KR101440843B1 - Metal oxide coated molybdenum sulfide electrode material for sodium rechargeable batteries and fabrication method for preparing the same, and sodium rechargeable batteries using the same - Google Patents

Abstract

The present invention relates to the production of molybdenum sulfide (MoS ₂ ) nanofibers coated with a metal oxide and an electrode active material for a sodium secondary battery using the same. The molybdenum sulfide (MoS ₂ ) nanofibers produced by the electrospinning method are characterized in that the individual nanofibers are bundled together as a cluster, and contain a large specific surface area and fine nano pores. Thus, the characteristics of the electrode active material for an excellent sodium secondary battery Lt; / RTI > In particular, an electrode active material for a sodium secondary battery having improved life characteristics can be manufactured by additionally coating a thin metal oxide on an electrode including molybdenum sulfide (MoS ₂ ) nanofibers by atomic layer deposition.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molybdenum sulfide electrode active material coated with a metal oxide for a sodium secondary battery, and a method for manufacturing the same. BACKGROUND ART [0002]

The present invention relates to a metal oxide-coated molybdenum sulfide (MoS ₂ ) nanofiber and to a next generation energy storage device using the same as an electrode active material for a sodium (Na) secondary battery. Unlike a commercial lithium secondary battery, in the case of a sodium secondary battery, when sodium ions are charged and discharged through an intercalation mechanism repeatedly inserted into and removed from the structure, sodium ions having a relatively larger ion radius than lithium ions (1) insertion into the structure, (2) desorption to the outside, and (3) ion diffusivity in the structure, which deteriorates the charge / discharge performance. In addition, there is a problem that sodium ions can not migrate from the inside of the structure and become traps during charge / discharge.

However, MoS ₂ nanofibers are not MoS ₂ + 4Na ⁺ + 4e ↔ 2Na ₂ S + Mo, which reacts with the structure itself, not intercalation mechanism in which sodium (Na) ion repeats insertion and desorption in the structure during charging and discharging. since the MoS ₂ nanofiber synthesized in the present invention contains a very high specific surface area and a fine nanopore structure, it is possible to realize excellent sodium secondary battery characteristics. And has significantly improved capacity characteristics as compared with known carbonaceous anode active materials. In addition, by coating a thin metal oxide thin layer on the MoS ₂ nanofibers, the lifetime characteristics are improved, so that an electrode active material for a sodium secondary battery having high capacity and long life can be manufactured.

The demand for electric vehicles and next-generation large energy storage devices as well as small-sized electronic devices such as mobile phones and notebooks has been rapidly increasing, and development of large-capacity secondary batteries capable of storing energy surplus and being used as needed has been actively developed. Conventional lithium secondary batteries have high energy density, long life characteristics, and excellent efficiency. However, since lithium reserves are limited, it is the next generation secondary battery for lowering the cost of lithium secondary batteries. Based sodium secondary battery has been attracting much attention recently. Sodium, which contains a large amount of seawater on the earth, is known to be a next-generation secondary battery that can replace lithium secondary batteries with superior price competitiveness than lithium.

For example, lithium carbonate (Li ₂ CO ₃ ), which is a raw material of lithium, is expensive at about $ 5000 per tonne (2012, http://lithiuminvestingnews.com). However, sodium, a typical sodium mineral, (trona, Na ₃ (CO ₃ ) (HCO ₃ ) ₂ H ₂ O) is very affordable as $ 135-165 / tonne (2012, Source: Minerals Commodity Summaries, USA) and is attractive for next-generation secondary batteries, can do.

The sodium secondary battery has been reported to have a driving mechanism in which sodium ions are repeatedly intercalated and deintercalated in a host material. In a conventional lithium secondary battery system, lithium is replaced with sodium, Efforts to achieve battery-like performance have continued in recent years.

As the cathode active material, a transition metal oxide system (NaMO ₂ , NaMPO _4, etc.) containing sodium is used. As the anode active material, sodium metal, graphite, hard carbon, tin (Sn), antimony And performance tests of secondary battery cells are under way in a carbonate electrolyte added with a sodium salt. In the case of the cathode, sodium metal has a problem of short-circuiting with the anode due to the formation of the resin phase during charging and discharging, and is much more reactive than lithium metal and has a lower melting point than lithium (Li: 180 ^° C, Na : 98 ^o C), and the battery using sodium metal as the negative active material has a disadvantage that the stability is very low. Therefore, it is important to develop a new anode material that can replace the sodium metal for stable operation of the sodium secondary battery.

Currently, it is used in lithium secondary batteries, and it is reported that performance deterioration is particularly serious when the anode active material is applied to the sodium battery in the same manner. For example, when graphite, which is currently widely used as a cathode active material of lithium secondary batteries, is used as a negative electrode active material of a sodium battery, the large ionic radius of sodium (Li ⁺ : 60 pm, Na ⁺ : 95 pm) It has been reported that an inert material having a capacitance value close to 0 mAh / g is obtained because of the impossibility of thecalation.

Examples of other carbon-based materials other than graphite include hard carbon or carbon spear as an anode active material for a sodium battery and have been reported to have a capacity of about 200 mAh / g. This is a significantly lower value than the theoretical capacity value (374 mAh / g) that can be implemented when graphite is applied to a lithium-ion secondary site.

In addition, when silicon (4200 mAh / g) or tin (994 mAh / g), which is reported to have a very high theoretical capacity in a lithium secondary battery, is applied as a sodium-metal alloy cathode material, (Sb) metal is about 500 ~ 600 mAh / g. However, it has a low lifetime due to high rate characteristics and volume expansion. And it has been reported that there is a limit to a practical application. Therefore, it is necessary to develop an anode active material optimized for a sodium secondary battery.

Most of the negative electrode materials for sodium secondary batteries reported so far have a low capacity of less than 300 mAh / g, so improvement of the capacity value and improvement of the long life characteristics are essential.

In order to increase the capacity of the anode active material for sodium secondary batteries, sodium ions having a large ionic radius easily intercalate and desorb (intercalation compound), (2) easy to alloy with the negative electrode structure (Na -M alloy, and (3) chemical bonding and decomposition reaction with sodium ions. Known Conversion Reaction cathodes in conventional lithium secondary batteries include metal oxides (MOx), metal sulfides (MSx), and metal fluorides (MFx). Conversion Reaction Molybdenum sulfide (MoS ₂ ), which is known as one of the negative electrodes, has a reversible capacity of about 1,000 mAh / g and has a two-dimensional layered structure, which has been reported as an anode active material of a lithium secondary battery.

However, to date, conversion cathodes such as MoS ₂ have not been applied to sodium secondary batteries, and the theoretical capacity (> 800 mAh / g) is much higher than the intercalation reaction. Conversion Reaction In the case of negative electrode, due to the chemical bonding with sodium, the structure should be rearranged and decomposed repeatedly. Therefore, it is advantageous to have a very large specific surface area and to have many nanometer sized pores for easy charging and discharging.

High Capacity Conversion Reaction There has been no report on the optimization of an anode material for a sodium secondary battery having a nanostructure from the viewpoint of a negative electrode material. In the present invention, the synthesis of MoS ₂ nanofiber and its use as an anode active material for a sodium secondary battery, Introduction of oxide coating layer to introduce the technology of sodium secondary battery technology with high capacity and long life characteristics.

An object of the present invention is to provide a high-capacity anode active material for a molybdenum sulfide (MoS ₂ ) nanofiber-based sodium secondary battery having uniform nanopores of a single phase and a method of manufacturing the same.

For other purposes, a cathode is prepared using molybdenum sulfide (MoS ₂ ) nanofibers having uniform nanopores of single phase in order to improve long life characteristics, and a post-treatment process of thinly coating a metal oxide thin layer And a method for manufacturing a negative electrode for a sodium secondary battery.

It is another object of the present invention to provide a method for mass-producing a high capacity anode active material for a molybdenum sulfide (MoS ₂ ) nanofiber-based sodium secondary battery using an electrospinning technique.

Another object of the present invention is to provide a sodium secondary battery comprising a molybdenum sulfide (MoS ₂ ) nanofiber-based high-capacity anode active material having uniform nanopores of a single phase coated with a metal oxide.

The molybdenum sulfide (MoS ₂ ) nanofiber for a sodium secondary battery anode active material having single-phase uniform nanopores, which is one aspect of the present invention, is a mixture of styrene-acrylonitrile (SAN) Ammonium tetrathiomolybdate mixed precursor Nanofibers can be prepared by heat treatment in a reducing atmosphere of H ₂ (5%) / N ₂ .

Another aspect of the present invention is a molybdenum sulfide (MoS ₂ ) nanofiber for a sodium secondary battery anode active material having uniform nanopores of a single phase, which has a uniform fiber diameter (thickness) distribution of 100 to 200 nm, MoS ₂ composite nanofibers composed of a plurality of nanofibers finally synthesized have a shape of composite nanofibers having a thickness of about 500 nm and are bound to each other in a curved shape unlike the linear nanofibers having a straight shape. There are features.

Another aspect of the present invention is a method for preparing molybdenum sulfide (MoS ₂ ) nanofibers for a sodium secondary battery anode active material having single-phase uniform nanopores, comprising the steps of: (a) mixing a Mo and S salt precursor with styrene acrylonitrile ) Radiating a spinning solution in which the polymer is dissolved; (b) preparing molybdenum sulfide (MoS ₂ ) nanofibers by preparing Mo and S salt precursor / SAN composite nanofibers and heat-treating them in a reducing atmosphere.

In another aspect of the present invention, molybdenum sulfide (MoS ₂ ) nanofibers for a sodium secondary battery anode active material having homogeneous nanopores of a single phase as an additional post-treatment process are coated with a uniform metal oxide thin layer of about 5 nm, It is possible to prevent the leaching of sulfur and improve the long life characteristics.

The secondary battery, which is another aspect of the present invention, may include the molybdenum sulfide (MoS ₂ ) nanofiber or the metal oxide coated molybdenum sulfide (MoS ₂ ) nanofiber.

According to the present invention, it is possible to synthesize molybdenum sulfide (MoS ₂ ) nanofibers having uniform nano-pores of a single phase and having a single fiber of 50 to 500 nm intertwined with each other in a large amount through electrospinning, When used as an anode active material, it can exhibit high capacity and high-rate characteristics of 600 mAh / g or more.

One-dimensional nanostructures and nanopores facilitate the transport of Na-containing electrolytes, minimizing the structural changes that occur during the conversion of MoS ₂ + 4Na ⁺ + 4e ↔ 2Na ₂ S + Mo.

In addition, it can be used as a negative electrode active material for a sodium secondary battery in which lifetime characteristics are greatly improved by relieving sulfur (S) leaching phenomenon caused by charging and discharging through a metal oxide coating.

FIG. 1 is a schematic view of synthesis of molybdenum sulfide (MoS ₂ ) nanofiber for a sodium secondary battery anode active material having uniform nano-pores of single phase through electrospinning and a post-treatment process after metal oxide coating.
2 is a scanning electron microscope (SEM) photograph of different magnifications of Mo and S salt / SAN composite nanofibers according to Example 1 of the present invention.
3 is a scanning electron microscope (SEM) photograph according to another magnification of the molybdenum sulfide (MoS ₂ ) nanofiber according to Example 1 of the present invention.
4 is a graph showing the specific surface area (a) and the pore size (b) of the molybdenum sulfide (MoS ₂ ) nanofiber according to Example 1 of the present invention.
5 is an X-ray diffraction (XRD) pattern analysis result of molybdenum sulfide (MoS ₂ ) nanofibers and bulk powder for molybdenum sulfide (MoS ₂ ) according to Example 1 and Comparative Example 1 of the present invention.
6 is a transmission electron microscope (TEM) photograph of a molybdenum sulfide (MoS ₂ ) nanofiber-based negative electrode obtained by the titanium dioxide (TiO _{2 )} coating obtained according to Example 2 of the present invention.
Figure 7 is an embodiment of the present invention 1, Example 2, Comparative Example molybdenum sulfide obtained in accordance with 1 (MoS ₂₎ nanofibers, TiO _2, a molybdenum sulfide treatment coating (MoS ₂₎ nano-fiber and molybdenum disulfide (MoS ₂₎ Commercial X-ray photoelectron spectroscopy (XPS) analysis of cathodes based on bulk powder.
8 is a scanning electron microscope (SEM) photograph according to another magnification of molybdenum sulfide (MoS ₂ ) bulk powder according to Comparative Example 1 of the present invention.
Embodiment 9 is Example 1, the practice of the invention Example 2, Comparative Example molybdenum sulfide obtained in accordance with 1 (MoS ₂₎ nanofibers, TiO _2, a molybdenum sulfide treatment coating (MoS ₂₎ nano-fiber and molybdenum disulfide (MoS ₂₎ Commercial This graph is a graph showing the characteristics of a sodium secondary battery with respect to cathodes based on bulk powder.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The single-phase molybdenum sulfide (MoS ₂ ) nanofibers, which undergo conversion and reaction with Na ions through a conversion reaction, are preferably small in diameter and have a large specific surface area and a uniform thickness distribution. The reaction with Na ions in the electrolyte It is preferable to include a plurality of nano pores so as to be smoothly performed.

The thickness of the single MoS ₂ nanofiber preferably ranges from 50 nm to 500 nm, and the thickness of the multiple MoS ₂ nanofibers entangled is preferably in the range of 50 nm to 3 μm, The pore size preferably ranges from 1 nm to 50 nm.

In the molybdenum sulfide (MoS ₂₎ secondary battery negative electrode comprising nanofibers having a single phase, a negative electrode active material is a molybdenum sulfide on a single (MoS ₂₎ Nanofiber 2 wt% - it may comprise in the range of 98 wt%. (MoS ₂ ) nanofiber-based anode active material is mainly involved in the reaction when it contains 2 wt% or more and is included in the form of additive in other negative electrode active material for sodium secondary battery. It will be done.

The secondary battery of the present invention comprises a current collector and an electrode formed on the current collector by using molybdenum sulfide (MoS ₂ ) nanofiber single phase obtained through the present invention. At least one selected from the group consisting of nickel (Ni), stainless steel (SUS), aluminum (Al), molybdenum (Mo), chrome (Cr), copper (Cu), and titanium Can be used.

Further, in order to constitute the secondary battery, an electrode, a case and a terminal including the electrolyte, the separator and the cathode active material may be further constituted. Examples of the electrolyte include a carbonate-based electrolyte solution containing a sodium salt such as NaClO _4, and an electrolyte capable of causing an electrochemical reaction with the molybdenum sulfide (MoS ₂ ) nanofiber electrode active material of the present invention, .

In one embodiment, FIG. 1 shows a method for manufacturing a negative electrode of the present invention, in which a single-phase molybdenum sulfide (MoS ₂ ) nanofiber anode active material for a sodium secondary battery and a thin metal oxide layer are additionally coated, Can:

(110) a step (110) of producing molybdenum and a sulfur precursor / SAN composite nanofiber by stirring and spinning a SAN spinning solution comprising a molybdenum precursor and a sulfide precursor, and heat treating the molybdenum and a sulfur precursor / SAN composite nanofiber in a reducing atmosphere A step 120 of producing a single phase molybdenum sulfide (MoS ₂ ) nanofiber, and a step 130 of preparing a negative electrode using the single phase molybdenum sulfide (MoS ₂ ) nanofiber as a negative electrode active material for a secondary battery, (140) uniformly coating the electrode with a thin layer of metal oxide using Atomic Layer Deposition (ALD) method, and step (140) comprises charging and discharging testing for the coating .

The precursors for electrospinning, that is, the molybdenum salts and the sulfur salts, include, but are not limited to, Ammonium Tetrathiomolybdate, Ammonium Heptamolybdate, Ammonium tTtrathiomolybdate, Sulfur, Hydrogen sulfide (H ₂ S) or the like can be used, and a precursor including a molybdenum salt and a sulfur salt which can be mixed with a SAN and radiated does not limit the specific precursor salt.

As the solvent used for the spinning, there are no restrictions on the solvent specific solvent in which the SAN, the molybdenum salt and the sulfur salt are simultaneously dissolved, and dimethylformaldehyde (DMF), dimethylacetamide (DMAc) and the like can be used.

In order to produce a one-dimensional nanofiber shape, electrospinning was used in the present invention. The electrospinning device consists of a spinning nozzle connected to a metering pump that contains molybdenum salts and sulfur salts and can quantitatively inject spinning fluid in which the SAN polymer is dissolved, a high voltage generator, and a grounded conductive substrate.

First, the current collector is placed on a grounded conductive substrate. At this time, a grounded conductive substrate is used as a cathode, and a spinning nozzle having a pump with a controlled amount of discharge per hour is used as an anode. A voltage of 8 - 30 kV is applied, and a solution discharge rate is adjusted to 5 - 200 μl / min to prepare molybdenum, sulfur / SAN composite nanofiber.

Especially, the electrospinning device can be realized by a multi-nozzle system composed of more than 10,000 needles, and mass production using a cylinder type drum is also possible. At this time, it is preferable that the diameter of the composite nanofiber is in the range of 50 nm - 3 μm.

In order to produce monolithic molybdenum sulfide (MoS ₂ ) nanofibers, heat treatment is performed in a reducing atmosphere. In a temperature range of 800 to 900 ^° C for 3 to 12 hours while flowing a gas under a nitrogen atmosphere containing hydrogen as a reducing gas The heat treatment allows the synthesis of monolithic molybdenum sulfide (MoS ₂ ) nanofibers while decomposing and recombining SAN polymers and salts. At this time, it is preferable that the solid sulfur is placed in a tube furnace for supplementing sulfur constituting the molybdenum sulfide (MoS ₂ ) nanofiber so that the MoS ₂ phase can be stabilized by the vaporized sulfur during the heat treatment.

By using a single phase molybdenum sulfide (MoS ₂ ) nanofiber as a negative electrode active material for a sodium secondary battery, a long process life characteristic can be greatly improved by coating on a conductive substrate and further coating a thin metal oxide layer on the fiber layer .

In the conversion reaction (MoS ₂ + 4Na ⁺ + 4e ↔ 2Na ₂ S + Mo), Na ₂ S, NaS, S, etc. may be partially dissolved in the electrolyte solution. Therefore, in order to prevent elution of sulfur salts into the electrolyte, It is preferable to further form it. Since the coating layer generally has a low electrical conductivity, the individual MoS ₂ nanofibers are each coated with a metal oxide coating layer and the molybdenum sulfide (MoS ₂ ) nanofiber is applied to the cathode It is preferable that an electrode for a secondary battery is first prepared as an active material together with a conductive agent and a metal oxide coating treatment is performed using ALD (Atomic Layer Deposition) as a post-treatment process.

If the electrical conductivity of individual coating material superior to coat the molybdenum sulfide (MoS ₂₎ nanofibers independently is also possible. The metal oxide of the coating layer is preferably a metal oxide having high corrosion resistance such as TiO ₂ , Al ₂ O ₃ , WO ₃ and ZrO _{2. In} order not to lower the electrical conductivity of the electrode, the thickness of the coating layer is preferably less than 20 nm Do. (RuO ₂ , IrO ₂ , SnO ₂ , SiO ₂ , and Co ₃ O ₄₎ as well as TiO ₂ , Al ₂ O ₃ , WO ₃ , and ZrO ₂ as well as other metal oxide coating layers having better ionic conductivity and electrical conductivity , FeO _x , NiO, MnO _x , MgO, HfO ₂ , Ag ₂ O, Cr ₂ O ₃ , VO _x , MoO ₃ ) can be alternatively selected.

In the present invention, an ALD process capable of uniformly manufacturing a thin layer is used for manufacturing the coating layer, but other processes such as sputtering and CVD (Chemical Vapor Deposition) may be used. Manufacturing process techniques that can coat thin metal oxide layers do not limit the specific deposition method.

Hereinafter, the present invention will be described in more detail by way of examples. However, it should be understood that the present invention is not limited thereto.

Example  One: Only everyday  The molybdenum sulfide ( MoS ₂ ) Synthesis of nanofiber and As an anode active material  Cathode manufacturing

As in the synthesis process shown in FIG. 1, ammonium tetramethylborate (ATTM) was used as molybdenum and a salt thereof, styrene acrylonitrile (SAN) was used as a polymer, and N, Ndimethylformamide ) Was used to prepare a spinning solution.

First, 1.2 g of ATTM was dissolved in 8 g of DMF for 6 hours through a magnetic stirrer, and 1.0 g of SAN was added to the mixed solution and further dissolved for 3 hours.

The electrospinning was carried out by applying a voltage of 15 kV and a nozzle size of 25 GA was used. The gap between the current collector and the nozzle was 15 cm, and electrospinning was performed at a discharge rate of 10 μl / min. A stainless steel substrate was used as the collector substrate.

2 is a scanning electron micrograph of the molybdenum and the sulfur / SAN composite nanofiber obtained on the current collector substrate. It can be seen from FIG. 2 that a highly uniform As-spun composite fiber having a diameter of 200 to 250 nm is well formed.

The resultant composite nanofibers were heat-treated at 900 ^° C for 6 hours under an atmosphere of H ₂ (5%) / N ₂ . FIG. 3 is a scanning electron microscope (SEM) photograph of the MoS ₂ nanofibers obtained through the above-described heat treatment to observe images of the finally obtained molybdenum sulfide (MoS ₂ ) nanofibers. The composite nanofibers electrospun during the heat treatment process are subjected to a salt and polymer decomposition process and a crystallization process of molybdenum sulfide (MoS ₂ ), finally shrinking to about 150 to 200 nm, and compared with the smooth composite fiber of FIG. 2, It was observed that unevenness was formed.

As compared with FIG. 2, the molybdenum sulfide (MoS ₂ ) nanofibers of FIG. 3 were bent in a streamline shape, and a plurality of nanofibers were clustered together to form aggregated nanofibers of 500 600 nm. MoS ₂ ) Aggregated nanofibers are relatively uniformly formed as a whole.

4 is a Brunauer-Emmett-Teller (BET) analysis showing the specific surface area and pore distribution of synthesized molybdenum sulfide (MoS ₂ ) nanofibers. In order to clearly confirm the structural and electrochemical advantages of the molybdenum sulfide (MoS ₂ ) nanofibers, the specific surface area and the electrochemical cell test analysis were performed in parallel using commercial molybdenum molybdenum (MoS ₂ ) bulk powder as a comparative sample. The molybdenum sulfide (MoS ₂ ) nanofiber was found to have a very high specific surface area (MoS ₂ bulk powder: 3.55 m ² / g, MoS ₂ nanofiber: 144.32 m ² / g ), It was observed that highly uniform nanopores of about 10 nm were present.

The micropores on the surface and inside of the nanofiber provide not only a buffer effect on the structural change during the conversion reaction of the molybdenum sulfide (MoS ₂ ) nanofiber but also a fast diffusion path of Na ion, And has a feature that plays a very important role in the improvement of the performance.

5 is a graph showing the results of X-ray diffraction analysis of commercial molybdenum molybdenum (MoS ₂ ) bulk powder and molybdenum sulfide (MoS ₂ ) nanofibers. As a result, the molybdenum sulfide (MoS ₂ ) (MoS ₂ ) as a single phase which does not exist. The molybdenum sulfide (MoS ₂ ) nanofiber prepared above was used as an anode active material to prepare molybdenum sulfide (MoS ₂ ) The negative electrode active material 80 wt%, the polyvinylidene fluoride (PVDF) binder 10 wt%, and the super-P carbon particles 10 wt% were mixed and slurry coated on the copper foil substrate and dried to prepare the secondary battery negative electrode Respectively.

Example  2: molybdenum sulfide ( MoS ₂ ) Nanofiber As an anode active material  On the cathode electrode Atomic layer  TiO2 by vapor deposition ₂ Nano layer  coating

The surface of the negative electrode for a sodium secondary battery prepared using the MoS ₂ nanofibers of Example 1 as a negative electrode active material was further coated with a TiO ₂ thin layer. TiO ₂ thin films were deposited by atomic layer deposition (ALD).

Atomic layer deposition (ALD) injects reactive gases sequentially in pulsed form, thus inducing surface reactions through self-limited adsorption on the substrate surface, depositing the thin film on an atomic layer basis Whereby a thin film having a very good uniformity and step-coverage can be deposited.

The precursor used for atomic layer deposition (ALD) in the TiO ₂ nanoclay coating is tetrakis-dimethyl-amino-titanium (TDMAT) and the intermediate reactant is thermal H ₂ O . One cycle was coated with 15 cycles totaling 3 seconds of TDMAT, 5 seconds of argon (Ar) purge, 4 seconds of H ₂ O and 5 seconds of argon (Ar) purge . The surface temperature of the negative electrode made of MoS ₂ nanofiber as the negative electrode active material was maintained at 150 캜 during the deposition.

Molybdenum sulfide (MoS ₂ ) nanofibers and Super-P carbon particles as a conductive material were mixed in advance to form a cathode, and then TiO ₂ When the thin layer is coated over the entire surface of the negative electrode, the molybdenum sulfide (MoS ₂ ) nanofiber and the conductive material are well contacted and bound, and the TiO ₂ coating layer is coated between the molybdenum sulfide (MoS ₂ ) and the conductive material, There is an advantage that it can be prevented to prevent it.

Figure 6 shows a molybdenum sulfide (MoS ₂₎ nanofibers are TiO ₂ nano-layer on top of the applied negative electrode mentioned in the results of coating the atomic layer deposition method. It was confirmed that amorphous TiO ₂ of about 5 nm was uniformly coated on the molybdenum sulfide (MoS ₂ ) nanofiber. As shown in FIG. 7, X-ray photoelectron spectroscopy (XPS) ) to result in a 465 eV and 458 eV in the molybdenum sulfide (MoS ₂₎ commercial bulk powder and molybdenum disulfide (MoS ₂₎ nanofibers analyzed using it was confirmed that the TiO ₂ is not observed peak is observed.

Comparative Example  1: molybdenum sulfide ( MoS ₂ ) Commercial Bulk powder As an anode active material  Cathode manufacturing

A negative electrode was prepared using molybdenum sulfide (MoS ₂ ) bulk powder (Sigma Aldrich Co., Ltd., USA) as a negative electrode active material for a sodium secondary battery at each time as Comparative Examples in Examples 1 and ₂ .

8 shows a scanning electron micrograph of high magnification (left) and low magnification (right) of molybdenum sulfide (MoS ₂ ) bulk powder. Unlike the molybdenum sulfide (MoS ₂ ) nanofiber synthesized in Example 1, the shape of the particles was in the form of a micro-plate, and the particle size was observed to be very different from several microns to several tens of microns.

To test the charging / discharging performance, a negative electrode active material was prepared by mixing 80 wt% of the negative electrode active material, 10 wt% of the PVDF binder, and 10 wt% of the Super-P carbon particles, using a bulk powder for molybdenum sulfide (MoS ₂ ) Each substrate was coated with a slurry and dried to prepare a secondary battery negative electrode.

Analysis example  1: molybdenum sulfide ( MoS ₂ ) Negative electrode prepared by using commercial powder, molybdenum sulfide ( MoS ₂ ) Nanofiber  The negative electrode and the negative electrode TiO ₂  Coated molybdenum sulfide ( MoS ₂ Evaluation of Characteristics of Sodium Secondary Battery Using Nanofiber Based Cathode

In order to confirm the performance of the negative electrode prepared in Examples 1, 2 and Comparative Example 1, a CR2032-type coin cell structure was prepared as follows. In the cell configuration, 1 M NaClO ₄ dissolved polycarbonate (PC, Polycarbonate) solution was used as the electrolyte.

A metal sodium foil having a purity of 99.99% was used as a reference electrode and a counter electrode, and a molybdenum sulfide (MoS ₂ ) commercial powder obtained through Example 1, Example 2 and Comparative Example 1 was used as a working electrode. A negative electrode, a negative electrode made of molybdenum sulfide (MoS ₂ ) nanofiber, and a negative electrode made of TiO ₂ coated molybdenum sulfide (MoS ₂ ) nanofiber were used. A glass microfibre filter (Whatman Co., Ltd., USA) was used as a separator to prevent an electrical short between the cathode and the anode. The fabrication of such a cell was performed using argon Ar) atmosphere.

The charge / discharge test device was a WBCS3000 model of WonATech Co., Ltd., and the change of the voltage under a constant current was examined with MPS (Multi Potentiostat System) which can measure 16 channels by adding 16 boards. The intensity of the current density used in charging and discharging was 100 mA / g, and the cut off voltage was 0.01 to 3.0 V.

FIG. 9 is a graph showing the results of a negative electrode prepared using molybdenum sulfide (MoS ₂ ) powder obtained through Examples 1 and 2 and Comparative Example 1, a negative electrode prepared using molybdenum sulfide (MoS ₂ ) nanofiber and a TiO ₂ coating process (MoS ₂ ) nanofiber-based negative electrode, and the change of the discharge and charge capacity according to the cycle change for each electrode under a constant current of 100 mA / g.

In the case of the molybdenum sulfide (MoS ₂ ) nanofiber-based negative electrode of Example 1, the initial discharge capacity value was 1,168 mAh / g, and the second discharge capacity value was 839 mAh / g, gave.

On the other hand, in the case of the molybdenum sulfide (MoS ₂ ) commercial powder of Comparative Example 1, the initial discharge capacity value was 562 mAh / g and the second discharge capacity value was 382 mAh / g. (MoS ₂ ) nanofibers were found to be much lower than those of molybdenum sulfide (MoS ₂ ) nanofibers.

However, in the case of the commercial powder of molybdenum sulfide (MoS ₂ ), which was a comparative group, the second discharge value after the initial charge / discharge except for the irreversible capacity was twice as high as that of the carbonaceous anodes known in the prior art. It is suggested that the molybdenum sulfide (MoS ₂ ) nanofiber has a very high capacity and it shows the highest capacity among the sodium secondary battery cathodes known so far.

However, it was confirmed that the reversible capacity decreased to 30% or less of the second discharge capacity as the cycle progressed in both cases of Example 1 and Comparative Example 1. This is due to the fact that Na ₂ S, NaS and S are continuously dissolved in the electrolyte during the conversion reaction (MoS ₂ + 4Na ⁺ + 4e ↔ 2Na ₂ S + Mo) through charge and discharge, This is a clear indication of the need.

Therefore, by coating the coating layer on the negative electrode, the elution of sulfur can be minimized and the cycle life can be expected to be increased. In the case of the negative electrode prepared by coating the TiO ₂ -coated molybdenum sulfide (MoS ₂ ) nanofiber-based negative electrode active material of Example 2 on the current collector, the molybdenum sulfide (MoS ₂ ) nanofiber cathode having no TiO ₂ coating layer of Example 1 It was observed that the initial discharge capacity (934 mAh / g) and the second discharge capacity (740 mAh / g) values were somewhat lower due to the presence of the coating layer, 18.1%) and Comparative Example 1 (9.6% of the second discharge capacity after 40 cycles), the long-term capacity value of the cycle can be greatly improved as 43.6% of the second discharge capacity after 40 cycles there was.

This is evidence that the cycle characteristics can be greatly improved by applying a very thin TiO ₂ layer of 5 nm on the MoS ₂ -based anode by atomic layer deposition. Optimization of the thickness of the coating layer and coating of the coating layer on TiO ₂ (Al ₂ O ₃ , WO ₃ , ZrO ₂ , RuO ₂ , IrO ₂ , SnO ₂ , SiO ₂ , Co ₃ O ₄ , FeO _x , NiO, and MnO _x , MgO, HfO ₂ , Ag ₂ O, Cr ₂ O ₃ , VO _x , MoO ₃ ) are introduced.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI > or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (19)

A single phase molybdenum sulfide (MoS ₂ ) nanofiber electrode active material for a sodium secondary cell having a plurality of nanofibers in an aggregate bundle and having a plurality of nanopores. The method according to claim 1,
The diameter of the molybdenum sulfide (MoS ₂ ) single nanofiber is in the range of 50 - 500 nm, and the diameter of the fiber bundle in which the plural nanofibers are aggregated is in the range of 50 nm - 3 μm. On a molybdenum sulfide (MoS ₂ ) nanofiber electrode active material. The method according to claim 1,
Wherein the plurality of nanopores in the molybdenum sulfide (MoS ₂ ) nanofiber have a size ranging from 1 to 50 nm, and the monolith sulfide molybdenum (MoS ₂ ) nanofiber electrode active material for a sodium secondary cell. The method according to claim 1,
On the surface of the single molybdenum sulfide (MoS ₂₎ nanofibers on the _{Al 2 O 3, WO 3,} ZrO 2, RuO 2, IrO 2, SnO 2, SiO 2, Co 3 O 4, FeO x, NiO, MnO x, (MoS ₂ ) nanofiber electrode active material for a single-phase sodium secondary battery, comprising at least one metal oxide coating layer selected from MgO, HfO ₂ , Ag ₂ O, Cr ₂ O ₃ , VO _x , MoO ₃ and mixtures thereof. A sodium secondary battery comprising a conductive current collector and an electrode including a plurality of nanofiber molybdenum (MoS ₂ ) nanofiber electrode active materials, the plurality of nanofibers being formed into an aggregate bundle and having a plurality of nanopores. 6. The method of claim 5,
Wherein the _first electrode is formed of a material selected from the group consisting of Al ₂ O ₃ , WO ₃ , ZrO ₂ , RuO ₂ , IrO ₂ , SnO ₂ , SiO ₂ , Co ₃ O ₄ , FeO _x , NiO, MnO _x , MgO, HfO ₂ , Ag ₂ O, Cr ₂ O ₃ , VO _x , MoO _3, and mixtures thereof. A method for producing a molybdenum sulfide (MoS ₂ ) nanofiber electrode active material comprising a plurality of nanofibers in an aggregate bundle and including a plurality of nanopores,
(a) preparing a spinning solution in which molybdenum, a sulfur salt, and a precursor polymer are dissolved in a solvent;
(b) electrospinning the spinning solution on the current collector to form molybdenum and a sulfur / salt / precursor polymer composite fiber; And
(c) heat-treating the molybdenum and the sulfide / precursor polymer composite fiber at a temperature of 700 ^° C or higher in a reducing atmosphere
(MoS ₂ ) nanofiber electrode active material comprising the metal oxide nanoparticles. 8. The method of claim 7,
The molybdenum and the sulfur salt may,
Ammonium Tetrathiomolybdate, Ammonium Heptamolybdate, Ammonium Tetrathiomolybdate, Sodium Molybdate, Trithio-chloro, and the like. (MoS ₂ ) nanofiber electrode active material corresponding to at least one of molybdate, polyoxomolybdate anion, vaporized sulfur, and hydrogen sulfide (H ₂ S). 8. The method of claim 7,
The precursor polymer,
(SAN, styrene-acrylonitrile), polyacrylonitrile (PAN), polyvinyl acetate (PVAc), polyvinylpyrrolidone (PVP), polyvinylpyrrolidone A molybdenum sulfide corresponding to one or a mixture of at least one of alcohol (PVA, polyvinyl alcohol), polyethylene oxide (PEO), polyacrylic acid (PAA), and hydroxypropyl cellulose (HPC) (MoS ₂ ) nanofiber electrode active material. 8. The method of claim 7,
The step (a) may be carried out by dissolving the molybdenum, the sulfur salt and the precursor polymer in a solvent selected from the group consisting of dimethylformamide (DMF), dimethylacetamide (DMAc), acetone, tetrahydrofuran and toluene, Wherein the molybdenum sulfide (MoS ₂ ) and the one-fiber electrode active material corresponding to the mixture are produced. 8. The method of claim 7,
Molybdenum sulfide (MoS ₂₎ process for producing a nanofiber electrode active material having a range of 90 wt% - content of 0.5 compared to the precursor polymers of the molybdenum and hwangyeom. 8. The method of claim 7,
Wherein the step (b) comprises electrospinning through a device composed of a spray nozzle, a high voltage generator, and a conductive current collector connected to a metering pump capable of quantitatively injecting a dispersion solution, wherein the molybdenum sulfide (MoS ₂ ) nanofiber electrode active material is electrospun. Claim 13 has been abandoned due to the set registration fee. 8. The method of claim 7,
The step (b) molybdenum disulfide for electrospinning through at least one injection nozzle (MoS ₂₎ process for producing a nanofiber electrode active material. 8. The method of claim 7,
The step (c) may be carried out in a gas atmosphere of at least one selected from nitrogen (N ₂ ), argon (Ar), hydrogen (H ₂ ), helium (He), hydrogen sulfide (H ₂ S) (MoS ₂ ) nanofiber electrode active material. 8. The method of claim 7,
In the step (c), a molybdenum sulfide (MoS ₂ ) nanofiber electrode active material is prepared by placing solid sulfur in a tube furnace for supplementing sulfur during heat treatment and stabilizing the molybdenum sulfide (MoS ₂ ) phase through vaporized sulfur . A method for manufacturing a sodium secondary battery using molybdenum sulfide (MoS ₂ ) comprising a plurality of nanofibers as an aggregate bundle and including a plurality of nanopores,
Coating a metal oxide layer directly on the molybdenum sulfide (MoS ₂ ) nanofiber electrode active material, or coating the metal oxide on an anode coated with an electrode active material on a collector substrate
≪ / RTI > 17. The method of claim 16,
The metal oxide is _{Al 2 O 3, WO 3,} ZrO 2, RuO 2, IrO 2, SnO 2, SiO 2, Co 3 O 4, FeO x, NiO, MnO x, MgO, HfO 2, Ag 2 O, Cr ₂ O ₃ , VO _x , MoO ₃ , or a mixture thereof. 18. The method according to any one of claims 16 to 17,
Wherein the thickness of the metal oxide ranges from 1 to 50 nm. 17. The method of claim 16,
Wherein the metal oxide layer is manufactured through a vacuum deposition process such as atomic layer deposition (ALD), chemical vapor deposition (CVD), or sputtering.

Images