Carboxymethyl cellulose and / or its salt, electrode composition for non-aqueous electrolyte secondary battery, electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

Abstract

To provide carboxymethyl cellulose and / or its salts capable of obtaining an electrode layer with a small electric resistance and that is used for a binding agent for an electrode of a non-aqueous electrolyte secondary battery.SOLUTION: Provided is carboxymethyl cellulose and / or its salts used for a binding agent for an electrode of a non-aqueous electrolyte secondary battery, in which a carboxymethyl substitution degree per anhydrous glucose unit is 0.5-1.2. A degree of dispersion measured by using a powder tester is 20-60%. A ratio ((particle size D90-particle size D50) / (particle size D50-particle size D10)) of a value obtained by subtracting a particle size D50 from a particle size D90 (particle size D90-particle size D50) and a value obtained by subtracting a particle size D10 from the particle size D50 (particle size D50-particle size D10) is 1.0-2.5.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to carboxymethyl cellulose and / or a salt thereof used as an electrode binder for a non-aqueous electrolyte secondary battery, an electrode composition for a non-aqueous electrolyte secondary battery using the carboxymethyl cellulose and / or the salt thereof, an electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery. [Background technology]

[0002] In recent years, the rapid spread of small portable devices such as smartphones and tablets, as well as stationary storage batteries, has led to an increasing demand for small, high-energy-density batteries to power them.

[0003] Generally, graphite-based materials are used for the negative electrodes of lithium-ion secondary batteries, but the theoretical capacity of graphite-based materials is 372 mAh / g (LiC6), which is currently approaching its limit.

[0004] Furthermore, in order to improve the energy density of lithium-ion secondary batteries, it is necessary to select new materials. Therefore, materials made by alloying lithium with silicon, tin, etc., which have the second lowest potential and large specific capacity after carbon and lithium, are attracting attention.

[0005] Among these materials, silicon can absorb up to 4.4 lithium atoms per 1 silicon atom in molar ratio, theoretically providing 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, leading to degradation and capacity loss with repeated charge-discharge cycles. Detailed analysis of this phenomenon has revealed that when lithium is inserted into silicon-containing active materials, the volume expansion causes microcracks to form within the electrode, allowing the electrolyte to penetrate these microcracks and form a new coating (SEI layer). This creates 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, minimizing changes in electrode structure due to this volume expansion is a key challenge when using silicon-containing active materials.

[0006] In view of these circumstances, Patent Document 1 aims to improve battery characteristics by using a binder containing three essential components: carboxymethyl cellulose or a metal salt thereof, polyacrylic acid or a metal salt thereof, and styrene-butadiene rubber or polyvinylidene fluoride. However, according to the examples and comparative examples of Patent Document 1, when only two components (carboxymethyl cellulose and styrene-butadiene rubber, or carboxymethyl cellulose and polyvinylidene fluoride) were used as the binder, desired battery characteristics were not obtained. [Prior art documents] [Patent documents]

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

[0008] Patent Document 1 states that three components including carboxymethyl cellulose or a metal salt thereof are essential as a binder, but does not specifically mention the physical properties of carboxymethyl cellulose or a metal salt thereof. The inventors' studies have revealed that these physical properties affect the battery characteristics, particularly the electrical resistance of the resulting electrode layer.

[0009] Specifically, an object of the present invention is to provide carboxymethyl cellulose and / or a salt thereof for use in an electrode binder for a non-aqueous electrolyte secondary battery, which enables the formation of an electrode layer with low electrical resistance, and to provide an electrode composition for a non-aqueous electrolyte secondary battery, an electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery, which use the carboxymethyl cellulose and / or the salt thereof. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have found that the above problems can be solved by using a material having a predetermined degree of dispersion.

[0011] That is, according to the present invention, (1) Carboxymethyl cellulose and / or a salt thereof used as an electrode binder for a non-aqueous electrolyte secondary battery, the degree of carboxymethyl substitution per anhydrous glucose unit being 0.5 to 1.2, the degree of dispersion measured using a powder tester being 20 to 60%, and the ratio ((particle diameter D90 - particle diameter D50) / (particle diameter D50 - particle diameter D10)) of the value obtained by subtracting particle diameter D50 from particle diameter D90 (particle diameter D90 - particle diameter D50) to the value obtained by subtracting particle diameter D10 from particle diameter D50 (particle diameter D50 - particle diameter D10) being 1.0 to 2.5; (2) The carboxymethyl cellulose and / or salt thereof according to (1), having a particle size D50 of 10 to 20 μm. (3) Carboxymethylcellulose and / or a salt thereof according to (1) or (2), having an angle of repose of 42° or more. (4) Carboxymethylcellulose and / or a salt thereof according to (1) or (2), having a collapse angle of 19° or more. (5) The carboxymethyl cellulose and / or salt thereof according to (1) or (2), having a viscosity of 1% by mass aqueous solution measured at 25°C with a Brookfield viscometer (30 rpm) of 1,000 to 20,000 mPa s. (6) The carboxymethyl cellulose and / or salt thereof according to (1) or (2), wherein 2 liters of a 0.3% by mass aqueous solution of the carboxymethyl cellulose or salt thereof having a dry mass m is prepared, and the whole is 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. When the ratio of the dry mass M to the dry mass m is less than 200 ppm, (7) An electrode composition for a non-aqueous electrolyte secondary battery, comprising the carboxymethyl cellulose and / or salt thereof according to (1) or (2) and a styrene-butadiene rubber having an average particle size of 50 nm to 300 nm. (8) The electrode composition for a nonaqueous electrolyte secondary battery according to (7), wherein the styrene-butadiene rubber has a glass transition temperature of −50° C. to 50° C. (9) An electrode for a non-aqueous electrolyte secondary battery, using the electrode composition for a non-aqueous electrolyte secondary battery according to (7). (10) A non-aqueous electrolyte secondary battery using the electrode composition for a non-aqueous electrolyte secondary battery according to (7). is provided. [Effects of the Invention]

[0012] The present invention provides carboxymethyl cellulose and / or a salt thereof for use as an electrode binder for a non-aqueous electrolyte secondary battery, which enables the formation of an electrode layer with low electrical resistance. The present invention also provides an electrode composition for a non-aqueous electrolyte secondary battery, an electrode for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery, which use the carboxymethyl cellulose and / or a salt thereof. DETAILED DESCRIPTION OF THE INVENTION

[0013] The carboxymethyl cellulose and / or salt thereof of the present invention is described below. The carboxymethyl cellulose and / or salt thereof of the present invention is used as an electrode binder for a non-aqueous electrolyte secondary battery, and has a degree of carboxymethyl substitution per anhydroglucose unit of 0.5 to 1.2 and a degree of dispersion of 20 to 60% as measured using a powder tester.

[0014] <Carboxymethylcellulose and / or its salt> Carboxymethyl cellulose and / or its salt (hereinafter sometimes abbreviated as CMC) contained in the active material layer of the present invention has a structure in which the hydroxyl groups in the glucose units constituting cellulose are substituted with carboxymethyl ether groups. Carboxymethyl cellulose may be in the form of a salt. Examples of carboxymethyl cellulose salts include metal salts such as sodium carboxymethyl cellulose.

[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, CMC can be produced by treating cellulose with a mercerizing agent (alkali) to prepare mercerized cellulose (alkali cellulose), and then adding an etherifying agent to the mercerized cellulose to cause an etherification reaction.

[0020] The cellulose used as the raw material can be any of the above-mentioned celluloses without any particular limitations, but cellulose with a high purity is preferred, and dissolving pulp or linter is more preferred. By using these, it is possible to obtain highly pure CMC.

[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 1.2. 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 1.2 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 1.2, preferably 0.5 to 1.0, and more preferably 0.6 to 1.0.

[0025] The degree of carboxymethyl substitution is measured as follows: Approximately 2.0 g of sample is weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of a solution of 1000 mL of methanol and 100 mL of concentrated nitric acid is added, and the mixture is shaken for 3 hours to convert the carboxymethyl cellulose salt (CMC) to H-CMC (hydrogen-form carboxymethyl cellulose). 1.5 to 2.0 g of the bone-dry H-CMC is weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. The H-CMC is moistened with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH is added, and the mixture is shaken at room temperature for 3 hours. Using phenolphthalein as an indicator, excess NaOH is back-titrated with 0.1 N H2SO4, and the degree of carboxymethyl substitution (DS value) is calculated 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) Furthermore, the viscosity of a 1% by mass aqueous solution of the carboxymethyl cellulose or salt thereof of the present invention, measured at 25°C using a Brookfield viscometer (30 rpm), is preferably 1,000 to 20,000 mPa·s, more preferably 1,000 to 15,000 mPa·s, and even more preferably 1,000 to 10,000 mPa·s. If this viscosity is too high, problems arise, such as difficulty in mixing with the active material and conductive additive during slurry preparation, or poor fluidity when applying the slurry to a current collector, making application difficult. If the viscosity is too low, problems arise, such as the slurry running off the current collector when applied to the current collector, making application difficult, 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] (Dispersion degree) The carboxymethyl cellulose and / or salt thereof of the present invention has a degree of dispersion measured using a powder tester of 20 to 60%, preferably 25 to 55%, and more preferably 30 to 50%. When the degree of dispersion is within the above range, CMC exhibits good dispersibility when used as a binder or dispersant in a negative electrode composition, thereby improving the electrical resistance value. On the other hand, if the degree of dispersion is too high, there will be a lot of dusting, making it impossible to dissolve the required amount of carboxymethyl cellulose, and the function as a binder and dispersant in the negative electrode will be reduced, resulting in the problem of high electrical resistance.If the degree of dispersion is too low, it will not mix well with other materials, resulting in the problem of high electrical resistance. Here, the degree of dispersion was measured using a powder tester (Powder Tester PT-X (manufactured by Hosokawa Micron Corporation)). 10 g of the sample was placed in the dispersion unit of the PT-X and dropped. The degree of dispersion was calculated from the amount of powder that fell onto the watch glass using the following formula. Dispersibility (%) = (10 (g) - amount of powder dropped onto the watch glass (g)) / 10 (g)

[0029] (Angle of repose) The angle of repose of the carboxymethyl cellulose and / or salt thereof of the present invention is preferably 42° or more, more preferably 45° or more. If the angle of repose is too small, the powder will flow out of the outlet of the feeder, making it impossible to dissolve the desired amount of carboxymethyl cellulose, and the function as a binder or dispersant in the negative electrode will be reduced, resulting in a problem of increased electrical resistance. Here, the angle of repose was measured using a powder tester (Powder Tester PT-X (manufactured by Hosokawa Micron Corporation)) with the angle measurement method set to "Peak Operation" using a sieve with a mesh size of 710 μm and a linearity of 450 μm. The moisture content of the carboxymethyl cellulose used in the measurement was adjusted to 6.0 to 9.0%.

[0030] (collapse angle) The collapse angle of the carboxymethyl cellulose and / or salt thereof of the present invention is preferably 19° or more, more preferably 21° or more. If the collapse angle is too small, the powder will flow out of the outlet of the feeder, making it impossible to dissolve the desired amount of carboxymethyl cellulose, and the function as a binder or dispersant in the negative electrode will be reduced, resulting in a problem of increased electrical resistance. Here, the collapse angle was measured using a powder tester (Powder Tester PT-X (manufactured by Hosokawa Micron Corporation)) with the angle measurement method set to "Peak Operation" using a sieve with a mesh size of 710 μm and a linearity of 450 μm. The moisture content of the carboxymethyl cellulose used in the measurement was adjusted to 6.0 to 9.0%. (difference angle) The value obtained by subtracting the value of the angle of collapse from the value of the angle of repose can be expressed as a difference angle.

[0031] (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. 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.

[0032] (particle size) The particle diameter D90 of the carboxymethyl cellulose and / or its salt according to the present invention minus the particle diameter D10 (particle diameter D90 - particle diameter D10) is preferably 10 to 50 μm, more preferably 10 to 30 μm, and even more preferably 20 to 30 μm. If this value is too large, the particles may undergo layer separation, resulting in an inhomogeneous solution and high electrical resistance.

[0033] Furthermore, the value obtained by subtracting the particle diameter D50 from the particle diameter D90 of the carboxymethyl cellulose and / or salt thereof of the present invention (particle diameter D90 - particle diameter D50) is preferably 5 to 30 μm, more preferably 10 to 30 μm, and even more preferably 10 to 20 μm. If this value is too large, the particles will undergo layer separation, resulting in an inhomogeneous solution and high electrical resistance.

[0034] Furthermore, the value obtained by subtracting the particle diameter D10 from the particle diameter D50 of the carboxymethyl cellulose and / or salt thereof of the present invention (particle diameter D50 - particle diameter D10) is preferably 5 to 20 μm, more preferably 5 to 15 μm, and even more preferably 8 to 12 μm. If this value is too large, the particles may undergo layer separation, resulting in a problem that a homogeneous solution cannot be obtained.

[0035] Here, D10 is the particle size that contains 10% of the particles when calculated from the minimum value in the particle size distribution based on the volume average particle size, D50 is the particle size that contains 50% of the particles when calculated from the minimum value, and is also called the average particle size. Furthermore, D90 is the particle size that contains 90% of the particles when calculated from the minimum value. The particle size distribution based on the volume average particle size can be measured using a laser diffraction / scattering particle size distribution analyzer, for example, using methanol as a dispersant.

[0036] The particle size D10 of the carboxymethyl cellulose and / or salt thereof of 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.

[0037] [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.

[0038] 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.

[0039] The following types of milling devices can be used in the present invention. 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.

[0040] 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.).

[0041] 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.).

[0042] 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.

[0043] 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.).

[0044] In the present invention, a step of classifying the pulverized carboxymethyl cellulose or a salt thereof based on particle size can be provided. 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.

[0045] 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.

[0046] <Binder for non-aqueous electrolyte secondary batteries> The carboxymethyl cellulose and / or its salt of the present invention is used as an electrode binder for a non-aqueous electrolyte secondary battery. Typically, an aqueous solution containing carboxymethyl cellulose and / or its salt is used as an electrode binder for a non-aqueous electrolyte secondary battery.

[0047] 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.

[0048] 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.

[0049] Furthermore, binders for non-aqueous electrolyte secondary batteries may contain other binders in addition to carboxymethyl cellulose and / or its salt. Examples of binders used in electrode compositions for negative electrodes 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. Examples of binders used in electrode compositions for positive electrodes include the synthetic rubber binders listed above as binders for negative electrodes, as well as polytetrafluoroethylene (PTFE).

[0050] The average particle size (D50) of the SBR is preferably 50 to 300 nm, and more preferably 50 to 200 nm. If the average particle size (D50) of the SBR is too large, the SBR will not adhere uniformly to the active material, reducing its binder function and resulting in a problem of high electrical resistance. If the average particle size (D50) of the SBR is too small, the SBR will cover the active material, resulting in a problem of high electrical resistance.

[0051] The glass transition temperature (Tg) of the SBR is preferably −50° C. to 50° C. When the SBR is within the above range, it mixes well with the carboxymethyl cellulose and / or salt thereof of the present invention and has appropriate flexibility when used in the negative electrode layer, making it less likely to have high electrical resistance.

[0052] <Electrode composition for nonaqueous electrolyte secondary batteries> The electrode composition for a non-aqueous electrolyte secondary battery of the present invention (hereinafter sometimes referred to as the "electrode composition") contains at least an electrode active material and the carboxymethyl cellulose and / or a salt thereof of the present invention as the binder for the non-aqueous electrolyte secondary battery.

[0053] That is, the carboxymethyl cellulose and / or its salt of the present invention can serve as an electrode binder and, together with an electrode active material, constitute an electrode composition. In this case, the content of the carboxymethyl cellulose and / or its salt in the electrode composition is preferably 0.1 to 4.0 mass% based on the total mass of the electrode composition.

[0054] When the other binders are used, the content of the binder for a non-aqueous electrolyte secondary battery in the electrode composition is preferably 1 to 10 mass %, more preferably 1 to 6 mass %, and even more preferably 1 to 2 mass %.

[0055] (electrode active material) The electrode active material contained in the active material layer constituting the present invention is a negative electrode active material when the electrode for a nonaqueous electrolyte secondary battery is a negative electrode, and is a positive electrode active material when the electrode is a positive electrode.

[0056] As the negative electrode active material, graphite materials such as graphite (natural graphite, artificial graphite, etc.), coke, and carbon fiber; elements capable of forming an alloy with lithium, that is, for example, elements such as silicon-based compounds, Al, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, Ti, etc.; compounds containing elements capable of forming an alloy with lithium; composites of elements capable of forming an alloy with lithium and the said compounds and carbon and / or the said graphite materials, or nitrides containing lithium, etc. can be exemplified. Among these, graphite materials and silicon-based compounds are preferred, and silicon particles or silicon oxide particles are more preferred as the graphite and silicon-based compounds.

[0057] In addition, the silicon oxide in the present invention means SiO x (represented by 0 < x ≦ 2). Also in the present invention, as the active material layer, a composite of a silicon-based compound and a graphite material is more suitable.

[0058] When the negative electrode active material is a composite of a graphite material and a silicon-based compound, the mixing ratio of the graphite material:silicon-based compound is preferably 10:90 to 90:10, and more preferably 50:50 to 80:20.

[0059] As the positive electrode active material, LiFePO4, LiMe x O y (Me means a transition metal containing at least one of Ni, Co, and Mn. x and y mean arbitrary numbers.)-based positive electrode active materials are preferred.

[0060] The content of the electrode active material in the electrode layer 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.

[0061] The electrode composition may also contain a conductive aid as needed. Examples of conductive aids include conductive carbons such as carbon black, acetylene black, and ketjen black. The content of the conductive aid in the electrode composition is usually 0.01 to 20% by mass, and preferably 0.1 to 10% by mass.

[0062] The solvent used in the electrode composition 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.

[0063] 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.

[0064] 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.

[0065] The conditions for producing the electrode composition are not particularly limited. For example, other components constituting the electrode composition are added to an aqueous solution of carboxymethyl cellulose and / or a salt thereof, and mixed with stirring as necessary. The form of the electrode composition is not particularly limited, and may be, for example, a liquid, a paste, a slurry, or any other form.

[0066] <Nonaqueous electrolyte secondary battery electrode> An electrode layer can be formed on a current collector by applying the electrode composition to 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 achieved by casting the electrode composition onto the current collector using a coating device such as a doctor blade. The lamination method is not limited to the specific example described above, and can also be achieved by discharging the electrode composition from an extrusion-type injector having a slot nozzle onto a running current collector wound around a backup roll. In blade coating, after casting, the electrode layer can be obtained by further drying, such as by heating (for example, at a temperature of 80 to 120°C, for example, for 4 to 12 hours) or by applying pressure using a roll press, as needed.

[0067] The shape of the electrode for a non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but is usually a sheet. The thickness of the sheet-shaped electrode plate (the thickness of the electrode layer formed from the electrode composition, excluding the current collector portion) is difficult to specify because it depends on the composition and production conditions of the composition, but is usually 30 to 150 μm.

[0068] (current collector) Any electrical conductor that does not cause a fatal chemical reaction in the constructed electrode or battery can be used as the current collector. If the electrode is a negative electrode, a negative electrode current collector can be used, and if the electrode is a positive electrode, a positive electrode current collector can be used.

[0069] Examples of materials 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, etc. Among these, copper or a copper alloy is preferred, and copper is more preferred. 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. <Nonaqueous electrolyte secondary battery> The electrode for a non-aqueous electrolyte secondary battery of the present invention is used as an electrode for a non-aqueous electrolyte secondary battery.

[0070] That is, the present invention also provides a nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery can have a structure in which positive electrodes and negative electrodes are alternately stacked with separators interposed therebetween and wound many times. The nonaqueous electrolyte secondary battery can be obtained by placing the wound stack of positive electrodes, separators, and negative electrodes in a battery container, injecting a nonaqueous electrolyte, and sealing the container.

[0071] The shape of the nonaqueous electrolyte secondary battery is not particularly limited, and may be a cylindrical shape, a prismatic shape, a flat shape, a coin shape, a button shape, a sheet shape, etc. The material of the battery container is not particularly limited as long as it can prevent moisture from entering the battery, and examples thereof include a laminate of metal, aluminum, etc.

[0072] The separator is usually impregnated with a non-aqueous electrolyte. The separator may be, for example, a microporous membrane or nonwoven fabric made of polyolefin such as polyethylene or polypropylene.

[0073] The non-aqueous electrolyte typically contains a lithium salt and a non-aqueous solvent. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, and LiClO4. Examples of non-aqueous solvents include ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, butylene carbonate, and methyl ethyl carbonate. One type of non-aqueous solvent may be used alone, or two or more types may be used in combination. The concentration of the lithium salt in the non-aqueous electrolyte is typically 0.5 to 2.5 mol / L.

[0074] Electrodes for non-aqueous electrolyte secondary batteries and non-aqueous electrolyte secondary batteries produced using an electrode composition using the carboxymethyl cellulose and / or a salt thereof of the present invention as an electrode binder for non-aqueous electrolyte secondary batteries have low resistance values ​​and excellent battery characteristics due to the small amount of undissolved gel. [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. <Measurement and evaluation methods> In the examples and comparative examples, measurements and evaluations were carried out as follows.

[0076] (Measurement of the degree of carboxymethyl substitution (DS value)) Approximately 2.0 g of sample was weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of a solution of 1000 mL of methanol and 100 mL of concentrated nitric acid was added, and the mixture was shaken for 3 hours to convert carboxymethylcellulose salt (CMC) to H-CMC (hydrogen-form carboxymethylcellulose). 1.5 to 2.0 g of the bone-dry H-CMC was weighed and placed in a 300 mL Erlenmeyer flask with a stopper. The H-CMC was moistened with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH was added, and the mixture was shaken at room temperature for 3 hours. Using phenolphthalein as an indicator, excess NaOH was back-titrated with 0.1 N H2SO4, and the degree of carboxymethyl substitution (DS value) was calculated using the following equation: 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

[0077] (Measurement of 1% by mass viscosity of CMC) 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 after 3 minutes was then measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) at 30 rpm according to the method of JIS-Z-8803.

[0078] (particle size) The particle diameters D10, D50 and D90 of the carboxymethyl cellulose or salts thereof used in the examples and comparative examples were determined from the particle diameter distribution based on the volume average particle diameter.

[0079] The particle size distribution was measured using a laser diffraction / scattering particle size distribution analyzer (Mastersizer 2000E, manufactured by Spectris Co., Ltd.). For the measurement, the sample was dispersed in methanol and then subjected to ultrasonic treatment for at least one minute.

[0080] (Dispersion degree) The dispersibility of carboxymethyl cellulose or its salt used in the examples and comparative examples was measured using a powder tester (Powder Tester PT-X, manufactured by Hosokawa Micron Corporation). Specifically, a 10 g sample was placed in the dispersion unit of the PT-X and dropped, and the dispersibility was calculated from the amount of powder that fell onto a watch glass using the following formula: Dispersibility (%) = (10 (g) - amount of powder dropped onto the watch glass (g)) / 10 (g)

[0081] (Angle of repose) The angle of repose of the carboxymethyl cellulose or its salt used in the examples and comparative examples was measured using a powder tester (Powder Tester PT-X, manufactured by Hosokawa Micron Corporation). Specifically, the angle was measured using a powder property tester (Powder Tester PT-X (manufactured by Hosokawa Micron Corporation)) with the angle measurement method set to "Peak Operation" using a sieve with a mesh size of 710 μm and a linearity of 450 μm. The moisture content of the carboxymethyl cellulose used in the measurements was adjusted to 6.0 to 9.0%.

[0082] (collapse angle) The collapse angle of the carboxymethyl cellulose or salt thereof used in the examples and comparative examples was measured using a powder tester (Powder Tester PT-X, manufactured by Hosokawa Micron Corporation) under the same conditions as those for measuring the angle of repose described above. (difference angle) Using the angle of repose and angle of collapse measured above, calculate the difference angle as follows: angle of repose = angle of repose - angle of collapse was calculated by

[0083] (impedance) The electrode compositions obtained in the examples and comparative examples were applied to a current collector (320 mm long x 170 mm wide x 17 μm thick copper foil (NC-WS, manufactured by Furukawa Electric Co., Ltd.)) and dried at room temperature for 30 minutes, followed by drying at 60°C for 30 minutes. After drying, the current collector was pressed at 5.0 kN using a small tabletop roll press (SA-602, manufactured by Tester Sangyo Co., Ltd.) to obtain a negative electrode plate having a negative electrode active material layer on the current collector. The obtained negative electrode plate and a LiCoO2 positive electrode plate (manufactured by Hosen Co., Ltd., basis weight: 227.1 g / m2, effective discharge capacity: 145 mAh / g) were each punched out into a circle with a diameter of 16 mm, and the punched negative electrode plate 1 and positive electrode plate were vacuum dried at 120°C for 12 hours. Similarly, a separator (20 μm thick polypropylene separator, manufactured by CS Tech Co., Ltd.) was punched out into a circle with a diameter of 17 mm and vacuum dried at 60°C for 12 hours. The negative electrode plate was then placed in a 20.0 mm diameter stainless steel circular dish-shaped container. Next, a separator, a positive electrode plate, a spacer (15.5 mm diameter, 1 mm thick), and a stainless steel washer (Hosen Co., Ltd.) were stacked in this order. 300 μL of electrolyte (1 mol / L LiPF6, ethylene carbonate and diethyl carbonate in a 1:1 volume ratio) was then added to the circular dish-shaped container. A stainless steel cap was placed over the container via a polypropylene packing and sealed using a coin battery crimping machine (Hosen Co., Ltd.), yielding a coin-type nonaqueous electrolyte secondary battery. The resulting coin-type battery was subjected to one charge-discharge cycle in a constant temperature bath at 25°C using a secondary battery charge-discharge tester (BTS2004, Nagano Co., Ltd.). Impedance measurements were then performed using an impedance tester (VPS, Toyo Corporation), and resistance values ​​were calculated using a ZView (Scribner Associates). The smaller the resistance value, the better the performance of the nonaqueous electrolyte battery obtained when it is used as a battery.

[0084] (Measurement of the amount of filtration residue of carboxymethyl cellulose or its salt) 2 liters of an aqueous solution containing 0.3% by mass (mass % based on the dry mass of carboxymethyl or its salt) of carboxymethyl cellulose or its salt were prepared. 2 liters of this aqueous solution were filtered using a filter (Separate, manufactured by Kiriyama Seisakusho) under a reduced pressure condition of -200 mmHg through a 250-mesh filter (made of stainless steel, aperture 63 μm). The residue remaining on the 250-mesh filter was dried by blowing air at a temperature of 105 °C for 16 hours, and then the mass of the dried residue was measured and expressed as mass percentage (ppm) with respect to the mass of carboxymethyl cellulose in the carboxymethyl cellulose aqueous solution. The above measurement and evaluation results are shown in Table 1.

[0085] <Preparation of electrode composition> (Example 1) <Manufacture of CMC> To a twin-screw kneader with the rotation speed adjusted to 100 rpm, 550 parts of isopropanol and a solution of 40 parts of sodium hydroxide dissolved in 80 parts of water were added, and 100 parts charged based on the dry weight when the linter pulp was dried at 100 °C for 60 minutes. Stirring and mixing were carried out at 30 °C for 90 minutes to prepare mercerized cellulose. While further stirring, 50 parts of monochloroacetic acid were added, and after stirring for 30 minutes, the temperature was raised to 70 °C and a carboxymethylation reaction was carried out for 90 minutes. After the reaction was completed, it was neutralized with acetic acid to a pH of about 7, de-liquored, dried, and pulverized to obtain CMC1. The DS value of CMC1 was 0.92, and the 1% viscosity was 1650 mPa·s. <Manufacture of electrode composition> As the negative electrode active material, 1.4 g of 98% by mass graphite powder and 0.6 g of 98% by mass SiO x powder, 0.01 g of 98% by mass acetylene black as a conductive assistant, 1.0 g of an aqueous dispersion (2% by mass) of CMC1 as a binder, 63 mg of 48% by mass styrene-butadiene rubber (SBR), and 1.5 g of water were mixed with a Magels star (manufactured by Kurashiki Boseki Co., Ltd., Magels star KK-250S) to prepare an electrode composition. The Tg of SBR was 7 °C, and the average particle diameter was 165 nm.

[0086] (Example 2) <Manufacture of CMC> To a two-shaft kneader with the rotation speed adjusted to 100 rpm, 650 parts of isopropanol and a solution of 60 parts of sodium hydroxide dissolved in 100 parts of water were added, and 100 parts of lint pulp was charged based on the dry weight when dried at 100 °C for 60 minutes. It was stirred and mixed at 30 °C for 90 minutes to prepare mercerized cellulose. While further stirring, 70 parts of monochloroacetic acid was added, and after stirring for 30 minutes, the temperature was raised to 70 °C and a carboxymethylation reaction was carried out for 90 minutes. After the reaction was completed, it was neutralized with acetic acid to a pH of about 7, de-liquored, dried, and pulverized to obtain CMC2. The DS value of CMC2 was 0.84, and the 1% viscosity was 4580 mPa·s. <Manufacture of Electrode Composition> The electrode composition was prepared in the same manner as in Example 1, except that the type of CMC was changed to CMC2 obtained above.

[0087] (Example 3) <Manufacture of CMC> To a two-shaft kneader with the rotation speed adjusted to 100 rpm, 600 parts of isopropanol and a solution of 55 parts of sodium hydroxide dissolved in 100 parts of water were added, and 100 parts of lint pulp was charged based on the dry weight when dried at 100 °C for 60 minutes. It was stirred and mixed at 30 °C for 90 minutes to prepare mercerized cellulose. While further stirring, 65 parts of monochloroacetic acid was added, and after stirring for 30 minutes, the temperature was raised to 70 °C and a carboxymethylation reaction was carried out for 90 minutes. After the reaction was completed, it was neutralized with acetic acid to a pH of about 7, de-liquored, dried, and pulverized to obtain CMC3. The DS value of CMC3 was 0.70, and the 1% viscosity was 4900 mPa·s. <Manufacture of Electrode Composition> The electrode composition was prepared in the same manner as in Example 1, except that the type of CMC was changed to CMC3 obtained above.

[0088] (Example 4) <Manufacture of CMC> A twin-screw kneader with the rotation speed adjusted to 100 rpm was charged with 600 parts of isopropanol and 38 parts of sodium hydroxide dissolved in 80 parts of water. 100 parts of linter pulp (dry weight after drying at 100°C for 60 minutes) was added. The mixture was stirred and mixed at 30°C for 90 minutes to prepare mercerized cellulose. While stirring, 46 parts of monochloroacetic acid was added. After stirring for 30 minutes, the mixture was heated to 70°C and carboxymethylation reaction was carried out for 90 minutes. After the reaction was complete, the mixture was neutralized with acetic acid to a pH of approximately 7, deliquored, dried, and pulverized to obtain CMC4. The DS value of CMC4 was 0.70 and the 1% viscosity was 8980 mPa·s. <Production of electrode composition> An electrode composition was prepared in the same manner as in Example 1, except that the type of CMC was changed to the CMC4 obtained above.

[0089] (Comparative Example 1) <Production of electrode composition> An electrode composition was prepared in the same manner as in Example 1, except that the type of CMC was changed to CMC5, which had a DS value of 0.93 and a 1% viscosity of 3460 mPa·s.

[0090] (Comparative Example 2) <Production of electrode composition> An electrode composition was prepared in the same manner as in Example 1, except that the type of CMC was changed to CMC6, which had a DS value of 0.69 and a 1% viscosity of 6340 mPa·S.

[0091] [Table 1]

[0092] As shown in Table 1, carboxymethyl cellulose and / or a salt thereof used as an electrode binder for non-aqueous electrolyte secondary batteries, which has a degree of carboxymethyl substitution per anhydrous glucose unit of 0.5 to 1.2 and a degree of dispersion measured using a powder tester of 20 to 60%, an electrode layer obtained from an electrode composition using carboxymethyl cellulose and / or a salt thereof has a low resistance value and is shown to have good battery performance when used in a non-aqueous electrolyte secondary battery.

Claims

1. Carboxymethyl cellulose and / or a salt thereof for use as an electrode binder for a non-aqueous electrolyte secondary battery, the carboxymethyl cellulose and / or a salt thereof having a degree of carboxymethyl substitution per anhydrous glucose unit of 0.5 to 1.2, a degree of dispersion measured using a powder tester of 20 to 60%, and a ratio ((particle diameter D90 - particle diameter D50) / (particle diameter D50 - particle diameter D10)) of the value obtained by subtracting particle diameter D50 from particle diameter D90 (particle diameter D90 - particle diameter D50) to the value obtained by subtracting particle diameter D10 from particle diameter D50 (particle diameter D50 - particle diameter D10) of 1.0 to 2.

5.

2. The carboxymethyl cellulose and / or salt thereof according to claim 1, having a particle size D50 of 10 to 20 μm.

3. The carboxymethyl cellulose and / or salt thereof according to claim 1 or 2, having an angle of repose of 42° or more.

4. The carboxymethyl cellulose and / or salt thereof according to claim 1 or 2, having a collapse angle of 19° or more.

5. The carboxymethyl cellulose and / or salt thereof according to claim 1 or 2, wherein the viscosity of a 1% by mass aqueous solution measured at 25 ° C. with a B-type viscometer (30 rpm) is 1,000 to 20,000 mPa s.

6. 3. The carboxymethyl cellulose and / or salt thereof according to claim 1 or 2, wherein 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 the entire solution is filtered through a 250-mesh filter under reduced pressure conditions of -200 mmHg. When 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 200 ppm.

7. 3. An electrode composition for a non-aqueous electrolyte secondary battery, comprising the carboxymethyl cellulose and / or salt thereof according to claim 1 or 2, and a styrene-butadiene rubber having an average particle size of 50 nm to 300 nm.

8. 8. The electrode composition for a non-aqueous electrolyte secondary battery according to claim 7, wherein the styrene-butadiene rubber has a glass transition temperature of -50°C to 50°C.

9. An electrode for a non-aqueous electrolyte secondary battery, which uses the electrode composition for a non-aqueous electrolyte secondary battery according to claim 7.

10. A non-aqueous electrolyte secondary battery using the electrode composition for a non-aqueous electrolyte secondary battery according to claim 7.

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