Flame retardant-containing particle, resin composition, fire-extinguishing sheet, and application thereof

Abstract

A flame retardant-containing particle (C) is obtained by polymerizing a monomer (A) in a composition containing: the monomer (A), which contains two or more monomers (A-1) having polymerizable unsaturated double bonds, and a monomer (A-2) having two or more polymerizable unsaturated double bonds; and a phosphorus-based flame retardant (B) dissolved in at least a part of the two or more monomers (A-1). The particle (C) includes a resin layer (D) formed by polymerizing the monomer (A), and the elution rate of the resin layer (D) into an electrolyte is 40 mass% or less.

Description

Flame retardant-containing particles, resin composition, fire extinguishing sheet, and their applications

[0001] The present disclosure relates to flame retardant-containing particles, a resin composition, a fire-extinguishing sheet, and applications thereof.

[0002] Lithium-ion secondary batteries have attracted attention due to their high energy density and high power output. In particular, lithium-ion secondary battery stacks having a stack structure in which multiple lithium-ion secondary batteries are stacked directly or via other layers have been adopted as power sources for electric vehicles, large-scale storage batteries, etc.

[0003] Because lithium-ion secondary batteries have high energy density and high output characteristics, when an internal short circuit occurs, a large current flows, causing rapid heat generation, and in the worst case scenario, the lithium may ignite.

[0004] One method for preventing fire ignition is to use fire-extinguishing agent-containing particles in which a fire-extinguishing agent is encapsulated in a resin layer. For example, Japanese Patent No. 5374309 proposes fire-extinguishing agent-containing particles in which a fire-extinguishing agent is encapsulated in a resin layer, the resin layer being made of a resin containing 0.1 to 30 wt % of a component derived from a crosslinkable monomer and 70 to 99.9 wt % of a component derived from a radical polymerizable monomer, and the fire-extinguishing agent has a trifluoromethyl group and a boiling point of 45 to 300°C.

[0005] Furthermore, JP 2021-118847 A proposes a fire extinguishing sheet that can be used in places, facilities, structures, etc. where a fire may occur and has an initial fire extinguishing function. The fire extinguishing sheet described in JP 2021-118847 A contains a fire extinguishing agent that thermally decomposes to generate a fire extinguishing component when it reaches a predetermined temperature, and the fire extinguishing function is exerted by generating an aerosol through thermal decomposition.

[0006] In addition, Japanese Patent Application Laid-Open No. 2020-130661 proposes a chemical fire extinguishing agent sheet that can extinguish a fire by automatic initial extinguishing at the point of ignition. The chemical fire extinguishing agent sheet of Japanese Patent Application Laid-Open No. 2020-130661 is a fire extinguishing sheet that detects a fire and automatically sprays a fluorocarbon-based fire extinguishing agent.

[0007] The fire-extinguishing agent-containing particles of Japanese Patent No. 5,374,309 use a fire-extinguishing agent with a low boiling point, such as 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (boiling point 56°C), which poses the problem of the fire-extinguishing agent easily evaporating. Therefore, in Japanese Patent No. 5,374,309, it is desirable to employ pressure polymerization during the production of the fire-extinguishing agent-containing particles in order to suppress evaporation of the fire-extinguishing agent, which poses the problem of limitations on the polymerization method. Therefore, it is desirable to produce fire-extinguishing agent-containing particles using a fire-extinguishing agent (e.g., a flame retardant) for which the polymerization method is not limited. Furthermore, even when such a fire-extinguishing agent is used, it is desirable to employ a monomer composition that allows the production of fire-extinguishing agent-containing particles.

[0008] Furthermore, the resin layer covering at least a part of the fire extinguishing agent (e.g., flame retardant) may be used in contact with the electrolyte of a secondary battery, etc. Therefore, a material capable of forming a resin layer that is inhibited from eluting into the electrolyte is desirable.

[0009] Next, the fire extinguishing sheet described in JP 2021-118847 A contains a fire extinguishing agent that thermally decomposes to generate a fire extinguishing component when it reaches a predetermined temperature. Specifically, the fire extinguishing agent generates thermal energy by burning a chlorate salt of component B, which is a strong oxidizing agent, and a potassium salt of component C, which generates an aerosol, which is a fire extinguishing component. In JP 2021-118847 A, it is necessary to generate thermal energy to generate the aerosol, which may promote ignition due to thermal runaway of the secondary battery, etc.

[0010] In the fire extinguishing sheet described in JP 2020-130661 A, a fluorocarbon-based fire extinguishing agent is dispersed as droplets within a fire extinguishing sheet made of synthetic resin. In JP 2020-130661 A, the synthetic resin plasticizes at around 80°C, which may cause the fluorocarbon-based fire extinguishing agent to leach out of the fire extinguishing sheet. Therefore, there is a risk that the fluorocarbon-based fire extinguishing agent may leach out of the fire extinguishing sheet in the operating temperature range of secondary batteries (e.g., 45°C to 80°C).

[0011] In view of the above circumstances, a first aspect of the present disclosure aims to provide flame-retardant-containing particles formed using a flame retardant that is not restricted by its polymerization method and that include a resin layer that is inhibited from leaching into an electrolyte solution, a resin composition that can form a resin layer that is inhibited from leaching into an electrolyte solution, and the like.

[0012] In view of the above circumstances, a second aspect of the present disclosure has an object to provide a fire-extinguishing sheet or the like that can suppress fire caused by thermal runaway or the like of a secondary battery.

[0013] Means for solving the above problems include the following embodiments. <1A> Particles (C) obtained by polymerizing two or more monomers (A) having a polymerizable unsaturated double bond in a composition containing the two or more monomers (A) and a phosphorus-based flame retardant (B) dissolved in at least a portion of the two or more monomers (A), the particles (C) including a resin layer (D) formed by polymerization of the two or more monomers (A), the resin layer (D) having an elution rate in an electrolytic solution of 40 mass % or less. <2A> The flame-retardant-containing particle according to <1A>, wherein the resin layer (D) covers at least a portion of the phosphorus-based flame retardant (B). <3A> A polymerizable resin composition comprising a monomer (1) capable of dissolving 70% by mass or more but less than 99% by mass of a phosphorus-based flame retardant (B), wherein the content of a monomer (2) having an acidic group is 0% by mass to 10% by mass, the content of a monomer (3) other than the monomers (1) and (2) is 0% by mass to 25% by mass, and the proportion of methyl methacrylate contained in the monomer (1) is 50% by mass or less based on the total amount of the monomers (1). <4A> The resin composition according to <3A>, which is used to form a resin layer (D) covering at least a portion of the phosphorus-based flame retardant (B). <5A> The resin composition according to <3A> or <4A>, wherein the monomer (1) is at least one selected from the group consisting of acrylonitrile, methyl methacrylate, butyl methacrylate, and styrene. <6A> The resin composition according to any one of <3A> to <5A>, wherein the monomer (2) is at least one selected from the group consisting of methacrylic acid and acrylic acid. <7A> The resin composition according to any one of <3A> to <6A>, wherein the monomer (3) contains one polymerizable unsaturated double bond. <8A> A flame-retardant-containing particle comprising: the phosphorus-based flame retardant (B); and a resin layer (D) formed from the resin composition according to any one of <3A> to <7A>, said resin layer (D) covering at least a part of the phosphorus-based flame retardant (B). <9A> A flame-retardant coating material comprising the flame-retardant-containing particle according to any one of <1A>, <2A> and <8A>. <10A> A laminate comprising the flame-retardant-containing particle according to any one of <1A>, <2A> and <8A>.<11A> A method for producing flame-retardant-containing particles, comprising the steps of preparing a mixed liquid containing the resin composition according to any one of <3A> to <7A> and the phosphorus-based flame retardant (B), and polymerizing the monomer (A) in the mixed liquid to form a resin layer (D). <12A> A method for producing flame-retardant-containing particles according to <11A>, in which the resin layer (D) covers at least a portion of the phosphorus-based flame retardant (B). <13A> A method for producing flame-retardant-containing particles according to <11A> or <12A>, in which a resin layer (D) is formed. <1B> A fire-extinguishing sheet comprising: a base layer; and a self-extinguishing layer containing fire-extinguishing-agent-supported particles comprising a fire-extinguishing agent and a resin layer covering at least a portion of the fire-extinguishing agent. <2B> The fire extinguishing sheet according to <1B>, wherein the self-extinguishing layer further contains a water-soluble resin and a binder, and the content of the fire extinguishing agent-carrying particles is 50% by mass to 80% by mass relative to the total amount of the self-extinguishing layer. <3B> The fire extinguishing sheet according to <1B> or <2B>, wherein the self-extinguishing layer further contains an inorganic filler. <4B> The fire extinguishing sheet according to any one of <1B> to <3B>, wherein the fire extinguishing agent contains a phosphorus-based flame retardant. <5B> The fire extinguishing sheet according to <4B>, wherein the content of the phosphorus-based flame retardant is 50% by mass to 100% by mass relative to the total amount of the fire extinguishing agent. <6B> The fire extinguishing sheet according to any one of <1B> to <5B>, wherein the base layer contains 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. <7B> The fire extinguishing sheet according to any one of <1B> to <6B>, wherein the base layer contains a flame retardant. <8B> A secondary battery comprising the fire extinguishing sheet according to any one of <1B> to <7B>, a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the fire extinguishing sheet is disposed inside or outside a battery exterior material. <9B> A method for producing a fire extinguishing sheet, comprising the step of applying to a base layer an aqueous composition containing fire extinguishing agent and fire extinguishing agent-supported particles including a resin layer covering at least a portion of the fire extinguishing agent.<10B> A method for releasing a fire extinguishing agent, comprising: a step in which the fire extinguishing agent-carrying particles contained in the fire extinguishing sheet according to any one of <1B> to <7B> change in shape between 110°C and 180°C; and a step in which the fire extinguishing agent is released from the fire extinguishing agent-carrying particles.

[0014] According to a first aspect of the present disclosure, there are provided flame retardant-containing particles formed using a flame retardant that is not restricted by polymerization method and that include a shell layer that is inhibited from leaching into an electrolyte solution, a resin composition capable of forming a shell layer that is inhibited from leaching into an electrolyte solution, etc. According to a second aspect of the present disclosure, there are provided fire extinguishing sheets that can inhibit ignition due to thermal runaway or the like in secondary batteries, etc.

[0015] In the present disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the upper and lower limits. In numerical ranges described in stages in the present disclosure, the upper or lower limit described in one numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in numerical ranges described in the present disclosure, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. In the present disclosure, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of that process is achieved. In the present disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in a composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified.

[0016] [Flame-retardant-containing particle] The flame-retardant-containing particle of the present disclosure is a particle (C) obtained by polymerizing two or more types of monomers (A) in a composition containing two or more types of 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 types of monomers (A), and the particle (C) includes a resin layer (D) formed by polymerization of the two or more types of monomers (A), and the elution rate of the resin layer (D) in an electrolyte solution is 40 mass% or less.

[0017] The flame retardant-containing particles of the present disclosure are formed using a phosphorus-based flame retardant (B), which is a flame retardant that has no boiling point or a high boiling point and is not restricted by its polymerization method. Furthermore, the particles include a resin layer (D) that is inhibited from leaching into an electrolyte solution. By including the resin layer (D) that has an elution rate into an electrolyte solution of 40% by mass or less, when the flame retardant-containing particles are applied to a secondary battery, for example, when the flame retardant-containing particles are used as an outermost separator, exterior material, etc., adverse effects on battery characteristics can be reduced. Specifically, it is believed that the inhibition of elution of the resin layer (B) into the electrolyte solution also inhibits the elution of the phosphorus-based flame retardant (B), thereby maintaining battery characteristics.

[0018] The flame retardant-containing particles of the present disclosure are particles (C) obtained by polymerizing two or more types of monomers (A) in a composition containing two or more types of monomers (A) and a phosphorus-based flame retardant (B).

[0019] (Monomer (A)) Monomer (A) is a monomer having a polymerizable unsaturated double bond. Monomer (A) preferably contains monomer (1) capable of dissolving phosphorus-based flame retardant (B), and may or may not contain a monomer other than monomer (1). Examples of monomers other than monomer (1) include monomer (2) having an acidic group, and monomer (3) other than monomer (1) and monomer (2). Specific examples of monomer (1), monomer (2), and monomer (3) are as described below, and preferred embodiments are also the same as those of the resin composition of the present disclosure described below.

[0020] The content of the monomer (1) is preferably 70% by mass or more and less than 99% by mass based on the total amount of the monomer (A). From the viewpoint of further suppressing the elution rate into the electrolyte solution, the content is preferably 75% by mass to 97% by mass, and more preferably 80% by mass to 95% by mass.

[0021] The content of the monomer (2) is 0 to 5% by mass, preferably 1 to 5% by mass, and more preferably 3 to 5% by mass, based on the total amount of the monomer (A).

[0022] The content of the monomer (3) is 0 to 25% by mass, preferably 0 to 20% by mass, and more preferably 0 to 10% by mass, based on the total amount of the monomer (A).

[0023] The content of the monomer (A) contained in the composition used to prepare the particles (C) may be 20% by mass to 80% by mass, 30% by mass to 70% by mass, or 40% by mass to 60% by mass, relative to the total amount of the composition.

[0024] (Phosphorus-based flame retardant (B)) The phosphorus-based flame retardant (B) is a flame retardant that contains phosphorus element and is soluble in at least a part of the two or more monomers (A). Examples of the phosphorus-based flame retardant (B) include phosphate ester-based flame retardants and condensed phosphate ester-based flame retardants. Of these, condensed phosphate ester-based flame retardants are preferred. The phosphorus-based flame retardants (B) may be used singly or in combination of two or more.

[0025] As the condensed phosphate ester-based flame retardant, commercially available products may be used, such as Adeka STAB FP-600, Adeka STAB PFR, and Adeka STAB FP-900L manufactured by ADEKA CORPORATION.

[0026] The content of the phosphorus-based flame retardant (B) contained in the composition used to prepare the particles (C) may be 20% by mass to 80% by mass, 30% by mass to 70% by mass, or 40% by mass to 60% by mass, based on the total amount of the composition.

[0027] The composition used to prepare the particles (C) may contain components (other components) other than the monomer (A) and the phosphorus-based flame retardant (B). Examples of other components include a polymerization initiator. Examples of the polymerization initiator include an azo polymerization initiator and a peroxide polymerization initiator. Examples of the azo polymerization initiator include 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 2,2-azobis(2,4-dimethylvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate), and 2,2'-azobis(2-methylbutyronitrile). Examples of the peroxide polymerization initiator include dibenzoyl peroxide and dilauroyl peroxide.

[0028] Particles (C), which are flame retardant-containing particles of the present disclosure, are particles obtained by polymerizing two or more types of monomers (A) in a composition. Examples of methods for polymerizing two or more types of monomers (A) include a method of 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). The pressure used for polymerizing two or more types of monomers (A) is not particularly limited, and may be atmospheric pressure of about 0.05 MPa to 0.15 MPa. Furthermore, particles (C), which are flame retardant-containing particles of the present disclosure, may be obtained by polymerizing two or more types of monomers (A) by suspension polymerization.

[0029] The average particle size of the particles (C) may be less than 10 μm, 5 μm or less, or 0.5 μm to 3 μm. The average particle size of the particles (C) can be determined by measuring the particle size with a particle size measuring device (MT3300EXII, manufactured by Microtrac-Bell).

[0030] The flame retardant-containing particle (C) of the present disclosure includes a resin layer (D) formed by polymerization of 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) may include one core containing a flame retardant and cover at least a portion of the core, or may include multiple cores containing a flame retardant and cover at least a portion of the multiple cores. The core may be entirely covered by the resin layer (D), or may be partially covered by the resin layer (D), with the remainder exposed from the resin layer (D).

[0031] The elution rate of the resin layer (D) in the electrolyte solution 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. The lower limit of the elution rate of the resin layer (D) in the electrolyte solution is not particularly limited as long as it is 0% by mass or more.

[0032] The elution rate of the resin layer (D) into the electrolyte solution refers to the elution rate of the resin layer (D) in an electrolyte solution obtained by mixing ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a mass ratio of 1:1:1. Specifically, the resin layer (D) or a sample having the same resin composition as the resin layer (D) is prepared, and 0.5 parts by mass of the resin layer (D) or sample is immersed in 10 parts by mass of the electrolyte solution at room temperature. After immersion, the electrolyte solution is filtered, and the filtrate is dried at 150 ° C. for 3 hours. The elution rate into the electrolyte solution is calculated by measuring the residue. The elution rate of the resin layer (D) into the electrolyte solution is a value calculated from the elution amount of the components constituting the resin layer (D), and does not take into account the elution amount of the flame retardant. Therefore, for example, the elution rate of the resin layer (D) into the electrolyte is determined from a sample having the same resin composition as the resin layer (D), or the elution rate of the resin layer (D) into the electrolyte is determined by subtracting the elution amount of the flame retardant from the total elution amount.

[0033]

[0034] The flame retardant-containing particles of the present disclosure may or may not contain a flame retardant other than the phosphorus-based flame retardant (B). For example, the content of the other flame retardant may be 0% by mass to 10% by mass, or 0% by mass to 5% by mass, based on the total amount of the phosphorus-based flame retardant (B) and the other flame retardant.

[0035] The flame retardant-containing particles of the present disclosure can be applied to components that may cause fires due to high temperatures. For example, the flame retardant-containing particles of the present disclosure may be applied to home appliances, secondary batteries, automobile parts, etc. The flame retardant-containing particles of the present disclosure may be used to prepare flame-retardant coating materials and laminates, which will be described later.

[0036] The flame retardant-containing particles of the present disclosure may be particles that release the phosphorus-based flame retardant (B) to the outside when certain conditions are met. For example, (1) the phosphorus-based flame retardant (B) may be released to the outside when the flame retardant-containing particles of the present disclosure or a member containing the flame retardant-containing particles is exposed to a certain temperature (e.g., 60°C or higher), (2) the phosphorus-based flame retardant (B) may be released to the outside when the flame retardant-containing particles of the present disclosure or a member containing the flame retardant-containing particles is subjected to an impact, or (3) the phosphorus-based flame retardant (B) may be released to the outside when the resin layer (D) contained in the flame retardant-containing particles of the present disclosure is altered by a chemical change or the like.

[0037] [Flame-retardant coating material] The flame-retardant coating material of the present disclosure includes the flame-retardant-containing particles of the present disclosure. The flame-retardant coating material may be applied to the surface of a substrate or a member, or may be used to impart fire resistance to home appliances, secondary batteries, automobile parts, etc.

[0038] The flame-retardant coating material may contain components other than the flame-retardant-containing particles of the present disclosure, such as solvents, pigments, inorganic materials such as fillers, and binder components.

[0039] The flame-retardant coating material may be, for example, a fire-extinguishing sheet including a substrate layer and a self-extinguishing layer containing the flame-retardant-containing particles of the present disclosure.

[0040] [Fire-extinguishing sheet] The fire-extinguishing sheet of the present disclosure includes a base layer and a self-extinguishing layer containing fire-extinguishing agent-carrying particles including a fire-extinguishing agent and a resin layer covering at least a portion of the fire-extinguishing agent. By including fire-extinguishing agent-carrying particles including a fire-extinguishing agent and a resin layer covering at least a portion of the fire-extinguishing agent in the self-extinguishing layer, it is possible to suppress ignition due to thermal runaway or the like, for example, to reduce the maximum heat generation temperature of secondary battery cells adjacent to a secondary battery cell that has experienced thermal runaway, and to delay the start of heat generation.

[0041] The fire extinguishing sheet may be placed inside or outside the battery exterior material, or may be placed in the gap between components that can generate heat, such as between secondary batteries. By placing the fire extinguishing sheet in the gap between components that can generate heat, it is possible to prevent the spread of fire to components adjacent to the heated component.

[0042] The fire extinguishing sheet can be applied to components that may cause a fire due to high temperatures. For example, the fire extinguishing sheet may be applied to home appliances, secondary batteries such as lithium-ion secondary batteries, automobile parts, etc.

[0043] (Substrate Layer) The material of the substrate layer in the flame-retardant coating material or fire-extinguishing sheet is not particularly limited, and examples thereof include metal materials such as aluminum and copper, fluorine-containing resins such as polyolefin, polyester, polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyamide imide (PAI), and polytetrafluoroethylene (PTFE), and resin materials such as acrylic resins, silicone resins, styrene resins, ethylene vinyl alcohol resins, polylactic acid resins, and vinyl chloride resins. The substrate layer may contain only one material, or may contain 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 a metal material and a resin material.

[0044] 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, acrylic acid esters, and methacrylic acid esters; blends, block copolymers, and graft copolymers of two or more of these polymers or of these polymers with other thermoplastic resins. Among these, polypropylene or polyethylene is preferred as the polyolefin.

[0045] Polyesters include, for example, polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate.

[0046] The substrate layer may contain a flame retardant. Examples of flame retardants that can be contained in the substrate layer include halogen-based flame retardants and inorganic flame retardants (alumina, magnesium hydroxide, antimony trioxide, etc.). When the substrate layer contains a flame retardant, the substrate layer may be made of a composition in which the flame retardant is mixed with the resin material constituting the substrate layer, or may be a laminate in which a flame retardant layer containing a flame retardant is laminated on a layer of a resin material. The flame retardants contained in the substrate layer may be used alone or in combination of two or more.

[0047] The thickness of the substrate layer is not particularly limited, and may be, for example, 100 μm to 300 μm, 150 μm to 250 μm, or 150 μm to 200 μm.

[0048] (Self-extinguishing layer) The fire extinguishing sheet of the present disclosure includes a self-extinguishing layer containing flame retardant-containing particles or fire extinguishing agent-carrying particles. The flame retardant-containing particles or fire extinguishing agent-carrying particles may be used alone or in combination of two or more.

[0049] The thickness of the self-extinguishing layer is not particularly limited, and may be, for example, 100 μm to 300 μm, 150 μm to 250 μm, or 150 μm to 200 μm.

[0050] The content of the flame retardant-containing particles or the fire extinguishing agent-carrying particles may be 30% by mass to 85% by mass, 50% by mass to 80% by mass, or 55% by mass to 70% by mass, based on the total amount of the self-extinguishing layer.

[0051] <Fire-extinguishing agent-carrying particles> The self-extinguishing layer may contain fire-extinguishing agent-carrying particles including a fire-extinguishing agent and a resin layer covering at least a portion of the fire-extinguishing agent. The fire-extinguishing agent-carrying particles are particles in which at least a portion of the fire-extinguishing agent is covered with a resin layer. The fire-extinguishing agents contained in the fire-extinguishing agent-carrying particles may be used alone or in combination of two or more.

[0052] The type of fire extinguishing agent contained in the self-extinguishing layer is not particularly limited. Examples of fire extinguishing agents include guanidine phosphate, melamine polyphosphate, phosphoric trichloride reaction products with 4,4'-isopropylidenediphenol and phenol (e.g., Adekastab FP-600), phosphoric ester, phosphoric trichloride polymer with 1,3-benzenediol, phenyl ester (e.g., Adekastab PFR), and phosphoric acid mixed esters with [1,1'-biphenyl]-4,4'-diol and phenol (e.g., Adekastab Examples of suitable flame retardants include phosphorus-based flame retardants such as ethylenebispentabromobenzene, 2,3-dibromopropyl ether, triallyl isocyanate hexabromide, bis[3,5-dibromo-4-(2,3-dibromopropoxy)phenyl]sulfone, and ethylenebispentabromobenzene / antimony trioxide; potassium perfluorobutanesulfonate; and inorganic flame retardants such as silicon carbide, spherical alumina, special carbon fiber, and titanium borate. Among these, the fire extinguishing agent preferably contains the aforementioned phosphorus-based flame retardant. Because phosphorus-based flame retardants have no or a high boiling point, no treatment to suppress volatilization of the fire extinguishing agent is required when polymerizing a resin material to prepare fire extinguishing agent-supported particles, and the polymerization method for the resin material is less likely to be restricted. Phosphorus-based flame retardants may be used alone or in combination of two or more.

[0053] The content of the phosphorus-based flame retardant may be 50% by mass to 100% by mass, 60% by mass to 100% by mass, or 80% by mass to 100% by mass, based on the total amount of the fire extinguishing agent.

[0054] The resin layer covering at least a portion of the extinguishing agent is preferably a layer formed by polymerization of two or more types of monomers (A'). The resin layer may include one core containing an extinguishing agent and cover at least a portion of the single core, or may include a plurality of cores containing an extinguishing agent and cover at least a portion of the plurality of cores. The core may be entirely covered by the resin layer, or may be partially covered by the resin layer with the remainder exposed from the resin layer.

[0055] The elution 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. The lower limit of the elution rate of the resin layer in the electrolyte is not particularly limited as long as it is 0% by mass or more. The elution rate of the resin layer in the electrolyte can be determined in the same manner as the elution rate of the resin layer (D) in the electrolyte described above.

[0056] The monomer (A') that can be used to form the resin layer is a monomer having a polymerizable unsaturated double bond. The monomer (A') preferably contains a monomer (1') that can dissolve a fire extinguishing agent (preferably a phosphorus-based flame retardant), and may or may not contain a monomer other than the monomer (1'). Examples of the monomer other than the monomer (1') include a monomer (2) having an acidic group and a monomer (3) having a polymerizable unsaturated double bond other than the monomer (1') and the monomer (2).

[0057] (Monomer (1')) The monomer (1') is preferably a monomer component capable of dissolving a fire extinguishing agent (preferably a phosphorus-based flame retardant), and further preferably contains one or more (preferably one) polymerizable unsaturated double bonds. The monomer (1') may be the same as the monomer (1) described below. The monomer (1') may be used alone or in combination of two or more.

[0058] Monomer (1') is preferably at least one selected from the group consisting of acrylonitrile, methyl methacrylate, butyl methacrylate, and styrene. Monomer (1') preferably contains at least one selected from the group consisting of acrylonitrile and methyl methacrylate.

[0059] The content of the monomer (1') may be 60% by mass or more and less than 99% by mass, 65% by mass to 97% by mass, or 70% by mass to 95% by mass, based on the total amount of the monomer (A').

[0060] When the monomer (1') contains at least one selected from the group consisting of acrylonitrile and methyl methacrylate, the total content of acrylonitrile and methyl methacrylate is preferably 50% by mass to 100% by mass, more preferably 80% by mass to 100% by mass, and even more preferably 90% by mass to 100% by mass, based on the total amount of the monomer (1'). This makes it possible to further suppress the elution rate into the electrolyte solution and tends to facilitate the formation of fire-extinguishing agent-supported particles.

[0061] The monomer (1') preferably contains acrylonitrile. The content of acrylonitrile in the monomer (1') is preferably 50% by mass to 100% by mass, more preferably 80% by mass to 100% by mass, and even more preferably 90% by mass to 100% by mass, based on the total amount of the monomer (1').

[0062] (Monomer (2)) Monomer (A') may or may not contain a monomer (2) having an acidic group. That is, in monomer (A'), monomer (2) is an optional component. Monomer (2) may be used alone or in combination of two or more. Preferred examples of monomer (2) that can be contained in monomer (A') are the same as the preferred examples of monomer (2) that can be contained in monomer (A) described above.

[0063] The content of the monomer (2) is preferably 0% by mass to 10% by mass, more preferably 1% by mass to 5% by mass, and even more preferably 3% by mass to 5% by mass, based on the total amount of the monomer (A').

[0064] (Monomer (3)) Monomer (A') may or may not contain a monomer (3) having a polymerizable unsaturated double bond other than monomer (1') and monomer (2). That is, in monomer (A'), monomer (3) is an optional component. Monomer (3) may be used alone or in combination of two or more. Preferred examples of monomer (3) that can be contained in monomer (A') are the same as the preferred examples of monomer (3) that can be contained in monomer (A) described above.

[0065] When the monomer (A') contains the monomer (3), the content of the monomer (3) is preferably 1.1% by mass to 25% by mass, more preferably 1.5% by mass to 20% by mass, and even more preferably 2% by mass to 10% by mass, based on the total amount of the monomer (A').

[0066] The content of the fire-extinguishing agent-carrying particles may be 30% by mass to 85% by mass, 50% by mass to 80% by mass, or 55% by mass to 70% by mass, based on the total amount of the self-extinguishing layer.

[0067] The content of the fire extinguishing agent contained in the fire extinguishing agent-carrying particles may be 20% by mass to 80% by mass, 30% by mass to 70% by mass, or 40% by mass to 60% by mass, relative to the total amount of the fire extinguishing agent-carrying particles.

[0068] The content of the resin layer contained in the fire extinguishing agent-carrying particle may be 20% by mass to 80% by mass, 30% by mass to 70% by mass, or 40% by mass to 60% by mass, relative to the total amount of the fire extinguishing agent-carrying particle.

[0069] The average particle diameter of the fire extinguishing agent-carrying particles may be 0.1 μm or more, or may be 0.5 μm or more. When the average particle diameter of the fire extinguishing agent-carrying particles is 0.1 μm or more, the number of adhesion points with the particulate binder increases, making the fire extinguishing agent-carrying particles less likely to crack under normal conditions and making it easier for the fire extinguishing sheet to deform along the shape of the component to which the fire extinguishing sheet is applied (e.g., a secondary battery). The average particle diameter of the fire extinguishing agent-carrying particles may be 6 μm or less, or may be 5 μm or less. When the average particle diameter of the fire extinguishing agent-carrying particles is 6 μm or less, the number of adhesion points with the particulate binder does not increase too much, making it easier for the fire extinguishing agent to be released from the fire extinguishing agent-carrying particles in the event of abnormal heat generation, etc. The average particle diameter of the fire extinguishing agent-carrying particles can be determined by measuring the particle diameter using a particle diameter measuring device (MT3300EXII, manufactured by Microtrac-Bell).

[0070] It is preferable that the resin layer of the fire extinguishing agent-carrying particles does not undergo structural deformation at temperatures below 100°C. Structural deformation of the resin layer means that the resin layer undergoes chemical alteration, causing the fire extinguishing agent to be released from the fire extinguishing agent-carrying particles to the outside of the fire extinguishing sheet. The absence of structural deformation of the resin layer at temperatures below 100°C suppresses the release of the fire extinguishing agent from the fire extinguishing agent-carrying particles to the outside of the fire extinguishing sheet in the operating temperature range of the secondary battery (e.g., 45°C to 80°C).

[0071] [Method for Releasing Fire Extinguishing Agent] The method for releasing fire extinguishing agent of the present disclosure includes a step (step 1) in which fire extinguishing agent-carrying particles contained in a fire extinguishing sheet undergo a morphological change between 110°C and 180°C, and a step (step 2) in which the fire extinguishing agent is released from the fire extinguishing agent-carrying particles. As a result, when abnormal heat generation or the like occurs, the fire extinguishing agent is released from the fire extinguishing agent-carrying particles, thereby suppressing ignition of secondary batteries or the like. Note that steps 1 and 2 may proceed simultaneously or may partially overlap. For example, the fire extinguishing agent may be released from the fire extinguishing agent-carrying particles while the fire extinguishing agent-carrying particles are undergoing a morphological change.

[0072] The method for producing fire extinguishing agent-supported particles includes the steps of preparing a mixed solution containing a monomer (A') and a fire extinguishing agent, and polymerizing the monomer (A') in the mixed solution to form a resin layer.

[0073] The method for producing a fire extinguishing agent-supported particle includes a step of preparing a mixed solution containing a monomer (A') and a fire extinguishing agent (preparation step). In this step, the fire extinguishing agent may be dissolved in at least a part of the two or more monomers (A') (preferably the monomer (1')).

[0074] The method includes a step (forming step) of polymerizing the monomer (A') in the mixed solution to form a resin layer. In the forming step, the composition may be heated, for example, 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'). The mixture may also contain the aforementioned polymerization initiator, such as an azo-based polymerization initiator or a peroxide-based polymerization initiator. The pressure during polymerization of the monomer (A') is not particularly limited and may be atmospheric pressure of about 0.05 MPa to 0.15 MPa.

[0075] In the forming step, the monomer (A') may be polymerized by suspension polymerization. For example, the mixed liquid and an aqueous liquid containing a solvent such as water may be stirred to disperse the mixed liquid in the aqueous liquid, and the monomer (A') in the mixed liquid may be polymerized to form a resin layer. By performing suspension polymerization, it is easy to control the particle size of the fire-extinguishing agent-carrying particles, and particles with small variations in particle size, shape, etc. tend to be formed.

[0076] (Water-Soluble Resin) From the viewpoint of processability, the self-extinguishing layer preferably further contains a water-soluble resin. Examples of water-soluble resins include resins having a hydroxy group. Examples of water-soluble resins include polyvinyl alcohol-based resins such as polyvinyl alcohol (PVA), cellulose-based resins such as hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC), hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose, and resins having an ether bond such as chitins, chitosans, starch, polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), and polyvinyl ether (PVE). The water-soluble resins may be used alone or in combination of two or more.

[0077] When the self-extinguishing layer contains a water-soluble resin, the content of the water-soluble resin may be 0.5% by mass to 10% by mass, 1% by mass to 8% by mass, or 1% by mass to 5% by mass, relative to the total amount of the self-extinguishing layer.

[0078] (Binder) The self-extinguishing layer preferably further contains a binder from the viewpoint of adhesion of flame retardant-containing particles, fire extinguishing agent-carrying particles, etc. Examples of binders include styrene-butadiene copolymers, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), acrylic resins, urethane resins, water-soluble resins, etc. The water-soluble resins described above may also serve as binders. One type of binder may be used alone, or two or more types may be used in combination.

[0079] The binder may be particulate. When the flame retardant-containing particles or fire extinguishing agent-carrying particles and binder that form the self-extinguishing layer are particulate and the self-extinguishing layer is formed from an aggregate of particles, the adhesion area between adjacent particles in the self-extinguishing layer is reduced, and the adhesion between adjacent particles is easily broken when abnormal heat generation or the like occurs. Furthermore, when abnormal heat generation or the like occurs, the resin layer that covers at least a portion of the fire extinguishing agent in the flame retardant-containing particles or fire extinguishing agent-carrying particles is likely to melt, and the fire extinguishing agent is quickly released from the flame retardant-containing particles or fire extinguishing agent-carrying particles dispersed in the self-extinguishing layer, which tends to suppress ignition.

[0080] When the self-extinguishing layer contains a binder, the content of the binder may be 1% by mass to 15% by mass, 2% by mass to 12% by mass, or 4% by mass to 10% by mass, relative to the total amount of the self-extinguishing layer.

[0081] (Inorganic Filler) From the viewpoint of improving processability and performance of the fire extinguishing sheet, the self-extinguishing layer preferably further contains an inorganic filler. Examples of inorganic fillers include alumina, magnesium hydroxide, silica, aluminum hydroxide, magnesium oxide, zirconium oxide, titanium oxide aluminum nitride, boron nitride, and graphite. One type of inorganic filler may be used alone, or two or more types may be used in combination.

[0082] When the self-extinguishing layer contains an inorganic filler, the content of the inorganic filler may be 3% by mass to 40% by mass, 5% by mass to 35% by mass, or 15% by mass to 30% by mass, relative to the total amount of the self-extinguishing layer.

[0083] The content of the fire extinguishing agent other than the flame retardant-containing particles of the present disclosure may 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 the fire extinguishing agent other than the flame retardant-containing particles 15% by mass or less relative to the total amount of the self-extinguishing layer, a fire extinguishing sheet can be obtained that can reduce the maximum heat generation temperature of secondary battery cells adjacent to a secondary battery cell that has experienced thermal runaway and can delay the time when heat generation begins.

[0084] [Method of Manufacturing Fire Extinguisher Sheet] The method of manufacturing a fire extinguisher sheet of the present disclosure includes a step of applying to a substrate layer an aqueous composition containing flame retardant-containing particles or fire extinguisher-supported particles, the flame retardant containing particles or fire extinguisher-supported particles including a fire extinguisher and a resin layer covering at least a portion of the fire extinguisher.

[0085] In the manufacturing method of the present disclosure, the aqueous composition described above is prepared and applied to a substrate layer. The aqueous composition contains the flame retardant-containing particles or fire extinguishing agent-carrying particles described above and water, and, if necessary, at least one of a water-soluble resin, a binder, and an inorganic filler. It may also contain other components (such as a surfactant, a fire extinguishing agent other than the flame retardant-containing particles or the fire extinguishing agent-carrying particles (e.g., a fire extinguishing agent not covered with a resin layer), or other components insoluble in the electrolyte).

[0086] Examples of methods for preparing the aqueous composition include a method in which powder components (such as flame retardant-containing particles or fire extinguishing agent-carrying particles, water-soluble resin, binder, and inorganic filler) are mixed by stirring, and then water as a solvent is added to disperse each powder component in water to prepare the aqueous composition.

[0087] The content of the flame retardant-containing particles or the fire extinguishing agent-carrying particles in the aqueous composition may be 30% by mass to 85% by mass, 50% by mass to 80% by mass, or 55% by mass to 70% by mass, based on all components excluding water from the aqueous composition.

[0088] When the aqueous composition contains a water-soluble resin, the content of the water-soluble resin may be 0.5% by mass to 10% by mass, 1% by mass to 8% by mass, or 1% by mass to 5% by mass, based on all components excluding water from the aqueous composition.

[0089] When the aqueous composition contains a binder, the content of the binder may be 1% by mass to 15% by mass, 2% by mass to 12% by mass, or 4% by mass to 10% by mass, based on all components excluding water from the aqueous composition.

[0090] When the aqueous composition contains an inorganic filler, the content of the inorganic filler may be 3% by mass to 40% by mass, 5% by mass to 35% by mass, or 15% by mass to 30% by mass, based on all components excluding water from the aqueous composition.

[0091] The method for applying the aqueous composition to the base layer is not particularly limited, and any conventionally known application method can be used. After applying the aqueous composition to the base layer, the aqueous composition may be dried as necessary.

[0092] [Laminate] The laminate of the present disclosure contains the flame retardant-containing particles of the present disclosure. The laminate of the present disclosure is not particularly limited as long as it contains two or more layers, and contains at least one layer containing the flame retardant-containing particles of the present disclosure. For example, the flame retardant coating material described above may be applied to the surface of a substrate, a member, or the like, and then heated, dried, or the like as necessary to form a layer containing the flame retardant-containing particles of the present disclosure on the surface of the substrate, a member, or the like, to form a laminate.

[0093] The flame retardant-containing particles, flame retardant coating material, fire extinguishing sheet, and laminate of the present disclosure may be used to impart fire protection to secondary batteries.

[0094] [Secondary Battery] A secondary battery may include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. For example, a laminate containing the flame retardant-containing particles of the present disclosure may be used as the outermost separator of a secondary battery, or may be used as an exterior material of the secondary battery. The laminate containing the flame retardant-containing particles of the present disclosure may be disposed so that at least a portion thereof is in contact with the electrolyte in the secondary battery. Examples of secondary batteries include lithium ion secondary batteries and magnesium ion secondary batteries.

[0095] The secondary battery comprises the fire-extinguishing sheet of the present disclosure, a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, and the fire-extinguishing sheet may be disposed inside or outside the battery exterior material.

[0096] When the fire-extinguishing sheet is disposed inside the battery exterior material, it is preferable that the self-extinguishing layer is located on the electrode side and the substrate layer is located on the opposite side from the electrode side. Even when the self-extinguishing layer is located on the electrode side, the charge / discharge characteristics of the secondary battery tend to be maintained. Furthermore, the positive electrode, the negative electrode, the separator disposed between the positive electrode and the negative electrode, and the nonaqueous electrolyte may be housed in the battery exterior material in a state where they are wrapped around the fire-extinguishing sheet. Furthermore, the positive electrode, the negative electrode, and the separator may be formed by stacking or winding.

[0097] As the positive electrode, negative electrode and separator in the secondary battery, conventionally known materials can be used.

[0098] For example, the positive electrode is usually composed of a positive electrode active material and a positive electrode current collector, and optionally contains a conductive additive, a binder, etc. The positive electrode active material is not particularly limited, and a commonly known material can be used, for example, lithium-containing composite oxides such as lithium cobalt oxide, lithium nickel oxide, lithium manganate, spinel-type lithium composite oxide, and lithium titanate.

[0099] For example, the negative electrode is usually composed of a negative electrode active material and a negative electrode current collector, and optionally contains a conductive additive, a binder, etc. The negative electrode active material is not particularly limited, and a generally known material can be used, for example, carbon materials such as graphite and hard carbon, Si, and Si alloys.

[0100] The electrolyte is preferably a non-aqueous electrolyte containing an electrolyte and a non-aqueous solvent. ６ , LiBF ４ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ CF ２ CF ３ ) ２ Examples of Li electrolytes include:

[0101] Examples of non-aqueous solvents include cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, fluorine-containing chain carbonates, aliphatic carboxylic acid esters, fluorine-containing aliphatic carboxylic acid esters, γ-lactones, fluorine-containing γ-lactones, cyclic ethers, fluorine-containing cyclic ethers, chain ethers, fluorine-containing chain ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, dimethyl sulfoxide phosphate, etc. The non-aqueous solvents may be used alone or in combination of two or more.

[0102] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of fluorine-containing cyclic carbonates include fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and trifluoropropylene carbonate. Examples of chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and dipropyl carbonate (DPC). Examples of fluorine-containing chain carbonates include methyl 2,2,2-trifluoroethyl carbonate. 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. Examples of fluorine-containing aliphatic carboxylic acid esters include methyl difluoroacetate, methyl 3,3,3-trifluoropropionate, ethyl difluoroacetate, and 2,2,2-trifluoroethyl acetate. Examples of γ-lactones include γ-butyrolactone and γ-valerolactone. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, and 1,4-dioxane. Examples of the chain ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, 1,2-dibutoxyethane, etc. Examples of the fluorine-containing chain ethers include HCF ２ CF ２ CH ２ OCF ２ CF ２ H, C.F. ３ CF ２ CH ２ OCF ２CF ２ H, HCF ２ CF ２ CH ２ OCF ２ CFHCF ３ , C.F. ３ CF ２ CH ２ OCF ２ CFHCF ３ , C ６ F １３ OCH ３ , C ６ F １３ O.C. ２ H ５ , C ８ F １７ OCH ３ , C ８ F １７ O.C. ２ H ５ , C.F. ３ CFHCF ２ CH (CH ３ ) OCF ２ CFHCF ３ , HCF ２ CF ２ OCH (C ２ H ５ ) ２ , HCF ２ CF ２ O.C. ４ H ９ , HCF ２ CF ２ OCH ２ CH(C ２ H ５ ) ２ , HCF ２ CF ２ OCH ２ CH (CH ３ ) ２ Examples of nitriles include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, etc. Examples of amides include N,N-dimethylformamide, etc. Examples of lactams include N-methylpyrrolidinone, N-methyloxazolidinone, N,N'-dimethylimidazolidinone, etc.

[0103] The content of the non-aqueous solvent is preferably 60% by mass to 99% by mass, more preferably 70% by mass to 97% by mass, and even more preferably 90% by mass to 97% by mass, based on the total amount of the non-aqueous electrolyte.

[0104] [Resin Composition] The resin composition of the present disclosure is a polymerizable composition comprising a monomer (1) capable of dissolving 70% by mass or more but less than 99% by mass of a phosphorus-based flame retardant (B), a content of a monomer (2) having an acidic group being 0% by mass to 10% by mass, a content of a monomer (3) other than the monomers (1) and (2) being 0% by mass to 25% by mass, and the proportion of methyl methacrylate contained in the monomer (1) being 50% by mass or less based on the total amount of the monomers (1). The resin composition of the present disclosure is a composition used for forming a resin layer.

[0105] The resin composition of the present disclosure may be used to form a resin layer (D) that covers at least a part of the phosphorus-based flame retardant (B), or may be used to form the flame-retardant-containing particles described above by combining with the phosphorus-based flame retardant (B).

[0106] Flame retardant-containing particles may be formed using the resin composition of the present disclosure. For example, the flame retardant-containing particles of the present disclosure may be particles comprising a phosphorus-based flame retardant (B) and a resin layer (D) formed from the resin composition of the present disclosure and covering at least a portion of the phosphorus-based flame retardant (B). The flame retardant-containing particles of the present disclosure may or may not satisfy the elution rate of the resin layer (D) in an electrolyte solution of 40 mass% or less.

[0107] (Monomer (1)) The resin composition of the present disclosure contains a monomer (1) capable of dissolving 70% by mass or more but less than 99% by mass of the phosphorus-based flame retardant (B), and the proportion of methyl methacrylate contained in the monomer (1) is 50% by mass or less based on the total amount of the monomer (1). The monomer (1) may be any monomer component capable of dissolving the phosphorus-based flame retardant (B), and preferably further contains one or more (preferably one) polymerizable unsaturated double bonds. The monomer (1) may be used singly or in combination of two or more.

[0108] Monomer (1) is preferably at least one selected from the group consisting of acrylonitrile, methyl methacrylate, butyl methacrylate, and styrene. Monomer (1) preferably contains at least one selected from the group consisting of acrylonitrile and methyl methacrylate.

[0109] From the viewpoint of easily forming a resin layer in which elution into the electrolytic solution is suppressed, the proportion of methyl methacrylate contained in the monomer (1) is 50% by mass or less, preferably 20% by mass or less, and more preferably 10% by mass or less, based on the total amount of the monomer (1).

[0110] 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 the present disclosure (or the total amount of monomer components contained in the resin composition). From the viewpoint of being able to further suppress the elution rate into the electrolyte solution and facilitating the formation of flame retardant-containing particles, the content is preferably 75% by mass to 97% by mass, and more preferably 80% by mass to 95% by mass.

[0111] When the monomer (1) contains at least one selected from the group consisting of acrylonitrile and methyl methacrylate, the total content of acrylonitrile and methyl methacrylate is preferably 50% by mass to 100% by mass, more preferably 80% by mass to 100% by mass, and even more preferably 90% by mass to 100% by mass, based on the total amount of the monomer (1). This makes it possible to further suppress the elution rate into the electrolyte solution and tends to facilitate the formation of flame retardant-containing particles.

[0112] The monomer (1) preferably contains acrylonitrile. The content of acrylonitrile in the monomer (1) is preferably 50% by mass to 100% by mass, more preferably 80% by mass to 100% by mass, and even more preferably 90% by mass to 100% by mass, based on the total amount of the monomer (1).

[0113] (Monomer (2)) The resin composition of the present disclosure may or may not contain a monomer (2) having an acidic group. That is, in the resin composition of the present disclosure, the monomer (2) is an optional component. The monomer (2) may be used alone or in combination of two or more.

[0114] Examples of the acidic group include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, etc. The monomer (2) is preferably at least one selected from the group consisting of methacrylic acid and acrylic acid.

[0115] The content of monomer (2) is 0% by mass to 10% by mass, preferably 1% by mass to 8% by mass, more preferably 1% by mass to 5% by mass, and even more preferably 3% by mass to 5% by mass, relative to the total amount of the resin composition of the present disclosure (or the total amount of the monomer components contained in the resin composition).

[0116] (Monomer (3)) The resin composition of the present disclosure may or may not contain a monomer (3) other than the monomer (1) and the monomer (2). That is, in the resin composition of the present disclosure, the monomer (3) is an optional component. The monomer (3) may be used alone or in combination of two or more.

[0117] Monomer (3) is a monomer other than monomer (1) and monomer (2), and preferably contains one or more polymerizable unsaturated double bonds, more preferably one. Examples of monomer (3) include (meth)acrylate compounds and vinyl compounds other than monomer (1) and monomer (2). Specific examples of monomer (3) containing one polymerizable unsaturated double bond include methyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl methacrylate, and isobornyl methacrylate. Specific examples of the monomer (3) containing two or more polymerizable unsaturated double bonds 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, polytetramethylene glycol di(meth)acrylate, tricyclodecanol di(meth)acrylate, trimethylolpropane (meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and methylenebis(meth)acrylamide.

[0118] The content of the monomer (3) is 0% by mass to 25% by mass, preferably 0% by mass to 20% by mass, and more preferably 0% by mass to 10% by mass, relative to the total amount of the resin composition of the present disclosure (or the total amount of the monomer components contained in the resin composition).

[0119] [Method for producing flame retardant-containing particles] The method for producing flame retardant-containing particles of the present disclosure includes the steps of preparing a mixed solution containing the resin composition of the present disclosure and a phosphorus-based flame retardant (B), and polymerizing a polymerizable monomer in the mixed solution to form a resin layer (D). The preferred conditions for the produced flame retardant-containing particles are the same as those for the flame retardant-containing particles of the present disclosure. For example, the flame retardant-containing particles produced may or may not satisfy the elution rate of the resin layer (D) in the electrolyte solution of 40 mass% or less.

[0120] The manufacturing method of the present disclosure includes a step (preparation step) of preparing a mixed liquid containing the resin composition of the present disclosure and a phosphorus-based flame retardant (B). In the preparation step, a mixed liquid containing the resin composition of the present disclosure and the phosphorus-based flame retardant (B) may be prepared. In this step, the phosphorus-based flame retardant (B) may be dissolved in at least a portion (preferably monomer (1)) of the two or more monomers (A) contained in the resin composition of the present disclosure.

[0121] The manufacturing method of the present disclosure includes a step (forming step) of polymerizing the polymerizable monomers in the mixed solution to form a resin layer (D). In the forming step, the composition may be heated, for example, 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 types of monomers (A). The mixture may also contain the aforementioned polymerization initiators, such as an azo-based polymerization initiator or a peroxide-based polymerization initiator. The pressure used to polymerize the two or more types of monomers (A) is not particularly limited and may be atmospheric pressure of about 0.05 MPa to 0.15 MPa.

[0122] In the forming step, two or more kinds of monomers (A) may be polymerized by suspension polymerization. For example, the mixed solution and an aqueous liquid containing a solvent such as water may be stirred to disperse the mixed solution in the aqueous liquid, and the two or more kinds of monomers (A) in the mixed solution may be polymerized to form the resin layer (D). By carrying out suspension polymerization, it is easy to control the particle size of the flame retardant-containing particles, and particles with small variations in particle size, shape, etc. tend to be formed.

[0123] The flame retardant-containing particles obtained by the production method of the present disclosure include a resin layer (D) formed by polymerization of 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) may include one core portion made of a flame retardant and cover at least a portion of the core portion, or may include multiple core portions made of a flame retardant and cover at least a portion of the multiple core portions. The core portion may be entirely covered by the resin layer (D), or may be partially covered by the resin layer (D) with the remainder exposed from the resin layer (D).

[0124] The present disclosure will be described in more detail below with reference to examples, but the invention of the present disclosure is not limited to these examples. In the following examples, parts means parts by mass.

[0125] <Preparation of Electrolyte Solution> 100 parts each of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were placed in a flask, and the mixture was stirred with a magnetic stirrer to prepare a homogeneous electrolyte solution.

[0126] <Calculation method of elution rate> An emulsion solution containing only the resin layer was prepared, dried at room temperature for 24 hours, and then 0.5 parts of the sample dried at 100 ° C for 2 minutes was immersed in 10 parts of electrolyte for 16 hours at room temperature. After immersion, the electrolyte was filtered, and the filtrate was dried at 150 ° C for 3 hours. The amount of elution into the electrolyte was calculated by weighing the residue. The elution rate was calculated from the amount of elution into the electrolyte using the following formula.

[0127]

[0128] Example 1 An oil phase mixture and an aqueous solution were prepared with the following compositions. V-65 refers to 2,2'-azobis(2,4-dimethylvaleronitrile). The obtained oil phase mixture and aqueous solution were vigorously stirred to obtain an emulsion. The entire amount of the obtained emulsion was charged into a separable flask equipped with a stirrer and reflux condenser, while washing with 393.5 parts of distilled water. After purging with nitrogen gas, the temperature was raised to 55°C and polymerization was completed over 2 hours with stirring. A dispersion of flame retardant-containing particles with a solids content of 30.0% by mass was obtained. The average particle size of the obtained dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 88.6 parts n-butyl acrylate 6.4 parts methacrylic acid 5.0 parts heptane 10.0 parts V-65 1.5 parts Adekastab FP-900L (manufactured by ADEKA Corporation) 100.0 parts (Aqueous solution) Poval PVA-210 10.0 parts Distilled water 90.0 parts

[0129] Example 2 An emulsion solution with a solid content of 30.0% by mass was obtained in the same manner as in Example 1, except that the oil phase mixture was changed to the following composition. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 89.5 parts 2-ethylhexyl acrylate 5.5 parts Methacrylic acid 5.0 parts Heptane 10.0 parts V-65 1.5 parts Adeka STAB FP-900L (manufactured by ADEKA Corporation) 100.0 parts

[0130] Example 3 An emulsion solution with a solid content of 30.0% by mass was obtained in the same manner as in Example 1, except that the oil phase mixture was changed to the following composition. The average particle size of the obtained dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 92.0 parts 2-hydroxyethyl methacrylate 3.0 parts Methacrylic acid 5.0 parts Heptane 10.0 parts V-65 1.5 parts Adeka STAB FP-900L (manufactured by ADEKA Corporation) 100.0 parts

[0131] Example 4 An emulsion solution with a solid content of 30.0% by mass was obtained in the same manner as in Example 1, except that the oil phase mixture was changed to the following composition. The average particle size of the obtained dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 95.0 parts Methacrylic acid 5.0 parts Heptane 10.0 parts V-65 1.5 parts Adeka STAB FP-900L (manufactured by ADEKA Corporation) 100.0 parts

[0132] Example 5 An emulsion solution with a solid content of 30.0% by mass was obtained in the same manner as in Example 1, except that the oil phase mixture was changed to the following composition. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 95.0 parts Acrylic acid 5.0 parts Heptane 10.0 parts V-65 1.5 parts Adeka STAB FP-900L (manufactured by ADEKA Corporation) 100.0 parts

[0133] Example 6 An emulsion solution with a solid content of 30.0% by mass was obtained in the same manner as in Example 1, except that the oil phase mixture was changed to the following composition. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 70.0 parts n-butyl acrylate 25.0 parts Methacrylic acid 5.0 parts Heptane 10.0 parts V-65 1.5 parts Adeka STAB FP-900L (manufactured by ADEKA Corporation) 100.0 parts

[0134] Example 7 An emulsion solution having a solids content of 30.0% by mass was obtained in the same manner as in Example 1, except that the oil phase mixture was changed to the following composition. The average particle size of the resulting dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 64.9 parts Methyl methacrylate 5.9 parts n-butyl acrylate 14.2 parts Isobornyl methacrylate 10.0 parts Methacrylic acid 5.0 parts Heptane 10.0 parts V-65 1.5 parts Adeka STAB FP-900L (manufactured by ADEKA Corporation) 100.0 parts

[0135] Example 8 An emulsion solution with a solid content of 30.0% by mass was obtained in the same manner as in Example 1, except that the oil phase mixture was changed to the following composition. The average particle size of the obtained dispersion was 1.0 μm. (Oil phase mixture) n-butyl methacrylate 95.0 parts Methacrylic acid 5.0 parts Heptane 10.0 parts V-65 1.5 parts Adeka STAB FP-900L (manufactured by ADEKA Corporation) 100.0 parts

[0136] Comparative Example 1 An emulsion solution having a solids content of 30.0% by mass was obtained in the same manner as in Example 1, except that the oil phase mixture was changed to the following composition. The average particle size of the obtained dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 33.2 parts Methyl methacrylate 37.8 parts n-butyl acrylate 14.0 parts Isobornyl methacrylate 10.0 parts Methacrylic acid 5.0 parts Heptane 10.0 parts V-65 1.5 parts Adeka STAB FP-900L (manufactured by ADEKA Corporation) 100.0 parts

[0137] Comparative Example 2 An emulsion solution having a solids content of 30.0% by mass was obtained in the same manner as in Example 1, except that the oil phase mixture was changed to the following composition. The average particle size of the obtained dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 40.3 parts Methyl methacrylate 18.6 parts n-Butyl acrylate 16.1 parts Isobornyl methacrylate 20.0 parts Methacrylic acid 5.0 parts Heptane 10.0 parts V-65 1.5 parts Adeka STAB FP-900L (manufactured by ADEKA Corporation) 100.0 parts

[0138] Comparative Example 3 An emulsion solution having a solid content of 30.0% by mass was obtained in the same manner as in Example 1, except that the oil phase mixture was changed to the following composition. The average particle size of the obtained dispersion was 1.0 μm. (Oil phase mixture) Acrylonitrile 65.0 parts n-butyl acrylate 30.0 parts Methacrylic acid 5.0 parts Heptane 10.0 parts V-65 1.5 parts Adeka STAB FP-900L (manufactured by ADEKA Corporation) 100.0 parts

[0139] 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 aggregation occurred. (Oil phase mixture) Acrylonitrile 99.0 parts Methacrylic acid 1.0 part Heptane 10.0 parts V-65 1.5 parts Adeka STAB FP-900L (manufactured by ADEKA Corporation) 100.0 parts

[0140] Comparative Example 5 An emulsion solution with a solid content of 30.0% by mass was obtained in the same manner as in Example 1, except that the oil phase mixture was changed to the following composition. The average particle size of the obtained dispersion was 1.0 μm. (Oil phase mixture) Methyl acrylate 100.0 parts Heptane 10.0 parts V-65 1.5 parts Adeka STAB FP-900L (manufactured by ADEKA Corporation) 100.0 parts

[0141] <Confirmation of Flame Retardant-Containing Particles> The dispersions of flame retardant-containing particles obtained in Examples 1 to 8 were visually inspected to confirm that there was no separation or precipitation of the flame retardant-containing particles after polymerization of the monomer. This confirmed that the flame retardant was encapsulated in the flame retardant-containing particles. Note that if the flame retardant is not encapsulated in the particles, phenomena such as "aggregation during polymerization," "separation or precipitation of the flame retardant at the bottom of the flask," and "adhesion of a viscous liquid to the surface of a glass plate after dripping the dispersion onto the glass plate and rinsing with water" may occur.

[0142] The compositions of the oil phase mixtures of Examples 1 to 8 and Comparative Examples 1 to 5 are summarized in Table 1.

[0143]

[0144] The abbreviations in Table 1 are as follows: AN: acrylonitrile, MMA: methyl methacrylate, BMA: n-butyl methacrylate, BA: n-butyl acrylate, 2EHA: 2-ethylhexyl acrylate, HEMA: 2-hydroxyethyl methacrylate, IBX: isobornyl methacrylate, MA: methyl acrylate, Mac: methacrylic acid, Aac: acrylic acid, V-65: 2,2'-azobis(2,4-dimethylvaleronitrile), FP-900L: Adeka Stab FP-900L manufactured by ADEKA Corporation, PVA-210: Poval PVA-210 manufactured by Kuraray Co., Ltd.

[0145] Example 9 65% by mass (solid content equivalent) of the flame retardant-containing particles obtained in Example 1 and 2% by mass of carboxymethyl cellulose (Cellogen 6, Dai-ichi Kogyo Seiyaku Co., Ltd.), a water-soluble resin, were mixed using a planetary mixer, and then alumina (Al ２ O ３ 30% by mass of water was added and the powder was further stirred. Thereafter, water as a solvent was added so that the mass ratio after drying would be 45% by mass, and the mixture was uniformly dispersed using a planetary mixer. Styrene-butadiene rubber (2001, manufactured by Nippon Zeon Co., Ltd.) was added so that the mass ratio after drying would be 4% by mass to prepare a self-extinguishing layer coating liquid.

[0146] <Preparation of Fire Extinguisher Sheet> The self-extinguishing layer coating liquid was applied to a 150 μm substrate using a bar coater so that the coating thickness after drying would be 150 μm or more, and the coating was dried at 60° C. for 30 minutes to form a self-extinguishing layer on the substrate, thereby preparing a fire extinguisher sheet. In Example 1, a PPS (polyphenylene sulfide) substrate was used.

[0147] <Preparation of Negative Electrode> 95 parts by mass of graphite as a negative electrode active material, 1 part by mass of SBR (styrene-butadiene rubber) as a binder, 1 part by mass of carboxymethyl cellulose (CMC) as a thickener, and 100 parts by mass of water as a solvent were mixed to prepare a negative electrode slurry. Next, a 10 μm thick copper foil (porous foil) was used as a negative electrode current collector, and a graphite slurry having a mass of 4 mg / cm after drying was prepared. ２ The negative electrode slurry was applied to a negative electrode current collector so as to obtain the following, and then dried to prepare a negative electrode.

[0148] <Preparation of Positive Electrode> 90 parts by mass of powdered activated carbon as a positive electrode active material, 6 parts by mass of polyacrylic acid (sodium neutralized 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 were mixed to prepare a positive electrode slurry. Next, a 15 μm thick aluminum foil (porous foil) was used as a positive electrode current collector, and the positive electrode slurry was dried so that the mass of the activated carbon was 4 mg / cm. ２ The positive electrode current collector was coated with the above-mentioned solution and dried to prepare a positive electrode.

[0149] <Preparation of Secondary Battery> The positive electrode and negative electrode prepared as described above were each punched out to form a rectangle measuring 60 mm × 40 mm, and the slurry coating film was peeled off from a 20 mm × 40 mm region on one end of the long side, leaving a 40 mm × 40 mm area of ​​the slurry coating film, and an electrode terminal was attached. The entire battery element, excluding the end of the battery element where the electrode terminal was attached and the other end opposite to that end, was wrapped in the fire-extinguishing sheet, and the positive electrode, separator, and negative electrode were fixed.

[0150] Examples 10 and 11 Fire extinguishing sheets and secondary batteries were produced in the same manner as in Example 9, except that the types and amounts of the components used in <Preparation of self-extinguishing layer coating liquid> were changed as shown in Table 2, and the composition and thickness of the substrate and the thickness of the coating film after drying in <Preparation of fire extinguishing sheet> were changed as shown in Table 2. PET means a polyethylene terephthalate substrate.

[0151] Comparative Example 6 A fire-extinguishing sheet was produced in the same manner as in Example 9, and a secondary battery was also produced, except that in the preparation of the self-extinguishing layer coating solution of Example 9, a fire-extinguishing agent (MPP, melamine polyphosphate) was used instead of the flame-retardant-containing particles, and the amounts of each component used were changed as shown in Table 2. In Comparative Example 6, Dispersant 5468 (San Nopco, ammonium polycarboxylate) was used as the surfactant in the preparation of the self-extinguishing layer coating solution. PP / L-190 refers to a polypropylene substrate containing a mixture of a halogen-based flame retardant and antimony trioxide in an amount of 10% to 30% by mass relative to the entire substrate.

[0152] Comparative Examples 7 and 8 Secondary batteries were fabricated in the same manner as in Example 9, except that no fire-extinguishing sheet was used and 10% by mass or 20% by mass of ADK STAB FP-900L, a viscous liquid, was added to the electrolyte solution.

[0153] <Charge / Discharge Test> A charge / discharge test was performed on the secondary batteries prepared in each Example and Comparative Example 1 under the following conditions. First, the secondary battery was placed in a thermostatic chamber set at 25°C and charged to 4.2 V at 0.2 C using CC-CV (constant current-constant voltage) charging. The discharge capacity was measured when the secondary battery was discharged to 3.0 V at 0.2 C, and this was taken as the initial capacity [Ah / g]. Next, the current and voltage during short-term discharge at 100%, 90%, and 50% charge were measured, and this data was plotted with current / A on the horizontal axis and voltage / V on the vertical axis. The slope of this data was calculated as DC resistance / Ω, which was taken as the internal resistance of the secondary battery. Furthermore, when the internal resistance was 3.00 Ω or less, the rate characteristics were considered to be good (evaluation A), and when the internal resistance was greater than 3.00 Ω, the rate characteristics were considered to be poor (evaluation B).

[0154] <Multiple Explosion Test> After adjusting the 1 Ah secondary batteries prepared in each Example and Comparative Example 1 to 100% SOC, three secondary batteries were stacked and secured at both ends 10 mm apart with Kapton tape. The assembled secondary batteries were sandwiched between a Bakelite jig with a 5 mm diameter hole drilled in the center. A 3 mm diameter nail with a triangular pyramid tip was used to drive the outermost secondary battery into thermal runaway at a nail insertion speed of 1 mm / min, and the heat generation initiation delay time and maximum heat generation temperature of the adjacent secondary batteries were measured. The results are shown in Table 2.

[0155]

[0156] As shown in Table 2, the results of the charge / discharge test in each example were equal to or better than those in Comparative Example 1, and the internal resistance was suppressed. The reason for this is presumably that the suppression of elution of the resin layer into the electrolyte also suppresses the elution of the flame retardant, thereby maintaining the battery characteristics.

[0157] The 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 in their entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. 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), the particles (C) including a resin layer (D) formed by polymerization of the two or more monomers (A), the elution rate of the resin layer (D) in an electrolyte solution being 40 mass% or less.

2. The flame retardant-containing particle according to 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 a monomer (1) capable of dissolving 70% by mass or more and less than 99% by mass of a phosphorus-based flame retardant (B), a content of a monomer (2) having an acidic group being 0% by mass to 10% by mass, a content of a monomer (3) other than the monomers (1) and (2) being 0% by mass to 25% by mass, and a proportion of methyl methacrylate contained in the monomer (1) being 50% by mass or less based on the total amount of the monomer (1).

4. The resin composition according to claim 3, which is used to form a resin layer (D) which covers at least a part of the phosphorus-based flame retardant (B).

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

6. A resin composition according to any one of claims 3 to 5, wherein the monomer (2) is at least one selected from the group 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. A flame retardant-containing particle comprising: the phosphorus-based flame retardant (B); and a resin layer (D) formed from the resin composition according to any one of claims 3 to 7, the resin layer (D) covering at least a portion of the phosphorus-based flame retardant (B).

9. A flame-retardant coating material comprising the flame-retardant-containing particles according to any one of claims 1, 2 and 8.

10. A laminate comprising the flame retardant-containing particles according to any one of claims 1, 2 and 8.

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

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

13. A method for producing flame retardant-containing particles as described in claim 11 or 12, wherein in the step of forming the resin layer (D), the monomer (A) is suspension polymerized to form the resin layer (D).

14. A fire-extinguishing sheet comprising: a base layer; and a self-extinguishing layer containing fire-extinguishing agent-carrying particles including a fire-extinguishing agent and a resin layer covering at least a portion of the fire-extinguishing agent.

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

16. The fire-extinguishing sheet according to claim 14 or 15, wherein the self-extinguishing layer further contains an inorganic filler.

17. A fire-extinguishing sheet according to any one of claims 14 to 16, wherein the fire-extinguishing agent contains a phosphorus-based flame retardant.

18. A fire extinguishing sheet as described in any one of claims 14 to 17, wherein the content of the phosphorus-based flame retardant is 50% by mass to 100% by mass based on the total amount of the fire extinguishing agent.

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

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

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