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

Abstract

Provided is a binder composition for a nonaqueous secondary battery electrode, which has excellent durability in terms of an electrolyte solution and excellent film-forming properties, and which makes it possible to form a secondary battery that has excellent battery characteristics such as charge / discharge efficiency and capacity retention rate.　The binder composition for a nonaqueous secondary battery electrode contains vinyl polymer-based resin particles (A) and an aqueous medium (B). The degree of swelling after a film formed of the vinyl polymer-based resin particles (A) is immersed in a specific organic solvent under specific conditions is 5 mass% to 100 mass% inclusive. When differential scanning calorimetry (DSC) is performed on the film formed of the vinyl polymer-based resin particles (A), one glass transition point is observed in the temperature range of -50°C to 70°C, and one glass transition point is observed in the temperature range of 70°C to 170°C. The lowest film formation temperature of a coating film that is formed of an adjustment liquid which is adjusted so as to have a solid content concentration of the vinyl polymer-based resin particles (A) of 25 mass% is 70°C or lower.

Description

Binder composition for non-aqueous secondary battery electrodes, method for manufacturing the binder composition for non-aqueous secondary battery electrodes, composition for non-aqueous secondary battery electrodes, non-aqueous secondary battery electrodes, and non-aqueous secondary battery

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

[0002] Non-aqueous secondary batteries (non-aqueous electrolyte secondary batteries), such as lithium-ion secondary batteries, are 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. 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 improve the performance of non-aqueous secondary batteries, improvements to various battery components such as electrodes are being considered. Electrodes for non-aqueous secondary batteries typically comprise a current collector and an electrode material layer formed on the current collector. This electrode material layer is formed using a slurry-like electrode composition in which a composition containing, for example, an active material (negative electrode active material or positive electrode active material) and a binder (binding agent) is dispersed in a dispersion medium. In the negative electrode of lithium-ion secondary batteries, styrene-butadiene copolymer (SBR) is commonly used as the binder component. However, with SBR-based binders, the bonding properties between the negative electrode active materials and between the negative electrode active materials and the current collector are not always sufficient. As a result, when producing a negative electrode with a small amount of binder, there is a problem in which some of the negative electrode active materials peel off during the process of cutting the current collector. Acrylic emulsion (AcEm) is also used in some cases as a binder composition because of its excellent heat resistance and mechanical properties. However, while SBR has excellent electrolyte resistance due to its hydrophobic resin skeleton, AcEm has a problem in that it has high affinity for electrolytes due to its ester group resin skeleton and therefore has poor electrolyte resistance.

[0003] To address these problems, for example, Patent Document 1 proposes using an aqueous emulsion obtained by emulsion polymerization of an ethylenically unsaturated monomer in the presence of a surfactant, containing 15 to 70% by mass of styrene, 0.1 to 10% by mass of an ethylenically unsaturated carboxylic acid ester having polar groups, 25 to 80% by mass of other ethylenically unsaturated carboxylic acid esters, an ethylenically unsaturated carboxylic acid, and 0.1 to 3% by mass of an internal crosslinking agent as essential components relative to the total ethylenically unsaturated monomer, as a binder for lithium-ion secondary battery electrodes. In the binder of Patent Document 1, it is stated that electrolyte resistance is achieved by a crosslinking structure formed throughout the binder particles. Furthermore, Patent Document 2 proposes a binder for secondary battery electrodes containing a copolymer latex obtained by emulsion polymerization of a monomer composition comprising 60 to 94.8% by weight of an unsaturated carboxylic acid alkyl ester monomer, 0.1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer containing a dicarboxylic acid, 5 to 20% by weight of an alkenyl aromatic monomer, and 0.1 to 10% by weight of other monomers copolymerizable with these (excluding cyano group-containing vinyl monomers, the aforementioned unsaturated carboxylic acid alkyl ester monomers, the aforementioned ethylenically unsaturated carboxylic acid monomers, and the aforementioned alkenyl aromatic monomers). The binder in Patent Document 2 is said to have excellent electrolyte resistance and improved bonding strength of the electrode coating layer because it does not contain cyano groups, which are easily soluble in electrolytes.

[0004] On the other hand, polyvinylidene fluoride (PVDF) is generally used as a binder component for the positive electrode of lithium-ion secondary batteries. However, dissolving PVDF requires N-methyl-2-pyrrolidone (NMP) as a solvent, which poses a problem in terms of environmental load. Furthermore, when PVDF is placed in a high-temperature environment of 50°C or higher, it swells and is plasticized by the electrolytic solution, which weakens the binding force, increases electrode resistance, and also has the problem of lacking high-temperature durability. Furthermore, the binding property between positive electrode active materials and the binding property between the positive electrode active material and the current collector are not necessarily sufficient. To address these problems, SBR and acrylic emulsions have been studied as alternatives to PVDF. For example, in Patent Document 3, a polymer containing a structural unit derived from (a3) a (meth)acrylic acid ester compound is obtained by polymerizing a monomer component containing (a1) 20 to 50 parts by mass of an aromatic vinyl compound, (a2) 25 to 60 parts by mass of a conjugated diene compound, (a3) 5 to 40 parts by mass of a (meth)acrylic acid ester compound, and (a4) 0.5 to 6 parts by mass of an ethylenically unsaturated carboxylic acid monomer, provided that the total of the monomer components is 100 parts by mass. A binder for a secondary battery electrode obtained by this polymerization is proposed. In addition, in Patent Document 4, a binder for a secondary battery electrode is proposed in which (A) polymer particles contain a diene-based polymer having a repeating unit Mc derived from an unsaturated carboxylic acid, a repeating unit Md derived from a conjugated diene compound, and a repeating unit Me derived from an aromatic vinyl compound.

[0005] Japanese Patent No. 5701519, Japanese Patent No. 5809636, Japanese Unexamined Patent Publication No. 2015-005523, Japanese Unexamined Patent Publication No. 2016-072235

[0006] In the binder described in Patent Document 1, a cross-linking structure is formed throughout the binder particles, making it difficult for the binder particles to fuse together. This results in insufficient bonding between the active materials and between the active materials and the current collector. Furthermore, while the binder described in Patent Document 2 attempts to improve electrolyte resistance by omitting cyano groups, which are easily soluble in electrolytes, simply omitting cyano groups is insufficient to achieve electrolyte resistance. Moreover, cyano groups have a high dielectric constant, which can be advantageous for lithium ion conductivity. The binders described in Patent Documents 3 and 4 also suffer from insufficient bonding between the active materials and between the active materials and the current collector. Therefore, there is a strong demand for an electrode binder that exhibits both excellent electrolyte resistance and excellent bonding strength. The present inventors have investigated an acrylic emulsion-based electrode binder composition that exhibits excellent electrolyte resistance and film-forming properties, such as binding properties between active materials (negative electrode active material or positive electrode active material) and binding properties between active materials and current collectors, as a binder (binder particle). As a result, we found that by using binder particles such that, when a film formed from the binder particles is immersed in a predetermined organic solvent under predetermined conditions, the degree of swelling is between 5% by mass and 100% by mass, and when differential scanning calorimetry (DSC) is performed on the film formed from the binder particles, one glass transition point is observed in the temperature range of -50°C to 70°C and another glass transition point is observed in the temperature range of 70°C to 170°C, and the minimum film formation temperature of a coated film formed with an adjusted solution adjusted to a solid content concentration of 25% by mass of the binder particles is 70°C or lower, the binder particles exhibit excellent electrolyte resistance and film formation properties, and are effective in improving battery characteristics such as charge / discharge efficiency and capacity retention rate of secondary batteries equipped with electrodes formed using such an electrode binder composition, thus completing the present invention.The object of the present invention is to provide a binder composition for a non-aqueous secondary battery electrode that can form a secondary battery with excellent durability to electrolytes (electrolyte resistance) and film-forming properties, and excellent battery characteristics such as charge-discharge efficiency and capacity retention rate; a method for producing such an electrode binder composition; a non-aqueous secondary battery electrode composition containing such an electrode binder composition; a non-aqueous secondary battery electrode containing such an electrode composition; and a non-aqueous secondary battery having such an electrode.

[0007] The present invention has the following aspects: [1] A binder composition for non-aqueous secondary battery electrodes containing vinyl polymer resin particles (A) and an aqueous medium (B), wherein a film formed from the vinyl polymer resin particles (A) is made of LiPF ６When a film formed from vinyl polymer resin particles (A) is immersed in a mixed solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 30 / 30 / 40 (volume ratio) at a concentration of 1 mol / L at 60°C for 72 hours, the degree of swelling after immersion is 5% by mass or more and 100% by mass or less, and differential scanning calorimetry (DSC) is performed on the film formed from the vinyl polymer resin particles (A) in accordance with JIS K7121, one glass transition point is observed in the temperature range of -50°C to 70°C, and one glass transition point is observed in the temperature range of 70°C to 170°C, and JIS K A binder composition for non-aqueous secondary battery electrodes, wherein a prepared solution, adjusted to a solid content concentration of 25% by mass of the vinyl polymer resin particles (A) as measured in accordance with 6828-2, is applied to a hot plate with a temperature gradient from 0 to 80°C to a coating thickness of 38 μm (1.5 ml), and then dried for 4 hours, the minimum film-forming temperature is 70°C or lower. [2] The binder composition for non-aqueous secondary battery electrodes of [1], wherein the vinyl polymer resin particles (A) contain structural units derived from an aromatic vinyl monomer, structural units derived from an unsaturated carboxylic acid ester monomer, and structural units derived from a vinyl monomer having an acidic group, wherein the content of structural units derived from the aromatic vinyl monomer is 18% by mass or more and 90% by mass or less, the content of structural units derived from the unsaturated carboxylic acid ester monomer is 8% by mass or more and 80% by mass or less, and the content of structural units derived from the vinyl monomer having an acidic group is 0.05% by mass or more and 10% by mass or less. [3] The binder composition for non-aqueous secondary battery electrodes of [2], wherein the vinyl polymer resin particles (A) are core-shell type particles having a shell portion made of polymer (a1) and a core portion made of polymer (a2). [4] The binder composition for non-aqueous secondary battery electrodes according to [3], wherein the polymer (a1) contains structural units derived from the unsaturated carboxylic acid ester monomer. [5] The binder composition for non-aqueous secondary battery electrodes according to [4], wherein the polymer (a1) further contains structural units derived from the aromatic vinyl monomer. [6] The binder composition for non-aqueous secondary battery electrodes according to [4], wherein the polymer (a1) further contains structural units derived from the acidic vinyl monomer.[7] The binder composition for non-aqueous secondary battery electrodes according to [3], wherein the polymer (a2) contains structural units derived from the aromatic vinyl monomer. [8] The binder composition for non-aqueous secondary battery electrodes according to [3], wherein the polymer (a2) does not contain structural units derived from the vinyl monomer having an acidic group. [9] The binder composition for non-aqueous secondary battery electrodes according to [3], wherein the content of polymer (a1) is X [mass%] and the content of polymer (a2) is Y [mass%], and X:Y is 5:95 to 99:1.

[10] The binder composition for non-aqueous secondary battery electrodes according to [3], wherein the polymer (a1) and the polymer (a2) are chemically bonded.

[11] The binder composition for non-aqueous secondary battery electrodes according to

[10] , wherein the chemical bond is at least one bond selected from ester bonds, siloxane bonds, amide bonds, and hydrazone bonds.

[12] The binder composition for non-aqueous secondary battery electrodes according to

[11] , wherein the chemical bond is formed by at least one reaction selected from the reaction between an epoxy group and a carboxyl group, the hydrolysis and condensation reaction of an alkoxysilyl group, the reaction between an oxazoline group and a carboxyl group, the condensation reaction of a methylol group and / or an alkyloxymethyl group, the reaction between a ketone group and a hydrazide group, and the reaction between an epoxy group and a hydrazide group.

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

[12] .

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

[13] .

[15] A non-aqueous secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein at least one of the positive electrode and the negative electrode is the non-aqueous secondary battery electrode according to

[14] .

[0008] The present invention provides a binder composition for a non-aqueous secondary battery electrode that can form a secondary battery with excellent durability to electrolytes (electrolyte resistance) and film-forming properties, as well as excellent battery characteristics such as charge-discharge efficiency and capacity retention rate; a method for producing such an electrode binder composition; a non-aqueous secondary battery electrode composition containing such an electrode binder composition; a non-aqueous secondary battery electrode containing such an electrode composition; and a non-aqueous secondary battery having such an electrode.

[0009] Figure 1 is a graph showing DSC measurement results of the electrode binder composition prepared in Example 1. Figure 2 is an image showing AFM measurement results of the electrode binder composition prepared in Example 1. Figure 3 is a graph showing DSC measurement results of the electrode binder composition prepared in Comparative Example 1.

[0010] Hereinafter, embodiments of the present invention will be described in detail. In the present specification, a numerical range indicated using "~" refers to a range including the numerical values described before and after "~" as the minimum value and maximum value, respectively. 1. Binder composition for non-aqueous secondary battery electrodes The present invention is a binder composition for non-aqueous secondary battery electrodes containing vinyl polymer resin particles (A) and an aqueous medium (B), wherein a film formed from the vinyl polymer resin particles (A) is immersed in a mixed solution prepared by dissolving LiPF ６ in ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate at a volume ratio of 30 / 30 / 40 at a concentration of 1 mol / L for 72 hours at 60°C has a swelling degree of 5 mass% to 100 mass%; and when differential scanning calorimetry (DSC) is performed in accordance with JIS K7121 on a film formed from the vinyl polymer resin particles (A), one glass transition temperature is observed in the temperature range of -50°C to 70°C, and one glass transition temperature is observed in the temperature range of 70°C to 170°C; and when a preparation liquid of the vinyl polymer resin particles (A) adjusted to a solid content concentration of 25 mass%, measured in accordance with JIS K 6828-2, is applied onto a hot plate adjusted to a temperature gradient of 0 to 80°C such that the coating thickness is 38 µm (1.5 mil), and then dried for 4 hours, the minimum film forming temperature is 70°C or lower. This is a binder composition for non-aqueous secondary battery electrodes (hereinafter sometimes simply referred to as "the electrode binder composition of the present invention"). The electrode binder composition of the present invention is an aqueous binder composition in which vinyl polymer resin particles (A) as a binder are dispersed in an aqueous medium (B), and may optionally further contain other components generally used in the field of non-aqueous secondary batteries.

[0011] A film formed from the vinyl polymer resin particles (A) is immersed in LiPF ６It is more preferable that the degree of swelling after immersion at 60°C for 72 hours in a mixed solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 30 / 30 / 40 (volume ratio) at a concentration of 1 mol / L is 5% by mass or more and 50% by mass or less. By using vinyl polymer resin particles (A) that satisfy this degree of swelling as a binder, both electrolyte resistance and film-forming properties are improved. Furthermore, the battery characteristics such as charge-discharge efficiency and capacity retention rate of secondary batteries equipped with electrodes formed using such electrode binder composition can be further improved. Details of the method for measuring the degree of swelling will be described later in the Examples section. In addition, when differential scanning calorimetry (DSC) is performed on a film formed from vinyl polymer resin particles (A) in accordance with JIS K7121, the observed low-temperature glass transition point is preferably in the temperature range of -25°C to 40°C, and the observed high-temperature glass transition point is preferably in the temperature range of 70°C to 140°C. By using vinyl polymer resin particles (A), in which glass transition points are observed in each of the above-mentioned temperature ranges, as a binder, the capacity retention rate of a secondary battery equipped with electrodes formed using such an electrode binder composition can be further improved, both at low temperatures (e.g., around 0°C) and high temperatures (e.g., around 60°C). This is thought to be because the component originating from the low-temperature glass transition point of the vinyl polymer resin particles (A) maintains molecular mobility at low temperatures, thus exhibiting excellent bonding (film-forming) properties even at low temperatures, and the component originating from the high-temperature glass transition point of the vinyl polymer resin particles (A) maintains heat resistance at high temperatures, thus exhibiting excellent bonding (film-forming) properties even at high temperatures. Furthermore, when a prepared solution, adjusted to a solid content concentration of 25% by mass of vinyl polymer resin particles (A) as measured in accordance with JIS K 6828-2, is applied to a hot plate with a temperature gradient from 0 to 80°C to a coating thickness of 38 μm (1.5 ml), and then dried for 4 hours, the minimum film-forming temperature at which a crack-free film is formed is more preferably 50°C or lower. By using vinyl polymer resin particles (A) that satisfy this minimum film-forming temperature as a binder, an electrode with excellent peel strength between the formed electrode material layer and the current collector can be obtained.The binder composition for an electrode of the present invention, which contains the vinyl polymer resin particles (A) satisfying the above characteristics, is excellent in both electrolyte resistance and film-forming property. Further, battery characteristics such as charge-discharge efficiency and capacity retention rate of a secondary battery including an electrode formed using such a binder composition for an electrode can be improved.

[0012] Note that the above LiPF ６ dissolved in a mixture of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate at a volume ratio of 30 / 30 / 40 at a concentration of 1 mol / L is an organic solvent having a dispersion term (δd) in the Hansen solubility parameter of 15 MPa ０．５ to 21 MPa ０．５ inclusive, a polarity term (δp) of 6 MPa ０．５ to 22 MPa ０．５ inclusive, and a hydrogen bonding term (δh) of 3 MPa ０．５ to 10 MPa ０．５ inclusive. Here, the dispersion term (δd), polarity term (δp), and hydrogen bonding term (δh) in the Hansen solubility parameter are parameters that take into account the polarity of a substance, obtained by dividing the solubility parameter (SP value: δ) introduced by Hildebrand into three components: the dispersion term δd, the polarity term δp, and the hydrogen bonding term δh, and expressing them in a three-dimensional space, and the relationship represented by the following formula holds. δ [(cal / cm ３ ) ０．５ = (δd ２ + δp ２ + δh ２ ) ０．５The dispersion term δd, polarity term δp, and hydrogen bonding term δh mentioned above have been determined by Hansen and subsequent researchers, and are published, for example, in the Polymer Handbook (4th edition), VII-698 to 711. In addition, Hansen's solubility parameters for many solvents and resins have been investigated, and these solubility parameters are described, for example, in the Industrial Solvents Handbook (by Wesley L. Archer). They can also be determined using the Hansen Solubility Parameters in Practice (HSPiP) software.

[0013] Examples of organic solvents that satisfy the above requirements are shown, based on the Hansen solubility parameters δd, δp, and δh calculated using HSPiP software (6th Edition, 6.0.03).

[0014]

[0015] Furthermore, as an organic solvent, the Hansen solubility parameter δd is 15 MPa. ０．５ Above 17 MPa ０．５ Less than δp is 10 MPa ０．５ Above 14 MPa ０．５ Less than δh is 3 MPa ０．５ Above 8 MPa ０．５ It is more preferable, from the viewpoint of being able to more practically evaluate the swelling (electrolyte resistance) and durability of the electrode material layer formed from the electrode composition containing the electrode binder composition of the present invention, if the organic solvent is less than δd, δp, and δh. The organic solvent that satisfies the ranges of δd, δp, and δh is the LiPF mentioned above. ６In addition to a mixed solution obtained by dissolving in ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 30 / 30 / 40 (volume ratio) at a concentration of 1 mol / L, the solvent may be a single solvent or a mixed solvent of two or more solvents. For example, a mixed solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC), which are carbonate-based solvents used as electrolytes for non-aqueous secondary batteries, in a volume ratio of EC:EMC = 30:70, has Hansen solubility parameters of δd = 16.2, δp = 12.6, and δh = 6.2, satisfying the more preferable δd, δp, and δh for the organic solvent described above.

[0016] Vinyl polymer resin particles (A) having the aforementioned properties with respect to organic solvents preferably contain structural units derived from aromatic vinyl monomers, structural units derived from unsaturated carboxylic acid ester monomers, and structural units derived from vinyl monomers having acidic groups. Furthermore, it is preferable that the content of structural units derived from aromatic vinyl monomers is 18% to 90% by mass, the content of structural units derived from unsaturated carboxylic acid ester monomers is 8% to 80% by mass, and the content of structural units derived from vinyl monomers having acidic groups is 0.05% to 10% by mass, relative to the total amount of units constituting the vinyl polymer resin particles (A). An electrode binder composition containing vinyl polymer resin particles (A) containing each of the above structural units within the above ranges has superior electrolyte resistance and film-forming properties. In addition, battery characteristics such as charge-discharge efficiency and capacity retention rate of a secondary battery equipped with electrodes formed using such an electrode binder composition can be further improved. Furthermore, it is more preferable that the content of structural units derived from aromatic vinyl monomers is 30% by mass or more and 80% by mass or less, relative to the total amount of units constituting the vinyl polymer resin particles (A). Furthermore, it is more preferable that the content of structural units derived from unsaturated carboxylic acid ester monomers is 12% by mass or more and 50% by mass or less, relative to the total amount of units constituting the vinyl polymer resin particles (A). Furthermore, it is preferable that the content of structural units derived from vinyl monomers having acidic groups is 0.05% by mass or more and 5% by mass or less, relative to the total amount of units constituting the vinyl polymer resin particles (A).

[0017] As vinyl polymer resin particles (A), various types of particles can be used, such as particles in which the entire particle has a uniform composition obtained by mixing and polymerizing various monomers that constitute vinyl polymer resin particles (A) (aromatic vinyl monomers, unsaturated carboxylic acid ester monomers, vinyl monomers having acidic groups, and other monomers having vinyl groups), particles obtained by blending polymers obtained by polymerizing various monomers separately, and core-shell type particles having different monomer compositions in the shell and core portions. Among these, it is preferable to use core-shell type particles as vinyl polymer resin particles (A) from the viewpoint that both the electrolyte resistance and film-forming properties of the binder can be improved by exhibiting different properties (binding properties, electrolyte resistance, etc.) in the shell and core portions. In the following description, each component of the electrode binder composition using core-shell type particles (A) as vinyl polymer resin particles (A) will be described.

[0018] <Core-shell type particles (A)> The electrode binder composition of this embodiment contains core-shell type particles (A) as vinyl polymer resin particles (A) (binder), which have a shell portion made of polymer (a1) and a core portion made of polymer (a2). When the vinyl polymer resin particles (A) are core-shell type particles (A), the "glass transition point in the temperature range of -50°C to 70°C" is observed based on the shell portion made of polymer (a1), and the "glass transition point in the temperature range of 70°C to 170°C" is observed based on the core portion made of polymer (a2). The polymer (a1) constituting the shell portion exhibits excellent binding properties (film-forming properties) to the core-shell type particles (A), while the polymer (a2) constituting the core portion exhibits excellent durability (electrolyte resistance) to the electrolyte to the core-shell type particles (A).

[0019] (Shell portion) The polymer (a1) constituting the shell portion preferably contains structural units derived from unsaturated carboxylic acid ester monomers, vinyl monomers having acidic groups, and aromatic vinyl monomers. Unsaturated carboxylic acid ester monomers are used in the formation of the shell portion (polymer (a1)) to improve the film-forming properties of the core-shell type particles (A). Examples of such unsaturated carboxylic acid ester monomers include (meth)acrylic acid ester monomers and dicarboxylic acid ester monomers such as maleic acid, fumaric acid, itaconic acid, and citraconic acid. Among these, (meth)acrylic acid ester monomers are preferred. 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 units constituting polymer (a1) is not particularly limited, but can be 5% by mass or more and 95% by mass 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 to promote 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 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. One type of vinyl monomer having acidic groups may be used alone, or two or more types may be used in combination. Among these, acrylic acid, methacrylic acid, or itaconic acid is preferred. Furthermore, it is preferable that the content of structural units derived from the vinyl monomer having acidic groups relative to the total amount of 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 acidic groups is within the above range, the core-shell particles (A) can exist more stably in the aqueous medium (B), and the fusion of the core-shell particles (A) with each other in the formed electrode material layer can be promoted, further improving the film-forming properties of the core-shell particles (A).

[0021] 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 units constituting polymer (a1) is not particularly limited, but can be 5% by mass or more and 95% by mass or less.

[0022] Furthermore, it is preferable that the polymer (a1) contains a reactive emulsifier. Core-shell type particles (A) can be obtained by polymerizing unsaturated carboxylic acid monomers such as (meth)acrylic acid ester monomers, vinyl monomers having acidic groups, and aromatic vinyl monomers in an aqueous medium (B) in the presence of a reactive emulsifier, to form polymer particles that will form the shell portion consisting of polymer (a1). Then, using the polymer particles as a reaction site, hydrophobic monomers constituting polymer (a2) are polymerized to form a core portion consisting of polymer (a2) inside the polymer particles. The reactive emulsifier, upon reaction, is incorporated into the shell portion as a component of polymer (a1), becoming a hydrophilic group of the polymer that forms the shell portion, and losing its function as a surfactant. Therefore, the polymerization of the core portion can be described as soap-free polymerization, which is carried out in the absence of surfactants. In the formation process of the core-shell particle (A) described above, the hydrophobic monomer that is to become the core portion (polymer (a2)) enters the interior of the hydrophilic polymer particle (polymer (a1)) formed by the reaction of the reactive emulsifier, and polymerizes inside the polymer particle to form the core-shell particle (A). Core-shell particles obtained in this way, by polymerizing a hydrophobic monomer inside a hydrophilic polymer particle that forms the shell portion to form the core portion, are called inverted core-shell particles.

[0023] Core-shell particles (A) formed through 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 generated as by-products in addition to core-shell particles. From this viewpoint, the electrode binder composition of this embodiment is advantageous in that each core-shell particle (A) possesses stable shell characteristics (film-forming ability) and core characteristics (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 high affinity for the aqueous medium (B) and can exist stably in the aqueous medium (B). Moreover, in the core-shell particle (A), the polymer (a1) and polymer (a2) are fused within the particle, resulting in separation at the nm size. Polymers (a1) and (a2) are phase-separated at a size sufficiently smaller than the size (μm size) of the negative electrode active material or positive electrode active material (hereinafter also simply referred to as "active material"). Therefore, for all types of active materials, the properties of both the core and shell portions can be expressed, and uniform performance can be achieved throughout the electrode. In contrast, when polymers (a1) and (a2) are simply blended (mixed), polymers (a1) and (a2) separate at the particle size level (μm size). As a result, depending on the active material used, products with poor electrolyte resistance or poor binding properties may occur, leading to deterioration of the overall performance of the electrode or non-uniform performance. Therefore, in an electrode binder composition using core-shell type particles (A) containing a reactive emulsifier as a component of polymer (a1) which forms the shell portion, both electrolyte resistance and film-forming properties are superior. Furthermore, the battery characteristics such as charge-discharge efficiency and capacity retention rate of secondary batteries equipped with electrodes formed using such electrode binder compositions can be further improved.

[0024] 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 electrode binder composition of this embodiment, 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 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).

[0025] As a reactive emulsifier, for example, emulsifiers represented by general formulas (1) to (5) can be used.

[0026] General formula (1) [Chemical formula 1] In general formula (1), R is an alkyl group and m is an integer between 10 and 40.

[0027] General formula (2) [Chemical formula 2] In general formula (2), x is an integer between 10 and 12, and y is an integer between 10 and 40.

[0028] General formula (3) [Chemical formula 3] In general formula (3), R is an alkyl group and M is NH ４ Or it is Na.

[0029] General formula (4) [Chemical formula 4] In general formula (4), R is an alkyl group.

[0030] General formula (5) [Chemical formula 5] In general formula (5), X is a hydrogen atom or SO₂ ３ NH ４ Here, m is an integer between 1 and 4 (inclusive), and n is an integer between 5 and 40 (inclusive). X is SO ３ NH ４It is preferable that m is between 1 and 3. It is preferable that n is between 8 and 40, more preferably between 8 and 25, and even more preferably between 8 and 15.

[0031] 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 Eleminol 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 of 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 better peel strength between the formed electrode material layer and the current collector can be obtained. In addition, as will be described later, when forming the shell portion (polymer a1), a non-reactive emulsifier may be used in combination with the 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, more preferably 1 / 5, and even more preferably 1 / 10 or less of the content of the reactive emulsifier.

[0032] Furthermore, the polymer (a1) may contain structural units derived from vinyl monomers having amide groups, in addition to structural units derived from each of the above components. When vinyl monomers having amide groups are used in the formation of the shell portion (polymer (a1)), they promote the fusion of core-shell type particles (A) in the formed electrode material layer through hydrogen bonding between amide groups and between amide groups and other functional groups, thereby improving the film-forming properties of the core-shell type particles (A). In addition, by using vinyl monomers having 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, and the polymerization of the core portion proceeds stably.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 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 particles (A) in the formed electrode material layer can be promoted, further improving the film-forming properties of the core-shell particles (A).

[0033] (Core portion) The polymer (a2) constituting the core portion preferably contains structural units derived from aromatic vinyl monomers. The aromatic vinyl monomers, when used in the formation of the core portion (polymer (a2)), improve the electrolyte resistance of the 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 polymer (a2) is preferably 10% by mass or more and 99% 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.

[0034] Furthermore, it is preferable that polymer (a2) contains a vinyl monomer having a crosslinking reactive group that chemically bonds polymer (a1) and polymer (a2). When the core portion (polymer (a2)) contains such a vinyl monomer having a crosslinking reactive group, polymer (a1) and polymer (a2) chemically bond during the formation of the core-shell type particle (A). As described above, in the core-shell type particle (A), polymer (a1) and polymer (a2) are fused within the particle and are separated at the nm size. Since polymer (a1) and polymer (a2) are phase-separated at a size sufficiently smaller than the size of the active material (μm size), the properties of both the core portion and the shell portion can be expressed for all types of active materials, and uniform performance can be expressed throughout the electrode. Furthermore, if the core portion (polymer (a2)) contains a vinyl monomer having the above-mentioned crosslinkable reactive group, the core portion (polymer a2) and the shell portion (polymer a1) are chemically bonded, forming a crosslinked structure (core-shell crosslinked structure) between polymer (a1) and polymer (a2), suppressing separation between the core and shell. It is presumed that the performance characteristics unique to core-shell particles are more likely to be uniformly expressed throughout the electrode containing the binder composition of the present invention. In addition, the chemical bond between the core portion (polymer a2) and the shell portion (polymer a1) allows for further suppression of the swelling of the core-shell particles, as shown in the examples described later. This enables the core-shell particles (A) to exhibit superior durability (electrolyte resistance).

[0035] The chemical bond between the shell portion (polymer a1) and the core portion (polymer a2) is preferably at least one bond selected from ester bonds, siloxane bonds, amide bonds, and hydrazone bonds. With these bonds, the separation between the core and shell is further suppressed by the crosslinking structure between polymer (a1) and polymer (a2), and the performance unique to core-shell particles is expressed more uniformly throughout the electrode containing the binder composition of the present invention. More specifically, the chemical bond between the shell portion (polymer a1) and the core portion (polymer a2) is preferably formed by at least one reaction selected from the reaction between epoxy groups and carboxyl groups, hydrolysis and condensation reactions of alkoxysilyl groups, reactions between oxazoline groups and carboxyl groups, condensation reactions of methylol groups and / or alkyloxymethyl groups, reactions between ketone groups and hydrazide groups, and reactions between epoxy groups and hydrazide groups. As the vinyl monomer having a crosslinkable reactive group that chemically bonds polymer (a1) and polymer (a2), compounds that cause the above-mentioned various reactions are preferred and not particularly limited, but glycidyl methacrylate (GMA), 3-(trimethoxysilyl)propyl methacrylate (MPTMS), N-methylolacrylamide (NMAM), 2-isopropenyl-2-oxazoline (OX), and diacetone acrylamide (DAAM) are preferred.

[0036] Furthermore, it is preferable that the content of structural units derived from the vinyl monomer having such 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 the vinyl monomer having such crosslinkable reactive groups is within the above range, the electrolyte resistance of the core-shell type particles (A) can be further improved. In addition, the polymer (a2) may contain not only a vinyl monomer having a crosslinkable reactive group that chemically bonds polymer (a1) and polymer (a2), but also a vinyl monomer having a crosslinkable reactive group that forms a crosslinked structure only on polymer (a2). By containing a vinyl monomer having a crosslinkable reactive group that forms a crosslinked structure only on polymer (a2), a crosslinked structure is formed on polymer (a2), and the electrolyte resistance (electrolyte resistance) of the core-shell type particles (A) can be further improved. Examples of vinyl monomers having such crosslinkable reactive groups include divinylbenzene and ethylene dimethacrylate.

[0037] Furthermore, polymer (a2) may further contain structural units derived from each of the above components, as well as structural units derived from (meth)acrylic acid ester monomers, structural units derived from conjugated diene monomers, and structural units derived from vinyl monomers having cyano groups. The (meth)acrylic acid ester monomer is used in the formation of the core portion (polymer (a2)) to improve the film-forming properties of the core-shell type particles (A). As such (meth)acrylic acid ester monomers, the various (meth)acrylic acid ester monomers mentioned above that can be used in the formation of polymer (a1) can be used, and it is particularly preferable to use 2-ethylhexyl acrylate, butyl acrylate, methyl methacrylate, or 2-hydroxyethyl methacrylate. In addition, it is preferable that the content of structural units derived from (meth)acrylic acid ester monomers relative to the total amount of units constituting polymer (a2) be 5% by mass or more and 90% by mass or less. If the content of structural units derived from (meth)acrylic acid ester monomers is within the above range, the film-forming properties of the core-shell type particles (A) can be further improved.

[0038] 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 (negative electrode active material) that exhibits large volume changes due to lithium absorption and release, such as a silicon-containing 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, resulting in separation 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.

[0039] As the conjugated diene monomer, either an aliphatic conjugated diene monomer or an aromatic conjugated diene monomer can be used, but the use of an aliphatic conjugated diene monomer is preferred. 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, the use of isoprene and butadiene is preferred.

[0040] 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 30% by mass or less, and more preferably 5% by mass or more and 20% by mass or less. If the content of structural units derived from conjugated diene monomers is within the above range, the elastic deformation characteristics and electrolyte resistance of the core-shell type particles (A) can be further improved.

[0041] When a vinyl monomer having a cyano group is used to form the core portion (polymer (a2)), the high dielectric constant of the cyano group improves the conductivity of lithium ions in the formed electrode, and as a result, the discharge capacity maintenance rate of the secondary battery equipped with such electrode is improved. Furthermore, since the structural units derived from the vinyl monomer having a cyano group are contained only in the polymer (a2) constituting the core portion, the vinyl monomer having a cyano group does not dissolve into the electrolyte, and the electrolyte resistance of the core-shell type particle (A) does not decrease. Examples of vinyl monomers having a cyano group include vinyl monomers having nitrile groups such as (meth)acrylonitrile, and the use of acrylonitrile is particularly preferred. Furthermore, 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 preferably 0.1% by mass or more and 10% by mass or less. If the content of structural units derived from the vinyl monomer having a cyano group is within the above range, the conductivity of lithium ions in the formed electrode is further improved, and as a result, the discharge capacity maintenance rate of the secondary battery equipped with such electrode can be further improved.

[0042] Furthermore, it is preferable that polymer (a2) does not contain structural units derived from the aforementioned vinyl monomer having an acidic group, or structural units derived from the fluorine-containing monomer, as constituent components of polymer (a1). If polymer (a2) contains structural units derived from the vinyl monomer having an acidic group, it becomes disadvantageous in terms of fusion between core-shell type particles (A) and peel strength between the electrode material layer and the current collector in the formed electrode material layer. Also, in the reverse-phase core-shell process, if the polymer (a2) that forms the core contains a vinyl monomer having an acidic group as a constituent monomer, it becomes difficult to balance the hydrophilicity between the polymer particles that form the shell and the constituent monomer of polymer (a2), making it difficult to form reverse-phase core-shell particles. Furthermore, if polymer (a2) contains structural units derived from the fluorine-containing monomer, similarly to the above, it becomes disadvantageous in terms of fusion between core-shell type particles (A) and peel strength between the electrode material layer and the current collector in the formed electrode material layer. Furthermore, in the reversed-phase core-shell process, if fluorine-containing monomers are included as constituent monomers in 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 reversed-phase core-shell particles.

[0043] 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 properties) due to the polymer (a1) constituting the shell portion, and excellent durability to electrolytes (electrolyte resistance) due to the polymer (a2) constituting the core portion. 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 properties) may decrease, and if the content of polymer (a2) in the core-shell type particle (A) is low, the core properties (electrolyte resistance) may decrease. In contrast, if the content of polymer (a1) and polymer (a2) in the core-shell type particle (A) are within the above range, an electrode binder composition containing core-shell type particle (A) that achieves both excellent film-forming properties and electrolyte resistance can be obtained.

[0044] <Aqueous medium (B)> The aqueous medium (B) functions as a dispersion medium for vinyl polymer resin particles (A) (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, an electrode binder composition using core-shell type particles (A) as vinyl polymer resin particles (A) is obtained by forming core-shell type particles (A) in the 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 electrode binder composition of the present invention, or it may be diluted with additional aqueous medium (B) as needed before being used as the electrode binder composition of this embodiment. The content of core-shell type particles (A) in the total electrode binder composition of this embodiment is preferably in the range of 10 to 60% by mass.

[0045] The electrode binder composition 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.

[0046] 2. Method for Manufacturing a Binder Composition for Non-Aqueous Secondary Battery Electrodes Next, a method for manufacturing the electrode binder composition of this embodiment, using core-shell type particles (A) as vinyl polymer resin particles (A), will be described. This embodiment is a method for manufacturing a binder composition for non-aqueous secondary battery electrodes containing 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), comprising: a shell portion forming step in which various monomers constituting polymer (a1), such as unsaturated carboxylic acid monomers like (meth)acrylic acid ester monomers, vinyl monomers having acidic groups, and aromatic vinyl monomers, are polymerized 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 in which various monomers constituting polymer (a2) are polymerized using the polymer particles as a reaction field to form the core portion made of polymer (a2) inside the polymer particles. The following describes each step in the manufacturing method of the electrode binder composition of this embodiment.

[0047] (Shell Formation Process) The shell formation process involves polymerizing various monomers constituting the polymer (a1) in an aqueous medium (B) in the presence of a reactive emulsifier to form polymer particles that will become the shell portion of the polymer (a1). The reactive emulsifier, unsaturated carboxylic acid monomer, vinyl monomer having an acidic group, aromatic vinyl monomer, and aqueous medium (B) that constitute the polymer (a1), as well as the components described later (vinyl monomer having an amide group, vinyl monomer having a crosslinkable reactive group that chemically bonds polymer (a1) and polymer (a2), and vinyl monomer having a cyano group), are all the same as those described in the electrode binder composition of the present invention. In addition to the reactive emulsifier, a non-reactive emulsifier may also be used in combination.

[0048] The reactive emulsifier, upon reaction, is incorporated into the shell portion as a component of the polymer (a1), becoming a hydrophilic group of the polymer that forms the shell portion, and losing its function as a surfactant. In addition to the above components, vinyl monomers having amide groups can be used as constituent monomers of the shell portion (polymer (a1)). In particular, by using vinyl monomers having amide groups, in the reverse-phase core-shell process, the amide groups improve the stability of the polymer particles that form the shell portion, and the polymerization of the core portion in the core portion formation process proceeds stably. The reactive emulsifier, unsaturated carboxylic acid monomer, vinyl monomer having an acidic group, aromatic vinyl monomer, 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 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.

[0049] In this step, 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 units constituting the polymer (a1) excluding structural units derived from the reactive emulsifier is preferably 0.01% by mass or more and 1% by mass or less. In addition, in this step, 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.

[0050] (Core Formation Process) The core formation process involves polymerizing vinyl monomers and aromatic vinyl monomers having crosslinkable reactive groups that chemically bond polymer (a1) and polymer (a2) using the polymer particles as a reaction site to form a core consisting of polymer (a2) inside the polymer particles. As mentioned above, in the shell formation process, 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 process can be described as soap-free polymerization 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 vinyl monomers and aromatic vinyl monomers having crosslinkable reactive groups 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 a reversed-phase core-shell process. Furthermore, during the process of forming core-shell type particles (A), vinyl monomers having crosslinkable reactive groups chemically bond with polymer particles (polymer (a1)), thereby forming a crosslinked structure between the core and shell.

[0051] Vinyl monomers having crosslinkable reactive groups, aromatic vinyl monomers, and other monomers 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.

[0052] In this step, it is preferable to include a radical polymerization initiator. Various radical polymerization initiators as 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. Also, in this step, 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.

[0053] 3. Compositions for Non-Aqueous Secondary Battery Electrodes The present invention also relates to a composition for non-aqueous secondary battery electrodes (hereinafter simply referred to as "the electrode composition of the present invention") which contains an active material (negative electrode active material or positive electrode active material) and the above-described binder composition for non-aqueous secondary battery electrodes of the present invention (i.e., the electrode binder composition of the present invention). Such a composition for non-aqueous secondary battery electrodes of the present invention includes a composition for the negative electrode of a non-aqueous secondary battery (hereinafter simply referred to as "the negative electrode composition of the present invention") and a composition for the positive electrode of a non-aqueous secondary battery (hereinafter simply referred to as "the positive electrode composition of the present invention"). The negative electrode composition of the present invention contains a negative electrode active material as an active material and the electrode binder composition of 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, silides, 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.

[0054] 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.

[0055] 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 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 to adjust the viscosity of the resulting negative electrode composition of the present invention and to improve 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.

[0056] Furthermore, the positive electrode composition of the present invention contains a positive electrode active material as an active material and the electrode binder composition of the present invention. The positive electrode active material is not particularly limited, and for example, when manufacturing a lithium-ion secondary battery 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 oxide (LiCoO) ２ Lithium-cobalt composite oxides (LCOs), lithium nickelate (LiNiO), etc. ２ ), lithium manganese (LiMnO ２ ) and their composite oxides (LiCo ｘ Ni ｙ Mn ｚ O ２ x + y + z = 1; Lithium nickel manganese cobalt composite oxide (NMC); Lithium manganese spinel (LiMn ２ O ４ ), lithium vanadium compound, V ２ O ５ , V ６ O １３ , VO ２ MnO ２ , TiO ２ MoV ２ O ８ TiS ２ , V２ S ５ , VS ２ MoS ２ MoS ３ , Cr ３ O ８ , Cr ２ O ５ Olivine type LiMPO ４ (wherein M is Co, Ni, Mn, or Fe); Examples include 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. Among these, olivine-type LiFePO is preferred from the viewpoint of operating voltage, volume density, theoretical capacity, high-temperature stability, and economics. ４ It is more preferable to use lithium iron phosphate compounds (LFPs) such as the above.

[0057] 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. Also, when lithium iron phosphate compound (LFP) is 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 above range, the positive electrode expansion rate during charging and discharging is small when used as 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 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.

[0058] The positive electrode active material may have at least a portion of its surface covered 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, such as electronically conductive materials like 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.

[0059] Furthermore, the positive 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.

[0060] The positive electrode composition of the present invention is obtained by mixing and dispersing the positive electrode active material described above, a conductive material, and the non-aqueous binder composition for secondary battery positive electrodes of the present invention. There are no particular restrictions on the order of addition during mixing. Furthermore, a non-aqueous solvent may be added as appropriate to adjust the viscosity of the resulting positive electrode composition of the present invention and to improve 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.

[0061] 4. Non-aqueous secondary battery The present invention also relates to a non-aqueous secondary battery electrode comprising an electrode material layer (negative electrode material layer or positive electrode material layer) formed using the electrode composition of the present invention described above. Such a non-aqueous secondary battery electrode of the present invention includes a non-aqueous secondary battery negative electrode (hereinafter also simply referred to as "the negative electrode of the present invention") and a non-aqueous secondary battery positive electrode (hereinafter also simply referred to as "the positive electrode of the present invention"). The present invention also relates to a non-aqueous secondary battery comprising a negative electrode, a positive electrode, an electrolyte, and a separator, wherein at least one of the positive electrode and the negative electrode is the non-aqueous secondary battery electrode of the present invention described above. The binder composition for non-aqueous secondary battery electrodes of the present invention has excellent durability against the electrolyte (electrolyte resistance) and film-forming properties. Therefore, the electrode material layer formed from the electrode composition containing the binder composition for non-aqueous secondary battery electrodes of the present invention has excellent charge-discharge capacity and capacity retention rate. That is, a non-aqueous secondary battery of the present invention having an electrode comprising such an electrode material layer exhibits good charge-discharge characteristics and has 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 an electrode material layer formed using the non-aqueous secondary battery 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 a negative electrode and a positive electrode, at least one of which is the non-aqueous secondary battery electrode of the present invention as described above, opposite each other with a separator in between, and injecting an electrolyte.

[0062] <Negative Electrode> The negative electrode of the present invention can be obtained, for example, by applying the above-described non-aqueous secondary battery 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 composition of the present invention may be molded into a sheet, pellet, or other shape and integrated with the current collector to obtain the negative electrode.

[0063] Examples of materials for the current collector include copper, nickel, titanium, and stainless steel. The shape of the current collector is preferably a strip shape 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. Examples of methods for applying the negative electrode composition to the current collector include 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 or calender roll as needed. Alternatively, the negative electrode material layer may be obtained by forming the paste-like negative electrode composition into a sheet or pellet and then integrating it with the current collector using a roll, press, or a combination thereof.

[0064] 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. This heat treatment removes the aqueous medium (B) derived from the binder composition for non-aqueous secondary battery electrodes of the present invention, promotes the fusion of core-shell type particles (A), and improves the adhesion between negative electrode active materials and between the 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, but it is usually in the range of 1 minute to 20 hours. It is preferable to perform the heat treatment in a non-oxidizing gas atmosphere such as helium, argon, or nitrogen, or in a vacuum atmosphere, from the viewpoint of preventing oxidation of the current collector during heat treatment. Furthermore, after heat treatment, the negative electrode, which consists of the negative electrode material layer formed on the current collector or the negative electrode material layer integrated with the current collector, is preferably pressurized from the viewpoint of adjusting the electrode density. The electrode density of the negative electrode is usually 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 negative electrode expansion rate and potentially reducing the capacity retention rate. Therefore, an optimal range for electrode density is selected.

[0065] <Positive Electrode> The positive electrode is obtained by forming a positive electrode material layer on the surface of the current collector, similar to the negative electrode. For example, a positive electrode material slurry is prepared by kneading the positive electrode active material and the non-aqueous secondary battery electrode composition of the present invention described above 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 be applied to a current collector (e.g., copper foil) to form a positive electrode material layer. Alternatively, the positive electrode composition of the present invention may be molded into a sheet, pellet, or other shape and integrated with the current collector to obtain the positive electrode. Furthermore, instead of the non-aqueous secondary battery electrode composition of the present invention, an organic binder other than the non-aqueous secondary battery electrode composition can be used as the positive electrode. Examples of such 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.

[0066] 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 content of organic binder is 1% by mass or more, adhesion is improved, and the destruction of the positive 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.

[0067] 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.

[0068] Examples of materials for the current collector include copper, nickel, titanium, and stainless steel. The shape of the current collector is preferably a strip shape 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. Examples of methods for applying the positive electrode material slurry to the current collector include metal mask printing, electrostatic painting, 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 or calender roll as needed. Alternatively, the positive electrode material layer may be obtained by forming the paste-like positive electrode material slurry into a sheet or pellet and then integrating it with the current collector using a roll, press, or a combination thereof.

[0069] 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. This heat treatment removes the aqueous medium (B) derived from the binder composition for non-aqueous secondary battery electrodes of the present invention, promotes the fusion of core-shell type particles (A), and improves the adhesion between positive electrode active materials and between positive 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, but it is usually in the range of 1 minute to 20 hours. If an organic binder with polyimide or polyamide-imide as the main backbone is used instead of the non-aqueous secondary battery electrode composition of the present invention, it is preferable to heat-treat at 150 to 450°C. It is preferable to perform the heat treatment in a non-oxidizing gas atmosphere such as helium, argon, or nitrogen, or in a vacuum atmosphere, from the viewpoint of preventing oxidation of the current collector during heat treatment.

[0070] 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 usually 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.

[0071] <Separator> 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 structure of the non-aqueous electrolyte secondary battery being manufactured is such that the positive and negative electrodes do not come into direct contact, a separator is not required.

[0072] <Electrolyte> For example, LiClO ４ LiPF ６ LiAsF ６ LiBF ４ LiSO ３ CF ３ A so-called organic electrolyte can be used, which is obtained by dissolving lithium salts such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidine-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, etc., in one or more non-aqueous solvents.

[0073] The structure of a secondary battery using the non-aqueous secondary battery electrode binder composition of the present invention is not particularly limited, but it is common to have a structure in which a positive electrode, a negative electrode, and a separator (if provided as needed) are wound in a flat spiral shape to form a wound electrode plate group, or these are stacked as flat plates to form a stacked electrode plate group, and these electrode plate groups are sealed in an outer casing. Secondary batteries using the non-aqueous secondary battery electrode binder composition of the present invention can be used as, for example, paper type batteries, button type batteries, coin type batteries, stacked type batteries, cylindrical type batteries, prismatic type batteries, etc. The non-aqueous secondary battery electrode binder composition of the present invention can also be applied to electrochemical devices in general that use the insertion and removal of lithium ions as a charge and discharge mechanism, such as hybrid capacitors and solid lithium secondary batteries.

[0074] The binder composition for non-aqueous secondary battery electrodes, the method for manufacturing the binder composition for non-aqueous secondary battery electrodes, the electrode composition, the electrode, and the secondary battery having the 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 non-aqueous secondary battery electrodes, the method for manufacturing the binder composition for non-aqueous secondary battery electrodes, the electrode composition, the electrode, and the secondary battery having the 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.

[0075] 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.

[0076] <Unsaturated Carboxylic Acid Ester Monomers> MMA: Methyl Methacrylate BA: Butyl Acrylate 2EHA: 2-Ethylhexyl Acrylate <Aromatic Vinyl Monomers> ST: Styrene <Vinyl Monomers with Acidic Groups> AA: Acrylic Acid MAA: Methacrylic Acid <Vinyl Monomers with Crosslinkable Reactive Groups> GMA: Glycidyl Methacrylate MPTMS: 3-(Trimethoxysilyl)propyl Methacrylate OX: 2-Isopropenyl-2-Oxazoline DAAM: Diacetone Acrylamide DVB: Divinylbenzene <Vinyl Monomers with Crosslinkable Reactive Groups and Amide Groups> NMAM: N-Methylolacrylamide <Vinyl Monomers with Amide Groups> AM: Acrylamide <Conjugated Diene Monomers> BD: Butadiene <Emulsifiers> SR-10: Ether sulfate type ammonium salt (Reactive surfactant Adekarya Soap SR-10 manufactured by ADEKA Corporation)

[0077] (Example 1) (1) Preparation of electrode binder composition <Shell formation process> 220 parts by mass of deionized water and 0.5 parts by mass of SR-10 were charged into a reaction vessel equipped with a stirrer, thermometer and cooler, 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, 52 parts by mass of ST, 47 parts by mass of 2EHA, and 1 part by mass of AA. This emulsion and an aqueous solution prepared by dissolving 0.2 parts by mass of ammonium persulfate in 10 parts by mass of deionized water were simultaneously added dropwise to the reaction vessel over 3 hours to carry out polymerization, and then maintained at 80°C for 2 hours after the dropwise addition was completed. After that, it 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> The reaction vessel was heated again to 80°C, and a mixture of 99 parts by mass of ST and 1 part by mass of GMA was added to it. This mixture was then simultaneously added dropwise to the reaction vessel over 3 hours along with an aqueous solution of 0.2 parts by mass of ammonium persulfate dissolved in 10 parts by mass of deionized water to carry out polymerization. After the addition was complete, the mixture was maintained at 80°C for 2 hours. The mixture was cooled to room temperature, the pH was adjusted to 7 with 25% aqueous ammonia, 1 part by mass of activide MBS and 0.1 parts by mass of activide MV4 were added, and the non-volatile content was adjusted to 40.0% with deionized water to obtain the electrode binder composition.

[0078] (2) DSC and AFM Measurement of Electrode Binder Composition The DSC measurement results and AFM measurement results of the electrode binder composition obtained above are shown in Figures 1 and 2, respectively. The DSC measurement method and AFM measurement method for the electrode binder composition prepared in Example 1 are described below. <DSC Measurement> The electrode binder composition prepared in Example 1, the other examples and comparative examples described later were applied to a release PET film and dried at 140°C for 2 hours, then at 110°C for 10 hours to create a film with a thickness of 40 μm. The film was measured using a differential scanning calorimeter (DSC) (TA Instruments Q100 heat flux type) in the range of -50°C to 150°C at a heating rate of 10°C / min. <AFM Measurement> The electrode binder composition prepared in Example 1 was applied to a glass substrate by spin coating and dried at room temperature for 3 hours. Subsequently, images were observed using an MFP-3D Origin manufactured by Oxford Instruments (Asylum Research).

[0079] From the DSC measurement results shown in Figure 1, the electrode binder composition prepared in Example 1 exhibited glass transition points at approximately 14°C on the low-temperature side and approximately 104°C on the high-temperature side. Furthermore, from the AFM image shown in Figure 2, it was found that the electrode binder composition prepared in Example 1 contained uniformly sized core-shell type particles (A) dispersed as vinyl polymer resin particles (A).

[0080] (3) Preparation of electrode composition 48.5 parts by mass of artificial graphite and 48.5 parts by mass of natural graphite were weighed out as negative electrode active materials and stirred in a rotary-orbit mixer for 30 seconds. 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 and mixed until the mixture became a paste, and then stirred in a rotary-orbit mixer for 2 minutes. Since heat was generated by stirring, it was cooled to room temperature with ice water, stirred again in a rotary-orbit mixer for 2 minutes, 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 mixed until the mixture was uniform, then stirred in a rotary-orbit mixer for 2 minutes, and then cooled to room temperature with ice water. Ten parts by weight of distilled water and 3.75 parts by mass (1.5 parts by mass in terms of solid content) of the electrode binder composition obtained in (1) above were added, and the mixture was stirred again in a rotary-orbit mixer for 2 minutes, and then cooled to room temperature with ice water. The viscosity of the obtained slurry was measured with a B-type viscometer at 25°C and 30 rpm, and distilled water was added until the viscosity was in the range of 2000 to 4000 mPa·s. Finally, the mixture was stirred in a rotary-orbit mixer for 30 seconds to prepare a slurry-like negative electrode composition.

[0081] (4) The coating amount (surface density) of the negative electrode composition after drying of the negative electrode is 12.56 mg / cm². ２ The gap of the bar coater was adjusted to achieve the desired result, and the negative electrode composition was coated onto the copper foil current collector using this bar coater. The mixture was then dried for 8 minutes in a forced-air dryer set to 80°C. The dried electrodes were cut to a width of 40 mm and pressed using a roll press machine (Small Desktop Roll Press SA-602, manufactured by Tester Industries Co., Ltd.) to achieve a layer density of 1.60 g / cm³. ３ After pressing in this manner, the material was vacuum-dried at 110°C for 10 hours to obtain the negative electrode.

[0082] (5) Preparation of the positive electrode composition As the positive electrode active material, olivine-type lithium iron phosphate (LiFePO) ４94.0 parts by mass of ) and 2.93 parts by mass of acetylene black as a conductive material were weighed out and stirred for 30 seconds in a rotating-orbit mixer (Thinky Co., Ltd. "ARE-310 (product name)") at a rotation speed of 1000 rpm and an orbital speed of 2000 rpm. Thereafter, stirring using the rotating-orbit mixer was performed using the same apparatus and conditions unless otherwise specified. 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 (Nippon Paper Industries Co., Ltd. "Sunrose MAC350HC") in distilled water and adjusting the non-volatile content concentration to 2% was added and mixed until the whole mixture became a paste, and then stirred in a rotating-orbit mixer for 2 minutes. Since heat was generated by stirring, it was cooled to room temperature with ice water, stirred again in a rotating-orbit mixer for 2 minutes, and then cooled to room temperature with ice water. Next, 27.0 parts by mass (0.54 parts by mass in terms of solid content) of the above CMC solution were added to this mixture, and after mixing until the whole was homogeneous, the mixture was stirred for 2 minutes in a rotary-orbit mixer and cooled to room temperature with ice water. 7.5 parts by mass (0.07 parts by mass in terms of solid content) of single-wall carbon nanotube aqueous dispersion (OCSiAl "TUBALL BATT H2O") as a conductive additive were added and stirred for 2 minutes in a rotary-orbit mixer. 3.75 parts by mass (1.5 parts by mass in terms of solid content) of the electrode binder composition obtained in (1) above were added and stirred again for 2 minutes in a rotary-orbit mixer and cooled to room temperature with ice water. While measuring the viscosity of the obtained slurry with a B-type viscometer at 25°C and 30 rpm, distilled water was added to bring it to a range of 10,000 to 12,000 mPa·s. Finally, the mixture was stirred for 30 seconds in a rotation-orbit mixer to prepare a slurry-like negative electrode composition.

[0083] (6) The coating amount (surface density) of the cathode composition after the preparation and drying of the cathode 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 80°C. The dried electrode was cut to a width of 40 mm and pressed using a roll press machine (Small Desktop Roll Press SA-602, manufactured by Tester Industries Co., Ltd.) to achieve a layer density of 2.4 g / cm³. ３ After pressing in this manner, the cathode was obtained by vacuum drying at 110°C for 10 hours.

[0084] (7) Fabrication of a secondary battery The negative electrode fabricated above was cut into a 24 mm x 24 mm square with a tab, and the positive electrode fabricated above was cut into a 22 mm x 22 mm square with a tab, using a die-cutting blade. Nickel tab leads were welded to the tab portion of the cut electrodes, and aluminum tab leads were welded to the tab portion of the negative electrode, and aluminum tab leads were welded to the tab portion of the positive electrode. On the other hand, a 25 μm thick polyethylene microporous membrane was cut into a 28 mm x 3.8 cm rectangle using a die-cutting blade as a separator. The positive 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, LiPF ６ The non-aqueous electrolyte solution obtained by dissolving the compound in a 30 / 30 / 40 mixed solution of ethylene carbonate / dimethyl carbonate / methyl ethyl carbonate (volume ratio) at a concentration of 1 mol / L, and then adding 1 vol% vinyl carbonate and 5 vol% fluoroethylene carbonate, was prepared by adding 300 μL of this solution and completely sealing it by vacuum lamination to produce the laminate-type secondary battery of Example 1.

[0085] (Examples 2-4 and 6-20) Except for using electrode binder compositions with modified material types and amounts as shown in Tables 2-3, negative electrode compositions, negative electrodes, positive electrode compositions, positive electrodes, and secondary batteries were obtained in the same manner as in Example 1.

[0086] (Example 5) A negative electrode composition, a negative electrode, a positive electrode composition, a positive electrode, and a secondary battery were obtained in the same manner as in Example 1, except that the electrode binder composition prepared by the method described below was used as the electrode binder composition. <Shell Formation Process> 220 parts by mass of deionized water and 0.5 parts by mass of SR-10 were charged into a reaction vessel equipped with a stirrer, thermometer, and cooler, 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, 51 parts by mass of ST, 47 parts by mass of 2EHA, 1 part by mass of AA, and 1 part by mass of AM. This emulsion and an aqueous solution prepared by dissolving 0.2 parts by mass of ammonium persulfate in 10 parts by mass of deionized water were simultaneously added dropwise to the reaction vessel over 3 hours to carry out polymerization. Subsequently, after the dropwise addition was completed, the temperature was maintained at 80°C for 2 hours. After that, 0.7 parts by mass of hydrazine monohydrate was added and the temperature was maintained for 10 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> The reaction vessel was heated again to 80°C, and a mixture of 99 parts by mass of ST and 1 part by mass of DAAM, along with an aqueous solution of 0.2 parts by mass of ammonium persulfate dissolved 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 completed, the temperature was maintained at 80°C for 2 hours. The mixture was cooled to room temperature, the pH was adjusted to 7 with 25% aqueous ammonia, 1 part by mass of activide MBS and 0.1 parts by mass of activide MV4 were added, and then the non-volatile content was adjusted to 40.0% with deionized water to obtain an electrode binder composition. In vinyl polymer resin particles (core-shell type particles) formed in such electrode binder compositions, a cross-linked structure is formed within the shell portion by the reaction between the hydrazide group of hydrazine monohydrate and the amide group of AM (acrylamide), and a cross-linked structure is formed between the core and shell by the reaction between the hydrazide group of hydrazine monohydrate in the shell portion and the amide group of DAAM (diacetone acrylamide) in the core portion.

[0087] (Comparative Example 1) A negative electrode composition, a negative electrode, a positive electrode composition, a positive electrode, and a secondary battery were obtained in the same manner as in Example 1, except that the electrode binder composition prepared by the method described below was used as the electrode binder composition. (1) Preparation of the electrode binder composition 220 parts by mass of deionized water and 0.5 parts by mass of SR-10 were charged into a reaction vessel equipped with a stirrer, thermometer and cooler, 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, 52 parts by mass of ST, 47 parts by mass of 2EHA, and 1 part by mass of AA, and 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 over 3 hours to carry out polymerization, and then maintained at 80°C for 2 hours after the dropwise addition was completed. The mixture was then cooled to room temperature, the pH was adjusted to 7 with 25% aqueous ammonia, 1 part by mass of activide MBS and 0.1 parts by mass of activide MV4 were added, and the non-volatile content was adjusted to 40.0% with deionized water to obtain an electrode binder composition.

[0088] (2) DSC and AFM measurements of the electrode binder composition Figure 3 shows the DSC measurement results of the electrode binder composition of Comparative Example 1 obtained above. From the DSC measurement results shown in Figure 3, one glass transition point was observed around 15°C in the electrode binder composition prepared in Comparative Example 1.

[0089] (Comparative Example 2) A negative electrode composition, a negative electrode, a positive electrode composition, a positive electrode, and a secondary battery were obtained in the same manner as in Example 1, except that the electrode binder composition prepared by the method described below was used as the electrode binder composition. (1) Preparation of the electrode binder composition <Synthesis of emulsion A> 220 parts by mass of deionized water and 0.5 parts by mass of SR-10 were charged into a reaction vessel equipped with a stirrer, thermometer and cooler, 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, 52 parts by mass of ST, 47 parts by mass of 2EHA, and 1 part by mass of AA, and 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 over 3 hours to carry out polymerization, and then maintained at 80°C for 2 hours after the dropwise addition was completed. Subsequently, the mixture was cooled to room temperature, the pH was adjusted to 7 with 25% aqueous ammonia, 1 part by mass of activide MBS and 0.1 parts by mass of activide MV4 were added, and the non-volatile content was adjusted to 40.0% with deionized water to obtain emulsion A. <Synthesis of Emulsion B> 220 parts by mass of deionized water and 0.5 parts by mass of SR-10 were charged into a reaction vessel equipped with a stirrer, thermometer, and condenser, and heated to 80°C. Next, a mixture of 50 parts by mass of deionized water, 0.5 parts by mass of SR-10, 99 parts by mass of ST, and 1 part by mass of GMA was simultaneously added dropwise over 3 hours to carry out polymerization, followed by maintaining the temperature at 80°C for 2 hours after the dropwise addition was completed. Subsequently, the mixture was cooled to room temperature, the pH was adjusted to 7 with 25% aqueous ammonia, 1 part by mass of activide MBS and 0.1 parts by mass of activide MV4 were added, and the non-volatile content was adjusted to 40.0% with deionized water to obtain emulsion B. <Preparation of blended emulsion> 50 parts of emulsion A and 50 parts of emulsion B were mixed and stirred at room temperature for 3 minutes to prepare a blended emulsion, which was used as the electrode binder composition.

[0090] (Comparative Examples 3-5) Except for using electrode binder compositions with modified material types and amounts as shown in Table 3, negative electrode compositions, negative electrodes, positive electrodes, and secondary batteries were obtained in the same manner as in Example 1.

[0091] [Evaluation] 1. Measurement of the minimum film-forming temperature For each example and comparative example, a prepared solution was made in which the solid content concentration of vinyl polymer resin particles (A) was adjusted to 25% by mass for the electrode binder composition prepared. Next, the prepared solution was applied to a hot plate adjusted to a temperature gradient from 0 to 80°C to a coating thickness of 38 μm (1.5 ml), and after drying for 4 hours, the minimum film-forming temperature at which a crack-free film was formed was measured using a film temperature tester manufactured by Imoto Seisakusho in accordance with the method of JIS K 6828-2.

[0092] 2. Swelling degree of vinyl polymer resin particles (films formed from such resin particles) constituting the electrode binder composition in relation to the electrolyte. The electrode binder compositions prepared in each example and comparative example were applied to a release PET film and dried at 140°C for 2 hours, then at 110°C for 10 hours to create a film with a thickness of 40 μm. A 1 cm × 1 cm test piece was cut out and its mass was measured (M1). This test piece was then subjected to LiPF ６ The sample was immersed in a non-aqueous electrolyte solution prepared by dissolving the sample in ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 30 / 30 / 40 (volume ratio) at a concentration of 1 mol / L at 60°C for 72 hours. After removal, the non-aqueous electrolyte solution was wiped off the surface of the test piece, and the mass was measured again (M2). The degree of swelling was calculated using the following formula: Swelling degree (%) = 100 × (M2 - M1) / M1

[0093] 3. 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 was attached to a stainless steel plate using double-sided tape (Nitto Denko Corporation "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 "Autograph AG-XPlus"). A 180° peel test was performed using the peel test machine, and the peel strength was measured.

[0094] 4. 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 and left at 25°C for 3 hours. After that, one charge / discharge cycle was performed at 0.1C, and the initial charge / discharge efficiency was measured. Next, the charge / discharge cycle was repeated 50 times at 0.2C at 60°C and 0°C respectively. The discharge capacity retention rate after 50 cycles at 60°C and after 50 cycles at 0°C were measured using the following formulas: Capacity retention rate (%) = 100 × Discharge capacity after 50 cycles (mAh / g) / Initial discharge capacity (mAh / g) The above results, along with the glass transition temperatures observed from the DSC measurement results of the negative electrode binder compositions prepared in each example and comparative example, are summarized in Tables 2 and 3.

[0095]

[0096]

[0097] The results in Tables 2-3 show that the electrode binder composition of the present invention exhibits excellent film-forming properties. Furthermore, electrodes (negative and positive electrodes) formed from the electrode binder composition of the present invention exhibit excellent durability against electrolytes, and secondary batteries equipped with such electrodes have a high initial charge-discharge efficiency of 90% or more. Moreover, they maintain a capacity of 88% or more at both low (0°C) and high (60°C) temperatures, demonstrating an excellent balance of battery characteristics. In particular, the core-shell type particles (A) in the electrode binder compositions of Examples 1-19 exhibited particularly suppressed swelling in the electrolyte due to the formation of a cross-linking structure between the core and shell, resulting in excellent electrolyte resistance.

[0098] The electrode binder composition of the present invention exhibits excellent durability to electrolytes (electrolyte resistance) and film-forming properties, enabling the formation of electrodes and secondary batteries with excellent battery characteristics such as charge-discharge efficiency and capacity retention. Secondary batteries equipped with such electrodes have excellent battery characteristics such as charge-discharge characteristics and can be effectively used in portable electronic devices, for example, as paper batteries, button batteries, coin batteries, stacked batteries, cylindrical batteries, prismatic batteries, etc.

Claims

1. A binder composition for non-aqueous secondary battery electrodes containing vinyl polymer resin particles (A) and an aqueous medium (B), wherein a film formed from the vinyl polymer resin particles (A) is made into a LiPF ６ When a film formed from vinyl polymer resin particles (A) is immersed in a mixed solution of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate = 30 / 30 / 40 (volume ratio) at a concentration of 1 mol / L at 60°C for 72 hours, the degree of swelling after immersion is 5% by mass or more and 100% by mass or less, and differential scanning calorimetry (DSC) is performed on the film formed from the vinyl polymer resin particles (A) in accordance with JIS K7121, one glass transition point is observed in the temperature range of -50°C to 70°C, and one glass transition point is observed in the temperature range of 70°C to 170°C, and JIS K A binder composition for non-aqueous secondary battery electrodes, wherein a prepared solution, adjusted to a solid content concentration of 25% by mass of the vinyl polymer resin particles (A) as measured in accordance with 6828-2, is applied to a hot plate with a temperature gradient from 0 to 80°C to a coating thickness of 38 μm (1.5 ml), and then dried for 4 hours, the minimum film-forming temperature is 70°C or lower.

2. The binder composition for non-aqueous secondary battery electrodes according to claim 1, wherein the vinyl polymer resin particles (A) contain structural units derived from aromatic vinyl monomers, structural units derived from unsaturated carboxylic acid ester monomers, and structural units derived from vinyl monomers having acidic groups, wherein the content of structural units derived from aromatic vinyl monomers is 18% by mass or more and 90% by mass or less, the content of structural units derived from unsaturated carboxylic acid ester monomers is 8% by mass or more and 80% by mass or less, and the content of structural units derived from vinyl monomers having acidic groups is 0.05% by mass or more and 10% by mass or less.

3. The binder composition for non-aqueous secondary battery electrodes according to claim 2, wherein the vinyl polymer resin particles (A) are core-shell type particles having a shell portion made of polymer (a1) and a core portion made of polymer (a2).

4. The binder composition for non-aqueous secondary battery electrodes according to claim 3, wherein the polymer (a1) contains structural units derived from the unsaturated carboxylic acid ester monomer.

5. The binder composition for non-aqueous secondary battery electrodes according to claim 4, wherein the polymer (a1) further contains structural units derived from the aromatic vinyl monomer.

6. The binder composition for non-aqueous secondary battery electrodes according to claim 4, wherein the polymer (a1) further contains structural units derived from the vinyl monomer having the acidic group.

7. The binder composition for non-aqueous secondary battery electrodes according to claim 3, wherein the polymer (a2) contains structural units derived from the aromatic vinyl monomer.

8. The binder composition for non-aqueous secondary battery electrodes according to claim 3, wherein the polymer (a2) does not contain structural units derived from a vinyl monomer having an acidic group.

9. The binder composition for non-aqueous secondary battery electrodes according to claim 3, wherein when the content of polymer (a1) is X [mass%] and the content of polymer (a2) is Y [mass%], X:Y is 5:95 to 99:

1.

10. The binder composition for non-aqueous secondary battery electrodes according to claim 3, wherein polymer (a1) and polymer (a2) are chemically bonded together.

11. The binder composition for non-aqueous secondary battery electrodes according to claim 10, wherein the chemical bond is at least one bond selected from ester bonds, siloxane bonds, amide bonds, and hydrazone bonds.

12. The binder composition for non-aqueous secondary battery electrodes according to claim 11, wherein the chemical bond is formed by at least one reaction selected from the reaction between an epoxy group and a carboxyl group, the hydrolysis and condensation reaction of an alkoxysilyl group, the reaction between an oxazoline group and a carboxyl group, the condensation reaction of a methylol group and / or an alkyloxymethyl group, the reaction between a ketone group and a hydrazide group, and the reaction between an epoxy group and a hydrazide group.

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

14. A non-aqueous secondary battery electrode comprising an electrode material layer formed using the non-aqueous secondary battery electrode composition described in claim 13.

15. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein at least one of the positive electrode and the negative electrode is the non-aqueous secondary battery electrode described in claim 14.

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