Method for producing a slurry composition for secondary battery electrodes, and method for producing secondary battery electrodes and secondary batteries.

Abstract

The present invention provides a production method for a slurry composition that makes it possible to obtain a secondary battery electrode which, in a case where said composition for a secondary battery electrode has a higher-than-conventional solid content concentration, preserves coatability as a result of said composition having reduced viscosity, and which exhibits excellent peel strength (adhesiveness).　This production method comprises: a step A for kneading a composition that has a 60-80 mass% solid content concentration and comprises an active material, a thickener, and water into a paste to obtain a first thick paste product; a step B for adding a hydrophilic binder (different from the thickener) and water to the first thick paste product and kneading to a paste to obtain a second thick paste product; and a step C for adjusting the solid content concentration of the second thick paste product to 40-60 mass%.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a slurry composition for a secondary battery electrode, and methods for manufacturing a secondary battery electrode and a secondary battery.

Background Art

[0002] As secondary batteries, various power storage devices such as nickel-metal hydride secondary batteries, lithium-ion secondary batteries, and electric double layer capacitors have been put into practical use. Electrodes used in these secondary batteries are produced by applying and drying a composition for forming an electrode mixture layer containing an active material, a binder, etc. on a current collector. For example, in a lithium-ion secondary battery, an aqueous binder containing styrene-butadiene rubber (SBR) latex and carboxymethyl cellulose (CMC) is used as the binder used in the negative electrode slurry composition. On the other hand, as the binder used in the positive electrode mixture layer, an N-methyl-2-pyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) is widely used.

[0003] Generally, a secondary battery electrode is obtained by applying and drying a slurry composition for a secondary battery electrode (hereinafter, also referred to as "electrode slurry") containing an active material, a thickener, and a binder on the surface of an electrode current collector. At this time, from the viewpoint of increasing the drying efficiency of the electrode slurry and improving the productivity of the electrode, it is advantageous to increase the solid content concentration of the slurry composition for the secondary battery electrode, but it becomes difficult to ensure good coating properties.

[0004] As a method for manufacturing a slurry composition for a secondary battery electrode having a high solid content concentration, for example, in Patent Document 1, a negative electrode active material, CMC, and water are kneaded to generate a primary kneaded body (solid content concentration: 70% by mass or less), and further, water is added to the primary kneaded body for dilution, and a binder is further added to generate a negative electrode paste for manufacturing a negative electrode. A method for manufacturing a non-aqueous electrolyte secondary battery including the steps is described. Patent Document 1 specifically discloses a method for producing a slurry composition for a negative electrode (hereinafter also referred to as "negative electrode slurry") using CMC as a thickening agent and SBR as an aqueous binder. It states that, in order to produce a non-aqueous electrolyte secondary battery with excellent output characteristics and cycle characteristics, peel strength can be ensured while using high-viscosity CMC in the negative electrode.

[0005] Furthermore, Patent Document 2 describes a method for producing a paste for manufacturing a negative electrode, comprising the steps of: (A) preparing a mixture (M1) containing at least the negative electrode active material and the first thickener by mixing the negative electrode active material and the first thickener; (B) preparing a paste precursor by wet mixing one or more liquid components selected from an emulsion aqueous solution containing an aqueous medium and an aqueous binder into the mixture (M1); and (C) preparing a paste for manufacturing a negative electrode by further adding the liquid components to the paste precursor and wet mixing. The step (B) includes at least the steps of: (B1) obtaining a mixture (M2) by incorporating the liquid components into the mixture (M1); (B2) obtaining a mixture (M3) by mixing the second thickener and the liquid components into the mixture (M2); and (B3) obtaining the paste precursor by kneading the mixture (M3) to solidify it. Patent Document 2 specifically discloses a method for producing a negative electrode slurry composition (negative electrode slurry) with a solid content of 51% by mass, using CMC as a thickening agent and SBR as an aqueous binder, and states that it is possible to stably obtain a negative electrode for batteries with excellent adhesion between the current collector layer and the negative electrode active material layer.

[0006] Furthermore, Patent Document 3 describes a multi-stage process comprising at least a first solid mixing step (solid content concentration: 68% to 79% by mass) and a second solid mixing step (solid content concentration: 59% to 66% by mass) in which a plurality of powdered materials containing at least a negative electrode active material and a thickener are dry-mixed in a powder state, and then an aqueous medium and an aqueous solution containing an aqueous binder are added and wet-mixed. Patent Document 3 specifically discloses a method for producing a negative electrode slurry composition (negative electrode slurry) with a solid content of 59-66% by mass, using CMC as a thickening agent and SBR as an aqueous binder. It states that the viscosity of the negative electrode slurry can be controlled within a certain range, and a secondary battery negative electrode with excellent adhesion between the negative electrode active material layer and the current collector layer can be stably obtained. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2014-11075 [Patent Document 2] Japanese Patent Publication No. 2019-164887 [Patent Document 3] International Publication No. 2019 / 107054 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In recent years, with the improvement of performance and productivity of secondary batteries, there has been a growing demand for further improvements in the coating properties of slurry compositions for secondary battery electrodes (electrode slurries), and the adhesion between the electrode active material layer and the current collector layer (hereinafter also referred to as "peel strength").

[0009] Although the manufacturing methods described in Patent Documents 1 and 2 can impart good peel strength, they do not show any relationship between the manufacturing method and the viscosity and coating properties of the electrode slurry. Furthermore, the manufacturing method described in Patent Document 3 is described as being able to impart good coating properties and peel strength. However, in the manufacturing methods described in Patent Documents 1 to 3, when a slurry composition for secondary battery electrodes is manufactured using a binder that is more hydrophilic than SBR as the aqueous binder, the viscosity of the composition tends to increase, resulting in the problem that it is not possible to achieve both coating properties and peel strength for the electrode slurry.

[0010] The present invention has been made in view of the above circumstances, and its object is to provide a method for producing a slurry composition for secondary battery electrodes that, when the solid content concentration of the slurry composition is higher than conventional methods, can produce a secondary battery electrode that exhibits excellent peel strength (binding properties) while ensuring coating properties by reducing the viscosity of the slurry composition. Furthermore, the present invention also provides a method for producing a secondary battery electrode using the above slurry composition and a method for producing a secondary battery. [Means for solving the problem]

[0011] As a result of diligent research to solve the above problems, the present inventors have found that by employing a method for producing a slurry composition for secondary battery electrodes, which includes the steps of: obtaining a first solid product by kneading a composition containing an active material, a thickener, and water, having a solid content concentration within a specific range; obtaining a second solid product by adding a hydrophilic binder and water to the first solid product and kneading it; and adjusting the solid content concentration of the second solid product to a specific range, it is possible to obtain a secondary battery electrode that exhibits excellent peel strength (binding properties) while ensuring the coating properties of the slurry composition, and thus the present invention has been completed.

[0012] The present invention is as follows: [1] A method for producing a slurry composition for secondary battery electrodes, comprising: step A, kneading a composition containing an active material, a thickener, and water with a solid content concentration of 60 to 80% by mass to obtain a first solid paste; step B, adding a hydrophilic binder (different from the thickener) and water to the first solid paste and kneading to obtain a second solid paste; and step C, adjusting the solid content concentration of the second solid paste to 40 to 60% by mass. [2] The method for producing a slurry composition for secondary battery electrodes according to [1], wherein step B includes step B1, in which an aqueous solution of the hydrophilic binder is added to the first solid paste and kneaded to obtain a second solid paste. [3] The method for producing a slurry composition for secondary battery electrodes according to [1], wherein step B includes step B2 of adding the hydrophilic binder to the first solid paste and kneading it, and step B3 of further adding water and kneading it to obtain a second solid paste. [4] The method for producing a slurry composition for secondary battery electrodes according to any one of [1] to [3], wherein the hydrophilic binder is obtained by polymerizing a monomer component containing an ethylenically unsaturated carboxylic acid monomer, and the monomer component contains 50% by mass or more and 100% by mass or less of the ethylenically unsaturated carboxylic acid monomer based on its total amount. [5] A method for producing a slurry composition for secondary battery electrodes according to any one of [1] to [4], wherein the hydrophilic binder is crosslinked with a crosslinkable monomer, and the amount of the crosslinkable monomer used is 0.001 mol% or more and 2.5 mol% or less relative to the total amount of non-crosslinkable monomers. [6] A method for producing a slurry composition for secondary battery electrodes according to any one of [1] to [5], wherein the hydrophilic binder has a degree of neutralization of 80 to 100 mol%. [7] A method for producing a slurry composition for secondary battery electrodes according to any one of [1] to [6], wherein the thickening agent comprises carboxymethylcellulose (CMC). [8] A method for producing a slurry composition for secondary battery electrodes according to any one of [1] to [7], wherein step C includes a step of adding styrene-butadiene rubber (SBR) latex. [9] A method for manufacturing a secondary battery electrode, comprising the step of forming a composite layer on the surface of a current collector, which is formed from a slurry composition for secondary battery electrodes obtained by the manufacturing method described in any one of [1] to [8]. A method for manufacturing a secondary battery, comprising a step of manufacturing a secondary battery equipped with secondary battery electrodes obtained by the manufacturing method described in

[10] and [9]. [Effects of the Invention]

[0013] According to the method for producing a slurry composition for secondary battery electrodes of the present invention, when the solid content concentration of the slurry composition is higher than conventional methods, it is possible to obtain a secondary battery electrode that exhibits excellent peel strength (binding properties) while ensuring coating properties by reducing the viscosity of the slurry composition. [Modes for carrying out the invention]

[0014] The slurry composition for a secondary battery electrode of the present invention contains a thickener, an active material, a hydrophilic binder, and water. The above slurry composition is in a slurry state that can be applied to a current collector. A secondary battery electrode of the present invention is obtained by forming a combined agent layer formed from the above composition on the surface of a current collector such as a copper foil or an aluminum foil. Here, the hydrophilic binder is preferable in that the effects exhibited by the present invention are particularly great when used in a slurry composition for a secondary battery electrode containing a silicon-based active material described later as an active material.

[0015] Hereinafter, each of the thickener, the active material, the hydrophilic binder, other components, a method for producing a slurry composition for a secondary battery electrode, a method for producing a secondary battery electrode obtained using the composition, and a method for producing a secondary battery will be described in detail. In addition, in this specification, “(meth)acrylic” means acrylic and / or methacrylic, and “(meth)acrylate” means acrylate and / or methacrylate. Further, “(meth)acryloyl group” means acryloyl group and / or methacryloyl group.

[0016] 1. Thickening agent The thickener is not particularly limited as long as it improves the coating property of the slurry composition for a secondary battery electrode (however, it is different from the hydrophilic binder according to the present invention). Examples of the thickener include cellulose-based water-soluble polymers, a substituted product obtained by substituting a cellulose-based water-soluble polymer with a carboxymethyl group or a salt thereof (hereinafter, the substituted product or its salt is also collectively referred to as “CMC”), alginic acid or its salt, oxidized starch, phosphorylated starch, casein, starch, and the like. Among these, CMC is preferable in terms of easily obtaining an electrode slurry having excellent coating property by adsorbing to the active material, and being able to obtain a secondary battery electrode that exhibits excellent peel strength (binding property).

[0017] Here, specific examples of the cellulose-based water-soluble polymer include alkyl celluloses such as methyl cellulose, methyl ethyl cellulose, ethyl cellulose, and microcrystalline cellulose; Examples include hydroxyethylcellulose, hydroxybutylmethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose stearoxy ether, carboxymethylhydroxyethylcellulose, alkylhydroxyethylcellulose, nonoxynylhydroxyethylcellulose, and other hydroxyalkylcelluloses.

[0018] 2.Active material As the positive electrode active material, lithium salts of transition metal oxides can be used, for example, layered rock salt type and spinel type lithium-containing metal oxides can be used. Specific compounds of the layered rock salt type positive electrode active material include lithium cobaltate, lithium nickelate, and NCM{Li(Ni}, which are called ternary systems. x Co y ,Mn z ), x+y+z=1} and NCA{Li(Ni 1-a-b Co a Al b Examples include )}. In addition, lithium manganate is an example of a spinel-type positive electrode active material. Besides oxides, phosphates, silicates, and sulfur can also be used, and examples of phosphates include olivine-type lithium iron phosphate. As a positive electrode active material, one of the above may be used alone, or two or more may be combined and used as a mixture or composite.

[0019] Furthermore, when a positive electrode active material containing layered rock salt-type lithium-containing metal oxide is dispersed in water, the dispersion becomes alkaline due to the exchange of lithium ions on the surface of the active material with hydrogen ions in the water. This may cause corrosion of common positive electrode current collector materials such as aluminum foil (Al). In such cases, it is preferable to neutralize the alkali leaching from the active material by using an unneutralized or partially neutralized polymer as a hydrophilic binder. It is also preferable to use an amount of the unneutralized or partially neutralized polymer such that the amount of unneutralized carboxyl groups in the polymer is equivalent to or greater than the amount of alkali leaching from the active material.

[0020] Since all positive electrode active materials have low electrical conductivity, they are generally used with the addition of a conductive additive. Examples of conductive additives include carbon-based materials such as carbon black, carbon nanotubes, carbon fibers, graphite powder, and carbon fibers. Of these, carbon black, carbon nanotubes, and carbon fibers are preferred because they easily provide excellent conductivity. Ketjenblack and acetylene black are preferred as carbon blacks. One of the above conductive additives may be used alone, or two or more may be used in combination. From the viewpoint of balancing conductivity and energy density, the amount of conductive additive used can be, for example, 0.2 to 20 parts by mass, or for example, 0.2 to 10 parts by mass, per 100 parts by mass of the total amount of active material. In addition, the positive electrode active material may be surface-coated with a conductive carbon-based material.

[0021] On the other hand, examples of negative electrode active materials include carbon-based materials, lithium metal, lithium alloys, and metal oxides, and one or more of these can be used in combination. Among these, active materials made of carbon-based materials such as natural graphite, artificial graphite, hard carbon, and soft carbon (hereinafter also referred to as "carbon-based active materials") are preferred, with graphite such as natural graphite and artificial graphite, and hard carbon being more preferred. In the case of graphite, spheroidized graphite is preferably used in terms of battery performance, and the preferred range of particle size is, for example, 1 to 20 μm, or for example, 5 to 15 μm. Furthermore, in order to increase the energy density, metals or metal oxides that can absorb lithium, such as silicon and tin, can also be used as negative electrode active materials. Among these, silicon has a higher capacity than graphite, and active materials made of silicon-based materials such as silicon, silicon alloys, and silicon oxides such as silicon monoxide (SiO) (hereinafter also referred to as "silicon-based active materials") can be used. However, while the silicon-based active material has high capacity, it undergoes large volume changes during charging and discharging. For this reason, it is preferable to use it in combination with the carbon-based active material. In this case, if the amount of silicon-based active material is too high, it can lead to the breakdown of the electrode material, and the cycle characteristics (durability) may be greatly reduced. From this perspective, when using silicon-based active material in combination, the amount used should be, for example, 60% by mass or less, or for example, 30% by mass or less, relative to the carbon-based active material.

[0022] Since carbon-based active materials possess good electrical conductivity on their own, it is not always necessary to add conductive additives. When conductive additives are added for purposes such as further reducing resistance, the amount used, from the perspective of energy density, should be, for example, 10 parts by mass or less, or for example, 5 parts by mass or less, per 100 parts by mass of the total amount of active material.

[0023] 3. Hydrophilic binder The hydrophilic binder used in the present invention has structural units derived from a hydrophilic vinyl monomer, and the monomer can be any radically polymerizable hydrophilic vinyl monomer, and is not particularly limited (however, it is different from the thickener mentioned above). Furthermore, the hydrophilic binder used in the present invention may be a crosslinked polymer (hereinafter also referred to as "the crosslinked polymer") or a non-crosslinked polymer (hereinafter also referred to as "the non-crosslinked polymer"). The crosslinked polymer and the non-crosslinked polymer may be used individually or in combination. In addition, one type of the crosslinked polymer or the non-crosslinked polymer may be used individually, or two or more types may be used in combination. Here, as the hydrophilic vinyl monomer, for example, a hydrophilic vinyl monomer having a polar group such as a carboxyl group, amide group, amino group, phosphate group, sulfonic acid group, hydroxyl group, quaternary ammonium group, or salts thereof (including partially and completely neutralized products) can be used.

[0024] Among these, hydrophilic vinyl monomers having carboxyl groups (hereinafter also referred to as "ethylenically unsaturated carboxylic acid monomers") are preferred because they improve adhesion to the current collector, and have excellent desolvation effect and ionic conductivity for lithium ions, resulting in electrodes with low resistance and excellent high-rate characteristics. Examples of ethylenically unsaturated carboxylic acid monomers include (meth)acrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid; (meth)acrylamide alkyl carboxylic acids such as (meth)acrylamidehexanoic acid and (meth)acrylamidedodecanoic acid; ethylenically unsaturated monomers having carboxyl groups such as monohydroxyethyl (meth)acrylate succinate, ω-carboxy-caprolactone mono(meth)acrylate, and β-carboxyethyl (meth)acrylate, or their (partially) alkali neutralized products. One of these may be used alone, or two or more may be used in combination. Among the above, compounds having an acryloyl group as a polymerizable functional group are preferred because they yield polymers with long primary chain lengths due to their high polymerization rate and good binding strength of hydrophilic binders, and acrylic acid is particularly preferred. When acrylic acid is used as the ethylenically unsaturated carboxylic acid monomer, polymers with a high carboxyl group content can be obtained.

[0025] Furthermore, hydrophilic vinyl monomers having an amide group (hereinafter also referred to as "amide group-containing ethylenically unsaturated monomers") are preferred because they exhibit excellent binding properties for hydrophilic binders. Examples of amide group-containing ethylenically unsaturated monomers include N-alkyl(meth)acrylamide compounds such as isopropyl(meth)acrylamide and t-butyl(meth)acrylamide; N-alkoxyalkyl(meth)acrylamide compounds such as Nn-butoxymethyl(meth)acrylamide and N-isobutoxymethyl(meth)acrylamide; N,N-dialkyl(meth)acrylamide compounds such as dimethyl(meth)acrylamide and diethyl(meth)acrylamide; and cyclic(meth)acrylamide compounds such as N-acryloylmorpholine. One of these may be used alone, or two or more may be used in combination. Among the above, N-acryloylmorpholine is preferred because it is easy to obtain high molecular weight polymers and has excellent binding properties.

[0026] 3-1. This cross-linked polymer This section describes crosslinked polymers when ethylenically unsaturated carboxylic acid monomers are used as hydrophilic vinyl monomers. <Structural units derived from ethylenically unsaturated carboxylic acid monomers> The crosslinked polymer contained in this hydrophilic binder may contain 50% to 100% by mass of structural units derived from ethylenically unsaturated carboxylic acid monomers (hereinafter also referred to as "component (a1)"). When the crosslinked polymer has carboxyl groups due to the presence of such structural units, adhesion to the current collector is improved, and the desolvation effect of lithium ions and ionic conductivity are excellent, resulting in electrodes with low resistance and excellent high-rate characteristics. In addition, water swelling properties are imparted, which can improve the dispersion stability of active materials in this slurry composition. The above component (a1) can be introduced into the polymer, for example, by polymerizing a monomer containing an ethylenically unsaturated carboxylic acid monomer. Alternatively, it can be obtained by (co)polymerizing a (meth)acrylic acid ester monomer and then hydrolyzing it. Furthermore, (meth)acrylamide and (meth)acrylonitrile may be polymerized and then treated with a strong alkali, or an acid anhydride may be reacted with a polymer having a hydroxyl group.

[0027] Examples of ethylenically unsaturated carboxylic acid monomers include those mentioned above. Among these, compounds having an acryloyl group as a polymerizable functional group are preferred, particularly acrylic acid, because they yield polymers with long primary chain lengths due to their high polymerization rate and good binding strength for hydrophilic binders. When acrylic acid is used as the ethylenically unsaturated carboxylic acid monomer, polymers with a high carboxyl group content can be obtained.

[0028] The content of component (a1) in this crosslinked polymer can be 50% by mass or more and 100% by mass or less relative to the total structural units of the crosslinked polymer. By including component (a1) within this range, excellent adhesion to the current collector can be easily ensured. When the lower limit is 50% by mass or more, the dispersion stability of this slurry composition is good and a higher binding strength can be obtained, which is preferable, and it may be 60% by mass or more, 70% by mass or more, or 80% by mass or more. The upper limit is, for example, 99.9% by mass or less, for example 99.5% by mass or less, for example 99% by mass or less, for example 98% by mass or less, for example 95% by mass or less, for example 90% by mass or less, or for example 80% by mass or less. The range can be a combination of these lower and upper limits as appropriate, for example, 50% by mass or more and 100% by mass or less, or for example, 50% by mass or more and 99.9% by mass or less, or for example, 50% by mass or more and 99% by mass or less, or for example, 50% by mass or more and 98% by mass or less.

[0029] <Other structural units> In addition to component (a1), this crosslinked polymer may contain structural units derived from other ethylenically unsaturated monomers copolymerizable with these components (hereinafter also referred to as "component (b1)"). Examples of component (b1) include structural units derived from ethylenically unsaturated monomer compounds having anionic groups other than carboxyl groups, such as sulfonic acid groups and phosphate groups, or from nonionic ethylenically unsaturated monomers. These structural units can be introduced by copolymerizing monomers containing ethylenically unsaturated monomer compounds having anionic groups other than carboxyl groups, such as sulfonic acid groups and phosphate groups, or nonionic ethylenically unsaturated monomers.

[0030] The proportion of component (b1) can be 0% by mass or more and 50% by mass or less with respect to the total structural units of the crosslinked polymer. The proportion of component (b1) may be 1% by mass or more and 50% by mass or less, 2% by mass or more and 50% by mass or less, 5% by mass or more and 50% by mass or less, or 10% by mass or more and 50% by mass or less. Furthermore, if component (b1) is contained at 1% by mass or more with respect to the total structural units of the crosslinked polymer, the affinity to the electrolyte will improve, and thus an effect of improving lithium ion conductivity can also be expected.

[0031] (b1) Among the above, structural units derived from nonionic ethylenically unsaturated monomers are preferred as components, from the viewpoint of obtaining electrodes with good flexibility. Examples of nonionic ethylenically unsaturated monomers include amide group-containing ethylenically unsaturated monomers, nitrile group-containing ethylenically unsaturated monomers, alicyclic structure-containing ethylenically unsaturated monomers, hydroxyl group-containing ethylenically unsaturated monomers, and the like.

[0032] Examples of amide group-containing ethylenically unsaturated monomers include those mentioned above, and one of these may be used alone or two or more may be used in combination.

[0033] Examples of nitrile group-containing ethylenically unsaturated monomers include (meth)acrylonitrile; cyanoalkyl ester compounds such as cyanomethyl (meth)acrylate and cyanoethyl (meth)acrylate; cyano group-containing unsaturated aromatic compounds such as 4-cyanostyrene and 4-cyano-α-methylstyrene; and vinylidene cyanide. One of these may be used alone, or two or more may be used in combination. Among the above, acrylonitrile is preferred due to its high nitrile group content.

[0034] Examples of ethylenically unsaturated monomers containing alicyclic structures include cycloalkyl (meth)acrylates which may have aliphatic substituents, such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, cyclodecyl (meth)acrylate, and cyclododecyl (meth)acrylate; isobornyl (meth)acrylate, adamantyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and cycloalkyl polyalcohol mono(meth)acrylates such as cyclohexanedimethanol mono(meth)acrylate and cyclodecanedimethanol mono(meth)acrylate. One of these may be used alone, or two or more may be used in combination.

[0035] Examples of hydroxyl group-containing ethylenically unsaturated monomers include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate. One of these may be used alone, or two or more may be used in combination.

[0036] The crosslinked polymer or its salt preferably contains structural units derived from amide group-containing ethylenically monounsaturated monomers, nitrile group-containing ethylenically unsaturated monomers, alicyclic structure-containing ethylenically unsaturated monomers, etc., due to its excellent binding properties for hydrophilic binders. Furthermore, when structural units derived from hydrophobic ethylenically unsaturated monomers with a water solubility of 1 g / 100 ml or less are introduced as component (c), strong interactions with the electrode material can be achieved, and good binding properties to the active material can be exhibited. As a result, a robust and well-integrated electrode mixture layer can be obtained, and therefore, alicyclic structure-containing ethylenically unsaturated monomers are particularly preferred as the "hydrophobic ethylenically unsaturated monomers with a water solubility of 1 g / 100 ml or less" mentioned above.

[0037] The crosslinked polymer or its salt preferably contains structural units derived from hydroxyl group-containing ethylenically unsaturated monomers, in that it improves the cycle characteristics of the resulting secondary battery, and preferably contains 0.5% by mass or more and 50% by mass or less of such structural units, more preferably 2.0% by mass or more and 50% by mass or less, and even more preferably 10.0% by mass or more and 50% by mass or less.

[0038] Furthermore, other nonionic ethylenically unsaturated monomers may be used, for example, (meth)acrylic acid esters. Examples of (meth)acrylic acid esters include alkyl (meth)acrylic acid ester compounds such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Aromatic (meth)acrylic acid ester compounds such as phenyl (meth)acrylate, phenylmethyl (meth)acrylate, and phenylethyl (meth)acrylate; Examples include alkoxyalkyl ester compounds of (meth)acrylates such as 2-methoxyethyl (meth)acrylate and 2-ethoxyethyl (meth)acrylate. One of these may be used alone, or two or more may be used in combination.

[0039] From the viewpoint of adhesion to the active material and cycle characteristics, aromatic (meth)acrylic acid ester compounds can be preferably used. From the viewpoint of further improving lithium ion conductivity and high-rate characteristics, compounds having an ether bond, such as (meth)acrylic acid alkoxyalkyl esters like 2-methoxyethyl (meth)acrylate and 2-ethoxyethyl (meth)acrylate, are preferred, and 2-methoxyethyl (meth)acrylate is more preferred.

[0040] Among nonionic ethylenically unsaturated monomers, compounds having an acryloyl group are preferred because they have a fast polymerization rate, resulting in polymers with long primary chain lengths and good binding strength for hydrophilic binders. Furthermore, among nonionic ethylenically unsaturated monomers, compounds with a homopolymer glass transition temperature (Tg) of 0°C or lower are preferred because they result in good flexural resistance of the resulting electrodes.

[0041] The crosslinked polymer may be in the form of a salt in which some or all of the carboxyl groups contained in the polymer are neutralized. The type of salt is not particularly limited, but examples include alkali metal salts such as lithium salts, sodium salts and potassium salts; alkaline earth metal salts such as magnesium salts, calcium salts and barium salts; other metal salts such as aluminum salts; ammonium salts and organic amine salts. Among these, alkali metal salts and alkaline earth metal salts are preferred because they do not adversely affect battery characteristics, and alkali metal salts are more preferred.

[0042] The polymer is preferably a polymer having a crosslinked structure (the crosslinked polymer). The crosslinking method for the crosslinked polymer is not particularly limited, and examples include the following methods. 1) Copolymerization of crosslinkable monomers 2) Utilizing chain transfer to polymer chains during radical polymerization 3) After synthesizing a polymer having reactive functional groups, a crosslinking agent is added as needed to perform post-crosslinking. Because this polymer has a crosslinked structure, a binder containing the polymer or a salt thereof can have excellent binding strength. Among the above methods, copolymerization of crosslinkable monomers is preferred because it is easy to operate and the degree of crosslinking can be easily controlled.

[0043] <Cross-linkable monomers> Examples of crosslinkable monomers include polyfunctional polymerizable monomers having two or more polymerizable unsaturated groups, and monomers having self-crosslinkable functional groups such as hydrolyzable silyl groups.

[0044] The above-mentioned polyfunctional polymerizable monomers are compounds having two or more polymerizable functional groups such as (meth)acryloyl groups and alkenyl groups in their molecules, and include polyfunctional (meth)acrylate compounds, polyfunctional alkenyl compounds, and compounds having both (meth)acryloyl and alkenyl groups. These compounds may be used individually or in combination of two or more. Among these, polyfunctional alkenyl compounds are preferred because they easily yield a uniform crosslinked structure, and polyfunctional allyl ether compounds having two or more allyl ether groups in their molecules are particularly preferred.

[0045] Examples of polyfunctional (meth)acrylate compounds include di(meth)acrylates of dihydric alcohols such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate; tri(meth)acrylates of trihydric or higher polyhydric alcohols such as trimethylolpropane tri(meth)acrylate, tri(meth)acrylate of trimethylolpropane ethylene oxide modified product, glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate; and bisamides such as methylenebisacrylamide and hydroxyethylenebisacrylamide.

[0046] Examples of polyfunctional alkenyl compounds include polyfunctional allyl ether compounds such as trimethylolpropanediallyl ether, trimethylolpropanetriallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, tetraallyloxyethane, and polyallyl saccharose; polyfunctional allyl compounds such as diallyl phthalate; and polyfunctional vinyl compounds such as divinylbenzene.

[0047] Examples of compounds having both a (meth)acryloyl group and an alkenyl group include allyl (meth)acrylate, isopropenyl (meth)acrylate, butenyl (meth)acrylate, pentenyl (meth)acrylate, and 2-(2-vinyloxyethoxy)ethyl (meth)acrylate.

[0048] Specific examples of monomers having self-crosslinkable functional groups include hydrolyzable silyl group-containing vinyl monomers and N-methylol(meth)acrylamide. These compounds can be used individually or in combination of two or more.

[0049] The hydrolyzable silyl group-containing vinyl monomer is not particularly limited as long as it is a vinyl monomer having at least one hydrolyzable silyl group. Examples include vinyl silanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, and vinyldimethylmethoxysilane; silyl group-containing acrylic acid esters such as trimethoxysilylpropyl acrylate, triethoxysilylpropyl acrylate, and methyldimethoxysilylpropyl acrylate; silyl group-containing methacrylic acid esters such as trimethoxysilylpropyl methacrylate, triethoxysilylpropyl methacrylate, methyldimethoxysilylpropyl methacrylate, and dimethylmethoxysilylpropyl methacrylate; silyl group-containing vinyl ethers such as trimethoxysilylpropyl vinyl ether; and silyl group-containing vinyl esters such as vinyl trimethoxysilylundecanoate.

[0050] When the crosslinked polymer is crosslinked with a crosslinkable monomer, the amount of the crosslinkable monomer used is preferably 0.01 parts by mass or more and 5.0 parts by mass or less, more preferably 0.05 parts by mass or more and 5.0 parts by mass or less, even more preferably 0.1 parts by mass or more and 3.0 parts by mass or less, and even more preferably 0.2 parts by mass or more and 2.0 parts by mass or less, based on 100 parts by mass of the total amount of monomers other than the crosslinkable monomer (non-crosslinkable monomer). Using 0.05 parts by mass or more of the crosslinkable monomer is preferable because it results in better binding properties and electrode slurry stability. Using 5.0 parts by mass or less tends to increase the stability of the polymer. Similarly, the amount of the above-mentioned crosslinkable monomer used is preferably 0.001 mol% to 2.5 mol%, more preferably 0.01 mol% to 2.0 mol%, even more preferably 0.03 mol% to 1.5 mol%, even more preferably 0.05 mol% to 1.0 mol%, and even more preferably 0.10 mol% to 0.50 mol% based on the total amount of monomers other than the crosslinkable monomer (non-crosslinkable monomer).

[0051] <Aqueous viscosity of this crosslinked polymer in aqueous solution> The crosslinked polymer preferably has a viscosity of 10,000 mPa·s or less in its 2% by mass aqueous solution. When the viscosity of the 2% by mass aqueous solution is 10,000 mPa·s or less, it can be made durable enough to follow the volume change of the active material during charging and discharging. The viscosity of the 2% by mass aqueous solution may be 5,000 mPa·s or less, 3,000 mPa·s or less, or 2,000 mPa·s or less. The viscosity of the aqueous solution is obtained by uniformly dissolving or dispersing a predetermined amount of the crosslinked polymer in water, and then measuring the B-type viscosity (25°C) at 12 rpm.

[0052] This crosslinked polymer or its salt swells in water by absorbing water. Generally, when a crosslinked polymer has an appropriate degree of crosslinking, the more hydrophilic groups it has, the more easily it absorbs water and swells. Also, regarding the degree of crosslinking, the lower the degree of crosslinking, the more easily the crosslinked polymer swells. However, even if the number of crosslinking points is the same, the larger the molecular weight (primary chain length), the more crosslinking points contribute to the formation of a three-dimensional network, making the crosslinked polymer less likely to swell. Therefore, the viscosity of an aqueous solution of the crosslinked polymer can be adjusted by adjusting the amount of hydrophilic groups, the number of crosslinking points, and the primary chain length of the crosslinked polymer. In this case, the number of crosslinking points can be adjusted, for example, by the amount of crosslinkable monomer used, the chain transfer reaction to the polymer chain, and the post-crosslinking reaction. Furthermore, the primary chain length of the polymer can be adjusted by setting conditions related to the amount of radical generation, such as the initiator and polymerization temperature, and by selecting a polymerization solvent that takes chain transfer into consideration.

[0053] <Particle size of this crosslinked polymer> In this slurry composition, it is preferable that the crosslinked polymer is well dispersed as water-swellable particles with an appropriate particle size, rather than existing as large-particle clumps (secondary aggregates), because this allows the binder containing the crosslinked polymer to exhibit good binding performance.

[0054] Preferably, the crosslinked polymer has a neutralization degree based on the carboxyl groups of 70 to 100 mol%. When dispersed in water, the particle size (water-swelled particle size) is in the range of 0.1 μm or more and 10.0 μm or less in volume-based median diameter. A more preferred range for the above particle size is 0.1 μm or more and 8.0 μm or less, an even more preferred range is 0.1 μm or more and 7.0 μm or less, an even more preferred range is 0.2 μm or more and 5.0 μm or less, and an even more preferred range is 0.5 μm or more and 3.0 μm or less. If the particle size is in the range of 0.1 μm or more and 10.0 μm or less, the particles will be uniformly present in the slurry composition at a suitable size, resulting in high stability and excellent binding properties for the slurry composition. If the particle size exceeds 10.0 μm, there is a risk that the binding properties will be insufficient as described above. Furthermore, there is a risk of insufficient coating properties due to the difficulty in obtaining a smooth coated surface. On the other hand, when the particle size is less than 0.1 μm, there are concerns from the viewpoint of stable manufacturing. Here, the water-swollen particle size is obtained by the method described in the examples.

[0055] Furthermore, the particle size of this crosslinked polymer when dry (dry particle size) is preferably in the range of 0.03 μm or more and 3 μm or less in terms of volume-based median diameter. A more preferred range for the above particle size is 0.1 μm or more and 1 μm or less, and an even more preferred range is 0.3 μm or more and 0.8 μm or less.

[0056] In this crosslinked polymer, it is preferable to use it in the slurry composition in the form of a salt, after the acidic groups such as carboxyl groups derived from the ethylenically unsaturated carboxylic acid monomer have been neutralized to a degree of neutralization of 20 mol% or more. The degree of neutralization is more preferably 50 mol% or more, even more preferably 70 mol% or more, even more preferably 75 mol% or more, even more preferably 80 mol% or more, and particularly preferably 85 mol% or more. The upper limit of the degree of neutralization is 100 mol%, but it may also be 98 mol% or 95 mol%. The range of the degree of neutralization can be appropriately combined from the lower and upper limits above, for example, it may be 50 mol% or more and 100 mol% or less, 75 mol% or more and 100 mol% or less, or 80 mol% or more and 100 mol% or less. A degree of neutralization of 20 mol% or more is preferable because it results in good water swelling and makes it easier to obtain a dispersion stabilization effect. In this specification, the degree of neutralization can be calculated from the input values ​​of monomers having acidic groups such as carboxyl groups and the neutralizing agent used for neutralization. The degree of neutralization can be confirmed by IR measurement of the powder obtained by drying the crosslinked polymer or its salt at 80°C for 3 hours under reduced pressure, and by the intensity ratio of the peak derived from the C=O group of the carboxylic acid and the peak derived from the C=O group of the carboxylate salt.

[0057] <Method for producing this cross-linked polymer> This crosslinked polymer can be produced using known polymerization methods such as solution polymerization, precipitation polymerization, suspension polymerization, and emulsion polymerization, but precipitation polymerization and suspension polymerization (reverse-phase suspension polymerization) are preferred in terms of productivity. Heterogeneous polymerization methods such as precipitation polymerization, suspension polymerization, and emulsion polymerization are preferred in terms of obtaining better performance in terms of binding properties, and among these, precipitation polymerization is more preferred. Precipitation polymerization is a method for producing polymers by carrying out a polymerization reaction in a solvent that dissolves the raw material unsaturated monomers but does not substantially dissolve the resulting polymer. As polymerization progresses, the polymer particles grow larger through aggregation and growth, and a dispersion of polymer particles is obtained in which primary particles of tens to hundreds of nanometers are secondary aggregated to several micrometers to tens of micrometers. Dispersion stabilizers can also be used to control the particle size of the polymer. Furthermore, secondary aggregation can be suppressed by selecting appropriate dispersion stabilizers and polymerization solvents. Generally, precipitation polymerization in which secondary aggregation is suppressed is also called dispersion polymerization.

[0058] In precipitation polymerization, the polymerization solvent can be selected from water and various organic solvents, taking into consideration the type of monomer used. To obtain polymers with longer primary chain lengths, it is preferable to use a solvent with a small chain transfer constant.

[0059] Specific polymerization solvents include water-soluble solvents such as methanol, t-butyl alcohol, acetone, methyl ethyl ketone, acetonitrile, and tetrahydrofuran, as well as benzene, ethyl acetate, dichloroethane, n-hexane, cyclohexane, and n-heptane. These can be used individually or in combination of two or more. Alternatively, they may be used as a mixed solvent with water. In this invention, a water-soluble solvent refers to a solvent whose solubility in water at 20°C is greater than 10 g / 100 ml. Of the above, methyl ethyl ketone and acetonitrile are preferred because they produce fewer coarse particles and adhere less to the reactor, resulting in good polymerization stability; the precipitated polymer fine particles are less prone to secondary aggregation (or even if secondary aggregation occurs, they dissolve easily in an aqueous medium); a small chain transfer constant is obtained, resulting in a polymer with a large degree of polymerization (primary chain length); and the process of neutralization described later is easy to handle.

[0060] The polymerization initiator can be any known polymerization initiator such as azo compounds, organic peroxides, or inorganic peroxides, but is not particularly limited. The usage conditions can be adjusted to achieve an appropriate amount of radical generation using known methods such as thermal initiation, redox initiation with a reducing agent, or UV initiation. In order to obtain a crosslinked polymer with a long primary chain length, it is preferable to set the conditions so that the amount of radical generation is reduced within an acceptable range of production time.

[0061] The preferred amount of polymerization initiator to use is, for example, 0.001 to 2 parts by mass, or for example, 0.005 to 1 part by mass, or for example, 0.01 to 0.1 parts by mass, when the total amount of monomer components used is 100 parts by mass. If the amount of polymerization initiator used is 0.001 parts by mass or more, the polymerization reaction can be carried out stably, and if it is 2 parts by mass or less, it is easy to obtain a polymer with a long primary chain length.

[0062] The polymerization temperature is preferably 0 to 100°C, and more preferably 20 to 80°C, although this depends on conditions such as the type and concentration of monomers used. The polymerization temperature may be constant or may change during the polymerization reaction. The polymerization time is preferably 1 minute to 20 hours, and more preferably 1 hour to 10 hours.

[0063] 3-2. This non-crosslinked polymer This section describes non-crosslinked polymers when ethylenically unsaturated carboxylic acid monomers are used as hydrophilic vinyl monomers. <Structural units derived from ethylenically unsaturated carboxylic acid monomers> The non-crosslinked polymer contained in the hydrophilic binder may contain 50% to 100% by mass of structural units (component (a1) above) derived from ethylenically unsaturated carboxylic acid monomers. The method for introducing component (a1) of the non-crosslinked polymer may be the same as the method described for component (a1) of the crosslinked polymer. Alternatively, the method may involve saponification of a polymer containing structural units derived from an alkyl (meth)acrylate compound (as described above as component (b1) of the crosslinked polymer). As the alkyl (meth)acrylate compound, methyl acrylate and methyl methacrylate are preferred from the viewpoint that the saponification reaction proceeds easily, and one type may be used alone or two or more types may be used in combination.

[0064] This non-crosslinked polymer has a higher viscosity than this crosslinked polymer. This is presumed to be because the molecular chains of this non-crosslinked polymer are spread out, while those of this crosslinked polymer are particulate, resulting in a smaller apparent molecular weight.

[0065] The content of component (a1) in this non-crosslinked polymer can be 50% by mass or more and 100% by mass or less relative to the total structural units of the non-crosslinked polymer, preferably 60% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, and even more preferably 80% by mass or more and 100% by mass or less.

[0066] <Other structural units> In addition to component (a1), this non-crosslinked polymer may also contain structural units derived from other ethylenically unsaturated monomers copolymerizable with these (component (b1)). The method for introducing component (b1) may be the same as the method described for component (b1) of this crosslinked polymer. Alternatively, it may be a method of saponifying a polymer containing structural units derived from vinyl ester compounds such as vinyl acetate and vinyl propionate. Vinyl acetate is preferred as the vinyl ester compound due to the ease of obtaining raw materials, and one type may be used alone or two or more types may be used in combination.

[0067] The proportion of component (b1) may be 0% by mass or more and 50% by mass or less with respect to the total structural units of the non-crosslinked polymer. The proportion of component (b1) may be 1% by mass or more and 50% by mass or less, 2% by mass or more and 50% by mass or less, 5% by mass or more and 50% by mass or less, or 10% by mass or more and 50% by mass or less.

[0068] The non-crosslinked polymer may be in the form of a salt in which some or all of the carboxyl groups contained in the polymer are neutralized. The type of salt is not particularly limited, but examples include alkali metal salts such as lithium, sodium, and potassium; magnesium salts; alkaline earth metal salts such as calcium salts and barium salts; other metal salts such as aluminum salts; ammonium salts and organic amine salts. Among these, alkali metal salts and alkaline earth metal salts are preferred because they do not adversely affect battery characteristics, and alkali metal salts are more preferred.

[0069] In this slurry composition, the non-crosslinked polymer is preferably used in the form of a salt, with the acidic groups such as carboxyl groups derived from the ethylenically unsaturated carboxylic acid monomer neutralized to a degree of neutralization of 20 mol% or more. The degree of neutralization is more preferably 50 mol% or more, even more preferably 70 mol% or more, even more preferably 75 mol% or more, even more preferably 80 mol% or more, and particularly preferably 85 mol% or more. The upper limit of the degree of neutralization is 100 mol%, but it may also be 98 mol% or 95 mol%. The range of the degree of neutralization can be appropriately combined from the lower and upper limits above, for example, it may be 50 mol% or more and 100 mol% or less, 75 mol% or more and 100 mol% or less, or 80 mol% or more and 100 mol% or less. A degree of neutralization of 20 mol% or more is preferable because it is easier to ensure solubility in water. In this specification, the degree of neutralization can be calculated from the input values ​​of monomers having acidic groups such as carboxyl groups and the neutralizing agent used for neutralization. The degree of neutralization can be confirmed by IR measurement of the powder obtained by drying the crosslinked polymer or its salt at 80°C for 3 hours under reduced pressure, and by the intensity ratio of the peak derived from the C=O group of the carboxylic acid and the peak derived from the C=O group of the carboxylate salt.

[0070] The weight-average molecular weight (Mw) of this non-crosslinked polymer is not particularly limited, but is preferably 5,000 or more, and more preferably 10,000 or more, in order to obtain an electrode mixture layer with excellent binding properties. Mw may be 100,000 or more, 500,000 or more, or 1,000,000 or more. The upper limit of Mw is also not particularly limited, but from the viewpoint of handling during manufacturing, it may be, for example, 10,000,000 or less, 7,000,000 or less, 5,000,000 or less, or 3,000,000 or less. Here, Mw is obtained by a method according to the method described in the examples, depending on the structural unit of the non-crosslinked polymer.

[0071] When the hydrophilic binder contains the crosslinked polymer and the non-crosslinked polymer, the amount of the non-crosslinked polymer used is preferably 7.5 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the total amount of the crosslinked polymer. The amount of the non-crosslinked polymer used may be 15 parts by mass or more, 25 parts by mass or more, 35 parts by mass or more, or 45 parts by mass or more. The upper limit may be 190 parts by mass or less, 180 parts by mass or less, 170 parts by mass or less, or 160 parts by mass or less. The range can be an appropriate combination of these lower and upper limits, for example, 15 parts by mass or more and 190 parts by mass or less, for example, 25 parts by mass or more and 180 parts by mass or less, for example, 35 parts by mass or more and 170 parts by mass or less, for example, 35 parts by mass or more and 160 parts by mass or less.

[0072] Thus, by using a specific amount of this non-crosslinked polymer in combination with this crosslinked polymer, it is possible to obtain a secondary battery that exhibits excellent cycle characteristics while ensuring coating properties by reducing the viscosity of the electrode slurry, even when the solid content concentration of the secondary battery electrode slurry composition is higher than conventional methods. This effect can be achieved when the amount of this non-crosslinked polymer used is 7.5 parts by mass or more. However, if the amount of this non-crosslinked polymer used exceeds 200 parts by mass, sufficient coating properties may not be obtained.

[0073] <Method for producing this non-crosslinked polymer> This non-crosslinked polymer can be polymerized using known polymerization methods such as solution polymerization, precipitation polymerization, suspension polymerization, and emulsion polymerization, and the appropriate polymerization method may be selected based on molecular weight or composition.

[0074] The polymerization initiator can be any known polymerization initiator such as azo compounds, organic peroxides, or inorganic peroxides, but is not particularly limited. The usage conditions can be adjusted to achieve an appropriate amount of radical generation using known methods such as thermal initiation, redox initiation with a reducing agent, or UV initiation. Furthermore, known chain transfer agents may be used as needed for purposes such as adjusting molecular weight.

[0075] <Aqueous viscosity of this non-crosslinked polymer in aqueous solution> The non-crosslinked polymer preferably has a viscosity of 10,000 mPa·s or less in its 2% by mass aqueous solution. When the viscosity of the 2% by mass aqueous solution is 10,000 mPa·s or less, it can be made durable enough to follow the volume change of the active material during charging and discharging. The viscosity of the 2% by mass aqueous solution may be 5,000 mPa·s or less, 3,000 mPa·s or less, or 2,000 mPa·s or less. The viscosity of the aqueous solution is obtained by uniformly dissolving or dispersing a predetermined amount of the non-crosslinked polymer in water, and then measuring the B-type viscosity (25°C) at 12 rpm.

[0076] 4. Other ingredients This slurry composition may also contain other binder components such as styrene-butadiene rubber (SBR) latex, acrylic latex, and polyvinylidene fluoride latex. When other binder components are used, the amount used can be, for example, 0.1 to 5 parts by mass or less, or 0.1 to 2 parts by mass or less, or 0.1 to 1 part by mass or less, per 100 parts by mass of the total amount of active material. If the amount of other binder components used exceeds 5 parts by mass, the resistance may increase, and the high-rate properties may become insufficient. Among the above, the use of SBR latex is more preferable because it offers an excellent balance of binding properties and flexural resistance. In this context, the timing of adding the latex is preferably in step C, in order to suppress the aggregation of the latex due to shearing.

[0077] The above-mentioned SBR-based latex refers to an aqueous dispersion of a copolymer having structural units derived from aromatic vinyl monomers such as styrene and structural units derived from aliphatic conjugated diene monomers such as 1,3-butadiene. Examples of aromatic vinyl monomers include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene, and one or more of these can be used. The amount of structural units derived from the aromatic vinyl monomers in the copolymer can be in the range of, for example, 20 to 70% by mass, or in the range of, for example, 30 to 60% by mass, mainly from the viewpoint of binding properties. Examples of the above-mentioned aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, etc., and one or more of these can be used. The structural units derived from the above-mentioned aliphatic conjugated diene monomers in the copolymer can be in the range of, for example, 30 to 70% by mass, or in the range of 40 to 60% by mass, in order to ensure good binder binding and flexibility of the resulting electrode. In addition to the monomers mentioned above, SBR-based latex may also use other monomers as copolymer monomers to further improve properties such as binding ability, including nitrile group-containing monomers such as (meth)acrylonitrile, carboxyl group-containing monomers such as (meth)acrylic acid, itaconic acid, and maleic acid, and ester group-containing monomers such as (meth)acrylate. The structural units derived from the other monomers in the copolymer can be in the range of, for example, 0 to 30% by mass, or in the range of, for example, 0 to 20% by mass.

[0078] 5. Method for producing slurry composition for secondary battery electrodes The present invention provides a method for producing a slurry composition for secondary battery electrodes, comprising an active material, a thickener, a hydrophilic binder, and water, and includes the following steps A, B, and C. Step A: A process of obtaining a solid paste by kneading a composition containing an active material, a thickener, and water with a solid content concentration of 60-80% by mass. Step B: Step B involves adding a hydrophilic binder (but different from the aforementioned thickener) and water to the solid paste obtained in Step A, and kneading it to obtain a second solid paste. Step C: A step to adjust the solid content concentration of the second solid paste to 40-60% by mass. Here, while a portion of the hydrophilic binder may be added in step A as long as the effects of the present invention are achieved, it is preferable to add all of the hydrophilic binder in step B in order to achieve a higher viscosity reduction of the slurry composition.

[0079] By kneading a composition containing a thickening agent in step A, and then adding part or all of the hydrophilic binder in step B, the viscosity of the electrode slurry can be reduced even when the solid content concentration of the slurry composition is high, resulting in excellent productivity. Unlike the manufacturing method of the present invention, when the entire amount of the thickener and hydrophilic binder is added before solid mixing, the viscosity of the slurry composition increases significantly, resulting in poor productivity. This is thought to be because the hydrophilic binder and thickener are competitively adsorbed to the active material, leading to a large amount of free thickener present in the medium. On the other hand, in the manufacturing method of the present invention, by kneading a composition containing a thickener but without a hydrophilic binder in step A, the amount of thickener adsorbed onto the active material increases, and the amount of thickener present free in the medium decreases, which is thought to reduce the viscosity of the slurry composition.

[0080] Here, the solid content concentration of the composition in step A is 60 to 80% by mass, preferably 61 to 78% by mass, more preferably 62 to 76% by mass, even more preferably 63 to 74% by mass, even more preferably 66 to 72% by mass, even more preferably 68 to 72% by mass, and particularly preferably 68 to 70% by mass, in that a strong shear force can be applied to the composition to promote the adsorption of the thickener to the active material, thereby further reducing the viscosity of the resulting electrode slurry. The kneading time in step A is preferably 10 to 60 minutes, more preferably 20 to 60 minutes, and even more preferably 25 to 60 minutes, as it promotes the adsorption of the thickener to the active material, reduces the viscosity of the resulting electrode slurry, and offers excellent productivity.

[0081] Furthermore, process B may include the following process B1. Step B1: A step in which an aqueous solution of a hydrophilic binder is added to the first solid paste obtained in Step A, and the mixture is kneaded to obtain a second solid paste. The inclusion of step B1 in step B is preferable because, by adding the hydrophilic binder in an aqueous solution beforehand rather than in powder form, the viscosity of the resulting electrode slurry can be further reduced, and the occurrence of so-called "stepping stones" can be suppressed, resulting in a smooth secondary battery electrode.

[0082] Furthermore, process B may also include the following processes B2 and B3. Process B2: A process in which a hydrophilic binder is added to the first solid paste obtained in process A, and the paste is kneaded. Process B3: Following process B2, water is added and the mixture is kneaded to obtain a second solid paste. The inclusion of steps B2 and B3 in step B is preferable because, when the hydrophilic binder is in powder form, the solid mixing step B2 uniformly disperses and dissolves the hydrophilic binder in the electrode slurry, thereby reducing the viscosity of the resulting electrode slurry.

[0083] The amount of thickener used in this slurry composition is, for example, 0.1 parts by mass to 20 parts by mass per 100 parts by mass of the total amount of active material. The above amount can also be, for example, 0.2 parts by mass to 10 parts by mass, for example, 0.3 parts by mass to 8 parts by mass, or for example, 0.4 parts by mass to 5 parts by mass. If the amount of thickener used is 0.1 parts by mass or more, sufficient binding properties can be obtained. Furthermore, the dispersion stability of the active material can be ensured, and a uniform mixture layer can be formed. If the amount of thickener used is 20 parts by mass or less, this slurry composition will not become highly viscous, and coating properties for current collectors can be ensured. As a result, a mixture layer with a uniform and smooth surface can be formed.

[0084] The amount of hydrophilic binder used in this slurry composition is, for example, 0.1 parts by mass to 20 parts by mass per 100 parts by mass of the total amount of active material. The above amount can also be, for example, 0.2 parts by mass to 10 parts by mass, for example, 0.3 parts by mass to 8 parts by mass, or for example, 0.4 parts by mass to 5 parts by mass. If the amount of hydrophilic binder used is 0.1 parts by mass or more, sufficient binding properties can be obtained. Furthermore, dispersion stability of the active material can be ensured, and a uniform mixture layer can be formed. If the amount of hydrophilic binder used is 20 parts by mass or less, this slurry composition will not become highly viscous, and coating properties for current collectors can be ensured. As a result, a mixture layer with a uniform and smooth surface can be formed.

[0085] The amount of active material used in this slurry composition is, for example, in the range of 20 to 40% by mass, or in the range of 25 to 40% by mass, relative to the total amount of the slurry composition. If the amount of active material used is 20% by mass or more, migration of hydrophilic binders, etc., is suppressed, and there is also an advantage in terms of the drying cost of the medium. On the other hand, if the amount of active material is 40% by mass or less, the fluidity and coating properties of the slurry composition can be ensured, and a uniform mixture layer can be formed.

[0086] This slurry composition uses water as the medium. Furthermore, to adjust the properties and drying properties of this slurry composition, a mixed solvent with lower alcohols such as methanol and ethanol, carbonates such as ethylene carbonate, ketones such as acetone, tetrahydrofuran, or N-methylpyrrolidone may be used. The proportion of water in the mixed medium is, for example, 50% by mass or more, and also, for example, 70% by mass or more.

[0087] When this slurry composition is made into a coatable slurry, the content of the water-containing medium in the total slurry composition can be in the range of 40 to 60% by mass, or for example, 40 to 55% by mass, from the viewpoint of the coatability of the slurry, the energy cost required for drying, and productivity.

[0088] The slurry composition for secondary battery electrodes according to the present invention comprises an active material, a thickener, a hydrophilic binder, and water as essential components, and is obtained by mixing each component using known means. The method of mixing each component is not particularly limited, and known methods can be used, but a method of dry-blending powder components such as the active material and thickener, and then mixing them with a dispersion medium such as water, and then dispersing and kneading is preferred. When obtaining this slurry composition in slurry form, it is preferable to produce a slurry without poor dispersion or aggregation. As a mixing means, known mixers such as planetary mixers, thin-film swirling mixers, and orbital mixers can be used, but it is preferable to use a planetary mixer because a good dispersion state can be obtained in a short time. Also, when using a thin-film swirling mixer, it is preferable to perform pre-dispersion with a stirrer such as a disperser beforehand. The pH of the above slurry composition is not particularly limited as long as the effects of the present invention are achieved, but it is preferably less than 12.5, and for example, when CMC is included, it is more preferable to have a pH of less than 11.5, and even more preferable to have a pH of less than 10.5, as there is less concern about hydrolysis. Furthermore, the viscosity of the slurry composition is not particularly limited as long as it achieves the effects of the present invention, but as a B-type viscosity (25°C) at 20 rpm, it can be in the range of, for example, 100 to 12,000 mPa·s, or for example, 500 to 11,000 mPa·s, or for example, 1,000 to 10,000 mPa·s. If the viscosity of the slurry is within the above range, good coating properties can be ensured.

[0089] 6. Method for manufacturing secondary battery electrodes The secondary battery electrode according to the present invention comprises a composite layer formed from the slurry composition for secondary battery electrodes according to the present invention on the surface of a current collector such as copper or aluminum. The composite layer is formed by coating the surface of the current collector with the slurry composition and then drying and removing a medium such as water. The method of coating with the slurry composition is not particularly limited, and known methods such as the doctor blade method, dip method, roll coat method, comma coat method, curtain coat method, gravure coat method, and extrusion method can be employed. Furthermore, the drying can be carried out by known methods such as hot air blowing, reduced pressure, (far) infrared radiation, and microwave irradiation. Typically, the mixture layer obtained after drying is subjected to compression treatment using a die press or roll press. Compression brings the active material and hydrophilic binder into close contact, improving the strength of the mixture layer and its adhesion to the current collector. Compression can adjust the thickness of the mixture layer to, for example, 30-80% of its original thickness, and the thickness of the mixture layer after compression is generally around 4-200 μm.

[0090] 7. Manufacturing method of secondary batteries A secondary battery can be manufactured by providing a separator and an electrolyte to the secondary battery electrode according to the present invention. The electrolyte may be in liquid form or gel form. The separator is placed between the positive and negative electrodes of a battery and plays a role in preventing short circuits caused by contact between the two electrodes and in retaining the electrolyte to ensure ionic conductivity. The separator is preferably a film-like insulating microporous membrane with good ionic permeability and mechanical strength. Specific materials that can be used include polyethylene, polyolefins such as polypropylene, and polytetrafluoroethylene.

[0091] The electrolyte can be a known one commonly used depending on the type of active material. In lithium-ion secondary batteries, specific solvents include cyclic carbonates with high dielectric constant and high electrolyte solubility, such as propylene carbonate and ethylene carbonate, as well as low-viscosity chain carbonates, such as ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate. These can be used alone or as mixed solvents. The electrolyte is used by dissolving lithium salts such as LiPF6, LiSbF6, LiBF4, LiClO4, and LiAlO4 in these solvents. In nickel-metal hydride secondary batteries, an aqueous potassium hydroxide solution can be used as the electrolyte. Secondary batteries are obtained by housing positive and negative electrode plates, separated by a separator, in a spiral or stacked structure in a case or the like.

[0092] As described above, a secondary battery equipped with an electrode having a composite layer formed from the slurry composition for secondary battery electrodes disclosed herein exhibits good durability (cycle characteristics) even after repeated charging and discharging, and is therefore suitable for automotive secondary batteries and the like. [Examples]

[0093] The present invention will be described in detail below based on examples. However, the present invention is not limited to these examples. In the following, "parts" and "%" mean parts by mass and mass%, respectively, unless otherwise specified. In the following example, the evaluation of the crosslinked polymer was carried out using the following method.

[0094] Hydrophilic Binder (Manufacturing Example 1: Manufacturing of hydrophilic binder R-1) For polymerization, a reactor equipped with a stirring blade, thermometer, reflux condenser, and nitrogen inlet tube was used. 567 parts acetonitrile, 2.2 parts deionized water, acrylic acid (hereinafter, 100 parts of AA, 0.9 parts of trimethylolpropanediallyl ether (manufactured by Osaka Soda Co., Ltd., trade name "Neoallyl T-20") (0.30 mol%) relative to the above AA, and triethylamine equivalent to 1.0 mol% relative to the above AA were charged. After thoroughly purging the reactor with nitrogen, the internal temperature was raised to 55°C. After confirming that the internal temperature had stabilized at 55°C, 0.040 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name "V-65") were added as a polymerization initiator. When turbidity was observed in the reaction solution, this point was taken as the polymerization initiation point. The monomer concentration was calculated to be 15.0%. Twelve hours after the start of polymerization, the polymerization reaction solution was cooled, and after the internal temperature dropped to 25°C, 52.4 parts of lithium hydroxide monohydrate (hereinafter referred to as "LiOH·H2O") powder were added. After the addition, stirring was continued at room temperature for 12 hours to obtain a slurry-like polymerization reaction solution in which particles of hydrophilic polymer R-1 (lithium salt, degree of neutralization 90 mol%) were dispersed in the medium.

[0095] The resulting polymerization reaction solution was centrifuged to settle the polymer particles, and the supernatant was removed. Then, the precipitate was redispersed in an equal mass of acetonitrile, and the washing operation, in which the polymer particles were settled by centrifugation and the supernatant was removed, was repeated twice. The precipitate was collected and dried under reduced pressure at 80°C for 3 hours to remove volatile components, thereby obtaining hydrophilic polymer R-1 powder. Since hydrophilic polymer R-1 is hygroscopic, it was stored in a sealed container with water vapor barrier properties. Furthermore, IR measurement of the hydrophilic polymer R-1 powder revealed a neutralization degree of 90 mol%, which was equal to the calculated value from the initial stage, based on the intensity ratio of the peaks originating from the C=O group of the carboxylic acid and the C=O group of the lithium carboxylate.

[0096] Furthermore, the particle size measured in the aqueous medium using the following method was 1.68 μm. (Measurement of particle size in an aqueous medium (water-swollen particle size)) 0.25 g of hydrophilic polymer R-1 powder and 49.75 g of deionized water were weighed into a 100 cc container and placed in a rotation / revolution type agitator (Sinky Co., Ltd., Awatori Rentaro AR-250). Next, stirring (rotation speed 2,000 rpm / revolution speed 800 rpm, 7 minutes) and degassing (rotation speed 2,200 rpm / revolution speed 60 rpm, 1 minute) were performed to prepare a hydrogel in which R-1 had swollen in water. Next, the particle size distribution of the hydrogel was measured using a laser diffraction / scattering particle size analyzer (Microtrac MT-3300EXII, Microtrac Bell Co., Ltd.) with deionized water as the dispersion medium. When an appropriate amount of hydrogel was added to a system circulating an excess amount of dispersion medium, the particle size distribution shape measured after a few minutes stabilized. Once stability was confirmed, the particle size distribution was measured, and the volume-based median diameter (D50), which is a representative value of the particle size, was obtained.

[0097] (Manufacturing Example 2: Manufacturing of hydrophilic binder R-2) For polymerization, a reactor equipped with a stirring blade, thermometer, reflux condenser, and nitrogen inlet tube was used. 567 parts acetonitrile, 2.2 parts deionized water, 80 parts AA, 0.9 parts neoallyl T-20 (0.33 mol%) relative to the total amount of AA and 2-hydroxyethyl acrylate), and triethylamine equivalent to 1.0 mol% relative to AA were charged into the reactor. After thoroughly purging the reactor with nitrogen, the internal temperature was raised to 55°C. After confirming that the internal temperature had stabilized at 55°C, 0.040 parts V-65 was added as a polymerization initiator. A white turbidity was observed in the reaction solution, and this point was designated as the polymerization initiation point. Two hours after the start of polymerization, 20.0 parts of 2-hydroxyethyl acrylate were added all at once. The monomer concentration was calculated to be 15.0%. Twelve hours after the start of polymerization, the polymerization reaction solution was cooled, and after the internal temperature had dropped to 25°C, 41.9 parts of LiOH·H2O powder were added. After addition, stirring was continued at room temperature for 12 hours to obtain a slurry-like polymerization reaction solution in which particles of hydrophilic polymer R-2 (lithium salt, degree of neutralization 90 mol%) were dispersed in the medium.

[0098] The obtained polymerization reaction solution was centrifuged to settle the polymer particles, and the supernatant was removed. Then, the precipitate was redispersed in an equal mass of acetonitrile, and the washing operation, in which the polymer particles were settled by centrifugation and the supernatant was removed, was repeated twice. The precipitate was collected and dried under reduced pressure at 80°C for 3 hours to remove volatile components, thereby obtaining hydrophilic polymer R-2 powder. Since hydrophilic polymer R-2 is hygroscopic, it was stored in a sealed container with water vapor barrier properties. Furthermore, the hydrophilic polymer R-2 powder was subjected to IR measurement, and the degree of neutralization was determined from the intensity ratio of the peak originating from the C=O group of the carboxylic acid and the peak originating from the C=O group of the lithium carboxylic acid, which was equal to the calculated value from the initial stage, at 90 mol%. The particle size in the aqueous medium, measured in the same manner as in Example 1, was 1.40 μm.

[0099] (Hydrophilic Binder R-3) Details of R-3 used in the examples and comparative examples are shown below. • R-3: Neutralized sodium polyacrylate (non-crosslinked). Product name "Aron® A-20P-X" (manufactured by Toagosei Co., Ltd., Mw 5,000,000) was used. The Mw obtained using GPC (Gel Permeation Chromatography HLC-8420, manufactured by Tosoh Corporation) was equivalent to the catalog value. In this case, an aqueous solution of sodium nitrate dissolved at a concentration of 0.1 M was used as the eluent, and sodium polyacrylate was used as the standard substance.

[0100] (Manufacturing Example 3: Manufacturing of hydrophilic binder R-4) For polymerization, a reactor equipped with a stirring blade, thermometer, reflux condenser, and nitrogen inlet tube was used. 400 parts of pure water and 100 parts of N-acryloylmorpholine (manufactured by Kojinsha, hereinafter referred to as "ACMO") were charged into the reactor. After thoroughly purging the reactor with nitrogen, the internal temperature was raised to 45°C. After confirming that the internal temperature had stabilized at 45°C, 0.084 parts of 2,2'-azobis[2-(2-imidazolin-2-yl)propane] disulfate dihydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name "VA-046B") were added as a polymerization initiator to start polymerization. Four hours after the start of polymerization, the polymerization reaction solution was cooled to obtain an aqueous solution of the hydrophilic polymer R-4. The molecular weight (Mw) obtained using GPC (Gel Permeation Chromatography HLC-8320, Tosoh Corporation) was 2,126,600, the number-average molecular weight (Mn) was 686,000, and the molecular weight distribution (PDI) was 3.1. Dimethylformamide in which lithium bromide monohydrate was dissolved at a concentration of 10 mM was used as the eluent, and polymethyl methacrylate was used as the standard substance. Furthermore, the polymerization rate of ACMO calculated from GC (Gas Chromatography GC-2014, Shimadzu Corporation) was 100%.

[0101] The resulting polymerization reaction solution was dried overnight at 100°C, and then pulverized to obtain hydrophilic polymer R-4 powder. Since hydrophilic polymer R-4 is hygroscopic, it was stored in a sealed container with water vapor barrier properties.

[0102] Example 1 (Manufacturing of slurry composition for secondary battery electrodes) 77.6 parts of artificial graphite (Showa Denko Corporation, product name "SCMG-CF") and 19.4 parts of silicon monoxide (Osaka Titanium Technologies Co., Ltd., particle size 5 μm) were added as active materials to a 0.6 L planetary mixer (Primix Corporation, Hibiscus Mix 2P-03 model), and 1.5 parts of sodium carboxymethylcellulose (CMC) were added as a thickener. Then, dry mixing was performed at a rotation speed of 40 rpm for 7 minutes to obtain a powder mixture. Next, in step A, 43.5 parts of deionized water were added to the powder mixture to adjust the solid content concentration to 69.4%, and then the mixture was kneaded in a planetary mixer at a rotation speed of 95 rpm for 30 minutes to obtain the first solid paste. At this time, 99.4 g of the mixture was being kneaded in the planetary mixer, and a current of 0.25 A was flowing at an applied voltage of 100 V (252 W / kg). The starting temperature for kneading was 26.1 °C, but due to the heat generated by stirring, the temperature of the solid paste rose to 36.4 °C by the end of mixing. Furthermore, in step B, 1.0 part of hydrophilic binder R-1 and 31.5 parts of deionized water were added to the first solid mixture to adjust the solid content to 57.0%, and then the mixture was kneaded in a planetary mixer at a rotation speed of 95 rpm for 20 minutes to obtain a second solid mixture. At this time, 122.15 g of the mixture was kneaded in the planetary mixer, and a current of 0.15 A was flowing at an applied voltage of 100 V (123 W / kg). The starting temperature of the kneading was 31.9 °C, but the temperature of the solid mixture was 32.6 °C at the end of the kneading, indicating that the temperature hardly changed. Finally, in step C, 1.5 parts of ion-exchanged water and styrene-butadiene rubber (SBR) latex were added to the second solid paste to adjust the solid content to 53%. The mixture was then gently mixed in a planetary mixer at 95 rpm for 10 minutes, followed by vacuum degassing in a planetary mixer at 10 rpm for 5 minutes to produce a slurry composition for the negative electrode (negative electrode slurry).

[0103] (Viscosity measurement of negative electrode slurry) The negative electrode slurries obtained in each of the following examples and comparative examples were adjusted to 25°C ± 1°C, and then the slurry viscosity was measured using a Type B viscometer (TVB-10, manufactured by Toki Sangyo Co., Ltd.) at 12 rpm.

[0104] (Fabrication of negative electrode plate) Next, the negative electrode slurry was applied to a 20 μm thick current collector (copper foil) using a variable applicator, and a composite layer was formed by drying in a forced-air dryer at 80°C for 30 minutes. After that, the composite layer was rolled to a thickness of 50 ± 5 μm and a composite density of 1.60 ± 0.10 g / cm³, punched out to a size of 1 cm × 6 cm for peel strength testing, and dried under reduced pressure at 130°C for 8 hours to obtain a negative electrode plate.

[0105] (180° peel strength (bonding properties)) A sample for peel testing was prepared by attaching the composite layer surface of the above-mentioned negative electrode plate, measuring 1 cm x 6 cm, to a 3 cm x 9 cm acrylic plate using double-sided tape (Nichiban NW-20). Using a tensile testing machine (Imada MX-500N electric stand, Imada DSY-5N digital force gauge), a 180° peel test was performed at a measurement temperature of 25°C and a tensile speed of 100 mm / min, and the adhesion was evaluated by measuring the peel strength between the composite layer and the copper foil. The peel strength was high at 20.8 N / m, which was good.

[0106] Example 2 In step B, a negative electrode slurry was prepared by performing the same procedure as in Example 1, except that in step B1, 1.0 part of hydrophilic binder R-1 was mixed with 31.5 parts of deionized water to create an aqueous solution of the hydrophilic binder in the state of a water-swollen gel, and the viscosity of the slurry was measured.

[0107] Examples 3, 5-14, and Comparative Examples 1-4 A negative electrode slurry was prepared by performing the same procedure as in Example 1, except that the formulation and preparation conditions for the negative electrode slurry were as shown in Table 1, and the viscosity of the slurry was measured.

[0108] Example 4 After obtaining a powder mixture using the same procedure as in Example 1, in step A, 43.5 parts of deionized water were added to the powder mixture to adjust the solid content to 69.4%, and then the mixture was kneaded in a planetary mixer at a rotation speed of 95 rpm for 25 minutes. Next, in step B, 1.0 part of hydrophilic polymer R-1 was added as step B2 and kneaded in a planetary mixer at a rotation speed of 95 rpm for 5 minutes, and 31.5 parts of ion-exchanged water were added as step B3 and kneaded in a planetary mixer at a rotation speed of 95 rpm for 20 minutes. For operations other than those described above, a negative electrode slurry was prepared by performing the same procedure as in Example 1, and its slurry viscosity was measured.

[0109] [Table 1]

[0110] [Table 2]

[0111] Details of the compounds used in Tables 1 and 2 are shown below. SiO: Silicon monoxide (manufactured by Osaka Titanium Technologies, particle size 5 μm) CMC: Sodium Carboxymethylcellulose SBR: Styrene-butadiene rubber

[0112] <<Evaluation Results>> As is clear from the results of Examples 1 to 14, by adding part or all of the hydrophilic binder after kneading a composition containing a thickening agent, the viscosity of the electrode slurry can be reduced even when the solid content concentration of the final negative electrode slurry is high, resulting in excellent productivity, high peel strength, and excellent binding properties. The reduction in electrode slurry viscosity by the manufacturing method of the present invention can be attributed to the fact that by delaying the addition of the hydrophilic binder, the thickening agent is preferentially adsorbed onto the active material rather than the hydrophilic binder, resulting in a reduced amount of free thickening agent present in the medium. In contrast, when the entire amount of the thickener and hydrophilic binder were added before solid mixing (Comparative Examples 1-4), the viscosity of the electrode slurry increased significantly compared to the examples, resulting in lower productivity. This can be attributed to the competitive adsorption of the hydrophilic binder and thickener to the active material, leading to a larger amount of free thickener present in the medium.

[0113] Here, comparing the effects of adding a portion of the hydrophilic binder during dry mixing of the active material and the thickener, the step without adding a portion of the hydrophilic binder (Example 1) resulted in a lower electrode slurry viscosity than the step with adding a portion of the hydrophilic binder during dry mixing (Example 3). This is thought to be because, in the former case, the adsorption of the thickener to the active material proceeded sufficiently, whereas in the latter case, the hydrophilic binder partially added during dry mixing inhibited the adsorption of the thickener to the active material in the first solid mixing step. Furthermore, comparing the effects of the mixing time in step A, the viscosity of the resulting electrode slurry was lower when the mixing time was longer (Example 1: 30 minutes) than when the mixing time in step A was shorter (Example 6: 15 minutes). This suggests that in step A, a longer mixing time allowed for sufficient adsorption of the thickener onto the active material, resulting in a lower electrode slurry viscosity. Furthermore, comparing the effect of the solid content concentration of the composition in the solid mixing process of step A, the electrode slurry viscosity obtained in Example 1 (69.4%) was lower than that of Examples 8 (65.0%) and 9 (71.1%). This is thought to be because in Example 1, a stronger shear force was applied to the composition in the solid mixing process of step A, resulting in sufficient adsorption of the thickener to the active material, thus exhibiting a lower electrode slurry viscosity. [Industrial applicability]

[0114] The slurry composition for secondary battery electrodes obtained by the manufacturing method of the present invention is expected to exhibit good durability (cycle characteristics) because, even at higher solid content concentrations than conventional methods, it maintains coating properties by reducing viscosity while exhibiting excellent peel strength (binding properties). Therefore, secondary batteries equipped with electrodes obtained using the above slurry composition are expected to maintain good integrity and exhibit good durability (cycle characteristics) even after repeated charging and discharging, contributing to the increase in capacity of automotive secondary batteries and the like. It can be suitably used in non-aqueous electrolyte secondary battery electrodes, and is particularly useful in non-aqueous electrolyte lithium-ion secondary batteries with high energy density.

Claims

1. Step A involves kneading a composition containing an active material, a thickener, and water with a solid content concentration of 60-80% by mass to obtain a first solid paste, Step B involves adding a hydrophilic binder (but different from the thickener) and water to the first solid paste and kneading it to obtain a second solid paste, The process includes step C, which involves adjusting the solid content concentration of the second solid paste to 40 to 60% by mass. A method for producing a slurry composition for secondary battery electrodes.

2. The aforementioned step B includes step B1, in which an aqueous solution of the hydrophilic binder is added to the first solid paste and kneaded to obtain a second solid paste. A method for producing a slurry composition for secondary battery electrodes according to claim 1.

3. Step B includes step B2 of adding the hydrophilic binder to the first solid paste and kneading it, and step B3 of further adding water and kneading it to obtain a second solid paste. A method for producing a slurry composition for secondary battery electrodes according to claim 1.

4. A method for producing a slurry composition for secondary battery electrodes according to any one of claims 1 to 3, wherein the hydrophilic binder is obtained by polymerizing a monomer component containing an ethylenically unsaturated carboxylic acid monomer, and the monomer component contains 50% by mass or more and 100% by mass or less of the ethylenically unsaturated carboxylic acid monomer based on its total amount.

5. A method for producing a slurry composition for secondary battery electrodes according to any one of claims 1 to 3, wherein the hydrophilic binder is crosslinked with a crosslinkable monomer, and the amount of the crosslinkable monomer used is 0.001 mol% or more and 2.5 mol% or less relative to the total amount of non-crosslinkable monomers.

6. A method for producing a slurry composition for secondary battery electrodes according to any one of claims 1 to 3, wherein the hydrophilic binder has a degree of neutralization of 80 to 100 mol%.

7. The method for producing a slurry composition for secondary battery electrodes according to any one of claims 1 to 3, wherein the thickening agent comprises carboxymethylcellulose (CMC).

8. The method for producing a slurry composition for secondary battery electrodes according to any one of claims 1 to 3, wherein step C includes the step of adding a styrene-butadiene rubber (SBR) latex.

9. A method for manufacturing a secondary battery electrode, comprising the step of forming a composite layer on the surface of a current collector, which is formed from a slurry composition for secondary battery electrodes obtained by a method for manufacturing a slurry composition for secondary battery electrodes according to any one of claims 1 to 3.

10. A method for manufacturing a secondary battery, comprising the step of manufacturing a secondary battery comprising a secondary battery electrode obtained by the manufacturing method described in claim 9.

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