Binder for nonaqueous electrolyte secondary battery electrode, electrode composition for nonaqueous electrolyte secondary battery, electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery

Abstract

This binder for a nonaqueous electrolyte secondary battery electrode comprises component A and component B, where the combination ratio of the components in the binder for a nonaqueous electrolyte secondary battery electrode, i.e., component A / component B, is 90 / 10 to 55 / 45. Component A is a carboxymethylcellulose and / or a salt thereof, an aqueous 1 mass% solution of component A having a viscosity of 1,000 to 20,000 mPa•s as determined by a type B viscometer (30 rpm) at 25°C. Component B is a carboxymethylcellulose and / or salt thereof, an aqueous 1 mass% solution of component B having a viscosity of 1 to 500 mPa•s as determined by a type B viscometer (30 rpm) at 25°C.

Description

Binder for non-aqueous electrolyte secondary battery electrodes, electrode composition for non-aqueous electrolyte secondary battery, electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

[0001] The present invention relates to a binder for electrodes of non-aqueous electrolyte secondary batteries, an electrode composition for non-aqueous electrolyte secondary batteries, an electrode for non-aqueous electrolyte secondary batteries, and a non-aqueous electrolyte secondary battery.

[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, and the theoretical capacity of graphite-based materials is 372 mAh / g (LiC ６ ) and 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 by approximately 3 to 4 times when they absorb lithium, leading to degradation and capacity loss with repeated charge / discharge cycles. Detailed analysis of this phenomenon has shown 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 significant, 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 view of this situation, 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.

[0007] JP 2015-198038 A

[0008] Patent Document 1 requires three components, including carboxymethyl cellulose or a metal salt thereof, 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 adhesive strength between the active material and the current collector, as well as the dispersibility of the active material and the conductive additive. Furthermore, improving the adhesive strength between the active material and the current collector, as well as the dispersibility of the active material and the conductive additive, also improves the battery performance.

[0009] That is, an object of the present invention is to provide a binder for electrodes of non-aqueous electrolyte secondary batteries that has a desired adhesive strength between an active material and a current collector and that exhibits good dispersibility of the active material and a conductive additive, and to provide an electrode composition for non-aqueous electrolyte secondary batteries, an electrode for non-aqueous electrolyte secondary batteries, and a non-aqueous electrolyte secondary battery that use the binder for electrodes of non-aqueous electrolyte secondary batteries.

[0010] As a result of extensive efforts, the present inventors have found that the problems can be solved by the following [1] to [6]. That is, the present invention provides the following [1] to [6]. [1] A binder for electrodes of non-aqueous electrolyte secondary batteries, comprising: component A: carboxymethyl cellulose and / or a salt thereof having a molecular weight of 6 million or more and a viscosity of 1% by mass aqueous solution of 1,000 to 20,000 mPa·s measured at 25°C with a Brookfield viscometer (30 rpm) of 1,000 to 20,000 mPa·s; and component B: carboxymethyl cellulose and / or a salt thereof having a viscosity of 1% by mass aqueous solution of 1 to 500 mPa·s measured at 25°C with a Brookfield viscometer (30 rpm), wherein the blending ratio of components A and B in the binder for electrodes of non-aqueous electrolyte secondary batteries is component A / component B=90 / 10 to 55 / 45. [2] The binder for electrodes of non-aqueous electrolyte secondary batteries according to [1], wherein the degree of carboxymethyl substitution per anhydrous glucose unit of Component A and Component B is 0.5 to 1.2. [3] The binder for electrodes of non-aqueous electrolyte secondary batteries according to [1], wherein the degree of dispersion of Component B measured using a powder tester is 20 to 60%. [4] An electrode composition for non-aqueous electrolyte secondary batteries, using the binder for electrodes of non-aqueous electrolyte secondary batteries according to [1]. [5] An electrode for non-aqueous electrolyte secondary batteries, using the binder for electrodes of non-aqueous electrolyte secondary batteries according to [1]. [6] A non-aqueous electrolyte secondary battery, using the binder for electrodes of non-aqueous electrolyte secondary batteries according to [1].

[0011] According to the present invention, there are provided a binder for electrodes of non-aqueous electrolyte secondary batteries that has a desired adhesive strength between an active material and a current collector and that exhibits good dispersibility of the active material and a conductive additive, as well as an electrode composition for non-aqueous electrolyte secondary batteries, an electrode for non-aqueous electrolyte secondary batteries, and a non-aqueous electrolyte secondary battery that use the binder for electrodes of non-aqueous electrolyte secondary batteries.

[0012] The binder for electrodes of non-aqueous electrolyte secondary batteries of the present invention is described below. The binder for electrodes of non-aqueous electrolyte secondary batteries of the present invention comprises: Component A: carboxymethyl cellulose and / or a salt thereof having a molecular weight of 6 million or more and a viscosity of 1% by mass aqueous solution of 1,000 to 20,000 mPa·s measured at 25°C with a Brookfield viscometer (30 rpm) of 1,000 to 20,000 mPa·s; and Component B: carboxymethyl cellulose and / or a salt thereof having a viscosity of 1% by mass aqueous solution of 1 to 500 mPa·s measured at 25°C with a Brookfield viscometer (30 rpm), wherein the blending ratio of Components A and B in the binder for electrodes of non-aqueous electrolyte secondary batteries is Component A / Component B=90 / 10 to 55 / 45.

[0013] <Component A: Carboxymethylcellulose and / or its salt having a viscosity of 1,000 to 20,000 mPa·s in a 1% by mass aqueous solution> (Viscosity) One of the carboxymethylcelluloses or salts thereof (hereinafter sometimes abbreviated as CMC) constituting the present invention (Component A) preferably has a viscosity of 1,000 to 20,000 mPa·s in a 1% by mass aqueous solution measured at 25°C using a Brookfield viscometer (30 rpm), more preferably 1,000 to 15,000 mPa·s, and even more preferably 1,000 to 10,000 mPa·s. A viscosity of 1,000 to 20,000 mPa·s allows for the production of a slurry with a viscosity suitable for coating. Furthermore, this can also prevent the structure of the coating layer from being damaged by expansion and contraction of the coating layer during charging and discharging.

[0014] The viscosity measurement method in the present invention is as follows: Carboxymethyl cellulose or a salt thereof is 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 is stirred at 600 rpm for 3 hours at 25°C using a stirrer. Thereafter, the viscosity after 3 minutes is measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) with a No. 1 rotor at a rotation speed of 30 rpm in accordance with the method of JIS-Z-8803.

[0015] (Molecular Weight) The molecular weight of component A is 6 million or more, preferably 7 million or more, more preferably 8 million or more, and preferably 15 million or less, more preferably 13 million or less, and even more preferably 12 million or less. The molecular weight can be measured by the following gel permeation chromatography analysis. Specifically, a 1% by mass CMC solution is prepared, and 1 g is sampled from the CMC solution. Next, 10 mL of ultrapure water is added, followed by 10 mL of 400 mM aqueous sodium nitrate solution to prepare a measurement sample. The measurement sample was placed in an HLC-8320GPC (manufactured by Tosoh Corporation). Two TSKgel GMPWxl columns and one G2500PWxl column, both manufactured by Tosoh Corporation, were used. A 200 mM aqueous sodium nitrate solution was used as the eluent. The measurement was performed at a flow rate of 1 mL / min, a column temperature of 50°C, and an injection volume of 100 μL. Pullulan (manufactured by Resonac Co., Ltd.) was used as a standard sample.

[0016] <Component B: Carboxymethylcellulose and / or its salt having a viscosity of 1 to 500 mPa·s in a 1% by mass aqueous solution> (Viscosity) One of the carboxymethylcelluloses or salts thereof constituting the present invention (Component B) preferably has a viscosity of 1 to 500 mPa·s in a 1% by mass aqueous solution measured at 25°C using a Brookfield viscometer (30 rpm), more preferably 5 to 300 mPa·s, and even more preferably 10 to 100 mPa·s. A viscosity of 1 to 500 mPa·s improves the dispersibility of the active material and conductive additive. The viscosity was measured as described above.

[0017] (Molecular Weight) The molecular weight of component B is preferably 100,000 or more, more preferably 200,000 or more, and even more preferably 300,000 or more, and is preferably 1,000,000 or less, more preferably 800,000 or less, and even more preferably 500,000 or less. The method for measuring the molecular weight is as described above.

[0018] <Physical Properties Other Than Viscosity of Carboxymethylcellulose and / or Its Salt, Which are Components A and B> The physical properties other than viscosity of carboxymethylcellulose and / or its salt, which are Components A and B, are described below. Note that the physical properties other than viscosity of carboxymethylcellulose and / or its salt, which are Components A and B, do not need to be the same and may be different.

[0019] The carboxymethyl cellulose and / or its salts constituting the present invention have a structure in which the hydroxyl groups in the glucose units constituting the 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.

[0020] (Cellulose Raw Material) In the present invention, cellulose refers to a polysaccharide having a structure in which D-glucopyranose (also simply referred to as "glucose unit" or "anhydroglucose") is linked together through β,1-4 bonds. Cellulose is generally classified into native cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose obtained by removing the amorphous region, etc., based on its origin, production method, etc.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] The carboxymethyl cellulose or one of its salts constituting 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.

[0025] The cellulose raw material can be any of the above-mentioned celluloses without any particular limitations, but cellulose with high purity is preferred, and dissolving pulp or linter is more preferred. By using these, CMC with high purity can be obtained.

[0026] 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.

[0027] 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 the side reaction of excess mercerizing agent and monochloroacetic acid from progressing and producing an alkali metal glycolate, which is economical. In the present invention, the CMC may be a commercially available product. An example of a commercially available product is "Sunrose" manufactured by Nippon Paper Industries Co., Ltd.

[0028] In the present invention, the degree of etherification of CMC refers to the ratio of carboxymethyl ether groups (—OCH ) to hydroxyl groups (—OH) in the glucose units constituting cellulose. ２ COOH) is substituted.

[0029] (Degree of substitution of carboxymethyl groups) The carboxymethyl cellulose or salt thereof constituting 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.

[0030] The degree of carboxymethyl group substitution is measured as follows: Approximately 2.0 g of sample is weighed out and placed in a 300 mL Erlenmeyer flask with a ground stopper. 100 mL of a solution of 100 mL of special-grade concentrated nitric acid in 1000 mL of methanol 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 ground 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 x F' - 0.1 N - H ２ SO ４ (mL) × F) × 0.1] / (bone dry mass (g) of H-CMC) Degree of carboxymethyl substitution = 0.162 × A / (1 - 0.058 × A) F': 0.1N-H ２ SO ４ F: Factor of 0.1N-NaOH

[0031] (Dispersion Degree) The carboxymethyl cellulose or its salt constituting the present invention has a dispersion degree measured using a powder tester of 20 to 60%, preferably 25 to 55%, and more preferably 30 to 50%. When the dispersion degree is within the above range, CMC exhibits good dispersibility when used as a binder or dispersant in a negative electrode composition, resulting in low electrical resistance. On the other hand, if the dispersion degree is too high, there will be a lot of dusting, making it impossible to dissolve a predetermined amount of carboxymethyl cellulose, and its function as a binder or dispersant in the negative electrode will be reduced, resulting in high electrical resistance. Furthermore, if the dispersion degree is too low, it will not mix well with other materials, resulting in high electrical resistance. Here, the dispersion degree was measured using a powder tester (Powder Tester PT-X (manufactured by Hosokawa Micron Corporation)). A 10 g sample was placed in the dispersion unit of the PT-X and dropped. The dispersion degree 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)

[0032] (Filtration Residue Amount) The carboxymethyl cellulose or salt thereof constituting the present invention preferably has a filtration residue amount within a predetermined range. That is, when 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 then 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, and 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 is reduced below the predetermined amount, resulting in a decrease in its function as a binder or dispersant, which leads to problems such as increased electrical resistance.

[0033] (Particle diameter) The particle diameter D10 of the carboxymethyl cellulose or salt thereof constituting the present invention is preferably 1 to 10 μm, the particle diameter D50 is preferably 10 to 20 μm, and the particle diameter D90 is preferably 20 to 40 μm.

[0034] Here, D10 is the particle size that includes 10% of the particles when integrated from the minimum value in the particle size distribution based on the volume average particle size, D50 is the particle size that includes 50% of the particles when integrated from the minimum value, and is also called the average particle size. Furthermore, D90 is the particle size that includes 90% of the particles when integrated from the minimum value. The particle size distribution based on the volume average particle size can be measured using, for example, methanol as a dispersant with a laser diffraction / scattering particle size distribution analyzer.

[0035] Furthermore, the value obtained by subtracting the particle diameter D10 from the particle diameter D90 of the carboxymethyl cellulose or salt thereof constituting the present invention (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, coarse undissolved matter in the particles may cause hole defects in the negative electrode layer.

[0036] Furthermore, the value obtained by subtracting the particle diameter D50 from the particle diameter D90 of carboxymethyl cellulose and / or its salt (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, coarse undissolved matter in the particles may cause hole defects in the negative electrode layer.

[0037] Furthermore, the value obtained by subtracting the particle diameter D10 from the particle diameter D50 of carboxymethyl cellulose and / or its salt (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, there is a problem in that undissolved matter in the particles may cause hole defects in the negative electrode layer.

[0038] (Pulverization Treatment) In the present invention, carboxymethyl cellulose or a salt thereof may be pulverized. As a method for pulverizing carboxymethyl cellulose or a salt thereof, either a dry pulverization method in which the carboxymethyl cellulose or a salt thereof is pulverized in a powder state or a wet pulverization method in which the carboxymethyl cellulose or a salt thereof is pulverized in a dispersed or dissolved state in a liquid may be selected.

[0039] 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.

[0040] Examples of fine grinding devices that can be used in the present invention include the following: Dry grinders include cutting mills, impact mills, and airflow mills. These can be used alone or in combination, and the same model can be used for multiple stages of processing.

[0041] 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 Co., Ltd.).

[0042] 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.).

[0043] 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.). Examples of media mills include a vibration ball mill.

[0044] Examples of the wet mill include Masscolloider (manufactured by Masuko Sangyo Co., Ltd.), and examples of the media mill include a bead mill (manufactured by Imex Co., Ltd.) and a high-pressure homogenizer (manufactured by Sanmaru Kikai Kogyo Co., Ltd.).

[0045] 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 can be provided during or after the pulverization step. Any known method can be used for classification. Examples of dry classifiers include cyclone classifiers, DS separators, turbo classifiers, microseparators, and air separators. On the other hand, examples of wet classifiers include liquid cyclone type, centrifugal settlers, and hydroshi separators.

[0046] <Binder for Non-Aqueous Electrolyte Secondary Batteries> In the binder for non-aqueous electrolyte secondary batteries (hereinafter sometimes referred to as "battery binder") of the present invention, the component A and the component B, carboxymethyl cellulose and / or its salt, are preferably used in a blending ratio of Component A / Component B = 90 / 10 to 55 / 45, more preferably 90 / 10 to 60 / 40, based on the solids mass of the binder for non-aqueous electrolyte secondary battery electrodes. More preferably, the blending amount of Component A is 10 parts by mass or more but less than 25 parts by mass, and the blending amount of Component B is more than 75 parts by mass but not more than 90 parts by mass, per 100 parts by mass of the total solids mass of Components A and B. Within these ranges, not only is the active material and conductive additive uniformly dispersed in the slurry, but also an electrode plate with excellent adhesion strength between the active material and the current collector can be obtained. Furthermore, the adhesion strength between the active materials, between the conductive additives, and between the active material and the conductive additive is improved, resulting in an electrode plate with less cracking in the coating layer.

[0047] The binder for non-aqueous electrolyte secondary batteries of the present invention can also be prepared as an aqueous solution. The conditions for producing such an aqueous solution are not particularly limited. For example, the electrode binder can be added to water (e.g., distilled water, purified water, tap water, etc.) and dissolved by stirring, etc., as necessary. Alternatively, carboxymethyl cellulose or a salt thereof can be dissolved in water, etc., and then a borate can be added and dissolved by stirring, etc. Similarly, a borate can be dissolved in water, etc., and then carboxymethyl cellulose or a salt thereof can be dissolved by stirring, etc.

[0048] The aqueous solution of such a binder for a non-aqueous electrolyte secondary battery preferably has a pH in the range of 1 to 8, more preferably in the range of 2 to 8, even more preferably in the range of 3 to 8, and particularly preferably in the range of 6 to 8. If the pH of the aqueous solution is biased toward the acidic side, it becomes difficult for the aqueous solution to exhibit the viscosity expected of the aqueous solution. Therefore, when the pH is in the range of 6 to 8, a particularly good balance between viscosity and solubility can be achieved, and an aqueous solution with excellent coatability can be obtained.

[0049] 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.

[0050] Furthermore, the viscosity of a 1% by mass aqueous solution of the binder for non-aqueous electrolyte secondary batteries, measured at 25° C. with a Brookfield viscometer (30 rpm), is preferably 400 mPa·s or more, more preferably 800 mPa·s or more, and is preferably 15,000 mPa·s or less, more preferably 10,000 mPa·s or less, and even more preferably 8,000 mPa·s or less. When the aqueous solution of the binder for non-aqueous electrolyte secondary batteries has a viscosity within the above range, it can exhibit suitable dispersibility, viscosity increasing properties, and binding properties when added to an electrode composition.

[0051] The binder for a non-aqueous electrolyte secondary battery may contain other binders in addition to carboxymethyl cellulose and / or its salt, which are components A and B. 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. Examples of binders used in the electrode composition for the positive electrode include the synthetic rubber binders listed above as binders for the negative electrode, as well as polytetrafluoroethylene (PTFE).

[0052] Here, 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.

[0053] 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 a salt thereof of the present invention and has appropriate flexibility when used in the negative electrode layer, so that the electrical resistance is less likely to be high.

[0054] <Electrode Composition for Non-Aqueous Electrolyte Secondary Battery> The electrode composition for a non-aqueous electrolyte secondary battery of the present invention (hereinafter may be referred to as "electrode composition") contains at least an electrode active material and two types of carboxymethyl cellulose and / or salts thereof as the binder for the non-aqueous electrolyte secondary battery.

[0055] The content of carboxymethyl cellulose and / or a salt thereof in the electrode composition is preferably 0.1 to 4.0% by mass based on the total mass of the electrode composition.

[0056] 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 %.

[0057] (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.

[0058] Examples of negative electrode active materials include graphite materials such as graphite (natural graphite, artificial graphite, etc.), coke, and carbon fiber; elements capable of forming an alloy with lithium, i.e., silicon-based compounds, elements such as Al, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, and Ti; compounds containing elements capable of forming an alloy with lithium; composites of elements and compounds capable of forming an alloy with lithium with carbon and / or the graphite materials, or nitrides containing lithium. Among these, graphite materials and silicon-based compounds are preferred, and silicon particles or silicon oxide particles are more preferred as graphite and silicon-based compounds.

[0059] In the present invention, silicon oxide refers to SiO ｘ (0<x≦2) In the present invention, the active material layer is more preferably a composite of a silicon-based compound and a graphite material.

[0060] When the negative electrode active material is a composite of a graphite material and a silicon-based compound, the blending ratio of the graphite material to the silicon-based compound is preferably 10:90 to 90:10, more preferably 50:50 to 80:20.

[0061] The positive electrode active material is LiFePO ４ , LiMe ｘ O ｙ (Me represents a transition metal including at least one of Ni, Co, and Mn, and x and y represent arbitrary numbers.)-based positive electrode active materials are preferred.

[0062] Here, when the electrode composition for the positive electrode is used, LiFePO ４ In view of the relationship between the capacitance and the electrode layer, it is preferable to make the electrode layer thicker, as will be described later, but thicker layers tend to cause cracks. Therefore, the electrode layer for the positive electrode is required to have excellent flexibility, and the electrode layer of the present invention has excellent flexibility by containing two types of carboxymethyl cellulose and / or a salt thereof, i.e., Component A and Component B, and further, can have an excellent balance between the flexibility of the electrode layer, the coatability of the electrode composition, and the battery performance obtained.

[0063] The content of the electrode active material in the electrode 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%.

[0064] 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.

[0065] 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.

[0066] The water-soluble organic solvent is an organic solvent that dissolves in water, and examples thereof 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.

[0067] 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 the effects of the invention are not impaired.

[0068] 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 its salt, and mixed while stirring as necessary. The state of the electrode composition is also not particularly limited. For example, the electrode composition may be in any form, such as a liquid, a paste, or a slurry.

[0069] <Electrode for Nonaqueous Electrolyte Secondary Battery> 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 performed by casting the electrode composition onto the current collector using a coating device such as a doctor blade. Furthermore, the lamination method is not limited to the specific example described above. Another example is a method in which the electrode composition is discharged 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 (at a temperature of, for example, 80 to 120°C for a heating time of, for example, 4 to 12 hours), or by applying pressure using a roll press, as needed.

[0070] The shape of the electrode for a nonaqueous 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 manufacturing conditions of the composition, but is usually 30 to 150 μm.

[0071] (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.

[0072] Examples of materials for the negative electrode current collector include stainless steel, nickel, copper, titanium, carbon, and copper or stainless steel surfaces with carbon, nickel, titanium, or silver attached thereto. 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. Examples of the shape of the current collector include mesh, punched metal, foam metal, and foil processed into a plate shape, with foil processed into a plate shape being preferred.

[0073] <Non-aqueous 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] The non-aqueous electrolyte usually contains a lithium salt and a non-aqueous solvent. Examples of the lithium salt include LiPF ６ , LiAsF ６ , LiBF ４ , LiClO ４Examples of the non-aqueous solvent 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 usually 0.5 to 2.5 mol / L.

[0078] When the binder for a non-aqueous electrolyte secondary battery of the present invention is added to an electrode composition, it not only uniformly disperses the active material and conductive additive, but also provides strong binding between the active material and the current collector foil, so that the electrode for a non-aqueous electrolyte secondary battery and the non-aqueous electrolyte secondary battery produced by the present invention have excellent battery characteristics.

[0079] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

[0080] In the present examples and comparative examples, the indices of carboxymethyl cellulose or a salt thereof were measured by the following methods.

[0081] <Method for measuring the degree of carboxymethyl substitution (CM-DS)> Approximately 2.0 g of a sample of pulverized carboxymethyl cellulose was weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of methanol (a solution of 1000 mL of methanol and 100 mL of special-grade concentrated nitric acid) was added, and the mixture was shaken for 3 hours to convert the carboxymethyl cellulose salt (CMC salt) into H-CMC (carboxymethyl cellulose). 1.5 to 2.0 g of bone-dried 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. Phenolphthalein was used as an indicator, and the CM-DS was measured using 0.1 N H ２ SO ４ The excess NaOH was back-titrated with 0.1N NaOH. CM-DS was calculated using the following formula 1: A = [(100 x F - (0.1N H ２ SO ４(mL) × F') × 0.1] / (bone dry weight of H-CMC (g)) Degree of carboxymethyl substitution (CM-DS) = 0.162 × A / (1-0.058 × A) A: amount of 1N NaOH (mL) required to neutralize 1 g of H-CMC F': amount of 0.1N H ２ SO ４ Factor F: Factor of 0.1N NaOH

[0082] <Viscosity> Carboxymethylated cellulose or a salt thereof 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. Thereafter, the viscosity after 3 minutes was measured at 30 rpm using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) in accordance with the method of JIS-Z-8803.

[0083] <Dispersibility> The dispersibility of carboxymethyl cellulose or a salt thereof was measured using a powder tester (Powder Tester PT-X, manufactured by Hosokawa Micron Corporation). Specifically, when a 10 g sample was placed in the dispersion unit of the PT-X and dropped, 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 that fell onto the watch glass (g)) / 10 (g).

[0084] <Measurement of the mass ratio of the mass of the filtration residue to the dry mass of carboxymethyl cellulose dissolved in the aqueous solution> Two liters of an aqueous solution containing 0.3% by mass (mass % based on the dry mass of carboxymethyl cellulose or its salt) of carboxymethyl cellulose or a salt thereof was prepared. Two liters of this aqueous solution was filtered through a 250-mesh filter (stainless steel, mesh size 63 μm) using a filter ("Separote", manufactured by Kiriyama Seisakusho) under a reduced pressure of -200 mmHg. The residue remaining on the 250-mesh filter was dried with air at a temperature of 105°C for 16 hours, and the mass of the dried residue was measured and expressed as a mass percentage (ppm) relative to the mass of carboxymethyl cellulose in the aqueous carboxymethyl cellulose solution.

[0085] The negative electrode plates 1 to 7 obtained in the examples and comparative examples were evaluated for adhesion strength as follows.

[0086] <Adhesion Strength Evaluation> The negative electrode plates obtained in the Examples and Comparative Examples were cut with a cutter to a width of 250 mm, and the coated surface of the negative electrode plate was attached to a wooden board (300 mm long x 200 mm wide x 3 mm thick) with double-sided tape (manufactured by Nitto Denko Corporation). The force required to peel the copper foil from the coating layer using TENSILON RTC-1210A (manufactured by A&D Co., Ltd.) was defined as the adhesion strength. A higher adhesion strength value indicates better adhesion.

[0087] The dispersibility of the active material and the conductive additive in the battery binders 1 and 7 was evaluated as follows.

[0088] <Evaluation of dispersibility of active material> 125 g of carboxymethyl cellulose containing 0.2 mass % of SiO ｘ 5 g of the above was added and stirred for 30 minutes at 2,500 rpm using a stirrer. The dispersion obtained by stirring was diluted 100 times with water, and the particle size was measured using a Zetasizer 3000HSA (manufactured by Malvern Instruments). A smaller particle size indicates better dispersibility.

[0089] <Evaluation of dispersibility of conductive additive> 0.1 g of acetylene black (manufactured by Stream Chemical Co.) was added to 125 g of 0.2 mass% carboxymethyl cellulose and stirred for 30 minutes at 2,500 rpm using a stirrer. The dispersion obtained by stirring was diluted 100 times with water, and the particle size was measured using a ZETASIZER 3000HSA (manufactured by Malvern Instruments). The smaller the particle size, the better the dispersibility.

[0090] (Example 1) (Production of CMC (a)) 600 parts of isopropanol and a solution of 38 parts of sodium hydroxide in 80 parts of water were added to a twin-screw kneader adjusted to a rotation speed of 100 rpm, and 100 parts of linter pulp was added in terms of dry weight after drying at 100°C for 60 minutes. The mixture was stirred and mixed at 30°C for 90 minutes to prepare mercerized cellulose. 46 parts of monochloroacetic acid was further added with stirring, and after stirring for 30 minutes, the mixture was heated to 70°C and subjected to a carboxymethylation reaction for 90 minutes. After completion of the reaction, the mixture was neutralized with acetic acid to a pH of about 7, deliquored, dried, and pulverized to obtain a sodium salt of carboxymethyl cellulose (hereinafter, sometimes referred to as "CMC(a)") having a degree of carboxymethyl substitution of 0.70, a viscosity of a 1% by mass aqueous solution of 7,900 mPa s measured at 25°C with a Brookfield viscometer, a molecular weight of 8 to 12,000,000, a filtration residue of 48 ppm relative to the dry mass of carboxymethyl cellulose dissolved in the aqueous solution, and a degree of dispersion of 36.1%.

[0091] (Production of CMC (b)) A solution of 550 parts of isopropanol and 45 parts of sodium hydroxide dissolved in 80 parts of water was added to a twin-screw kneader adjusted to a rotation speed of 100 rpm, and 100 parts of softwood pulp (NDP-T, manufactured by Nippon Paper Industries Co., Ltd.) was added in dry weight form after drying at 100°C for 60 minutes. The mixture was stirred and mixed at 30°C for 90 minutes to prepare mercerized cellulose. 50 parts of monochloroacetic acid was further added with stirring, and after stirring for 30 minutes, the mixture was heated to 70°C and subjected to a carboxymethylation reaction for 90 minutes. After completion of the reaction, the mixture was neutralized with acetic acid to a pH of about 7, deliquored, dried, and pulverized to obtain a sodium salt of carboxymethyl cellulose (hereinafter, sometimes referred to as "CMC(b)") having a degree of carboxymethyl substitution of 0.71, a viscosity of a 1% by mass aqueous solution measured at 25°C with a Brookfield viscometer of 10 mPa s, a molecular weight of 395,000, a filtration residue of 35 ppm relative to the dry mass of carboxymethyl cellulose dissolved in the aqueous solution, and a degree of dispersion of 30%.

[0092] (Preparation of Battery Binder 1) The above-mentioned CMC(a) and CMC(b) were mixed so that the weight ratio of CMC(a) / CMC(b) was 8 / 2, and an electrode binder 1 was obtained, having a viscosity of 3,140 mPa s as a 1% by mass aqueous solution measured at 25°C with a B-type viscometer.

[0093] (Preparation of negative electrode plate) SiO as a negative electrode active material ｘ , acetylene black (manufactured by Stream Chemical Co., Ltd.) (hereinafter sometimes referred to as "AB"), electrode binder 1, and styrene butadiene rubber (SBR, manufactured by JSR Corporation, product number S2910(E)-12-Na) were mixed so that the solids weight ratio was 100:0.5:1.0:1.5, water was added so that the slurry concentration was 45.6% by mass, and the mixture was thoroughly stirred using a Mazerustar (manufactured by Kurabo Industries, Ltd., KK-250S) to obtain slurry 1. This slurry was applied with an applicator to a copper foil (manufactured by Furukawa Electric Co., Ltd., NC-WS) measuring 320 mm in length, 170 mm in width, and 17 μm in thickness, and then air-dried for 30 minutes, followed by drying in a dryer at 60 ° C. for 30 minutes. Further, using a small tabletop roll press (manufactured by Tester Sangyo Co., Ltd., SA-602), the fabric was pressed under conditions of 5 kN and a roll peripheral speed of 50 m / min, resulting in a fabric weight of 19.7 g / m ２ Thus, a negative electrode plate 1 having an effective discharge capacity of 2100 mAh / g was obtained.

[0094] (Example 2) The active material was changed to graphite, the compounding ratio of CMC (a) and CMC (b) was changed to 7.5 / 2.5, and the weight per unit area was changed to 62.9 g / m ２ An electrode binder 2 and a negative electrode plate 2 using the same with an effective discharge capacity of 330 mAh / g were obtained in the same manner as in Example 1, except that the above-mentioned change was made.

[0095] Example 3 An electrode binder 3 and a negative electrode plate 3 using the same were obtained in the same manner as in Example 2, except that the compounding ratio of CMC(a) and CMC(b) was changed to 6 / 4.

[0096] Comparative Example 1 An electrode binder 4 and a negative electrode plate 4 using the same were obtained in the same manner as in Example 2, except that the compounding ratio of CMC(a) and CMC(b) was changed to 5 / 5.

[0097] Comparative Example 2 An electrode binder 5 and a negative electrode plate 5 using the same were obtained in the same manner as in Example 2, except that the compounding ratio of CMC (a) and CMC (b) was changed to 2.5 / 7.5.

[0098] Comparative Example 3 An electrode binder 6 and a negative electrode plate 6 using the same were obtained in the same manner as in Example 2, except that CMC(b) was used alone as the CMC.

[0099] Comparative Example 4 An electrode binder 7 and a negative electrode plate 7 using the same were obtained in the same manner as in Example 1, except that CMC (c) (manufactured by Nippon Paper Industries Co., Ltd., degree of carboxymethyl substitution: 0.9, viscosity of a 1% by mass aqueous solution measured with a B-type viscometer at 25°C: 3,360 mPa s, molecular weight: 5,660,000, filtration residue: 240 ppm, dispersity: 14.6%) was used alone as the CMC.

[0100] The evaluation results of the adhesive strength in Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1 below.

[0101]

[0102] The results of evaluation of the dispersibility of the above-mentioned battery binders 1 and 7 are shown in Table 2 below as Experimental Examples 1 to 4.

[0103]

[0104] As shown in Table 1, the active material was SiO ｘ In this case, Example 1, which used the electrode binder of the present invention, had a superior adhesive strength to Comparative Example 4. Similarly, even when the active material was graphite, Examples 2 and 3, which used the electrode binder of the present invention, had a superior adhesive strength to Comparative Examples 1 to 3. ｘ The electrode plate of Comparative Example 4 using SiO has a better adhesion strength than the electrode plates of Examples 2 and 3 using graphite as the active material. ｘ This is thought to be due to the interaction between the hydroxyl groups on the surface and the carboxyl groups of CMC. As shown in Table 2, when the electrode binder of the present invention was used, the dispersion was dissolved in acetylene black, SiO ｘExperimental Examples 1 and 2, in which the electrode binder of the present invention was used, showed improved dispersibility (decreased particle size) compared to Experimental Examples 3 and 4, in which the electrode binder of the present invention was not used. From the above, it was found that the electrode binder of the present invention had excellent adhesive strength to the current collector regardless of the active material, and further had excellent dispersibility of the active material and the conductive additive.

[0105] Furthermore, the flexibility of the positive electrode plates 1 to 3 obtained in Example 4 and Comparative Examples 5 to 6 was measured as follows, and the coatability of the positive electrode slurries 1 to 3 obtained in Example 4 and Comparative Examples 5 to 6 was evaluated as follows. Furthermore, the battery performance was evaluated as follows using the positive electrode plates 1 to 3 obtained in Example 4 and Comparative Examples 5 to 6.

[0106] <Flexibility> Each of the positive electrode plates 1 to 3 obtained in Example 4 and Comparative Examples 5 to 6 was cut into a width of 2.5 cm, and the flexibility was evaluated using a cylindrical mandrel bending tester. That is, the diameter of the mandrel when cracks occurred in the coating film was shown as the evaluation value, and a smaller value indicates better flexibility.

[0107] <Coatability> Each of the positive electrode slurries 1 to 3 obtained in Example 4 and Comparative Examples 5 and 6 was coated on an aluminum foil and air-dried, and then the presence or absence of coating unevenness and streaks was visually evaluated according to the following criteria: A: Almost no irregularities or streaks were observed on the coating layer surface, and the coating property was excellent. B: Roughness or streaks were observed on the coating layer surface, and the coating property was poor.

[0108] <Electrolyte Penetration> Each of the positive electrode plates 1 to 3 obtained in Example 4 and Comparative Examples 5 to 6 was cut into a circle having a diameter of 15.9 mm and dried in a vacuum at 120° C. for 12 hours. Then, the positive electrode plates were filled with 1.0 M LiPF 6 as an electrolyte in a glove box. ６ A drop of EC / DEC (Sigma-Aldrich) was dropped onto the coated surface using a 200 μL pipette tip, and the time until the electrolyte penetrated (electrolyte penetration time) was measured. A shorter electrolyte penetration time indicates better penetration.

[0109] <Capacity Retention Rate> A charge / discharge rate test was carried out on the coin-type nonaqueous electrolyte secondary batteries 1 to 3 obtained in Example 4 and Comparative Examples 5 and 6. Specifically, a Nagano Corporation BTS2004 was used in a thermostatic chamber at 25°C, and 52 cycles were carried out, with one cycle consisting of a charge treatment followed by a discharge treatment. Note that the charge treatment conditions for all cycles were a constant current / constant voltage (CC-CV) method (CC current 0.2 C, CV voltage 4.2 V, and final current 0.02 C).

[0110] As a condition for the discharge treatment, the final voltage was set to 3.0 V. In the first cycle, the discharge treatment was performed at a constant current of 0.2 C, and the discharge capacity (mAh) after one cycle was measured and used as the initial capacity.

[0111] Thereafter, up to the 52nd cycle, the constant current for the discharge treatment was set as follows, and the discharge capacity (mAh) was measured after discharge of each cycle.

[0112] The constant current for discharge treatment in each cycle was as follows: 2 to 10 cycles: constant current of 0.2 C for discharge treatment 11 to 20 cycles: constant current of 1 C for discharge treatment 21 cycle: constant current of 0.2 C for discharge treatment 22 to 31 cycles: constant current of 2 C for discharge treatment 32 cycle: constant current of 0.2 C for discharge treatment 33 to 42 cycles: constant current of 3 C for discharge treatment 43 to 52 cycles: constant current of 0.2 C for discharge treatment

[0113] In the above charge-discharge rate test, the discharge capacity after 20 cycles was defined as the 1C rate capacity, and the discharge capacity after 31 cycles was defined as the 2C rate capacity. The capacity retention rates were calculated as follows: Capacity retention rate 1 (%) = 1C rate capacity (mAh) / initial capacity (mAh) × 100, and Capacity retention rate 2 (%) = 2C rate capacity (mAh) / initial capacity (mAh) × 100.

[0114] (Example 4) (Preparation of Positive Electrode Plate) LiFePO was used as the positive electrode active material. ４(hereinafter sometimes referred to as "LFP").), acetylene black (manufactured by Stream Chemical Co.), electrode binder 1, styrene butadiene rubber (SBR, manufactured by JSR Corporation, product number S2910(E)-12-Na) were mixed so that the solids weight ratio was 92:4:1:3, water was added so that the slurry concentration was 59.1% by mass, and the mixture was thoroughly stirred using a Mazerustar (manufactured by Kurabo Industries, Ltd., KK-250S) to obtain a positive electrode slurry 1. This slurry was applied with an applicator to a copper foil (manufactured by Furukawa Electric Co., Ltd., NC-WS) measuring 320 mm in length x 170 mm in width x 17 μm in thickness, and then air-dried for 30 minutes. After that, it was dried in a dryer at 60 ° C. for 30 minutes. Further, using a small tabletop roll press (manufactured by Tester Sangyo Co., Ltd., SA-602), the fabric was pressed under conditions of 5 kN and a roll peripheral speed of 50 m / min, resulting in a fabric weight of 27.2 g / m ２ A positive electrode plate 1 having an effective discharge capacity of 170 mAh / g was obtained.

[0115] (Preparation of negative electrode plate for positive electrode evaluation) As negative electrode active material, artificial graphite, AB, CMC (a), styrene butadiene rubber (SBR, manufactured by JSR Corporation, product number S2910(E)-12-Na) were mixed so that the solids weight ratio was 100: 0.5: 1.0: 1.5, water was added so that the slurry concentration was 45.6% by mass, and Mazerustar (manufactured by Kurabo Industries, KK-250S) was used for thorough stirring to obtain slurry 1. This slurry was applied to a copper foil (manufactured by Furukawa Electric Co., Ltd., NC-WS) measuring 320 mm in length x 170 mm in width x 17 μm in thickness with an applicator and air-dried for 30 minutes, and then dried at 60 ° C. for 30 minutes in a dryer. Further, using a small tabletop roll press (manufactured by Tester Sangyo Co., Ltd., SA-602), it was pressed under the conditions of 5 kN and a roll peripheral speed of 50 m / min, and the basis weight was 13.0 g / m ２ A negative electrode plate with an effective discharge capacity of 330 mAh / g was obtained.

[0116] (Fabrication of coin-shaped non-aqueous electrolyte secondary battery) The obtained positive electrode plate 1 and the negative electrode plate for positive electrode evaluation were punched out into circles with a diameter of 15.9 mm, and the punched negative electrode plate and positive electrode plate were vacuum dried at 120° C. for 12 hours.

[0117] Similarly, a separator (a 20 μm thick polypropylene separator manufactured by CS Tech) was punched out into a circle having a diameter of 17 mm, and vacuum dried at 60° C. for 12 hours.

[0118] Thereafter, the negative electrode plate was placed in a stainless steel circular dish-shaped container having a diameter of 20.0 mm, and then a separator, a positive electrode plate 1, a spacer (diameter 15.5 mm, thickness 1 mm), and a stainless steel washer (manufactured by Hosen Co., Ltd.) were stacked in this order, and then an electrolyte (1 mol / L LiPF ６ 300 μL of a mixture of ethylene carbonate and diethyl carbonate (volume ratio of 1:1) was added to the container, which was then covered with a stainless steel cap via a polypropylene packing and sealed using a coin battery crimping machine (Hosen Co., Ltd.) to obtain a coin-type nonaqueous electrolyte secondary battery 1.

[0119] Comparative Example 5 A positive electrode slurry, a positive electrode plate, and a coin-type non-aqueous electrolyte secondary battery were prepared in the same manner as in Example 4, except that CMC (a) was used alone instead of the electrode binder 1, thereby obtaining a positive electrode slurry 2, a positive electrode plate 2, and a coin-type non-aqueous electrolyte secondary battery 2.

[0120] Comparative Example 6 A positive electrode slurry, a positive electrode plate, and a coin-type non-aqueous electrolyte secondary battery were prepared in the same manner as in Example 4, except that CMC(b) was used alone instead of electrode binder 1, thereby obtaining a positive electrode slurry 3, a positive electrode plate 3, and a coin-type non-aqueous electrolyte secondary battery 3.

[0121] The results of measurement or evaluation of flexibility, coatability and capacity retention in Example 4 and Comparative Examples 5 and 6 are shown in Table 3 below.

[0122]

[0123] As shown in Table 3, a binder for a non-aqueous electrolyte secondary battery electrode comprising: Component A: carboxymethyl cellulose and / or a salt thereof having a molecular weight of 6 million or more and a viscosity of 1,000 to 20,000 mPa·s in a 1% by mass aqueous solution measured at 25°C with a Brookfield viscometer (30 rpm) and Component B: carboxymethyl cellulose and / or a salt thereof having a viscosity of 1 to 500 mPa·s in a 1% by mass aqueous solution measured at 25°C with a Brookfield viscometer (30 rpm), wherein the blending ratio of Components A and B in the binder for a non-aqueous electrolyte secondary battery electrode was Component A / Component B = 90 / 10 to 55 / 45. The coating properties of a positive electrode slurry using the binder for a non-aqueous electrolyte secondary battery electrode and the flexibility of a positive electrode plate obtained using this positive electrode slurry were good. Furthermore, the capacity retention rate of a non-aqueous electrolyte secondary battery using this positive electrode plate was also good. Furthermore, the electrolyte permeability was also good.

Claims

1. A binder for electrodes of non-aqueous electrolyte secondary batteries, comprising: component A: carboxymethyl cellulose and / or a salt thereof having a molecular weight of 6 million or more and a viscosity of 1% by mass aqueous solution of 1,000 to 20,000 mPa·s measured at 25°C with a B-type viscometer (30 rpm); and component B: carboxymethyl cellulose and / or a salt thereof having a viscosity of 1% by mass aqueous solution of 1 to 500 mPa·s measured at 25°C with a B-type viscometer (30 rpm), wherein a blending ratio of components A and B in the binder for electrodes of non-aqueous electrolyte secondary batteries is component A / component B=90 / 10 to 55 / 45.

2. The binder for a non-aqueous electrolyte secondary battery electrode according to claim 1, wherein the degree of carboxymethyl substitution per anhydrous glucose unit of said component A and said component B is 0.5 to 1.

2.

3. The electrode binder for a non-aqueous electrolyte secondary battery according to claim 1, wherein the degree of dispersion of said component B as measured using a powder tester is 20 to 60%.

4. An electrode composition for a non-aqueous electrolyte secondary battery, which uses the electrode binder for a non-aqueous electrolyte secondary battery according to claim 1.

5. An electrode for a non-aqueous electrolyte secondary battery, which uses the electrode binder for a non-aqueous electrolyte secondary battery according to claim 1.

6. A non-aqueous electrolyte secondary battery using the electrode binder for a non-aqueous electrolyte secondary battery according to claim 1.

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