Flame retardant-containing particles, resin composition, fire-extinguishing sheet, and uses thereof

Abstract

The flame retardant-containing particles are particles (C) obtained by polymerizing two or more monomers (A) in a composition containing two or more monomers (A) having a polymerizable unsaturated double bond and a phosphorus-based flame retardant (B) dissolved in at least a portion of the two or more monomers (A), and the particles (C) include a resin layer (D) formed by polymerizing the two or more monomers (A). The elution rate of the resin layer (D) in the electrolyte solution is 40 mass% or less.

Description

Technical Field

[0001] This disclosure relates to particles containing flame retardants, resin compositions, fire-extinguishing sheets, and their applications. Background Technology

[0002] Lithium-ion batteries have long been recognized for their high energy density and high output characteristics. In particular, electric vehicle power supplies and large-capacity batteries utilize stacked lithium-ion batteries with a stacked structure obtained by directly or indirectly stacking multiple lithium-ion batteries through other layers.

[0003] In lithium-ion secondary batteries, due to their high energy density and high output characteristics, a large current flows through them when an internal short circuit occurs, resulting in rapid heating. In the worst case, lithium may even catch fire.

[0004] As a method for preventing fires, there is a method using fire extinguishing agent-containing particles obtained by encapsulating a fire extinguishing agent in a resin layer. For example, Japanese Patent No. 5374309 discloses fire extinguishing agent-containing particles obtained by encapsulating a fire extinguishing agent in a resin layer, characterized in that the aforementioned resin layer is formed of a resin containing 0.1 to 30% by weight of a component derived from a crosslinking monomer and 70 to 99.9% by weight of a component derived from a free radical polymerizable monomer, and the aforementioned fire extinguishing agent is a fire extinguishing agent having trifluoromethyl groups and a boiling point of 45 to 300°C.

[0005] Furthermore, Japanese Patent Application Publication No. 2021-118847 discloses fire extinguishing sheets that can be used in places, equipment, structures, etc., where fires may occur, and have initial fire extinguishing capabilities. The fire extinguishing sheets described in Japanese Patent Application Publication No. 2021-118847 contain a fire extinguishing agent that thermally decomposes upon reaching a specified temperature to produce fire extinguishing components. This fire extinguishing function is achieved by generating an aerosol through thermal decomposition.

[0006] Furthermore, Japanese Patent Application Publication No. 2020-130661 discloses a chemical extinguishing agent sheet capable of extinguishing fires based on automatic initial extinguishing at the point of ignition. The chemical extinguishing agent sheet disclosed in Japanese Patent Application Publication No. 2020-130661 is an extinguishing sheet that automatically sprays a fluorocarbon-based extinguishing agent upon detecting a fire. Summary of the Invention

[0007] The problem that the invention aims to solve Japanese Patent No. 5374309 discloses fire extinguishing agent-containing particles that use low-boiling-point fire extinguishing agents such as 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (boiling point 56°C), which suffers from the problem of easy evaporation of the fire extinguishing agent. Therefore, in Japanese Patent No. 5374309, pressure polymerization is desired to suppress the evaporation of the fire extinguishing agent during the manufacture of fire extinguishing agent-containing particles, but this results in a constraint on the polymerization method. Therefore, it is desirable to use fire extinguishing agents (e.g., flame retardants) whose polymerization methods are not constrained to produce fire extinguishing agent-containing particles. Furthermore, it is desirable to use a monomer composition that allows for the production of fire extinguishing agent-containing particles even when using such fire extinguishing agents.

[0008] Furthermore, there are cases where the resin layer covering at least a portion of the fire extinguishing agent (e.g., flame retardant) is used in contact with the electrolyte of a secondary battery or similar source. Therefore, it is desirable to form a resin layer that inhibits dissolution in the electrolyte.

[0009] Secondly, the fire extinguishing sheet material described in Japanese Patent Application Publication No. 2021-118847 contains a fire extinguishing agent that thermally decomposes upon reaching a specified temperature to produce fire extinguishing components. Specifically, it generates heat energy through the combustion of chlorate (component B) and potassium salt (component C), which act as strong oxidants, thereby producing an aerosol as the fire extinguishing component. However, the requirement for heat energy to generate the aerosol in Japanese Patent Application Publication No. 2021-118847 raises the possibility of promoting fires caused by thermal runaway from secondary batteries.

[0010] In the fire extinguishing sheet described in Japanese Patent Application Publication No. 2020-130661, fluorocarbon-based fire extinguishing agents are dispersed in droplet form within the fire extinguishing sheet formed of synthetic resin. However, the synthetic resin in Japanese Patent Application Publication No. 2020-130661 is plasticizable at around 80°C, raising concerns about the leaching of fluorocarbon-based fire extinguishing agents from the fire extinguishing sheet. Therefore, there are concerns about the leaching of fluorocarbon-based fire extinguishing agents from the fire extinguishing sheet within the operating temperature range of secondary batteries (e.g., 45°C to 80°C).

[0011] In view of the above, the object of the first aspect of this disclosure is to provide flame retardant-containing particles that form a resin layer containing a flame retardant using an unrestricted polymerization method and whose dissolution in an electrolyte is suppressed, and a resin composition that can form a resin layer in an electrolyte with suppressed dissolution.

[0012] In view of the above, the purpose of the second aspect of this disclosure is to provide fire-extinguishing sheets and the like that can suppress fires caused by thermal runaway of secondary batteries.

[0013] Methods for solving problems <1A> Flame retardant-containing particles, which are obtained by polymerizing the two or more monomers (A) in a composition comprising two or more monomers (A) having polymerizable unsaturated double bonds and a phosphorus-based flame retardant (B) dissolved in at least a portion of the two or more monomers (A). The aforementioned particle (C) comprises a resin layer (D) formed by polymerizing two or more of the aforementioned monomers (A), and the dissolution rate of the aforementioned resin layer (D) in the electrolyte is less than 40% by mass.

[0014] <2A> Particles containing a flame retardant as described in <1A>, wherein the aforementioned resin layer (D) covers at least a portion of the aforementioned phosphorus-based flame retardant (B).

[0015] <3A> A polymerizable resin composition comprising 70% by mass and less than 99% by mass of a monomer (1) capable of dissolving phosphorus-based flame retardant (B). The content of monomers (2) with acidic groups is 0% to 10% by mass. The content of monomer (3) other than monomer (1) and monomer (2) is 0% to 25% by mass. The proportion of methyl methacrylate contained in the aforementioned monomer (1) is less than 50% by mass relative to the total amount of monomer (1).

[0016] <4A> The resin composition as described in <3A> is used to form a resin layer (D) covering at least a portion of the aforementioned phosphorus-based flame retardant (B).

[0017] <5A> The resin composition as described in <3A> or <4A>, wherein the aforementioned monomer (1) is at least one selected from the group consisting of acrylonitrile, methyl methacrylate, butyl methacrylate and styrene.

[0018] <6A> The resin composition of any one of <3A> to <5A>, wherein the aforementioned monomer (2) is at least one selected from the group consisting of methacrylic acid and acrylic acid.

[0019] <7A> The resin composition as described in any one of <3A> to <6A>, wherein the aforementioned monomer (3) comprises a polymerizable unsaturated double bond.

[0020] <8A> Flame retardant-containing particles, which possess the following characteristics: The aforementioned phosphorus-based flame retardant (B); and The resin layer (D) is formed from any one of the resin compositions <3A> to <7A> and covers at least a portion of the aforementioned phosphorus-based flame retardant (B).

[0021] <9A> Flame-retardant coating material comprising particles containing a flame retardant as described in any one of <1A>, <2A> and <8A>.

[0022] <10A> laminate, comprising particles containing a flame retardant as described in any one of <1A>, <2A> and <8A>.

[0023] <11A> A method for manufacturing particles containing flame retardants, comprising: The step of preparing a mixture comprising the aforementioned phosphorus-based flame retardant (B) and any one of <3A> to <7A>; and The process of polymerizing the aforementioned monomer (A) in the aforementioned mixture to form a resin layer (D).

[0024] <12A> A method for manufacturing particles containing a flame retardant as described in <11A>, wherein the aforementioned resin layer (D) covers at least a portion of the aforementioned phosphorus-based flame retardant (B).

[0025] <13A> A method for manufacturing particles containing flame retardants as described in <11A> or <12A>, wherein a resin layer (D) is formed.

[0026] <1B> Fire extinguishing sheets, which possess the following characteristics: Substrate layer; and The self-extinguishing layer includes particles carrying an extinguishing agent, wherein the particles carrying the extinguishing agent include the extinguishing agent and a resin layer covering at least a portion of the extinguishing agent.

[0027] <2B> As described in <1B>, the fire-extinguishing sheet further comprises a water-soluble resin and a binder. The content of the aforementioned particles carrying the extinguishing agent is 50% to 80% by mass relative to the total amount of the aforementioned self-extinguishing layer.

[0028] <3B> The fire-extinguishing sheet as described in <1B> or <2B>, wherein the aforementioned self-extinguishing layer further comprises an inorganic filler.

[0029] <4B> The fire extinguishing sheet as described in any one of <1B> to <3B>, wherein the aforementioned fire extinguishing agent comprises a phosphorus-based flame retardant.

[0030] <5B> The fire-extinguishing sheet as described in <4B>, wherein the content of the aforementioned phosphorus-based flame retardant is 50% to 100% by mass relative to the total amount of the aforementioned fire extinguishing agent.

[0031] <6B> The fire-extinguishing sheet as described in any one of <1B> to <5B>, wherein the aforementioned substrate layer comprises at least one resin selected from the group consisting of aluminum, copper, polyolefin, polyester, polyphenylene sulfide, polyether ether ketone, polyamide imide and polytetrafluoroethylene, and a flame retardant.

[0032] <7B> Fire extinguishing sheet as described in any one of <1B> to <6B>, wherein the aforementioned substrate layer contains a flame retardant.

[0033] <8B> A secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the aforementioned positive electrode and the aforementioned negative electrode, a non-aqueous electrolyte, and any one of <1B> to <7B> a fire extinguishing sheet, wherein the aforementioned fire extinguishing sheet is disposed inside or outside the battery outer packaging material.

[0034] <9B> A method for manufacturing a fire-extinguishing sheet, comprising the step of imparting an aqueous composition containing particles carrying a fire extinguishing agent to a substrate layer, wherein the particles carrying the fire extinguishing agent contain a fire extinguishing agent and a resin layer covering at least a portion of the aforementioned fire extinguishing agent.

[0035] <10B> A method for releasing an extinguishing agent, comprising the steps of subjecting the particles carrying the aforementioned extinguishing agent contained in any one of <1B> to <7B> to undergo morphological changes between 110°C and 180°C, and the step of releasing the extinguishing agent from the aforementioned particles carrying the extinguishing agent.

[0036] Invention Effects According to the first aspect of this disclosure, flame retardant-containing particles that are formed using an unrestricted polymerization method and whose dissolution in an electrolyte is suppressed, and resin compositions that can form a shell in an electrolyte with suppressed dissolution, etc., can be provided.

[0037] According to the second aspect of this disclosure, fire-extinguishing sheets or the like can be provided to suppress fires caused by thermal runaway of secondary batteries. Detailed Implementation

[0038] In this publication, the numerical range indicated by "~" refers to the range including the values ​​before and after "~" as the lower and upper limits.

[0039] In the numerical ranges described in this disclosure, the upper or lower limit of one numerical range can be replaced by the upper or lower limit of other numerical ranges described in the same period. Furthermore, the upper or lower limit of a numerical range described in this disclosure can also be replaced by the values ​​shown in the embodiments.

[0040] In this disclosure, the term "process" refers not only to a standalone process, but also to any process that achieves its intended purpose, even if it cannot be clearly distinguished from other processes.

[0041] Each component in this disclosure may also include multiple substances belonging to the stated component. In the case of multiple substances belonging to each component in the composition, unless otherwise specified, the content or percentage of each component refers to the total content or percentage of the multiple substances present in the composition.

[0042] [Particles containing flame retardants] The flame retardant particles disclosed herein are obtained by polymerizing two or more monomers (A) in a composition comprising at least two monomers (A) having polymerizable unsaturated double bonds and a phosphorus-based flame retardant (B) dissolved in at least a portion of the two or more monomers (A). The particles (C) comprise a resin layer (D) formed by polymerizing the two or more monomers (A), and the resin layer (D) has a dissolution rate of 40% by mass or less in an electrolyte.

[0043] The flame retardant-containing particles of this disclosure are formed using a phosphorus-based flame retardant (B) that is a flame retardant with no boiling point or a high boiling point and whose polymerization method is unrestricted. The flame retardant-containing particles of this disclosure also include a resin layer (D) whose dissolution in the electrolyte is suppressed. By including a resin layer (D) with a dissolution rate of 40% by mass or less in the electrolyte, when the flame retardant-containing particles are used in secondary batteries, for example, as an outermost separator, outer packaging material, etc., adverse effects on battery characteristics can be reduced. Specifically, it can be inferred that this is because by suppressing the dissolution of the resin layer (B) in the electrolyte, the dissolution of the phosphorus-based flame retardant (B) is also suppressed, thus maintaining battery characteristics.

[0044] The flame retardant-containing particles disclosed herein are particles (C) obtained by polymerizing two or more monomers (A) in a composition comprising two or more monomers (A) and a phosphorus-based flame retardant (B).

[0045] (Single (A)) Monomer (A) is a monomer having an unsaturated double bond capable of polymerization. Monomer (A) preferably contains a monomer (1) capable of dissolving phosphorus-based flame retardant (B), and may contain monomers other than monomer (1), or may not contain monomers other than monomer (1). Examples of monomers other than monomer (1) include monomers (2) having acidic groups, monomers (3) other than monomer (1) and monomer (2).

[0046] As specific examples of monomers (1), (2), and (3), as described below, the preferred embodiments are also the same as those of the resin compositions described later in this disclosure.

[0047] The content of monomer (1) is preferably 70% by mass or more and less than 99% by mass relative to the total amount of monomer (A). From the viewpoint of being able to further suppress the dissolution rate in the electrolyte, it is preferably 75% by mass to 97% by mass, and more preferably 80% by mass to 95% by mass.

[0048] The content of monomer (2) is 0% to 5% by mass relative to the total amount of monomer (A), preferably 1% to 5% by mass, and more preferably 3% to 5% by mass.

[0049] The content of monomer (3) is 0% to 25% by mass relative to the total amount of monomer (A), preferably 0% to 20% by mass, and more preferably 0% to 10% by mass.

[0050] The monomer (A) contained in the composition used to make particles (C) may be 20% to 80% by mass, 30% to 70% by mass, or 40% to 60% by mass relative to the total amount of the composition.

[0051] (Phosphorus-based flame retardant (B)) Phosphorus-based flame retardants (B) contain phosphorus and are flame retardants that can dissolve in at least a portion of two or more monomers (A).

[0052] Examples of phosphorus-based flame retardants (B) include phosphate ester flame retardants and condensed phosphate ester flame retardants. Among these, condensed phosphate ester flame retardants are preferred.

[0053] Phosphorus-based flame retardants (B) can be used alone or in combination of two or more.

[0054] As a condensed phosphate ester-based flame retardant, commercially available products can be used, such as ADKSTAB FP-600, ADK STAB PFR, and ADK STAB FP-900L manufactured by ADEKA Corporation.

[0055] The content of phosphorus-based flame retardant (B) in the composition used to make particles (C) can be 20% to 80% by mass, 30% to 70% by mass, or 40% to 60% by mass relative to the total amount of the composition.

[0056] The composition used to produce particles (C) may also contain components other than monomers (A) and phosphorus-based flame retardants (B). Examples of such components include polymerization initiators. Examples of polymerization initiators include azo polymerization initiators and peroxide polymerization initiators.

[0057] Examples of azo polymerization initiators include 2,2'-azobis(4-methoxy-2,4-dimethylpentanonitrile), 2,2'-azobisisobutyronitrile, 2,2-azobis(2,4-dimethylpentanonitrile), dimethyl 2,2'-azobis(2-methylpropionate), and 2,2'-azobis(2-methylbutyronitrile).

[0058] Examples of peroxide-based polymerization initiators include benzoyl peroxide and dilauryl peroxide.

[0059] The particles (C) containing flame retardants as described in this disclosure are particles obtained by polymerizing two or more monomers (A) in the composition. As a method for polymerizing the two or more monomers (A), for example, heating the composition at 40°C to 70°C (55°C in one example) for 30 minutes to 5 hours (2 hours in one example) is an example. The pressure used to polymerize the two or more monomers (A) is not particularly limited and can be atmospheric pressure of about 0.05 MPa to 0.15 MPa.

[0060] In addition, two or more monomers (A) can be polymerized by suspension polymerization to obtain particles (C) containing flame retardants, which are the contents of this disclosure.

[0061] The average particle size of the particles (C) can be less than 10 μm, less than 5 μm, or 0.5 μm to 3 μm.

[0062] The average particle size of the particles (C) can be determined by measuring the particle size using a particle size measuring device (manufactured by MicrotracBEL Corp., MT3300EXII).

[0063] The particles (C) containing flame retardants as disclosed herein comprise a resin layer (D) formed by polymerizing two or more monomers (A). The resin layer (D) preferably covers at least a portion of the phosphorus-based flame retardant (B). The resin layer (D) can be in the form of comprising a core containing flame retardant and covering at least a portion of that core, or it can be in the form of comprising multiple cores containing flame retardants and covering at least a portion of those multiple cores. The cores can be entirely covered by the resin layer (D), or they can be partially covered by the resin layer (D) with the remainder exposed.

[0064] The dissolution rate of the resin layer (D) in the electrolyte is 40% by mass or less, preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, and particularly preferably 15% by mass or less.

[0065] There is no particular limitation on the lower limit of the dissolution rate of the resin layer (D) in the electrolyte as long as it is above 0% by mass.

[0066] The dissolution rate of resin layer (D) in the electrolyte refers to the dissolution rate of resin layer (D) with respect to an electrolyte obtained by mixing ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a mass ratio of 1:1:1. Specifically, prepare a resin layer (D) or a sample having the same resin composition as resin layer (D), impregnate 0.5 parts by mass of resin layer (D) or the sample with 10 parts by mass of electrolyte at room temperature, filter the electrolyte after impregnation, dry the filtrate at 150°C for 3 hours, weigh the resulting residue, and calculate the amount dissolved in the electrolyte. Furthermore, the dissolution rate can be calculated from the amount dissolved in the electrolyte using the following formula. The dissolution rate of resin layer (D) in the electrolyte is a value calculated based on the amount dissolved of the components constituting resin layer (D), and does not consider the amount dissolved by flame retardants. Therefore, for example, the dissolution rate of the resin layer (D) in the electrolyte can be determined from a sample having the same resin composition as the resin layer (D), or the dissolution rate of the resin layer (D) in the electrolyte can be determined by subtracting the dissolution rate of the flame retardant from the total dissolution rate.

[0067] [Mathematical Expression 1] The flame retardant particles disclosed herein may contain flame retardants other than phosphorus-based flame retardants (B), or may not contain flame retardants other than phosphorus-based flame retardants (B). For example, the content of other flame retardants may be 0% to 10% by mass or 0% to 5% by mass relative to the total amount of phosphorus-based flame retardants (B) and other flame retardants.

[0068] The flame-retardant particles disclosed herein are suitable for use in components that may become a cause of fire due to high temperatures. For example, the flame-retardant particles disclosed herein can also be used in household appliances, secondary batteries, automotive parts, etc.

[0069] The flame-retardant particles disclosed herein can also be used in the production of flame-retardant coating materials, laminates, etc., as described later.

[0070] The flame retardant particles in this disclosure may also be particles that release phosphorus-based flame retardants (B) to the outside when certain conditions are met.

[0071] For example, (1) when the particles containing the flame retardant of this disclosure, or a component containing the particles containing the flame retardant, are exposed to a specific temperature (e.g., above 60°C), the phosphorus-based flame retardant (B) can be released to the outside. (2) When the particles containing the flame retardant in this disclosure, or the component containing the particles containing the flame retardant, are impacted, the phosphorus-based flame retardant (B) may be released to the outside. (3) When the resin layer (D) contained in the flame retardant particles of this disclosure deteriorates due to chemical changes, the phosphorus-based flame retardant (B) can be released to the outside.

[0072] [Flame-retardant coating material] The flame-retardant coating material disclosed herein contains particles containing flame retardants.

[0073] Flame-retardant coating materials can be applied to the surface of substrates and components, and can also be used to impart fire resistance to household appliances, secondary batteries, automotive parts, etc.

[0074] Flame-retardant coating materials may also contain components other than the flame-retardant particles described in this disclosure. Examples of components other than flame-retardant particles include solvents, pigments, fillers, inorganic materials, and binder components.

[0075] Flame-retardant coating materials can also be, for example, fire-extinguishing sheets having a substrate layer and a self-extinguishing layer, the self-extinguishing layer containing particles containing flame retardants as described in this disclosure.

[0076] [Fire-extinguishing sheet] The fire-extinguishing sheet disclosed herein comprises a substrate layer and a self-extinguishing layer. The self-extinguishing layer includes particles carrying an extinguishing agent, the particles carrying the extinguishing agent comprising the extinguishing agent and a resin layer covering at least a portion of the extinguishing agent. By including the particles carrying the extinguishing agent and the resin layer covering at least a portion of the extinguishing agent, the self-extinguishing layer can suppress fires caused by thermal runaway, for example, reducing the maximum heating temperature of secondary battery cells adjacent to thermally runaway secondary battery cells and delaying the onset of heating.

[0077] Fire-extinguishing sheets can be placed inside or outside the battery packaging material, or in gaps between potentially heat-generating components such as secondary batteries. By placing fire-extinguishing sheets in gaps between potentially heat-generating components, the spread of fire to components adjacent to heat-generating components can be suppressed.

[0078] Fire-extinguishing sheets can be used on components that may become a cause of fire due to high temperatures. For example, fire-extinguishing sheets can also be used on household appliances, secondary batteries such as lithium-ion batteries, and automotive parts.

[0079] (Substrate layer) There are no particular limitations on the material of the substrate layer in flame-retardant coating materials or fire-extinguishing sheets. Examples include metal materials such as aluminum and copper, polyolefins, polyesters, polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyamide imide (PAI), polytetrafluoroethylene (PTFE) and other resins containing fluorine, acrylic resins, silicone resins, styrene resins, ethylene vinyl alcohol resins, polylactic acid resins, and vinyl chloride resins.

[0080] The substrate layer may contain only one material or two or more materials. The substrate layer may be a layer containing a metal material, a layer containing a resin material, or a layer containing both a metal material and a resin material.

[0081] Examples of polyolefins include homopolymers or copolymers of α-olefins such as ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, and 3-methyl-1-butene; copolymers of α-olefins with other copolymerizable monomers, such as styrene, acrylonitrile, vinyl chloride, vinyl acetate, acrylates, and methacrylates; blends, block copolymers, and graft copolymers of two or more of these polymers or with other thermoplastic resins. Polypropylene or polyethylene is preferred among these.

[0082] Examples of polyesters include polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate.

[0083] The substrate layer may also contain flame retardants. Examples of flame retardants that may be included in the substrate layer include halogenated flame retardants and inorganic flame retardants (alumina, magnesium hydroxide, antimony trioxide, etc.).

[0084] When the substrate layer contains a flame retardant, the substrate layer may be formed by a composition obtained by mixing the flame retardant with the aforementioned resin material constituting the substrate layer, or it may be a laminate in which a flame retardant layer containing a flame retardant is laminated on a layer of resin material.

[0085] The flame retardant contained in the substrate layer can be a single type or a combination of two or more types.

[0086] The thickness of the substrate layer is not particularly limited; for example, it can be 100μm~300μm, 150μm~250μm, or 150μm~200μm.

[0087] (Self-extinguishing fire layer) The fire-extinguishing sheet disclosed herein comprises a self-extinguishing layer containing particles containing flame retardants or particles carrying extinguishing agents. The particles containing flame retardants or particles carrying extinguishing agents may be used alone or in combination of two or more types.

[0088] There is no particular limitation on the thickness of the self-extinguishing layer. For example, it can be 100μm~300μm, 150μm~250μm, or 150μm~200μm.

[0089] The content of flame retardant particles or fire extinguishing agent-carrying particles relative to the total amount of self-extinguishing layer can be 30% to 85% by mass, 50% to 80% by mass, or 55% to 70% by mass.

[0090] <Particles carrying extinguishing agents> The self-extinguishing layer may also contain particles carrying an extinguishing agent, wherein the particles carrying the extinguishing agent contain the extinguishing agent and a resin layer covering at least a portion of the aforementioned extinguishing agent.

[0091] The particles carrying the extinguishing agent are particles in which at least a portion of the extinguishing agent is covered by a resin layer.

[0092] The extinguishing agent contained in the particles carrying the extinguishing agent can be used alone or in combination with two or more types of extinguishing agents.

[0093] There are no particular restrictions on the types of extinguishing agents contained in self-extinguishing fire-resistant layers.

[0094] Examples of fire extinguishing agents include, for example, guanidine phosphate, melamine polyphosphate, tetraphenylbisphenol A diphosphate (reaction products with 4,4'-isopropylidenediphenol and phenol) (e.g., ADK STAB FP-600), phosphate esters, resorcinol bis(diphenyl phosphate) (polymer with 1,3-benzenediol, phenyl ester) (e.g., ADK STAB PFR), and phosphate acid, mixed esters with [1,1'-biphenyl]-4,4'-diol and phenol (e.g., ADK STAB). Phosphorus-based flame retardants such as FP-900L; antimony trioxide; ethylenebis(pentabromobenzene), 2,3-dibromopropyl ether, triallyl isocyanate hexabromide, bis[3,5-dibromo-4-(2,3-dibromopropoxy)phenyl] sulfone, ethylenebis(pentabromobenzene) / antimony trioxide and other bromine-based flame retardants; potassium perfluorobutanesulfonate salts; inorganic flame retardants such as silicon carbide, spherical alumina, special carbon fibers, titanium borate, etc. The extinguishing agent preferably includes the aforementioned phosphorus-based flame retardants. Phosphorus-based flame retardants have no boiling point or a high boiling point; therefore, when polymerizing resin materials to produce particles carrying the extinguishing agent, no treatment to inhibit the volatilization of the extinguishing agent is required, and the polymerization method of the resin material is not restricted.

[0095] Phosphorus-based flame retardants can be used alone or in combination of two or more.

[0096] The content of phosphorus-based flame retardant relative to the total amount of the aforementioned fire extinguishing agent can be 50% to 100% by mass, 60% to 100% by mass, or 80% to 100% by mass.

[0097] The resin layer covering at least a portion of the extinguishing agent is preferably a layer formed by polymerizing two or more monomers (A'). The resin layer may be in the form of including a core containing the extinguishing agent and covering at least a portion of the core, or it may be in the form of including multiple cores containing the extinguishing agent and covering at least a portion of the multiple cores. The core may be entirely covered by the resin layer, or it may be partially covered by the resin layer with the remainder exposed.

[0098] The dissolution rate of the resin layer in the electrolyte is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, even more preferably 20% by mass or less, even more preferably 15% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 1% by mass or less.

[0099] There is no particular limitation on the lower limit of the dissolution rate of the resin layer in the electrolyte, as long as it is above 0% by mass.

[0100] The dissolution rate of the resin layer in the electrolyte can be calculated in the same way as the dissolution rate of the aforementioned resin layer (D) in the electrolyte.

[0101] The monomer (A') used to form the resin layer is a monomer having polymerizable unsaturated double bonds. The monomer (A') preferably contains a monomer (1') that can dissolve the fire extinguishing agent (preferably a phosphorus-based flame retardant), and may contain monomers other than monomer (1'), or may not contain monomers other than monomer (1'). Examples of monomers other than monomer (1') include monomers (2) having acidic groups, monomers (1'), and monomers (3) other than monomer (2) having polymerizable unsaturated double bonds.

[0102] (monomer (1')) The monomer (1') is preferably a monomeric component capable of dissolving the fire extinguishing agent (preferably a phosphorus-based flame retardant), and preferably also contains one or more (preferably one) polymerizable unsaturated double bonds. The monomer (1') may also be the same as the monomer (1) described later.

[0103] Monomer (1') can be used alone or in combination of two or more.

[0104] The monomer (1') is preferably at least one selected from the group consisting of acrylonitrile, methyl methacrylate, butyl methacrylate and styrene. The monomer (1') preferably includes at least one selected from the group consisting of acrylonitrile and methyl methacrylate.

[0105] The content of monomer (1') relative to the total amount of monomer (A') can be more than 60% by mass and less than 99% by mass, can be 65% to 97% by mass, or can be 70% to 95% by mass.

[0106] When the monomer (1') comprises at least one selected from the group consisting of acrylonitrile and methyl methacrylate, the total content of acrylonitrile and methyl methacrylate relative to the total amount of monomer (1') is preferably 50% to 100% by mass, more preferably 80% to 100% by mass, and even more preferably 90% to 100% by mass. This further suppresses the dissolution rate in the electrolyte and makes it easier to form particles carrying the extinguishing agent.

[0107] The monomer (1') preferably contains acrylonitrile. The content of acrylonitrile in the monomer (1') is preferably 50% to 100% by mass relative to the total amount of monomer (1'), more preferably 80% to 100% by mass, and even more preferably 90% to 100% by mass.

[0108] (Single(2)) The monomer (A') may contain a monomer (2) having an acidic group or may not contain a monomer (2) having an acidic group. That is, in the monomer (A'), the monomer (2) is an optional component.

[0109] Monomer (2) can be used alone or in combination of two or more.

[0110] Preferred examples of monomer (2) that may be contained in monomer (A') are the same as the preferred examples of monomer (2) that may be contained in monomer (A) mentioned above.

[0111] The content of monomer (2) is preferably 0% to 10% by mass relative to the total amount of monomer (A'), more preferably 1% to 5% by mass, and even more preferably 3% to 5% by mass.

[0112] (Monomer (3)) The monomer (A') may contain monomer (3) other than monomer (1') and monomer (2) that has a polymerizable unsaturated double bond, or it may not contain monomer (3). That is, in monomer (A'), monomer (3) is an optional component.

[0113] Monomer (3) can be used alone or in combination of two or more.

[0114] Preferred examples of monomer (3) that may be contained in monomer (A') are the same as the aforementioned preferred examples of monomer (3) that may be contained in monomer (A).

[0115] When the monomer (A') includes monomer (3), the content of monomer (3) is preferably 1.1% to 25% by mass relative to the total amount of monomer (A'), more preferably 1.5% to 20% by mass, and even more preferably 2% to 10% by mass.

[0116] The content of particles carrying extinguishing agent relative to the total amount of self-extinguishing layer can be 30% to 85% by mass, 50% to 80% by mass, or 55% to 70% by mass.

[0117] The content of extinguishing agent in the particles carrying the extinguishing agent can be 20% to 80% by mass, 30% to 70% by mass, or 40% to 60% by mass relative to the total amount of particles carrying the extinguishing agent.

[0118] The resin layer content of the particles carrying the extinguishing agent can be 20% to 80% by mass, 30% to 70% by mass, or 40% to 60% by mass relative to the total amount of particles carrying the extinguishing agent.

[0119] The average particle size of the extinguishing agent-carrying particles can be 0.1 μm or more, or 0.5 μm or more. When the average particle size of the extinguishing agent-carrying particles is 0.1 μm or more, there are more bonding points with the particulate binder. Under normal circumstances, the extinguishing agent-carrying particles are less likely to break, making it easier to deform the extinguishing sheet according to the shape of the component (e.g., a secondary battery) to which the extinguishing sheet is applied.

[0120] The average particle size of the extinguishing agent-carrying particles can be less than 6 μm or less than 5 μm. When the average particle size of the extinguishing agent-carrying particles is less than 6 μm, the number of bonding points with the particulate binder will not increase, and the extinguishing agent will be more easily released from the extinguishing agent-carrying particles in the event of abnormal heating.

[0121] The average particle size of the fire extinguishing agent-carrying particles can be determined by measuring the particle size using a particle size analyzer (MicrotracBEL Corp., MT3300EXII). Regarding the particles carrying the extinguishing agent, it is preferable to have a structure without resin layer deformation below 100°C. Resin layer deformation refers to the release of the extinguishing agent from the particles carrying the extinguishing agent to the outside of the extinguishing sheet due to chemical deterioration of the resin layer. By eliminating resin layer deformation below 100°C, the release of the extinguishing agent from the particles carrying the extinguishing agent to the outside of the extinguishing sheet is suppressed within the operating temperature range of the secondary battery (e.g., 45°C to 80°C).

[0122] [Methods for releasing fire extinguishing agents] The method for releasing the extinguishing agent disclosed herein includes a step (step 1) of causing the particles carrying the extinguishing agent contained in the fire-extinguishing sheet to undergo morphological changes between 110°C and 180°C, and a step (step 2) of releasing the extinguishing agent from the particles carrying the extinguishing agent. As a result, when abnormal heating or other phenomena occur, the extinguishing agent is released from the particles carrying the extinguishing agent, thus suppressing phenomena such as fires caused by secondary batteries. It should be noted that steps 1 and 2 can be performed simultaneously or partially repeated; for example, the extinguishing agent can be released from the particles carrying the extinguishing agent while the particles undergo morphological changes.

[0123] The method for manufacturing particles carrying extinguishing agent includes a step of preparing a mixture containing monomer (A') and extinguishing agent, and a step of polymerizing the monomer (A') in the aforementioned mixture to form a resin layer.

[0124] The method for manufacturing particles carrying extinguishing agents includes a step of preparing a mixture containing monomers (A') and extinguishing agents (preparation step). In this step, the extinguishing agent may also be dissolved in at least a portion of two or more monomers (A') (preferably monomer (1')).

[0125] The process includes the step of polymerizing the monomer (A') in the aforementioned mixture to form a resin layer (forming step). In the forming step, for example, the composition can be heated at 50°C to 90°C (75°C in one example) for 30 minutes to 5 hours (2 hours in one example) to polymerize the monomer (A'). Additionally, the mixture may also contain the aforementioned polymerization initiators such as azo-based polymerization initiators and peroxide-based polymerization initiators. The pressure during monomer (A') polymerization is not particularly limited and can be atmospheric pressure of approximately 0.05 MPa to 0.15 MPa.

[0126] In the formation process, the monomer (A') can also be polymerized through suspension polymerization. For example, the mixture can be stirred with an aqueous liquid containing a solvent such as water, dispersing the mixture in the aqueous liquid, and allowing the monomer (A') in the mixture to polymerize to form a resin layer. By performing suspension polymerization, it is easy to control the particle size of the particles carrying the extinguishing agent, and there is a tendency to form particles with small deviations in particle size, shape, etc.

[0127] (Water-soluble resin) From a processability point of view, it is preferable that the self-extinguishing layer also includes a water-soluble resin. Examples of water-soluble resins include resins containing hydroxyl groups. Examples of water-soluble resins include polyvinyl alcohol (PVA) and other polyvinyl alcohol-based resins, cellulose-based resins such as hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC), hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose, chitosans, deacetylated chitosans, starch, polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), and polyvinyl ether (PVE), etc., which contain ether bonds.

[0128] Water-soluble resins can be used alone or in combination of two or more.

[0129] When the self-extinguishing layer contains water-soluble resin, the content of water-soluble resin relative to the total amount of the self-extinguishing layer can be 0.5% to 10% by mass, 1% to 8% by mass, or 1% to 5% by mass.

[0130] (Adhesive) Regarding the self-extinguishing layer, from the viewpoint of bonding flame-retardant particles and extinguishing agent-carrying particles, it is preferable to also include an adhesive. Examples of adhesives include styrene-butadiene copolymers, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), acrylic resins, urethane resins, and water-soluble resins. The aforementioned water-soluble resins can also function as adhesives.

[0131] One type of adhesive can be used alone, or two or more types can be used in combination.

[0132] The binder can also be in particulate form. By making the flame-retardant-containing particles or extinguishing agent-carrying particles forming the self-extinguishing layer and the binder particulate, the self-extinguishing layer is formed by aggregates of particles. This reduces the adhesion area between adjacent particles within the self-extinguishing layer, making it easier to dissolve the adhesion between adjacent particles in the event of abnormal heating. Furthermore, in the event of abnormal heating, the resin layer covering at least a portion of the extinguishing agent in relation to the flame-retardant-containing particles or extinguishing agent-carrying particles readily melts, tending to release the extinguishing agent from the flame-retardant-containing particles or extinguishing agent-carrying particles dispersed in the self-extinguishing layer at an early stage, thereby suppressing ignition.

[0133] When the self-extinguishing layer contains an adhesive, the content of the adhesive relative to the total amount of the self-extinguishing layer can be 1% to 15% by mass, 2% to 12% by mass, or 4% to 10% by mass.

[0134] (Inorganic filler) Regarding the self-extinguishing layer, from the viewpoint of improving processability and the performance of the fire-extinguishing sheet, it is preferable to also include an inorganic filler. Examples of inorganic fillers include alumina, magnesium hydroxide, silicon dioxide, aluminum hydroxide, magnesium oxide, zirconium oxide, aluminum titanium nitride, boron nitride, and graphite.

[0135] Inorganic fillers can be used alone or in combination of two or more.

[0136] When the self-extinguishing layer contains inorganic filler, the content of inorganic filler relative to the total amount of the self-extinguishing layer can be 3% to 40% by mass, 5% to 35% by mass, or 15% to 30% by mass.

[0137] The content of extinguishing agent other than flame retardant particles in this disclosure can be 0% to 15% by mass, 0% to 10% by mass, or 0% to 5% by mass relative to the total amount of the self-extinguishing layer. By making the content of extinguishing agent other than flame retardant particles 15% by mass or less relative to the total amount of the self-extinguishing layer, it is possible to obtain a fire-extinguishing sheet that can reduce the maximum heating temperature of secondary battery cells adjacent to thermally runaway secondary battery cells and delay the heating start time.

[0138] [Manufacturing method of fire extinguishing sheet] The method for manufacturing a fire-extinguishing sheet disclosed herein includes a step of imparting an aqueous composition comprising particles containing a flame retardant or particles carrying a fire extinguishing agent to a substrate layer, wherein the particles containing the flame retardant or particles carrying a fire extinguishing agent comprise a fire extinguishing agent and a resin layer covering at least a portion of the aforementioned fire extinguishing agent.

[0139] In the manufacturing method disclosed herein, the aforementioned aqueous composition is prepared, and the prepared aqueous composition is applied to a substrate layer. The aqueous composition comprises the aforementioned flame-retardant-containing particles or fire-extinguishing agent-carrying particles and water, and may, as needed, comprise at least one of a water-soluble resin, a binder, and an inorganic filler, and may also comprise other components (surfactants, fire-extinguishing agents other than flame-retardant-containing particles or fire-extinguishing agent-carrying particles (e.g., fire-extinguishing agents not covered by the resin layer), other components insoluble in the electrolyte, etc.).

[0140] One method for preparing an aqueous composition is to stir and mix powder components (particles containing flame retardants or particles carrying fire extinguishing agents, water-soluble resins, binders, inorganic fillers, etc.), and then add water as a solvent to disperse the powder components in the water.

[0141] The content of flame retardant particles or fire extinguishing agent-carrying particles in the aqueous composition can be 30% to 85% by mass, 50% to 80% by mass, or 55% to 70% by mass relative to the total components after removing water from the aqueous composition.

[0142] When the aqueous composition contains a water-soluble resin, the content of the water-soluble resin may be 0.5% to 10% by mass, 1% to 8% by mass, or 1% to 5% by mass relative to the total components after removing water from the aqueous composition.

[0143] When the aqueous composition contains a binder, the binder content relative to the total components after removing water from the aqueous composition can be 1% to 15% by mass, 2% to 12% by mass, or 4% to 10% by mass.

[0144] When the aqueous composition contains an inorganic filler, the content of the inorganic filler relative to the total components after removing water from the aqueous composition can be 3% to 40% by mass, 5% to 35% by mass, or 15% to 30% by mass.

[0145] There are no particular limitations on the method for applying the aqueous composition to the substrate layer, and conventionally known coating methods can be used. Alternatively, the aqueous composition can be dried as needed after it has been applied to the substrate layer.

[0146] [Layered Body] The laminate of this disclosure includes the flame-retardant particles of this disclosure. The laminate of this disclosure includes two or more layers, and there is no particular limitation as long as it includes at least one layer containing the flame-retardant particles of this disclosure. For example, the aforementioned flame-retardant coating material can be applied to the surface of a substrate, component, etc., and then heated and dried as needed to form a layer containing the flame-retardant particles of this disclosure on the surface of the substrate, component, etc., thus creating a laminate.

[0147] The flame-retardant particles, flame-retardant coatings, fire-extinguishing sheets, and laminates disclosed herein can also be used to impart fire resistance to secondary batteries.

[0148] [Rechargeable Battery] The secondary battery may also include a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte. For example, a laminate containing flame-retardant particles as described in this disclosure may be used as the outermost separator of the secondary battery, or as the outer packaging material of the secondary battery. The laminate containing flame-retardant particles as described in this disclosure may also be configured such that at least a portion of it is in contact with the electrolyte within the secondary battery. Examples of secondary batteries include lithium-ion secondary batteries and magnesium-ion secondary batteries.

[0149] The secondary battery includes the fire-extinguishing sheet described in this disclosure, a positive electrode, a negative electrode, a separator disposed between the aforementioned positive electrode and the aforementioned negative electrode, and a non-aqueous electrolyte. The aforementioned fire-extinguishing sheet may also be disposed inside or outside the battery outer packaging material.

[0150] When the fire-extinguishing sheet is disposed inside the battery outer packaging material, it is preferable that the fire-extinguishing layer is located on the electrode side and the substrate layer is located on the opposite side to the electrode side.

[0151] Even when the self-extinguishing layer is located on the electrode side, there is a tendency for the charging and discharging characteristics of the secondary battery to be maintained.

[0152] Furthermore, the positive electrode, negative electrode, separator disposed between the aforementioned positive and negative electrodes, and non-aqueous electrolyte can also be contained within the battery outer packaging material while being surrounded by a fire-extinguishing sheet. Additionally, the positive electrode, negative electrode, and separator can also be formed by lamination or winding.

[0153] The positive electrode, negative electrode, and separator in a secondary battery can each use previously known components.

[0154] For example, the positive electrode is typically composed of a positive electrode active material and a positive electrode current collector, and may include conductive additives, binders, etc., as needed. There are no particular limitations on the positive electrode active material; generally known positive electrode active materials can be used, such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, spinel-type lithium composite oxides, lithium titanate, and other lithium-containing composite oxides.

[0155] For example, the negative electrode is typically composed of a negative electrode active material and a negative electrode current collector, and may include conductive additives, binders, etc., depending on the requirements. There are no particular limitations on the negative electrode active material; generally known negative electrode active materials can be used, such as carbon materials like graphite and hard carbon, Si and Si alloys, etc.

[0156] As an electrolyte, a non-aqueous electrolyte containing an electrolyte and a non-aqueous solvent is preferred.

[0157] Examples of Li electrolytes include LiPF6, LiBF4, LiN(SO2CF3)2, and LiN(SO2CF2CF3)2.

[0158] Examples of non-aqueous solvents include cyclic carbonates, fluorinated cyclic carbonates, chain carbonates, fluorinated chain carbonates, aliphatic carboxylic acid esters, fluorinated aliphatic carboxylic acid esters, γ-lactones, fluorinated γ-lactones, cyclic ethers, fluorinated cyclic ethers, chain ethers, fluorinated chain ethers, nitriles, amides, lactams, nitromethane, nitrobenzene, sulfolane, trimethyl phosphate, dimethyl sulfoxide, and dimethyl sulfoxide phosphoric acid. One non-aqueous solvent can be used alone or in combination of two or more.

[0159] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butene carbonate (BC).

[0160] Examples of fluorinated cyclic carbonates include, for example, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and trifluoropropylene carbonate.

[0161] Examples of chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and dipropyl carbonate (DPC).

[0162] Examples of fluorinated chain carbonates include, for example, 2,2,2-trifluoroethyl methyl carbonate.

[0163] Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylbutyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, ethyl isobutyrate, and ethyl trimethylbutyrate.

[0164] Examples of fluorinated aliphatic carboxylic acid esters include, for example, methyl difluoroacetate, methyl 3,3,3-trifluoropropionate, ethyl difluoroacetate, and 2,2,2-trifluoroethyl acetate.

[0165] Examples of γ-lactones include, for example, γ-butyrolactone and γ-valerolactone.

[0166] Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxacyclopentane, 4-methyl-1,3-dioxacyclopentane, 1,3-dioxacyclohexane, and 1,4-dioxacyclohexane.

[0167] Examples of chain ethers include, for example, 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane.

[0168] Examples of fluorinated chain ethers include HCF2CF2CH2OCF2CF2H, CF3CF2CH2OCF2CF2H, HCF2CF2CH2OCF2CFHCF3, CF3CF2CH2OCF2CFHCF3, and C6F. 13 OCH3, C6F 13 OC2H5, C8F 17 OCH3, C8F 17 OC2H5, CF3CFHCF2CH (CH3) OCF2CFHCF3, HCF2CF2OCH (C2H5) 2, HCF2CF2OC4H9, HCF2CF2OCH2CH (C2H5) 2, HCF2CF2OCH2CH (CH3) 2, etc.

[0169] Examples of nitrile compounds include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, and 3-methoxypropionitrile.

[0170] Examples of amides include, for instance, N,N-dimethylformamide.

[0171] Examples of lactams include N-methylpyrrolidone, N-methyloxazolidinone, and N,N'-dimethylimidazolinone.

[0172] The content of non-aqueous solvent relative to the total amount of non-aqueous electrolyte is preferably 60% to 99% by mass, more preferably 70% to 97% by mass, and even more preferably 90% to 97% by mass.

[0173] [Resin Composition] The resin composition disclosed herein is a polymerizable composition comprising 70% by mass and less than 99% by mass of a monomer (1) capable of dissolving a phosphorus-based flame retardant (B), a monomer (2) having an acidic group in a content of 0% to 10% by mass, a monomer (3) other than the aforementioned monomer (1) and monomer (2) in a content of 0% to 25% by mass, and wherein the proportion of methyl methacrylate contained in the aforementioned monomer (1) is 50% by mass or less relative to the total amount of monomer (1). The resin composition disclosed herein is a composition for forming a resin layer.

[0174] The resin composition of this disclosure may be a resin composition for forming a resin layer (D) covering at least a portion of the phosphorus-based flame retardant (B), or a resin composition for forming the aforementioned flame retardant-containing particles by combining with the phosphorus-based flame retardant (B).

[0175] The resin composition of this disclosure can also be used to form particles containing flame retardants. For example, the flame retardant particles of this disclosure may be particles comprising a phosphorus-based flame retardant (B) and a resin layer (D) formed from the resin composition of this disclosure, covering at least a portion of the aforementioned phosphorus-based flame retardant (B). Regarding the flame retardant particles of this disclosure, the dissolution rate of the resin layer (D) in the electrolyte may or may not be satisfied with 40% by mass or less.

[0176] (monomer(1)) The resin composition disclosed herein contains 70% by mass and less than 99% by mass of a monomer (1) capable of dissolving phosphorus-based flame retardant (B), wherein the proportion of methyl methacrylate contained in the monomer (1) is 50% by mass or less relative to the total amount of the monomer (1). The monomer (1) may be any monomeric component capable of dissolving phosphorus-based flame retardant (B), and preferably also contains one or more (preferably one) polymerizable unsaturated double bonds.

[0177] Monomer (1) can be used alone or in combination of two or more.

[0178] The monomer (1) is preferably at least one selected from the group consisting of acrylonitrile, methyl methacrylate, butyl methacrylate and styrene. The monomer (1) preferably includes at least one selected from the group consisting of acrylonitrile and methyl methacrylate.

[0179] From the viewpoint that a resin layer that is easily formed in the electrolyte can be suppressed by dissolution, the proportion of methyl methacrylate contained in monomer (1) is 50% by mass or less, preferably 20% by mass or less, and more preferably 10% by mass or less, relative to the total amount of monomer (1).

[0180] The content of monomer (1) is 70% by mass or more and less than 99% by mass relative to the total amount of the resin composition of this disclosure (or the total amount of monomer components contained in the resin composition). From the viewpoint that it can further suppress the dissolution rate in the electrolyte and easily form particles containing flame retardants, it is preferably 75% by mass to 97% by mass, and more preferably 80% by mass to 95% by mass.

[0181] When the monomer (1) comprises at least one selected from the group consisting of acrylonitrile and methyl methacrylate, the total content of acrylonitrile and methyl methacrylate relative to the total amount of monomer (1) is preferably 50% to 100% by mass, more preferably 80% to 100% by mass, and even more preferably 90% to 100% by mass. This further suppresses the dissolution rate in the electrolyte and reduces the tendency to easily form particles containing flame retardants.

[0182] The monomer (1) preferably contains acrylonitrile. The content of acrylonitrile in the monomer (1) is preferably 50% to 100% by mass relative to the total amount of monomer (1), more preferably 80% to 100% by mass, and even more preferably 90% to 100% by mass.

[0183] (Single(2)) The resin composition of this disclosure may contain a monomer (2) having an acidic group, or may not contain a monomer (2) having an acidic group. That is, in the resin composition of this disclosure, the monomer (2) is an optional component.

[0184] Monomer (2) can be used alone or in combination of two or more.

[0185] Examples of acidic groups include carboxylic acid groups, sulfonic acid groups, and phosphate groups.

[0186] The monomer (2) is preferably at least one selected from the group consisting of methacrylic acid and acrylic acid.

[0187] The content of monomer (2) is 0% to 10% by mass relative to the total amount of the resin composition of this disclosure (or the total amount of monomer components contained in the resin composition), preferably 1% to 8% by mass, more preferably 1% to 5% by mass, and even more preferably 3% to 5% by mass.

[0188] (Monomer (3)) The resin composition of this disclosure may contain monomer (3) other than monomer (1) and monomer (2), or may not contain monomer (3). That is, in the resin composition of this disclosure, monomer (3) is an optional component.

[0189] Monomer (3) can be used alone or in combination of two or more.

[0190] Monomer (3) is a monomer other than monomer (1) and monomer (2), preferably containing one or more polymerizable unsaturated double bonds, more preferably containing one polymerizable unsaturated double bond.

[0191] Regarding monomers (3), examples include (meth)acrylate compounds, vinyl compounds, etc., other than monomers (1) and (2).

[0192] As monomers containing one polymerizable unsaturated double bond (3), examples include methyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, isobornyl methacrylate, etc.

[0193] As monomers containing two or more polymerizable unsaturated double bonds (3), examples include divinylbenzene, divinylnaphthalene, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polybutylene glycol di(meth)acrylate, tricyclodecyl di(meth)acrylate, trimethylolpropane (meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, methylenebis(meth)acrylamide, etc.

[0194] The content of monomer (3) is 0% to 25% by mass relative to the total amount of the resin composition of this disclosure (or the total amount of monomer components contained in the resin composition), preferably 0% to 20% by mass, and more preferably 0% to 10% by mass.

[0195] [Method for manufacturing particles containing flame retardants] The method for manufacturing flame retardant-containing particles disclosed herein includes a step of preparing a mixture comprising the aforementioned resin composition of this disclosure and a phosphorus-based flame retardant (B), and a step of polymerizing polymerizable monomers in the aforementioned mixture to form a resin layer (D). The preferred conditions for the manufactured flame retardant-containing particles are the same as those for the flame retardant-containing particles disclosed herein. For example, regarding the manufactured flame retardant-containing particles, the dissolution rate of the aforementioned resin layer (D) in the electrolyte may or may not be satisfied with 40% by mass or less.

[0196] The manufacturing method of this disclosure includes a step (preparation step) of preparing a mixture comprising the aforementioned resin composition of this disclosure and a phosphorus-based flame retardant (B). In the preparation step, a mixture obtained by mixing the aforementioned resin composition of this disclosure with the phosphorus-based flame retardant (B) is prepared. In this step, the phosphorus-based flame retardant (B) may also be dissolved in at least a portion of two or more monomers (A) contained in the aforementioned resin composition of this disclosure (preferably monomer (1)).

[0197] The manufacturing method disclosed herein includes a step (forming step) of polymerizing polymerizable monomers in the aforementioned mixture to form a resin layer (D). In the forming step, for example, the composition may be heated at 40°C to 70°C (55°C in one example) for 30 minutes to 5 hours (2 hours in one example) to polymerize two or more monomers (A). Furthermore, the mixture may also contain the aforementioned polymerization initiators such as azo-based polymerization initiators and peroxide-based polymerization initiators. The pressure used to polymerize two or more monomers (A) is not particularly limited and may be atmospheric pressure of approximately 0.05 MPa to 0.15 MPa.

[0198] In the formation process, two or more monomers (A) can be polymerized by suspension polymerization. For example, a mixture and an aqueous liquid containing a solvent such as water can be stirred, the mixture can be dispersed in the aqueous liquid, and two or more monomers (A) in the mixture can be polymerized to form a resin layer (D). By performing suspension polymerization, it is easy to control the particle size of the particles containing flame retardants, and there is a tendency to form particles with small deviations in particle size, shape, etc.

[0199] The flame retardant-containing particles obtained by the manufacturing method of this disclosure comprise a resin layer (D) formed by polymerizing two or more monomers (A). The resin layer (D) preferably covers at least a portion of the phosphorus-based flame retardant (B). The resin layer (D) can be in the form of including a core formed of a flame retardant and covering at least a portion of that core, or it can be in the form of including multiple cores formed of flame retardants and covering at least a portion of those multiple cores. The core can be entirely covered by the resin layer (D), or it can be partially covered by the resin layer (D) with the remainder exposed.

[0200] Example The present disclosure is further described in detail below with reference to embodiments, but the invention of the present disclosure is not limited to these embodiments. In the following embodiments, parts refer to parts by mass.

[0201] <Preparation of Electrolyte> Ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, each in 100 parts, were added to a flask and stirred with a magnetic stirrer to prepare a homogeneous electrolyte.

[0202] <Methods for calculating dissolution rate> Prepare an emulsion solution containing only the resin layer. After drying at room temperature for 24 hours, 0.5 parts of the dried sample (at 100°C for 2 minutes) are immersed in 10 parts of electrolyte at room temperature for 16 hours. After immersion, filter the electrolyte and dry the filtrate at 150°C for 3 hours. Weigh the resulting residue to calculate the amount dissolved in the electrolyte. Calculate the dissolution rate from the amount dissolved in the electrolyte using the following formula.

[0203] [Mathematical Expression 2] <Example 1> Prepare an oil-phase mixture and an aqueous solution with the following compositions. It should be noted that V-65 refers to 2,2'-azobis(2,4-dimethylpentanonitrile).

[0204] The resulting oil-phase mixture and aqueous solution were vigorously stirred to obtain an emulsion. The emulsion was then added to the total volume while being washed with 393.5 parts by volume of distilled water in a separable flask equipped with a stirrer and reflux condenser. After purging with nitrogen, the mixture was heated to 55°C and stirred for 2 hours to complete polymerization. A dispersion containing flame retardant particles with a solid content of 30.0% by mass was obtained. The average particle size of the obtained dispersion was 1.0 μm.

[0205] (Oil phase mixture) Acrylonitrile 88.6 parts 6.4 parts of n-butyl acrylate 5.0 parts methacrylic acid 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies (Aqueous solution) POVAL PVA-210 10.0 copies 90.0 parts distilled water <Example 2> Except for changing the composition of the oil phase mixture to the following, the procedure was the same as in Example 1 to obtain an emulsion solution with a solid content of 30.0% by mass. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 89.5 parts 5.5 parts of 2-ethylhexyl acrylate 5.0 parts methacrylic acid 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies <Example 3> Except for changing the composition of the oil phase mixture to the following, the procedure was the same as in Example 1 to obtain an emulsion solution with a solid content of 30.0% by mass. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) 92.0 parts acrylonitrile 3.0 parts of 2-hydroxyethyl methacrylate 5.0 parts methacrylic acid 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies <Example 4> Except for changing the composition of the oil phase mixture to the following, the procedure was the same as in Example 1 to obtain an emulsion solution with a solid content of 30.0% by mass. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 95.0 parts 5.0 parts methacrylic acid 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies <Example 5> Except for changing the composition of the oil phase mixture to the following, the procedure was the same as in Example 1 to obtain an emulsion solution with a solid content of 30.0% by mass. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 95.0 parts 5.0 parts acrylic acid 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies <Example 6> Except for changing the oil phase mixture to the following composition, the procedure was the same as in Example 1 to obtain an emulsion solution with a solid content of 30.0% by mass. The average particle size of the resulting dispersion was 1.0 μm.

[0206] (Oil phase mixture) Acrylonitrile 70.0 parts 25.0 parts of n-butyl acrylate 5.0 parts methacrylic acid 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies <Example 7> Except for changing the composition of the oil phase mixture to the following, the procedure was the same as in Example 1 to obtain an emulsion solution with a solid content of 30.0% by mass. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 64.9 parts 5.9 parts of methyl methacrylate 14.2 parts of n-butyl acrylate 10.0 parts of isobornyl methacrylate 5.0 parts methacrylic acid 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies <Example 8> Except for changing the composition of the oil phase mixture to the following, the procedure was the same as in Example 1 to obtain an emulsion solution with a solid content of 30.0% by mass. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) 95.0 parts of n-butyl methacrylate 5.0 parts methacrylic acid 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies <Comparative Example 1> Except for changing the composition of the oil phase mixture to the following, the procedure was the same as in Example 1 to obtain an emulsion solution with a solid content of 30.0% by mass. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 33.2 parts 37.8 parts of methyl methacrylate 14.0 parts of n-butyl acrylate 10.0 parts of isobornyl methacrylate 5.0 parts methacrylic acid 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies <Comparative Example 2> Except for changing the composition of the oil phase mixture to the following, the procedure was the same as in Example 1 to obtain an emulsion solution with a solid content of 30.0% by mass. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 40.3 parts 18.6 parts of methyl methacrylate 16.1 parts of n-butyl acrylate 20.0 parts of isobornyl methacrylate 5.0 parts methacrylic acid 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies <Comparative Example 3> Except for changing the composition of the oil phase mixture to the following, the procedure was the same as in Example 1 to obtain an emulsion solution with a solid content of 30.0% by mass. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 65.0 parts 30.0 parts of n-butyl acrylate 5.0 parts methacrylic acid 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies <Comparative Example 4> Polymerization was carried out in the same manner as in Example 1, except that the oil phase mixture was changed to the following composition, but an emulsion solution was not obtained and coagulation occurred.

[0207] (Oil phase mixture) 99.0 parts acrylonitrile 1.0 part methacrylic acid 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies <Comparative Example 5> Except for changing the composition of the oil phase mixture to the following, the procedure was the same as in Example 1 to obtain an emulsion solution with a solid content of 30.0% by mass. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) 100.0 parts of methyl acrylate 10.0 parts of heptane V-65 1.5 copies ADK STAB FP-900L (manufactured by ADEKA Co., Ltd.) 100.0 copies <Confirmation of particles containing flame retardants> Regarding the dispersions of flame retardant-containing particles obtained in Examples 1-8, visual inspection confirmed that no separation or precipitation of flame retardant-containing particles occurred after monomer polymerization. This confirms that the flame retardant is encapsulated within the flame retardant-containing particles. It should be noted that without flame retardant encapsulation within the particles, phenomena such as "aggregation during polymerization," "flame retardant separation or settling to the bottom of the flask," and "viscous liquid adhering to the surface of a glass plate after the dispersion is dropped onto the glass plate and washed with water" may occur.

[0208] The compositions of the oil phase mixtures of Examples 1-8 and Comparative Examples 1-5 are summarized in Table 1.

[0209] [Table 1] The abbreviations in Table 1 are as follows.

[0210] AN: Acrylonitrile MMA: Methyl methacrylate BMA: n-Butyl methacrylate BA: n-Butyl acrylate 2EHA: 2-Ethylhexyl acrylate HEMA: 2-Hydroxyethyl methacrylate IBX: Isoborneol Methacrylate MA: Methyl acrylate Mac: Methacrylic Acid Aac: Acrylic acid V-65: 2,2'-Azobis(2,4-dimethylpentanonitrile) FP-900L: ADK STAB FP-900L made by ADEKA Co., Ltd. PVA-210: POVAL PVA-210 made by KURARAY CO., LTD. <Example 9> 65% by mass (based on solid content) of the flame retardant-containing particles obtained in Example 1, 2% by mass of carboxymethyl cellulose (Daiichi Kogyo Pharmaceutical Co., Ltd.: CELOGEN 6) as a water-soluble resin, were stirred using a planetary mixer. Then, 30% by mass of alumina (Al2O3) as an inorganic filler was added, and the powder was further stirred. Next, water as a solvent was added at a dried mass ratio of 45% by mass, and the mixture was uniformly dispersed using a planetary mixer. Finally, styrene-butadiene rubber (Zeon Corporation: 2001) was added at a dried mass ratio of 4% by mass to prepare a self-extinguishing coating liquid.

[0211] <Production of Fire Extinguishing Sheets> The self-extinguishing coating liquid was applied to a substrate to a thickness of 150 μm or more after drying using a bar coater. The coating was then dried at 60°C for 30 minutes to form a self-extinguishing layer on the substrate, thus producing a fire-extinguishing sheet. In Example 1, a PPS (polyphenylene sulfide) substrate was used.

[0212] <Making the Negative Electrode> A slurry for the negative electrode is prepared by mixing 95 parts by mass of graphite as the negative electrode active material, 1 part by mass of SBR (styrene-butadiene rubber) as the binder, 1 part by mass of carboxymethyl cellulose (CMC) as the thickener, and 100 parts by mass of water as the solvent.

[0213] Next, a 10 μm thick copper foil (porous foil) was used as the negative electrode current collector, with the mass of the dried graphite being 4 mg / cm³. 2 The negative electrode is produced by coating the negative current collector with a slurry and then drying it.

[0214] <The Making of Positive Electrode> A slurry for the positive electrode is prepared by mixing 90 parts by mass of activated carbon powder (as the positive electrode active material), 6 parts by mass of polyacrylic acid (sodium neutral salt of polyacrylic acid) (as a binder), 15 parts by mass of acetylene black (as a conductive additive), and 345 parts by mass of water (as a solvent).

[0215] Next, using a 15μm thick aluminum foil (porous foil) as the positive electrode current collector, the positive electrode slurry was prepared with a mass of 4 mg / cm³ of dried activated carbon. 2 The positive electrode is coated onto the positive current collector and then dried to produce the positive electrode.

[0216] <Making a Secondary Battery> The positive and negative electrodes, as described above, are each punched into a rectangle measuring 60mm × 40mm, leaving a 40mm × 40mm slurry coating. The slurry coating in a 20mm × 40mm area on one end of the long side is peeled off, and electrode terminals are then installed.

[0217] Except for the end of the battery element with the electrode terminals installed and the other ends opposite to that end, the entire battery element is wrapped with the fire-extinguishing sheet to fix the positive electrode, the separator, and the negative electrode.

[0218] <Examples 10 and 11> The types and amounts of each component used in the "Preparation of Self-Extinguishing Layer Coating Liquid" in Example 9 are changed as shown in Table 2. The composition and thickness of the substrate and the thickness of the coating after drying in the "Preparation of Fire-Extinguishing Sheet" are changed as shown in Table 2. Otherwise, the same procedure as in Example 9 is followed to prepare the fire-extinguishing sheet and the secondary battery.

[0219] PET refers to polyethylene terephthalate (PET) as a base material.

[0220] <Comparative Example 6> In Example 9, "Preparation of Self-Extinguishing Layer Coating Liquid", fire extinguishing agent (MPP, melamine polyphosphate) was used instead of particles containing flame retardant, and the amounts of each component used were changed as shown in Table 2. Otherwise, the same procedure as in Example 9 was followed to produce fire-extinguishing sheets and secondary batteries.

[0221] In addition, in Comparative Example 6, DISPERSANT 5468 (SANNOPCO, ammonium polycarboxylate) was used as a surfactant in the preparation of the self-extinguishing coating liquid.

[0222] PP / L-190 refers to a polypropylene substrate containing a mixture of halogenated flame retardants and antimony trioxide in a proportion of 10% to 30% by mass relative to the total substrate.

[0223] <Comparative Examples 7 and 8> The secondary battery was manufactured in the same manner as in Example 9, except that fire-extinguishing sheets were not used and 10% or 20% by mass of ADKSTAB FP-900L, which is a viscous liquid, was added to the electrolyte.

[0224] <Charge and Discharge Test> Charge-discharge tests were conducted on the secondary batteries prepared in each embodiment and Comparative Example 1 under the following conditions.

[0225] First, place the secondary battery in a constant temperature bath set to 25°C and charge it to 4.2V using CC-CV (constant current-constant voltage) at 0.2C. Then, measure the discharge capacity when discharging to 3.0V at 0.2C and set it as the initial capacity [Ah / g].

[0226] Next, the current and voltage during short-term discharge at 100%, 90%, and 50% charge levels were measured. Based on this data, the horizontal axis was set as the current value / A and the vertical axis as the voltage / V. The DC resistance / Ω, which represents the slope at this point, was calculated and used as the internal resistance of the secondary battery.

[0227] In addition, a speed characteristic of 3.00Ω or less is considered good (evaluation A), and a speed characteristic of more than 3.00Ω is considered poor (evaluation B).

[0228] <Chain Explosion Test> After adjusting the 1Ah secondary battery prepared in each embodiment and Comparative Example 1 to 100% SOC, three secondary batteries were stacked and secured 10mm from both ends with Kapton tape. The assembled secondary battery was then clamped into the centrally located... A bakelite plate with a 5mm hole was used in a fixture. Using a 3mm rivet with a triangular pyramidal tip, the outermost secondary cell was thermally runaway at a needle penetration rate of 1mm / min. The onset delay time and maximum temperature of the adjacent secondary cells were measured. The results are shown in Table 2.

[0229] [Table 2] As shown in Table 2, in each embodiment, the results of the charge-discharge test were equal to or better than those of Comparative Example 1, and the internal resistance was suppressed. It can be inferred that this is because by suppressing the dissolution of the resin layer in the electrolyte, the dissolution of the flame retardant is also suppressed, thus maintaining the battery characteristics.

[0230] The full disclosures of Japanese Patent Application No. 2023-132173, filed on August 14, 2023, and Japanese Patent Application No. 2023-161502, filed on September 25, 2023, are incorporated herein by reference.

[0231] All documents, patent applications and technical standards described in this specification are incorporated herein by reference to the same extent as the specific and separately described herein.

Claims

1. A particle containing a flame retardant, which is a particle (C) obtained by polymerizing the two or more monomers (A) in a composition comprising two or more monomers (A) having polymerizable unsaturated double bonds and a phosphorus-based flame retardant (B) dissolved in at least a portion of the two or more monomers (A). The particle (C) comprises a resin layer (D) formed by polymerizing two or more monomers (A), and the resin layer (D) has a dissolution rate of less than 40% by mass in the electrolyte.

2. The flame retardant-containing particles as described in claim 1, wherein, The resin layer (D) covers at least a portion of the phosphorus-based flame retardant (B).

3. A polymerizable resin composition comprising 70% by mass and less than 99% by mass of a monomer (1) capable of dissolving a phosphorus-based flame retardant (B). The content of monomers (2) with acidic groups is 0% to 10% by mass. The content of monomer (3) other than monomer (1) and monomer (2) is 0% to 25% by mass. The proportion of methyl methacrylate contained in the monomer (1) is less than 50% by mass relative to the total amount of monomer (1).

4. The resin composition of claim 3, wherein it is used to form a resin layer (D) covering at least a portion of the phosphorus-based flame retardant (B).

5. The resin composition according to claim 3 or claim 4, wherein, The monomer (1) is selected from at least one of the group consisting of acrylonitrile, methyl methacrylate, butyl methacrylate and styrene.

6. The resin composition according to any one of claims 3 to 5, wherein, The monomer (2) is selected from at least one of the groups consisting of methacrylic acid and acrylic acid.

7. The resin composition according to any one of claims 3 to 6, wherein, The monomer (3) contains one polymerizable unsaturated double bond.

8. Particles containing flame retardants, which possess the following characteristics: The phosphorus-based flame retardant (B); and A resin layer (D) is formed from the resin composition of any one of claims 3 to 7 and covers at least a portion of the phosphorus-based flame retardant (B).

9. A flame-retardant coating material comprising particles containing a flame retardant as described in any one of claims 1, 2 and 8.

10. A laminate comprising particles containing a flame retardant as described in any one of claims 1, 2 and 8.

11. A method for manufacturing particles containing flame retardants, comprising: A step of preparing a mixture comprising the resin composition according to any one of claims 3 to 7 and the phosphorus-based flame retardant (B); and The process of polymerizing the monomer (A) in the mixture to form a resin layer (D).

12. The method for manufacturing particles containing a flame retardant as described in claim 11, wherein, The resin layer (D) covers at least a portion of the phosphorus-based flame retardant (B).

13. The method for manufacturing particles containing a flame retardant as described in claim 11 or claim 12, wherein, In the process of forming the resin layer (D), the monomer (A) is suspended and polymerized to form the resin layer (D).

14. Fire extinguishing sheets, which possess the following characteristics: Substrate layer; and The self-extinguishing layer comprises particles carrying an extinguishing agent, the particles carrying the extinguishing agent comprising the extinguishing agent and a resin layer covering at least a portion of the extinguishing agent.

15. The fire-extinguishing sheet as described in claim 14, wherein, The self-extinguishing layer also includes water-soluble resin and binder. The content of the particles carrying the extinguishing agent is 50% to 80% by mass relative to the total amount of the self-extinguishing layer.

16. The fire-extinguishing sheet as described in claim 14 or claim 15, wherein, The self-extinguishing layer also contains an inorganic filler.

17. The fire-extinguishing sheet according to any one of claims 14 to 16, wherein, The extinguishing agent contains phosphorus-based flame retardants.

18. The fire-extinguishing sheet according to any one of claims 14 to 17, wherein, The content of the phosphorus-based flame retardant is 50% to 100% by mass relative to the total amount of the extinguishing agent.

19. The fire-extinguishing sheet according to any one of claims 14 to 18, wherein, The substrate layer comprises at least one material selected from the group consisting of aluminum, copper, polyolefin, polyester, polyphenylene sulfide, polyether ether ketone, polyamide imide, and polytetrafluoroethylene.

20. The fire-extinguishing sheet according to any one of claims 14 to 19, wherein, The substrate layer contains a flame retardant.

21. A secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, a non-aqueous electrolyte, and a fire-extinguishing sheet according to any one of claims 14 to 20, wherein, The fire-extinguishing sheet is disposed inside or outside the battery outer packaging material.

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