Journal of Energy Storage

Journal of Energy Storage 81 (2024) 110361
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Journal of Energy Storage

journal homepage: www.elsevier.com/locate/est
Review Article
Fundamental chemical and physical properties of electrolytes in energy

storage devices: A review
Rudramani Tiwari a, b, Devendra Kumar a, Dipendra Kumar Verma a, Km Parwati a,
Pushpesh Ranjan c, d, Rajshree Rai a, S. Krishnamoorthi a, *, Raju Khan c, d
a
Department of Chemistry, Institute of Science, Banaras Hindu University, Varanasi 221005, India
b
Department of Chemistry, CCRAS - Regional Ayurveda Research Institute, Gwalior 474009, India
c
CSIR – Advanced Materials and Processes Research Institute (AMPRI), Bhopal 462026, India
d
Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
A R T I C L E I N F O A B S T R A C T
Keywords: Electrolytes are indispensable and essential constituents of all types of energy storage devices (ESD) including
Electrolytes, energy storage materials batteries and capacitors. They have shown their importance in ESD by charge transfer and ionic balance between
Ionic properties two electrodes with separation. Nevertheless, they significantly affect the charge storage performance, energy
Electrolyte impedance
density, cycle life, safety, and operating conditions of an ESD. Therefore, the understanding of the primary role,
Dielectric properties
Electrode compatibility
working principle and mechanism of the electrolytes are crucial for the development of high-performance ESD. In
this review, we gathered the most important properties of the electrolytes i.e. ionic conductivity, electrochemical
stability window (ESW), electrolyte impedance, matrix relaxation, loss tangent, dielectric permittivity, dielectric
modulus, ionic mobility, ionic diffusivity, drift ionic velocity, ionic transference number, solid electrolyte
interface (SEI), electrode compatibility, electrolyte phase, salt effect, temperature effect, and solvent effect which
are influencing factors in the ESD. Moreover, we also focused on the study in the progress of electrolyte research,
their challenges and future perspectives. The present review provides supportive information on the electrolyte's
Abbreviations: 1SP, solvent-shared ion-pair; 2SP, solvent-separated ion pair; AFCs, alkaline fuel cells; AFM, atomic force microscope; Al, aluminum; ARC,
accelerated rate calorimetry; BEMA, bisphenol A ethoxylate dimethacrylate; BMIM, 1-butyl-3-methylimidazolium; BMPyBF4, butyl-1-methylpyrrolidinium tetra
fluoroborate; Ca, calcium; CB, conduction band; Cd, cadmium; CDC, circuit description code; CEI, cathode electrolyte interphase; CIP, contact-ion pair; COFs, co
valent organic frameworks; CPE, constant phase behavior; Cs, cesium; CV, cyclic voltammetry; DEC, diethyl carbonate; DEE, diethyl ether-based electrolytes; DFT,
density functional theory; DMC, dimethyl carbonate; DMF, dimethylformamide; DMSO, dimethyl sulfoxide; DSC, differential scanning calorimetry; EC, ethylene
carbonate; ECM, equivalent circuit modeling; EDL, electrical double layer; EDLC, electric double-layer capacitor; EFPN, ethoxy(pentafluoro)-cyclotriphosphazene;
EMC, ethylene-methyl carbonate; EMIM, 1-ethyl-3-methylimidazolium; ePC-SAFT, electrolyte perturbed-chain statistical associating fluid theory; ESD, energy
storage devices; ESW, electrochemical stability window; FEC, fluoroethylene carbonate; GITT, galvanostatic intermittent titration technique; GSEs, gel state elec
trolytes; H2SO4, sulfuric acid; H3PO4, phosphoric acid; HER, the hydrogen evolution reaction; HMPP, 2-hydroxy-2-methylpropiophenone; HOMO, highest occupied
molecular orbital; HOPG, highly oriented pyrolytic graphite; ILs, ionic liquids; Im, imidazolium; K, potassium; KOH, potassium hydroxide; Li, lithium; Li+, lithium
ion; LIBs, lithium-ion batteries; LiODFB/EC-DMC-FEC, lithium oxalyldifluoroborate/ethylenecarbonate/dimethyl carbonate/fluoroethylene carbonate; LMBs, lithium
metal batteries; LMWA, law of matching water affinities; LSEs, liquid state electrolytes; LSV, linear sweep voltammetry; LUMO, lowest unoccupied molecular orbital;
MEEP, poly[bis(methoxy-ethoxy-ethoxy)phosphazene; Mg, magnesium; MIACs, mean ionic activity coefficients; MOFs, metal-organic frameworks; MoS2, molyb
denum disulfide; Na, sodium; Na+, sodium ion; NaCF3SO3, sodium trifluoromethanesulfonate; NaClO4, sodium perchlorate; NaOH, sodium hydroxide; NaPF6, sodium
hexafluorophosphate; Ni, nickel; NMP, N-methylpyrrolidone; NMR, nuclear magnetic resonance; OER, oxygen evolution reaction; OH− 1, hydroxide ion; ORR, and
oxygen reduction reaction; P(VDF-HFP), poly-(vinylidene fluoride-hexafluoropropylene); PAA, polyacrylic acid; PAN, polyacrylonitrile; PC, propylene carbonate;
PCL, polycaprolactone; PE, polyethylene; PEA, poly(ethyl acrylate); PEC, poly(ethylene carbonate); PEGMA, poly(ethylene glycol) methyl ether methacrylate; PEI,
polyethyleneimine; PEMFC, proton exchange membrane fuel cells; PEO, polyethylene oxide; PES, prop-1-ene-1,3-sultone; PF6, hexafluorophosphate; PIL, polymeric
ionic liquid; PITT, potentiostatic intermittent titration technique; PK, polyketone; PMMA, polymethyl methacrylate; PPO, polypropylene oxide; PSi, polysiloxane;
PTMA, poly (2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate); PTMC, poly(trimethylene carbonate); PVA, polyvinyl alcohol; PVC, polyvinyl chloride; PVDF,
polyvinylidene fluoride; PVF, polyvinyl fluoride; PVP, polyvinyl pyrrolidone; Py, pyridinium; SEI, solid electrolyte interface; SIBs, sodium ion batteries; SPEs, solid
polymer electrolytes; SSEs, solid state electrolytes; TFSI, bis(trifluorosulfonyl)imide; TGA, thermogravimetric analysis; TTFP, tris(2,2,2-trifluoroethyl) phosphite; VB,
valence band; WCAs, weakly coordinating anions; WIS, water-in-salt; Zn, zinc.
* Corresponding author.
E-mail address: skmoorthi@bhu.ac.in (S. Krishnamoorthi).
https://doi.org/10.1016/j.est.2023.110361
Received 6 September 2023; Received in revised form 3 December 2023; Accepted 28 December 2023
Available online 9 January 2024
2352-152X/© 2024 Elsevier Ltd. All rights reserved.
R. Tiwari et al. Journal of Energy Storage 81 (2024) 110361
chemistry and physics to design superior electrolytes for the development of ESD or other fields, where elec
trolytes are applicable.
1. Introduction solvation. The fundamental characteristics required for an ionic system

to be referred to as an electrolyte are (i) high ionic conductivity, (ii) low
With the high demand in the sphere of electrochemical energy electronic conductivity, (iii) a wide electrochemical window, (iv)
storage technologies for stationary and transportation applications, the chemical inertness, (v) easy wetting of the electrode's surface, (vi)
ESD, i.e. secondary batteries are the best choice. They are safe, cost- thermal stability, and (vii) matrix stability [7,8]. These properties play
effective, easy to manufacture, require low maintenance and capable an important role in the selection of a perfect electrolyte system for
of delivering high performance [1]. The energy economy will emerge particular device.
with its inexpensive and sustainable supply for many lavish activities, Apart from this, some other factors are also considered for the se
such as transport, electronic gadgets, etc. Nowadays, batteries are used lection of an electrolyte including the electrode dissolution factor, safety
in diverse applications from heavy vehicles to small electronics such as concerns associated with the solvent, chemical and electrochemical
electric vehicles, electronic devices, solar devices, satellites etc. stability of materials and solvents, the transport mechanism of ions
Although the concept of a battery is simple, but the progress in their within the matrix, thermal stability, and the strength of ionic conduc
development is slow due to the unavailability of appropriate electrode tivity, etc. [9]. The electrolyte compositions are widely investigated by
materials, electrolytes, and complications in the electrode-electrolyte considering the properties of electrode materials which include solvents
interfaces. Battery consists of two major components, one is the elec with high voltage operations, low viscous, highly mobile, nonflam
trodes, i.e., the cathode and the anode, with diverse chemical potentials, mable, high electrochemical stability, polymers for solid-state batteries,
and the second is an electrolyte material that couples them together. The size-exclusion membranes, aqueous systems for their cheap, safe and
electrodes are where the conduction takes place while the electrolytes high-power density properties. However, a considerable concern asso
offer a suitable medium to provide the necessary ions to complete the ciated with electrolytes include their limited operating voltage for
cell. In battery systems, several factors such as electrode, and electrolyte aqueous electrolytes (<1.5 V) [10], the toxic and flammable nature of
materials, their potential, current, stability, etc. affect the performance. organic solvents, high viscosity, and poor ionic conduction [11,12].
Whereas, the cell potential and capacity of the battery is most consid Therefore, the selection of raw materials for electrolyte preparation can
erable properties which depends on the chemistry of the electrode- be made based on considerations such as functional groups, polarity,
electrolyte system, where electrolytes play a major role by providing a synthesis cost, ion conduction, and solvent systems [13]. In ESD the
suitable ionic media to conduct the electrochemical activities [2]. The most common electrolytes are based on liquid solvents (aqueous and
electrodes in electrochemical systems as primary and secondary batte non-aqueous), salts and additives. Liquid electrolytes are polar, have
ries based on different metals such as Li, Na, K, Mg, Ca, Zn, Al, Ni, Cd, low toxicity, exhibit electrochemical stability, and possess high ionic
etc. The metal-based electrode offers several advantages such as cost- conductivity. However, safety concerns related to flammability and
effectiveness, long shelf-life, low rate of self-discharge, high power leakage are associated with these systems. When current passes through
density, and rapid charging rate. Nevertheless, they are also stable over the electrolyte system, it can undergo for oxidation (at the cathode) or
time and charge-discharge cycles to maintain their efficiency and reduction (at the anode) due to the flow of electrons to or from the
restrict the formation of any by-products for safety issues. However, the electrode, respectively. It's important to note that this property of elec
limited abundance, resource distribution, and recycling-related issues trolytes is not solely intrinsic but also a result of electrode-electrolyte
raise serious concerns to the large-scale production of metal-based interactions. The degradation of materials depends on the chemical
batteries [3]. In addition to the selection of metals employed in the nature of the electrode and electrolyte components. The multi-step
electrode preparation, an electrolyte due to the profound influence of degradation of electrolytes in batteries and capacitors results in the
the intrinsic properties on the overall performance and functionality of formation of several unwanted products, both organic and inorganic,
the ESD is also a notable concern. which are deposited on the electrode surface [14]. The deposition of
Electrolytes are an indispensable and critical constituent of all types these unwanted products on the electrode surface forms both thin and
of battery and capacitor systems. They demonstrate their importance in thick layers (known as the SEI layer), which reduce the porosity of the
ESD by facilitating charge transfer and ionic balance between two electrode and disrupt the ionic reactions inside the device. However,
electrodes separated by a medium. It has noted that the charge storage electron transfer reactions continue through quantum tunneling, but
performance, energy density, cycle life, safety, and operating conditions tunneling also ceases as the thickness of the SEI layer increases [15].
of an ESD are directly affected by the electrolyte. They also influence the Therefore, reducing the formation of the SEI layer in batteries and ca
reversible capacity of electrode materials where the interaction between pacitors is one of the most challenging aspects. Apart from this, the
the electrode and electrolyte in electrochemical processes impacts the several other properties such as electrolytes impedance, dielectric
formation of the SEI layer and the internal morphology of the active properties, ionic diffusivity, ionic transference number are also kept in
electrode material. Nevertheless, the specific capacity of devices is also view before the selection of electrolytes, since they directly influence the
affected by the electrolyte which attracts more attention to specified working of the ESD. Moreover, the pH effect, and salt effect are also
research in this field [4]. The electrolyte composition also determines considered, since the very low or very high pH may decline the perfor
the ESW and thermodynamic stability of the devices. These are related mance of EDS. Hence, the optimization of operating pH is necessary to
to the energy gap between the HOMO and the LUMO of the constituent improve the efficiency of ESD.
mixture. Moreover, the kinetics of electrochemical reactions are To point out all the concerns related to electrolytes, there are several
controlled by the ionic transference number and the formation of the SEI comprehensive review articles [1,16–23] are available, which focus on
layer in the electrochemical system [5]. Ponrouch et al [6]. reported that the progress of electrolyte research, electrolyte formulation, new elec
an appropriate SEI film formed by the electrolyte on an anode can trolyte systems, their synthesis strategies, and applications in different
enhance the performance by the cycling of devices. Hence, improved aqueous and non-aqueous-based electrolyte systems for Li+-ion and
electrolyte-electrode compatibility can enhance the overall device per Na+-ion based ESD. To the best of our knowledge, there is a lack of
formance, making the development of compatible electrolytes crucial articles that provide fundamental knowledge of an electrolyte, covering
for their application. On the other hand, the rate of charge transfer re all its important properties and factors that affect the performance of
action is affected by oppositely charged counter-ions and the degree of ESD. This review addresses the existing gap by providing comprehensive
2
coverage of all the basic aspects and factors affecting parameters, as well employing LSEs. Owing to their low cost, low volatility, non-
as the development and challenges associated with electrolyte materials. flammability, and high solubilizing capacity, aqueous electrolyte sys
Nevertheless, we extensively discuss the fundamental features of tems based on acids, bases, or salts were the most studied LSEs between
different electrolyte systems, covering their role in ESD and associated year 1990 and 2014. However, the low working potential and temper
drawbacks. Subsequently, we delve into various aspects of electrolyte ature range further imitated their application.
properties, including ionic conductivity and transference, ESW, elec Various organic solvent-based electrolyte systems were designed,
trolyte impedance, matrix relaxation, loss tangent, dielectric properties which are based on EC, DMC, EMC, DMF, DMSO, etc. Although organic
(permittivity and modulus), ionic mobility, matrix diffusivity, and drift solvent-based LSEs exhibit a wider ESW than aqueous electrolytes.
ionic velocity. Furthermore, we explore the factors that affect electrolyte However, they suffer from volatility, flammability, toxicity, poor solu
properties, such as the nature of the solvent, pH effects, thermal stability bility of ionic salts, and a low working temperature range. Both aqueous
and activation, salt effects, physical phase of the electrolyte material, and non-aqueous solvent-based LSEs exhibit a risk of leakage, which
SEI, and electrode compatibility. Our aim is to present a comprehensive poses problems regarding their packaging and fabrication and makes it
overview in progress in the field of electrolyte research, encompassing difficult to use them easily for ESD for portable and wearable
basic characteristics, development, challenges, and future perspectives, electronics.
which can assist early researchers in selecting the appropriate electro
lyte for ESD systems. 2.3. Gel electrolytes
2. Electrolytes types and modern fabrication techniques Gelled electrolytes are a hybrid between liquid and solid electrolytes.
They contain a gelling agent to immobilize the liquid electrolyte. The
The choice of electrolyte depends on the specific requirements of the issues of lower ionic conductivity, poor electrode-electrolyte interac
application, with a trade-off between performance, safety, and ease of tion, volatility, flammability, poor solubility, and a lower working po
manufacturing. As far as ESD is concerned, electrolytes are going to play tential and temperature range imposed by SSEs and LSEs were overcome
key role in their performances. Based on their physical state, they are by utilizing GSEs. They are based on hydrogel materials, ILs, and poly
broadly classified into SSEs, LSEs, and GSEs. Ongoing research is aimed meric matrices, in which either liquid electrolytes such as H2SO4, or
to addressing the challenges associated with each type of electrolyte and ionic salts dissolved in an appropriate solvent, are used as the ion source.
improving their prospects for various electrochemical devices. Over the Ionic transport occurs through the polymeric matrix, which acts as the
time, advances in materials science and engineering continue to drive host for ionic species. PVA is the most suitable polymeric system for
innovation in this field. Each type has its own set of advantages and GSEs. Due to the presence of a liquid phase, GSEs exhibit improved ionic
challenges. In this section, we have discussed the essential properties of conductivity compared to SSEs. GSEs also offer a large ESW and a
the different type of electrolytes employed in the ESD. working temperature range, and allow water as a solvent to dissolve
ionic salts in this phase. Owing to improved thermal, chemical, me
2.1. Solid electrolytes chanical, and electrochemical properties, GSEs are utilized for devel
oping various types of flexible, wearable, portable, stretchable,
Solid electrolytes are typically non-liquid, and non-gelled materials printable, and micro-electronic devices. Along with several advantages
that conduct ions. They can be ceramics, polymers, or composites. of GSEs, they also face challenges such as viscosity, complex
Owing to the ease of packaging and fabrication, SSEs have attracted manufacturing, and longevity issues.
remarkable scientific attention for their widespread application in
various fields of electronics, such as portable, flexible, wearable, micro, 2.4. Evolution of different electrolytes
and printable electronics. Polymer-based SSEs such as PEO, PMMA,
PVDF, PAN, etc. are broadly recognized SPEs and polyelectrolytes. Only In the early phase, the progress of the electrolyte's development in
a few reports are available for SSEs based on inorganic solid materials the ESD was very slow. The first electrolyte “ionic conductive polymer”
(ceramics) and hybrid inorganic-organic materials (composites). In the of a mixture of alkaline salt and PEO was reported by D. E. Fenton in
case of SPEs, the polymeric matrix acts as the host for the electrolyte salt, 1973 [24]. After a few years, Feuillade and Perche in 1975, a polymer, Li
and ionic transport occurs throughout the polymeric matrix. Experi salts, and organic solvent-based GPEs were reported which was utilized
mental observations have revealed that better ionic conductivity is in the Li cell [25]. After that, Bannister and colleagues conceptualized a
achieved in an amorphous matrix. However, in the case of poly single Li+ conducting polymer electrolyte. The primary mechanism of
electrolytes, charged polymeric chains based on PAA are used as a ionic conduction is attributed to the transfer of lithium cations [26]. Due
means to conduct ions. SPEs serve a dual function as a medium to the high efficiency of Li-based electrolytes in the energy system, it
responsible for transporting ions and as an electrode separator. They gains remarkable attention and is widely considered a good electrolyte
also possess excellent mechanical strength. SSEs electrolytes are less with improved working performance in batteries. Consequently, a
prone to leakage or thermal runaway and offer higher energy density rechargeable Li-battery made of diethyl ether-based electrolytes (DEE/
compared to liquid electrolyte batteries. They function effectively over a LiAsF6) was introduced [27]. Nevertheless, a rubbery solid polymer
broad temperature range. Along with several advantages of SSEs, they electrolyte known as “polymer-in-salt,” characterized by commendable
also face challenges of low ionic conductivity and poor interfacial Li+ conductivity having high electrochemical stability was reported by
interaction between the electrolyte and electrode materials. Moreover, Angell and colleagues [28]. Progressively, the biopolymer electrolyte of
they are brittle and prone to cracking, which can affect the long-term Li-acylated chitosan for the polymeric battery was prepared. This elec
stability of the device. trolyte possesses 10− 4 S cm− 1 of electrical conductivity. However, the
short lifetime and low discharge limited their efficiency [29]. To
2.2. Liquid electrolytes continuously rise in the electrolyte research, a liquid-based electrolyte
was developed. Successively, in 2010, Mizuno et al. developed a
Liquid electrolytes are solutions or solvents that contain dissolved carbonate-based liquid electrolyte for rechargeable Li-air batteries. The
ions. They are composed of electrolyte salts dissolved in organic and/or electrolyte possesses high efficiency such as rechargeability over 100
inorganic solvents or aqueous acid and/or alkali solutions. LSEs offer the cycles, and 60 % of capacity retention [30]. Progressively, Pan et al. in
highest obtained ionic conductivity, which depends on the ionic size and 2012, a silica-based gel electrolyte was reported having considerable
their concentration. Hence, the problem of lower ionic conductivity and physical and electrochemical properties, rendering it a promising choice
poor electrode-electrolyte interaction was easily overcome by for lead acid batteries [31]. Nevertheless, Suo et al. introduced a highly
3
Fig. 1. Evolution timeline of different types of electrolytes.
efficient liquid electrolyte termed “WIS”, characterized for the Li+-based chemical stability, excellent ionic transport, a wider ESW, and excellent
high voltage aqueous electrolyte having 3 V of an electrochemical cycle stability.
window for battery applications [32]. Lahiri et al. reported an ionic Electrolyte systems based on aqueous and/or organic solvents pose
liquid-organic solvent-based hybrid polymer-gel electrolyte. The elec various challenges such as the lower ESW of aqueous solvents, flam
trolyte was optimized for a high lithium concentration and conducted a mability, volatility, and solubility issues of inorganic salts in organic
study on its performance and formation of SEI for all types of solid-state solvents, as well as leakage and working temperature range problems.
Li+-batteries. With the continuous research progress and growing de To overcome these challenges, ILs are being suggested as suitable al
mand in the energy sector, the development of highly efficient novel ternatives to aqueous and organic solvents. ILs are ionic compounds
electrolytes is need of hour. A detailed timeline of the development of (salt-like materials) made up of organic cations based on ammonium,
solid, liquid, and gel-based electrolytes is shown in Fig. 1. imidazolium [34], pyrrolidinium [35] etc., and organic or inorganic
anions. They are more thermally and electrochemically stable, more
viscous than aqueous and organic solvents, which solve the leakage
2.5. Modern electrolyte fabrication techniques problems to a sufficient extent. Due to their ionic nature, they are also
capable of dissolving a wide range of inorganic salts. Although their
The design and development of electrolytes need to meet several comparatively high viscosity has a detrimental effect on ionic mobility.
requirements, such as exhibiting excellent thermal, chemical, and me In contrast to aqueous and various organic solvents, ILs exhibit negli
chanical properties. The highest possible ionic transport, a wide ESW, gible vapour pressure which can dissolve various types of organic,
non-flammability, non-combustibility, non-volatility, excellent cycling inorganic, and polymeric moieties, and exhibit electrochemical stability
stability, as well as not undergoing decomposition of electrolytes are up to 6 V [36].
crucial for high performance ESD. To meet all of the above-mentioned Among aqueous, organic, and IL solvents, aqueous solvent has su
criteria, several new approaches have been adopted in the preparation periority over others in terms of safety, low volatility and flammability,
of electrolytes, which are based on the utilization of nanoparticle fillers, ionic conductivity, cost-effectiveness, and the solubility of wide range of
ILs, and various types of suitable organic and inorganic additives. ionic salts. However, aqueous electrolytes pose problems for metallic
Currently, LIBs are the most widely used ESD, where SPEs including anodes, such as zinc anodes, which are associated with the growth of
PMMA, PVDF, PEO, and PAN are commonly utilized for LIBs [33]. zinc dendrites and other side reactions. These drawbacks of aqueous
Among them, owing to its commercial availability and environmentally electrolytes can be mitigated by the application of various types of
friendly nature, PEO establishes itself as one of the most promising electrolyte additives. Trace amounts of electrolyte additives can also
electrolytes. Experimental findings reveal that the transport of Li+ ions play an important role in improving the ESW. Nowadays, various types
mainly occurs through the amorphous zone of the polymer. To achieve of electrolyte additives are used for superior electrolyte design and
better transport of active ionic species and good ionic conductivity, it development, including metal ion additives, surface electrolyte interface
has been proposed to enhance the amorphousness of the polymeric film-forming additives, complexing additives, and surfactant additives.
candidate of SPEs by introducing nanoparticles [33]. Consequently, Additives are compounds that are more easily reducible than the parent
nanoparticle-containing electrolyte systems exhibit good thermal and
4
Fig. 2. Schematic illustration of the different characteristics of electrolytes and factors affecting the ESD.
solvents used in the ESD. Therefore, they reduce themselves prior to the The most important property of the electrolyte material is its ionic
solvent and salts used for electrolyte design, thus protecting against their conductivity of active ion (i.e. Li+ or Na+ for LIBs and SIBs) that has to be
degradation. All these various types of additives prevent dendritic intercalated with the electrode. In LIBs and SIBs, there are no chemical
growth and side reactions by modulating the electrode/electrolyte changes involved in battery operation, while the movement of ions takes
interface environment [37]. The introduction of additives in SPE design place at lower and higher voltages to find the maximum energy den
is a cutting-edge technology for achieving possible high-performance sities. Since these parameters do not have any higher or lower threshold
SPEs. Additive addition also reduces the flammability issue of organic values, they always need to be optimized separately for specific cell
solvents to a certain extent [38]. In summary, it can be concluded that systems e.g. ionic conductivity (>1 mS cm− 1), optimization for room
modern approaches utilized for the design of electrolytes using nano temperature operation, electrolyte salt optimization, matrix diffusivity,
particles, ILs, and additives provide extra stability to ESD, thereby etc., So measurement of a single property cannot decide the applicability
enhancing their lifespan. of electrolyte in a full cell system. There is some fundamental difference
in physical and chemical aspect for example, moving from Li+ to Na+
3. Fundamental characteristics of electrolytes ionic size, acidity, charge/radius ratio, redox potential, etc. can change.
The differences are not limited to the properties of the ions but are also
Electrolytes play an important role and are mainly responsible for observed in electrode properties such as intercalation/interface forma
the possible energy output to the ESD. There are several physical and tion. For example, both Li+ and Na+ show good interaction with
chemical properties and factors that affect the performance of electro carbonaceous materials. Li+ shows good intercalation with graphite
lytes as well as ESD (Fig. 2). Because electrolytes are the bridge for ion while Na+ does not, however, Na+ shows better interaction with hard
transport from one electrode to another to complete the circuit. Tradi carbon materials. It was also observed that a Na+ complex i.e. [Na
tional electrolytes are prepared by dissolving metal salts in a particular (diglyme)2]+ shows good intercalation with graphite which shows the
solvent [39]. Depending on metal ion concentration (dilute/concen need for solvent optimization [42]. These results strongly suggest that
trate) the behavior of the electrolyte gets changed, because the con each component of electrolyte affect the performance in different grade
centration directly influences the electrochemical performance of the and empower to optimization of the electrolyte constituents by varying
electrolyte system. Apart from this, the Lewis acidic and basic nature of the concentration of salts, particular ion salts, solvents, additives, salt/
solvents allows for solvation processes. The solvation amount of metal additive ratio, etc. The selection of a particular ionic salt and solvent
ion allows high migration rates and increases the ionic conductivity of always affects ionic conductivity, chemical and electrochemical stabil
electrolyte in dilute electrolyte systems [40]. However, shortcomings ity. The strength of opposite ionic interaction affects the ionic conduc
associated due to solvents i.e. thermodynamic stability, ESW and tion in the electrolyte system by availing the number of charge carriers.
chemical stability can be eliminated by using a concentrated electrolyte For the example of Li+ and Na+, moving from Li+ to Na+ the interaction
system [32,41]. between cation and anion gets reduced up to 80 % limit [43]. The ionic
5
pairing and salt solubility also depend upon the temperature that relies Table 1
upon the optimization of salt concentration in a particular cell system. Molar ionic conductivity of some cations and anions in water at 25 ◦ C [53,54].
The solvent also governs the ionic conductivity, mobility, diffusivity Cation Molar ionic conductivity [S Anions Molar ionic conductivity [S
and drift velocity due to their viscosity characteristic which are cm2 mol− 1] cm2 mol− 1]
inversely proportional to these all parameters. Ionic conductivity de H+ 349.6 F− 54.8
pends on several factors, including ionic transference, ionic mobility, Li+ 38.7 Cl− 76.2
ionic diffusivity, and ionic velocity. The ionic transference number is a Na+ 50.0 Br− 75.5
measure of the efficiency of ionic transport in the electrolyte. It repre K+ 73.6 I− 76.8
Cs+ 77.3 OH− 197.9
sents the ratio of the current carried by a particular ion concerning the Be2+ 90.0 HSO−4 50.0
total current obtained from the electrolyte. The ionic transference Mg2+ 105.1 NO−3 71.4
number governing the mobility and transport of the solvated ions Ca2+ 119.1 HCO−3 44.3
effected by the solvation factor. Since an anion has a lower charge/ Ba2+ 127.4 CO2−3 143.5
Al3+ 188.9 CN− 78.0
radius ratio and gets weakly solvated shows higher mobility. In contrast,
Cu2+ 110.1 SO2−4 160.7
a cation has a larger charge/radius ratio which results in a higher sol Pb2+ 142.0 S2− 109.8
vation number and shows poor mobility inside the matrix. This factor Zn2+ 107.4 NO−2 71.7
results from more anionic conduction in electrolytes which are opti Ni2+ 99.2 PO3−4 206.8
mized with simple salts and show the cationic transference number in a
range of 0.2–0.4 and the anionic transference number in a range of
energy and deliver it more quickly, which increases its high power and
0.6–0.8. Similarly, changing the cation also changes the solvation which
energy density [52]. The ionic conductivity of some cations and anions
can improve the cationic transference number due to the charge/radius
are shown in Table 1.
ratio i.e. Na+ shows a lower solvation number compared to the Li+ [44].
The conduction mechanism of ions in different electrolytes can vary
The ionic mobility is the ability of an ion to move inside the matrix
depending on the chemical and physical properties including its chem
and it is related to the ionic transference by the Einstein equation (μ =
ical composition, concentration, and structure. In a strong electrolyte
ezD / kbT) [45], which states that ionic mobility is proportional to ionic
solution, it is mainly through a migration process, where the ions move
charge and inversely proportional to the size of the ion. The fast
through the electrolyte in response to an electric field. The migration of
migration of ions inside the matrix reduces the rate of ion intercalation
ions is facilitated by the solvent molecules, which help to stabilize the
at the electrode surface, ion transfer across the interface, charge transfer
ions and reduce their interaction with each other. Whereas, the con
and polarization resistance. This property of electrolytes also gets
duction mechanism of ions in weak electrolytes solution is mainly
affected by ion size, ionic coordination and solvation of ions. For
through a combination of migration and diffusion processes. The degree
example, Li+ has a smaller charge/radius ratio which reduces binding
of dissociation of an electrolyte determines the concentration of the ions,
energy compared to Na+ and shows better transport at the interface.
and hence their mobility in the solution. The conduction mechanism of
Instead of that the transport rate of Li+ is poor compared to Na+ due to
ions in polymer/hydrogel electrolytes is mainly through a hopping
the high coordination of Na+ in the solvent system [43,46]. Although
process, where the ions move from one site to another in the polymer
poor de-solvation energy enables lower Ea for faster charge-discharge
matrix through a series of jumps. The hopping process is facilitated by
processes inside the ESD i.e. Na+ has lower Ea than Li+ and hence SIBs
the flexible and mobile polymer/hydrogel chains, which allow the ions
show faster charge-discharge processes than LIBs [47]. Nevertheless,
to move through the polymer matrix. However, in ceramic, composite,
ionic diffusivity measure how quickly an ion can diffuse through the
crystalline electrolytes, it is mainly through a vacancy-mediated process,
electrolyte. It is related to the ionic mobility by the Stokes-Einstein
where the ions move through the lattice by exchanging places with
equation (D = μkbT = kbT / 6πηr) [48] which states that ionic diffu
vacant sites in the crystal structure. The vacancy-mediated process is
sivity is directly proportional to the ionic mobility and inversely pro
facilitated by defects in the crystal structure, such as vacancies or dis
portional to the size of the ion. Ionic velocity is another important factor
locations, which provide sites for the ions to move through the lattice
that measures the speed at which an ion moves in response to an applied
[55].
electric field, and it is related to ionic mobility and ionic diffusivity.
For an electrolyte system, conductivity can be calculated by using
Electrochemical impedance, dielectric permittivity, dielectric loss, and
several techniques such as transference number measurements, NMR,
dielectric modulus are all also valuable properties of electrolytes that
conductivity meters, and EIS. The ionic conductivity (σ ) of liquid elec
can affect their performance in electrochemical systems. These funda
trolytes and ILs can be easily measured by using conductivity meters
mental characteristics of electrolytes can be analyzed based on their
(Eq. (1)) [56]:
bulk properties [49]. In this section, we have briefly discussed the
different characteristics of the electrolytes. σ = Λρ/M (1)
Here Λ is molar conductivity, ρ is the narrow range temperature
3.1. Ionic conductivity
parameter and M is molar concentration. Conductivity meters work by
applying an electric field across the electrolyte and measuring the
Ionic conductivity (σ) refers to the ability of ions to move through the
resulting current. This method is relatively simple and quick, but it re
electrolyte. The higher the ionic conduction allows the faster ionic
quires a steady-state condition and is limited for high-viscosity or low-
movement. In a rechargeable ESD, ions move from the anode to the
concentration solutions. EIS is also utilize for conductivity measure
cathode during discharge, and vice-versa during charging. It has a
ment which provide information about the complex resistance and
paramount importance in ESD, particularly in batteries and super
capacitance of the electrolyte, used to determine ionic conductivity
capacitors. These ESD rely on the movement of ions between electrodes
(Fig. 3A) using relation (Eq. (2)) [57,58]:
through the electrolyte to store and release energy. The faster the ions
can move through the electrolyte, the more efficiently the device can σ = (1/Rb)(l/A) (2)
store and release energy. Therefore, high ionic conductivity leads to
Here, Rb is bulk resistance, l is the distance between two electrodes
faster charging and discharging, which can increase the device's power
and A the area of the sample electrode interface. Due to the notable
and energy density [50]. A lower ionic conductivity can lead to slow ion
information's, this method can be used for a wide range of electrolytes i.
transport, which can cause the electrodes to degrade over time. This
e. solid, liquid, composite, hydrogel, etc. A detail of EIS technique is
degradation can reduce the device's lifespan and lead to reduced per
discussed in Section 3.3. The conductivity of electrolytes can also
formance [51]. Higher ionic conduction enables the device to store more
6
Fig. 3. (A) Bulk resistance of electrolyte material (B) Arrhenius type relationship of conductivity with temperature change, (C) frequency-dependent conductivity
showing different depressed regions, and (D) scaled master curve for frequency-reliant conductivities.
measure by transference number measurements [59] (detail mention in barriers. The conductivity of electrolyte relates to the temperature
Section 3.9). This method is useful for measuring the ionic conductivity which is Arrhenius type and follows the thermally activated process
of multicomponent electrolytes. Nevertheless, NMR is also capable to (Fig. 3B). This property of electrolyte is applicable for the determination
measure ionic conductivity by observing the dynamics of ions in the of the Ea, which is necessary for the ionic movement from one place to
electrolyte. It can provide information about the diffusion coefficient another and the creation of a migration path. The relationship of con
and the correlation time of the ions. This method is non-destructive and ductivity with the temperature can be represented as Eq. (3) [65]:
can provide detailed information about the electrolyte structure and
σ T = σ o exp − Ea /kT (3)
dynamics [60].
The ionic conductivity is also related to its viscosity (σ ∝ 1 / ηo) [56], where σ o is the pre-exponential factor. Ea is conquered by the migration
ionic diffusivity (σ = Di q2N / kbT) [61], ionic mobility (σ = nqμ) [62], energy at all temperatures, but salt dissociation energy can considered
drift ionic velocity (σ = z Vd N) [63], ionic transference number (σ ion = as Ea only at the higher temperature [65]. Ionic conductivity determines
qion cion tion / KbT) [59], density, stability, electrolyte composition, the efficiency, power and energy density, and lifespan of ESD. However,
microstructure, and processing conditions [59,64,65]. The viscosity of high ionic conductivity can lead to safety concerns [71]. Since, high
the electrolyte directly influencing the ionic movements. Lower viscos conductive electrolyte can cause a short circuit and lead to thermal
ity allows ions to move more freely and quickly through the electrolyte runaway, which can result in a fire or explosion. Therefore, finding the
and results in higher conductivity. This, in turn, increases the battery's proper balance between ionic conductivity and safety is critical for
power and energy density. Nevertheless, a high ionic conductivity can battery performance. It is also noticeable that the conductivity of ions
lead to a lower density of the electrolyte, which can reduce the overall can vary depending on the solvent and temperature. Also, the concen
weight of the battery. Optimizing the physical parameters (i.e. electro tration of the ions and the presence of other species in the electrolyte can
lyte concentration and selecting an appropriate aliovalent dopant) [66], affect their conductivity.
processing conditions (different sintering processes to prepare electro The ionic conductivity of dielectric properties having electrolytes are
lyte matrix) [67], and microstructure to achieve maximum ionic con frequency dependent. The frequency-dependent conductivity investi
ductivity. Microstructures are related to the possessions of grain and gation of unstructured, polymeric, glassy, hydrogel and film electrolyte
grain boundary. Grain boundaries can deliver a region of rapid mass systems are widely applied for understanding the ionic transport
transport in some of the polycrystalline electrolytes compared to the mechanism and dynamics. For these materials, the frequency-dependent
bulk crystallites. Its properties can be determined by the disparity of the conductivity vs. frequency spectrum is anticipated to obey Jonscher's
lattice parameters, impurities, phase segregation, microcracks, and also Power law (JPL, σ ac = σ dc + Afn where, σ dc is the frequency-independent
space charge [68]. conductivity, A is constant, n is the power exponent) [72]. The values of
Beside these, the conductivity of the electrolyte is kinetically and power exponent are restricted to below or equal to 1, and it indicates the
thermodynamically related to the temperature, the concentration of different ionic transport mechanisms inside the electrolyte matrix. The
ions, the partial pressure of gas and the matrix structure [69,70]. value of n = 0 indicates a free ionic hopping mechanism, whereas, the 0
Thermodynamic dependence of electrolyte conductivity can be obtained < n < 1 indicate correlated hopping inside the electrolyte matrix.
by using thermally activated voltage fluctuations transversely on the Moreover, the n > 0 indicates a caged movement of ions over the
insulating area of the surface, which controls the effective conduction
7
Fig. 4. Correlative notations of negative and positive potential limits for the electrolyte stability, and the energy levels of HOMO and LUMO.
electrolyte materials [73–75]. The AC conductivity curve of a typical studies of 10 polymer electrolytes PEO, PPO, PVA, PK, PCL, PMMA, PEA,
dielectric material-based film is shown in Fig. 3C, which consists of three PE, PVC, and PVDF and found that they exhibit ESW of ≥4.7 eV which
different regions, (i) a dispersion region at a low-frequency region owing show good agreement in the utilization of Li-based battery. However,
to the gathering of ions at the electrode-electrolyte interface, (ii) a the morphological disordering of the polymer may alter the energy band
plateau region at mid-frequency region due to frequency-independent gap which declines the ESW [78]. Peljo and Girault et al. correlate the
conductivity, and (iii) a dispersion region with increasing conductivity effect of the energy gap of the HOMO and LUMO, redox potential and
at high-frequency region due to capacitive behavior reactance (Xc = 1 / fermi level of electron on the ESW (Fig. 4). They revealed that based on
2πf). It is also conceivable to scale frequency-dependent conductivities, HOMO-LUMO, it is hard to decide the choice of materials. Since water
that are arises by changing the temperature or different material com possesses an 8.7–8.9 eV band gap, therefore they could be the best
positions in a single master curve by scaling the frequency axis and choice for a Na-based battery, however, it is not possible the same. So,
conductivity axis with the help of hopping frequency (fH) and σ dc the HOMO-LUMO gap, redox potential of electrolyte and solvent/poly
derived from mid region of the plot (Fig. 3D) [76,77]. This scaled plot mer cannot directly relate to the ESW. However, doping the PEO with
indicates that the conduction mechanism in the electrolyte system fol Li+ salt can reduce the ESW [78].
lows concentration and temperature-independent conductivity Mery et al. gathered the ESW of the commonly used SPEs and solid
formalism. composites electrolytes having the range of 3.0–6.5 V estimated through
the CV and LSV techniques. They also stated that the accurate ESW can
be calculated by keeping the appropriate cell configuration to enhance
3.2. Electrochemical stability window
the interfacial contact and proper method of estimation which is
frequently used in electrochemical techniques such as CV, LSV, and EIS
The ESW is the most significant parameter for choosing an electro
[79]. Recently, Wang et al. listed the ESW of 308 electrolytes based on
lyte when dealing with the ESD. It is measured by the electrochemical
thermodynamic cycle calculation. These studies revealed the suitability
potential of an electrolyte which is restricted to reduce or oxidize. It
for the utilization of non-aqueous solvents for broad application in the
should be noted that the both solvent and the host polymeric materials
assembly of rechargeable batteries [81]. In a recent study, Marchiori
must possess wide ESW which will be measured based on their redox
et al. estimated the ESW of PVA, PEO, PEC, PTMC, PCL, PAN, and PEI for
potential which is governed by the energy gap between the VB and CB.
Li+-based battery through the calculation of Gibbs free energy of the
Since high ESW restricted the redox process caused self-reaction in the
reduction reaction. They found that the PAN has an oxidation potential
battery system. Additionally, the ESW controls the open circuit voltage
of 4.46 V and a reduction potential of − 3.65 V which display a wide-
which influences the life cycle of the batteries. However, if electrolytes
ranging ESW of 8.11 V. The reduction potential is quite a match with
fail to meet such criteria, it causes the formation of a passivated
the Li+-salt. However, the lower stability of the PAN with Li+-salt may
electrode-electrolyte layer to block the movement of the ions. Hence, the
cause less suitability in battery formations. Nevertheless, other poly
life cycle of the battery may decline. Therefore, the wide ESW must be
mers, PVA, PEO, PEC, PTMC, and PCL also show broad ESW and
considered during the selection of solvent and polymeric electrolytes.
comparative redox potential close to the Li+-salt which shows good
The ESW of the polymeric electrolyte has been experimentally measured
agreement in the Li-based battery [82]. Very recently, Schwietert et al.
through optical absorption spectra, CV, and LSV. Additionally, the DFT
used the computational approach to determine the ESW of the solid
has been also used to theoretically calculate the ESW [78,79].
electrolytes through the stability of the decomposition product based on
Several studies revealed that organic solvents such as IL, polymeric
the Gibbs free energy calculation and evaluation of the intrinsic window
electrolytes such as PEO, PVDF, PPO, MEEP, PSi, PC, PVC, PAN, PMMA,
(delithiation) of the solid electrolytes [83]. Apart from the solid elec
P(VDF-HFP), etc. are commonly used since they exhibit high ESW [80]
trolytes, other non-aqueous solvents such as ILs considered as most
However, several investigations could be performed to study the
fascinating in battery systems due to their wide ESW. They are
particular interactions of the salt with the polymers or solvent to explore
composed of an organic cation and an inorganic anion; however, their
the nature of the electrode-electrolyte interface. Chen et al. did the DFT
8
Fig. 5. Comparative ESW ranges of different ionic salts of Na and Li based electrolytes.
Reproduced from Ref. [95] with permission from the Royal Society of Chemistry. (This article is licensed under a Creative Commons Attribution 3.0 Unpor
ted Licence.)
properties can be improved by choosing the correct pair of cation and [94,95]. Other than these electrolytes, an aqueous electrolyte has also
anion [84]. Researchers revealed that they potentially serve for both Li- shown high suitability in Na-based batteries. It was seen that the satu
[85–87] and Na-based batteries [88–91]. It was shown that the rated aqueous solution of NaClO4 displays an ESW of 2.7 V which was
methylimidazolium-based IL having the [PF−6 ] anion shows wide ESW in due to the formation of stable SEI and the prevention of the decompo
comparison to the [TFSI− ], [TfO− ], and [BF− ] anion containing IL. sition of water in a Na-based battery [96]. Another study shows that the
However, the length of the alkyl chain significantly influences the ESW NaCF3SO3 in an aqueous solution has an ESW of 2.5 V for the Na-battery.
where, by the increasing number of carbons in the alkyl chain, the ESW In this system, the electrolyte diminishes the hydrogen production on
become decreases for Li-based batteries [85]. the anode and also forms the stable SEI [97]. Very recently, an aqueous
Apart from the Li-based battery, Na-based battery also gains polymeric electrolyte “water-in-ionogel” was tested for Na-battery. The
tremendous attention in rechargeable batteries. To support the better ionogel consisted of PEGMA, BEMA, FEC, and HMPP polymers in 10 wt
functioning of the Na-battery, the carbonate ester-based solvent has % water. These ionogel electrolytes in the presence of NaTFSI show ESW
been widely utilized. This is mainly due to the wide ESW and excellent of 3.0 V for Na/Na+. In this system, the huge number of hydrogen
ability to dissolve Na salts. These carbonate esters are EC, PC, DMC, bonding stabilizes the electrolytes responsible for the high stability.
EMC, and DEC. The use of combinations of two or more solvents is Moreover, the fluoride additive significantly improves the working at
commonly reported instead of the use of a single solvent for the best lower temperatures which can potentially be operated at − 25 ◦ C [98].
operation of Na-batteries [91]. A mixture of EC and DMC (30:70 wt%) Beyond this, further studies are also needed to explore the highly suit
was studied by Bhide et al. in the presence of NaPF6, NaClO4, and able electrolyte which possesses wide ESW to fulfill the construction of
NaCF3SO3, where the NaPF6 and NaClO4 show ESW of 4.5 V vs Na/Na+. high performance of ESD. A comparative ESW ranges of different ionic
However, in these three electrolytes, NaPF6 was found the best suitable salts of Na and Li based electrolytes are provided in Fig. 5.
candidate for Na-battery. Since, the anionic decomposition product of
PF−6 show better stability compared to the ClO−4 and CF3SO−3 . In NaClO4, 3.3. Electrolyte impedance
the first reaction is observed at 3.0 V. However, such reactions are not
found in NaPF6. Furthermore, the compatibility of these electrolytes was EIS is a powerful non-destructive technique to study the interfacial
tested with the Na0.7CoO2 cathode where NaPF6 was found more suit properties of electroactive (redox) materials. In which, they examine the
able for these Na-batteries [92]. Apart from this, the ESW of boron-based impedimetric response at the electrode-electrolyte interface. Through
electrolytes such as CB9H10 and CB11H12 has been tested against both Na the impedance, the adsorption, charge transfer process, mass transport,
and Li-based batteries. For the CB9H10, the stability of the 3.5 V and 3.9 the thickness of electrolyte, bias potential, and diffusion processes in the
V has been achieved vs Na and Li respectively. However, for CB11H12 the electrochemical system at different rates are frequently examined. In
stability was attained at 4.2 V vs Na and Li. Overall, both electrolytes EIS, the two graphs i.e. Nyquist and Bode represent the impedimetric
display superior electrochemical stability against Na compared to Li-ion behavior. In the Nyquist plot (Zreal vs Zimag), the semicircle portion
[93]. Nonetheless, other organic electrolytes like SSE are also a better exhibits the kinetic control reaction, which shows the charge transfer
choice for Na-based batteries. Since, SSE possesses the most fascinating resistance or bulk resistance (Rct ot Rb). The Rct is so-called the elec
properties such as excellent ionic conductivity, low grain boundary trolyte resistance at the electrode in an electrochemical system. More
resistance, long ESW, and high stability. The mainly used SSE are over, the straight line in low frequency region displays the Warburg
β-alumina (β-Al2O3), NASICON (Na3Zr2Si2PO12), sulfur-based (Na3PS4, impedance due to the diffusion control reaction which designates the
Na3PSe4, Na3SbSe4), complex hydride {Na2(B12H12)0.5(B10H10)0.5} etc. diffusion effects of ions on the host electrolyte. However, for an EDLC,
9
Fig. 6. (A) Showing different regions of the Nyquist plot with the corresponding electrode-electrolyte phenomenon, and (B) different natures of the Lissajous plot.
the Rct represents the sum of the electrode resistance, electrolyte resis ∫ ∞
tance, and resistance between the current collector and electrode. In the 2 xZ˝ (x) − ωZ˝ (ω)
Z′ (ω) = R∞ + dx (5)
case of the Bode plot, the graphs give notable information on the phase π 0 x2 − ω2
shift, EDLC, change in resistance, and ion diffusion of the electrode ∫
(Fig. 6A) [99–103]. 2ω ∞
xZ′(x) − ωZ' (ω)
Z″ (ω) = dx (6)
EIS provides kinetic and mechanistic data i.e. electrochemical, π 0 x2 − ω2
chemical, and physical processes and their electrochemical stimulation Notably, Kramers–Kronig relationships are applicable at standard
to equivalent electrical circuits (resistances, capacitance, inductance, conditions only and helpful in the determination of the past frequency
etc.) of electrolyte systems. EIS methodology depends on the solicitation which is present in non-stationary artifacts. Fittings of Kramers–Kronig
of the small-amplitude stimulus and its response over a broad frequency relationships obeying impedance plots with a Voigt circuit at a partic
range. EIS measurement needs specials condition of small-amplitude ular time constant (τ ) are possible which results in the accurate esti
perturbation to ensure a linear relationship between input and output mation of the real electrochemical systems. If any system shows
signals. In an electrochemical system, a linear domain measurement can accuracy with these fittings and gives a stabilized electrical circuit it can
be done by using amplitude perturbation. The change in the phase of be said Kramers− Kronig transformation [107].
input and output signal can be explained by the Lissajous plot (Fig. 6B) Apart from this, the information regarding the time constant/relax
that provides important characteristics of impedance data at both lower ation time (τ ) is calculated using the Nyquist plot based on semicircle
and higher frequencies based on amplitude and phase shift. The Lissa region. The peak frequency/relaxation frequency (fr) that has the
jous plot gives a typical oval/eclipse shape in ideal conditions, but highest value of the semicircle arc is related with τ (as fr = 1 / 2πτ ), but
distortion is observed when applied amplitude perturbation is reduced an idea semicircle plot follows relation 2πτ fr ≫ 1 which represents
in the frequency field which results in degenerated diagonal and circular different processes with different τ such as τ x, τ y which fulfill the con
plots at phase shift between 0◦ or 90◦ angle (Fig. 6B). The symmetry of dition of τ x ≫ τ y [108,109]. It should be strictly considered that the
the Lissajous plot of electrochemical system indicate the linearity re Nyquist plot is plotted by taking the same ranges of both the x and y axis
strictions (distorted plot for a non-linear system) [103] and time- for better data interpretation. The unsymmetrical axis of the plot results
invariance (immobile plot for a stable system) [104]. The shift of the in major disadvantages such as (i) the non-distinct representation of
signal usually occurs at lower frequency regions that suggest the system plots at high-frequency regions and (ii) the lake of direct impedance
is in a stationary state [105]. EIS can shorten the frequency-dependent matching [103]. Another important characteristic of EIS can be obtained
complex electrochemical process into individual processes with partic by applying a Bode plot that results from the frequency-dependent
ular time constants. Notably, slow processes can be analyzed at very low impedance modulus (|Z|) and phase angles (ϕ) for the systems. The
frequencies and fast processes, ionic motion, etc. of electrolyte materials two curves in the Bode plot are plotted as log |Z| versus f(log f), and the
are observed at high-frequency regions [106]. Since EIS is a transfer − phase angle versus f(log f), which are simultaneously providing the
function measurement, it requires four different standards such as values of |Z| and ϕ at particular frequencies. This analysis provides the
linearity, causality, stability and finiteness [107]. The measured accurate assumption for wide-scale data response as well as scattered
response of perturbation will provide a calculated transfer function data values that arise from both real and imaginary parts of the mea
termed as electrochemical impedance (Z) of the system and expressed as surements. Since the Bode plot illustrates the change in impedance with
Eq. (4): changing the frequency, the phase change with frequency illustrates
different properties. The ohmic resistance was concluded when the
Z(ω) = |V(ω)/I(ω)|(cos ϕ (ω) + jsin ϕ (ω) ) = Z′ − i Z″ (4)
phase angle tends towards the 0◦ at higher frequencies but for a polar
Here V and I denote the variables, ω is the angular frequency (ω = izable electrode system, it has a value of 90◦ at the same frequency.
2πf), and ϕ represents the phase angle. The electrochemical impedance However, the CPE shows a phase angle value < 90◦ at a higher frequency
is a complex entity that is a combined result of its real (Z′) part which [105].
associates with the frequency-dependent resistance of the system and EIS allows its transformations to a particular electrical circuit or a
imaginary part (− Z″) which associates with the frequency-dependent combination of electrical circuits relaying the inductance, capacitance,
reactance of the system. Further, the validation of EIS data can be resistance and faradic impedance. In the case of thin film electrolytes,
assessed by applying Kramers–Kronig relationships, which allow the the electrode-electrolyte interface is acting as an electrical double layer
detection of various errors in impedance measurements and enable the and dielectrics take place. Hence it is needful to analyze the interface
calculations of the real (Z') and imaginary (Z") part of the impedance by properties during the circuit transformation [110]. It is considerable
the following equations (Eqs. (5) & (6)): that there is not a single circuit model available for data transformation
from Nyquist/Bode plot to an electrical circuit, but simulation is possible
10
Fig. 7. (A–C): Ideal mathematical relations, accordingly approved electrical circuits, Nyquist and Bode plots for simple systems.
for some ideal circuits when they are mathematically identical. Bou containing a capacitor, resistor, and inductor. However, the combina
kamp [111] proposed several notations named “CDC” for different tion of the electrical circuit could be varying from battery to battery
electrical circuit transformations and the notation for series connections [112]. Mei et al. interpreted the impedance of organic electrolytes in
is put in a general way e.g. ‘RC’ but circuits present in parallel con LiNi0.6Co0.2Mn0.2O2 and MoS2 electrodes interface. They revealed that
nections denote in parenthesis e.g. ‘(RC)’ etc. There are several ideal the semicircle diameter at high frequency has been equal to the resis
mathematically approved electrical circuits are available for Nyquist tance of bulk electrolytes. However, the semicircle diameter at lower
and Bode plots which are provided in Fig. 7A–C for simple systems and frequencies decreases by increasing the thickness of the electrolyte
Fig. 8A–D for complex systems. [102].
Impedance allows for rapid analysis of the electrochemical devices In another report, Zhang et al. tested the efficiency of Li+-battery in
such as a battery (Li+/Na+-and solid electrolyte battery), capacitor, fuel PIL-based SPE through the EIS measurements in the frequency range of
cell, etc. through the charge discharge method to examine the degra 7.0 × 106–0.1 Hz. They found that the PIL has several crystalline regions
dation, lifetime, rate capacity, and temperature dependence for quality which reduce the ionic conductivity (σ) which was calculated using the
assessment. Through this, the kinetics, reaction mechanism, charge formula (σ = L / RS), where L, R, and S are the thickness of the elec
transfer property, ionic-electronic conducting interphase, and SEI film trolyte, the resistance of the electrolyte, and effective surface area of
on the electroactive materials have been analyzed. Frequently, ECM is electrode respectively. To improve this, they did the co-polymerization
applied to interpret the EIS. In this analysis, the data has been inter of PIL with PEG which decrease the crystallinity. In this PIL-based SPE,
preted through the fitting of EIS data by constructing an electrical circuit the specific capacity of the LiFePO4 (LFP) in LFP|P(IL-PEGDA) SPE|Li
11
Fig. 8. (A–D): Ideal mathematical relations, accordingly approved electrical circuits, Nyquist and Bode plots for complex systems.
battery was calculated of 140 mA h g− 1 at 0.2C at 25 ◦ C. It has been DMC-FEC electrolyte for Li-S batteries. Such electrolytes inhibited the
examined that these SPE efficiently reduce the dendrite growth of Li in formation of dendritic Li which improves the cyclic efficiency. Along
charge-discharge cycling which improves the performance of the bat with they also stabilized the sulfur cathode, as a result, the overall ef
tery. Moreover, the high cycling stability up to 70 cycles demonstrated ficiency of the battery may significantly improve where it is stable at
~100 % Coulombic efficiency [113]. Xu et al. proposed a LiODFB/EC- cycle for more than 2000H. Moreover, the reversible capacity of the Li-S
12
Fig. 9. Representations of the (A) loss of permittivity over the frequency region, (B) Nyquist plot using real and imaginary parts of permittivity, (C) generation of tan
δ and its relation with ESR and capacitive reactance, (D) loss tangent relation over the frequency region, and (E) scaling plot of the loss tangent at different tem
peratures shows a collapsed single master curve.
battery was calculated as 1400 mA h g− 1, a capacity of 1100 mA h g− 1 at results in the distribution of relaxation time, modifications include in
10C, and excellent Coulombic efficiency of 98.8 %. Additionally, the Cole and Cole's semiempirical equation (Fig. 9B) and led to the new
battery was stable up to 60 ◦ C without self-discharging. Therefore, such equation, Eq. (10) [120]:
electrolytes potentially be utilized for the making of high-performance /( ( )α )β
Li-S batteries [114]. The EC-DMC-based electrolyte suffers due to its Ɛ' = Ɛ∞ + Ɛo − Ɛ∞ 1 + ω2 τ 2 (10)
flammable nature which adversely reduces the battery life and can cause
an explosion. To resolve this, TTFP has been added which turns them where α and β are in the range of 0 and 1 and there is no physical
into a flame-inhibiting electrolyte. The non-flammability remarkably meaning assigned for these parameters. This modified equation results
improves the performance of the sulfur-based cathode. However, it also in a broader peak with a smaller loss value that shows asymmetrical
improved the capacity which was calculated at >800 mA h g− 1 (at 10C), features. The dielectric constant and dielectric loss are frequencies and
and also prevent the reduction of capacity beyond the 750 cycles for the temperatures reliant [121]. With the rising temperature, chain mobility
Li-S battery [115]. begins to increase and results in the shortening of the relaxation time.
On the other hand, by changing the frequency, the polymeric chain's
dipole polarization can bring it into line and increase in dielectric con
3.4. Matrix relaxation and loss tangent
stant. However, this arrangement of chain matrix with the applied
oscillating field gradually failed with increasing frequency and the op
The foremost model of electrolyte matrix relaxation behavior was
timum dielectric constant rate occurs at a higher frequency which cor
derived from the Debye relaxation model [116]. This model illustrates
responds to the maximum dielectric loss. Similarly, at higher
the real and imaginary (Ɛ' and Ɛ") parts of the dielectric constant and
temperatures, a large dielectric loss occurs at higher frequencies
relates the dielectric properties with the matrix relaxation time (Eqs.
compared to those of lower temperatures [122]. It can be concluded that
(7)–(9)) [117]:
dielectric loss shifted towards the higher frequencies with increasing
/
Ɛ' = Ɛ ∞ + Ɛ o − Ɛ ∞ 1 + ω 2 τ 2 (7) temperature.
The dielectric loss tangent (tan δ) [123] is related to the dielectric
/ relaxation process such as transport behavior, polarization effect and
Ɛ˝ = (Ɛo − Ɛ∞ ) ωτ 1 + ω2 τ 2 (8)
matrix relaxation phenomenon, which is helpful for different kinds of
ionic transport at different temperatures. This is also known as the
(Ɛ' − Ɛs + Ɛ∞ /2) + Ɛ″2 = (Ɛs − Ɛ∞ /2) (9)
2 2
dissipation factor and it is defined as the ratio of energy loss to energy
The plot between Ɛ' and Ɛ" give Nyquist or Cole-Cole plot [118] stored in a periodic field. Tan δ can be calculated using the following
which shows the relationship between dielectric constant and dielectric relation (Eq. (11)) [124]:
loss (Fig. 9A). It shows that there is no loss of dielectric constant at the
tan δ = 1/2πfRC (11)
infinite frequency (Ɛ∞), and static dielectric constant (Ɛs); the highest
loss occurs at the center of the two dielectric values. The greater dif
where δ is the dielectric loss angle, C is the capacitance, R is the resis
ference between the Ɛs and Ɛ∞, suggests the higher dielectric loss. This
tance and f is the frequency (Fig. 9C). Loss tangent is also related to the
model is very appropriate for polar small molecular liquids. However,
ratio of the imaginary part Ɛ" and the real part Ɛ ' (tan δ = Ɛ″ / Ɛ') [124]
the case of polymeric materials, which contribute both viscous and
and illustrates the change of the loss tangent against frequency. The loss
elastic characteristics properties require some changes to this model.
tangent plot shows that loss increases on increasing frequency and at a
Since the Debye relaxation model involved only one specific relaxation
given frequency (Fig. 9D), it reached maximum loss and again decreases
time. For the polymeric systems, this is determined by the mobility of
at high frequencies, due to the enhancement in matrix flexibility. The
dipoles, which depends upon the local environments [119]. These
13
Fig. 10. Dielectric properties of electrolyte and its relation with ESD.
dominated ohmic component is associated with two frequencies region. represents that on increasing flexibility of the polymer matrix at the
One is a low-frequency region observed at the left side of the peak and higher temperature, the ionic transport mechanism is also get affected
the other maxima is observed at a specific frequency (relaxation fre by the change in matrix properties. To understand the dependence of
quency) region, where the maximum power transfer takes place [125]. relaxation time on the applied electric field and temperature, the scaling
In this situation, the frequency of the applied electric field resonates of the tan δ value can be done by taking tan δ/tan δmax and f/fmax for loss
with the frequency of molecule rotation. This is the high-frequency re tangent and frequency axis respectively [127]. The frequency and
gion characterized by dominated capacitive behavior. The component temperature reliance of loss tangent explained by Kohlrauch Wil
that is in phase with the applied voltage causes loss at a particular angle liams–Watt's law, f (t) = exp(− t / τ )β, where β denotes Kohlrauch
δ termed the loss angle. The highest value of tan δ is obtained at a exponent (β = 1.44/FWHM) [128]. The scaling plot of the loss tangent at
particular frequency range that satisfies the equation ωτ = 1, where ω different temperatures shows a collapsed single master curve which
represents the applied field's angular frequency and τ denotes Debye indicates the matrix relaxation process is time- temperature independent
relaxation time [126]. with common β values for different temperatures (Fig. 9E).
An increase in dielectric relaxation frequency and a higher value of
tan δ arise due to an increase in matrix flexibility, where the matrix
shows its highest ionic conductivity. At the low-frequency region, a 3.5. Dielectric properties
lower value of tan δ and relaxation frequency occurs due to the accu
mulation of ions at the electrode surface, which is responsible for a The dielectric properties (dielectric constant, dielectric loss and
particular ionic transport mechanism and it observed that on the dielectric modulus) provide useful information about the electrical
increasing temperature the value of relaxation frequency increases. This properties and behavior of ions, atoms, and molecules, within the ma
trix. These electrolytes have been studied as a function of temperature
Fig. 11. Showing (A–B) frequency dependence of real and imaginary part of the dielectric permittivity, (C–D) frequency dependence of real and imaginary part of the
dielectric modulus, (E) showing polarization under applied electrical field which is responsible for the retardation and relaxation process and intercorrelation be
tween dielectric permittivity, dielectric modulus and tan δ.
14
and frequency. The structure of compounds, grain boundary, charge about charge transport and dielectric polarization in polymer electro
storage capabilities of dielectric material and transport properties were lytes. However, it has been rarely exploited to study the dielectric
explained by dielectric spectroscopic analysis. Since dielectric materials behavior of insulating polymers. The study of electric modulus also
are very poor electrical conductors under an applied electrical field, supplies a better understanding of the dielectric behavior of polymer
these materials cannot flow current in them due to the absence of charge electrolyte material and examines the conductivity relaxation at low
carriers. The dielectric constant decreased rapidly as frequency frequency by suppressing the electrode polarization effect. So, with the
increased due to a decrease in the space charge polarization effect. At a help of this, the dielectric data is converted into the modulus data and it
given frequency, it remained nearly constant but increased with can be related to permittivity by the following relation. The electric
increasing temperature. However, it was high at low frequencies due to modulus is represented as the reciprocal of complex dielectric permit
the accumulation of space charge at the grain boundaries, which creates tivity (M = 1 / Ɛ). The common role of electric modulus and complex
a potential barrier. The charge accumulation at the grain boundary, permittivity are similar to those of the elastic modulus and complex
resulting in higher values of the real part of permittivity. The dominance elastic compliance in the viscoelasticity of solids, typically noticeable in
of the grain boundaries effect can explain the dielectric dispersion more organic polymers. For dielectrics, which show a loss, the electric
moderately than the grains [129]. This is accredited to Maxwell–Wagner modulus is a real number. If the dielectrics show loss its complex
[130] type of interfacial polarization in harmony with Koop's phenom permittivity (Ɛ* = Ɛ' − iƐ") and the modulus becomes complex (M* =
enological theory. The use of dielectric material and its effect on ESD is M' + jM″) [137]. It is introduced by Macedo to study the space charge
shown in Fig. 10. polarization phenomenon. Nowadays electric modulus is widely used to
analyze ionic conductivities. The relationship of the different imaginary
3.5.1. Dielectric permittivity and real parts of modulus with the imaginary and real part of permit
It is important to study the concept of permittivity to understand the tivity can be written as (Eqs. (16) & (17)):
closely related properties of capacitance. Capacitance is defined as the /( )
ability of a system to collect and store electrical charge [131,132]. So, M' = Ɛ' Ɛ'2 + Ɛ″2 (16)
the permeability related to the dielectric constant, which can be repre /( )
sented as Eq. (12) [133]: M″ = Ɛ″ Ɛ'2 + Ɛ″2 (17)
k = Ɛr = Ɛm /Ɛo (12) A distorted semicircle designates the occurrence of heterogeneous/

broad relaxation mechanisms. The presence of a regular single semi
where k is the dielectric constant, Ɛr is relative permittivity, Ɛm is the circle curve indicates that the electrolyte system is experiencing a single
permittivity of material and Ɛo represents the permittivity of vacuum. In relaxation process. Its complex permittivity becomes a function of fre
the presence of an electric field, the behavior of molecule/polymeric quency (ω) and satisfies the following Debye formula (Eq. (18)):
material is characterized by permittivity. The energy storage application /
of electrolyte material was determined by two important properties i.e. Ɛ* (ω) = Ɛ' (ω) − iƐ˝ (ω) = Ɛ∞ + Ɛs − Ɛ∞ 1 + (iωτ )β (18)
dielectric storage and dielectric loss. Dielectric analyses of electrolytes
are necessary to reach a better intuition into ion dynamics and are When the complex permittivity satisfies the Cole-Cole formula, M*
examined in terms of the real (Ɛ′) and imaginary (Ɛ″) parts of complex can be written as (Eq. (19)):
permittivity (Ɛ *) [134]. This parameter defines the polarizing aptitude / / / / / /
M* = 1 Ɛ∞ + Ɛs − Ɛ∞ 1 + (iωτ )β = 1 Ɛ∞ − 1 Ɛ∞ − 1 Ɛs 1 + (iωτ ' M )β
of charge carriers under the applied external electric field as a function
of frequency. This can be represented as (Eqs. (13)–(15)) [135]: (19)
* Here β = 1.0 indicates that the material exhibits a single relaxation
Ɛ =Ɛ− jƐ′ ˝
(13)
Debye process, while, β > 1.0 indicates that the multiple relaxation
/( ) process [138]. The highest capacitance is associated with the smallest
Ɛ′ = − Z″ Z2 + Z″2 (14)
semi-circle diameter. In the high-frequency region, the electric modulus
/( ) versus frequency plot of the real and imaginary parts and dispersion is
Ɛ″ = Z′ Z′2 + Z″2 (15)
visible. The ideal modulus graph (Fig. 11C) shows that M′ → 0 at low
frequency due to the association of a large amount of the capacitance
where Ɛ′ and Ɛ″ denote the dielectric permittivity of real and imaginary
arises from the electrode polarization effect. The increase in M′ in the
parts and j is imaginary unity (j2 = − 1). The higher value of Ɛ′ and Ɛ"
high-frequency window is linked to dispersion in the electrolyte-less
shows the formation of space charge polarization at the electrode-
restoring force for mobile charge carriers on field application. The
electrolyte interface. This is also studied as the electrode polarization
value of the M′ and M″ is independent of frequency, indicating that the
effect which is observed in the short-frequency region (Fig. 11A–B).
electric field does not affect dipole orientation. The lower value in the
Dielectric loss Ɛ″ is related to the conductivity of the electrolyte and
modulus spectra (M″) indicates ion transport. The nature of the M″
appears as a result of conductivity loss [136]. The electrode polarization
spectrum (Fig. 11D) shows the modulus relaxation at the higher fre
effect of the electrolyte matrix is suppressed at higher frequencies due to
quency region, which is not an experimental frequency range. A low
a decrease in the fast-periodic reversal of the electric field, and it be
relaxation time indicates rapid cation migration from one coordinating
comes saturated as the frequency approaches infinity. The relaxation
site to another, increasing the ionic conductivity of the polymer matrix.
bands for the electrolyte matrix are discovered to shift towards higher
Complete set of dielectric permittivity and dielectric modulus is origi
frequencies as the sample film's temperature rises due to a change in the
nated from by applying external electrical field on ionic conducting
matrix phase. The study of temperature-dependent dielectric permit
system. This applied electric field generate both retardation and relax
tivity represents that there is an increase in capacitance, electrode po
ation on electrolyte matrix and made it be understandable to the origi
larization and loss of energy by displacement of charge with the increase
nation of loss tangent (Fig. 11E).
in temperature.
3.5.2. Dielectric modulus 3.6. Ionic mobility

The electric modulus was first proposed for the study of electrical
relaxation phenomena in ionic conductors that are made from hard The conductivity obtained from the electrolyte system is due to ionic
glassy material. Electric modulus has also offered valuable information transport across the matrix. There are several factors present which are
act as resistance for the ionic transport such as counterions, ionic size,
15
Table 2 circumstances, the collision frequency of mobile species presents in the

Showing diffusivity [151] and mobility [152,153] of some cations and anions in solution going to increase, which is mainly responsible for the increment
water at 25 ◦ C. of α and η values. Also, the new interactions between mobile species and
Cations μ × 10− 8
(m2 D × 10− 9 Anions μ × 10− 8
(m2 D × 10− 9 separator/polymer chain arise new factors for α and η [144,145]. At the
s− 1
V− 1) (m2 s− 1) s− 1
V− 1 ) (m2 s− 1) separator/polymer surfaces, pore walls and pore sites cause new com
H+ 36.26 9.310 F− 5.74 1.460 ponents for all microviscosity (α, η, and β). Distinct determination of
Li+ 4.00 1.030 Cl− 7.91 2.030 different microviscosity recommends the perfect directions and paths for
Na+ 5.19 1.330 Br− 8.09 2.010 ionic transport and suggests that the reduction in microviscosity can
K+ 7.16 1.960 I− 7.96 2.045
improve the device's performance. The porosity, porous sites, polar
Cs+ 8.00 2.030 OH− 20.53 5.270
Rb+ 7.92 2.070 CO2− 14.38 0.955 groups and swelling properties of the separator/polymer act as physical
3
Mg2+ 1.10 0.705 NO−3 7.41 1.900 barriers for mobile species and are responsible for larger microviscosity
Ca2+ 12.34 0.793 HCO−3 4.61 1.180 compare to the free electrolyte solution [60]. These factors indicate the
NH+ 4 7.60 1.96 SO2−4 8.29 1.070 need for an ideal separator/polymer in terms of their physical structure
i.e. pore size, path tortuosity, and porosity for significant ionic transport
interactive forces (Van der Waals forces between neutral species and inside the porous paths. Thus, it can able to reduce its interference with
coulombic forces between charged species and polar groups), solvents ionic movement and resistance. It is much better to design a separator/
(polar group or sites), high matrix viscosity, etc., that obstacles the ionic polymer chain that can increase the ionic mobility itself.
movement inside the electrolyte materials. The ionic mobility of some Eq. (20) describes that the ionic mobility of electrolyte material is
cations and anions is shown in Table 2. The role of the different effects of directly proportional to its conductivity. The conductivity of the elec
parameters can be more understandable by the Stoke-Einstein relation trolyte is also affected by the number of charge carriers (charge carrier
and Stoke's law [139,140]. The aptitude of the ionic transport across the density) present in the electrolyte matrix. From a charge carrier ion's
matrix/medium is defined as the ionic mobility (μ) of the system. Ionic point of view, salt dissolution or its degree of dissolution plays a sig
mobilities play an important role in ESD as it determines the power nificant role in the scene of the availability of free ions. For better salt
performance, density and stiffness [141,142]. Electrolyte systems with dissolution solvent properties i.e. dielectric constant (Ɛ) and bulk vis
high ionic mobilities enable the path to fabricate high power and high cosity (ηb) play an imperative role in salt dissolution. Coulomb's law
capacity batteries. High ionic mobility allows ions to have wide, deep, suggests that the higher dielectric constant of solvents can make more
homogenous and strong electrode penetration, which results in more separation between cations and anions [146]. Solvent with a high
active sites for charge transfer reaction and a large capacitive effect. The dielectric constant can increase the salt dissolution and avail a greater
ionic mobility also related to the ionic conductivity (σ) of electrolyte number of charge carriers in the electrolyte matrix. On the other hand,
which can calculated by the relation (Eq. (20)). the viscosity (ηb) of solvent shows reciprocal effects on ionic mobility
which can easily be understandable from the Stokes-Einstein equation.
σ = nqμ (20) By optimizing these two parameters (Ɛ and ηb) of solvent by applying a
mixture of polar and non-polar solvents, the mobilities of ions can be
where, q is ionic charge and n is charge carrier density. The role of ionic increased. A higher mole fraction of polar solvent in the solvent mixture
mobility on ionic conductivity can be more understandable by taking the allows higher Ɛ and ηb and vice-versa that are responsible for the change
example of the low conductivity of solid electrolytes compare to the in the values of degree of dissociation (x), α, and η [143]. The parameter
liquid electrolyte systems due to the higher ionic mobility of the liquid x and η shows analogs relations but α shows an inverse relationship with
phase compared to the solid phase [142]. Ɛ and ηb.
The solvated size and solvation number of cations of the electrolyte is The interaction of mobile ions with solid phase separator/polymer
depends upon the nature of the solvent and the concentration of the salt. chains causes both physical and chemical obstacles. The physical ob
The interactive forces involved in the system also affect the micro stacles (porosity, path width, path tortuosity, crystalline size, gelation
viscosity (microviscosity related to the coulombic force α, the Van der properties, cross-section shape of path) involve the morphological
Waals force (η) and the path β) of the movable species. The lower parameter that affects the ionic collision and transport behavior. On the
microviscosity of the electrolyte matrix is providing higher mobility. other hand, chemical obstacles (functional ions, polar groups and Lewis
The polar acidic and basic sites present in the electrolyte matrix can acidic/basic groups) involve the strength of attractive/repulsive inter
discriminatorily interact with cations and anions and reduce their mo action between ions and functional sites of separator/polymer chains
bilities, even then it is possible to control the ionic mobilities of an [147]. The porosity and pore size of the separator are depending upon
electrolyte by modifying the polar sites of the matrix and solvation the preparation method of the separator film and are responsible for the
structure of ions [143]. The aptitude of ionic mobility separately de paths for ionic transport through the membrane and path diameter. A
pends upon the interactions between the ion and the electrolyte con membrane with high porosity provides a larger pore diameter that al
stituents present close to the ions, separators and electrodes. Since lows the low collision of mobile ions with pore walls and low coulombic
efficient battery performance demands smooth and higher ionic trans interactions between opposite ions due to the presence of large path
port in side devices. Therefore, the influence of electrolyte constituents space, thus porosity and pore diameter increase ionic mobility of the
on ionic motion cannot be avoidable. It was observed that the separator/ system. The effect of porosity on microviscosity was also observed.
polymer chain present in the device has an excessive influence on the There is a low impact of porosity change reported on η, but α shows an
mobilities of ions. inverse relationship with porosity, and β shows an analog relationship
The ionic mobility also depends upon the diffusivity coefficient of with cations but an inverse relationship with anions accordingly by
ions while using separator/polymer membranes in ESD. The diffusion changing the porosity. A decrease in the porosity of the membrane re
coefficient of ions in separator/polymer and ion-separator/ion-polymer sults in a small pore diameter that is responsible for a new type of
interaction affects the ionic conditions and ionic migration inside the resistance factor i.e. path tortuosity. Path tortuosity is defined as
matrix. Moreover, it is specify the separator/polymer chain effects randomness or degree of curve in the ionic transport path, in other
depending on its chemical structure, morphology (pore size & porosity), words, it is the ratio of mean path distance of transport path and
and ion-separator/ion-polymer chain interaction [143]. Microviscosities membrane thickness. Higher path tortuosity allows more collision be
(α and η) can be increased when electrolytes are limited on the ion- tween ions and walls of the migration path due to an increase in wall
separator/ion-polymer chain due to the restricted ionic motion at the area, which generates more resistance on ionic transport and hence
pores of the separator/polymer in free electrolyte systems. In these shows an inverse effect with ionic mobility [148–150].
16
3.7. Ionic diffusivity
Ionic diffusivity is a measure of the ability of ions to move through a

medium, typically a liquid or solid electrolyte. Modern electrolyte
research is principally focused on ion-conducting polymer electrolytes
which are providing high resistance, ionic transference and diffusion
paths compare to liquid electrolytes [154]. In the solid electrolyte sys
tem, there is no diffusion motion is observed until there is any applied
electrical field is present and it is also observed that the diffusion process
under an applied electrical field is completely different from the self-
diffusion process. For solid electrolyte systems, cation-anion and salt
species all components are participating in the diffusion process [155].
Matrix diffusivity is defined as the ratio of the ionic flow rate to the
concentration gradient of the ion. Ionic conductivity and ionic diffu
sivity are related, as the ionic conductivity of a material is determined by
both the ionic diffusivity and the concentration of mobile ions in the
material. Usually, a material with high ionic diffusivity and high ionic
concentration will have high ionic conductivity. An increase in ionic
diffusivity will increase ionic conductivity, and conversely, a decrease in
ionic diffusivity will result in a decrease in ionic conductivity [59,156].
The diffusion property of electrolyte materials (both liquid and solid)
regulates some of the specific parameters of a cell such as charge-
discharge rate, cyclic stability and capacity. The diffusion process of
ions can be understood by Fick's law [157] and for an electrolyte matrix
diffusivity constant can be determined by using the Stoke-Einstein Fig. 12. Showing the inter correlation between ionic conductivity, ionic
equation (for liquid Di = kbT / 6πηRo and solid Di = a2Γ) [59]. Both mobility, diffusivity, drift velocity, and ionic transference number; and factors
experimental and theoretical e. g. molecular dynamics confirm that the affecting the particular parameters.
solvent diffusivity sways the ionic transport inside the mixture [158].
When the size of the ion and solvent molecule, the slipping boundary terms of the ionic transport mechanism and diffusion coefficients at each
conditions are applied in the study of different solvent systems (organic component. In SEI, ionic transport takes place through the pore, inter
solvents or IL solvents) [159–161]. In the electrolyte solution Stokes stitial spaces and vacancies. The diffusion coefficient and diffusion
radii depend upon the salt concentration which was affected by the mechanism in the SEI layer are highly susceptive to the temperature and
solvation and counterions, which results in ionic conductivity and applied electrical field. It is generally observed that with increasing
diffusivity [162]. The diffusion process is directed by the random ionic temperature ionic diffusivity increases and vice-versa. It is observed that
jumps. Its kinetics is temperature dependent and follows an Arrhenius- both knock-off and vacancy diffusion is observed in high-temperature
type relationship (rate ≈ eT−b ΔG/k) with it [163]. Although it was conditions and show a linear relationship with it. This temperature-
observed that the temperature dependence of diffusivity is less for liquid dependence behavior of diffusivity also follows the Arrhenius law (D
electrolytes compare to solid electrolytes. The determination of diffu = Do e− Ea/RT), where Do is the pre-exponential factor [168]. On the
sivity in liquid electrolytes was not easy due to an inadequate under other hand, the diffusivity increases exponentially with increasing the
standing of the liquid electrolyte structure but can be easily determined applied electrical field showing the effect of changing the applied
for solid electrolyte systems [157,164]. electrical field [169].
The relationship of ionic diffusivity with ionic conductivity can Various dynamic properties of both liquid and solid electrolytes
describe the ionic motion inside the matrix. The resistance inside the depend upon the inherent diffusivity coefficients of the cation (DC),
battery arises from the electrode-electrolyte interface and by electrolyte anion (DA) ion pairs (DP) and solvent (Ds). These parameters of an
matrix itself. Transport of charge carriers present inside electrolyte de inherent ionic species in an electrolyte system can be theoretically
pends upon externally applied electrical field and concentration. The determined by applying a few theoretical models fashioned with ionic
relationship between ionic conductivity and diffusivity can be achieved conductivity [170]. Different diffusivity parameters of the electrolyte
by using the relation (Eq. (21)) [61]: system and different microviscosity (η, α, and βc) can be determined
/
Di = σ kb T q2 N (21) [171], which indicate the path structure of the electrolyte matrix. In
solid electrolyte systems, the matrix porosity affects the different
This relationship confirms that the ionic conductivity is directly diffusivity coefficients in a proportionality manner, with increasing
proportional to the ionic diffusivity [165]. The measurement of ionic porosity a monotonous increment in DC and D was observed. It is also
conductivity is easy to measure by using CV, GITT, PITT and EIS from reported that the temperature shows a reciprocal effect on DC, DA, DP
using ionic conductivity, diffusivity value can be computed. Using EIS and Ds [60]. The ionic diffusivity of some cations and anions is shown in
dielectric study diffusivity can be calculated by using the relation (Eq. Table 2. The inter correlation between ionic conductivity, ionic
(22)) [61]: mobility, diffusivity, drift velocity, and ionic transference number; and
/ factors affecting the particular parameters is shown in Fig. 12.
D = 2f max l2 32 (tan δmax )3 (22)
The interface between two grains known as grain boundary also

plays an important role in diffusivity parameters and depends upon the 3.8. Drift ionic velocity
bonding state, composition, crystallographic orientation and lattice di
mensions. Grain boundary generates small resistance and a large num The drift ionic velocity (Vd) of the electrode system defines the ve
ber of defects at the electrode surface which results in higher diffusion at locity of ionic transport from one electrode to another electrode under
grain boundary compare to within grain [59,166,167]. Except for grain an applied electrical field. The conductivity in an electrolyte system
boundary, another focused on the SEI, which has more attention in arises from the transport of the ions present inside the matrix from one
electrode to another. There are several random paths present for ion
17
transport in both liquid and solid electrolyte systems [55]. These paths Overall, the ionic drift velocity and its relationship with ionic conduc
are not present in well-organized mannaric i.e. straight or linear but they tivity are important considerations in the design and optimization of
are present in zig-zag or random in nature. The transport of ions through materials for various electrolyte materials in electrochemical devices,
these paths is showing different times due to different path lengths, including batteries, capacitors, and electrolysis cells.
structures, pore sizes, etc. In other words, all the physical and chemical Drift ionic velocity is a critical parameter that influences the trans
obstacles that derive the ionic mobilities are responsible for the Tyndall port of ions through an electrolyte solution in batteries. The speed at
motion of ionic species under the applied electrical field [172]. It is more which ions move through the electrolyte is directly related to the overall
necessary to understand that the ionic drift velocity is a completely performance of the ESD. The drift ionic velocity affects the conductivity
different entity from the ionic mobility since it is concerned with it. For of the electrolyte, which determines how efficiently ions can move
better understanding, it can be said that ionic mobility shows the ability through the solution. In general, a higher drift ionic velocity leads to a
of ionic movement inside the electrolyte matrix but drift ionic velocity more conductive electrolyte and faster ion transport [177]. This results
shows how faster of ionic transport takes place through the medium. in improved device performance, including higher current and power
However, both the ionic mobility and drift ionic velocity designate the densities, faster charging and discharging rates, and improved energy
drive of both anions and cations. Drift ionic velocity is a measure of the efficiency. However, there are also potential drawbacks to high drift
average speed of ions moving over the medium under an applied elec ionic velocity. As the ions move more rapidly through the electrolyte,
trical field, which can be expressed as Eq. (23) [173,174]: they can create additional resistance and heating within the device
[178]. This can reduce the battery's lifespan and even pose safety risks.
V d = μE (23)
The choice of the electrolyte solution can significantly impact the drift
The current density of a cell is directly related to the ionic transport ionic velocity and thus the overall performance of the battery. For
inside the electrolyte material under the applied electrical field [175]. example, organic solvents have higher drift ionic velocities but are less
The ions present inside the electrolyte materials feel an external force stable and more prone to degradation than inorganic electrolytes. In
that enhances the speed of mobile ions under an applied electrical field. summary, the drift ionic velocity plays a vital role in determining the
This acceleration would observe until the ion reaches the respective performance of electrolytes in batteries.
electrode. It is also considered that the large ion density, solvent mole
cules, additive molecules, polymer chains, separator film, etc. also 3.9. Ionic transference number
present in electrolyte systems that will collide with each other and try to
stop the ionic migration and slow down the acceleration. This resistive Ionic transference number (tion) can affect the output of ESD in terms
phenomenon results in different speeds and directions of ions at of the efficiency, stability, and selectivity of the electrochemical re
different times. Thus, the external electrical field made a random ionic actions, particularly those that use liquid or polymer electrolytes. It is a
movement towards the oppositely charged electrode by applying elec measure of the ability of an ion to carry current through the electrolyte
trostatic force (F) with a particular collision frequency (τ ). So the rela and designates the amount of ionic/electronic contribution to the total
tion between applied frequency and drift velocity can be also defined as electrolyte conductivity. In a typical rechargeable battery, such as a Li+/
Eq. (24) [176]: Na+ battery, the electrolyte consists of Li/Na salts dissolved in an
V d = F τ /m (24) aqueous/organic solvent. A higher ionic transference number of the
electrolyte results in higher power density and efficiency of the ESD. It
Here m represents the mass of ionic species, and Eq. (5) confirms that can be defined through Eq. (26) [179]:
the applied electrical field is directly proportional to the drift ionic ve
locity. If the τ /m is constant for the any of electrolyte systems, the drift tion = 1 − te (26)
velocity at that time represents the ionic mobility of the electrolyte Here, te is the electronic transference number. Eq. (7) shows that the
matrix. Applied current from different positive and negative electrodes sum of the transference numbers of all charge carriers is always equal to
attracts ions with opposite charges, the migration of oppositely charged 1 which is the total conductivity (It) of the electrolyte. The extant of tion
ions in opposite directions may form a diffusion layer in the electrolyte and te can be determined by using the relation (Eqs. (27), (28)) [179]:
matrix which feels electric flux due to ionic migration. In this situation,
the current density of the electrolyte system is directly proportional to tion = Iion /It (27)
the drift velocity of ionic species (J = CVdzF, here J = current density, C
= total ionic concentration, z = charge on ionic species and F = Faraday te = Ie /It (28)
constant). The value of drift velocity is also temperature reliant and Iion and Ie can easily determine by using Wagner's DC polarization
obeys the Arrhenius-type relationship (Vd = Vdoe− Ea/KT). At a particular method [179]. Ionic conductivity is a measure of how easily ions can
electrical field, drift ionic velocity is directly proportional to the ionic move through a solution under the influence of an electric field. It is
mobility and hence the relationship between of logVd – 1 / T and logμ – related to the ionic transference number by the Nernst-Einstein equa
1 / T are similar with the same amount of activation energies [63]. These tion, Eq. (29):
factors and the relationship of drift velocity with ionic mobility confirm ∑( )
that the drift ionic velocity of the electrolyte system is an important σ=F z2 c μ (29)
parameter that affects the conductivity of electrolyte material. It is
related to the ionic conductivity of a material, which is a measure of how where σ is the ionic conductivity, F is Faraday's constant, z is the charge
well an electrolyte conducts electricity. The relationship between ionic on the ion, c is the concentration of the ion, and μ is the ionic mobility.
drift velocity and ionic conductivity can be described by the following More specifically the relationship between the ionic conductivity of a
Eq. (25) [63]: particular ion and its transference number can be written as Eq. (30)
[59]:
σ = z Vd N (25) /
σ ion = qion cion tion Kb T (30)
This equation shows that the ionic conductivity is directly propor
tional to the ionic charge (z) and the ionic drift velocity, and inversely Additionally, the ionic transference number affects the rate and ki
proportional to the number density (N) of ions. On the other hand, the netics of the electrochemical reactions at the electrodes [180]. For
presence of impurities, defects, or other species that can interfere with example, in a Li+/Na+ battery, the Li+/Na+ must shuttle between the
the movement of ions can decrease the drift velocity and conductivity. two electrodes during charge and discharge cycles. If the transference
number of the ions is low, the rate of ion transport between the
18
electrodes may be limited, leading to slower charge/discharge rates and reduce conductivity. Some electrolytes, such as acids and bases, can be
reduced power density. Furthermore, If one ion species has a signifi corrosive to materials they come into contact with due to their ability to
cantly lower transference number than the others, it may preferentially react with certain substances. These factors can have a significant
accumulate at one of the electrodes and cause dendrite formation [181], impact on the characteristics of electrolytes and their ability to conduct
which can short-circuit the battery and lead to thermal runaway and electricity. It can also impact the performance of devices that rely on
even explosion which concern the safety of the battery. them, such as batteries, capacitors, and fuel cells. A brief discussion of
In a two-electrode electrochemical cell, the ionic transference num factors that affect electrolyte performance is provided below:
ber of the electrolyte determines the fraction of the total current that
flows through each electrode. If one ion species has a significantly lower 4.1. Nature of solvent
transference number than the others, it may preferentially accumulate at
one of the electrodes [182] and cause concentration polarization, which Along with electrode material and ionic salts, inorganic and organic
can reduce the cell performance and limit the current density. Similarly, salts, the nature of the solvent used for the electrolyte preparation plays
in a three-electrode electrochemical cell, the ionic transference number a crucial role in the successful and long-lasting operation of the charge
of the supporting electrolyte affects the selectivity and yield of the storage devices such as batteries. Solvents should have the ability to
electrode reactions [183]. For example, if the transference number of efficiently dissolve the ionic salts, and a higher boiling point to reduce
the cation is much higher than that of the anion, the cation may domi the vapour pressure, thereby mitigating flammability issue. A higher
nate the current and react preferentially at the working electrode, while dielectric constant keeps the cations and anions of the salt apart, pre
the anion may remain largely unreacted and accumulate at the counter venting the formation of ion pairs. Low viscosity prevents the restriction
electrode, leading to side reactions and reduced efficiency. Furthermore, of ionic movement towards the respective electrode, while a low melting
the ionic transference number affects the transport properties of the point prevents solvent solidification at operational temperatures.
electrolyte, such as ionic conductivity, mobility, and diffusivity [64], Additionally, the solvent should be readily available, cost-effective, and
which in turn influence the rate and kinetics of the electrochemical re environmentally benign. Furthermore, an ideal solvent should exhibit
actions. For example, if the transference number of the ion species that chemical stability, maintaining its molecular nature consistently and
participate in the rate-limiting step is low, the reaction rate may be remaining electrochemically stable. The solvent should prevent to
slower due to the lower mobility and diffusivity of that ion. Therefore, oxidize and reduce within the operating voltage range of the device
optimizing the ionic transference number of the electrolyte is important [184]. The nature of solvents significantly affects various parameters
for achieving high-performance batteries with high efficiency, power discussed below, and the choice of solvent leaves a profound impact on
density, cycle life, safety and electrochemical cells with high efficiency, the electrolyte and, consequently, device performance.
selectivity, and stability. This can be done by selecting appropriate
electrolyte compositions, concentrations and additives, optimizing the 4.1.1. Solubility
electrode/electrolyte interface, developing new electrolytes with high For the successful formulation of electrolytes of considerable salt
transference numbers and good stability as well as optimizing the strength, by dissolving salts into the solvent, the solubility of salt plays a
electrode and cell designs. pronounced impact. Most of the salts used for formulate electrolytes are
consist of acidic/cationic and basic/anionic parts that are attracted to
4. Factors affecting electrolyte characteristics each other by strong electrostatic forces. In an ionic lattice of salt, each
anion is surrounded by several cations and vice-versa. Salt solubility is a
The electrolytes can be affected by a variety of factors, such as the measure of the amount of salt that can be dissolved in a given amount of
salt concentration in a solution, solvent, pH, salt effect, structure, solvent at a constant temperature, which largely depends on the nature
electrode-electrolyte interphase and compatibility. Usually, the higher of the solvent, whether it's polar or nonpolar. The polarity of solvent has
salt concentrations in electrolytes typically result in higher conductivity. a pronounced impact on salt solubility. The rule of thumb ‘like dissolve
However, if the concentration becomes too high, the ions can become like’ [185] stated that polar solutes have better solubility in polar sol
crowded, and this can interfere with their ability to move, reducing vents while non-polar solutes have excellent solubility in non-polar
conductivity. The type of solvent used can also affect the conductivity of solvents. Since all salts are highly polar solutes, they dissolve rapidly
electrolytes. Different solvents may have different dielectric constants, in polar solvents. Water is a very well-known polar solvent with a dipole
which can affect the strength of the electric field between the ions in the moment of 1.84D. They have ability to dissolve a wider variety salts.
electrolyte solution. Additionally, the viscosity of the solvent can affect Solubility of salts i.e. chloride, sulfate, carbonate and bicarbonate based
the mobility of the ions. Temperature can also affect the conductivity of on alkali metal ions namely Na, K and Cs are always higher in water than
electrolytes. Generally, as the temperature increases, the conductivity of in any other solvents i.e. organic and ionic liquids. The solubility of salt
electrolytes also increases. This is because higher temperatures can in water depends mainly on the size of basic radicals. Many organic
provide more energy to the ions, allowing them to move more freely. solvents, like methanol, ethanol, DMSO, DMF, and NMP, are commonly
However, at very high temperatures, electrolytes can decompose, which used for electrolyte formulation due to the presence of a polar functional
can reduce their conductivity. The size and charge of ions in an elec group. But the solubility of various alkali metal ions-based salts have
trolyte can affect its conductivity. Smaller ions with higher charges tend been investigated and found that their solubility in organic solvents is
to have higher conductivity. nearly one order of magnitude lower than in water. The knowledge of
Apart from these, the impurities in electrolyte solution can affect its solubility product (Ksp) value and the determined value of MIACs [186]
conductivity. Impurities can interfere with the movement of ions and allows us to model the salt solubility in organic solvents. It has been
reduce conductivity. Since, impurities can absorb some of the electrical observed that, in contrast to aqueous solution, the solubility of ionic
charges, making it harder for the ions to move. The addition of certain salts in organic solvent does not depend linearly on the size of the cation.
additives, such as salts or surfactants, can also affect the conductivity of Therefore, experimental attempts to determine salt solubility in organic
the electrolyte by changing its properties, such as the viscosity or the solvents can be significantly reduced by using theoretical approaches,
solvation of the ions. The pH of an electrolyte solution can also affect its such as ePC-SAFT [187,188]. The ePC-SAFT approach has been exten
conductivity. This is because changes in pH can affect the degree of sively used to model the solubility of 1:1 (uni-univalent) and 1:2 (uni-
dissociation of the electrolyte into ions, which in turn affects conduc bivalent) electrolytes in organic solvents and the results are in good
tivity. The materials used for the electrodes can also affect electrolyte agreement with experimental data. Similar to the organic solvent pres
conductivity. For example, if the electrode materials react with the ence of a polar functional group in the polymer chain allows the polymer
electrolyte or corrode, this can interfere with the movement of ions and matrix to dissolve ionic salts in it and conduct the ions from one
19
Table 3 decreases rapidly with increasing size, for example, water molecule
Showing melting point, boiling point, dielectric constant value, viscosity and made bilayer solvation sheath around unipositive smaller size Li+ while
ESW values of some common solvents [7,192–195]. only one-layer solvation sheath formed around comparatively larger size
Solvent MP (◦ C) BP Dielectric Viscosity ESW Na+ and makes the superiority of Na+ based electrolyte over the Li+
(◦ C) constant (mPa s) based electrolytes. Dielectric constant of some solvents is listed in
EC 36.4 244 89.6 1.9 6.2 Table 3.
PC − 48.8 242 66.1 2.5 7.3
BC 74 55.9 3.2 4.1.3. Viscosity
DMC 2–4 90 3.1 0.58 6.7
Ionic transport towards the respective electrode is also adversely
DEC − 43 125.8 2.82 0.75 6.4
EMC − 14.5 107 2.4 0.65 6.7 affected by the viscosity of solvents. The higher will be the viscosity
FEC 18 249 78.4 2.35 employed for electrolyte formulation lower will be the ionic trans
TEP − 56.4 215 13.01 1.6 portation rate [196]. Solvents of higher dielectric constant facilitate the
TMP − 46 197 21.6 1.3 ionic transport by solvating and hence preventing ion-pair formation
DMMP − 50 181 1.75
126GBL − 43.5 204 39 1.7 7.6
usually being of higher viscosity retard the ionic transport. The viscosity
AND 1 295 30 6.1 of solvent also depends on the polarity of solvents, higher polarity
VC 22 162 126 2.23 usually of higher viscosity. The viscosity of a given solvent increases
DME − 58 84 7.2 0.46 5.1 further by adding more and more salt to it due to the formation of
DEGDME − 64 162 7.18 1.06
prominent ion-dipole interaction between polar functional groups of
TEGDME − 46 216 7.53 3.39
DOL − 95 75.6 0.6 solvents (aqueous and organic solvent, polymer electrolyte, ILs) and
THF − 108.4 66 7.58 0.46 5.4 radical of salts. Lower the charge-by-size ratio of radicals greater will be
DMF − 61 153 7.2 0.455 3.9 the extent of ion-dipole interaction which results in a higher viscosity of
DMSO 19 189 46.68 1.69 3.7 the resulting electrolyte. Owing to the larger charge by size ratio Na+-
NMP − 24 203 32.2 1.89
based electrolytes will be of lower viscosity and hence they have better
Ethanol − 114 78.3 24.55 1.040 2.6
Methanol − 98 65.4 32.70 0.5435 2.3 rate of ionic transport than Li+-based electrolytes. The detrimental
Acetonitrile − 44 82 37.5 0.334 6.3 impact of the high viscosity of EC and PC over the ionic mobility can be
Dichloromethane − 97 39.6 8.9 0.41 3.5 overcome significantly by combining them with linear ester derivatives
Chloroform − 63.49 61.27 4.72 5.55 2.6
such as DMC and EMC used as co-solvents.
Acetone − 95.4 58 20.7 3.02 2.6
Water 0 100 78.4 1.0016 2.4 A combination of high dielectric constant organic solvents with low
viscosity organic solvent can serve as a better solvent having an
attractive range of ESW for electrolyte preparation. Ponrouch et al.
electrode to another much like other solvents. The polymeric material [197] have revealed that binary solvent-based electrolytes have higher
used for the ion transport medium should have an either polar substit ionic conductivity as compared to the single component solvent. Ther
uent as a side chain and/or end groups or possess electronegative lone modynamic and kinetic factor studied by Kamath et.al [198] using the
pair containing heteroatoms such as nitrogen, oxygen, sulfur, halogens, theoretical and experimental approach for various binary solvent-based
etc. in their backbone to solvate the ions of the salt. Polymeric matrices electrolyte system reveals that electrolytes based on the binary solvent
most commonly used for the ion transport medium in alkali metal ion system of EC:DMC and EC:EMC has kinetic advantages to exhibit the
batteries include PEO, PVA, PVC, PMMA, PVP, PVF, PEG, PC, and PILs best formulation for SIBs. In this way, the combination of high dielectric
[189] being highly polar can dissolve salts to a considerable extent into with low viscosity solvent prevents the slower rate of ionic transport.
it. The solubility of salts in a solvent largely depends on the charge-to- Most of the well-known RTILs are based on the cationic organic
size ratio of the acidic and basic radicals of the salts. The larger the component such as Im, Py, ammonium, and sulfonium and both organic,
charge-to-size ratio of the radicals, the higher their solubility will be. triflate and inorganic fluoroborate, fluorophosphate anionic compo
nents are known, imposes higher values of viscosities in the order of ten
4.1.2. Dielectric constant of centipoise at room temperature, which also further increases upon
It is the measure of the ability of the solvent molecule to insulate the dissolving ionic salts in it due to much stronger ion-ion interaction. The
acidic and basic radicals from one another. Once the salts are transferred stronger ion-ion interaction present in ILs-based electrolytes results in
into the solvent they dissociate into their acidic and basic radicals and lower ionic mobility. Despite the negligible leakage problem presented
the solvent molecule surrounds the acidic and basic radicals by ion- by polymer electrolyte-based alkali metal batteries, polymer electrolyte
dipole interaction. At this condition, solvent molecules made a layer faces the huge challenge of ionic mobility owing to the very high vis
of themselves around the cation and anion referred to as a solvation cosity of the polymeric matrix employed as an ion-conducting medium.
sheath [190]. The extent of ion-dipole interaction and hence the insu Once again, the viscosity of polymer electrolytes enhances with
lating ability of the solvent molecule depends on the polarity of the increasing concentration of dissolved salts, the unit of charge residing
solvent. The formation of the solvent layer around the radicals not only over acidic and basic radicals, decreasing the size of cation and anion
stabilizes the charges but also prevents the ion pair formation. This is a and also the molecular weight of the polymer matrix employed. The
very important criterion regarding the better transport of ionic species higher viscosity of polymer electrolytes can also be overcome to a
towards the respective electrode in the battery. Solvents of high certain extent by utilizing low molecular weight polymer [199] and
dielectric constant such as water, EC, PC, etc. solvate the salts and monovalent salts based on bigger ionic sizes. In the above context, Na+-
prevent ion-pair formation even at high salt concentrations. The extent based polymer electrolytes would be more feasible over Li+-based. Ionic
of solvation of radicals by solvent molecules depends on both, the nature mobility in polymer electrolyte can also be enhanced by the inclusion of
of salts and solvents. For a given salt the extent of solvation increases plasticizers which enhances the dissociation of salt into its ion and
with increasing the polarity of solvents. However, the solvation effi prevent strong intra and inter-chain ion-polymer interaction. Viscosity
ciency of a solvent increases with increasing the charge-by-size ratio of of some solvents is listed in Table 3.
ions. Since for a given quantity of electronic charge the size of the cation
is usually smaller than that of the anions so ion-dipole interaction and 4.1.4. Electrochemical stability
solvation efficiency are more effective for cations than anions. Excessive In addition to good dissolving power, low viscosity and high
solvation of ionic species results in larger and heavier ions and hence dielectric constant of the solvent electrochemical stability is an impor
reduces their transportation rate [191]. The degree of solvation of cation tant criterion for the selection of appropriate solvent for electrolyte
20
Fig. 13. Showing (A) major factors affecting the stability and performance of electrolytes in energy storage systems, (B) the effect of pH on aqueous electro
lyte system.
preparation. The potential range over which a solvent does not exhibit So here we can conclude that solvents have an interesting impact on
any redox property is referred to as an ESW. A good solvent used for the electrolyte formulation and their various striking features such as
electrolyte preparation should have higher ESW. Despite various strik high dielectric constant, low viscosity, electrochemical stability, high
ing features exhibited by water as a solvent for electrolytes, it has a vapour pressure, and eco-friendly required for the high solubility of salt
serious drawback of low electrochemical stability of 1.23 V at 25 ◦ C, in a given volume of solvent, In-flammability, high ionic conductivity, a
which limits its wider applicability as a potential solvent for electrolyte wide range of electrochemical stability low leaking problem is not
formulation. On the other hand, most of the organic solvent have wider achievable in any one specific solvent. The selection of the proper sol
ESW of up to 5 V at 25 ◦ C, the striking feature of wider ESW exhibited by vent for electrolyte formulation for a particular application largely de
organic solvents make them suitable to be used for the preparation of the pends on the requirements. Table 3 shows the melting point and boiling
electrolyte solution. Best examples of high dielectric constant organic point of some common solvents which are frequently used in battery
solvents exhibiting quite significant ESW are based on cyclic alkyl car systems. Fig. 13A showing the major factors affecting the stability and
bonate moiety [200] i.e. PC and EC, which dissolve various alkali metal performance of electrolytes in energy storage systems.
salt significantly. ILs possess comparable electrochemical stability and
inorganic salt solubility to various organic solvents making them suit
able alternatives to organic solvents. Imidazole-based ILs such as EMIM 4.2. pH effect
and BMIM have some problems with the cathodic limit of ESW however
pyrrolidine-based ILs do not face the ESW limitation challenges [201]. The pH of the electrolyte can have a significant impact on the per
ESW of some solvents is listed in Table 3. formance of a battery, particularly for those that use aqueous electro
lytes. The pH is a measure of the acidity or basicity of a solution, and it
4.1.5. Chemical stability can affect the electrochemical reactions that take place at the electrodes.
The role of an ideal solvent used for the formulation of electrolytes The pH can affect the stability of the electrode materials in terms of the
involves the dissolution of the ionic salts in it. The solvents should be dissolution and corrosion of active electrode materials under acidic or
chemically stable enough to neither react with the salts nor with the basic conditions, which can limit the device lifespan [206]. This effect is
electrode material. The solvent molecules have to stabilize the metal ion particularly observed in aqueous electrolyte systems. The stability of the
of metal salt via ion-dipole interaction [202] but it should not have to electrolyte is critical for the performance and safety of the battery, as the
form stable complexes with the metal ion. The solvent has to exhibit breakdown of the electrolyte can lead to gas evolution, corrosion, and
wide ESW to not exhibit any type of redox behavior over the working other issues that can damage the battery and pose a safety hazard.
range of the device. The solvent should not react with moisture and air Generally, electrolytes with a pH closer to neutral (pH 7) tend to be more
to form other various unwanted side products which can result in stable than those with extreme lower or higher pH values. Since, they
corrosion of the electrode material or separator [203] used to separate accelerate the breakdown of the electrolyte and lead to gas evolution
the anode and cathode compartment of the ESD. and other issues. In acidic electrolytes, they lead to the corrosion of the
electrode materials as well as the current collector material [207]. This
4.1.6. Thermal stability can result in the release of gas, which can cause the battery to swell or
Like ESW and chemical stability, the solvent also should be highly even rupture. Moreover, in basic electrolytes, the high pH can lead to the
thermally stable. It should not decompose or does not undergo any formation of passivation layers on the electrode surface, which can limit
condensation reaction to form undesired side products which result in the battery's performance and reduce its lifespan. Therefore, it is
the breakdown or deposition of the electrode material. In addition to important to carefully select the pH of the electrolyte to ensure that it is
this, the solvent has a higher boiling point to prevent the flammability stable under the operating conditions of the ESD.
issue [204] and a low freezing point to overcome the solidification issue The pH of the electrolyte can also have an impact on the stability of
[205] at operating temperature. Where, excellent, chemical, thermal the solvent in which the electrolyte is dissolved. The solvent stability is
and electrochemical stability exhibited by the EC, PC, or binary solvent important because it affects the solubility of the salts in the electrolyte
system is good for the electrolyte formulation. and the ability of the solvent to support the electrochemical reactions
that occur in the battery [208]. In some cases, the pH of the electrolyte
21
can cause hydrolysis of the solvent, which can result in the formation of 4.3. Thermal stability and activation
acidic or basic species, which can lead to the degradation of the solvent.
Solvent degradation can occur through a variety of chemical reactions, The thermal stability of any electrolyte system plays a crucial role in
including oxidation or reduction of the solvent molecules, which can the better working efficiency and long-lasting characteristic of batteries
result in the formation of reactive species. The pH of the electrolyte can based on either SIBs or LIBs. The thermal stability of ESD depends on
also affect the solubility of the salts in the electrolyte [209]. This can be two factors which include the thermal stability of the electrolyte itself as
important because if the salts are not sufficiently soluble, they can form well as the thermal stability of the battery system under operational
a solid phase that can clog the pores in the electrode, reducing the de conditions. Since electrolytes of any ESD usually have three important
vice's performance. The pH of the electrolyte can also affect the corro components i.e. salts, solvents, and additives, their thermal stability was
sion of the electrode materials, which can lead to the formation of metal determined by the product of the thermal stability of their components.
ions that can react with the matrix and lead to its breakdown [210]. Thermal stability study of electrolytes is generally carried out by the
Water stability refers to the ability of water to resist changes in its TGA/DSC technique. For example, among various commonly used so
physical and chemical properties over time. The HER, OER and ORR are dium salts, NaClO4 exhibits higher thermal stability, NaTFSI exhibits
the most important characteristics that are the most common reactions lower thermal stability and NaPF6 shows intermediate thermal stability.
that take place by changing the pH of aqueous electrolytes (Fig. 13B). The second important component of an electrolyte is the solvent
The HER is a process that occurs when water is split into its constituent employed. It has been observed that organic liquid electrolytes based on
parts such as hydrogen and oxygen. The pH of the solution in which the more electrochemically stable organic solvents such as EC, PC, DME,
HER occurs can have a significant effect on the reaction rate and effi DMC and their various combination, are prone to get decompose during
ciency [211] Generally, the HER is more favorable at acidic conditions charge/discharge process of ESD. The decomposition of organic liquid
and less favorable at alkaline conditions. At low pH levels, the HER is electrolytes is associated with heat release and a rise in the operating
generally faster due to the higher concentration of protons (H+) in the temperature. The endothermic peak temperature of various solvents
solution, which serves as a reactant for the reaction. However, the low increases from about 90.1 ◦ C for DME to nearly 235.1 ◦ C for PC. Mixing
pH can also lead to the corrosion of the electrode used for the HER, two different solvents does not lead to the occurrence of a eutectic point.
which can limit the reaction efficiency. At high pH levels, the HER is Among various solvents, ILs have proven themselves one of the most
generally slower due to the lower concentration of protons in the solu thermally stable liquid solvents. NaBF4/EMIBF4, NaTFSI/Pyr18TFSI,
tion. However, the higher pH can also lead to the formation of surface NaTFSI/BMP-TFSI etc. IL electrolyte systems are the most widely used
oxides on the electrode, which can hinder the reaction and limit its ef for safe electrolyte formulation. The thermal stability of all mentioned IL
ficiency. The OER is a process that occurs during the electrochemical electrolytes is found to be stable even if the temperature rises above
splitting of water into hydrogen and oxygen. This reaction is important 350.1 ◦ C [215–219].
for various applications, including the production of oxygen and the Special additives such as EFPN use for the formulation of electrolyte
development of renewable energy technologies [212]. Similar to the provide outstanding thermal stability and causes resistance to flamma
HER, the pH of the solution in which the OER occurs can have a sig bility [220,221]. Moreover, overcharging and heating can initiate the
nificant effect on the reaction rate and efficiency. However, unlike the self-heating process of a battery resulting in a series of various types of
HER, the OER is generally more favorable at alkaline conditions and less chemical reactions such as electrolyte decomposition and interaction
favorable at acidic conditions. At higher pH, the OER is generally faster with the electrode material. These chemical reactions resulted in high
due to the higher concentration of OH− in the solution, which serves as a internal pressure within the ESD and even sometimes cause explosions
reactant for the reaction. In addition, the high pH can also stabilize [222]. In this regard, the thermal stability behavior of ESD is essential to
certain metal oxide catalysts that are commonly used for the OER, study and improve to ensure battery safety. Thermal stability of LIBs
leading to higher reaction rates and efficiencies. At lower pH, the OER is based on various types of electrolyte composition has been studied
generally slower due to the lower concentration of hydroxide ions in the extensively and found to be dependent on several factors namely the
solution. However, the low pH can also lead to the formation of surface composition of SEI layers over the electrode material, several possible
oxides on the electrode, which can hinder the reaction and limit its ef states of charge of cathode material, the extent of lithiation of graphite
ficiency. The ORR is a process that involves the electrochemical reduc and also over the electrolyte type [223,224]. However, only limited data
tion of oxygen to water. This reaction is critical in a variety of are available for thermal stability in the SIBs. The thermal stability of
applications, including fuel cells and metal-air batteries. The pH of the sodiated hard carbon of SIBs with organic solvent and electrolyte was
solution in which the ORR occurs can significantly affect the reaction investigated by Xia et al. and compared to the thermal stability of
rate and efficiency [213]. Generally, the ORR is more favorable at high lithiated graphite of LIBs. They observed that the addition of NaPF6 to
pH levels and less favorable at low pH levels. At high pH levels, the ORR various carbonated solvents such as EC and/or DEC does not lead to any
is generally faster due to the higher concentration of OH− in the solu improvement in the thermal stability of sodiated hard carbon [225]. As
tion, which serves as a reactant for the reaction. In addition, the high pH NaPF6 does not decompose into NaF to form a passivated layer and
can also improve the stability of certain catalysts used for the ORR, protect the electrode material as LiF from LiPF6 in the LiBs. ARC and DSC
leading to higher reaction rates and efficiencies. At low pH levels, the technique were employed to deduce the reactivity of cathode material
ORR is generally slower due to the lower concentration of OH− in the such as NaxFeO2, NaxCrO2 and NaxCoO2, with electrolytes [225–227].
solution. In addition, the low pH can also lead to the formation of surface All these Na-based cathode materials generally have similar exothermic
oxides on the electrode, which can hinder the reaction and limit its behavior, which involves the thermal decomposition of cathode mate
efficiency. rial into either their metal oxide or metal and oxygen, which reacted
The pH can affect the mobility of the ions in the electrolyte, which with the electrolyte. Usually, two types of electrolyte systems are
can affect the device's ability to deliver current. Higher pH levels can commonly used for the SIBs namely liquid electrolyte systems and
improve the ionic conductivity of the electrolyte, which can enhance the electrolyte systems based on solid or semi-solid phases. Electrolyte
battery's performance. Additionally, it can also affect the electro design for SIBs is based on three important factors viz. ionic conduc
chemical reactions that take place at the electrodes by affecting the rate tivity, electrochemical stability and thermal stability. As thermal sta
of charge transfer, the voltage of the ESD, and the formation of passiv bility of the electrolyte utilized is a basic parameter for designing the
ation layers on the electrode surface [214]. ESD. Since, the thermal stability of electrolytes is a function of the
thermal stability of salts, solvents and additives used for preventing
several side reactions. Thus, the thermal stability issue of the full cell is
complex and it largely depends on the extent of electrode-electrolyte
22
interaction along with the formation of SEI. ionic charge and its nature, the charge/size ratio of ions, the concen
SEI breaks down or cracks upon heating which resulted in an tration and the molecular property of solvent molecules i.e. polarity,
exothermic reaction to happen subsequently between now SEI-free viscosity, dielectric constant, vapour pressure, chemical, thermal and
electrode and electrolyte, which in turn leads to the formation of new electrochemical stability. Based on the charge/size ratio, the concen
SEI over the electrode surface. Upon heating the re-formed SEI undergo tration of ions and the polarity of the solvent one can observe 1SP, 2SP
thermal decomposition in the next round, along with the reaction with a and CIP. In CIP, the cation and anion are in direct contact with one
binder which in turn generates an additional amount of heat and this another, this type of ion-pairing is generally observed when the charge/
process continues till the complete decomposition of the electrode ma size ratio is large and the concentration of salt in the solvent is high or
terial [228]. The positive electrode of the batteries involved the thermal when the solvent having a low dielectric constant is implied. In 1SP,
decomposition of the active material itself with simultaneous oxygen cation and anion are separated from one another by a single solvation
evolution and exothermic reactions with solvents are the major shell. In 2SP, both cation and anion have their solvation shell. Hence the
contributing factor for the generation of heat [229]. Several exothermic distance between cation and anion is minimum in CIP and maximum in
processes were found to be the most probable sources for the disastrous 2SP but always < λB [232]. At the moderate salt concentration (1 mol
thermal runaway of the battery system. DSC and ARC studies were L− 1) most of the ions in organic solvents predominantly form 2SP. At
utilized to deduce the thermal stability of only a few electrode- higher salt concentrations, ionic aggregation was observed particularly
electrolyte combinations for both SIBs and LIBs. The thermal response for the Li+-based salt having bulky anionic components such as TFSI.
of individuals and selected combinations of cell components were Ionic aggregation is commonly observed in super-concentrated elec
measured by the DSC technique over wide temperature ranges at a fixed trolytes or solvents in salt electrolytes i.e. WIS electrolytes [32,97,233].
rate of scanning. ARC analyses are conducted for fuel cell and cell In the case of solvent in salt electrolytes, there is a low amount of solvent
components operated under adiabatic conditions. The cell heating rate is molecules available that are responsible for the formation of partial
a function of the intrinsic heat generated from various exothermic re solvation shells around the ions [234,235]. Super-concentrated elec
actions within the cell and the thermal heat capacitance of the cell trolyte systems based on various types of salts and solvent molecules
components namely electrode material, electrolyte, etc. [230]. For high have been explored concerning their potential application in LIBs and
carbon electrodes, DSC results indicate that 1 M NaPF6 in EC:PC solvent LMBs. Initial results in acetonitrile, water, PC and sulfonate solvent are
system shows the highest exothermic peak onset temperature and lowest quite interesting owing to their relatively high electrochemical stability
enthalpy of reaction among a variety of electrolytes. It has been and large enough ionic conductivity. Thus, it can be concluded that the
observed that fully sodiated high carbon in 1 M NaPF6 in the EC:PC number of ion complexes increases with an increasing salt concentration
solvent system appears to be quite comparable with lithiated graphite in in a given solvent system. However, a detailed understanding concern
terms of safety issues. ARC studies conducted by various authors ing the mechanism and structure of ion-pair is still missing and
exhibited that lithiated graphite in 1 M LiPF6 in EC:DEC solvent system controversial [236,237].
is thermally more stable in comparison to the high carbon sodiated 1 M Various studies suggest that in some solvents specifically in water
NaPF6 in the same solvent system. distinct ion exhibit differences in complex formation tendency, which is
commonly referred as specific ion effects [232,238,239]. These effects
are more pronounced for the aqueous system and very little information
4.4. Salt effect is available for the organic system. Various Li salts exhibit the following
order of solubility in acetonitrile solvents, LiPF6 < LiFSI < LiTFSI <
For the proper functioning of a battery to have a better lifetime, the LiClO4 < LiBF4, the order of solubility strongly coincides with the
choice of salts is an essential factor. There are different concerns complex formation tendency of ions. To account for this specific ion
regarding the selection of salt in electrochemical ESD, which include (i) effect first empirical attempt was based on distinguishing ions according
high solubility (ii) high electrochemical stability (iii) chemical stability to their chaotropic and kosmotropic properties [239,240]. Smaller-size
(iv) salt dissociation (v) cost-effective and (vi) environment friendly. ions are referred to as kosmotrops (i.e. LiF) while large-size ions are
Most of the salt after introduction to the appropriate solvent ionizes referred to as chaotropes (i.e. CsI), It has been proposed that pair of
and ion complexes in electrolyte solution form. Electrostatic interaction kosmotropes and pair of chaotropes results in the most stable ion com
governs the ionic complex's formation in the electrolyte solution. plex. An extension of this model introduces the LMWA [232,241] which
Stronger the electrostatic interaction more stable the ion complexes is based on the difference in the hydration energies of individual ions
formed. For two oppositely charged ion present in a solvent having a and a little bit similar to the hard/soft acid base concept. In the LMWA
definite dielectric constant the electrostatic interaction which is of approach, kosmotrope and chaotrope terms are related to the degree of
coulombic origin decreases with the increasing distance between hydration of ions. Being smaller in size, kosmotropic ions will be more
oppositely charged ionic species. The electrostatic interaction between hydrated as compared to the chaotropic ion. The LMWA approach was
two ions in a dilute electrolyte solution is inversely related to the square also studied for organic solvents like DMSO, formamide, methanol and
of the ionic distance. However, at abundant salt concentrations, ions PC. Results reveal that this approach is more or less equally applicable
mutually influence each other. In dilute electrolyte solutions, the elec for this system [242]. In SIBs presence of larger-size Na+ modifies the
trostatic interaction becomes screened significantly beyond the electrostatic interaction between ionic species, and between ion-solvent
distinctive distance termed as Bjerrum length (λB) [231] and is defined molecules to some extent in the aqueous system. But for the organic
by Eq. (31): solvent systems; these differences are marginal compared to the LIBs,
which may due to the presence of low charge on both ions. Compare to
λB = e2 4πe0 erkBT (31)
monovalent ions, the properties of salts with multivalent ion changes
At Bjerrum length, electrostatic interactions are of comparable value significantly higher due to the higher charge/size ratio of ions and the
to that of thermal energy kBT and can define the maximum distance for complex formation tendency of salt with multivalent ions in a given
electrostatic ionic interactions. Recent theoretical and experimental solvent. Specific ion effect which is related to the ion complex formation
results strongly suggested the existence of various ion complex states. As tendency of distinct ions has a strong influence over the ionic conduc
soon as salt ionizes into their respective cation and anion in a solvent tivity in a given solvent. Due to the different cation-anion interactions
some of the molecules of the solvent arrange themselves around the and solvent volume, the difference in ionic conductivity has been
cation and anion based on their polarity and resulting in the formation of observed for different Li and Na salts. Ponrouch et al. [197] and Bhide
the ion-solvent complex of specific stoichiometry within the Bjerrum et al. [92] studies that the value of conductivities of 1 M NaTFSI,
length. The formation of the ion-solvent complex gets influenced by the NaClO4, and NaPF6 salts in polycarbonate-based electrolytes are found
23
Table 4
The effect of ionic size in bare and hydrated form and corresponding conductivity of different ions (some data taken from Patent: Naphthalene Alkylation Process, PCT/
US91/02337) [53,54,248–250].
Ionic Size of bare ion Size of hydrated ion Ionic conductivity (S cm2 Ionic Size of bare ion Size of hydrated ion Ionic conductivity (S cm2
species (Å) (Å) mol− 1) species (Å) (Å) mol− 1)
H+ 1.15 2.80 350.1 Cl− 1.81 3.32 76.31

Li+ 0.60 3.82 38.69 NO−3 2.64 3.35 71.42
Na+ 0.95 3.58 50.11 SO2−4 2.90 3.79 160.0
K+ 1.33 3.31 73.5 OH− 1.76 3.00 198.0
NH+ 4 1.48 3.31 73.7 ClO−4 2.92 3.38 67.3
Mg2+ 0.72 4.28 106.12 PO43− 2.23 3.39 207.0
2+
Ca 1.00 4.12 119.0 CO2−3 2.66 3.94 138.6
Ba2+ 1.35 4.04 127.8 F− 1.24 2.63 54.8
Al3+ 0.54 9 188.9 Br− 1.98 3.37 75.5
Cu2+ 0.72 4.2 110.1 I− 2.25 3.65 76.8
Zn2+ 0.74 4.3 107.4 S2− 1.84 109.8
Ni2+ 0.70 4.04 99.2 HSO−4 2.21 50.0
Cs+ 1.69 3.29 77.3 CN− 1.87 78.0
Be2+ 0.25 90.0 HCO−3 2.07 3.64 44.3
to be 6.2, 6.5 and 8.0 mS cm− 1 respectively. However, the conductivity bicarbonate salts increases with increasing the size of alkali metal ions
values of 0.8 M NaOTf and NaPF6 salts in EC/EMC-based electrolytes (Na+ < K+ < Cs+). The solubility of chloride and bicarbonates of alkali
obtained 3.7 and 6.6 mS cm− 1 respectively. For both the solvent system metal ions get decreases and the solubility of alkali metal carbonate to
it was observed that the conductivity value of NaPF6 salt was relatively methanol > ethanol > NMP. On the other hand, the solubility of alkali
higher than the other salts due to the less polarization of PF6 anion, more metal carbonate decreases to NMP > methanol > ethanol [245]. The ion
solubility and ionic mobility. The conductivity of electrolyte based on pair and complex formation are most frequently observed in solvent
Na salts in general increases gradually with concentration to the having low dielectric constants. The salt dissociation is moderate or low
maximum and then decrease in common ester solvents such as EC, EMC, in organic solvents such as methanol, ethanol, and NMP, whose
PC and DMC etc. this observation of salt concentration over conductivity dielectric constant is <0.2.
can be explained based on free ion and viscosity. At lower salt concen
tration; free ions are a dominant factor but further addition of salt allows
more interaction between cations and anions followed by complexation 4.5. Influence of ion size
in electrolyte and enhances the viscosity of electrolytes. As a result, it
reduces the ionic mobility and hence conductivity. This decrement in The efficiency of an electrolyte depends on the ionic conductivity of
conductivity with increasing salt concentration and viscosity is mono the ions that constitute the electrolyte. Ionic conductivity relies on the
tonic. At maximum observed conductivity, there is a proper balance nature of the ionic species, their concentration, and the properties of the
between ionic mobility and viscosity [216,243,244]. solvent. Generally, the nature of ionic species includes the size of ions
The selection of salt for the design of an ESD depends on the nature of and the number of electronic charges on each ion. In the molten state of
the cationic as well as anionic components, due to their specific role in a salt, homovalent ions with smaller sizes tend to move rapidly, resulting
salt solubility, ion-pair formation and ion-solvent complex formation. in higher observed ionic conductivity. However, larger size ions exhibit
Inorganic anions, with electron-withdrawing central atoms, are restricted transport, corresponding to lower observed ionic conductivity
responsible for the delocalization of negative charge that gives weakly [246]. When salts are dissolved in an appropriate solvent, they ionize
coordinating anions (WCAs). Due to negative charge, delocalization according to their ionization potential, resulting in the formation of
WCAs are also more likely stable to oxidation. Li or Na salts based on cationic and anionic species. These species form ion-solvent complexes
perchlorate, tetrafluoroborate, hexafluorophosphate, triflate, and bis- in the electrolyte solution. The tendency for ion-solvent complex for
(trifluorosulfonylimide) are most commonly used for the designing of mation depends on the charge-to-size ratio, the dielectric constant of the
LIBs and SIBs. However, the anions mentioned above exhibit some solvent, and the concentration of the salt. Ion-solvent complex formation
problems as perchlorate is a strong oxidizing agent and because of this, is less pronounced when the amount of charge on the ion is smaller, the
these are avoidable in device fabrication. Tetrafluoroborate anion pro ions are larger in size, and nonpolar solvents (typically organic solvents)
duces comparatively less conductive electrolyte system owing to their are employed. Since most well-known electrolytes are based on aqueous
stronger interaction with the cation, decreasing the number of free systems, water molecules, owing to their higher polarity, exhibit a
charge carriers present in the system. PF6 being the anion of choice also strong tendency to form ion-solvent complexes with various ions based
has some safety issues. Since they involve in hydrolysis of PF6 anion at on inorganic salts. In aqueous electrolytes, smaller-sized homovalent
raised temperature and in the presence of humidity to form HF, POF3, ions have higher charge density than larger-sized ions [247]. As a result,
PF5, etc. Triflate anion possesses similar issues as tetrafluoroborate i. e. smaller-sized ions interact strongly with water molecules and form
low conductivity and corrosive nature. Similarly, bis-(tri strong ion-solvent complexes, resulting in the formation of a solvation
fluorosulfonylimide) anion was also reported for its corroding property shell around the ions, making them “hydrated.” Smaller-sized homo
for current collectors. valent ions are more hydrated than larger-sized ions. Consequently,
The solubility and ionization capacity of salts are important factors strongly hydrated smaller-sized ions have a larger effective size than
for ESD efficiency as these factors are directly related to the ionic con weakly hydrated larger-sized ions. Therefore, the ionic conductivity
ductivity of the electrolyte medium. Nearly all alkali metal halide, car trend observed in the molten state unlikely going to change in an elec
bonate, and bicarbonate are highly soluble in water and their degree of trolyte solution. In solution electrolyte the effectively larger size of
dissociation reached up to 0.8 at room temperature over a broad con smaller cation ions, imposes higher hydrodynamic resistance than
centration range. However, the solubility of chloride salts of alkali metal larger-sized ions. As a result, smaller ions exhibit lower ionic conduc
has a different order in different organic solvents i.e. CsCl and NaCl both tivity than larger-sized ions. Experimental observations regarding the
have better solubility in alcohol than KCl. Whereas NaCl and KCl have correlation between ionic conductivity and effective size are provided in
better solubility in NMP than CsCl. The solubility of alkali carbonate and the Table 4. These experimental results indicate that larger-sized ions,
which are weakly hydrated, interact more strongly with the electrode
24
Fig. 14. Showing different ionic conduction mechanisms under different physical phases of electrolyte materials.
than smaller-sized, heavily hydrated ions. This interaction results in size of these anions [253–255].
more energy being stored. In summary, in an aqueous electrolyte sys Additionally, the size of ions presents in polymer and composite
tem, larger-sized ions lead to both higher ionic conductivity and the electrolytes plays a pivotal role in determining their overall conductiv
storage of more energy. ity. Smaller ions generally exhibit higher mobility within polymer
Besides solution electrolytes, ionic size significantly influences the matrices. The smaller size allows them to more easily navigate through
ionic conductivity of solid-state electrolytes. In crystalline electrolytes, the polymer chains, overcoming steric hindrance and enhancing their
smaller ions can more easily navigate through the lattice structure of the diffusion [256]. Ionic size also influences the degree of polymer
solid electrolyte, as they require less energy to overcome lattice distor swelling. Smaller ions may cause less swelling as they can more readily
tions and move between interstitial sites (vacancies). A lattice with fit between polymer chains, whereas larger ions may induce more sig
higher vacancy concentration and smaller ions shows enhanced con nificant swelling due to increased steric effects [257]. The ionic diffu
ductivity due to more facile diffusion through these vacancies. More sion within the polymer matrix is affected by its size. Smaller ions
over, smaller ions have a weaker electrostatic interaction with the experience less resistance in moving through the polymer structure,
surrounding lattice, resulting in reduced coupling between ions and contributing to faster ion transport and higher conductivity than larger
lattice vibrations. In certain materials, smaller ions can promote phase ions and vice-versa [258]. Moreover, larger ions may disrupt the poly
transitions that lead to a more open lattice structure. Smaller ions mer matrix, affecting its mechanical strength and durability. An un
generally exhibit higher mobility and conductivity due to reduced lattice derstanding of the relationship between ion size and ionic conductivity
distortion, enhanced vacancy diffusion, weaker coupling strength and is essential for tailoring polymer and composite electrolytes to specific
potential phase transitions [251,252]. For instance, Li+-conducting solid applications. While smaller ions generally enhance conductivity, a
electrolytes, such as LiPON and LLZO, exhibit high conductivity due to careful consideration of other factors such as polymer swelling and
the small size of the Li+. Similarly, F− and O−2 conducting solid elec mechanical properties is crucial for optimizing overall electrolyte per
trolytes, such as LiF and BaF2, display high conductivity due to the small formance. For instance, Na+ is larger than Li+ and K+. This larger size
25
can have a significant impact on Na+ conduction in composite and by simple diffusion of ions either freely or under an applied electrical
polymer electrolytes. Na+ has a harder time diffusing through the nar field. But SSEs have faced issues to reach the desired ionic conductivity
row pores of the inorganic filler material and are more strongly solvated same as liquid electrolytes till now. Different types of SSEs i.e. ceramic,
by the polymer matrix. These factors result in lower Na+ conduction polymer, polymer-ceramic composite and MOFs are made up of different
than that of Li+ or K+ ions in both composite and polymer electrolytes microstructures. Ceramic electrolytes are offered higher room temper
(ionic conduction = Li+ > K+ > Na+). However, there are a number of ature conductivities (in the range of 10− 3 S cm− 1) but this is difficult to
strategies that can be used to improve larger size ion conduction in incorporate ceramic electrolytes due to their poor integration with
composite and polymer electrolytes i.e. using a larger pore size filler electrodes, which generate a large interfacial resistance [265]. Polymer
material, modifying the surface of the filler material to make it more electrolytes offer better electrode intimation interface but they offer
hydrophilic, using a plasticizer to increase the free volume of the elec lower ionic conductivity compared to ceramic electrolytes. Since it is
trolyte, using a polymer matrix with a lower glass transition temperature observed that the ceramic and polymer electrolyte act as complement
(Tg) and by using a polymer matrix with a higher dielectric constant material for each other. Hence, the incorporation of both forms a
[259–261]. polymer-ceramic composite electrolyte that offers intermediate con
ductivity [266]. These types of electrolytes show different conductivities
4.6. Physical phase and structure due to their different matrix structure and ionic transport mechanism.
For example, different ceramic electrolytes i.e. perovskite oxides, garnet
The physical phase of an electrolyte can have a significant impact on oxides, NASICONs, sulfides, halides and phosphates have different
its properties. Since, the properties of an electrolyte are determined by bottleneck sizes for ionic diffusion and lattice volume of crystal struc
the behavior of its constituent ions, the physical phase of the electrolyte ture, which govern the ionic conductivities of these electrolytes.
can affect how these ions interact with each other and with the sur In ceramic electrolytes, ionic transport depends upon diffusion type,
rounding environment. It can affect the viscosity, mobility, availability diffusion path, charge carrier type and crystal defects i. e. electron
of ions, and diffusivity, therefore influencing the ionic conductivity of defect, point defect, line defect, volume defect and planner defect. The
the electrolyte [262]. In a solid electrolyte, ions are typically held in charge carrier type and their concentrations are depending upon the
fixed positions either in the crystal lattice or a cavity. As a result, the point defects present in the crystal structure and show interaction with
mobility of ions is limited and the ionic conductivity may be relatively other carriers and the surrounding matrix during their migration. Hence,
low. In a liquid or molten electrolyte, ions are free to move around and they affecting the conductivity of the electrolyte. Among the other de
interact with each other. This results in higher ionic conductivity fects, point defects influence more ionic transport by it's accomplishing
compared to solid electrolytes. Whereas in a solution electrolyte, the the ionic transport via a random walk of ionic diffusion in mobile point
ions are dispersed in a solvent. The mobility of ions in solution is greater defects. In the different types of ceramic materials ion transport takes
than in solid electrolytes but typically lower than in liquid electrolytes. place by interstitial mechanism, vacancy mechanism and interstitial-
The ionic conductivity of a solution electrolyte is affected by factors such substitutional exchange mechanism. In the interstitial mechanism, the
as the concentration of the electrolyte, the type of solvent used, and the interstitial ion present in the lattice diffuses through the Frenkel defects
temperature. Gel and hydrogel electrolytes can provide high ionic con via continuous displacement of other ions. Instead of that in the vacancy
ductivity, similar to liquid electrolytes, due to their ability to retain a mechanism, a lot of vacancies are available through Schottky defects in
large amount of solvent and ions. It can be designed to have specific lattice and ion migration takes place by hopping which generates a new
properties i.e. mechanical strength, composition and structure. This al vacancy for migration of another ion [267–270]. Another charge
lows for tailoring of the electrolyte properties by better tunability to transport mechanism termed the “paddle-wheel” mechanism has been
specific applications and requirements i.e. they can also be used in reported for higher ionic conducting crystals to interpret the cation-
flexible and wearable devices due to their mechanical flexibility [263]. anion interchange. In this mechanism, cation transport takes place via
Additionally, the physical phase of an electrolyte can have a signif a “paddle-wheel” of “revolving doors” generated by the interchange of
icant impact on its stability. Electrolyte stability refers to the ability of transitionally static anions [271]. The grain boundary formation in ce
an electrolyte to maintain its chemical and physical properties over time ramics allows the higher resistance compare to the intragrain resistance
and under different conditions. Thus, stability is an important consid and increases the Ea of ion transport. There are distinct structural and
eration for ESD. Nevertheless, electrolyte degradation can lead to chemical alterations observed at the grain boundary and bulk grain that
decreased device performance, safety issues, and reduced device life made it not favorable in ionic transport [272]. There are three major ion
time [264]. SSEs are generally more stable than liquid or solution transport paths i.e. intragranular ion transport, intergranular ion
electrolytes because they are less prone to evaporation, leakage, and transport and ion transport at grain boundaries are reported for poly
other types of degradation. These can also provide improved stability crystalline ceramics [273]. The granular ionic transport mechanism is
against chemical reactions that can occur between the electrodes and the observed when the resistance of the grain boundary is higher than the
electrolyte. However, the stability of SSEs can be affected by factors such bulk grain. Hence, the ion migration takes via grain to grain by crossing
as temperature, humidity, and mechanical stress. The stability of liquid the grain boundaries. The grain boundary ionic transport mechanism is
electrolytes can be influenced by their chemical composition, tempera observed when the resistance of grain boundary is comparable to the
ture, and exposure to air or other contaminants. Some liquid electrolytes bulk grain and ion migration takes via grain boundaries. This is observed
can be prone to evaporation or degradation over time, which can lead to in sulfides and a few oxide-based ceramic electrolytes [274]. In polymer
changes in their composition and properties. However, few may also electrolytes, ionic transport takes place by segmental motion which is
react with the electrodes, leading to degradation and reduced device the most common mechanism for this system. The ionic hopping/Grot
performance. Solution electrolytes can be subject to the same types of thuss mechanism is infrequently observed for polymers electrolytes as
degradation as liquid electrolytes, but their stability can be improved by well as mass diffusion (vehicle mechanism). In segmental motion, the
carefully controlling their composition and concentration. For example, ionic transport is completely reliant on the mobility of the polymer chain
adding stabilizing agents or controlling the pH of the solution can pre segment which takes place above the glass transition temperature of the
vent degradation and maintain the stability of the electrolyte. polymer. This type of transport mechanism is observed in polymer
The physical phase and matrix structure also show a great influence electrolytes where the salt is dissolved in macromolecules having ion-
on the ionic conductivity and ion transport mechanism of any electrolyte coordination sites and polar groups i.e. amine (-NH2), imide (-NH-),
system (Fig. 14). In liquid and solution electrolytes (ionic liquids or any alcohol (-OH), ether (–O–), thiol (-SH), thioether (–S–), etc. [275].
inorganic electrolyte solution) vehicle mechanism of ionic transport is The lower lattice energy of salt with a higher dielectric constant host
observed very commonly. In this mechanism, ionic transport takes place polymer allows greater salt dissociation [276]. Polar groups on host
26
Fig. 15. (A) Showing ion transport through the SEI layer (B) process of SEI formation (C) SEI formation on different surfaces.
polymer are plays an important role in ion coordination and lowering and COFs show covalent bonding with a ligand that allows the single ion
the hindrance due to the presence of bond rotations, and hence this transport mechanism. On the other hand, pseudo-solid MOFs and COFs
matrix enables the cationic transport [277]. The ionic hopping mecha allow ionic transport via abundant pores either for ionic hopping or
nism is observed in crystalline and semi-crystalline polymer electrolytes, vehicle mechanism [282].
where lattice structure shows point defects without any rearrangement. The physical phase of an electrolyte can also play a critical role in the
In polymer electrolytes, the cation-polymer interactions are stronger performance of ESD. In a battery, the physical phase of the electrolyte
and the mean available free path for ionic hopping is larger, ionic con can affect the mobility of ions, which can impact the rate of electro
ductivity takes place via the hopping mechanism. Temperature- chemical reactions. For example, solid-state batteries use solid electro
dependent linear Arrhenius change indicates the migration of ions lytes that can provide higher energy densities and improved stability
through simple hopping which is completely free from segmental mo compared to liquid electrolytes, but they may have lower ion mobility
tion [278]. In polymer electrolytes it is also possible that the ionic and slower reaction rates. In a flow battery, energy is stored and released
hopping can be convoyed by segmental motion, relaxation and breath through redox reactions between the electrolyte and the electrodes. The
ing of polymer chains. It is also observed that the hopping and segmental physical phase of the electrolyte can affect the solubility of the redox-
motion cooperatively act in polymer chains and ion jump from one chain active species and the ability of the electrolyte to flow through the
to another [279,280]. Vehicle mechanism is rarely observed in polymer battery [283]. For example, some flow batteries use liquid electrolytes
electrolytes, where transport of proton in the porous polymer (e.g. that can be recharged by replacing the spent electrolyte with fresh
Nafion) takes place via this mechanism. Ceramic-polymer composite electrolyte, while others use SSEs that can offer improved stability and
electrolytes are made-up of polymer and passive inorganic fillers which safety. In capacitors and supercapacitors, energy is stored through
can reduce the glass transition temperature of polymer chains and in electrostatic charge accumulation at the surface of the electrodes. The
crease the amorphousness of the matrix. In this system, ionic transport physical phase of the electrolyte can affect the ability of ions to access
takes place similar to the SPE such as segmental motion [281]. Since the the surface of the electrodes, which can impact the charge storage ca
ceramic-polymer composite matrix consists of ceramic and polymer pacity and rate of the supercapacitor. For example, some super
materials the ionic transport can take place via intra-ceramic, intra- capacitors use electrolytes with high ion mobility, such as ILs, to
polymer and interfacial transport [282]. It is observed that the higher improve charge storage capacity and power density. Gel and hydrogel
concentrations of fillers introduce higher resistance on composite elec electrolytes can offer improved safety compared to traditional liquid
trolytes due to the agglomeration of inorganic particles that reduce the electrolytes, which can be flammable and prone to leakage. Gel and
ceramic-polymer interface. Whereas, a lower concentration of inorganic hydrogel electrolytes can be designed to be non-volatile and non-
fillers shows a percolation effect at the interphase region and introduced flammable, reducing the risk of fire and explosion [284].
the hopping channels at the interphase which is responsible for the
higher ionic conduction. Besides the other SSEs, MOFs and COFs are
present in two classes i. e. pure solid and pseudo solid. Pure solid MOFs
27
4.7. Solid electrolyte interphase the reaction kinetics are powerful tools that restrict the electrochemical
reactivity of the system [296]. Differences in chemical potential also
The SEI is a passivated layer formed by the decomposition of elec motivate the spontaneous chemical reactions at the anode and cathode
trolyte material on the Li or Na-ion anode surface. The formation of SEI material's surface which is responsible for the chemical reaction origi
is closely related to the electrode-electrolyte properties and it is gov nated SEIs. These SEIs are beneficial when they are conducting for the
erned during the charging and discharging of the device. When elec cation but not for the electrons [286]. These chemical reactions can be
trolytes react with the anode, the solvent of the electrolyte reacts and mitigated by using inert electrode materials with a protective coat.
decomposes on the anode to make a thin layer called SEI. The formation In a study by Li et al., the positive effects of SEI formation on the Li-
of SEI is least understood but can play a significant role in the de based battery were observed. They tested the carbonate-based electro
terminations of the rated capacity, efficiency, safety, lifetime, cycling lyte using an additive of PES in LiMn2O4/graphite Li+ battery at high
ability, and stability of the device (Fig. 15A). The formation of SEI has temperature (60 ◦ C) and found excellent cyclability and dimensional
been importantly considered when designing the device. The porous stability. However, it was stable up to 150 cycles with 91 % of capacity
structure of a few nanometers (nm) thick layers of SEI can remarkably retention. The high performance was due to the formation of stable SEI
enhance the conductivity of ions (Li+ or Na+), since they allow the fast in the presence of PES which prevent the decomposition of electrolyte
transfer of ions from the electrolyte, low consumption of electrolyte, [297]. Furthermore, the effect of SEI on Li+ intercalation and dein
stabilize the electrode, and prevent the corrosion and degradation of the tercalation on the graphitic anode at varied temperatures was studied
anode [285,286]. using EIS and an AFM. For the model, a study has been conducted on the
There are several spontaneous chemical reactions between elec LiNi0.6Co0.2Mn0.2O2 cathode and graphite anode in the electrolyte of
trodes and electrolytes are takes place incompatibility of their chemical LiPF6 in EC-EMC. It was examined that anions (PF−6 ) and functional
potential. These chemical reactions produce a resistive interface be groups of electrolytes other than Li+ also move through SEI which is
tween anode and electrolyte known as SEI; and also, between cathode involved in the intercalation/deintercalation process. Furthermore, the
and electrolyte known as CEI. These SEI and CEI restrict the ionic dielectric constant of the SEI layer was measured through EIS and found
diffusion and charge transfer processes inside the ESD [287,288]. The to be ~57 and ~93 for Si and highly oriented pyrolytic graphite (HOPG)
study of SEI properties e.g. thickness, thermal and mechanical stability, respectively at 24 ◦ C. However, the AFM results stated the SEI thickness
composition, structure, ionic conductivity, etc. is meaningful to under of ~39 nm on HOPG. Both studies have shown good agreement with the
standing its evolution [289]. Initial SEI induction is observed either due high performance of Li+-battery due to the formation of stable SEI
to cation solvation by anions/solvent molecules, or adsorption of an [298]. Successively, a mixture of fluorosulfonate and commercial elec
ions/solvent molecules on electrode material which forms an EDL that trolyte on the SEI layer formation has been studied for the Li+ battery. It
affects the interface formation [290,291]. Both solvation and adsorption was noticed that the fluoro sulfonate reacts with the alkyl of the elec
mechanism are significantly responsible for SEI formation (Fig. 15B). trolyte to form a flexible SEI layer which enhances the concentration of
The inner Helmholtz layer of EDL was consisting adsorbed anions/sol LiF. They improved the stability and rapid charging of the battery by
vent molecules that are going to decompose and form the initial inter inhibiting the formation of Li-dendrimers which allow the uniform
face, while the solvated structure present on the outer Helmholtz layer deposition of Li. As a result, they achieved a high current density of 20
consists of bulk electrolyte material which forms secondary SEI by redox mA cm− 2, and were deposited stable for 300 h. Moreover, at 5C the
reaction [292]. SEI structure and its components play a critical role in capacitive retention rate of Li-LiFePO4 was 90.6 % even after the 1000
device performance. It was reported that both organic and inorganic cycle. These suggested that stable SEI can remarkably enhance the ca
components are participating in SEI formation, which can understand pacity of the battery even far better than the commercially available
able by using mosaic and multilayer models [293]. The electrolyte electrolytes [299].
components i.e. additives, salts, and solvents can affect the SEI forma Apart from this, the Na-based aqueous electrolytes are also utilized
tion via their reduction, growth-supporting carriers, and distributions on a broad scale for Na-based batteries which show better SEI to improve
that also provide advancement for electrolyte preparations [4,294]. the efficiency. In a study by Lee et al., the saturated aqueous solution of
Notably, there is a restriction on solid electrolytes that they cannot drift about 17 M NaClO4 at Na4Fe3(PO4)2(P2O7) cathode, and NaTi2(PO4)3
into voids/interstitial spaces of electrode material which results in poor anode exhibit the stable SEI layer without reduction of anions. They
interaction between solid electrolytes and electrodes. By altering the have better cycle stability at 1C for 200 cycles, ~99 % of coulombic
electrolyte components, it is possible to regulate the electrolyte solva efficiency and 900 for storage stability. The high efficiency was due to
tion structures as well as the adsorption structure that regulates SEI the NaClO4 diminishing the decomposition of water and forming the SEI
properties [295]. These interfaces can be categorized according to their layer of Na2CO3 and Na–O compound in NaOH and through the
origination such as based on chemical or electrochemical origin, inter reduction of oxygen and carbon dioxide which improves the battery
stitial/void origin, or orange from grain boundaries (Fig. 15C). Grain stability [96]. Similarly, the NaSF3SO3 electrolyte in an aqueous solu
boundary-based interfaces originated due to different electrochemical tion exhibits high stability up to the 350-cycle having coulombic effi
potentials of electrolyte and electrode materials. At this condition, inter- ciency of >99.2 % at 0.2 C due to the formation of stable SEI and
grain cation transport generates a cation-deficient layer which is reducing the hydrogen evolution on the electrode surface. Moreover,
responsible for the suppression of ionic conduction. Interstitial/void- this was retained up to 92.7 % after the 1200 cycles suggesting the high
based interfaces are originated either due to the improper contact of efficiency of such electrolytes for Na-batteries [97]. Beyond the aqueous
electrode-electrolyte material in device fabrication which results in the electrolyte, three SSE Na2.25Y0.25Zr0.75Cl6, (NYZC), Na3PS4 (NPS), and
porosity at the interface; or electrode pulverization which results Na2(B10H10)0.5(B12H12)0.5 (NBH) was utilized by Deysher for Na-battery.
dendrite formation at the interface. This type of interface could increase They found that NBH electrolyte exhibits superior stability due to they
resistance by restricting the charge transfer and energy density by prevent the reduction and degradation in cell reaction and achieves
enhancing the dendrite growth and cell volume. Electrochemical-based ~99 % Coulombic efficiency. However, NYZC reduces to form an
SEIs originate due to a mismatch in electrode-electrolyte potentials and insulating phase which resulted in capacity loss and increases the
low ESW of solid electrolyte materials which refers to the redox resistance of the cell. Nevertheless, NPS also reduced into the Na2S and
decomposition (oxidation at high voltage and reduction at low voltage) Na3P which also reduces the cell performance [300]. Apart from this,
of electrolyte materials at the electrode surfaces and leads towards SEI/ further research is required to explore the exact mechanism of SEI for
CEI formation. This effect restricts the cell application at the full voltage battery systems.
range of electrode materials. To overcome this issue, the use of
electrode-electrolyte materials with matching potential and minimizing
28
Table 5 reduces self-discharge in PTMA by minimizing the dissolution of active

Some stabilized electrolytes for particular electrode systems for sodium-ion materials and preventing capacity loss during cycling processes [314].
batteries. However, a few times reduced specific capacity was also observed in the
Electrode system Solvents Salts PTMA system with concentrated electrolytes due to lowering the ionic
Hard carbon (Carbotorn P PC 1 M NaPF6/NaClO4
mobility and electrode surface wetting [315].
(J))/Na EC + DEC (1:1 v/v) 1 M NaClO4 Electrolyte-electrode compatibility can also impact the durability of
Na3V2(PO4)2F3/hard carbon EC + PC + DMC 1 M NaClO4 ESD. When the electrolyte and electrode are not compatible, it can lead
(0.45:0.45:0.1 v/v) to a range of issues such as poor ion transport, formation of passivation
Graphite/Na DEGDME 1 M NaPF6/NaClO4/
layers, and electrochemical reactions that can degrade the electrode or
NaCF3CS3
Na[Ni0.25Fe0.5Mn0.25]O2/C- EMS + 2 v% FEC 1 M NaClO4 the electrolyte. One approach to enhance electrolyte-electrode
Fe3O4 compatibility is to design or modify the electrode surface to make it
Na2FePO4F/Na EC + DEC (1:1 w/w) 1 M NaPF6 more compatible with the electrolyte. This can involve surface treat
BF-rGO/Na EC + DEC + FEC (1:1:5 w/ 1 M NaClO4 ments such as coating the electrode with a thin layer of a protective
w)
Na0.7CoO2/Na EC + DMC (3:7 w/w) 0.5 M NaPF6
material [316] or modifying the surface chemistry to promote better
Hard carbon/Na EC + PC (1:1 v/v) 1 M NaPF6/NaClO4 interactions with the electrolyte. Another approach is to design or
Polymeric/oligomeric Schiff Me-THF 1 M NaFSI modify the electrolyte to make it more compatible with the electrode
base/Na [234]. For example, electrolytes with lower viscosity and higher ionic
Na2FeP2O7/NaTi2(PO4)3 Water 2 M Na2SO4
conductivity can improve the transport of ions to and from the electrode,
Na0.7CoO2/graphite TEGDME 1 M NaClO4
Hard carbon C1600/Na EC + DMC (1:1 v/v) 1 M NaClO4 leading to improved performance. Additionally, using additives in the
electrolyte can improve compatibility with the electrode by reducing the
formation of passivation layers or improving the wettability of the
4.8. Electrode compatibility electrode surface. Overall, enhancing electrolyte-electrode compati
bility requires a deep understanding of the interactions between the
Electrolyte compatibility with electrode materials is a critical electrolyte and the electrode, as well as a careful selection of materials
consideration in the design of efficient and durable ESD. The choice of and design parameters to optimize performance and durability [192].
electrode material and electrolyte can significantly impact the perfor
mance and lifespan of these devices. In general, the electrolyte should be 5. Outcome and future perspective
compatible with the electrode material, meaning that it should not
induce significant chemical reactions or degrade the electrode during In this review, a detail overview of the factors affecting the electro
operation. For example, several stabilized electrochemical systems for lyte properties including ionic conductivity, ESW, electrolyte imped
Na+ batteries are provided in Table 5 [4]. However, these solvents can ance, ionic mobility and diffusivity, and transference number is
react with other electrode materials, such as Li metal or some transition discussed. Nevertheless, it also describes the impact of the solubility, pH
metal oxides, leading to the formation of SEI layers that can degrade effects, stability (chemical and thermal), salt effect etc. on electrolytes
battery performance over time. In SSEs, electrode-electrolyte compati properties in ESD. However, some of the consideration made before the
bility depends upon the electrode/electrolyte interface. A better inter selection of better electrolyte materials with improved properties to
face requires chemical and electrochemical stability during application, fulfill the criteria of high performing ESD. (i) Electrolytes must have
higher contact area, and fast ionic transport. Maintaining the mechan higher ionic conductivity, lower viscosity, and better stability under
ical and chemical stability of both the electrode and electrolyte during different operating conditions. It is also important to understand the
device operation remains a major challenge in the field of solid-state molecular mechanisms of electrolytes that govern ion transport. How
ESD development. Similarly, in fuel cells, the choice of electrolyte can ever, these studies can be performed using experimental as well as
affect the stability and durability of the electrode catalyst. For example, computational methods to how different electrolytes interact with ions
acidic electrolytes such as H3PO4 or H2SO4 are commonly used with Pt- and facilitate their transport. Also, the low viscous electrolyte freely
based catalysts in PEMFCs, while alkaline electrolytes such as KOH or moves the ions which improves the ionic conductivity. (ii) Electrode
NaOH are used with Ni-based catalysts in AFCs. Overall, the compati compatibility is also a critical consideration when designing new elec
bility of electrolytes with electrode materials is a complex issue that trolytes. The focus is on developing new electrolytes that are compatible
depends on many factors, including the chemical and physical proper with a range of electrodes. Although, electrolytes can be sensitive to
ties of the materials, the operating conditions of the device, and the temperature, which can affect their performance and safety. Therefore,
desired performance characteristics. Consequently, careful consider the development of thermally stable electrolytes is needed to improve
ation and testing of different electrolyte-electrode material combina the operational performance of ESD. Since, the stable electrolytes in
tions are required to optimize the performance and durability of ESD different environment restricted the degradation, gas and other by-
[301–307]. product formations, leakage, and explosion which ensure the safety of
The active dissolution of electrodes in the solvent of the electrolyte is ESD. (iii) The performance of electrochemical devices is often limited by
a well-known drawback that reduces the cyclic stability of ESD and leads the SEI. It is critical for the stable and efficient operation of many ESD. A
to self-discharge of active materials, particularly in the presence of small better understanding of the formation and interaction of the SEI layers
carbonyl compounds [308]. For example, in PTMA self-discharge takes with ions is crucial to explore the high reliability of SEI. Since the
place by the shuttle effect of the dissolved electrode in electrolyte [309]. exploration of the functioning mechanism on the electrode-electrolyte
To outcome of this issue, several approaches are introduced to the active interfaces can open a new avenue to the designing of high-
material i.e. side group introduction to increase the material's polarity performance storage devices. Along with this, the designing of new
[310], polymerization [311] and crosslinking [312]. These approaches electrode-electrolyte interfaces required that can facilitate faster ion
increase the molar mass of active materials and decrease the gravimetric transport, reduce interfacial resistance, and improve the overall per
capacity. Another approach to reducing electrode compatibility is to use formance of the ESD. (iv) ESW is the other considerable factor in elec
high conducting concentrated (>1 M) electrolyte [313], which offer trolyte research is to expand the of electrolytes, particularly for high-
several benefits i.e. increasing electrolyte viscosity to kinetically slow voltage applications. This can be achieved by designing new electro
the dissolution rate of active materials, reducing unwanted side re lyte materials with higher oxidative and reductive stability, or by
actions, enhancing thermal stability, and lowering the risk of flamma modifying existing materials to improve their electrochemical stability.
bility. For example, increasing the concentration of BMPyBF4 in PC (v) The accurate measurements of ionic mobility, diffusivity, drift
29
Fig. 16. Showing overall chemical and physical aspects related to the electrolytes and their factors affecting constituents.
velocity, and ionic transference number are also essential for advancing the work reported in this paper.
electrolyte research. Since, they offer insight view of the movements of
ions in various electrolytes system. (vi) The dielectric properties of the Data availability
electrolytes, such as permittivity and dielectric constant also play a
critical role in ion transport and electrochemical behavior. It is needful Data will be made available on request.
to explore the relationship between dielectric properties and electro
chemical behavior in the context of high-voltage applications. (vii) The Acknowledgments
structure of the matrix in which an electrolyte is embedded can also
have several impacts on ionic conductivity, electrochemical stability, Authors are grateful to BHU for the financial and research facility
ionic transport mechanism and mechanical strength which can help to support. Dipendra Kumar Verma, Km Parwati, Rajshree Rai are thankful
identify superior materials and formulations that are more effective in to UGC, New Delhi, India for financial support. Pushpesh Ranjan is
specific applications (Fig. 16). thankful to CSIR, New Delhi, India for financial support.
In the future, with technological advancement, the electrolyte field is
continuously growing, and preparing the advanced electrolytes system
References
which has the potential to develop high-performance ESD for broad
applications such as energy, catalysis, biomedical devices, and electro [1] B. Dunn, H. Kamath, J.-M. Tarascon, Electrical energy storage for the grid: a
catalysis to solve the future demands of the energy systems. battery of choices, Science 334 (2011) 928–935.
[2] R.M. May, S.A. Levin, G. Sugihara, Ecology for bankers, Nature 451 (2008)
893–894.
CRediT authorship contribution statement [3] R. Schmuch, R. Wagner, G. Hörpel, T. Placke, M. Winter, Performance and cost of
materials for lithium-based rechargeable automotive batteries, Nature, Energy 3
(2018) 267–278.
Rudramani Tiwari: Conceptualization, Investigation, Writing –
[4] H. Che, S. Chen, Y. Xie, H. Wang, K. Amine, X.-Z. Liao, Z.-F. Ma, Electrolyte
original draft. Devendra Kumar: Methodology, Writing – original draft. design strategies and research progress for room-temperature sodium-ion
Dipendra Kumar Verma: Formal analysis, Writing – original draft. Km batteries, Energy Environ. Sci. 10 (2017) 1075–1101.
Parwati: Visualization. Pushpesh Ranjan: Validation, Writing – orig [5] A. Heist, S.-H. Lee, Improved stability and rate capability of ionic liquid
electrolyte with high concentration of LiFSI, J. Electrochem. Soc. 166 (2019)
inal draft. Rajshree Rai: Formal analysis. S. Krishnamoorthi: Super A1860.
vision. Raju Khan: Writing – review & editing. [6] A. Ponrouch, R. Dedryvère, D. Monti, A.E. Demet, J.M.A. Mba, L. Croguennec,
C. Masquelier, P. Johansson, M.R. Palacín, Towards high energy density sodium
ion batteries through electrolyte optimization, Energy Environ. Sci. 6 (2013)
Declaration of competing interest 2361–2369.
[7] K. Xu, Nonaqueous liquid electrolytes for lithium-based rechargeable batteries,
Chem. Rev. 104 (2004) 4303–4418.
The authors declare that they have no known competing financial [8] L.M. Rodriguez-Martinez, N. Omar, Emerging Nanotechnologies in Rechargeable
interests or personal relationships that could have appeared to influence Energy Storage Systems, William Andrew, 2017.
30
[9] J. Kalhoff, G.G. Eshetu, D. Bresser, S. Passerini, Safer electrolytes for lithium-ion [40] D.S. Hall, R. Gauthier, A. Eldesoky, V.S. Murray, J.R. Dahn, New chemical
batteries: state of the art and perspectives, ChemSusChem 8 (2015) 2154–2175. insights into the beneficial role of Al2O3 cathode coatings in lithium-ion cells,
[10] Z. Yang, J. Zhang, M.C. Kintner-Meyer, X. Lu, D. Choi, J.P. Lemmon, J. Liu, ACS Appl. Mater. Interfaces 11 (2019) 14095–14100.
Electrochemical energy storage for green grid, Chem. Rev. 111 (2011) [41] J.-Y. Luo, W.-J. Cui, P. He, Y.-Y. Xia, Raising the cycling stability of aqueous
3577–3613. lithium-ion batteries by eliminating oxygen in the electrolyte, Nat. Chem. 2
[11] M. Watanabe, M.L. Thomas, S. Zhang, K. Ueno, T. Yasuda, K. Dokko, Application (2010) 760–765.
of ionic liquids to energy storage and conversion materials and devices, Chem. [42] B. Jache, P. Adelhelm, Use of graphite as a highly reversible electrode with
Rev. 117 (2017) 7190–7239. superior cycle life for sodium-ion batteries by making use of co-intercalation
[12] Q. Yang, Z. Zhang, X.-G. Sun, Y.-S. Hu, H. Xing, S. Dai, Ionic liquids and derived phenomena, Angew. Chem. Int. Ed. 53 (2014) 10169–10173.
materials for lithium and sodium batteries, Chem. Soc. Rev. 47 (2018) [43] E. Jónsson, P. Johansson, Modern battery electrolytes: ion–ion interactions in Li
2020–2064. +/Na+ conductors from DFT calculations, Phys. Chem. Chem. Phys. 14 (2012)
[13] R. Chen, D. Bresser, M. Saraf, P. Gerlach, A. Balducci, S. Kunz, D. Schröder, 10774–10779.
S. Passerini, J. Chen, A comparative review of electrolytes for organic-material- [44] D. Monti, E. Jónsson, A. Boschin, M.R. Palacín, A. Ponrouch, P. Johansson,
based energy-storage devices employing solid electrodes and redox fluids, Towards standard electrolytes for sodium-ion batteries: physical properties, ion
ChemSusChem 13 (2020) 2205–2219. solvation and ion-pairing in alkyl carbonate solvents, Phys. Chem. Chem. Phys.
[14] F. Wang, J. Graetz, M.S. Moreno, C. Ma, L. Wu, V. Volkov, Y. Zhu, Chemical 22 (2020) 22768–22777.
distribution and bonding of lithium in intercalated graphite: identification with [45] M. Gouverneur, J. Kopp, L. Van Wüllen, M. Schönhoff, Direct determination of
optimized electron energy loss spectroscopy, ACS Nano 5 (2011) 1190–1197. ionic transference numbers in ionic liquids by electrophoretic NMR, Phys. Chem.
[15] E. Peled, Film forming reaction at the lithium/electrolyte interface, J. Power Chem. Phys. 17 (2015) 30680–30686.
Sources 9 (1983) 253–266. [46] M. Okoshi, Y. Yamada, A. Yamada, H. Nakai, Theoretical analysis on de-solvation
[16] D. Aurbach, Y. Talyosef, B. Markovsky, E. Markevich, E. Zinigrad, L. Asraf, J. of lithium, sodium, and magnesium cations to organic electrolyte solvents,
S. Gnanaraj, H.-J. Kim, Design of electrolyte solutions for Li and Li-ion batteries: a J. Electrochem. Soc. 160 (2013) A2160.
review, Electrochim. Acta 50 (2004) 247–254. [47] Y. Mizuno, M. Okubo, D. Asakura, T. Saito, E. Hosono, Y. Saito, K. Oh-ishi,
[17] J.W. Fergus, Ceramic and polymeric solid electrolytes for lithium-ion batteries, T. Kudo, H. Zhou, Impedance spectroscopic study on interfacial ion transfers in
J. Power Sources 195 (2010) 4554–4569. cyanide-bridged coordination polymer electrode with organic electrolyte,
[18] H. Kim, J. Hong, K.-Y. Park, H. Kim, S.-W. Kim, K. Kang, Aqueous rechargeable Li Electrochim. Acta 63 (2012) 139–145.
and Na ion batteries, Chem. Rev. 114 (2014) 11788–11827. [48] M. Young, P. Carroad, R. Bell, Estimation of diffusion coefficients of proteins,
[19] A.S. Nagelberg, W.L. Worrell, A thermodynamic study of sodium-intercalated Biotechnol. Bioeng. 22 (1980) 947–955.
TaS2 and TiS2, J. Solid State Chem. 29 (1979) 345–354. [49] W. Liu, C. Yi, L. Li, S. Liu, Q. Gui, D. Ba, Y. Li, D. Peng, J. Liu, Designing polymer-
[20] Y. Xia, K. Tatsumi, T. Fujieda, P.P. Prosini, T. Sakai, Solid-state lithium-polymer in-salt electrolyte and fully infiltrated 3D electrode for integrated solid-state
batteries using lithiated MnO2 cathodes, J. Electrochem. Soc. 147 (2000) 2050. lithium batteries, Angew. Chem. 133 (2021) 13041–13050.
[21] A. Ponrouch, D. Monti, A. Boschin, B. Steen, P. Johansson, M.R. Palacín, Non- [50] G. Li, Regulating mass transport behavior for high-performance lithium metal
aqueous electrolytes for sodium-ion batteries, J. Mater. Chem. A 3 (2015) 22–42. batteries and fast-charging lithium-ion batteries, Adv. Energy Mater. 11 (2021)
[22] B. Zakeri, S. Syri, Corrigendum to “Electrical energy storage systems: a 2002891.
comparative life cycle cost analysis”[Renew. Sustain. Energy Rev. 42 (2015) [51] M. Kabir, D.E. Demirocak, Degradation mechanisms in Li-ion batteries: a state-of-
569–596], Renew. Sust. Energ. Rev., 100 (2016) 1634–1635. the-art review, Int. J. Energy Res. 41 (2017) 1963–1986.
[23] D. Patteeuw, K. Bruninx, A. Arteconi, E. Delarue, W. D’haeseleer, L. Helsen, [52] E. Pomerantseva, F. Bonaccorso, X. Feng, Y. Cui, Y. Gogotsi, Energy storage: the
Integrated modeling of active demand response with electric heating systems future enabled by nanomaterials, Science 366 (2019) eaan8285.
coupled to thermal energy storage systems, Appl. Energy 151 (2015) 306–319. [53] D. Parkhurst, C. Appelo, PhreeqC. A computer program for speciation, batch-
[24] D. Fenton, Complex of alkali metal ions with poly (ethylene oxide), Polymer 14 reaction, one-dimensional transport, and inverse geochemical calculations, US
(1973) 589. Geological Survey, (2003).
[25] G. Feuillade, P. Perche, Ion-conductive macromolecular gels and membranes for [54] P. Vanysek, Ionic conductivity and diffusion at infinite dilution, in: CRC Hand
solid lithium cells, J. Appl. Electrochem. 5 (1975) 63–69. Book of Chemistry and Physics, 1993, pp. 5–92.
[26] J. Gao, C. Wang, D.-W. Han, D.-M. Shin, Single-ion conducting polymer [55] H. Yang, N. Wu, Ionic conductivity and ion transport mechanisms of solid-state
electrolytes as a key jigsaw piece for next-generation battery applications, Chem. lithium-ion battery electrolytes: a review, Energy Sci. Eng. 10 (2022) 1643–1671.
Sci. 12 (2021) 13248–13272. [56] S. Seki, K. Hayamizu, S. Tsuzuki, K. Fujii, Y. Umebayashi, T. Mitsugi,
[27] K. Abraham, J. Goldman, D. Natwig, Characterization of ether electrolytes for T. Kobayashi, Y. Ohno, Y. Kobayashi, Y. Mita, Relationships between center atom
rechargeable lithium cells, J. Electrochem. Soc. 129 (1982) 2404. species (N, P) and ionic conductivity, viscosity, density, self-diffusion coefficient
[28] C. Angell, C. Liu, E. Sanchez, Rubbery solid electrolytes with dominant cationic of quaternary cation room-temperature ionic liquids, Phys. Chem. Chem. Phys. 11
transport and high ambient conductivity, Nature 362 (1993) 137–139. (2009) 3509–3514.
[29] N. Mohamed, R. Subban, A. Arof, Polymer batteries fabricated from lithium [57] R. Tiwari, E. Sonker, D. Kumar, K. Kumar, P. Adhikary, S. Krishnamoorthi,
complexed acetylated chitosan, J. Power Sources 56 (1995) 153–156. Preparation, characterization and electrical properties of alkali metal ions doped
[30] F. Mizuno, S. Nakanishi, Y. Kotani, S. Yokoishi, H. Iba, Rechargeable Li-air co-polymers based on TBF, Mater. Sci. Eng. B 262 (2020) 114687.
batteries with carbonate-based liquid electrolytes, Electrochemistry 78 (2010) [58] K. Parwati, R. Tiwari, D.K. Verma, D. Kumar, S. Yadav, R. Rai, S. Singh, P.
403–405. Srivastava, S. Krishnamoorthi, Ionic liquid-supported vat dye (Congo Red)-based
[31] K. Pan, G. Shi, A. Li, H. Li, R. Zhao, F. Wang, W. Zhang, Q. Chen, H. Chen, donor–acceptor type conjugated polymeric material as photosensitizer for dye-
Z. Xiong, The performance of a silica-based mixed gel electrolyte in lead acid sensitized solar cells, Energy Technology, 2300598.
batteries, J. Power Sources 209 (2012) 262–268. [59] M. Park, X. Zhang, M. Chung, G.B. Less, A.M. Sastry, A review of conduction
[32] L. Suo, O. Borodin, T. Gao, M. Olguin, J. Ho, X. Fan, C. Luo, C. Wang, K. Xu, phenomena in Li-ion batteries, J. Power Sources 195 (2010) 7904–7929.
“Water-in-salt” electrolyte enables high-voltage aqueous lithium-ion chemistries, [60] Y. Saito, W. Morimura, R. Kuratani, S. Nishikawa, Factors controlling the ionic
Science 350 (2015) 938–943. mobility of lithium electrolyte solutions in separator membranes, J. Phys. Chem.
[33] Y. Xu, J. Li, W. Li, A strategy for preparing solid polymer electrolytes containing C 120 (2016) 3619–3624.
in situ synthesized ZnO nanoparticles with excellent electrochemical [61] R. Tiwari, D.K. Verma, D. Kumar, S. Yadav, K. Kumar, S. Krishnamoorthi, Ionic
performance, Nanomaterials 12 (2022) 2680. conductivity and dielectric properties of bulk SPP-PEG hydrogels as Na+ ion-
[34] H. Srour, H. Rouault, C. Santini, Imidazolium based ionic liquid electrolytes for based SPE materials for energy storage applications, Materials Chemistry,
Li-ion secondary batteries based on graphite and LiFePO4, J. Electrochem. Soc. Frontiers 5 (2021) 5857–5866.
160 (2012) A66. [62] R. Tiwari, D.K. Verma, D. Kumar, S. Yadav, K. Kumar, P. Adhikary,
[35] J. Pitawala, M.A. Navarra, B. Scrosati, P. Jacobsson, A. Matic, Structure and S. Krishnamoorthi, Single-ion-conducting SPP–SPA blend hydrogel-based pseudo-
properties of Li-ion conducting polymer gel electrolytes based on ionic liquids of solid polymeric electrolyte material for Na+-ion constructed energy storage
the pyrrolidinium cation and the bis (trifluoromethanesulfonyl) imide anion, devices, Energy Fuel 36 (2022) 6459–6467.
J. Power Sources 245 (2014) 830–835. [63] A. Chandra, A. Bhatt, A. Chandra, Ion conduction in superionic glassy
[36] E. Kim, J. Han, S. Ryu, Y. Choi, J. Yoo, Ionic liquid electrolytes for electrolytes: an overview, J. Mater. Sci. Technol. 29 (2013) 193–208.
electrochemical energy storage devices, Materials 14 (2021) 4000. [64] M. Chintapalli, K. Timachova, K.R. Olson, S.J. Mecham, D. Devaux, J.
[37] Q. Shen, Y. Wang, G. Han, X. Li, T. Yuan, H. Sun, Y. Gong, T. Chen, Recent M. DeSimone, N.P. Balsara, Relationship between conductivity, ion diffusion, and
progress in electrolyte additives for highly reversible zinc anodes in aqueous zinc transference number in perfluoropolyether electrolytes, Macromolecules 49
batteries, Batteries 9 (2023) 284. (2016) 3508–3515.
[38] A. Pfrang, A. Kriston, V. Ruiz, N. Lebedeva, F. Di Persio, Safety of rechargeable [65] S.R. Hui, J. Roller, S. Yick, X. Zhang, C. Decès-Petit, Y. Xie, R. Maric, D. Ghosh,
energy storage systems with a focus on Li-ion technology, in: Emerging A brief review of the ionic conductivity enhancement for selected oxide
Nanotechnologies in Rechargeable Energy Storage Systems, Elsevier, 2017, electrolytes, J. Power Sources 172 (2007) 493–502.
pp. 253–290. [66] N.Q. Minh, T. Takahashi, Science and Technology of Ceramic Fuel Cells, Elsevier,
[39] Y. Cui, H. Yao, B. Gao, Y. Qin, S. Zhang, B. Yang, C. He, B. Xu, J. Hou, Fine-tuned 1995.
photoactive and interconnection layers for achieving over 13% efficiency in a [67] J. Baumard, P. Abelard, Defect structure and transport properties of ZrO 2-based
fullerene-free tandem organic solar cell, J. Am. Chem. Soc. 139 (2017) solid electrolytes, in: Science and Technology of Zirconia II, 1983.
7302–7309. [68] O.T. Sørensen, Nonstoichiometric Oxides, Elsevier, 2012.
[69] H. Tuller, in: T. Sorensen (Ed.), Nonstozchrometrzc Oxzdes, Academic Press, New
York, 1981.
31
[70] N.M. Tallan, Electrical Conductivity in Ceramics and Glass, M. Dekker, 1974. [100] N.O. Laschuk, E.B. Easton, O.V. Zenkina, Reducing the resistance for the use of
[71] H. Cavers, P. Molaiyan, M. Abdollahifar, U. Lassi, A. Kwade, Perspectives on electrochemical impedance spectroscopy analysis in materials chemistry, RSC
improving the safety and sustainability of high voltage lithium-ion batteries Adv. 11 (2021) 27925–27936.
through the electrolyte and separator region, Adv. Energy Mater. 12 (2022) [101] B.-A. Mei, O. Munteshari, J. Lau, B. Dunn, L. Pilon, Physical interpretations of
2200147. Nyquist plots for EDLC electrodes and devices, J. Phys. Chem. C 122 (2018)
[72] R. Kumar, S.A. Suthanthiraraj, Ion dynamics and segmental relaxation of CeO2 194–206.
nanoparticles loaded soft-matter like gel polymer electrolyte, J. Non-Cryst. Solids [102] B.-A. Mei, J. Lau, T. Lin, S.H. Tolbert, B.S. Dunn, L. Pilon, Physical interpretations
405 (2014) 76–82. of electrochemical impedance spectroscopy of redox active electrodes for
[73] N. Srivastava, M. Kumar, Ion dynamics and relaxation behavior of NaPF 6-doped electrical energy storage, J. Phys. Chem. C 122 (2018) 24499–24511.
polymer electrolyte systems, J. Solid State Electrochem. 20 (2016) 1421–1428. [103] A.C. Lazanas, M.I. Prodromidis, Electrochemical Impedance Spectroscopy — A
[74] W. Li, Y. Pang, J. Liu, G. Liu, Y. Wang, Y. Xia, A PEO-based gel polymer Tutorial, ACS Measurement Science Au, 2022.
electrolyte for lithium ion batteries, RSC Adv. 7 (2017) 23494–23501. [104] K.J. Szekeres, S. Vesztergom, M. Ujvári, G.G. Láng, Methods for the determination
[75] A. Khiar, R. Puteh, A. Arof, Conductivity studies of a chitosan-based polymer of valid impedance spectra in non-stationary electrochemical systems: concepts
electrolyte, Phys. B Condens. Matter 373 (2006) 23–27. and techniques of practical importance, ChemElectroChem 8 (2021) 1233–1250.
[76] R. Murugaraj, Ac conductivity and its scaling behavior in borate and bismuthate [105] S. Wang, J. Zhang, O. Gharbi, V. Vivier, M. Gao, M.E. Orazem, Electrochemical
glasses, J. Mater. Sci. 42 (2007) 10065–10073. impedance spectroscopy, Nat. Rev. Methods Primers 1 (2021) 41.
[77] D. Almond, A. West, Mobile ion concentrations in solid electrolytes from an [106] E. Barsoukov, J.R. Macdonald, Impedance Spectroscopy Theory, Experiment, and,
analysis of ac conductivity, Solid State Ionics 9 (1983) 277–282. Applications, 2nd ed.(Hoboken, NJ: John Wiley &Sons, Inc., 2005), (2005).
[78] L. Chen, S. Venkatram, C. Kim, R. Batra, A. Chandrasekaran, R. Ramprasad, [107] M.E. Orazem, B. Tribollet, Electrochemical impedance spectroscopy, New Jersey
Electrochemical stability window of polymeric electrolytes, Chem. Mater. 31 1 (2008) 383–389.
(2019) 4598–4604. [108] E. Ivers-Tiffee, A. Weber, Evaluation of electrochemical impedance spectra by the
[79] A. Méry, S. Rousselot, D. Lepage, M. Dollé, A critical review for an accurate distribution of relaxation times, J. Ceram. Soc. Jpn. 125 (2017) 193–201.
electrochemical stability window measurement of solid polymer and composite [109] S. Dierickx, A. Weber, E. Ivers-Tiffée, How the distribution of relaxation times
electrolytes, Materials 14 (2021) 3840. enhances complex equivalent circuit models for fuel cells, Electrochim. Acta 355
[80] L. Long, S. Wang, M. Xiao, Y. Meng, Polymer electrolytes for lithium polymer (2020) 136764.
batteries, J. Mater. Chem. A 4 (2016) 10038–10069. [110] D.D. Macdonald, Reflections on the history of electrochemical impedance
[81] D. Wang, T. He, A. Wang, K. Guo, M. Avdeev, C. Ouyang, L. Chen, S. Shi, spectroscopy, Electrochim. Acta 51 (2006) 1376–1388.
A thermodynamic cycle-based electrochemical windows database of 308 [111] B.A. Boukamp, A nonlinear least squares fit procedure for analysis of immittance
electrolyte solvents for rechargeable batteries, Adv. Funct. Mater. 33 (11) (2023) data of electrochemical systems, Solid State Ionics 20 (1986) 31–44.
2212342. [112] B.-R. Chen, Y.R. Police, M. Li, P.R. Chinnam, T.R. Tanim, E.J. Dufek,
[82] C.F. Marchiori, R.P. Carvalho, M. Ebadi, D. Brandell, C.M. Araujo, Understanding A mathematical approach to survey electrochemical impedance spectroscopy for
the electrochemical stability window of polymer electrolytes in solid-state aging in lithium-ion batteries, Front. Energy Res. 11 (2023) 167.
batteries from atomic-scale modeling: the role of Li-ion salts, Chem. Mater. 32 [113] F. Zhang, Y. Sun, Z. Wang, D. Fu, J. Li, J. Hu, J. Xu, X. Wu, Highly conductive
(2020) 7237–7246. polymeric ionic liquid electrolytes for ambient-temperature solid-state lithium
[83] T.K. Schwietert, A. Vasileiadis, M. Wagemaker, First-principles prediction of the batteries, ACS Appl. Mater. Interfaces 12 (2020) 23774–23780.
electrochemical stability and reaction mechanisms of solid-state electrolytes, [114] X. Han, S.J. Zhou, Y.Z. Tan, X. Wu, F. Gao, Z.J. Liao, R.B. Huang, Y.Q. Feng, X. Lu,
JACS Au 1 (2021) 1488–1496. S.Y. Xie, Crystal structures of saturn-like C50Cl10 and pineapple-shaped C64Cl4:
[84] P. Gentile, M.G. Scioli, A. Bielli, B. De Angelis, C. De Sio, D. De Fazio, geometric implications of double-and triple-pentagon-fused chlorofullerenes,
G. Ceccarelli, A. Trivisonno, A. Orlandi, V. Cervelli, Platelet-rich plasma and Angew. Chem. Int. Ed. 47 (2008) 5340–5343.
micrografts enriched with autologous human follicle mesenchymal stem cells [115] J. Wang, F. Lin, H. Jia, J. Yang, C.W. Monroe, Y. NuLi, Towards a safe
improve hair re-growth in androgenetic alopecia. Biomolecular pathway analysis lithium–sulfur battery with a flame-inhibiting electrolyte and a sulfur-based
and clinical evaluation, Biomedicines 7 (2019) 27. composite cathode, Angew. Chem. Int. Ed. 53 (2014) 10099–10104.
[85] G.G. Gochev, E. Scoppola, R.A. Campbell, B.A. Noskov, R. Miller, E. Schneck, [116] S.B. Aziz, Z.H.Z. Abidin, Ion-transport study in nanocomposite solid polymer
β-Lactoglobulin adsorption layers at the water/air surface: 3, Neutron electrolytes based on chitosan: electrical and dielectric analysis, J. Appl. Polym.
reflectometry study on the effect of pH, J. Phys. Chem. B 123 (2019) Sci. 132 (2015).
10877–10889. [117] B.K. Faris, A.A. Hassan, S.B. Aziz, M.A. Brza, A.M. Abdullah, A.A. Abdalrahman,
[86] K. Liu, Z. Wang, L. Shi, S. Jungsuttiwong, S. Yuan, Ionic liquids for high O.A. Abu Ali, D.I. Saleh, Impedance, electrical equivalent circuit (EEC) modeling,
performance lithium metal batteries, J. Energy Chem. 59 (2021) 320–333. structural (FTIR and XRD), dielectric, and electric modulus study of MC-based
[87] H. Qi, Y. Ren, S. Guo, Y. Wang, S. Li, Y. Hu, F. Yan, High-voltage resistant ionic ion-conducting solid polymer electrolytes, Materials 15 (2022) 170.
liquids for lithium-ion batteries, ACS Appl. Mater. Interfaces 12 (2019) 591–600. [118] M. Kato, K. Hiraoka, S. Seki, Investigation of the ionic conduction mechanism of
[88] P.J. Fischer, M.P. Do, R.M. Reich, A. Nagasubramanian, M. Srinivasan, F.E. Kühn, polyether/Li7La3Zr2O12 composite solid electrolytes by electrochemical
Synthesis and physicochemical characterization of room temperature ionic impedance spectroscopy, J. Electrochem. Soc. 167 (2020) 070559.
liquids and their application in sodium ion batteries, Phys. Chem. Chem. Phys. 20 [119] J.C. Hooker, W.R. Burghardt, J.M. Torkelson, Birefringence and second-order
(2018) 29412–29422. nonlinear optics as probes of polymer cooperative segmental mobility:
[89] G.A. Giffin, Ionic liquid-based electrolytes for “beyond lithium” battery demonstration of Debye-type relaxation, J. Chem. Phys. 111 (1999) 2779–2788.
technologies, J. Mater. Chem. A 4 (2016) 13378–13389. [120] J. Mijović, J. Kenny, A. Maffezzoli, A. Trivisano, F. Bellucci, L. Nicolais, The
[90] K. Sirengo, A. Babu, B. Brennan, S.C. Pillai, Ionic liquid electrolytes for sodium- principles of dielectric measurements for in situ monitoring of composite
ion batteries to control thermal runaway, J. Energy Chem. 81 (2023) 321–338. processing, Compos. Sci. Technol. 49 (1993) 277–290.
[91] D.C. Hoekstra, K. Nickmans, J. Lub, M.G. Debije, A.P. Schenning, Air-curable, [121] C. Abed, A. Ben Gouider Trabelsi, F.H. Alkallas, S. Fernandez, H. Elhouichet,
high-resolution patternable oxetane-based liquid crystalline photonic films via Transport mechanisms and dielectric features of Mg-doped ZnO nanocrystals for
flexographic printing, ACS Appl. Mater. Interfaces 11 (2019) 7423–7430. device applications, Materials 15 (2022) 2265.
[92] A. Bhide, J. Hofmann, A.K. Dürr, J. Janek, P. Adelhelm, Electrochemical stability [122] W. Wang, X. Wang, J. He, Y. Liu, S. Li, Y. Nie, Electric stress and dielectric
of non-aqueous electrolytes for sodium-ion batteries and their compatibility with breakdown characteristics under high-frequency voltages with multi-harmonics
Na 0.7 CoO 2, Phys. Chem. Chem. Phys. 16 (2014) 1987–1998. in a solid-state transformer, Int. J. Electr. Power Energy Syst. 129 (2021) 106861.
[93] O. Tutusaus, H. Kuwata, M.J. Counihan, R. Mohtadi, Improved synthesis enables [123] C. Ramya, S. Selvasekarapandian, G. Hirankumar, T. Savitha, P. Angelo,
assessment of the electrochemical window of monocarborate solid state Investigation on dielectric relaxations of PVP–NH4SCN polymer electrolyte,
electrolytes, Chem. Commun. 59 (2023) 4746–4749. J. Non-Cryst. Solids 354 (2008) 1494–1502.
[94] Y. Lu, L. Li, Q. Zhang, Z. Niu, J. Chen, Electrolyte and interface engineering for [124] M. Hashim, S. Kumar, B. Koo, S.E. Shirsath, E. Mohammed, J. Shah, R. Kotnala,
solid-state sodium batteries, Joule 2 (2018) 1747–1770. H. Choi, H. Chung, R. Kumar, Structural, electrical and magnetic properties of
[95] V. Lacivita, Y. Wang, S.-H. Bo, G. Ceder, Ab initio investigation of the stability of Co–Cu ferrite nanoparticles, J. Alloys Compd. 518 (2012) 11–18.
electrolyte/electrode interfaces in all-solid-state Na batteries, J. Mater. Chem. A 7 [125] R. Bilkees, A.A. Khan, M. Javed, J. Kazmi, M.A. Mohamed, M.N. Khan, A.Y. Abid,
(2019) 8144–8155. A. Majeed, Dielectric relaxation and variable range hopping conduction in sol-gel
[96] M.H. Lee, S.J. Kim, D. Chang, J. Kim, S. Moon, K. Oh, K.-Y. Park, W.M. Seong, auto combustion derived La0. 7Bi0. 3Fe0. 5Mn0. 5O3 manganite, Materials
H. Park, G. Kwon, Toward a low-cost high-voltage sodium aqueous rechargeable Science and Engineering: B, 269 (2021) 115153.
battery, Mater. Today 29 (2019) 26–36. [126] R. Das, R. Choudhary, Dielectric relaxation and magneto-electric characteristics
[97] L. Suo, O. Borodin, Y. Wang, X. Rong, W. Sun, X. Fan, S. Xu, M.A. Schroeder, A. of lead-free double perovskite: Sm 2 NiMnO 6, J. Adv. Ceram. 8 (2019) 174–185.
V. Cresce, F. Wang, “Water-in-salt” electrolyte makes aqueous sodium-ion battery [127] M. Fadhlullah, A. Shukur, Characterization of Ion Conducting Solid Biopolymer
safe, green, and long-lasting, Adv. Energy Mater. 7 (2017) 1701189. Electrolytes Based on Starch-Chitosan Blend and Application in Electrochemical
[98] J.-Z. Rong, T.-X. Cai, Y.-Z. Bai, X. Zhao, T. Wu, Y.-K. Wu, W. Zhao, W.-J. Dong, S.- Devices, Universiti Malaya, 2015.
M. Xu, J. Chen, A free-sealed high-voltage aqueous polymeric sodium battery [128] S. Das, A. Ghosh, Effect of plasticizers on ionic conductivity and dielectric
enabling operation at− 25◦ C, Cell Rep. Phys. Sci. 3 (2022) 100805. relaxation of PEO-LiClO4 polymer electrolyte, Electrochim. Acta 171 (2015)
[99] P. Vadhva, J. Hu, M.J. Johnson, R. Stocker, M. Braglia, D.J. Brett, A.J. Rettie, 59–65.
Electrochemical impedance spectroscopy for all-solid-state batteries: theory, [129] E.V. Gopalan, K. Malini, S. Saravanan, D.S. Kumar, Y. Yoshida, M. Anantharaman,
methods and future outlook, ChemElectroChem 8 (2021) 1930–1947. Evidence for polaron conduction in nanostructured manganese ferrite, J. Phys. D.
Appl. Phys. 41 (2008) 185005.
32
[130] S. Karmakar, H.S. Mohanty, D. Behera, Exploration of alternating current [161] K. Hayamizu, Y. Aihara, S. Arai, C.G. Martinez, Pulse-gradient spin-echo 1H, 7Li,
conduction mechanism and dielectric relaxation with Maxwell–Wagner effect in and 19F NMR diffusion and ionic conductivity measurements of 14 organic
NiO–CdO–Gd 2 O 3 nanocomposites, Eur. Phys. J. Plus, 136 (2021) 1–21. electrolytes containing LiN (SO2CF3) 2, J. Phys. Chem. B 103 (1999) 519–524.
[131] A. Arya, A. Sharma, Structural, electrical properties and dielectric relaxations in [162] J. Cui, T. Kobayashi, R.L. Sacci, R.A. Matsumoto, P.T. Cummings, M. Pruski,
Na+-ion-conducting solid polymer electrolyte, J. Phys. Condens. Matter 30 Diffusivity and structure of room temperature ionic liquid in various organic
(2018) 165402. solvents, J. Phys. Chem. B 124 (2020) 9931–9937.
[132] R. Tiwari, E. Sonker, D.K. Verma, K. Kumar, P. Adhikary, S. Krishnamoorthi, [163] D.A. Porter, K.E. Easterling, M.Y. Sherif, Phase Transformations in Metals and
Synthesis of in-situ doped hydrazine-oxalyl chloride based polyamides and their Alloys, CRC Press, 2021.
ionic conductivity studies, J. Phys. Chem. Solids 141 (2020) 109424. [164] H. Mehrer, Interdiffusion and Kirkendall Effect, Diffusion in Solids:
[133] W.S. Mohammed, G.L. Hornyak, Optical behavior of periodic nanostructured Fundamentals, Methods, Materials, Diffusion-Controlled Processes, 2007,
media: a classical electromagnetic (mesoscopic) approach, in: Handbook of pp. 161–177.
Nanoscience, Engineering, and Technology, CRC Press, 2018, pp. 216–261. [165] C. Wang, J. Hong, Ionic/electronic conducting characteristics of LiFePO4 cathode
[134] S. Yadav, R. Tiwari, D.K. Verma, D. Kumar, P. Adhikary, S. Krishnamoorthi, materials: the determining factors for high rate performance, Electrochem. Solid-
Synthesis of hydrazine-fumaryl chloride-based polyamide and its electrical State Lett. 10 (2007) A65.
conductivity studies, Polym. Eng. Sci. 63 (2023) 584–592. [166] D. McLean, Grain Boundaries in Metals, Clarendon Press, Oxford, 1957.
[135] Z. Ahmad, Polymer dielectric materials, in: Dielectric Material, IntechOpen, 2012. [167] L. Wang, Y. Lin, Z. Zeng, W. Liu, Q. Xue, L. Hu, J. Zhang, Electrochemical
[136] K.J. Hamam, F. Salman, Dielectric constant and electrical study of solid-state corrosion behavior of nanocrystalline Co coatings explained by higher grain
electrolyte lithium phosphate glasses, Appl. Phys. A 125 (2019) 621. boundary density, Electrochim. Acta 52 (13) (2007) 4342–4350.
[137] S. Altındal Yerişkin, M. Balbaşı, A. Tataroğlu, Frequency and voltage dependence [168] H. Mehrer, Diffusion in Solids: Fundamentals, Methods, Materials, Diffusion-
of dielectric properties, complex electric modulus, and electrical conductivity in controlled Processes, Springer Science & Business Media, 2007.
Au/7% graphene doped-PVA/n-Si (MPS) structures, J. Appl. Polym. Sci. 133 [169] L. Benitez, J.M. Seminario, Ion diffusivity through the solid electrolyte interphase
(2016). in lithium-ion batteries, J. Electrochem. Soc. 164 (2017) E3159.
[138] D.C. Elton, The origin of the Debye relaxation in liquid water and fitting the high [170] K. Abraham, B. Scrosati, Applications of electroactive polymers, in: B. Scrossati
frequency excess response, Phys. Chem. Chem. Phys. 19 (2017) 18739–18749. (Ed.), Highly Conductive Polymer Electrolytes, 1993, pp. 75–112.
[139] L.J. Gagliardi, D.H. Shain, Electrostatic mechanism for depolymerization-based [171] S. Takeda, Y. Saito, I. Kaneko, H. Yoshitake, Effect of cross-sectional shape of
poleward force generation at kinetochores, Open, J. Biophys. 9 (2019) 198–203. pathway on ion migration in polyethylene separators for lithium-ion batteries,
[140] Y. Saito, H. Kataoka, C. Capiglia, H. Yamamoto, Ionic conduction properties of J. Phys. Chem. C 124 (2019) 1827–1835.
PVDF− HFP type gel polymer electrolytes with lithium imide salts, J. Phys. Chem. [172] R. Cumeras, E. Figueras, C. Davis, J.I. Baumbach, I. Gracia, Review on ion
B 104 (2000) 2189–2192. mobility spectrometry. Part 1: current instrumentation, Analyst 140 (2015)
[141] T.R. Jow, K. Xu, O. Borodin, M. Ue, Electrolytes for Lithium And Lithium-ion 1376–1390.
Batteries, Springer, 2014. [173] D.K. Verma, R. Tiwari, D. Kumar, S. Yadav, K. Parwati, P. Adhikary,
[142] A. Carvalho, S. Negi, A.H.C. Neto, Direct calculation of the ionic mobility in S. Krishnamoorthi, Development of Na+ Ion Conducting Solid Biopolymer
superionic conductors, Sci. Rep. 12 (2022) 19930. Electrolyte Based on Na-CMC-SPA Hydrogel for Energy Storage Devices, 2022.
[143] Y. Saito, M. Okano, K. Kubota, T. Sakai, J. Fujioka, T. Kawakami, Evaluation of [174] D.K. Verma, R. Tiwari, D. Kumar, S. Yadav, K. Parwati, P. Adhikary,
interactive effects on the ionic conduction properties of polymer gel electrolytes, S. Krishnamoorthi, Development of Na+ ion conducting solid biopolymer
J. Phys. Chem. B 116 (2012) 10089–10097. electrolytes based on Na-CMC-SPA hydrogel, Mater. Sci. Eng. B 297 (2023)
[144] F. Gutmann, L. Simmons, The temperature dependence of the viscosity of liquids, 116800.
J. Appl. Phys. 23 (1952) 977–978. [175] Z. Lei, Z. Liu, H. Wang, X. Sun, L. Lu, X. Zhao, A high-energy-density
[145] J.-P. Hsu, S.-H. Lin, Temperature dependence of the viscosity of nonpolymeric supercapacitor with graphene–CMK-5 as the electrode and ionic liquid as the
liquids, J. Chem. Phys. 118 (2003) 172–178. electrolyte, J. Mater. Chem. A 1 (2013) 2313–2321.
[146] J.N. Israelachvili, Intermolecular and Surface Forces, Academic press, 2011. [176] M. Dalal, A Textbook of Inorganic Chemistry–Volume 1, Dalal Institute, 2017.
[147] Y. Saito, Ion transport in solid medium—evaluation of ionic mobility for design of [177] J.W. Daily, M.M. Micci, Ionic velocities in an ionic liquid under high electric fields
ion transport pathways in separator and gel electrolyte, Membranes 11 (2021) using all-atom and coarse-grained force field molecular dynamics, J. Chem. Phys.
277. 131 (2009) 094501.
[148] Y. Saito, W. Morimura, S. Kuse, R. Kuratani, S. Nishikawa, Influence of the [178] A. Anders, Self-organization and self-limitation in high power impulse magnetron
morphological characteristics of separator membranes on ionic mobility in sputtering, Appl. Phys. Lett. 100 (2012) 224104.
lithium secondary batteries, J. Phys. Chem. C 121 (2017) 2512–2520. [179] R. Agrawal, R. Kumar, R. Gupta, Estimation of ionic drift velocity on some fast Ag
[149] D. Ihm, J. Noh, J. Kim, Effect of polymer blending and drawing conditions on + ion conducting systems, Mater. Sci. Eng. B 57 (1998) 46–51.
properties of polyethylene separator prepared for Li-ion secondary battery, [180] J. Fleig, Voltage-assisted 18 O tracer incorporation into oxides for obtaining
J. Power Sources 109 (2002) 388–393. shallow diffusion profiles and for measuring ionic transference numbers: basic
[150] P. Abba, J. Gongwala, S. Laminsi, J. Brisset, The effect of the humid air plasma on considerations, Phys. Chem. Chem. Phys. 11 (2009) 3144–3151.
the conductivity of distilled water: contribution of ions, Int. J. Res. Chem. [181] L. Deng, Y. Wang, C. Cai, Z. Wei, Y. Fu, 3D-cellulose acetate-derived hierarchical
Environ. (IJRCE) 4 (2014) 25–30. network with controllable nanopores for superior Li+ transference number,
[151] D.L. Parkhurst, C. Appelo, User’s guide to PHREEQC (Version 2): a computer mechanical strength and dendrites hindrance, Carbohydr. Polym. 274 (2021)
program for speciation, batch-reaction, one-dimensional transport, and inverse 118620.
geochemical calculations, in: Water-resources Investigations Report vol. 99, 1999, [182] S. Kondou, Y. Sakashita, A. Morinaga, Y. Katayama, K. Dokko, M. Watanabe,
p. 312. K. Ueno, Concentrated nonaqueous polyelectrolyte solutions: high Na-ion
[152] A. Revil, Ionic diffusivity, electrical conductivity, membrane and thermoelectric transference number and surface-tethered polyanion layer for sodium-metal
potentials in colloids and granular porous media: a unified model, J. Colloid batteries, ACS Appl. Mater. Interfaces 15 (2023) 11741–11755.
Interface Sci. 212 (1999) 503–522. [183] Y. Lu, M. Tikekar, R. Mohanty, K. Hendrickson, L. Ma, L.A. Archer, Stable cycling
[153] A. Regberg, K. Singha, M. Tien, F. Picardal, Q. Zheng, J. Schieber, E. Roden, S. of lithium metal batteries using high transference number electrolytes, Adv.
L. Brantley, Electrical conductivity as an indicator of iron reduction rates in Energy Mater. 5 (2015) 1402073.
abiotic and biotic systems, Water Resour. Res. 47 (2011). [184] S.Y. Hong, Y. Kim, Y. Park, A. Choi, N.-S. Choi, K.T. Lee, Charge carriers in
[154] C.-W. Huang, M.G. Mohamed, C.-Y. Zhu, S.-W. Kuo, Functional supramolecular rechargeable batteries: Na ions vs, Li ions, Energy Environ. Sci. 6 (2013)
polypeptides involving π–π stacking and strong hydrogen-bonding interactions: a 2067–2081.
conformation study toward carbon nanotubes (CNTs) dispersion, Macromolecules [185] K. Krisorncharoen, P. Weschayanwiwat, Separation of PCE via Liquid-Liquid
49 (2016) 5374–5385. Extraction and Reverse Micellar Extraction for Surfactant Recovery, Greater
[155] Y. Choo, D.M. Halat, I. Villaluenga, K. Timachova, N.P. Balsara, Diffusion and Mekong Subregion Academic and Research Network, 2011, p. 243.
migration in polymer electrolytes, Prog. Polym. Sci. 103 (2020) 101220. [186] S. Müller, Application and Refinement of COSMO-RS-ES for Calculating Phase
[156] D.K. Verma, R. Tiwari, D. Kumar, S. Yadav, P. Adhikary, S. Krishnamoorthi, Equilibria of Electrolyte Systems at High Concentrations in Mixed and Non-
Introduction of Al (III)-ion-based solid polymer electrolyte material for energy aqueous Solvents, Technische Universität Hamburg, 2020.
storage device applications, ChemistrySelect 8 (2023) e202302287. [187] L.F. Cameretti, G. Sadowski, J.M. Mollerup, Modeling of aqueous electrolyte
[157] D.S. Wilkinson, Mass Transport in Solids and Fluids, Cambridge University Press, solutions with perturbed-chain statistical associated fluid theory, Ind. Eng. Chem.
2000. Res. 44 (2005) 3355–3362.
[158] J.L. Bañuelos, G. Feng, P.F. Fulvio, S. Li, G. Rother, N. Arend, A. Faraone, S. Dai, [188] C. Held, T. Reschke, S. Mohammad, A. Luza, G. Sadowski, ePC-SAFT revised,
P.T. Cummings, D.J. Wesolowski, The influence of a hierarchical porous carbon Chem. Eng. Res. Des. 92 (2014) 2884–2897.
network on the coherent dynamics of a nanoconfined room temperature ionic [189] J.F. Brennecke, E.J. Maginn, Ionic liquids: innovative fluids for chemical
liquid: a neutron spin echo and atomistic simulation investigation, Carbon 78 processing, American Institute of Chemical Engineers, AICHE J. 47 (2001) 2384.
(2014) 415–427. [190] X. Wang, S. Wang, H. Wang, W. Tu, Y. Zhao, S. Li, Q. Liu, J. Wu, Y. Fu, C. Han,
[159] W. Sutherland LXXV, A dynamical theory of diffusion for non-electrolytes and the Hybrid electrolyte with dual-anion-aggregated solvation sheath for stabilizing
molecular mass of albumin, The London, Edinburgh, and Dublin Philosophical high-voltage lithium-metal batteries, Adv. Mater. 33 (2021) 2007945.
Magazine and Journal of, Science 9 (1905) 781–785. [191] B. Van der Bruggen, A. Koninckx, C. Vandecasteele, Separation of monovalent and
[160] H. Tokuda, K. Hayamizu, K. Ishii, M.A.B.H. Susan, M. Watanabe, Physicochemical divalent ions from aqueous solution by electrodialysis and nanofiltration, Water
properties and structures of room temperature ionic liquids. 2. Variation of alkyl Res. 38 (2004) 1347–1353.
chain length in imidazolium cation, J. Phys. Chem. B 109 (2005) 6103–6110.
33
[192] Y. Huang, L. Zhao, L. Li, M. Xie, F. Wu, R. Chen, Electrolytes and electrolyte/ [220] J. Feng, Y. An, L. Ci, S. Xiong, Nonflammable electrolyte for safer non-aqueous
electrode interfaces in sodium-ion batteries: from scientific research to practical sodium batteries, J. Mater. Chem. A 3 (2015) 14539–14544.
application, Adv. Mater. 31 (2019) 1808393. [221] L. Xia, Y. Xia, Z. Liu, A novel fluorocyclophosphazene as bifunctional additive for
[193] G.G. Eshetu, G.A. Elia, M. Armand, M. Forsyth, S. Komaba, T. Rojo, S. Passerini, safer lithium-ion batteries, J. Power Sources 278 (2015) 190–196.
Electrolytes and interphases in sodium-based rechargeable batteries: recent [222] J. Gnanaraj, E. Zinigrad, L. Asraf, H. Gottlieb, M. Sprecher, M. Schmidt,
advances and perspectives, Adv. Energy Mater. 10 (2020) 2000093. W. Geissler, D. Aurbach, A detailed investigation of the thermal reactions of LiPF6
[194] C. Schotten, T.P. Nicholls, R.A. Bourne, N. Kapur, B.N. Nguyen, C.E. Willans, solution in organic carbonates using ARC and DSC, J. Electrochem. Soc. 150
Making electrochemistry easily accessible to the synthetic chemist, Green Chem. (2003) A1533.
22 (2020) 3358–3375. [223] J. Jiang, J. Dahn, ARC studies of the reaction between Li0FePO4 and LiPF6 or
[195] M. Yoshimura, K. Honda, T. Kondo, R. Uchikado, Y. Einaga, T.N. Rao, D. Tryk, LiBOB EC/DEC electrolytes, Electrochem. Commun. 6 (2004) 724–728.
A. Fujishima, Factors controlling the electrochemical potential window for [224] M. Richard, J. Dahn, Accelerating rate calorimetry study on the thermal stability
diamond electrodes in non-aqueous electrolytes, Diam. Relat. Mater. 11 (2002) of lithium intercalated graphite in electrolyte. II. Modeling the results and
67–74. predicting differential scanning calorimeter curves, J. Electrochem. Soc. 146
[196] R. Komiya, L. Han, R. Yamanaka, A. Islam, T. Mitate, Highly efficient quasi-solid (1999) 2078.
state dye-sensitized solar cell with ion conducting polymer electrolyte, [225] X. Xia, J. Dahn, NaCrO2 is a fundamentally safe positive electrode material for
J. Photochem. Photobiol. A Chem. 164 (2004) 123–127. sodium-ion batteries with liquid electrolytes, Electrochem. Solid-State Lett. 15
[197] A. Ponrouch, E. Marchante, M. Courty, J.-M. Tarascon, M.R. Palacin, In search of (2011) A1.
an optimized electrolyte for Na-ion batteries, Energy Environ. Sci. 5 (2012) [226] X. Xia, J. Dahn, A study of the reactivity of de-intercalated P2-NaxCoO2 with non-
8572–8583. aqueous solvent and electrolyte by accelerating rate calorimetry, J. Electrochem.
[198] G. Kamath, R.W. Cutler, S.A. Deshmukh, M. Shakourian-Fard, R. Parrish, Soc. 159 (2012) A647.
J. Huether, D.P. Butt, H. Xiong, S.K. Sankaranarayanan, In silico based rank-order [227] X. Xia, J. Dahn, A study of the reactivity of de-intercalated NaNi0. 5Mn0. 5O2
determination and experiments on nonaqueous electrolytes for sodium ion with non-aqueous solvent and electrolyte by accelerating rate calorimetry,
battery applications, J. Phys. Chem. C 118 (2014) 13406–13416. J. Electrochem. Soc. 159 (2012) A1048.
[199] P.G. Bruce, C. Vincent, Polymer electrolytes, J. Chem. Soc. Faraday Trans. 89 [228] A. Boschin, P. Johansson, Characterization of NaX (X: TFSI, FSI)–PEO based solid
(1993) 3187–3203. polymer electrolytes for sodium batteries, Electrochim. Acta 175 (2015) 124–133.
[200] E. Quartarone, P. Mustarelli, Electrolytes for solid-state lithium rechargeable [229] I. Villaluenga, X. Bogle, S. Greenbaum, I.G. de Muro, T. Rojo, M. Armand, Cation
batteries: recent advances and perspectives, Chem. Soc. Rev. 40 (2011) only conduction in new polymer–SiO 2 nanohybrids: Na+ electrolytes, J. Mater.
2525–2540. Chem. A 1 (2013) 8348–8352.
[201] J. Pérez-Flores, P. Ocón, Applications of ionic liquids as innovative electrolytes [230] Y.L. Ni’mah, M.-Y. Cheng, J.H. Cheng, J. Rick, B.-J. Hwang, Solid-state polymer
for fuel cells, J. Magnetohydrodyn. Plasma Res. 21 (2016) 245–288. nanocomposite electrolyte of TiO2/PEO/NaClO4 for sodium ion batteries,
[202] K.H. Sippel, F.A. Quiocho, Ion–dipole interactions and their functions in proteins, J. Power Sources 278 (2015) 375–381.
Protein Sci. 24 (2015) 1040–1046. [231] D. Andelman, Electrostatic properties of membranes: the Poisson-Boltzmann
[203] Y. Song, P. Ruan, C. Mao, Y. Chang, L. Wang, L. Dai, P. Zhou, B. Lu, J. Zhou, Z. He, theory, in: Handbook of Biological Physics, Elsevier, 1995, pp. 603–642.
Metal–organic frameworks functionalized separators for robust aqueous zinc-ion [232] K.D. Collins, Ions from the Hofmeister series and osmolytes: effects on proteins in
batteries, Nano-Micro Lett. 14 (2022) 218. solution and in the crystallization process, Methods 34 (2004) 300–311.
[204] A. Curzons, D. Constable, V. Cunningham, Solvent selection guide: a guide to the [233] O. Borodin, L. Suo, M. Gobet, X. Ren, F. Wang, A. Faraone, J. Peng, M. Olguin,
integration of environmental, health and safety criteria into the selection of M. Schroeder, M.S. Ding, Liquid structure with nano-heterogeneity promotes
solvents, Clean Prod. Process. 1 (1999) 82–90. cationic transport in concentrated electrolytes, ACS Nano 11 (2017)
[205] M.P. Vikram, V. Kumaresan, S. Christopher, R. Velraj, Experimental studies on 10462–10471.
solidification and subcooling characteristics of water-based phase change [234] J. Zheng, J.A. Lochala, A. Kwok, Z.D. Deng, J. Xiao, Research progress towards
material (PCM) in a spherical encapsulation for cool thermal energy storage understanding the unique interfaces between concentrated electrolytes and
applications, Int. J. Refrig. 100 (2019) 454–462. electrodes for energy storage applications, Adv. Sci. 4 (2017) 1700032.
[206] W. Tong, M. Forster, F. Dionigi, S. Dresp, R. Sadeghi Erami, P. Strasser, A. [235] Y. Yamada, K. Furukawa, K. Sodeyama, K. Kikuchi, M. Yaegashi, Y. Tateyama,
J. Cowan, P. Farràs, Electrolysis of low-grade and saline surface water, Nature, A. Yamada, Unusual stability of acetonitrile-based superconcentrated electrolytes
Energy 5 (2020) 367–377. for fast-charging lithium-ion batteries, J. Am. Chem. Soc. 136 (2014) 5039–5046.
[207] K. Ehelebe, D. Escalera-López, S. Cherevko, Limitations of aqueous model systems [236] Y. Marcus, G. Hefter, Ion pairing, Chem. Rev. 106 (2006) 4585–4621.
in the stability assessment of electrocatalysts for oxygen reactions in fuel cell and [237] N.F. Van Der Vegt, K. Haldrup, S. Roke, J. Zheng, M. Lund, H.J. Bakker, Water-
electrolyzers, Curr. Opin. Electrochem. 29 (2021) 100832. mediated ion pairing: occurrence and relevance, Chem. Rev. 116 (2016)
[208] S. Carquigny, O. Segut, B. Lakard, F. Lallemand, P. Fievet, Effect of electrolyte 7626–7641.
solvent on the morphology of polypyrrole films: application to the use of [238] A.N. Krishnamoorthy, C. Holm, J. Smiatek, Specific ion effects for polyelectrolytes
polypyrrole in pH sensors, Synth. Met. 158 (2008) 453–461. in aqueous and non-aqueous media: the importance of the ion solvation behavior,
[209] D. Pahari, S. Puravankara, Greener, safer, and sustainable batteries: an insight Soft Matter 14 (2018) 6243–6255.
into aqueous electrolytes for sodium-ion batteries, ACS Sustain. Chem. Eng. 8 [239] P. Lo Nostro, B.W. Ninham, Hofmeister phenomena: an update on ion specificity
(2020) 10613–10625. in biology, Chem. Rev. 112 (2012) 2286–2322.
[210] Q. Li, B. Chen, B. Xing, Aggregation kinetics and self-assembly mechanisms of [240] Y. Zhang, P.S. Cremer, Interactions between macromolecules and ions: the
graphene quantum dots in aqueous solutions: cooperative effects of pH and Hofmeister series, Curr. Opin. Chem. Biol. 10 (2006) 658–663.
electrolytes, Environ. Sci. Technol. 51 (2017) 1364–1376. [241] K.D. Collins, Charge density-dependent strength of hydration and biological
[211] A. Goyal, M.T. Koper, The interrelated effect of cations and electrolyte pH on the structure, Biophys. J. 72 (1997) 65–76.
hydrogen evolution reaction on gold electrodes in alkaline media, Angew. Chem. [242] V. Mazzini, V.S. Craig, Volcano plots emerge from a sea of nonaqueous solvents:
Int. Ed. 60 (2021) 13452–13462. the law of matching water affinities extends to all solvents, ACS Cent. Sci. 4
[212] J.C. Fornaciari, L.-C. Weng, S.M. Alia, C. Zhan, T.A. Pham, A.T. Bell, T. Ogitsu, (2018) 1056–1064.
N. Danilovic, A.Z. Weber, Mechanistic understanding of pH effects on the oxygen [243] J.S. Moreno, G. Maresca, S. Panero, B. Scrosati, G. Appetecchi, Sodium-
evolution reaction, Electrochim. Acta 405 (2022) 139810. conducting ionic liquid-based electrolytes, Electrochem. Commun. 43 (2014) 1–4.
[213] Y. Pang, H. Xie, Y. Sun, M.-M. Titirici, G.-L. Chai, Electrochemical oxygen [244] M. Hilder, M. Gras, C.R. Pope, M. Kar, D.R. MacFarlane, M. Forsyth, L.A. O’Dell,
reduction for H 2 O 2 production: catalysts, pH effects and mechanisms, J. Mater. Effect of mixed anions on the physicochemical properties of a sodium containing
Chem. A 8 (2020) 24996–25016. alkoxyammonium ionic liquid electrolyte, Phys. Chem. Chem. Phys. 19 (2017)
[214] A.M.E. Badawy, T.P. Luxton, R.G. Silva, K.G. Scheckel, M.T. Suidan, T. 17461–17468.
M. Tolaymat, Impact of environmental conditions (pH, ionic strength, and [245] D. Pabsch, P. Figiel, G. Sadowski, C. Held, Solubility of electrolytes in organic
electrolyte type) on the surface charge and aggregation of silver nanoparticles solvents: solvent-specific effects and ion-specific effects, J. Chem. Eng. Data 67
suspensions, Environ. Sci. Technol. 44 (2010) 1260–1266. (2022) 2706–2718.
[215] F. Wu, N. Zhu, Y. Bai, L. Liu, H. Zhou, C. Wu, Highly safe ionic liquid electrolytes [246] A. Dukhin, S. Parlia, P. Somasundaran, Ion-pair conductivity theory V: critical ion
for sodium-ion battery: wide electrochemical window and good thermal stability, size and range of ion-pair existence, J. Electrochem. Soc. 165 (2018) E784.
ACS Appl. Mater. Interfaces 8 (2016) 21381–21386. [247] H. Aghajani, A.T. Tabrizi, R. Ghorbani, S. Behrangi, M. Stupavska, N. Abdian,
[216] N. Wongittharom, T.-C. Lee, C.-H. Wang, Y.-C. Wang, J.-K. Chang, Evaluation of electrochemical hydrogen storage capability of three-dimensional
Electrochemical performance of Na/NaFePO 4 sodium-ion batteries with ionic nano-structured nitrogen-doped graphene, J. Alloys Compd. 906 (2022) 164284.
liquid electrolytes, J. Mater. Chem. A 2 (2014) 5655–5661. [248] C. Zhong, Y. Deng, W. Hu, J. Qiao, L. Zhang, J. Zhang, A review of electrolyte
[217] C.-H. Wang, Y.-W. Yeh, N. Wongittharom, Y.-C. Wang, C.-J. Tseng, S.-W. Lee, W.- materials and compositions for electrochemical supercapacitors, Chem. Soc. Rev.
S. Chang, J.-K. Chang, Rechargeable Na/Na0. 44MnO2 cells with ionic liquid 44 (2015) 7484–7539.
electrolytes containing various sodium solutes, J. Power Sources 274 (2015) [249] C. Kikuchi, H. Kurane, T. Watanabe, M. Demura, T. Kikukawa, T. Tsukamoto,
1016–1023. Preference of Proteomonas Sulcata Anion Channelrhodopsin for Nitrate Revealed
[218] I. Hasa, S. Passerini, J. Hassoun, Characteristics of an ionic liquid electrolyte for Using a pH Electrode Method, 2021.
sodium-ion batteries, J. Power Sources 303 (2016) 203–207. [250] S. Kubota, S. Ozaki, J. Onishi, K. Kano, O. Shirai, Selectivity on ion transport
[219] T. Tamura, K. Yoshida, T. Hachida, M. Tsuchiya, M. Nakamura, Y. Kazue, across bilayer lipid membranes in the presence of gramicidin A, Anal. Sci. 25
N. Tachikawa, K. Dokko, M. Watanabe, Physicochemical properties of glyme–Li (2009) 189–193.
salt complexes as a new family of room-temperature ionic liquids, Chem. Lett. 39
(2010) 753–755.
34
[251] G. Li, G.R. Blake, T.T. Palstra, Vacancies in functional materials for clean energy [282] J. Zheng, Y.-Y. Hu, New insights into the compositional dependence of Li-ion
storage and harvesting: the perfect imperfection, Chem. Soc. Rev. 46 (2017) transport in polymer–ceramic composite electrolytes, ACS Appl. Mater. Interfaces
1693–1706. 10 (2018) 4113–4120.
[252] Y. Gao, A.M. Nolan, P. Du, Y. Wu, C. Yang, Q. Chen, Y. Mo, S.-H. Bo, Classical and [283] J.A. Kowalski, L. Su, J.D. Milshtein, F.R. Brushett, Recent advances in molecular
emerging characterization techniques for investigation of ion transport engineering of redox active organic molecules for nonaqueous flow batteries,
mechanisms in crystalline fast ionic conductors, Chem. Rev. 120 (2020) Curr. Opin. Chem. Eng. 13 (2016) 45–52.
5954–6008. [284] Y. Wang, W.H. Zhong, Development of electrolytes towards achieving safe and
[253] F. Tan, H. An, N. Li, J. Du, Z. Peng, Stabilization of Li0. 33La0. 55TiO3 solid high-performance energy-storage devices: a review, ChemElectroChem 2 (2015)
electrolyte interphase layer and enhancement of cycling performance of LiNi0. 22–36.
5Co0. 3Mn0. 2O2 battery cathode with buffer layer, Nanomaterials, 11 (2021) [285] Y. Zhang, N. Du, D. Yang, Designing superior solid electrolyte interfaces on silicon
989. anodes for high-performance lithium-ion batteries, Nanoscale 11 (2019)
[254] W. Lu, M. Xue, C. Zhang, Modified Li7La3Zr2O12 (LLZO) and LLZO-polymer 19086–19104.
composites for solid-state lithium batteries, Energy Storage Mater. 39 (2021) [286] S.K. Heiskanen, J. Kim, B.L. Lucht, Generation and evolution of the solid
108–129. electrolyte interphase of lithium-ion batteries, Joule 3 (2019) 2322–2333.
[255] M. Sural, A. Ghosh, Conductivity and relaxation in ZrF4–BaF2–YF3–LiF glasses: [287] K. Takada, N. Ohta, L. Zhang, K. Fukuda, I. Sakaguchi, R. Ma, M. Osada, T. Sasaki,
effect of substitution of BaF2 by LiF, Solid State Ionics 126 (1999) 315–321. Interfacial modification for high-power solid-state lithium batteries, Solid State
[256] Y. Li, S. Wang, G. He, H. Wu, F. Pan, Z. Jiang, Facilitated transport of small Ionics 179 (2008) 1333–1337.
molecules and ions for energy-efficient membranes, Chem. Soc. Rev. 44 (2015) [288] A. Sakuda, A. Hayashi, M. Tatsumisago, Interfacial observation between LiCoO2
103–118. electrode and Li2S− P2S5 solid electrolytes of all-solid-state lithium secondary
[257] O.E. Philippova, A.M. Rumyantsev, E.Y. Kramarenko, A.R. Khokhlov, New type of batteries using transmission electron microscopy, Chem. Mater. 22 (2010)
swelling behavior upon gel ionization: theory vs experiment, Macromolecules 46 949–956.
(2013) 9359–9367. [289] Y. Liang, C.Z. Zhao, H. Yuan, Y. Chen, W. Zhang, J.Q. Huang, D. Yu, Y. Liu, M.
[258] A. Karatrantos, Y. Koutsawa, P. Dubois, N. Clarke, M. Kröger, Miscibility and M. Titirici, Y.L. Chueh, A review of rechargeable batteries for portable electronic
nanoparticle diffusion in ionic nanocomposites, Polymers 10 (2018) 1010. devices, InfoMat 1 (2019) 6–32.
[259] Y. Hou, Z. Chen, R. Zhang, H. Cui, Q. Yang, C. Zhi, Recent advances and [290] K. Xu, Y. Lam, S.S. Zhang, T.R. Jow, T.B. Curtis, Solvation sheath of Li+ in
interfacial challenges in solid-state electrolytes for rechargeable Li-air batteries, nonaqueous electrolytes and its implication of graphite/electrolyte interface
in: Exploration, Wiley Online Library, 2023, p. 20220051. chemistry, J. Phys. Chem. C 111 (2007) 7411–7421.
[260] W. Zhang, J. Lu, Z. Guo, Challenges and future perspectives on sodium and [291] C. Yan, R. Xu, Y. Xiao, J.F. Ding, L. Xu, B.Q. Li, J.Q. Huang, Toward critical
potassium ion batteries for grid-scale energy storage, Mater. Today 50 (2021) electrode/electrolyte interfaces in rechargeable batteries, Adv. Funct. Mater. 30
400–417. (2020) 1909887.
[261] F. Cheng, J. Liang, Z. Tao, J. Chen, Functional materials for rechargeable [292] C. Yan, H. Yuan, H.S. Park, J.-Q. Huang, Perspective on the critical role of
batteries, Adv. Mater. 23 (2011) 1695–1715. interface for advanced batteries, Journal of Energy, Chemistry 47 (2020)
[262] M.R. Singh, E.L. Clark, A.T. Bell, Effects of electrolyte, catalyst, and membrane 217–220.
composition and operating conditions on the performance of solar-driven [293] E. Peled, The electrochemical behavior of alkali and alkaline earth metals in
electrochemical reduction of carbon dioxide, Phys. Chem. Chem. Phys. 17 (2015) nonaqueous battery systems—the solid electrolyte interphase model,
18924–18936. J. Electrochem. Soc. 126 (1979) 2047.
[263] R. Agrawal, R. Gupta, Superionic solid: composite electrolyte phase–an overview, [294] K. Zhang, F. Wu, K. Zhang, S. Weng, X. Wang, M. Gao, Y. Sun, D. Cao, Y. Bai,
J. Mater. Sci. 34 (1999) 1131–1162. H. Xu, Chlorinated dual-protective layers as interfacial stabilizer for dendrite-free
[264] F. Bella, J. Popovic, A. Lamberti, E. Tresso, C. Gerbaldi, J. Maier, Interfacial lithium metal anode, Energy Storage Mater. 41 (2021) 485–494.
effects in solid–liquid electrolytes for improved stability and performance of dye- [295] Y. Li, M. Liu, X. Feng, Y. Li, F. Wu, Y. Bai, C. Wu, How can the electrode influence
sensitized solar cells, ACS Appl. Mater. Interfaces 9 (2017) 37797–37803. the formation of the solid electrolyte interface? ACS Energy Lett. 6 (2021)
[265] C. Sun, J. Liu, Y. Gong, D.P. Wilkinson, J. Zhang, Recent advances in all-solid- 3307–3320.
state rechargeable lithium batteries, Nano Energy 33 (2017) 363–386. [296] A. Banerjee, X. Wang, C. Fang, E.A. Wu, Y.S. Meng, Interfaces and interphases in
[266] S. Li, S.Q. Zhang, L. Shen, Q. Liu, J.B. Ma, W. Lv, Y.B. He, Q.H. Yang, Progress and all-solid-state batteries with inorganic solid electrolytes, Chem. Rev. 120 (2020)
perspective of ceramic/polymer composite solid electrolytes for lithium batteries, 6878–6933.
Adv. Sci. 7 (2020) 1903088. [297] B. Li, Y. Wang, H. Rong, Y. Wang, J. Liu, L. Xing, M. Xu, W. Li, A novel electrolyte
[267] B. Zhang, R. Tan, L. Yang, J. Zheng, K. Zhang, S. Mo, Z. Lin, F. Pan, Mechanisms with the ability to form a solid electrolyte interface on the anode and cathode of a
and properties of ion-transport in inorganic solid electrolytes, Energy Storage LiMn 2 O 4/graphite battery, J. Mater. Chem. A 1 (2013) 12954–12961.
Mater. 10 (2018) 139–159. [298] F. Dinkelacker, P. Marzak, J. Yun, Y. Liang, A.S. Bandarenka, Multistage
[268] X. He, Y. Zhu, Y. Mo, Origin of fast ion diffusion in super-ionic conductors, Nat. mechanism of lithium intercalation into graphite anodes in the presence of the
Commun. 8 (2017) 15893. solid electrolyte interface, ACS Appl. Mater. Interfaces 10 (2018) 14063–14069.
[269] Z. Gao, H. Sun, L. Fu, F. Ye, Y. Zhang, W. Luo, Y. Huang, Promises, challenges, [299] D. Zhang, R. Gu, W. Guo, Q. Xu, H. Li, Y. Min, Long-life and high-rate-charging
and recent progress of inorganic solid-state electrolytes for all-solid-state lithium lithium metal batteries enabled by a flexible active solid electrolyte interphase
batteries, Adv. Mater. 30 (2018) 1705702. layer, ACS Appl. Mater. Interfaces 13 (2021) 60678–60688.
[270] S. Qian, H. Chen, Z. Wu, D. Li, X. Liu, Y. Tang, S. Zhang, Designing ceramic/ [300] G. Deysher, Y.-T. Chen, B. Sayahpour, S.W.-H. Lin, S.-Y. Ham, P. Ridley, A. Cronk,
polymer composite as highly ionic conductive solid-state electrolytes, Batter. E.A. Wu, D.H. Tan, J.-M. Doux, Evaluating electrolyte–anode interface stability in
Supercaps 4 (2021) 39–59. sodium all-solid-state batteries, ACS Appl. Mater. Interfaces 14 (2022)
[271] Z. Zhang, L.F. Nazar, Exploiting the paddle-wheel mechanism for the design of 47706–47715.
fast ion conductors, Nat. Rev. Mater. 7 (2022) 389–405. [301] M. Tatsumisago, M. Nagao, A. Hayashi, Recent development of sulfide solid
[272] C. Ma, K. Chen, C. Liang, C.-W. Nan, R. Ishikawa, K. More, M. Chi, Atomic-scale electrolytes and interfacial modification for all-solid-state rechargeable lithium
origin of the large grain-boundary resistance in perovskite Li-ion-conducting solid batteries, J. Asian Ceramic Soc. 1 (2013) 17–25.
electrolytes, Energy Environ. Sci. 7 (2014) 1638–1642. [302] S.P. Ong, Y. Mo, W.D. Richards, L. Miara, H.S. Lee, G. Ceder, Phase stability,
[273] J.A. Dawson, P. Canepa, T. Famprikis, C. Masquelier, M.S. Islam, Atomic-scale electrochemical stability and ionic conductivity of the Li 10±1 MP 2 X 12 (M=
influence of grain boundaries on Li-ion conduction in solid electrolytes for all- Ge, Si, Sn, Al or P, and X= O, S or Se) family of superionic conductors, Energy
solid-state batteries, J. Am. Chem. Soc. 140 (2018) 362–368. Environ. Sci. 6 (2013) 148–156.
[274] J.-F. Wu, X. Guo, Origin of the low grain boundary conductivity in lithium ion [303] L.J. Miara, W.D. Richards, Y.E. Wang, G. Ceder, First-principles studies on cation
conducting perovskites: Li 3x La 0.67− x TiO 3, Phys. Chem. Chem. Phys. 19 dopants and electrolyte| cathode interphases for lithium garnets, Chem. Mater. 27
(2017) 5880–5887. (2015) 4040–4047.
[275] F. Croce, G. Appetecchi, L. Persi, B. Scrosati, Nanocomposite polymer electrolytes [304] W.D. Richards, L.J. Miara, Y. Wang, J.C. Kim, G. Ceder, Interface stability in solid-
for lithium batteries, Nature 394 (1998) 456–458. state batteries, Chem. Mater. 28 (2016) 266–273.
[276] W.S. Young, W.F. Kuan, T.H. Epps III, Block copolymer electrolytes for [305] N. Ohta, K. Takada, I. Sakaguchi, L. Zhang, R. Ma, K. Fukuda, M. Osada, T. Sasaki,
rechargeable lithium batteries, J. Polym. Sci. B Polym. Phys. 52 (2014) 1–16. LiNbO3-coated LiCoO2 as cathode material for all solid-state lithium secondary
[277] S.B. Aziz, Li+ ion conduction mechanism in poly (ε-caprolactone)-based polymer batteries, Electrochem. Commun. 9 (2007) 1486–1490.
electrolyte, Iran. Polym. J. 22 (2013) 877–883. [306] K.H. Kim, Y. Iriyama, K. Yamamoto, S. Kumazaki, T. Asaka, K. Tanabe, C.
[278] R. Agrawal, G. Pandey, Solid polymer electrolytes: materials designing and all- A. Fisher, T. Hirayama, R. Murugan, Z. Ogumi, Characterization of the interface
solid-state battery applications: an overview, J. Phys. D. Appl. Phys. 41 (2008) between LiCoO2 and Li7La3Zr2O12 in an all-solid-state rechargeable lithium
223001. battery, J. Power Sources 196 (2011) 764–767.
[279] M.A. Ratner, P. Johansson, D.F. Shriver, Polymer electrolytes: ionic transport [307] S. Wenzel, T. Leichtweiss, D. Krüger, J. Sann, J. Janek, Interphase formation on
mechanisms and relaxation coupling, MRS Bull. 25 (2000) 31–37. lithium solid electrolytes—an in situ approach to study interfacial reactions by
[280] S.B. Aziz, T.J. Woo, M. Kadir, H.M. Ahmed, A conceptual review on polymer photoelectron spectroscopy, Solid State Ionics 278 (2015) 98–105.
electrolytes and ion transport models, J. Sci. Adv. Mater. Dev. 3 (2018) 1–17. [308] Q. Zhao, C. Guo, Y. Lu, L. Liu, J. Liang, J. Chen, Rechargeable lithium batteries
[281] D. Zhou, D. Shanmukaraj, A. Tkacheva, M. Armand, G. Wang, Polymer with electrodes of small organic carbonyl salts and advanced electrolytes, Ind.
electrolytes for lithium-based batteries: advances and prospects, Chem 5 (2019) Eng. Chem. Res. 55 (2016) 5795–5804.
2326–2352. [309] K. Nakahara, J. Iriyama, S. Iwasa, M. Suguro, M. Satoh, E.J. Cairns, Cell
properties for modified PTMA cathodes of organic radical batteries, J. Power
Sources 165 (2007) 398–402.
35
[310] Y. Liang, Y. Yao, Advancing electrolytes towards stable organic batteries, Gen. [314] P. Gerlach, R. Burges, A. Lex-Balducci, U. Schubert, A. Balducci, Influence of the
Chem. 3 (2017) 207. salt concentration on the electrochemical performance of electrodes for polymeric
[311] S. Lee, G. Kwon, K. Ku, K. Yoon, S.K. Jung, H.D. Lim, K. Kang, Recent progress in batteries, Electrochim. Acta 306 (2019) 610–616.
organic electrodes for Li and Na rechargeable batteries, Adv. Mater. 30 (2018) [315] P. Gerlach, R. Burges, A. Lex-Balducci, U. Schubert, A. Balducci, The influence of
1704682. the electrolyte composition on the electrochemical behaviour of cathodic
[312] T. Suga, H. Konishi, H. Nishide, Photocrosslinked nitroxide polymer cathode- materials for organic radical batteries, J. Power Sources 405 (2018) 142–149.
active materials for application in an organic-based paper battery, Chem. [316] T.Y. Kim, H.W. Lee, M. Stoller, D.R. Dreyer, C.W. Bielawski, R.S. Ruoff, K.S. Suh,
Commun. (2007) 1730–1732. High-performance supercapacitors based on poly (ionic liquid)-modified
[313] J. Wang, Y. Yamada, K. Sodeyama, C.H. Chiang, Y. Tateyama, A. Yamada, graphene electrodes, ACS Nano 5 (2011) 436–442.
Superconcentrated electrolytes for a high-voltage lithium-ion battery, Nat.
Commun. 7 (2016) 12032.
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Journal of Energy Storage 81 (2024) 110361

Contents lists available at ScienceDirect

Journal of Energy Storage

Fundamental chemical and physical properties of electrolytes in energy

1. Introduction solvation. The fundamental characteristics required for an ionic system

Fig. 1. Evolution timeline of different types of electrolytes.

k = Ɛr = Ɛm /Ɛo (12) A distorted semicircle designates the occurrence of heterogeneous/

3.5.2. Dielectric modulus 3.6. Ionic mobility

Table 2 circumstances, the collision frequency of mobile species presents in the

3.7. Ionic diffusivity

Ionic diffusivity is a measure of the ability of ions to move through a

The interface between two grains known as grain boundary also

H+ 1.15 2.80 350.1 Cl− 1.81 3.32 76.31

Table 5 reduces self-discharge in PTMA by minimizing the dissolution of active

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