Binder polymer for nonaqueous secondary battery, binder for nonaqueous secondary battery, binder composition for nonaqueous secondary battery, electrode slurry for nonaqueous secondary battery, electrode for nonaqueous secondary battery, nonaqueous secondary battery, method of producing binder polymer for nonaqueous secondary battery, method of producing binder for nonaqueous secondary battery, method of producing binder composition for nonaqueous secondary battery, method of producing electrode slurry for nonaqueous secondary battery, and method of producing electrode for nonaqueous secondary battery

Abstract

A binder polymer for a nonaqueous secondary battery according to the present invention includes: a first structural unit derived from an aromatic hydrocarbon monomer (a1) which is an aromatic compound that contains a hydrocarbon and has one ethylenically unsaturated bond; a second structural unit derived from a nonionic monomer (a2) which is a nonionic (meth)acrylic acid ester and has one ethylenically unsaturated bond; a third structural unit derived from a carboxylic acid monomer (a3) which is a compound having at least one moiety selected from the group consisting of a single ethylenically unsaturated bond, a carboxyl group, and a carboxyl group forming a salt; and a fourth structural unit derived from an isocyanate monomer (a4) which is a compound having at least one moiety selected from the group consisting of a single ethylenically unsaturated bond, an isocyanato group, and a blocked isocyanato group.

Description

Binder polymer for non-aqueous secondary battery, binder for non-aqueous secondary battery, binder composition for non-aqueous secondary battery, electrode slurry for non-aqueous secondary battery, electrode for non-aqueous secondary battery, non-aqueous secondary battery, method for producing binder polymer for non-aqueous secondary battery, method for producing binder for non-aqueous secondary battery, method for producing binder composition for non-aqueous secondary battery, method for producing electrode slurry for non-aqueous secondary battery, and method for producing electrode for non-aqueous secondary battery

[0001] The present disclosure relates to a binder polymer for non-aqueous secondary batteries, a binder for non-aqueous secondary batteries, a binder composition for non-aqueous secondary batteries, an electrode slurry for non-aqueous secondary batteries, an electrode for non-aqueous secondary batteries, a non-aqueous secondary battery, a method for producing a binder polymer for non-aqueous secondary batteries, a method for producing a binder for non-aqueous secondary batteries, a method for producing a binder composition for non-aqueous secondary batteries, a method for producing an electrode slurry for non-aqueous secondary batteries, and a method for producing an electrode for non-aqueous secondary batteries.

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

[0003] A non-aqueous secondary battery includes a positive electrode using a metal oxide or the like as an active material, a negative electrode using a carbon material such as graphite as an active material, and an electrolyte. The positive electrode and negative electrode each include 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. Examples of binders used in non-aqueous secondary batteries include those described in Patent Document 1 and Patent Document 2.

[0004] Patent Document 1 describes a secondary battery electrode having an electrode layer containing 100 parts by mass of at least one polymer selected from the group consisting of styrene-butadiene copolymers and copolymers obtained from a (meth)acrylic acid ester and a vinyl monomer having an acid component, and 1 to 20 parts by mass of at least one nonionic surfactant having a cloud point of 70°C or lower and selected from the group consisting of polyoxyethylene alkyl ether derivatives, polyoxyethylene-polyoxypropylene condensates, and polyoxyethylene-polyoxypropylene alkyl ether derivatives.

[0005] Patent Document 2 describes a binder for lithium ion secondary battery electrodes, which has a glass transition temperature of 30°C or lower and is obtained by emulsion polymerization of ethylenically unsaturated monomers containing, as essential components, 15 to 70% by mass of styrene relative to the total amount of ethylenically unsaturated monomers, an ethylenically unsaturated carboxylic acid ester, an ethylenically unsaturated carboxylic acid, and an internal crosslinking agent in the presence of a surfactant.

[0006] Furthermore, Patent Document 3 describes an electrode binder containing a polymer having a constituent unit derived from a (meth)acrylic acid alkyl ester monomer, a constituent unit derived from a monomer with a specific structure having an aromatic group, and a constituent unit derived from a monomer having at least one group selected from the group consisting of an epoxy group, a (blocked) isocyanate group, and a urethane group.

[0007] JP 2014-239070 A JP 2011-243464 A International Publication No. 2023-053863

[0008] In recent years, non-aqueous secondary batteries have been required to maintain sufficient battery performance even when exposed to a high-temperature environment for a long period of time, that is, to have excellent high-temperature storage properties.

[0009] Therefore, an object of the present disclosure is to provide a binder polymer for non-aqueous secondary batteries, a binder for non-aqueous secondary batteries, a binder composition for non-aqueous secondary batteries, an electrode slurry for non-aqueous secondary batteries, and an electrode for non-aqueous secondary batteries, which are capable of producing a non-aqueous secondary battery with excellent high-temperature storage stability. Another object of the present disclosure is to provide a non-aqueous secondary battery with excellent high-temperature storage stability. Another object of the present disclosure is to provide methods for producing the binder polymer for non-aqueous secondary batteries, the binder for non-aqueous secondary batteries, the binder composition for non-aqueous secondary batteries, the electrode slurry for non-aqueous secondary batteries, and the electrode for non-aqueous secondary batteries.

[0010] The present disclosure includes the following aspects: <1> A binder polymer for a non-aqueous secondary battery, comprising: a first structural unit derived from an aromatic hydrocarbon monomer (a1) which is an aromatic compound having one ethylenically unsaturated bond and composed of a hydrocarbon; a second structural unit derived from a nonionic monomer (a2) which is a nonionic (meth)acrylic acid ester having one ethylenically unsaturated bond; a third structural unit derived from a carboxylic acid monomer (a3) ​​which is a compound having one ethylenically unsaturated bond and at least one selected from the group consisting of a carboxy group and a salt-forming carboxy group; and a fourth structural unit derived from an isocyanate monomer (a4) which is a compound having one ethylenically unsaturated bond and at least one selected from the group consisting of an isocyanato group and a blocked isocyanato group. <2> The binder polymer for a non-aqueous secondary battery according to <1>, wherein the blocked isocyanato group has a structure that generates an isocyanato group in response to at least one selected from the group consisting of heating, voltage application, and a chemical reaction. <3> The binder polymer for a non-aqueous secondary battery according to <1> or <2>, wherein a content of the first structural unit in the total amount of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit is 35 mol % to 80 mol %. <4> The binder polymer for a non-aqueous secondary battery according to any one of <1> to <3>, wherein a content of the second structural unit in the total amount of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit is 10 mol % to 55 mol %. <5> The binder polymer for a non-aqueous secondary battery according to any one of <1> to <4>, wherein a content of the third structural unit in the total amount of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit is 1.0 mol % to 20 mol %. <6> The binder polymer for a nonaqueous secondary battery according to any one of <1> to <5>, wherein a content of the fourth structural unit in a total amount of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit is 0.10 mol % to 15 mol %.<7> The binder polymer for a non-aqueous secondary battery according to any one of <1> to <6>, further comprising a fifth structural unit derived from a polyfunctional monomer (a5) that is a compound having a plurality of independent ethylenically unsaturated bonds. <8> The binder polymer for a non-aqueous secondary battery according to <7>, in which a content of the fifth structural unit relative to a total content of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit is 0.010 mol % to 5.0 mol %. <9> The binder polymer for a non-aqueous secondary battery according to any one of <1> to <8>, in which a total content of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit is 90 mass % or more. <10> A binder for a non-aqueous secondary battery comprising the binder polymer for a non-aqueous secondary battery according to any one of <1> to <9>. <11> A binder composition for a non-aqueous secondary battery, comprising the binder polymer for a non-aqueous secondary battery according to any one of <1> to <9>, and an aqueous medium. <12> An electrode slurry for a non-aqueous secondary battery, comprising the binder polymer for a non-aqueous secondary battery according to any one of <1> to <9>, an electrode active material, and an aqueous medium. <13> An electrode for a non-aqueous secondary battery, comprising the binder polymer for a non-aqueous secondary battery according to any one of <1> to <9>. <14> A non-aqueous secondary battery, comprising the electrode for a non-aqueous secondary battery according to <13>. <15> A method for producing the binder polymer for a non-aqueous secondary battery according to any one of <1> to <9>, comprising copolymerizing the aromatic hydrocarbon monomer (a1), the nonionic monomer (a2), the carboxylic acid monomer (a3), and the isocyanate monomer (a4). <16> A method for producing a binder for a non-aqueous secondary battery, comprising mixing the binder polymer for a non-aqueous secondary battery according to any one of <1> to <9>. <17> A method for producing a binder composition for a non-aqueous secondary battery, comprising mixing the binder polymer for a non-aqueous secondary battery according to any one of <1> to <9> with an aqueous medium. <18> A method for producing a binder composition for a non-aqueous secondary battery, comprising mixing the binder for a non-aqueous secondary battery according to <10> with an aqueous medium.<19> A method for producing an electrode slurry for a non-aqueous secondary battery, comprising mixing the binder polymer for a non-aqueous secondary battery according to any one of <1> to <9>, an electrode active material, and an aqueous medium. <20> A method for producing an electrode slurry for a non-aqueous secondary battery, comprising mixing the binder for a non-aqueous secondary battery according to <10>, an electrode active material, and an aqueous medium. <21> A method for producing an electrode slurry for a non-aqueous secondary battery, comprising mixing the binder composition for a non-aqueous secondary battery according to <11> and an electrode active material. <22> A method for producing an electrode for a non-aqueous secondary battery, comprising applying the electrode slurry for a non-aqueous secondary battery according to <12> to at least a part of the surface of a current collector, and drying.

[0011] The present disclosure provides a binder polymer for a non-aqueous secondary battery, a binder for a non-aqueous secondary battery, a binder composition for a non-aqueous secondary battery, an electrode slurry for a non-aqueous secondary battery, and an electrode for a non-aqueous secondary battery, which are capable of producing a non-aqueous secondary battery with excellent high-temperature storage properties. The present disclosure also provides a non-aqueous secondary battery with excellent high-temperature storage properties. The present disclosure also provides methods for producing the binder polymer for a non-aqueous secondary battery, the binder for a non-aqueous secondary battery, the binder composition for a non-aqueous secondary battery, the electrode slurry for a non-aqueous secondary battery, and the electrode for a non-aqueous secondary battery.

[0012] The following describes the embodiments in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0013] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in the present disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in a composition, etc., the content or amount of each component means the total content or amount of the multiple substances present in the composition, etc., unless otherwise specified. In the present disclosure, the term "layer" includes cases where, when the region in which the layer exists is observed, the layer is formed over the entire region, as well as cases where the layer is formed only in a portion of the region.

[0014] In this disclosure, "(meth)acrylic" is a general term for acrylic and methacrylic. "(meth)acrylate" is a general term for acrylate and methacrylate. In this disclosure, "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerizability, unless otherwise specified.

[0015] (1) Binder polymer for non-aqueous secondary batteries The binder polymer for non-aqueous secondary batteries of the present disclosure includes: a first structural unit derived from an aromatic hydrocarbon monomer (a1), which is an aromatic compound having one ethylenically unsaturated bond and composed of a hydrocarbon; a second structural unit derived from a nonionic monomer (a2), which is a nonionic (meth)acrylic acid ester having one ethylenically unsaturated bond; a third structural unit derived from a carboxylic acid monomer (a3), which is a compound having one ethylenically unsaturated bond and at least one selected from the group consisting of a carboxy group and a salt-forming carboxy group; and a fourth structural unit derived from an isocyanate monomer (a4), which is a compound having one ethylenically unsaturated bond and at least one selected from the group consisting of an isocyanato group and a blocked isocyanato group. Hereinafter, the "binder polymer for non-aqueous secondary batteries" in the present disclosure will also be referred to as the "binder polymer (P)."

[0016] Use of the binder polymer (P) having the above-described configuration makes it possible to obtain a nonaqueous secondary battery with excellent high-temperature storage properties. The reason for this effect is unclear, but is presumed to be as follows. It is believed that the isocyanato groups present in the binder polymer (P), or in the case of blocked isocyanato groups, are generated by heating, voltage application, chemical reactions, etc., and generate active species through an oxidation-reduction reaction during charge and discharge in the nonaqueous secondary battery electrode. It is believed that these active species react with at least one of the electrolyte solution and the coating (SEI) that forms on the surface of the electrode active material due to the oxidation-reduction of the electrolyte solution, thereby allowing the binder polymer (P) to strongly protect the surface of the electrode active material. The surface of the electrode active material strongly protected by the binder polymer (P) has excellent durability at high temperatures such as 60°C. This is believed to suppress undesired decomposition reactions of the electrolyte solution and electrolyte that occur on the surface of the electrode active material during high-temperature storage, thereby improving high-temperature storage properties.

[0017] The above-mentioned action is thought to be particularly effective on electrode active materials, but it is also thought that the effect can be sufficiently obtained on components other than electrode active materials as long as they are exposed to the electrolyte and react with isocyanato groups.

[0018] The binder polymer (P) contains at least a first structural unit derived from an aromatic hydrocarbon monomer (a1), a second structural unit derived from a nonionic monomer (a2), a third structural unit derived from a carboxylic acid monomer (a3), and a fourth structural unit derived from an isocyanate monomer (a4). Here, the structural units contained in the polymer are bonded to each other by a polymerization reaction of the ethylenically unsaturated bonds possessed by each monomer. Furthermore, unless otherwise specified, the structural units contained in the polymer are bonded to each other by a covalent bond.

[0019] In addition, in the case of a polymer having a structural unit A derived from a compound A having an ethylenically unsaturated bond, the chemical structure of the portion of the structural unit A of the polymer other than the portion corresponding to the ethylenically unsaturated bond of the compound A is the same as the chemical structure of the portion other than the ethylenically unsaturated bond in the compound A before polymerization. For example, a structural unit derived from styrene is represented by "-CH ２ CH(C ６ H ５ It has the structure "(phenyl group))-".

[0020] In the present disclosure, a monomer derived from a certain structural unit in a polymer refers to a compound having a structure in which the bond between two carbon atoms forming the main chain of the polymer in that structural unit is replaced with an ethylenically unsaturated bond and separated from other structural units.

[0021] Furthermore, when a portion other than the main chain structure corresponding to the ethylenically unsaturated bond in a polymer, for example, the structure of a functional group such as a carboxy group, is changed by a chemical reaction or the like, the structural unit is classified based on the chemical structure after the change. For example, when vinyl acetate is polymerized and then saponified, this structural unit is referred to as a structural unit derived from vinyl alcohol, not as a structural unit derived from vinyl acetate. For example, when ion exchange is performed after polymerization of a monomer having an ionic functional group, the structural unit is classified based on the chemical structure after ion exchange. Specifically, for example, after polymerization of sodium acrylate, the corresponding structural unit is converted by ion exchange into "-CH ２When the structural unit is expressed as "CH(COOH)-", this structural unit is referred to as a structural unit derived from acrylic acid, not as a structural unit derived from sodium acrylate.

[0022] The binder polymer (P) may further contain one or more other structural units that do not fall under any of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit. Examples of other structural units include, but are not limited to, a fifth structural unit derived from a polyfunctional monomer (a5), which is a compound having multiple independent ethylenically unsaturated bonds. Here, the multiple independent ethylenically unsaturated bonds refer to multiple ethylenically unsaturated bonds that do not form a conjugated diene with each other.

[0023] The fifth structural unit may have one or more ethylenically unsaturated bonds remaining in the structural unit. For example, in the case of a divinylbenzene polymer, the structural unit derived from divinylbenzene may have a structure without an ethylenically unsaturated bond (a form in which both of the moieties corresponding to the two ethylenically unsaturated bonds of divinylbenzene are incorporated into the polymer chain), or may have a structure with one ethylenically unsaturated bond (a form in which only the moiety corresponding to one of the ethylenically unsaturated bonds is incorporated into the polymer chain).

[0024] [First Structural Unit] The aromatic hydrocarbon monomer (a1) from which the first structural unit is derived is composed of a hydrocarbon and does not contain atoms such as oxygen atoms. The aromatic hydrocarbon monomer (a1) contains an aromatic ring. The first structural unit may have one aromatic ring or two or more aromatic rings within one structural unit. The number of aromatic rings contained within one first structural unit is preferably 1 to 4, and more preferably 1. An example of the aromatic ring contained in the aromatic hydrocarbon monomer (a1) is a benzene ring. The aromatic ring contained in the aromatic hydrocarbon monomer (a1) may have a substituent. When the aromatic ring has a substituent, the number of substituents contained in the aromatic ring may be one or two or more. Examples of the substituent that the aromatic ring may have include an alkyl group, an alkoxy group, an acetyl group, an amino group, and a halogen atom. When the substituent that the aromatic ring may have is an alkyl group, the alkyl group preferably has 1 to 3 carbon atoms, and a methyl group is more preferred. The binder polymer (P) may contain one type of first structural unit alone or two or more types.

[0025] Examples of the aromatic hydrocarbon monomer (a1) from which the first structural unit is derived include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, and 1,1-diphenylethylene.

[0026] The aromatic hydrocarbon monomer (a1) from which the first structural unit is derived preferably contains at least one selected from the group consisting of styrene and alkylated styrene in which at least one hydrogen atom of styrene is substituted with an alkyl group. The total proportion of structural units derived from styrene and alkylated styrene in the first structural unit is preferably 80 mol% or more, may be 90 mol% or more, or may be 100 mol%. The proportion of structural units derived from styrene in the first structural unit is preferably 80 mol% or more, may be 90 mol% or more, or may be 100 mol%.

[0027] [Second structural unit] The nonionic monomer (a2) from which the second structural unit is derived is a nonionic (meth)acrylic acid ester having one ethylenically unsaturated bond and having neither an anionic functional group nor a cationic functional group. The binder polymer (P) may contain one type of second structural unit alone or two or more types.

[0028] The nonionic monomer (a2) from which the second structural unit is derived preferably contains a (meth)acrylic acid ester, more preferably a (meth)acrylic acid alkyl ester. The proportion of the structural unit derived from the (meth)acrylic acid ester in the second structural unit is preferably 60 mol% or more, may be 75 mol% or more, may be 90 mol% or more, or may be 100 mol%. The proportion of the structural unit derived from the (meth)acrylic acid alkyl ester in the second structural unit is preferably 60 mol% or more, may be 75 mol% or more, may be 90 mol% or more, or may be 100 mol%.

[0029] The number of carbon atoms in the alkyl group in the (meth)acrylic acid alkyl ester is preferably 1 to 20, more preferably 1 to 18, and even more preferably 4 to 16. The alkyl group in the (meth)acrylic acid alkyl ester may be linear, branched, or cyclic.

[0030] Examples of (meth)acrylic acid alkyl esters 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, stearyl (meth)acrylate, etc. Among these, from the viewpoint of forming an electrode active material layer having excellent electrolyte resistance, it is preferable that the (meth)acrylic acid alkyl ester contains 2-ethylhexyl (meth)acrylate.

[0031] The second structural unit may have a polar functional group. Examples of the polar functional group include, but are not limited to, a hydroxy group and a cyano group. The hydroxy group as a polar functional group is a concept that does not include an OH structure contained in an ionic functional group such as a carboxy group or a sulfo group (sulfonic acid group). The second structural unit may have one polar functional group within one structural unit, or may have two or more polar functional groups. Furthermore, when one structural unit has two or more polar functional groups, the two or more polar functional groups may be the same or different. Furthermore, the binder polymer (P) may contain two or more types of second structural units having different polar functional groups.

[0032] Examples of the nonionic monomer (a2) having a polar functional group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and (meth)acrylonitrile.

[0033] [Third structural unit] The third structural unit has at least one selected from the group consisting of a carboxy group and a carboxy group that forms a salt. The carboxy group that forms a salt refers to a group in which the carboxy group forms a salt with a basic substance. The third structural unit may have one carboxy group or two or more carboxy groups within one structural unit. The third structural unit may have one carboxy group that forms a salt within one structural unit, or two or more carboxy groups that form a salt. In the third structural unit, the total number of carboxy groups and carboxy groups that form a salt contained within one structural unit is preferably 1 to 4, and more preferably 1 to 2. The binder polymer (P) may contain one type of third structural unit alone, or two or more types.

[0034] Examples of the carboxylic acid monomer (a3) ​​from which the third structural unit is derived include unsaturated monocarboxylic acids such as methacrylic acid, acrylic acid, and crotonic acid; and unsaturated dicarboxylic acids such as itaconic acid and fumaric acid. From the viewpoint of suppressing peeling of the electrode active material layer from the current collector, the carboxylic acid monomer (a3) ​​preferably contains at least one selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid. The proportion of structural units derived from acrylic acid, methacrylic acid, and itaconic acid in the third structural unit (when two or more types are contained, the total proportion of structural units derived from these) is preferably 80 mol% or more, and may be 90 mol% or more, or may be 100 mol% or more.

[0035] Furthermore, from the viewpoint of improving the adhesion between the binder polymer and the active material or the current collector, the carboxylic acid monomer (a3) ​​may contain both an unsaturated monocarboxylic acid and an unsaturated dicarboxylic acid. When the carboxylic acid monomer (a3) ​​contains both an unsaturated monocarboxylic acid and an unsaturated dicarboxylic acid, the content of the unsaturated dicarboxylic acid relative to the total amount of the unsaturated monocarboxylic acid and the unsaturated dicarboxylic acid is preferably 1 mol% or more, or may be 5 mol% or more, or may be 10 mol% or more, or may be 15 mol% or more. Furthermore, the content of the unsaturated dicarboxylic acid relative to the total amount of the unsaturated monocarboxylic acid and the unsaturated dicarboxylic acid is preferably 70 mol% or less, more preferably 50 mol% or less, or may be 40 mol% or less, or may be 30 mol% or less.

[0036] Examples of the salt include metal salts and ammonium salts. Examples of the metal salt include alkali metal salts such as lithium salts, sodium salts, and potassium salts. Examples of the carboxylic acid monomer (a3) ​​from which the third structural unit having a carboxy group forming a salt is derived include lithium (meth)acrylate, lithium itaconate, dilithium itaconate, sodium (meth)acrylate, sodium itaconate, disodium itaconate, ammonium (meth)acrylate, ammonium itaconate, and diammonium itaconate.

[0037] [Fourth structural unit] The fourth structural unit has at least one selected from the group consisting of an isocyanato group and a blocked isocyanato group. The binder polymer (P) may contain one type of fourth structural unit alone or two or more types.

[0038] The isocyanate monomer (a4) from which the fourth structural unit is derived may be a compound having a (meth)acryloyl group, a vinyl group, or an allyl group, and from the viewpoints of availability and polymerization reactivity, a compound having a (meth)acryloyl group is preferred. The isocyanate monomer (a4) is preferably a compound having at least one selected from the group consisting of an isocyanato group and a blocked isocyanato group and a (meth)acryloyl group, and more preferably a (meth)acrylic acid ester having at least one selected from the group consisting of an isocyanato group and a blocked isocyanato group. The proportion of structural units derived from a (meth)acrylic acid ester having at least one selected from the group consisting of an isocyanato group and a blocked isocyanato group in the fourth structural unit is preferably 80 mol% or more, may be 90 mol% or more, or may be 99 mol% or more.

[0039] The proportion of the blocked isocyanato groups in the total amount of isocyanato groups and blocked isocyanato groups in the binder polymer (P) is preferably 50 mol % or more, or may be 70 mol % or more, or may be 90 mol % or more, or may be 100 mol %. When the isocyanato groups are blocked, conversion of the isocyanato groups to amino groups by hydrolysis is easily suppressed.

[0040] A blocked isocyanato group refers to a functional group formed by bonding an isocyanato group with a blocking agent. The blocked isocyanato group preferably has a structure that allows control of its conversion to an isocyanato group. The blocked isocyanato group preferably has a structure that generates an isocyanato group in response to an external stimulus, a chemical reaction, or the like, and more preferably has a structure that generates an isocyanato group in response to at least one reaction selected from the group consisting of heating, voltage application, and chemical reaction. The conversion of a blocked isocyanato group to an isocyanato group can occur when the blocking agent is eliminated by a redox reaction, such as a reaction due to heating, a chemical reaction with a Lewis acid, a Bronsted acid, or the like, or an electrochemical reaction due to voltage application. Examples of blocking agents include methyl salicylate, 3,5-dimethylpyrazole, 2-butanone oxime (methyl ethyl ketoxime), ε-caprolactam, and 1-methoxy-2-propanol. The blocking agent preferably contains at least one selected from the group consisting of methyl salicylate, 3,5-dimethylpyrazole, and 2-butanone oxime, because it is easily removed.

[0041] [Fifth structural unit] The binder polymer (P) may or may not contain a fifth structural unit derived from the polyfunctional monomer (a5). From the viewpoint of ensuring the electrolyte resistance of the binder polymer (P), it is preferable that the binder polymer (P) contains the fifth structural unit. The binder polymer (P) may have a crosslinked structure formed by the fifth structural unit. The binder polymer (P) may contain one type of fifth structural unit alone, or may contain two or more types. The number of ethylenically unsaturated bonds contained in the polyfunctional monomer (a5) is two or more, preferably 2 to 6, and may be 2 to 4, or may be 2 or 3.

[0042] Examples of the polyfunctional monomer (a5) from which the fifth structural unit is derived 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. From the viewpoint of polymerization stability when producing the binder polymer (P), the fifth structural unit preferably contains a structural unit derived from divinylbenzene. The proportion of the structural unit derived from divinylbenzene in the fifth structural unit is preferably 80 mol or more, and may be 90 mol% or more, or may be 100 mol%.

[0043] [Other structural units] Examples of compounds from which other structural units not corresponding to any of the first to fifth structural units are derived include, but are not limited to, compounds having one ethylenically unsaturated bond and having an anionic functional group other than a carboxyl group, such as a sulfo group or a phosphate group, or salts thereof, surfactants having one ethylenically unsaturated bond (hereinafter may be referred to as "polymerizable surfactants"), and compounds having one ethylenically unsaturated bond and functioning as a silane coupling agent (hereinafter may be referred to as "polymerizable silane coupling agents").

[0044] Examples of the compound having one ethylenically unsaturated bond and a sulfo group and a salt thereof include an aromatic vinyl compound having a sulfo group, an aromatic vinyl compound having a sulfo group in the form of a salt, etc. Among these, the binder polymer (P) preferably contains a structural unit derived from p-styrenesulfonic acid, and from the viewpoint of polymerization stability when producing the binder polymer (P), it is more preferable that some or all of the sulfo groups form a salt.

[0045] Examples of polymerizable surfactants from which other structural units can be derived include compounds represented by the following formulas (1) to (4).

[0046]

[0047] In formula (1), R １ represents an alkyl group, and p represents an integer of 10 to 40. １ The alkyl group represented by the formula (R) preferably has 5 to 20 carbon atoms. １ The alkyl group represented by R may be linear, branched, or cyclic, and is preferably linear. １ The alkyl group represented by the formula (I) may have a substituent, but is preferably unsubstituted. １ is more preferably a straight-chain unsubstituted alkyl group having 5 to 20 carbon atoms.

[0048]

[0049] In formula (2), R ２ represents an alkyl group, and q represents an integer of 10 to 40. ２ The alkyl group represented by the formula (R) preferably has 5 to 20 carbon atoms. ２ The alkyl group represented by R may be linear, branched, or cyclic, and is preferably linear. ２ The alkyl group represented by the formula (I) may have a substituent, but is preferably unsubstituted. ２ is more preferably a straight-chain unsubstituted alkyl group having 5 to 20 carbon atoms.

[0050] Examples of the compound represented by formula (2) include polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt (Aqualon KH-10, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0051]

[0052] In formula (3), R ３ represents an alkyl group, M １ is NH ４ or Na. ３ The alkyl group represented by the formula (R) preferably has 5 to 20 carbon atoms. ３ The alkyl group represented by R may be linear, branched, or cyclic, and is preferably linear. ３The alkyl group represented by the formula (I) may have a substituent, but is preferably unsubstituted. ３ is more preferably a straight-chain unsubstituted alkyl group having 5 to 20 carbon atoms.

[0053]

[0054] In formula (4), R ４ represents an alkyl group, M ２ is NH ４ or Na. ４ The alkyl group represented by the formula (R) preferably has 5 to 20 carbon atoms. ４ The alkyl group represented by R may be linear, branched, or cyclic, and is preferably linear. ４ The alkyl group represented by the formula (I) may have a substituent, but is preferably unsubstituted. ４ is more preferably a straight-chain unsubstituted alkyl group having 5 to 20 carbon atoms.

[0055] Examples of polymerizable silane coupling agents from which other structural units can be derived include vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, and γ-methacryloxypropyltriethoxysilane.

[0056] [Content of each structural unit in binder polymer (P)] The total content of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit (hereinafter, the "first structural unit, the second structural unit, the third structural unit, and the fourth structural unit" may also be referred to as "first to fourth structural units") in the binder polymer (P) is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 97% by mass or more. It may be 98% by mass or more, or even 100% by mass. The total content of the first to fourth structural units in the binder polymer (P) may be 99.5% by mass or less.

[0057] The total content of the first to fourth structural units in the binder polymer (P) may be 90% by mass to 100% by mass, 95% by mass to 100% by mass, 97% by mass to 99.5% by mass, or 98% by mass to 99.5% by mass. Hereinafter, the content of each of the first to fourth structural units means the proportion of the amount of each structural unit in the total amount of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit.

[0058] The content of the first structural unit among the first to fourth structural units is preferably 35 mol% or more, more preferably 40 mol% or more, and even more preferably 45 mol% or more. The content of the first structural unit among the first to fourth structural units may be 53 mol% or more, or may be 59 mol% or more. When the content of the first structural unit is within the above range, the heat resistance of the binder polymer (P) is improved, and electrodes using the binder polymer (P) and batteries including the electrodes tend to have excellent durability during high-temperature storage.

[0059] The content of the first structural unit among the first to fourth structural units is preferably 80 mol% or less, more preferably 70 mol% or less, and even more preferably 65 mol% or less. The content of the first structural unit among the first to fourth structural units may be 59 mol% or less, or may be 53 mol% or less. When the content of the first structural unit is within the above range, the flexibility of the binder polymer (P) is improved, and the processability of an electrode using the binder polymer (P) tends to be easily ensured.

[0060] The content of the first structural unit in the first to fourth structural units may be 35 mol% to 80 mol%, 40 mol% to 70 mol%, 45 mol% to 65 mol%, 53 mol% to 59 mol%, 59 mol% to 65 mol%, or 45 mol% to 53 mol%.

[0061] The content of the second structural unit in the first to fourth structural units is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more. The content of the second structural unit in the first to fourth structural units may be 25 mol% or more, or may be 34 mol% or more. When the content of the second structural unit is within the above range, the flexibility of the binder polymer (P) is improved, and the processability of an electrode using the binder polymer (P) tends to be easily ensured.

[0062] The content of the second structural unit among the first to fourth structural units is preferably 55 mol% or less, more preferably 50 mol% or less, and even more preferably 45 mol% or less. The content of the first structural unit among the first to fourth structural units may be 40 mol% or less, or may be 34 mol% or less. When the content of the second structural unit is within the above range, swelling and elution of the binder polymer (P) in the electrolyte solution are suppressed, and peeling of the electrode active material layer from the current collector in an electrolyte solution immersion environment tends to be further suppressed.

[0063] The content of the second structural unit in the first to fourth structural units may be 10 mol% to 55 mol%, 15 mol% to 50 mol%, 20 mol% to 45 mol%, 25 mol% to 40 mol%, 34 mol% to 40 mol%, or 25 mol% to 34 mol%.

[0064] With respect to the first structural unit and the second structural unit, it is preferable to appropriately set the type and amount of the monomer from the viewpoint of adjusting the glass transition temperature of the binder polymer (P) or adjusting the polymerization rate according to the molecular design.

[0065] From the viewpoint of further suppressing peeling of the electrode active material layer from the current collector, the content of the third structural unit among the first to fourth structural units is preferably 1.0 mol% or more, more preferably 4.0 mol% or more, even more preferably 6.0 mol% or more, and particularly preferably 7.5 mol% or more.

[0066] From the viewpoint of polymerization stability during production of the binder polymer (P), the content of the third structural unit among the first to fourth structural units is preferably 20 mol % or less, more preferably 15 mol % or less, and even more preferably 10 mol % or less.

[0067] The content of the third structural unit in the first to fourth structural units may be 1.0 mol % to 20 mol %, 4.0 mol % to 15 mol %, or 7.5 mol % to 10 mol %.

[0068] The content of the fourth structural unit among the first to fourth structural units is preferably 0.10 mol% or more, more preferably 0.40 mol% or more, and even more preferably 0.60 mol% or more. The content of the fourth structural unit among the first to fourth structural units may be 0.90 mol% or more, 2.5 mol% or more, or even 4.5 mol% or more. When the content of the fourth structural unit is within the above range, the high-temperature storage properties of an electrode containing the binder polymer (P) tend to be further improved.

[0069] The content of the fourth structural unit among the first to fourth structural units is preferably 15 mol% or less, more preferably 10 mol% or less, even more preferably 7.5 mol% or less, and particularly preferably 6.5 mol% or less. The content of the fourth structural unit among the first to fourth structural units may be 4.5 mol% or less, 2.5 mol% or less, or even 0.90 mol% or less. When the content of the fourth structural unit is within the above range, polymerization stability during production of the binder polymer (P) is improved, thereby improving yield and tending to reduce the production cost of the binder polymer (P).

[0070] The content of the fourth structural unit in the first to fourth structural units may be 0.10 to 15 mol%, 0.40 to 10 mol%, 0.60 to 7.5 mol%, 0.60 to 6.5 mol%, 0.60 to 4.5 mol%, 0.60 to 2.5 mol%, 0.60 to 0.90 mol%, 0.90 to 6.5 mol%, 2.5 to 6.5 mol%, or 4.5 to 6.5 mol%.

[0071] When the binder polymer (P) contains the fifth structural unit, the content of the fifth structural unit relative to the total content of the first to fourth structural units is preferably 0.010 mol % or more, more preferably 0.020 mol % or more, and even more preferably 0.030 mol % or more. When the content of the fifth structural unit is within the above range, the number of internal crosslinking sites in the binder polymer (P) increases, which suppresses deterioration of the binder polymer (P), and tends to result in a nonaqueous secondary battery with better cycle characteristics.

[0072] From the viewpoint of suppressing gelation of the binder polymer (P), the content of the fifth structural unit relative to the total content of the first to fourth structural units is preferably 5.0 mol % or less, more preferably 1.0 mol % or less, even more preferably 0.10 mol % or less, and particularly preferably 0.070 mol parts or less.

[0073] The content of the fifth structural unit relative to the total content of the first to fourth structural units may be 0.010 mol% to 5.0 mol%, 0.020 mol% to 1.0 mol%, 0.030 mol% to 0.10 mol%, or 0.030 mol% to 0.070 mol%.

[0074] When the binder polymer (P) contains, as another structural unit, a structural unit derived from a compound having one ethylenically unsaturated bond and having a sulfo group or a salt thereof (also referred to as a "structural unit having a sulfo group"), the content of the structural unit having a sulfo group relative to the total content of the first to fourth structural units is preferably 0.10 mol% or more, more preferably 0.20 mol% or more, and even more preferably 0.30 mol% or more. When the content of the structural unit having a sulfo group is within the above range, the polymerization stability during production of the binder polymer (P) is improved, thereby improving the yield and tending to reduce the production cost of the binder polymer (P).

[0075] The content of the structural unit having a sulfo group relative to the total content of the first to fourth structural units is preferably 5.0 mol % or less, more preferably 3.0 mol % or less, even more preferably 1.0 mol % or less, and may be 0.50 mol % or less. When the content of the structural unit having a sulfo group is within the above range, it tends to be easier to appropriately adjust the particle size, viscosity, etc. of the binder polymer (P).

[0076] The content of the structural unit having a sulfo group relative to the total content of the first to fourth structural units may be 0.10 mol% to 5.0 mol%, 0.20 mol% to 3.0 mol%, 0.30 mol% to 1.0 mol%, or 0.30 mol% to 0.50 mol%.

[0077] [Glass transition temperature Tg of binder polymer (P)] The glass transition temperature Tg of the binder polymer (P) is preferably −30° C. or higher, more preferably −20° C. or higher, even more preferably −10° C. or higher, and particularly preferably 0° C. or higher. When the glass transition temperature Tg of the binder polymer (P) is within the above range, a nonaqueous secondary battery equipped with an electrode containing the binder polymer (P) tends to 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 30° C. or lower, and may be 20° C. or lower, or may be 10° C. or lower. When the glass transition temperature Tg is within the above range, the film-forming properties of the binder polymer (P) are improved, and a nonaqueous secondary battery equipped with an electrode containing the binder polymer (P) tends to have excellent cycle characteristics. The glass transition temperature Tg of the binder polymer (P) may be −30° C. to 100° C., −20° C. to 50° C., −10° C. to 30° C., 0° C. to 30° C., 0° C. to 20° C., or 0° C. to 10° C.

[0078] The glass transition point Tg of the binder polymer (P) is the peak top temperature of a chart obtained as a temperature derivative when measurement is performed using a differential scanning calorimetry (DSC) device (e.g., EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Corporation) at a temperature rise rate of 10°C / min under a nitrogen gas atmosphere.

[0079] [Method for producing binder polymer (P)] The binder polymer (P) of the present disclosure can be produced by copolymerizing monomers for forming each structural unit (polymerization step). The monomers used to synthesize the binder polymer (P) include an aromatic hydrocarbon monomer (a1), a nonionic monomer (a2), a carboxylic acid monomer (a3), and an isocyanate monomer (a4), and may further include other monomers. These multiple types of monomers are collectively referred to as "monomer (a)."

[0080] Examples of the method for copolymerizing the monomer (a) include an emulsion polymerization method in which the monomer (a) is emulsion-polymerized in an aqueous medium (b). When producing the binder polymer (P) by the emulsion polymerization method, in addition to the monomer (a) and the aqueous medium (b), components such as a non-polymerizable surfactant (c), a basic substance (d), a radical polymerization initiator (e), and a chain transfer agent (f) can be used.

[0081] -Aqueous Medium (b)- The aqueous medium (b) is preferably at least one selected from the group consisting of water and hydrophilic solvents. The hydrophilic solvent may be used alone or in combination of two or more. Examples of the hydrophilic solvent include methanol, ethanol, isopropyl alcohol, and N-methylpyrrolidone. From the viewpoint of polymerization stability, the aqueous medium (b) is preferably water. A mixture of water and a hydrophilic solvent may also be used as the aqueous medium (b).

[0082] -Non-polymerizable surfactant (c)- When producing the binder polymer (P) by emulsion polymerization, a liquid containing an aqueous medium (b) and a monomer (a) may contain a non-polymerizable surfactant (c) and undergo emulsion polymerization. The non-polymerizable surfactant (c) is a surfactant (c) that does not have an ethylenically unsaturated bond in its chemical structure. The surfactant (c) improves the dispersion stability of at least one of the liquid during emulsion polymerization and the dispersion liquid (emulsion) obtained after polymerization. It is preferable to use an anionic surfactant or a nonionic surfactant as the surfactant (c).

[0083] 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 alkyl phenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. The surfactant (c) may be used alone or in combination of two or more.

[0084] - Basic substance (d) - When producing the binder polymer (P) by emulsion polymerization, a basic substance (d) may be added to at least one of the liquid to be emulsion-polymerized containing the aqueous medium (b) and the monomer (a) and the dispersion liquid after emulsion polymerization. By adding the basic substance (d), the acidic component contained in the monomer (a) is neutralized. As a result, the pH of the liquid to which the basic substance (d) has been added falls within an appropriate range, and the stability of the liquid is improved.

[0085] Examples of the basic substance (d) include ammonia, triethylamine, sodium hydroxide, lithium hydroxide, etc. The basic substance (d) may be used alone or in combination of two or more.

[0086] -Radical Polymerization Initiator (e)- When producing the binder polymer (P) by emulsion polymerization, a radical polymerization initiator (e) may be used. Examples of the radical polymerization initiator (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.

[0087] When the binder polymer (P) is produced by emulsion polymerization, redox polymerization may be carried out by using a reducing agent such as sodium bisulfite, Rongalite, or ascorbic acid together with the radical polymerization initiator (e).

[0088] The amount of radical polymerization initiator (e) added (including the reducing agent when used in combination) is preferably 0.001 parts by mass or more, more preferably 0.002 parts by mass or more, even more preferably 0.005 parts by mass or more, and particularly preferably 0.01 parts by mass or more, relative to 100 parts by mass of monomer (a). When the amount of radical polymerization initiator (e) added is within the above range, there is a tendency for the conversion rate of monomer (a) to binder polymer (P) to be increased when producing binder polymer (P) by emulsion polymerization. The amount of radical polymerization initiator (e) added is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less, even more preferably 2.0 parts by mass or less, and particularly preferably 1.0 part by mass or less, relative to 100 parts by mass of monomer (a). When the amount of radical polymerization initiator (e) added is within the above range, the molecular weight of the binder polymer (P) can be increased, and the swelling ratio of a non-aqueous secondary battery electrode containing the binder polymer (P) in an electrolytic solution tends to be reduced. The amount of radical polymerization initiator (e) added may be 0.001 to 10 parts by mass, 0.002 to 5.0 parts by mass, 0.005 to 2.0 parts by mass, or 0.01 to 1.0 part by mass, relative to 100 parts by mass of the monomer (a).

[0089] Chain Transfer Agent (f) When producing the binder polymer (P) by emulsion polymerization, a chain transfer agent (f) may be used from the viewpoint of adjusting the molecular weight of the binder polymer (P) obtained by emulsion polymerization. Examples of the chain transfer agent (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, benzyl alcohol, and α-methylstyrene dimer.

[0090] (Emulsion Polymerization Method) Examples of the emulsion polymerization method used in producing the binder polymer (P) include a method in which emulsion polymerization is carried out while continuously supplying each component to be used in emulsion polymerization into a reaction vessel. The temperature of the emulsion polymerization is not particularly limited and may be, for example, 30°C to 90°C, 50°C to 85°C, or 55°C to 80°C. The emulsion polymerization is preferably carried out with stirring. Furthermore, it is preferable to continuously supply the monomer (a) and the radical polymerization initiator (e) to the liquid during emulsion polymerization so that the concentrations of the monomer (a) and the radical polymerization initiator (e) in the liquid during emulsion polymerization are uniform.

[0091] (2) Binder for Non-Aqueous Secondary Battery The binder for non-aqueous secondary battery of the present disclosure includes the binder polymer (P) of the present disclosure. Note that in the binder for non-aqueous secondary battery, functional groups contained in the binder polymer (P) may react with other components, resulting in a partial change in the structure of the binder polymer (P). In this case, the structure of the binder polymer (P) after the reaction is also referred to as the binder polymer (P). That is, in the binder for non-aqueous secondary battery, the binder polymer (P) includes the corresponding polymer and the structure of the polymer after reaction with other components.

[0092] The binder for a non-aqueous secondary battery may contain a polymer other than the binder polymer (P), a surfactant, etc. The binder for a non-aqueous secondary battery is obtained by mixing these components.

[0093] The binder for a non-aqueous secondary battery is composed of components that remain without volatilizing even when a heating step is performed in the manufacturing method for a non-aqueous secondary battery, which will be described later with respect to the binder composition for a non-aqueous secondary battery. Specifically, the components that constitute the binder for a non-aqueous secondary battery are components that remain as a solid or liquid after weighing out 1 g of the binder composition for a non-aqueous secondary battery containing the binder polymer (P), placing it on an aluminum dish with a diameter of 5 cm, placing it in a dryer, and drying it at 1 atmosphere (1013 hPa) and a temperature of 105°C for 1 hour while circulating air in the dryer.

[0094] The content of the binder polymer (P) contained in the binder for a non-aqueous secondary battery is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and still more preferably 98% by mass or more, because the effect of including the binder polymer (P) becomes significant.

[0095] (3) Binder Composition for Non-Aqueous Secondary Batteries The binder composition for non-aqueous secondary batteries of the present disclosure (hereinafter sometimes abbreviated as the binder composition) includes the binder polymer (P) of the present disclosure and an aqueous medium (B). The binder composition may be obtained by mixing the binder polymer (P) of the present disclosure with an aqueous medium, or by mixing the binder for non-aqueous secondary batteries of the present disclosure with an aqueous medium. Note that in the binder composition, functional groups contained in the binder polymer (P) may react with other components, causing a partial change in the structure of the binder polymer (P). In this case, the structure of the binder polymer (P) after the reaction is also referred to as the binder polymer (P). In other words, in the binder composition, the binder polymer (P) includes the corresponding polymer and the structure of the polymer after reaction with other components.

[0096] The binder composition is preferably an emulsion in which particles containing the binder polymer (P) are dispersed in an aqueous medium (B). Examples of the particles containing the binder polymer (P) include particles made of the binder polymer (P), particles containing the binder polymer (P) and a surfactant, and particles containing other components. The binder composition may also contain both particles containing the binder polymer (P) and particles not containing the binder polymer (P).

[0097] The binder composition may contain other components in addition to the binder polymer (P) and the aqueous medium (B). Specifically, the binder composition may contain the components used in the synthesis of the binder polymer (P), etc.

[0098] The binder composition of the present disclosure may be a dispersion obtained by emulsion polymerization of the monomer (a). Alternatively, the binder composition of the present disclosure may be a dispersion in which a binder polymer (P) obtained by a method other than emulsion polymerization is dispersed in an aqueous medium (B).

[0099] [Aqueous Medium (B)] The aqueous medium (B) in the binder composition of the present disclosure is preferably at least one selected from the group consisting of water and hydrophilic solvents. The hydrophilic solvents may be used alone or in combination of two or more.

[0100] Examples of hydrophilic solvents include the same hydrophilic solvents as 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). When the binder composition is an emulsion obtained by emulsion polymerization, the aqueous medium (B) may be the aqueous medium (b) used in the synthesis of the binder polymer (P). The aqueous medium (B) may also be the aqueous medium (b) used in the synthesis of the binder polymer (P) to which a new aqueous medium has been added. The aqueous medium (B) may also be the aqueous medium obtained by replacing part or all of the aqueous medium (b) contained in the dispersion obtained by emulsion polymerization with a new aqueous solvent. The new aqueous medium used in this case may have the same composition as the aqueous medium (b) or a different composition.

[0101] [Non-volatile content concentration of binder composition] The non-volatile content concentration of the binder composition of the present disclosure is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, from the viewpoint of increasing the amount of active ingredients contained in the binder composition. The non-volatile content concentration of the binder composition can be adjusted by the content of the aqueous medium (B) contained in the binder composition. From the viewpoint of suppressing an increase in the viscosity of the binder composition and facilitating the preparation of the non-aqueous secondary battery electrode slurry described below, the non-volatile content concentration of the binder composition is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. The non-volatile content concentration of the binder composition is determined by weighing 1 g of the binder composition, placing it on an aluminum dish with a diameter of 5 cm, placing it in a dryer, and measuring the mass remaining as a solid or liquid after drying at 1 atmosphere (1013 hPa) and a temperature of 105°C for 1 hour while circulating air in the dryer.

[0102] (4) Electrode Slurry for Non-Aqueous Secondary Battery The electrode slurry for non-aqueous secondary battery (hereinafter also referred to as electrode slurry) of the present disclosure contains the binder polymer (P) of the present disclosure, an electrode active material, and an aqueous medium. Note that in the electrode slurry, functional groups contained in the binder polymer (P) may react with other components, causing the structure of the binder polymer (P) to partially change. In this case, the structure of the binder polymer (P) after the reaction is also referred to as the binder polymer (P). That is, in the electrode slurry, the binder polymer (P) includes the corresponding polymer and the structure of the polymer after reaction with other components.

[0103] The binder polymer (P) and the electrode active material contained in the electrode slurry are preferably dispersed in an aqueous medium. The electrode slurry may contain a thickener, a conductive additive, components used in the synthesis of the binder polymer (P), and the like.

[0104] The content of the binder polymer (P) in the electrode slurry is preferably 0.50 parts by mass or more, and more preferably 1.0 part by mass or more, relative to 100 parts by mass of the electrode active material. When the content of the binder polymer (P) is within the above range, the effect of including the binder polymer (P) tends to be more sufficiently exhibited.

[0105] The content of the binder polymer (P) in the electrode slurry 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, relative to 100 parts by mass of the electrode active material. When the content of the binder polymer (P) is within the above range, the content of the electrode active material in the electrode slurry can be increased, and the charge-discharge characteristics tend to be excellent.

[0106] [Electrode active material] The electrode active material contained in the electrode slurry is a material that allows intercalation and deintercalation of ions that serve as charge carriers, such as lithium ions. The ions that serve as charge carriers are preferably alkali metal ions, more preferably lithium ions, sodium ions, and potassium ions, and even more preferably lithium ions.

[0107] When the electrode for a nonaqueous secondary battery produced using the electrode slurry is a negative electrode, the electrode active material is a negative electrode active material. The negative electrode active material preferably includes at least one material selected from the group consisting of a carbon material, a silicon-containing material, and a titanium-containing material. These materials used as the negative electrode active material may be used alone, in combination with two or more types, or in a composite.

[0108] Examples of carbon materials used as negative electrode active materials include cokes such as petroleum coke, pitch coke, and coal coke, carbonized organic polymers, and graphites such as artificial graphite and natural graphite. Examples of silicon-containing materials used as negative electrode active materials include elemental silicon and silicon compounds such as silicon oxide. Examples of titanium-containing materials used as negative electrode active materials include lithium titanate.

[0109] The negative electrode active material preferably contains at least one selected from the group consisting of a carbon material and a silicon-containing material. When the negative electrode active material is the above material, the binder polymer (P) contained in the electrode slurry tends to have a greater effect of improving the binding between the negative electrode active materials and between the negative electrode active material and the current collector.

[0110] When the electrode for a non-aqueous secondary battery manufactured using the electrode slurry is a positive electrode, the electrode active material is a positive electrode active material. As the positive electrode active material, a material having a more noble standard electrode potential than the negative electrode active material is used. Specifically, as the positive electrode active material, lithium composite oxides containing nickel, such as Ni-Co-Mn-based lithium composite oxides, Ni-Mn-Al-based lithium composite oxides, and Ni-Co-Al-based lithium composite oxides, lithium cobalt oxide (LiCoO ２ ), spinel-type lithium manganese oxide (LiMn ２ O ４ ), olivine-type lithium iron phosphate, TiS ２ , MnO ２ , MoO ３ , V ２ O ５ These substances used as the positive electrode active material may be used alone or in combination of two or more.

[0111] [Aqueous Medium] The aqueous medium contained in the electrode slurry of the present disclosure is preferably one selected from the group consisting of water and hydrophilic solvents. Examples of the hydrophilic solvent include the same hydrophilic solvents as those exemplified as the aqueous medium (b) used in the synthesis of the binder polymer (P). The aqueous medium contained in the electrode slurry may be the same as or different from the aqueous medium (b) used in the synthesis of the binder polymer (P).

[0112] [Thickener] Examples of thickeners that can be contained in the electrode slurry include cellulose derivatives such as carboxymethyl cellulose (CMC), hydroxyethyl cellulose, and hydroxypropyl cellulose, ammonium salts of cellulose derivatives, alkali metal salts of cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, poly(meth)acrylates, poly(meth)acrylamide, poly(meth)N-hydroxyalkylacrylamide, etc. From the viewpoint of dispersibility of the electrode active material in the electrode slurry, it is preferable that the thickener contains at least one selected from the group consisting of carboxymethyl cellulose, ammonium salts of carboxymethyl cellulose, and alkali metal salts of carboxymethyl cellulose.

[0113] The content of the thickener contained in the electrode slurry 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 the electrode active material. When the content of the thickener is within the above range, the coating properties of the electrode slurry for a non-aqueous secondary battery tend to be good. The content of the thickener contained in the electrode slurry 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 the electrode active material. The binding between the electrode active materials contained in the electrode for a non-aqueous secondary battery prepared using the electrode slurry, and between the electrode active material and the current collector, tend to be good.

[0114] [Conductive Aid] Examples of conductive aids that can be contained in the electrode slurry include carbon black and carbon fiber. Examples of carbon black include furnace black, acetylene black, Denka Black (manufactured by Denka Co., Ltd.), and Ketjen Black (manufactured by Ketjen Black International Co., Ltd.). Examples of carbon fiber include carbon nanotubes and carbon nanofibers. Examples of carbon nanotubes include VGCF (manufactured by Resonac Co., Ltd.), which is a vapor-grown carbon fiber.

[0115] [Method for Producing Electrode Slurry] The electrode slurry of the present disclosure can be produced, for example, by mixing the binder polymer (P) of the present disclosure, an electrode active material, an aqueous medium, a thickener (if necessary), a conductive additive (if necessary), and other components (if necessary). Alternatively, the electrode slurry of the present disclosure can be obtained by mixing the binder for a non-aqueous secondary battery of the present disclosure, an electrode active material, an aqueous medium, a conductive additive (if necessary), and other components (if necessary). Alternatively, the electrode slurry of the present disclosure can be obtained by mixing the binder composition of the present disclosure, an electrode active material, a conductive additive (if necessary), and other components (if necessary). The mixing order of the components that are the raw materials for the electrode slurry is not particularly limited and can be determined as appropriate. Examples of methods for mixing the components include methods using a stirring, rotating, or shaking mixer.

[0116] (5) Electrode for Non-Aqueous Secondary Battery The electrode for a non-aqueous secondary battery of the present disclosure includes the binder polymer (P) of the present disclosure. In the following description, unless otherwise specified, the term "electrode" refers to an electrode for a non-aqueous secondary battery. In addition, functional groups contained in the binder polymer (P) may react in the electrode, causing the structure of the binder polymer (P) to partially change. In this case, the structure of the binder polymer (P) after the reaction is also referred to as the binder polymer (P). In other words, in the electrode, the binder polymer (P) includes the corresponding polymer and the structure of the polymer after the reaction and change.

[0117] The electrode generally comprises a current collector and an electrode active material layer formed on the current collector. The shape of the electrode is not particularly limited, and examples thereof include a laminate and a wound body.

[0118] The area on the current collector where the electrode active material layer is formed is not particularly limited, and the electrode active material layer may be formed on the entire surface of the current collector, or may be formed on only a part of the surface of the current collector. When the current collector is in the shape of a plate, foil, or the like, the electrode active material layer may be formed on both surfaces of the current collector, or may be formed on only one surface.

[0119] [Current Collector] The current collector is preferably a metal sheet. Examples of metals forming the metal sheet include iron, copper, aluminum, nickel, and stainless steel. When the electrode of the present disclosure is a negative electrode of a lithium ion secondary battery, the current collector is preferably a copper foil. The thickness of the metal sheet is not particularly limited, and is preferably 0.001 mm to 0.5 mm.

[0120] [Electrode active material layer] The electrode active material layer contains the binder polymer (P) of the present disclosure and an electrode active material. The electrode active material layer may contain a conductive aid, a thickener, etc. The electrode active material, the conductive aid, and the thickener may all be the same as those exemplified as components of the electrode slurry.

[0121] [Method for manufacturing an electrode] The electrode of the present disclosure can be manufactured, for example, by the method described below. First, the electrode slurry of the present disclosure is applied to a current collector. Next, the electrode slurry is dried to obtain an electrode sheet in which an electrode active material layer is formed on the current collector. Thereafter, if necessary, the electrode sheet is cut to a size and shape appropriate for the size and shape of the nonaqueous secondary battery to obtain an electrode. Note that if cutting is not necessary, the electrode sheet may be used as an electrode as is.

[0122] The method for applying the electrode slurry to the current collector is not particularly limited, and examples thereof include a reverse roll method, a direct roll method, a doctor blade method, a knife method, an extrusion method, a curtain method, a gravure method, a bar method, a dip method, and a squeeze method. Among these application methods, in consideration of the physical properties such as viscosity of the electrode slurry and drying properties, it is preferable to use at least one method selected from the group consisting of a direct roll method, a doctor blade method, a knife method, and an extrusion method. When these methods are applied, an electrode active material layer having a smooth surface and small thickness variation tends to be obtained.

[0123] When the electrode slurry is applied to both sides of the current collector, it may be applied to each side sequentially or simultaneously. The electrode slurry may be applied to the current collector continuously or intermittently. The amount of electrode slurry to be applied can be determined appropriately depending on the design capacity of the battery, the composition of the electrode slurry, and the like.

[0124] The method for drying the electrode slurry applied to the current collector is not particularly limited, and for example, hot air drying, reduced pressure drying, vacuum drying, (far) infrared drying, low temperature air drying, or a combination thereof can be used.

[0125] The drying temperature and drying time when drying the electrode slurry can be appropriately adjusted depending on the nonvolatile content concentration in the electrode slurry, the amount of the electrode slurry applied to the current collector, etc. The drying temperature is preferably 40°C to 350°C, and from the viewpoint of productivity, more preferably 60°C to 100°C. The drying time is preferably 1 minute to 30 minutes.

[0126] The electrode sheet in which the electrode active material layer is formed on the current collector may be cut to a size and shape appropriate for the electrode. The method for cutting the electrode sheet is not particularly limited, and slitting, laser cutting, wire cutting, a cutter, a Thomson cutter, or the like may be used.

[0127] In the present disclosure, the electrode sheet may be pressed as needed before or after cutting, which allows the electrode active material to be more firmly bound to the current collector and also reduces the thickness of the electrode, thereby enabling the nonaqueous secondary battery to be made smaller.

[0128] The electrode sheet can be pressed by a general method, and it is particularly preferable to use a mold pressing method or a roll pressing method.

[0129] When using the mold pressing method, the pressing pressure is not particularly limited, and is preferably 0.5 t / cm ２ ~5t / cm ２ It is preferable to set the following.

[0130] When the roll press method is used, the press load is not particularly limited, but is preferably 0.5 t / cm to 8 t / cm. When the press load is in this range, the above-mentioned effects of pressing can be easily obtained, and a decrease in the insertion and desorption capacity of charge carriers such as lithium ions into and from the electrode active material tends to be suppressed.

[0131] (6) Nonaqueous Secondary Battery The nonaqueous secondary battery of the present disclosure includes the electrode for a nonaqueous secondary battery of the present disclosure. Hereinafter, a lithium ion secondary battery will be described as a preferred example of the nonaqueous secondary battery according to the present disclosure. Note that the configuration of the nonaqueous secondary battery of the present disclosure is not limited to the example shown below.

[0132] An example of a lithium ion secondary battery has a configuration in which a positive electrode, a negative electrode, and an electrolyte are housed in an exterior body. In addition to the above configuration, the lithium ion secondary battery may include, for example, a separator between the positive electrode and the negative electrode, or may include other components. The shape of the lithium ion secondary battery may be any shape, such as a coin type, a button type, a sheet type, a cylindrical type, a prismatic type, or a flat type.

[0133] [Positive electrode and negative electrode] In the lithium ion secondary battery of the present disclosure, one or both of the positive electrode and the negative electrode contain the binder polymer (P) of the present disclosure. The binder polymer (P) is preferably contained in an electrode active material layer of the electrode. Of the positive electrode and the negative electrode, at least the negative electrode preferably contains the binder polymer (P), and it is more preferable that the negative electrode has an electrode active material layer containing the binder polymer (P).

[0134] In the lithium ion secondary battery of the present disclosure, when only one of the positive electrode and the negative electrode contains the binder polymer (P) of the present disclosure, the other electrode contains polyvinylidene fluoride or the like as a binder.

[0135] [Electrolyte] It is preferable to use a non-aqueous liquid having ion conductivity as the electrolyte. Examples of the electrolyte include a solution in which an electrolyte is dissolved in an organic solvent, an ionic liquid, etc. The former is preferable from the viewpoint of obtaining a lithium ion secondary battery with low production cost and low internal resistance.

[0136] The electrolyte can be an alkali metal salt, and can be appropriately selected depending on the type of electrode active material, etc. The electrolyte can be LiClO ４ , LiBF ６ , LiPF ６ , LiCF ３ SO ３ , LiCF ３ CO ２, LiAsF ６ , LiSbF ６ , LiB １０ Cl １０ , LiAlCl ４ , LiCl, LiBr, LiB(C ２ H ５ ) ４ , C.F. ３ SO ３ Li, C.H. ３ SO ３ Li, LiCF ３ SO ３ , LiC ４ F ９ SO ３ , Li(CF ３ SO ２ ) ２ Examples of the electrolyte include lithium carboxylate, lithium cations of N, and aliphatic carboxylates. Other alkali metal salts can also be used as the electrolyte.

[0137] The organic solvent for dissolving the electrolyte is not particularly limited, and examples thereof 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), and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The organic solvent may be used alone or in combination of two or more. Among these, it is preferable to use two or more linear carbonate solvents in combination as the organic solvent.

[0138] The electrolyte may contain additives in addition to the above components. Examples of additives include nitrile compounds, sulfur-containing compounds, and boron-containing compounds. Examples of nitrile compounds include succinonitrile and acetonitrile. Examples of sulfur-containing compounds include compounds having a sulfonyl group, sulfonate group, or sultone structure, such as methyl ethyl sulfone and 1,3-propane sultone. Examples of boron-containing compounds include boric acid esters.

[0139] [Exterior Body] As the exterior body, an exterior body formed of an aluminum laminate material made of aluminum foil and a resin film can be appropriately used, but is not limited to this.

[0140] Hereinafter, one example of the embodiment of the present disclosure will be specifically described using examples, but the embodiment is not limited to these examples.

[0141] In the following examples, a negative electrode of a lithium ion secondary battery was fabricated as an example of an electrode for a nonaqueous secondary battery according to the present disclosure, and a lithium ion secondary battery was fabricated as an example of a nonaqueous secondary battery, and these were compared with the negative electrode of a lithium ion secondary battery and the lithium ion secondary battery of comparative examples. Furthermore, unless otherwise specified, the water used in the following examples and comparative examples is ion-exchanged water.

[0142] <Production of binder polymer and non-aqueous secondary battery binder composition> In each example and comparative example, an emulsion was prepared by mixing the respective monomers in the amounts shown in Table 1 or Table 2. The values ​​in the "mass %" column in Table 1 and Table 2 represent the content (mass %) of each monomer relative to the total amount of monomers. The values ​​in the "mol %" column in Table 1 and Table 2 represent the content (mol %) of each monomer relative to the total amount (mol) of (a1) to (a4). Next, an aqueous solution was prepared by dissolving the polymerization initiator (e) in the amount shown in Table 1 or Table 2 in 50 parts by mass of water. 150 parts by mass of water was placed in a separable flask equipped with a cooling tube, thermometer, stirrer, and dropping funnel, and the temperature was raised to 80°C. The monomer emulsion and the aqueous solution in which the polymerization initiator (e) was dissolved were continuously supplied to the separable flask over a period of 3 hours at 80°C while being stirred, thereby carrying out emulsion polymerization, thereby obtaining emulsions containing particles containing the binder polymer of Examples 1 to 7 or Comparative Examples 1 to 4 and an aqueous medium.

[0143] The resulting emulsion was cooled to room temperature (25°C). Then, 133 parts by mass of water and 25% by mass of aqueous ammonia were added. This produced the nonaqueous secondary battery binder compositions of Examples 1 to 7 and Comparative Examples 1 to 4, which were emulsions in which particles containing the binder polymer of Examples 1 to 7 or Comparative Examples 1 to 4 were dispersed in an aqueous medium.

[0144]

[0145]

[0146] The abbreviations for the monomers in Tables 1 and 2 represent the following: St: styrene 2-EHA: 2-ethylhexyl acrylate BA: butyl acrylate BzMA: benzyl methacrylate 2-HEMA: 2-hydroxyethyl methacrylate AA: acrylic acid IA: itaconic acid DVB: divinylbenzene p-StSANa: sodium p-styrenesulfonate GMA: glycidyl methacrylate KH-10: polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt (Aqualon KH-10, polymerizable surfactant, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)

[0147] As the isocyanate monomer (a4), a compound having a methacryloyloxy group and a blocked isocyanate group was used. Specifically, they are as follows: MOI-SM: 2-[[[[2-[(2-methyl-1-oxo-2-propen-1-yl)oxy]ethyl]amino]carbonyl]oxy]-methyl benzoate (Karenz (registered trademark) MOI-SM (manufactured by Resonac Co., Ltd.)) MOI-BP: 2-[(3,5-dimethylpyrazolyl)carbonylamino]ethyl methacrylate (Karenz MOI-BP (manufactured by Resonac Co., Ltd.)) MOI-BM: 2-[0-(1'-methylpropylideneamino)carboxyamino]ethyl methacrylate (Karenz MOI-BM (manufactured by Resonac Co., Ltd.))

[0148] Rongalit SFS in the polymerization initiator (e) is the trade name of Rongalit manufactured by Sumitomo Seika Chemicals Co., Ltd. The amount of ammonia as the basic substance (d) shown in Table 1 or Table 2 is the amount (parts by mass) of ammonia contained in aqueous ammonia. The amount of water as the aqueous medium (b) shown in Table 1 or Table 2 is the total amount (parts by mass) of water contained in the nonaqueous secondary battery binder composition.

[0149] [Measurement of Glass Transition Temperature Tg] The nonaqueous secondary battery binder compositions of Examples 1 to 7 or Comparative Examples 1 to 4 were 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 the binder polymer. Square test pieces measuring 2 mm in length and 2 mm in width were cut from the obtained film. The test pieces were sealed in aluminum pans, and differential scanning calorimetry (DSC) measurements were performed on the test pieces at a heating rate of 10°C / min under a nitrogen gas atmosphere using a differential scanning calorimeter (EXSTAR DSC / SS7020, manufactured by Hitachi High-Tech Science Corporation). The temperature range for DSC measurements was -40°C to 200°C. The peak-top temperature of the DDSC chart obtained as the temperature derivative of DSC was then measured, and this temperature was designated as the glass transition temperature Tg (°C) of the binder polymer.

[0150] [Measurement of Nonvolatile Content of Binder Composition] 1 g of each of the binder compositions for nonaqueous secondary batteries of Examples 1 to 7 or Comparative Examples 1 to 4 was weighed out, placed on an aluminum dish with a diameter of 5 cm, and placed in a dryer. While circulating air in the dryer, the composition was dried at 1 atmosphere (1013 hPa) and a temperature of 105°C for 1 hour, and the mass of the remaining components was measured. The mass ratio (mass%) of the components remaining after drying relative to the mass (1 g) of the binder composition for nonaqueous secondary batteries before drying was calculated, and this was taken as the nonvolatile content concentration (mass%).

[0151] <Production of Non-Aqueous Secondary Battery> Negative electrodes were produced by the method described below using the binder compositions for non-aqueous secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 4, respectively, and lithium ion secondary batteries, which are the non-aqueous secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 4, were produced using these negative electrodes.

[0152] (Preparation of Positive Electrode) LiNi as Positive Electrode Active Material ０．６ Mn ０．２ Co ０．２ O ２ 94 parts by mass of the cathode active material, 3 parts by mass of acetylene black as a conductive additive, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to obtain a mixture, and 50 parts by mass of N-methylpyrrolidone was added to the obtained mixture and further mixed to obtain a positive electrode slurry.

[0153] A 15 μm thick aluminum foil was prepared as a positive electrode current collector. The positive electrode slurry was applied to both sides of the positive electrode current collector by a 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 below 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 pressed by a roll press method using a roll press (manufactured by Thank Metals, press load 5 t / cm, roll width 7 cm) to obtain a positive electrode sheet having a positive electrode active material layer on both sides of the positive electrode current collector. The obtained positive electrode sheet was cut into a rectangle 50 mm long and 40 mm wide, and a conductive tab was attached to form a positive electrode.

[0154] (Preparation of negative electrode (electrode for non-aqueous secondary battery)) 96.9 parts by mass of artificial graphite (G49, manufactured by Jiangxi Zishen Technology Co., Ltd.) as a negative electrode active material, 3.6 parts by mass of any of the binder compositions for non-aqueous secondary batteries produced in Examples 1 to 7, and Comparative Examples 1 to 4 (non-volatile content (binder polymer) 1.4 parts by mass), and 60 parts by mass of a 2% by mass aqueous solution of CMC (carboxymethyl cellulose-sodium salt, manufactured by Nippon Paper Chemicals Co., Ltd., Sunrose MAC500LC), were mixed, and 16 parts by mass of water was added, and the mixture was mixed using a planetary centrifugal mixer (ARE-310, manufactured by Thinky Corporation) to obtain a negative electrode slurry (slurry for electrodes for non-aqueous secondary batteries).

[0155] A copper foil with a thickness of 10 μm was prepared as the negative electrode current collector. The negative electrode slurry was applied to both sides of the negative electrode current collector by a 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 below 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 pressed by a roll press method using a roll press (manufactured by Thank Metals, press load 8 t / cm, roll width 7 cm) to obtain a negative electrode sheet having a negative electrode active material layer on both sides of the negative electrode current collector. The obtained negative electrode sheet was cut into a rectangle with a length of 52 mm and a width of 42 mm, and a conductive tab was attached to form a negative electrode.

[0156] (Fabrication of Lithium-Ion Secondary Battery (Nonaqueous Secondary Battery)) A separator (made of polyethylene, 25 μm thick) made of a polyolefin-based porous film was interposed between the positive electrode and the negative electrode, and the positive electrode active material layer and the negative electrode active material layer were laminated so that they faced each other, and then housed in an exterior body (battery pack) made of aluminum laminate material. An electrolyte solution was then poured into the exterior body, vacuum impregnation was performed, and the battery was packed with a vacuum heat sealer to obtain a lithium-ion secondary battery. The electrolyte solution was a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:DEC = 30:50:20, and LiPF 5 at a concentration of 1.0 mol / L. ６ A mixture of 99 parts by mass of a solution in which the above was dissolved and 1 part by mass of vinylene carbonate was used.

[0157] <Evaluation of Nonaqueous Secondary Batteries> The lithium ion secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 4 were evaluated by the following methods for the discharge capacity retention rate after 500 cycles, the discharge capacity retention rate after 4 weeks of storage at 60° C., and the rate of increase in internal resistance (DCR) after 4 weeks of storage at 60° C. The results are shown in Table 3.

[0158] [Discharge Capacity Retention Rate After 500 Cycles] Charge and discharge were performed under the condition of 45°C, with one cycle consisting of a series of operations of the following steps (i) to (iv). The time-integrated value of the current in steps (i) and (ii) was taken as the charge capacity, and the time-integrated value of the current in step (iv) was taken as the discharge capacity. The discharge capacity at the first cycle and the discharge capacity at the 500th cycle were measured, and the discharge capacity retention rate after 500 cycles was calculated using the following formula: Discharge capacity retention rate after 500 cycles (%) = 100 × (discharge capacity at the 500th cycle / discharge capacity at the first cycle)

[0159] (i) Charge at a current of 1 C until the voltage reaches 4.2 V (constant current (CC) charging). (ii) Charge at a voltage of 4.2 V until the current reaches 0.05 C (constant voltage (CV) charging). (iii) Leave to stand for 30 minutes. (iv) Discharge at a current of 1 C until the voltage reaches 2.75 V (constant current (CC) discharging).

[0160] [Discharge Capacity Retention Rate After 4 Weeks of Storage at 60°C] CC charging was performed at a current of 1C at 25°C until the voltage reached 4.2V, followed by CV charging until the current reached 0.05C. CC discharging was then performed at a current of 1C until the voltage reached 2.75V, and the resulting discharge capacity was recorded as the discharge capacity before storage. CC charging was then performed again at a current of 1C until the voltage reached 4.2V, followed by CV charging until the current reached 0.05C to obtain a fully charged battery. The resulting fully charged battery was left standing at 60°C for 4 weeks. CC discharging was then performed again at a current of 1C until the voltage reached 2.75V at 25°C, and the resulting discharge capacity was recorded as the discharge capacity after storage. The discharge capacity retention rate after 4 weeks of storage at 60°C was calculated from the discharge capacity before storage and the discharge capacity after storage using the following formula: Discharge capacity retention rate (%) after 4 weeks of storage at 60°C = 100 × (discharge capacity after storage / discharge capacity before storage).

[0161] [Rate of increase in internal resistance (DCR) after storage at 60°C for 4 weeks] The internal resistance (DCR (Ω)) of a lithium ion secondary battery was measured under the condition of 25°C according to the following procedure. That is, the battery was charged and discharged at a constant current of 0.2 C from the rest potential until the voltage reached 3.6 V, and the state of charge was set to 50% of the initial capacity (SOC 50%). Thereafter, the battery was discharged for 60 seconds at current values ​​of 0.2 C, 0.5 C, 1 C, and 2 C. The internal resistance DCR (Ω) at SOC 50% was determined from the relationship between these four current values ​​(values ​​for 1 second) and voltage.

[0162] The internal resistance (DCR) obtained by the above procedure was measured at the following stages (1) and (2): (1) Before storing for 4 weeks under the condition of being fully charged and at 60°C; (2) After storing for 4 weeks under the condition of being fully charged and at 60°C. The internal resistance (DCR) measured in (1) was defined as the DCR before storage, and the internal resistance (DCR) measured in (2) was defined as the DCR after storage. The rate of increase in internal resistance (DCR) after 4 weeks of storage at 60°C was calculated using the following formula: Rate of increase in internal resistance (DCR) after 4 weeks of storage at 60°C (%) = 100 × (DCR after storage / DCR before storage).

[0163]

[0164] <Evaluation Results> As shown in Table 3, it was confirmed that the lithium ion secondary batteries of Examples 1 to 7 had higher discharge capacity retention rates after 4 weeks of storage at 60°C than the lithium ion secondary batteries of Comparative Examples 1 to 4. This is presumably because the binder polymer contained in the negative electrodes of the lithium ion secondary batteries of Examples 1 to 7 was a copolymer containing structural units derived from monomers (a1) to (a4) shown in Table 1.

[0165] Furthermore, as shown in Table 3, it was confirmed that the lithium ion secondary batteries of Examples 1 to 7 had a lower DCR increase rate after 4 weeks of storage at 60°C than the lithium ion secondary batteries of Comparative Examples 1 to 4. This is presumably because the binder polymer contained in the negative electrodes of the lithium ion secondary batteries of Examples 1 to 7 is a copolymer containing structural units derived from monomers (a1) to (a4) shown in Table 1.

[0166] As shown in Table 3, it was confirmed that the lithium ion secondary batteries of Examples 1 to 7 all had discharge capacity retention rates after 500 cycles equal to or higher than those of the lithium ion secondary batteries of Comparative Examples 1 to 4. This is presumably because the binder polymer contained in the negative electrodes of the lithium ion secondary batteries of Examples 1 to 7 is a copolymer containing structural units derived from the monomers (a1) to (a4) shown in Table 1.

[0167] The disclosures of Japanese Patent Application Nos. 2023-214286, 2024-188626, and 2024-188627 are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A binder polymer for non-aqueous secondary batteries comprising: a first structural unit derived from an aromatic hydrocarbon monomer (a1) which is an aromatic compound having one ethylenically unsaturated bond and made of a hydrocarbon; a second structural unit derived from a nonionic monomer (a2) which has one ethylenically unsaturated bond and is a nonionic (meth)acrylic acid ester; a third structural unit derived from a carboxylic acid monomer (a3) ​​which is a compound having one ethylenically unsaturated bond and at least one selected from the group consisting of a carboxy group and a carboxy group forming a salt; and a fourth structural unit derived from an isocyanate monomer (a4) which is a compound having one ethylenically unsaturated bond and at least one selected from the group consisting of an isocyanato group and a blocked isocyanato group.

2. The binder polymer for non-aqueous secondary batteries according to claim 1, wherein the blocked isocyanato group has a structure that generates an isocyanato group by at least one selected from the group consisting of heating, applying voltage, and chemical reaction.

3. The binder polymer for non-aqueous secondary batteries according to claim 1, wherein a content of the first structural unit in the total amount of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit is 35 mol % to 80 mol %.

4. The binder polymer for non-aqueous secondary batteries according to claim 1, wherein a content of the second structural unit in the total amount of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit is 10 mol % to 55 mol %.

5. The binder polymer for non-aqueous secondary batteries according to claim 1, wherein a content of the third structural unit in the total amount of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit is 1.0 mol % to 20 mol %.

6. The binder polymer for non-aqueous secondary batteries according to claim 1, wherein a content of the fourth structural unit in the total amount of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit is 0.10 mol % to 15 mol %.

7. The binder polymer for a non-aqueous secondary battery according to claim 1, further comprising a fifth structural unit derived from a polyfunctional monomer (a5) which is a compound having a plurality of independent ethylenically unsaturated bonds.

8. The binder polymer for non-aqueous secondary batteries according to claim 7, wherein a content of the fifth structural unit relative to a total content of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit is 0.010 mol % to 5.0 mol %.

9. The binder polymer for non-aqueous secondary batteries according to claim 1, wherein the total content of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit is 90 mass % or more.

10. A binder for non-aqueous secondary batteries, comprising the binder polymer for non-aqueous secondary batteries according to any one of claims 1 to 9.

11. A binder composition for a non-aqueous secondary battery, comprising the binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 9 and an aqueous medium.

12. An electrode slurry for a non-aqueous secondary battery, comprising the binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 9, an electrode active material, and an aqueous medium.

13. An electrode for a non-aqueous secondary battery, comprising the binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 9.

14. A non-aqueous secondary battery comprising the electrode for a non-aqueous secondary battery according to claim 13.

15. A method for producing a binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 9, comprising copolymerizing the aromatic hydrocarbon monomer (a1), the nonionic monomer (a2), the carboxylic acid monomer (a3) ​​and the isocyanate monomer (a4).

16. A method for producing a binder for a non-aqueous secondary battery, comprising mixing the binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 9.

17. A method for producing a binder composition for a non-aqueous secondary battery, comprising mixing the binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 9 with an aqueous medium.

18. A method for producing a binder composition for a non-aqueous secondary battery, comprising mixing the binder for a non-aqueous secondary battery according to claim 10 with an aqueous medium.

19. A method for producing an electrode slurry for a non-aqueous secondary battery, comprising mixing the binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 9, an electrode active material, and an aqueous medium.

20. A method for producing an electrode slurry for a non-aqueous secondary battery, comprising mixing the binder for a non-aqueous secondary battery according to claim 10, an electrode active material, and an aqueous medium.

21. A method for producing an electrode slurry for a non-aqueous secondary battery, comprising mixing the binder composition for a non-aqueous secondary battery according to claim 11 with an electrode active material.

22. A method for producing an electrode for a non-aqueous secondary battery, comprising applying the electrode slurry for a non-aqueous secondary battery according to claim 12 to at least a part of the surface of a current collector, and drying the applied electrode slurry.

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