Binder resin composition, slurry composition, separator and lithium ion battery

Abstract

To provide a binder resin composition for lithium ion battery separator capable of realizing a lithium ion battery which is capable of discharging a redox shuttle agent into an electrolyte when a temperature rises, a slurry composition, a separator and the lithium ion battery which is capable of discharging the redox shuttle agent into the electrolyte when the temperature rises.SOLUTION: The present invention relates to: [1] a binder resin composition for lithium ion battery separator containing a binder resin and a redox shuttle agent; [2] a slurry composition for lithium ion battery separator containing a binder resin composition described in [1] and an inorganic filler; [3] a separator for lithium ion battery comprising a separator substrate and a functional layer disposed on at least one surface of the separator substrate and formed from the binder resin composition described in [1] or the slurry composition described in [2]; and [4] a lithium ion battery comprising a cathode, an anode, an electrolyte and a separator disposed between the cathode and the anode, wherein the separator includes the separator described in [3].SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a binder resin composition, a slurry composition, a separator, and a lithium ion battery. [Background technology]

[0002] In lithium-ion batteries, redox shuttle agents are sometimes added to the electrolyte to improve safety. Redox shuttle agents are a type of oxidation-reduction reagent that, during overcharge, shuttling between the positive and negative electrodes consumes the overcharge current through a chemical reaction, thereby establishing an overcharge suppression mechanism. Examples of techniques relating to such redox shuttle agents include those disclosed in Patent Documents 1 and 2.

[0003] Patent Document 1 (JP 9-17447 A) describes a non-aqueous electrolyte secondary battery that uses a metal mainly composed of lithium or a carbon material capable of doping and dedoping lithium for the negative electrode and a composite oxide of lithium and a transition metal for the positive electrode, and that is characterized in that the non-aqueous electrolyte secondary battery contains an organic compound having a structure in which two methoxy groups and a halogen group are introduced into a benzene ring. The battery is capable of providing overcharge protection for lithium secondary batteries (nonaqueous electrolyte secondary batteries) with high energy density and voltages of 4 V or more at low cost and without a protective device that reduces energy density.

[0004] Patent Document 2 (JP 2009-514149 A) ​​describes that by adding one or more compounds selected from the group consisting of vinylene carbonates, ethylene carbonates, cyclic sulfites, and unsaturated sultones to an electrolyte, it is possible to suppress the reaction between a redox shuttle agent in the electrolyte and the negative electrode, thereby improving the life of the redox shuttle agent that circulates through an oxidation-reduction reaction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-17447 [Patent Document 2] Special Publication No. 2009-514149 Summary of the Invention [Problem to be solved by the invention]

[0006] The redox shuttle agent in the electrolyte may react with the negative electrode and become inactive (see Patent Document 2). Therefore, there is a demand for a lithium-ion battery that can release the redox shuttle agent into the electrolyte when the battery reaches a high temperature, such as during overcharging.

[0007] The present invention has been made in view of the above circumstances, and provides a binder resin composition for a lithium ion battery separator, a slurry composition, and a separator, which can realize a lithium ion battery that can release a redox shuttle agent into an electrolyte solution when exposed to high temperatures, as well as a lithium ion battery that can release a redox shuttle agent into an electrolyte solution when exposed to high temperatures. [Means for solving the problem]

[0008] According to the present invention, there are provided a binder resin composition, a slurry composition, a separator, and a lithium ion battery as described below.

[0009] [1] A binder resin, A redox shuttle agent; A binder resin composition for a lithium ion battery separator, comprising: [2] further comprising an aqueous medium; the binder resin is dispersed in the aqueous medium in the form of particles, The binder resin composition according to [1] above, wherein the redox shuttle agent is contained in particles of the binder resin. [3] The binder resin composition according to [1] or [2] above, wherein the binder resin is an emulsion particle. [4] The binder resin composition according to any one of [1] to [3], wherein the redox shuttle agent comprises a compound having a structure in which at least one functional group selected from the group consisting of a hydroxy group and an alkoxy group is introduced into a benzene ring. [5] The binder resin composition according to any one of [1] to [4] above, wherein the redox shuttle agent comprises a compound represented by the following formula (1): [ka] (In the formula (1), R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently a hydrogen atom, a hydroxy group, a halogen atom, an aryl group, an alkyl group having 1 to 4 carbon atoms, a fluorine-substituted alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a fluorine-substituted alkoxy group having 1 to 4 carbon atoms, and at least one of these substituents is a hydroxy group or an alkoxy group. [6] The binder resin composition according to any one of [1] to [5] above, wherein the redox shuttle agent comprises at least one selected from the group consisting of tert-butylcatechol, hydroquinone monomethyl ether, hydroquinone, and dibutylhydroxytoluene. [7] The binder resin composition according to any one of [1] to [6], wherein the binder resin comprises at least one selected from the group consisting of an aliphatic conjugated diene / aromatic monovinyl copolymer, a (meth)acrylic polymer, a fluorine-containing polymer, a (meth)acrylic acid / (meth)acrylamide copolymer, a (meth)acrylonitrile polymer, and an aromatic monovinyl / (meth)acrylic copolymer. [8] A slurry composition for a lithium ion battery separator, comprising the binder resin composition according to any one of [1] to [7] above and an inorganic filler. [9] A separator substrate; a functional layer formed from the binder resin composition according to any one of [1] to [7] above or the slurry composition according to [8] above, which is disposed on at least one surface of the separator substrate; A separator for a lithium ion battery comprising:

[10] a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode; A lithium ion battery, wherein the separator comprises the separator according to [9]. [Effects of the Invention]

[0010] The present invention provides a binder resin composition for a lithium ion battery separator, a slurry composition, and a separator that can realize a lithium ion battery that can release a redox shuttle agent into an electrolyte solution when the temperature becomes high, as well as a lithium ion battery that can release a redox shuttle agent into an electrolyte solution when the temperature becomes high. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described. In this specification, unless otherwise specified, the symbol "to" in a numerical range indicates a range from above to below.

[0012] [Binder resin composition] The binder resin composition of the present invention is a binder resin composition for a lithium ion battery separator, which contains a binder resin and a redox shuttle agent. The binder resin composition of the present invention makes it possible to realize a lithium ion battery that can release a redox shuttle agent into the electrolyte when exposed to high temperatures. The reason why such an effect is obtained is presumed to be as follows.

[0013] First, a lithium ion battery generally includes a positive electrode, a negative electrode, and a separator that separates the positive electrode from the negative electrode to prevent short-circuiting between the positive electrode and the negative electrode. The binder resin composition according to the present invention can be used to form a functional layer that improves the mechanical strength, binding property, heat resistance, and other properties of the separator in the lithium ion battery. When the lithium ion battery reaches a high temperature, the binder resin in the functional layer formed from the binder resin composition softens, and the redox shuttle agent contained in the functional layer made of the binder resin composition is released into the electrolyte solution. In this way, the binder resin composition of the present invention can realize a lithium ion battery that can release a redox shuttle agent into the electrolyte when the temperature becomes high.

[0014] Hereinafter, each component constituting the binder resin composition according to the present invention will be described.

[0015] (binder resin) The binder resin is a component that imparts binding properties to the functional layer formed on the separator substrate using the binder resin composition or slurry composition, that prevents components such as inorganic fillers from being detached from the functional layer, and that enables the battery components to be bonded together via the functional layer.

[0016] The binder resin is not particularly limited as long as it can be used in a lithium ion battery, but a polymer obtained by polymerizing a monomer composition containing a monomer that can exhibit binding properties is preferred, and an addition polymer obtained by addition polymerization is more preferred. Such polymers include aliphatic conjugated diene / aromatic monovinyl copolymers (polymers mainly containing aliphatic conjugated diene monomer units and aromatic monovinyl monomer units), (meth)acrylic polymers (polymers mainly containing (meth)acrylic acid alkyl ester monomer units), fluorine-containing polymers (polymers mainly containing fluorine-containing monomer units), (meth)acrylic acid / (meth)acrylamide copolymers (polymers mainly containing (meth)acrylic acid units and (meth)acrylamide units), (meth)acrylonitrile polymers (polymers mainly containing (meth)acrylonitrile units), and aromatic monovinyl / (meth)acrylic acid copolymers. p) At least one selected from the group consisting of acrylic copolymers (polymers mainly containing aromatic monovinyl monomer units and (meth)acrylic acid alkyl ester monomer units) is preferred, at least one selected from the group consisting of aliphatic conjugated diene / aromatic monovinyl copolymers, (meth)acrylic acid / (meth)acrylamide copolymers, (meth)acrylonitrile polymers, and (meth)acrylic polymers is more preferred, and at least one selected from the group consisting of aliphatic conjugated diene / aromatic monovinyl copolymers, (meth)acrylonitrile polymers, and (meth)acrylic polymers is even more preferred. Here, the aliphatic conjugated diene monomer capable of forming an aliphatic conjugated diene monomer unit, the aromatic monovinyl monomer capable of forming an aromatic monovinyl monomer unit, the (meth)acrylic acid alkyl ester monomer capable of forming a (meth)acrylic acid alkyl ester monomer unit, and the fluorine-containing monomer capable of forming a fluorine-containing monomer unit are not particularly limited, and for example, various known monomers used as monomers for forming binder resins can be used. As used herein, "(meth)acrylic" means acrylic and / or methacrylic, "(meth)acrylo" means acrylo and / or methacrylo, "(meth)acrylate" means acrylate and / or methacrylate, and "(meth)allyl" means allyl and / or methallyl. In addition, in this specification, "containing a monomer unit" means that "a polymer obtained using that monomer contains a structural unit derived from the monomer." In this specification, "mainly comprising" a monomer unit means that the content ratio of that monomer unit is the highest, and "mainly comprising" multiple types of monomer units means that "when the amount of all repeating units contained in the polymer is 100 mass%, the total content ratio of the multiple types of monomer units exceeds 50 mass%." In this specification, the content ratio of various monomer units (repeating units) in a polymer is expressed as 1 H-NMR and 13 It can be measured using a nuclear magnetic resonance (NMR) method such as C-NMR.

[0017] Examples of the aliphatic conjugated diene / aromatic monovinyl copolymer include butadiene / styrene copolymer rubber and acrylonitrile / butadiene / styrene copolymer rubber. Examples of fluorine-based polymers include polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene copolymer, and fluorine rubber.

[0018] The polymer used as the binder resin preferably contains a functional group from the viewpoint of improving binding properties. From the viewpoint of improving the binding strength of the functional layer and the rate characteristics of the lithium ion battery, the functional group contained in the binder resin is preferably at least one functional group selected from the group consisting of a carboxylic acid group, a hydroxyl group, an amino group, an epoxy group, an oxazoline group, a sulfonic acid group, a nitrile group, and an amide group, more preferably at least one functional group selected from the group consisting of a carboxylic acid group, a hydroxyl group, an amino group, an epoxy group, a nitrile group, and an amide group, and even more preferably at least one functional group selected from the group consisting of a carboxylic acid group, an epoxy group, and a nitrile group. These functional groups may be used alone or in combination of two or more in any ratio. The polymer having two or more types of functional groups is not particularly limited, but examples thereof include a polymer having an epoxy group and a nitrile group; a polymer having a carboxylic acid group and a nitrile group; a polymer having a carboxylic acid group and a hydroxyl group; a polymer having a carboxylic acid group and an amide group; a polymer having a carboxylic acid group, a nitrile group, and an amino group; and a polymer having a carboxylic acid group, an epoxy group, a hydroxyl group, and a nitrile group.

[0019] The method for introducing the specific functional group into a polymer is not particularly limited. A polymer containing the functional group-containing monomer unit described above may be obtained by preparing a polymer using a monomer containing the functional group described above, or a polymer having the functional group described above at its terminal may be obtained by terminal-modifying any polymer.

[0020] Here, examples of the carboxylic acid group-containing monomer capable of forming the carboxylic acid group-containing monomer unit include monocarboxylic acids and derivatives thereof, dicarboxylic acids and acid anhydrides thereof and derivatives thereof. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of the monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and the like. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters such as nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate. Examples of the acid anhydrides of dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Furthermore, as the carboxylic acid group-containing monomer, for example, an acid anhydride that generates a carboxylic acid group by hydrolysis can also be used. Among these, acrylic acid and methacrylic acid are preferred as the carboxylic acid group-containing monomer. The carboxylic acid group-containing monomer may be used alone or in combination of two or more kinds in any ratio.

[0021] Examples of hydroxyl group-containing monomers capable of forming hydroxyl group-containing monomer units include ethylenically unsaturated alcohols such as (meth)allyl alcohol, 3-butene-1-ol, and 5-hexene-1-ol; alkanol esters of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, and di-2-hydroxypropyl itaconate; and esters of ethylenically unsaturated carboxylic acids having the general formula: CH═CR a -COO-(C q H 2q O) p -H (wherein p is an integer of 2 to 9, q is an integer of 2 to 4, R arepresents a hydrogen atom or a methyl group) and (meth)acrylic acid esters; mono(meth)acrylic acid esters of dihydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2'-(meth)acryloyloxyphthalate and 2-hydroxyethyl-2'-(meth)acryloyloxysuccinate; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; mono(meth)allyl ethers of alkylene glycols such as (meth)allyl-2-hydroxyethyl ether, (meth)allyl-2-hydroxypropyl ether, (meth)allyl-3-hydroxypropyl ether, (meth)allyl-2-hydroxybutyl ether, (meth)allyl-3-hydroxybutyl ether, (meth)allyl-4-hydroxybutyl ether, and (meth)allyl-6-hydroxyhexyl ether; diethylene glycol mono(meth)allyl ether, dipropyl Examples of the hydroxyl group-containing monomer include polyoxyalkylene glycol mono(meth)allyl ethers such as ethylene glycol mono(meth)allyl ether; mono(meth)allyl ethers of halogen- and hydroxy-substituted (poly)alkylene glycols such as glycerin mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether, and (meth)allyl-2-hydroxy-3-chloropropyl ether; mono(meth)allyl ethers of polyhydric phenols such as eugenol and isoeugenol and their halogen-substituted derivatives; (meth)allyl thioethers of alkylene glycols such as (meth)allyl-2-hydroxyethyl thioether and (meth)allyl-2-hydroxypropyl thioether; and amides having a hydroxyl group such as N-hydroxymethylacrylamide (N-methylolacrylamide), N-hydroxymethylmethacrylamide, N-hydroxyethylacrylamide, and N-hydroxyethylmethacrylamide. The hydroxyl group-containing monomer may be used alone or in combination of two or more in any ratio.

[0022] Examples of amino group-containing monomers capable of forming amino group-containing monomer units include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, aminoethyl vinyl ether, dimethylaminoethyl vinyl ether, etc. The amino group-containing monomers may be used alone or in combination of two or more at any ratio.

[0023] Examples of epoxy group-containing monomers capable of forming epoxy group-containing monomer units include monomers containing a carbon-carbon double bond and an epoxy group. Examples of monomers containing a carbon-carbon double bond and an epoxy group include unsaturated glycidyl ethers such as vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, and o-allylphenyl glycidyl ether; diene or polyene monoepoxides such as butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, and 1,2-epoxy-5,9-cyclododecadiene; and 3,4-epoxy-1-butene. glycidyl esters of unsaturated carboxylic acids such as glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl 4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl 4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexenecarboxylic acid, and glycidyl ester of 4-methyl-3-cyclohexenecarboxylic acid. The epoxy group-containing monomer may be used alone or in combination of two or more kinds in any ratio.

[0024] Examples of oxazoline group-containing monomers capable of forming oxazoline group-containing monomer units include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, etc. The oxazoline group-containing monomers may be used alone or in combination of two or more in any ratio.

[0025] Examples of sulfonic acid group-containing monomers capable of forming sulfonic acid group-containing monomer units include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, etc. The sulfonic acid group-containing monomers may be used alone or in combination of two or more at any ratio.

[0026] Examples of nitrile group-containing monomers capable of forming nitrile group-containing monomer units include α,β-ethylenically unsaturated nitrile monomers. Specifically, the α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group, and examples thereof include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. One type of nitrile group-containing monomer may be used alone, or two or more types may be used in combination at any ratio.

[0027] Examples of the amide group-containing monomer capable of forming the amide group-containing monomer unit include acrylamide, methacrylamide, etc. The amide group-containing monomer may be used alone or in combination of two or more kinds in any ratio.

[0028] The binder resin composition of the present invention preferably further comprises an aqueous medium in which the binder resin is dispersed in particulate form, thereby further suppressing the redox shuttle agent from leaching into the electrolyte during use or storage, since the redox shuttle agent is contained in the binder resin particles.

[0029] The method for preparing the polymer as a binder resin is not particularly limited. The polymer as a binder resin is produced, for example, by polymerizing a monomer composition containing the above-mentioned monomers in an aqueous solvent. The content ratio of each monomer in the monomer composition can be determined based on the content ratio of the desired monomer unit (repeating unit) in the polymer. The polymerization method is not particularly limited, and any of solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used. The polymerization reaction can be any of ionic polymerization, radical polymerization, living radical polymerization, various condensation polymerizations, addition polymerization, etc. An emulsifier or a polymerization initiator can be used during the polymerization, if necessary. Among these, the binder resin is preferably produced by emulsion polymerization, which allows the binder resin to be obtained in the form of latex particles. The binder resin is preferably in the form of emulsion particles, and is preferably dispersed in an aqueous medium to be used as an aqueous emulsion solution.

[0030] The volume average particle diameter of the binder resin according to the present invention is preferably 10 nm or more, more preferably 30 nm or more, even more preferably 50 nm or more, even more preferably 100 nm or more, and even more preferably 130 nm or more from the viewpoint of improving binding properties, and is preferably 1000 nm or less, more preferably 600 nm or less, even more preferably 400 nm or less, even more preferably 200 nm or less, and even more preferably 170 nm or less from the viewpoint of improving the rate characteristics of lithium ion batteries. The volume-average particle diameter is the particle diameter D at which the cumulative volume calculated from the smallest diameter side becomes 50% in the particle diameter distribution (volume basis) measured using a laser diffraction particle size distribution analyzer. 50 can be adopted.

[0031] The binder resin according to the present invention has a glass transition temperature of preferably −50° C. or higher, more preferably −40° C. or higher, and even more preferably −30° C. or higher, from the viewpoint of suppressing elution of the redox shuttle agent into the electrolyte during use or storage, and preferably 150° C. or lower, more preferably 100° C. or lower, and even more preferably 80° C. or lower, from the viewpoint of improving elution of the redox shuttle agent into the electrolyte at high temperatures. In this specification, the "glass transition temperature" can be measured using the method described in the examples.

[0032] The content of the binder resin in the binder resin composition according to the present invention, when the total amount of the binder resin and redox shuttle agent is taken as 100 parts by mass, is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, even more preferably 90 parts by mass or more, even more preferably 95 parts by mass or more, and even more preferably 97 parts by mass or more, from the viewpoint of improving binding strength; and is preferably 99.99 parts by mass or less, more preferably 99.9 parts by mass or less, even more preferably 99.7 parts by mass or less, and even more preferably 99.5 parts by mass or less, from the viewpoint of suppressing a decrease in ionic conductivity and suppressing effects on battery characteristics such as input / output characteristics and battery life.

[0033] (redox shuttle agent) The redox shuttle agent is preferably a compound having a reversible oxidation-reduction potential, the value of which is close to the desired overcharge potential. Here, "having a reversible oxidation-reduction potential" means that irreversible reactions such as decomposition or polymerization of the compound are unlikely to occur at the electrode, and the compound undergoes repeated reactions of alternating between its oxidized and reduced forms. In this specification, the term "reversible oxidation-reduction potential" refers to a potential determined by cyclic voltammetry (CV) measurements. The "overcharge potential to be set" varies depending on the type of positive electrode active material and is determined by each battery manufacturer within a range that does not cause irreversible reactions such as decomposition of the nonaqueous electrolyte. For example, for lithium-ion batteries using LiCoO2 for the positive electrode and graphite for the negative electrode, it is often set to approximately 4.2 to 4.4 V; for lithium-ion batteries using Li2Mn2O4 for the positive electrode and graphite for the negative electrode, it is often set to approximately 4.0 to 4.2 V; and for lithium-ion batteries using LiFePO4 for the positive electrode and graphite for the negative electrode, it is often set to approximately 3.6 to 3.8 V. Furthermore, "in the vicinity" is preferably ±0.05 V from the overcharge potential to be set.

[0034] From the viewpoint of improving diffusibility in the electrolyte, the molecular weight of the redox shuttle agent is preferably 100 or more, more preferably 110 or more, even more preferably 120 or more, and is preferably 500 or less, more preferably 400 or less, even more preferably 300 or less, even more preferably 250 or less, even more preferably 200 or less.

[0035] As the redox shuttle agent, a compound having a structure in which at least one functional group selected from the group consisting of a hydroxy group and an alkoxy group is introduced into a benzene ring is preferred, and a compound represented by the following formula (1) is more preferred.

[0036] [ka] Here, in the formula (1), R 1 , R 2 , R 3 , R 4 , R 5 and R 6 (Hereinafter referred to as “R 1 ~R 6") are each independently a hydrogen atom, a hydroxy group, a halogen atom, an aryl group, an alkyl group having 1 to 4 carbon atoms, a fluorine-substituted alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a fluorine-substituted alkoxy group having 1 to 4 carbon atoms, and at least one of these substituents is a hydroxy group or an alkoxy group.

[0037] Examples of halogen atoms include fluorine, chlorine, bromine, and iodine atoms. Examples of aryl groups include phenyl groups. Examples of alkyl groups having 1 to 4 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and tert-butyl groups. Examples of fluorine-substituted alkyl groups having 1 to 4 carbon atoms include trifluoromethyl groups. Examples of alkoxy groups having 1 to 4 carbon atoms include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, and tert-butoxy groups. Examples of fluorine-substituted alkoxy groups having 1 to 4 carbon atoms include monofluoromethoxy, difluoromethoxy, 2,2,2-trifluoroethoxy, and 2,2,3,3-tetrafluoropropoxy groups. The substituents may be any combination of these substituents.

[0038] Among the compounds represented by the formula (1), at least one selected from the group consisting of tert-butylcatechol, hydroquinone monomethyl ether, hydroquinone, and dibutylhydroxytoluene is preferred.

[0039] The content of the redox shuttle agent in the binder resin composition according to the present invention, when the total amount of the binder resin and redox shuttle agent is taken as 100 parts by mass, is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, from the viewpoint of improving the overcharge prevention effect due to the circulation action of the redox reaction; and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, from the viewpoint of suppressing a decrease in ionic conductivity and suppressing the effects on battery characteristics such as input / output characteristics and battery life.

[0040] (aqueous medium) The aqueous medium according to the present invention is not particularly limited as long as it can disperse the binder resin, but examples thereof include distilled water, ion-exchanged water, city water, and industrial water. Among these, distilled water and ion-exchanged water are preferred. Furthermore, water may be mixed with a solvent that is highly hydrophilic to water, such as alcohol.

[0041] The total content of the binder resin and redox shuttle agent in the binder resin composition according to the present invention, when the entire binder resin composition according to the present invention is taken as 100% by mass, is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less.

[0042] The pH value of the binder resin composition according to the present invention is, for example, 4 or more and 9 or less, from the viewpoint of improving storage stability.

[0043] (Other ingredients) The binder resin composition of the present invention may contain components other than the binder resin, redox shuttle agent, and aqueous medium, such as an organic solvent, a thickener, and a pH adjuster, as long as the effects of the present invention are not impaired. These additives may be used singly or in combination of two or more.

[0044] The method for preparing the binder resin composition according to the present invention is not particularly limited, but for example, it can be prepared by polymerizing a binder resin in the presence of an aqueous medium and a redox shuttle agent.

[0045] [Slurry Composition] The slurry composition according to the present invention is a slurry composition for a lithium ion battery separator, which contains the binder resin composition according to the present invention described above and an inorganic filler. The slurry composition according to the present invention can be used to form a functional layer that improves the mechanical strength, binding property, heat resistance, etc. of the separator in a lithium ion battery. That is, the functional layer according to the present invention is formed from the binder resin composition according to the present invention or the slurry composition according to the present invention.

[0046] (inorganic filler) Examples of inorganic fillers include oxides such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitrides such as silicon nitride, titanium nitride, and boron nitride; carbides such as silicon carbide and calcium carbonate; sulfates such as magnesium sulfate and aluminum sulfate; hydroxides such as aluminum hydroxide and aluminum oxide hydroxide; talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, and glass; and potassium titanate, among which oxides and hydroxides are preferred, and aluminum oxide and aluminum hydroxide are more preferred.

[0047] The content of the inorganic filler in the slurry composition according to the present invention is, for example, 50 parts by mass or more and 99.7 parts by mass or less, when the total of the binder resin and the inorganic filler is 100 parts by mass.

[0048] (Other ingredients) The slurry composition of the present invention may contain components other than the binder resin composition of the present invention and the inorganic filler, as long as the effects of the present invention are not impaired. Examples of other components include dispersants, organic solvents, thickeners, wetting agents, antifoaming agents, foaming agents, pH adjusters, flame retardants, organic fine particles, other polymers having different compositions and properties from the binder resin, wetting agents, viscosity adjusters, electrolyte additives, and other additives that can be added to the functional layer. These additives may be used singly or in combination of two or more.

[0049] The method for preparing the slurry composition according to the present invention is not particularly limited, and the slurry composition can be prepared by mixing the above-mentioned components.

[0050] [Separator] The separator according to the present invention is a separator for a lithium-ion battery, comprising: a separator substrate; and a functional layer formed from the binder resin composition or slurry composition according to the present invention described above, which is disposed on at least one surface of the separator substrate. The separator according to the present invention has a functional layer formed from the binder resin composition or slurry composition according to the present invention, and therefore can release the redox shuttle agent in the functional layer into the electrolyte when the lithium ion battery reaches a high temperature.

[0051] (separator substrate) The separator substrate is not particularly limited, but examples thereof include organic separator substrates and inorganic separator substrates, with organic separator substrates being preferred. The organic separator substrate is a porous member made of an organic material, and from the viewpoint of improving strength, is preferably a microporous membrane or nonwoven fabric containing a polyolefin resin such as polyethylene or polypropylene, or an aromatic polyamide resin, more preferably a microporous membrane or nonwoven fabric made of a polyolefin resin, and even more preferably a microporous membrane or nonwoven fabric made of polyethylene.

[0052] The thickness of the separator substrate is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more from the viewpoint of improving strength, and is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less from the viewpoint of improving the rate characteristics of the lithium ion battery.

[0053] As described above, the functional layer is formed from the binder resin composition or the slurry composition according to the present invention. Since each component contained in the functional layer is the same as that contained in the binder resin composition or slurry composition of the present invention, excluding volatile components such as solvents, the suitable content of each component is the same as the suitable content of each component in the binder resin composition or slurry composition of the present invention.

[0054] Examples of methods for forming a functional layer on a separator substrate include a method in which the binder resin composition or slurry composition according to the present invention is applied to the surface of the separator substrate and then dried; a method in which the separator substrate is immersed in the binder resin composition or slurry composition according to the present invention and then dried; and a method in which the binder resin composition or slurry composition according to the present invention is applied to a release substrate and dried to produce a functional layer, and the obtained functional layer is transferred to the surface of the substrate.

[0055] The thickness of the functional layer is preferably 0.1 μm or more, more preferably 1 μm or more, and even more preferably 3 μm or more from the viewpoint of improving functions such as mechanical strength, binding property, and heat resistance, and is preferably 10 μm or less, more preferably 8 μm or less from the viewpoint of improving the rate characteristics of the lithium ion battery.

[0056] [Lithium-ion battery] The lithium-ion battery according to the present invention includes a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode, the separator including the separator according to the present invention. The lithium-ion battery according to the present invention includes a separator having a functional layer formed from the binder resin composition or slurry composition according to the present invention. Therefore, when the lithium-ion battery reaches high temperatures, the redox shuttle agent in the functional layer can be released into the electrolyte. Therefore, the lithium-ion battery according to the present invention can prevent the redox shuttle agent in the electrolyte from reacting with the negative electrode and becoming inactive during use or storage.

[0057] (positive and negative electrodes) The positive electrode and negative electrode are not particularly limited, and positive electrodes and negative electrodes for lithium ion batteries can be used. Examples of the positive electrode include an electrode including a positive electrode current collector and a positive electrode active material laminated on the positive electrode current collector. Examples of the positive electrode current collector include aluminum foil, titanium foil, stainless steel foil, nickel foil, baked carbon, conductive polymer, and conductive glass. Examples of the positive electrode active material include lithium-containing transition metal oxides, lithium-containing phosphates, and lithium-containing sulfates. These positive electrode active materials may be used alone or in combination of two or more in any ratio. The negative electrode may be, for example, an electrode including a negative electrode current collector and a negative electrode active material laminated on the negative electrode current collector. Examples of the negative electrode current collector include copper foil and nickel foil. Examples of the negative electrode active material include carbon active materials such as graphite, soft carbon, and hard carbon. These negative electrode active materials may be used alone or in combination of two or more in any ratio.

[0058] (electrolyte) As the electrolyte, for example, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent can be used. The supporting electrolyte may be, for example, a lithium salt. Examples of the lithium salt include at least one selected from the group consisting of LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. Among these, at least one selected from the group consisting of LiPF6, LiClO4, and CF3SO3Li is preferred. One supporting electrolyte may be used alone, or two or more may be used in combination.

[0059] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte, and examples thereof include at least one selected from the group consisting of carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide. A mixture of these organic solvents may also be used. Among these, carbonates are preferred from the viewpoint of their favorable dielectric constant and stable potential range.

[0060] The lithium ion battery according to the present invention can be produced, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the stack as necessary, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the container. Furthermore, the battery container may contain, as necessary, an expanded metal, a fuse, an overcurrent protection element such as a PTC element, a lead plate, or the like, to prevent pressure buildup within the battery and overcharging and discharging. Examples of the shape of the battery include coin, button, sheet, cylindrical, rectangular, and flat types.

[0061] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations can also be adopted. The present invention is not limited to the above-described embodiment, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. [Example]

[0062] The present embodiment will be described in detail below with reference to examples and comparative examples, but the present embodiment is not limited to the descriptions of these examples.

[0063] Example 1 A separable flask equipped with a stirrer and reflux cooling was charged with 200 parts by mass of distilled water, 1 part by mass of tert-butylcatechol as a redox shuttle agent, and 0.1 part by mass of sodium dodecylbenzenesulfonate (emulsifier), and the temperature was raised to 70° C. Next, 2.2 parts by mass of potassium persulfate (initiator) was added to the separable flask. Next, the following monomer components, 100 parts by mass of distilled water, and 0.3 parts by mass of sodium dodecylbenzenesulfonate (emulsifier) ​​were mixed and stirred to obtain an emulsion. The obtained emulsion was continuously added to the above-mentioned separable flask, whose atmosphere had been purged with nitrogen gas, at 70°C over 180 minutes. The mixture was then stirred at 75°C for 4 hours to complete the polymerization. This resulted in an aqueous dispersion of the binder resin, a binder resin composition for lithium-ion battery separators. The binder resin composition had a solids concentration of 25.0% by mass, a glass transition temperature of -24°C, and a volume-average particle diameter of 120 nm. The volume-average particle diameter of the binder resin was measured using a laser diffraction particle size distribution analyzer (Otsuka Electronics Co., Ltd., Concentrated Particle Size Analyzer FPAR1000). The particle diameter D at which the cumulative volume calculated from the smallest diameter side in the particle size distribution (volume basis) reached 50% was determined. 50 Shows. (monomer component) n-Butyl acrylate 41 parts by mass Ethyl acrylate 42 parts by mass Acrylonitrile 15 parts by mass Glycidyl methacrylate 2 parts by mass

[0064] The glass transition temperature (Tg, unit: ° C.) of the binder resin was calculated by the following FOX formula. 1 / Tg=W1 / Tg1+W2 / Tg2++W n / Tg n (1) [Wherein, Tg is the glass transition temperature of the copolymer (unit: K), Tg i (i=1, 2, . . . n) is the glass transition temperature (unit: K) when monomer i forms a homopolymer, W i (i=1, 2,...n) represents the mass fraction of monomer i in all monomers.]

[0065] Example 2 A separable flask equipped with a stirrer and reflux cooling was charged with 200 parts by mass of distilled water, 1 part by mass of hydroquinone monomethyl ether as a redox shuttle agent, and 0.1 part by mass of sodium dodecylbenzenesulfonate (emulsifier), and the temperature was raised to 70° C. Next, 2.2 parts by mass of potassium persulfate (initiator) was added to the separable flask. Next, the following monomer components, 100 parts by mass of distilled water, and 0.3 parts by mass of sodium dodecylbenzenesulfonate (emulsifier) ​​were mixed and stirred to obtain an emulsion. The obtained emulsion was continuously added to the separable flask, the atmosphere of which had been purged with nitrogen gas, at 70°C over 180 minutes. The mixture was then stirred at 75°C for 4 hours to complete the polymerization. This resulted in a binder resin composition for lithium-ion battery separators, in the form of an aqueous dispersion of the binder resin. The solids concentration of the binder resin composition was 25.1% by mass, the glass transition temperature of the binder resin was 49°C, and the volume average particle diameter of the binder resin was 150 nm. (monomer component) Acrylonitrile 42 parts by mass n-Butyl acrylate 25 parts by mass Methacrylic acid 3 parts by mass Styrene 30 parts by mass

[0066] Comparative Example 1 A separable flask equipped with a stirrer and reflux cooling was charged with 200 parts by mass of distilled water and heated to 70° C. Next, 1.5 parts by mass of potassium persulfate (initiator) and 0.1 parts by mass of sodium dodecylbenzenesulfonate (emulsifier) ​​were added to the separable flask. Next, the following monomer components, 100 parts by mass of distilled water, and 0.3 parts by mass of sodium dodecylbenzenesulfonate (emulsifier) ​​were mixed and stirred to obtain an emulsion. The obtained emulsion was continuously added to the separable flask, the atmosphere of which had been purged with nitrogen gas, at 70°C over 180 minutes. The mixture was then stirred at 75°C for 4 hours to complete the polymerization. This yielded a binder resin composition. The binder resin composition had a solids concentration of 25.0% by mass, a glass transition temperature of 49°C, and a volume average particle diameter of 130 nm. (monomer component) Acrylonitrile 42 parts by mass n-Butyl acrylate 25 parts by mass Methacrylic acid 3 parts by mass Styrene 30 parts by mass

[0067] [evaluation] (1) The amount of redox shuttle agent (also called "RS agent") in the water The binder resin compositions obtained in Examples 1 and 2 were centrifuged at 85,000 rpm for 1 hour using an ultracentrifuge (manufactured by Eppendorf-Himac Technologies, product name: HITACHI Micro Ultracentrifuge CS100FNX), and the resulting supernatant was dissolved in isopropanol (IPA) and then subjected to GC / MS to quantify the amount of redox shuttle agent dissolved in water in the binder resin composition. (GC-MS device) Agilent 7890B-5977 (Agilent Technologies) Inlet: 240℃ Column: DB-WAX 30m x 0.25mm ID x 0.25μm Column flow rate: 1.7mL / min (constant flow rate control, average linear velocity: 30cm / sec) Split ratio: 10 / 1 Heating conditions: After holding at 40°C for 3 minutes, heat up to 250°C at a rate of 10°C / min, then hold at 250°C for 10 minutes Measurement mode: SIM (selected ion monitoring) Quantitative ion: m / z 57

[0068] (2) Amount of redox shuttle agent in the electrolyte The binder resin compositions obtained in Examples 1 and 2 were dried at room temperature to prepare test pieces. The test pieces were immersed in an electrolytic solution prepared with a volume ratio of ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) = 3 / 2 / 5 under two immersion conditions: 1 hour at 25°C and 1 hour at 70°C. In addition, the binder resin composition obtained in Comparative Example 1 was dried at room temperature, and the obtained sample piece was immersed in the above-mentioned electrolyte solution, and tert-butylcatechol was added as a redox shuttle agent in a ratio of 1 part by mass per 100 parts by mass of the binder resin. The redox shuttle agent present in each electrolyte was dissolved in IPA in the same manner as in (1) above, and then subjected to GC / MS to quantify the amount of redox shuttle agent dissolved in each electrolyte.

[0069] (Evaluation results) The above evaluation results are summarized in Table 1.

[0070] [Table 1]

[0071] In Examples 1 and 2, the amount of redox shuttle agent in the water in the binder resin composition was 0 ppm, which indicated that the redox shuttle agent was contained in the emulsion particles of the binder resin. Furthermore, it was found that the binder resin compositions of Examples 1 and 2 contained a larger amount of redox shuttle agent in the electrolyte when immersed in an electrolyte at 70° C. than when immersed in an electrolyte at 25° C. That is, it can be seen that the binder resin composition according to the present invention can release the redox shuttle agent into the electrolyte when exposed to high temperatures.

Claims

1. A binder resin, A redox shuttle agent; an aqueous medium; Including, the binder resin is dispersed in the aqueous medium in the form of particles, The binder resin composition for a lithium-ion battery separator, wherein the redox shuttle agent is contained in the binder resin in particulate form.

2. The binder resin composition according to claim 1 , wherein the binder resin is an emulsion particle.

3. 3. The binder resin composition according to claim 1, wherein the redox shuttle agent comprises a compound having a structure in which at least one functional group selected from the group consisting of a hydroxy group and an alkoxy group is introduced into a benzene ring.

4. 4. The binder resin composition according to claim 1, wherein the redox shuttle agent comprises a compound represented by the following formula (1): 【Chemistry 1】 (In the formula (1), R １ , R ２ , R ３ , R ４ , R ５ and R ６ are each independently a hydrogen atom, a hydroxy group, a halogen atom, an aryl group, an alkyl group having 1 to 4 carbon atoms, a fluorine-substituted alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a fluorine-substituted alkoxy group having 1 to 4 carbon atoms, and at least one of these substituents is a hydroxy group or an alkoxy group.

5. 5. The binder resin composition according to claim 1, wherein the redox shuttle agent comprises at least one selected from the group consisting of tert-butylcatechol, hydroquinone monomethyl ether, hydroquinone, and dibutylhydroxytoluene.

6. 6. The binder resin composition according to claim 1, wherein the binder resin comprises at least one selected from the group consisting of an aliphatic conjugated diene / aromatic monovinyl copolymer, a (meth)acrylic polymer, a fluorine-based polymer, a (meth)acrylic acid / (meth)acrylamide copolymer, a (meth)acrylonitrile polymer, and an aromatic monovinyl / (meth)acrylic copolymer.

7. A binder resin composition described in any one of claims 1 to 6, wherein the glass transition temperature of the binder resin is -50°C or higher and 80°C or lower.

8. A binder resin composition described in any one of claims 1 to 7, wherein the molecular weight of the redox shuttle agent is 100 or more and 500 or less.

9. A slurry composition for a lithium ion battery separator, comprising the binder resin composition according to any one of claims 1 to 8 and an inorganic filler.

10. A separator substrate; a functional layer formed from the binder resin composition according to any one of claims 1 to 8 or the slurry composition according to claim 9, which is disposed on at least one surface of the separator substrate; A separator for a lithium ion battery comprising:

11. a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode; A lithium ion battery, wherein the separator comprises the separator of claim 10.

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