Binder polymers for non-aqueous secondary batteries, binder compositions for non-aqueous secondary batteries, and electrodes for non-aqueous secondary batteries

Abstract

A non-aqueous secondary battery binder polymer which has a structural unit derived from a monomer (a1), a structural unit derived from a monomer (a2), a third structural unit and a structural unit derived from an internal crosslinking agent, wherein: the monomer (a1) is a nonionic compound which has an ethyleny unsaturated bond, the monomer (a2) is a compound which has an ethyleny unsaturated bond and an anionic functional group, the internal crosslinking agent is a compound which has a plurality of independent ethyleny unsaturated bonds, and the third structural unit is represented by the following formula (Z is a hydrogen atom, a C1-30 organic group, a metal element or an ammonium group).

Description

[Technical Field]

[0001] This invention relates to binder polymers for non-aqueous secondary batteries, binder compositions for non-aqueous secondary batteries, and electrodes for non-aqueous secondary batteries. This application claims priority based on Japanese Patent Application No. 2021-214135, filed in Japan on December 28, 2021, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] Non-aqueous secondary batteries are widely used as power sources for laptop computers, mobile phones, power tools, and electronic and communication equipment because they can be made smaller and lighter. In recent years, non-aqueous secondary batteries have also been used as power sources for electric vehicles and hybrid vehicles. A typical example of a non-aqueous secondary battery is the lithium-ion secondary battery.

[0003] Non-aqueous secondary batteries include a positive electrode with a metal oxide or the like as the active material, a negative electrode with a carbon material such as graphite as the active material, and an electrolyte. The positive and negative electrodes each comprise a current collector and an electrode active material layer formed on the current collector. The electrode active material layer typically contains a binder that binds the active materials together and between the active materials and the current collector, thereby fixing the electrode active material layer on the current collector. Conventionally, binders used in non-aqueous secondary batteries are known from those described in Patent Documents 1 and 2.

[0004] Patent Document 1 describes a binder composition for secondary battery electrodes containing 100 parts by mass of at least one polymer aqueous dispersion selected from the group consisting of styrene-butadiene copolymer latex and acrylic emulsion, and 1 to 20 parts by mass of a compound having a cloud point of 70°C or lower.

[0005] Furthermore, it is known that cyclopolymerization of α-(allyloxymethyl)acrylate (AOMA) compounds yields polymers having a tetrahydrofuran (THF) ring structure in the main chain. Patent document 2 describes a medical device material containing a polymer of α-(allyloxymethyl)acrylate. Patent Document 3 describes an electronic component that includes a cured product obtained by curing a curable resin composition containing an α-(allyloxymethyl)acrylate compound. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2014-239070 [Patent Document 2] Japanese Patent Publication No. 2016-214840 [Patent Document 3] Japanese Patent Publication No. 2021-130773 [Overview of the project] [Problems that the invention aims to solve]

[0007] In recent years, there has been a strong demand for higher power output, higher capacity, and longer lifespan in non-aqueous secondary batteries. Therefore, binders used in non-aqueous secondary batteries are required to form electrodes that are less prone to peeling of the electrode active material layer from the current collector, thereby improving the cycle characteristics of non-aqueous secondary batteries using these binders.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a binder polymer for non-aqueous secondary batteries that can be used as a binder material to form electrodes in which the electrode active material layer is less likely to peel off from the current collector and to obtain non-aqueous secondary batteries with excellent cycle characteristics, a binder composition for non-aqueous secondary batteries containing the same, a binder for non-aqueous secondary batteries, and a slurry for non-aqueous secondary battery electrodes. Furthermore, the present invention aims to provide a non-aqueous secondary battery electrode containing the binder polymer for non-aqueous secondary batteries of the present invention, which makes it difficult for the electrode active material layer to peel off from the current collector and provides a non-aqueous secondary battery with excellent cycle characteristics, and a non-aqueous secondary battery equipped with the same. [Means for solving the problem]

[0009] The present invention includes the following aspects. The first aspect of the present invention provides a binder polymer for a non-aqueous secondary battery as follows. [1] A first structural unit derived from monomer (a1), a second structural unit derived from monomer (a2), a third structural unit, and a fourth structural unit derived from internal crosslinking agent (a4), and the monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond, the monomer (a2) is a compound having only one ethylenically unsaturated bond and an anionic functional group, the internal crosslinking agent (a4) is a compound having a plurality of independent ethylenically unsaturated bonds, the third structural unit is a structural unit represented by the following general formula (1), a binder polymer for a non-aqueous secondary battery, characterized in that.

[0010] [Chemical formula] (In formula (1), Z is a hydrogen atom, an organic group having 1 to 30 carbon atoms, a metal atom, or an ammonium group.)

[0011] The binder polymer for a non-aqueous secondary battery according to the first aspect of the present invention preferably has the following characteristics [2] to [6]. It is also preferable to combine two or more of the following characteristics. [2] The binder polymer for a non-aqueous secondary battery according to [1], wherein Z in the formula (1) is a linear or branched chain saturated hydrocarbon group. [3] The binder polymer for a non-aqueous secondary battery according to [1] or [2], wherein Z in the formula (1) is at least one selected from the group consisting of a methyl group, an n-propyl group, and an n-hexyl group.

[0012] [4] The anionic functional group is a compound having at least one of a carboxy group and a sulfo group, and is the binder polymer for non-aqueous secondary batteries according to any one of [1] to [3]. [5] The binder polymer for non-aqueous secondary batteries according to any one of [1] to [4], which contains 80% by mass or more in total of the first structural unit and the second structural unit. [6] The content of the third structural unit with respect to 100 parts by mass of the first structural unit is 0.050 parts by mass or more, and is the binder polymer for non-aqueous secondary batteries according to any one of [1] to [5].

[0013] The second aspect of the present invention provides the following binder composition for non-aqueous secondary batteries. [7] A binder composition for non-aqueous secondary batteries, which contains the binder polymer for non-aqueous secondary batteries according to any one of [1] to [6] and an aqueous medium. The third aspect of the present invention provides the following binder for non-aqueous secondary batteries. [8] A binder for non-aqueous secondary batteries, which contains the binder polymer for non-aqueous secondary batteries according to any one of [1] to [6]. The fourth aspect of the present invention provides the following slurry for non-aqueous secondary battery electrodes. [9] It contains the binder polymer for non-aqueous secondary batteries according to any one of [1] to [6], an electrode active material, and an aqueous medium, The aqueous medium is one selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent, and is a slurry for non-aqueous secondary battery electrodes. The fifth aspect of the present invention provides the following non-aqueous secondary battery electrodes.

[0014]

[10] A non-aqueous secondary battery electrode, which contains the binder polymer for non-aqueous secondary batteries according to any one of [1] to [6]. The sixth aspect of the present invention provides the following non-aqueous secondary batteries.

[11] A non-aqueous secondary battery, which includes the non-aqueous secondary battery electrode described in

[10] .

[0015] A seventh aspect of the present invention provides a method for producing the following binder polymer for non-aqueous secondary batteries.

[12] A method for producing a binder polymer for non-aqueous secondary batteries, characterized by copolymerizing monomer (a1), monomer (a2), monomer (a3), and internal crosslinking agent (a4), The monomer (a1) is a nonionic compound having an ethylenically unsaturated bond and not having multiple independent ethylenically unsaturated bonds. The monomer (a2) is a compound having an ethylenically unsaturated bond and an anionic functional group, and lacking multiple independent ethylenically unsaturated bonds. The monomer (a3) ​​is a compound represented by the following general formula (2), A method for producing a binder polymer for non-aqueous secondary batteries, characterized in that the internal crosslinking agent (a4) is a compound having a plurality of independent ethylenically unsaturated bonds.

[0016] [ka] (In formula (2), Z is a hydrogen atom, an organic group having 1 to 30 carbon atoms, a metal atom, or an ammonium group.) [Effects of the Invention]

[0017] According to the present invention, it is possible to form electrodes in which the electrode active material layer is less likely to peel off from the current collector, and a binder polymer for non-aqueous secondary batteries that can be used as a binder material to obtain non-aqueous secondary batteries with excellent cycle characteristics can be provided. Furthermore, according to the present invention, it is possible to form electrodes in which the electrode active material layer is less likely to peel off from the current collector, and to obtain non-aqueous secondary batteries with excellent cycle characteristics. This provides a binder composition for non-aqueous secondary batteries, a binder for non-aqueous secondary batteries, and a slurry for non-aqueous secondary battery electrodes. Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery electrode in which the electrode active material layer is less likely to peel off from the current collector and a non-aqueous secondary battery with excellent cycle characteristics, and a non-aqueous secondary battery equipped with the same that has excellent cycle characteristics. [Modes for carrying out the invention]

[0018] The following describes in detail preferred examples of the binder polymer for non-aqueous secondary batteries, binder composition for non-aqueous secondary batteries, binder for non-aqueous secondary batteries, slurry for non-aqueous secondary battery electrodes, and non-aqueous secondary batteries of the present invention. It should be noted that the present invention is not limited to the embodiments shown below. For example, additions, omissions, substitutions, and changes can be made to the number, types, positions, quantities, ratios, materials, and configurations, without departing from the spirit of the present invention.

[0019] Herein, we will explain the following terms used in this specification. "(Meth)acrylic" is a general term for acrylic and methacrylic. "(Meth)acrylate" is a general term for acrylate and methacrylate. Unless otherwise specified, "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond that exhibits radical polymerization properties.

[0020] In a polymer using a compound having an ethylenically unsaturated bond, the structural unit derived from the compound having the ethylenically unsaturated bond may mean a structural unit in which the chemical structure of the part of the compound other than the ethylenically unsaturated bond is the same as the chemical structure of the part of the polymer other than the part corresponding to the ethylenically unsaturated bond. The ethylenically unsaturated bond of the compound may be changed to a single bond when forming the polymer. For example, in a polymer of methyl methacrylate, the structural unit derived from methyl methacrylate is represented by -CH2-C(CH3)(COOCH3)-.

[0021] Furthermore, in the case of polymers of compounds having ionic functional groups and ethylenically unsaturated bonds, for example, as shown in the second structural unit described later, structural units having ionic functional groups such as carboxyl groups may be considered structural units derived from the same ionic compound even if some of the functional groups are ion-exchanged or not. For example, the structural unit represented by -CH2-C(CH3)(COONa)- may also be considered a structural unit derived from methacrylic acid.

[0022] Furthermore, for compounds having multiple independent ethylenically unsaturated bonds, one or more ethylenically unsaturated bonds may remain within the structural unit as a structural unit of the polymer of the compound. Multiple independent ethylenically unsaturated bonds mean multiple ethylenically unsaturated bonds that do not form conjugated dienes with each other. For example, in the case of a polymer of divinylbenzene, the structural unit derived from divinylbenzene may be a structure without ethylenically unsaturated bonds (a form in which both parts corresponding to the two ethylenically unsaturated bonds of divinylbenzene are incorporated into the polymer chain), or it may be a structure having one ethylenically unsaturated bond (a form in which only the part corresponding to one of the ethylenically unsaturated bonds is incorporated into the polymer chain).

[0023] Furthermore, if, after polymerization, the parts of the polymer other than the chain structure corresponding to the ethylenically unsaturated bond, such as functional groups like carboxyl groups, no longer correspond to the chemical structure of the monomer due to chemical reactions, then the structural units of the polymer shall be considered to be structural units derived from the compound containing the ethylenically unsaturated bond in the polymer. For example, when vinyl acetate is polymerized and then saponified, the structural units of the polymer shall be considered to be derived from vinyl alcohol, rather than from vinyl acetate, based on the chemical structure of the polymer.

[0024] In this embodiment, the term "class" attached to a compound name refers to a group of compounds that include the compound structure in question, and also includes compounds having substituents. For example, "α-allyloxymethyl acrylate class" refers to a group of compounds that include the α-allyloxymethyl acrylate structure.

[0025] <1. Binder polymer (P) for non-aqueous secondary batteries> The binder polymer for non-aqueous secondary batteries of this embodiment is a polymer used as a binder for non-aqueous secondary batteries, and may hereinafter be referred to as the "binder polymer." The binder polymer (P) of this embodiment has a first structural unit derived from the monomer (a1) shown below, a second structural unit derived from the monomer (a2) shown below, a third structural unit derived from the monomer (a3) ​​shown below, and a fourth structural unit derived from the internal crosslinking agent (a4) shown below. The binder polymer (P) of this embodiment may also contain structural units derived from other monomers (a5) that do not fall under any of monomers (a1), monomer (a2), monomer (a3), or internal crosslinking agent (a4).

[0026] [First structural unit] In the binder polymer (P) of this embodiment, the first structural unit is derived from monomer (a1). Monomer (a1) is a nonionic compound (having neither anionic nor cationic functional groups) having only one ethylenically unsaturated bond. Monomer (a1) may consist of only one compound or may contain two or more compounds.

[0027] The monomer (a1) is preferably at least one of a (meth)acrylic acid ester and an aromatic compound having an ethylenically unsaturated bond, and more preferably both. The (meth)acrylic acid ester is more preferably an alkyl (meth)acrylate ester. The monomer (a1) preferably does not have either a hydroxyl group or a cyano group, and more preferably does not have a polar functional group.

[0028] When monomer (a1) contains an alkyl (meth)acrylate and an aromatic compound having an ethylenically unsaturated bond, the total content of the alkyl (meth)acrylate and aromatic compound in monomer (a1) is preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass.

[0029] Examples of alkyl (meth)acrylate esters included in the (meth)acrylate ester used in monomer (a1) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate. Among these, it is preferable to include 2-ethylhexyl (meth)acrylate because it forms a binder polymer (P) that can form an electrode active material layer with excellent electrolyte resistance.

[0030] Examples of aromatic compounds having ethylenically unsaturated bonds used in monomer (a1) include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, and 1,1-diphenylethylene. When monomer (a1) contains an aromatic vinyl compound, it is more preferable to contain at least one of styrene and α-methylstyrene, and it is even more preferable to contain styrene because it results in a binder polymer (P) with excellent dispersibility in aqueous media.

[0031] Examples of monomers (a1) other than (meth)acrylic acid esters and aromatic compounds having ethylenically unsaturated bonds include aliphatic hydrocarbon compounds having ethylenically unsaturated bonds and alicyclic hydrocarbon compounds having ethylenically unsaturated bonds.

[0032] Regarding the composition of monomer (a1), it is preferable to appropriately adjust the preferred compounds and their amounts within the range specified in the present invention in order to adjust the glass transition temperature of the binder polymer (P) or to adjust the polymerization rate according to the molecular design.

[0033] [Second structural unit] In this embodiment, the second structural unit in the binder polymer (P) is derived from the monomer (a2). Monomer (a2) is a compound having only one ethylenically unsaturated bond and an anionic functional group. Monomer (a2) may consist of only one compound or may contain two or more compounds.

[0034] Examples of anionic functional groups of monomer (a2) include carboxyl groups, sulfol groups, and phosphate groups. Since monomer (a2) is a binder polymer (P) that can form an electrode in which the electrode active material layer is less likely to peel off from the current collector, it is preferable that monomer (a2) contains a compound having at least one of a carboxyl group and a sulfol group, and it is more preferable that it contains both a compound having a carboxyl group and a compound having a sulfol group.

[0035] Monomer (a2) may contain compounds having multiple identical anionic functional groups in one molecule. That is, the binder polymer (P) may contain multiple identical anionic functional groups in one structural unit. Monomer (a2) may contain compounds having two or more different anionic functional groups in one molecule. That is, the binder polymer (P) may contain two or more different anionic functional groups in one structural unit. Furthermore, monomer (a2) may contain two or more compounds containing different anionic functional groups. That is, the binder polymer (P) may contain two or more structural units containing different anionic functional groups.

[0036] Examples of monomers (a2) include unsaturated monocarboxylic acids such as methacrylic acid, acrylic acid, and crotonic acid; and unsaturated dicarboxylic acids such as itaconic acid and fumaric acid. Among these, monomer (a2) is preferable because it forms a binder polymer (P) that can create an electrode in which the electrode active material layer is less likely to peel off from the current collector, and therefore contains at least one of acrylic acid, methacrylic acid, and itaconic acid.

[0037] At least some of the structural units derived from monomer (a2) may form salts with basic substances. Examples of monomer (a2) that form salts include sodium (meth)acrylate and sodium p-styrenesulfonate (also known as sodium p-styrenesulfonate).

[0038] The monomer (a2) preferably contains at least one of a sulfonic acid having an ethylenically unsaturated bond and a salt thereof, and more preferably contains a sulfonate having an ethylenically unsaturated bond. The sulfonic acid preferably contains an aromatic vinyl compound having a sulfo group, and more preferably contains parastyrene sulfonic acid. The sulfonate preferably contains a salt of an aromatic vinyl compound having a sulfo group, more preferably contains parastyrene sulfonate, and even more preferably contains sodium parastyrene sulfonate because good polymerization stability is obtained when producing the binder polymer (P).

[0039] [Third structural unit] The third structural unit in the binder polymer (P) of this embodiment is a structural unit represented by the following general formula (1). The third structural unit may be one type or may contain two or more types.

[0040] [ka] (In formula (1), Z is a hydrogen atom, an organic group having 1 to 30 carbon atoms, a metal atom, or an ammonium group.)

[0041] The binder polymer (P) has a third structural unit represented by general formula (1), which allows for the formation of electrodes in which the electrode active material layer is less likely to peel off from the current collector, resulting in a non-aqueous secondary battery with excellent cycle characteristics. The mechanism by which these effects are obtained is not entirely clear, but the inventors estimate that it is due to the following. In other words, it is presumed that the non-aqueous secondary battery electrode containing the binder polymer (P) of this embodiment will have close contact between the electrode active materials and between the electrode active materials and the current collector due to the following reasons.

[0042] Because the binder polymer (P) contains a ring structure (tetrahydrofuran ring) of the third structural unit represented by general formula (1) in its main chain, the binder polymer (P) exhibits good adhesion to the electrode active material.

[0043] As a result, the non-aqueous secondary battery electrode containing the binder polymer (P) has the electrode active material layer firmly attached to the current collector. Therefore, it is estimated that a non-aqueous secondary battery equipped with this non-aqueous secondary battery electrode will have excellent cycle characteristics. The effects of the binder polymer (P) of this embodiment are particularly effective when the binder polymer (P) is applied to the material of the negative electrode active material layer provided in the negative electrode.

[0044] The third structural unit is derived from monomer (a3). Monomer (a3) ​​is not particularly limited and can be any compound represented by general formula (1) that can form a polymer having a third structural unit. In this embodiment, if the compound corresponding to monomer (a3) ​​is one or more compounds selected from monomer (a1), monomer (a2), monomer (a4), and monomer (a5), then it is considered to be the compound corresponding to monomer (a3).

[0045] As the monomer (a3), it is preferable to use α-allyloxymethyl acrylates represented by the following general formula (2). The compound represented by general formula (2), which is the monomer (a3), is preferred because it allows for the simpler formation of the third structural unit represented by general formula (1) of the binder polymer (P) by cyclization polymerization.

[0046] [ka] (In equation (2), Z is the same as in general equation (1).)

[0047] In formulas (1) and (2), Z represents a hydrogen atom, an organic group having 1 to 30 carbon atoms, a metal atom, or an ammonium group. That is, Z in general formula (2) is the same as Z in general formula (1). As monomer (a3), only one type of compound may be used, or, for example, two or more different compounds with different Z values ​​in formula (2) may be used.

[0048] In formula (2), α-allyloxymethyl acrylates in which Z is an organic group having 1 to 30 carbon atoms are preferably organic groups having 1 to 30 carbon atoms and a valency of 1 to 6. α-allyloxymethyl acrylates having 1 to 30 carbon atoms and a valency of 1 to 6 can be produced by a dehydration reaction of α-allyloxymethylacrylic acid with a valency of 1 to 6 having an organic group having 1 to 30 carbon atoms, or by a transesterification reaction of an ester of α-allyloxymethylacrylic acid with a valency of 1 to 6 having an organic group having 1 to 30 carbon atoms.

[0049] When Z in formula (2) is a 2-6 valent organic group having 1-30 carbon atoms, the third structural unit represented by general formula (1) obtained by cyclopolymerization may be bonded to 1-5 other structural units via the 1-30 carbon atom organic group of Z in formula (1). Specifically, for example, the third structural unit represented by general formula (1) may be bonded to 1-5 other third structural units represented by general formula (1) by sharing Z in formula (1). In this case, the main chain containing the tetrahydrofuran ring of the binder polymer (P) is -CO-OZ'(-O-CO-) n1 It has a bridging structure represented by (wherein Z' is Z in formula (1), which is a linking group consisting of organic groups having 1 to 30 carbon atoms. n1 is an integer from 1 to 5, which is the number of other third structural units that share Z in formula (1).)

[0050] α-allyloxymethyl acrylates in which Z in formula (2) is a metal atom or an ammonium group can be produced by a neutralization reaction between α-allyloxymethylacrylic acid and a metal hydroxide or ammonium compound. α-allyloxymethyl acrylates in formula (2) where Z is a metal atom or an ammonium group may be produced by the hydrolysis reaction of α-allyloxymethyl acrylic acid esters having a structure corresponding to the target α-allyloxymethyl acrylate.

[0051] When Z in formulas (1) and (2) is an organic group having 1 to 30 carbon atoms, it is preferably a hydrocarbon group having 1 to 30 carbon atoms, and more preferably a 1 to 6-valent hydrocarbon group having 1 to 30 carbon atoms. The hydrocarbon group having 1 to 30 carbon atoms may have a linear, branched, or cyclic structure, and may have substituents. Examples of substituents that the hydrocarbon group having 1 to 30 carbon atoms may have include alkoxy groups, hydroxyl groups, cyano groups, amino groups, and amide groups. In order to obtain good polymerization stability when producing the binder polymer (P), the hydrocarbon group when Z is a hydrocarbon group having 1 to 30 carbon atoms does not need to have substituents.

[0052] Specific examples of organic groups having 1 to 30 carbon atoms corresponding to Z in formulas (1) and (2) include linear or branched linear saturated hydrocarbon groups such as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, s-butyl group, t-butyl group, n-hexyl group, and 2-ethylhexyl group; Alkoxy-substituted linear saturated hydrocarbon groups, in which some of the hydrogen atoms of a linear saturated hydrocarbon group such as methoxyethyl group, methoxyethoxyethyl group, methoxyethoxyethoxyethyl group, 3-methoxybutyl group, ethoxyethyl group, ethoxyethoxyethyl group, phenoxyethyl group, and phenoxyethoxyethyl group are replaced with alkoxy groups; Hydroxy-substituted chain saturated hydrocarbon groups, such as hydroxyethyl, hydroxypropyl, hydroxybutyl, and 2,3-dihydroxypropyl groups, in which some of the hydrogen atoms of a chain saturated hydrocarbon group are replaced with hydroxyl groups; Amino-substituted chain saturated hydrocarbon groups, such as dimethylaminoethyl group and diethylaminoethyl group, in which some of the hydrogen atoms of a chain saturated hydrocarbon group are replaced with amino groups; Amide-substituted chain saturated hydrocarbon groups, such as acetamidoethyl group, N-methylacetamidoethyl group, propioamidoethyl group, and pyrrolidonylethyl group, in which some of the hydrogen atoms of a chain saturated hydrocarbon group are replaced with an amide group; Alicyclic hydrocarbon groups such as cyclohexyl groups and isobornyl groups, and alicyclic hydrocarbon groups in which some of the hydrogen atoms are replaced with alkoxy groups, hydroxyl groups, or amino groups; Cyclic ether structure-containing groups having a cyclic ether structure in which carbon atoms of alicyclic hydrocarbon groups such as tetrahydrofurfuryl group, tetrahydrofurfuryloxyethyl group, tetrahydrofurfuryloxyethoxyethyl group, tetrahydropyranyl group, and dioxanyl group are replaced with oxygen atoms; Aromatic hydrocarbon groups such as phenyl groups, benzyl groups, and naphthyl groups, and aromatic hydrocarbon groups in which some of the hydrogen atoms are replaced with alkoxy groups, hydroxyl groups, or amino groups; Examples include combinations of two or more of these hydrocarbon groups. In this embodiment, the chain-like structure includes not only linear structures but also structures having branched chains.

[0053] In formulas (1) and (2), Z is preferably a linear or branched linear saturated hydrocarbon group, as this allows for better polymerization stability when producing the binder polymer (P) and makes the effects of the binder polymer (P) of this embodiment described above more pronounced. In particular, Z is preferably a linear or branched linear saturated hydrocarbon group having 1 to 6 carbon atoms, and more preferably one selected from the group consisting of a methyl group, an n-propyl group, and an n-hexyl group, as this prevents the molecular weight of Z from becoming too large and ensures sufficient effect in forming an electrode in which the electrode active material layer is less likely to peel off from the current collector, even with a small content of the third structural unit in the binder polymer (P).

[0054] Examples of α-allyloxymethyl acrylates in which Z in formula (2) is a hydrogen atom or a monovalent hydrocarbon group which may have a substituent include α-allyloxymethylacrylic acid, methyl α-allyloxymethylacrylate (a compound in which Z in general formula (2) is a methyl group), ethyl α-allyloxymethylacrylate, n-propyl α-allyloxymethylacrylate (a compound in which Z in general formula (2) is an n-propyl group), i-propyl α-allyloxymethylacrylate, n-butyl α-allyloxymethylacrylate, s-butyl α-allyloxymethylacrylate, t-butyl α-allyloxymethylacrylate, n-hexyl α-allyloxymethylacrylate (a compound in which Z in general formula (2) is an n-hexyl group), and 2-ethylhexyl α-allyloxymethylacrylate; α-Allyloxymethylacrylate methoxyethyl, α-Allyloxymethylacrylate methoxyethoxyethyl, α-Allyloxymethylacrylate methoxyethoxyethoxyethyl, α-Allyloxymethylacrylate 3-Methoxybutyl, α-Allyloxymethylacrylate ethoxyethyl, α-Allyloxymethylacrylate ethoxyethoxyethyl, α-Allyloxymethylacrylate phenoxyethyl, α-Allyloxymethylacrylate phenoxyethoxyethyl; α-Allyloxymethylacrylate hydroxyethyl, α-Allyloxymethylacrylate hydroxypropyl, α-Allyloxymethylacrylate hydroxybutyl, α-Allyloxymethylacrylate 2,3-dihydroxypropyl; Dimethylaminoethyl α-allyloxymethylacrylate, diethylaminoethyl α-allyloxymethylacrylate; α-Allyloxymethylacrylate acetamidoethyl, α-Allyloxymethylacrylate N-methylacetamidoethyl, α-Allyloxymethylacrylate propioamide ethyl, α-Allyloxymethylacrylate pyrrolidonyl ethyl; α-Allyloxymethylacrylate cyclohexyl, α-Allyloxymethylacrylate isobornyl; α-Allyloxymethylacrylate tetrahydrofurfuryl, α-Allyloxymethylacrylate tetrahydrofurfuryloxyethyl, α-Allyloxymethylacrylate tetrahydrofurfuryloxyethoxyethyl, α-Allyloxymethylacrylate tetrahydropyranyl, α-Allyloxymethylacrylate (5-methyl-5-m-dioxanyl)methyl; Examples include phenyl α-allyloxymethylacrylate, benzyl α-allyloxymethylacrylate, and naphthyl α-allyloxymethylacrylate.

[0055] Among these α-allyloxymethyl acrylates represented by formula (2), it is preferable that Z in formula (2) be a monovalent hydrocarbon group which may have substituents, in order to obtain good polymerization stability when producing the binder polymer (P). Specifically, it is preferable that Z be at least one of α-allyloxymethylacrylate, α-allyloxymethylacrylate n-propyl, and α-allyloxymethylacrylate n-hexyl, and more preferably α-allyloxymethylacrylate, in which Z in formula (2) is a methyl group.

[0056] [Fourth structural unit] The fourth structural unit in the binder polymer (P) of this embodiment is derived from the internal crosslinking agent (a4). In this embodiment, the internal crosslinking agent (a4) is a compound having multiple independent ethylenically unsaturated bonds. In this embodiment, the internal crosslinking agent (a3) ​​is a compound capable of forming a crosslinked structure in the radical polymerization of monomers including monomer (a1), monomer (a2), and monomer (a3). As the internal crosslinking agent (a4), only one compound may be used, or two or more different compounds may be used.

[0057] Examples of internal crosslinking agents (a4) include compounds having two ethylenically unsaturated bonds, such as divinylbenzene, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 2-hydroxy-3-acryloyloxypropyl methacrylate, and compounds having three or more ethylenically unsaturated bonds, such as trimethylolpropane tri(meth)acrylate. It is preferable that the internal crosslinking agent (a4) contains at least one of divinylbenzene and trimethylolpropane tri(meth)acrylate, as this provides good polymerization stability when producing the binder polymer (P).

[0058] [Other monomers (a5)] Other monomers (a5) do not fall under any of monomers (a1), monomers (a2), monomers (a3), or internal crosslinking agents (a4). Examples of other monomers (a5) include, but are not limited to, compounds having ethylenically unsaturated bonds and polar functional groups, surfactants having ethylenically unsaturated bonds (hereinafter sometimes referred to as "polymerizable surfactants"), and compounds having ethylenically unsaturated bonds and functioning as silane coupling agents.

[0059] In compounds having an ethylenically unsaturated bond and a polar functional group, the polar functional group preferably includes at least one of a hydroxyl group and a cyano group, and more preferably a hydroxyl group. Examples of compounds having ethylenically unsaturated bonds and polar functional groups include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and (meth)acrylonitrile, with the inclusion of 2-hydroxyethyl (meth)acrylate being preferable.

[0060] As an example of a polymerizable surfactant, which is another monomer (a5), compounds having an ethylenically unsaturated bond and functioning as a surfactant can be used. Examples of polymerizable surfactants include compounds represented by the following chemical formulas (3) to (6).

[0061] [Chemical formula]

[0062] In formula (3), R 1 is an alkyl group. p is an integer from 10 to 40. R 1 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a straight-chain unsubstituted alkyl group having 10 to 40 carbon atoms.

[0063] [Chemical formula]

[0064] In formula (4), R 2 is an alkyl group. q is an integer from 10 to 12. R 2 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a straight-chain unsubstituted alkyl group having 10 to 40 carbon atoms. Examples of the compound represented by formula (4) include polyoxyethylene alkyl ether sulfate (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., Aqualon KH-10), etc.

[0065] [Chemical formula]

[0066] In formula (5), R 3 is an alkyl group. M 1 is NH4 or Na. R 3 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a straight-chain unsubstituted alkyl group having 10 to 40 carbon atoms.

[0067] [Chemical formula]

[0068] In formula (6), R 4 is an alkyl group. M 2R is either NH4 or Na. 4 It is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms.

[0069] Examples of other monomers (a5) that have an ethylenically unsaturated bond and function as silane coupling agents include vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, and γ-methacryloxypropyltriethoxysilane.

[0070] [Content of each structural unit in the binder polymer (P)] The binder polymer (P) of this embodiment preferably contains 80% by mass or more of the first structural units and the second structural units in total, more preferably 85% by mass or more, and even more preferably 87% by mass or more. This is because increasing the content of the first structural units and the second structural units in the binder polymer (P) provides better polymerization stability when manufacturing the binder polymer (P), and also allows for the formation of electrodes in which the electrode active material layer is less likely to peel off from the current collector. The binder polymer (P) may contain 90% by mass or more of the first structural units and the second structural units in total, or 95% by mass or more.

[0071] In this embodiment, the binder polymer (P) preferably contains 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 3.0 parts by mass or more, of the second structural unit derived from monomer (a2) per 100 parts by mass of the first structural unit derived from monomer (a1). This is because better polymerization stability can be obtained when manufacturing the binder polymer (P), and an electrode can be formed in which the electrode active material layer is less likely to peel off from the current collector.

[0072] In this embodiment, the binder polymer (P) preferably contains 30 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 7.5 parts by mass or less, of second structural units derived from monomer (a2) per 100 parts by mass of first structural units derived from monomer (a1). This is because better polymerization stability can be obtained when producing the binder polymer (P).

[0073] In this embodiment, the binder polymer (P) preferably contains 0.050 parts by mass or more, more preferably 0.100 parts by mass or more, and even more preferably 0.150 parts by mass or more, of third structural units derived from monomer (a3) ​​per 100 parts by mass of first structural units derived from monomer (a1). This is because the binder polymer (P) can be used as a binder material to form electrodes in which the electrode active material layer is less likely to peel off from the current collector, and to obtain a non-aqueous secondary battery with superior cycle characteristics.

[0074] In this embodiment, the binder polymer (P) preferably contains 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, of third structural units derived from monomer (a3) ​​per 100 parts by mass of first structural units derived from monomer (a1). This is because it is easier to obtain a binder polymer (P) with a sufficiently high molecular weight, and the gel fraction of the binder composition for non-aqueous secondary batteries containing it becomes sufficiently high.

[0075] In this embodiment, the binder polymer (P) preferably contains 0.050 parts by mass or more, more preferably 0.075 parts by mass or more, and even more preferably 0.50 parts by mass or more, of fourth structural units derived from the internal crosslinking agent (a4) per 100 parts by mass of first structural units derived from the monomer (a1). This is because it suppresses the degradation of the binder polymer (P) and makes it usable as a binder material for obtaining non-aqueous secondary batteries with superior cycle characteristics.

[0076] In this embodiment, the binder polymer (P) preferably contains 20 parts by mass or less, more preferably 7.5 parts by mass or less, and even more preferably 2.5 parts by mass or less, of the fourth structural unit derived from the internal crosslinking agent (a4) per 100 parts by mass of the first structural unit derived from the monomer (a1). This is because it is possible to suppress the gelation of the binder polymer (P).

[0077] In this embodiment, when the binder polymer (P) contains a fifth structural unit derived from another monomer (a5), and the other monomer (a5) is a polymerizable surfactant, the content of the fifth structural unit derived from the other monomer (a5) relative to 100 parts by mass of the first structural unit derived from monomer (a1) is preferably 0.05 parts by mass or more, and more preferably 0.075 parts by mass or more. This is because good polymerization stability can be obtained when producing the binder polymer (P).

[0078] Furthermore, if the other monomer (a5) is a polymerizable surfactant, the content of the fifth structural unit derived from the other monomer (a5) relative to 100 parts by mass of the first structural unit derived from monomer (a1) is preferably 30 parts by mass or less, and more preferably 15 parts by mass or less. This is because the particle size, viscosity, etc. of the binder polymer (P) can be appropriately adjusted.

[0079] [Glass transition temperature (Tg) of binder polymer (P)] The glass transition temperature Tg of the binder polymer (P) in this embodiment is the peak top temperature of the DDSC chart obtained as the temperature derivative of the DSC measurement, performed using a Differential Scanning Calorimetry (DSC) instrument (EXSTAR DSC / SS7020, Hitachi High-Tech Science Corporation) at a heating rate of 10°C / min under a nitrogen gas atmosphere.

[0080] The glass transition temperature Tg of the binder polymer (P) is preferably -30°C or higher, more preferably -10°C or higher, and even more preferably 0°C or higher. This is because a non-aqueous secondary battery equipped with an electrode containing a binder for non-aqueous secondary batteries containing the binder polymer (P) will have excellent cycle characteristics. The glass transition temperature (Tg) of the binder polymer (P) is preferably 100°C or lower, more preferably 50°C or lower, and even more preferably 40°C or lower. This is because it improves the film-forming properties of the binder polymer (P), resulting in a non-aqueous secondary battery equipped with an electrode containing the binder polymer (P) for non-aqueous secondary batteries having excellent cycle characteristics.

[0081] [Method for producing polymer (P) for binders] The binder polymer (P) is obtained by copolymerizing monomers containing monomer (a1), monomer (a2), monomer (a3), and an internal crosslinking agent (a4), and optionally other monomers (a5). The monomers (components (a1) to (a5)) used to synthesize the binder polymer (P) are sometimes collectively referred to as monomer (a).

[0082] One method for copolymerizing monomer (a) is emulsion polymerization, in which monomer (a) is emulsion polymerized in an aqueous medium (b). When producing a binder polymer (P) by emulsion polymerization, in addition to monomer (a) and aqueous medium (b), components such as a surfactant (c) that does not polymerize, a basic substance (d), a radical polymerization initiator (e), and a chain transfer agent (f) can be used.

[0083] [Aqueous medium (b)] The aqueous medium (b) is selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent. Examples of hydrophilic solvents include methanol, ethanol, isopropyl alcohol, and N-methylpyrrolidone. From the viewpoint of polymerization stability, the aqueous medium (b) is preferably water. As long as polymerization stability is not impaired, a mixture of water and a hydrophilic solvent may be used as the aqueous medium (b).

[0084] [Non-polymerizable surfactants (c)] When producing a binder polymer (P) by emulsion polymerization, a nonpolymerizable surfactant (c) may be included in a solution containing an aqueous medium (b) and a monomer (a) during emulsion polymerization. A nonpolymerizable surfactant (c) is a surfactant (c) that does not have polymerizable unsaturated bonds in its chemical structure. The surfactant (c) improves the dispersion stability of the solution during emulsion polymerization and / or the dispersion (emulsion) obtained after polymerization. It is preferable to use an anionic surfactant or a nonionic surfactant as the surfactant (c).

[0085] Examples of anionic surfactants include alkylbenzene sulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, and fatty acid salts. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. The surfactant (c) described above may be used alone or in combination of two or more types.

[0086] [Basic substances (d)] When producing a binder polymer (P) by emulsion polymerization, a basic substance (d) may be added to the emulsion polymerization solution and / or the dispersion after emulsion polymerization, which contain an aqueous medium (b) and monomer (a). Adding the basic substance (d) neutralizes the acidic components contained in monomer (a). As a result, the pH of the solution during emulsion polymerization and / or the dispersion after emulsion polymerization becomes within an appropriate range, and the stability of the solution during emulsion polymerization and / or the dispersion after emulsion polymerization is improved.

[0087] When manufacturing electrodes using a slurry containing a binder polymer (P) for non-aqueous secondary batteries and electrode active material, the dispersion after emulsion polymerization preferably has a pH of 1.5 to 10, more preferably 5.0 to 9.0, and even more preferably 6.0 to 9.0 at 23°C. This is because it suppresses the settling of the electrode active material in the slurry containing the binder for non-aqueous secondary batteries and electrode active material.

[0088] Examples of basic substances (d) to be added to the emulsion polymerization solution and / or the dispersion after emulsion polymerization include ammonia, triethylamine, sodium hydroxide, and lithium hydroxide. These basic substances (d) may be used individually or in combination of two or more.

[0089] [Radical polymerization initiator (e)] The radical polymerization initiator (e) used when producing the binder polymer (P) by emulsion polymerization is not particularly limited, and known ones can be used. Examples of radical polymerization initiators (e) include persulfates such as ammonium persulfate and potassium persulfate; hydrogen peroxide; azo compounds; and organic peroxides such as tert-butyl hydroperoxide, tert-butyl peroxybenzoate, and cumene hydroperoxide. It is preferable to use persulfates and organic peroxides as radical polymerization initiators (e).

[0090] In this embodiment, when producing the binder polymer (P) by emulsion polymerization, a reducing agent such as sodium bisulfite, rongalit, or ascorbic acid may be used in combination with the radical polymerization initiator (e) for redox polymerization.

[0091] The amount of radical polymerization initiator (e) added (including the reducing agent if used in combination) is preferably 0.001 parts by mass or more, and more preferably 0.005 parts by mass or more, per 100 parts by mass of monomer (a). This is because it is possible to increase the conversion rate of monomer (a) to binder polymer (P) when producing binder polymer (P) by emulsion polymerization. The amount of radical polymerization initiator (e) added is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of monomer (a). This is because it is possible to increase the molecular weight of binder polymer (P) and reduce the swelling rate of the non-aqueous secondary battery electrode containing the binder polymer (P) of this embodiment in relation to the electrolyte.

[0092] [Chain transfer agent (f)] The chain transfer agent (f) used in the production of the binder polymer (P) by emulsion polymerization is used to adjust the molecular weight of the binder polymer (P) obtained by emulsion polymerization. Examples of chain transfer agents (f) include n-dodecyl mercaptan, tert-dodecyl mercaptan, n-butyl mercaptan, 2-ethylhexyl thioglycolate, 2-mercaptoethanol, β-mercaptopropionic acid, methyl alcohol, n-propyl alcohol, isopropyl alcohol, t-butyl alcohol, and benzyl alcohol.

[0093] [Emulsion polymerization method] Examples of emulsion polymerization methods used in producing the binder polymer (P) include a method in which each component used for emulsion polymerization is continuously supplied into the reaction vessel while emulsion polymerization is carried out. The temperature of emulsion polymerization is not particularly limited, but is preferably 30 to 90°C, preferably 50 to 85°C, and more preferably 55 to 80°C. Emulsion polymerization is preferably carried out while stirring. Furthermore, it is preferable to continuously supply monomer (a) and radical polymerization initiator (e) to the solution during emulsion polymerization so that the concentrations of monomer (a) and radical polymerization initiator (e) in the solution during emulsion polymerization become uniform.

[0094] <2. Binder for non-aqueous secondary batteries> The binder for non-aqueous secondary batteries of this embodiment includes the binder polymer (P) of this embodiment. The electrode binder for non-aqueous secondary batteries may contain other components along with the binder polymer (P). Specifically, the electrode binder for non-aqueous secondary batteries may contain, for example, polymers other than the binder polymer (P), surfactants, etc.

[0095] The binder for non-aqueous secondary batteries consists of components that remain without volatilizing even after heating processes in the manufacturing method of non-aqueous secondary batteries described later. Specifically, the components constituting the binder for non-aqueous secondary batteries are those that remain after weighing 1 g of a binder composition for non-aqueous secondary batteries containing a binder polymer (P), placing it on a 5 cm diameter aluminum dish, and drying it in a dryer at 1 atmosphere (1013 hPa) and a temperature of 105°C for 1 hour while circulating the air inside the dryer.

[0096] The content of the binder polymer (P) in the binder for non-aqueous secondary batteries is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 98% by mass or more. This is because the effects of including the binder polymer (P) become significant.

[0097] <3. Binder composition for non-aqueous secondary batteries> The binder composition for non-aqueous secondary batteries of this embodiment comprises the binder polymer (P) and an aqueous medium (B). Preferably, in the binder composition for non-aqueous secondary batteries of this embodiment, the binder polymer (P) is dispersed in the aqueous medium (B). The binder composition for non-aqueous secondary batteries may also contain other components along with the binder polymer (P) and the aqueous medium (B). Specifically, the binder composition for non-aqueous secondary batteries may contain, for example, the above-mentioned components used in the synthesis of the binder polymer (P).

[0098] The binder composition for non-aqueous secondary batteries of this embodiment may be a dispersion obtained by producing a binder polymer (P) by emulsion polymerization. Alternatively, the binder composition for non-aqueous secondary batteries of this embodiment may be a dispersion obtained by dispersing a binder polymer (P) obtained by a method other than emulsion polymerization in an aqueous medium (B). In this case, a known method can be used to disperse the binder polymer (P) in the aqueous medium (B).

[0099] [Aqueous medium (B)] The aqueous medium (B) in the binder composition for non-aqueous secondary batteries of this embodiment is water, a hydrophilic solvent, or a mixture thereof. Examples of hydrophilic solvents include those exemplified as the aqueous medium (b) used in the synthesis of the binder polymer (P). The aqueous medium (B) may be the same as, or different from, the aqueous medium (b) used in the synthesis of the binder polymer (P).

[0100] If the binder composition for non-aqueous secondary batteries is a dispersion obtained by producing a binder polymer (P) by emulsion polymerization, the aqueous medium (B) may be the aqueous medium (b) used in the synthesis of the binder polymer (P). Alternatively, the aqueous medium (B) may be the aqueous medium (b) used in the synthesis of the binder polymer (P) with a new aqueous medium added. Alternatively, the aqueous medium (B) may be obtained by replacing part or all of the aqueous medium (b) contained in the dispersion obtained by producing the binder polymer (P) by emulsion polymerization with a new aqueous solvent. In this case, the new aqueous medium used may have the same composition as the aqueous medium (b) used in the synthesis of the binder polymer (P), or it may have a different composition.

[0101] [Non-volatile content concentration of binder compositions for non-aqueous secondary batteries] The non-volatile content concentration of the binder composition for non-aqueous secondary batteries in this embodiment is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. This is to increase the amount of active ingredients contained in the binder composition for non-aqueous secondary batteries. The non-volatile content concentration of the binder composition for non-aqueous secondary batteries can be adjusted by the content of the aqueous medium (B) contained in the binder composition for non-aqueous secondary batteries. The non-volatile content concentration of the binder composition for non-aqueous secondary batteries is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. This is because it suppresses the increase in viscosity of the binder composition for non-aqueous secondary batteries, making it easier to prepare a slurry for non-aqueous secondary battery electrodes.

[0102] [Gel fraction] The binder composition for non-aqueous secondary batteries of this embodiment preferably has a gel fraction of 80% or more, more preferably 85% or more, and even more preferably 90% or more, as measured by the method described later. This is because it results in a binder composition for non-aqueous secondary batteries that can form non-aqueous secondary battery electrodes with excellent solvent resistance.

[0103] <4. Slurry for non-aqueous secondary battery electrodes> Next, the slurry for non-aqueous secondary battery electrodes of this embodiment will be described in detail. The slurry for non-aqueous secondary battery electrodes includes the binder polymer (P) of this embodiment, an electrode active material, and an aqueous medium. Preferably, the binder polymer (P) and electrode active material contained in the slurry for non-aqueous secondary battery electrodes are dispersed in the aqueous medium. In addition to the binder polymer (P), electrode active material, and aqueous medium, the slurry for non-aqueous secondary battery electrodes may also contain a thickener, a conductive additive, the above-mentioned components used in the synthesis of the binder polymer (P), etc.

[0104] [Content of binder polymer (P)] The amount of binder polymer (P) contained in the slurry for non-aqueous secondary battery electrodes is preferably 0.50 parts by mass or more, and more preferably 1.0 part by mass or more, per 100 parts by mass of electrode active material. This is to allow the effects of including binder polymer (P) to be fully realized. The content of the binder polymer (P) in the slurry for non-aqueous secondary battery electrodes is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less, per 100 parts by mass of electrode active material. This is because it allows for a higher content of electrode active material in the slurry for non-aqueous secondary battery electrodes.

[0105] [Electrode active material] The electrode active material contained in the slurry for non-aqueous secondary battery electrodes is a material that can intercarry and deintercalate charge carrier ions such as lithium ions. The charge carrier ions are preferably alkali metal ions, more preferably lithium ions, sodium ions, and potassium ions, and even more preferably lithium ions.

[0106] When a non-aqueous secondary battery electrode manufactured using a slurry for non-aqueous secondary battery electrodes is the aqueductor, the electrode active material is the aqueductor active material. The aqueductor active material preferably contains at least one of the following: carbon materials, silicon-containing materials, and titanium-containing materials. Examples of carbon materials used as aqueductor active materials include coke such as petroleum coke, pitch coke, and coal coke; carbonized organic polymers; and graphite such as artificial graphite and natural graphite. Examples of silicon-containing materials used as aqueductor active materials include elemental silicon and silicon compounds such as silicon oxide. Examples of titanium-containing materials used as aqueductor active materials include lithium titanate. These materials used as aqueductor active materials may be used individually, or they may be used in mixtures or composites.

[0107] The negative electrode active material preferably contains at least one of a carbon material or a silicon-containing material, and more preferably a carbon material. This is because the binder polymer (P) contained in the non-aqueous secondary battery electrode slurry has a significant effect in improving the binding between negative electrode active materials and between the negative electrode active material and the current collector.

[0108] When a non-aqueous secondary battery electrode manufactured using a slurry for non-aqueous secondary battery electrodes is the positive electrode, the electrode active material is the positive electrode active material. As the positive electrode active material, a material with a higher standard electrode potential than the negative electrode active material is used. Specifically, examples of positive electrode active materials include lithium composite oxides containing nickel, such as Ni-Co-Mn lithium composite oxides, Ni-Mn-Al lithium composite oxides, and Ni-Co-Al lithium composite oxides, as well as chalcogen compounds such as lithium cobalt oxide (LiCoO2), spinel-type lithium manganate (LiMn2O4), olivine-type lithium iron phosphate, TiS2, MnO2, MoO3, and V2O5. These materials used as positive electrode active materials may be used individually or in combination of two or more types.

[0109] [Aqueous medium] The aqueous medium contained in the slurry for non-aqueous secondary battery electrodes of this embodiment is selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent. Examples of the hydrophilic solvent include the same hydrophilic solvent exemplified as the aqueous medium (b) used in the synthesis of the binder polymer (P). The aqueous medium contained in the slurry for non-aqueous secondary battery electrodes may be the same as or different from the aqueous medium (b) used in the synthesis of the binder polymer (P).

[0110] [Thickening agent] Examples of thickeners that may be included in the slurry for non-aqueous secondary battery electrodes include celluloses such as carboxymethylcellulose (CMC), hydroxyethylcellulose, and hydroxypropylcellulose, ammonium salts of celluloses, alkali metal salts of celluloses, polyvinyl alcohol, and polyvinylpyrrolidone. It is preferable that the thickener contains at least one of carboxymethylcellulose, ammonium salts of carboxymethylcellulose, or alkali metal salts of carboxymethylcellulose, as this facilitates the dispersion of the electrode active material in the slurry for non-aqueous secondary battery electrodes.

[0111] The amount of thickener contained in the slurry for non-aqueous secondary battery electrodes is preferably 0.50 parts by mass or more, and more preferably 0.80 parts by mass or more, per 100 parts by mass of electrode active material. This is because it improves the bonding between the electrode active materials contained in the non-aqueous secondary battery electrodes prepared using the slurry, and between the electrode active materials and the current collector. The amount of thickener contained in the slurry for non-aqueous secondary battery electrodes is preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, and even more preferably 1.5 parts by mass or less, per 100 parts by mass of electrode active material. This is because it improves the coating properties of the slurry for non-aqueous secondary battery electrodes.

[0112] [Conductive additive] Examples of conductive additives that may be included in the slurry for non-aqueous secondary battery electrodes of this embodiment include carbon black and carbon fibers. Examples of carbon black include furnace black, acetylene black, Denka Black (registered trademark) (manufactured by Denka Co., Ltd.), and Ketjen Black (registered trademark) (manufactured by Ketjen Black International Co., Ltd.). Examples of carbon fibers include carbon nanotubes and carbon nanofibers. As a carbon nanotube, VGCF (registered trademark, manufactured by Showa Denko K.K.), which is a gas-phase carbon fiber, is a preferred example.

[0113] [Method for manufacturing slurry for non-aqueous secondary battery electrodes] A method for producing the slurry for non-aqueous secondary battery electrodes according to this embodiment involves mixing, for example, the binder polymer (P) of this embodiment, the electrode active material, an aqueous medium, a thickener as needed, a conductive additive as needed, and other components as needed. The mixing order of the components that make up the slurry for non-aqueous secondary battery electrodes is not particularly limited and can be determined as appropriate. Methods for mixing the components include using a mixing device such as a stirring type, rotary type, or shaking type.

[0114] <5. Non-aqueous secondary battery electrode> Next, the non-aqueous secondary battery electrode (hereinafter sometimes referred to as "electrode") of this embodiment will be described in detail. The electrode of this embodiment includes the binder polymer (P) of this embodiment. The electrode of this embodiment comprises a current collector and an electrode active material layer formed on the current collector. The shape of the electrode of this embodiment is not particularly limited and includes, for example, a laminate or a wound body. The area in which the electrode active material layer is formed on the current collector is not particularly limited, and the electrode active material layer may be formed on the entire surface of the current collector, or on only a part of the surface of the current collector. If the current collector is in the shape of a plate, foil, etc., the electrode active material layer may be formed on both sides of the current collector, or on only one side.

[0115] [Current collector] The current collector is preferably a metal sheet with a thickness of 0.001 mm or more and 0.5 mm or less. Examples of metals forming the metal sheet include iron, copper, aluminum, nickel, and stainless steel. When the electrode in this embodiment is the negative electrode of a lithium-ion secondary battery, the current collector is preferably copper foil.

[0116] [Electrode active material layer] The electrode active material layer includes the binder polymer (P) and electrode active material of this embodiment. The electrode active material layer may also contain conductive additives, thickeners, etc. The electrode active material, conductive additives, and thickeners can all be the same as those exemplified as components of the slurry for non-aqueous secondary battery electrodes.

[0117] [Method for manufacturing non-aqueous secondary battery electrodes] The electrode of this embodiment can be manufactured, for example, by the method shown below. First, the slurry for non-aqueous secondary battery electrodes of this embodiment is applied to a current collector. Next, the slurry for non-aqueous secondary battery electrodes is dried. This forms an electrode active material layer containing a binder polymer (P) on the current collector, forming an electrode sheet. After that, the electrode sheet is cut to an appropriate size as needed. By performing the above steps, the electrode of this embodiment is obtained.

[0118] There are no particular limitations on the method for applying the slurry for non-aqueous secondary battery electrodes onto a current collector, but examples include the reverse roll method, direct roll method, doctor blade method, knife method, extrusion method, curtain method, gravure method, bar method, dip method, and squeeze method. Among these application methods, considering the viscosity and other physical properties and drying properties of the slurry for non-aqueous secondary battery electrodes, it is preferable to use one of the methods selected from the doctor blade method, knife method, or extrusion method. This is because it is possible to obtain an electrode active material layer with a smooth surface and small variation in thickness.

[0119] When applying a slurry for non-aqueous secondary battery electrodes to both sides of a current collector, it may be applied sequentially to one side at a time, or to both sides simultaneously. Furthermore, the slurry for non-aqueous secondary battery electrodes may be applied continuously or intermittently to the current collector. The amount of slurry applied to the non-aqueous secondary battery electrode can be appropriately determined according to the battery's design capacity and the composition of the slurry.

[0120] The method for drying the slurry for non-aqueous secondary battery electrodes applied to the current collector is not particularly limited, but for example, methods selected from hot air, reduced pressure or vacuum environment, (far) infrared radiation, and low-temperature air can be used alone or in combination. The drying temperature and drying time when drying the slurry for non-aqueous secondary battery electrodes can be appropriately adjusted depending on the concentration of non-volatile components in the slurry, the amount applied to the current collector, etc. The drying temperature is preferably 40°C to 350°C, and more preferably 60°C to 100°C from the viewpoint of productivity. The drying time is preferably 1 minute to 30 minutes.

[0121] An electrode sheet, on which an electrode active material layer is formed on a current collector, may be cut to a size and shape suitable for use as an electrode. The method of cutting the electrode sheet is not particularly limited, and for example, slitting, laser cutting, wire cutting, cutting machines, die cutting machines, etc., can be used.

[0122] In this embodiment, the electrode sheet may be pressed before or after cutting, if necessary. This allows the electrode active material to be firmly bonded to the current collector, and the non-aqueous secondary battery can be miniaturized by reducing the thickness of the electrode. A general method can be used for pressing the electrode sheet. In particular, it is preferable to use a die press method or a roll press method. When using the die pressing method, the press pressure is not particularly limited, but 0.5 t / cm 2 5 t / cm² or more 2 The following is preferable. When using the roll press method, the press load is not particularly limited, but it is preferable to set it to 0.5 t / cm or more and 8 t / cm or less. This is because it is possible to obtain the above-mentioned effects of pressing while suppressing a decrease in the insertion and desorption capacity of charge carriers such as lithium ions into the electrode active material.

[0123] [Peel strength] In this embodiment, the non-aqueous secondary battery electrode preferably has a peel strength of 10.0 mN / mm or more, more preferably 12.5 mN / mm or more, and even more preferably 15.0 mN / mm or more, relative to the current collector, as measured by the method described later. This is because the cycle characteristics and durability of the non-aqueous secondary battery using the non-aqueous secondary battery electrode are improved.

[0124] <6.Nonaqueous secondary battery> Next, a lithium-ion secondary battery will be described as a preferred example of a non-aqueous secondary battery according to this embodiment. Note that the configuration of the non-aqueous secondary battery of the present invention is not limited to the example shown below. The lithium-ion secondary battery of this embodiment has a positive electrode, a negative electrode, an electrolyte, and known components such as separators, which may be provided as needed, housed in an outer casing. The shape of the lithium-ion secondary battery may be any shape, such as coin-shaped, button-shaped, sheet-shaped, cylindrical, prismatic, or flat.

[0125] [Positive electrode / Negative electrode] In this embodiment, the lithium-ion secondary battery comprises an electrode active material layer containing the binder polymer (P) of this embodiment in one or both of the positive and negative electrodes. In this embodiment, it is preferable that at least the negative electrode of the lithium-ion secondary battery comprises an electrode active material layer containing the binder polymer (P). In the lithium-ion secondary battery of this embodiment, if only one of the electrodes, the positive electrode or the negative electrode, is equipped with an electrode active material layer containing the binder polymer (P) of this embodiment, then, as an electrode that does not contain the binder polymer (P) of this embodiment, a known binder such as polyvinylidene fluoride is used instead of the binder polymer (P) of this embodiment.

[0126] [Electrolyte] As the electrolyte, a non-aqueous liquid with ionic conductivity is used. Examples of electrolytes include solutions in which the electrolyte is dissolved in an organic solvent, and ionic liquids, with the former being preferred. This is because it allows for the production of lithium-ion secondary batteries with low manufacturing costs and low internal resistance.

[0127] Alkali metal salts can be used as electrolytes and can be appropriately selected depending on the type of electrode active material, etc. Examples of electrolytes include LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, and LiB 10 Cl 10 Examples include LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiCF3SO3, LiC4F9SO3, Li(CF3SO2)2N, and lithium aliphatic carboxylates. Other alkali metal salts can also be used as electrolytes.

[0128] The organic solvent used to dissolve the electrolyte is not particularly limited, but examples include carbonate ester compounds such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC); nitrile compounds such as acetonitrile; and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. These organic solvents may be used individually or in combination of two or more. Among these, it is preferable to use a combination of linear carbonate solvents as the organic solvent.

[0129] [Exterior] As for the exterior, for example, a material formed from aluminum laminate consisting of aluminum foil and resin film can be used as appropriate, but is not limited to this. [Examples]

[0130] The present invention will be described in detail below with reference to examples and comparative examples. The following examples are provided to facilitate understanding of the present invention. The present invention is not limited to these examples. In the following embodiments, a negative electrode for a lithium-ion secondary battery was fabricated as an example of a non-aqueous secondary battery electrode of the present invention, and a lithium-ion secondary battery was fabricated as an example of a non-aqueous secondary battery. The effects of the present invention were confirmed by comparing it with the negative electrode and lithium-ion secondary battery of the comparative example. Furthermore, unless otherwise specified, the water used in the following examples and comparative examples is deionized water.

[0131] <1. Manufacturing of Binder Polymers> 150 parts by mass of water were placed in a separable flask equipped with a condenser, thermometer, stirrer, and dropping funnel, and the temperature was raised to 80°C. Monomers (a1), (a2), (a3), an internal crosslinking agent (a4), a polymerizable surfactant (a5), and a radical polymerization initiator (e), as shown in Tables 1 to 3, were continuously supplied to this separable flask in the proportions shown in Tables 1 to 3 over 3 hours while stirring at 80°C to carry out emulsion polymerization and obtain aqueous emulsions containing the binder polymers of Examples 1 to 10 and Comparative Examples 1 to 3.

[0132] The obtained aqueous emulsion was cooled to room temperature, and 160 parts by mass of water and 25% by mass of aqueous ammonia were added. This produced the non-aqueous binder compositions for secondary batteries of Examples 1 to 10 and Comparative Examples 1 to 3, in which the particulate binder polymers of Examples 1 to 10 and Comparative Examples 1 to 3 were dispersed in an aqueous medium (b).

[0133] [Table 1]

[0134] [Table 2]

[0135] [Table 3]

[0136] The amounts of ammonia as a basic substance (d) shown in Tables 1 to 3 represent the amount of ammonia contained in aqueous ammonia (parts by mass). The amount of water as the aqueous medium (b) shown in Tables 1 to 3 represents the total amount of water (parts by mass) contained in the binder composition for non-aqueous secondary batteries.

[0137] The polymerizable surfactant (a5) shown in Tables 1 to 3 is polyoxyethylene alkyl ether sulfate (Aqualon KH-10, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). The polymerization initiator (e2) is tert-butyl peroxybenzoate (Kayabutyl B, manufactured by Kayaku Akzo Co., Ltd.). The polymerization initiator (e3) is tert-butyl hydroperoxide (manufactured by Kayaku Akzo Co., Ltd., Kayabutyl H-70).

[0138] <2. Evaluation of binder polymers and binder compositions for non-aqueous secondary batteries> The glass transition temperature (Tg) of the binder polymers in Examples 1 to 10 and Comparative Examples 1 to 3 was measured using the method described below. The results are shown in Tables 1 to 3. Furthermore, the non-volatile content concentration and gel fraction of the binder compositions for non-aqueous secondary batteries of Examples 1 to 10 and Comparative Examples 1 to 3 were measured using the methods described below. The results are shown in Tables 1 to 3.

[0139] [Glass transition temperature Tg] A binder composition for non-aqueous secondary batteries was applied to a release PET (polyethylene terephthalate) film and dried at 50°C for 5 hours to obtain a 2 mm thick film made of a binder polymer. Square test specimens measuring 2 mm in length and 2 mm in width were cut from the obtained film. The test specimens were sealed in aluminum pans, and differential scanning calorimetry (DSC) measurements were performed on the specimens using a differential scanning calorimeter (EXSTAR DSC / SS7020, Hitachi High-Tech Science Corporation) under a nitrogen gas atmosphere at a heating rate of 10°C / min. The temperature range for DSC measurement was -40°C to 200°C. The peak top temperature of the DDSC chart obtained as the temperature derivative of the DSC was measured, and this temperature was defined as the glass transition temperature Tg (°C) of the binder polymer.

[0140] [Non-volatile content concentration] One g of the binder composition for non-aqueous secondary batteries was weighed, placed on a 5 cm diameter aluminum dish, and placed in a drying oven. The mixture was dried for one hour at 1 atmosphere (1013 hPa) and 105°C while circulating the air inside the oven, and the mass of the remaining components was measured. The mass ratio (mass%) of the components remaining after drying to the mass (1 g) of the binder composition for non-aqueous secondary batteries before drying was calculated and defined as the non-volatile content concentration.

[0141] [Gel fraction] A binder composition for non-aqueous secondary batteries was applied to a release PET film and dried at 160°C for 1 hour to obtain a spot film with a diameter of 5 mm made of binder polymer. 0.1000 to 0.2000 g of the obtained spot film was weighed (A2) and placed in a 300-mesh wire cage whose mass (A1) had been measured in advance.

[0142] Next, the wire mesh cage containing the spot film was placed in a glass bottle containing 20g of THF (tetrahydrofuran), ensuring that the spot film inside the cage was immersed in the THF. The cage was left standing at 20°C for 24 hours. The wire mesh cage containing the spot film was removed from the glass bottle, and the THF adhering to the cage was wiped off with a Kimwipe. Then, the wire mesh cage containing the spot film was placed in a drying oven and dried at 160°C for 10 minutes. Subsequently, the wire mesh cage containing the spot film was removed from the drying oven, cooled at 23°C for 20 minutes, and its mass (A3) was measured.

[0143] Subsequently, the gel fraction was calculated using the following formula. In the formula, (A1) is the mass (g) of the 300-mesh wire cage. (A2) is the mass (g) of the spot film placed in the wire cage. (A3) is the mass of the wire cage containing the spot film after immersion in THF and drying (total mass (g) of the spot film and wire cage). Gel fraction (%) = 100 - {A2 - (A3 - A1) / A2} × 100

[0144] <3. Manufacturing of non-aqueous secondary batteries> Using the binder compositions for non-aqueous secondary batteries of Examples 1 to 10 and Comparative Examples 1 to 3, negative electrodes were prepared by the methods described below, and lithium-ion secondary batteries, which are non-aqueous secondary batteries of Examples 1 to 10 and Comparative Examples 1 to 3, were prepared using these negative electrodes.

[0145] [Fabrication of the positive electrode] LiNi as a positive electrode active material 0.6 Mn 0.2 Co 0.2 A mixture was obtained by mixing 4 parts by mass of O294, 3 parts by mass of acetylene black as a conductive additive, and 3 parts by mass of polyvinylidene fluoride as a binder. 50 parts by mass of N-methylpyrrolidone were added to the mixture and further mixed to obtain a positive electrode slurry.

[0146] A 15 μm thick aluminum foil was prepared as the positive electrode current collector. The positive electrode slurry was applied to both sides of the positive electrode current collector using the direct roll method. The amount of positive electrode slurry applied to the positive electrode current collector was adjusted so that the thickness after the roll press treatment described later was 125 μm per side. The positive electrode slurry applied to the positive electrode current collector was dried at 120°C for 5 minutes, and then pressed using a roll press (manufactured by Sankmetal Co., Ltd., press load 5 t / cm, roll width 7 cm) by the roll press method to obtain a positive electrode sheet having positive electrode active material layers on both sides of the positive electrode current collector. The obtained positive electrode sheet was cut into a rectangle measuring 50 mm in length and 40 mm in width, and conductive tabs were attached to form the positive electrode.

[0147] [Fabrication of negative electrode (non-aqueous secondary battery electrode)] 100 parts by mass of artificial graphite (G49, manufactured by Jiangxi Zichen Technology Co., Ltd.) as the negative electrode active material, 3.9 parts by mass of any non-aqueous secondary battery binder composition produced in Examples 1 to 10 or Comparative Examples 1 to 3 (1.5 parts by mass of non-volatile content (binder polymer)), and 62 parts by mass of a 2% by mass aqueous solution of CMC (carboxymethylcellulose-sodium salt, manufactured by Nippon Paper Chemicals Co., Ltd., Sunrose® MAC500LC) were mixed, and 28 parts by mass of water were added. The mixture was then mixed using a rotation-orbit mixer (ARE-310, manufactured by Thinky Co., Ltd.) to obtain a negative electrode slurry (slurry for non-aqueous secondary battery electrodes).

[0148] A 10 μm thick copper foil was prepared as the negative electrode current collector. The negative electrode slurry was applied to both sides of the negative electrode current collector using the direct roll method. The amount of negative electrode slurry applied to the negative electrode current collector was adjusted so that the thickness after the roll press treatment described later was 170 μm per side. The negative electrode slurry applied to the negative electrode current collector was dried at 90°C for 10 minutes, and then pressed using a roll press (manufactured by Sankmetal Co., Ltd., press load 8 t / cm, roll width 7 cm) by the roll press method to obtain a negative electrode sheet having negative electrode active material layers on both sides of the negative electrode current collector. The obtained negative electrode sheet was cut into a rectangle measuring 52 mm in length and 42 mm in width, and conductive tabs were attached to form the negative electrode.

[0149] [Peeling strength of the negative electrode active material layer] Test specimens measuring 25 mm in width and 70 mm in length were cut from the negative electrode sheets manufactured to obtain the negative electrodes of Examples 1 to 10 and Comparative Examples 1 to 3. The peel strength of the negative electrode active material layer of each obtained test specimen was measured using a peel tester (Tensilon®, manufactured by A&D Co., Ltd.) in an atmosphere of 23°C and 50% relative humidity by mass, according to the method described below. The results are shown in Tables 1 to 3.

[0150] Double-sided tape (NITTOTAPE® No. 5, manufactured by Nitto Denko Corporation) was applied to the entire surface of the negative electrode active material layer of the test specimen. Then, the negative electrode active material layer of the test specimen and a metal plate measuring 50 mm in width and 200 mm in length were attached together using the double-sided tape so that the widthwise centers of the test specimen and the widthwise centers of the metal plate coincided, and left for 10 minutes.

[0151] Next, the negative electrode current collector (copper foil) was peeled 20 mm from one end of the test specimen's negative electrode active material layer and folded back 180°. The portion of the negative electrode current collector that had been peeled from the test specimen was then grasped by the upper chuck of the peeling test machine. The end of the metal plate in the longitudinal direction from which the negative electrode current collector had been peeled was also grasped by the lower chuck of the peeling test machine. In this state, the upper chuck was pulled at a speed of 100 ± 10 mm / min in the direction that widened the gap between the upper and lower chucks, thereby peeling the negative electrode current collector from the negative electrode active material layer.

[0152] Then, the average value (mN) of the peeling force when the length of the negative electrode current collector peeled off from the negative electrode active material layer was within the range of 10 to 45 mm was calculated, and the value obtained by dividing this by the width of the test piece (25 mm) was taken as the peeling strength (mN / mm) of the negative electrode active material layer. When measuring the peel strength of the negative electrode active material layer, no peeling occurred between the double-sided tape and the metal plate, nor between the double-sided tape and the negative electrode active material layer, in any of the test specimens from Examples 1 to 10 and Comparative Examples 1 to 3.

[0153] [Fabrication of non-aqueous secondary batteries] A separator made of a porous polyolefin film (polyethylene, 25 μm thick) was interposed between the positive and negative electrodes, and the positive electrode active material layer and the negative electrode active material layer were laminated so that they faced each other. These were then housed in an outer casing (battery pack) made of aluminum laminate material. Subsequently, an electrolyte solution was injected into the outer casing, vacuum impregnation was performed, and the battery was packed using a vacuum heat sealer to obtain a lithium-ion secondary battery. As the electrolyte, a mixture was used consisting of 99 parts by mass of a solution in which LiPF6 was dissolved at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:DEC = 30:50:20, and 1 part by mass of vinylene carbonate.

[0154] <4. Evaluation of non-aqueous secondary batteries> The internal resistance and discharge capacity retention rate after 100 cycles were evaluated for the lithium-ion secondary batteries of Examples 1 to 10 and Comparative Examples 1 to 3, respectively, using the methods described below. The results are shown in Tables 1 to 3.

[0155] [Internal resistance (DCR)] Under conditions of 25°C, the internal resistance (DCR(Ω)) of a lithium-ion secondary battery was measured using the following procedure. Specifically, the battery was charged at a constant current of 0.2C from rest potential until the voltage reached 3.6V, bringing the charge state to 50% of the initial capacity (SOC50%). Subsequently, discharge was performed for 60 seconds at current values ​​of 0.2C, 0.5C, 1C, and 2C. The internal resistance DCR(Ω) at SOC50% was determined from the relationship between these four current values ​​(values ​​per second) and voltage.

[0156] [Discharge capacity retention rate after 100 cycles] Under conditions of 45°C, charging and discharging were performed with each cycle consisting of the following steps (i) to (iv) as defined. The time integral of the current in steps (i) and (ii) was defined as the charging capacity, and the time integral of the current in step (iv) was defined as the discharging capacity. The discharging capacity after the first cycle and the discharging capacity after the 100th cycle were measured, and the discharge capacity retention rate after 100 cycles was calculated using the following formula. Discharge capacity retention rate (%) = 100 × (Discharge capacity at 100 cycles / Discharge capacity at 1 cycle)

[0157] (i) Charge at a current of 1C until the voltage reaches 4.2V (constant current (CC) charging). (ii) Charge at a voltage of 4.2V until the current reaches 0.05C (constant voltage (CV) charging). (iii) Let stand for 30 minutes. (iv) Discharge at a current of 1C until the voltage reaches 2.75V (constant current (CC) discharge).

[0158] <5. Evaluation Results> As shown in Tables 1 to 3, the lithium-ion secondary batteries of Examples 1 to 10 all demonstrated higher capacity retention rates compared to the lithium-ion secondary batteries of Comparative Examples 1 to 3. Furthermore, the lithium-ion secondary batteries of Examples 1 to 10 all exhibited sufficiently high peel strength of the negative electrode active material layer. This is presumed to be because the binder polymer contained in the negative electrode of the lithium-ion secondary batteries of Examples 1 to 10 is a copolymer formed by emulsion polymerization of monomer (a1), monomer (a2), monomer (a3), and internal crosslinking agent (a4) as shown in Table 1 or Table 2. Furthermore, as shown in Tables 1 to 3, it was confirmed that the lithium-ion secondary batteries of Examples 1 to 10 and Comparative Examples 1 to 3 had sufficiently low internal resistance values ​​for practical use. [Industrial applicability]

[0159] According to the present invention, it is possible to form electrodes in which the electrode active material layer is less likely to peel off from the current collector, and a binder can be provided that yields a non-aqueous secondary battery with excellent cycle characteristics.

Claims

1. The first structural unit derived from the monomer (a1), The second structural unit derived from the monomer (a2), The third structural unit, It has a fourth structural unit derived from an internal crosslinking agent (a4), The monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond, The monomer (a2) is a compound having only one ethylenically unsaturated bond and an anionic functional group. The internal crosslinking agent (a4) is a compound having a plurality of independent ethylenically unsaturated bonds, A binder polymer for non-aqueous secondary batteries, characterized in that the third structural unit is a structural unit represented by the following general formula (1). 【Chemistry 1】 (In formula (1), Z is a hydrogen atom, an organic group having 1 to 30 carbon atoms, a metal atom, or an ammonium group.)

2. The binder polymer for non-aqueous secondary batteries according to claim 1, wherein Z in formula (1) is a linear or branched chain-like saturated hydrocarbon group.

3. The binder polymer for non-aqueous secondary batteries according to claim 1, wherein Z in formula (1) is at least one selected from the group consisting of a methyl group, an n-propyl group, and an n-hexyl group.

4. The binder polymer for non-aqueous secondary batteries according to claim 1, wherein the anionic functional group is at least one of a carboxyl group and a sulfo group.

5. A binder polymer for a non-aqueous secondary battery according to claim 1, comprising a total of 80% by mass or more of the first structural unit and the second structural unit.

6. The binder polymer for non-aqueous secondary batteries according to claim 1, wherein the content of the third structural unit is 0.050 parts by mass or more per 100 parts by mass of the first structural unit.

7. A binder composition for a non-aqueous secondary battery, comprising a binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 6, and an aqueous medium.

8. A binder for a non-aqueous secondary battery, comprising the binder polymer for a non-aqueous secondary battery described in any one of claims 1 to 6.

9. A binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 6, an electrode active material, and an aqueous medium, The aqueous medium is one selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent, wherein the slurry is for a non-aqueous secondary battery electrode.

10. A non-aqueous secondary battery electrode comprising a binder polymer for non-aqueous secondary batteries according to any one of claims 1 to 6.

11. A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode described in claim 10.

12. A method for producing a binder polymer for non-aqueous secondary batteries, characterized by copolymerizing monomer (a1), monomer (a2), monomer (a3), and internal crosslinking agent (a4), The monomer (a1) is a nonionic compound having an ethylenically unsaturated bond and not having multiple independent ethylenically unsaturated bonds. The monomer (a2) is a compound having an ethylenically unsaturated bond and an anionic functional group, and lacking a plurality of independent ethylenically unsaturated bonds. The monomer (a3) ​​is a compound represented by the following general formula (2), A method for producing a binder polymer for non-aqueous secondary batteries, characterized in that the internal crosslinking agent (a4) is a compound having a plurality of independent ethylenically unsaturated bonds. 【Chemistry 2】 (In formula (2), Z is a hydrogen atom, an organic group having 1 to 30 carbon atoms, a metal atom, or an ammonium group.)

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