KR101486658B1 - Electrode material based upon graphene for high-performance supercapacitor and supercapacitor comprising the same - Google Patents

Abstract

The present invention relates to a graphene based electrode material for a super capacitor electrode with high performance and a super capacitor including the same. According to the embodiment of the present invention, provided is the graphene based electrode material for the super capacitor electrode with high performance and the super capacitor including the same, capable of suppressing an irreversible stack layer of rGO sheets which reduce capacitance in SC. The graphene based electrode material includes a reduction graphene oxide sheet.

Description

TECHNICAL FIELD The present invention relates to a graphene-based electrode material for a high-performance supercapacitor electrode, and a supercapacitor including the same,

The present invention relates to a graphene-based electrode material for a high performance supercapacitor electrode, and more particularly to a graphene-based electrode material for a high performance supercapacitor electrode, and more particularly to a graphene- Based electrode material.

The use of renewable energy resources, represented by solar and wind energy, is becoming increasingly important as the energy and environmental challenges of using fossil fuels are becoming significant. A grid-scale energy storage system (ESS) in which the availability of these resources varies over time is essential for effective use of such renewable energy resources. In this direction, supercapacitors (SC) are attracting much attention as one of the ESSs, and their inherent high power capacity (about 10 kW / kg) can support instant load and energy leveling, which is important for the operation of grid type ESS It is because. The long service life of the SC (> 100,000 cycles) is also desirable for the operation of these ESSs. In addition, the SC has been considered in systems primarily combined with rechargeable batteries for ESS, since the short-term transients required during electrical grid operation exceed the discharge capacity of a typical rechargeable battery. In addition to the ESS, SCs are expanding their reach to a variety of applications where high-power operation is required, and wireless electric appliances and hybrid electric vehicles (HEVs) are typical examples.

In a so-called electrical double layer capacitor (EDLC), which belongs to one class of SCs, energy is stored and released by adsorption and desorption of EDI carrier ions at the electrode surface. Thus, the capacitance is generally proportional to the surface area of the electrode, which makes various carbonaceous nanomaterials attractive as SC electrodes. For this reason, the Carbon Society is now focusing on active carbon (AC), carbon nanotubes (CNT), carbon nanofibers (CNF), and graphene for SC electrodes. Of these broad carbon nanomaterials, graphene, a two-dimensional (2d) hexagonal lattice of sp2-hybridized carbon atoms, is considered a promising candidate due to its high conductivity and greater theoretical specific surface area (about 2650 m2 / g) than expected. For reference, this high theoretical surface area can be such that it can carry the mass capacitance of SC as high as 550 F / g. Despite these promising intrinsic properties, typical graphene SC exhibits only 100-120 F / g of organic electrolyte when prepared in the form of reduced graphene oxide (rGO) through the conventional solution process, Hummer's method. This low non-capacitance originates primarily from the irreversible reclamation of the individual rGO sheets during the reduction and drying process, which makes the substantial surface of rGO unavailable for charge storage. During the conventional synthesis process, a weakly resilient layer means that the capacitance of graphene SC is highly dependent on the detailed characteristics of graphene such as functional groups, size, pore structure and surface accessibility.

To address the grafting problem of graphene sheets, it is necessary to identify the cause of this phenomenon. In Hummer's method, one or a few GO sheets were known to be well dispersed in the GO solution. Interestingly, even after the GO solution has dried, the water molecules remain trapped within the GO powder through the hydrogen bonding interaction between the water molecules and the oxygen-containing functional groups of the GO (Fig. 1A), and these water molecules are predominantly " . The intercalated water molecules play a crucial role in the redistribution of the final rGO by allowing the hydrogen bonds to promote the interaction between the GO sheets, resulting in the GO sheets being aligned in the same orientation.

It is an object of the present invention to provide a novel electrode material for suppressing the irreversible re-layering of rGO sheets which causes a decrease in capacitance in SC, and a method for manufacturing the same.

In order to solve the above problems, the present invention provides a graphene-based electrode material characterized by containing a graphene sheet functionalized with a monomer of a nitrogen-containing resin.

According to one embodiment of the present invention, the nitrogen-containing resin is a melamine resin.

According to one embodiment of the present invention, the reduced graphene graphene is reduced by a heat treatment method after the melamine resin monomer is bonded.

According to one embodiment of the present invention, the melamine resin is condensation-polymerized with a functional group on the surface of the graphene oxide in the form of a monomer.

According to one embodiment of the present invention, the functional group of the graphene oxide surface is a hydroxyl or carboxylic acid group, and the melamine resin monomer includes a hydroxyl group.

The present invention also provides a supercapacitor including the above-described reduced oxidation graphene.

The present invention provides a graphene-based electrode material manufacturing method comprising: mixing a melamine resin monomer dispersion solution into a graphene oxide dispersion solution; And a step of heat treating the graphene oxide functionalized by the melamine resin monomer and reducing the graphene based electrode material after the mixing step.

According to one embodiment of the present invention, the graphene oxide is produced by a modified Hummer method from graphite powder.

According to an embodiment of the present invention, a functional group which is a hydroxyl group or a carboxyl group is bonded to the surface of the graphene oxide.

According to the present invention, the final graphene molecules after carbonization of the MR monomers have substantially reduced redeposition properties and, accordingly, increased specific surface area and porosity characteristics. Furthermore, when used as an electrode of an energy element such as a supercapacitor, excellent electrochemical performance can be achieved as a supercapacitor electrode since it exhibits improved electrode characteristics by doped nitrogen atoms.

Fig. 1 is a schematic diagram illustrating a comparison of the synthesis route of rGO inhibited with re-growth layer, which is a structure of interest currently under investigation, and conventional rGO.
FIG. 2A shows the MR-GO, 2b shows the SEM image of the GO, FIGS. 2C and 2D show TEM images of the same sample, and 2e shows the XRD spectrum.
FIG. 3A shows (A) SEM of cMR-rGOth, and FIG. 3B shows a TEM image. 3C is a photograph of cMR-rGOth, rGOH, and CNT-rGOth in the same mass (= 70 mg).
Figure 4 is a scanning transmission electron microscope (STEM) image of MR-GO and cMR-rGOth restrained forms (A, B).
FIGS. 5A and 5B are XPS analysis results of MR-GO and cMR-rGOth, respectively, and FIG. 5C are high resolution N 1s XPS data.
6 is a high-resolution SEM image of (A) cMR-rGO _th , (B) rGO _H , (C) CNT-rGO _th , and (D) CNTs.
FIG. 7A shows the cMR-rGOth, and 7b shows the nitrogen adsorption-desorption isotherm of rGOH. Here, the black line and the red line correspond to adsorption and desorption curves, respectively. 7C and 7D are pore size distributions of cMR-rGOth (C) and rGOH (D), respectively, and 7e is an XRD pattern of cMR-rGOth (black) and rGOH (red).
Fig. 8 shows pore size distribution (PSD) results of the BJH method for cMR-rGOth (A) and rGOH (B).
9 is an N2 adsorption-desorption isotherm graph of CNT-rGOth and CNTs, and Table 2 below shows specific surface area and pore volume data of all carbonaceous materials used in the present invention.
Fig. 10a shows the charge and discharge profiles of cMR-rGOth (black line) and rGOH (red line) measured at the same current density of 0.5 A / g, Fig. 10C shows the weight capacitances of all four samples measured at various current densities, Fig. 10D shows the fast charge of cMR-rGOth and rGOH for evaluating a given sample as a future flash energy storage device, Fig. And a delayed discharge test.
Figure 11 shows the cycling performance of cMR-rGOth measured at (A) 0.5 A / g and (B) 2.0 A / g.

In order to fully understand the present invention, operational advantages of the present invention, and objects achieved by the practice of the present invention, reference should be made to the accompanying drawings and the accompanying drawings which illustrate preferred embodiments of the present invention.

Hereinafter, the present invention will be described in detail with reference to the preferred embodiments of the present invention with reference to the accompanying drawings. However, the present invention can be implemented in various different forms, and is not limited to the embodiments described. In order to clearly describe the present invention, parts that are not related to the description are omitted, and the same reference numerals in the drawings denote the same members.

The present invention solves the restacking problem of graphene sheets by functionalizing graphene oxide sheets with monomers of nitrogen containing resins and reducing them. Thereby solving the reclamation problem of the graphene oxide sheet by water and further improving the electrochemical performance of the graphene based electrode material according to the present invention.

Fig. 1 is a schematic diagram illustrating a comparison of the synthesis route of rGO inhibited with re-growth layer, which is a structure of interest currently under investigation, and conventional rGO.

Referring to FIG. 1, both of the synthesis routes start with the GO solution, but when the redeposited layer is suppressed in the initial stage, it involves a nitrogenous resin, a melamine resin treatment, which makes a dramatic difference in microscopic form. Hereinafter, the nitrogen-containing resin is described as a melamine resin, but condensation polymerization can be carried out with a hydroxyl group or a carboxyl group of graphene oxide,

As described above, in the case of reduced graphene oxide (rGO), the dried graphene oxide contains water molecules inserted through hydrogen bonds promoting the re-entrainment to a considerable degree in the intermediate stage. That is, reloading power is transferred to final rGO through van der Waals forces between rGO sheets upon subsequent reduction by hydrazine treatment. On the other hand, graphene oxide (hereinafter referred to as MR-GO) functionalized with a melamine resin (hereinafter referred to as MR) is obtained by condensation of the hydroxyl end group of the MR monomer with the hydroxyl or carboxylic acid group on the GO sheet The possibility of hydrogen bonding is completely eliminated by the reaction in advance. Thus, the reclaimed layer is suppressed in the dried MR-GO manufacturing step, and such reclaimed layer-retained features are retained until the end of the subsequent carbonization.

In the experiment according to one embodiment of the present invention, after a specific period when the MR monomer solution was continuously added to the GO solution, MR-GO colored MR-GO was spontaneously precipitated due to increased hydrophobicity of the GO sheet it started. Hereinafter, a method for producing a redeposited layer-inhibiting graphene according to the present invention will be described as a specific experimental example. However, the scope of the present invention is not limited by the following experimental examples.

Example

Preparation of cMR-rGOth, rGOH, and CNT-rGOth

First, graphite powder (Alfa Aesar, APC 7-11) was oxidized by modified Hummer method to obtain GO. 2 g of graphite and 1 g of sodium nitrate (NaNO3, Sigma Aldrich) were mixed with sulfuric acid (H2SO4, 50 mL, Sigma Aldrich) in an ice bath at 0 DEG C for 3 hours with vigorous stirring. To this suspension was slowly added 8 g of potassium permanganate (KMnO4, Sigma Aldrich), and the suspension was stirred until dark gray. Next, deionized water (DI) (96 mL) was slowly added to the suspension, and the suspension was kept at 98 DEG C for 1 hour. Finally, warm brown deionized water (280 mL) and a hydrogen peroxide solution (H2O2, 50 wt%, 20 mL, Sigma Aldrich) were slowly added to obtain a light brown graphite oxide solution.

This solution was filtered, washed several times with deionized water, and then subjected to a drying step to obtain a "graphite oxide powder ". The next step was to obtain the GO solution from the oxidized graphite powder by ultrasonic treatment. Typically, 4.2 g of graphite oxide powder was added to 350 mL of deionized water and the solution was tip-sonicated at 80 W for 2 hours. The sonicated solution was centrifuged at 9500 rpm for 1 hour, and the supernatant solution was dried to obtain a GO powder.

The resulting GO sheet was functionalized with a melamine resin (MR-GO) and heat-treated in vacuum (0.1 bar) to prepare cMR-rGOth. First, 2.5 g of melamine (Sigma Aldrich) An MR solution was first prepared by adding 4.425 mL aldehyde aqueous solution (Sigma Aldrich) to 40 mL deionized water. After the solution was heat treated at 70 ° C for 10 minutes, the solution turned transparent, indicating that the MR monomer was well dissolved in the aqueous medium. Next, GO solution (20 mL, 10 mg / mL) was introduced into the MR monomer solution and stirred at 98 ° C for 3 hours.

During the stirring, a condensation reaction occurred between the MR and the GO sheet, and the brown MR-GO powder precipitated. The MR-GO was thoroughly washed several times with deionized water and ethanol. Finally, cMR-rGOth was obtained (120 DEG C for 20 minutes, 400 DEG C for 2 hours, 600 DEG C for 2 hours, and 800 DEG C for 2 hours) by multi-stage heat treatment of MR-GO at an increasing rate of 1 DEG C / min.

Alternatively, 200 mL of 1 mg / mL GO solution was reduced to 400 μL of hydrazine monohydrate (H2N-NH2 · H2O, Sigma Aldrich) to produce rGOH as a control sample. To this end, both components were placed in a 50 mL flask and incubated for 5 hours at 98 ° C. Heat treated. Once the reduction process was complete, the black rGO was filtered through an alumina membrane (pore size = 200 nm, Whatman) with deionized water and ethanol several times. Finally, rGO powder was obtained by vacuum drying at 70 DEG C for 12 hours.

As another control, a microwave-assisted polyol process is used to prepare CNT-rGOth. 40 mL of CNT (Hanwa Nanotech, Korea) was dispersed by tip ultrasonication in 20 mL of ethylene glycol (EG, Sigma Aldrich) at 80 W for 5 hours. Next, 5 mL of GO solution (10 mg / mL) and 0.5 mL of sodium hydroxide solution (0.5 M, Sigma Aldrich) were added to the CNT solution. After further sonication for 1 hour, the solution was treated in a domestic microwave oven (700 W) for 90 seconds. Next, the agglomerated powder was washed several times with acetone and dried at 70 DEG C in a vacuum for 12 hours. The CNT-rGOth synthesis was completed by heat treatment at 800 ° C in a vacuum (about 0.1 bar) for 1 hour.

Character analysis

The chemical functionalities on the surface of a given sample were analyzed by X-ray photoelectron spectroscopy (XPS, Thermo VG scientific, Sigma Probe). X-ray diffraction (XRD, Rigaku) was used to analyze the crystallinity of the graphite arrays in each sample. The specific surface area, pore volume and pore size distribution were obtained from N2 adsorption-desorption measurements (Quantachrome, Quadrasorb SI). The sample morphology was observed using a field emission scanning electron microscope (FE-SEM, Sitrion) and a field emission transmission electron microscope (FE-TEM, TECNAI). The electrodes were all first treated with an active material, Super-P (TIMCAL) and poly (vinylidene difluoride) (PVDF) dispersed in 1-methyl-2- , Sigma Aldrich). The slurry was cast on a Ni mesh and the cast sample was dried in a vacuum oven at 70 DEG C for 12 hours. A co-solvent of ethylene carbonate (EC) and diethylene carbonate (DEC) (1: 1 = v: v) containing 1M lithium hexafluorophosphate (LiPF6) (PANAX E-TEC, Korea) was used as the electrolyte. 2032 coin cells were assembled in a glove box filled with argon using a porous membrane (polypropylene, Celgard 2400) as a separator. Galvanostatic charge / discharge measurements were performed at a voltage range of 0-2 V using a WBCS 3000 battery cycler (WonATech, Korea) at 25 [deg.] C for an actual electrochemical test of all samples. (Cs, F / g), energy density (ED, Wh / kg) and power density (PD, W / kg) were obtained from the galvanic nosteet results.

A non-capacitance was obtained based on the following equation:

Cs = I / [- DELTA V / DELTA t] m = I / [- slope]

Where I, m, and slope are the discharge current, the mass of active material at one electrode, and the slope of the discharge curve after iR drop. ED was calculated by multiplying the integrated area of the galvanic nystic discharge curve (voltage vs. discharge time) by the current density (A / g). PD was calculated by dividing ED by discharge time. The exact equations for ED and PD are:

, PD =

ED =

, PD =

Where V, M, I, and t are the voltage, the mass of the active material at both electrodes, the discharge current, and the discharge time.

analysis

FIG. 2A shows an MR-GO, 2b shows a SEM image of GO, FIGS. 2C and 2D show TEM images of the same sample, and 2E shows an XRD spectrum.

Referring to Figures 2A-2E, the re-layering inhibitory properties of GO-functionalized GOs were reflected in scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization.

When two samples according to this example were compared on a micrometer scale, a corrugated form ranging from tens to hundreds of nanometers was observed (Fig. 2a), which may be the earliest indication of the re-deposition inhibiting nature of MR-GO . On the other hand, the dried GO was seen as micrometer scale particles with a smooth surface morphology (Fig. 2B). These distinct forms of both samples were characterized in more detail by TEM characterization.

That is, MR-GO exhibited individual sheets scattered in a random 3D orientation (Fig. 2C) and the GO sheet in the dried GO appeared to be generally aligned along the TEM grid (Fig. 2D).

Also, in the high magnification TEM image (Fig. 2c, insert) of MR-GO, dark lines corresponding to cross sections of individual MR-GO flakes were frequently observed. From the average thicknesses of these dark lines (about 20 nm), each graphene flake constituting the local structure of the MR-GO powder was evaluated for the MR-sensibility in consideration of the thickness of each GO sheet (0.6 to 1.2 nm) It is proved that it is composed of approximately several sheets of the GO. In the case of dried GO (Fig. 2d, insert), the black / white contrast was much less pronounced due to repositioned features.

In addition, x-ray diffraction (XRD) analysis provides structural information for both samples (Fig. 2e), in particular this is concentrated on crystallinity and interlayer distance. The dried GO powder exhibited a sharp peak at 2? = 12.3 °, which indicated an ordered interlayer distance (about 7.25 Å) due to the ordered crystallinity of the GO layers aligned along the stack and the oxygen- . On the other hand, the MR-GO powder exhibited only a broad peak at 2? = 24 °, corresponding to graphite arrays properly aligned along the (002) direction. These graphite arrays actually correspond to graphene flakes visible as black lines in the TEM image of Figure 2D. Elemental analysis using X-ray photoelectron spectroscopy (XPS) also provides a consistent picture (Table 1 and Figure S1A). The hydrogen bonds removed in the MR-GO are reflected in a substantially lower oxygen content (8.8%) compared to the dried GO powder (33.40%).

FIG. 3A shows (A) SEM of cMR-rGOth, and FIG. 3B shows a TEM image. FIG. 3C also shows photographs of cMR-rGOth, rGOH, and CNT-rGOth in the same mass (= 70 mg).

Referring to Figures 3A and 3B, the re-layering inhibiting properties of MR-GO were transferred to the same sample after thermal reduction. During this heat treatment the MRs were carbonized at the same time, so in the present invention this heat treated sample is labeled cMR-rGOth. As in the case of MR-GO, cMR-rGOth also exhibited SEM analysis results (see FIG. 3A), corrugated shapes ranging from tens to hundreds of nanometers, and TEM analysis (see FIG. 3B) Individual or few rGO sheets emerged. Observed forms containing such voided voids of varying dimensions are actually judged to be of a wide pore size in the porosity measurement.

Figure 4 is a scanning transmission electron microscope (STEM) image of MR-GO and cMR-rGOth restrained forms (A, B).

Referring to FIG. 4, it can be seen that both the MR-GO and the cMR-rGOth are maintained in a layer-restrained form.

FIGS. 5A and 5B are XPS analysis results of MR-GO and cMR-rGOth, respectively, and FIG. 5C are high resolution N 1s XPS data. Table 1 also shows the elemental contents of GO, MR-GO and cMR-rGOth.

The elemental contents of GO, MR-GO, rGO _H , and cMR-rGO _th obtained by XPS analysis C (atomic%) N (atomic%) O (atomic%) GO 66.60 0 33.40 MR-GO 56.20 35.00 8.80 rGO _H 82.00 2.31 15.69 cMR-rGO _th 86.76 5.24 8.00

Referring to the above results, XPS elemental analysis of the two samples showed that the carbon content increased from 56.20% (MR-GO) to 86.76% (cMR-rGOth), suggesting that the MR was mostly carbonized after the heat treatment.

In fact, the carbon content of cMR-rGOth is similar to the carbon content (82.00%) of well-established rGO (designated rGOH) reduced by hydrazine. On the other hand, high resolution N 1s XPS data showed two peaks at 398.4 eV and 400.9 eV, which correspond to N-6 (pyridine-like) and NQ (graphite-like) nitrogen forms, respectively (see FIG. These N-forms are consistent with those already reported on similar MR-based materials and are also expected to enhance the conductivity of cMR-rGOth through the excess electrons of NQ.

6 is a high-resolution SEM image of (A) cMR-rGO _th , (B) rGO _H , (C) CNT-rGO _th , and (D) CNTs.

In Figure 6, the CNT-rGOth composite was added as another control sample to further compare the volume of the sample at a given mass before the quantitative porosity measurement, showing a dramatic difference in porosity between the samples.

6, it can be seen that the pores of the cMR _rGO-th also very large in accordance with the present invention. The results show that at the same mass of 70 mg, cMR-rGOth corresponds to a significantly larger volume compared to the other two controls (see Figure 3c), which correctly reflects the re-deposition inhibition characteristics of cMR-rGOth.

FIG. 7A shows the cMR-rGOth, and 7b shows the nitrogen adsorption-desorption isotherm of rGOH. Here, the black line and the red line correspond to adsorption and desorption curves, respectively. 7C and 7D are pore size distributions of cMR-rGOth (C) and rGOH (D), respectively, and 7e is an XRD pattern of cMR-rGOth (black) and rGOH (red).

The results provide a more quantitative set of information on the porosity of cMR-rGOth and rGOH, cMR-rGOth exhibiting a Type IV isotherm with a small hysteresis around P / P0 = 0.9, This shows the coexistence of macropores and mesopores in the powder and is consistent with the SEM image of Fig. 3A.

On the other hand, rGOH showed a different isotherm shape with large hysteresis in the P / P0 range of 0.5 to 1.0 (see Fig. 7b), which is the predominance of the relatively small mesopores existing between the resurfaced rGOH sheets Indicates presence. Based on the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) models from these isotherms, it was found that cMR-rGOth possesses significantly higher surface area and pore volume than rGOH, M < 2 > / g, and 2.6 to 0.6 cm < 3 > / g. In addition, the pore size distribution (PSD) obtained on the basis of the density function theory (DFT) method in adsorption basins also provides a consistent picture in terms of pore size. cMR-rGOth showed more pores in the range of 50-80 nm (Fig. 7c), which is due to the formation of pores between the rGO flakes. On the other hand, most of the pores in rGOH have been found to be in the sub-10 nm region (Fig. 7d), which is associated with small meso- and micro-pores formed between the rGO sheets by irreversible redeposition.

Fig. 8 shows pore size distribution (PSD) results of the BJH method for cMR-rGOth (A) and rGOH (B).

Referring to Figure 8, the PSD obtained from the BJH method also showed consistent results with respect to the dominant pore dimensions in the two samples.

9 is a N2 adsorption-desorption isotherm graph of CNT-rGOth and CNTs, and Table 2 below shows specific surface area and pore volume data of all carbonaceous materials used in the present invention.

The specific surface area and pore volume data of all the carbonaceous materials used in the present invention Specific surface area (m ² / g) Pore volume (cm ³ / g) cMR-rGO _th 1040 2.6 rGO _H 466 0.6 CNT-rGO _th 233 0.9 CNTs 176 0.7

9 and Table 2, it can be seen that cMR-rGOth according to the present invention has a very large specific surface area and pore size, and this is due to the melanin resin (MR) and the anti-redeposition effect through the carbonization process . Further, the XRD spectra of cMR-rGOth and rGOH in Figure 7e also clearly demonstrate the distinct structural features of both samples, both spectra exhibiting peaks at 2 [theta] = 24 [deg.] Corresponding to the (002) plane of the graphite array. In addition, the peak of cMR-rGOth was broader than the peak of rGOH because of the re-deposition inhibition characteristics of cMR-rGOth.

Experimental Example

To evaluate the effect of restraining layer on electrochemical performance, in the present invention, cMR-rGOth was evaluated as an active material of a symmetric SC electrode by preparing a coin battery. Most electrochemical characterization was performed under the galvanic nystic mode at a potential range of 0-2.0V. Detailed cell preparation and measurement conditions are described in the experimental section. Other control samples including rGOH, CNT-rGOth, and CNTs were also tested for comparison.

Fig. 10a shows the charge and discharge profiles of cMR-rGOth (black line) and rGOH (red line) measured at the same current density of 0.5 A / g, Fig. 10C shows the weight capacitances of all four samples measured at various current densities, Fig. 10D shows the fast charge of cMR-rGOth and rGOH for evaluating a given sample as a future flash energy storage device, Fig. And a delayed discharge test. Here 5.0 and 0.5 A / g were applied for rapid charging and delayed discharging, respectively.

Referring to Figures 10a-10d, considerably longer charging and discharging periods for cMR-rGOth exhibit better capacitance than rGOH (Figure 10a). Compared with CNT-rGOth and CNTs (Fig. 10b), the capacitance of cMR-rGOth was found to be much higher. At the same current density of 0.5 A / g, cMR-rGOth, rGOH, CNT-rGOH, and CNTs exhibited 210, 110, 33, and 15 F / g, respectively. From these apparently distinct capacitances, the following features are noted:

1. cMR-rGOth exhibited about two times more capacitance than rGOH, indicating significant morphological effects on capacitance as well as the importance of MR restraining by increased resistivity towards increased capacitance. Also, the increased nitrogen content (2.31% vs. 5.24%) must contribute to improved capacitance, since the N-doped region is known to have a higher affinity for carrier ions. Therefore, the melanin swell according to the present invention not only prevents re-deposition of graphene but also contributes to the movement of the carrier, thereby contributing to the improvement of the performance of the electrode.

2. CNTs exhibited the lowest capacitance, even though they were fairly free in the deep reloading layer, which is known to have a higher affinity for carrier ions than for a large inner tube surface and basal plane that does not contribute substantially to the adsorption of carrier ions It is believed that this is due to the absence of edge regions.

3. CNT proved to be less effective than MR in mitigating the redeposition of rGO in the final composite. This difference should be related to the degree of effectiveness of a given treatment to prevent hydrogen bonding between the inserted water and the GO sheet, thereby preventing redeposition in the dried GO state (see FIG. 1). In this sense, a conclusion can be drawn that a well-defined condensation reaction between the MR monomer and a significant portion of the GO functional group is very effective in mitigating hydrogen bonding and consequently re-deposition of the final rGO.

In addition, the outstanding capacitance of cMR-rGOth was also preserved at higher current densities (Fig. 10c). At a 20 times increased current density (10 A / g) 154 F / g was maintained, which corresponds to a capacitance retention of 73% for the capacitance at the original current density. At the same increased current density, rGOH exhibited a capacitance retention of only 51% (111 57 F / g), indicating that the well-developed pore structure of cMR-rGOth originating from restrained layer suppression Meaning that it plays a role in effective ion diffusion. In addition, the substantial content of the N-Q type must assure an excellent discharge capacity ratio performance by the enhanced electronic conductivity. Utilizing this combined effect, cMR-rGOth delivered a high non-capacitance of 140 F / g even at a high current density of 15 A / g. Therefore, cMR-rGOth according to the present invention showed a consistently higher energy density at a given power density, as compared to the rest of the control, which is attributed to the restructuring structure of cMR-rGOth and improved carrier transport efficiency do.

Additional SC measurements were performed to reflect the actual operation of EVs and portable electronic devices that require more rapid charge and delay discharge characteristics. Thus, rapid charging at 5 A / g for cMR-rGOth and rGOH and delayed discharge at 0.5 A / g were tested (Fig. 10d). The cMR-rGOth showed a capacitance of about 180 F / g even in this rapid charge mode, which is 2.5 times larger than the rCOH (about 70 F / g) capacitance measured under the same conditions, Suggesting that performance can be achieved even under difficult operating conditions of rapid charging. This result implies that cMR-rGOth can be a valuable option as electrode material for future flash-filled SC applications.

Figure 11 shows the cycling performance of cMR-rGOth measured at (A) 0.5 A / g and (B) 2.0 A / g.

Referring to FIG. 11, cMR-rGOth according to the present invention exhibited excellent cycling performance. When measured at 0.5 A / g (Fig. 11A), its non-capacitance gradually increased within the first 5000 cycles to reach 120% of the initial value, which is due to a specific activation process, such as progressive penetration of the electrolyte deep inside the electrode film . The increased capacitance with the use of the electrode material according to the present invention remained saturated until 9000 cycles. Note that this cycle number corresponds to a continuous measurement of three months. The cMR-rGOth was also tested at a higher current density of 2A / g (Fig. 6B) to extend the cycle count of the cycling test, and cMR-rGOth exhibited an excellent capacitance retention of 96% even after 20,000 cycles.

In conclusion, the present invention addresses the problem of chronic redeposition of rGO in conventional solution processes and has demonstrated significantly improved SC performance. In particular, recognizing that the water molecules inserted in the initially dried GO step play a crucial role in re-depositing the final rGO, the GO is functionalized with the MR monomer in solution to prevent hydrogen bonding, I kept it. As a result, the final cMR-rGOth had a high surface area (about 1040 m 2 / g) and a pore volume (about 2.6 cm 3 / g) as rGO flakes and showed excellent performance as SC electrodes in various electrochemical aspects. Overall, a series of results from cMR-rGOth suggests that various condensation reactions in conjunction with GO sheets in solution can be a general design principle for the synthesis of rGO with re-deposition in a scalable solution process .

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the scope of the present invention . Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (9)

A graphene-based electrode material comprising a reduced graphene oxide sheet functionalized with a melamine resin monomer,
The reduced graphene graphene sheet is formed by binding a melamine resin monomer to a graphene oxide sheet and then reducing it by a heat treatment method,
Wherein the melamine resin monomer is condensation-polymerized with a functional group on the surface of the graphene oxide sheet. delete delete delete The method according to claim 1,
Wherein the functional group on the graphene oxide sheet surface is a hydroxyl or carboxylic acid group and the melamine resin monomer contains a hydroxyl group. 6. A supercapacitor comprising a graphene based electrode material according to any one of claims 1 to 5. As a method of manufacturing a graphene based electrode material,
Mixing a melamine resin monomer dispersion solution into a graphene oxide dispersion solution; And
Heat-treating and reducing the graphene oxide functionalized by the melamine resin monomer after the step of mixing,
The graphene oxide is produced by a modified Hummer method from graphite powder,
Wherein a functional group that is a hydroxyl group or a carboxyl group is bonded to the surface of the graphene oxide. delete delete

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