Binder composition for anode of non-aqueous secondary battery, method for manufacturing binder composition for anode of non-aqueous secondary battery, composition for anode of non-aqueous secondary battery, anode of non-aqueous secondary battery and non-aqueous secondary battery

Abstract

This invention provides a binder composition for a negative electrode of a non-aqueous secondary battery that can form a secondary battery with excellent elastic deformation properties that can follow volume changes of the active material, excellent film-forming properties, excellent durability to the electrolyte (electrolyte resistance), and excellent battery characteristics such as charge-discharge efficiency and capacity retention rate. [Solution] A binder composition for a negative electrode of a non-aqueous secondary battery, comprising core-shell type particles (A) having a shell portion made of polymer (a1) and a core portion made of polymer (a2), and an aqueous medium (B), wherein polymer (a1) contains structural units derived from a reactive emulsifier, structural units derived from a vinyl monomer having an acidic group, and structural units derived from a (meth)acrylic acid ester monomer, and polymer (a2) contains structural units derived from a conjugated diene monomer and structural units derived from an aromatic vinyl monomer.

Description

[Technical Field]

[0001] The present invention relates to a binder composition for a negative electrode of a non-aqueous secondary battery, a method for producing a binder composition for a negative electrode of a non-aqueous secondary battery, a composition for a negative electrode of a non-aqueous secondary battery, a negative electrode of a non-aqueous secondary battery, and a non-aqueous secondary battery. [Background technology]

[0002] Non-aqueous secondary batteries (non-aqueous electrolyte secondary batteries), such as lithium-ion secondary batteries, are rapidly being deployed in hybrid vehicles, electric vehicles, and home energy storage systems, leveraging their high energy density and the ability to repeatedly charge and discharge, thus expanding their range of applications. Furthermore, in recent years, with the advancement of high performance and miniaturization of various portable electronic and communication devices, there has been a growing demand for secondary batteries that are small, lightweight, have higher capacity, and exhibit further improvements in various battery characteristics such as cycle characteristics and discharge rate characteristics. To further enhance the performance of non-aqueous secondary batteries, improvements to various battery components such as electrodes are being considered. The negative electrode for a non-aqueous secondary battery typically comprises a current collector and an electrode material layer (negative electrode material layer) formed on the current collector. This negative electrode material layer is formed using, for example, a slurry-like negative electrode composition in which a negative electrode active material and a composition containing a binder (binding agent) are dispersed in a dispersion medium.

[0003] One method for increasing the capacity of non-aqueous secondary batteries is to use silicon-containing active materials (silicon-based active materials), which have a higher lithium absorption capacity than conventional graphite-based active materials, as the negative electrode active material. However, silicon-containing active materials undergo large volume changes due to lithium absorption and release, causing the negative electrode material layer to expand and contract violently during charging and discharging. As a result, there are problems such as a decrease in electronic conductivity between negative electrode active materials, isolation of silicon-containing active materials within the negative electrode material layer, and disruption of the conductive path between the negative electrode active material and the current collector, which worsens the cycle characteristics of the secondary battery. To address these problems, for example, Patent Documents 1 and 2 suggest creating a negative electrode using a negative electrode slurry containing both a (meth)acrylic acid polymer (PAA), which has excellent elastic deformation properties that can follow the volume change of silicon-containing active material, and a styrene-butadiene copolymer (SBR), which has excellent adhesion to the current collector and bonding properties between active materials, as binders. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 7496854 [Patent Document 2] Japanese Patent Publication No. 2022-64465 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the binders described in Patent Documents 1 and 2 have poor compatibility between PAA and SBR, and because they exist separately within the electrode, the areas where PAA is locally present become hard and brittle, and the areas where SBR is locally present become brittle, resulting in a decrease in the overall performance of the electrode. Therefore, when silicon-containing active materials are used as the negative electrode active material, there is a strong demand for a binder component that exhibits excellent elastic deformation characteristics that can follow the volume changes of the silicon-containing active material, excellent adhesion to the current collector and bonding between active materials, and also excellent durability to the electrolyte (electrolyte resistance). The present inventors investigated emulsion-based binder compositions for negative electrodes that exhibit excellent film-forming properties, including elastic deformation characteristics, bonding properties between negative electrode active materials, and bonding properties between negative electrode active materials and current collectors, as well as excellent electrolyte resistance. As a result, they found that using core-shell type particles (A) as a binder, which have a shell portion made of polymer (a1) containing structural units derived from a reactive emulsifier, an acidic vinyl monomer, and a (meth)acrylic acid ester monomer, and a core portion made of polymer (a2) containing structural units derived from a conjugated diene monomer and an aromatic vinyl monomer, results in excellent elastic deformation characteristics and film-forming properties, as well as excellent electrolyte resistance. Furthermore, they found that this composition is effective in improving battery characteristics such as charge-discharge efficiency and capacity retention rate of secondary batteries equipped with a negative electrode formed using such a binder composition, thus completing the present invention. The object of the present invention is to provide a binder composition for a negative electrode of a non-aqueous secondary battery that, even when a silicon-containing active material is used as the negative electrode active material, exhibits excellent elastic deformation characteristics that can follow the volume change of the silicon-containing active material, excellent film-forming properties, excellent durability to the electrolyte (electrolyte resistance), and excellent battery characteristics such as charge-discharge efficiency and capacity retention rate, a method for producing such a binder composition for a negative electrode, a binder composition for a non-aqueous secondary battery containing such a binder composition for a non-aqueous secondary battery, a negative electrode for a non-aqueous secondary battery containing such a negative electrode composition, and a non-aqueous secondary battery having such a negative electrode. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] A binder composition for a negative electrode of a non-aqueous secondary battery, comprising core-shell type particles (A) having a shell portion made of polymer (a1) and a core portion made of polymer (a2), and an aqueous medium (B), The polymer (a1) contains structural units derived from a reactive emulsifier, structural units derived from a vinyl monomer having an acidic group, and structural units derived from a (meth)acrylic acid ester monomer. A binder composition for a negative electrode of a non-aqueous secondary battery, wherein the polymer (a2) contains structural units derived from a conjugated diene monomer and structural units derived from an aromatic vinyl monomer. [2] The binder composition for a negative electrode of a non-aqueous secondary battery according to [1], wherein the reactive emulsifier is an emulsifier having an ethylenically unsaturated group. [3] The binder composition for a negative electrode of a non-aqueous secondary battery according to [1], wherein the content of structural units derived from the reactive emulsifier is 0.01% by mass or more and 3% by mass or less, relative to the total amount obtained by excluding the structural units derived from the reactive emulsifier from the units constituting the polymer (a1). [4] The binder composition for a negative electrode of a non-aqueous secondary battery according to [1], wherein the content of structural units derived from the acidic vinyl monomer is 0.1% by mass or more and 10% by mass or less, relative to the total amount obtained by excluding the structural units derived from the reactive emulsifier from the units constituting the polymer (a1). [5] The binder composition for a negative electrode of a non-aqueous secondary battery according to [1], wherein the polymer (a1) further contains structural units derived from an aromatic vinyl monomer. [6] The binder composition for a negative electrode of a non-aqueous secondary battery according to [1], wherein the polymer (a1) further contains structural units derived from a vinyl monomer having an amide group. [7] The binder composition for a negative electrode of a non-aqueous secondary battery according to [1], wherein the conjugated diene monomer contains isoprene. [8] The binder composition for a negative electrode of a non-aqueous secondary battery according to [1], wherein the polymer (a2) further contains structural units derived from a vinyl monomer having a cyano group. [9] The binder composition for a negative electrode of a non-aqueous secondary battery according to [8], wherein the content of structural units derived from the vinyl monomer having a cyano group is 0.1% by mass or more and 10% by mass or less, relative to the total amount of units constituting the polymer (a2).

[10] The binder composition for a negative electrode of a non-aqueous secondary battery according to [1], wherein the polymer (a2) does not contain structural units derived from a vinyl monomer having an acidic group.

[11] The binder composition for a non-aqueous secondary battery negative electrode according to [1], wherein the polymer (a2) does not contain structural units derived from fluorine-containing monomers.

[12] A binder composition for a negative electrode of a non-aqueous secondary battery according to [1], wherein the content of polymer (a1) in the core-shell particle (A) is X [mass%] and the content of polymer (a2) in the core-shell particle (A) is Y [mass%], and X:Y is 5:95 to 99:1.

[13] A method for producing a binder composition for a non-aqueous secondary battery negative electrode, comprising core-shell type particles (A) having a shell portion made of polymer (a1) and a core portion made of polymer (a2), and an aqueous medium (B), A shell formation step is performed in which a vinyl monomer having an acidic group and a (meth)acrylic acid ester monomer are polymerized in the aqueous medium (B) in the presence of a reactive emulsifier to form polymer particles that will become the shell portion, consisting of the polymer (a1). A method for producing a binder composition for a negative electrode of a non-aqueous secondary battery, comprising: a core formation step of polymerizing a conjugated diene monomer and an aromatic vinyl monomer using polymer particles as a reaction field to form the core portion consisting of the polymer (a2) inside the polymer particles.

[14] A composition for a negative electrode of a non-aqueous secondary battery, comprising a negative electrode active material and any of the non-aqueous secondary battery negative electrode binder compositions of [1] to

[12] . A non-aqueous secondary battery anode comprising a negative electrode material layer formed using the non-aqueous secondary battery anode composition of

[15]

[14] .

[16]

[15] A non-aqueous secondary battery comprising a negative electrode, a positive electrode, an electrolyte, and a separator. [Effects of the Invention]

[0007] According to the present invention, even when a silicon-containing active material is used as the negative electrode active material, it has elastic deformation characteristics that can follow the volume change of the silicon-containing active material, excellent film-forming properties, excellent durability (electrolyte resistance) against the electrolyte, and excellent battery characteristics such as charge-discharge efficiency and capacity retention rate. Provided are a non-aqueous secondary battery negative electrode binder composition capable of forming a secondary battery, a method for manufacturing such a negative electrode binder composition, a non-aqueous secondary battery negative electrode composition containing such a negative electrode binder composition, a non-aqueous secondary battery negative electrode containing such a negative electrode composition, and a non-aqueous secondary battery having such a negative electrode.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described in detail. In this specification, a numerical range indicated by using "~" indicates a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. 1. Binder composition for anode of non-aqueous secondary batteries The present invention is a non-aqueous secondary battery negative electrode binder composition containing core-shell type particles (A) having a shell portion composed of a polymer (a1) and a core portion composed of a polymer (a2), and an aqueous medium (B). The polymer (a1) contains a structural unit derived from a reactive emulsifier, a structural unit derived from a vinyl monomer having an acidic group, and a structural unit derived from a (meth)acrylate monomer. The polymer (a2) contains a structural unit derived from a conjugated diene monomer and a structural unit derived from an aromatic vinyl monomer (hereinafter, also simply referred to as "the negative electrode binder composition 1 of the present invention"). The negative electrode binder composition 1 of the present invention is an aqueous binder composition in which a binder (binding material) is dispersed in an aqueous medium (B), and optionally, other components generally used in the field of non-aqueous secondary batteries can be further contained. First, each constituent component of the negative electrode binder composition 1 of the present invention will be described.

[0009] <Core-Shell Type Particles (A)> The binder composition 1 for the negative electrode of the present invention contains, as a binder, a polymer (a1) containing structural units derived from a reactive emulsifier, a vinyl monomer having an acidic group, and a (meth)acrylate monomer, and a core-shell type particle (A) having a core part composed of a polymer (a2) containing structural units derived from a conjugated diene monomer and an aromatic vinyl monomer. The polymer (a1) constituting the shell part exhibits excellent binding property (film-forming property) to the core-shell type particle (A), and the polymer (a2) constituting the core part imparts to the core-shell type particle (A) elastic deformation characteristics that can follow the volume change of the active material and excellent durability (electrolyte resistance) against the electrolyte.

[0010] As will be described later, the core-shell type particle (A) is obtained by polymerizing a vinyl monomer having an acidic group and a (meth)acrylate monomer in an aqueous medium (B) in the presence of a reactive emulsifier to form polymer particles that become the shell part composed of the polymer (a1), and then polymerizing a conjugated diene monomer and an aromatic vinyl monomer using the polymer particles as a reaction field to form a core part composed of the polymer (a2) inside the polymer particles. The reactive emulsifier is incorporated into the shell part as a component of the polymer (a1) by reacting, becoming a hydrophilic group of the polymer that forms the shell part, and losing its function as a surfactant. Therefore, the polymerization of the core part can be said to be soap-free polymerization carried out without the presence of a surfactant. In the formation process of the above core-shell type particle (A), the hydrophobic monomers (conjugated diene monomer and aromatic vinyl monomer) that should become the core part (polymer (a2)) enter the inside of the polymer particles (polymer (a1)) having a hydrophilic group formed by the reaction of the reactive emulsifier, and polymerize inside the polymer particles to form the core-shell type particle (A). Thus, the core-shell particles obtained by polymerizing hydrophobic monomers inside the polymer particles having a hydrophilic group that become the shell part to form the core part are called inverted core-shell particles.

[0011] Core-shell particles (A) formed by a reverse-phase core-shell process using a reactive emulsifier ensure that each particle reliably possesses a core-shell structure. In contrast, when a normal-phase core-shell process is used, in which a shell portion is formed on the surface of polymer particles that form the core portion using a non-reactive emulsifier, particles formed solely of the polymer components constituting the shell are easily produced as by-products in addition to core-shell particles. From this perspective, the negative electrode binder composition 1 of the present invention is advantageous in that each core-shell particle (A) possesses stable shell characteristics (film-forming properties) and core characteristics (elastic deformation properties, electrolyte resistance). Furthermore, as described above, since the polymer (a1) that forms the shell portion of the core-shell particle (A) has hydrophilic groups derived from the reactive emulsifier, the core-shell particle (A) has a high affinity for the aqueous medium (B) and can exist stably in the aqueous medium (B). Furthermore, in core-shell type particles (A), polymers (a1) and (a2) are fused within the particle, resulting in separation at the nm size. Since polymers (a1) and (a2) are phase-separated at a size sufficiently smaller than the size of the negative electrode active material (μm size), both the core and shell characteristics can be expressed for all types of negative electrode active materials, resulting in uniform performance throughout the negative electrode. In contrast, when polymers (a1) and (a2) are simply blended (mixed), polymers (a1) and (a2) are separated at the particle size level (μm size). Therefore, depending on the negative electrode active material used, products with poor elastic deformation characteristics, film-forming properties, or electrolyte resistance may occur, resulting in degraded or non-uniform performance throughout the negative electrode. Therefore, the negative electrode binder composition 1 of the present invention, by using core-shell type particles (A) as a binder, exhibits excellent elastic deformation characteristics, film-forming properties, and electrolyte resistance. Furthermore, it is possible to improve battery characteristics such as charge-discharge efficiency and capacity retention rate of a secondary battery equipped with a negative electrode formed using such negative electrode binder composition 1.

[0012] (Shell part) The shell portion is composed of a polymer (a1) containing structural units derived from a reactive emulsifier, a vinyl monomer having an acidic group, and a (meth)acrylic acid ester monomer, respectively. The reactive emulsifier used to form the shell portion (polymer (a1)) is an emulsifier having polymerizable ethylenically unsaturated groups such as vinyl groups and hydrophilic groups in its molecule. While ordinary non-reactive emulsifiers are merely adsorbed onto the surface of the generated particles, the reactive emulsifier is incorporated into the polymer (a1) as a component of the copolymer during the polymerization process of the polymer (a1). Therefore, it has the characteristic that the emulsifier does not bleed out (become free) from the polymer (a1) in the aqueous medium (B), or is less likely to bleed out. In the negative electrode binder composition 1 of the present invention, it is possible to prevent or suppress the bleeding out of the reactive emulsifier from the core-shell type particles (A), so that an electrode with excellent peel strength between the formed negative electrode material layer and the current collector can be obtained. Furthermore, since the shell portion (polymer (a1)) has hydrophilic groups derived from the reactive emulsifier, it has high affinity with the aqueous medium (B), and the core-shell type particles (A) can exist stably in the aqueous medium (B).

[0013] As a reactive emulsifier, for example, emulsifiers represented by general formulas (1) to (5) can be used.

[0014] General formula (1) [C1] JPEG2026078999000001.jpg19167 In general formula (1), R is an alkyl group and m is an integer between 10 and 40.

[0015] General formula (2) [C2] JPEG2026078999000002.jpg19167 In general formula (2), x is an integer between 10 and 12, and y is an integer between 10 and 40.

[0016] General formula (3) [C3] JPEG2026078999000003.jpg29167 In general formula (3), R is an alkyl group and M is NH4 or Na.

[0017] General formula (4) [C4] JPEG2026078999000004.jpg18166 In general formula (4), R is an alkyl group.

[0018] General formula (5) [5] In general formula (5), X is a hydrogen atom or SO3NH4, m is an integer between 1 and 4, and n is an integer between 5 and 40. X is preferably SO3NH4. m is preferably between 1 and 3. n is preferably between 8 and 40, more preferably between 8 and 25, and even more preferably between 8 and 15.

[0019] Specific examples of reactive emulsifiers include alkyl ether type (commercial products such as Adekarya Soap SR-10, SR-10N, SR-20N from ADEKA Corporation, Aqualon KH-05, KH-10, KH-20 from Daiichi Kogyo Seiyaku Co., Ltd., and Latemul PD-104 from Kao Corporation), sulfosuccinate ester type (commercial products such as Latemul S-120, S-120A, S-180P, S-180A from Kao Corporation, and Eleminor JS-2 from Sanyo Chemical Industries, Ltd.), alkylphenyl ether type or alkylphenyl ester type (commercial products such as Aqualon AR-10, AR-2 from Daiichi Kogyo Seiyaku Co., Ltd.) Examples include 0, H-2855A, H-3855B, H-3855C, H-3856, HS-05, HS-10, HS-20, HS-30, Adekarya Soap SDX-222, SDX-223, SDX-232, SDX-233, SDX-259, SE-10N, SE-20N, etc. manufactured by ADEKA Corporation, (meth)acrylate sulfate ester type (commercial products include, for example, Antox MS-60, MS-2N manufactured by Nippon Emulsifier Co., Ltd., and Eleminor RS-30 manufactured by Sanyo Chemical Industries, Ltd.), phosphate ester type (commercial products include, for example, H-3330PL manufactured by Daiichi Kogyo Seiyaku Co., Ltd., and Adekarya Soap PP-70 manufactured by ADEKA Corporation). These reactive emulsifiers may be used individually or in combination of two or more types. Furthermore, the content of structural units derived from the reactive emulsifier, relative to the total amount obtained by excluding the structural units derived from the reactive emulsifier from the units constituting the polymer (a1), is preferably 0.01% by mass or more and 3% by mass or less. If the content of structural units derived from the reactive emulsifier is within the above range, the core-shell type particles (A) can exist more stably in the aqueous medium (B), and an electrode with superior peel strength between the formed negative electrode material layer and the current collector can be obtained. Furthermore, as will be described later, when forming the shell portion (polymer a1), a non-reactive emulsifier may be used in combination with a reactive emulsifier, so that the shell portion (polymer a1) contains a non-reactive emulsifier. In that case, the content of the non-reactive emulsifier is preferably 1 / 2 or less of the content of the reactive emulsifier, more preferably 1 / 5, and even more preferably 1 / 10 or less.

[0020] The vinyl monomer having acidic groups is used in the formation of the shell portion (polymer (a1)) to improve the particle stability of the core-shell type particles (A) in the aqueous medium (B), and also promotes the fusion of the core-shell type particles (A) with each other through hydrogen bonding between acidic groups and between acidic groups and other functional groups in the formed negative electrode material layer, thereby improving the film-forming properties of the core-shell type particles (A). Examples of vinyl monomers having acidic groups include monocarboxylic acids and dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, as well as their anhydrides. These vinyl monomers having acidic groups may be used individually or in combination of two or more. Among these, acrylic acid, methacrylic acid, or itaconic acid is preferred. Furthermore, it is preferable that the content of structural units derived from a vinyl monomer having an acidic group, relative to the total amount of structural units derived from the reactive emulsifier from the units constituting the polymer (a1), is 0.1% by mass or more and 10% by mass or less. If the content of structural units derived from a vinyl monomer having an acidic group is within the above range, the core-shell type particles (A) can exist more stably in the aqueous medium (B), and the fusion of the core-shell type particles (A) with each other in the formed negative electrode material layer can be promoted, further improving the film-forming properties of the core-shell type particles (A).

[0021] (Meth)acrylic acid monomers are used in the formation of the shell portion (polymer (a1)) to improve the film-forming properties of core-shell type particles (A). Examples of (meth)acrylic acid monomers include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate Examples include alkyl methacrylates such as ropil, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate; and hydroxyl group-containing (meth)acrylic acid ester monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. These (meth)acrylic acid ester monomers may be used individually or in combination of two or more. Among these, 2-ethylhexyl acrylate, butyl acrylate, or methyl methacrylate is preferred. Furthermore, the content of structural units derived from (meth)acrylic acid ester monomers relative to the total amount of structural units derived from the reactive emulsifier from the units constituting polymer (a1) is not particularly limited, but can be 5% by mass or more and 95% by mass or less.

[0022] Furthermore, polymer (a1) may further contain structural units derived from aromatic vinyl monomers and structural units derived from vinyl monomers having amide groups, in addition to structural units derived from each of the above components. Aromatic vinyl monomers are used in the formation of the shell portion (polymer (a1)) to improve the electrolyte resistance and film-forming properties of core-shell type particles (A). Examples of aromatic vinyl monomers include styrene, α-methylstyrene, and vinyltoluene. These aromatic vinyl monomers may be used individually or in combination of two or more. Among these, styrene is preferred. Furthermore, the content of structural units derived from aromatic vinyl monomers relative to the total amount of structural units derived from reactive emulsifiers from the units constituting polymer (a1) is not particularly limited, but can be 5% by mass or more and 95% by mass or less.

[0023] Vinyl monomers containing amide groups are used in the formation of the shell portion (polymer (a1)) to promote the fusion of core-shell type particles (A) in the formed negative electrode material layer through hydrogen bonding between amide groups and between amide groups and other functional groups, thereby improving the film-forming properties of core-shell type particles (A). Furthermore, by using vinyl monomers containing amide groups in the formation of the shell portion (polymer (a1)), the stability of the polymer particles in which the amide groups form the shell portion is improved in the reverse-phase core-shell process, resulting in the stable progression of polymerization of the core portion. Examples of vinyl monomers having an amide group include (meth)acrylamide; alkylol(meth)acrylamide compounds such as N-methylolacrylamide, N,N-di(methylol)acrylamide, and N-methylol-N-methoxymethyl(meth)acrylamide; monoalkoxy(meth)acrylamide compounds such as N-methoxymethyl-(meth)acrylamide, N-ethoxymethyl-(meth)acrylamide, N-propoxymethyl-(meth)acrylamide, N-butoxymethyl-(meth)acrylamide, and N-pentoxymethyl-(meth)acrylamide; and N,N-di(methoxymethyl)acrylamide, N-ethoxymethyl-N-methoxymethylmethacrylamide, N,N-di(ethoxymethyl)acrylamide, and N-ethoxymethyl-N-propoxymethylmethacrylamide. Examples include dialkoxy(meth)acrylamide compounds such as N,N-di(propoxymethyl)acrylamide, N-butoxymethyl-N-(propoxymethyl)methacrylamide, N,N-di(butoxymethyl)acrylamide, N-butoxymethyl-N-(methoxymethyl)methacrylamide, N,N-di(pentoxymethyl)acrylamide, and N-methoxymethyl-N-(pentoxymethyl)methacrylamide; dialkylamino(meth)acrylamide compounds such as N,N-dimethylaminopropylacrylamide and N,N-diethylaminopropylacrylamide; dialkyl(meth)acrylamide compounds such as N,N-dimethylacrylamide and N,N-diethylacrylamide; and keto group-containing (meth)acrylamide compounds such as diacetone(meth)acrylamide. These vinyl monomers having amide groups may be used individually or in combination of two or more. Among these, acrylamide, dimethylacrylamide, N-methylolacrylamide, or N-methylolmethacrylamide is preferred. Furthermore, it is preferable that the content of structural units derived from vinyl monomers having amide groups, relative to the total amount of structural units derived from reactive emulsifiers from the units constituting the polymer (a1), is 0.1% by mass or more and 10% by mass or less. If the content of structural units derived from vinyl monomers having amide groups is within the above range, the fusion of core-shell type particles (A) in the formed negative electrode material layer can be promoted, further improving the film-forming properties of the core-shell type particles (A).

[0024] (Core part) The core is composed of a polymer (a2) containing structural units derived from conjugated diene monomers and aromatic vinyl monomers, respectively. By using conjugated diene monomers in the formation of the core (polymer (a2)), the core-shell particle (A) is given elastic deformation properties that can follow the volume changes of the active material, even when using an active material with large volume changes due to lithium absorption and release, such as a silicon-containing active material, as the negative electrode active material. Furthermore, core-shell particle (A) containing structural units derived from conjugated diene monomers can suppress excessive swelling even when containing electrolyte, and has excellent durability to electrolyte (electrolyte resistance). In addition, as mentioned above, in core-shell particle (A), polymer (a1) and polymer (a2) are fused within the particle, and are separated at the nm size. In such core-shell particle (A), by using a material with excellent elastic deformation properties and electrolyte resistance in the core, the core-shell particle (A) as a whole can exhibit the properties of both the core and the shell, resulting in a core-shell particle (A) that is excellent in elastic deformation properties, film-forming properties, and electrolyte resistance.

[0025] As the conjugated diene monomer, either an aliphatic conjugated diene monomer or an aromatic conjugated diene monomer can be used, but it is preferable to use an aliphatic conjugated diene monomer. Examples of aliphatic conjugated diene monomers include isoprene (2-methyl-1,3-butadiene), butadiene (1,3-butadiene), 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene (chloroprene), substituted linear conjugated pentadienes, and substituted and side-chain conjugated hexadienes. These aliphatic conjugated diene monomers may be used individually or in combination of two or more. Among these, isoprene and butadiene are preferred, and isoprene is particularly preferred. Isoprene is more hydrophobic than other aliphatic conjugated diene monomers such as 1,3-butadiene, and easily penetrates into the polymer particles constituting the shell in the reversed-phase core-shell process. Therefore, core-shell particles (A) with more stable and uniform properties can be obtained. Furthermore, core-shell type particles (A) containing structural units derived from isoprene exhibit superior electrolyte resistance, and the conductivity of lithium ions in the resulting negative electrode is improved. As a result, the discharge capacity maintenance rate of secondary batteries equipped with such negative electrodes can be improved.

[0026] Furthermore, the content of structural units derived from conjugated diene monomers relative to the total amount of units constituting the polymer (a2) is preferably 1% by mass or more and 99% by mass or less, and more preferably 5% by mass or more and 90% by mass or less. If the content of structural units derived from conjugated diene monomers is within the above range, the elastic deformation properties and electrolyte resistance of the core-shell type particles (A) can be further improved.

[0027] Aromatic vinyl monomers are used in the formation of the core portion (polymer (a2)) to improve the electrolyte resistance of core-shell type particles (A). As such aromatic vinyl monomers, the various aromatic vinyl monomers mentioned above that can be used in the formation of polymer (a1) can be used, and styrene is particularly preferred. Furthermore, the content of structural units derived from aromatic vinyl monomers relative to the total amount of units constituting the polymer (a2) is preferably 1% by mass or more and 99% by mass or less, and more preferably 5% by mass or more and 90% by mass or less. If the content of structural units derived from aromatic vinyl monomers is within the above range, the electrolyte resistance of the core-shell type particles (A) can be further improved.

[0028] Furthermore, polymer (a2) may further contain structural units derived from each of the above components, as well as structural units derived from vinyl monomers having crosslinkable reactive groups and structural units derived from vinyl monomers having cyano groups. Vinyl monomers having crosslinkable reactive groups are used in the formation of the core portion (polymer (a2)), thereby forming a crosslinked structure in polymer (a2). This further improves the excellent durability (electrolyte resistance) of the core-shell type particles (A) to electrolytes.

[0029] A vinyl monomer having a crosslinkable reactive group preferably has at least one selected from an ethylenically unsaturated group, a monofunctional or polyfunctional alkoxysilyl group, a methylol group, and an alkyloxymethyl group as the crosslinkable reactive group. Examples of vinyl monomers having an ethylenically unsaturated group as a crosslinkable reactive group include divinyl compounds such as divinylbenzene and divinyl adipate; polyfunctional (meth)acrylic acid esters such as ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, 1,1,1-trishydroxymethylethane diacrylate, 1,1,1-trishydroxymethylethane triacrylate, and 1,1,1-trishydroxymethylpropanetriacrylic acid; allyl (meth)acrylate, 1-methylallyl (meth)acrylate, 2-methylallyl (meth)acrylate, 1-butenyl (meth)acrylate, and 2-butenyl (meth)acrylate. Examples include ethylenically unsaturated group-containing (meth)acrylic acid esters such as (meth)acrylate 3-butenyl (meth)acrylate, (meth)acrylate 1,3-methyl-3-butenyl (meth)acrylate, (meth)acrylate 2-chlorallyl (meth)acrylate, (meth)acrylate 3-chlorallyl (meth)acrylate, (meth)acrylate o-allylphenyl (meth)acrylate, (meth)acrylate 2-(allyloxy)ethyl (meth)acrylate, (meth)acrylate allyl lactyl (meth)acrylate, (meth)acrylate citronellyl (meth)acrylate, (meth)acrylate geranyl (meth)acrylate, (meth)acrylate rhodinyl (meth)acrylate, (meth)acrylate cinnamyl (meth)acrylate, diallyl maleate, diallyl lutaconic acid, (meth)acrylate vinyl, vinyl crotate, vinyl oleate, vinyl linolenate, and (meth)acrylate 2-(2'-vinyloxyethoxy)ethyl (meth)acrylate; and diallyls such as diallyl isophthalate, diallyl phthalate, and diallyl maleate. These vinyl monomers having ethylenically unsaturated groups as crosslinking reactive groups may be used individually or in combination of two or more. Among these, divinylbenzene or ethylene glycol diacrylate is preferred.

[0030] Examples of vinyl monomers having monofunctional or polyfunctional alkoxysilyl groups as crosslinkable reactive groups include γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropyltributoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-acryloxypropylmethyldimethoxysilane, γ-methacryloxymethyltrimethoxysilane, γ-acryloxymethyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltributoxysilane, and vinylmethyldimethoxysilane. These vinyl monomers having monofunctional or polyfunctional alkoxysilyl groups as crosslinkable reactive groups may be used individually or in combination of two or more. Among these, it is preferable to use γ-methacryloxypropyltrimethoxysilane (3-(trimethoxysilyl)propyl methacrylate).

[0031] Examples of vinyl monomers having a methylol group as a crosslinking reactive group include N-methylol(meth)acrylamide and N,N-di(methylol)acrylamide. These vinyl monomers having a methylol group as a crosslinking reactive group may be used individually or in combination of two or more. Among these, N-methylol(meth)acrylamide is preferred. Examples of vinyl monomers having an alkyloxymethyl group as a crosslinking reactive group include N-methoxymethyl(meth)acrylamide and N-butoxymethyl(meth)acrylamide. These vinyl monomers having an alkyloxymethyl group as a crosslinking reactive group may be used individually or in combination of two or more.

[0032] Furthermore, it is preferable that the content of structural units derived from vinyl monomers having crosslinkable reactive groups relative to the total amount of units constituting the polymer (a2) is 0.1% by mass or more and 10% by mass or less. If the content of structural units derived from vinyl monomers having crosslinkable reactive groups is within the above range, the electrolyte resistance of core-shell type particles (A) can be further improved.

[0033] When vinyl monomers containing cyano groups are used to form the core (polymer (a2)), the high dielectric constant of the cyano groups improves the conductivity of lithium ions in the resulting negative electrode, thereby improving the discharge capacity retention rate of secondary batteries equipped with such negative electrodes. Furthermore, since the polymer (a2) constituting the core contains structural units derived from vinyl monomers containing cyano groups, vinyl monomers containing cyano groups do not dissolve into the electrolyte, and the electrolyte resistance of the core-shell type particles (A) does not decrease. Examples of vinyl monomers having a cyano group include vinyl monomers having a nitrile group, such as (meth)acrylonitrile, and it is particularly preferable to use acrylonitrile. Furthermore, it is preferable that the content of structural units derived from vinyl monomers having cyano groups relative to the total amount of units constituting the polymer (a2) be 0.1% by mass or more and 10% by mass or less. If the content of structural units derived from vinyl monomers having cyano groups is within the above range, the conductivity of lithium ions in the formed negative electrode is further improved, and as a result, the discharge capacity maintenance rate of a secondary battery equipped with such a negative electrode can be further improved.

[0034] Furthermore, it is preferable that polymer (a2) does not contain structural units derived from the aforementioned acidic vinyl monomer and structural units derived from the fluorine-containing monomer as components of polymer (a1). If the polymer (a2) contains structural units derived from vinyl monomers having acidic groups, it becomes disadvantageous in terms of fusion between core-shell particles (A) and peel strength between the negative electrode material layer and the current collector in the formed negative electrode material layer. Furthermore, in the reverse-phase core-shell process, if vinyl monomers having acidic groups are included as constituent monomers of the polymer (a2) that forms the core, it becomes difficult to balance the hydrophilicity between the polymer particles that form the shell and the constituent monomers of the polymer (a2), making it difficult to form reverse-phase core-shell particles. Similarly, if the polymer (a2) contains structural units derived from fluorine-containing monomers, it becomes disadvantageous in terms of fusion between core-shell particles (A) and peel strength between the negative electrode material layer and the current collector in the formed negative electrode material layer. Furthermore, in the reverse-phase core-shell process, if fluorine-containing monomers are included as constituent monomers of the polymer (a2) that forms the core, it becomes difficult to balance the hydrophilicity between the polymer particles that form the shell and the constituent monomers of polymer (a2), making it difficult to form reverse-phase core-shell particles.

[0035] Furthermore, when the content of polymer (a1) in the core-shell type particle (A) is X [mass%] and the content of polymer (a2) in the core-shell type particle (A) is Y [mass%], it is preferable that X:Y be 5:95 to 99:1, and more preferably that X:Y be 10:90 to 95:5. The core-shell type particle (A) exhibits excellent binding properties (film-forming ability) in the polymer (a1) constituting the shell portion, and the polymer (a2) constituting the core portion exhibits elastic deformation characteristics that can follow volume changes of the active material, as well as excellent durability to the electrolyte (electrolyte resistance). Therefore, depending on the type of material used, if the content of polymer (a1) in the core-shell type particle (A) is low, the shell properties (film-forming ability) may deteriorate, and if the content of polymer (a2) in the core-shell type particle (A) is low, the core properties (elastic deformation properties, electrolyte resistance) may deteriorate. On the other hand, if the content of polymer (a1) and polymer (a2) in the core-shell type particle (A) are within the above range, a negative electrode binder composition 1 can be obtained that contains core-shell type particles (A) that have excellent elastic deformation properties, film-forming ability, and electrolyte resistance.

[0036] <Aqueous medium (B)> The aqueous medium (B) functions as a dispersion medium for the core-shell type particles (A). Examples of aqueous mediums include water (distilled water, deionized water, tap water, etc.) and water to which various alcohols have been added. As described later, the anode binder composition 1 of the present invention is obtained by forming core-shell type particles (A) in an aqueous medium (B) in the presence of a reactive emulsifier via a reverse-phase core-shell process. The liquid containing the core-shell type particles (A) and aqueous medium (B) obtained in this way can be used as is as the anode binder composition 1 of the present invention, or it may be diluted with additional aqueous medium (B) as needed before being used as the anode binder composition 1 of the present invention. Preferably, the content of core-shell type particles (A) relative to the total anode binder composition 1 of the present invention is in the range of 10 to 100% by mass.

[0037] The negative electrode binder composition 1 of the present invention may further contain various additives as needed, such as other resins, surfactants, antioxidants, light stabilizers, plasticizers, viscosity modifiers, and organic or inorganic fillers, to the extent that they do not impair the effects of the present invention.

[0038] 2. Method for producing a binder composition for the negative electrode of a non-aqueous secondary battery The present invention also relates to a method for producing a binder composition for a non-aqueous secondary battery negative electrode, comprising a core-shell type particle (A) having a shell portion made of polymer (a1) and a core portion made of polymer (a2), and an aqueous medium (B), the method comprising: a shell portion forming step of polymerizing an acidic vinyl monomer and a (meth)acrylic acid ester monomer in the aqueous medium (B) in the presence of a reactive emulsifier to form polymer particles that will become the shell portion made of polymer (a1); and a core portion forming step of polymerizing a conjugated diene monomer and an aromatic vinyl monomer using the polymer particles as a reaction field to form the core portion made of polymer (a2) inside the polymer particles, the method for producing a binder composition for a non-aqueous secondary battery negative electrode (hereinafter also simply referred to as "the method for producing a binder composition for a negative electrode of the present invention"). The following describes each step in the method for producing the negative electrode binder composition of the present invention.

[0039] (Shell formation process) The shell formation step involves polymerizing a vinyl monomer having an acidic group and a (meth)acrylic acid ester monomer in an aqueous medium (B) in the presence of a reactive emulsifier to form polymer particles that will become the shell portion, consisting of polymer (a1). The reactive emulsifier, the vinyl monomer having an acidic group, the (meth)acrylic acid ester monomer, and the aqueous medium (B), as well as each of the components described later (aromatic vinyl monomer, vinyl monomer having an amide group, conjugated diene monomer, vinyl monomer having a crosslinkable reactive group, and vinyl monomer having a cyano group), are all the same as those described in the negative electrode binder composition 1 of the present invention. In addition to the reactive emulsifier, a non-reactive emulsifier may also be used in combination.

[0040] The reactive emulsifier, upon reaction, is incorporated into the shell portion as a component of polymer (a1), becoming a hydrophilic group of the polymer shell, and losing its function as a surfactant. Furthermore, in addition to the above components, aromatic vinyl monomers and / or vinyl monomers having amide groups can be used as constituent monomers for the shell portion (polymer (a1)). In particular, by using vinyl monomers having amide groups, the stability of the polymer particles that form the shell portion is improved in the reversed-phase core-shell process, and the polymerization of the core portion in the core portion formation process proceeds stably. Reactive emulsifiers, vinyl monomers having acidic groups, (meth)acrylic acid ester monomers, and other monomers may be added directly to the aqueous medium (B), but it is preferable to prepare these components in advance as an emulsion in the aqueous medium and add this emulsion to the aqueous medium (B). By adding each monomer as an emulsion to the aqueous medium (B), polymer particles with a more uniform size are formed, and the properties of the formed core-shell type particles (A) are stabilized.

[0041] In this process, it is preferable to include a radical polymerization initiator. Examples of radical polymerization initiators include ammonium persulfate, potassium persulfate, hydrogen peroxide, and t-butyl hydroperoxide. The content of the radical polymerization initiator relative to the total amount of polymer (a1) after excluding structural units derived from the reactive emulsifier is preferably 0.01% by mass or more and 1% by mass or less. Furthermore, in this process, the polymerization temperature of each component should be equal to or higher than the polymerization initiation temperature of the radical polymerization initiator used. For example, when using ammonium persulfate as the radical polymerization initiator, the polymerization temperature should be approximately 60°C to 90°C. The polymerization time is not particularly limited, but is usually 2 to 24 hours.

[0042] (Core formation process) The core formation step involves polymerizing a conjugated diene monomer and an aromatic vinyl monomer using the polymer particles as a reaction field to form a core consisting of polymer (a2) inside the polymer particles. As mentioned above, in the shell formation step, the reactive emulsifier becomes a hydrophilic group of the polymer that will become the shell, and loses its function as a surfactant. Therefore, the polymerization that forms the core (polymer a2) in the core formation step can be described as soap-free polymerization, which is carried out in the absence of surfactants. The polymer particles that will become the shell have hydrophilic groups derived from the reactive emulsifier, which increases their hydrophilicity with respect to the conjugated diene monomer and aromatic vinyl monomer that are to become the core (polymer (a2)). As a result, the hydrophobic monomers that are to become the core (polymer (a2)) enter the interior of the polymer particles (polymer (a1)) that have hydrophilic groups, and polymerize inside the polymer particles, thereby forming a core-shell type particle (A) through an inverted-phase core-shell process.

[0043] Conjugated diene monomers, aromatic vinyl monomers, and other monomers (such as vinyl monomers with crosslinkable reactive groups and vinyl monomers with cyano groups) may be added directly to the aqueous medium (B) in which the polymer particles are dispersed, or they may be added as an emulsion that has been emulsified in the aqueous medium beforehand, but it is preferable to add these monomers directly.

[0044] In this step, it is preferable to include a radical polymerization initiator. As the radical polymerization initiator, the various radical polymerization initiators described above can be used. Furthermore, the content of the radical polymerization initiator relative to the total amount of units constituting the polymer (a2) is preferably 0.01% by mass or more and 1% by mass or less. Furthermore, in this process, the polymerization temperature of each component should be equal to or higher than the polymerization initiation temperature of the radical polymerization initiator used. For example, when using ammonium persulfate as the radical polymerization initiator, the polymerization temperature should be approximately 60°C to 90°C. The polymerization time is not particularly limited, but is usually 2 to 24 hours.

[0045] 3. Composition for non-aqueous secondary battery negative electrode The present invention also relates to a composition for a negative electrode in a non-aqueous secondary battery (hereinafter also simply referred to as "the negative electrode composition of the present invention"), which contains a negative electrode active material and the above-described binder composition for a negative electrode in a non-aqueous secondary battery (i.e., binder composition 1 for the negative electrode in the present invention or binder composition 2 for the negative electrode in the present invention). The negative electrode active material is not particularly limited and examples include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that combine these. Carbon-based anode active materials refer to active materials with a carbon-based skeleton that can be doped with lithium. Examples of carbon-based anode active materials include graphite materials and carbonaceous materials. Examples of graphite materials include natural graphite and artificial graphite. Examples of carbonaceous materials include easily graphitizable carbon such as coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fibers, and pyrolysis vapor-grown carbon fibers, and examples of difficult-to-graphitize carbon such as phenolic resin calcined bodies, polyacrylonitrile carbon fibers, pseudoisotropic carbon, furfuryl alcohol resin calcined bodies (PFA), and hard carbon. Furthermore, as metallic anode active materials, for example, lithium metal, elemental metals that can form lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and their alloys, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc., can be used. Among these, silicon-containing active materials (silicon-based anode active materials) are preferred as metallic anode active materials. By using silicon-based anode active materials, the capacity of lithium-ion secondary batteries can be increased. Examples of silicon-based anode active materials include silicon (Si), silicon-containing alloys, SiO, SiO x Examples include composites of Si-containing material and conductive carbon, which are obtained by coating or compounding Si-containing material with conductive carbon.

[0046] Furthermore, the negative electrode composition of the present invention may further contain a conductive material. Examples of conductive materials include conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene, as well as porous carbon. These may be used individually or in combination of two or more types.

[0047] The negative electrode composition of the present invention is obtained by mixing and dispersing the aforementioned negative electrode active material with the non-aqueous secondary battery negative electrode binder composition of the present invention. There are no particular restrictions on the order of addition during mixing. Furthermore, an aqueous medium may be added as appropriate from the viewpoint of adjusting the viscosity of the obtained negative electrode composition of the present invention and improving dispersion stability. Dispersion can be carried out using dispersion equipment such as a stirrer, a rotary-orbit mixer, a ball mill, a super sand mill, or a pressurized kneader.

[0048] 4.Nonaqueous secondary battery The present invention also relates to a non-aqueous secondary battery anode comprising a negative electrode material layer formed using the negative electrode composition of the present invention described above. The present invention also relates to a non-aqueous secondary battery comprising a negative electrode, a positive electrode, an electrolyte, and a separator. The binder composition for a negative electrode of the non-aqueous secondary battery of the present invention exhibits excellent elastic deformation characteristics that can follow volume changes of the active material, film-forming properties, and durability against electrolytes (electrolyte resistance). Therefore, the negative electrode material layer formed from a negative electrode composition containing the binder composition for a negative electrode of the present invention exhibits excellent charge-discharge capacity and capacity retention rate. In other words, the non-aqueous secondary battery of the present invention having a negative electrode equipped with such a negative electrode material layer exhibits good charge-discharge characteristics and excellent capacity retention rate. As the non-aqueous secondary battery of the present invention, non-aqueous electrolyte secondary batteries and solid-state electrolyte secondary batteries are preferred, and in particular, non-aqueous electrolyte secondary batteries equipped with a negative electrode material layer formed using the non-aqueous secondary battery negative electrode composition of the present invention tend to exhibit superior performance. For example, if the secondary battery of the present invention is a wet electrolyte secondary battery, it can be constructed by arranging the negative electrode containing the negative electrode material layer and the positive electrode opposite each other via a separator, and injecting an electrolyte.

[0049] <Negative electrode> The negative electrode of the present invention can be obtained, for example, by applying the above-described non-aqueous secondary battery negative electrode composition of the present invention to a current collector to form a negative electrode material layer as a thin film. Alternatively, the negative electrode can be obtained by molding the negative electrode composition of the present invention into a sheet, pellet, or other shape and integrating it with a current collector.

[0050] Examples of materials for the current collector include copper, nickel, titanium, and stainless steel. The current collector is preferably in the form of a strip, such as foil, perforated foil, or mesh. Porous materials such as porous metal (foamed metal) and carbon paper can also be used as current collectors. Methods for applying the negative electrode composition to the current collector include, for example, metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, gravure coating, and screen printing. After application, it is preferable to perform rolling treatment using a flat plate press, calender roll, etc., as needed. Alternatively, a negative electrode material layer may be obtained by forming a paste-like negative electrode composition into a sheet or pellet, and then integrating it with a current collector using a roll, press, or a combination thereof.

[0051] The negative electrode material layer formed on the current collector or the negative electrode material layer integrated with the current collector is preferably heat-treated. Such heat treatment removes the aqueous medium (B) derived from the non-aqueous secondary battery negative electrode binder composition of the present invention, promotes the fusion of core-shell type particles (A), and further improves the adhesion between negative electrode active materials and between negative electrode active materials and the current collector. The heat treatment temperature is preferably in the range of 50 to 220°C, and more preferably in the range of 100 to 200°C. There are no particular restrictions on the heat treatment time, which is usually in the range of 1 minute to 20 hours. Furthermore, it is preferable to perform the heat treatment under a non-oxidizing gas atmosphere such as helium, argon, or nitrogen, or under a vacuum atmosphere, from the viewpoint of preventing oxidation of the current collector during the heat treatment. Furthermore, after heat treatment, the negative electrode, which consists of a negative electrode material layer formed on the current collector or a negative electrode material layer integrated with the current collector, is preferably subjected to pressurization from the viewpoint of adjusting the electrode density. The electrode density of the negative electrode is typically 1 to 1.8 g / cm³. 3 Preferably, it is 1.1 to 1.7 g / cm³. 3 It is more preferable that the concentration be 1.2 to 1.6 g / cm³. 3 It is even more preferable that this be the case. While higher electrode density tends to improve adhesion and electrode volumetric density, excessively high density can reduce voids within the electrode, making it difficult to suppress positive electrode expansion and potentially lowering capacity retention. Therefore, an optimal range for electrode density must be selected.

[0052] The positive electrode is obtained in the same way as the negative electrode by forming a positive electrode material layer on the surface of the current collector. For example, a positive electrode material slurry is prepared by kneading a positive electrode active material and an organic binder with a solvent using a dispersion device such as a stirrer, ball mill, super sand mill, or pressurized kneader. This positive electrode material slurry can then be applied to a current collector (e.g., copper foil) to form a positive electrode material layer.

[0053] The positive electrode active material is not particularly limited. In the case of manufacturing a lithium-ion secondary battery, for example, among non-aqueous electrolyte secondary batteries, examples include metal compounds, metal oxides, metal sulfides, and conductive polymers that can dope or intercalate lithium ions. Specifically, lithium cobalt oxides (LCOs) such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2) and their composite oxides (LiCoxNiyMnzO2, x+y+z=1; lithium-nickel-manganese-cobalt composite oxide (NMC)); lithium manganese spinel (LiMn2O4), lithium vanadium compounds, V2O5, V6O 13Examples include VO2, MnO2, TiO2, MoV2O8, TiS2, V2S5, VS2, MoS2, MoS3, Cr3O8, Cr2O5, olivine-type LiMPO4 (where M is Co, Ni, Mn, or Fe); conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene; and porous carbon. These may be used individually or in combination of two or more types. In particular, from the viewpoint of operating voltage, volume density, theoretical capacity, high-temperature stability, and economic efficiency, it is more preferable to use lithium iron phosphate compounds (LFPs) such as olivine-type LiFePO4.

[0054] The average particle size of the positive electrode active material is not particularly limited, but for example, when lithium-cobalt composite oxide (LCO) or lithium-nickel-manganese-cobalt composite oxide (NMC) is used as the positive electrode active material, the average particle size is usually preferably 1 μm to 100 μm, and more preferably 5 μm to 50 μm. Furthermore, when lithium iron phosphate-based compounds (LFP) are used as the positive electrode active material, the average particle size is usually preferably 0.01 μm to 5 μm, and more preferably 0.1 μm to 1 μm. When the average particle size of the positive electrode active material is within the aforementioned range, the positive electrode expansion rate during charging and discharging is small when used in a secondary battery, and it is easier to prevent a decrease in the reversible charge-discharge capacity per unit volume. Furthermore, it is easier to suppress the peeling of the electrode film (positive electrode material layer) from the current collector during electrode film fabrication. The average particle size of the positive electrode active material is the particle size (D50) at which the cumulative volume reaches 50% when the volume cumulative distribution curve is drawn from the smallest diameter side, based on the particle size distribution measured by dynamic light scattering using a laser diffraction particle size analyzer or the like.

[0055] The positive electrode active material may be coated on at least a portion of its surface with a coating material. The coating material is preferably a substance that exhibits electronic conductivity, lithium-ion conductivity, and an effect of suppressing electrolyte decomposition. Examples of electronically conductive substances include carbon, titanium, and nickel. Among these, carbon is preferred, and low-crystallinity carbon is more preferred, from the viewpoint of improving the chemical and thermal stability of the positive electrode active material and suppressing a decrease in the charge-discharge performance of the resulting secondary battery. When at least a portion of the surface of the positive electrode active material is covered with a coating material, the average thickness of the coating layer is preferably 10 nm to 300 nm, and more preferably 20 nm to 200 nm. Furthermore, the content of the coating material is preferably 1 to 30% by mass relative to the total amount of the components of the positive electrode active material and the coating material. Examples of the organic binders include styrene-butadiene rubber copolymers (hereinafter also referred to as "SBR"); ethylenically unsaturated carboxylic acid copolymers such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate, and unsaturated carboxylic acid copolymers such as (meth)acrylic copolymers made from ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid; and polymer compounds such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide, polyamideimide, and carboxymethylcellulose (hereinafter also referred to as "CMC"). Depending on their physical properties, these organic binders may be dispersed or dissolved in water, or dissolved in an organic solvent such as N-methyl-2-pyrrolidone.

[0056] The content of organic binder in the positive electrode material layer of the lithium-ion secondary battery positive electrode is preferably 1 to 30% by mass, more preferably 2 to 20% by mass, and even more preferably 3 to 15% by mass. When the organic binder content is 1% by mass or more, adhesion is improved, and the destruction of the negative electrode structure due to expansion or contraction during charging and discharging is more easily suppressed. On the other hand, when it is 30% by mass or less, the increase in electrode resistance is more easily suppressed.

[0057] The positive electrode slurry may further contain conductive additives as needed. Examples of conductive additives include carbon black, graphite, acetylene black, conductive oxides, and nitrides. If the positive electrode slurry further contains conductive additives, the amount is preferably in the range of 1 to 15% by mass relative to the positive electrode active material.

[0058] Examples of materials for the current collector include copper, nickel, titanium, and stainless steel. The current collector is preferably in the form of a strip, such as foil, perforated foil, or mesh. Porous materials such as porous metal (foamed metal) and carbon paper can also be used as current collectors. Methods for applying the positive electrode material slurry to the current collector include, for example, metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, gravure coating, and screen printing. After application, it is preferable to perform rolling treatment using a flat plate press, calender roll, etc., as needed. Alternatively, a positive electrode material layer may be obtained by forming a paste-like positive electrode material slurry into a sheet or pellet, and then integrating it with a current collector using a roll, press, or a combination thereof.

[0059] The positive electrode material layer formed on the current collector or the positive electrode material layer integrated with the current collector is preferably heat-treated according to the type of organic binder used. For example, when using a water-based styrene-butadiene rubber copolymer (SBR), heat treatment at 100 to 130°C is preferable, and when using an organic binder with polyimide or polyamide-imide as the main backbone, heat treatment at 150 to 450°C is preferable. This heat treatment removes solvents derived from the organic binder and promotes increased strength due to the hardening of the organic binder, thereby improving adhesion between particles and between particles and the current collector. It is preferable to perform the heat treatment under a non-oxidizing gas atmosphere such as helium, argon, or nitrogen, or under a vacuum atmosphere, from the viewpoint of preventing oxidation of the current collector during the heat treatment.

[0060] Furthermore, after heat treatment, the positive electrode, which consists of a positive electrode material layer formed on the current collector or a positive electrode material layer integrated with the current collector, is preferably subjected to pressure treatment from the viewpoint of adjusting the electrode density. The electrode density of the positive electrode is typically 1 to 1.8 g / cm³. 3 Preferably, it is 1.1 to 1.7 g / cm³. 3 It is more preferable that the concentration be 1.2 to 1.6 g / cm³. 3 It is even more preferable that the electrode density is as follows: While higher electrode density tends to improve adhesion and electrode volumetric density, if it is too high, the voids in the electrode decrease, making it difficult to suppress the positive electrode expansion rate and potentially reducing the capacity retention rate. Therefore, an optimal range for electrode density is selected.

[0061] As a separator, nonwoven fabrics, cloths, microporous films, or combinations thereof, mainly composed of polyolefins such as polyethylene and polypropylene can be used. However, if the positive and negative electrodes of the non-aqueous electrolyte secondary battery being manufactured are not in direct contact, a separator is not required.

[0062] As the electrolyte, a so-called organic electrolyte can be used, which is obtained by dissolving lithium salts such as LiClO4, LiPF6, LiAsF6, LiBF4, and LiSO3CF3 in one or more non-aqueous solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidine-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, and ethyl acetate.

[0063] The structure of a secondary battery using the non-aqueous secondary battery positive electrode binder composition of the present invention is not particularly limited, but it is common to have a structure in which the positive electrode, negative electrode, and a separator provided as needed are wound in a flat spiral shape to form a wound electrode plate group, or these are stacked as flat plates to form a stacked electrode plate group, and these electrode plate groups are sealed in an outer casing. A secondary battery using the non-aqueous secondary battery negative electrode binder composition of the present invention can be used as, for example, a paper-type battery, a button-type battery, a coin-type battery, a stacked-type battery, a cylindrical battery, a prismatic battery, etc. The binder composition for the negative electrode of a non-aqueous secondary battery of the present invention is also applicable to electrochemical devices in general that use the insertion and deinsertion of lithium ions as a charge and discharge mechanism, such as hybrid capacitors and solid lithium secondary batteries.

[0064] The binder composition for a non-aqueous secondary battery negative electrode, the method for manufacturing the binder composition for a non-aqueous secondary battery negative electrode, the negative electrode composition, the negative electrode, and the secondary battery having the negative electrode of the present invention have been described above. However, the present invention is not limited to the configurations of the embodiments described above. For example, the binder composition for a non-aqueous secondary battery negative electrode, the method for manufacturing the binder composition for a non-aqueous secondary battery negative electrode, the negative electrode composition, the negative electrode, and the secondary battery having the negative electrode of the present invention may each have additional configurations in addition to the configurations of the embodiments described above, or may be replaced with any configuration that performs similar functions. [Examples]

[0065] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples described below. The raw materials used in each example and comparative example are listed below.

[0066] <Vinyl monomers containing acidic groups> AA: Acrylic acid MAA: Methacrylic acid IA: Itaconic acid <(meth)acrylic acid monomer> MMA: Methyl methacrylate BA: Butyl acrylate 2EHA: 2-ethylhexyl acrylate <Aromatic vinyl monomers> ST: Styrene <Vinyl monomers containing amide groups> AM: Acrylamide DM: Dimethylacrylamide <Vinyl monomer having an amide group and a crosslinkable reactive group> NMAM: N-methylolacrylamide MAC:N-methylol methacrylamide NBAM: Nn-Butoxymethylacrylamide <Conjugated diene monomers> IP: Isoprene BD: Butadiene <Vinyl monomers containing cyano groups> AN: Acrylonitrile <Vinyl monomers having crosslinkable reactive groups> GMA: Glycidyl methacrylate DVB: Divinylbenzene MPTMS: 3-(trimethoxysilyl)propyl methacrylate <Fluorine-containing monomers> TF3F: 2,2,2-trifluoroethyl acrylate <Emulsifier> SR-10: Ether sulfate type ammonium salt (Reactive surfactant Adekaria Soap SR-10, manufactured by ADEKA Corporation) 08E: Polyoxyethylene oleyl cetyl ether ammonium sulfate (non-reactive surfactant, Hythenol 08E, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)

[0067] Example 1 (1) Preparation of binder composition for negative electrode <Shell Formation Process> In a reaction vessel equipped with a stirrer, thermometer, and condenser, 220 parts by mass of deionized water and 0.5 parts by mass of SR-10 were charged and heated to 80°C. Next, an emulsion was prepared by mixing 50 parts by mass of deionized water, 0.5 parts by mass of SR-10, parts by mass of ST26, 68 parts by mass of 2EHA, and 6 parts by mass of AA. This emulsion, along with an aqueous solution prepared by dissolving 0.2 parts by mass of ammonium persulfate in 10 parts by mass of deionized water, was simultaneously added dropwise to the reaction vessel over 3 hours to carry out polymerization. After the dropwise addition was complete, the temperature was maintained at 80°C for 2 hours. Subsequently, the mixture was cooled to room temperature, and the non-volatile content was adjusted to 26.0% with deionized water to obtain an emulsion in which polymer particles were dispersed in an aqueous medium (deionized water). <Core formation process> In a nitrogen-purged autoclave with a stirrer, 400 parts by mass of polymer particles (100 parts by mass of solids), 0.3 parts by mass of ethylenediaminetetraacetic acid, 0.4 parts by mass of tert-dodecyl mercaptan, and 50 parts by mass of ST and 50 parts by mass of IP as monomers were charged. 0.05 parts by mass of ammonium persulfate was added, and the mixture was heated to 80°C while stirring, and emulsion polymerization was carried out for 15 hours. Unreacted monomers were removed by steam distillation, the pH was adjusted to 7 with 25% aqueous ammonia, and the non-volatile content was adjusted to 30% with deionized water to obtain a binder composition for the negative electrode.

[0068] (2) Preparation of the negative electrode composition Ten parts by mass of SiO-based negative electrode active material and 86 parts by mass of artificial graphite were weighed out as negative electrode active materials and stirred for 30 seconds in a rotary-orbit mixer. Next, 48.0 parts by mass (0.96 parts by mass in terms of solid content) of an aqueous solution (hereinafter referred to as "CMC solution") prepared by dissolving carboxymethylcellulose sodium salt ("Sunrose MAC350HC" manufactured by Nippon Paper Industries Co., Ltd.) in distilled water and adjusting the non-volatile content to 2% was added, along with 250 parts by mass (1 part by mass in terms of solid content) of single-wall carbon nanotube aqueous dispersion ("TUBALL BATT H2O" manufactured by OCSiAl). After mixing until the mixture became a paste, it was stirred for 2 minutes in a rotary-orbit mixer. Since heat was generated by stirring, it was cooled to room temperature with ice water, stirred again for 2 minutes in a rotary-orbit mixer, and then cooled to room temperature with ice water. Subsequently, 27.0 parts by mass (0.54 parts by mass in terms of solid content) of the above CMC solution was added to this mixture, and after mixing until the whole became uniform, it was stirred with a planetary mixer for 2 minutes and cooled to room temperature with ice water. Then, 5 parts by mass (1.5 parts by mass in terms of solid content) of the negative electrode binder composition obtained in the above (1) was added, stirred again with a planetary mixer for 2 minutes, and cooled to room temperature with ice water. While measuring the viscosity of the obtained slurry at 25 °C and 30 rpm with a B-type viscometer, distilled water was added so that the viscosity was in the range of 2000 - 4000 mPa·s. Finally, it was stirred with a planetary mixer for 30 seconds to prepare a slurry-like negative electrode composition.

[0069] (3) Preparation of negative electrode The coating amount (areal density) of the dried negative electrode composition was adjusted to 8.8 mg / cm 2 by adjusting the gap of the bar coater, and the negative electrode composition was coated on a copper foil as a current collector with this bar coater and dried at 80 °C for 8 minutes in a blowing dryer. The dried electrode was cut to a width of 40 mm, and using a roll press machine (「Small desktop roll press SA-602」manufactured by Tester Sangyo Co., Ltd.), it was pressed so that the layer density became 1.55 g / cm 3 and then vacuum dried at 110 °C for 10 hours to obtain a negative electrode.

[0070] (4) Preparation of positive electrode composition 94.0 parts by mass of olivine-type lithium iron phosphate (LiFePO4) as a positive electrode active material and 3.0 parts by mass of acetylene black as a conductive material were weighed, and stirred with a planetary mixer (「ARE-310 (trade name)」manufactured by Thinky Co., Ltd.) at a rotation speed of 1000 rpm and a revolution speed of 2000 rpm for 30 seconds. Thereafter, stirring using a planetary mixer was carried out under the same apparatus and conditions unless otherwise specified. Next, 2.1,6 parts by mass of polyvinylidene fluoride (PVDF) and 19.0 parts by mass of NMP were added and mixed until the whole became paste-like, and then stirred with a planetary mixer for 2 minutes. Since heat was generated by the stirring, it was cooled to room temperature with ice water, stirred again with a planetary mixer for 2 minutes, and cooled to room temperature with ice water. Next, 0.84 parts by mass of polyvinylidene fluoride (PVDF) and 5 parts by mass of NMP were added to this mixture and mixed until the mixture was homogenized. The viscosity of the obtained slurry was measured using a B-type viscometer at 25°C and 30 rpm, and NMP was added to bring it within the range of 2000-4000 mPa·s. Finally, the mixture was stirred for 30 seconds in a rotary-orbit mixer to prepare a slurry-like cathode composition.

[0071] (5) Preparation of the positive electrode The coating density (surface density) of the cathode composition after drying is 25.0 mg / cm². 2 The gap of the bar coater was adjusted to achieve the desired result, and the positive electrode composition obtained above was coated onto the carbon-coated aluminum foil, which served as the current collector, using this bar coater. The mixture was then dried for 10 minutes in a forced-air dryer set to 100°C. The dried electrodes were cut to a width of 40 mm and pressed using a roll press machine (Tester Industries Co., Ltd. "Small Tabletop Roll Press SA-602") to obtain a layer density of 2.5 g / cm³. 3 After pressing in this manner, the cathode was obtained by vacuum drying at 110°C for 10 hours.

[0072] (6) Manufacturing of secondary batteries The negative electrode prepared above was cut into a 24mm x 24mm square with a tab, and the positive electrode prepared above was cut into a 22mm x 22mm square with a tab, using a die-cutting blade. Nickel tab leads were welded to the tab portion of the cut electrodes, and aluminum tab leads were welded to the tab portion of the positive electrode. Meanwhile, a 25μm thick polyethylene microporous membrane was cut into a 28mm x 3.8cm rectangle using a die-cutting blade as a separator. The positive and negative electrodes were placed facing each other with this separator in between, wrapped in laminate film, and the tab portion was fixed by heat sealing. Then, LiPF6 was dissolved in a 30 / 30 / 40 mixed solution of ethylene carbonate / dimethyl carbonate / methyl ethyl carbonate at a concentration of 1 mol / L. 300 μL of a non-aqueous electrolyte solution, obtained by adding 1 vol% vinyl carbonate and 5 vol% fluoroethylene carbonate, was added, and the solution was completely sealed by vacuum lamination to produce the laminate-type secondary battery of Example 1.

[0073] Comparative Example 1 Except for using a negative electrode binder composition prepared by the method described below, a negative electrode composition, a positive electrode, and a secondary battery were obtained in the same manner as in Example 1. (1) Preparation of binder composition for negative electrode <Synthesis of Emulsion A> 200 parts by mass of deionized water were charged into a reaction vessel equipped with a stirrer, thermometer, and condenser, and heated to 80°C. Next, an emulsion prepared by dissolving 50 parts by mass of ST, 47 parts by mass of 2EHA, and 3 parts by mass of MAA as monomers in a solution of 12 parts by mass of SR-10, 0.05 parts by mass of ammonium persulfate, and 40 parts by mass of deionized water was added dropwise to the reaction vessel over 2 hours, and emulsion polymerization was carried out by maintaining the mixture for 2 hours. After that, the mixture was cooled to room temperature, the pH was adjusted to 7 with 25% aqueous ammonia, and the non-volatile content was adjusted to 25% with deionized water to obtain emulsion A. <Synthesis of Emulsion B> In a nitrogen-purged autoclave with a stirrer, 150 parts by mass of deionized water, 12 parts by mass of SR-10, 0.3 parts by mass of ethylenediaminetetraacetic acid, 0.4 parts by mass of tert-dodecyl mercaptan, and 50 parts by mass of ST and 50 parts by mass of IP as monomers were charged. 0.05 parts by mass of ammonium persulfate was added, and the mixture was heated to 80°C with stirring and emulsion polymerization was carried out for 15 hours. Unreacted monomers were removed by steam distillation, the pH was adjusted to 7 with 25% aqueous ammonia, and the non-volatile content was adjusted to 35% with deionized water to obtain emulsion B. <Preparation of Blend Emulsion> By mixing 100 parts by mass of emulsion A and 100 parts by mass of emulsion B, a blended emulsion with a non-volatile component content of 30% was prepared to form a binder composition for the negative electrode.

[0074] Examples 2-40, Comparative Examples 2-3 Except for using a negative electrode binder composition with modified material types and amounts as shown in Tables 1-4, a negative electrode composition, a negative electrode, a positive electrode, and a secondary battery were obtained in the same manner as in Example 1.

[0075] [evaluation] 1. Peel strength of the negative electrode Test pieces measuring 25 mm wide x 100 mm long were cut from the negative electrodes prepared in each example and comparative example. The negative electrode active material side of the test piece was used as the adhesion surface and attached to a stainless steel plate using double-sided tape (Nitto Denko Corporation's "No. 5015"). On the other hand, approximately 10 mm of the edge of the carbon-coated aluminum foil was peeled off, and polyimide tape was attached to it to serve as the attachment point for the peel test equipment (Shimadzu Corporation's "Autograph AG-XPlus"). A 180° peel test was performed using the peel test machine, and the peel strength was measured.

[0076] 2. Battery characteristics (initial charge / discharge efficiency and capacity retention rate) The secondary batteries prepared in each example and comparative example were mounted on a charge / discharge device, left at 25°C for 3 hours, and then charged and discharged once at 0.1C. The initial charge / discharge efficiency was then measured. Next, the charge-discharge cycle was repeated 50 times at 60°C and 0.2C, and the discharge capacity retention rate after 50 cycles at 60°C (relative to the initial discharge capacity at 0.2C) was measured using the following formula. Capacity retention rate (%) = 100 × Discharge capacity after 50th discharge (mAh / g) / Initial discharge capacity (mAh / g) The results above are summarized in Tables 1-4.

[0077] [Table 1]

[0078] [Table 2]

[0079] [Table 3]

[0080] [Table 4]

[0081] The results in Tables 1-4 show that the negative electrode binder composition of the present invention exhibits excellent film-forming properties. Furthermore, the negative electrode formed from the negative electrode binder composition of the present invention exhibits excellent resistance to electrolyte, and secondary batteries equipped with such negative electrodes have a high initial charge-discharge efficiency of 90% or more, and moreover, a capacity retention rate of 90% or more, indicating an excellent balance of battery characteristics. In addition, although the negative electrode composition using the negative electrode binder composition of the present invention contained a silicon-containing active material (silicon carbide-based negative electrode active material) as the negative electrode active material, which undergoes a large volume change due to lithium absorption and release, the discharge capacity retention rate after 50 cycles of the fabricated secondary battery was sufficiently high, indicating that it has sufficient cycle characteristics when used as a secondary battery. [Industrial applicability]

[0082] The negative electrode binder composition of the present invention, even when a silicon-containing active material is used as the negative electrode active material, exhibits excellent elastic deformation characteristics that can follow the volume change of the silicon-containing active material, as well as excellent film-forming properties and excellent durability to the electrolyte (electrolyte resistance), enabling the formation of a negative electrode and secondary battery with excellent battery characteristics such as charge-discharge efficiency and capacity retention rate. A secondary battery equipped with such a negative electrode has excellent battery characteristics such as charge-discharge characteristics and can be effectively used in portable electronic devices, for example, as a paper battery, button battery, coin battery, stacked battery, cylindrical battery, prismatic battery, etc.

Claims

1. A binder composition for a negative electrode of a non-aqueous secondary battery, comprising core-shell type particles (A) having a shell portion made of polymer (a1) and a core portion made of polymer (a2), and an aqueous medium (B), The polymer (a1) contains structural units derived from a reactive emulsifier, structural units derived from a vinyl monomer having an acidic group, and structural units derived from a (meth)acrylic acid ester monomer. A binder composition for a negative electrode of a non-aqueous secondary battery, wherein the polymer (a2) contains structural units derived from a conjugated diene monomer and structural units derived from an aromatic vinyl monomer.

2. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the reactive emulsifier is an emulsifier having an ethylenically unsaturated group.

3. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the content of structural units derived from the reactive emulsifier is 0.01% by mass or more and 3% by mass or less, relative to the total amount obtained by excluding the structural units derived from the reactive emulsifier from the units constituting the polymer (a1).

4. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the content of structural units derived from the acidic vinyl monomer is 0.1% by mass or more and 10% by mass or less, relative to the total amount obtained by excluding the structural units derived from the reactive emulsifier from the units constituting the polymer (a1).

5. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the polymer (a1) further contains structural units derived from an aromatic vinyl monomer.

6. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the polymer (a1) further contains structural units derived from a vinyl monomer having an amide group.

7. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the conjugated diene monomer contains isoprene.

8. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the polymer (a2) further contains structural units derived from a vinyl monomer having a cyano group.

9. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 8, wherein the content of structural units derived from the vinyl monomer having a cyano group, relative to the total amount of units constituting the polymer (a2), is 0.1% by mass or more and 10% by mass or less.

10. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the polymer (a2) does not contain structural units derived from a vinyl monomer having an acidic group.

11. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein the polymer (a2) does not contain structural units derived from a fluorine-containing monomer.

12. The binder composition for a negative electrode of a non-aqueous secondary battery according to claim 1, wherein when the content of the polymer (a1) in the core-shell type particle (A) is X [mass%] and the content of the polymer (a2) in the core-shell type particle (A) is Y [mass%], X:Y is 5:95 to 99:

1.

13. A method for producing a binder composition for a negative electrode of a non-aqueous secondary battery, comprising core-shell type particles (A) having a shell portion made of polymer (a1) and a core portion made of polymer (a2), and an aqueous medium (B), A shell-forming step in which a vinyl monomer having an acidic group and a (meth)acrylic acid ester monomer are polymerized in the aqueous medium (B) in the presence of a reactive emulsifier to form polymer particles that will become the shell portion, the polymer (a1) A method for producing a binder composition for a negative electrode of a non-aqueous secondary battery, comprising: a core formation step of polymerizing a conjugated diene monomer and an aromatic vinyl monomer using polymer particles as a reaction field to form the core portion consisting of the polymer (a2) inside the polymer particles.

14. A composition for a negative electrode of a non-aqueous secondary battery, comprising a negative electrode active material and a binder composition for a negative electrode of a non-aqueous secondary battery according to any one of claims 1 to 12.

15. A non-aqueous secondary battery anode comprising a negative electrode material layer formed using the non-aqueous secondary battery anode composition described in claim 14.

16. A non-aqueous secondary battery comprising a negative electrode, a positive electrode, an electrolyte, and a separator, as described in claim 15.

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