Nonaqueous secondary battery electrode binder composition and method for producing same, nonaqueous secondary battery electrode composition, nonaqueous secondary battery electrode, and nonaqueous secondary battery

Abstract

A nonaqueous secondary battery electrode binder composition comprising a water soluble vinyl polymer that includes a structural unit (a) derived from a vinyl monomer (A) that has an acid component, a structural unit (b) derived from a vinyl monomer (B) that exhibits a solubility of 8-300 g with respect to 100 g of water at 25°C, and a structural unit (c) derived from a vinyl monomer (C) that exhibits a solubility of not less than 1 g to less than 8 g with respect to 100 g of water at 25°C, wherein the content proportion of the structural unit (c) derived from the vinyl monomer (C) is 5-80 mol% with respect to all monomer units of the water soluble vinyl polymer.

Description

Binder composition for non-aqueous secondary battery electrodes and method for producing the same, composition for non-aqueous secondary battery electrodes, non-aqueous secondary battery electrodes, and non-aqueous secondary battery

[0001] The present invention relates to a binder composition for non-aqueous secondary battery electrodes and a method for producing the same, a composition for non-aqueous secondary battery electrodes, a non-aqueous secondary battery electrode, and a non-aqueous secondary battery.

[0002] Non-aqueous secondary batteries (non-aqueous electrolyte secondary batteries), such as lithium-ion secondary batteries, are small, lightweight, have high energy density, and can be repeatedly charged and discharged, making them suitable for a wide range of applications. Therefore, in recent years, improvements to battery components such as electrodes have been considered to further enhance the performance of non-aqueous secondary batteries.

[0003] Here, the electrodes of a non-aqueous secondary battery typically comprise a current collector and an electrode active material layer formed on the current collector. This electrode active material layer is formed using an electrode composition, for example, which comprises a binder composition containing a binder resin and an electrode active material dispersed in a dispersion medium.

[0004] In order to achieve further performance improvement of the secondary battery, as the binder composition, for example, styrene-butadiene copolymer (SBR), acrylic acid copolymer (PAA), etc. are used. In particular, PAA has a high elastic modulus and excellent elastic deformation characteristics, so it is used in silicon-based negative electrode active materials with large volume expansion and contraction due to insertion and desorption of lithium ions. Specifically, for example, in Patent Document 1, a binder resin composition containing a copolymer containing a structural unit derived from a nitrile group-containing monomer and a structural unit derived from an acidic functional group-containing monomer, and a basic compound capable of neutralizing the acidic functional group is disclosed. Further, in the examples of Patent Document 1, a binder composition prepared using a nitrile group-containing monomer, an acidic functional group-containing monomer (at a ratio of 0.523 mol with respect to 1 mol of the nitrile group-containing monomer), polyethylene glycol (meth)acrylate and / or (meth)acrylate alkyl ester (alkyl group having 8 carbon atoms), and a basic compound is specifically disclosed. Also, in Patent Document 2, a binder composition characterized by containing 78 to 95% of acrylonitrile units, 1 to 10% of acrylate-based units, 2 to 15% of acrylamide-based units, and 2 to 8% of acrylate-based units in terms of constituent units represented by mass percentage is proposed.

[0005] Japanese Patent Application Laid-Open No. 2012-051999, Japanese Patent Application Laid-Open No. 2019-526693

[0006] However, in the above conventional binder compositions, there is room for improvement in terms of improving the capacity retention rate of non-aqueous secondary batteries produced using the binder composition.

[0007] In particular, in recent years, along with the improvement of the capacity retention rate of non-aqueous secondary batteries, improvement in productivity in electrode manufacturing is also required. To increase the productivity of the electrode, for example, there is a method of shortening the process of applying and drying the electrode composition on the current collector compared to the conventional method. However, when forming an electrode using the above conventional binder composition, there is a problem that battery characteristics such as the capacity retention rate of non-aqueous secondary batteries produced from the obtained electrode deteriorate as the drying speed is increased.

[0008] Therefore, an object of the present invention is to provide an electrode binder composition capable of forming a non-aqueous secondary battery exhibiting excellent battery performance such as a capacity retention rate, a method for producing the same, a non-aqueous secondary battery electrode composition containing such an electrode binder composition, a non-aqueous secondary battery electrode formed by such an electrode composition, and a secondary battery having such an electrode.

[0009] As a result of intensive studies, the present inventors have found that in the drying step after applying an electrode composition containing a water-soluble resin as a binder resin to a current collector, the water-soluble resin easily floats (migrates) from the current collector interface to the coating film surface as the solvent volatilizes. As a result of further studies, it was considered that the above migration is one of the factors causing a decrease in battery performance such as the capacity retention rate. More specifically, in the drying step, convection occurs in the coating film formed by the electrode composition from the current collector interface toward the coating film surface. At this time, the binder resin having low adhesion to the current collector and a low specific gravity floats on the coating film surface of the current collector and becomes unevenly distributed as the solvent volatilizes. As a result, the density of the binder resin decreases on the current collector surface, which causes a decrease in the peel strength of the produced electrode, as well as peeling and collapse of the electrode active material layer, and it was found that the capacity retention rate of the produced secondary battery decreases. It was also found that the decrease in peel strength due to the above migration becomes more prominent as the drying speed is faster.

[0010] On the other hand, the present inventors have found that the above problems can be solved by using a vinyl polymer obtained by polymerizing two types of vinyl monomers having different solubilities in water and a vinyl monomer having an acid component as the binder resin, and have completed the present invention.

[0011] In other words, the present invention relates to the following: [1] A binder composition for a non-aqueous secondary battery containing a water-soluble vinyl polymer, comprising: a constituent unit (a) derived from a vinyl monomer (A) having an acid component; a constituent unit (b) derived from a vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C; and a structural unit (c) derived from a vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C, wherein the content ratio of the constituent unit (c) derived from the vinyl monomer (C) is 5 mol% or more and 80 mol% or less with respect to the total monomer units of the water-soluble vinyl polymer. [2] The binder composition for a non-aqueous secondary battery electrode according to [1], further comprising a basic compound. [3] The binder composition for non-aqueous secondary battery electrodes according to [1] or [2], wherein the water-soluble vinyl polymer further comprises a constituent unit (d) derived from a vinyl monomer (D) that is miscible with water, and the content of the constituent unit (d) derived from the vinyl monomer (D) is 0.1 mol% or more and 35 mol% or less with respect to the total monomer units of the water-soluble vinyl polymer. [4] The binder composition for non-aqueous secondary battery electrodes according to any one of [1] to [3], wherein the content of the constituent unit (c) derived from the vinyl monomer (C) is 10 mol% or more and 30 mol% or less with respect to the total monomer units of the water-soluble vinyl polymer. [5] The binder composition for non-aqueous secondary battery electrodes according to any one of [1] to [4], wherein the vinyl monomer (A) comprises at least one selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid. [6] The binder composition for non-aqueous secondary battery electrodes according to any one of [1] to [5], wherein the vinyl monomer (B) comprises at least one selected from the group consisting of vinyl monomers containing an amide group and vinyl monomers containing a nitrile group. [7] The binder composition for non-aqueous secondary battery electrodes according to any one of [1] to [6], wherein the vinyl monomer (C) comprises an alkyl (meth)acrylate having an alkyl group having 1 to 2 carbon atoms. [8] The binder composition for non-aqueous secondary battery electrodes according to any one of [3] to [7], wherein the vinyl monomer (D) comprises an N,N-disubstituted (meth)acrylamide.[9] A binder composition for non-aqueous secondary battery electrodes containing a vinyl polymer having the following characteristics (1) to (4): (1) The solubility of a film formed from the vinyl polymer after immersion in water at 25°C for 24 hours is 100%. (2) The water absorption of a film formed from the vinyl polymer after standing in an environment with 20% humidity for 24 hours is 0.1% by mass or more and 15% by mass or less. (3) The water absorption of a film formed from the vinyl polymer after standing in an environment with 40% humidity for 24 hours is 5% by mass or more and 30% by mass or less. (4) The electrolyte swelling degree of the vinyl polymer is 0.1% by mass or more and 100% by mass or less.

[10] The binder composition for non-aqueous secondary battery electrodes according to [9], wherein the vinyl polymer comprises a constituent unit (a) derived from a vinyl monomer (A) having an acid component, a constituent unit (b) derived from a vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C, and a structural unit (c) derived from a vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C, and the content ratio of the constituent unit derived from the vinyl monomer (C) is 5 mol% or more and 80 mol% or less with respect to the total monomer units of the vinyl polymer.

[11] A composition for non-aqueous secondary battery electrodes comprising an electrode active material, a conductive material, and the binder composition for non-aqueous secondary battery electrodes according to any one of [1] to

[10] .

[12] A non-aqueous secondary battery electrode comprising an electrode active material layer formed using the non-aqueous secondary battery electrode composition according to

[11] .

[13] A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode described in

[12] , an electrolyte, and a separator.

[14] A method for producing a binder composition for a non-aqueous secondary battery electrode, comprising: step 1 obtaining a reaction solution containing a monomer mixture comprising a vinyl monomer (A) having an acid component, a vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C, and a vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C; step 2 adjusting the pH of the reaction solution obtained in step 1 to 3 to 7; step 3 reducing the dissolved oxygen concentration of the reaction solution obtained in step 2 to 20 mg / L or less; and step 4 adding an initiator to the reaction solution obtained in step 3 and polymerizing the monomer mixture.

[0012] According to the present invention, an electrode binder composition and a method for producing the same can be obtained, which can form a non-aqueous secondary battery exhibiting excellent battery performance such as capacity retention rate; a non-aqueous secondary battery electrode composition containing the electrode binder composition; a non-aqueous secondary battery electrode formed by the electrode composition; and a secondary battery having the electrode.

[0013] Embodiments of the present invention will be described below. A binder composition for non-aqueous secondary battery electrodes according to a first aspect of the present invention (hereinafter also referred to as "binder composition 1") comprises: a constituent unit (a) derived from a vinyl monomer (A) having an acid component; a constituent unit (b) derived from a vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C; and a structural unit (c) derived from a vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C, wherein the content ratio of the constituent unit (c) derived from the vinyl monomer (C) is 5 mol% or more and 80 mol% or less with respect to the total monomer units of the water-soluble vinyl polymer.

[0014] Furthermore, a binder composition for non-aqueous secondary battery electrodes according to a second aspect of the present invention (hereinafter also referred to as "binder composition 2") is a binder composition for non-aqueous secondary battery electrodes containing a vinyl polymer having the following characteristics (1) to (4): (1) The solubility of a film formed from the vinyl polymer after immersion in water at 25°C for 24 hours is 100%. (2) The water absorption of a film formed from the vinyl polymer after standing in an environment with 20% humidity for 24 hours is 1% by mass or more and 15% by mass or less. (3) The water absorption of a film formed from the vinyl polymer after standing in an environment with 40% humidity for 24 hours is 5% by mass or more and 30% by mass or less. (4) The electrolyte swelling degree of the vinyl polymer is 0.1% by mass or more and 100% by mass or less. Hereinafter, unless otherwise specified, "the binder composition for non-aqueous secondary battery electrodes of the present invention" (hereinafter also referred to as "the binder composition of the present invention") refers to all of the binder compositions for non-aqueous secondary battery electrodes according to the first and second embodiments described above.

[0015] In this specification, in copolymers produced by copolymerizing two or more monomers, the proportion of a constituent unit formed by polymerizing a certain monomer in the copolymer is, unless otherwise specified, usually equal to the ratio of the mass of that particular monomer to the total mass of monomers used in the polymerization of the copolymer (the charging ratio). Furthermore, the content of each constituent unit of the copolymer can also be determined by performing NMR measurements on the copolymer.

[0016] Furthermore, in this specification, "(meth)acrylic acid" means either or both methacrylic acid and acrylic acid. "(meth)acrylate" means either or both methacrylate and acrylate.

[0017] Furthermore, in this specification, "vinyl monomer" means a compound having a polymerizable carbon-carbon double bond (>C=C<), and may be a monomer containing a vinyl group, a vinylene group, a vinylidene group, an acryloyl group, a methacryloyl group, or a derivative group thereof.

[0018] ≪Binder composition for non-aqueous secondary battery electrodes according to the first embodiment≫ The binder composition for non-aqueous secondary battery electrodes according to the first embodiment of the present invention (hereinafter referred to as "binder composition 1") is a binder composition for non-aqueous secondary batteries containing a water-soluble vinyl polymer, comprising: a constituent unit (a) derived from a vinyl monomer (A) having an acid component; a constituent unit (b) derived from a vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C; and a structural unit (c) derived from a vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C, wherein the content ratio of the constituent unit derived from the vinyl monomer (C) is 5 mol% or more and 80 mol% or less with respect to the total monomer units of the water-soluble vinyl polymer.

[0019] <Water-soluble vinyl polymer> Binder composition 1 contains a water-soluble vinyl polymer (hereinafter also simply referred to as "vinyl polymer"). The vinyl polymer includes a constituent unit (a) derived from a vinyl monomer (A) having an acid component, a constituent unit (b) derived from a vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C, and a structural unit (c) derived from a vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C.

[0020] As described above, the present inventors have found that by using a vinyl polymer obtained from two types of vinyl monomers with different solubility in water and a constituent unit (a) derived from a vinyl monomer (A) having an acid component as a binder composition, migration during electrode formation can be suppressed, and the peel strength of the electrode formed using the binder composition 1 can be improved. Furthermore, they have found that this can improve battery characteristics such as the capacity retention rate of secondary batteries. More specifically, in the electrode composition containing the binder composition, the binder resin (vinyl polymer) is dissolved in water, ensuring the dispersibility and stability of the electrode active material. In the drying process, in which this electrode composition is applied to an electrode and moisture is evaporated, the solubility in water decreases starting with structural unit (c) derived from vinyl monomer (C), which has a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C that constitutes the vinyl polymer. Subsequently, the solubility in water decreases starting with structural unit (b) derived from vinyl monomer (B), which has a solubility of 8 g or more and 300 g in 100 g of water at 25°C that constitutes the vinyl polymer. In this way, in binder composition 1, the solubility of the vinyl polymer decreases stepwise during the drying process, thus suppressing the migration of the vinyl polymer to the coating surface (air interface) of the current collector as moisture evaporates. However, if the vinyl polymer is composed only of structural unit (a) derived from vinyl monomer (A) having the acid component, it becomes a polymer with excellent water solubility, making it easy for the polymer to migrate to the air interface as water evaporates during drying, making it difficult to suppress the migration. Furthermore, if the vinyl polymer consists only of the constituent unit (a) and the constituent unit (b), the polymer will not be sufficiently insoluble in water, making it difficult to suppress migration. Also, if the vinyl polymer consists only of the constituent unit (a) and the constituent unit (c), insolubilization in water occurs in the early stages of the drying process, leading to a decrease in the smoothness and leveling properties of the electrode layer and a reduction in battery performance. Furthermore, if the vinyl polymer consists only of the constituent unit (b) and the constituent unit (c), the solubility of the vinyl polymer in the electrode composition will be insufficient, reducing the stability of the electrode active material.This reduces the coating properties of the non-aqueous secondary battery electrode composition, leading to a deterioration in battery performance. The constituent units of the vinyl polymer are described below.

[0021] (Constituent units (a) derived from vinyl monomer (A) having an acid component) The vinyl polymer constituting the binder composition 1 has constituent units (a) derived from vinyl monomer (A) having an acid component. The inclusion of constituent units (a) derived from vinyl monomer (A) having an acid component in the vinyl polymer increases the solubility of the resulting vinyl polymer in water. This results in improved dispersion stability and storage stability of the electrode composition made using the binder composition 1, and improves the capacity retention rate of the non-aqueous secondary battery formed using the electrode composition.

[0022] Specifically, the vinyl monomer (A) may be, for example, a vinyl monomer having a -COOH group (carboxylic acid group), -SO ３ Vinyl monomer having an H group (sulfonic acid group), -PO ３ H ２ Examples include vinyl monomers having a group, vinyl monomers having a -PO(OH)(OR) group (where R represents a hydrocarbon group), etc. These may be used individually or in combination of two or more types.

[0023] Examples of vinyl monomers having the carboxylic acid group include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, their derivatives, and combinations thereof. In this specification, "derivative" means a compound having a structure in which one or more groups of the original compound are replaced by other groups (substituents). Specific examples of monocarboxylic acids include (meth)acrylic acid and crotonic acid. Specific examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Examples of derivatives of dicarboxylic acids include methyl allyl maleate such as methyl maleic acid, dimethyl maleic acid, phenyl maleic acid, chloro maleic acid, dichloro maleic acid, and fluoro maleic acid; and maleic acid esters such as diphenyl maleic acid, nonyl maleic acid, decyl maleic acid, dodecyl maleic acid, octadecyl maleic acid, and fluoroalkyl maleic acid.

[0024] Examples of vinyl monomers having a sulfonic acid group include, for example, monomers in which one of the conjugated double bonds of a diene compound such as isoprene and butadiene is sulfonated; vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate, sulfobutyl methacrylate, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and 3-alyloxy-2-hydroxypropanesulfonic acid (HAPS).

[0025] The aforementioned - PO ３ H ２ Examples of vinyl monomers having a group and / or a -PO(OH)(OR) group (where R represents a hydrocarbon group) include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate.

[0026] Among these, the vinyl monomer (A) preferably includes a vinyl monomer having a carboxylic acid group, more preferably includes at least one selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid, and even more preferably includes acrylic acid.

[0027] Furthermore, if a vinyl monomer corresponds to vinyl monomer (A) and also corresponds to any of the vinyl monomers (B) to (D) described later, then that vinyl monomer shall be deemed to belong to vinyl monomer (A). Specifically, for example, methacrylic acid has a solubility of 8.9 g in 100 g of water at 25°C, and therefore corresponds to vinyl monomer (B) described later, which has a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C. However, it also corresponds to vinyl monomer (A) having an acid component, so in this invention, methacrylic acid shall be deemed to belong to vinyl monomer (A).

[0028] The content of the constituent unit (a) derived from the vinyl monomer (A) is preferably 1 mol% to 80 mol% of the total monomer units constituting the vinyl polymer. When the content of the constituent unit (a) is 1 mol% or more, the dispersion stability of the electrode composition made using the binder composition 1 can be improved, and the battery characteristics can be further enhanced. The content of the constituent unit (a) is more preferably 5 mol% or more, even more preferably 10 mol% or more, and particularly preferably 15 mol% or more. Furthermore, when the content of the constituent unit (a) derived from the vinyl monomer (A) is 80 mol% or less, migration can be further suppressed. The content of the constituent unit (a) is more preferably 70 mol% or less, even more preferably 60 mol% or less, and particularly preferably 50 mol% or less.

[0029] (Constituent units (b) derived from vinyl monomer (B) having a solubility of 8 g to 300 g in 100 g of water at 25°C) The vinyl polymer constituting the binder composition 1 contains constituent units (b) derived from vinyl monomer (B) having a solubility of 8 g to 300 g in 100 g of water at 25°C. By containing constituent units (b) derived from vinyl monomer (B) in the vinyl polymer, migration can be suppressed. This increases the peel strength of electrodes formed using the binder composition 1 and improves the capacity retention rate of non-aqueous secondary batteries. In addition, it can withstand high-temperature drying during the manufacturing of secondary batteries, improving production efficiency.

[0030] The vinyl monomer (B) that can form the constituent unit (b) is not particularly limited as long as it is a vinyl monomer whose solubility in 100 g of water at 25°C is 8 g or more and 300 g or less. Specifically, examples of the vinyl monomer (B) include (meth)acrylamide, acrylonitrile, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, etc. These may be used individually or in combination of two or more. Among these, from the viewpoint of having strong hydrogen bonding properties, being easily adsorbed to the electrode active material, and further suppressing the migration, it is preferable that the vinyl monomer (B) includes at least one selected from the group consisting of vinyl monomers containing an amide group and vinyl monomers containing a nitrile group, it is preferable that it includes a vinyl monomer containing an amide group, and it is even more preferable that it includes acrylamide.

[0031] The content of the constituent unit (b) derived from the vinyl monomer (B) is preferably 5 mol% to 80 mol% of the total monomer units constituting the vinyl polymer. When the content of the constituent unit (b) is 5 mol% or more, the dispersion stability of the electrode composition made using the binder composition 1 can be improved, and the battery characteristics can be further enhanced. The content of the constituent unit (b) is more preferably 10 mol% or more, and even more preferably 15 mol% or more. Furthermore, when the content of the constituent unit (b) is 80 mol% or less, migration can be further suppressed. The content of the constituent unit (b) is more preferably 70 mol% or less, and even more preferably 60 mol% or less.

[0032] (Structural units (c) derived from vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C) The vinyl polymer constituting the binder composition 1 has structural units (c) derived from vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C. By including structural units (c) derived from vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C in the vinyl polymer, migration can be suppressed. This increases the peel strength of the electrodes formed using the binder composition 1 and improves the capacity retention rate of the secondary battery. In addition, it can withstand high-temperature drying during the manufacturing of the secondary battery, improving production efficiency.

[0033] The vinyl monomer (C) is not particularly limited as long as it is a vinyl monomer that has a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C. Specifically, examples of the vinyl monomer (C) include methyl (meth)acrylate, ethyl acrylate, 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, methacrylonitrile, glycidyl (meth)acrylate, and tetrahydrofurfuryl (meth)acrylate. These may be used individually or in combination of two or more. Among these, in this embodiment, from the viewpoint of suppressing migration, it is preferable to use an alkyl (meth)acrylate ester having an alkyl group with 1 to 2 carbon atoms as the vinyl monomer (C), and it is more preferable to use at least one of methyl acrylate and ethyl acrylate. Also, from a similar viewpoint, a vinyl monomer that has a solubility of 3 g or more and less than 8 g in 100 g of water at 25°C may be used. Examples of such vinyl monomers include methyl acrylate and tetrahydrofurfuryl acrylate.

[0034] The content of constituent units (c) derived from the vinyl monomer (C) is 5 mol% to 80 mol% of the total monomer units constituting the vinyl polymer. When the content of constituent units (c) derived from the vinyl monomer (C) is 5 mol% or more, migration can be suppressed and the peel strength of the electrode made using the binder composition 1 can be improved. The content of constituent units (c) is preferably 7 mol% or more, and more preferably 10 mol% or more. Furthermore, when the content of constituent units (c) is 80 mol% or less, the water solubility of the vinyl polymer can be ensured and the uniformity of the mixing between the vinyl polymer and the electrode active material when the binder composition 1 and the electrode active material are mixed is improved. The content of constituent units (c) is more preferably 50 mol% or less, and even more preferably 30 mol% or less.

[0035] In the binder composition 1, the total content ratio of constituent units (a) derived from vinyl monomer (A), constituent units (b) derived from vinyl monomer (B), and constituent units (c) derived from vinyl monomer (C) relative to the total monomer units constituting the vinyl polymer is preferably 60 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more. By keeping the total content ratio of constituent units (a) to (c) within the above range, the capacity retention rate of a non-aqueous secondary battery equipped with electrodes formed using the binder composition 1 can be further improved. The upper limit of the total content ratio of constituent units (a) to (c) relative to the total monomer units constituting the vinyl polymer may be 100 mol%, 95 mol%, or 90 mol%. In other words, the total content ratio of constituent units (a) to (c) may be 60 mol% or more and 100 mol% or less.

[0036] (Constituent unit (d) derived from water-miscible vinyl monomer (D)) The vinyl polymer constituting the binder composition 1 may be a vinyl polymer consisting only of the constituent units (a) to (c), but it is preferable that it further contains a constituent unit (d) derived from water-miscible vinyl monomer (D). By the vinyl polymer containing the constituent unit (d) derived from water-miscible vinyl monomer (D), the uniformity of the mixing between the vinyl polymer and the electrode active material is increased when the binder composition 1 and the electrode active material are mixed. This further improves the capacity retention rate of the non-aqueous secondary battery made using the binder composition 1. In this specification, "miscible" means that the substance can be mixed with water in any ratio (i.e., it has no saturation point and can be uniformly mixed at any concentration).

[0037] Examples of the water-miscible vinyl monomer (D) include polyethylene glycol acrylate, (meth)allyl alcohol, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-cyanoethyl (meth)acrylate, acrylamide derivatives such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide, N-vinylacetamide, and N-vinylpyrrolidone. These may be used individually or in combination of two or more. Among these, it is preferable to use an acrylamide derivative as the vinyl monomer (D), more preferably to use N,N-disubstituted (meth)acrylamide, and even more preferably to use at least one of N,N-dimethylacrylamide and N,N-diethylacrylamide.

[0038] When the vinyl polymer contains the constituent unit (d), its content is preferably 0.1 mol% to 35 mol% relative to the total monomer units constituting the vinyl polymer. When the content of the constituent unit (d) derived from the vinyl monomer (D) is 0.1 mol% or more, the uniformity of the mixing between the vinyl polymer and the electrode active material when the binder composition 1 is mixed with the electrode active material is increased, and the battery characteristics of the non-aqueous secondary battery made using the binder composition 1 can be further improved. The content of the constituent unit (d) is more preferably 0.5 mol% or more, even more preferably 1 mol% or more, and particularly preferably 2 mol% or more. Furthermore, when the content of the constituent unit (d) is 35 mol% or less, the migration can be further suppressed. The content of the constituent unit (d) is more preferably 30 mol% or less, even more preferably 20 mol% or less, and particularly preferably 10 mol% or less.

[0039] However, if the vinyl polymer contains constituent units derived from 2-hydroxyethyl (meth)acrylate, the content of such units is preferably 1 mol% or less, more preferably 0.5 mol% or less, even more preferably 0.3 mol% or less, and particularly preferably substantially absent, relative to the total constituent units of the vinyl polymer. By keeping the content of constituent units derived from 2-hydroxyethyl (meth)acrylate within the above range, it is possible to suppress the excessive swelling of the electrolyte of the vinyl polymer and further improve its electrolyte resistance. Furthermore, the lower limit of the content of constituent units derived from 2-hydroxyethyl (meth)acrylate in the vinyl monomer (D) is 0 mol%. That is, the content of 2-hydroxyethyl (meth)acrylate may be 0 mol% or more and 1 mol% or less. In this specification, "substantially absent from a certain constituent unit" means that the content of that monomer unit relative to the total monomer units constituting the copolymer is less than 0.1 mol%.

[0040] In the binder composition 1, if the vinyl polymer contains a constituent unit (d) derived from the vinyl monomer (D) in addition to the constituent units (a) to (c), the total content ratio of constituent units (a) to (d) relative to the total monomer units constituting the vinyl polymer is preferably 80 mol% or more, and more preferably 90 mol% or more. By keeping the total content ratio of constituent units (a) to (d) within the above range, the capacity retention rate of a non-aqueous secondary battery equipped with an electrode formed using the binder composition 1 can be further improved. The upper limit of the total content ratio of constituent units (a) to (d) relative to the total monomer units constituting the vinyl polymer may be 100 mol%, 95 mol%, or 90 mol%. In other words, the total content ratio of constituent units (a) to (d) may be 80 mol% or more and 100 mol% or less.

[0041] (Constituent units (e) derived from other monomers (E)) The vinyl polymer constituting the binder composition 1 may further have constituent units (e) derived from other monomers (E) other than the constituent units (a) to (d) mentioned above.

[0042] Examples of constituent units (e) derived from the aforementioned other monomers (E) include constituent units derived from (meth)acrylic acid esters, constituent units derived from aromatic vinyl monomers, constituent units derived from polyfunctional monomers, constituent units derived from compounds that can function as crosslinking agents and / or monomers that can form self-crosslinking structures. These may be used individually or in combination of two or more types.

[0043] Examples of (meth)acrylic acid esters that can form constituent units derived from the (meth)acrylic acid ester include propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, heptyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, and benzyl (meth)acrylate.

[0044] Examples of aromatic vinyl monomers that can form structural units derived from the aforementioned aromatic vinyl monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, vinylnaphthalene, benzyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, and phenyl (meth)acrylate.

[0045] The polyfunctional monomer that can be used as a constituent unit derived from the aforementioned polyfunctional monomer is not particularly limited as long as it is a monomer having two or more reactive functional groups, especially polymerizable functional groups, within its molecule.

[0046] Examples of compounds that can function as the crosslinking agent and monomers that can form the self-crosslinking structure include (poly)ethylene glycol di(meth)acrylate, pentaerythritol diacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate.

[0047] If the vinyl polymer contains the constituent unit (e), its content may be 0 mol% to 40 mol%, 0 mol% to 15 mol%, 0 mol% to 10 mol%, 0 mol% to 5 mol%, or 0 mol% to 3 mol% relative to the total constituent units of the vinyl polymer. If the content of the constituent unit (d) is within the above range, the migration suppression effect is improved, and the battery characteristics such as the capacity retention rate of the secondary battery formed using the binder composition 1 can be further enhanced.

[0048] However, if the vinyl polymer contains a constituent unit (e) derived from a polyfunctional monomer, its content is preferably 5 mol% or less relative to the total constituent units of the vinyl polymer. If the content of the constituent unit derived from the polyfunctional monomer is within the above range, the uniformity of the mixing when the binder composition 1 is mixed with the electrode active material can be further improved, and migration when the binder composition 1 is dried at high speed can be suppressed to a greater extent. The content of the constituent unit derived from the crosslinkable monomer is more preferably 1 mol% or less, and even more preferably substantially absent.

[0049] Furthermore, if the vinyl polymer contains a constituent unit (e) derived from a compound that can function as a crosslinking agent and / or a monomer that can form a self-crosslinking structure, the content of such constituent unit is preferably 5 mol% or less, more preferably 1 mol% or less, and even more preferably substantially absent, relative to the total constituent units of the vinyl polymer. In other words, it is preferable that the vinyl polymer does not have a gel structure. By the vinyl polymer not containing a gel structure, the uniformity of the mixture can be further improved when the binder composition 1 is mixed with the active material, and migration can be further suppressed.

[0050] The content of the constituent units derived from polyfunctional monomers and / or compounds that can function as crosslinking agents, and constituent units derived from monomers that can form self-crosslinked structures in the vinyl polymer is preferably 10 mol% or less in total, more preferably 6 mol% or less, even more preferably 2 mol% or less, and particularly preferably substantially absent, relative to the total constituent units of the vinyl polymer. If the content of the constituent units is within the above range, migration can be further suppressed.

[0051] The content of the vinyl polymer in the binder composition 1 is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, when the nonvolatile content of the binder composition 1 is set to 100% by mass. When the content of the vinyl polymer is within the above range, the peel strength of the electrode formed using the obtained binder composition 1 is improved. The content of the vinyl polymer may be 100% by mass or less, 95% by mass or less, or 90% by mass or less, when the nonvolatile content of the binder composition 1 is set to 100% by mass. In other words, the content of the vinyl polymer may be 50% by mass or more and 100% by mass.

[0052] (Characteristics of water-soluble vinyl polymer) The vinyl polymer is water-soluble. Hereinafter, "water-soluble" means that the solubility of a film formed from the vinyl polymer after immersion in water at 25°C for 24 hours is 95% or more, preferably 100%. The solubility can be measured by the method described in the examples below.

[0053] The weight-average molecular weight (Mw) of the vinyl polymer is preferably between 100,000 and 8,000,000, and more preferably between 500,000 and 5,000,000. When the weight-average molecular weight of the vinyl polymer is within the above range, the binding strength of the electrode active material layer is increased, and the battery performance is further improved. The weight-average molecular weight can be measured by the method described in the examples.

[0054] The water absorption and electrolyte swelling of the vinyl polymer are preferably within the range described in the binder composition according to the second embodiment described later.

[0055] <Basic Compounds> The binder composition 1 preferably further contains basic compounds. The basic compound is a compound that can neutralize a vinyl monomer (A) having an acidic component. By including the basic compound, the solubility of the vinyl polymer in water can be improved. This increases the uniformity of the mixing of the vinyl polymer and the electrode active material when the binder composition 1 and the electrode active material are mixed, and improves the peel strength of the electrode formed using the binder composition 1.

[0056] Examples of the basic compound include inorganic bases and organic bases. The basic compound may be used alone or in combination of two or more types.

[0057] Examples of the inorganic bases include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; alkali metal salts of silica such as sodium orthosilicate, sodium metasilicate, and sodium sesquisilicate; alkali metal salts of phosphoric acid such as trisodium phosphate; alkali metal salts of carbonic acid such as disodium carbonate, sodium bicarbonate, and dipotassium carbonate; alkali metal salts of boric acid such as sodium borate; and ammonia.

[0058] Examples of the organic bases include alkylamines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, and triethylamine; alkanolamines such as aminoethanol, methylaminoethanol, dimethylaminoethanol, ethylaminoethanol, diethylaminoethanol, diethanolamine, and triethanolamine; and amines having a nonionic group such as methoxypoly(oxyethylene / oxypropylene)-2-propylamine.

[0059] Among these, in binder composition 1, it is preferable to use a compound containing at least one metal element selected from the group consisting of lithium, sodium, and potassium as the basic compound, and it is more preferable to use a compound containing at least one metal element from lithium and sodium.

[0060] If the vinyl polymer contains a basic compound, its content is preferably in the range of 0.5 to 1.5, and more preferably in the range of 0.9 to 1.1, based on 1 mole of the acidic component contained in the vinyl monomer (A).

[0061] <Solvent> When manufacturing electrodes using binder composition 1, binder composition 1 may be prepared as a binder composition containing a solvent. That is, binder composition 1 may contain a solvent. Examples of the solvent include aqueous solvents and non-aqueous solvents, and it is preferable that it contains an aqueous solvent. Examples of non-aqueous solvents include aromatic solvents such as benzene, toluene, and xylene; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone; aliphatic alcohol solvents such as isopropyl alcohol and n-butanol; alkylene glycol monoalkyl ether solvents such as ethylene glycol monomethyl ether and diethylene glycol monomethyl ether; ether solvents such as diethyl ether, dibutyl ether, tetrahydrofuran, and ethylene glycol dimethyl ether; and other organic solvents. These may be used individually or in combination of two or more in any ratio.

[0062] If the binder composition 1 contains a solvent, the amount of the solvent is preferably such that the solid content concentration of the binder composition 1 is within the range of 50% by mass or less, and more preferably within the range of 10% by mass or less. When the solid content concentration of the binder composition 1 is within the above range, the workability when manufacturing the non-aqueous secondary battery electrode composition described later is improved.

[0063] <Other Resins> Binder composition 1 may contain resins other than the vinyl polymer (hereinafter referred to as "other resins"). When binder composition 1 contains the other resins, the content ratio is preferably 50% by mass or less, more preferably 40% by mass or less, and particularly preferably 30% by mass or less, based on 100% by mass of the nonvolatile content of binder composition 1. Furthermore, the lower limit of the content ratio of other resins may be 0% by mass. That is, the content ratio of other resins may be 0% by mass or more and 50% by mass or less.

[0064] <Additives> Binder composition 1 may further contain various additives as needed, such as preservatives, surfactants, antioxidants, light stabilizers, plasticizers, viscosity modifiers, and organic or inorganic fillers, to the extent that they do not impair the effects of the present invention. When binder composition 1 contains the above-mentioned additives, the content ratio is preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably 2% by mass or less, based on 100% by mass of the non-volatile content of binder composition 1. Furthermore, the lower limit of the content ratio of the above-mentioned additives may be 0% by mass. In other words, the content ratio of the additives may be 0% by mass or more and 10% by mass or less.

[0065] Any known preservative can be used. Specifically, examples of preservatives include organic sulfur compounds, organic nitrogen sulfur compounds, organic halogen compounds, haloallyl sulfone compounds, iodopropagyl compounds, N-haloalkylthio compounds, nitrile compounds, pyridine compounds, 8-oxyquinoline compounds, benzothiazole compounds, isothiazoline compounds, dithiol compounds, pyridine oxide compounds, nitropropane compounds, organotin compounds, phenol compounds, quaternary ammonium salt compounds, triazine compounds, thiazine compounds, anilide compounds, adamantane compounds, dithiocarbamate compounds, brominated indanone compounds, benzyl bromacetate compounds, inorganic salt compounds, alcohols such as ethanol and isopropyl alcohol, and benzalkonium chloride. These may be used alone or in combination of two or more. In addition, commercially available preservatives can be used. Examples of commercially available products include Actiside MBS and Actiside MV4 (manufactured by So Japan Co., Ltd.).

[0066] ≪Second Embodiment of a Binder Composition for Non-Aqueous Secondary Battery Electrodes≫ The second embodiment of the present invention is a binder composition for non-aqueous secondary battery electrodes, characterized by containing a vinyl polymer having the following features (1) to (4): (1) The solubility of a film formed from the vinyl polymer after immersion in water at 25°C for 24 hours is 100%. (2) The water absorption of a film formed from the vinyl polymer after standing in an environment with 20% humidity for 24 hours is 0.1% by mass or more and 15% by mass or less. (3) The water absorption of a film formed from the vinyl polymer after standing in an environment with 40% humidity for 24 hours is 5% by mass or more and 30% by mass or less. (4) The electrolyte swelling degree of the vinyl polymer is 0.1% by mass or more and 100% by mass or less.

[0067] The binder composition 2 contains a vinyl polymer having the characteristics described in (1) to (4) above, thereby increasing its adhesion to the current collector and ensuring sufficient peel strength of the electrode. This improves the capacity retention rate of the non-aqueous secondary battery produced from the electrode. Furthermore, even when the binder composition 2 is dried at high speed to produce the electrode, the excellent adhesion of the vinyl polymer to the current collector allows for excellent peel strength. More specifically, when the binder composition 2 containing the vinyl polymer having the characteristics described in (1) to (4) above is applied to the electrode and dried, the solubility of the vinyl polymer decreases in stages, thus suppressing the migration of the vinyl polymer to the coating surface (air interface) of the current collector along with water. This improves the peel strength of the electrode formed by the binder composition 2, and improves the capacity retention rate of the non-aqueous secondary battery equipped with the electrode. In addition, because it has resistance to electrolytes while possessing appropriate swelling properties, the battery performance of the non-aqueous secondary battery equipped with the electrode formed by the binder composition 2 is easily improved.

[0068] The method for measuring solubility in (1) above can be measured by the method described in the examples below.

[0069] In (2) above, the water absorption after being left standing for 24 hours in an environment with 20% humidity is 0.1% by mass or more and 15% by mass or less, preferably 1% by mass or more and 10% by mass or less. In (3) above, the water absorption after being left standing for 24 hours in an environment with 40% humidity is 5% by mass or more and 30% by mass or less, preferably 10% by mass or more and 25% by mass or less, and more preferably 10% by mass or more and 24% by mass or less. The water absorption in (2) and (3) above can be measured by the method described in the examples below.

[0070] In (4) above, from the viewpoint of increasing resistance to the electrolyte, the degree of swelling of the vinyl polymer in the electrolyte is preferably 0.1% by mass or more and 100% by mass or less, and preferably 0.5% by mass or more and 50% by mass or less.

[0071] Incidentally, the electrolyte swelling degree is a value obtained by the following measurement method. (Measurement method) A vinyl polymer is applied onto a release PET film, dried at 80°C for 10 minutes and then at 110°C for 10 hours to produce a film with a film thickness of 50 μm. A test piece of 1 cm × 1 cm is cut out from the obtained film, and its mass is measured (M1). ６ Next, the test piece is immersed in an electrolyte solution (a mixed solution in which LiPF ６ is dissolved, composition: ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 30 / 30 / 40 (volume ratio)) at 60°C for 72 hours. Then, the test piece is taken out, the electrolyte solution adhering to the surface is wiped off, and the mass is measured again (M2), and the electrolyte swelling degree is calculated by the following formula. Electrolyte swelling degree (%) = 100 × (M2 - M1) / M1

[0072] Incidentally, the above ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 30 / 30 / 40 mixed solution (volume ratio) has a dispersion term (δd) in the Hansen solubility parameter of 15 MPa ０．５ or more and 21 MPa ０．５ less than, a polar term (δp) of 6 MPa ０．５ or more and 22 MPa ０．５ less than, and a hydrogen bond term (δh) of 3 MPa ０．５ or more and 10 MPa ０．５ less than, and is also an organic solvent. In the present embodiment, in (4) above, the film formed of the vinyl polymer has a dispersion term (δd) in the Hansen solubility parameter of 15 MPa ０．５ or more and 21 MPa ０．５ less than, a polar term (δp) of 6 MPa ０．５ or more and 22 MPa ０．５ less than, and a hydrogen bond term (δh) of 3 MPa ０．５ or more and 10 MPa ０．５ less than, and the swelling degree after immersion in an organic solvent S1 at 60°C for 24 hours may be 0.1 mass% or more and 100 mass% or less.

[0073] Here, the dispersion term (δd), polarity term (δp), and hydrogen bonding term (δh) in the Hansen solubility parameter are parameters that take into account the polarity of a substance, obtained by dividing the solubility parameter (SP value: δ), introduced by Hildebrand, into three components: dispersion term δd, polarity term δp, and hydrogen bonding term δh, and representing them in three-dimensional space, and the following relationship holds: δ[(cal / cm²) ３ ) ０．５ ]] = (δd ２ +δp ２ +δh ２ ) ０．５ The dispersion term δd, polarity term δp, and hydrogen bonding term δh mentioned above have been determined by Hansen and subsequent researchers, and are published, for example, in the Polymer Handbook (4th edition), VII-698 to 711. In addition, Hansen's solubility parameters for many solvents and resins have been investigated, and these solubility parameters are described, for example, in the Industrial Solvents Handbook (by Wesley L. Archer). They can also be determined using the Hansen Solubility Parameters in Practice (HSPiP) software.

[0074] An example of an organic solvent S1 that satisfies the above requirements is shown, based on the Hansen solubility parameters δd, δp, and δh calculated using HSPiP software (6th Edition, 6.0.03).

[0075]

[0076] Furthermore, the organic solvent S1 has a Hansen solubility parameter δd of 15 MPa. ０．５ Above 17 MPa ０．５ Less than δp = 10 MPa ０．５ Above 14 MPa ０．５ Less than δh is 3 MPa ０．５ Above 8 MPa ０．５It is more preferable that the organic solvent S1 has a value less than δd, δp, and δh, from the viewpoint of being able to more practically evaluate the swelling and durability of the electrode active material layer formed from the electrode composition containing the binder composition 2 in relation to the electrolyte. The organic solvent S1 that satisfies the ranges of δd, δp, and δh may be a single type or a mixed solvent obtained by mixing two or more solvents. For example, a mixed solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC), which are carbonate-based solvents used as electrolytes for non-aqueous secondary batteries, at a volume ratio of EC:EMC = 30:70, has Hansen solubility parameters of δd = 16.2, δp = 12.6, and δh = 6.2, satisfying the more preferable δd, δp, and δh for the organic solvent S1 described above.

[0077] A vinyl polymer having the characteristics of (1) to (4) above can be obtained by adjusting the types of monomers constituting the vinyl polymer and the proportion of their constituent units. As the composition of the vinyl polymer, the composition described in Binder Composition 1 above can be applied. For example, it may include constituent units (a) derived from vinyl monomer (A) having an acid component, constituent units (b) derived from vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C, and structural units (c) derived from vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C, wherein the content ratio of constituent units derived from vinyl monomer (C) is preferably 5 mol% or more and 80 mol% or less with respect to the total monomer units of the water-soluble vinyl polymer. Here, specific examples and preferred embodiments of vinyl monomer (A) having an acid component capable of forming the constituent units (a) to (c), vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C, and vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C, as well as the preferred range of the content ratio of the constituent units (a) to (c), are the same as those described in Binder Composition 1.

[0078] Furthermore, in binder composition 2, specific examples of constituent units other than the constituent units (a) to (c) that the vinyl polymer may contain, preferred embodiments, and preferred embodiments of properties such as the weight-average molecular weight of the vinyl polymer are the same as those described in binder composition 1.

[0079] Furthermore, specific examples of other resins and additives that binder composition 2 may contain, as well as preferred embodiments such as their content ratios, are the same as those described for binder composition 1.

[0080] ≪Method for Producing a Binder Composition for Non-Aqueous Secondary Battery Electrodes≫ The present invention provides a method for producing a binder composition, comprising: step 1 obtaining a reaction solution containing a monomer mixture comprising a vinyl monomer (A) having an acid component, a vinyl monomer (B) having a solubility of 8 g to 300 g in 100 g of water at 25°C, and a vinyl monomer (C) having a solubility of 1 g to less than 8 g in 100 g of water at 25°C; step 2 adjusting the pH of the reaction solution obtained in step 1 to 3 to 7; step 3 reducing the dissolved oxygen concentration of the reaction solution obtained in step 2 to 20 mg / L or less; and step 4 adding an initiator to the reaction solution obtained in step 3 and polymerizing the monomer mixture.

[0081] <Step 1> Step 1 is a step to obtain a reaction solution containing a monomer mixture comprising a vinyl monomer (A) having an acid component, a vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C, and a vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C.

[0082] Specific examples and preferred embodiments of the vinyl monomer (A) having the acid component, the vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C, and the vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C are the same as those described in section 1 of Binder Composition.

[0083] The amount of vinyl monomer (A) having the acid component is preferably 1 mol% to 80 mol%, more preferably 5 mol% to 70 mol%, even more preferably 10 mol% to 60 mol%, and particularly preferably 15 mol% to 50 mol% relative to the total amount of monomers constituting the monomer mixture. When the amount of vinyl monomer (A) is within the above range, the dispersion stability of the electrode composition containing the prepared binder composition can be improved, and the battery characteristics can be further enhanced. In addition, migration can be further suppressed.

[0084] The amount of vinyl monomer (B), which has a solubility of 8 g to 300 g in 100 g of water at 25°C, is preferably 5 mol% to 80 mol%, more preferably 10 mol% to 70 mol%, and even more preferably 15 mol% to 60 mol% relative to the total amount of monomers constituting the monomer mixture. When the amount of vinyl monomer (B) is within the above range, the dispersion stability of the electrode composition containing the prepared binder composition can be improved, and the battery characteristics can be further enhanced. In addition, migration can be further suppressed.

[0085] The amount of vinyl monomer (C), which has a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C, is preferably 5 mol% or more and 80 mol% or less, more preferably 7 mol% or more and 50 mol% or less, and even more preferably 10 mol% or more and 30 mol% or less, relative to the total monomers constituting the monomer mixture. When the amount of vinyl monomer (C) is within the above range, migration can be suppressed and the peel strength of the electrode made using the binder composition can be improved.

[0086] Furthermore, the total amount of vinyl monomers (A) to (C) is preferably 60 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more, relative to the total amount of monomers constituting the monomer mixture. By setting the amount of vinyl monomers (A) to (C) within the above range, the capacity retention rate of the non-aqueous secondary battery formed using the prepared binder composition can be further improved. The upper limit of the total amount of vinyl monomers (A) to (C) may be 100 mol%, 95 mol%, or 90 mol%, relative to the total amount of monomers constituting the monomer mixture. In other words, the total amount of vinyl monomers (A) to (C) may be 60 mol% or more and 100 mol% or less.

[0087] In the method for producing a binder composition for non-aqueous secondary battery electrodes according to the present invention, the monomer mixture may contain components other than the vinyl monomers (A) to (C). Examples of components other than the vinyl monomers (A) to (C) include the "water-miscible vinyl monomer (D)" and "other monomers (E)" described in the section on binder composition 1. The monomer mixture may further contain at least one of the water-miscible vinyl monomer (D) and the other monomers (E), and it is preferable that it contains the water-miscible vinyl monomer (D). Specific examples and preferred embodiments of the water-miscible vinyl monomer (D) and other monomers (E) are the same as those described in the section on binder composition 1.

[0088] When adding the water-miscible vinyl monomer (D), the amount added is preferably 0.1 mol% to 30 mol%, more preferably 0.5 mol% to 20 mol%, and even more preferably 1 mol% to 10 mol%, relative to the total amount of monomers constituting the monomer mixture. When the amount of vinyl monomer (D) is within the above range, the uniformity of the mixture between the vinyl polymer and the electrode active material when the binder composition is mixed with the electrode active material can be improved.

[0089] Furthermore, when 2-hydroxyethyl (meth)acrylate is added as the vinyl monomer (D), the amount added is preferably 0 mol% to 1 mol%, more preferably 0 mol% to 0.5 mol%, even more preferably 0 mol% to 0.3 mol%, and may be substantially omitted, from the viewpoint of suppressing excessive swelling of the electrolyte of the vinyl polymer.

[0090] Furthermore, when vinyl monomer (D) is incorporated, the total amount of vinyl monomers (A) to (D) is preferably 60 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more, relative to the total monomer units constituting the monomer mixture. By keeping the total amount of vinyl monomers (A) to (D) within the above range, the capacity retention rate of a non-aqueous secondary battery equipped with electrodes formed using the manufactured binder composition can be further improved. Also, the upper limit of the total amount of vinyl monomers (A) to (D) may be 100 mol%, 95 mol%, or 90 mol%.

[0091] Furthermore, when the other vinyl monomer (E) is added, the amount added may be 0 mol% to 40 mol%, 0 mol% to 15 mol%, 0 mol% to 10 mol%, 0 mol% to 5 mol%, or 0 mol% to 3 mol% relative to the total monomers constituting the monomer mixture. When the amount of vinyl monomer (E) is within the above range, the binder composition produced is used to form the binder. When a polyfunctional monomer is added as the vinyl monomer (E), the amount added is preferably 0 mol% to 5 mol%, more preferably 0 mol% to 1 mol%, and even more preferably substantially absent. Furthermore, when a compound that can function as a crosslinking agent and / or a monomer that can form a self-crosslinking structure is added as the vinyl monomer (D), the amount added is preferably 0 mol% to 5 mol%, more preferably 0 mol% to 1 mol%, and even more preferably substantially absent.

[0092] In step 1, it is preferable to add and mix each vinyl monomer with a solvent from the viewpoint of suppressing gelation. That is, the reaction solution may contain a solvent. Examples of the solvent include aqueous solvents and non-aqueous solvents. Examples of non-aqueous solvents include aromatic solvents such as benzene, toluene, and xylene; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone; aliphatic alcohol solvents such as isopropyl alcohol and n-butanol; alkylene glycol monoalkyl ether solvents such as ethylene glycol monomethyl ether and diethylene glycol monomethyl ether; ether solvents such as diethyl ether, dibutyl ether, tetrahydrofuran, and ethylene glycol dimethyl ether; and other organic solvents. These may be used individually or in combination of two or more in any ratio.

[0093] The amount of solvent used may be such that the total weight of the vinyl monomer is preferably 50 to 99% by mass, more preferably 70 to 95% by mass, of the total weight of (solvent + vinyl monomer). In step 1, the method for obtaining the reaction solution is not particularly limited, and various conventionally known compounding methods can be used. The order in which each monomer is added is not particularly limited; some may be mixed first and then added, or they may be added separately.

[0094] <Step 2> Step 2 is a step of adjusting the pH of the reaction solution obtained in Step 1 to 3 to 7. In this step, by adjusting the pH of the reaction solution to within the above range, the acid component of the vinyl monomer (A) having the acid component is neutralized, making it easier to react more uniformly with other vinyl monomers. This makes it possible to further improve the battery characteristics such as the capacity retention rate of the secondary battery made using the obtained binder composition. It is preferable to adjust the pH to within the range of 3.5 to 6.5.

[0095] A method for adjusting the pH of the reaction solution obtained in step 1 can be, for example, by using a basic compound or an acid. Examples of basic compounds include those described in section 1 of the binder composition section. Specific examples of acids include inorganic acids such as phosphoric acid, hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as acetic acid and citric acid. These may be used individually or in combination of two or more.

[0096] In the method for producing the binder composition of the present invention, it is preferable to add the basic compound in step 2. By adding the basic compound in step 2, the solubility of the resulting vinyl polymer in water can be improved. This increases the uniformity of the mixing when the binder composition produced by the present invention is mixed with the electrode active material, and improves the peel strength of the electrode formed using the binder composition. The amount of the basic compound to be added can be set as appropriate, but it is preferable to be in the range of 0.5 to 1.5, and more preferably in the range of 0.9 to 1.1, based on 1 mole of the acid component contained in the vinyl monomer (A). The basic compound may also be added in steps other than step 2. That is, the basic compound may be added in multiple steps, for example, in step 2 and in step 4 described later. When the basic compound is added in multiple steps, it is preferable that the total amount added in each step falls within the above range.

[0097] <Step 3> Step 3 is a step to reduce the dissolved oxygen concentration in the reaction solution obtained in Step 2 to 20 mg / L or less. In this step, by reducing the dissolved oxygen concentration in the reaction solution to 20 mg / L or less, the peel strength of the electrode made from the binder composition containing the vinyl polymer obtained is improved, thereby improving the battery characteristics of the secondary battery. The dissolved oxygen concentration is preferably 15 mg / L or less, more preferably 10 mg / L or less, and even more preferably 5 mg / L or less. The lower limit of the dissolved oxygen concentration is not particularly limited, for example, 0.1 mg / L. That is, the dissolved oxygen concentration may be 0.1 mg / L or more and 20 mg / L or less. The dissolved oxygen concentration in the reaction solution can be measured by a dissolved oxygen meter (for example, the UC-12-OL model manufactured by Central Scientific Co., Ltd., or the U-50 series manufactured by Horiba, Ltd.).

[0098] Methods for adjusting the dissolved oxygen concentration are not particularly limited, but include methods such as thoroughly bubbling an inert gas such as nitrogen, repeatedly reducing pressure and replacing with an inert gas, and repeatedly pressurizing and opening the pressure with an inert gas. These methods may be carried out individually or in combination.

[0099] <Step 4> Step 4 is a step in which an initiator is added to the reaction solution obtained in Step 3 and the monomer mixture is polymerized.

[0100] The polymerization method is not particularly limited, and the monomer mixture may be polymerized using polymerization methods such as radical polymerization, cationic polymerization, anionic polymerization, or coordination anionic polymerization.

[0101] Furthermore, there are no particular limitations on the initiators, and various known and conventional ones can be used. For example, when performing radical polymerization, initiators such as 2,2'-azobis-(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis-2-methylpropionate methyl, 2,2'-azobisisobutyrate dimethyl, 2,2'-azobis-2-methylvaleronitrile, 1,1'-azobis-1-cycloheptanenitrile, 1,1'-azobis-1-phenylethane, phenylazotriphenylmethane, and phenylazotriphenylmethane can be used. Examples include potassium ruoxodisulfate, sodium peroxodisulfate, ammonium peroxodisulfate, benzoyl peroxide, acetyl peroxide, tert-butyl peroxide, propionyl peroxide, lauroyl peroxide, tert-butyl peracetate, tert-butyl perbenzoate, tert-butyl hydroperoxide, tert-butyl peroxypivalate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and t-butylperoxy-2-ethylhexanoate.

[0102] The temperature during the polymerization reaction is not particularly limited, but is preferably 0°C or higher, more preferably 20°C or higher, particularly preferably 40°C or higher, and also preferably 150°C or lower, more preferably 125°C or lower, particularly preferably 100°C or lower. The specific polymerization temperature is set appropriately depending on the type of monomer used, the type of polymerization initiator, etc.

[0103] Furthermore, a basic compound may be added in step 4. Specifically, the basic compound may be added after polymerizing the monomer mixture. By adding a basic compound, the solubility in water of the vinyl polymer obtained by the polymerization reaction can be increased. Examples of the basic compound are the same as those described in section 1 of the binder composition.

[0104] The present invention may include a step of purifying the vinyl polymer-containing solution obtained in step 4. Purification methods include reprecipitation of the manufactured vinyl polymer in a poor solvent, followed by filtration and subsequent drying under reduced pressure, evaporation of unreacted monomers and solvent, and GPC preparative separation. These methods may be carried out in combination.

[0105] Furthermore, the obtained vinyl polymer-containing solution can be used as is as the binder composition of the present invention. However, if necessary, resins other than the vinyl polymer or additives may be added, or it may be diluted with a solvent before being used as the binder composition of the present invention. The additives and solvents are the same as those described in section 1 of Binder Composition 1.

[0106] The concentration of the vinyl polymer is preferably adjusted to 1% by mass or more, more preferably 2% by mass or more, and even more preferably 5% by mass or more, based on 100% by mass of the nonvolatile content of the binder composition. When the content of the vinyl polymer is within the above range, the peel strength of the electrode formed using the binder composition is improved. Furthermore, the content of the vinyl polymer may be 50% by mass or less, 40% by mass or less, or 30% by mass or less, based on 100% by mass of the nonvolatile content of the binder composition.

[0107] Furthermore, when a resin other than the vinyl polymer is added, the amount added is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on 100% by mass of the nonvolatile content of the resulting binder composition. The lower limit of the amount of the resin other than the vinyl polymer added may be 0% by mass. Furthermore, when the additive is added, the amount blended is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less, based on 100% by mass of the nonvolatile content of the resulting binder composition. The lower limit of the amount of the additive added may be 0% by mass.

[0108] ≪Composition for Non-Aqueous Secondary Battery Electrodes≫ The composition for non-aqueous secondary battery electrodes according to the present invention contains an electrode active material, a conductive material, and the above-mentioned binder composition for non-aqueous secondary battery electrodes of the present invention.

[0109] (Electrode Active Material) The electrode active material can be selected and blended in various ways depending on the type of electrode to be manufactured. That is, the non-aqueous secondary battery electrode composition of this embodiment includes a non-aqueous secondary battery positive electrode composition and a non-aqueous secondary battery negative electrode composition. Specifically, by using the positive electrode active material described later as the electrode active material, a non-aqueous secondary battery positive electrode composition can be obtained. Similarly, by using the negative electrode active material described later as the electrode active material, a non-aqueous secondary battery negative electrode composition can be obtained.

[0110] When the non-aqueous secondary battery electrode composition of this embodiment is used to manufacture the negative electrode of a lithium-ion secondary battery, the electrode active material (negative electrode active material) may be a metal compound, metal oxide, metal sulfide, or conductive polymer material capable of doping or intercalating lithium ions, and is not particularly limited. The negative electrode active material is not particularly limited and examples include carbon materials such as graphite, natural graphite, and artificial graphite; silicon-based materials such as silicon, silicon oxide, and silicon-containing alloys; tin-based materials; polyacene-based conductive polymers; and composite metal oxides such as lithium titanate.

[0111] When the non-aqueous secondary battery electrode composition of this embodiment is used to manufacture the positive electrode of a lithium-ion secondary battery, the electrode active material (positive electrode active material) may be a metal compound, metal oxide, metal sulfide, or conductive polymer material capable of doping or intercalating lithium ions, and is not particularly limited. A specific example of the positive electrode active material is lithium cobalt oxide (LiCoO2). ２ ), lithium nickelate (LiNiO ２ ), lithium manganese (LiMnO ２ ), and their composite oxides (LiCoxNiyMnzo ２ , x + y + z = 1), lithium manganese spinel (LiMn ２ O ４), lithium vanadium compound, V ２ O ５ , V ６ O １３ , VO ２ MnO ２ , TiO ２ MoV ２ O ８ TiS ２ , V ２ S ５ , VS ２ MoS ２ MoS ３ , Cr ３ O ８ , Cr ２ O ５ Olivine type LiMPO ４ Conductive polymers such as (M: Co, Ni, Mn, Fe), polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene, as well as porous carbon, can be used individually or in combination.

[0112] (Conductive materials) Examples of conductive materials include acetylene black, Ketjen black, carbon black, vapor-grown carbon fibers, and conductive carbon such as carbon nanotubes. Carbon powder such as graphite, and fibers and foils of various metals may also be used. These may be used individually or in combination of two or more types.

[0113] (Other Components) The electrode composition of the present invention may contain components other than the electrode active material, the conductive material, and the binder composition for non-aqueous secondary battery electrodes of the present invention. Examples of other components that the electrode composition of the present invention may contain include preservatives and pH adjusters. Examples of preservatives include those described in Binder Composition 1.

[0114] (Method for producing a composition for non-aqueous secondary battery electrodes) The electrode composition of the present invention is obtained by mixing and dispersing the electrode active material, the conductive material, and the binder composition for non-aqueous secondary battery electrodes of the present invention. There are no particular restrictions on the order of addition during mixing. Furthermore, a non-aqueous solvent may be added as appropriate from the viewpoint of adjusting the viscosity of the obtained electrode composition of the present invention and improving dispersion stability. Dispersion can be carried out using a dispersion device such as a stirrer, a rotary-orbit mixer, a ball mill, a super sand mill, or a pressurized kneader.

[0115] ≪Non-aqueous secondary battery electrode≫ The non-aqueous secondary battery electrode of the present invention comprises an electrode active material layer formed using a non-aqueous secondary battery electrode composition. Specifically, for example, it can be obtained by coating the non-aqueous secondary battery electrode composition of the present invention onto a current collector to form an electrode active material layer as a thin film. Alternatively, the non-aqueous secondary battery electrode composition may be molded into a sheet, pellet, or other shape and integrated with a current collector to obtain the electrode. The non-aqueous secondary battery electrode of the present invention includes both a non-aqueous secondary battery negative electrode and a non-aqueous secondary battery positive electrode. Specifically, a non-aqueous secondary battery negative electrode can be formed by using the non-aqueous secondary battery negative electrode composition. Similarly, a non-aqueous secondary battery positive electrode can be formed by using the non-aqueous secondary battery positive electrode composition.

[0116] The material and shape of the current collector are not particularly limited; for example, copper, nickel, titanium, stainless steel, etc., can be used in the form of foil, perforated foil, mesh, or other strip-like material. Porous materials, such as porous metal (foamed metal) or carbon paper, can also be used.

[0117] The method for applying the non-aqueous secondary battery electrode composition to the current collector is not particularly limited, but known methods include, for example, metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, gravure coating, and screen printing. After application, it is preferable to perform rolling treatment using a flat plate press, calender roll, etc., as needed.

[0118] Furthermore, the integration of electrode compositions molded into sheet-like, pellet-like, or other shapes with current collectors can be carried out by known methods such as rolling, pressing, or a combination thereof. The electrode density after integration is, for example, 1.0 to 1.8 g / cm³. ３ Preferably, 1.1 to 1.7 g / cm³ ３ That is the case.

[0119] The electrode composition formed on the current collector and the electrode active material layer integrated with the current collector are preferably subjected to heat treatment. The heat treatment conditions are, for example, 80 to 150°C for 5 to 20 hours. This heat treatment removes the solvent, hardens the binder, and increases strength, thereby improving the adhesion between particles and between particles and the current collector. These heat treatments are preferably carried out in an inert atmosphere such as helium, argon, or nitrogen, or in a vacuum atmosphere, in order to prevent oxidation of the current collector during the treatment.

[0120] ≪Non-aqueous secondary battery≫ The non-aqueous secondary battery of the present invention (hereinafter also simply referred to as "secondary battery") is equipped with the electrodes of the present invention. When the secondary battery of the present invention is used, for example, in a wet electrolyte secondary battery, it can be constructed by arranging a positive electrode and a negative electrode opposite each other with a separator in between, and injecting an electrolyte.

[0121] As the separator, for example, a nonwoven fabric, cloth, microporous film, or a combination thereof, mainly composed of polyolefins such as polyethylene and polypropylene can be used. However, if the positive and negative electrodes of the non-aqueous electrolyte secondary battery to be manufactured are not in direct contact, a separator does not need to be used.

[0122] The electrolyte can be, for example, LiClO ４ LiPF ６ LiAsF ６ LiBF ４ LiSO ３ CF ３A so-called organic electrolyte can be used, which is obtained by dissolving lithium salts such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidine-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, etc., in one or more non-aqueous solvents.

[0123] The structure of the secondary battery of the present invention is not particularly limited, but for example, a structure may be adopted in which a positive electrode, a negative electrode, and a separator, if provided as needed, are wound in a flat spiral shape to form a wound electrode plate group, or these are stacked as flat plates to form a stacked electrode plate group, and these electrode plate groups are sealed in an outer casing.

[0124] The secondary battery of the present invention can be used as, for example, a paper-type battery, a button-type battery, a coin-type battery, a stacked battery, a cylindrical battery, a prismatic battery, etc. Furthermore, the secondary battery of the present invention can be applied to all electrochemical devices that use the insertion and removal of lithium ions as a charge and discharge mechanism, such as hybrid capacitors and solid lithium secondary batteries.

[0125] The binder composition for non-aqueous secondary battery electrodes, electrode composition, electrode, and secondary battery having the electrode of the present invention have been described above, but the present invention is not limited to the configurations of the embodiments described above. For example, the binder composition for non-aqueous secondary battery electrodes, electrode composition, electrode, and secondary battery having the electrode of the present invention may each have any other configuration added to the configuration of the embodiments described above, or may be replaced with any configuration that performs a similar function.

[0126] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples. The raw materials used in each example and comparative example are listed below.

[0127] <Vinyl Monomers> AA: Acrylic acid MAA: Methacrylic acid IA: Itaconic acid AM: Acrylamide (water solubility 204 g / 100 g) 2MTA: 2-Methoxyethyl acrylate (water solubility 12 g / 100 g) AN: Acrylonitrile (water solubility 9 g / 100 g) THFA: Tetrahydrofurfuryl acrylate (water solubility 7.9 g / 100 g) MA: Methyl acrylate (water solubility 6 g / 100 g) GMA: Glycidyl methacrylate (water solubility 2.3 g / 100 g) THFMA: Tetrahydrofurfuryl methacrylate (water solubility 1.9 g / 100 g) MMA: Methyl methacrylate (water solubility 1.59 g / 100 g) EA : Ethyl acrylate (water solubility 1.5 g / 100 g) HEA: 2-hydroxyethyl acrylate (water soluble) PEGDA: Polyethylene glycol (14 repeating units) diacrylate (water soluble) DMAA: N,N-dimethylacrylamide (water soluble) DEAA: N,N-diethylacrylamide (water soluble) BA: Butyl acrylate (water solubility 0.08 g / 100 g) 2EHA: 2-ethylhexyl acrylate (water solubility 0.01 g / 100 g)

[0128] (Preparation of Binder Composition) (Synthesis Example 1) In a reaction vessel equipped with a stirrer, thermometer, condenser, and nitrogen gas introduction tube, 2082 parts by mass of deionized water, 72 parts by mass (20 mol%) of acrylic acid, 213 parts by mass (60 mol%) of acrylamide, and 86 parts by mass (20 mol%) of methyl acrylate were charged and stirred for 10 minutes. Then, 21 parts by mass (10 mol%) of lithium hydroxide monohydrate was added and stirred for 30 minutes. The pH of the reaction solution after stirring was 5. The reaction solution was heated to 40°C while stirring, and nitrogen was bubbled in at 40°C for 1 hour. The dissolved oxygen concentration in the reaction solution was measured using a dissolved oxygen meter (UC-12-SOL type, manufactured by Central Scientific Co., Ltd.) and was found to be 6 mg / L. Subsequently, the reaction solution was heated to 70°C, and 0.2 parts by mass of ammonium peroxodisulfate dissolved in 2 parts by mass of deionized water was added. After reacting at 70°C for 10 hours, 10 parts by mass (5 mol%) of lithium hydroxide monohydrate was added, and the solid content concentration was adjusted to 10% with deionized water to obtain binder composition 1. The weight-average molecular weight (standard polystyrene equivalent) of the vinyl polymer constituting binder composition 1 was measured using the following apparatus and measurement conditions and was found to be 2,000,000. Apparatus: Tosoh Corporation "HLC-8420 GPC (product name)" Guard column: Tosoh Corporation "GF-1G (product name)" Columns: "GF-7MHQ", "GF-7MHQ", "GF-7MHQ" connected in series in this order (all Tosoh Corporation products, product names) Column temperature: 40°C Developing solvent: Deionized water (containing 0.1 mol% sodium chloride) Developing solvent flow rate: 0.6 ml / min Detector: RI (differential refractometer) Data processing: Calibration curve created using Tosoh Corporation's "GPC workstation EcoSEC-WorkStation" and Tosoh Corporation's pullulan with known molecular weight "Shodex standard P-82" (both product names) as standard samples.

[0129] (Synthesis Example 2) In a reaction vessel equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet tube, 2082 parts by mass of deionized water, 72 parts by mass (20 mol%) of acrylic acid, 213 parts by mass (60 mol%) of acrylamide, and 86 parts by mass (20 mol%) of methyl acrylate were added and stirred for 10 minutes. Then, 42 parts by mass (10 mol%) of a 48% aqueous solution of sodium hydroxide was added and stirred for 30 minutes. The pH was measured to be 5. The reaction solution was heated to 40°C while stirring, and nitrogen was bubbled in at 40°C for 1 hour. The dissolved oxygen was measured to be 6 mg / L. Subsequently, the reaction solution was heated to 70°C, and 0.2 parts by mass of ammonium peroxodisulfate dissolved in 2 parts by mass of deionized water was added. After reacting at 70°C for 10 hours, 21 parts by mass (5 mol%) of a 48% aqueous solution of sodium hydroxide was added, and the solid content concentration was adjusted to 10% with deionized water to obtain binder composition 2.

[0130] (Synthesis Examples 3-22) Binder compositions 3-22 were obtained in the same manner as in Synthesis Example 1, except that the type and amount of vinyl monomer used were changed as shown in Table 2.

[0131] (Synthesis Example 23) Binder composition 23 was obtained in the same manner as in Synthesis Example 1, except that the type and amount of vinyl monomer used were changed as shown in Table 2, and lithium hydroxide monohydrate was not added.

[0132] (Synthesis Examples 24-29) Binder compositions 24-29 were obtained in the same manner as in Synthesis Example 1, except that the type and amount of vinyl monomer used were changed as shown in Table 2.

[0133] (Example 1) (1) Preparation of composition for non-aqueous secondary battery anode 8.8 parts by mass of silicon carbide anode active material, 87.2 parts by mass of artificial graphite, and 0.97 parts by mass of acetylene black as a conductive material were weighed out and stirred for 30 seconds in a rotary-orbit mixer (Thinky Co., Ltd. "ARE-310 (product name)"; from now on, stirring using the rotary-orbit mixer will be carried out using the same apparatus and conditions unless otherwise specified). Next, 12.5 parts by mass (0.50 parts by mass in terms of solid content) of an aqueous solution (hereinafter referred to as "CMC solution") prepared by dissolving carboxymethylcellulose sodium salt (Nippon Paper Industries Co., Ltd. "Sunrose MAC350HC") in distilled water and adjusting the non-volatile content to 4% was added, and 10 parts by mass (1.0 part by mass in terms of solid content) of the binder composition 1 obtained above were added, and distilled water was added to bring the solid content to a range of 63-65%, and the mixture was stirred for 2 minutes in a rotary-orbit mixer. Since heat was generated by stirring, it was cooled to room temperature with ice water, 6.25 parts by mass of CMC solution (0.25 parts by mass in terms of solid content) and 5 parts by mass of the binder composition 1 obtained above (0.5 parts by mass in terms of solid content) were added, and it was stirred again for 2 minutes with a rotary-orbit mixer, and cooled to room temperature with ice water. Subsequently, 6.25 parts by mass of CMC solution (0.25 parts by mass in terms of solid content) and 5 parts by mass of the binder composition 1 obtained above (0.5 parts by mass in terms of solid content) were added, and it was stirred again for 2 minutes with a rotary-orbit mixer, and cooled to room temperature with ice water. Single-wall carbon nanotube aqueous dispersion (OCSiAl "TUBALL BATT H ２ 7.5 parts by mass (0.03 parts by mass in terms of solid content) of "O") were added and mixed until the mixture became a paste, then stirred for 2 minutes in a rotary-orbit mixer. Distilled water was added to the mixture obtained above at 25°C and 30 rpm, while measuring with a B-type viscometer, until the viscosity was in the range of 2000 to 4000 mPa·s. Finally, the mixture was stirred for 30 seconds in a rotary-orbit mixer to prepare a slurry-like negative electrode composition 1.

[0134] (2) Preparation of a negative electrode for a non-aqueous secondary battery The negative electrode composition 1 obtained in (1) above is used, and the coating amount (surface density) of the negative electrode composition 1 after drying is 9.1 mg / cm². ２The gap of the bar coater was adjusted so that the negative electrode composition 1 was coated onto the copper foil current collector using this bar coater, and dried for 8 minutes in a forced-air dryer set to 80°C. The dried electrode was cut to a width of 40 mm, and a roll press machine (Small Desktop Roll Press SA-602, manufactured by Tester Industries Co., Ltd.) was used to create a layer with a density of 1.60 g / cm³. ３ After pressing in this manner, the electrode was vacuum-dried at 110°C for 10 hours to obtain the negative electrode 1A.

[0135] (3) Preparation of non-aqueous secondary electrode composition As positive electrode active material, olivine-type lithium iron phosphate (LiFePO) ４ 94.0 parts by mass of [unclear] and 3.0 parts by mass of acetylene black as a conductive material were weighed out and stirred for 30 seconds in a rotary-orbit mixer at a rotation speed of 1000 rpm and an orbit speed of 2000 rpm. Next, 2.16 parts by mass of polyvinylidene fluoride (PVDF) and 19.0 parts by mass of N-methylpyrrolidone (NMP) were added and mixed until the mixture became a paste, then stirred for 2 minutes in a rotary-orbit mixer. Since the mixture generated heat during stirring, it was cooled to room temperature in ice water, stirred again for 2 minutes in a rotary-orbit mixer, and cooled to room temperature in ice water. Subsequently, 0.84 parts by mass of polyvinylidene fluoride (PVDF) and 5 parts by mass of NMP were added to this mixture and mixed until the mixture was homogenized. The viscosity of the obtained mixture was measured using a B-type viscometer at 25°C and 30 rpm, and NMP was added to bring it to a range of 2000 to 4000 mPa·s. Finally, the mixture was stirred for 30 seconds in a rotary-orbit mixer to prepare a slurry-like cathode composition.

[0136] (4) Preparation of the positive electrode The positive electrode composition obtained above is used to prepare the coating amount (surface density) of the positive electrode composition after drying to 25.0 mg / cm². ２ The gap of the bar coater was adjusted so that the positive electrode composition obtained above was coated onto the carbon-coated aluminum foil, which is the current collector, using this bar coater, and dried for 10 minutes in a forced-air dryer set to 100°C. The dried electrode was cut to a width of 40 mm and pressed using a roll press machine (Small Desktop Roll Press SA-602 manufactured by Tester Industries Co., Ltd.) to obtain a layer density of 2.5 g / cm³. ３ After pressing in this manner, the cathode was obtained by vacuum drying at 110°C for 10 hours.

[0137] (5) Fabrication of the secondary battery The negative electrode 1A fabricated in (2) above was cut into a 24 mm x 24 mm square with a tab, and the positive electrode fabricated above was cut into a 22 mm x 22 mm square with a tab, using a die-cutting blade. Nickel tab leads were welded to the tab portion of the cut electrodes, and aluminum tab leads were welded to the tab portion of the negative electrode 1A and the positive electrode, respectively. On the other hand, a 25 μm thick polyethylene microporous membrane was cut into a 28 mm x 3.8 cm rectangle using a die-cutting blade as a separator. The positive electrode and negative electrode 1A were placed facing each other with this separator in between, wrapped in laminate film, and the tab portion was fixed by heat sealing. Then, LiPF ６ A laminate-type secondary battery 1 was fabricated by dissolving the compound in a 30 / 30 / 40 mixed solution of ethylene carbonate / dimethyl carbonate / methyl ethyl carbonate at a concentration of 1 mol / L, adding 1 vol% vinyl carbonate and 5 vol% fluoroethylene carbonate to obtain a non-aqueous electrolyte solution, adding 300 μL of the solution, and completely sealing it by vacuum lamination.

[0138] (Examples 2-24, Comparative Examples 1-5) In Example 1 (1), the same procedure as in Example 1 was performed except that binder compositions 2-29 obtained in Synthesis Examples 2-29 were used instead of binder composition 1 obtained in Synthesis Example 1. Negative electrode compositions 2-29, negative electrodes 2-29, and laminate-type secondary batteries 2-29 were prepared using each binder composition.

[0139] ≪Characteristics of Vinyl Polymers≫ <Solubility of Vinyl Polymers in Water> The binder compositions prepared in each example and comparative example were coated onto a release PET film and dried at 80°C for 10 minutes, then at 110°C for 10 hours to produce a film with a thickness of 50 μm. A 1 cm × 1 cm test piece was cut out and its mass was measured (M1). This test piece was immersed in deionized water at 25°C for 24 hours, then removed and its mass was measured again (M2). The solubility was calculated using the following formula: Solubility (%) = 100 × (M1 - M2) / M1

[0140] <Water Absorption of Vinyl Polymers (20% Humidity, 40% Humidity)> The binder compositions prepared in each example and comparative example were coated onto a release PET film and dried at 80°C for 10 minutes, then at 110°C for 10 hours to produce a film with a thickness of 50 μm. A 1 cm × 1 cm test piece was cut out and its mass was measured (M1). This test piece was left to stand in an environmental test chamber with 20% / 40% humidity for 24 hours, then removed and its mass was measured again (M2). The water absorption was calculated using the following formula: Swelling degree (%) = 100 × (M2 - M1) / M1

[0141] <Electrolyte Swelling Degree of Vinyl Polymers> The binder compositions prepared in each example and comparative example were coated onto a release PET film, dried at 80°C for 10 minutes, and then at 110°C for 10 hours to produce a film with a thickness of 50 μm. A 1 cm × 1 cm test piece was cut out and its mass was measured (M1). This test piece was then subjected to LiPF ６ The sample was dissolved in an organic solvent S1 (non-aqueous electrolyte) at a concentration of 1.2 mol / L in a mixed solution of ethylene carbonate / ethyl methyl carbonate = 30 / 70 (volume ratio). After immersion at 60°C for 24 hours, the sample was removed, the non-aqueous electrolyte was wiped off the surface of the sample, and the mass was measured again (M2). The degree of electrolyte swelling was calculated using the following formula: Degree of electrolyte swelling (%) = 100 × (M2 - M1) / M1

[0142] <Peel Strength of Negative Electrode> Negative electrodes 1A and 1B were prepared using the electrode compositions prepared in each example and comparative example, following the procedures in (1) and (2) below. The obtained negative electrodes 1A and 1B were each cut into strips 25 mm wide and 100 mm long. Next, using double-sided tape (Nitto Denko No. 5015), the electrode active material side was attached to a stainless steel plate to create a sample for peel strength testing. Approximately 10 mm was peeled off the end of the copper foil, and polyimide tape was attached there to create a mounting part for the peel tester. The sample for peel strength testing was mounted on a peel tester (Shimadzu Corporation Autograph AG-XPlus) and a 180-degree peel test was performed. Furthermore, if the peel strength under drying condition A is 18 N / m or more, and the peel strength under drying condition B is 10 N / m or more, it can be evaluated that the peel strength is excellent and migration is suppressed even when the negative electrode composition is dried at high speed. The peel strength under drying condition A is more preferably 20 N / m or more, and even more preferably 25 N / m or more, and the peel strength under drying condition B is more preferably 15 N / m or more, and even more preferably 20 N / m or more.

[0143] (1) Drying conditions for the preparation of the negative electrode A For the negative electrode compositions prepared in each example and comparative example, the coating amount (surface density) after drying was 9.1 mg / cm². ２ The gap of the bar coater was adjusted to achieve the desired result, and the negative electrode composition was coated onto the copper foil current collector using this bar coater. The mixture was then dried for 8 minutes in a forced-air dryer set to 80°C. The dried electrodes were cut to a width of 40 mm and pressed using a roll press machine (Small Desktop Roll Press SA-602, manufactured by Tester Industries Co., Ltd.) to achieve a layer density of 1.60 g / cm³. ３ After pressing in this manner, the electrode was vacuum-dried at 110°C for 10 hours to obtain the negative electrode 1A.

[0144] (2) Drying conditions for the preparation of the negative electrode B For the negative electrode compositions prepared in each example and comparative example, the coating amount (surface density) after drying was 9.1 mg / cm². ２The gap of the bar coater was adjusted to achieve the desired result, and the negative electrode composition was coated onto the copper foil current collector using this bar coater. The mixture was then dried for 30 seconds in a forced-air dryer set to 140°C. The dried electrodes were cut to a width of 40 mm and pressed using a roll press machine (Small Desktop Roll Press SA-602, manufactured by Tester Industries Co., Ltd.) to achieve a layer density of 1.60 g / cm³. ３ After pressing in this manner, the electrode was vacuum-dried at 110°C for 10 hours to obtain the negative electrode 1B.

[0145] <Initial Charge / Discharge Efficiency and Capacity Retention Rate of Secondary Batteries> The secondary batteries prepared in each example and comparative example were mounted on a charge / discharge device and left at 25°C for 3 hours. After that, one charge / discharge cycle was performed at 0.1C, and the initial charge / discharge efficiency was measured. Next, the charge / discharge cycle at 0.2C was repeated 50 times, and the discharge capacity retention rate after 50 cycles (relative to the first discharge capacity at 0.2C) was measured using the following formula: Capacity retention rate (%) = 100 × Discharge capacity after 50 cycles (mAh / g) / Initial discharge capacity (mAh / g)

[0146]

[0147] As shown in Table 2, the negative electrodes of Examples 1 to 24 formed using negative electrode binder compositions 1 to 24 exhibited superior peel strength compared to the comparative example, and the capacity retention of secondary batteries equipped with negative electrodes formed from these negative electrode binder compositions 1 to 24 was excellent at over 90%. In particular, negative electrode binder compositions 1 to 24 showed higher peel strength compared to the comparative example even at drying speed B, where the negative electrode was manufactured at a faster drying speed. Furthermore, secondary batteries equipped with negative electrodes formed from the negative electrode binder compositions 1 to 24 of the present invention showed high initial charge-discharge efficiency of over 90%, demonstrating an excellent balance of battery characteristics.

Claims

1. A binder composition for non-aqueous secondary batteries containing a water-soluble vinyl polymer, comprising: a constituent unit (a) derived from a vinyl monomer (A) having an acid component; a constituent unit (b) derived from a vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C; and a structural unit (c) derived from a vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C, wherein the content ratio of the constituent unit (c) derived from the vinyl monomer (C) is 5 mol% or more and 80 mol% or less with respect to the total monomer units of the water-soluble vinyl polymer.

2. The binder composition for non-aqueous secondary battery electrodes according to claim 1, further comprising a basic compound.

3. The binder composition for non-aqueous secondary battery electrodes according to claim 1, wherein the water-soluble vinyl polymer further comprises a constituent unit (d) derived from a vinyl monomer (D) that is miscible with water, and the content ratio of the constituent unit (d) derived from the vinyl monomer (D) is 0.1 mol% or more and 35 mol% or less with respect to the total monomer units of the water-soluble vinyl polymer.

4. The binder composition for non-aqueous secondary battery electrodes according to claim 1, wherein the content of constituent units (c) derived from the vinyl monomer (C) is 10 mol% or more and 30 mol% or less with respect to the total monomer units of the water-soluble vinyl polymer.

5. The binder composition for non-aqueous secondary battery electrodes according to claim 1, wherein the vinyl monomer (A) comprises at least one selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid.

6. The binder composition for non-aqueous secondary battery electrodes according to claim 1, wherein the vinyl monomer (B) comprises at least one selected from the group consisting of vinyl monomers containing an amide group and vinyl monomers containing a nitrile group.

7. The binder composition for non-aqueous secondary battery electrodes according to claim 1, wherein the vinyl monomer (C) comprises an alkyl (meth)acrylate having an alkyl group having 1 to 2 carbon atoms.

8. The binder composition for non-aqueous secondary battery electrodes according to claim 1, wherein the vinyl monomer (D) comprises an N,N-disubstituted (meth)acrylamide.

9. A binder composition for non-aqueous secondary battery electrodes containing a vinyl polymer having the following characteristics (1) to (4): (1) The solubility of a film formed from the vinyl polymer after immersion in water at 25°C for 24 hours is 100%. (2) The water absorption of a film formed from the vinyl polymer after standing in an environment with 20% humidity for 24 hours is 0.1% by mass or more and 15% by mass or less. (3) The water absorption of a film formed from the vinyl polymer after standing in an environment with 40% humidity for 24 hours is 5% by mass or more and 30% by mass or less. (4) The electrolyte swelling degree of the vinyl polymer is 0.1% by mass or more and 100% by mass or less.

10. The binder composition for non-aqueous secondary battery electrodes according to claim 9, wherein the vinyl polymer comprises a constituent unit (a) derived from a vinyl monomer (A) having an acid component, a constituent unit (b) derived from a vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C, and a structural unit (c) derived from a vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C, wherein the content ratio of the constituent unit derived from the vinyl monomer (C) is 5 mol% or more and 80 mol% or less with respect to the total monomer units of the vinyl polymer.

11. A composition for a non-aqueous secondary battery electrode, comprising an electrode active material, a conductive material, and the binder composition for a non-aqueous secondary battery electrode according to any one of claims 1 to 10.

12. A non-aqueous secondary battery electrode comprising an electrode active material layer formed using the non-aqueous secondary battery electrode composition described in claim 11.

13. A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode described in claim 12, an electrolyte, and a separator.

14. A method for producing a binder composition for non-aqueous secondary battery electrodes, comprising: step 1 obtaining a reaction solution containing a monomer mixture comprising a vinyl monomer (A) having an acid component, a vinyl monomer (B) having a solubility of 8 g or more and 300 g or less in 100 g of water at 25°C, and a vinyl monomer (C) having a solubility of 1 g or more and less than 8 g in 100 g of water at 25°C; step 2 adjusting the pH of the reaction solution obtained in step 1 to 3 to 7; step 3 reducing the dissolved oxygen concentration of the reaction solution obtained in step 2 to 20 mg / L or less; and step 4 adding an initiator to the reaction solution obtained in step 3 and polymerizing the monomer mixture.

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