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

Abstract

The present invention contains: a component A that is a carboxymethyl cellulose having a degree of carboxymethyl substitution of 0.45 or more per anhydroglucose unit, or a salt of this carboxymethyl cellulose; and a component B that is a saturated carboxylic acid having 6 or less carbon atoms, or a salt of this saturated carboxylic acid.

Description

Technical Field

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

Background Art

[0002] In recent years, electronic devices, particularly portable devices such as mobile phones, PDAs (personal digital assistants), and notebook computers, have become smaller, lighter, thinner, and more highly performant, and the spread of portable devices has advanced. Along with the diversification of the usage range of such portable devices, the batteries that drive them have become extremely important components. Among batteries, non-aqueous electrolyte secondary batteries typified by lithium-ion secondary batteries, which have a high energy density and high capacity, are widely used.

[0003] Normally, a non-aqueous electrolyte secondary battery is manufactured as follows. That is, a negative electrode containing a negative electrode active material made of a carbon material capable of occluding and releasing lithium ions and the like, and a positive electrode containing a positive electrode active material made of a lithium-containing transition metal composite oxide (for example, LiCoO2, LiNiO2, LiMn2O4, etc.) are each formed in a sheet shape on the surface of a metal foil as a current collector substrate (current collector), to obtain a sheet-shaped positive electrode and a sheet-shaped negative electrode. Then, the sheet-shaped positive electrode and the sheet-shaped negative electrode are wound or laminated via a separator also formed in a sheet shape and housed in a case. The sheet-shaped positive electrode and the sheet-shaped negative electrode have a structure including a metal foil serving as a current collector substrate (current collector) and a binder layer containing an active material formed on the surface thereof, and a negative electrode active material slurry (or paste) or a positive electrode active material slurry (or paste) can be applied and dried on the current collector material to be formed.

[0004] The negative electrode active material slurry (paste) contains a binder (binder) in addition to a negative electrode active material made of a carbon material capable of occluding and releasing lithium ions and the like. As a binder, a binder for a negative electrode mainly composed of styrene / butadiene latex (SBR) is disclosed in Patent Document 1.

[0005] According to Patent Document 1, carboxymethyl cellulose as a water-soluble thickener is dissolved in water to prepare an aqueous solution, and SBR and a negative electrode active material are mixed therein to produce a slurry. The slurry is applied onto a substrate as a coating liquid and dried to form a sheet-like negative electrode.

[0006] On the other hand, in the production of the positive electrode of a non-aqueous electrolyte secondary battery, organic solvents such as N-methyl-2-pyrrolidone (NMP) have conventionally been used as the solvent. However, in recent years, water has been used as the solvent in view of reducing the cost required for handling and the impact on the environmental load during discharge.

[0007] The positive electrode active material slurry (paste) contains a binder in addition to a lithium-containing transition metal composite oxide (such as LiCoO2, LiNiO2, LiMn2O4, etc.) as the positive electrode active material and carbon as the conductive material. As the binder, cellulose having a viscosity of 4000 mPa·s or more in a 1% aqueous solution, such as carboxymethyl cellulose, is described in Patent Document 2. Patent Document 2 describes that carboxymethyl cellulose is put into pure water together with a conductive material, polytetrafluoroethylene (PTFE), etc. to prepare an active material paste.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

[0009] However, in both Patent Document 1 and Patent Document 2, there has been a concern that undissolved matter of carboxymethyl cellulose used as the binder remains in the slurry, resulting in streak-like defects on the current collector substrate coated with the slurry.

[0010] Therefore, an object of the present invention is to obtain a binder for a non-aqueous electrolyte secondary battery electrode, which can reduce the generation of undissolved matter of carboxymethyl cellulose and has excellent solubility of carboxymethyl cellulose. Furthermore, in addition to the above, an object of the present invention is to obtain a binder for a non-aqueous electrolyte secondary battery electrode, which has excellent coatability when added to an electrode composition and also has excellent coating film strength.

Summary of the Invention

Means for Solving the Problems

[0011] As a result of intensive efforts, the present inventors have found that the problems can be solved by the following [1] to

[17] . That is, according to the present invention, (1) A binder for a non-aqueous electrolyte secondary battery electrode, comprising component A: carboxymethyl cellulose or a salt thereof having a carboxymethyl substitution degree of 0.45 or more per anhydrous glucose unit, and component B: a saturated carboxylic acid having 6 or less carbon atoms or a salt thereof. (2) The binder for a non-aqueous electrolyte secondary battery electrode according to (1), wherein the component B contains at least a lithium salt of a saturated carboxylic acid having 6 or less carbon atoms. (3) The binder for a non-aqueous electrolyte secondary battery electrode according to (1) or (2), characterized by satisfying the following condition (I). Condition (I): When the component A is carboxymethyl cellulose or a salt thereof having a carboxymethyl substitution degree of 0.45 or more and 1.0 or less, the component B is contained in the range of 1 to 100 parts by weight with respect to 100 parts by weight of the component A. (4) The binder for a non-aqueous electrolyte secondary battery electrode according to (1) or (2), characterized by satisfying the following condition (II). Condition (II): When the component A is carboxymethyl cellulose or a salt thereof having a carboxymethyl substitution degree exceeding 1.0, the component B is contained in the range of 1 to 200 parts by weight with respect to 100 parts by weight of the component A. (5) The binder for a non-aqueous electrolyte secondary battery electrode according to any one of (1) to (4), wherein the component B is a lithium salt of a hydroxy acid having 6 or less carbon atoms. 〔6〕 The binder for non-aqueous electrolyte secondary battery electrodes according to any one of 〔1〕 to 〔5〕, wherein the component B contains at least a lithium citrate salt. 〔7〕 The binder for non-aqueous electrolyte secondary battery electrodes according to any one of 〔1〕 to 〔6〕, wherein the carboxymethyl cellulose or its salt has a volume cumulative 100% particle diameter of less than 100 μm as measured by a laser diffraction / scattering particle size distribution analyzer using methanol as a dispersion medium. 〔8〕 The binder for non-aqueous electrolyte secondary battery electrodes according to 〔1〕, wherein the carboxymethyl cellulose or its salt has a viscosity of 1,000 to 20,000 mPa·s for a 1 mass% aqueous solution measured by a B-type viscometer (30 rpm) at 25°C. 〔9〕 The binder for non-aqueous electrolyte secondary battery electrodes according to 〔1〕 or 〔8〕, wherein the carboxymethyl cellulose or its salt has a volume cumulative 100% particle diameter of less than 50 μm as measured by a laser diffraction / scattering particle size distribution analyzer using methanol as a dispersion medium. 〔10〕 The binder for non-aqueous electrolyte secondary battery electrodes according to any one of 〔1〕, 〔8〕 or 〔9〕, wherein the saturated carboxylic acid or its salt is contained in the range of 10 to 120% by weight with respect to the carboxymethyl cellulose or its salt. 〔11〕 The binder for non-aqueous electrolyte secondary battery electrodes according to any one of 〔1〕 to 〔10〕, wherein the carboxymethyl cellulose or its salt is prepared by preparing 2 liters of a 0.3 mass% aqueous solution of the carboxymethyl cellulose or its salt with a dry mass m, filtering all of it through a 250-mesh filter under reduced pressure conditions of -200 mmHg, and measuring the dry mass M of the residue on the filter after filtration, and the ratio of the dry mass M to the dry mass m is less than 50 ppm. 〔12〕 The binder for non-aqueous electrolyte secondary battery electrodes according to any one of 〔1〕 to 〔11〕, wherein the carboxymethyl cellulose or its salt is a mechanically pulverized product. 〔13〕 An aqueous solution containing the binder for non-aqueous electrolyte secondary battery electrodes according to any one of 〔1〕 to 〔12〕. An aqueous solution as described in

[13] , which is characterized in that the pH is in the range of 2 to 8. An electrode composition for a non-aqueous electrolyte secondary battery, comprising the aqueous solution as described in

[13] or

[14] . The electrode composition for a non-aqueous electrolyte secondary battery as described in

[15] , which is characterized by containing a silicon-based active material. An electrode for a non-aqueous electrolyte secondary battery, formed by the electrode composition as described in

[15] or

[16] . is provided.

Advantages of the Invention

[0012] According to the present invention, it is possible to obtain a binder for a non-aqueous electrolyte secondary battery electrode, which has excellent solubility of carboxymethyl cellulose and can reduce the generation of undissolved matter of carboxymethyl cellulose. Further, according to the present invention, it is possible to obtain a binder for a non-aqueous electrolyte secondary battery electrode, which has excellent coating properties when added to an electrode composition and also has excellent coating film strength.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the binder for a non-aqueous electrolyte secondary battery electrode of the present invention (hereinafter, sometimes referred to as "binder for electrode") will be described. The binder for electrode of the present invention contains Component A: carboxymethyl cellulose or a salt thereof having a carboxymethyl substitution degree of 0.45 or more per anhydrous glucose unit, and Component B: a saturated carboxylic acid having 6 or less carbon atoms or a salt thereof.

[0014] <Component A: Carboxymethyl Cellulose or a Salt Thereof> In the present invention, carboxymethyl cellulose or a salt thereof has a structure in which a hydroxyl group in a glucose residue constituting cellulose is substituted with a carboxymethyl ether group. Carboxymethyl cellulose may be in the form of a salt. Examples of the salt of carboxymethyl cellulose may include metal salts such as sodium carboxymethyl cellulose salt.

[0015] In the present invention, cellulose means a polysaccharide having a structure in which D-glucopyranose (also simply referred to as "glucose residue" or "anhydroglucose") is linked by β,1-4 bonds. Cellulose is generally classified into natural cellulose, regenerated cellulose, microcrystalline cellulose, microcrystalline cellulose excluding amorphous regions, etc., according to its origin, production method, etc.

[0016] Examples of natural cellulose include bleached pulp or unbleached pulp (bleached wood pulp or unbleached wood pulp); lint, purified lint; cellulose produced by microorganisms such as acetic acid bacteria, etc. The raw materials for bleached pulp or unbleached pulp are not particularly limited, and examples include wood, cotton, straw, bamboo, etc. Also, the production method of bleached pulp or unbleached pulp is not particularly limited, and it may be a mechanical method, a chemical method, or a method combining the two in the middle. Examples of bleached pulp or unbleached pulp classified by production method include mechanical pulp, chemical pulp, groundwood pulp, sulfite pulp, kraft pulp, etc. Furthermore, dissolving pulp may be used in addition to pulp for papermaking. Dissolving pulp is chemically purified pulp, which is mainly dissolved in chemicals and used as the main raw material for artificial fibers, cellophane, etc.

[0017] Examples of regenerated cellulose include those obtained by dissolving cellulose in a solvent such as a copper ammonia solution, a cellulose xanthate solution, a morpholine derivative, etc. and then spinning it again.

[0018] Examples of microcrystalline cellulose include those obtained by depolymerizing cellulose-based materials such as the above natural cellulose and regenerated cellulose (e.g., acid hydrolysis, alkaline hydrolysis, enzymatic hydrolysis, blasting treatment, vibration ball mill treatment, etc.), and those obtained by mechanically treating the cellulose-based materials.

[0019] The carboxymethyl cellulose or its salt of the present invention is importantly such that the degree of carboxymethyl substitution per anhydroglucose unit is 0.45 or more, and more preferably 0.5 or more. If the degree of carboxymethyl substitution is less than 0.45, there is a risk that dissolution in water will be insufficient.

[0020] In the present invention, the anhydroglucose unit means each individual anhydroglucose (glucose residue) constituting cellulose. Further, the degree of carboxymethyl substitution (also referred to as the degree of etherification) indicates the ratio of the hydroxyl groups (-OH) in the glucose residue constituting cellulose that are substituted with carboxymethyl ether groups (-OCH2COOH). Note that the degree of carboxymethyl substitution may be abbreviated as DS or CM-DS.

[0021] The upper limit of the degree of carboxymethyl substitution per anhydroglucose unit of the carboxymethyl cellulose or its salt is preferably 2.0 or less, and more preferably 1.5 or less.

[0022] The degree of carboxymethyl substitution can be confirmed by measuring the amount of a base such as sodium hydroxide required to neutralize the carboxymethyl cellulose in the sample. In this case, when the carboxymethyl ether group of the carboxymethyl cellulose or its salt is in the form of a salt, it is converted to carboxymethyl cellulose in advance before measurement. During measurement, back titration using a base and an acid, and indicators such as phenolphthalein can be appropriately combined.

[0023] In the present invention, the carboxymethyl cellulose or its salt preferably has a viscosity of 1,000 to 20,000 mPa·s, more preferably 1,500 to 15,000 mPa·s, and even more preferably 2,000 to 10,000 mPa·s for a 1 mass% aqueous solution measured with a B-type viscometer (30 rpm) at 25°C. Since the viscosity within the above range makes it difficult to sediment and enables the production of an electrode slurry with good coatability, it is suitable for non-aqueous electrolyte secondary batteries.

[0024] In addition, for carboxymethyl cellulose or a salt thereof, when the dry mass of the residue on a filter when filtering all 2 liters of an aqueous solution containing 0.3% by mass of the carboxymethyl cellulose or a salt thereof through a 250-mesh filter under a reduced pressure condition of -200 mmHg is defined as mass M, and the mass of the carboxymethyl cellulose or a salt thereof dissolved in the aqueous solution is defined as mass m, the ratio of mass M to mass m is preferably less than 50 ppm. If it is 50 ppm or more, when an electrode is formed using carboxymethyl cellulose or a salt thereof, appearance defects such as streaks and pinholes may occur in the electrode, and the quality of the battery may deteriorate. The lower limit of the ratio of mass M to mass m is not particularly limited, and the smaller it is, the better.

[0025] In the present invention, the production method of carboxymethyl cellulose or a salt thereof is not limited, and a known production method of carboxymethyl cellulose or a salt thereof can be applied. That is, the carboxymethyl cellulose or a salt thereof in the present invention can be produced by treating cellulose as a raw material with a mercerizing agent (alkali) to prepare mercerized cellulose (alkali cellulose), and then adding an etherifying agent to cause an etherification reaction.

[0026] As the cellulose of the raw material, any of the above-mentioned celluloses can be used without particular limitation, but those with high cellulose purity are preferred, and in particular, it is preferable to use dissolving pulp and linter. By using these, carboxymethyl cellulose or a salt thereof with high purity can be obtained.

[0027] As the mercerizing agent, alkali metal hydroxide salts such as sodium hydroxide and potassium hydroxide can be used. As the etherifying agent, monochloroacetic acid, sodium monochloroacetate, etc. can be used.

[0028] In the case of a general method for producing water-soluble carboxymethyl cellulose, the molar ratio of the mercerizing agent to the etherifying agent is generally 2.00 to 2.45 when monochloroacetic acid is used as the etherifying agent. The reason is that if it is less than 2.00, the etherification reaction may not proceed sufficiently, so unreacted monochloroacetic acid may remain and cause waste, and if it exceeds 2.45, side reactions due to the excess mercerizing agent and monochloroacetic acid may proceed to form alkali metal glycolate, which may be uneconomical.

[0029] In the present invention, carboxymethyl cellulose or its salt may be used as it is a commercially available product or after being processed as necessary. Examples of commercially available products include the product named "Sunrose" (sodium salt of carboxymethyl cellulose) manufactured by Nippon Paper Industries Co., Ltd.

[0030] [Grinding treatment] In the present invention, carboxymethyl cellulose or its salt may be used as it is the carboxymethyl cellulose or its salt as described above, or it may be further subjected to a grinding treatment (ground product). The grinding treatment is usually a mechanical grinding treatment using a machine. Examples of the method for grinding carboxymethyl cellulose or its salt include a dry grinding method for treating in a powder state and a wet grinding method for treating in a state of being dispersed or dissolved in a liquid. In the present invention, any of these may be selected.

[0031] When an aqueous solution of carboxymethyl cellulose or a salt thereof is prepared, gel particles derived from carboxymethyl cellulose or a salt thereof remain in the aqueous solution as undissolved matter. By mechanically dry- or wet-milling carboxymethyl cellulose or a salt thereof, the gel particles are refined in an aqueous solution of the mechanically milled product of carboxymethyl cellulose or a salt thereof. As a result, when an electrode is formed using an aqueous solution of the mechanically milled product of carboxymethyl cellulose or a salt thereof, it is considered that coarse undissolved matter that causes streak-like defects (streaks), peeling, pinholes, etc. generated on the surface of the electrode can be further suppressed.

[0032] Examples of the grinding device that can be used for mechanical grinding treatment in the present invention include the following dry grinders and wet grinders.

[0033] Examples of the dry grinder include a cutting mill, an impact mill, a pneumatic mill, and a media mill. These can be used alone or in combination, and further can be processed in multiple stages with the same model, but a pneumatic mill is preferred.

[0034] Examples of the cutting mill include a mesh mill (manufactured by Horai Co., Ltd.), an atoms (manufactured by Yamamoto Hyakuba Seisakusho Co., Ltd.), a knife mill (manufactured by Pallmann), a granulator (manufactured by Herbold), a rotary cutter mill (manufactured by Nara Kikai Seisakusho Co., Ltd.), etc.

[0035] Examples of the impact mill include a pulpizer (manufactured by Hosokawa Micron Corporation), a fine impact mill (manufactured by Hosokawa Micron Corporation), a super micron mill (manufactured by Hosokawa Micron Corporation), a sample mill (manufactured by Seishin Co., Ltd.), a bantam mill (manufactured by Seishin Co., Ltd.), an atomizer (manufactured by Seishin Co., Ltd.), a tornado mill (manufactured by Nikkiso Co., Ltd.), a turbo mill (manufactured by Turbo Kogyo Co., Ltd.), a bevel impactor (manufactured by Aikawa Tekko Co., Ltd.), etc.

[0036] Examples of the pneumatic mill include CGS type jet mill (manufactured by Mitsui Mining Co., Ltd.), jet mill (manufactured by Sanjo Industry Co., Ltd.), Ebara jet micronizer (manufactured by Ebara Corporation), Selene mill (manufactured by Masayuki Sangyo Co., Ltd.), supersonic jet mill (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the like.

[0037] Examples of the media mill include vibration ball mill and the like.

[0038] Examples of the wet pulverizer include Mascoloider (manufactured by Masayuki Sangyo Co., Ltd.), high-pressure homogenizer (manufactured by Sanmaru Kikai Kogyo Co., Ltd.), and media mill. Examples of the media mill include bead mill (manufactured by Aimex Co., Ltd.) and the like.

[0039] [Particle size of carboxymethyl cellulose] In the present invention, the particle size of carboxymethyl cellulose or its salt is preferably small. That is, the value of the volume cumulative 100% particle diameter measured by a laser diffraction / scattering type particle size distribution analyzer using methanol as a dispersion medium (hereinafter sometimes referred to as "maximum particle diameter" in this specification) is desirably less than 100 μm, more desirably less than 50 μm, and even more desirably less than 45 μm. If the maximum particle diameter of carboxymethyl cellulose or its salt is too large, the amount of undissolved matter in the aqueous solution of carboxymethyl cellulose or its salt tends to increase.

[0040] Further, in the present invention, carboxymethyl cellulose or its salt may be subjected to granulation treatment. Thereby, handling becomes easy. By performing the granulation treatment, the maximum particle diameter of carboxymethyl cellulose or its salt may become equal to or greater than the above value, but the maximum particle diameter of carboxymethyl cellulose or its salt before the granulation treatment is preferably less than the above value. Note that the lower limit of the maximum particle diameter is not particularly limited. The smaller, the better, and it may exceed 0.

[0041] The volume median diameter (hereinafter referred to as the average particle diameter) of carboxymethyl cellulose or a salt thereof, measured by a laser diffraction / scattering particle size distribution analyzer using methanol as a dispersion medium, is usually 30 μm or less, preferably 20 μm or less, and more preferably 15 μm or less. The lower limit of the average particle diameter is not particularly limited, but is usually 5 μm or more, preferably 10 μm or more, and more preferably 12 μm or more.

[0042] In the present invention, carboxymethyl cellulose or a salt thereof can be classified based on the particle size (preferably the maximum particle size). Classification means a process of sieving particles to be classified into those having a particle size greater than a certain particle size and those having a particle size less than that.

[0043] Classification is preferably carried out based on whether the maximum particle size is less than or greater than the above value. Thereby, carboxymethyl cellulose or a salt thereof having a maximum particle size less than the above value can be selectively collected.

[0044] When using a pulverized product of carboxymethyl cellulose or a salt thereof as carboxymethyl cellulose or a salt thereof, the timing of the above classification is not particularly limited, and it may be provided during the pulverization process or after the completion of the pulverization process.

[0045] As the classification method, a known method, for example, a method using a dry classifier or a wet classifier may be used. Examples of the dry classifier include a cyclone classifier, a DS separator, a turbo classifier, a micro separator, an air separator, etc. On the other hand, examples of the wet classifier include a liquid cyclone classifier, a centrifugal sedimentation machine, a hydro classifier, etc. Among these, a dry classifier is preferred, and a cyclone classifier is more preferred.

[0046] <Component B: Saturated carboxylic acid having 6 or less carbon atoms or a salt thereof> It is important that the binder for the electrode of the present invention contains a saturated carboxylic acid having 6 or less carbon atoms or a salt thereof. The saturated carboxylic acid having 6 or less carbon atoms in the present invention represents aliphatic hydroxy acids, aromatic hydroxy acids, saturated fatty acids, dicarboxylic acids, tricarboxylic acids, etc. having 6 or less carbon atoms, and aliphatic hydroxy acids having 6 or less carbon atoms are more preferable. Such aliphatic hydroxy acids can include citric acid, malic acid, gluconic acid, succinic acid, etc.

[0047] Examples of the saturated carboxylate having 6 or less carbon atoms can include salts of the saturated carboxylic acids exemplified above, etc. As such a salt form, potassium saturated carboxylate, calcium saturated carboxylate, and lithium saturated carboxylate are preferable. Among these, lithium saturated carboxylate is more preferable, and lithium citrate is even more preferable.

[0048] When such a saturated carboxylic acid having 6 or less carbon atoms or a salt thereof is used as a binder for the electrode together with carboxymethyl cellulose, the hydroxy group or carboxy group in the saturated carboxylic acid having 6 or less carbon atoms forms a cross-linked structure via hydrogen bonding with the carboxy group of carboxymethyl cellulose. In this cross-linked structure, since more hydroxy groups and carboxyl groups are contained in the molecule than in carboxymethyl cellulose alone, the reactivity with the negative electrode material such as SiOx dispersed in the negative electrode slurry via hydrogen bonding is increased. As a result, it is presumed that a stable oxide film can be formed on the surface of the negative electrode material such as SiOx, the decomposition of the electrolytic solution is suppressed, and the excessive thickness of the SEI film (Solid Electrolyte Interface) on the electrode surface does not occur, leading to an effect of improving battery characteristics.

[0049] In addition, when using a lithium salt of a saturated carboxylic acid having 6 or fewer carbon atoms, the saturated carboxylic acid can exhibit neutral or weak alkalinity when added to the electrode composition. When the saturated carboxylic acid is not in the form of a lithium salt, the electrode composition in the form of an aqueous solution becomes strongly acidic, resulting in a decrease in the viscosity of the electrode composition and uneven distribution of polarity, which causes unevenness when applying the electrode composition to the current collector, so this is not preferable. Furthermore, since the saturated carboxylic acid having 6 or fewer carbon atoms is a lithium salt, the incorporation of impurities is reduced when using a lithium-based active material, making it easier to exhibit electrical performance.

[0050] <Binder for electrode> It is important that the binder for the non-aqueous electrolyte secondary battery electrode of the present invention contains the above-described component A: carboxymethyl cellulose or a salt thereof and component B: a saturated carboxylic acid having 6 or fewer carbon atoms or a salt thereof. Such a binder for an electrode preferably contains the saturated carboxylic acid having 6 or fewer carbon atoms or a salt thereof in the range of 10 to 120% by weight, more preferably in the range of 20 to 100% by weight, and even more preferably in the range of 30 to 50% by weight, based on 100% by weight of carboxymethyl cellulose or a salt thereof. When the blending ratio is within this range, it is presumed that the formation of a cross-linked structure of carboxymethyl cellulose and a saturated carboxylic acid having 6 or fewer carbon atoms or a salt thereof described above occurs more effectively.

[0051] The binder for the electrode for the non-aqueous secondary battery of the present invention preferably satisfies the following condition (I) or condition (II). Condition (I): When component A is carboxymethyl cellulose or a salt thereof having a carboxymethyl substitution degree of 0.45 or more and 1.0 or less, component B is contained in the range of 1 to 100 parts by weight with respect to 100 parts by weight of component A. Condition (II): When component A is carboxymethyl cellulose or a salt thereof having a carboxymethyl substitution degree exceeding 1.0, component B is contained in the range of 1 to 200 parts by weight with respect to 100 parts by weight of component A.

[0052] When the degree of carboxymethyl substitution of Component A increases, the number of cross-linking points in carboxymethyl cellulose increases, so even if the addition amount of Component B increases, aggregation or the like will not be caused.

[0053] Therefore, when Component A is carboxymethyl cellulose or a salt thereof having a degree of carboxymethyl substitution of 0.45 or more and 1.0 or less, it is preferable that Component B is contained in the range of 1 to 100 parts by weight with respect to 100 parts by weight of Component A, more preferably in the range of 1 to 80 parts by weight, and even more preferably in the range of 10 to 50 parts by weight.

[0054] Further, when Component A is carboxymethyl cellulose or a salt thereof having a degree of carboxymethyl substitution exceeding 1.0, it is preferable that Component B is contained in the range of 1 to 200 parts by weight with respect to 100 parts by weight of Component A, more preferably in the range of 1 to 180 parts by weight, even more preferably in the range of 10 to 150 parts by weight, and particularly preferably exceeding 100 parts by weight and 150 parts by weight or less.

[0055] When the mixing ratio is within the above range, it is presumed that the formation of the cross-linked structure of the above-mentioned carboxymethyl cellulose and the saturated carboxylic acid having 6 or less carbon atoms or a salt thereof occurs more effectively.

[0056] The binder for an electrode of the present invention can also be made into an aqueous solution. The production conditions of such an aqueous solution are not particularly limited. For example, the binder for an electrode can be added to water (such as distilled water, purified water, tap water, etc.) and dissolved by stirring or the like as necessary. Further, after dissolving carboxymethyl cellulose or a salt thereof in water or the like, a saturated carboxylic acid having 6 or less carbon atoms or a salt thereof can be added and dissolved by stirring or the like. Similarly, after dissolving a saturated carboxylic acid having 6 or less carbon atoms or a salt thereof in water or the like, carboxymethyl cellulose or a salt thereof can be dissolved by stirring or the like.

[0057] The aqueous solution of such a binder for an electrode preferably has a pH in the range of 1 to 8, more preferably in the range of pH 2 to 8, still more preferably in the range of pH 3 to 8, and particularly preferably in the range of pH 6 to 8. When the pH of the aqueous solution is biased toward the acidic side, it becomes difficult to exhibit the expected viscosity of the aqueous solution. Therefore, when the pH is in the range of 6 to 8, an aqueous solution with a particularly good balance between viscosity and solubility and excellent coatability can be obtained.

[0058] In addition, for the aqueous solution of the binder for an electrode, the viscosity of a 1 mass% aqueous solution measured with a B-type viscometer (30 rpm) at 25°C is preferably 5 mPa·s or more, more preferably 250 mPa·s or more, preferably 15,000 mPa·s or less, more preferably 10,000 mPa·s or less, and still more preferably 7,000 mPa·s or less. When the aqueous solution of the binder for an electrode is within the above viscosity range, suitable thickening properties and binding properties can be exhibited when added to the electrode composition.

[0059] The binder for an electrode of the present invention can also contain components constituting other electrode compositions as long as the effects of the present invention are not inhibited. Examples of such additive components include inorganic salts that ionize into cations in an aqueous solution. The presence of cations reinforces the cross-linked structure of carboxymethyl cellulose, so that an excellent effect on electrical properties can be exhibited. As such cations, monovalent, divalent, trivalent, etc. cations can be appropriately used, and specifically, those containing Fe ions, etc. are preferred.

[0060] <Electrode composition> The binder for an electrode of the present invention can form an electrode composition together with the active material of the electrode. The properties of the electrode composition are not particularly limited and can be either slurry-like or paste-like.

[0061] In the present invention, the content of carboxymethyl cellulose or its salt in the electrode composition is preferably 0.1 to 4.0 mass% based on the whole electrode composition.

[0062] The electrode composition may include various components depending on whether the electrode formed from the composition is a negative electrode or a positive electrode.

[0063] In the case of an electrode composition for a negative electrode, a negative electrode active material is usually included. Examples of the negative electrode active material include graphite materials such as graphite (natural graphite, artificial graphite), coke, and carbon fiber; elements capable of forming an alloy with lithium, such as elements such as Al, Si, Sn, Ag, Bi, Mg, Zn, In, Ge, Pb, and Ti; compounds containing the elements capable of forming an alloy with lithium; composites of the elements and compounds capable of forming an alloy with lithium with carbon and / or the graphite materials; and nitrides containing lithium. Among these, graphite materials and / or silicon-based compounds are preferred, and those containing graphite and / or silicon-based compounds are more preferred, with those containing at least a silicon-based compound being preferred.

[0064] In the case of an electrode composition for a positive electrode, a positive electrode active material is usually included. The positive electrode active material is LiMe x O y (Me represents a transition metal containing at least one of Ni, Co, and Mn. x and y represent arbitrary numbers.)-based positive electrode active materials are preferred. x O y Although the positive electrode active material is not particularly limited, LiMn2O4-, LiCoO2-, and LiNiO2-based positive electrode active materials are preferred. Examples of LiMn2O4-, LiCoO2-, and LiNiO2-based positive electrode active materials include compounds with LiMnO2, LiMn2O4, LiCoO2, or LiNiO2 as the main skeleton, substituted with various metal elements. LiMn2O4-, LiCoO2-, and LiNiO2-based positive electrode active materials have excellent performance as positive electrode active materials, such as excellent electron and lithium ion diffusion performance, and thus can provide lithium-ion secondary batteries with high charge / discharge efficiency and good cycle characteristics. Among these, LiCoO2-based positive electrode active materials are preferred, with LiCoO2 being more preferred. On the other hand, due to their low material cost, LiMn2O4-based positive electrode active materials are preferred.

[0065] The content of the active material in the electrode composition is usually 90 to 99 mass %, preferably 91 to 99 mass %, and more preferably 92 to 99 mass %.

[0066] In the case of an electrode composition for a positive electrode, the electrode composition preferably contains a conductive material. When the electrode composition contains a conductive material, the characteristics of the produced positive electrode are improved. Furthermore, the conductive material can ensure the electrical conductivity of the positive electrode. Examples of conductive materials include one or a mixture of two or more carbon materials such as carbon black, acetylene black, and graphite. Of these, carbon black is preferred.

[0067] The electrode composition may also contain a binder other than the aqueous solution of carboxymethyl cellulose or its salt. Examples of binders for 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 for electrode compositions for positive electrodes include the synthetic rubber binders listed above as binders for negative electrodes, as well as polytetrafluoroethylene (PTFE), with polytetrafluoroethylene (PTFE) being preferred.

[0068] The content of the binder in the electrode composition is usually 1 to 10 mass %, preferably 1 to 6 mass %, and more preferably 1 to 2 mass %.

[0069] 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 or a salt thereof, and the mixture is mixed with stirring as necessary.

[0070] The state of the electrode composition is not particularly limited, and may be, for example, a liquid, a paste, a slurry, or any other state.

[0071] The electrode composition is used for manufacturing an electrode for a non-aqueous electrolyte secondary battery. The manufacturing of the electrode for a non-aqueous electrolyte secondary battery may be carried out by a method of laminating the electrode composition on a current collector substrate (current collector). Examples of the lamination method include blade coating, bar coating, and die coating, and blade coating is preferred. For example, in the case of blade coating, a method of casting the electrode composition on the current collector substrate using a coating device such as a doctor blade is exemplified. Further, the lamination method is not limited to the above specific examples, and a method of discharging and applying the electrode composition from an extrusion type injector having a slot nozzle onto a current collector substrate wound around a backup roll and running is also exemplified. In blade coating, after casting, drying by heating (temperature is, for example, 80 to 120 °C, heating time is, for example, 4 to 12 hours), etc. as necessary, and pressing by roll pressing, etc. can be performed.

[0072] As the current collector substrate, any electric conductor that does not cause a fatal chemical change in the constructed battery can be used.

[0073] As the current collector substrate for the negative electrode active material, stainless steel, nickel, copper, titanium, carbon, copper with carbon, nickel, titanium, or silver adhered to the surface of the stainless steel, etc. can be used. Among these, copper or a copper alloy is preferred, and copper is most preferred.

[0074] Examples of the material of the current collector substrate for the positive electrode include metals such as aluminum and stainless steel, and aluminum is preferred. As the shape of the current collector substrate, a net, punched metal, foam metal, a foil processed into a plate shape, etc. can be used, and a foil processed into a plate shape is preferred.

[0075] The shape of the electrode for a non-aqueous electrolyte secondary battery formed by the electrode composition is not particularly limited, but is usually sheet-shaped. The thickness (the thickness of the mixture layer formed from the electrode composition, excluding the current collector substrate part) in the case of a sheet-shaped electrode plate is difficult to uniquely define because it is also appropriately selected according to the composition of the composition, manufacturing conditions, etc., but is usually 30 to 150 μm.

[0076] The electrode formed by the composition is used as the electrode of a non-aqueous electrolyte secondary battery. That is, the present invention provides an electrode formed by the composition, and a non-aqueous electrolyte secondary battery can be manufactured using this electrode. The non-aqueous electrolyte secondary battery may have a structure in which a positive electrode and a negative electrode are alternately laminated via a separator and wound multiple times. The separator is usually impregnated with a non-aqueous electrolyte. As this negative electrode and / or positive electrode, the negative electrode and / or positive electrode formed by the above-described electrode composition can be used. Such a non-aqueous electrolyte secondary battery uses carboxymethyl cellulose or a salt thereof having excellent solubility, and can omit processes such as filtration by a filter, so it is excellent in productivity, and the initial irreversible capacity is significantly improved, and high battery characteristics can be exhibited.

Examples

[0077] Hereinafter, embodiments of the present invention will be described by way of examples, but the present invention is not limited thereto.

[0078] In this example and the comparative example, each index of carboxymethyl cellulose or a salt thereof was measured by the following method. <Method for Measuring Carboxymethyl Substitution Degree (CM-DS)> Approximately 2.0 g of a sample of carboxymethyl cellulose pulverized product was precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of methanol (a solution prepared by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol) was added, and the mixture was shaken for 3 hours to convert carboxymethyl cellulose salt (CMC salt) to H-CMC (carboxymethyl cellulose). 1.5 to 2.0 g of absolutely dried H-CMC was precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. H-CMC was moistened with 15 mL of 80% methanol, 100 mL of 0.1N NaOH was added, and the mixture was shaken at room temperature for 3 hours. Using phenolphthalein as an indicator, the excess NaOH was back-titrated with 0.1N H2SO4. CM-DS was calculated by the following formula 1. (Formula 1) A = [(100 × F - (0.1 N H2SO4 (mL)) × F') × 0.1] / (dry weight of H-CMC (g)) Degree of carboxymethyl substitution (CM-DS) = 0.162 × A / (1 - 0.058 × A) A: Amount of 1 N NaOH (mL) required for neutralization of 1 g of H-CMC F': Factor of 0.1 N H2SO4 F: Factor of 0.1 N NaOH

[0079] <Viscosity> Carboxymethylated cellulose or its salt was weighed into a 1000 mL glass beaker, dispersed in 900 mL of distilled water, and a water dispersion was prepared to have a solid content of 1% (w / v). The water dispersion was stirred at 25 °C using a stirrer at 600 rpm for 3 hours. Then, in accordance with the method of JIS-Z-8803, using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.), the viscosity after 3 minutes at No. 1 rotor / rotation speed of 30 rpm was measured.

[0080] <Measurement of maximum particle diameter, average particle diameter, and particle size distribution> The maximum particle diameter and average particle diameter of carboxymethyl cellulose were measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac Model-9220-SPA, manufactured by Nikkiso Co., Ltd.). Here, the maximum particle diameter indicates the value of the volume cumulative 100% particle diameter, and the average particle diameter indicates the value of the volume cumulative 50% particle diameter. For the measurement, after dispersing the sample in methanol, the measurement was performed on the sample that had been subjected to ultrasonic treatment for at least 1 minute or more. In Examples 2 and 10, the measurement of the maximum particle diameter and average particle diameter was not performed.

[0081] <Measurement of the mass ratio of the mass of the filtration residue to the dry mass of carboxymethyl cellulose dissolved in an aqueous solution> 2 liters of an aqueous solution containing 0.3 mass% of carboxymethyl cellulose or its salt (mass% based on the dry mass of carboxymethyl methylcellulose or its salt) was prepared. 2 liters of this aqueous solution was filtered through a 250-mesh filter (made of stainless steel, with an opening of 63 μm) using a filter (Separate, manufactured by Kiriyama Seisakusho) under a reduced pressure condition of -200 mmHg. 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 a mass percentage (ppm) with respect to the mass of carboxymethyl cellulose in the carboxymethyl cellulose aqueous solution.

[0082] Also, for the electrode binders obtained in the examples and comparative examples, measurements and evaluations were carried out as follows.

[0083] <Solubility of the electrode binder dissolved in the aqueous solution> The solubility of the electrode binder dissolved in the aqueous solution was measured by weighing 100 mass% of an organic acid with respect to carboxymethyl cellulose and carboxymethyl cellulose into a 300 mL glass beaker, adding distilled water so that the solid content concentration of carboxymethyl cellulose became 2% (w / v) to obtain an aqueous dispersion of the electrode binder. The aqueous dispersion was stirred at 500 rpm for 1 hour at 25 °C using a stirrer. Then, the presence or absence of lumps (dissolved powders in a lump form) of commercially available carboxymethyl cellulose was visually judged, and the solubility was evaluated according to the following criteria. A: No lumps occurred and the solubility was good. B: Lumps occurred and the solubility was poor.

[0084] <pH of the electrode binder dissolved in the aqueous solution> The pH (hydrogen ion index) of the electrode binder dissolved in the aqueous solution was measured at a temperature of 25 °C using a glass electrode pH meter (HM-30P, manufactured by Toa DKK). This measurement was carried out for Examples 8 to 10.

[0085] <Viscosity of the electrode binder dissolved in the aqueous solution> The viscosity of the binder for electrodes dissolved in an aqueous solution was measured as follows: the aqueous dispersion of the binder for electrodes described above was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) in the same manner as carboxymethyl cellulose, and the viscosity after 3 minutes at a rotor No. 1 / rotation speed of 30 rpm was measured.

[0086] In addition, for the binders for electrodes 8 to 11 obtained in Examples 8 to 10 and Comparative Example 1, film evaluation was performed as follows.

[0087] <Film Evaluation of Binder for Electrodes> (Film Formation of Binder for Electrodes) The obtained binders for electrodes 1 to 4 were adjusted so that the solid content concentration of carboxymethyl cellulose was 2% (w / v), and then glycerol was added so that the solid content was 50% by weight based on the solid content of carboxymethyl cellulose, and stirred well until dissolved. Next, defoaming was performed using a Mazelsstar (manufactured by Kurashiki Boseki Co., Ltd., KK-250S), 80 g was poured into a polytetrafluoroethylene petri dish with a diameter of 14 cm, spread evenly over the entire surface of the petri dish so that no bubbles entered, and then dried in a forced-air dryer at 30 °C for 30 hours to obtain films 1 to 4 of the binders for electrodes 1 to 4.

[0088] (Film Evaluation) The obtained films 1 to 4 were each left standing in a room maintained at a room temperature of 23 °C and a humidity of 50% for one day and night for humidity conditioning, cut into a width of 1.5 cm, and then a tensile test was performed using a Tensilon universal testing machine. The test was carried out under the conditions of a sample distance of 5 cm and a speed of 1 cm / min to obtain an elongation rate correlated with the coating film strength.

[0089] In addition, using the binders for electrodes 1 to 3, 6 to 11 obtained in the examples and comparative examples, the evaluation of the electrode composition was performed as follows.

[0090] <Coatability of Electrode Composition> The slurry obtained when preparing the negative electrode plates in each example and comparative example was coated on a copper foil, and after drying, the coated surface after roll pressing was visually confirmed and evaluated according to the following criteria. A: There are no aggregates or coating peeling on the slurry-coated surface of the copper foil, and there is no coating unevenness at all. B: Aggregates or coating peeling are observed on a part of the slurry-coated surface of the copper foil, but there is no problem when used in a battery. C: Aggregates, coating peeling, coating unevenness, etc. are observed over the entire slurry-coated surface of the copper foil.

[0091] In addition, using the coin-type non-aqueous electrolyte secondary batteries obtained in Examples 1 to 3, 7, 9, 10 and Comparative Examples 1 to 2, the batteries were evaluated as follows.

[0092] <Battery Evaluation> (Discharge Capacity (Charge-Discharge Rate Test)) The charge-discharge rate test of the coin-type non-aqueous electrolyte secondary batteries obtained in the examples and comparative examples was carried out using BTS2004 of Nagano Corporation in a constant temperature bath at 25°C. Using the coin-type non-aqueous electrolyte secondary battery, the charge-discharge performed in the order of charge treatment - discharge treatment was regarded as 1 cycle, and 52 cycles were carried out. As the conditions for the charge treatment, in all cycles, the constant current constant voltage (CC-CV) method (CC current 0.2C, CV voltage 4.2V, termination current 0.02C) was used. As the conditions for the discharge treatment, the termination voltage was set to 3.0V. In the first cycle, the constant current of the discharge treatment was carried out at 0.2C, and after discharge, the discharge capacity (mAh / g) after 1 cycle was measured. Up to the 52nd cycle thereafter, the constant current of the discharge treatment was set as follows, and the discharge capacity (mAh / g) was measured after discharge in each cycle. (Constant Current of Discharge Treatment in Each Cycle) 2 to 10 cycles: Constant current of discharge treatment 0.2C 11 to 20 cycles: Constant current of discharge treatment 1C 21st cycle: Constant current of discharge treatment 0.2C 22 to 31 cycles: Constant current of discharge treatment 2C 32nd cycle: Constant current of discharge treatment 0.2C 33 to 42 cycles: Constant current of discharge treatment 3C 43 to 52 cycles: Constant current of discharge treatment 0.2C

[0093] (Capacity retention rate) The capacity retention rate is calculated from the discharge capacity (mAh / g) in each of the cycle tests described above, using the formula "Capacity retention rate = Discharge capacity (mAh / g) after 1 cycle / Discharge capacity (mAh / g) after 52 cycles × 100".

[0094] (Example 1) (Preparation of electrode binder) To a twin-screw kneader with the rotation speed adjusted to 100 rpm, 2720 g of isopropyl alcohol, 170 g of sodium monochloroacetate, and a solution of 58 g of sodium hydroxide dissolved in 480 g of water were added, and 160 g of lint pulp was charged based on the dry weight when dried at 30 °C for 60 minutes. After stirring and mixing at 30 °C for 90 minutes to prepare mercerized cellulose, the temperature was raised to 70 °C and a carboxymethylation reaction was carried out for 90 minutes. After the reaction, it was neutralized with acetic acid to a pH of about 7, de-liquored, dried, and pulverized to obtain a sodium salt of carboxymethyl cellulose (hereinafter sometimes referred to as "CMC1") having a carboxymethyl substitution degree of 0.70, a viscosity of 7,900 mPa·s for a 1 mass% aqueous solution measured with a B-type viscometer at 25 °C, and a filtration residue of 48 ppm with respect to the dry weight of the carboxymethyl cellulose dissolved in the aqueous solution. 100 mass% of citric acid (manufactured by Fujifilm Wako Pure Chemical Corporation) with respect to the above-mentioned sodium carboxymethyl cellulose and sodium carboxyethyl cellulose was measured into a 300 mL glass beaker, and distilled water was added to prepare an aqueous dispersion so that the solid content concentration of the carboxymethyl cellulose became 2% (w / v). The aqueous dispersion was stirred at 500 rpm for 1 hour using a stirrer at 25 °C to obtain Electrode Binder 1.

[0095] (Preparation of negative electrode plate) As a negative electrode material, SiOx, acetylene black (manufactured by Strem Chemicals), binder 1 for electrodes, and styrene-butadiene rubber (SBR, manufactured by JSR, product number S2910(E)-12-Na) were mixed so that the solid content weight ratio was 97:0.5:1.0:1.5, water was added so that the slurry concentration became 45.6 mass%, and it was stirred well using a Maelstrom (manufactured by Kurashiki Boseki, KK-250S) to obtain Slurry 1. This slurry was applied to a copper foil (manufactured by Furukawa Electric Co., Ltd., NC-WS) with a size of 320 mm in length × 170 mm in width × 17 μm in thickness using an applicator, air-dried for 30 minutes, and then dried at 60 °C for 30 minutes in a dryer. Further, using a small bench-top 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 62.9 g / m 2 , and a negative electrode plate 1 with a discharge effective capacity of 330 mAh / g was obtained.

[0096] <Fabrication of Coin-Type Non-Aqueous Electrolyte Secondary Battery> The obtained negative electrode plate 1 and a LiCoO2 positive electrode plate (manufactured by Hozen Co., Ltd., basis weight 110.2 g / m 2 , discharge effective capacity 145 mAh / g) were punched into a circular shape with a diameter of 16 mm, and the punched negative electrode plate and positive electrode plate were vacuum-dried at 120 °C for 12 hours.

[0097] Similarly, a separator (manufactured by CS Tech, polypropylene separator with a thickness of 20 μm) was punched into a circular shape with a diameter of 17 mm and vacuum-dried at 60 °C for 12 hours.

[0098] Thereafter, the negative electrode plate 1 was placed in a stainless steel circular dish-shaped container with a diameter of 20.0 mm, and then a separator, a positive electrode plate, a spacer (diameter 15.5 mm, thickness 1 mm), and a stainless steel washer (manufactured by Hozen Co., Ltd.) were laminated in this order. Then, 300 μL of an electrolytic solution (1 mol / L LiPF6, volume ratio of ethylene carbonate to diethyl carbonate 1:1) was added to the circular dish-shaped container. A stainless steel cap was placed over this through a polypropylene packing and sealed with a coin battery caulking machine (manufactured by Hozen Co., Ltd.) to obtain a coin-type non-aqueous electrolyte secondary battery 1.

[0099] (Example 2) To a twin-screw kneader with the rotation speed adjusted to 100 rpm, 170 g of sodium monochloroacetate and 58 g of sodium hydroxide dissolved in 480 g of water were added, and 160 g of softwood pulp (manufactured by Nippon Paper Industries Co., Ltd., NDP-T) was charged based on the dry weight when dried at 30 °C for 60 minutes. Stirring and mixing were carried out at 30 °C for 90 minutes to prepare mercerized cellulose. While further stirring, 2720 g of isopropyl alcohol 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 completion of the reaction, it was neutralized with acetic acid to a pH of about 7, de-liquored, dried, and pulverized to obtain a sodium salt of carboxymethyl cellulose with a degree of carboxymethyl substitution of 0.80 and a viscosity of 17,260 mPa·s for a 1 mass% aqueous solution measured with a B-type viscometer at 25 °C. 300 mL of citric acid (manufactured by Fujifilm Wako Pure Chemical Corporation) at 100 mass% with respect to the above-mentioned sodium carboxymethyl cellulose salt was measured into a 300 mL glass beaker, and distilled water was added to prepare an aqueous dispersion so that the solid content concentration of carboxymethyl cellulose was 2% (w / v). The electrode binder 2 was obtained by stirring the aqueous dispersion at 25 °C for 1 hour at 500 rpm using a stirrer.

[0100] A slurry, a negative electrode plate, and a coin-type nonaqueous electrolyte secondary battery were prepared in the same manner as in Example 1, except that the electrode binder 2 was used instead of the electrode binder 1.

[0101] (Example 3) Commercially available carboxymethyl cellulose (the Brookfield viscosity of a 1% by mass aqueous solution at 25°C is 4,700 mPa·s, the degree of carboxymethyl substitution is 0.70, product name "Sunrose" manufactured by Nippon Paper Chemicals Co., Ltd.) and 100% by mass of citric acid (manufactured by Fujifilm Wako Pure Chemical Corporation) with respect to carboxymethyl cellulose were measured into a 300 mL glass beaker, and distilled water was added so that the solid content concentration of carboxymethyl cellulose became 2% (w / v) to prepare an aqueous dispersion. Further, iron(II) sulfate heptahydrate (manufactured by Fujifilm Wako Pure Chemical Corporation) was added so as to be 50% by mass with respect to carboxymethyl cellulose, and the aqueous dispersion was stirred at 500 rpm for 1 hour at 25°C using a stirrer to obtain a binder for electrode 3.

[0102] A slurry, a negative electrode plate, and a coin-type nonaqueous electrolyte secondary battery were produced in the same manner as in Example 1, except that binder for electrode 3 was used instead of binder for electrode 1.

[0103] (Example 4) A binder for electrode 4 was obtained in the same manner as in Example 1, except that malic acid (manufactured by Fujifilm Wako Pure Chemical Corporation) was used instead of citric acid.

[0104] (Example 5) A binder for electrode 5 was obtained in the same manner as in Example 1, except that succinic acid (manufactured by Fujifilm Wako Pure Chemical Corporation) was used instead of citric acid.

[0105] (Example 6) A binder for electrode 6 was obtained in the same manner as in Example 1, except that sodium citrate (manufactured by Fujifilm Wako Pure Chemical Corporation) was used instead of citric acid. Also, a slurry was prepared in the same manner as in Example 1, except that binder for electrode 6 was used instead of binder for electrode 1.

[0106] (Example 7) Electrode binder 7 was obtained in the same manner as in Example 1, except that calcium gluconate (manufactured by Fujifilm Wako Pure Chemical Corporation) was used instead of citric acid. Further, a slurry, a negative electrode plate, and a coin-type nonaqueous electrolyte secondary battery were produced in the same manner as in Example 1, except that electrode binder 7 was used instead of electrode binder 1.

[0107] (Example 8) The above-mentioned CMC1 and 100% by mass of lithium citrate (manufactured by Fujifilm Wako Pure Chemical Corporation) with respect to CMC1 were weighed into a 300 mL glass beaker, and distilled water was added so that the solid content concentration of carboxymethyl cellulose became 2% (w / v) to prepare an aqueous dispersion. The electrode binder 8 was obtained by stirring the aqueous dispersion at 25 °C for 1 hour at 500 rpm using a stirrer.

[0108] A slurry was prepared in the same manner as in Example 1, except that electrode binder 8 was used instead of electrode binder 1.

[0109] (Example 9) Electrode binder 9 was obtained in the same manner as in Example 8, except that 10% by mass of lithium citrate with respect to CMC1 was used. Further, a slurry, a negative electrode plate, and a coin-type nonaqueous electrolyte secondary battery were produced in the same manner as in Example 1, except that electrode binder 9 was used instead of electrode binder 1.

[0110] (Example 10) To a twin-screw kneader with the rotation speed adjusted to 100 rpm, 1000 g of isopropyl alcohol, 240 g of sodium monochloroacetate, and 83 g of sodium hydroxide dissolved in 120 g of water were added, and 160 g of linter pulp was charged based on the dry weight when dried at 30°C for 60 minutes. After stirring and mixing at 30°C for 90 minutes to prepare mercerized cellulose, 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 a sodium salt of carboxymethylated cellulose with a carboxymethyl substitution degree of 1.34, a viscosity of 2,800 mPa·s for a 1 mass% aqueous solution measured with a B-type viscometer at 25°C, and a filtration residue of 46 ppm based on the dry weight of the carboxymethyl cellulose dissolved in the aqueous solution. 150 mass% of lithium citrate (manufactured by Fujifilm Wako Pure Chemical Corporation) with respect to the above-mentioned sodium carboxymethyl cellulose and sodium carboxyethyl cellulose was weighed into a 300 mL glass beaker, and distilled water was added to prepare an aqueous dispersion so that the solid content concentration of the carboxymethyl cellulose was 2% (w / v). The electrode binder 10 was obtained by stirring the aqueous dispersion at 25°C for 1 hour at 500 rpm using a stirrer.

[0111] A slurry, a negative electrode plate, and a coin-type nonaqueous electrolyte secondary battery were prepared in the same manner as in Example 1, except that the electrode binder 10 was used instead of the electrode binder 1.

[0112] (Comparative Example 1) An electrode binder 11 was obtained in the same manner as in Example 1, except that citric acid was not added. Also, a slurry, a negative electrode plate, and a coin-type nonaqueous electrolyte secondary battery were prepared in the same manner as in Example 1, except that the electrode binder 11 was used instead of the electrode binder 1.

[0113] (Comparative Example 2) An electrode binder 12 was obtained in the same manner as in Example 1, except that sodium fumarate (manufactured by Fujifilm Wako Pure Chemical Corporation) was used instead of citric acid. Also, a slurry, a negative electrode plate, and a coin-type nonaqueous electrolyte secondary battery were prepared in the same manner as in Example 1, except that the electrode binder 12 was used instead of the electrode binder 1.

[0114] The measurement and evaluation results for the examples and comparative examples are shown in Table 1 below. [Table 1]

[0115] As shown in Table 1, the electrode binder for non-aqueous electrolyte secondary batteries, which contains Component A: carboxymethylcellulose or a salt thereof having a carboxymethyl substitution degree per anhydroglucose unit of 0.45 or more, and Component B: a saturated carboxylic acid or a salt thereof having 6 or less carbon atoms, has excellent solubility and a good elongation rate when formed into a film. In addition, a composition (slurry) using this electrode binder has excellent coatability. Furthermore, a non-aqueous electrolyte secondary battery using this electrode binder in a negative electrode plate has excellent capacity retention.

Claims

1. Component A: Carboxymethyl cellulose or a salt thereof having a carboxymethyl substitution degree of 0.45 or more per anhydrous glucose unit, and Component B: At least one selected from aliphatic hydroxy acids that are saturated acids having 6 or fewer carbon atoms, aromatic hydroxy acids that are saturated acids having 6 or fewer carbon atoms, saturated dicarboxylic acids having 6 or fewer carbon atoms, and saturated tricarboxylic acids having 6 or fewer carbon atoms, or a salt thereof, The carboxymethyl cellulose or a salt thereof has a viscosity of 1,000 to 20,000 mPa·s for a 1% by mass aqueous solution measured with a B-type viscometer (30 rpm) at 25°C, A binder for a non-aqueous electrolyte secondary battery electrode, wherein the component B is contained in the range of 1 to 200 parts by weight with respect to 100 parts by weight of the component A.

2. The binder for a non-aqueous electrolyte secondary battery electrode according to claim 1, wherein the component B contains at least a lithium salt of a saturated carboxylic acid having 6 or fewer carbon atoms.

3. The binder for a non-aqueous electrolyte secondary battery electrode according to claim 1 or 2, characterized by satisfying the following condition (I). Condition (I): When the component A is carboxymethyl cellulose or a salt thereof having a carboxymethyl substitution degree of 0.45 or more and 1.0 or less, The component B is contained in the range of 1 to 100 parts by weight with respect to 100 parts by weight of the component A.

4. The binder for a non-aqueous electrolyte secondary battery electrode according to claim 1 or 2, characterized by satisfying the following condition (II). Condition (II): When the component A is carboxymethyl cellulose or a salt thereof having a carboxymethyl substitution degree exceeding 1.0, The component B is contained in the range of 1 to 200 parts by weight with respect to 100 parts by weight of the component A.

5. The binder for a non-aqueous electrolyte secondary battery electrode according to any one of claims 1 to 4, wherein the component B is a lithium salt of a hydroxy acid having 6 or fewer carbon atoms.

6. The binder for a non-aqueous electrolyte secondary battery electrode according to any one of claims 1 to 5, wherein the component B is a lithium citrate salt.

7. The binder for a non-aqueous electrolyte secondary battery electrode according to any one of claims 1 to 6, wherein the carboxymethyl cellulose or a salt thereof has a volume cumulative 100% particle diameter of less than 100 μm measured with a laser diffraction / scattering particle size distribution analyzer using methanol as a dispersion medium.

8. The carboxymethyl cellulose or a salt thereof has a cumulative volume particle diameter of less than 50 μm as measured by a laser diffraction / scattering particle size distribution analyzer using methanol as a dispersion medium, and is a binder for a non-aqueous electrolyte secondary battery electrode according to claim 1 or 7.

9. The binder for a non-aqueous electrolyte secondary battery electrode according to claim 1 or 8, wherein the component B is contained in a range of 10 to 120% by weight with respect to the component A.

10. The carboxymethyl cellulose or a salt thereof is prepared by preparing 2 liters of a 0.3% by mass aqueous solution of the carboxymethyl cellulose or a salt thereof with a dry mass m, filtering all of it with a 250-mesh filter under a reduced pressure condition of -200 mmHg, and measuring the dry mass M of the residue on the filter after filtration. When the ratio of the dry mass M to the dry mass m is less than 50 ppm, the binder for a non-aqueous electrolyte secondary battery electrode according to any one of claims 1 to 9.

11. The carboxymethyl cellulose or a salt thereof is a mechanically pulverized product, and is a binder for a non-aqueous electrolyte secondary battery electrode according to any one of claims 1 to 10.

12. An aqueous solution containing the binder for a non-aqueous electrolyte secondary battery electrode according to any one of claims 1 to 11.

13. The aqueous solution according to claim 12, which has a pH in the range of 2 to 8.

14. An electrode composition for a non-aqueous electrolyte secondary battery containing the aqueous solution according to claim 12 or 13.

15. The electrode composition for a non-aqueous electrolyte secondary battery according to claim 14, which contains a silicon-based active material.

16. An electrode for a non-aqueous electrolyte secondary battery formed from the electrode composition according to claim 14 or 15.

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