Electrode for all-solid battery and the all-solid battery

Abstract

To provide an electrode for an all-solid-state battery capable of improving a charge capacity and reducing a resistance by using a binder containing carboxymethyl cellulose or a salt thereof.SOLUTION: An electrode for an all-solid-state battery contains an electrode active material layer using an electrode composition for the all-solid-state battery including an ingredient A: carboxymethyl cellulose or a salt thereof having a degree of carboxymethyl substitution per anhydroglucose unit of 0.5 to 1.4 and a component B: a silicon-based active material. The thickness of the electrode active material layer is 1 to 40 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrode for an all-solid-state battery and an all-solid-state battery. [Background technology]

[0002] In recent years, electronic devices, particularly mobile devices such as mobile phones such as smartphones, tablets, and laptop computers, have become increasingly smaller, lighter, thinner, and more powerful. As the range of uses for such mobile devices has diversified, batteries that power them have become extremely important components. Batteries are also extremely important components in hybrid vehicles, electric vehicles, and the like. While nonaqueous electrolyte secondary batteries using an electrolytic solution in which an electrolyte is dissolved in a liquid have been used as such batteries, all-solid-state batteries using a solid electrolyte have been considered for further safety improvements.

[0003] In all-solid-state batteries, a sulfide-based solid electrolyte such as Li3PS4 is used as the solid electrolyte in the solid electrolyte layer, and in Patent Document 1, for example, a sulfide-based solid electrolyte is also contained in the electrode active material layer to be used as a conduction path for lithium ions.

[0004] In Patent Document 1, a graphite-based material is used as the negative electrode active material, but the theoretical capacity of the graphite-based material is 372 mAh / g (LiC6), and there is a limit to the energy density.

[0005] Therefore, in order to improve energy density, active materials such as silicon have been investigated for batteries using nonaqueous electrolytes (electrolytes dissolved in a liquid), which theoretically offer approximately 10 times the capacity of graphite-based carbon materials. However, silicon particles expand in volume approximately three to four times when they absorb lithium, which causes degradation and capacity loss with repeated charge and discharge cycles. Detailed analysis of this phenomenon has revealed that when lithium is inserted into a silicon-containing active material, the volume expansion causes microcracks in the electrode, allowing the electrolyte to penetrate these microcracks and form a new coating (SEI layer). This results in irreversible capacity loss, resulting in a decrease in battery capacity. This phenomenon manifests itself in changes in charge / discharge efficiency during cycling. The decrease in cycle efficiency, especially during the early stages of cycling when volume change is large, significantly impacts the battery's lifespan when combined with a positive electrode with high charge / discharge efficiency. Therefore, when using silicon-containing active materials, minimizing changes in electrode structure due to this volume expansion is a key challenge.

[0006] In light of this situation, Patent Document 2 also considers aqueous binders (binders) that use water as a solvent or dispersion medium, such as carboxymethyl cellulose or its salts. However, there is a concern that hydrogen sulfide may be generated when a sulfide-based solid electrolyte is used in the electrode active material layer of an all-solid-state battery, as in Patent Document 1, and therefore there are limitations to the use of aqueous binders. In addition, there are concerns about the environmental impact of organic solvent-based binders used in such cases. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-176484 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-198038 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide an electrode for an all-solid-state battery and an all-solid-state battery that can improve charge capacity and reduce resistance by using a binder containing carboxymethyl cellulose or a salt thereof. [Means for solving the problem]

[0009] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by setting the film thickness of the active material layer within a predetermined range.

[0010] That is, according to the present invention, (1) An electrode for an all-solid-state battery comprising an electrode active material layer using an electrode composition for an all-solid-state battery comprising component A: carboxymethylcellulose or a salt thereof having a carboxymethyl substitution degree per anhydroglucose unit of 0.5 to 1.4, and component B: a silicon-based active material, wherein the thickness of the electrode active material layer is 1 to 40 μm; (2) The electrode for an all-solid-state battery according to (1), wherein the component A is obtained by preparing 2 liters of a 0.3 mass % aqueous solution of the carboxymethyl cellulose or a salt thereof having a dry mass m, filtering the entire solution through a 250-mesh filter under a reduced pressure of −200 mmHg, and measuring the dry mass M of the residue on the filter after filtration, such that the ratio of the dry mass M to the dry mass m is less than 50 ppm. (3) The electrode for an all-solid-state battery according to (1), wherein the viscosity of a 1% by mass aqueous solution of the component A measured at 25°C using a Brookfield viscometer (30 rpm) is 500 to 20,000 mPa·s. (4) The electrode for an all-solid-state battery according to (1), wherein the component A is a carboxymethyl cellulose lithium salt. (5) The electrode for an all-solid-state battery according to (1), wherein the electrode composition for an all-solid-state battery further contains component C: at least one selected from citric acid, citrate salts, and metal-crosslinked products of citric acid. (6) The electrode for an all-solid-state battery according to (1), which contains carbon nanotubes as a conductive additive. (7) An all-solid-state battery using the electrode for an all-solid-state battery according to any one of (1) to (6). is provided. [Effects of the Invention]

[0011] According to the present invention, there are provided an electrode for an all-solid-state battery that uses a binder containing carboxymethyl cellulose or a salt thereof to improve charge capacity and reduce resistance, and an all-solid-state battery that uses this electrode for an all-solid-state battery. DETAILED DESCRIPTION OF THE INVENTION

[0012] The electrode for an all-solid-state battery of the present invention will be described below. The electrode for an all-solid-state battery of the present invention is an electrode for an all-solid-state battery comprising an electrode active material layer using an electrode composition for an all-solid-state battery comprising Component A: carboxymethylcellulose or a salt thereof having a carboxymethyl substitution degree per anhydroglucose unit of 0.5 to 1.4, and Component B: a silicon-based active material, and the film thickness of the electrode active material layer is 1 to 40 μm.

[0013] (All-solid-state battery electrode composition) The electrode composition for an all-solid-state battery (hereinafter, sometimes referred to as "electrode composition") used in the electrode active material layer contained in the all-solid-state battery electrode of the present invention includes an electrode active material layer using an electrode composition for an all-solid-state battery containing Component A: carboxymethylcellulose or a salt thereof having a carboxymethyl substitution degree per anhydroglucose unit of 0.5 to 1.4, and Component B: a silicon-based active material. Optionally, the electrode composition further contains Component C: at least one selected from citric acid, citrate salts, and metal-crosslinked products of citric acid.

[0014] <Component A: Carboxymethylcellulose and / or its salt> The carboxymethyl cellulose and / or its salt (hereinafter sometimes abbreviated as CMC) contained in the electrode composition for an all-solid-state battery used in the present invention has a structure in which the hydroxyl groups in the glucose units constituting cellulose are substituted with carboxymethyl ether groups. The carboxymethyl cellulose may be in the form of a salt. Examples of the salt of carboxymethyl cellulose include metal salts such as sodium carboxymethyl cellulose and lithium carboxymethyl cellulose, and carboxymethyl cellulose lithium salt (CMC-Li) is preferred. The more lithium in CMC-Li, the better the lithium ion conductivity. When carboxymethyl cellulose lithium salt (CMC-Li) is used, the lithium content is preferably 10,000 ppm or more, and more preferably 20,000 ppm or more.

[0015] In the present invention, cellulose refers to a polysaccharide having a structure in which D-glucopyranose units (also simply referred to as "glucose units" or "anhydroglucose") are linked together via β,1-4 bonds. Cellulose is generally classified into native cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose (which is cellulose obtained by removing the amorphous region), etc., based on its origin and manufacturing method.

[0016] Examples of natural cellulose include bleached or unbleached pulp, purified linters, and cellulose produced by microorganisms such as acetic acid bacteria. The raw materials for bleached or unbleached pulp are not particularly limited, and examples include wood, cotton, straw, bamboo, etc. The method for producing bleached or unbleached pulp is also not particularly limited, and examples include mechanical methods, chemical methods, and methods that combine mechanical and chemical methods. Examples of bleached or unbleached pulp include mechanical pulp, chemical pulp, groundwood pulp, sulfite pulp, kraft pulp, and papermaking pulp. Another example of bleached or unbleached pulp is dissolving pulp, which is chemically refined and used primarily by dissolving it in chemicals, and is used as a main raw material for artificial fibers, cellophane, etc.

[0017] Examples of regenerated cellulose include regenerated cellulose obtained by dissolving cellulose in a solvent such as a cuprammonium solution, a cellulose xanthate solution, or a morpholine derivative, and then spinning the resulting solution.

[0018] Examples of fine cellulose include fine cellulose obtained by depolymerizing cellulosic materials such as natural cellulose and regenerated cellulose through acid hydrolysis, alkali hydrolysis, enzymatic decomposition, blasting treatment, vibrating ball mill treatment, etc., and fine cellulose obtained by mechanically treating cellulosic materials.

[0019] The CMC used in the present invention can be produced by a known CMC production method. For example, cellulose is treated with a mercerizing agent (alkali) to prepare mercerized cellulose (alkali cellulose), and then an etherifying agent is added to the mercerized cellulose to cause an etherification reaction, thereby producing CMC.

[0020] The cellulose raw material can be any of the above-mentioned celluloses, but those with high cellulose purity are preferred, and dissolving pulp or linter are more preferred. By using these, CMC with high purity can be obtained.

[0021] Examples of the mercerizing agent include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, etc. Examples of the etherifying agent include monochloroacetic acid, sodium monochloroacetate, etc.

[0022] In a typical method for producing water-soluble carboxymethyl cellulose, the molar ratio of the mercerizing agent to the etherifying agent (mercerizing agent / etherifying agent) is generally 2.00 to 2.45 when monochloroacetic acid is used as the etherifying agent. A ratio of 2.00 or more allows the etherification reaction to proceed sufficiently, preventing unreacted monochloroacetic acid from being wasted. A ratio of 2.45 or less prevents a side reaction between the excess mercerizing agent and monochloroacetic acid from progressing, resulting in the production of an alkali metal glycolate, which is economical. In the present invention, the CMC may be a commercially available product, for example, a product under the trade name "Sunrose" manufactured by Nippon Paper Industries Co., Ltd.

[0023] In the present invention, the degree of etherification of CMC refers to the proportion of hydroxyl groups (-OH) in the glucose units constituting cellulose that have been substituted with carboxymethyl ether groups (-OCH2COOH).

[0024] (Degree of substitution of carboxymethyl group) The CMC used in the present invention has a degree of substitution of carboxymethyl groups per anhydroglucose unit (hereinafter sometimes referred to as DS value) of 0.5 to 1.4. A DS value of 0.5 or more can maintain good solubility in water and suppress the generation of undissolved matter. Furthermore, a DS value of 1.4 or less can suppress an increase in spinnability of the liquid and maintain easy handling. Therefore, the DS value of the CMC of the present invention is 0.5 to 1.4, preferably 0.5 to 1.2, and more preferably 0.6 to 1.0.

[0025] The degree of substitution of carboxymethyl groups is measured as follows: Weigh out approximately 2.0 g of sample and place it in a 300 mL Erlenmeyer flask with a stopper. Add 100 mL of a solution of 1000 mL of methanol and 100 mL of concentrated nitric acid, and shake for 3 hours to convert carboxymethyl cellulose salt (CMC) to H-CMC (hydrogen-form carboxymethyl cellulose). Weigh out 1.5 to 2.0 g of the bone-dry H-CMC and place it in a 300 mL Erlenmeyer flask with a stopper. Wet the H-CMC with 15 mL of 80% methanol, add 100 mL of 0.1 N NaOH, and shake for 3 hours at room temperature. Using phenolphthalein as an indicator, back-titrate the excess NaOH with 0.1 N H2SO4, and calculate the degree of carboxymethyl substitution (DS value) using the following formula: A = [(100 × F' - 0.1N-H2SO4 (mL) × F) × 0.1] / (bone-dry mass of H-CMC (g)) Carboxymethyl substitution degree = 0.162 x A / (1 - 0.058 x A) F': Factor of 0.1N-H2SO4 F: Factor of 0.1N-NaOH

[0026] (viscosity) The viscosity of a 1% by mass aqueous solution of the carboxymethyl cellulose or salt thereof used in the present invention, measured at 25°C using a Brookfield viscometer (30 rpm), is preferably 500 to 20,000 mPa·s, more preferably 500 to 15,000 mPa·s, and even more preferably 500 to 10,000 mPa·s. If this viscosity is too high, problems arise, such as the inability to uniformly mix with the active material and conductive additive during slurry preparation, or the poor fluidity of the slurry when applied to a current collector, making it difficult to apply. If the viscosity is too low, problems arise, such as the slurry flowing off the current collector when applied to the current collector, preventing a uniform film thickness, or migration of the active material and binders such as SBR, resulting in high electrical resistance.

[0027] The viscosity was measured as follows: Carboxymethylcellulose or its salt was weighed into a 1000 mL glass beaker and dispersed in 900 mL of distilled water to prepare an aqueous dispersion with a solids content of 1% (w / v). The aqueous dispersion was stirred at 600 rpm for 3 hours at 25°C using a stirrer. The viscosity was then measured after 3 minutes at 30 rpm using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) according to the method of JIS-Z-8803.

[0028] (Amount of filtration residue) Furthermore, the carboxymethyl cellulose and / or salt thereof of the present invention preferably has a filtration residue amount within a predetermined range. That is, when 2 L of a 0.3% by mass aqueous solution of the carboxymethyl cellulose or salt thereof having a dry mass m is prepared and completely filtered through a 250-mesh filter under reduced pressure conditions of −200 mmHg, and the dry mass M of the residue on the filter after filtration is measured, the ratio of the dry mass M to the dry mass m is preferably less than 200 ppm, more preferably less than 50 ppm.

[0029] If this value is too large, clogging occurs easily when filtering the electrode slurry, and the amount of carboxymethyl cellulose in the filtered slurry becomes less than the specified amount, which reduces its function as a binder and dispersant, resulting in the problem of increased electrical resistance.

[0030] (particle size) The particle size D10 of the carboxymethyl cellulose and / or salt thereof used in the present invention is preferably 1 to 10 μm, the particle size D50 is preferably 10 to 20 μm, and the particle size D90 is preferably 20 to 40 μm.

[0031] Here, particle diameter D10 (hereinafter sometimes referred to as D10) is the particle diameter that contains 10% of the particles when calculated from the minimum value in the particle diameter distribution based on the volume average particle diameter, and particle diameter D50 (hereinafter sometimes referred to as D50) is the particle diameter that contains 50% of the particles when calculated from the minimum value, and is also called the average particle diameter. Furthermore, particle diameter D90 (hereinafter sometimes referred to as D90) is the particle diameter that contains 90% of the particles when calculated from the minimum value. The particle diameter distribution based on the volume average particle diameter can be measured using, for example, methanol as a dispersant with a laser diffraction / scattering particle size distribution analyzer.

[0032] The BET specific surface area of ​​the carboxymethyl cellulose and / or its salt used in the present invention is 0.5 to 5.0 m 2 / g is preferred, and 1.0 to 4.0m 2 / g is more preferable, and 1.5 to 3.0m 2 If this value is too small, water does not easily penetrate into the CMC, and the amount of undissolved CMC increases, resulting in a decrease in adhesion between active materials and an increase in resistance.

[0033] The BET specific surface area was measured by weighing 0.1 g of powdered CMC into a test tube, drying it at 105°C for 1 hour while blowing nitrogen gas into it using a FlowPrep060 manufactured by Micromeritics, and then measuring the BET specific surface area using a Gemini VII2390 manufactured by Shimadzu Corporation.

[0034] [Crushing process] In the present invention, carboxymethyl cellulose or a salt thereof may be finely pulverized. As a method for finely pulverizing carboxymethyl cellulose or a salt thereof, either a dry pulverization method in which the carboxymethyl cellulose or a salt thereof is treated in a powder state or a wet pulverization method in which the carboxymethyl cellulose or a salt thereof is treated in a dispersed or dissolved state in a liquid may be selected.

[0035] By subjecting carboxymethyl cellulose or a salt thereof to mechanical dry or wet grinding, gel particles derived from carboxymethyl cellulose or a salt thereof that exist as undissolved matter in an aqueous solution are reduced in size, which is thought to prevent the formation of coarse undissolved matter that can cause streak defects, peeling, pinholes, and the like on the surface of the negative electrode. The following types of milling devices can be used in the present invention.

[0036] Dry mills include cutting mills, impact mills, and airflow mills. These can be used alone or in combination, and the same type of mill can be used for multiple stages of processing.

[0037] Examples of cutting-type mills include Mesh Mill (manufactured by Horai Co., Ltd.), Atoms (manufactured by Yamamoto Hyakuma Seisakusho Co., Ltd.), Knife Mill (manufactured by Parman Co., Ltd.), Granulator (manufactured by Herbolt Co., Ltd.), and Rotary Cutter Mill (manufactured by Nara Machinery Works Co., Ltd.).

[0038] Examples of impact mills include Pulperizer (manufactured by Hosokawa Micron Corporation), Fine Impact Mill (manufactured by Hosokawa Micron Corporation), Super Micron Mill (manufactured by Hosokawa Micron Corporation), Sample Mill (manufactured by Seishin Corporation), Bantam Mill (manufactured by Seishin Corporation), Atomizer (manufactured by Seishin Corporation), Tornado Mill (Nikkiso Co., Ltd.), Turbo Mill (Turbo Kogyo Co., Ltd.), and Bevel Impactor (Aikawa Iron Works Co., Ltd.).

[0039] Examples of airflow mills include a CGS-type jet mill (manufactured by Mitsui Mining Co., Ltd.), a jet mill (manufactured by Sansho Industry Co., Ltd.), an Ebara Jet Micronizer (manufactured by Ebara Corporation), a Selenium Mirror (manufactured by Masuko Sangyo Co., Ltd.), and a supersonic jet mill (manufactured by Nippon Pneumatic Mfg. Co., Ltd.). An example of a media mill is a vibrating ball mill.

[0040] Examples of the wet mill include Masscolloider (manufactured by Masuko Sangyo Co., Ltd.), and examples of the media mill include Bead Mill (manufactured by Imex Co., Ltd.) and High Pressure Homogenizer (manufactured by Sanmaru Machinery Industry Co., Ltd.). In the present invention, a step of classifying the pulverized carboxymethyl cellulose or a salt thereof based on particle size can be provided.

[0041] The classification step may be performed during or after the pulverization step. Any known method may be used for classification. Examples of dry classifiers include cyclone classifiers, DS separators, turbo classifiers, microseparators, and air separators. Examples of wet classifiers include liquid cyclone type, centrifugal settlers, and hydroseparators. The CMC used in the present invention may be one type, or a combination of two or more types of CMC differing in degree of etherification, DS value, viscosity, molecular weight, etc.

[0042] The carboxymethyl cellulose or a salt thereof used in the present invention serves as an electrode binder for an all-solid-state battery, and constitutes an electrode composition for the all-solid-state battery together with an electrode active material such as a silicon-based active material. Usually, an aqueous solution containing carboxymethyl cellulose or a salt thereof is used as an electrode binder for the all-solid-state battery.

[0043] The concentration of carboxymethyl cellulose or a salt thereof in the aqueous solution of carboxymethyl cellulose and / or a salt thereof is usually 0.1 to 10% by mass, preferably 0.2 to 4% by mass, and more preferably 0.5 to 2% by mass.

[0044] There are no particular limitations on the conditions for producing an aqueous solution of carboxymethyl cellulose and / or a salt thereof. For example, the aqueous solution is prepared by adding carboxymethyl cellulose and / or a salt thereof to water (e.g., distilled water, purified water, tap water, etc.) and dissolving it by stirring, etc., as necessary.

[0045] In addition, the content of carboxymethyl cellulose or its salt in the electrode composition for all-solid-state batteries is preferably 0.1 to 4.0% by mass based on the whole electrode composition for all-solid-state batteries.

[0046] <Component B: Silicon-based active material> The electrode composition for all-solid-state batteries used in the present invention contains Component B: a silicon-based active material. Silicon particles or silicon oxide particles containing a silicon-based active material are preferred. The silicon oxide in the present invention is SiO x (represented by 0 < x ≦ 2).

[0047] In addition to the silicon-based active material, it may contain components as active materials. Examples of such components include graphite materials such as graphite (natural graphite, artificial graphite, etc.), coke, and carbon fibers; elements capable of forming an alloy with lithium, that is, for example, elements such as Al, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Ti; compounds containing elements capable of forming an alloy with lithium; composites of elements capable of forming an alloy with lithium and the above compounds with carbon and / or the above graphite materials, or nitrides containing lithium, etc. Among these, graphite materials are preferred, and graphite is more preferred. In the present invention, a composite of a silicon-based active material and a graphite material can also be used as the active material.

[0048] When using a silicon-based active material and a graphite material, the silicon-based active material and the graphite material are preferably used in a mass ratio of silicon-based active material:graphite material = 10:90 to 90:10, and more preferably in a mass ratio of 50:50 to 80:20.

[0049] The content of the electrode active material in the electrode active material layer of the present invention is usually 90 to 99% by mass, preferably 91 to 99% by mass, more preferably 92 to 99% by mass, still more preferably 95 to 99% by mass, particularly preferably 96 to 99% by weight, and most preferably 98 to 99% by mass.

[0050] <Component C: At least one selected from citric acid, citrate salts, and metal-crosslinked citric acid> The electrode composition for an all-solid-state battery used in the present invention may further contain, in addition to component A: carboxymethyl cellulose or a salt thereof and component B: a silicon-based active material, component C: at least one selected from citric acid, citrate salts, and metal-crosslinked products of citric acid.

[0051] Here, component C may be at least one selected from carboxylic acids having 6 or less carbon atoms, carboxylic acid salts having 6 or less carbon atoms, and metal-crosslinked products of carboxylic acids having 6 or less carbon atoms. The saturated carboxylic acids having 6 or less carbon atoms include aliphatic hydroxy acids, aromatic hydroxy acids, saturated fatty acids, dicarboxylic acids, tricarboxylic acids, etc., each having 6 or less carbon atoms, with aliphatic hydroxy acids having 6 or less carbon atoms being more preferred. Examples of such aliphatic hydroxy acids include citric acid, malic acid, gluconic acid, and succinic acid.

[0052] Examples of saturated carboxylic acid salts having 6 or less carbon atoms include salts of the saturated carboxylic acids exemplified above, and preferred forms of such salts include saturated carboxylic acid potassium salts, saturated carboxylic acid calcium salts, and saturated carboxylic acid lithium salts. Of these, saturated carboxylic acid lithium salts are more preferred, and among these, lithium citrate salts are even more preferred. Examples of metal-bridged carboxylic acids having 6 or less carbon atoms include metal organic frameworks (MOFs) in which the saturated carboxylic acids exemplified above serve as ligands.

[0053] That is, when a citrate is used as component C, potassium citrate, calcium citrate, and lithium citrate are preferred, and among these, lithium citrate is more preferred.

[0054] When a metal-bridged product of citric acid is used as component C, examples include metal organic frameworks (MOFs) with citric acid as a ligand, and copper organic frameworks (MOFs-Cu), cobalt organic frameworks (MOFs-Co), and zinc organic frameworks (MOFs-Zn) with citric acid as a ligand are preferred. MOFs-Cu can be obtained, for example, from citric acid and copper nitrate or copper carbonate, MOFs-Co can be obtained, for example, from citric acid and cobalt nitrate or cobalt carbonate, and MOFs-Zn can be obtained, for example, from citric acid and zinc nitrate.

[0055] When component C is used as a binder together with carboxymethylcellulose or its salt, the hydroxyl or carboxyl groups in citric acid form a crosslinked structure via hydrogen bonding with the carboxyl groups of carboxymethylcellulose or its salt. This crosslinked structure contains more hydroxyl and carboxyl groups per molecule than carboxymethylcellulose alone, making it more reactive with the anode material, such as SiOx, dispersed in the anode slurry via hydrogen bonding. As a result, a stable oxide film can be formed on the surface of the anode material, such as SiOx, which suppresses electrolyte decomposition and prevents the formation of an excessively thick SEI (Solid Electrolyte Interface) film on the electrode surface, which is thought to lead to improved battery performance.

[0056] When component C is used, the component C is preferably contained in the range of 0.1 to 20 mass % of the carboxymethyl cellulose or a salt thereof, more preferably in the range of 0.1 to 15 mass %, and even more preferably in the range of 0.3 to 12 mass %. When the blending ratio is within this range, it is presumed that the formation of a crosslinked structure between the carboxymethyl cellulose or a salt thereof and at least one selected from citric acid, citrate salts, and metal crosslinked products of citric acid can be more effectively generated.

[0057] (Conductive additive) The electrode composition for an all-solid-state battery used in the present invention may contain a conductive aid as needed. Examples of the conductive aid include conductive carbon such as carbon black, acetylene black, carbon nanotubes, and ketjen black. Among these, acetylene black and carbon nanotubes are preferred. The content of the conductive aid in the electrode composition for an all-solid-state battery is usually 0.01 to 10% by mass, preferably 0.01 to 1% by mass.

[0058] (Other binders) The binder in the electrode composition for an all-solid-state battery used in the present invention may contain other binders in addition to carboxymethyl cellulose or a salt thereof. Examples of binders used in the electrode composition for the negative electrode include synthetic rubber binders. Examples of synthetic rubber binders that can be used include one or more selected from the group consisting of styrene butadiene rubber (SBR), nitrile butadiene rubber, methyl methacrylate butadiene rubber, chloroprene rubber, carboxy-modified styrene butadiene rubber, and latexes of these synthetic rubbers. Among these, styrene butadiene rubber (SBR) is preferred.

[0059] When the other binder is used, the content of the other binder in the electrode composition for an all-solid-state battery is preferably 1 to 10 mass %, more preferably 1 to 6 mass %, and even more preferably 1 to 2 mass %.

[0060] (solvent) The solvent used in the electrode composition for an all-solid-state battery is preferably an aqueous solvent. The type of aqueous solvent is not particularly limited, but is preferably water, a water-soluble organic solvent, or a mixed solvent thereof, and more preferably water.

[0061] The water-soluble organic solvent is an organic solvent that dissolves in water. Examples of water-soluble organic solvents include methanol, ethanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), N,N-dimethylacetamide, dimethyl sulfoxide (DMSO), acetonitrile, methyl succinate triglycol diester, acetic acid, and combinations thereof.

[0062] When the mixed solvent is used as the aqueous solvent, the amount of the water-soluble organic solvent in the mixed solvent is preferably 10% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more. There is no upper limit to this amount, but it is preferably 95% by mass or less, more preferably 90% by mass or less. Furthermore, the aqueous solvent may contain a water-insoluble organic solvent as long as it does not impair the effects of the invention.

[0063] (Production of electrode composition for all-solid-state battery) The conditions for producing the electrode composition for an all-solid-state battery are not particularly limited. For example, other components constituting the electrode composition for an all-solid-state battery are added to an aqueous solution of carboxymethyl cellulose or a salt thereof, and mixed with stirring as necessary. The form of the electrode composition for an all-solid-state battery is not particularly limited, and may be, for example, a liquid, a paste, a slurry, or the like.

[0064] (Formation of electrodes for all-solid-state batteries) By applying the above-mentioned electrode composition for all-solid-state batteries to a current collector, an electrode for all-solid-state batteries can be formed, in which an electrode active material layer is formed on the current collector. Examples of application methods include blade coating, bar coating, and die coating, with blade coating being preferred. For example, blade coating can be performed by casting the electrode composition for all-solid-state batteries onto the current collector using a coating device such as a doctor blade. Furthermore, the lamination method is not limited to the above specific example, and can also be performed by discharging the electrode composition from an extrusion-type injector with a slot nozzle onto a running current collector wound around a backup roll. In blade coating, after casting, an electrode active material layer can be obtained by further drying, such as by heating (at a temperature of, for example, 80 to 120°C for a heating time of, for example, 4 to 12 hours), or by pressing (a pressing step) using a roll press or the like, as needed.

[0065] The shape of the electrode for an all-solid-state battery of the present invention is not particularly limited, but is usually a sheet. The thickness of the electrode active material layer after the above-mentioned pressing step is 1 to 40 μm, preferably 1 to 20 μm, and more preferably 1 to 10 μm. By keeping the thickness of the electrode active material layer within this range, it is possible to prevent the phenomenon in which lithium ions cannot migrate to the current collector side and therefore the battery does not function. In other words, lithium ions can move and enter and exit the electrode active material layer as a whole, allowing the battery to function.

[0066] (current collector) Any electrical conductor can be used as the current collector as long as it does not cause a fatal chemical change in the constructed electrode or battery. The electrode for the all-solid-state battery of the present invention preferably uses a negative electrode current collector, and examples of the material for the negative electrode current collector include stainless steel, nickel, copper, titanium, carbon, copper, or stainless steel surfaces treated with carbon, nickel, titanium, or silver. Of these, copper or a copper alloy is preferred, and copper is more preferred.

[0067] <All-solid-state battery> The all-solid-state battery of the present invention includes the all-solid-state battery electrode (negative electrode) of the present invention, an electrode (positive electrode) as a counter electrode to the all-solid-state battery electrode, and a solid electrolyte layer disposed between the negative electrode and the positive electrode.

[0068] (solid electrolyte layer) The solid electrolyte layer includes a solid electrolyte. Materials known for use in all-solid-state batteries can be used as the solid electrolyte, including oxide solid electrolytes, sulfide solid electrolytes, halide solid electrolytes, complex hydride solid electrolytes, and polymer solid electrolytes. Among these, sulfide solid electrolytes are preferred from the viewpoint of lithium ion conductivity, and Li2S-P2S5 glass electrolytes and argyrodite-type Li6PS5X (X = Cl, Br, I) are more preferred. The solid electrolyte layer may contain a known binder, although from the viewpoint of safety, an organic solvent-based binder is preferred, and it is preferable that the solid electrolyte layer does not contain a water-based binder.

[0069] (positive electrode) The electrode (positive electrode) serving as the counter electrode of the all-solid-state electrode of the present invention may be a known electrode, such as a lithium foil or an indium foil, or may be formed by applying a positive electrode composition containing a positive electrode active material, a positive electrode binder, and, if necessary, a conductive additive, onto a positive electrode current collector.

[0070] The positive electrode active material is LiFePO4, LiMe x O y (Me represents a transition metal including at least one of Ni, Co, and Mn. x and y represent any numbers.)-based positive electrode active materials can be used. In this case, the content of the positive electrode active material in the positive electrode active material layer is usually 90 to 99 mass%, preferably 91 to 99 mass%, more preferably 92 to 99 mass%, even more preferably 95 to 99 mass%, particularly preferably 96 to 99 mass%, and most preferably 98 to 99 mass%.

[0071] Examples of binders for the positive electrode include the synthetic rubber binders listed above as binders for the negative electrode, as well as poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP). The content of the binder for the positive electrode in the positive electrode composition is preferably 1 to 10 mass%, more preferably 1 to 6 mass%, and even more preferably 1 to 2 mass%. Examples of the conductive additive include the same ones that can be used in the above-mentioned electrode composition for an all-solid-state battery. Examples of materials for the positive electrode current collector include metals such as aluminum and stainless steel, with aluminum being preferred. The current collector may be in the form of a mesh, punched metal, foam metal, or foil processed into a plate shape, with foil processed into a plate shape being preferred. When the positive electrode composition is used, the positive electrode can be formed by the same method as that described above for forming the electrode for the all-solid-state battery.

[0072] (Manufacturing method of all-solid-state batteries) The method for producing the all-solid-state battery of the present invention is not particularly limited, but for example, a solid electrolyte layer can be formed by pressing a material for forming the solid electrolyte layer, and an electrode for the all-solid-state battery of the present invention (negative electrode), a solid electrolyte layer, and a positive electrode are stacked in this order, followed by further pressing to produce an all-solid-state battery. The stacking is performed so that the electrode active material layer side of the negative electrode and the electrode active material layer side of the positive electrode are in contact with the solid electrolyte layer, respectively.

[0073] Alternatively, an all-solid-state battery may be produced by forming a solid electrolyte layer on the electrode active material layer side of a negative electrode, then disposing a positive electrode so that the electrode active material layer of the positive electrode is in contact with the solid electrolyte layer side, and pressing the positive electrode. Alternatively, an all-solid-state battery may be produced by forming a solid electrolyte layer on the electrode active material layer side of a positive electrode, then disposing a negative electrode so that the electrode active material layer of the negative electrode is in contact with the solid electrolyte layer side, and pressing the negative electrode.

[0074] The all-solid-state battery may be housed in a housing such as a predetermined cell, and in this case, pressure may be applied from the negative electrode side and the positive electrode side of the cell. [Example]

[0075] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[0076] Example 1 <Preparation of electrode binder> A twin-screw kneader adjusted to 100 rpm was charged with 2720 g of isopropyl alcohol, 170 g of sodium monochloroacetate, and 58 g of sodium hydroxide dissolved in 480 g of water. The resulting mixture was then dried at 30°C for 60 minutes, yielding 160 g of linter pulp (dry weight). The mixture was stirred and mixed at 30°C for 90 minutes to prepare mercerized cellulose, which was then heated to 70°C and carboxymethylated for 90 minutes. After the reaction was complete, the mixture was neutralized with acetic acid to a pH of approximately 7, dewatered, dried, and pulverized to obtain a sodium salt of carboxymethyl cellulose (hereinafter sometimes referred to as "CMCa"). The sodium salt had a carboxymethyl substitution degree of 0.70, a viscosity of a 1% by weight aqueous solution measured at 25°C of 7,900 mPa·s using a Brookfield viscometer, and a filter residue of 48 ppm relative to the dry mass of carboxymethyl cellulose dissolved in the aqueous solution.

[0077] CMCa was weighed into a 300 mL glass beaker, and distilled water was added to prepare an aqueous dispersion with a carboxymethyl cellulose solids concentration of 2% (w / v). The aqueous dispersion was stirred at 500 rpm for 2 hours at 25°C using a stirrer to obtain electrode binder 1.

[0078] <Preparation of negative electrode plate> Silicon (Alfa Aesar), acetylene black (Stream Chemical), and electrode binder 1 were mixed as anode materials at a solids weight ratio of 100:0.5:1.0, and water was added to a slurry concentration of 45.6% by mass. The mixture was thoroughly stirred using a Mazerustar (Kurashiki Boseki, KK-250S) to obtain a slurry. This slurry was applied to a copper foil (Furukawa Electric, NC-WS) measuring 320 mm in length, 170 mm in width, and 17 μm in thickness using an applicator. The foil was then air-dried for 30 minutes and then dried in a dryer at 60°C for 30 minutes. The foil was then pressed using a small benchtop roll press (Tester Sangyo, SA-602) at 5 kN and a roll peripheral speed of 50 m / min to obtain a coating weight of 325 μg / cm. 2 A negative electrode plate with an effective discharge capacity of 4200 mAh / g was obtained. The film thickness of the obtained negative electrode plate was measured and found to be 4 μm.

[0079] <Fabrication of all-solid-state batteries> The obtained negative electrode plate was punched out into a circle having a diameter of 9.5 mm, and the punched negative electrode plate was vacuum dried at 60° C. for 12 hours. 80 mg of powdered glass solid electrolyte Li3PS4 (Li2S:P2S5=75:25 (molar ratio)) was placed in a cylindrical cell and pressed with a press at 56 MPa for 30 seconds. The negative electrode plate was set on one side of the cell and pressed in a press at 333 MPa for 1 minute.

[0080] Indium foil (0.1 mm thick) was punched out to a circle with a diameter of 8 mm. Lithium foil (0.2 mm thick) was punched out to a circle with a diameter of 4.5 mm. The indium foil and lithium foil were laminated in this order on the side of the cell opposite the negative electrode plate. The foil was then pressed in a press at 111 MPa for 1 minute.

[0081] The cell was sandwiched between metal plates on the top and bottom and screwed together to create a confining pressure of 75 MPa, creating an all-solid-state battery.

[0082] Example 2 50 g of CMCa was added to 500 mL of 10 vol% nitric acid methanol and stirred for 2 hours. The resulting slurry was centrifuged to separate H-type CMCa (hereinafter sometimes referred to as "CMCa-H"). This was then poured into 100 mL of distilled water, stirred for 30 minutes, and centrifuged to recover CMCa-H. The CMCa was again poured into 100 mL of distilled water, stirred for 30 minutes, and centrifuged to recover CMCa-H.

[0083] 1.27 g of lithium hydroxide was dissolved in 150 mL of 75 vol% methanol. 15 g of the recovered CMCa-H was added to this solution and stirred for 3 hours. The pH was adjusted to 7 with acetic acid, and the solution was filtered to recover the Li-type CMCa (hereinafter sometimes referred to as "CMCa-Li").

[0084] The recovered CMCa-Li was added to 150 mL of 90% methanol, stirred for 30 minutes, and then filtered to recover the CMCa-Li. This process was repeated once more to obtain CMCb, which had a carboxymethyl substitution degree of 0.70, a viscosity of a 1% by mass aqueous solution measured at 25°C using a Brookfield viscometer of 2,750 mPa·s, a filter residue of 49 ppm relative to the dry mass of carboxymethyl cellulose dissolved in the aqueous solution, and a Li content of 22,700 ppm.

[0085] CMCb was weighed into a 300 mL glass beaker to give a solids concentration of 2% (w / v), and distilled water was added to prepare an aqueous dispersion. The aqueous dispersion was stirred at 500 rpm at 25°C for 2 hours using a stirrer to obtain electrode binder 2.

[0086] Electrode binder 2 was used instead of electrode binder 1, and the weight of the negative electrode plate was 917 μg / cm 2 A slurry, a negative electrode plate, and an all-solid-state battery were prepared in the same manner as in Example 1, except that the thickness of the film was changed to 6 μm.

[0087] Example 3 Citric acid (Fujifilm Wako Pure Chemical Industries, Ltd.) was weighed out in a 300 mL glass beaker at a ratio of 1% by mass to CMCa, and distilled water was added to make the carboxymethyl cellulose solids concentration 2% (w / v) to prepare an aqueous dispersion. The aqueous dispersion was stirred at 500 rpm for 2 hours at 25°C using a stirrer to obtain electrode binder 3.

[0088] Instead of the electrode binder 1, the electrode binder 3 was used, and the weight of the negative electrode plate was 480 μg / cm 2 A slurry, a negative electrode plate, and an all-solid-state battery were prepared in the same manner as in Example 1, except that the thickness of the film was changed to 9 μm.

[0089] Example 4 An electrode binder 4 was obtained in the same manner as in Example 3, except that 1% by mass of citric acid was changed to 10% by mass of trilithium citrate (Fujifil Wako Pure Chemical Industries, Ltd.).

[0090] Instead of the electrode binder 1, the electrode binder 4 was used, and the weight of the negative electrode plate was 547 μg / cm 2 A slurry, a negative electrode plate, and an all-solid-state battery were prepared in the same manner as in Example 1, except that the thickness of the film was changed to 7 μm.

[0091] Example 5 An electrode binder 5 was obtained in the same manner as in Example 3, except that CMCb was used instead of CMCa. As the negative electrode material, silicon (manufactured by Alfa Aesar), carbon nanotubes (manufactured by OCSiAL), and electrode binder 5 were mixed so that the solid weight ratio was 100:0.05:1.0, and the weight of the negative electrode plate was 684 μg / cm 2 A slurry, a negative electrode plate, and an all-solid-state battery were prepared in the same manner as in Example 1, except that the thickness of the film was changed to 4 μm.

[0092] Example 6 50 g of carboxymethyl cellulose (manufactured by Nippon Paper Industries Co., Ltd., "Sunrose A350SH") was added to 500 mL of 10 vol% nitric acid methanol and stirred for 2 hours. The resulting slurry was filtered to separate H-type Sunrose A350SH (hereinafter sometimes referred to as "A350SH-H"), which was then poured into 600 mL of 75% methanol solution, stirred for 30 minutes, and then filtered to recover A350SH-H. A350SH-H was again poured into 600 mL of 75% methanol solution, stirred for 30 minutes, and then filtered to recover A350SH-H.

[0093] 2.76 g of lithium hydroxide was dissolved in 80 mL of 75 vol% methanol. 5 g of the recovered A350SH-H was added to this solution and stirred for 3 hours. The pH was adjusted to 7 with acetic acid, and then the solution was filtered to recover the Li-type A350SH (hereinafter sometimes referred to as "A350SH-Li").

[0094] The recovered A350SH-Li was added to 80 mL of 90% methanol, stirred for 30 minutes, and filtered to recover A350SH-Li. This process was repeated once more to obtain CMCc. The carboxymethyl substitution degree of CMCc was 1.34, and the viscosity of a 1% by weight aqueous solution measured at 25°C using a Brookfield viscometer was 630 mPa·s. The filtration residue relative to the dry mass of carboxymethyl cellulose dissolved in the aqueous solution was 47 ppm, and the Li content was 36,800 ppm.

[0095] CMCc was weighed into a 300 mL glass beaker to give a solids concentration of 2% (w / v), and distilled water was added to prepare an aqueous dispersion. The aqueous dispersion was stirred at 500 rpm at 25°C for 2 hours using a stirrer to obtain electrode binder 6. A slurry, a negative electrode plate, and an all-solid-state battery were prepared in the same manner as in Example 1, except that electrode binder 6 was used instead of electrode binder 1, the coating weight of the negative electrode plate was set to 968 μg / cm2, and the film thickness was set to 6 μm.

[0096] Example 7 Citric acid (Fujifilm Wako Pure Chemical Industries, Ltd.) and copper(II) nitrate trihydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) were weighed into a 300 mL glass beaker and distilled water was added to prepare an aqueous solution with a solids concentration of 0.2%. CMCa was added to this aqueous solution with a solids concentration of 2% to prepare an aqueous dispersion. The aqueous dispersion was stirred at 500 rpm at 25°C using a stirrer for 2 hours to obtain electrode binder 7. Electrode binder 7 was used instead of electrode binder 1, and the weight of the negative electrode plate was 894 μg / cm 2 A slurry, a negative electrode plate, and an all-solid-state battery were prepared in the same manner as in Example 1, except that the thickness of the film was changed to 6 μm.

[0097] (Comparative Example 1) The weight of the negative electrode plate is 4526 μg / cm 2 A slurry, a negative electrode plate, and an all-solid-state battery were prepared in the same manner as in Example 1, except that the thickness of the film was 50 μm.

[0098] <Measurement and evaluation methods> The all-solid-state batteries obtained in the examples and comparative examples were measured and evaluated as follows.

[0099] <Battery evaluation> (Charge capacity (charge / discharge cycle test)) The charge-discharge cycle test of the all-solid-state batteries obtained in the examples and comparative examples was carried out using Nagano Corporation's BTS2004 in a thermostatic chamber at 30° C., with 15 cycles being one cycle consisting of a discharge treatment followed by a charge treatment. Note that the discharge treatment conditions were a constant current-constant voltage (CC-CV) method (CC current 0.05 mA, CV voltage −0.58 V, final current 0.005 mA) for all cycles. The charging conditions were a cut-off voltage of 0.88 V and a constant current of 0.05 mA, and the charge capacity (mAh / g) after one cycle was measured.

[0100] (Film thickness measurement) The film thickness was measured using TM600 (manufactured by Kumagai Riki Kogyo Co., Ltd.).

[0101] (impedance measurement) The batteries obtained in the examples and comparative examples were subjected to an Ametech Versa STAT3 test, where an AC voltage with an amplitude of 10 mV superimposed thereon was applied from 1 MHz to 0.005 Hz with an OCV (open circuit voltage) of 0 V, and the impedance (Ω) was calculated from the response current, and this value was taken as the resistance value. The results of the above measurements and evaluations are shown in Table 1.

[0102] [Table 1]

[0103] As shown in Table 1, all-solid-state batteries using electrodes for all-solid-state batteries including an electrode active material layer using an electrode composition for all-solid-state batteries containing Component A: carboxymethylcellulose or its salt having a carboxymethyl substitution degree per anhydroglucose unit of 0.5 to 1.2, and Component B: a silicon-based active material, and in which the film thickness of the electrode active material layer is 1 to 40 μm, were shown to function as batteries. Furthermore, when CMC-Li was used as the CMC (Examples 2 and 6), when citric acid was added to the CMC (Example 3), when lithium citrate was added to the CMC (Example 4), when citric acid was added to the CMC and carbon nanotubes were used as a conductive additive (Example 5), and when citric acid and copper nitrate were added to the CMC (Example 7), the charge capacity of the all-solid-state batteries was further improved even when the film thickness was increased compared to Example 1. When CMC-Li was used as the CMC (Examples 2 and 6) and when citric acid was added to the CMC (Example 3), the charge capacity after 15 cycles was improved compared to Example 1.

Claims

1. An electrode for an all-solid-state battery comprising an electrode active material layer using an electrode composition for an all-solid-state battery comprising: component A: carboxymethylcellulose or a salt thereof having a carboxymethyl substitution degree per anhydroglucose unit of 0.5 to 1.4; and component B: a silicon-based active material, wherein the film thickness of the electrode active material layer is 1 to 40 μm.

2. 2. The electrode for an all-solid-state battery according to claim 1, wherein, when 2 L of a 0.3 mass % aqueous solution of carboxymethyl cellulose or a salt thereof having a dry mass m is prepared, the solution is completely filtered through a 250-mesh filter under a reduced pressure condition of −200 mmHg, and the dry mass M of the residue on the filter after filtration is measured, the ratio of the dry mass M to the dry mass m is less than 50 ppm.

3. 2. The electrode for an all-solid-state battery according to claim 1, wherein the viscosity of a 1% by mass aqueous solution of component A measured at 25°C with a Brookfield viscometer (30 rpm) is 500 to 20,000 mPa·s.

4. 2. The electrode for an all-solid-state battery according to claim 1, wherein the component A is a carboxymethyl cellulose lithium salt.

5. 2. The electrode for an all-solid-state battery according to claim 1, wherein the electrode composition for an all-solid-state battery further comprises component C: at least one selected from citric acid, citrate salts, and metal-crosslinked products of citric acid.

6. The electrode for an all-solid-state battery according to claim 1 , wherein the electrode composition for an all-solid-state battery contains carbon nanotubes as a conductive additive.

7. An all-solid-state battery using the electrode for an all-solid-state battery according to any one of claims 1 to 6.

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