Hierarchical porous carbon material based on benzoic acid compound derivation as well as preparation method and application of hierarchical porous carbon material

Abstract

The invention discloses a hierarchical porous carbon material based on benzoic acid compound derivation and a preparation method and application thereof, and relates to the field of electrochemical energy storage materials. Comprising the following steps: weighing a benzoic acid compound and potassium-containing inorganic salt according to the molar ratio of carboxylate radical to potassium ion of 1: (1-2), dissolving in deionized water, stirring and dissolving, carrying out rotary evaporation to remove a solvent, and drying to obtain a salinized precursor; placing the salinized precursor in a crucible, carbonizing for 1-3 hours in an inert atmosphere, switching carbon dioxide gas, and carrying out chambering treatment for 5-20 minutes to obtain a crude product; and washing and drying the crude product to obtain the graded porous carbon material. According to the invention, the ratio of micro-mesopores (0.9-2nm) is obviously increased to be greater than or equal to 49% by adopting a CO2 gas phase reaming technology, and a mesopore transmission channel is provided; the obtained material has better performance, and the specific surface area is greater than or equal to 2000m < 2

Description

Technical Field

[0001] The present invention relates to the field of electrochemical energy storage materials, and in particular to a hierarchical porous carbon material derived from benzoic acid compounds, and a preparation method and application thereof. Background Art

[0002] Supercapacitors have attracted much attention due to their advantages such as high power density and long cycle life. However, their energy density is limited by the single pore structure of traditional carbon materials, especially when using organic electrolyte systems with a high voltage window (≥2.7V), including but not limited to:

[0003] (a) Quaternary ammonium salt system: tetraethylammonium (TEA + ), spirocyclic quaternary ammonium salt (SBP + ), N-methyl-N-ethylpyrrolidine (MEP + ), N,N-dimethylpyrrolidine (DMP + ) and other cations with tetrafluoroborate (BF4 - ), hexafluorophosphate (PF6 - ), bis(fluorosulfonyl imide) - ) and other anions;

[0004] (b) Ionic liquid system: 1-ethyl-3-methylimidazole (EMIM + ), 1-butyl-3-methylimidazole (BMIM + ) and other cations with BF4 - PF6 - 、FSI - Anionic combination;

[0005] (c) organic solvent: at least one of acetonitrile (AN), propylene carbonate (PC), γ-butyrolactone (GBL), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC);

[0006] Typical combinations include DMPBF4 / AN, SBPBF4 / AN, TEABF4 / PC, EMIMBF4 / PC, LiPF6 / EC-DMC, etc.

[0007] Commercial activated carbon has poor micropore clogging and surface wettability in the above-mentioned electrolytes, and its pore size is poorly matched with the organic electrolyte ions (usually 0.7-1.3nm in size). It is difficult to achieve high energy density, high power density and long cycle life simultaneously. Most existing electrode materials are based on carbon-based materials such as activated carbon and carbon nanotubes. Although they have good electrical conductivity and high specific surface area, their pore structure is not optimized enough, resulting in ion transmission channels that are too small or too large, and the energy density of the electrode material cannot be fully improved. In order to break through this bottleneck, how to increase the specific surface area of ​​the material and optimize the transmission path of the electrolyte ions by regulating the pore distribution and structure of the electrode material has become a key issue that needs to be solved urgently.

[0008] Previous studies have attempted to construct hierarchical porous structures using methods such as metal-organic framework (MOF)-derived carbon and carbonization of aromatic carboxylates, but these methods generally suffer from complex synthetic routes, poor controllability, and high energy consumption. Therefore, the development of porous carbon materials with optimized structures, simple synthesis, and excellent performance is urgent, especially addressing the compatibility issues of high specific volume and high-rate performance in organic electrolyte systems. An existing patent (CN201310297767) discloses porous carbon materials derived from unsubstituted benzoates, but their pore size distribution control capabilities are insufficient, and they do not disclose methods for regulating aromatization and nitrogen doping through the synergistic effects of amino groups. An existing patent (CN2018106170432) prepares porous carbon materials using wheat straw alkali lignin as a carbon source and adding sodium p-aminobenzoate and silica for reaction. Although sodium p-aminobenzoate is used, the specific surface area of ​​the material produced by this preparation method is not ideal.

[0009] The present invention first discovered that the synergistic effect of the amino-carboxyl group in single-phenyl ring aminobenzoic acid derivatives (such as p-aminobenzoic acid) can significantly improve the aromatization efficiency. This effect can be extended to the aminobenzoic acid-containing compound system described in the present invention. Summary of the Invention

[0010] To address the problems of existing porous carbon materials, such as irrational pore distribution and structure, and complex and uncontrollable preparation processes, this paper proposes a method for preparing hierarchical porous carbon materials using benzoic acid compounds as precursors, through stoichiometric control and synergistic carbonization with carbon dioxide vapor phase pore expansion, resulting in a one-step carbonization and activation process. This simple and efficient method creates a hierarchical pore structure dominated by micropores and supplemented by mesopores, significantly improving the energy storage capacity and rate performance of the electrode material.

[0011] The technical solution adopted in the present invention is:

[0012] A method for preparing a hierarchical porous carbon material derived from a benzoic acid compound comprises the following steps:

[0013] Step 1: Weigh a benzoic acid compound and a potassium-containing inorganic salt in a molar ratio of carboxylate to potassium ion of 1:1-2, dissolve in deionized water with stirring, remove the solvent by rotary evaporation, and dry at 100-150°C for 12-24 hours to obtain a salt precursor;

[0014] Step 2: Place the salt precursor in a crucible, heat to 700-900°C at 5-15°C / min under an inert atmosphere and carbonize for 1-3 hours, switch to carbon dioxide gas at a flow rate of 50-150 mL / min, and perform pore expansion treatment for 5-20 minutes to obtain a crude product;

[0015] Step 3: The crude product is washed with 0.5-2M acid solution until neutral, and dried to obtain the hierarchical porous carbon.

[0016] Furthermore, the benzoic acid compound contains at least one amino group (-NH2).

[0017] Furthermore, the benzoic acid compound is selected from p-aminobenzoic acid, 3-aminophthalic acid or one of their derivatives.

[0018] Furthermore, the benzene ring of the benzoic acid compound includes a carboxyl group and an amino group, and the remaining four positions on the benzene ring are selected from any combination of -H, hydroxyl (-OH), methyl, and ethyl.

[0019] Furthermore, the potassium-containing inorganic salt is at least one of potassium carbonate, potassium hydroxide, and potassium phosphate, preferably potassium carbonate, and preferably has a carboxylate / potassium ion molar ratio of 1:2.

[0020] In the above scheme, the benzoic acid compound is preferably a molecule that also contains at least one amino group (-NH2), such as p-aminobenzoic acid, 3-aminophthalic acid, etc. The amino group can promote the electrophilic substitution reaction, accelerate the aromatization process of the carbon skeleton, and is conducive to the formation of a stable nitrogen-doped defective carbon skeleton at a relatively low carbonization temperature. The nitrogen-doped skeleton cooperates with K + The template effect and CO2 pore expansion process can significantly increase the proportion of 0.9-2nm micro-mesopores (≥49%) and optimize the mesoporous channels. In addition to carboxyl and amino groups, the benzene ring can also be substituted by 0 to 4 substituents independently selected from C1-C3 alkyl groups such as hydroxyl (-OH), methyl, ethyl, etc. These substituents can assist in the dissolution and dispersion of the precursor. It should be noted that the benzoic acid compounds should exclude molecules containing halogen (such as F, Cl, Br, I) or nitro (-NO2) substituents. The reason is that: halogens may produce corrosive or toxic byproducts (such as hydrogen halide) during high-temperature carbonization, interfere with the reaction process, damage the equipment, and may have residual effects on the purity and electrochemical properties of the carbon material; the nitro group is unstable at high temperatures and may undergo violent decomposition or even explosion, posing a safety hazard. At the same time, its decomposition products may also contaminate the carbon material and introduce unfavorable heteroatoms.

[0021] Through the above method, the present invention prepares a hierarchical porous carbon material derived from benzoic acid compounds.

[0022] Furthermore, the specific surface area of ​​the hierarchical porous carbon material is ≥1800m 2 / g, micropores (0.9-2nm) account for 40-55%, and mesopores account for 8-30%.

[0023] More specifically, the specific surface area of ​​the hierarchical porous carbon material is ≥2000 m 2 / g, micropores (0.9-2nm) account for 43-55%, and mesopores account for 17-30%.

[0024] The material prepared by the method of the present invention has a high specific surface area (≥1800m 2 / g) and an optimized hierarchical pore network (micropores + micromesopores ≥ 70%). When an aminobenzoic acid-containing precursor (such as p-aminobenzoic acid) is used and the method of the present invention is adopted, the resulting material contains a nitrogen-doped defect skeleton with a specific surface area ≥ 2000 m 2 / g(typical value 2861m 2 / g), pore volume ≥1.4cm 3 / g(typical value 1.46cm 3 / g), the pore size distribution is significantly optimized: micropores (<0.9nm) account for 25-30%, micromesopores (0.9-2nm) account for ≥49% (typical value 49%), and mesopores (2-50nm) account for 18-26% (typical value 26%). The total micro / mesopore volume ratio refers to the ratio of the sum of the volumes of micropores (<0.9nm), micromesopores (0.9-2nm) and mesopores (2-50nm) to the total pore volume, which is calculated from nitrogen adsorption and desorption test data. This pore structure with 0.9-2nm micromesopores as the core and mesopores as the transmission channel is particularly matched to the size of organic electrolyte ions (such as DMP+, with a solvation size of approximately 0.82nm), solving the balance problem between ion transport and effective adsorption surface area.

[0025] Finally, the present invention provides the use of a hierarchical porous carbon material derived from a benzoic acid compound in preparing a working electrode for a capacitor. The hierarchical porous carbon material derived from a benzoic acid compound is mixed with a conductive agent and a binder in a mass ratio of (70-90):(5-20):(5-15) and prepared according to a method for making an electrode sheet.

[0026] The conductive agent is selected from at least one of conductive carbon black, carbon nanotubes, and graphene.

[0027] The binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and sodium carboxymethyl cellulose / styrene-butadiene rubber (CMC / SBR) composite systems.

[0028] Using N-methylpyrrolidone as the solvent, grind until uniform to obtain a slurry. Apply the slurry evenly to the surface of an aluminum foil current collector and dry the solvent in an oven at 50-80°C. Once the electrode material is dried, compact it using a roller press and cut it into 1cm x 2cm electrode sheets. Finally, place the treated electrode sheets in a vacuum oven at 100-150°C and dry them for 12-24 hours.

[0029] The application of benzoic acid compound-derived hierarchical porous carbon materials in supercapacitors comprises the following steps:

[0030] Weigh two identical pieces of electrode material made from graded porous carbon derived from benzoic acid compounds and weld the aluminum tabs to the electrodes using an ultrasonic welder. The active material-coated surfaces of the two electrodes face each other, with a cellulose separator placed between them. After securing them with high-temperature tape on all sides, the electrode assembly is placed into an aluminum plastic shell and sealed. The sealed device is dried in a vacuum oven at 100-150°C for 12-24 hours, then removed and placed in a glove box. An organic electrolyte is added to the glove box, vacuum-exhausted, and the plastic seal is completed, allowing it to rest for 12-24 hours.

[0031] The technical solution of the present invention obtains benzoic acid compound-derived hierarchical porous carbon through one-step carbonization, constructs a suitable pore structure, and has the following advantages:

[0032] (1) The method is simple and efficient, and carbonization and activation are completed simultaneously in one step, avoiding the traditional multi-step process; hierarchical pores are constructed through the synergistic effect of stoichiometric regulation and CO2 gas phase pore expansion.

[0033] (2) The obtained material has a high specific surface area (≥1800m 2 / g) and an optimized hierarchical pore network (micropores + micromesopores ≥ 70%), which is particularly suitable for the ion size of organic electrolytes.

[0034] (3) In particular, when using aminobenzoic acid precursors and adopting the corresponding methods: CO2 gas phase pore expansion technology significantly increases the proportion of micro-mesopores (0.9-2nm) to ≥49%, and provides mesoporous transmission channels; the resulting material has better performance and a specific surface area of ​​≥2000m 2 / g, achieving a specific capacitance of 165F / g and an energy density of 48.5Wh / kg (power density 1458.2W / kg) in an organic electrolyte (DMPBF4 / AN), which is 47% higher than that of commercial activated carbon YP-80F, and a capacity retention rate of ≥86% after 10,000 cycles.

[0035] This approach, through the synergistic effects of chemical activation and carbon dioxide vapor-phase pore expansion, successfully constructed a hierarchical pore network with 0.9-2 nm micro-mesopores as the core and mesopores as the transmission channels. The hierarchical porous carbon materials synthesized via this method have demonstrated high rate performance, long cycle stability, and high energy density in supercapacitors, resolving the existing conflict between high energy density and high rate performance, particularly in organic electrolyte systems. Furthermore, they offer the advantages of low cost and simple processing, promising broad commercialization prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 are scanning electron microscope images, wherein a is a scanning electron microscope (SEM) image of a benzoic acid-derived hierarchical porous carbon material; b is a SEM image of a trimesic acid-derived hierarchical porous carbon material; c is a SEM image of a p-aminobenzoic acid-derived hierarchical porous carbon material;

[0037] Figure 2 The nitrogen adsorption-desorption curve and pore size distribution of p-aminobenzoic acid-derived hierarchical porous carbon materials. The H4-type hysteresis loop (P / P0 = 0.4-0.8) confirms the microporous-mesoporous interconnected structure.

[0038] Figure 3 Cyclic voltammetry (CV) curve of p-aminobenzoic acid-derived hierarchical porous carbon electrode;

[0039] Figure 4 This is the galvanostatic charge-discharge (GCD) curve of the p-aminobenzoic acid-derived hierarchical porous carbon electrode;

[0040] Figure 5 This is the cycling performance diagram of the supercapacitor based on p-aminobenzoic acid-derived hierarchical porous carbon electrode, with a capacity retention rate of 86% after 10,000 cycles. DETAILED DESCRIPTION

[0041] Example 1

[0042] A method for preparing a hierarchical porous carbon material derived from p-aminobenzoic acid, comprising the following steps:

[0043] This example illustrates the effects of different precursors (with and without amino groups) on the product structure. Para-aminobenzoic acid represents a preferred embodiment of the present invention, while benzoic acid and trimesic acid are used to illustrate the differences in the effects of precursors without amino groups or with multiple carboxyl groups (no amino groups).

[0044] Step 1: Respectively react the following benzoic acid compounds with potassium carbonate (at a molar ratio of carboxylate / potassium ion = 1:2):

[0045] Para-aminobenzoic acid (preferred precursor of the present invention): 10.0 g compound + 10.08 g potassium carbonate Benzoic acid (Comparative Example 1): 10.0 g compound + 11.31 g potassium carbonate

[0046] Trimesic acid (Comparative Example 2): 10.0 g compound + 13.14 g potassium carbonate

[0047] Place in a beaker, add 1000 mL of deionized water, and stir until completely dissolved. Rotary evaporate the solution to remove the solvent, and then dry at 100-150°C for 12-24 hours to obtain a salt precursor.

[0048] Step 2: Place 10g of the salted precursor in a corundum crucible and flow nitrogen gas. Raise the temperature to 700-900°C and hold for 1-3 hours at a rate of 5-15°C / min. Then, introduce carbon dioxide gas for 5-20 minutes at a flow rate of 50-150mL / min to expand the pores. Cool to room temperature to obtain a crude product.

[0049] Step 3: Wash with 0.5-2M hydrochloric acid and deionized water until the waste liquid is neutral, filter and dry in an oven for 12-24 hours to obtain the final hierarchical porous carbon material.

[0050] Scanning electron microscopy ( Figure 1 ac), all three materials have porous structures. Table 1 shows the BET specific surface area and pore size distribution analysis results:

[0051]

[0052] Para-aminobenzoic acid (preferred solution): Successfully prepared ultra-high specific surface area (2861m 2 / g), macropore volume (1.46cm 3 / g) of graded porous carbon. Its core feature is that micropores (0.9-2nm) account for as much as 49%, while mesopores (2-50nm) account for 26%, forming a through-hole structure with micropores as the main and mesopores as the auxiliary. Nitrogen adsorption and desorption curve ( Figure 2 ) shows an obvious H4-type hysteresis loop in the range of P / P0=0.4-0.8, confirming the coexistence of micropores and mesopores.

[0053] Benzoic acid (Comparative Example 1): Although the specific surface area (2434m 2 / g) and pore volume (1.40 cm 3 The pore size (g / g) is also high, but the micro-mesopore ratio (43%) is lower than the threshold of the preferred solution (49%). Furthermore, the mesopore ratio is relatively low (17%), while the micropore ratio is relatively high (40%). The resulting material has a hierarchical pore structure dominated by micro-mesopores and supplemented by micropores, and the effect is not as good as the preferred solution.

[0054] Trimellitic acid (Comparative Example 2): The specific surface area of ​​the obtained material (1850m 2 / g) and pore volume (1.00 cm 3 The pore size (g / g) is relatively low. Its pores are primarily micropores (<0.9 nm, 51%), with the micro-mesopore ratio (41%) significantly lower than the preferred solution, and the mesopore ratio (8%) is too low. The resulting material has an 8% mesopore ratio, while its micropore ratio is too high (51%) and lacks the amino group's regulatory effect, resulting in a hierarchical pore structure dominated by micropores and supplemented by micro-mesopores, which is not as good as the preferred solution.

[0055] Conclusion: Example 1 fully demonstrates the unique advantages of aminobenzoic acid as a precursor. The amino group in its molecule effectively promotes aromatization, nitrogen doping and synergistic K + / CO2 regulation forms a high proportion (≥49%) of 0.9-2nm micro-mesopores and suitable mesoporous channels (18-26%), and has a high specific surface area ≥2000m 2 / g, macropore volume ≥1.4cm 3 The benzoic acid solution produced a material that basically met the requirements, but its structural parameters (especially the mesopore ratio) were significantly inferior to those of the preferred solution. The material obtained with trimesic acid had an 8% mesopore ratio, but its high micropore ratio (51%) led to performance degradation, highlighting the necessity of an amino-containing precursor.

[0056] Example 2

[0057] A method for preparing a capacitor electrode, using the hierarchical porous carbon material prepared from p-aminobenzoic acid in Example 1, comprises the following steps:

[0058] The amino-derived hierarchical porous carbon material prepared in step 3 is mixed with a conductive agent and a binder in any of the following proportions:

[0059] Formula A: active material 80wt% + conductive carbon black 10wt% + PVDF 10wt%;

[0060] Formula B: active material 85wt% + carbon nanotubes 7wt% + PTFE 8wt%;

[0061] Formula C: active material 90wt% + conductive carbon black 5wt% + CMC / SBR (1:1) 5wt%;

[0062] Use N-methylpyrrolidone (Formula A, B) or deionized water (Formula C) as the solvent and grind until uniform to obtain a slurry. Apply the slurry evenly on the surface of the aluminum foil current collector and dry the solvent in an oven at 50-80°C. After the electrode material is dried, use a roller press to compact it at room temperature and cut it into 1cm×2cm electrode sheets. Finally, place the treated electrode sheet in a vacuum oven at 100-150°C and dry it for 12-24 hours as a working electrode.

[0063] The performance of the working electrode was evaluated in a two-electrode system. A symmetric double-layer supercapacitor was assembled using it as the working electrode and N,N-dimethylpyrrolidine tetrafluoroborate / acetonitrile (DMPBF4 / AN) solution as the electrolyte. Cyclic voltammetry and galvanostatic charge-discharge tests were performed on the assembled device at room temperature using a Chenhua CHI 660E electrochemical workstation.

[0064] like Figure 3 The p-aminobenzoic acid-derived hierarchical porous carbon material shown was tested for specific capacitance in a 3.0 V voltage window: the CV curve was rectangular at a scan rate of 10 mV / s.

[0065] like Figure 4 The electrochemical constant current charge / discharge diagrams of the p-aminobenzoic acid-derived hierarchical porous carbon material at different current densities show that the electrode material exhibits highly reversible double-layer energy storage behavior during the charge and discharge process. At a current density of 1 A / g, the specific capacitance reaches 165 F / g, a 50% increase over the commercial activated carbon YP-80F (110 F / g) under the same test conditions. This fully demonstrates the significant performance advantages of the present materials, particularly porous carbon prepared from precursors containing aminobenzoic acids (such as p-aminobenzoic acid), in organic electrolyte systems.

[0066] Example 3

[0067] This example uses the electrode prepared by the method described in Example 2 (using formula A), weighs two pieces of electrode material made of p-aminobenzoic acid-derived graded porous carbon of the same weight, and uses an ultrasonic welding machine to weld the aluminum tab to the electrode; the active material coated surfaces of the two pole pieces are facing each other, and a cellulose separator is placed in the middle. After fixing it with high-temperature tape on all sides, the electrode assembly is placed in an aluminum plastic shell and sealed. The sealed device is placed in a vacuum oven at 100-150°C for 12-24 hours, taken out and placed in a glove box. N,N-dimethylpyrrolidine tetrafluoroborate / acetonitrile (DMPBF4 / AN) electrolyte is added to the glove box, vacuum exhaust treatment is performed, and the plastic sealing operation is completed, and it is left to stand for 12-24 hours. After the soft-pack device is left to stand for 12-24 hours, performance testing is performed using the Xinwei battery testing system. The device has an energy density of 48.5Wh / kg when the power density is 1458W / kg under the test conditions of 3.0V voltage window and current density 1A / g. After 10,000 continuous charge and discharge cycles ( Figure 5 ), capacity retention rate ≥86%.

[0068] Although DMPBF4 / AN electrolyte is used as an example in this embodiment, other quaternary ammonium salt / fluoride anion / organic solvent combinations (such as TEABF4 / PC, SBPBF4 / AN, etc.) are also applicable to the hierarchical porous carbon electrode prepared by the present invention.

Claims

1. A method for preparing hierarchical porous carbon materials derived from benzoic acid compounds, characterized in that: The following steps are involved: Weigh a benzoic acid compound and a potassium-containing inorganic salt in a molar ratio of carboxylate to potassium ion of 1:1-2, dissolve in deionized water with stirring, remove the solvent by rotary evaporation, and dry at 100-150°C for 12-24 hours to obtain a salt precursor; The salt precursor is placed in a crucible, heated to 700-900°C at 5-15°C / min under an inert atmosphere and carbonized for 1-3 hours, then the carbon dioxide gas is switched to a flow rate of 50-150 mL / min, and the pores are expanded for 5-20 minutes to obtain a crude product; The crude product was washed with 0.5-2 M acid solution until neutral, and dried to obtain the hierarchical porous carbon.

2. The method for preparing a hierarchical porous carbon material derived from benzoic acid compounds according to claim 1, characterized in that: The benzoic acid compound contains at least one amino group (-NH2).

3. The method for preparing a hierarchical porous carbon material derived from benzoic acid compounds according to claim 1 or 2, characterized in that: The benzoic acid compound is selected from p-aminobenzoic acid, 3-aminophthalic acid or one of their derivatives.

4. The method for preparing a hierarchical porous carbon material derived from benzoic acid compounds according to claim 1, characterized in that: The benzene ring of the benzoic acid compound includes a carboxyl group and an amino group, and the remaining four positions on the benzene ring are selected from any combination of -H, hydroxyl (-OH), methyl, and ethyl.

5. The method for preparing a hierarchical porous carbon material derived from benzoic acid compounds according to claim 1, characterized in that: The potassium-containing inorganic salt is at least one of potassium carbonate, potassium hydroxide and potassium phosphate.

6. A hierarchical porous carbon material derived from a benzoic acid compound, characterized in that: Prepared by the method according to any one of claims 1 to 5.

7. The hierarchical porous carbon material derived from benzoic acid compounds according to claim 6, characterized in that: The specific surface area of ​​the hierarchical porous carbon material is ≥1800 m 2 / g, micropores (0.9-2nm) account for 40-55%, and mesopores account for 8-30%.

8. The hierarchical porous carbon material derived from benzoic acid compounds according to claim 7, characterized in that: The specific surface area of ​​the hierarchical porous carbon material is ≥2000m 2 / g, micropores (0.9-2nm) account for 43-55%, and mesopores account for 17-30%.

9. Use of the hierarchical porous carbon material derived from benzoic acid compounds according to any one of claims 6 to 8 in preparing a working electrode for a capacitor.

10. The application according to claim 9, characterized in that: The hierarchical porous carbon material derived from benzoic acid compounds is mixed with a conductive agent and a binder in a mass ratio of (70-90): (5-20): (5-15) and prepared according to a method for making an electrode sheet.

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