Organic particle dispersion for secondary battery functional layer, composition for secondary battery functional layer, battery member for secondary battery, and secondary battery

Abstract

Provided are organic particles including a polyfunctional monomer unit at a ratio of 50 mass% or more, and an organic particle dispersion for a secondary cell functional layer containing a solvent. Said organic particle dispersion has a polymerization initiator decomposition product content of 50 ppm or less, the total content of the polymerization initiator decomposition product and an unreacted polyfunctional monomer being 500 ppm or less.

Description

[Technical Field]

[0001] The present invention relates to an organic particle dispersion for a secondary battery functional layer, a composition for a secondary battery functional layer, a battery member for a secondary battery, and a secondary battery. [Background technology]

[0002] Secondary batteries such as lithium-ion secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications.

[0003] Here, a secondary battery generally includes battery components such as electrodes (positive electrode, negative electrode) and a separator that separates the positive electrode and negative electrode to prevent short-circuiting between them. A porous membrane layer for improving heat resistance and strength, or an adhesive layer for improving adhesion between battery components (hereinafter, these may be collectively referred to as "functional layers") may be provided on the surface of the electrode and / or separator. Specifically, an electrode formed by forming a functional layer on an electrode base material formed by providing an electrode mixture layer on a current collector, or a separator formed by forming a functional layer on a separator base material, are used as battery components.

[0004] Conventionally, attempts have been made to improve functional layers in order to further enhance the performance of secondary batteries. For example, Patent Document 1 describes a composition for a functional layer of a non-aqueous secondary battery, which contains organic particles containing 55% to 90% by mass of polyfunctional ethylenically unsaturated monomer units and having a volume average particle diameter of 50 to 370 nm, and a solvent. The functional layer composition according to Patent Document 1 can form a functional layer that has excellent heat shrinkage resistance and can enable a non-aqueous secondary battery to exhibit excellent cycle characteristics. Furthermore, for example, Patent Document 2 describes the use of non-conductive particles having a predetermined specific surface area and containing 50% or more by mass of (meth)acrylic polyfunctional monomer units in the formation of a porous membrane for a secondary battery. Furthermore, for example, Patent Document 3 discloses a composition for forming a protective film for an electrical storage device, the composition containing polymer particles (A1), polymer particles (A2), and a liquid medium, wherein the content of repeating units derived from a compound having two or more polymerizable unsaturated groups per 100 parts by mass of the polymer particles (A2) is 20 parts by mass or more and 100 parts by mass or less. Furthermore, for example, Patent Document 4 discloses a composition for forming a protective film for an electrical storage device, the composition containing polymer particles (A) containing polymer particles (A2) having a content of repeating units derived from a compound having two or more polymerizable unsaturated groups of 20% by mass or more and 100% by mass or less, a metal complex salt (B), and a liquid medium (C). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 065416 [Patent Document 2] Patent No. 6052174 [Patent Document 3] Patent No. 5488857 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-219358 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been a demand for secondary batteries with even higher performance and capacity. However, it is known that secondary batteries lose capacity during the initial charge / discharge cycle. Therefore, secondary batteries are required to achieve higher capacity by reducing this loss and increasing the initial coulombic efficiency. Furthermore, secondary batteries using battery components with functional layers are required to suppress the thermal shrinkage of the functional layer (i.e., to improve the thermal shrinkage resistance) and thereby sufficiently suppress the occurrence of short circuits between the positive and negative electrodes in high-temperature environments, thereby further improving the stability of the secondary battery.

[0007] Therefore, an object of the present invention is to provide an organic particle dispersion for a secondary battery functional layer, which is capable of forming a functional layer that has excellent heat shrinkage resistance and can enable a secondary battery to exhibit excellent initial coulombic efficiency, and a composition for a secondary battery functional layer containing the same. Another object of the present invention is to provide a battery member for a secondary battery that has excellent heat shrinkage resistance and is provided with a functional layer that can enable the secondary battery to exhibit excellent initial coulomb efficiency. Another object of the present invention is to provide a secondary battery that is excellent in stability and initial coulombic efficiency. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems, and have newly discovered that a functional layer having excellent heat shrinkage resistance and capable of causing a secondary battery to exhibit excellent initial Coulombic efficiency can be formed by using a dispersion obtained by dispersing organic particles in a solvent, the organic particles containing polyfunctional monomer units in a proportion of 50% by mass or more, and in which the content of polymerization initiator decomposition products and the total content of the polymerization initiator decomposition products and unreacted polyfunctional monomer are not more than predetermined upper limits, and thus have completed the present invention.

[0009] The present invention aims to advantageously solve the above-mentioned problems, and provides an organic particle dispersion for a secondary battery functional layer, comprising organic particles and a solvent, wherein the organic particles contain polyfunctional monomer units in a proportion of 50% by mass or more, the content of polymerization initiator decomposition products in the organic particle dispersion for a secondary battery functional layer is 50 ppm or less, and the total content of the polymerization initiator decomposition products and unreacted polyfunctional monomer is 500 ppm or less. By using an organic particle dispersion containing polyfunctional monomer units in a proportion of 50% by mass or more, the content of polymerization initiator decomposition products is 50 ppm or less, and the total content of the polymerization initiator decomposition products and unreacted polyfunctional monomer is 500 ppm or less, a functional layer having excellent heat shrinkage resistance can be formed, and a battery component including the functional layer can be used to enable a secondary battery to exhibit excellent initial coulombic efficiency. Here, the "content of polymerization initiator decomposition products" and the "total content of polymerization initiator decomposition products and unreacted polyfunctional monomer" in the organic particle dispersion liquid for a secondary battery functional layer are the proportions (ppm) of the contents of the above substances based on the total mass of the organic particle dispersion liquid for a secondary battery functional layer, and can be measured by the method described in the Examples of this specification. Furthermore, in this specification, when a component consisting of a polymer such as organic particles "contains a monomer unit," it means that "a polymer obtained using that monomer contains a repeating unit derived from that monomer." In addition, in this specification, in a polymer produced by copolymerizing multiple types of monomers, the "content ratio of a monomer unit" formed by polymerizing a certain monomer usually coincides with the ratio (feed ratio) of that certain monomer to all the monomers used in the polymerization of that polymer, unless otherwise specified. In addition, the "content ratio of each monomer unit" in the polymer is 1 H-NMR and 13 It can be measured using nuclear magnetic resonance (NMR) techniques such as C-NMR.

[0010] In the organic particle dispersion for a secondary battery functional layer of the present invention, the organic particles preferably have a volume average particle diameter of 50 nm to 900 nm, which can further improve the heat shrinkage resistance of the resulting functional layer and the initial coulombic efficiency of the resulting secondary battery. The "volume average particle size" of the organic particles can be measured using the method described in the examples.

[0011] The present invention also aims to advantageously solve the above-mentioned problems, and provides a composition for a secondary battery functional layer of the present invention, which is characterized by comprising a binder and any of the organic particle dispersions for a secondary battery functional layer described above. By using such a composition for a secondary battery functional layer, a functional layer having excellent heat shrinkage resistance can be formed, and by using a battery component including such a functional layer, the secondary battery can exhibit excellent initial coulombic efficiency.

[0012] The present invention also aims to advantageously solve the above-mentioned problems, and provides a battery component for a secondary battery of the present invention, characterized in that it includes a functional layer for a secondary battery formed using the above-mentioned composition for a functional layer for a secondary battery. As described above, a battery component including a functional layer formed using the above-mentioned composition for a functional layer has excellent heat shrinkage resistance and can enable a secondary battery including the battery component to exhibit excellent initial coulombic efficiency.

[0013] Furthermore, by using the battery member for a secondary battery of the present invention, a secondary battery excellent in stability and initial coulomb efficiency can be obtained. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide an organic particle dispersion for a secondary battery functional layer, which is capable of forming a functional layer that has excellent heat shrinkage resistance and can enable a secondary battery to exhibit excellent initial Coulombic efficiency, and a composition for a secondary battery functional layer containing the same. Furthermore, according to the present invention, it is possible to provide a battery member for a secondary battery that has excellent resistance to heat shrinkage and can enable the secondary battery to exhibit excellent initial coulomb efficiency. Furthermore, according to the present invention, a secondary battery excellent in stability and initial coulombic efficiency can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail. Here, the organic particle dispersion for a secondary battery functional layer of the present invention and the composition for a secondary battery functional layer containing the same are used to form a functional layer for a secondary battery. The battery member for a secondary battery of the present invention includes such a functional layer for a secondary battery. More specifically, the battery member for a secondary battery of the present invention may be a separator or electrode including a functional layer for a secondary battery formed using the organic particle dispersion for a secondary battery functional layer of the present invention or the composition for a secondary battery functional layer containing the same. Furthermore, the secondary battery of the present invention includes at least the battery member for a secondary battery of the present invention.

[0016] (Organic particle dispersion for secondary battery functional layer) The organic particle dispersion of the present invention contains organic particles and a solvent, and may optionally contain other additives. Here, the organic particles contained in the organic particle dispersion of the present invention contain polyfunctional monomer units in a proportion of 50 mass% or more. Furthermore, the content of polymerization initiator decomposition products in the organic particle dispersion of the present invention is 50 ppm or less, and the total content of polymerization initiator decomposition products and unreacted polyfunctional monomer is 500 ppm or less.

[0017] The organic particle dispersion of the present invention contains polyfunctional monomer units in a proportion of 50 mass% or more, has a content of polymerization initiator decomposition products of 50 ppm or less, and has a total content of polymerization initiator decomposition products and unreacted polyfunctional monomers of 500 ppm or less. Therefore, the organic particle dispersion can impart excellent heat shrinkage resistance to a functional layer formed using the organic particle dispersion, and can enable a secondary battery having a battery component equipped with the functional layer to exhibit excellent initial coulombic efficiency.

[0018] <Organic particles> The organic particles are particles made of a polymer, and are a component that can mainly improve the heat shrinkage resistance and strength of the functional layer.

[0019] <<Composition>> Here, as described above, the organic particles may contain polyfunctional monomer units in a proportion of 50% by mass or more, and may contain repeating units other than the polyfunctional monomer units (other repeating units) in a proportion of 50% by mass or less.

[0020] [Polyfunctional Monomer Unit] In the present invention, examples of polyfunctional monomers capable of forming polyfunctional monomer units include polyfunctional ethylenically unsaturated monomers. As the polyfunctional ethylenically unsaturated monomer, a monomer having two or more ethylenically unsaturated bonds per molecule (excluding conjugated diene monomers such as 1,3-butadiene) can be used.

[0021] Here, examples of the polyfunctional ethylenically unsaturated monomer include polyfunctional (meth)acrylic acid ester monomers such as allyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate; Polyfunctional aromatic vinyl monomers such as divinylbenzene and diisopropenylbenzene; Examples include dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane diallyl ether, allyl or vinyl ethers of polyfunctional alcohols other than those mentioned above, triallylamine, and methylenebisacrylamide. In the present invention, the term "(meth)acrylate" means acrylate and / or methacrylate.

[0022] These polyfunctional ethylenically unsaturated monomers can be used alone or in combination of two or more. Among these, from the viewpoint of further improving the heat shrinkage resistance of the functional layer, polyfunctional (meth)acrylic acid ester monomers and polyfunctional aromatic vinyl monomers are preferred, polyfunctional (meth)acrylic acid ester monomers are more preferred, and ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate are even more preferred.

[0023] The content of the polyfunctional monomer units in the organic particles must be 50% by mass or more, preferably 64% by mass or more, more preferably 70% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 83% by mass or less, assuming that the total repeating units of the polymer constituting the organic particles is 100% by mass. By ensuring that the content of the polyfunctional monomer units in the organic particles is 50% by mass or more, the degree of crosslinking of the organic particles can be sufficiently increased, thereby ensuring sufficient heat shrinkage resistance of the functional layer. On the other hand, by ensuring that the content of the polyfunctional monomer units in the organic particles is 90% by mass or less, polymerization stability during preparation of the organic particles can be improved, thereby suppressing the generation of fine particles and the remaining of unreacted materials. This can improve the initial coulombic efficiency and cycle characteristics of secondary batteries.

[0024] [Other repeating units] Other repeating units contained in the organic particles are not particularly limited, but include monofunctional (meth)acrylic acid ester monomer units, nitrile group-containing monomer units, and acidic group-containing monomer units. In the present invention, "(meth)acrylic" means acrylic and / or methacrylic.

[0025] -Monofunctional (meth)acrylic acid ester monomer unit- Examples of (meth)acrylic acid ester monomers that can form monofunctional (meth)acrylic acid ester monomer units include acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate. Acid alkyl esters; methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate; and the like. These may be used alone or in combination of two or more. Among these, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and 2-ethylhexyl methacrylate are preferred, and n-butyl acrylate is more preferred.

[0026] The content of the monofunctional (meth)acrylic acid ester monomer units in the organic particles is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 45% by mass or less, more preferably 35% by mass or less, and even more preferably 29% by mass or less, assuming that the total repeating units of the polymer constituting the organic particles is 100% by mass. When the content of the monofunctional (meth)acrylic acid ester monomer units in the organic particles is 10% by mass or more, polymerization stability during preparation of the organic particles can be ensured, suppressing the generation of fine particles, and improving the initial coulombic efficiency and cycle characteristics of the secondary battery. On the other hand, when the content of the monofunctional (meth)acrylic acid ester monomer units in the organic particles is 45% by mass or less, the degree of crosslinking of the organic particles can be ensured, further improving the heat resistance of the functional layer. Furthermore, the cycle characteristics of the secondary battery can be further improved.

[0027] -Nitrile group-containing monomer unit- Examples of nitrile group-containing monomers capable of forming nitrile group-containing monomer units include α,β-ethylenically unsaturated nitrile monomers. Specifically, the α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group. Examples include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. These may be used alone or in combination of two or more. Among these, acrylonitrile and methacrylonitrile are preferred.

[0028] The content of the nitrile group-containing monomer units in the organic particles is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, and preferably 10% by mass or less, and more preferably 5% by mass or less, when the total repeating units of the polymer constituting the organic particles is taken as 100% by mass. If the content of the nitrile group-containing monomer units in the organic particles is 0.1% by mass or more and 10% by mass or less, polymerization stability during preparation of the organic particles can be ensured, the generation of fine particles can be suppressed, and the cycle characteristics of the secondary battery can be improved.

[0029] -Acidic group-containing monomer units- Examples of acidic group-containing monomers capable of forming acidic group-containing monomer units include carboxylic acid group-containing monomers, sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers.

[0030] Examples of the carboxylic acid group-containing monomer include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides and their derivatives. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid. Examples of the monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters such as nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate. Examples of the acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Furthermore, as the carboxylic acid group-containing monomer, an acid anhydride that generates a carboxylic acid group upon hydrolysis can also be used.

[0031] Examples of sulfonic acid group-containing monomers include styrene sulfonic acid, vinyl sulfonic acid (ethylene sulfonic acid), methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, and 3-allyloxy-2-hydroxypropane sulfonic acid. In the present invention, "(meth)allyl" means allyl and / or methallyl.

[0032] Furthermore, examples of the phosphate group-containing monomer include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate. In the present invention, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0033] The above-mentioned acidic group-containing monomers can be used alone or in combination of two or more. Among these acidic group-containing monomers, carboxylic acid group-containing monomers are preferred, and acrylic acid and methacrylic acid are more preferred.

[0034] The content of the acidic group-containing monomer units in the organic particles is preferably 0.1% by mass or more, more preferably 1% by mass or more, and preferably 10% by mass or less, and more preferably 5% by mass or less, assuming that the total repeating units of the polymer constituting the organic particles is 100% by mass. If the content of the acidic group-containing monomer units in the organic particles is 0.1% by mass or more, polymerization stability during preparation of the organic particles can be ensured, the generation of fine particles can be suppressed, and the cycle characteristics of the secondary battery can be improved. On the other hand, if the content of the acidic group-containing monomer units in the organic particles is 10% by mass or less, the amount of moisture carried over into the secondary battery can be reduced, thereby improving the cycle characteristics of the secondary battery.

[0035] <<Method of manufacturing organic particle dispersion liquid>> An organic particle dispersion liquid in which organic particles capable of satisfying the above-mentioned various attributes are dispersed in a solvent can be produced by polymerizing a monomer composition containing the above-mentioned monomer in a solvent such as water in the presence of a polymerization initiator and a reducing agent. In other words, the organic particle dispersion liquid of the present invention can be a polymerization liquid obtained by polymerizing the monomer composition in a solvent. In this case, the content ratio of each monomer in the monomer composition can be determined based on the content ratio of each repeating unit (monomer unit) in the organic particles.

[0036] [Polymerization initiator] The polymerization initiator is not particularly limited, and an oil-soluble polymerization initiator can be suitably used. Examples of the oil-soluble polymerization initiator include benzoyl peroxide, α,α'-azobisisobutyronitrile (AIBN), α,α'-azobis(2-methylbutyronitrile) (AMBN), t-butylperoxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylacetate, t-butylperoxyacetate, cumeneperoxyneodecanoate, t-butylperoxyneodecanoate, t-hexylperoxyneodecanoate, t-butylperoxylaurate, t-hexylperoxybenzoate, and 3,5,5-trimethylhexanoyl peroxide. Among these, t-butylperoxy-2-ethylhexanoate and α,α'-azobis(2-methylbutyronitrile) are preferably used. The amount of the polymerization initiator used can be adjusted appropriately depending on the mass of the monomer composition, etc. For example, the amount of the polymerization initiator used can be 1.0 part by mass or more and 5.0 parts by mass or less, where the mass of the monomer composition (solid content equivalent) is 100 parts by mass.

[0037] [Reducing agent] The reducing agent is not particularly limited, and examples thereof include ascorbic acid and its salts (e.g., sodium ascorbate), sodium hydrogensulfite, sodium hyposulfite, and sodium formaldehyde sulfoxylate, and methods in which at least one of these is used in combination with Fe ions. Among these, ascorbic acid and its salts are preferred from the viewpoints of polymerizability and dispersibility of the resulting organic particles in the dispersion. The amount of the reducing agent used can be appropriately adjusted depending on the mass of the monomer composition and the amount of the polymerization initiator used. For example, the amount of the reducing agent used can be 1.0 to 5.0 parts by mass, where the mass of the monomer composition (solids content equivalent) is 100 parts by mass.

[0038] [Polymerization mode and polymerization reaction] The polymerization method for preparing the organic particles is not particularly limited, and any of solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used. Among these, emulsion polymerization is preferred. Furthermore, any of ionic polymerization, radical polymerization, living radical polymerization, etc. can be used as the polymerization reaction. In the polymerization, seed polymerization is preferably carried out using seed particles. The polymerization conditions can be appropriately adjusted depending on the polymerization method, etc.

[0039] [Polymerization temperature] The temperature at which the polymerization reaction of the polyfunctional monomer is carried out in the presence of a reducing agent is preferably less than 80°C, more preferably 60°C or less, and even more preferably 50°C or less. The temperature at which the polymerization reaction is carried out is not particularly limited and may be, for example, 25°C or higher. By carrying out the polymerization reaction of the polyfunctional monomer at a temperature of less than 80°C, the content of polymerization initiator decomposition products and the content of unreacted polyfunctional monomer in the resulting organic particle dispersion can be reduced. When organic particles are produced by seed polymerization, the temperature conditions for the polymerization reaction during the preparation of seed particles are not particularly limited. For example, the polymerization reaction during the preparation of seed particles can be carried out at a temperature range of 25°C or higher and 100°C or lower. This also applies when the seed particles contain polyfunctional monomer units.

[0040] [Additives] In addition, known additives such as emulsifiers and chain transfer agents can be used in the polymerization for preparing the organic particles, and the amounts used can be those generally used.

[0041] <<Volume average particle size of organic particles>> The volume average particle diameter of the organic particles obtained as described above is preferably 50 nm or more, more preferably 100 nm or more, and preferably 900 nm or less, more preferably 500 nm or less, and even more preferably 200 nm or less. When the volume average particle diameter of the organic particles is 50 nm or more, an excessive increase in the resistance of the functional layer can be suppressed, thereby improving the initial coulombic efficiency and cycle characteristics of the secondary battery. On the other hand, when the volume average particle diameter of the organic particles is 900 nm or less, an excessive decrease in coating density when the functional layer composition is applied to a substrate to form a functional layer can be suppressed, thereby improving the heat shrinkage resistance of the resulting functional layer.

[0042] The volume average particle diameter of the organic particles can be adjusted by changing the type and amount of the polymerization initiator, chain transfer agent, and / or emulsifier used in preparing the organic particles. For example, when preparing organic particles by seed polymerization, increasing the amount of emulsifier used in preparing the seed particles can make the seed particles smaller, thereby reducing the volume average particle diameter of the resulting organic particles. Conversely, decreasing the amount of emulsifier used in preparing the seed particles can make the seed particles larger, thereby increasing the volume average particle diameter of the resulting organic particles.

[0043] <<Glass transition temperature of organic particles>> The glass transition temperature of the organic particles obtained as described above is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. If the glass transition temperature of the organic particles is 100°C or higher, the heat shrinkage resistance of the functional layer can be further improved. The upper limit of the glass transition temperature of the organic particles is not particularly limited, but is usually 500°C or lower. The glass transition temperature of the organic particles can be adjusted by changing the type and ratio of the monomers used in preparing the organic particles, and can be measured according to the method described in the Examples.

[0044] <Content of polymerization initiator decomposition products in organic particle dispersion> The content of polymerization initiator decomposition products in the organic particle dispersion must be 50 ppm or less, preferably 30 ppm or less, more preferably 15 ppm or less, and even more preferably 10 ppm or less. If the content of polymerization initiator decomposition products in the organic particle dispersion is equal to or less than the above upper limit, the initial coulombic efficiency of the resulting secondary battery can be further improved. Polymerization initiator decomposition products remaining in the resulting functional layer can cause side reactions during initial charging and result in capacity loss in the secondary battery. Therefore, if the amount of polymerization initiator decomposition products contained in the functional layer is small, capacity loss in the secondary battery can be reduced and the initial coulombic efficiency can be effectively improved. The content of polymerization initiator decomposition products is not particularly limited, but may be below the detection limit. The content of polymerization initiator decomposition products in the organic particle dispersion can be controlled by appropriately adjusting the polymerization reaction conditions. More specifically, the content of polymerization initiator decomposition products in the organic particle dispersion can be controlled to 50 ppm or less by proceeding with the polymerization reaction of polymerizing the polyfunctional monomer in the presence of a polymerization initiator and a reducing agent under appropriate temperature conditions (for example, below 80°C).

[0045] <Content of Unreacted Polyfunctional Monomer in Organic Particle Dispersion> The content of unreacted polyfunctional monomer in the organic particle dispersion must be 500 ppm or less, preferably 450 ppm or less, and more preferably 250 ppm or less. If the content of unreacted polyfunctional monomer is equal to or less than the upper limit, the initial coulombic efficiency of the secondary battery can be further improved. Unreacted polyfunctional monomer remaining in the resulting functional layer can cause side reactions during initial charging, resulting in capacity loss in the secondary battery. Therefore, if the amount of unreacted polyfunctional monomer contained in the functional layer is small, capacity loss in the secondary battery can be reduced, and the initial coulombic efficiency can be effectively improved. The content of unreacted polyfunctional monomer is not particularly limited, but may be below the detection limit. The content of unreacted polyfunctional monomer in the organic particle dispersion can be controlled by appropriately adjusting the polymerization reaction conditions. More specifically, the content of unreacted polyfunctional monomer in the organic particle dispersion can be controlled to 500 ppm or less by proceeding the polymerization reaction for polymerizing the polyfunctional monomer in the presence of a polymerization initiator and a reducing agent under appropriate temperature conditions (for example, below 80°C).

[0046] <Total Content of Decomposition Products of Polymerization Initiator and Unreacted Polyfunctional Monomer in Organic Particle Dispersion> The total content of polymerization initiator decomposition products and unreacted polyfunctional monomer in the organic particle dispersion must be 500 ppm or less, preferably 450 ppm or less, and more preferably 250 ppm or less. If the total content of polymerization initiator decomposition products and unreacted polyfunctional monomer in the organic particle dispersion is equal to or less than the above upper limit, the initial coulombic efficiency of the secondary battery can be further improved. The lower limit of the total content of polymerization initiator decomposition products and unreacted polyfunctional monomer in the organic particle dispersion is not particularly limited, but may be less than the detection limit. The total content of polymerization initiator decomposition products and unreacted polyfunctional monomer in the organic particle dispersion can be controlled by the same method as that for controlling the content of polymerization initiator decomposition products and unreacted polyfunctional monomer.

[0047] <Components derived from reducing agents in organic particle dispersions> The organic particle dispersion may contain components derived from the reducing agent, such as unreduced reducing agent and oxides of the reducing agent.

[0048] <Solvent> As the solvent for the organic particle dispersion of the present invention, any known solvent capable of dispersing the above-mentioned organic particles can be used. Among them, it is preferable to use water as the solvent. The solvent for the organic particle dispersion may be the polymerization solvent used when preparing the organic particles.

[0049] <Other ingredients> The components other than the organic particles and the solvent that may be contained in the organic particle dispersion of the present invention are not particularly limited. Examples of such components include known inorganic particles and known additives. Examples of known inorganic particles include those described in JP 2017-103034 A. The known additives are not particularly limited and may include, for example, wetting agents, dispersants, leveling agents, antioxidants, thickeners, antifoaming agents, and electrolyte additives. These additives are not particularly limited as long as they do not affect the battery reaction, and known additives can be used (see, for example, Japanese Patent No. 6052174). These other components may be used alone or in combination of two or more in any ratio.

[0050] <Solid content concentration of organic particle dispersion> The solid content concentration of the organic particle dispersion of the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, and is preferably 40% by mass or less, more preferably 35% by mass or less.

[0051] (Composition for secondary battery functional layer) The functional layer composition of the present invention contains a binder and the organic particle dispersion liquid of the present invention described above, and may optionally contain other components described above. Because the functional layer composition of the present invention contains the organic particle dispersion liquid of the present invention, it can form a functional layer having excellent heat shrinkage resistance, and when a battery component including the functional layer is used, it can enable a secondary battery to exhibit excellent initial coulombic efficiency.

[0052] <Binding material> The binder is a polymer component that can hold components such as the organic particles contained in a functional layer formed using a functional layer composition so that they do not detach from the functional layer.

[0053] <<Composition>> Here, the binder preferably contains crosslinkable monomer units in a proportion of 0.05% by mass to 5% by mass, and is made of a polymer containing repeating units other than the crosslinkable monomer units (other repeating units).

[0054] [Crosslinkable monomer unit] The crosslinkable monomer that can form the crosslinkable monomer unit is not particularly limited, and includes a monomer that can form a crosslinked structure by polymerization.Examples of the crosslinkable monomer usually include a monomer having thermal crosslinkability.More specifically, it includes a monomer having a thermal crosslinkable crosslinkable group and one ethylenically unsaturated bond per molecule; a polyfunctional ethylenically unsaturated monomer (a monomer having two or more ethylenically unsaturated bonds per molecule).

[0055] Examples of the thermally crosslinkable crosslinkable group include an epoxy group, an N-methylolamide group, an oxetanyl group, an oxazoline group, and combinations thereof. Among these, an epoxy group is more preferred because it is easy to adjust the crosslinking and crosslink density.

[0056] Examples of the monomer having an epoxy group as a thermally crosslinkable crosslinking group and having an ethylenically unsaturated bond include unsaturated glycidyl ethers such as vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, and o-allylphenyl glycidyl ether; diene or polyene monoepoxides such as butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, and 1,2-epoxy-5,9-cyclododecadiene; 3,4- Examples include alkenyl epoxides such as epoxy-1-butene, 1,2-epoxy-5-hexene, and 1,2-epoxy-9-decene; and glycidyl esters of unsaturated carboxylic acids such as glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexenecarboxylic acid, and glycidyl ester of 4-methyl-3-cyclohexenecarboxylic acid.

[0057] Furthermore, examples of monomers having an N-methylolamide group as a thermally crosslinkable crosslinking group and having an ethylenically unsaturated bond include (meth)acrylamides having a methylol group, such as N-methylol(meth)acrylamide.

[0058] Furthermore, examples of monomers having an oxetanyl group as a thermally crosslinkable crosslinkable group and having an ethylenically unsaturated bond include 3-((meth)acryloyloxymethyl)oxetane, 3-((meth)acryloyloxymethyl)-2-trifluoromethyloxetane, 3-((meth)acryloyloxymethyl)-2-phenyloxetane, 2-((meth)acryloyloxymethyl)oxetane, and 2-((meth)acryloyloxymethyl)-4-trifluoromethyloxetane.

[0059] Furthermore, examples of monomers having an oxazoline group as a thermally crosslinkable crosslinkable group and having an ethylenically unsaturated bond include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

[0060] Furthermore, examples of polyfunctional ethylenically unsaturated monomers (monomers having two or more ethylenically unsaturated bonds per molecule) include the same as the "polyfunctional ethylenically unsaturated monomers" described above in the section "organic particles."

[0061] The above-mentioned crosslinkable monomers can be used alone or in combination of two or more. Among these crosslinkable monomers, allyl methacrylate and allyl glycidyl ether are preferred.

[0062] The content of the crosslinkable monomer units in the binder is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 1% by mass or more, particularly preferably 2% by mass or more, and preferably 5% by mass or less, more preferably 3.5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 2.5% by mass or less, assuming that the total repeating units of the polymer constituting the binder is 100% by mass. If the content of the crosslinkable monomer units in the binder is 0.05% by mass or more, the degree of crosslinking of the binder is ensured, thereby suppressing excessive swelling in the electrolyte, and further improving the cycle characteristics of the secondary battery. On the other hand, if the content of the crosslinkable monomer units in the binder is 5% by mass or less, the binding ability of the binder is ensured, thereby improving the adhesiveness of the functional layer and further increasing the heat shrinkage resistance of the functional layer.

[0063] [Other repeating units] Other repeating units contained in the polymer forming the binder are not particularly limited, but include monofunctional (meth)acrylic acid ester monomer units, aromatic monovinyl monomer units, and acidic group-containing monomer units.

[0064] -Monofunctional (meth)acrylic acid ester monomer unit- Examples of monofunctional (meth)acrylic acid ester monomers capable of forming monofunctional (meth)acrylic acid ester monomer units include those mentioned above in the section on "organic particles." These can be used alone or in combination of two or more. Among these, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and 2-ethylhexyl methacrylate are preferred, with 2-ethylhexyl acrylate being more preferred.

[0065] The content of the monofunctional (meth)acrylic acid ester monomer units in the binder is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and preferably 80% by mass or less, and more preferably 75% by mass or less, when the total repeating units of the polymer constituting the binder is taken as 100% by mass. If the content of the monofunctional (meth)acrylic acid ester monomer units in the binder is 60% by mass or more, an excessive increase in the glass transition temperature of the binder is suppressed, and the adhesiveness of the functional layer is ensured. On the other hand, if the content of the monofunctional (meth)acrylic acid ester monomer units in the binder is 80% by mass or less, the cycle characteristics of the secondary battery can be further improved.

[0066] - Aromatic monovinyl monomer unit - Examples of aromatic monovinyl monomers that can form aromatic monovinyl monomer units include styrene, styrenesulfonic acid and its salts (e.g., sodium styrenesulfonate), α-methylstyrene, vinyltoluene, and 4-(tert-butoxy)styrene. These can be used alone or in combination of two or more. Among these, styrene is preferred.

[0067] The content of aromatic monovinyl monomer units in the binder is preferably 10% by mass or more, more preferably 20% by mass or more, and preferably 40% by mass or less, and more preferably 30% by mass or less, assuming that the total repeating units of the polymer constituting the binder is 100% by mass. If the content of aromatic monovinyl monomer units in the binder is 10% by mass or more, the glass transition temperature of the binder does not decrease excessively, and blocking of battery components having functional layers can be suppressed. On the other hand, if the content of aromatic monovinyl monomer units in the binder is 40% by mass or less, the glass transition temperature of the binder does not increase excessively, and the adhesiveness of the functional layer can be ensured.

[0068] -Acidic group-containing monomer units- Examples of the acidic group-containing monomer capable of forming the acidic group-containing monomer unit include those mentioned above in the section "organic particles." These can be used alone or in combination of two or more. Among these, carboxylic acid group-containing monomers are preferred, and acrylic acid is more preferred.

[0069] The content of the acidic group-containing monomer units in the binder is preferably 2% by mass or more, more preferably 2.5% by mass or more, and preferably 8% by mass or less, and more preferably 5% by mass or less, when the total repeating units of the polymer constituting the binder is taken as 100% by mass. If the content of the acidic group-containing monomer units in the binder is 2% by mass or more, polymer stability is ensured when preparing the binder, thereby suppressing the generation of aggregates and improving the cycle characteristics of the secondary battery. On the other hand, if the content of the acidic group-containing monomer units in the binder is 8% by mass or less, the amount of moisture carried over into the secondary battery can be reduced, thereby improving the cycle characteristics of the secondary battery.

[0070] <<Preparation method>> The binder can be produced by polymerizing a monomer composition containing the above-mentioned monomers in an aqueous solvent such as water. In this case, the content of each monomer in the monomer composition can be determined based on the content of each repeating unit (monomer unit) in the binder.

[0071] The polymerization method is not particularly limited, and any of solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used. Furthermore, any of ionic polymerization, radical polymerization, living radical polymerization, etc. can be used as the polymerization reaction. The polymerization conditions can be appropriately adjusted depending on the polymerization method, etc. In addition, known additives such as emulsifiers, polymerization initiators, and chain transfer agents can be used in the polymerization, and the amounts used are also generally used amounts.

[0072] <<Glass transition temperature>> The glass transition temperature of the binder obtained as described above is preferably −40° C. or higher, preferably 0° C. or lower, and more preferably −15° C. or lower. If the binder has a glass transition temperature of −40° C. or higher, blocking of battery components including a functional layer can be suppressed. On the other hand, if the binder has a glass transition temperature of 0° C. or lower, the adhesiveness of the functional layer can be sufficiently ensured. The glass transition temperature of the binder can be adjusted by changing the type and ratio of the monomers used in preparing the binder. For example, the glass transition temperature of the binder can be increased by increasing the ratio of aromatic monovinyl monomers such as styrene used in preparing the binder, and the glass transition temperature of the binder can be decreased by decreasing the ratio.

[0073] <<Content ratio of organic particles to binder>> The content ratio of the organic particles to the binder in the functional layer composition is not particularly limited, but the proportion of the binder in the total of the organic particles and the binder is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 5% by mass or more, particularly preferably 9% by mass or more, and preferably 20% by mass or less, and more preferably 15% by mass or less. If the proportion of the binder in the total of the organic particles and the binder is 1% by mass or more, powdering of the organic particles is suppressed, and the heat shrinkage resistance of the functional layer can be sufficiently ensured. On the other hand, if the proportion of the binder in the total of the organic particles and the binder is 20% by mass or less, an excessive increase in the resistance of the functional layer can be suppressed, and the cycle characteristics of the secondary battery can be sufficiently ensured.

[0074] <Method for preparing composition for secondary battery functional layer> The composition for a functional layer of the present invention can be prepared by stirring and mixing the above-mentioned organic particle dispersion, a binder, and any other components in the presence of a solvent such as water. Note that the liquid contained in the organic particle dispersion may be used as the solvent for the composition for a functional layer as it is. The solid content of the composition for functional layer of the present invention is usually 10% by mass or more and 40% by mass or less.

[0075] The stirring method is not particularly limited and can be performed by a known method. Specifically, a slurry composition for functional layers can be prepared by mixing the above components with the solvent using a general stirring vessel, ball mill, sand mill, bead mill, pigment disperser, ultrasonic disperser, crusher, homogenizer, planetary mixer, Filmix, etc. The mixing of the above components with the solvent can usually be performed at room temperature to 80°C for 10 minutes to several hours.

[0076] (Battery materials for secondary batteries) The battery member for a secondary battery of the present invention includes a functional layer for a secondary battery formed using the functional layer composition described above. Such a battery member for a secondary battery can be formed, for example, by applying the functional layer composition described above to the surface of an appropriate substrate to form a coating film, and then drying the formed coating film. That is, the battery member for a secondary battery of the present invention includes a functional layer formed on a substrate and composed of a dried product of the functional layer composition described above. The functional layer contains the organic particles described above and, optionally, the binder and other components. The organic particles and binder may be crosslinked during drying of the functional layer composition or during a heat treatment optionally performed after drying. (That is, the functional layer provided in the battery member for a secondary battery of the present invention may include crosslinked organic particles, binders, and / or organic particles and a binder.) Furthermore, the components contained in the functional layer are the same as those contained in the functional layer composition described above, and the preferred ratios of the components are the same as the preferred ratios of the components in the functional layer composition. The battery member for a secondary battery of the present invention has a functional layer formed using the above-mentioned functional layer composition, and therefore has excellent heat shrinkage resistance. Furthermore, the use of the battery member for a secondary battery allows the secondary battery to exhibit excellent initial coulombic efficiency.

[0077] <Base material> Here, there are no limitations on the substrate to which the functional layer composition is applied. For example, a coating film of the functional layer composition may be formed on the surface of a release substrate, the coating film may be dried to form a functional layer, and the release substrate may then be peeled off from the functional layer. In this way, the functional layer peeled off from the release substrate can be used as a free-standing film to form a battery component for a secondary battery. Specifically, the functional layer peeled off from the release substrate may be laminated on a separator substrate to form a battery component of the present invention that is a separator comprising a functional layer, or the functional layer peeled off from the release substrate may be laminated on an electrode substrate to form a battery component of the present invention that is an electrode comprising a functional layer. However, from the viewpoint of increasing the manufacturing efficiency of battery components by eliminating the step of peeling off the functional layer, it is preferable to use a separator substrate or an electrode substrate, rather than a release substrate, as the substrate to which the functional layer composition is applied.

[0078] <<Separator substrate>> The separator substrate is not particularly limited, but examples include known separator substrates such as organic separator substrates. The organic separator substrate is a porous member made of an organic material. Examples of organic separator substrates include microporous membranes or nonwoven fabrics containing polyolefin resins such as polyethylene and polypropylene, or aromatic polyamide resins. Microporous membranes and nonwoven fabrics made of polyethylene are preferred due to their excellent strength. The thickness of the separator substrate can be any thickness, preferably 5 μm to 30 μm, more preferably 5 μm to 20 μm, and even more preferably 5 μm to 18 μm. A separator substrate thickness of 5 μm or more ensures sufficient safety. Furthermore, a separator substrate thickness of 30 μm or less can suppress a decrease in ionic conductivity and a decrease in the output characteristics of the secondary battery, while suppressing an increase in the thermal contraction force of the separator substrate, thereby improving heat resistance.

[0079] <<Electrode base material>> The electrode substrates (positive electrode substrate and negative electrode substrate) are not particularly limited, but examples thereof include electrode substrates in which an electrode mixture layer is formed on a current collector. Here, the current collector, the electrode active materials (positive electrode active material, negative electrode active material) and binders for the electrode composite layer (binders for the positive electrode composite layer, binders for the negative electrode composite layer) in the electrode composite layer, and the method for forming the electrode composite layer on the current collector may be known, and for example, the method described in Japanese Patent No. 6052174 may be used.

[0080] <Method for forming functional layer for secondary battery> Examples of methods for forming a functional layer on a substrate such as the separator substrate or electrode substrate described above include the following methods. 1) A method in which the functional layer composition of the present invention is applied to the surface of a separator substrate or an electrode substrate (in the case of an electrode substrate, the surface on the electrode mixture layer side; the same applies hereinafter) and then dried; 2) A method of immersing a separator substrate or an electrode substrate in the functional layer composition of the present invention and then drying it; and 3) A method in which the functional layer composition of the present invention is applied to a release substrate, dried to produce a functional layer, and the resulting functional layer is transferred to the surface of a separator substrate or electrode substrate. Among these, the method 1) is particularly preferred because it allows for easy control of the thickness of the functional layer. Specifically, the method 1) includes a step of applying a functional layer composition onto a substrate (application step) and a step of drying the functional layer composition applied onto the substrate to form a functional layer (functional layer formation step). The functional layer may be formed on only one side or both sides of the separator substrate or electrode substrate depending on the structure of the secondary battery to be manufactured. Here, when a separator substrate is used as the substrate, it is preferable to form the functional layer on both sides of the separator substrate, and when an electrode substrate is used as the substrate, it is preferable to form the functional layer on one side of the electrode substrate, particularly on the electrode mixture layer.

[0081] <<Coating process>> In the coating process, the method for coating the functional layer composition onto the substrate is not particularly limited, and examples thereof include the doctor blade method, reverse roll method, direct roll method, gravure method, extrusion method, and brush coating method.

[0082] <<Functional layer formation process>> In the functional layer forming step, the method for drying the functional layer composition on the substrate is not particularly limited and any known method can be used. Examples of drying methods include drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with infrared rays or electron beams. The drying conditions are not particularly limited, but the drying temperature is preferably 40 to 150°C, and the drying time is preferably 2 to 30 minutes.

[0083] <Functional layer thickness> The thickness of each functional layer formed on the substrate is preferably 0.5 μm or more, preferably 1.5 μm or less, more preferably 1.3 μm or less, and even more preferably 1.1 μm or less. If the thickness of the functional layer is 0.5 μm or more, the heat shrinkage resistance of the functional layer can be sufficiently ensured. On the other hand, if the thickness of the functional layer is 1.5 μm or less, an excessive increase in the resistance of the functional layer can be suppressed, and the cycle characteristics and initial coulombic efficiency of the secondary battery can be improved.

[0084] <Other components> In addition, the battery components (e.g., separators and electrodes) of the present invention may have other components in addition to the separator substrate or electrode substrate and the functional layer formed using the functional layer composition of the present invention, as long as the effects of the present invention are not significantly impaired.

[0085] (Secondary battery) The secondary battery of the present invention includes the battery component of the present invention described above. More specifically, the secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte solution, and includes at least one of the battery components of the positive electrode, the negative electrode, and the separator described above. Because the secondary battery of the present invention includes the battery component of the present invention, it has excellent initial coulombic efficiency and is also excellent in stability because the occurrence of short circuits between the positive electrode and the negative electrode in a high-temperature environment is sufficiently suppressed.

[0086] <Positive electrode, negative electrode, and separator> At least one of the positive electrode, negative electrode, and separator used in the secondary battery of the present invention is the battery component of the present invention. The positive electrode, negative electrode, and separator that do not fall under the battery component of the present invention are not particularly limited, and an electrode made of the above-mentioned electrode base material and a separator made of the above-mentioned separator base material can be used.

[0087] <Electrolyte> As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is typically used. For example, in lithium-ion secondary batteries, which are a type of non-aqueous secondary battery, a lithium salt is used as the supporting electrolyte. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, CF4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. Among these, LiPF6, LiClO4, and CF3SO3Li are preferred because they are easily soluble in solvents and exhibit a high degree of dissociation. One type of electrolyte may be used alone, or two or more types may be used in combination. Generally, the lithium ion conductivity tends to increase as the supporting electrolyte has a higher degree of dissociation. Therefore, the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0088] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. For example, in lithium ion secondary batteries, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC) are preferred; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. Mixtures of these solvents may also be used. Among these, carbonates are preferred due to their high dielectric constant and wide stable potential range. Generally, the lower the viscosity of the solvent used, the higher the lithium ion conductivity, so the lithium ion conductivity can be adjusted by the type of solvent. The concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate. Known additives may also be added to the electrolytic solution.

[0089] <Secondary battery manufacturing method> The secondary battery of the present invention described above can be produced, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the stack as necessary, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the container. At least one of the battery components, the positive electrode, the negative electrode, and the separator, is a battery component with a functional layer. If necessary, the battery container may contain an expanded metal, a fuse, an overcurrent prevention element such as a PTC element, or a lead plate to prevent pressure buildup within the battery and overcharging and discharging. The shape of the battery may be, for example, a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, or any other suitable shape. [Example]

[0090] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. In the examples and comparative examples, various measurements and evaluations were carried out as follows.

[0091] <Volume average particle size of organic particles> The volume-average particle diameter of the polymers obtained in the examples and comparative examples was measured by laser diffraction. Specifically, an aqueous dispersion containing the prepared particles (solid content concentration: 0.1 to 2% by mass) was used as a sample, and the particle size distribution (volume basis) was obtained using a laser diffraction particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name "LS-13 320"), and the particle diameter at which the cumulative volume calculated from the smallest diameter side reached 50% was determined as the volume-average particle diameter D50 (nm). <Glass transition temperature (Tg)> The aqueous dispersions of organic particles and binder obtained in the examples and comparative examples were each dried at a temperature of 130° C. for 1 hour to obtain measurement samples. A 10 mg sample was weighed into an aluminum pan and measured using a differential scanning calorimetry (DSC) analyzer (SII NanoTechnology, Inc., EXSTAR DSC6220) under the conditions specified in JIS Z 8703. The temperature range was between -100°C and 200°C, with a heating rate of 10°C / min. A differential scanning calorimetry (DSC) curve was obtained. An empty aluminum pan was used as a reference. The glass transition temperature (°C) was calculated by measuring the intersection of the baseline just before the endothermic peak of the DSC curve, where the differential signal (DDSC) was 0.05 mW / min / mg or greater, and the tangent to the DSC curve at the first inflection point after the endothermic peak. <Contents of polymerization initiator decomposition products and unreacted polyfunctional monomers> The amounts of polymerization initiator decomposition products and unreacted polyfunctional monomer in the organic particle dispersion were measured using a gas chromatograph (Shimadzu Corporation, "GC-2010") and a non-polar column (Agilent Corporation, "DB-1", size: 0.25 mm × 30 m × 1 μm) according to the following procedure. (1) Preparation and quantification of internal standard solution Dodecane was used as the internal standard substance and diluted with dimethylformamide (DMF) to a concentration of 1% to obtain an internal standard solution. Next, various multifunctional monomers (EDMA or TMPTMA) and polymerization initiators (perbutyl O or AMBN) used in producing organic particles in the Examples and Comparative Examples were diluted with DMF to a concentration of 0.1% to obtain a sample solution. 2 g of the sample solution and 0.2 g of the internal standard solution were each precisely weighed, and 5 g of acetone was added and mixed to prepare a measurement solution. 1 μl of the resulting measurement solution was introduced into the device and measured by gas chromatography. A correction factor was determined from the integrated value of the sample and dodecane. (2) Measurement of the sample 5 g of the organic particle dispersion and 0.2 g of the above internal standard solution were precisely weighed, and 5 g of acetone was added and mixed to obtain a mixed solution. The resulting mixed solution was left to stand for at least one day and night, and the supernatant was filtered through a 0.45 μm filter to obtain a sample. 1 μl of the resulting sample was introduced into the device and measured by gas chromatography. The concentrations of unreacted polyfunctional monomer and polymerization initiator decomposition products in the organic particle dispersion (concentration [ppm] based on the total mass of the organic particle dispersion) were calculated from the integrated value of the sample and the correction factor obtained according to the procedure in (1) above. <Functional layer thickness> The thickness of the functional layer was calculated by subtracting the thickness of the substrate without the functional layer from the thickness of the battery component consisting of the functional layer and the substrate (separator substrate or electrode substrate). The thicknesses of the battery component and the substrate were each measured at 10 random points using a contact thickness meter (Digimatic Indicator Code No.: 543-575, manufactured by Mitutoyo Precision Instruments Co., Ltd.) and calculated as the average value.

[0092] <Heat shrinkage resistance of functional layer> A single-layer polyethylene separator (thickness: 9 μm) manufactured by a wet method was prepared as a separator substrate. The functional layer compositions obtained in the Examples and Comparative Examples were applied to one side of this separator substrate, and the functional layer compositions on the separator substrate were dried at 50°C for 10 minutes to form a functional layer (thickness: 1.0 μm). The separator with this functional layer was used as the separator for evaluation. The prepared separator for evaluation was cut into a 12 cm x 12 cm square, and a square with sides of 10 cm was drawn inside the square to form a test piece. The test piece was then placed in a thermostatic chamber at 130°C and left for 1 hour, after which the change in the area of ​​the square drawn inside (= {(area of ​​square before leaving - area of ​​square after leaving) / area of ​​square before leaving} x 100%) was calculated as the thermal shrinkage rate and evaluated according to the following criteria. The smaller this thermal shrinkage rate, the better the thermal shrinkage resistance of the functional layer formed using the functional layer composition. A: Heat shrinkage rate is less than 2% B: Heat shrinkage rate is 2% or more and less than 3% C: Heat shrinkage rate is 3% or more and less than 5% D: Heat shrinkage rate is 5% or more <Initial Coulomb efficiency> The lithium-ion secondary batteries fabricated in the examples and comparative examples were poured with electrolyte and then allowed to stand at 25°C for 5 hours. Next, they were charged to a cell voltage of 3.65V at a constant current of 0.2C at 25°C (the charge capacity at this time was designated C1). Subsequently, they were aged for 12 hours at 60°C. Then, they were subjected to CC-CV charging (upper cell voltage of 4.30V) at a constant current of 0.2C at 25°C (the charge capacity at this time was designated C2), and CC discharging to 3.00V at a constant current of 0.2C (the discharge capacity at this time was designated D). Using the charge capacities C1, C2, and discharge capacity D thus obtained, the initial coulombic efficiency was calculated according to the following formula and evaluated according to the following criteria. A higher initial coulombic efficiency indicates better initial characteristics of the secondary battery. Initial Coulomb efficiency = D / (C1+C2) x 100(%) A: 90.5% or more B: 90% or more but less than 90.5% C: Less than 90% <Cycle characteristics> Using the lithium ion secondary batteries prepared in the Examples and Comparative Examples and whose initial coulombic efficiency was measured, 100 cycles of charge / discharge were performed at a cell voltage of 4.30-3.00 V and a charge / discharge rate of 1.0 C in an environment at a temperature of 25°C. The capacity at the first cycle, i.e., the initial discharge capacity X1, and the discharge capacity at the 100th cycle X2 were measured, and the capacity retention rate (%) = (X2 / X1) × 100 was calculated and evaluated according to the following criteria. A higher value of this capacity retention rate indicates that the secondary battery has better cycle characteristics. A: Capacity retention rate is 80% or more B: Capacity retention rate is 70% or more but less than 80% C: Capacity retention rate is less than 70%

[0093] Example 1 <Production of organic particle dispersion> (1) Preparation of Monomer Composition for Seed Particles In a reactor A equipped with a stirrer, 1.0 part of sodium dodecyl sulfate, 0.40 parts of ammonium persulfate, and 180 parts of ion-exchanged water were mixed to form a mixture, and the mixture was heated to 65° C. Meanwhile, in a separate vessel, 80.0 parts of n-butyl acrylate as a monofunctional (meth)acrylic acid ester monomer, 10.0 parts of methacrylic acid as an acidic group-containing monomer, 10.0 parts of acrylonitrile as a nitrile group-containing monomer, 0.6 parts of sodium dodecyl sulfate, and 40 parts of ion-exchanged water were mixed to prepare a monomer composition for seed particles. This monomer composition for seed particles was continuously added to the above-mentioned reactor A over a period of 4 hours to carry out a polymerization reaction. The temperature inside the reactor was maintained at 65°C during the continuous addition of the monomer composition for seed particles. After the continuous addition was completed, the polymerization reaction was continued for an additional 3 hours at 80°C. This resulted in an aqueous dispersion of seed particles. The volume average particle diameter of the seed particles was measured in the same manner as for the organic particles and was found to be 95 nm. (2) Seeded polymerization of multifunctional monomers Next, 20 parts of the aqueous dispersion of the seed particles (solids equivalent: 16 parts n-butyl acrylate units, 2 parts methacrylic acid units, and 2 parts acrylonitrile units), 80 parts ethylene glycol dimethacrylate (Kyoeisha Chemical Co., Ltd., product name "Light Ester EG") as a polyfunctional monomer, 5 parts sodium dodecylbenzenesulfonate, and 1.6 parts t-butylperoxy-2-ethylhexanoate (NOF Corporation, product name "Perbutyl O") as a polymerization initiator were added to a reactor equipped with a stirrer. 160 parts of ion-exchanged water was then added and the mixture was stirred at 35°C for 12 hours to completely absorb the polyfunctional monomer and polymerization initiator into the seed particles. The temperature inside the reactor was then maintained at 40°C, and an aqueous ascorbic acid solution (solids equivalent: 1.3 parts) as a reducing agent was added dropwise over 1 hour. The polymerization reaction (seed polymerization) was then carried out for another 2 hours to obtain an aqueous dispersion of organic particles. The obtained organic particle dispersion was cooled to 25°C, and an aqueous sodium hydroxide solution was added to adjust the pH to 8.0. The solid content was further adjusted with ion-exchanged water to obtain an organic particle dispersion (solid content: 20%) in which organic particles were dispersed in water. The volume average particle size and glass transition temperature of the obtained organic particles were measured. The results are shown in Table 1. In the measurement of the glass transition temperature, no peak was observed within the measurement temperature range (-100°C to 200°C), confirming that the glass transition temperature of the organic particles was above 200°C (the same applies to Examples 2 to 10 and Comparative Examples 1 to 3, 5, and 6). <Preparation of binder> 70 parts of ion-exchanged water, 0.20 parts of polyoxyethylene lauryl ether (manufactured by Kao Chemical Corporation, product name "Emulgen (registered trademark) 120") as an emulsifier, and 0.5 parts of ammonium persulfate were supplied to a reactor B equipped with a stirrer, the gas phase was replaced with nitrogen gas, and the temperature was raised to 60°C. Meanwhile, in a separate vessel, 50 parts of ion-exchanged water, 0.5 parts of polyoxyethylene lauryl ether (manufactured by Kao Chemical Corporation, product name "Emulgen (registered trademark) 120") as an emulsifier, 70 parts of 2-ethylhexyl acrylate as a monofunctional (meth)acrylic acid ester monomer, 25 parts of styrene as an aromatic monovinyl monomer, 1.7 parts of allyl glycidyl ether and 0.3 parts of allyl methacrylate as crosslinkable monomers, and 3 parts of acrylic acid as an acidic group-containing monomer were mixed to obtain a monomer composition. This monomer composition was continuously added to the reactor B over 4 hours to carry out polymerization. During the continuous addition, the reaction was carried out at 70° C. After the continuous addition was completed, the mixture was further stirred at 80° C. for 3 hours to terminate the reaction, thereby obtaining an aqueous dispersion of the binder. The obtained aqueous dispersion of the binder was cooled to 25°C, and then an aqueous sodium hydroxide solution was added to adjust the pH to 8.0, and the solid content was adjusted with ion-exchanged water to obtain an aqueous dispersion of the binder (solid content: 40%). The volume average particle diameter of the binder was measured in the same manner as for the organic particles and was found to be 180 nm. <Preparation of Functional Layer Composition> The organic particle dispersion obtained above, the binder aqueous dispersion obtained above, carboxymethylcellulose (Daicel Corporation, product name "Daicel 1220") as a thickener, and a wetting agent (San Nopco Co., Ltd., product name "SN Wet 980") were mixed in water to obtain a functional layer composition (solids concentration: 20%) at a solids mass ratio of organic particles:binder:thickener:wetting agent of 82:12:5:1 (approximately 13% of the total binder content of the organic particles and binder). The resulting functional layer composition was used to prepare a separator for evaluation, and the heat shrinkage resistance of the functional layer was evaluated. The results are shown in Table 1. <Preparation of separator with functional layers on both sides> A single-layer polyethylene separator (thickness: 9 μm) manufactured by a wet process was prepared as the separator substrate. The functional layer composition obtained above was applied to one side of this separator substrate, and the functional layer composition on the separator substrate was dried at 50°C for 10 minutes to form a functional layer (thickness: 1.0 μm). Furthermore, the functional layer composition obtained above was applied to the other side of the separator substrate, and the functional layer composition on the separator substrate was dried at 50°C for 10 minutes to form a functional layer (thickness: 1.0 μm), thereby producing a separator with functional layers on both sides. <Preparation of positive electrode> To 295 parts of LiCoO as the positive electrode active material, 3 parts (solids equivalent) of polyvinylidene fluoride (PVDF, manufactured by Kureha Chemical Industry Co., Ltd., product name "KF-1100") as a positive electrode binder was added, and 2 parts of acetylene black as a conductive material and 20 parts of N-methylpyrrolidone as a solvent were further added and mixed in a planetary mixer to obtain a positive electrode slurry composition. This positive electrode slurry composition was applied to one side of an 18 μm thick aluminum foil, dried at 120°C for 3 hours, and then rolled using a roll press to obtain a positive electrode (thickness: 100 μm) having a positive electrode composite layer. <Preparation of negative electrode> 98 parts graphite (particle size: 20 μm, specific surface area: 4.2 m) as the negative electrode active material 21.0 part of carboxymethyl cellulose was added to the mixture, and the mixture was mixed in a planetary mixer to obtain a slurry composition for the negative electrode. This slurry composition for the negative electrode was applied to one side of a copper foil with a thickness of 18 μm, dried at 120°C for 3 hours, and then rolled using a roll press to obtain a negative electrode (thickness: 100 μm) having a negative electrode composite layer. <Secondary battery manufacturing> The positive electrode obtained above was cut into a size of 49 cm x 5 cm and placed on a stand with the surface on the positive electrode composite layer facing up. The separator obtained above (with functional layers on both sides) was cut into a size of 120 cm x 5.5 cm and placed on top of the positive electrode composite layer of this positive electrode, with the positive electrode positioned on the left side of the separator in the longitudinal direction. Furthermore, the negative electrode obtained above was cut into a size of 50 cm x 5.2 cm and placed on top of this separator with the surface on the negative electrode composite layer in contact with the separator and the negative electrode positioned on the right side of the separator in the longitudinal direction, to obtain a laminate. This laminate was then wound using a winding machine around the center of the separator in the longitudinal direction to obtain a wound body. This wound body was wrapped in an aluminum packaging material that served as the battery exterior, and an electrolyte solution (solvent: ethylene carbonate / ethyl methyl carbonate / vinylene carbonate (volume ratio) = 30.0 / 70.0 / 1.5, electrolyte: 1M LiPF6) was poured into the battery so that no air remained. The aluminum packaging material was then heat-sealed at 150°C to produce a wound lithium-ion secondary battery. The initial coulombic efficiency and cycle characteristics of the resulting lithium-ion secondary battery were evaluated. The results are shown in Table 1.

[0094] Example 2 In preparing the organic particles, various operations and evaluations were carried out in the same manner as in Example 1, except that trimethylolpropane trimethacrylate was used instead of ethylene glycol dimethacrylate as the polyfunctional monomer. The results are shown in Table 1.

[0095] Example 3 In preparing the organic particles, the amount of n-butyl acrylate in the monomer composition for seed particles was changed to 84.6 parts, the amount of methacrylic acid to 7.7 parts, and the amount of acrylonitrile to 7.7 parts to prepare the seed particles, and further, in the seed polymerization, the amount of solids equivalent of the seed particles was changed to 13 parts (of which n-butyl acrylate units were 11 parts, methacrylic acid units were 1 part, and acrylonitrile units were 1 part) and the amount of ethylene glycol dimethacrylate was changed to 87 parts. Except for this, various operations and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0096] Example 4 In preparing the organic particles, the amount of n-butyl acrylate in the monomer composition for seed particles was changed to 83.4 parts, the amount of methacrylic acid to 8.3 parts, and the amount of acrylonitrile to 8.3 parts to prepare the seed particles, and further, in the seed polymerization, the solids equivalent amount of the seed particles was changed to 36 parts (of which n-butyl acrylate units were 30 parts, methacrylic acid units were 3 parts, and acrylonitrile units were 3 parts) and the amount of ethylene glycol dimethacrylate was changed to 64 parts. Except for this, various operations and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0097] (Examples 5 to 6) During the preparation of the organic particles, the amount of sodium dodecyl sulfate charged into reactor A equipped with a stirrer was changed from 1.0 part to 0.15 parts (Example 5) and 0.05 parts (Example 6), respectively, to adjust the volume average particle diameter of the seed particles to 160 nm (Example 5) and 400 nm (Example 6), respectively. Except for this, various operations and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0098] Example 7 During the preparation of the organic particles, the polymerization reaction (seed polymerization) in the step (2) of seed polymerization of the polyfunctional monomer was carried out under a temperature condition of 60°C. Except for this, various operations and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0099] Example 8 During the preparation of organic particles, in the step (2) of seed polymerization of polyfunctional monomer, the amount of polymerization initiator added was changed to 3.2 parts and the amount of reducing agent added was changed to 2.6 parts. Except for this, various operations and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0100] Example 9 During the preparation of organic particles, in the step (2) of seed polymerization of polyfunctional monomer, the amount of polymerization initiator added was changed to 1.2 parts and the amount of reducing agent added was changed to 1.0 part. Except for this, various operations and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0101] Example 10 During the preparation of organic particles, in the step (2) of seed polymerization of polyfunctional monomer, the type of reducing agent was changed to sodium ascorbate, and the amount of reducing agent added was changed to 1.5 parts. Except for these points, various operations and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0102] Example 11 In preparing the organic particles, various operations and evaluations were carried out in the same manner as in Example 1, except that in the (2) step of seed polymerization of a polyfunctional monomer, 1.6 parts of sodium ascorbate was added as a reducing agent and the polymerization initiator used was changed to α,α'-azobis(2-methylbutyronitrile). The results are shown in Table 1. In measuring the glass transition temperature of the organic particles, no peak was observed within the measurement temperature range (-100°C to 200°C), confirming that the glass transition temperature of the organic particles was above 200°C.

[0103] (Comparative Example 1) During the preparation of organic particles, various operations were carried out in the same manner as in Example 1 up to the step of absorbing the monomer in the step of (2) seed polymerization of the polyfunctional monomer. Thereafter, without adding a reducing agent, the temperature inside the reactor was maintained at 90°C, and a polymerization reaction (seed polymerization) was carried out for 5 hours to obtain an organic particle dispersion. The obtained organic particles were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0104] (Comparative Example 2) In preparing the organic particles, various operations and evaluations were carried out in the same manner as in Comparative Example 1, except that the amount of the polymerization initiator was changed to 4 parts in the step (2) of seed polymerization of the polyfunctional monomer. The results are shown in Table 1.

[0105] (Comparative Example 3) In preparing the organic particles, various operations and evaluations were carried out in the same manner as in Comparative Example 1, except that in the step (2) of seed polymerization of the polyfunctional monomer, the amount of the polymerization initiator was changed to 1 part. The results are shown in Table 1.

[0106] Comparative Example 4 In preparing the organic particles, the amount of n-butyl acrylate in the monomer composition for seed particles was changed to 95.2 parts, the amount of methacrylic acid to 1.0 parts, and the amount of acrylonitrile to 3.8 parts. Furthermore, in the seed polymerization, the solids equivalent amount of the seed particles was changed to 52 parts (of which n-butyl acrylate units were 49.5 parts, methacrylic acid units were 0.5 parts, and acrylonitrile units were 2 parts), and the amount of ethylene glycol dimethacrylate was changed to 48 parts. The procedures and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1. In measuring the glass transition temperature of the organic particles, no peak was observed within the measurement temperature range (-100°C to 200°C), confirming that the glass transition temperature of the organic particles was above 200°C.

[0107] (Comparative Example 5) During the preparation of the organic particles, the step (2) of seed polymerization of the polyfunctional monomer was carried out in the same manner as in Comparative Example 1, and steam was introduced into the obtained organic particle dispersion at a temperature of 90°C for 12 hours to remove unreacted monomers and decomposition products of the polymerization initiator, thereby obtaining an aqueous dispersion of organic particles. Except for these points, various operations and evaluations were carried out in the same manner as in Comparative Example 1. The results are shown in Table 1.

[0108] (Comparative Example 6) In preparing the organic particles, various operations and evaluations were carried out in the same manner as in Comparative Example 5, except that the steam introduction time in the step (2) of seed polymerization of the polyfunctional monomer was changed to 24 hours. The results are shown in Table 1.

[0109] In addition, in Table 1 shown below, "EDMA" refers to ethylene glycol dimethacrylate units; "TMPTMA" indicates trimethylolpropane-trimethacrylate units; "BA" indicates n-butyl acrylate units; "AN" indicates an acrylonitrile unit; "MAA" indicates a methacrylic acid unit, "AMA" indicates an allyl methacrylate unit; "AGE" represents an allyl glycidyl ether unit, "2EHA" indicates 2-ethylhexyl acrylate units, "ST" indicates a styrene unit; "AA" represents an acrylic acid unit; "AMBN" refers to α,α'-azobis(2-methylbutyronitrile).

[0110] [Table 1]

[0111] From Table 1, it can be seen that in Examples 1 to 11, when a functional layer was formed using a functional layer composition containing an organic particle dispersion liquid containing 50 mass% or more of polyfunctional monomer units, in which the content of polymerization initiator decomposition products was 50 ppm or less, and the total content of polymerization initiator decomposition products and unreacted polyfunctional monomers was 500 ppm or less, the resulting functional layer had excellent heat shrinkage resistance, and the resulting secondary battery was able to exhibit high initial coulombic efficiency. Table 1 also shows that in Comparative Examples 1 to 3 and 5 to 6, in which functional layers were formed using functional layer compositions containing organic particle dispersions in which both or at least one of (i) the content of polymerization initiator decomposition products and (ii) the total content of polymerization initiator decomposition products and unreacted polyfunctional monomers was outside the specified range, the resulting secondary batteries had poor initial coulombic efficiency. Furthermore, Table 1 also shows that in Comparative Example 4, in which a functional layer was formed using a functional layer composition containing an organic particle dispersion that did not contain organic particles containing 50% or more by mass of polyfunctional monomer units, a functional layer with excellent heat resistance could not be formed. [Industrial Applicability]

[0112] According to the present invention, it is possible to provide an organic particle dispersion for a secondary battery functional layer, which is capable of forming a functional layer that has excellent heat shrinkage resistance and can enable a secondary battery to exhibit excellent initial Coulombic efficiency, and a composition for a secondary battery functional layer containing the same. Furthermore, according to the present invention, it is possible to provide a battery member for a secondary battery that has excellent resistance to heat shrinkage and can enable the secondary battery to exhibit excellent initial coulomb efficiency. Furthermore, according to the present invention, a secondary battery excellent in stability and initial coulombic efficiency can be provided.

Claims

1. An organic particle dispersion for a secondary battery functional layer, comprising organic particles and a solvent, the organic particles contain a polyfunctional (meth)acrylic acid ester monomer as a polyfunctional monomer unit in a proportion of 64% by mass or more, and further contain a monofunctional (meth)acrylic acid ester monomer unit, an acidic group-containing monomer unit, and a nitrile group-containing monomer unit; the volume average particle diameter of the organic particles is 100 nm or more and 650 nm or less; the content of polymerization initiator decomposition products in the organic particle dispersion liquid for a secondary battery functional layer is 15 ppm or less, and the total content of the polymerization initiator decomposition products and unreacted polyfunctional monomers is 500 ppm or less; Organic particle dispersion liquid for secondary battery functional layer.

2. 2. The organic particle dispersion for a secondary battery functional layer according to claim 1, wherein the volume average particle diameter of the organic particles is 150 nm or more and 500 nm or less.

3. A composition for a secondary battery functional layer, comprising a binder and the organic particle dispersion liquid for a secondary battery functional layer according to claim 1 .

4. A battery member for a secondary battery, comprising a functional layer for a secondary battery formed using the composition for a secondary battery functional layer according to claim 3 .

5. A secondary battery comprising the battery member for a secondary battery according to claim 4 .

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