Matrix material for electrolyte, solid electrolyte, and power storage device

Abstract

To provide a matrix material for an electrolyte, capable of giving a solid electrolyte having excellent flexibility while exhibiting high ion conductivity at room temperature.SOLUTION: The matrix material for an electrolyte contains a polymer which has a repeating unit represented by formula (1) and does not substantially have a repeating unit represented by -(R1-O)- (where R1 is a linear or branched alkylene group). In the formula (1), R represents a hydrogen atom or an alkyl group; and m represents an integer of 0-10.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a matrix material for an electrolyte, a solid electrolyte, and an electricity storage device. [Background technology]

[0002] Various types of secondary batteries have been put to practical use, including nickel-metal hydride secondary batteries, lithium-ion secondary batteries, electric double-layer capacitors, etc. Among these, lithium-ion secondary batteries are used in a wide range of applications because of their high energy density and battery capacity.

[0003] A lithium ion secondary battery is a secondary battery that has a negative electrode, a positive electrode, and an electrolyte, and is charged and discharged by transferring lithium ions between the two electrodes via the electrolyte. Conventionally, an organic electrolyte solution in which lithium metal salt is dissolved in an organic solvent such as ethylene carbonate has mainly been used as the electrolyte. In recent years, however, a solid electrolyte using an organic polymer has been proposed instead of an organic electrolyte solution as a technology to eliminate concerns about electrolyte leakage and short circuits inside the battery due to overcharging and overdischarging (see, for example, Non-Patent Document 1).

[0004] Known organic polymers used as matrix resins for solid electrolytes include polyether polymers such as poly(ethylene oxide) (hereinafter, also referred to as "PEO"). In particular, PEO has a glass transition temperature of approximately -60°C and a molecular structure that can strongly coordinate with lithium ions, so that solid electrolytes using PEO exhibit high ionic conductivity.

[0005] In addition, as a matrix resin used in the production of a solid electrolyte, it has been disclosed to use a block copolymer having a polymer block made of polytetrahydrofuran and a polymer block made of polycaprolactone (see, for example, Patent Document 1), and to introduce a branched structure into a polyether-based polymer (see, for example, Non-Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2021-512200 [Non-patent literature]

[0007] [Non-Patent Document 1] Polymer, 2005, Vol. 54, December issue, p. 870-873 [Non-Patent Document 2] Soft Matter, 2020, Vol. 16, pp. 1979-1988 Summary of the Invention [Problem to be solved by the invention]

[0008] However, polyether-based polymers are highly crystalline, and ionic conductivity is significantly reduced below the melting point of the polyether-based polymer. In addition, increasing the lithium salt concentration tends to decrease ionic conductivity. Furthermore, solid electrolytes made of polyether-based polymers are hard and insufficiently flexible, so that voids are likely to occur at the contact surface with other components when incorporated into a secondary battery. In addition, if the flexibility of the solid electrolyte is insufficient, this leads to an increase in internal resistance, and furthermore, it is easily damaged by impact, making it difficult to mount it in a flexible power storage device, etc.

[0009] The present invention has been made in view of the above circumstances, and has as its object to provide a matrix material for an electrolyte that can provide a solid electrolyte having high ionic conductivity at room temperature and excellent flexibility, and another object to provide a solid electrolyte having high ionic conductivity at room temperature and excellent flexibility. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above problems, and have found that a solid electrolyte that exhibits high ionic conductivity at room temperature and is flexible can be produced by using a polyester polymer having a specific structure, thereby completing the present invention.

[0011] [1] The following formula (1): [ka] (In formula (1), R represents a hydrogen atom or an alkyl group, and m represents an integer of 0 to 10.) The repeating unit represented by -(R 1 Repeating units represented by -O)- (where R 1 A matrix material for an electrolyte, comprising a polymer substantially free of a group (wherein is a linear or branched alkylene group).

[0012] [2] The matrix material for electrolytes according to [1], wherein the content of the repeating unit represented by the above formula (1) in the polymer is 80 mass % or more based on the total repeating units of the polymer. [3] The matrix material for an electrolyte according to [1] or [2], wherein the polymer is a star polymer. [4] The matrix material for electrolytes according to [3], wherein the star polymer has a branch number of 3 to 24. [5] The matrix material for an electrolyte according to [1] or [2], wherein the polymer is a linear polymer. [6] The matrix material for an electrolyte according to any one of [1] to [5], wherein the polymer has a weight average molecular weight of 5,000 to 100,000. [7] The matrix material for an electrolyte according to any one of [1] to [6], wherein the polymer has a tertiary alkyl group or an alicyclic hydrocarbon group at one or more ends.

[0013] [8] A solid electrolyte comprising the matrix material for an electrolyte according to any one of [1] to [7] and an alkali metal salt. [9] The solid electrolyte according to [8], wherein the alkali metal salt includes an imide-based alkali metal salt.

[10] The solid electrolyte according to [9], wherein the alkali metal salt includes lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide.

[11] The solid electrolyte according to any one of [8] to

[10] , wherein the content of the alkali metal salt in the solid electrolyte is 40 mass % or more.

[12] An electricity storage device comprising the solid electrolyte according to any one of [8] to

[11] . Effect of the Invention

[0014] According to the matrix material for electrolyte of the present invention, a solid electrolyte having high ionic conductivity at room temperature and excellent flexibility can be obtained. In addition, by using a solid electrolyte containing the matrix material for electrolyte of the present invention and an alkali metal salt as an electrolyte for an electricity storage device such as a secondary battery or a capacitor, it is possible to obtain an electricity storage device that combines high ionic conductivity with the assurance of safety due to the solidification of the electrolyte. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The matrix material for an electrolyte, the solid electrolyte, and the electricity storage device according to the present disclosure will be described in detail below.

[0016] <Electrolyte matrix material> The matrix material for electrolytes according to the present disclosure (hereinafter also referred to as the present matrix material) is preferably used as a material constituting the matrix of a solid electrolyte. [ka] (In formula (1), R represents a hydrogen atom or an alkyl group, and m represents an integer of 0 to 10.) The repeating unit represented by -(R 1 Repeating units represented by -O)- (where R 1 is an alkylene group) (hereinafter, also referred to as "polyester polymer (A)").

[0017] <Polyester polymer (A)> In the above formula (1), R is preferably a hydrogen atom or a methyl group from the viewpoints of availability of raw materials and ease of synthesis of the polyester polymer (A). m is preferably an integer of 0 to 8, more preferably an integer of 0 to 6, and more preferably an integer of 0 to 4, from the viewpoint of easy availability of raw materials.

[0018] Monomers used to introduce the repeating unit represented by the above formula (1) into a polymer include lactones and lactides. Specific examples of these include lactones such as β-propiolactone, γ-butyrolactone, β-butyrolactone, pivalolactone, δ-valerolactone, and ε-caprolactone. Lactides include glycolide obtained by dehydration condensation of two glycolic acid molecules, dilactide obtained by dehydration condensation of two lactic acid molecules, and tetramethylglycolide. The polyester polymer (A) may contain only one type of repeating unit represented by the above formula (1), or may contain two or more types. When the above lactides are used as monomers, two repeating units represented by the above formula (1) are introduced into the polymer by one lactide molecule.

[0019] In terms of obtaining a solid electrolyte having higher ion conductivity, the monomer used to introduce the repeating unit represented by the above formula (1) into the polymer is preferably at least one selected from the group consisting of γ-butyrolactone, δ-valerolactone, ε-caprolactone, and dilactide. Among these, δ-valerolactone is particularly preferred because of its excellent ion conductivity.

[0020] The number of repeating units represented by the above formula (1) contained in the polyester polymer (A) can be appropriately set according to the desired molecular weight. The number of repeating units represented by the above formula (1) contained in the polyester polymer (A) is, for example, 10 to 1,500, preferably 20 to 1,200, more preferably 30 to 1,000, and even more preferably 30 to 800.

[0021] The polyester polymer (A) may be a polymer consisting of only the repeating unit represented by the above formula (1), or may be a polymer further having a repeating unit (another repeating unit) different from the repeating unit represented by the above formula (1). Examples of the other repeating units include dioxepanone, ethylene oxalate, dioxanone, γ-nonalactone, γ-decalactone, γ-undecalactone, cyclopentadecanolide, and cyclohexedecanolide.

[0022] In the polyester polymer (A), the content of the repeating unit represented by the above formula (1) is preferably 80 mass % or more, more preferably 85 mass % or more, even more preferably 90 mass % or more, and even more preferably 95 mass % or more, based on all repeating units of the polyester polymer (A), from the viewpoint of obtaining a solid electrolyte having higher ion conductivity.

[0023] The polyester polymer (A) is -(R 1 Repeating units represented by -O)- (where R 1 is a linear or branched alkylene group). 1 The repeating unit represented by -(R -O)- is typically a repeating unit derived from an alkylene oxide or a cyclic ether. 1 The proportion of the repeating units represented by R-O- is preferably 2 mass% or less, more preferably 1 mass% or less, even more preferably 0.5 mass% or less, and still more preferably 0.1 mass% or less, based on the total repeating units of the polyester polymer (A). 1 The number of carbon atoms is, for example, 1 to 10.

[0024] The polyester polymer (A) may be linear or branched. When the polyester polymer (A) is branched, the polyester polymer (A) is preferably a star polymer having a core portion and three or more branched chains (arm portions) extending from the core portion, since crystallization of the polyester polymer (A) is suppressed and molecular motion is facilitated.

[0025] When the polyester polymer (A) is a star polymer, the structure of the core portion of the polyester polymer (A) is not particularly limited and can be appropriately set according to the desired structure of the polyester polymer (A). In terms of inexpensive and easy production of the star polymer, it is preferable that the core portion has a structure derived from a polyhydric alcohol having three or more hydroxyl groups.

[0026] Specific examples of polyhydric alcohols constituting the core portion include polyhydric alcohols having three hydroxyl groups, such as glycerin, trimethylolethane, trimethylolpropane, tris(2-hydroxyethyl)isocyanurate, trihydric alcohols such as hexanetriol, octanetriol, and decanetriol, and alkylene oxide adducts of trihydric alcohols.

[0027] Specific examples of polyhydric alcohols having four hydroxyl groups include tetrahydric alcohols such as ditrimethylolethane, ditrimethylolpropane, diglycerol and pentaerythritol, as well as alkylene oxide adducts of tetrahydric alcohols.

[0028] Specific examples of polyhydric alcohols having five hydroxyl groups include pentahydric alcohols such as tritrimethylolethane, tritrimethylolpropane and triglycerin, as well as alkylene oxide adducts of pentahydric alcohols.

[0029] Specific examples of polyhydric alcohols having six or more hydroxyl groups include hexahydric or higher alcohols such as polytrimethylolethane, polytrimethylolpropane, polyglycerin, dipentaerythritol, tripentaerythritol, sorbitol, and polypentaerythritol, as well as alkylene oxide adducts of hexahydric or higher alcohols.

[0030] The molecular weight of the polyhydric alcohol constituting the core portion is preferably 300 or less, more preferably 250 or less, and even more preferably 200 or less, from the viewpoint of obtaining a solid electrolyte exhibiting good ion conductivity.

[0031] From the viewpoint of ease of synthesis and availability of raw materials, the number of branched chains in the polyester polymer (A) is preferably 3 to 24. From the viewpoint of ease of synthesis, the number of branched chains in the polyester polymer (A) is more preferably 3 to 10, and further preferably 3 to 8. The degree of polymerization in each branched chain of the polyester polymer (A) may be the same or different between the branched chains.

[0032] The terminal structure of the polyester polymer (A) is not particularly limited. For example, the polyester polymer (A) may have a hydroxyl group or a carboxyl group derived from a monomer at the polymer terminal. The terminal of the polyester polymer (A) may be modified by utilizing the hydroxyl group or the carboxyl group present at the polymer terminal. By modifying the terminal hydroxyl group or the terminal carboxyl group of the polyester polymer (A), the heat resistance (durability) of the polyester polymer (A) can be improved.

[0033] When the terminal of the polyester polymer (A) is modified, the terminal structure is not particularly limited. For example, a monovalent hydrocarbon group having one or more carbon atoms may be introduced into the terminal of the polyester polymer (A) to improve the heat resistance of the polyester polymer (A).

[0034] In order to reduce the crystallinity of the polyester polymer (A), a monovalent hydrocarbon group having 3 or more carbon atoms may be introduced into the polymer terminal. When the polyester polymer (A) has a monovalent hydrocarbon group having 3 or more carbon atoms at its terminal, the crystallinity of the polyester polymer (A) is reduced, which promotes an ion conduction path in a solid electrolyte produced using the polyester polymer (A) and an alkali metal salt, and is considered to contribute to improving ion conductivity. The effects of improving heat resistance by modifying the terminals of the polyester polymer (A) and improving ion conductivity by reducing crystallinity are more clearly observed in a region where the concentration of the alkali metal salt is low in a solid electrolyte obtained using the polyester polymer (A) and an alkali metal salt.

[0035] Examples of the monovalent hydrocarbon group having 3 or more carbon atoms to be introduced into the polymer terminal of the polyester polymer (A) include a monovalent linear or branched alkyl group having 3 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, and a monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms. Among these, a branched alkyl group having 4 to 20 carbon atoms or a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms is preferred from the viewpoint of being able to reduce the crystallinity of the polymer while suppressing the inhibition of molecular motion due to the interaction between the terminals, thereby sufficiently obtaining the effect of improving the ionic conductivity of the solid electrolyte.

[0036] Specific examples of these include branched alkyl groups having 3 to 20 carbon atoms, such as isopropyl, isobutyl, tert-butyl, 1,1-dimethylpropyl, 1-ethyl-1-methylpropyl, 1,1-dimethylbutyl, and 1-ethyl-1-methylpropyl. Examples of monovalent alicyclic hydrocarbon groups having 3 to 20 carbon atoms include cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cyclooctyl; and polycyclic alicyclic hydrocarbon groups such as norbornyl and adamantyl. In terms of being able to fully obtain the effect of improving the ion conductivity of the solid electrolyte by modifying the polymer terminal, the hydrocarbon group introduced at the end of the polyester polymer (A) is preferably a tertiary alkyl group or an alicyclic hydrocarbon group, more preferably a tertiary alkyl group, a cycloalkyl group, a norbornyl group, or an adamantyl group, and even more preferably a norbornyl group or an adamantyl group.

[0037] When a polymer having a monovalent hydrocarbon group having 3 or more carbon atoms at its terminal is used as the polyester polymer (A), the polyester polymer (A) may have a monovalent hydrocarbon group having 3 or more carbon atoms at some of its terminals or may have a monovalent hydrocarbon group having 3 or more carbon atoms at all of its terminals.

[0038] The method for producing the polyester polymer (A) is not particularly limited, and it can be produced by using a conventionally known method as appropriate. In terms of being able to easily and inexpensively produce the polyester polymer (A) having the repeating unit represented by the above formula (1), it is preferable to produce the polyester polymer (A) by ring-opening polymerization using at least one monomer selected from the group consisting of the above lactones and lactides.

[0039] In the ring-opening polymerization, for example, a polymerization solvent and monomers are charged into a reactor, and an initiator is added to polymerize to obtain the target polyester polymer (A). The method of charging each raw material including the monomer may be a batch-type initial lump-sum charging in which all raw materials are charged at once, a semi-continuous charging in which at least a part of the raw materials are continuously fed into the reactor, or a continuous polymerization method in which all raw materials are continuously fed and the produced resin is continuously withdrawn from the reactor at the same time.

[0040] As the initiator, a monoalcohol or a polyhydric alcohol can be preferably used because the target polymer can be easily obtained. The monoalcohol is preferably an alkyl alcohol, such as methanol, ethanol, propanol, tert-butanol, 1,1-dimethylpropyl alcohol, 1-ethyl-1-methylpropyl alcohol, 1,1-dimethylbutyl alcohol, and 1-ethyl-1-methylpropyl alcohol. Specific examples of the polyhydric alcohol include the alcohols exemplified in the description of the case where the polyester polymer (A) is a star polymer.

[0041] In producing the polyester polymer (A), the amount of the initiator used is, for example, 0.01 to 15 parts by mass, and preferably 0.02 to 10 parts by mass, based on 100 parts by mass of the total amount of the monomers used in the polymerization.

[0042] The ring-opening polymerization is preferably carried out in the presence of a catalyst from the viewpoint of carrying out the reaction efficiently. As the catalyst, a conventionally known acid catalyst or base catalyst can be appropriately used. Specific examples of the acid catalyst include sulfonic acid, methanesulfonic acid, trifluoroacetic acid, 10-camphorsulfonic acid, phosphoric acid, phosphoric acid monoester (methyl phosphate, ethyl phosphate, octyl phosphate, phenyl phosphate, etc.), phosphoric acid diester (dimethyl phosphate, diethyl phosphate, dibutyl phosphate, diphenyl phosphate, etc.), phosphorous acid, phosphorous acid ester, tin tetrachloride, phosphorus pentafluoride, boron trifluoride complex, etc.

[0043] Specific examples of the base catalyst include hydroxides such as sodium hydroxide and potassium hydroxide; tertiary amine compounds such as tetrabutylammonium bromide, tetrabutylammonium chloride, tetramethylammonium bromide, tetramethylammonium chloride, 1,8-diazabicyclo[5,4,0]-7-undecene, and 1,4-diazabicyclo[2,2,2]octane; phosphorus compounds such as ethylphosphine, phenylphosphine, dimethylphosphine, diphenylphosphine, triphenylphosphine, and tributylphosphine; imidazole compounds such as 2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, and 2-ethyl-4-methylimidazole; and the like.

[0044] In producing the polyester polymer (A), the amount of the catalyst used is, for example, 0.01 to 20 parts by mass, and preferably 0.05 to 10 parts by mass, based on 100 parts by mass of the total amount of the monomers used in the polymerization.

[0045] As the polymerization solvent, an organic solvent can be preferably used. Examples of the organic solvent include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane and heptane; esters such as ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; and ethers such as propylene glycol monomethyl ether. As the polymerization solvent, one or more kinds can be used. The amount of the polymerization solvent used is, for example, 10 to 1,500 parts by mass, preferably 20 to 1,000 parts by mass, relative to 100 parts by mass of the total amount of the monomers used in the polymerization.

[0046] The polymerization temperature and polymerization time are not particularly limited and may be set appropriately. From the viewpoint of increasing the reaction rate while suppressing side reactions, the polymerization temperature is, for example, in the temperature range of 0°C to 120°C, and preferably in the temperature range of 5°C to 100°C. The polymerization time is, for example, 0.5 to 72 hours, and preferably 1 to 48 hours. The pressure during polymerization may be any pressure that can maintain the polymerization temperature. From the viewpoint of suppressing a decrease in the degree of polymerization, the reaction may be carried out under dry air (for example, under conditions where the dew point at atmospheric pressure is -40°C or less). Instead of dry air, the reaction may be carried out under dry nitrogen or dry argon. The polymerization reaction is preferably carried out while stirring the inside of the reactor.

[0047] A polyester polymer having a hydroxyl group at the polymer end can be obtained by carrying out ring-opening polymerization of lactones or lactides using a monoalcohol or polyhydric alcohol as an initiator. The polyester polymer thus obtained may be contained in the matrix material as it is (i.e., in a state in which the terminal hydroxyl group is present) as the polyester polymer (A). Alternatively, the terminal hydroxyl group of the polyester polymer obtained by the above polymerization reaction may be reacted with a compound having a reactive functional group capable of reacting with the hydroxyl group (hereinafter also referred to as a "modifier") to introduce a structure derived from the modifier into the terminal of the polyester polymer, and the obtained polymer may be used as the polyester polymer (A).

[0048] The reaction between the polyester polymer having a hydroxyl group at its terminal and the modifying agent (hereinafter, this reaction may be referred to as "modification reaction") can be carried out, for example, in a suitable solvent, using a catalyst as necessary.

[0049] As the modifier, a compound having a monovalent hydrocarbon group having one or more carbon atoms can be preferably used in terms of improving the heat resistance of the polyester polymer (A). Furthermore, a compound having a monovalent hydrocarbon group having three or more carbon atoms can be preferably used in terms of reducing the crystallinity of the polyester polymer (A) while suppressing the decrease in ion conductivity of the solid electrolyte. For specific and preferred examples of the monovalent hydrocarbon group having three or more carbon atoms, the explanation of the monovalent hydrocarbon group having three or more carbon atoms introduced into the polymer terminal of the polyester polymer (A) is applied. As the reactive group of the modifier, a carboxyl group is preferred in terms of high reactivity with a hydroxyl group.

[0050] Specific examples of the modifying agent include monocarboxylic acids having 5 to 20 carbon atoms, and aliphatic monocarboxylic acids having 5 to 20 carbon atoms can be preferably used. Specific examples thereof include tert-butyl acetic acid, 3-cyclopentylpropionic acid, 4-butylcyclohexane carboxylic acid, 4-isobutylcyclohexane carboxylic acid, 4-propylcyclohexane carboxylic acid, 4-pentylcyclohexane carboxylic acid, cyclohexane carboxylic acid, cyclohexane acetic acid, cyclooctane acetic acid, norbornane-2-carboxylic acid, and 1-adamantane acetic acid. In the above modification reaction, one type of modifying agent may be used alone, or two or more types may be used in combination.

[0051] In the above modification reaction, the amount of the modifying agent used is, for example, 0.5 to 100 parts by mass, preferably 1 to 50 parts by mass, and more preferably 2 to 30 parts by mass, relative to 100 parts by mass of the total amount of the polymer used in the modification reaction.

[0052] As the solvent, an organic solvent can be preferably used.Specific examples include aromatic compounds such as benzene, toluene, xylene, and anisole; esters such as methyl acetate, ethyl acetate, propyl acetate, and butyl acetate; ketones such as acetone and methyl ethyl ketone; and aprotic polar solvents such as dimethylformamide, acetonitrile, and dimethylsulfoxide.The amount of the solvent used is, for example, 10 to 1,200 parts by mass, and preferably 20 to 800 parts by mass, relative to 100 parts by mass of the total amount of the polymer used in the modification reaction.

[0053] As the catalyst, a known nucleophilic agent can be appropriately used. As the catalyst, for example, triethylenediamine, N-methylimidazole, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, quinuclidine, 3-quinuclidinone, 3-hydroxyquinuclidine, pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, N,N-dimethyl-4-aminopyridine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, imidazole, N-methylimidazole, N-ethylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, etc. can be mentioned. As the catalyst, one type may be used alone, or two or more types may be used in combination.

[0054] In the above modification reaction, the amount of the catalyst used is, for example, 1 to 100 parts by mass, and preferably 2 to 50 parts by mass, per 100 parts by mass of the total amount of the polymer used in the modification reaction.

[0055] The reaction temperature and reaction time in the modification reaction are not particularly limited, and may be appropriately set depending on the type of polymer and modifying agent used. The reaction temperature is, for example, within a temperature range of 0°C to 120°C, and preferably within a temperature range of 5°C to 100°C. The reaction time is, for example, 0.5 to 48 hours, and preferably 1 to 24 hours. The modification reaction may be carried out under atmospheric pressure, or under reduced or increased pressure. In order to allow the reaction to proceed sufficiently, the modification reaction is preferably carried out while stirring the inside of a reactor.

[0056] When the polyester polymer (A) is produced by a solution polymerization method, the polyester polymer (A) dissolved in a solvent can be isolated by a known solvent removal method such as a reprecipitation method, and a drying method such as a heat treatment. The polyester polymer (A) may also be produced in a manner such as bulk polymerization without using a solvent.

[0057] The weight average molecular weight (Mw) of the polyester polymer (A) is preferably 5,000 to 100,000. When the Mw of the polyester polymer (A) is within the above range, a solid electrolyte having both strength and flexibility can be obtained. From this viewpoint, the Mw of the polyester polymer (A) is preferably 6,000 or more, more preferably 7,000 or more, even more preferably 8,000 or more, and even more preferably 10,000 or more. The upper limit of the Mw of the polyester polymer (A) is preferably 80,000 or less, more preferably 70,000 or less, even more preferably 50,000 or less, even more preferably 45,000 or less, and even more preferably 40,000 or less, in terms of increasing the flexibility of the solid electrolyte.

[0058] The preferred range of Mw of the polyester polymer (A) can be set by appropriately combining the upper and lower limits of the preferred range of Mw described above. The range of Mw of the polyester polymer (A) is more preferably 6,000 to 80,000, even more preferably 7,000 to 70,000, and still more preferably 8,000 to 50,000.

[0059] The number average molecular weight (Mn) of the polyester polymer (A) is preferably 2,000 or more, more preferably 3,000 or more, and even more preferably 4,000 or more. The upper limit of Mn of the polyester polymer (A) is preferably 100,000 or less, more preferably 80,000 or less, and even more preferably 50,000 or less. The range of Mn of the polyester polymer (A) is preferably 2,000 or more and 100,000 or less, more preferably 3,000 or more and 80,000 or less, and even more preferably 4,000 or more and 50,000 or less.

[0060] The molecular weight distribution (Mw / Mn) of the polyester polymer (A), which is expressed by the ratio of Mw to Mn, is preferably 4.5 or less, more preferably 4.0 or less, even more preferably 3.5 or less, even more preferably 3.0 or less, and even more preferably 2.8 or less, from the viewpoint of obtaining a solid electrolyte exhibiting good ion conductivity. The lower limit of Mw / Mn of the polyester polymer (A) is not particularly limited, and can be 1.0 or more. In this specification, Mw and Mn of the polymer are values ​​calculated in terms of standard polystyrene obtained by gel permeation chromatography (GPC).

[0061] The matrix material may contain the polyester polymer (A) as a resin component. Therefore, the matrix material may contain only the polyester polymer (A), or may further contain a component different from the polyester polymer (A). Examples of the component different from the polyester polymer (A) include an antioxidant and a colorant. In the matrix material, the content of the polyester polymer (A) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 99% by mass or more, based on the total amount of the matrix material. The polyester polymer (A) contained in the matrix material may be one type alone or two or more types.

[0062] ≪Solid electrolyte≫ The solid electrolyte of the present disclosure (hereinafter also referred to as the "solid electrolyte of the present disclosure") contains the above-mentioned electrolyte matrix material of the present disclosure and an alkali metal salt. The solid electrolyte of the present disclosure has high ionic conductivity at room temperature (24°C) and excellent flexibility.

[0063] <Alkali metal salt> The alkali metal salt is not particularly limited as long as it is a salt that generates an alkali metal ion, and examples of the alkali metal salt include lithium salt, sodium salt, and potassium salt.

[0064] Specific examples of alkali metal salts include Li2CO3, LiBr, LiCl, LiI, LiSCN, LiBF4, LiAsF6, LiClO4, CH3COOLi, CF3COOLi, LiCF3SO3, LiPF6, LiC(CF3SO2)3, and lithium bis(fluorosulfonyl)imide (Li + (FSO2)2N - ), lithium bis(trifluoromethanesulfonyl)imide (Li + (CF3SO2)2N - and salts of the anions of these lithium salts with alkali metals other than lithium (e.g., sodium, potassium, etc.). Among these, the lithium salts or sodium salts are preferred, and the lithium salts are more preferred, since they have high ion dissociation properties and can further increase the ionic conductivity of the present solid electrolyte.

[0065] In terms of being able to further increase the ion conductivity of the present solid electrolyte, the alkali metal salt contained in the present solid electrolyte preferably contains an imide-based alkali metal salt. Among them, imide-based lithium salts are preferred in terms of high ion dissociation, and among the imide-based lithium salts, bis(fluorosulfonyl)imide lithium, bis(trifluoromethanesulfonyl)imide lithium, or (fluorosulfonyl)(trifluoromethanesulfonyl)imide=lithium are particularly preferred, bis(fluorosulfonyl)imide lithium or bis(trifluoromethanesulfonyl)imide lithium are more preferred, and bis(fluorosulfonyl)imide lithium is even more preferred.

[0066] The molecular weight of the alkali metal salt is, for example, 500 or less, preferably 400 or less, more preferably 350 or less, and even more preferably 300 or less. The lower limit of the molecular weight of the alkali metal salt is, for example, 20 or more, preferably 50 or more, more preferably 100 or more, and even more preferably 150 or more. As the alkali metal salt, one type may be used alone, or two or more types may be used in combination.

[0067] The melting point of the alkali metal salt is, for example, 60° C. or higher, preferably 70° C. or higher, and more preferably 80° C. or higher. The upper limit of the melting point of the alkali metal salt is not particularly limited, but may be, for example, 300° C. or lower, or 250° C. or lower.

[0068] The solid electrolyte may further contain a component other than the polyester polymer (A) and the alkali metal salt, as long as the effect of the present disclosure is not impaired. Examples of the component other than the polyester polymer (A) and the alkali metal salt include a solvent (e.g., an organic solvent, water, or a mixture of an organic solvent and water), a binder, etc.

[0069] <Electricity storage device> The power storage device of the present disclosure (hereinafter also referred to as "the device") includes the solid electrolyte of the present disclosure. Examples of the device include a secondary battery and a capacitor. When the device is a secondary battery, one embodiment of the device is an all-solid-state battery, and a lithium-ion secondary battery is preferable in terms of excellent ion conductivity.

[0070] An all-solid-state lithium ion secondary battery, which is one aspect of the device, will be described. The lithium ion secondary battery is a laminate including electrodes consisting of a positive electrode and a negative electrode, and a solid electrolyte, and the solid electrolyte is disposed between the positive electrode and the negative electrode so that the solid electrolyte is in contact with the electrode. The materials constituting the positive electrode and the negative electrode are not particularly limited, and can be appropriately selected from materials known as electrode materials for lithium ion secondary batteries. For example, metal foils such as aluminum and stainless steel can be used as the positive electrode current collector. Metal foils such as copper foil and lithium foil can be used as the negative electrode current collector.

[0071] In the lithium ion secondary battery of the present disclosure, the solid electrolyte is formed using a polyester polymer (A) and an alkali metal salt. The thickness of the solid electrolyte is not particularly limited and can be appropriately set depending on the application of the secondary battery. The thickness of the solid electrolyte is, for example, 5 to 500 μm.

[0072] The method for producing the solid electrolyte and the lithium ion secondary battery is not particularly limited, and a known method can be appropriately adopted depending on the battery structure, etc. For example, a laminate including a positive electrode, a solid electrolyte, and a negative electrode may be produced by preparing a powder composition containing a polyester polymer (A) and an alkali metal salt, annealing a molded body formed using the powder composition, and sandwiching the solid electrolyte obtained by this between a positive electrode and a negative electrode. Alternatively, an electrolyte material including a powder composition containing a polyester polymer (A) and an alkali metal salt may be sandwiched between a positive electrode and a negative electrode and contained in a container, and the container may be annealed to produce a laminate including a positive electrode, a solid electrolyte, and a negative electrode. The laminate including a positive electrode, a solid electrolyte, and a negative electrode is usually contained in a case and used as a secondary battery.

[0073] The device is not limited to the above-mentioned configuration in which the carrier for ion conduction is lithium ions, and may be a secondary battery in which other ions such as sodium ions are used as the carrier. The device may also be a capacitor. One embodiment of the capacitor has an anode body, a cathode body, and a solid electrolyte, and the solid electrolyte is disposed between the anode body and the cathode body so that the solid electrolyte is in contact with the electrode.

[0074] Here, one of the means for obtaining a solid electrolyte exhibiting high ionic conductivity is to increase the concentration of alkali metal salt in the solid electrolyte. However, when poly(ethylene oxide), which has been known as a matrix resin for solid electrolytes, is used, if the concentration of alkali metal salt in the solid electrolyte is increased, the strong coordination force for alkali metal ions inhibits the molecular motion of poly(ethylene oxide), and the ionic conductivity tends to decrease. On the other hand, when the above-mentioned polyester polymer (A) is used as the matrix resin for the solid electrolyte, if the concentration of alkali metal salt in the solid electrolyte is increased, the ionic conductivity can be increased with the increase in the concentration of alkali metal salt. This can increase the ionic conductivity of the solid electrolyte. The reason for obtaining such an effect is that, although it does not limit the present invention, the polyester polymer (A) does not have as strong a coordination force for alkali metal ions as the polyether polymer, and therefore, even if the concentration of alkali metal salt is increased, it is assumed that the molecular motion is less likely to decrease. In addition, it is considered that the plasticity of the alkali metal salt can impart flexibility to the solid electrolyte.

[0075] The power storage device including the solid electrolyte of the present disclosure can be used for various purposes. Specifically, it can be used as a power source for various mobile devices such as mobile phones, personal computers, smartphones, game devices, and wearable devices, various moving objects such as electric cars, hybrid cars, robots, and drones, various electric and electronic devices such as digital cameras, video cameras, music players, power tools, and home appliances, and the like. EXAMPLES

[0076] The present invention will be specifically described below based on examples. Note that the present invention is not limited to these examples. In the following, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0077] <Molecular weight measurement> The molecular weight of the polymer was determined using a gel permeation chromatography (hereinafter also referred to as "GPC") apparatus according to the following procedure. A sample solution was obtained by dissolving 4 mg of the polymer in 4 mL of tetrahydrofuran. The obtained sample solution was filtered through a polytetrafluoroethylene membrane filter, and 100 μL was injected into a GPC device to measure the weight average molecular weight and number average molecular weight (hereinafter also referred to as "Mw" and "Mn", respectively). Column: Tosoh TSKgel SuperMultiporeHZ-M x 4 Temperature: 40℃ Eluent: Tetrahydrofuran Detector: Differential refractometer Flow rate: 600μL / min Standard material: polystyrene

[0078] <Ionic conductivity measurement> The ionic conductivity of the solid electrolyte was determined by the AC impedance method according to the following procedure. The solid electrolyte was sandwiched between two stainless steel plates, and the impedance between the plates was measured at 24°C. During the measurement, an alternating current was applied between the electrodes, and the ionic conductivity was calculated from the real impedance intercept of the obtained Cole-Cole plot. All of the above operations were carried out in a dry room with a dew point of -60°C or less. The ionic conductivity (σ) was calculated by the following formula (1). σ = L / (R × S) (1) (In formula (1), σ is the ionic conductivity (unit: S cm -1 ), R is the real impedance intercept (unit: Ω), and S is the cross-sectional area of ​​the solid electrolyte at the time of measurement (unit: cm 2 ), L is the distance between the electrodes (unit: cm). Measuring equipment: Keysight E4990A Applied voltage: 10mV Frequency: 20Hz~120MHz

[0079] <Flexibility assessment> The flexibility of the solid electrolyte was evaluated according to the following criteria based on the bending angle at which a solid electrolyte having a thickness of 0.250 mm was bent and broke. ◯: The solid electrolyte is deformable and does not break even when bent by 90° or more. △: The solid electrolyte is deformable, but breaks when bent by 90° or more. ×: The solid electrolyte breaks when bent at an angle of 90° or less.

[0080] <Production of matrix material for electrolyte> [Production Example 1: Production of Polymer A] In a 100 mL test tube, 100 parts by mass of ε-caprolactone, 0.65 parts by mass of 1-butanol, 2.2 parts by mass of diphenyl phosphate, 423 parts by mass of toluene, and a stirrer were placed and stirred for 24 hours at 25°C under dry air (dew point -60°C or less). However, ε-caprolactone, 1-butanol, and toluene were used after dehydration treatment with molecular sieves. The polymerization solution was poured into a large amount of isopropyl alcohol to precipitate the polymer. The precipitate was collected by filtration under reduced pressure and dried in vacuum to obtain polymer A. Mn of polymer A was 15,900 and Mw was 18,500. In addition, for the structural units of polymer A, R and m in the above formula (1) and the degree of polymerization of polymer A are also shown in Table 1.

[0081] [Production Examples 2 to 6: Production of Polymers B to F] Polymers B to F were obtained by the same operation as in Production Example 1, except that the types and amounts of raw materials charged in the test tube were changed as shown in Table 1 and the reaction time and reaction temperature were appropriately adjusted. For the structural units possessed by Polymers B to F, R, n, and m in the above formula (1) are also shown in Table 1. The measurement results of Mn and Mn of Polymers B to F are also shown in Table 1.

[0082] [Production Example 7: Production of Polymer G] In a 20 mL beaker, 1.13 g of polymer B obtained in Production Example 2, 0.070 g of 1-adamantaneacetic acid, 0.046 g of N,N-dimethyl-4-aminopyridine, 0.078 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 3.0 g of acetonitrile, and a stirrer were placed, and the mixture was stirred at 40° C. for 5 hours in the air. The reaction solution was poured into a large amount of isopropyl alcohol to precipitate a polymer. The precipitated polymer was dried in a vacuum to obtain polymer G. Polymer G had an Mn of 18,000 and an Mw of 20,000.

[0083] [Production Example 8: Production of Polymer H] Polymer H was obtained in the same manner as in Production Example 7, except that the types and amounts of raw materials charged in the beaker were changed as shown in Table 2. The measurement results of Mn and Mn of Polymer H are shown in Table 2.

[0084] [Table 1]

[0085] [Table 2]

[0086] Details of the compounds used in Tables 1 and 2 are shown below. CL: ε-caprolactone (Tokyo Chemical Industry Co., Ltd.) VL: δ-valerolactone (Tokyo Chemical Industry Co., Ltd.) ·DLLA: DL-lactide (Tokyo Chemical Industry Co., Ltd.) ·BuOH: 1-butanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) TMP: Trimethylolpropane (Tokyo Chemical Industry Co., Ltd.) DPET: Dipentaerythritol [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.] DPP: Diphenyl phosphate (Tokyo Chemical Industry Co., Ltd.) DBU: 1,8-diazabicyclo[5.4.0]-7-undecene (Tokyo Chemical Industry Co., Ltd.) Toluene: Toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) THF: Tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) AcCN: Acetonitrile (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) AdAc: 1-Adamantaneacetic acid (Tokyo Chemical Industry Co., Ltd.) DMAP: N,N-dimethyl-4-aminopyridine (Tokyo Chemical Industry Co., Ltd.) EDC-HCl: 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (Tokyo Chemical Industry Co., Ltd.)

[0087] <Production of solid electrolyte> [Example 1] 100 parts by mass of Polymer A and 251 parts by mass of LiFSI were dissolved in acetonitrile to obtain a solid electrolyte composition. Next, a 300 μm thick silicone rubber sheet having an opening with a diameter of 6 mm was placed on a 10 mm square stainless steel plate, the opening was filled with the above solid electrolyte composition, and the solid electrolyte was dried in vacuum at 60° C. for 48 hours to obtain a solid electrolyte. The above operations were carried out in a dry room with a dew point of -60°C or less. The solid electrolyte thus obtained had a mass ratio of LiFSI of 71.5% and a thickness of 0.300 mm. The ionic conductivity of the solid electrolyte was measured at 24°C and found to be 3.5 × 10 -6 S / cm.

[0088] [Examples 2 to 11 and Comparative Examples 1 and 2] A solid electrolyte was obtained in the same manner as in Example 1, except that the solid electrolyte composition was prepared by changing the types and amounts of raw materials as shown in Table 3. The measurement results of ionic conductivity are shown in Table 3.

[0089] [Table 3]

[0090] Details of the compounds used in Table 3 are shown below. PEO: Polyethylene oxide (Mw 100,000) [Aldrich] LiFSI: Lithium bis(fluorosulfonyl)imide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0091] <Evaluation Results> As is clear from the results of Table 3, the solid electrolytes containing the polyester-based polymers of Examples 1 to 11 exhibited high ionic conductivity at room temperature (24°C) and good flexibility. In addition, the higher the alkali metal salt concentration of the solid electrolyte, the higher the tendency of the ionic conductivity to be. Among these, the solid electrolytes of Examples 1 to 8, which have a sufficiently high alkali metal salt concentration of 40 mass% or more, were excellent in flexibility as well as ionic conductivity. Furthermore, in the region where the alkali metal salt concentration is low, when a terminal-modified polyester-based polymer was used as a matrix material for the solid electrolyte, the effect of improving the ionic conductivity by terminal modification was large (comparison between Examples 10 and 11). In addition, from the results of Examples 1 to 3, the higher the number of branches of the polyester-based polymer, the higher the tendency of the ionic conductivity to be.

[0092] In contrast, the solid electrolytes (Comparative Examples 1 and 2) containing a polyether polymer instead of a polyester polymer together with an alkali metal salt were hard, did not follow bending, and broke, resulting in poor flexibility. In addition, when the ionic conductivity at room temperature (24°C) was examined, a decrease in the ionic conductivity was observed when the alkali metal salt concentration was increased, and it was not possible to improve the ionic conductivity by increasing the concentration of the alkali metal salt.

[0093] From the above results, it is considered that the compound having the repeating unit represented by the above formula (1) and -(R 1 Repeating units represented by -O)- (where R 1 It has been revealed that a solid electrolyte formed by using a polymer substantially free of a alkylene group (wherein R is a linear or branched alkylene group) as an electrolyte matrix material exhibits high ionic conductivity at room temperature and also has sufficient flexibility.

Claims

1. The following formula (1): 【Chemistry 1】 (In formula (1), R represents a hydrogen atom or an alkyl group, and m represents an integer from 0 to 10.) It has repeating units represented by -(R １ Repeating units represented by -O)- (where R １ An electrolyte matrix material containing a polymer that substantially lacks (where is a linear or branched alkylene group).

2. The electrolyte matrix material according to claim 1, wherein the proportion of repeating units represented by formula (1) in the polymer is 80% by mass or more of the total repeating units of the polymer.

3. The electrolyte matrix material according to claim 1, wherein the polymer is a star-shaped polymer.

4. The electrolyte matrix material according to claim 3, wherein the number of branches of the star-shaped polymer is 3 to 24.

5. The electrolyte matrix material according to claim 1, wherein the polymer is a linear polymer.

6. The electrolyte matrix material according to claim 1, wherein the weight-average molecular weight of the polymer is 5,000 to 100,000.

7. The electrolyte matrix material according to claim 1, wherein one or more terminals of the polymer are tertiary alkyl groups or alicyclic hydrocarbon groups.

8. A solid electrolyte comprising an electrolyte matrix material according to any one of claims 1 to 7 and an alkali metal salt.

9. The solid electrolyte according to claim 8, wherein the alkali metal salt includes an imide-based alkali metal salt.

10. The solid electrolyte according to claim 9, wherein the alkali metal salt comprises lithium bis(fluorosulfonyl)imide and / or lithium bis(trifluoromethanesulfonyl)imide.

11. The solid electrolyte according to claim 8, wherein the content of the alkali metal salt in the solid electrolyte is 40% by mass or more.

12. An energy storage device comprising the solid electrolyte described in claim 8.

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