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

Abstract

To provide a binder composition for a secondary battery, an electrode sheet and a secondary battery, as well as manufacturing methods for electrode sheet and secondary battery, which can sufficiently enhance the cycle characteristics (sufficiently prolong the cycle life) of the secondary battery even when using electrode active materials with large volume changes during charging and discharging.SOLUTION: The binder composition for a secondary battery, including a water-soluble polymer (X) and a water-soluble polymer (Y), in which the water-soluble polymer (X) is a polymer containing 20 mass% or more of a component having a specific structure represented by general formula (B-2), in which the ratio of the weight-average molecular weight of the water-soluble polymer (Y) to that of the water-soluble polymer (X) is from 0.300 to 10.0.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a binder composition for a secondary battery, an electrode sheet and a secondary battery, and methods for manufacturing the electrode sheet and the secondary battery. [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 have electrode active material layers (positive and negative electrode active material layers), which contain electrode active material particles capable of absorbing and releasing lithium ions during charging and discharging, and also contain a conductive additive, etc., as necessary. The electrode active material, conductive additive, etc. are so-called solid particles, and the electrical conductivity between the solid particles is easily impaired due to the expansion and contraction of the electrode active material particles accompanying the charging and discharging (intercalation and release of lithium ions) of the lithium-ion secondary battery. If the electrical conductivity is impaired, the internal resistance of the battery increases and the battery capacity decreases. To improve the cycle characteristics (extend the cycle life) of a lithium-ion secondary battery, it is important to be able to maintain adhesion between the solid particles even after repeated charging and discharging, and therefore the electrode active material layers usually contain a binder. For example, Patent Document 1 describes a binder composition for lithium ion secondary battery electrodes that includes a particulate polymer and a water-soluble polymer. Patent Document 1 also describes that the water-soluble polymer that constitutes this composition contains ethylenically unsaturated carboxylic acid monomer units, one or more carboxylic acid amide monomer units selected from (meth)acrylamide, N-2-dimethylaminoethyl(meth)acrylamide, and N-3-dimethylaminopropyl(meth)acrylamide, and crosslinkable monomer units other than the carboxylic acid amide monomer units, each in specific proportions; and that by combining this composition with an electrode active material and a carboxymethyl cellulose salt and applying it to form an electrode for a lithium ion secondary battery, gas generation in the resulting lithium ion secondary battery is suppressed and the cycle characteristics of the lithium ion secondary battery are improved. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2014 / 196547 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, the expansion of secondary battery applications has led to demands for higher energy density and improved cycle characteristics. To achieve even higher capacity in lithium-ion secondary batteries, the use of silicon-based active materials as negative electrode active materials has been actively investigated. 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 in turn leads to a correspondingly large contraction 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, resulting in a deterioration in battery performance with repeated charging and discharging. This means that there are limitations to improving cycle characteristics. As a result of further investigations, the present inventors have found that when conventional electrode binders, including the binder described in Patent Document 1, are used, the cycle characteristics of the resulting secondary batteries, particularly secondary batteries using a silicon-based active material that undergoes a large volume change during charging and discharging as the negative electrode active material, are not sufficient.

[0006] An object of the present invention is to provide a binder composition for secondary batteries 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 binder composition for a secondary battery, and a method for manufacturing the electrode sheet and the secondary battery. [Means for solving the problem]

[0007] That is, 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) and a water-soluble polymer (Y), wherein the water-soluble polymer (X) is a polymer containing 20 mass % or more of a constituent component represented by the following general formula (B-2), and the ratio of the weight-average molecular weight of the water-soluble polymer (Y) to the weight-average molecular weight of the water-soluble polymer (X) is 0.300 to 10.0: [ka] 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). <2> The content of the component represented by the general formula (B-2) in the water-soluble polymer (X) is 80 mass% or more. <1> The binder composition for a secondary battery according to claim 1. <3> The component represented by the general formula (B-2) contains a (meth)acrylamide component. <1> or <2> The binder composition for a secondary battery according to claim 1. <4> The water-soluble polymer (X) is a polymer further containing at least one of an acrylonitrile component and an N-vinyl-2-pyrrolidone component. <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. <5> The weight average molecular weight of the water-soluble polymer (X) is 10,000 to 1,000,000. <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. <6> The molecular weight distribution of the water-soluble polymer (X) is 5.0 or less. <1> ~ <5> 10. The binder composition for a secondary battery according to claim 9, wherein the binder composition is a binder for a secondary battery. <7> The water-soluble polymer (Y) is a polysaccharide. <1> ~ <6> 10. The binder composition for a secondary battery according to claim 9, wherein the binder composition is a binder for a secondary battery. <8> The water-soluble polymer (Y) contains at least one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and xanthan gum. <7> The binder composition for a secondary battery according to claim 1. <9> The weight average molecular weight of the water-soluble polymer (Y) is 100,000 to 500,000. <1> ~ <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> containing polymer particles, <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 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; <10> The binder composition for a secondary battery according to claim 1. <12> Contains water, <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 active material includes an active material capable of inserting and releasing ions of a metal belonging to Group 1 or Group 2 of the periodic table. <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 active material includes a silicon-based active material. <13> The binder composition for a secondary battery according to claim 1. <15> <13> or <14> 10. An electrode sheet having a layer formed using the binder composition for a secondary battery according to claim 9. <16> At least one of the positive electrode active material layer and the negative electrode active material layer is <13> or <14> A secondary battery, wherein the layer is formed using the binder composition for a secondary battery according to claim 1. <17> <13> or <14> and forming an electrode active material layer using the binder composition for a secondary battery according to claim 1. <18> <17> 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.

[0008] 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 in an amount of 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, 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 expression of a compound, a component, or a substituent includes a partial modification of the structure within the scope of the effects of the present invention. Furthermore, in the present invention, a compound or a component not specified as substituted or unsubstituted may have any substituent within the scope of the effects of the present invention. 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]

[0009] The binder composition for secondary batteries and the electrode sheet of the present invention can 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. 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]

[0010] [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

[0011] [Binder composition for secondary batteries] The binder composition for a secondary battery of the present invention (hereinafter also referred to as "the binder composition of the present invention") comprises a water-soluble polymer (X) and a water-soluble polymer (Y), wherein the water-soluble polymer (X) is a polymer containing 20 mass % or more of a constituent component represented by general formula (B-2) described below, and the ratio of the weight-average molecular weight of the water-soluble polymer (Y) to the weight-average molecular weight of the water-soluble polymer (X) is 0.300 to 10.0. 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 binder composition of the present invention preferably contains water as a liquid medium. Typically, the binder composition of the present invention can be suitably used for forming an electrode active material layer in an electrode (positive electrode or negative electrode) of a secondary battery. For example, the binder composition of the present invention can be used to form an electrode (positive electrode or negative electrode) active material layer of a secondary battery by adding an electrode active material (positive electrode active material or negative electrode active material, collectively referred to as "active material").

[0012] The water-soluble polymer (X) contained in the binder composition of the present invention and the polymer particles described below that may be contained in the binder composition of the present invention are thought to function, for example, 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 these solid particles. They may also function as a binder that binds the current collector and the solid particles. The adsorption of the water-soluble polymer (X) and the 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 polymer (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.

[0013] The binder composition of the present invention can be used to prepare an electrode sheet containing an active material, and by applying this to an electrode of a secondary battery, the cycle characteristics of the secondary battery can be improved. Although the reason for this is not clear, it is thought to be as follows. The binder composition of the present invention is thickened by the inclusion of the water-soluble polymer (Y), thereby improving the dispersibility of the binder composition. Therefore, even in an electrode active material layer formed using this binder composition, the water-soluble polymer (X), the water-soluble polymer (Y), and solid particles such as the active material can be substantially uniformly dispersed. Furthermore, when the water-soluble polymer (X) contains 20 mass% or more of a component having a specific structure represented by the general formula (B-2) described below, and the ratio of the weight-average molecular weight of the water-soluble polymer (Y) to the weight-average molecular weight of the water-soluble polymer (X) is 0.300 to 10.0, the formation of intermolecular bonds such as hydrogen bonds promotes the interaction between the water-soluble polymer (X) and the water-soluble polymer (Y), improving the fracture energy of the composite of the water-soluble polymer (X) and the water-soluble polymer (Y). Furthermore, the adhesiveness of the solid particles is also improved, thereby maintaining a good electrical continuity state even when the volume of the electrode active material changes during charge and discharge of the secondary battery. This is thought to be one of the reasons for the improved cycle performance of the secondary battery.

[0014] The components contained in the binder composition of the present invention will be described below.

[0015] (Water-soluble polymer (X)) The water-soluble polymer (X) is a polymer containing 20% ​​by mass or more of a constituent component represented by the following general formula (B-2).

[0016] [ka]

[0017] 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. 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 21 and R 22 is preferably a hydrogen atom. R 23 is preferably a hydrogen atom or methyl, more preferably a hydrogen atom. R 24 represents a hydrogen atom, an acyl group (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, and may be linear or branched. R 21 ~R 23 As the alkyl group, an alkyl group having 1 to 6 carbon atoms can be preferably used. R 24 is preferably a hydrogen atom or a hydroxy group, more preferably a hydrogen atom.

[0018] L 21 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. 21may 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 21 When L represents a linking group other than a single bond, 21 The chemical formula weight of L is preferably 14 to 2000, more preferably 14 to 500, and even more preferably 28 to 200. 21 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 21 is preferably a single bond, methylene, ethylene, propylene, 2-hydroxypropylene or butylene, more preferably a single bond, ethylene or butylene, further preferably a single bond or ethylene, and particularly preferably a single bond. * indicates a binding site for incorporation into the main chain of the polymer (water-soluble polymer (X)).

[0019] 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.

[0020] 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 (meth)acrylamide component, more preferably an acrylamide component. The content of the (meth)acrylamide component (preferably an 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.

[0021] The water-soluble polymer (X) used in the present invention may contain components other than the component represented by the general formula (B-2) above, within the scope that does not impair the effects of the present invention. Examples of such components include the component represented by the following general formula (B-1), an acrylonitrile component, an N-vinyl-2-pyrrolidone component, and a styrene component. It is preferable that the water-soluble polymer (X) contains at least one of the acrylonitrile component and the N-vinyl-2-pyrrolidone component, and it is more preferable that the water-soluble polymer (X) contains an acrylonitrile component.

[0022] [ka]

[0023] 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. R 13 is preferably a hydrogen atom or methyl, more preferably a hydrogen atom. 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.

[0024] L 11is 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. * indicates a binding site for incorporation into the main chain of the polymer (water-soluble polymer (X)).

[0025] 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.

[0026] 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, even more preferably 1 to 3 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.

[0027] In the water-soluble polymer (X), the content of the constituents represented by the general formula (B-2) is 20% by mass or more in total, preferably 40% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, particularly preferably 85% by mass or more, and even more preferably 90% by mass or more, most preferably 95% by mass or more, and may be 100% by mass. There is no particular upper limit, as long as it is 100% by mass or less. In the water-soluble polymer (X), the total content of the component represented by the general formula (B-1), the acrylonitrile component, the N-vinyl-2-pyrrolidone component, and the styrene component is 80% by mass or less, preferably 60% by mass or less, more preferably 40% by mass or less, even more preferably 20% by mass or less, still more preferably 15% by mass or less, even more preferably 10% by mass or less, and most preferably 5% by mass or less. It is also preferable that the water-soluble polymer (X) does not contain any of the component represented by the general formula (B-1), the acrylonitrile component, the N-vinyl-2-pyrrolidone component, and the styrene component.

[0028] The weight-average molecular weight (Mw) of the water-soluble polymer (X) used in the present invention is not particularly limited, and is, for example, preferably 10,000 to 1,000,000, and from the viewpoint of improving cycle characteristics, more preferably 100,000 to 900,000. The lower limit is more preferably 200,000 or more, and even more preferably 300,000 or more. The upper limit is more preferably 800,000 or less, and even more preferably 700,000 or less. The water-soluble polymer (X) preferably does not have a cross-linked structure, that is, it is preferably a chain polymer.

[0029] From the viewpoint of further improving cycle characteristics, the molecular weight distribution of the water-soluble polymer (X) is preferably 5.0 or less, while the molecular weight distribution of the water-soluble polymer (X) is practically preferably 1.0 or more, more preferably 1.5 or more, and even more preferably 2.0 or more. When the molecular weight distribution of the water-soluble polymer (X) is within the above-mentioned preferred range, it is believed that the variation in the molecular weight of the water-soluble polymer (X) is suppressed, and the interaction between the water-soluble polymer (X) and the water-soluble polymer (Y), which contributes to improving the tensile modulus of the binder composition, is more easily expressed. 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)].

[0030] The ratio (Y / X) of the weight-average molecular weight of the water-soluble polymer (X) to the weight-average molecular weight of the water-soluble polymer (Y) described below is 0.300 to 10.0. If Y / X is less than 0.300 or exceeds 10.0, the difference in weight-average molecular weight between the water-soluble polymer (X) and the water-soluble polymer (Y) is too large, making it difficult to form sufficient intermolecular bonds such as hydrogen bonds between the water-soluble polymer (X) and the water-soluble polymer (Y), and this is thought to be due to the insufficient effect of the interaction between the water-soluble polymer (X) and the water-soluble polymer (Y). The upper limit of Y / X is preferably 7.00 or less, more preferably 6.00 or less, even more preferably 5.00 or less, and particularly preferably 4.00 or less.

[0031] When the weight average molecular weight of the water-soluble polymer (X) is 10,000 or more and less than 70,000, the above Y / X is preferably 1.50 to 10.0, more preferably 2.00 to 10.0. When the weight average molecular weight of the water-soluble polymer (X) is 70,000 or more and less than 130,000, the above Y / X is preferably 0.700 to 7.00, more preferably 1.00 to 5.00. When the weight average molecular weight of the water-soluble polymer (X) is 130,000 or more and less than 200,000, the above Y / X is preferably 0.350 to 5.00, more preferably 0.600 to 3.50. When the weight average molecular weight of the water-soluble polymer (X) is 200,000 or more and less than 800,000, the above Y / X is preferably 0.300 to 5.00, more preferably 0.350 to 4.00. When the weight average molecular weight of the water-soluble polymer (X) is 800,000 or more and 10,000,000 or less, the above Y / X is preferably 0.300 to 5.00, more preferably 0.300 to 4.00. The above Y / X has three significant digits.

[0032] (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 the water-soluble polymer (X) are measured by gel permeation chromatography (GPC). The molecular weight refers to the weight-average molecular weight converted into polyethylene glycol. The measurement method is basically the value measured by the method under 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.

[0033] 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 can be determined in the same manner as in the method for calculating the tensile modulus of a binder composition described in the Examples below, except that a test piece is prepared using an aqueous solution of the water-soluble polymer (X) instead of the binder composition.

[0034] 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.

[0035] - 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.

[0036] The water-soluble polymer (X) used in the present invention can be obtained by a conventional polymer synthesis method. 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.

[0037] 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 (% by mass) of each component. a = 99 to 20, b = 1 to 80, and a + b = 100.

[0038] [ka]

[0039] In the present invention, the water-soluble polymer (X) may be used alone or in combination of two or more.

[0040] (Water-soluble polymer (Y)) In the present invention, the water-soluble polymer (Y) is a water-soluble polymer having a structure different from that of the water-soluble polymer (X), and a wide variety of water-soluble polymers can be used that function as thickeners for the slurry for forming the electrode active material layer of a secondary battery. Examples of the thickener include polysaccharides that function as thickeners, and may be either natural or synthetic polysaccharides, and the following examples are given: Examples of cellulose compounds that are thickening polysaccharides 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 compounds may be in the form of salts such as ammonium salts, sodium salts, and lithium salts. In cellulose compounds, the degree of ether substitution is usually 0.5 to 1.5, and preferably 0.5 to 1.0. The degree of ether substitution means the average number of hydroxyl groups substituted with ether groups per glucose ring unit of cellulose, and can be measured by titration or the like. Examples of natural polysaccharides other than the above-mentioned cellulose compounds 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 polymer (Y) preferably contains at least one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, carrageenan, and xanthan gum, and from the viewpoint of further improving cycle characteristics, it is more preferable that the water-soluble polymer (Y) contains at least one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and xanthan gum.

[0041] The weight average molecular weight (Mw) of the water-soluble polymer (Y) used in the present invention is not particularly limited, and is, for example, preferably from 100,000 to 500,000, more preferably from 150,000 to 500,000, and even more preferably from 200,000 to 500,000.

[0042] (Measurement of weight average molecular weight) In the present invention, the weight average molecular weight of the water-soluble polymer (Y) is a value measured by the method described above for the water-soluble polymer (X).

[0043] In the present invention, the water-soluble polymer (Y) may be used alone or in combination of two or more.

[0044] (polymer particles) The binder composition of the present invention preferably contains polymer particles from the viewpoint of further improving cycle characteristics. The polymer particles that may be contained are particulate polymers, and the "particulate" may be flat, amorphous, etc., and are preferably spherical or granular. The polymer particles are particles of a water-insoluble polymer, i.e., particles of a polymer whose solubility in water at 20°C is less than 10 g / L-H2O (no more than 10 g dissolves in 1 liter of water).

[0045] 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 calculating the tensile modulus of a binder composition described in the Examples below, except that a test piece is prepared using an aqueous solution of the polymer particles instead of the binder composition.

[0046] 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, and even more preferably from 0 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.

[0047] - 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.

[0048] 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.

[0049] The average particle size (median diameter based on volume in water) of the polymer particles is not particularly limited, and 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 unavailable or when synthetic polymer particles are used, the average particle size of the polymer particles is the particle size at which the cumulative volume calculated from the smallest diameter side in the particle size distribution measured by laser diffraction / scattering method becomes 50% (the median diameter based on volume in water).

[0050] 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.

[0051] 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 (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, ethylene glycol di(meth)acrylate, and 2,2,2-trifluoroethyl (meth)acrylate. Examples of vinyl fluoride monomers that lead to vinyl fluoride monomer components include vinylidene fluoride.

[0052] 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.

[0053] 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. The acrylic polymer means a polymer containing the above-mentioned ethylenically unsaturated carboxylic acid component and / or the above-mentioned ethylenically unsaturated carboxylic acid ester component. Examples of styrene / butadiene copolymers include those described in WO 2021 / 172208, WO 2021 / 153516, WO 2021 / 065457, WO 2019 / 188722, WO 2018 / 173717, WO 2017 / 056466, WO 2014 / 141721, JP 2014-203771 A, WO 2013 / 141140 A, JP 2014-116263 A, JP 2003-151560 A, JP 2000-123838 A, and JP 2000-123838 A. 2000-100436, WO 1999 / 048953, WO 2020 / 226035, WO 2014 / 057749, JP 2019-179631, JP 2017-126456, JP 2017-084621, JP 2015-191876, JP 2012-169112, JP 2012-094506, JP 2011-108373, JP 2010-205722 or JP 2010-140684 It is possible to use those described in. Examples of acrylic polymers include those described in JP 2020-123590 A, WO 2018 / 173717 A, JP 2016-024985 A, WO 2015 / 107896 A, WO 2014 / 148064 A, WO 2014 / 073647 A, JP 2014-203805 A, JP 2014-116265 A, JP 2015-106488 A, and WO 2018 / 194101 A. No. 2015 / 012366, WO 2012 / 049971, JP 2012-212537 A, JP 2011-171181 A, JP 2010-245035 A, JP 2010-192434 A, JP 2010-182439 A, JP 2010-146870 A, JP 2010-146869 A, or JP 2002-319403 A can be used. Examples of poly(vinylidene fluoride) that can be used include those described in JP 2014-229406 A, WO 2013 / 005796, WO 2011 / 040474, WO 2009 / 123168, WO 2014 / 057749, and WO 2012 / 117910. Other examples that can be used include those described in paragraphs 0120 to 0123 of International Publication No. 2013 / 005796.

[0054] In the present invention, the polymer particles may be used alone or in combination of two or more kinds.

[0055] The binder composition of the present invention may contain, in addition to the water-soluble polymer (X) and the water-soluble polymer (Y) and the polymer particles that may be contained, other polymers that are commonly used as binders for batteries. The proportion of the water-soluble polymer (X) and the water-soluble polymer (Y) in the total of the water-soluble polymer (X), the water-soluble polymer (Y) and other polymers contained in the binder composition of the present invention is preferably 80 mass % or more, more preferably 90 mass % or more, even more preferably 95 mass % or more, particularly preferably 99 mass % or more, and most preferably 100 mass %. In the binder composition of the present invention, the mass ratio of the water-soluble polymer (X) to the water-soluble polymer (Y) (mass of the water-soluble polymer (X):mass of the water-soluble polymer (Y)) is not particularly limited, and is preferably 20-90:10-80, more preferably 40-80:20-60.

[0056] When the binder composition of the present invention contains polymer particles, the total proportion of the water-soluble polymer (X), the water-soluble polymer (Y), and the polymer particles in the total of the water-soluble polymer (X), the water-soluble polymer (Y), the polymer particles, and other polymers contained in the binder composition of the present invention is preferably 80 mass % or more, more preferably 90 mass % or more, even more preferably 95 mass % or more, particularly preferably 99 mass % or more, and most preferably 100 mass %. In the binder composition of the present invention, the mass ratio of the water-soluble polymer (X), the water-soluble polymer (Y), and the polymer particles (mass of the water-soluble polymer (X): mass of the water-soluble polymer (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.

[0057] The binder composition of the present invention preferably 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.

[0058] In the binder composition of the present invention, the contents of the water-soluble polymer (X), the water-soluble polymer (Y), and the polymer particles that may be contained may be appropriately set depending on the purpose. For example, the total content of the water-soluble polymer (X), the water-soluble polymer (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) and the water-soluble polymer (Y), the polymer particles that may be contained, water, and a liquid medium other than water, depending on the purpose. Examples of the other components include polyhydric alcohols (alcohols having two or more hydroxy groups). The binder composition of the present invention can also be prepared by diluting the synthesis solutions of the water-soluble polymer (X) and the water-soluble polymer (Y), and the polymer particles that may be contained therein, etc. Therefore, the binder composition of the present invention may contain compounds used in the synthesis of the water-soluble polymer (X) and the water-soluble polymer (Y), and the polymer particles that may be contained therein, or by-products thereof after the reaction.

[0059] <Composition for electrodes> In one embodiment, the binder composition of the present invention may contain, in addition to the water-soluble polymer (X) and the water-soluble polymer (Y), the optional polymer particles, and water, an active material capable of inserting and releasing ions of a metal belonging to Group 1 or Group 2 of the periodic table. When the binder composition of the present invention contains an active material, it is particularly referred to as an electrode composition of the present invention. The electrode composition of the present invention may further contain a conductive additive and 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.

[0060] The content of the water-soluble polymer (X) and the water-soluble polymer (Y) 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) to the water-soluble polymer (Y) (mass of the water-soluble polymer (X):mass of the water-soluble polymer (Y)) is not particularly limited, and is preferably 20-90:10-80, more preferably 40-80:20-60. When the electrode composition of the present invention contains polymer particles, the total content of the water-soluble polymer (X), the water-soluble polymer (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%, 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 polymer (Y), and the polymer particles (mass of the water-soluble polymer (X):mass of the water-soluble polymer (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.

[0061] -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.

[0062] (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, a compound containing an element such as sulfur that can be composited with Li, a composite of sulfur and a metal, or the like. 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.

[0063] (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]), LiNi 1 / 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.

[0064] The shape of the positive electrode active material is not particularly limited, but 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 conventional methods using a pulverizer or classifier. The method for adjusting the particle size of the negative electrode active material to a predetermined particle size, described below, can also be applied. The positive electrode active material obtained by the calcination 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 average particle size of the positive electrode active material 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 synthesized positive electrode active material is used, the average particle size of the positive electrode active material is measured and calculated by the method described later in the section on negative electrode active material, and a value is adopted.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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 %.

[0070] (Negative electrode active material) The negative electrode active material is an active material capable of inserting and releasing ions of a metal belonging to Group 1 or 2 of the periodic table, and among these, those capable of reversibly inserting and releasing lithium ions are preferred. The material is not particularly limited as long as it has the above-mentioned properties, and examples thereof include carbonaceous materials, silicon-based materials (meaning materials containing silicon element), tin-based materials (meaning materials containing tin element), metal oxides, metal composite oxides, elemental lithium, and lithium alloys. Among these, carbonaceous materials and silicon-based materials are preferably used from the viewpoint of reliability.

[0071] 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.

[0072] Examples of tin-based materials (tin-based active materials) used as negative electrode active materials include Sn, SnO, SnO2, SnS, and SnS2.

[0073] 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.

[0074] 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.

[0075] The negative electrode active material preferably contains titanium element. More specifically, TiNb2O7 (niobium titanate oxide [NTO]), Li4Ti5O 12 (lithium titanate [LTO]) is preferable in that it has excellent rapid charge-discharge characteristics because of its small volume change during lithium ion insertion and extraction, suppresses electrode deterioration, and enables improvement of the cycle characteristics of the lithium ion secondary battery.

[0076] 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.

[0077] The silicon-based material (silicon-based active material) is a negative electrode active material containing silicon element. For example, silicon materials such as Si, SiOx (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-mentioned metal oxides and metal composite oxides, active materials containing silicon element and tin element such as SnSiO3, SnSiS3, etc. can be mentioned. SiOx can be used as a negative electrode active material (semimetal oxide) itself, and can also 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.

[0078] In the above, the negative electrode active material has been described focusing on the components. From the viewpoint 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. Examples of such active materials include negative electrode active materials containing the above-mentioned silicon element and / or tin element, and various metals such as Al and In. A silicon-based active material is preferable in that it enables a higher battery capacity, and a silicon-based active material having a silicon element content of 40 mol% or more of all constituent elements is more preferable. Generally, negative electrodes containing these negative electrode active materials capable of forming an alloy with lithium (e.g., Si negative electrodes containing a silicon-containing active material, Sn negative electrodes containing a tin-based active material) can store 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 stored 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 capable of forming an alloy with lithium, such as negative electrode active materials containing silicon and / or tin, are also referred to as high-capacity active materials.

[0079] 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.

[0080] 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.

[0081] The negative electrode active material may be doped with a metal element. In the negative electrode active material doped with a metal element (also referred to as "metal-doped active material"), the metal element to be doped is preferably at least one of Li, Ni, and Ti, and more preferably Li.

[0082] 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. For example, referring to JP-A-2019-204686, it can also be prepared by carbon-coating silicon oxide. [[ID=I3]] 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. 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.

[0083] 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. A negative electrode active material that is unstable in water may be measured and calculated by other methods such as observation with a SEM (Scanning Electron Microscope).

[0084] 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 and / or carbon-coated silicon oxide with 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.

[0085] When forming a negative electrode active material layer, the unit area (cm 2 The mass (mg) (weight per unit area) of the negative electrode active material is not particularly limited and can be determined appropriately depending on the designed battery capacity.

[0086] 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 %.

[0087] 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.

[0088] (Conductive additive) The electrode composition of the present invention may contain a conductive auxiliary agent, 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 agent. 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.

[0089] 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.

[0090] The shape of the conductive additive is not particularly limited, but is preferably particulate. The average particle size (median diameter D50 in terms of volume in water (volume basis)) of the conductive additive is not particularly limited, but 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).

[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 secondary batteries of the present invention can be prepared as a mixture, preferably as a slurry, by mixing the water-soluble polymer (X) and the water-soluble polymer (Y), preferably polymer particles, water, and optionally any other components, for example, using any of various commonly used mixers. In the case of the electrode composition of the present invention, an active material is mixed in addition to the above, and optionally, a conductive aid and other additives are also 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 binder composition (electrode composition) can be obtained by mixing the water-soluble polymer (X), the water-soluble polymer (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 in space. 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 in the present invention. Room temperature refers to 25°C. Composition ratios, blend ratios, and contents are based on mass unless otherwise specified.

[0112] Example I [Synthesis of water-soluble polymer (X)] Solution A was prepared by mixing 75.0 g of acrylamide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 75.0 g of distilled water, and 0.52 g of VA-057 (trade name, water-soluble azo polymerization initiator manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at room temperature. 337.5 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 75°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 75°C for 3 hours. The mixture was cooled to room temperature to obtain an aqueous solution of polyacrylamide (PAAm). The solids concentration of the resulting aqueous solution was 14.0 mass%, and the weight-average molecular weight (Mw) of the resulting polyacrylamide was 360,000, with a molecular weight distribution (Mw / Mn) of 2.40.

[0113] Water-soluble polymers (X) shown in Table 1 or 2 were synthesized in the same manner as in the synthesis of the polyacrylamides described above, except that in the synthesis of the polyacrylamides described above, the monomer composition was changed as shown in Table 1 or 2 below, and / or the amount of polymerization initiator added was adjusted so that Mw and Mw / Mn would have the values ​​shown in Table 1 or 2 below. The solids concentration of each of the aqueous solutions of water-soluble polymer (X) prepared above was 14.0% by mass, and the solubility of each of the water-soluble polymers (X) obtained above in water at 20°C was 100 g / L-H2O or more. The weight average molecular weight (Mw) and number average molecular weight (Mn) of the water-soluble polymer (X) were measured as described above.

[0114] [Preparation of binder composition] Binder compositions containing the water-soluble polymers (X) and (Y) shown in Table 1 were prepared as follows. 7.50 g of an aqueous solution of water-soluble polymer (X) (solid content: 1.05 g) and 8.00 g of an aqueous solution of water-soluble polymer (Y) (solid content: 0.40 g) were added to a 60 mL ointment container (Umano Chemical Co., Ltd.), and the mixture was stirred at 2000 rpm for 4 minutes using a THINKY Awatori Mixer (trade name), to obtain a binder composition. The solid content concentration of the binder composition was 9.35 mass%.

[0115] Furthermore, binder compositions containing the water-soluble polymer (X), the water-soluble polymer (Y) and polymer particles shown in Table 2 were prepared as follows. 7.50 g of an aqueous solution of water-soluble polymer (X) (solid content: 1.05 g) and 8.00 g of an aqueous solution of water-soluble polymer (Y) (solid content: 0.40 g) were added to a 60 mL ointment container (Umano Chemical Co., Ltd.), and dispersed at 2000 rpm for 4 minutes using a THINKY THINKY Mixer. 2.09 g of polymer particles (containing water as a liquid medium, solid content: 1.05 g) were then added to the dispersion and dispersed at 2000 rpm for 2 minutes using a THINKY Mixer to obtain a binder composition. The solid content of the binder composition was 14.2% by mass.

[0116] The binder compositions prepared above were subjected to tensile tests as follows to calculate the tensile modulus of elasticity. The results are shown in Tables 1 and 2.

[0117] (Tensile Test: Calculation of Tensile Modulus of Binder Composition) The binder composition prepared above was applied to a peelable polyethylene terephthalate (PET) film (5 cm long, 0.5 cm wide, 0.1 mm thick) and dried. The binder composition coating was peeled off from the PET film to obtain a binder composition coating test piece measuring 5 cm long, 0.5 cm wide, and 0.100 to 0.150 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 (product name: 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. The obtained tensile modulus was evaluated according to the following evaluation ranks. -Evaluation rank of tensile modulus (when polymer particles are not included)- 5: Over 6000 MPa 4: 4500 MPa or more, less than 6000 MPa 3: 3500 MPa or more, less than 4500 MPa 2: 3000 MPa or more, less than 3500 MPa 1: Less than 3000 MPa -Evaluation rank of tensile modulus (when polymer particles are included)- 5:2500MPa or more 4: 2000 MPa or more, less than 2500 MPa 3: 1500 MPa or more, less than 2000 MPa 2: 1000 MPa or more, less than 1500 MPa 1: Less than 1000 MPa

[0118] [Preparation Example 1 of Negative Electrode Composition] A negative electrode composition containing the water-soluble polymer (X) and the water-soluble polymer (Y) shown in Table 1 was prepared as follows. A 60 mL ointment container (manufactured by Umano Chemical Co., Ltd.) was charged with 1.78 g of carbon-coated silicon oxide (carbon element content: 1.3 mass%, average particle size: 5 μm, manufactured by Osaka Titanium Co., Ltd.), 7.12 g of graphite (trade name: MAG-D, manufactured by Showa Denko Materials Co., Ltd.), 0.60 g of acetylene black (trade name: Denka Black, manufactured by Denka Co., Ltd.), 2.59 g of an aqueous solution of water-soluble polymer (X) (solid content: 0.362 g), 2.76 g of an aqueous solution of water-soluble polymer (Y) (solid content: 0.138 g), and 3.33 g of distilled water. The mixture was dispersed at 2000 rpm for 6 minutes using a THINKY mixer (trade name). 0.69 g of distilled water was added to the dispersed solution, and the mixture was dispersed at 2000 rpm for 12 minutes using a THINKY mixer to obtain a negative electrode composition. The solid content of the negative electrode composition was 53 mass %.

[0119] [Preparation Example 2 of Negative Electrode Composition] Furthermore, a negative electrode composition containing the water-soluble polymer (X), the water-soluble polymer (Y) and the polymer particles shown in Table 2 was prepared as follows. A 60 mL ointment container (Umano Chemical Co., Ltd.) was charged with 1.78 g of carbon-coated silicon oxide (carbon element content: 1.3 mass%, average particle size: 5 μm, Osaka Titanium Co., Ltd.), 7.12 g of graphite (trade name: MAG-D, Showa Denko Materials Co., Ltd.), 0.60 g of acetylene black (trade name: Denka Black, Denka Co., Ltd.), 1.49 g of an aqueous solution of water-soluble polymer (X) (solid content: 0.208 g), 1.68 g of an aqueous solution of water-soluble polymer (Y) (solid content: 0.084 g), and 5.6 g of distilled water, and the mixture was dispersed at 2000 rpm for 6 minutes using a THINKY THINKY Mixer (trade name). 0.27 g of distilled water was added to the dispersed solution, and the mixture was dispersed at 2000 rpm for 12 minutes using a THINKY THINKY Mixer. Further, 0.41 g of polymer particles (solid content: 0.208 g) was added to the dispersion liquid, and the mixture was dispersed at 2000 rpm for 3 minutes using a mixer to obtain a negative electrode composition having a solid content of 53 mass %.

[0120] For secondary batteries equipped with negative electrode sheets obtained from the negative electrode compositions prepared above, the discharge capacity retention rate was measured as follows, and cycle characteristics were evaluated. The results are summarized in Tables 1 and 2.

[0121] [Preparation of non-aqueous electrolyte secondary battery (2032 type coin battery) 1] The negative electrode composition prepared above was applied to a copper foil with a thickness of 20 μm 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 so that the negative electrode active material layer surface was in contact with the separator. A 2032-type coin case was then crimped to fabricate a nonaqueous electrolyte secondary battery (a battery having a laminate consisting of Li foil, separator, negative electrode active material layer, and copper foil).

[0122] (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 rank of cycle characteristics - (without polymer particles) 5: 90% or more 4: 88% or more, less than 90% 3: 86% or more, less than 88% 2: 84% or more, less than 86% 1: Less than 84% - Evaluation rank of cycle characteristics - (when polymer particles are included) 5: 93% or more 4: 91% or more, less than 93% 3: 89% or more, less than 91% 2: 87% or more, less than 89% 1: Less than 87%

[0123] [Table 1-1]

[0124] [Table 1-2]

[0125] [Table 1-3]

[0126] [Table 2-1]

[0127] [Table 2-2]

[0128] "-": Indicates that the corresponding ingredient is not contained. (Water-soluble polymer (X)) AAm: acrylamide HEA: 2-hydroxyethyl acrylate AN: Acrylonitrile AA: acrylic acid HEAA: N-(2-hydroxyethyl)acrylamide NVP: N-vinyl-2-pyrrolidone Mw: Weight average molecular weight of water-soluble polymer (X), 3 significant digits Mn: Number average molecular weight of water-soluble polymer (X) Mw / Mn: Molecular weight distribution of water-soluble polymer (X) Composition ratio: indicates the proportion of each monomer-derived constituent component in the total of the monomer-derived constituent components that make up the water-soluble polymer (X), and is expressed in mass %. (Water-soluble polymer (Y)) CMC: Carboxymethyl cellulose (manufactured by Daicel Millize) HEC: Hydroxyethyl cellulose (manufactured by Daicel Millize Co., Ltd.) HPC: Hydroxypropyl cellulose (Nippon Soda Co., Ltd.) HPMC: Hydroxypropyl methylcellulose (Shin-Etsu Chemical Co., Ltd.) Carrageenan: Sansho Co., Ltd. Xanthan gum: manufactured by Sansho Co., Ltd. Mw: Weight average molecular weight of water-soluble polymer (Y), 3 significant digits Y / X: Ratio of the weight average molecular weight (Mw) of the water-soluble polymer (Y) to the weight average molecular weight (Mw) of the water-soluble polymer (X), with three significant digits (polymer particles) Polymer particles 1: Synthesized according to the preparation example of copolymer latex 1 described in paragraph 0038 of JP-A No. 2012-212537. Polymer particles 2: Synthesized according to the synthesis example of copolymer latex (B-2) described in paragraph 0044 of JP-A No. 2011-171181. Polymer particles 3: Synthesized according to the preparation example of polymer (A) described in paragraph 0134 of WO 2020 / 226035. Polymer particles 4: Synthesized according to the preparation example of particulate polymer Z1 described in paragraph 0141 of JP-A-2020-123590. The solubility of all of the polymer particles 1 to 4 in water at 20°C was less than 10 g / L-H2O. "Not measurable" in the column for tensile modulus of elasticity of Comparative Example 8 means that the binder composition was too brittle to prepare a test piece for measurement, and therefore the tensile modulus of elasticity could not be measured.

[0129] The following can be seen from Tables 1 and 2: The negative electrode compositions of Comparative Examples 1 to 6 and 11 to 21 are not electrode compositions of the present invention in that the ratio (Y / X) of the weight-average molecular weight of the water-soluble polymer (Y) to the weight-average molecular weight of the water-soluble polymer (X) is outside the range specified in the present invention. Furthermore, the negative electrode composition of Comparative Example 7 does not contain a water-soluble polymer (Y), the negative electrode composition of Comparative Example 8 does not contain a water-soluble polymer (X), and the negative electrode compositions of Comparative Examples 9 and 10 contain only 10 mass% of the component represented by general formula (B-2), so they are not electrode compositions of the present invention. The tensile moduli of the binder compositions used in the negative electrode compositions of Comparative Examples 1 to 21 were all small, and secondary batteries having negative electrode sheets fabricated using the negative electrode compositions of Comparative Examples 1 to 21 all exhibited poor cycle characteristics. In contrast, the negative electrode compositions of Examples 1 to 74 are all electrode compositions of the present invention. The tensile modulus of the binder compositions used in these negative electrode compositions of Examples 1 to 74 was all large, and it was found that all secondary batteries having negative electrode sheets fabricated using the negative electrode compositions of Examples 1 to 74 exhibited excellent cycle characteristics.

[0130] Example II [Preparation Example 3 of Negative Electrode Composition] For the negative electrode compositions of Examples 1 to 4, 9 to 15, 19 to 21, 24 to 32, 34, 36 to 42, and 46 to 50 and Comparative Examples 1, 2, 4, and 7 to 10 listed in Table 1, negative electrode compositions were prepared in the same manner as in the above-mentioned [Preparation Example 1 of Negative Electrode Composition], except that the type of negative electrode active material was changed from carbon-coated silicon oxide (carbon element content: 1.3 mass%, average particle size: 5 μm, manufactured by Osaka Titanium Co., Ltd.) to a metal-doped active material prepared as follows. [Preparation Example 4 of Negative Electrode Composition] For the negative electrode compositions of Examples 51, 53, 54, 56, 57, 59, 60, 62, 63, 65, 66, 68, 69, 71, 72, and 74 and Comparative Examples 14 to 21 listed in Table 2, negative electrode compositions were prepared in the same manner as in [Preparation Example 2 of Negative Electrode Composition] above, except that the type of negative electrode active material was changed from carbon-coated silicon oxide (carbon element content: 1.3 mass%, average particle size: 5 μm, manufactured by Osaka Titanium Co., Ltd.) to a metal-doped active material prepared as follows. In the above-mentioned Preparation Examples 3 and 4 of the Negative Electrode Layer Composition, three types of negative electrode compositions were prepared for each Example: negative electrode composition a containing silicon oxide that is both lithium-doped and carbon-coated (LiSiOC), negative electrode composition b containing silicon oxide that is both nickel-doped and carbon-coated (NiSiOC), and negative electrode composition c containing silicon oxide that is both titanium-doped and carbon-coated (TiSiOC). The same applies to the Comparative Examples.

[0131] [Preparation of metal-doped active materials] (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 a constant atmosphere. Argon gas was then introduced to the furnace, and the atmosphere was replaced with argon. The furnace was then heated 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 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.

[0132] (2) 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 A carbon coating was formed on a metal-doped silicon-based material (NiSiO or TiSiO) by thermal CVD. For thermal CVD, the metal-doped silicon-based material after mechanical milling was 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 a carbon film. This resulted in 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)). After the temperature reached room temperature, the powder was collected. The content of carbon element 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.

[0133] [Table A]

[0134] <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. The mixing ratio indicates the ratio of each component (Si alloy or SiO powder) to the total amount of Si alloy and SiO powder added when obtaining the metal element-doped silicon-based material (NiSiO or TiSiO), and is expressed in mass%.

[0135] [Preparation of non-aqueous electrolyte secondary battery (2032 type coin battery) 2] A nonaqueous electrolyte secondary battery was fabricated in the same manner as in the above [Fabrication of a nonaqueous electrolyte secondary battery (2032-type coin battery) 1], except that the negative electrode composition prepared in the negative electrode composition preparation example 3 or 4 was used as the negative electrode composition.

[0136] (Evaluation of cycle characteristics) The discharge capacity retention rate of each secondary battery prepared as described above was measured by the method described above in (Evaluation of cycle characteristics). The discharge capacity retention rate after 80 cycles of charge and discharge (the ratio of the discharge capacity after 80 cycles of charge and discharge 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 rank. The results are summarized in Tables 3 and 4. In addition, regardless of whether the negative electrode composition of the Examples or Comparative Examples was used, the evaluation rank of the cycle characteristics did not differ depending on the metal-doped active material (LiSiOC, NiSiOC, or TiSiOC). Therefore, in Tables 3 and 4, the evaluation results for the three negative electrode compositions a, b, and c, each containing a different metal-doped active material, are listed together in one column. For example, the cycle characteristics evaluation of "4" in the Example 1-abc column means that the cycle characteristics were evaluated as "4" when the negative electrode composition a of Example 1 containing LiSiOC, the negative electrode composition b of Example 1 containing NiSiOC, and the negative electrode composition c of Example 1 containing TiSiOC were all used. - Evaluation rank of cycle characteristics - (without polymer particles) 5: 92% or more 4: 90% or more, less than 92% 3: 88% or more, less than 90% 2: 86% or more, less than 88% 1: Less than 86% - Evaluation rank of cycle characteristics - (when polymer particles are included) 5: 95% or more 4: 93% or more, less than 95% 3: 91% or more, less than 93% 2: 89% or more, less than 91% 1: Less than 89%

[0137] [Table 3-1]

[0138] [Table 3-2]

[0139] [Table 4-1]

[0140] [Table 4-2]

[0141] The descriptions in the columns for water-soluble polymer (X), water-soluble polymer (Y), Y / X, and polymer particles in the table are the same as those in the notes to Tables 1 and 2 above. The entries in the tensile modulus column are the evaluation results of the tensile modulus of the binder composition, and therefore correspond to the evaluation results of the tensile modulus of the binder composition in Tables 1 and 2 above.

[0142] Tables 3 and 4 reveal the following: When any of the following negative electrode active materials was used instead of carbon-coated silicon oxide: 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, the evaluation of cycle characteristics showed trends similar to those when carbon-coated silicon oxide was used, as shown in Tables 1 and 2. That is, it was found that, compared to the secondary batteries having negative electrode sheets prepared using the negative electrode compositions a, b, and c of Comparative Examples 1, 2, 4, 7 to 10, and 14 to 21, the secondary batteries having negative electrode sheets prepared using the negative electrode compositions a, b, and c of Examples 1 to 4, 9 to 15, 19 to 21, 24 to 32, 34, 36 to 42, 46 to 50, 51, 53, 54, 56, 57, 59, 60, 62, 63, 65, 66, 68, 69, 71, 72, and 74 all exhibited excellent cycle characteristics. [Explanation of symbols]

[0143] 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) and a water-soluble polymer (Y), wherein the water-soluble polymer (X) is a polymer containing 20 mass % or more of a constituent component represented by the following general formula (B-2), and the ratio of the weight-average molecular weight of the water-soluble polymer (Y) to the weight-average molecular weight of the water-soluble polymer (X) is 0.300 to 10.0: 【Chemistry 1】 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).

2. 2. The binder composition for a secondary battery according to claim 1, wherein the content of the component represented by general formula (B-2) in the water-soluble polymer (X) is 80 mass % or more.

3. 2. The binder composition for a secondary battery according to claim 1, wherein the constituent component represented by the general formula (B-2) includes a (meth)acrylamide component.

4. 2. The binder composition for a secondary battery according to claim 1, wherein the water-soluble polymer (X) is a polymer further containing at least one of an acrylonitrile component and an N-vinyl-2-pyrrolidone component.

5. 5. The binder composition for a secondary battery according to claim 1, wherein the water-soluble polymer (X) has a weight average molecular weight of 10,000 to 1,000,000.

6. 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.

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

8. 8. The binder composition for a secondary battery according to claim 7, wherein the water-soluble polymer (Y) comprises at least one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and xanthan gum.

9. 5. The binder composition for a secondary battery according to claim 1, wherein the water-soluble polymer (Y) has a weight average molecular weight of 100,000 to 500,000.

10. The binder composition for a secondary battery according to claim 1 , comprising polymer particles.

11. 11. The binder composition for a secondary battery according to claim 10, 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.

12. The binder composition for a secondary battery according to any one of claims 1 to 4, further comprising water.

13. 2. The binder composition for a secondary battery according to claim 1, comprising an active material capable of inserting and releasing ions of a metal belonging to Group 1 or 2 of the periodic table.

14. The binder composition for a secondary battery according to claim 13 , wherein the active material comprises a silicon-based active material.

15. An electrode sheet having a layer formed using the binder composition for a secondary battery according to claim 13 or 14.

16. 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 binder composition for secondary batteries according to claim 13 or 14.

17. A method for producing an electrode sheet, comprising forming an electrode active material layer using the binder composition for a secondary battery according to claim 13 or 14.

18. A method for producing a secondary battery, comprising incorporating an electrode sheet obtained by the production method according to claim 17 as an electrode of the secondary battery.

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