Binder composition for secondary battery, electrode composition, electrode sheet and secondary battery, and manufacturing methods for electrode sheet and secondary battery

Abstract

To provide a binder composition for secondary battery, an electrode composition, an electrode sheet and a secondary battery, as well as a manufacturing method for the electrode sheet and secondary battery, which can sufficiently enhance the cycle characteristics (sufficiently prolong the cycle life) of the resulting secondary battery even when using electrode active materials with significant volume changes during charging and discharging.SOLUTION: The binder composition for secondary battery, electrode composition, electrode sheet and secondary battery including a water-soluble polymer (X) polymerized using an azo polymerization initiator, a water-soluble compound (Y), polymer particles and water, and a manufacturing method for the electrode sheet and secondary battery.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a binder composition for a secondary battery, a composition for an electrode, an electrode sheet and a secondary battery, and methods for manufacturing these electrode sheets and secondary batteries. [Background technology]

[0002] Secondary batteries, such as lithium-ion secondary batteries, are used as power sources for portable electronic devices such as personal computers, video cameras, and mobile phones. Recently, against the backdrop of the global environmental challenge of reducing carbon dioxide emissions, they have become increasingly popular as power sources for transportation equipment such as automobiles, and for storing electricity such as nighttime power and electricity generated by natural energy sources.

[0003] The electrodes (positive and negative electrodes) of a lithium ion secondary battery generally have electrode active material layers (positive and negative electrode active material layers), and these electrode active material layers contain electrode active material particles that can occlude or release lithium ions during charging and discharging, and also contain a conductive additive and the like as necessary. In recent years, with the expansion of secondary battery applications, the use of silicon-based active materials as negative electrode active materials has been actively investigated to further increase the capacity of lithium-ion secondary batteries. Using silicon-based active materials in negative electrodes enables higher energy density. However, silicon-based active materials occlude a large amount of lithium ions and expand significantly during charging, which leads to a corresponding increase in the degree of contraction of the silicon-based active material during discharging. Therefore, lithium-ion secondary batteries using silicon-based active materials as negative electrode active materials experience large volume changes during charging and discharging, which can easily impair the electrical conductivity (adhesion) between so-called solid particles, such as the electrode active material and conductive additive. Loss of electrical conductivity due to repeated charging and discharging increases the internal resistance of the battery, resulting in a decrease in battery performance. This limits the improvement of cycle characteristics.

[0004] In order to improve the cycle characteristics of lithium-ion secondary batteries (extend their cycle life), development is underway to develop binders to be contained in the electrode active material layer so that the adhesion between solid particles can be maintained even after repeated charging and discharging. For example, while a high-modulus polyimide binder improves cycle life, it requires a baking process, which creates a significant process load. Furthermore, when a high-Tg (glass transition temperature) monomer is introduced into the binder polymer to increase the modulus, the binder tends to become more hydrophilic, which reduces the dispersibility (adsorption rate) of the conductive additive. In recent years, the use of water-soluble acrylic binders with high modulus and good dispersibility in electrode slurries has been investigated. As a binder that solves these problems, Patent Document 1 describes a binder for secondary batteries, which comprises a first copolymer unit containing a carboxyl group-containing acrylic monomer, and one or more of an acrylic acid derivative monomer and a substituted or unsubstituted styrene, and a second copolymer unit containing a residue of a polymeric azo initiator, wherein the mass ratio of the second copolymer unit to the total mass of the first copolymer unit and the second copolymer unit is 10 to 40 mass %. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-101519 Summary of the Invention [Problem to be solved by the invention]

[0006] As a result of further investigations, the inventors have found that the cycle characteristics of the resulting secondary battery are insufficient when conventional electrode binders, including the binder described in Patent Document 1, are used. Therefore, there is a need to develop a binder that can further improve the cycle characteristics.

[0007] An object of the present invention is to provide a binder composition for secondary batteries and a composition for electrodes that can sufficiently improve the cycle characteristics (sufficiently extend the cycle life) of the resulting secondary battery even when an electrode active material that undergoes a large volume change during charge and discharge is used. Another object of the present invention is to provide an electrode sheet and a secondary battery using the above-mentioned binder composition for secondary batteries or electrode composition, and a method for manufacturing the above-mentioned electrode sheet and secondary battery. [Means for solving the problem]

[0008] The above-mentioned problems of the present invention have been solved by the following means. <1> A binder composition for a secondary battery, comprising: a water-soluble polymer (X) polymerized using an azo polymerization initiator; a water-soluble compound (Y); polymer particles; and water. <2> The azo polymerization initiator is a water-soluble azo polymerization initiator. <1> The binder composition for a secondary battery according to claim 1. <3> The azo polymerization initiator has a carboxy group. <1> or <2> The binder composition for a secondary battery according to claim 1. <4> The following <Condition I> is met: <1> ~ <3> 10. The binder composition for a secondary battery according to claim 9, wherein the binder composition is a binder for a secondary battery. <Condition I> Average particle size is 1 to 10 μm and specific surface area is 1 to 10 m 2 / g powdered carbon-coated silicon oxide with an average particle size of 15 to 25 μm and a specific surface area of ​​1 to 10 m 2 / g powdered graphite and graphite with an average particle size of 30-40 nm and a specific surface area of ​​65-75 m 2 In a slurry prepared by mixing acetylene black in powder form at a concentration of 0.1% / g and the binder composition for a secondary battery in the following quantitative ratio, the difference between the storage modulus G' at a shear strain of 0.1% and the storage modulus G' at a shear strain of 75% is 50 to 400 Pa, and the value of the storage modulus G' at a shear strain of 0.1% is 60 Pa or more. -Quantity ratio- With respect to 100 parts by mass of the total solid content in the slurry, the content of the carbon-coated silicon oxide is 17.8 parts by mass, the content of the graphite is 71.2 parts by mass, the content of the acetylene black is 6 parts by mass, the content of the solid content of the binder composition for secondary batteries is 5 parts by mass, and the total solid content in the slurry is 52% by mass. <5> The water-soluble polymer (X) is a polymer containing a component represented by the following general formula (B-1) and / or a component represented by the following general formula (B-2): <1> ~ <4> 10. The binder composition for a secondary battery according to claim 9, wherein the binder composition is a binder for a secondary battery. [ka] In general formula (B-1), R 11 ~R 13 represents a hydrogen atom, a cyano group, or an alkyl group having 1 to 6 carbon atoms; R 14 represents a hydrogen atom, a hydroxy group, an alkoxy group having 1 to 6 carbon atoms, a cyano group, a phenyl group, a carboxy group, a sulfo group, a phosphate group, or a phosphonate group; L 11 represents a single bond, an alkylene group having 1 to 16 carbon atoms, an arylene group having 6 to 12 carbon atoms, an oxygen atom, a sulfur atom, a carbonyl group, an imino group, or a linking group combining these. * represents a bonding site for incorporation into the main chain of the water-soluble polymer (X). In general formula (B-2), R 21 ~R 23 represents a hydrogen atom, a cyano group, or an alkyl group having 1 to 6 carbon atoms; R 24 represents a hydrogen atom, an acyl group, a hydroxy group, a phenyl group, or a carboxy group, and L 21 represents a single bond, an alkylene group having 1 to 16 carbon atoms, an arylene group having 6 to 12 carbon atoms, an oxygen atom, a sulfur atom, a carbonyl group, an imino group, or a linking group combining these. * represents a bonding site for incorporation into the main chain of the water-soluble polymer (X). <6> The water-soluble polymer (X) is a polymer containing a component represented by the general formula (B-2). <5> The binder composition for a secondary battery according to claim 1. <7> The content of the component represented by the general formula (B-2) in the water-soluble polymer (X) is 80 mass% or more. <6> The binder composition for a secondary battery according to claim 1. <8> The component represented by the general formula (B-2) contains an acrylamide component. <6> or <7> The binder composition for a secondary battery according to claim 1. <9> The water-soluble polymer (X) is a polymer further containing at least one of an acrylonitrile component, an N-vinyl-2-pyrrolidone component, and a styrene component. <5> ~ <8> 10. The binder composition for a secondary battery according to claim 9, wherein the binder composition is a binder for a secondary battery. <10> The water-soluble compound (Y) is a polysaccharide. <1> ~ <9> 10. The binder composition for a secondary battery according to claim 9, wherein the binder composition is a binder for a secondary battery. <11> The water-soluble compound (Y) contains at least one of carboxymethyl cellulose, cellulose nanofiber, hydroxyethyl cellulose, hydroxypropyl cellulose, and xanthan gum. <10> The binder composition for a secondary battery according to claim 1. <12> The weight average molecular weight of the water-soluble polymer (X) is 100,000 to 900,000. <1> ~ <11> 10. The binder composition for a secondary battery according to claim 9, wherein the binder composition is a binder for a secondary battery. <13> The molecular weight distribution of the water-soluble polymer (X) is 5.0 or less. <1> ~ <12> 10. The binder composition for a secondary battery according to claim 9, wherein the binder composition is a binder for a secondary battery. <14> The tensile modulus of the water-soluble polymer (X) is 4000 MPa or more. <1> ~ <13> 10. The binder composition for a secondary battery according to claim 9, wherein the binder composition is a binder for a secondary battery. <15> the polymer constituting the polymer particles is a polymer containing at least one of a conjugated diene component, an ethylenically unsaturated carboxylic acid component, a cyano group-containing ethylenic monomer component, and an aromatic vinyl monomer component; <1> ~ <14> 10. The binder composition for a secondary battery according to claim 9, wherein the binder composition is a binder for a secondary battery. <16> The glass transition temperature of the polymer particles is −50 to 150° C. <1> ~ <15> 10. The binder composition for a secondary battery according to claim 9, wherein the binder composition is a binder for a secondary battery. <17> <1> ~ <16> 1. A composition for an electrode, comprising the binder composition for a secondary battery according to any one of 1 to 10 above, an active material capable of inserting and releasing ions of a metal belonging to Group 1 or 2 of the periodic table, and a conductive additive. <18> The active material includes a silicon-based active material. <17> The electrode composition according to claim 1. <19> <17> or <18> An electrode sheet having a layer formed using the electrode composition according to claim 1. <20> At least one of the positive electrode active material layer and the negative electrode active material layer is <17> or <18> A secondary battery, wherein the layer is formed using the electrode composition according to claim 1. <21> <17> or <18> and forming an electrode active material layer using the electrode composition according to claim 1. <22> <21> 10. A method for manufacturing a secondary battery, comprising incorporating an electrode sheet obtained by the manufacturing method described in claim 1 as an electrode of the secondary battery.

[0009] In the present invention, the term "water-soluble polymer" refers to a polymer having a solubility in water of 10 g / L-H2O or more at 20°C, i.e., a polymer that dissolves 10 g or more in 1 liter of water. The solubility of the "water-soluble polymer" is preferably 100 g / L-H2O or more. In the present invention, the term "water-soluble compound" refers to a compound having a solubility in water of 10 g / L-H2O or more at 20°C, i.e., a compound that dissolves 10 g or more in 1 liter of water. The solubility of the "water-soluble compound" is preferably 100 g / L-H2O or more. In the present invention, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In the present invention, the description of compounds, components, or substituents includes those in which the structure has been partially modified, as long as the effects of the present invention are achieved. Furthermore, in the present invention, compounds or components that are not specified as substituted or unsubstituted may have any substituent, as long as the effects of the present invention are achieved. This also applies to substituents (e.g., groups expressed as "alkyl group," "methyl group," "methyl," etc.) and linking groups (e.g., groups expressed as "alkylene group," "methylene group," "methylene," etc.). Among such optional substituents, preferred substituents in the present invention are those selected from the substituent group T described below. In the present invention, when there are a plurality of substituents or linking groups, etc. (hereinafter referred to as "substituents, etc.") represented by a specific symbol or formula, or when a plurality of substituents, etc. are simultaneously defined, the respective substituents, etc. may be the same or different from each other unless otherwise specified. This also applies to the constituent components of the polymer. In the present invention, one kind of each component may be contained, or two or more kinds thereof may be contained. In the present invention, (meth)acrylic means one or both of acrylic and methacrylic. The same applies to (meth)acrylate. In the present invention, the term "secondary battery" refers to a general device in which ions pass between positive and negative electrodes via an electrolyte upon charging and discharging, and energy is stored and released at the positive and negative electrodes. That is, the term "secondary battery" in the present invention encompasses both batteries and capacitors (e.g., lithium ion capacitors). From the viewpoint of energy storage capacity, the secondary battery of the present invention is preferably used for battery applications (not as a capacitor). Secondary batteries can be broadly classified into aqueous secondary batteries and nonaqueous secondary batteries depending on the electrolyte used, with nonaqueous secondary batteries being preferred. In the present invention, "aqueous secondary battery" refers to a secondary battery using an aqueous electrolyte solution as the electrolyte. In the present invention, "nonaqueous secondary battery" encompasses nonaqueous electrolyte secondary batteries and all-solid-state secondary batteries. In the present invention, "nonaqueous electrolyte secondary battery" refers to a secondary battery using a nonaqueous electrolyte solution as the electrolyte. In the present invention, "nonaqueous electrolyte solution" refers to an electrolyte solution that is substantially free of water. An electrolyte solution that is substantially free of water means that the "nonaqueous electrolyte solution" may contain a trace amount of water as long as it does not impair the effects of the present invention. In the present invention, the "nonaqueous electrolyte solution" has a water concentration of 200 ppm (by mass) or less, preferably 100 ppm or less, and more preferably 20 ppm or less. It is practically difficult to make a nonaqueous electrolyte solution completely anhydrous, and it usually contains 1 ppm or more of water. In the present invention, the term "all-solid-state secondary battery" refers to a secondary battery that does not use a liquid electrolyte, but uses a solid electrolyte such as an inorganic solid electrolyte or a solid polymer electrolyte. In the present invention, when the number of carbon atoms of a certain group is specified, this number of carbon atoms means the number of carbon atoms of the group itself unless otherwise specified in the present invention or this specification. In other words, when this group further has a substituent, the number of carbon atoms means the number of carbon atoms counted excluding the carbon atoms of the substituent. In the present invention, the term "solid content" used when describing the content or content ratio means components other than water and the liquid medium described below. [Effects of the Invention]

[0010] The binder composition for secondary batteries, the electrode composition, and the electrode sheet of the present invention can sufficiently extend the cycle life of the resulting secondary batteries, even when using electrode active materials that undergo large volume changes during charge and discharge. The secondary battery of the present invention can achieve a sufficiently long cycle life even when an electrode active material that undergoes a large volume change during charging and discharging is used. The electrode sheet of the present invention can be obtained by the method for producing an electrode sheet of the present invention, and the secondary battery of the present invention can be obtained by the method for producing a secondary battery of the present invention. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a longitudinal sectional view showing a schematic basic layer structure of an embodiment of a secondary battery according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Binder composition for secondary batteries] The binder composition for secondary batteries of the present invention (hereinafter also referred to as "the binder composition of the present invention") contains a water-soluble polymer (X) (in the present invention, also simply referred to as "the water-soluble polymer (X)") polymerized using an azo polymerization initiator, a water-soluble compound (Y), polymer particles, and water. The binder composition of the present invention is suitable for use in forming members or constituent layers of preferably non-aqueous secondary batteries, more preferably non-aqueous electrolyte secondary batteries. The water contained in the binder composition of the present invention functions as a liquid medium. Typically, the binder composition of the present invention is suitable for use as an electrode composition containing the binder composition of the present invention, an electrode active material (a positive electrode active material or a negative electrode active material, collectively also simply referred to as "active material"), and a conductive additive, and is suitable for use in forming an electrode active material layer (a positive electrode active material layer or a negative electrode active material layer) in an electrode (a positive electrode or a negative electrode) of a secondary battery.

[0013] The water-soluble polymer (X) and polymer particles contained in the binder composition of the present invention are thought to function primarily as a binder that binds solid particles (electrode active material, conductive additive, etc.) together in a layer formed by mixing the binder composition of the present invention with solid particles. They may also function as a binder that binds the current collector and solid particles. The adsorption of the water-soluble polymer (X) and polymer particles to the solid particles and current collector includes not only physical adsorption but also chemical adsorption (adsorption by chemical bond formation, adsorption by electron exchange, etc.). On the other hand, the water-soluble compound (Y) contained in the binder composition of the present invention is thought to function mainly as a thickener (dispersant) in the binder composition of the present invention.

[0014] The binder composition of the present invention can be used, for example, to prepare an electrode sheet as an electrode composition containing an active material and a conductive additive, and by applying this to the electrode of a secondary battery, the cycle characteristics of the secondary battery can be improved. Although the reason for this is unclear, it is thought to be as follows. The water-soluble polymer (X) polymerized using the azo polymerization initiator contained in the binder composition of the present invention has superior breaking elongation compared to water-soluble polymers polymerized using persulfates such as ammonium persulfate (ammonium peroxodisulfate), potassium persulfate (potassium peroxodisulfate), or sodium persulfate (sodium peroxodisulfate) or inorganic peroxides such as hydrogen peroxide as a polymerization initiator. Furthermore, the coexistence of this water-soluble polymer (X) with a water-soluble compound (Y) functioning as a thickener and polymer particles increases the dispersion stability of the slurry, and the binder of the water-soluble polymer (X) with superior breaking elongation and the particulate binder act in combination to bind solid particles, etc., allowing good conductivity to be maintained even with volume changes in the electrode active material associated with charge and discharge of the secondary battery, which is thought to be one of the reasons for the improved cycle characteristics of the secondary battery.

[0015] (Water-soluble polymer (X)) The binder composition of the present invention contains a water-soluble polymer (X) obtained by polymerization using an azo polymerization initiator. The azo polymerization initiator is an azo compound having an azo group (-N=N-) that decomposes into nitrogen molecules and carbon radicals by heat or light, and functions as a polymerization initiator for polymer synthesis (polymerization). As the azo polymerization initiator, any commonly used azo polymerization initiator can be used without any particular limitation, and examples thereof include water-soluble azo polymerization initiators, oil-soluble azo polymerization initiators, and polymeric azo polymerization initiators. Of these, a water-soluble azo polymerization initiator is preferred, from the viewpoints that the water-soluble polymer (X) exhibiting high elasticity as a binder can be easily polymerized in an aqueous solvent, and further, the obtained aqueous solution of the water-soluble polymer (X) can be used as is for preparing a binder composition. A polymeric azo polymerization initiator is a polymer having a structure in which polymer segments and azo groups are repeatedly bonded, and having two or more radical generating points (azo groups) per molecule. In contrast, water-soluble azo polymerization initiators and oil-soluble azo polymerization initiators are usually compounds having one radical generating point (azo group) per molecule.

[0016] Examples of water-soluble azo polymerization initiators include azonitrile polymerization initiators, azoamide polymerization initiators, azoamidine polymerization initiators, and azoimidazoline polymerization initiators. Specific examples include 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] disulfate dihydrate, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate, 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], and 4,4'-azobis(4-cyanovaleric acid). As the water-soluble azo polymerization initiator, for example, VA-044, VA-046B, V-50, VA-057, VA-061, VA-086, and V-501 (all trade names) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. can be used.

[0017] From the viewpoint of further improving dispersibility and cycle characteristics, the azo polymerization initiator preferably has a carboxy group, and more preferably is a water-soluble azo polymerization initiator having a carboxy group.

[0018] The amount of the azo polymerization initiator used in the polymerization of the water-soluble polymer (X) is preferably 0.05 parts by mass or more and less than 10 parts by mass, more preferably 0.05 to 5 parts by mass, still more preferably 0.05 to 1 part by mass, and particularly preferably 0.1 to 1 part by mass, relative to 100 parts by mass of the total amount of the monomers (monomers do not include the polymerization initiator) used in the polymerization of the water-soluble polymer (X). The content of the azo polymerization initiator-derived component in the water-soluble polymer (X) roughly corresponds to the amount of the azo polymerization initiator used in the polymerization of the water-soluble polymer (X) relative to the total amount of the monomers used in the polymerization of the water-soluble polymer (X), and is preferably 0.05 parts by mass or more but less than 10 parts by mass, more preferably 0.05 to 5 parts by mass, even more preferably 0.05 to 1 part by mass, and particularly preferably 0.1 to 1 part by mass, relative to 100 parts by mass of the total amount of the monomer-derived components of the water-soluble polymer (X). In the present invention, the "constituent derived from the azo polymerization initiator" corresponds to a carbon radical structure obtained by elimination of a nitrogen molecule from the azo polymerization initiator.

[0019] The water-soluble polymer (X) is preferably a polymer containing a component represented by the following general formula (B-1) and / or a component represented by the following general formula (B-2) (a polymer containing at least one of a component represented by the following general formula (B-1) and a component represented by the following general formula (B-2)).

[0020] [ka]

[0021] In general formula (B-1), R 11 ~R 13 represents a hydrogen atom, a cyano group, or an alkyl group having 1 to 6 carbon atoms. This alkyl group having 1 to 6 carbon atoms may be linear or branched. This alkyl group having 1 to 6 carbon atoms is preferably an alkyl group having 1 to 4 carbon atoms, more preferably methyl or ethyl, and even more preferably methyl. R 11 and R 12 is preferably a hydrogen atom. R13 is preferably a hydrogen atom or methyl, more preferably a hydrogen atom.

[0022] R 14 represents a hydrogen atom, a hydroxy group, an alkoxy group (alkyloxy group) having 1 to 6 carbon atoms, a cyano group, a phenyl group, a carboxy group, a sulfo group (-S(=O)2(OH)), a phosphate group (-OP(=O)(OH)2), or a phosphonate group (-P(=O)(OH)2). The alkyl group in the alkoxy group having 1 to 6 carbon atoms may be linear or branched. The alkoxy group having 1 to 6 carbon atoms is preferably an alkoxy group having 1 to 4 carbon atoms, and more preferably methoxy or ethoxy. R 14 is preferably a hydrogen atom, a hydroxy group, methoxy or ethoxy, more preferably a hydrogen atom.

[0023] L 11 is a single bond, an alkylene group having 1 to 16 carbon atoms, an arylene group having 6 to 12 carbon atoms, an oxygen atom, a sulfur atom, a carbonyl group (>C=O), or an imino group (>NR N ), or a linking group combining these. 11 may have a substituent selected from the group T of substituents described below, and this substituent is preferably a hydroxy group. Above R N represents a hydrogen atom or an alkyl group. L 11 When L represents a linking group other than a single bond, 11 The chemical formula weight of L is preferably 14 to 2000, more preferably 14 to 500, and even more preferably 28 to 200. 11 The alkylene group having 1 to 16 carbon atoms may be linear or branched. The alkylene group preferably has 1 to 12 carbon atoms, more preferably 1 to 10 carbon atoms, still more preferably 1 to 6 carbon atoms, and particularly preferably 1 to 4 carbon atoms. L 11 is preferably a single bond, methylene, ethylene, propylene, 2-hydroxypropylene or butylene, more preferably a single bond, ethylene or butylene.

[0024] * indicates a binding site for incorporation into the main chain of the polymer (water-soluble polymer (X)).

[0025] In general formula (B-2), R 21 ~R 23 is the above R 11 ~R 13 The same definition and preferred form are also the same. R 24 represents a hydrogen atom, an acyl group (an alkylcarbonyl group), a hydroxy group, a phenyl group, or a carboxy group. Examples of the alkyl group in the acyl group include the alkyl groups in the substituent group T described below, which may be linear or branched. Preferably, R 11 ~R 13 As the alkyl group, an alkyl group having 1 to 6 carbon atoms can be used. R 24 is preferably a hydrogen atom or a hydroxy group, more preferably a hydrogen atom. L 21 is the above L 11 The preferred form is L 11 A single bond or ethylene is more preferred, and a single bond is even more preferred. * indicates a binding site for incorporation into the main chain of the polymer (water-soluble polymer (X)).

[0026] Specific examples of the constituent component represented by the general formula (B-1) above include a (meth)acrylic acid component; alkyl (meth)acrylate components such as a methyl (meth)acrylate component, an ethyl (meth)acrylate component, a propyl (meth)acrylate component, and a butyl (meth)acrylate component; hydroxyalkyl (meth)acrylate components such as a 2-hydroxyethyl (meth)acrylate component, a 4-hydroxybutyl (meth)acrylate component, and a 2,3-dihydroxypropyl (meth)acrylate component; and alkoxyalkyl (meth)acrylate components such as a methoxyethyl (meth)acrylate component and an ethoxyethyl (meth)acrylate component, with a (meth)acrylic acid component or a hydroxyalkyl (meth)acrylate component being preferred. Specific examples of the component represented by the general formula (B-2) include a (meth)acrylamide component; and an N-(hydroxyalkyl)(meth)acrylamide component such as an N-(2-hydroxyethyl)(meth)acrylamide component, with a (meth)acrylamide component being preferred and an acrylamide component being more preferred.

[0027] From the viewpoint of effectively suppressing the volume change of the electrode active material layer and improving the cycle characteristics, the water-soluble polymer (X) preferably contains a constituent component represented by the above general formula (B-2), and more preferably contains an acrylamide component. The content of the acrylamide component in the constituent component represented by general formula (B-2) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be 100% by mass.

[0028] The water-soluble polymer (X) used in the present invention may contain components other than the component represented by the general formula (B-1) above and / or the component represented by the general formula (B-2) above (hereinafter referred to as "other components"), within the range that does not impair the effects of the present invention. Examples of the other components include an acrylonitrile component, an N-vinyl-2-pyrrolidone component, and a styrene component. The water-soluble polymer (X) used in the present invention preferably contains at least one of an acrylonitrile component, an N-vinyl-2-pyrrolidone component, and a styrene component as other constituent components, and more preferably contains an acrylonitrile component. The types of constituent components contained in the water-soluble polymer (X) are not particularly limited, and are preferably 1 to 10 types, more preferably 1 to 5 types, and particularly preferably 1 or 2 types. Specific examples of the water-soluble polymer (X) described below describe polymers having one or two types of constituent components. In these specific examples, the polymer having one type of constituent component is polyacrylamide. When counting the types of the above constituent components, the constituent component derived from the azo polymerization initiator is not counted. The content of the following constituent components is the content of all the constituent components constituting the water-soluble polymer (X), excluding the constituent component derived from the azo polymerization initiator. In the water-soluble polymer (X), the content of the component represented by the general formula (B-1) above and / or the component represented by the general formula (B-2) above is preferably 60% by mass or more in total, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 85% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass. The content of the component represented by the general formula (B-1) in the water-soluble polymer (X) is preferably 40% by mass or less, more preferably less than 20% by mass, and even more preferably 15% by mass or less. On the other hand, the content of the component represented by the general formula (B-2) in the water-soluble polymer (X) is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more. In addition, when the water-soluble polymer (X) contains a component (other component) other than the component represented by the general formula (B-1) above and other than the component represented by the general formula (B-2) above, the content of the component represented by the general formula (B-2) above is preferably 65% ​​by mass or more, and more preferably 75% by mass or more. When the water-soluble polymer (X) contains a component represented by the general formula (B-1) and a component represented by the general formula (B-2), the mass ratio of the content of the component represented by the general formula (B-2) to the content of the component represented by the general formula (B-1) in the water-soluble polymer (X) (content of the component represented by the general formula (B-2) / content of the component represented by the general formula (B-1)) is not particularly limited, and is preferably 99 / 1 to 60 / 40.

[0029] The weight average molecular weight (Mw) of the water-soluble polymer (X) used in the present invention is not particularly limited, and is preferably from 100,000 to 900,000, more preferably from 200,000 to 500,000, from the viewpoint of improving cycle characteristics. The water-soluble polymer (X) preferably does not have a crosslinked structure, that is, it is preferably a chain polymer.

[0030] From the viewpoint of improving cycle characteristics, the molecular weight distribution of the water-soluble polymer (X) is preferably 5.0 or less, more preferably 3.0 or less, while a molecular weight distribution of 1.0 or more is practical. The molecular weight distribution of the water-soluble polymer (X) is also called dispersity and is calculated by [weight average molecular weight (Mw)] / [number average molecular weight (Mn)].

[0031] (Measurement of weight average molecular weight and number average molecular weight) In the present invention, the weight-average molecular weight and number-average molecular weight of a polymer are measured by gel permeation chromatography (GPC). The molecular weight refers to the weight-average molecular weight in terms of polyethylene oxide. The measurement method is basically the value measured under the method of measurement condition 1 below. However, depending on the type of polymer, an appropriate eluent may be selected and used. (Measurement condition 1) Measuring instrument: HLC-8220GPC (product name, manufactured by Tosoh Corporation) Columns: TOSOH TSKgel 5000PWXL (trade name, manufactured by Tosoh Corporation), TOSOH TSKgel G4000PWXL (trade name, manufactured by Tosoh Corporation), and TOSOH TSKgel G2500PWXL (trade name, manufactured by Tosoh Corporation) were connected together. Carrier: 200mM sodium nitrate aqueous solution Measurement temperature: 40℃ Carrier flow rate: 1.0 ml / min Sample concentration: 0.2% by mass Detector: RI (refractive index) detector If the molecular weight cannot be measured under the above measurement condition 1 due to crosslinking or other reasons, the molecular weight is measured by static light scattering under the following measurement condition 2. (Measurement condition 2) Measuring instrument: DLS-8000 (product name, manufactured by Otsuka Electronics Co., Ltd.) Measured concentration: 0.25, 0.50, 0.75, 1.00mg / mL Diluent: 0.1M NaCl aqueous solution Laser wavelength: 633nm Pinhole: PH1=Open, PH2=Slit Measurement angles: 60, 70, 80, 90, 100, 110, 120, 130 degrees Analysis method: The molecular weight is measured from the Zimm square root plot. The dn / dc required for analysis is measured using an Abbe refractometer.

[0032] The tensile modulus of the water-soluble polymer (X) used in the present invention is preferably 3500 MPa or more, more preferably 4000 MPa or more, even more preferably 5000 MPa or more, and particularly preferably 6000 MPa or more, from the viewpoint of effectively suppressing the volume change of the electrode active material layer and improving the cycle characteristics. On the other hand, the tensile modulus is practically 15000 MPa or less. In the present invention, the tensile modulus is a value obtained by the method described in the examples below.

[0033] The water-soluble polymer (X) may further have a substituent in each of the above-mentioned structures or partial structures, and examples of this substituent include substituents selected from the following substituent group T. Furthermore, for each substituent in the water-soluble polymer (X), unless otherwise specified, the description of the corresponding substituent in the following substituent group T can be applied. For each linking group in the water-soluble polymer (X), unless otherwise specified, the description of the linking group obtained by removing a hydrogen bond from the corresponding substituent in the following substituent group T can be applied.

[0034] - Substituent group T - alkyl groups (preferably alkyl groups having 1 to 20 carbon atoms, for example, methyl, ethyl, isopropyl, t-butyl, pentyl, heptyl, 1-ethylpentyl, benzyl, 2-ethoxyethyl, 1-carboxymethyl, etc.), alkenyl groups (preferably alkenyl groups having 2 to 20 carbon atoms, for example, vinyl, allyl, oleyl, etc.), alkynyl groups (preferably alkynyl groups having 2 to 20 carbon atoms, for example, ethynyl, butadiynyl, phenylethynyl, etc.), cycloalkyl groups (preferably cycloalkyl groups having 3 to 20 carbon atoms, for example , cyclopropyl, cyclopentyl, cyclohexyl, 4-methylcyclohexyl, etc.), aryl groups (preferably aryl groups having 6 to 26 carbon atoms, for example, phenyl, 1-naphthyl, 4-methoxyphenyl, 2-chlorophenyl, 3-methylphenyl, etc.), heterocyclic groups (preferably heterocyclic groups having 2 to 20 carbon atoms, more preferably 5- or 6-membered heterocyclic groups having at least one of oxygen atom, sulfur atom, and nitrogen atom as a ring-constituting atom. Heterocyclic groups include aromatic heterocyclic groups and aliphatic heterocyclic groups. For example, tetrahydropyran a tetrahydrofuran ring group, 2-pyridyl, 4-pyridyl, 2-imidazolyl, 2-benzimidazolyl, 2-thiazolyl, 2-oxazolyl, etc.), an alkoxy group (preferably an alkoxy group having 1 to 20 carbon atoms, for example, methoxy, ethoxy, isopropyloxy, benzyloxy, etc.), an aryloxy group (preferably an aryloxy group having 6 to 26 carbon atoms, for example, phenoxy, 1-naphthyloxy, 3-methylphenoxy, 4-methoxyphenoxy, etc.), a heterocyclic oxy group (a group in which an -O- group is bonded to the above heterocyclic group ... Examples of the alkoxycarbonyl group include an alkoxycarbonyl group (preferably an alkoxycarbonyl group having 2 to 20 carbon atoms, such as ethoxycarbonyl or 2-ethylhexyloxycarbonyl), an aryloxycarbonyl group (preferably an aryloxycarbonyl group having 7 to 26 carbon atoms, such as phenoxycarbonyl, 1-naphthyloxycarbonyl, 3-methylphenoxycarbonyl or 4-methoxyphenoxycarbonyl), an amino group (preferably an amino group having 0 to 20 carbon atoms, including an amino group substituted with a group selected from an alkyl group and an aryl group).For example, amino (-NH2), N,N-dimethylamino, N,N-diethylamino, N-ethylamino, anilino, etc.), sulfamoyl group (preferably a sulfamoyl group having 0 to 20 carbon atoms, including sulfamoyl groups substituted with a group selected from an alkyl group and an aryl group, for example, sulfamoyl (-SON2NH2), N,N-dimethylsulfamoyl, N-phenylsulfamoyl, etc.), acyl group (including an alkylcarbonyl group, an alkenylcarbonyl group, an alkynylcarbonyl group, an arylcarbonyl group, and a heterocyclic carbonyl group, preferably an acyl group having 1 to 20 carbon atoms, for example, formyl, acetyl, propionyl, butyryl, octanoyl, hexadecanoyl, acryloyl, methacryloyl, crotonoyl, benzoyl, naphthoyl, nicotinoyl, etc.), acyloxy group (alkylcarbonyloxy group, alkenyl Examples of the acyl group include an acylcarbonyloxy group, an alkynylcarbonyloxy group, an arylcarbonyloxy group, and a heterocyclic carbonyloxy group, and preferably an acyloxy group having 1 to 20 carbon atoms, such as formyloxy, acetyloxy, propionyloxy, butyryloxy, octanoyloxy, hexadecanoyloxy, acryloyloxy, methacryloyloxy, crotonoyloxy, benzoyloxy, naphthoyloxy, and nicotinoyloxy; a carbamoyl group (preferably a carbamoyl group having 1 to 20 carbon atoms, and including a carbamoyl group substituted with a group selected from an alkyl group and an aryl group, such as N,N-dimethylcarbamoyl and N-phenylcarbamoyl); and an acylamino group (preferably an acylamino group having 1 to 20 carbon atoms, and preferred examples of the acyl group in the acylamino group include the above-mentioned acyl groups).For example, acetylamino, benzoylamino, etc.), alkylthio groups (preferably alkylthio groups having 1 to 20 carbon atoms, for example, methylthio, ethylthio, isopropylthio, benzylthio, etc.), arylthio groups (preferably arylthio groups having 6 to 26 carbon atoms, for example, phenylthio, 1-naphthylthio, 3-methylphenylthio, 4-methoxyphenylthio, etc.), arylsilyl groups (preferably arylsilyl groups having 6 to 42 carbon atoms, for example, triphenylsilyl, etc.), heterocyclic thio groups (the above heterocyclic groups to which an -S- group is bonded), groups), alkylsulfonyl groups (preferably alkylsulfonyl groups having 1 to 20 carbon atoms, for example, methylsulfonyl, ethylsulfonyl, etc.), arylsulfonyl groups (preferably arylsulfonyl groups having 6 to 22 carbon atoms, for example, benzenesulfonyl, etc.), alkylsilyl groups (preferably alkylsilyl groups having 1 to 20 carbon atoms, for example, monomethylsilyl, dimethylsilyl, trimethylsilyl, triethylsilyl, etc.), phosphite groups (preferably phosphite groups having 0 to 20 carbon atoms, for example, -OP(=O)(-OH)(R P )), a hypophosphite group (preferably a hypophosphite group having 0 to 20 carbon atoms, for example, —OP(═O)(R P )2), a phosphoryl group (preferably a phosphoryl group having 0 to 20 carbon atoms, for example, —P(═O)(R P )2), a phosphinyl group (preferably a phosphinyl group having 0 to 20 carbon atoms, for example, —P(R P ) 2), sulfo group, phosphate group, phosphonate group, carboxy group, hydroxy group, sulfanyl group, cyano group, halogen atom (e.g., fluorine atom, chlorine atom, bromine atom, iodine atom). P is a hydrogen atom or a substituent (preferably a group selected from the substituent group T). Furthermore, each of the groups listed in the substituent group T may further have each of the groups listed in the substituent group T above as a substituent.

[0035] The water-soluble polymer (X) used in the present invention can be obtained by a conventional polymer synthesis method using an azo polymerization initiator as a polymerization initiator. In the synthesis of the water-soluble polymer (X) used in the present invention, the method and conditions for chain polymerization etc. are not particularly limited, and conventional methods and conditions can be appropriately applied depending on the purpose. The "water solubility" of the water-soluble polymer (X) can be controlled, for example, by the type and content of the constituent components.

[0036] Preferred specific examples of the water-soluble polymer (X) used in the present invention are shown below, but the present invention is not limited to these. In the following specific examples, a and b represent the proportions (mass%) of each component. a = 99 to 60, and b = 1 to 40, provided that a + b = 100. In the following specific examples, description of components derived from azo polymerization initiators is omitted.

[0037] [ka]

[0038] In the present invention, the water-soluble polymer (X) may be used alone or in combination of two or more.

[0039] (Water-soluble compound (Y)) In the present invention, the water-soluble compound (Y) is a water-soluble compound (monomer or polymer) having a structure different from that of the water-soluble polymer (X), and a wide variety of compounds can be used that function as a thickener for the slurry for forming the electrode active material layer of a secondary battery. Examples of the thickener include cellulose compounds and polysaccharides such as natural polysaccharides. Examples of cellulose compounds include methyl cellulose, ethyl cellulose, benzyl cellulose, triethyl cellulose, cyanoethyl cellulose, nitrocellulose, hydroxymethyl cellulose, hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC), hydroxybutyl methyl cellulose, carboxymethyl cellulose (CMC), aminomethyl hydroxypropyl cellulose, aminoethyl hydroxypropyl cellulose, cellulose nanofiber (CNF), cellulose nanocrystal (CNC), etc. Furthermore, the cellulose compound may be in the form of a salt such as an ammonium salt, a sodium salt, or a lithium salt. Examples of natural polysaccharides include carrageenan, xanthan gum, guar gum, tamarind gum (tamarind seed gum), diutan gum, welan gum, gellan gum, locust bean gum, and tara gum. Among these, the water-soluble compound (Y) preferably contains at least one of carboxymethyl cellulose, cellulose nanofiber, hydroxyethyl cellulose, hydroxypropyl cellulose, and xanthan gum. In the present invention, the water-soluble compound (Y) may be used alone or in combination of two or more.

[0040] (polymer particles) The polymer particles used in the present invention are particulate polymers, and the "particulate" may be flat, amorphous, etc., and is preferably spherical or granular. The polymer particles are water-insoluble polymers, i.e., polymers whose solubility in water at 20°C is less than 10 g / L-H2O (10 g or more do not dissolve in 1 liter of water).

[0041] From the viewpoint of improving cycle characteristics, the tensile modulus of the polymer particles is preferably 100 to 3000 MPa, more preferably 100 to 1000 MPa. In the present invention, the tensile modulus can be determined in the same manner as in the method for measuring the tensile modulus of a water-soluble polymer described in the Examples below, except that polymer particles are used instead of the water-soluble polymer.

[0042] The glass transition temperature of the polymer particles is not particularly limited, and is preferably from -50 to 150°C, more preferably from -30 to 100°C, from the viewpoint of improving the adhesion and cycle characteristics of the electrode sheet. When the polymer particles have two or more glass transition temperatures, it is preferable that all of them fall within the above-mentioned preferred range.

[0043] - Glass transition temperature - When commercially available polymer particles are used, the glass transition temperature of the polymer particles is the value listed in the manufacturer's catalog. When glass transition temperature information from the manufacturer is unavailable or when synthetic polymer particles are used, the glass transition temperature value from the table in Chapter 36 of POLYMER HANDBOOK 4th Edition is used. When the glass transition temperature is not listed in the above literature, the glass transition temperature value obtained by measurement under the following measurement conditions is used.

[0044] The glass transition temperature (Tg) is calculated by measuring a dried sample of polymer particles using a differential scanning calorimeter: X-DSC7000 (trade name, manufactured by SII Nano Technology Co., Ltd.) under the following measurement conditions. The measurement is carried out twice on the same sample, and the result of the second measurement is used. (Measurement conditions) Atmosphere in the measurement chamber: Nitrogen gas (50 mL / min) Heating rate: 5℃ / min Measurement start temperature: -80℃ Measurement end temperature: 250℃ Sample pan: Aluminum pan Measurement sample mass: 5 mg Calculation of Tg: Tg is calculated by rounding off the decimal point of the midpoint between the start and end points of the decline in a DSC (differential scanning calorimetry) chart.

[0045] The average particle size (average primary particle size) of the polymer particles is not particularly limited, but is preferably from 50 to 300 nm, more preferably from 50 to 250 nm, and even more preferably from 50 to 200 nm. When commercially available polymer particles are used, the average particle size of the polymer particles is the value listed in the manufacturer's catalog. When information on the average particle size from the manufacturer is not available or when synthesized polymer particles are used, the average particle size of the polymer particles may be a value obtained by applying the measurement method for the average particle size (volume-based median diameter D50 in water) of the negative electrode active material described below.

[0046] The polymer particles may be either step-polymerized or chain-polymerized, with chain-polymerized particles being preferred. The chain-polymerized polymer particles may be either a homopolymer or a copolymer. The copolymer may be either random or block polymerized. Examples of the constituent components of the polymer particles (chain polymerization polymers) include a conjugated diene component, an aromatic vinyl monomer component, an ethylenically unsaturated carboxylic acid component, a cyano group-containing ethylenic monomer component, an ethylenically unsaturated carboxylic acid ester component, and a fluorinated vinyl monomer component, and it is preferable that the polymer particles contain at least one of the conjugated diene component, the ethylenically unsaturated carboxylic acid component, the cyano group-containing ethylenic monomer component, and the aromatic vinyl monomer component. Among the above constituent components, it is preferable that the polymer particles contain a conjugated diene component and an aromatic vinyl monomer component. In the above, the term "aromatic vinyl monomer component" refers to a component derived from a monomer having a carbon-carbon double bond (preferably one or two, more preferably one) and an aryl group (preferably one); the term "ethylenically unsaturated carboxylic acid component" refers to a component derived from a monomer having a carbon-carbon double bond (preferably one) and a carboxy group (preferably one or two); the term "cyano group-containing ethylenic monomer component" refers to a component derived from a monomer having a carbon-carbon double bond (preferably one) and a cyano group (preferably one or two, more preferably one); the term "ethylenically unsaturated carboxylic acid ester component" refers to a component derived from a monomer having a carbon-carbon double bond (preferably one) and a carboxylic acid ester moiety (esterified carboxy group) (preferably one); and the term "vinyl fluoride monomer component" refers to a component derived from ethylene having 1 to 4 (preferably 2) fluorine atoms. The above "carbon-carbon double bond" does not include a carbon-carbon double bond in an aromatic ring.

[0047] Examples of conjugated dienes that lead to the conjugated diene component include aliphatic conjugated dienes such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3-butadiene. Examples of aromatic vinyl monomers that lead to the aromatic vinyl monomer component include styrene, α-methylstyrene, 4-tert-butylstyrene, 4-tert-butoxystyrene, vinyltoluene (3-vinyltoluene, 4-vinyltoluene), and divinylbenzene (m-divinylbenzene, p-divinylbenzene). Examples of the ethylenically unsaturated carboxylic acid from which the ethylenically unsaturated carboxylic acid component is derived include (meth)acrylic acid, maleic acid, itaconic acid, and fumaric acid. Examples of cyano group-containing ethylenic monomers that lead to the cyano group-containing ethylenic monomer component include (meth)acrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, and vinylidene cyanide. Examples of the ethylenically unsaturated carboxylic acid ester from which the ethylenically unsaturated carboxylic acid ester component is derived include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Examples of vinyl fluoride monomers that lead to vinyl fluoride monomer components include vinylidene fluoride.

[0048] The polymer particles used in the present invention can be obtained by a conventional polymer synthesis method. In the synthesis of the polymer particles used in the present invention, the method and conditions for chain polymerization etc. are not particularly limited, and conventional methods and conditions can be appropriately applied depending on the purpose. The polymer particles may be particles obtained by subjecting the step-polymerized polymer particles and chain-polymerized polymer particles described above to a modification treatment such as carboxy modification. The method and conditions for the modification treatment are not particularly limited, and the modification treatment can be carried out by a conventional method. The water solubility, tensile modulus, glass transition temperature and average particle size of the polymer particles can be adjusted, for example, by the type and content of the constituent components in the polymer.

[0049] Specific examples of polymer particles include styrene / butadiene copolymers, acrylic polymers, and poly(vinylidene fluoride), with styrene / butadiene copolymers being preferred. The styrene / butadiene copolymer means a copolymer having the above aromatic vinyl monomer component and the above conjugated diene component, and may be a modified copolymer such as a carboxy-modified copolymer. In the present invention, the polymer particles may be used alone or in combination of two or more kinds.

[0050] The binder composition of the present invention may contain, in addition to the water-soluble polymer (X), the water-soluble compound (Y) and the polymer particles, other polymers that are commonly used as binders for batteries. The total proportion of the water-soluble polymer (X), the water-soluble compound (Y), and the polymer particles in the total solid content of the binder composition of the present invention is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. Most preferably, the total solid content of the binder composition of the present invention is the water-soluble polymer (X), the water-soluble compound (Y), and the polymer particles. In the binder composition of the present invention, the mass ratio of the water-soluble polymer (X), the water-soluble compound (Y), and the polymer particles (mass of the water-soluble polymer (X): mass of the water-soluble compound (Y): mass of the polymer particles) is not particularly limited, and is preferably 10-80:10-80:10-50, and more preferably 20-70:10-60:20-50.

[0051] The binder composition of the present invention contains water as the liquid medium. The water content in the binder composition of the present invention is not particularly limited and can be, for example, 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more. The binder composition of the present invention may contain 60% by mass or more of water, 70% by mass or more, or 80% by mass or more. On the other hand, it is practical for the water content in the binder composition of the present invention to be 99.5% by mass or less. The binder composition of the present invention may contain a liquid medium other than water. Examples of the liquid medium other than water include organic solvents that are miscible with water without phase separation when mixed with water (hereinafter referred to as water-soluble organic solvents), and preferred examples thereof include N-methylpyrrolidone, methanol, ethanol, acetone, and tetrahydrofuran.

[0052] The contents of the water-soluble polymer (X), the water-soluble compound (Y), and the polymer particles in the binder composition of the present invention may be appropriately set depending on the purpose. For example, the total content of the water-soluble polymer (X), the water-soluble compound (Y), and the polymer particles in the binder composition may be 0.5 to 50% by mass, preferably 5 to 30% by mass, and more preferably 10 to 20% by mass. The binder composition of the present invention may contain other components in addition to the water-soluble polymer (X), the water-soluble compound (Y), the polymer particles, water, and a liquid medium other than water, depending on the purpose. Examples of other components include polyhydric alcohols (alcohols having two or more hydroxy groups). The binder composition of the present invention can also be prepared by, for example, diluting a synthesis liquid of the water-soluble polymer (X), the water-soluble compound (Y), and the polymer particles. Therefore, the binder composition of the present invention may contain compounds used in the synthesis of the water-soluble polymer (X), the water-soluble compound (Y), and the polymer particles, or by-products produced after the reaction thereof.

[0053] The binder composition of the present invention preferably satisfies the following <Condition I>. <Condition I> Average particle size is 1 to 10 μm and specific surface area is 1 to 10 m 2 / g powdered carbon-coated silicon oxide with an average particle size of 15 to 25 μm and a specific surface area of ​​1 to 10 m 2 / g powdered graphite and graphite with an average particle size of 30-40 nm and a specific surface area of ​​65-75 m 2 In a slurry prepared by mixing acetylene black in powder form at a concentration of 0.1% / g and the binder composition for a secondary battery in the following quantitative ratio, the difference between the storage modulus G' at a shear strain of 0.1% and the storage modulus G' at a shear strain of 75% is 50 to 400 Pa, and the value of the storage modulus G' at a shear strain of 0.1% is 60 Pa or more. -Quantity ratio- With respect to 100 parts by mass of the total solid content in the slurry, the content of the carbon-coated silicon oxide is 17.8 parts by mass, the content of the graphite is 71.2 parts by mass, the content of the acetylene black is 6 parts by mass, the content of the solid content of the binder composition for secondary batteries is 5 parts by mass, and the total solid content in the slurry is 52% by mass. In the present invention, the term "slurry" refers to a dispersion composition obtained by thoroughly and uniformly mixing the components, as in the mixing method in the Examples. In the present invention, "adjusting the total solid content of the slurry to 52% by mass" means that when the total solid content is adjusted from a state higher than 52% by mass to 52% by mass, the slurry is diluted with water, and when the total solid content is adjusted from a state lower than 52% by mass to 52% by mass, the slurry is concentrated by evaporating the solvent, for example. Evaporation of the solvent can be performed, for example, by vacuum drying or reduced pressure. The slurry used in the strain dispersion measurement under the above <Condition I> is preferably prepared by adding and mixing the polymer particles or a composition containing polymer particles last, from the viewpoint of easily obtaining a dispersion composition in which each component is sufficiently mixed uniformly. For example, it is preferable to prepare a slurry containing components other than the polymer particles, then add the polymer particles and further mix them to prepare a slurry. In the present invention, "the difference between the storage modulus G' at a shear strain of 0.1% and the storage modulus G' at a shear strain of 75%" means the value obtained by subtracting the storage modulus G' at a shear strain of 75% from the storage modulus G' at a shear strain of 0.1%. Alternatively, whether or not the above <Condition I> is satisfied can be determined by strain dispersion measurement using a rheometer. Detailed measurement conditions are as described in the Examples below.

[0054] The average particle size (volume-based median diameter D50) of the carbon-coated silicon oxide, graphite, and acetylene black used in the above <Condition I> is in the range of 1 to 10 μm (preferably 2 to 7 μm) for carbon-coated silicon oxide, 15 to 25 μm (preferably 17 to 22 μm) for graphite, and 30 to 40 nm (preferably 32 to 37 nm) for acetylene black. The specific surface area of ​​each of the carbon-coated silicon oxide, graphite, and acetylene black used in the above <Condition I> is 1 to 10 m for carbon-coated silicon oxide. 2 / g (preferably 2 to 7 m 2 / g), 1 to 10 m for graphite 2 / g (preferably 2 to 7 m 2 / g), the range for acetylene black is 65 - 75 m 2 / g (preferably 66 - 70 m 2 / g). If within the ranges of these average particle diameters and specific surface areas, the values of the storage elastic modulus obtained are substantially the same. Also, the "powder form" in the carbon-coated silicon oxide, graphite, and acetylene black used in the above <Condition I> represents a powder shape (powder containing primary particles and / or aggregates (secondary particles) formed by aggregation of primary particles), for example, it does not include those obtained by pressing the powder, granular ones, etc. Incidentally, the carbon-coated silicon oxide used in the above <Condition I> refers to silicon oxide (SiO x (0 < x ≤ 1.5)) on the surface of which a carbon material is supported, and the proportion of the carbon element content in the carbon-coated silicon oxide is in the range of 0.5 - 5 mass% (preferably 1 - 3 mass%). Note that the carbon-coated silicon oxide used in the above <Condition I> is not doped with metal elements. For example, the carbon-coated silicon oxide doped with lithium element used in the examples described later does not correspond to the carbon-coated silicon oxide used in the above <Condition I>. As commercially available products of carbon-coated silicon oxide, for example, carbon-coated silicon oxide powder manufactured by Osaka Titanium Technologies Co., Ltd. (grade: SiO NC, average particle diameter: 5 μm, specific surface area: 2.6 m 2 / g), as commercially available products of graphite, for example, massive artificial graphite powder manufactured by Showa Denko Materials Co., Ltd. (product name: MAG-D, average particle diameter: 21 μm, specific surface area: 4 m 2 / g), as commercially available products of acetylene black powder, for example, acetylene black manufactured by Denka Co., Ltd. (product name: Denka Black, grade: powder product, average particle diameter: 35 nm, specific surface area: 68 m 2 / g) can be used.

[0055] When the binder composition of the present invention satisfies the above <Condition I>, a more excellent effect of improving cycle characteristics can be obtained. The reason for this is not clear, but it is considered as follows. That is, (1) the difference between the storage modulus G' at a shear strain of 0.1% (low shear strain) and the storage modulus G' at a shear strain of 75% (high shear strain) indicates the degree of dispersion of solid particles in the slurry (the extent to which solid particles that aggregated under high shear strain are disintegrated and finely dispersed under low shear strain), and it is believed that when this difference is in the range of 50 to 400 Pa, the dispersibility of solid particles in a slurry containing the binder composition of the present invention is sufficiently enhanced, improving cycle characteristics. Also, (2) the value of the storage modulus G' at a shear strain of 0.1% indicates the degree of dispersion of solid particles in a slurry (the extent to which they are dispersed without agglomeration under low shear strain), and it is believed that when this value is 60 Pa or more, the state of dispersion of solid particles in a slurry containing the binder composition of the present invention is good, improving cycle characteristics. Therefore, even in an active material layer formed using the electrode composition of the present invention containing the binder composition of the present invention, solid particles such as the water-soluble polymer (X), the water-soluble polymer (Y), the polymer particles, the active material, and the conductive additive can be dispersed substantially uniformly, and it is thought that specific particles such as the active material are less likely to be unevenly distributed in the active material layer. As a result, it is thought that the generation or expansion of voids due to charge and discharge can be suppressed, and the cycle characteristics of the secondary battery can be improved.

[0056] In the above <Condition I>, the difference between the storage modulus G' at a shear strain of 0.1% and the storage modulus G' at a shear strain of 75% (the value obtained by subtracting the storage modulus G' at a shear strain of 75% from the storage modulus G' at a shear strain of 0.1%) is preferably 100 to 200 Pa. The storage modulus G' at a shear strain of 0.1% in the above <Condition I> is preferably 60 to 420 Pa, more preferably 120 to 220 Pa.

[0057] <Composition for electrodes> The electrode composition of the present invention contains the water-soluble polymer (X), the water-soluble compound (Y), the polymer particles, and water, as well as an active material capable of inserting and releasing ions of a metal belonging to Group 1 or 2 of the periodic table, and a conductive additive. The electrode composition of the present invention can also be obtained by adding an active material and a conductive additive to the binder composition of the present invention. The electrode composition of the present invention may further contain other additives as needed. The active material may be a positive electrode active material or a negative electrode active material. When the electrode composition contains a positive electrode active material, the electrode composition can be used as a slurry for forming a positive electrode active material layer of a secondary battery. When the electrode composition contains a negative electrode active material, the electrode composition can be used as a slurry for forming a negative electrode active material layer. While the binder composition of the present invention can be used for either a positive electrode or a negative electrode, it is preferably used for a negative electrode, and particularly preferably for a negative electrode containing a silicon-based active material. The active material, conductive aid, and other additives are not particularly limited, and may be appropriately selected from those commonly used in secondary batteries according to the purpose.

[0058] The content of the water-soluble polymer (X), the water-soluble compound (Y), and the polymer particles in the electrode composition of the present invention is not particularly limited, and is preferably 0.5 to 30 mass% in total, more preferably 1.0 to 20 mass%, even more preferably 1.5 to 15 mass%, and particularly preferably 2.5 to 10 mass%, based on the total solid content. In the electrode composition of the present invention, the mass ratio of the water-soluble polymer (X), the water-soluble compound (Y), and the polymer particles (mass of the water-soluble polymer (X): mass of the water-soluble compound (Y): mass of the polymer particles) is not particularly limited, and is preferably 10-80:10-80:10-50, and more preferably 20-70:10-60:20-50. The content of water in the electrode composition of the present invention is preferably 30 to 70 mass%, more preferably 40 to 60 mass%, and even more preferably 45 to 55 mass%. When the electrode composition of the present invention contains the binder composition of the present invention, the electrode composition of the present invention contains water derived from the binder composition of the present invention and may further contain water added during the preparation of the electrode composition. The solid content of the composition for an electrode of the present invention is preferably 30 to 70 mass %, more preferably 40 to 60 mass %, and even more preferably 45 to 55 mass %. The total proportion of the water-soluble polymer (X), water-soluble compound (Y), polymer particles, active material, and conductive aid in the total solid content contained in the electrode composition of the present invention is preferably 70 mass % or more, more preferably 80 mass % or more, even more preferably 90 mass % or more, and particularly preferably 95 mass % or more. It is most preferable that the total solid content contained in the electrode composition of the present invention is the water-soluble polymer (X), water-soluble compound (Y), polymer particles, active material, and conductive aid.

[0059] When the electrode composition of the present invention is used to form an electrode for a secondary battery, it is preferred that the difference between the storage modulus G' at a shear strain of 0.1% and the storage modulus G' at a shear strain of 75% be between 50 and 400 Pa, and that the value of the storage modulus G' at a shear strain of 0.1% be at least 60 Pa. By doing so, it is thought that highly uniform dispersion of solid particles such as the water-soluble polymer (X), the water-soluble polymer (Y), the polymer particles, the active material, and the conductive additive in the electrode composition of the present invention and in the active material layer formed using the same can be more easily achieved, thereby further improving the cycle characteristics of the secondary battery. The storage modulus G' at a shear strain of 0.1% and the storage modulus G' at a shear strain of 75% can be measured using a rheometer. Specifically, the measurement can be performed under the same measurement conditions as in the measurement for determining whether the above <Condition I> is satisfied, except that the electrode composition of the present invention is used instead of the measurement slurry. The "storage modulus G' at a shear strain of 0.1%" and the "difference between the storage modulus G' at a shear strain of 0.1% and the storage modulus G' at a shear strain of 75%" in the electrode composition of the present invention can be respectively within the preferred ranges for the "storage modulus G' at a shear strain of 0.1%" and the "difference between the storage modulus G' at a shear strain of 0.1% and the storage modulus G' at a shear strain of 75%".

[0060] -Active material- The electrode composition of the present invention contains an active material capable of inserting and releasing ions of a metal belonging to Group 1 or 2 of the periodic table.

[0061] (Cathode active material) The positive electrode active material may be any active material capable of inserting and releasing ions of a metal belonging to Group 1 or 2 of the periodic table, and is preferably one capable of reversibly inserting and releasing lithium ions. The material is not particularly limited as long as it has the above properties, and may be a transition metal oxide, an organic substance, an element capable of forming a composite with Li, such as sulfur, or a composite of sulfur and a metal. Among these, it is preferable to use a transition metal oxide as the positive electrode active material, and a transition metal element M a A transition metal oxide containing at least one element selected from Co, Ni, Fe, Mn, Cu, and V is more preferred. b (Elements of Group 1 (Ia) of the periodic table other than lithium, elements of Group 2 (IIa) of the periodic table, Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, etc.) may be mixed. b The amount of the transition metal element M a The amount of the transition metal element M is preferably 0 to 30 mol % relative to 100 mol %. a The molar ratio of Li to a ) is more preferably 0.3 to 2.2. Specific examples of transition metal oxides include (MA) transition metal oxides having a layered rock salt structure, (MB) transition metal oxides having a spinel structure, (MC) lithium-containing transition metal phosphate compounds, (MD) lithium-containing transition metal halide phosphate compounds, and (ME) lithium-containing transition metal silicate compounds.

[0062] (MA) Specific examples of transition metal oxides with a layered rock salt structure include LiCoO2 (lithium cobalt oxide [LCO]), LiNi2O2 (lithium nickel oxide), and LiNi 0.85 Co 0.10 Al 0.05 O2 (nickel cobalt lithium aluminate [NCA]), LiNi1 / 3 Co 1 / 3 Mn 1 / 3 O2 (lithium nickel manganese cobalt oxide [NMC]) and LiNi 0.5 Mn 0.5 O2 (lithium manganese nickel oxide). (MB) Specific examples of transition metal oxides having a spinel structure include LiMn2O4 (LMO), LiCoMnO4, Li2FeMn3O8, Li2CuMn3O8, Li2CrMn3O8, and Li2NiMn3O8. (MC) Examples of lithium-containing transition metal phosphate compounds include olivine-type iron phosphates such as LiFePO4 and Li3Fe2(PO4)3, iron pyrophosphates such as LiFeP2O7, cobalt phosphates such as LiCoPO4, and monoclinic Nasicon-type vanadium phosphates such as Li3V2(PO4)3 (lithium vanadium phosphate). (MD) Examples of lithium-containing transition metal halide phosphate compounds include iron fluorophosphates such as Li2FePO4F, manganese fluorophosphates such as Li2MnPO4F, and cobalt fluorophosphates such as Li2CoPO4F. (ME) Examples of lithium-containing transition metal silicate compounds include Li2FeSiO4, Li2MnSiO4, and Li2CoSiO4. In the present invention, transition metal oxides having a layered rock salt structure (MA) are preferred, and LCO or NMC are more preferred.

[0063] The shape of the positive electrode active material is not particularly limited, but a particulate form is preferred. The average particle size (volume-based median diameter D50) of the positive electrode active material is not particularly limited. For example, it can be 0.1 to 50 μm. The positive electrode active material can be adjusted to a predetermined particle size by a conventional method using a grinder or classifier. The method for adjusting the particle size of the negative electrode active material to a predetermined particle size, which will be described later, can also be applied. The positive electrode active material obtained by the firing method may be used after washing with water, an acidic aqueous solution, an alkaline aqueous solution, an organic solvent, or the like. When a commercially available positive electrode active material is used, the value described in the manufacturer's catalog is used as the average particle size of the positive electrode active material. When the information on the average particle size from the manufacturer is not available or when a synthesized positive electrode active material is used, the value measured and calculated by the method described below in the section on negative electrode active materials is used.

[0064] The chemical formula of the compound obtained by the above calcination method can be measured by inductively coupled plasma (ICP) emission spectroscopy, or simply calculated from the difference in mass of the powder before and after calcination.

[0065] The surface of the positive electrode active material may be coated with an oxide such as another metal oxide, a carbon-based material, etc. As the surface coating material, a surface coating material that can be used to coat the surface of a negative electrode active material, which will be described later, can be used.

[0066] The surface of the positive electrode active material may be treated with sulfur or phosphorus. Furthermore, the particle surfaces of the positive electrode active material may be subjected to a surface treatment with actinic rays or an active gas (plasma, etc.) before or after the above surface coating.

[0067] The positive electrode active materials may be used singly or in combination of two or more. When forming a positive electrode active material layer, the unit area (cm 2 The mass (mg) (weight per unit area) of the positive electrode active material is not particularly limited and can be determined appropriately depending on the designed battery capacity.

[0068] The content of the positive electrode active material in the electrode composition of the present invention is not particularly limited, and is preferably 10 to 99 mass % relative to the total solid content, more preferably 30 to 98 mass %, even more preferably 50 to 97 mass %, and particularly preferably 55 to 95 mass %.

[0069] (Negative electrode active material) The negative electrode active material may be any active material capable of inserting and releasing ions of a metal belonging to Group 1 or 2 of the periodic table, and is preferably one that can reversibly insert and release lithium ions. The material is not particularly limited as long as it has the above properties, and examples include carbonaceous materials, silicon-based materials (meaning materials containing silicon), tin-based materials (meaning materials containing tin), metal oxides, metal composite oxides, elemental lithium, and lithium alloys. Of these, carbonaceous materials and silicon-based materials are preferably used from the viewpoint of reliability.

[0070] The carbonaceous material used as the negative electrode active material is a material essentially composed of carbon. Examples include carbon black such as petroleum pitch and acetylene black, graphite (natural graphite such as flake graphite and block graphite, artificial graphite such as vapor-grown graphite and fibrous graphite, and expanded graphite obtained by specially processing flake graphite), activated carbon, carbon fiber, coke, soft carbon, hard carbon, and carbonaceous materials obtained by calcining various synthetic resins such as PAN (polyacrylonitrile)-based resins and furfuryl alcohol resins. Further examples include various carbon fibers such as PAN-based carbon fiber, cellulose-based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, dehydrated PVA (polyvinyl alcohol)-based carbon fiber, lignin carbon fiber, glassy carbon fiber, and activated carbon fiber, mesophase microspheres, graphite whiskers, and tabular graphite.

[0071] Examples of tin-based materials (tin-based active materials) used as negative electrode active materials include Sn, SnO, SnO2, SnS, and SnS2.

[0072] The metal oxides and metal composite oxides used as the negative electrode active material are not particularly limited as long as they are oxides that can insert and release (preferably store and release) ions of a metal belonging to Group 1 or 2 of the periodic table (preferably lithium ions). Examples of metal oxides include oxides of metal elements (metal oxides) and oxides of metalloid elements (metalloid oxides). Examples of metal composite oxides include composite oxides of metal elements, composite oxides of metal elements and metalloid elements, and composite oxides of metalloid elements. These metal oxides and metal composite oxides are preferably amorphous oxides, and further preferred examples include chalcogenides, which are reaction products between metal elements and elements of Group 16 of the periodic table. The term "amorphous" as used herein means that the oxides have a broad scattering band with a peak in the 2θ range of 20° to 40° when measured by X-ray diffraction using CuKα radiation, and may also have crystalline diffraction lines. Among the compounds consisting of the amorphous oxides and chalcogenides, amorphous oxides or chalcogenides of metalloid elements are more preferred, and oxides or composite oxides or chalcogenides consisting of one or a combination of two or more elements selected from Groups 13 (IIIB) to 15 (VB) of the Periodic Table (e.g., Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi) are particularly preferred. Specific examples of amorphous oxides and chalcogenides include Ga2O3, GeO, PbO, PbO2, Pb2O3, Pb2O4, Pb3O4, Sb2O3, Sb2O4, Sb2O8Bi2O3, Sb2O8Si2O3, Sb2O5, Bi2O3, Bi2O4, GeS, PbS, PbS2, Sb2S3, and Sb2S5.

[0073] The metal (composite) oxides and the chalcogenides preferably contain at least one of titanium and lithium as a constituent component from the viewpoint of high current density charge / discharge characteristics. Examples of lithium-containing metal composite oxides (lithium composite metal oxides) include composite oxides of lithium oxide and the metal (composite) oxides or the chalcogenides, more specifically Li2SnO2.

[0074] The negative electrode active material preferably contains titanium element. More specifically, TiNb2O7 (niobium titanate oxide [NTO]), Li4Ti5O 12 (lithium titanate [LTO]) is preferable because it has small volume fluctuations during the insertion and release of lithium ions, thus having excellent rapid charge-discharge characteristics, suppressing the deterioration of the electrode, and enabling improvement of the cycle characteristics of the lithium-ion secondary battery.

[0075] The lithium alloy as the negative electrode active material is not particularly limited as long as it is an alloy commonly used as the negative electrode active material of a secondary battery. For example, a lithium aluminum alloy can be mentioned.

[0076] The silicon-based material (silicon-based active material) is a negative electrode active material containing silicon element. For example, silicon materials such as Si, SiO x (0 < x ≤ 1.5), and further, silicon-containing alloys containing titanium, vanadium, chromium, manganese, nickel, copper or lanthanum (for example, LaSi2, VSi2), or organized active materials (for example, LaSi2 / Si). In addition, oxides or composite oxides containing silicon element in the description of the above metal oxides and metal composite oxides, active materials containing silicon element and tin element such as SnSiO3, SnSiS3, etc. can be mentioned. SiO x can be used as a negative electrode active material (semimetal oxide) itself, and also can be used as an active material (its precursor material) capable of forming an alloy with lithium because Si is generated during the operation of the battery.

[0077] In the above, the negative electrode active material has been described focusing on the components. However, from the perspective of characteristics, the negative electrode active material is preferably a negative electrode active material capable of forming an alloy with lithium. The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is commonly used as the negative electrode active material of a secondary battery. Such active materials include the above-mentioned negative electrode active materials containing silicon element and / or tin element, and various metals such as Al and In. The silicon-based active material is preferable in terms of enabling a higher battery capacity, and the silicon-based active material with a silicon element content of 40 mol% or more of all constituent elements is more preferable. Generally, negative electrodes containing negative electrode active materials capable of forming an alloy with lithium (e.g., Si negative electrodes containing silicon-based active materials, Sn negative electrodes containing tin-based active materials) can absorb more Li ions than negative electrodes made solely of carbonaceous materials (e.g., graphite, carbon black, etc.). In other words, the amount of Li ions absorbed per unit mass increases. This allows for a larger battery capacity (energy density). As a result, there is the advantage that the battery operating time can be extended. Thus, negative electrode active materials containing silicon and / or tin are also referred to as high-capacity active materials.

[0078] The surface of the negative electrode active material may be coated with an oxide such as another metal oxide, a carbon-based material, or the like (hereinafter, being surface-coated with a carbon-based material may be referred to as being "carbon-coated"). Examples of surface coating materials include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specific examples include titanate spinel, tantalum-based oxides, niobium-based oxides, and lithium niobate-based compounds. More specifically, Li4Ti5O 12 , Li2Ti2O5, LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, Li2MoO4, Li3BO3, LiBO2, Li2CO3, Li2SiO3, SiO2, TiO2, ZrO2, Al2O3, B2O3, etc. Carbon-based materials such as C, SiC, and carbon-added silicon oxides can also be used as surface coating materials.

[0079] The surface of the negative electrode active material may be treated with sulfur or phosphorus. Furthermore, the particle surfaces of the negative electrode active material may be subjected to a surface treatment with actinic rays or an active gas (plasma, etc.) before or after the above surface coating.

[0080] The negative electrode active material may be doped with a metal element. In the negative electrode active material doped with a metal element, the doped metal element is preferably at least one of Li, Ni, and Ti, and more preferably Li.

[0081] In the present invention, it is preferable to use a silicon-based active material as the negative electrode active material, and it is more preferable to use silicon oxide (SiO x (0 < x ≤ 1.5)) or carbon-coated silicon oxide (carbon-coated SiO x (0 < x ≤ 1.5)), and it is even more preferable to use carbon-coated silicon oxide. The carbon-coated silicon oxide may be further doped with a metal element. The proportion of the content of the carbon element in the carbon-coated silicon oxide is not particularly limited. For example, 0.5 to 5% by mass is preferable, and 1 to 3% by mass is more preferable. Commercially available products may be used for silicon oxide or carbon-coated silicon oxide. Also, the carbon-coated silicon oxide can be prepared by carbon-coating silicon oxide, for example, referring to Japanese Patent Application Laid-Open No. 2019-204686. The content of silicon oxide or carbon-coated silicon oxide in the negative electrode active material is not particularly limited. For example, it can be 10 to 90% by mass, preferably 10 to 50% by mass, and more preferably 15 to 40% by mass. When the negative electrode active material is silicon oxide or carbon-coated silicon oxide, the average particle size is preferably 5 to 20 μm. In the present invention, it is also preferable to use a silicon-based material doped with a metal element as the negative electrode active material, and a silicon-based material doped with at least one of Li, Ni, and Ti is more preferable, and a silicon-based material doped with Li is even more preferable. As the silicon-based material to be doped with the metal element, silicon oxide or carbon-coated silicon oxide is preferable. Commercially available products may be used as silicon oxide doped with a metal element and silicon oxide doped with a metal element and carbon coated. For example, see JP-A-2022-121582, WO 14 / 188851, and JP-A-2021-150077. Silicon oxide or carbon-coated silicon oxide may be doped with a metal element, or silicon oxide may be doped with a metal element and, if necessary, further coated with carbon. In the present invention, the phrase "both doped with a metal element and carbon coated" is used to mean both a material that has been doped with a metal element and then carbon coated, and a material that has been carbon coated and then doped with a metal element. In the present invention, it is also preferable to use, as the negative electrode active material, a silicon-based material that is both doped with a metal element and coated with carbon. As such a negative electrode active material, silicon oxide that is both doped with a metal element and coated with carbon is more preferable, and silicon oxide that is both lithium-doped and coated with carbon is particularly preferable.

[0082] The shape of the negative electrode active material is not particularly limited, but a particulate form is preferred. The average particle size (volume-based median diameter D50) of the negative electrode active material is preferably 0.1 to 60 μm. To achieve a predetermined particle size, it can be prepared by a conventional method using a grinder or classifier. For example, a mortar, ball mill, sand mill, vibration ball mill, satellite ball mill, planetary ball mill, swirling airflow jet mill, or sieve is preferably used. Wet grinding in the presence of water or an organic solvent such as methanol can also be performed during grinding. Classification is preferably performed to achieve a desired particle size. The classification method is not particularly limited, and a sieve, air classifier, or the like can be used as desired. Classification can be performed using either a dry method or a wet method. When a commercially available negative electrode active material is used, the average particle size of the negative electrode active material is the value listed in the manufacturer's catalog. When information on the average particle size from the manufacturer is unavailable or when a synthesized negative electrode active material is used, the negative electrode active material is dispersed in water and measured using a laser diffraction / scattering particle size distribution analyzer (e.g., HORIBA Particle LA-960V2), and the average particle size (volume-based median diameter D50 in water) obtained is used.

[0083] The negative electrode active material may be used alone or in combination of two or more. Among them, a combination of a silicon-based active material and a carbonaceous material is preferred, a combination of a silicon-based active material and graphite is more preferred, and a combination of silicon oxide or carbon-coated silicon oxide and graphite is even more preferred. The silicon oxide and carbon-coated silicon oxide may be silicon oxide doped with the above-mentioned metal element and silicon oxide doped with the metal element and carbon-coated, respectively. The doped metal element is preferably at least one of Li, Ni, and Ti, and more preferably Li. When a silicon-based active material is combined with graphite, the mass ratio of the silicon-based active material to the graphite (silicon-based active material / graphite) is preferably 2 or less, more preferably 1 or less, and even more preferably 0.5 or less. There is no particular lower limit to the mass ratio of the silicon-based active material to the graphite, but a mass ratio of 0.05 or more is practical.

[0084] The specific surface area (BET specific surface area) of the negative electrode active material is 0.1 to 50 m 2 / g is preferred. When a commercially available negative electrode active material is used, the specific surface area of ​​the negative electrode active material is the value listed in the manufacturer's catalog. When the manufacturer's specific surface area information is unavailable or when a synthesized negative electrode active material is used, the negative electrode active material is packed into a sample tube and dried by flowing nitrogen, and the specific surface area (BET specific surface area) is calculated by the BET (single point) method using a nitrogen adsorption method using a specific surface area / pore distribution measuring device (e.g., Microtrack-Bel BELSORP MINI).

[0085] The content of the negative electrode active material in the electrode composition of the present invention is not particularly limited, and is preferably 10 to 99 mass % relative to the total solid content, more preferably 30 to 98 mass %, even more preferably 45 to 97 mass %, and particularly preferably 55 to 95 mass %.

[0086] In the present invention, when the negative electrode active material layer is formed by charging the battery, ions of a metal belonging to Group 1 or 2 of the periodic table that are generated in the secondary battery can be used instead of the above-mentioned negative electrode active material. The negative electrode active material layer can be formed by bonding these ions with electrons and depositing them as a metal.

[0087] (Conductive additive) The electrode composition of the present invention contains a conductive auxiliary, and it is particularly preferred that the silicon-based active material as the negative electrode active material is used in combination with a conductive auxiliary. The conductive additive is not particularly limited, and may be any of those known as general conductive additives. For example, it may be an electron conductive material such as carbon blacks (e.g., acetylene black, ketjen black, furnace black, etc.), amorphous carbon (e.g., needle coke, etc.), carbon fibers (e.g., vapor-grown carbon fiber or carbon nanotube, etc.), carbonaceous materials (e.g., graphene or fullerene, etc.), metal powders (e.g., copper, nickel, etc.), metal fibers, or conductive polymers (e.g., polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylene derivatives, etc.). In the present invention, when an active material and a conductive additive are used in combination, the conductive additive is one among the above-mentioned conductive additives that does not undergo Li insertion and release during charging and discharging of the battery and does not function as an active material. Therefore, among conductive additives, one that can function as an active material in the active material layer during charging and discharging of the battery is classified as an active material rather than a conductive additive. Whether or not a conductive additive functions as an active material during charging and discharging of the battery is not uniquely determined, but is determined by the combination with the active material.

[0088] The conductive assistant may be used alone or in combination of two or more kinds. The content of the conductive auxiliary in the electrode composition of the present invention is preferably 0.5 to 60 mass %, more preferably 1.0 to 50 mass %, still more preferably 1.5 to 40 mass %, and particularly preferably 2.5 to 35 mass %, based on the total solid content.

[0089] The shape of the conductive additive is not particularly limited, but is preferably particulate. The average particle size (volume-based median diameter D50) of the conductive additive is not particularly limited, and is, for example, preferably 0.01 to 50 μm, and more preferably 0.02 to 10.0 μm. When using a commercially available conductive additive, the average particle size of the conductive additive is the value listed in the manufacturer's catalog. When information on the average particle size from the manufacturer is not available or when a synthetic conductive additive is used, the average particle size of the conductive additive may be the value obtained by applying the above-mentioned method for measuring the average particle size of the negative electrode active material (volume-based median diameter D50 in water).

[0090] The specific surface area (BET specific surface area) of the conductive additive is 10 to 100 m 2 / g is preferred. When a commercially available conductive additive is used, the specific surface area of ​​the conductive additive is the value listed in the manufacturer's catalog. When the information on the specific surface area from the manufacturer is not available or when a synthetic conductive additive is used, the value obtained by applying the above-mentioned method for measuring the specific surface area (BET specific surface area) of the negative electrode active material (BET method using nitrogen adsorption) may be used.

[0091] (Other additives) The electrode composition of the present invention may contain, as desired, other components in addition to the above components, such as a lithium salt, an ionic liquid, a thickener, an antifoaming agent, a leveling agent, a dehydrating agent, and an antioxidant. For details of the active materials, conductive aids, and other additives, reference can be made to, for example, International Publication No. 2019 / 203334 and Japanese Patent Application Laid-Open No. 2015-46389.

[0092] [Method for preparing binder composition for secondary battery and electrode composition] The binder composition for a secondary battery of the present invention can be prepared as a mixture, preferably as a slurry, by mixing the water-soluble polymer (X), the water-soluble compound (Y), polymer particles, and water, as well as any other components, using, for example, any of various commonly used mixers. In the case of the electrode composition of the present invention, an active material and a conductive aid are mixed in addition to the above, and further, as needed, other additives are mixed. The mixing method is not particularly limited, and the components may be mixed all at once or sequentially. Alternatively, a mixture obtained by mixing a plurality of components may be mixed with other components. For example, the electrode composition of the present invention can be obtained by mixing the water-soluble polymer (X), the water-soluble compound (Y), the active material, the conductive additive, and water, and then adding water and polymer particles and further mixing.

[0093] [Electrode sheet] The electrode sheet of the present invention has a layer (electrode active material layer, i.e., a negative electrode active material layer or a positive electrode active material layer) formed using the electrode composition of the present invention. The electrode sheet of the present invention may be an electrode sheet having an electrode active material layer formed using the electrode composition of the present invention, and may be a sheet in which the electrode active material layer is formed on a substrate such as a current collector, or a sheet in which there is no substrate and which is formed only of the electrode active material layer (a negative electrode active material layer or a positive electrode active material layer). This electrode sheet is usually a sheet configured by laminating the electrode active material layer on a current collector. The electrode sheet of the present invention may have other layers, for example, a protective layer such as a release sheet, or a coating layer. The electrode sheet of the present invention can be suitably used as a material constituting an anode active material layer or a cathode active material layer of a secondary battery, or as a laminate of an anode current collector and an anode active material layer (anode layer) or a laminate of a cathode current collector and a cathode active material layer (cathode layer).

[0094] When the electrode sheet of the present invention has a current collector, the current collector constituting the electrode sheet of the present invention is an electron carrier and is usually in the form of a film sheet. The current collector can be appropriately selected depending on the active material. Examples of materials for the positive electrode current collector include aluminum, aluminum alloys, stainless steel, nickel, and titanium, and aluminum or aluminum alloys are preferred. Examples of the positive electrode current collector include those in which the surface of aluminum or stainless steel is treated with carbon, nickel, titanium, or silver to form a coating layer (thin film). Examples of materials for the negative electrode current collector include aluminum, copper, copper alloys, stainless steel, nickel, and titanium, and aluminum, copper, copper alloys, and stainless steel are preferred. Examples of the negative electrode current collector include those in which the surface of aluminum, copper, copper alloys, or stainless steel is treated with carbon, nickel, titanium, or silver to form a coating layer (thin film).

[0095] There are no particular limitations on the thickness of the positive electrode active material layer that constitutes the electrode sheet of the present invention, and it can be, for example, 5 to 500 μm, and preferably 20 to 200 μm. The thickness of the positive electrode current collector constituting the electrode sheet of the present invention is not particularly limited, and can be, for example, 10 to 100 μm, preferably 10 to 50 μm.

[0096] There are no particular limitations on the thickness of the negative electrode active material layer that constitutes the electrode sheet of the present invention, and it can be, for example, 5 to 500 μm, preferably 20 to 200 μm. The thickness of the negative electrode current collector constituting the electrode sheet of the present invention is not particularly limited, and can be, for example, 10 to 100 μm, preferably 10 to 50 μm.

[0097] [Electrode sheet manufacturing method] The electrode sheet of the present invention can be obtained by forming an electrode active material layer using the electrode composition of the present invention. For example, the electrode sheet of the present invention can be manufactured by forming a film using the electrode composition of the present invention. Specifically, the electrode composition of the present invention is applied to a substrate such as a current collector (optionally via another layer) to form a coating film, which is then dried to obtain an electrode sheet having an active material layer (coated and dried layer) on the substrate. The secondary battery of the present invention can be obtained by incorporating the electrode sheet obtained by the above-described method for producing an electrode sheet into at least one of the electrodes (positive electrode and negative electrode) of the secondary battery.

[0098] [Secondary battery] In the secondary battery of the present invention, at least one of the positive electrode active material layer and the negative electrode active material layer is a layer formed using the electrode composition of the present invention. The secondary battery of the present invention will be described taking a non-aqueous electrolyte secondary battery as an example, but the secondary battery of the present invention is not limited to a non-aqueous electrolyte secondary battery and broadly includes secondary batteries in general.

[0099] A nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The positive electrode includes a positive electrode current collector and a positive electrode active material layer in contact with the positive electrode current collector, and the negative electrode includes a negative electrode current collector and a negative electrode active material layer in contact with the negative electrode current collector. In the nonaqueous electrolyte secondary battery of the present invention, at least one of the positive electrode active material layer and the negative electrode active material layer is formed using the electrode composition of the present invention. The nonaqueous electrolyte secondary battery of the present invention also includes a nonaqueous electrolyte secondary battery having only one of a positive electrode active material layer and a negative electrode active material layer, the electrode active material layer being formed using the electrode composition of the present invention. The nonaqueous electrolyte secondary battery of the present invention functions as a secondary battery upon charge and discharge by filling the space between the positive electrode and the negative electrode with a nonaqueous electrolyte.

[0100] FIG. 1 is a cross-sectional view showing a schematic representation of the laminated structure of a typical nonaqueous electrolyte secondary battery 10, including the working electrodes when the battery is in operation. The nonaqueous electrolyte secondary battery 10 has a laminated structure, viewed from the negative electrode side, having a negative electrode current collector 1, a negative electrode active material layer 2, a separator 3, a positive electrode active material layer 4, and a positive electrode current collector 5, in this order. The space between the negative electrode active material layer 2 and the positive electrode active material layer 4 is filled with a nonaqueous electrolyte (not shown), and they are separated by the separator 3. The separator 3 has pores, and during normal battery use, it functions as a positive / negative electrode separator that insulates the positive and negative electrodes, allowing the electrolyte and ions to pass through the pores. With this structure, for example, in the case of a lithium-ion secondary battery, electrons (e - ) is supplied, and at the same time, lithium ions (Li + ) moves and accumulates in the negative electrode. On the other hand, during discharge, the lithium ions (Li + ) is returned to the positive electrode side through the electrolyte, and electrons are supplied to the operating part 6. In the example shown, a light bulb is used as the operating part 6, and it is lit by the discharge. In the present invention, the negative electrode current collector 1 and the negative electrode active material layer 2 are collectively referred to as the negative electrode, and the positive electrode active material layer 4 and the positive electrode current collector 5 are collectively referred to as the positive electrode.

[0101] The secondary battery of the present invention includes at least one of a positive electrode active material layer and a negative electrode active material layer formed using the electrode composition of the present invention. The electrolyte (aqueous electrolyte, non-aqueous electrolyte) or a solid electrolyte material, and other components such as a separator are not particularly limited. These materials and components can be appropriately applied to those used in conventional secondary batteries. Furthermore, for the method of manufacturing the secondary battery of the present invention, conventional methods can be appropriately adopted, except that at least one of a positive electrode active material layer and a negative electrode active material layer is formed using the electrode composition of the present invention. For details of components and manufacturing methods typically used in these secondary batteries, see, for example, JP 2016-201308 A, JP 2005-108835 A, JP 2012-185938 A, and WO 2020 / 067106 A. A preferred form of the non-aqueous electrolyte will now be described in more detail.

[0102] (electrolyte) The electrolyte used in the non-aqueous electrolyte is preferably a salt of a metal ion belonging to Group 1 or 2 of the periodic table. The salt of the metal ion used is appropriately selected depending on the intended use of the non-aqueous electrolyte. Examples include lithium salt, potassium salt, sodium salt, calcium salt, magnesium salt, etc., and when used in a secondary battery, etc., lithium salt is preferred from the viewpoint of output. When the non-aqueous electrolyte is used as an electrolyte for a lithium ion secondary battery, lithium salt may be selected as the salt of the metal ion. As the lithium salt, lithium salts commonly used in electrolytes for lithium ion secondary batteries are preferred, and examples thereof include the following lithium salts.

[0103] (L-1) Inorganic lithium salts: inorganic fluoride salts such as LiPF6, LiBF4, LiAsF6, and LiSbF6; perhalogenates such as LiClO4, LiBrO4, and LiIO4; inorganic chloride salts such as LiAlCl4;

[0104] (L-2) Fluorine-containing organic lithium salts: perfluoroalkanesulfonates such as LiCF3SO3, perfluoroalkanesulfonylimide salts such as LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiN(FSO2)2, LiN(CF3SO2)(C4F9SO2), perfluoroalkanesulfonylmethide salts such as LiC(CF3SO2)3, perfluoroalkyl fluorophosphates such as Li[PF5(CF2CF2CF3)], Li[PF4(CF2CF2CF3)2], Li[PF3(CF2CF2CF3)3], Li[PF5(CF2CF2CF2CF3)], Li[PF4(CF2CF2CF2CF3)2], Li[PF3(CF2CF2CF2CF3)3], etc.

[0105] (L-3) Oxalatoborate salts: lithium bis(oxalato)borate, lithium difluorooxalatoborate, etc.

[0106] Among these, LiPF6, LiBF4, LiAsF6, LiSbF6, LiClO4, Li(R f1 SO3), LiN(R f1 SO2)2, LiN(FSO2)2, or LiN(R f1 SO2)(R f2 SO2) are preferred, LiPF6, LiBF4, LiN(R f1 SO2)2, LiN(FSO2)2, or LiN(R f1 SO2)(R f2 SO2) is more preferred, where R f1 and R f2 represents a perfluoroalkyl group, preferably having 1 to 6 carbon atoms. The electrolytes used in the non-aqueous electrolytic solution may be used alone or in any combination of two or more.

[0107] The salt concentration of the electrolyte (preferably ions of a metal belonging to Group 1 or 2 of the periodic table or a metal salt thereof) in the non-aqueous electrolyte is appropriately selected depending on the intended use of the non-aqueous electrolyte, but is generally 10 to 50 mass % of the total mass of the non-aqueous electrolyte, and preferably 15 to 30 mass %. The molar concentration is preferably 0.5 to 1.5 M. When evaluating the ion concentration, it may be calculated in terms of a salt with the suitably applied metal.

[0108] (non-aqueous solvent) The non-aqueous electrolyte contains a non-aqueous solvent. The non-aqueous solvent is preferably an aprotic organic solvent, and more preferably an aprotic organic solvent having 2 to 10 carbon atoms. Examples of such non-aqueous solvents include linear or cyclic carbonate compounds, lactone compounds, linear or cyclic ether compounds, ester compounds, nitrile compounds, amide compounds, oxazolidinone compounds, nitro compounds, linear or cyclic sulfone or sulfoxide compounds, and phosphate ester compounds. Compounds having an ether bond, a carbonyl bond, an ester bond, or a carbonate bond are preferred. These compounds may have a substituent, for example, a substituent selected from the above-mentioned substituent group T.

[0109] Examples of non-aqueous solvents include ethylene carbonate, fluorinated ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, methyl acetate, Examples of the solvent include methyl acrylate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, ethyl trimethylacetate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, N,N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N,N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, dimethyl sulfoxide phosphate, etc. These may be used alone or in combination of two or more. Among these, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone is preferred, and a combination of a high-viscosity (high-dielectric constant) solvent (e.g., relative dielectric constant ε≧30) such as ethylene carbonate or propylene carbonate with a low-viscosity solvent (e.g., viscosity≦1 mPa s) such as dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate is more preferred. By using a mixed solvent with such a combination, the dissociation of the electrolyte salt and the mobility of the ions are improved. However, the non-aqueous solvent used in the present invention is not limited to these.

[0110] The secondary battery of the present invention can be installed in electronic devices such as notebook computers, pen-input PCs, mobile PCs, electronic book players, mobile phones, cordless phone handsets, pagers, handheld terminals, portable fax machines, portable copiers, portable printers, headphone stereos, video camcorders, LCD televisions, handheld vacuum cleaners, portable CD players, mini-discs, electric shavers, transceivers, electronic organizers, calculators, portable tape recorders, radios, backup power supplies, and memory cards. It can also be installed in consumer products such as automobiles, electric vehicles, motors, lighting fixtures, toys, game devices, road conditioners, clocks, flash devices, cameras, and medical devices (pacemakers, hearing aids, shoulder massagers, etc.). It can also be used for various military applications and space applications. It can also be combined with solar cells. [Example]

[0111] The present invention will be described in more detail based on examples. It should be noted that the present invention is not limited to these examples except as specified herein. Room temperature refers to 27°C. Composition ratios, blend ratios, and contents are based on mass unless otherwise specified.

[0112] [Synthesis of water-soluble polymers] (1) Synthesis of polymer 1 Polymer 1 shown in Table 1 below was synthesized as follows. Solution A was prepared by mixing 75.0 g of acrylamide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 115.0 g of distilled water, and 0.53 g of VA-057 (trade name, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., a carboxyl group-containing water-soluble azo polymerization initiator) at room temperature. 349.5 g of distilled water was added to a 1 L three-neck flask equipped with a reflux condenser and a gas inlet valve. Nitrogen gas was introduced at a flow rate of 200 mL / min for 60 minutes, and then the temperature was raised to 77°C. Solution A prepared above was added dropwise to the distilled water in the 1 L three-neck flask over 1 hour. After completion of the addition, stirring was continued at 77°C for 3 hours. The mixture was cooled to room temperature to obtain an aqueous solution of polymer 1 (polyacrylamide (PAAm)).

[0113] (2) Synthesis of Polymers 2 to 9 and Comparative Polymers 1 and 2 Polymers 2 to 9 and comparative polymers 1 and 2 were synthesized in the same manner as in the synthesis of polymer 1, except that in the synthesis of polymer 1, the monomers, polymerization initiator and their amounts, and reaction temperature were changed as shown in Table 1 below.

[0114] Here, polymers 1 to 9 are water-soluble polymers (X) defined in the present invention, and comparative polymers 1 and 2 are water-soluble polymers for comparison. The solids concentration of the aqueous solutions of the water-soluble polymers prepared above was 13.9% by mass. The solubility in water at 20°C of each of Polymers 1 to 9 and Comparative Polymers 1 and 2 was 100 g / L-H2O or more.

[0115] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the water-soluble polymers synthesized above were measured as described above. Tensile tests were also conducted as described below to calculate the elongation at break and tensile modulus. The results are summarized in Table 2.

[0116] (Tensile test: Measurement of breaking elongation and tensile modulus of water-soluble polymer) The aqueous solution of the water-soluble polymer synthesized above was applied to a peelable polyethylene terephthalate (PET) film and dried. The water-soluble polymer sheet was peeled off from the PET film to obtain a water-soluble polymer test piece measuring 5 cm in length, 0.5 cm in width, and 0.10 mm thick. The test piece was fixed to a jig at a position 1 cm from one end and a position 1 cm from the other end in the longitudinal direction, and a tensile test was performed using a tensile tester (FGS-TV, manufactured by Nidec-Shimpo Corporation). This test was performed at 23°C and a tensile speed of 5 mm / min. The tensile modulus was calculated from the average value in the elastic region of the stress-strain curve obtained from the results of measuring the load versus displacement, and the breaking elongation was calculated using the following formula. The obtained breaking elongation was evaluated according to the following evaluation ranks. Breaking elongation (%) = 100 × (L-Lo) / Lo In the above formula, Lo is the length of the sample before the tensile test (distance between the jigs), and L is the length of the sample at the time of break (distance between the jigs measured by butting the broken test piece together). -Evaluation rank of elongation at break- 4: 1.8% or more 3: 1.5% or more and less than 1.8% 2: 1.2% or more, less than 1.5% 1: Less than 1.2%

[0117] [Preparation of binder composition] (1) Preparation of Binder Composition No. 101 Binder composition No. 101 shown in Table 2 below was prepared as follows. 7.50 g of the aqueous solution of polymer 1 (PAAm) (solid content: 1.05 g) and 8.00 g of an aqueous solution of carboxymethyl cellulose (CMC) (solid content: 0.40 g) as the water-soluble compound (Y) were added to a 60 mL ointment container (Umano Chemical Co., Ltd.) and dispersed for 4 minutes at 2000 rpm using a THINKY Mixer. Furthermore, 2.09 g of polymer particles (containing water as a liquid medium, solid content: 1.05 g) of Narstar SR-151 (product name, styrene butadiene rubber latex, manufactured by Nippon A&L Co., Ltd.) were added to the dispersion and dispersed for 2 minutes at 2000 rpm using a THINKY Mixer to prepare binder composition No. 101. The solid content of binder composition No. 101 was 14.2% by mass.

[0118] (2) Preparation of binder compositions Nos. 102 to 109 and c11 to c15 Binder compositions Nos. 102 to 109 and c11 to c15 were prepared in the same manner as in the preparation of binder composition No. 101, except that in the preparation of binder composition No. 101, the composition was changed to that shown in Table 2 below, and the amount of water was adjusted so that the solid content concentration of the binder composition was 14.2 mass%.

[0119] Here, binder compositions Nos. 101 to 109 are binder compositions of the present invention, and binder compositions Nos. c11 to c15 are binder compositions for comparison.

[0120] The binder compositions prepared above were subjected to tensile tests as follows, and the breaking energy was calculated. The results are summarized in Table 2.

[0121] (Tensile test: measurement of the breaking energy of the binder composition) The binder composition prepared above was applied to a peelable polyethylene terephthalate (PET) film and dried. The binder composition coating was peeled off from the PET film to obtain a binder composition coating test piece measuring 5 cm in length, 0.5 cm in width, and 0.10 mm in thickness. The test piece was fixed to a jig at a position 1 cm from one end and a position 1 cm from the other end in the longitudinal direction, and a tensile test was performed using a tensile tester (FGS-TV, manufactured by Nidec-Shimpo Corporation). This test was performed at 23°C and a tensile speed of 5 mm / min. The fracture energy was calculated from the stress-strain curve obtained from the results of measuring the load versus displacement. The obtained fracture energy was evaluated according to the following evaluation ranks. -Rating of breaking energy- 4: 1.5 MPa or more 3: 1.0 MPa or more, less than 1.5 MPa 2: 0.5 MPa or more, less than 1.0 MPa 1: Less than 0.5 MPa

[0122] [Table 1]

[0123] "-": Indicates that the corresponding ingredient is not contained. (monomer) AAm: acrylamide AA: acrylic acid NVP: N-vinyl-2-pyrrolidone HEA: 2-hydroxyethyl acrylate (Water-soluble azo polymerization initiator) VA-057: Trade name, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] tetrahydrate VA-044: Trade name, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride V-50: Trade name, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 2,2'-azobis(2-methylpropionamidine) dihydrochloride V-501: Trade name, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 4,4'-azobis(4-cyanovaleric acid) (polymeric azo polymerization initiator) VPE-0201: Product name, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., a polymeric azo polymerization initiator containing polyethylene glycol units (persulfate polymerization initiator) APS: ammonium peroxodisulfate KPS: potassium peroxodisulfate Composition ratio: The ratio of each monomer-derived component to the total of all monomer-derived components constituting the water-soluble polymer, expressed in mass %. Note that the monomer-derived components do not include components derived from the polymerization initiator. Amount blended: indicates the amount of polymerization initiator blended relative to 100 parts by mass of the total amount of monomers (monomers do not include polymerization initiators) used in the polymerization of the water-soluble polymer, and is expressed in parts by mass.

[0124] [Table 2]

[0125] "-": Indicates that the corresponding ingredient is not contained. Polymers 1 to 9, Comparative Polymers 1 and 2: Polymers 1 to 9 and Comparative Polymers 1 and 2 listed in Table 1 CMC: Cellogen WS-C (trade name), carboxymethyl cellulose manufactured by Daiichi Kogyo Seiyaku Co., Ltd., degree of etherification 0.66. SR-151: Nalstar SR-151 (trade name), a styrene butadiene rubber manufactured by Nippon A&L Co., Ltd. Two Tg points (-27°C and 15°C) are observed (catalog values ​​from Nippon A&L Co., Ltd.). The solubility of the above-mentioned Narstar SR-151 in water at 20°C was less than 10 g / L-H2O. Content: Indicates the percentage of each solid content in the total solid content contained in the binder composition, expressed in mass %. Mw: weight average molecular weight of water-soluble polymer Mn: Number average molecular weight of water-soluble polymer Mw / Mn: Molecular weight distribution of water-soluble polymer

[0126] As can be seen from Table 2, all of Polymers 1 to 9, which are water-soluble polymers (X) defined in the present invention, exhibited breaking elongation equal to or greater than that of Comparative Polymers 1 and 2. The breaking energy of films formed using any of Polymers 1 to 9 and Binder Compositions Nos. 101 to 109 of the present invention, which contain a water-soluble compound (Y), polymer particles, and water, was large and the films had excellent tensile breaking resistance.

[0127] [Preparation of Electrode Compositions Nos. C-1 to C-9 and BC-1 to BC-5] (1) Preparation of electrode composition No. C-1 A 60 mL ointment container (Umano Chemical Co., Ltd.) was filled with carbon-coated silicon oxide (carbon element content: 1.3 mass%, Osaka Titanium Technologies Co., Ltd., grade: SiO NC, average particle size: 5 μm, specific surface area: 2.6 m). 2 / g), 1.78 g of graphite (product name: MAG-D, manufactured by Showa Denko Materials Co., Ltd., average particle size: 21 μm, specific surface area: 4 m 2 / g) 7.12 g, acetylene black (trade name: Denka Black, manufactured by Denka Co., Ltd., average particle size: 35 nm, specific surface area: 68 m 20.60 g of cellulose acetate (PAAm / g), 1.41 g of an aqueous solution of the polymer 1 (PAAm) (solid content: 0.21 g), 1.68 g of an aqueous solution of CMC (solid content: 0.08 g) as the water-soluble compound (Y), and 3.8 g of distilled water were added and dispersed for 6 minutes at 2000 rpm using a THINKY THINKY Mixer. 2.4 g of distilled water was added to the dispersed solution, and the resulting solution was dispersed for 12 minutes at 2000 rpm using a THINKY THINKY Mixer. Furthermore, 0.41 g of polymer particles (containing water as a liquid medium, solid content: 0.21 g) of Nalstar SR-151 (a styrene-butadiene rubber latex manufactured by Nippon A&L Co., Ltd.) were added to the dispersed solution, and the resulting solution was dispersed for 3 minutes at 2000 rpm using a THINKY THINKY Mixer. Electrode Composition No. C-1 was obtained.

[0128] (2) Preparation of Electrode Compositions Nos. C-2 to C-9 and BC-1 to BC-5 Electrode Compositions Nos. C-2 to C-9 and BC-1 to BC-5 were prepared in the same manner as in the preparation of electrode composition No. C-1, except that the compositions were changed as shown in Table 3 below.

[0129] Here, electrode composition Nos. C-1 to C-9 are electrode compositions of the present invention, and electrode composition Nos. BC-1 to BC-5 are electrode compositions for comparison.

[0130] [Preparation of Electrode Compositions Nos. D-1 to D-9, BD-1 and BD-2] (1) Preparation of lithium-doped and carbon-coated silicon oxide In the same manner as in Example 1-1 of JP 2022-121582 A, lithium-doped and carbon-coated silicon oxide (LiSiOC) was produced. Specifically, the procedure was as follows. A mixture of silicon metal and silicon dioxide (vaporized starting material) was placed in a reactor. Vaporization occurred under a vacuum of 10 Pa. The material was deposited on an adsorption plate. After sufficient cooling, the deposit (silicon oxide) was removed and pulverized in a ball mill. After adjusting the particle size, a carbon coating was formed by thermal chemical vapor deposition (thermal CVD). For thermal CVD, the pulverized silicon oxide was placed in a silicon nitride tray and placed in a furnace capable of maintaining an argon atmosphere. Argon gas was then introduced into the furnace, and the atmosphere was replaced with argon. The temperature was then increased at a rate of 300°C / hr while a methane-argon gas mixture was introduced at 2 NL / min. The temperature was then maintained at 600–1,100°C for 3–10 hours, yielding a carbon-coated silicon oxide (SIOC). After the temperature reached room temperature, the powder was collected. Next, the carbon-coated silicon oxide was modified by doping with lithium using a redox method. First, the carbon-coated silicon oxide was immersed in a solution (Solution A) prepared by dissolving lithium pieces and naphthalene in tetrahydrofuran (hereinafter referred to as THF). Specifically, Solution A was prepared by dissolving naphthalene in THF solvent at a concentration of 0.2 mol / L and then adding 10% by mass of lithium pieces to the mixture of THF solvent and naphthalene. The temperature of Solution A when the carbon-coated silicon oxide was immersed was 20°C, and the immersion time was 20 hours. The solid matter was then filtered. The carbon-coated silicon oxide was doped with lithium through the above process. The obtained solid matter was heat-treated at 600°C for 24 hours in an argon atmosphere to stabilize the Li compound. In this way, the carbon-coated silicon oxide was modified to obtain silicon oxide (LiSiOC) that was both lithium-doped and carbon-coated. The carbon element content was 3 mass %, and the average particle size (volume-based median diameter D50) of the LiSiOC particles was 6.7 μm.

[0131] (2) Preparation of electrode compositions Nos. D-1 to D-9 and BD-1 to BD-2 Electrode composition No. D-1 was prepared in the same manner as in the preparation of electrode composition No. C-1, except that the carbon-coated silicon oxide was changed to the lithium-doped and carbon-coated silicon oxide (LiSiOC). In addition, electrode compositions Nos. D-2 to D-9 and BD-1 to BD-2 were prepared in the same manner as electrode composition No. D-1, except that the composition was changed to that shown in Table 3 below.

[0132] Here, electrode composition Nos. D-1 to D-9 are electrode compositions of the present invention, and electrode composition Nos. BD-1 and BD-2 are electrode compositions for comparison.

[0133] [Preparation of Electrode Compositions E-1 to E-9, F-1 to F-9, BE-1 to BE-2, and BF-1 to BF-2] (1) Preparation of silicon oxide that is both nickel-doped and carbon-coated, and silicon oxide that is both titanium-doped and carbon-coated In the same manner as in the preparation of the powder material for the negative electrode described in the examples of JP 2021-150077 A, silicon oxide (NiSiOC) having both nickel doping and carbon coating and silicon oxide (TiSiOC) having both titanium doping and carbon coating were prepared. Specifically, this was done as follows. (i) Preparation of Si alloy Each raw material was weighed to obtain the Si alloy composition shown in Table A below. The weighed raw materials were heated and melted using a high-frequency induction furnace to obtain a molten alloy. A powdered Si alloy was produced from the obtained molten alloy by gas atomization. An argon atmosphere was used during the preparation of the molten alloy and the gas atomization. During the gas atomization, high-pressure (4 MPa) argon gas was sprayed onto the molten alloy falling in a rod-like shape inside the atomization chamber. The obtained powder was sieved to a size of 25 μm or less and used as the Si alloy in the subsequent steps. (ii) Preparation for mechanical milling Si alloy and SiO2 powder as a metal oxide were placed in a stainless steel pot together with 30 metal balls (size: Φ3 / 8 inch, material: SUJ2) in the mixing ratio shown in Table A below. For example, to prepare 10 g of the target product, 9.5 g of Si alloy and 0.5 g of SiO2 powder were placed. After the addition, the atmosphere inside the pot was replaced with Ar gas. (iii) Mechanical milling The pot was placed in a planetary ball mill (Fritsch, P-5 / 4) and milled at 300 rpm for 150 hours. The resulting mixed powder was used as a metal-doped silicon-based material (nickel-doped silicon oxide (NiSiO) or titanium-doped silicon oxide (TiSiO)) in the subsequent steps. (iv) Carbon coating treatment on silicon-based materials doped with metal elements Carbon coatings were formed on metal-doped silicon-based materials (NiSiO or TiSiO) by thermal CVD. For thermal CVD, the metal-doped silicon-based materials after mechanical milling were placed in a silicon nitride tray and placed in a furnace capable of maintaining a constant atmosphere. Argon gas was then introduced to replace the atmosphere inside the furnace. The temperature was then increased at a rate of 300°C / hr while a methane-argon gas mixture was introduced at 2 NL / min. The temperature was then maintained at 600–1,100°C for 3–10 hours, resulting in thermal CVD of a carbon film. Silicon-based materials that were both metal-doped and carbon-coated (nickel-doped and carbon-coated silicon oxide (NiSiOC) and titanium-doped and carbon-coated silicon oxide (TiSiOC)) were obtained. After the temperature reached room temperature, the temperature was lowered and the powder was collected. The carbon element content was 3 mass %, and the average particle size (volume-based median diameter D50) of both the NiSiOC particles and the TiSiOC particles was 7 μm.

[0134] [Table A]

[0135] <Notes for Table A> NiSiO: Nickel-doped silicon oxide TiSiO: Titanium-doped silicon oxide Alloy composition: Indicates the percentage of each metal element in the Si alloy, which accounts for 100% by mass of the Si alloy and SiO powder added when obtaining the metal-doped silicon-based material (NiSiO or TiSiO), and the total alloy composition is 95% by mass. Mixing ratio: Indicates the ratio of each component (Si alloy or SiO2 powder) to the total amount of Si alloy and SiO2 powder added when obtaining a silicon-based material doped with a metal element (NiSiO or TiSiO), and is expressed in mass%.

[0136] (2) Preparation of electrode compositions Nos. E-1 to E-9 and BE-1 to BE-2 Electrode composition No. E-1 was prepared in the same manner as in the preparation of electrode composition No. C-1, except that the carbon-coated silicon oxide was changed to the silicon oxide that was both nickel-doped and carbon-coated (NiSiOC). In addition, electrode compositions Nos. E-2 to E-9 and BE-1 to BE-2 were prepared in the same manner as electrode composition No. E-1, except that the composition was changed to that shown in Table 4 below.

[0137] (3) Preparation of electrode compositions Nos. F-1 to F-9 and BF-1 to BF-2 Electrode composition No. F-1 was prepared in the same manner as in the preparation of electrode composition No. C-1, except that the carbon-coated silicon oxide was changed to the titanium-doped and carbon-coated silicon oxide (TiSiOC). In addition, electrode compositions Nos. F-2 to F-9 and BF-1 to BF-2 were prepared in the same manner as electrode composition No. F-1, except that the composition was changed to that shown in Table 4 below.

[0138] Here, electrode compositions Nos. E-1 to E-9 and F-1 to F-9 are electrode compositions of the present invention, and electrode compositions Nos. BE-1 to BE-2 and BF-1 to BF-2 are electrode compositions for comparison.

[0139] The electrode compositions prepared above were subjected to strain dispersion measurement as follows. Furthermore, the discharge capacity retention rate of secondary batteries equipped with negative electrode sheets obtained from the electrode compositions prepared above was measured as follows, and cycle characteristics were evaluated. The results are summarized in Tables 3 and 4.

[0140] (Measurement of strain distribution of electrode composition) Using 1 mL of the electrode composition prepared above, strain dispersion measurements were performed using a modular compact rheometer MCR102 (trade name, manufactured by Anton Paar) at 25°C, 10 rad / s, and a rheometer jig PP50. The difference between G' at a shear strain of 0.1% and G' at a shear strain of 75% was recorded as the "difference in electrode slurry G'," and G' at a shear strain of 0.1% was recorded as the "electrode slurry G'."

[0141] [Fabrication of non-aqueous electrolyte secondary battery (2032 type coin battery)] The electrode composition prepared above was applied to a 20 μm-thick copper foil using an applicator and dried at 80 ° C for 1 hour. After that, pressure was applied using a press and the foil was dried in a vacuum at 150 ° C for 6 hours to obtain a negative electrode sheet with a negative electrode active material layer thickness of 25 μm. A disk with a diameter of 13.0 mm was cut out from this negative electrode sheet and used to form a negative electrode. A lithium foil (50 μm thick, 14.5 mm diameter) and a polypropylene separator (25 μm thick, 16.0 mm diameter) were stacked in this order, and 200 μL of LiPF6 ethylene carbonate / ethyl methyl carbonate (volume ratio 1:2) electrolyte (concentration 1 M) was impregnated into the separator. Another 200 μL of the above electrolyte was impregnated on top of the separator, and a disk-shaped negative electrode sheet was placed on top of the separator with the negative electrode active material layer surface in contact with the separator. A 2032-type coin case was then closed to produce a nonaqueous electrolyte secondary battery (a battery having a laminate consisting of Li foil, separator, negative electrode active material layer, and copper foil).

[0142] (Evaluation of cycle characteristics) The discharge capacity retention rate of each secondary battery prepared as described above was measured using a charge / discharge evaluation device: TOSCAT-3000 (trade name, manufactured by Toyo Systems Co., Ltd.). Charging was performed at a C rate (capacity rate) of 0.2C (a rate at which full charge is achieved in 5 hours) until the battery voltage reached 0.02V. Discharging was performed at a C rate of 0.2C until the battery voltage reached 1.5V. Three cycles of charging and discharging, each consisting of one charge and one discharge, were repeated to initialize the secondary battery. The initialized secondary battery was charged at 0.5 C until it reached 0.02 V, and then discharged at 0.5 C until it reached 1.5 V. This cycle of charging and discharging was counted as one charge / discharge cycle, and the cycle characteristics were evaluated by repeating the charge / discharge cycle 80 times. The discharge capacity retention rate after 80 charge / discharge cycles (the ratio of the discharge capacity after 80 charge / discharge cycles to the initial discharge capacity) was calculated, assuming that the discharge capacity at the first cycle after initialization (initial discharge capacity) was 100%, and the cycle characteristics were evaluated according to the following evaluation ranks. All charging and discharging was carried out at 25°C. -Evaluation ranking of cycle characteristics- 6: 90% or more 5: 85% or more, less than 90% 4: 80% or more, less than 85% 3: 70% or more, but less than 80% 2: 50% or more, less than 70% 1: Less than 50%

[0143] [Table 3]

[0144] [Table 4]

[0145] SiOC: Carbon-coated silicon oxide (carbon element content: 1.3 mass%, manufactured by Osaka Titanium Technologies Co., Ltd., grade: SiO NC, average particle size: 5 μm, specific surface area: 2.6 m 2 / g) LiSiOC: silicon oxide prepared above that was both lithium-doped and carbon-coated (carbon content: 3% by mass, average particle size: 6.7 μm) NiSiOC: Silicon oxide prepared as above, doped with nickel and coated with carbon (carbon content: 3% by mass, average particle size: 7 μm) TiSiOC: The titanium-doped and carbon-coated silicon oxide prepared above (carbon content: 3% by mass, average particle size: 7 μm) Graphite: MAG-D (product name, manufactured by Showa Denko Materials Co., Ltd., average particle size: 21 μm, specific surface area: 4 m 2 / g) AB: Acetylene black (trade name: Denka Black, manufactured by Denka Co., Ltd., average particle size: 35 nm, specific surface area: 68 m 2 / g) Corresponding composition No.: Binder composition No. corresponding to the combination of binder components (water-soluble polymer (X), water-soluble compound (Y), and polymer particles) blended into the electrode composition. Content: Indicates the proportion of each component (solid content) in the total of all components (solid content) contained in the negative electrode composition, expressed in mass %. Difference in electrode slurry G': Indicates the difference between G' at a shear strain of 0.1% and G' at a shear strain of 75%, and is expressed in Pa. Electrode slurry G': G' at a shear strain of 0.1%, unit is Pa.

[0146] The following can be seen from Tables 3 and 4. Comparative electrode compositions Nos. BC-1 and BC-2 contain comparative polymers 1 and 2 polymerized using a persulfate polymerization initiator, while comparative electrode compositions Nos. BC-3 and BC-4 contain no polymer particles, and comparative electrode composition No. BC-5 contains no water-soluble compound or polymer particles. In these respects, none of these are electrode compositions of the present invention. Secondary batteries having negative electrode sheets fabricated using these comparative electrode compositions BC-1 to BC-5 all exhibited poor cycle characteristics. In contrast, it was found that all of the secondary batteries having negative electrode sheets fabricated using electrode compositions Nos. C-1 to C-9 of the present invention exhibited excellent cycle characteristics. When silicon oxide that was both lithium-doped and carbon-coated, silicon oxide that was both nickel-doped and carbon-coated, or silicon oxide that was both titanium-doped and carbon-coated was used as the high-capacity active material, as in the case of using carbon-coated silicon oxide, it was found that secondary batteries having negative electrode sheets fabricated using electrode compositions Nos. D-1 to D-9, E-1 to E-9, and F-1 to F-9 of the present invention all exhibited superior cycle characteristics compared to batteries using comparative electrode compositions Nos. BD-1 to BD-2, BE-1 to BE-2, and BF-1 to BF-2, which contained comparative polymers 1 and 2 polymerized using a persulfate polymerization initiator.

[0147] Furthermore, the above results indicate that, among azo polymerization initiators, when a water-soluble azo polymerization initiator is used, compared to a polymeric azo polymerization initiator, the combination of a water-soluble polymer (X), a water-soluble compound (Y), and polymer particles can be adjusted to satisfy Condition I when combined with an electrode active material and a conductive additive, and the resulting secondary battery exhibits superior cycle characteristics. For example, when a water-soluble polymer (X) polymerized using a polymeric azo polymerization initiator was used, the cycle characteristics were evaluated as 2 when electrode composition No. BC-3 (without polymer particles) was used, whereas the cycle characteristics were evaluated as 4 when electrode composition No. C-9 (with polymer particles) was used. In contrast, when a water-soluble polymer (X) polymerized using a water-soluble azo polymerization initiator was used, the cycle characteristics were evaluated as 2 when electrode composition No. BC-4 (without polymer particles) was used, whereas the cycle characteristics were evaluated as 6 when electrode composition No. C-1 (with polymer particles) was used. [Explanation of symbols]

[0148] 10 Nonaqueous electrolyte secondary battery 1 Negative electrode current collector 2 Negative electrode active material layer 3 Separator 4 Cathode active material layer 5 Positive electrode current collector 6. Working part (bulb)

Claims

1. A binder composition for a secondary battery, comprising: a water-soluble polymer (X) polymerized using an azo polymerization initiator; a water-soluble compound (Y); polymer particles; and water.

2. The binder composition for a secondary battery according to claim 1 , wherein the azo polymerization initiator is a water-soluble azo polymerization initiator.

3. The binder composition for a secondary battery according to claim 1 , wherein the azo polymerization initiator has a carboxy group.

4. The binder composition for a secondary battery according to claim 1 , which satisfies the following <Condition I>: <Condition I> Average particle size is 1 to 10 μm and specific surface area is 1 to 10 m ２ / g powdered carbon-coated silicon oxide, and a powder having an average particle size of 15 to 25 μm and a specific surface area of ​​1 to 10 m ２ / g of powdered graphite and a graphite powder having an average particle size of 30 to 40 nm and a specific surface area of ​​65 to 75 m ２ In a slurry prepared by mixing acetylene black in powder form having a molecular weight of 1 / g and the binder composition for a secondary battery in the following quantitative ratio, the difference between the storage modulus G' at a shear strain of 0.1% and the storage modulus G' at a shear strain of 75% of the slurry is 50 to 400 Pa, and the value of the storage modulus G' at a shear strain of 0.1% is 60 Pa or more. -Quantity ratio- With respect to 100 parts by mass of the total solid content in the slurry, the content of the carbon-coated silicon oxide is 17.8 parts by mass, the content of the graphite is 71.2 parts by mass, the content of the acetylene black is 6 parts by mass, the content of the solid content of the binder composition for secondary batteries is 5 parts by mass, and the total solid content in the slurry is 52% by mass.

5. 2. The binder composition for a secondary battery according to claim 1, wherein the water-soluble polymer (X) is a polymer containing a constituent component represented by the following general formula (B-1) and / or a constituent component represented by the following general formula (B-2): 【Chemistry 1】 In general formula (B-1), R １１ ~R １３ represents a hydrogen atom, a cyano group, or an alkyl group having 1 to 6 carbon atoms; R １４ represents a hydrogen atom, a hydroxy group, an alkoxy group having 1 to 6 carbon atoms, a cyano group, a phenyl group, a carboxy group, a sulfo group, a phosphate group, or a phosphonate group; L １１ represents a single bond, an alkylene group having 1 to 16 carbon atoms, an arylene group having 6 to 12 carbon atoms, an oxygen atom, a sulfur atom, a carbonyl group, an imino group, or a linking group combining these. * represents a bonding site for incorporation into the main chain of the water-soluble polymer (X). In general formula (B-2), R ２１ ~R ２３ represents a hydrogen atom, a cyano group, or an alkyl group having 1 to 6 carbon atoms; R ２４ represents a hydrogen atom, an acyl group, a hydroxy group, a phenyl group, or a carboxy group; L ２１ represents a single bond, an alkylene group having 1 to 16 carbon atoms, an arylene group having 6 to 12 carbon atoms, an oxygen atom, a sulfur atom, a carbonyl group, an imino group, or a linking group combining these. * represents a bonding site for incorporation into the main chain of the water-soluble polymer (X).

6. 6. The binder composition for a secondary battery according to claim 5, wherein the water-soluble polymer (X) is a polymer containing a constituent component represented by general formula (B-2).

7. 7. The binder composition for a secondary battery according to claim 6, wherein the content of the component represented by general formula (B-2) in the water-soluble polymer (X) is 80 mass% or more.

8. 7. The binder composition for a secondary battery according to claim 6, wherein the constituent component represented by general formula (B-2) includes an acrylamide component.

9. 6. The binder composition for a secondary battery according to claim 5, wherein the water-soluble polymer (X) is a polymer further containing at least one of an acrylonitrile component, an N-vinyl-2-pyrrolidone component, and a styrene component.

10. The binder composition for a secondary battery according to claim 1 , wherein the water-soluble compound (Y) is a polysaccharide.

11. The binder composition for a secondary battery according to claim 10 , wherein the water-soluble compound (Y) comprises at least one of carboxymethyl cellulose, cellulose nanofiber, hydroxyethyl cellulose, hydroxypropyl cellulose, and xanthan gum.

12. 2. The binder composition for a secondary battery according to claim 1, wherein the water-soluble polymer (X) has a weight average molecular weight of 100,000 to 900,000.

13. 2. The binder composition for a secondary battery according to claim 1, wherein the water-soluble polymer (X) has a molecular weight distribution of 5.0 or less.

14. 2. The binder composition for a secondary battery according to claim 1, wherein the water-soluble polymer (X) has a tensile modulus of elasticity of 4000 MPa or more.

15. 2. The binder composition for a secondary battery according to claim 1, wherein the polymer constituting the polymer particles is a polymer containing at least one of a conjugated diene component, an ethylenically unsaturated carboxylic acid component, a cyano group-containing ethylenic monomer component, and an aromatic vinyl monomer component.

16. 2. The binder composition for a secondary battery according to claim 1, wherein the polymer particles have a glass transition temperature of −50 to 150° C.

17. 10. A composition for an electrode comprising the binder composition for a secondary battery according to claim 1, an active material capable of inserting and releasing ions of a metal belonging to Group 1 or 2 of the periodic table, and a conductive additive.

18. The electrode composition according to claim 17 , wherein the active material comprises a silicon-based active material.

19. An electrode sheet having a layer formed using the electrode composition according to claim 17 or 18.

20. A secondary battery, wherein at least one of a positive electrode active material layer and a negative electrode active material layer is formed using the electrode composition according to claim 17 or 18.

21. A method for producing an electrode sheet, comprising forming an electrode active material layer using the electrode composition according to claim 17 or 18.

22. A method for producing a secondary battery, comprising incorporating an electrode sheet obtained by the production method according to claim 21 as an electrode of the secondary battery.

Images