Modifier for solid electrolytes and power storage device

Abstract

The present invention provides a modifier for solid electrolytes that comprises: an ionic compound which comprises a pyrrolidinium cation and an anion including fluorine or a cyano group; a borate ester which has a polymerizable functional group; and a lithium salt.

Description

Modifier for solid electrolyte and power storage device

[0001] The present invention relates to a modifier for a solid electrolyte and an electricity storage device using the same. Here, the term "modifier for a solid electrolyte" refers to a material used to form a member (e.g., a membrane between a solid electrolyte and an electrode) that exists between the solid electrolyte and an electrode to reduce the interfacial resistance between them, or a member that exists between two solid electrolytes to reduce the interfacial resistance between them.

[0002] The use of solid electrolytes as electrolytes for electricity storage devices such as secondary batteries and electric double layer capacitors has been studied. ２ S.P. ２ S ５ sulfide-based solid electrolytes such as Li ７ La ３ Zr ２ O １２ Known examples of such solid electrolytes include oxide-based solid electrolytes and plastic crystal-based solid electrolytes. Furthermore, known examples of plastic crystals include ionic compounds composed of an N-ethyl-N-methylpyrrolidinium cation and a bis(fluorosulfonyl)imide anion.

[0003] A plastic crystal-based solid electrolyte has a parent phase, which serves as a medium for ion conduction, formed of a plastic crystal, and contains an electrolyte (e.g., lithium salt) doped into the plastic crystal. Plastic crystals, also known as plastic crystals, have an ordered arrangement and a disordered orientation. That is, "plastic crystals" refer to crystals that have a three-dimensional crystal lattice structure in which anions and cations are regularly arranged, but these anions and cations have rotational disorder.

[0004] In a plastic crystal solid electrolyte, anions and cations generated by dissociation of the doped electrolyte hop through the voids in the crystal lattice due to the rotation of the anions and cations in the plastic crystal. Such a plastic crystal solid electrolyte is disclosed, for example, in Patent Document 1.

[0005] Japanese Patent Application Laid-Open No. 2020-167025

[0006] In an electricity storage device using a solid electrolyte (e.g., a lithium-ion secondary battery), the volume of the solid electrolyte expands during charging and contracts during discharging. A membrane in contact with such a solid electrolyte is pressurized by the volume expansion of the solid electrolyte during charging, and the pressure is released by the volume contraction during discharging. Therefore, such a membrane is required to have excellent adaptability to the volume change of the solid electrolyte. Furthermore, such a membrane is required to have high ionic conductivity.

[0007] The present invention has been made in light of the above-mentioned circumstances, and an object of the present invention is to provide a modifier capable of forming a membrane that is in contact with a solid electrolyte, has excellent adaptability to volume changes of the solid electrolyte, and exhibits high ionic conductivity.

[0008] In order to achieve the above object, the present inventors have conducted extensive research and have found that a modifier containing a specific ionic compound, a borate ester having a polymerizable functional group, and a lithium salt can be used to form a membrane that is excellent in adaptability to volume changes of a solid electrolyte and exhibits high ionic conductivity. The present invention, based on this finding, is as follows.

[0009] [1] A modifier for a solid electrolyte, comprising: an ionic compound comprising an anion containing a fluorine atom or a cyano group and a pyrrolidinium cation; a borate ester having a polymerizable functional group; and a lithium salt. [2] The modifier according to [1], wherein the content of the ionic compound is 10 to 90 mass %, the content of the borate ester having a polymerizable functional group is 1 to 20 mass %, and the content of the lithium salt is 5 to 70 mass % relative to the total of the ionic compound, the borate ester having a polymerizable functional group, and the lithium salt. [3] The borate ester having a polymerizable functional group is represented by Formula (1):

[0010]

[0011] [In formula (1), Y １ ~Y ３are each independently an acryloyl group, a methacryloyl group, or an alkyl group having 1 to 4 carbon atoms, and at least one of them is an acryloyl group or a methacryloyl group; A １ O-A ３ The modifier according to the above [1] or [2], which is a borate ester represented by the formula (2):

[0012]

[0013] [In formula (2), R １ and R ２ are each independently a methyl group, an ethyl group, a propyl group, an isopropyl group, a methoxymethyl group, or a methoxyethyl group.] [5] The anion containing a fluorine atom or a cyano group is a cation represented by the formula: NH ２ － An imide anion in which two hydrogen atoms of the anion are each independently substituted with a perfluoroalkylsulfonyl group or a fluorosulfonyl group (the above-mentioned NH ２ －when two hydrogen atoms of the anion are each independently substituted with the perfluoroalkylsulfonyl group, the two perfluoroalkyl groups contained therein may be linked to each other), an anion containing a fluorine atom selected from the group consisting of a tris(trifluoromethanesulfonyl)methanide anion, a hexafluorophosphate anion, a (perfluoroalkyl)fluorophosphate anion in which some fluorine atoms of the hexafluorophosphate anion are substituted with perfluoroalkyl groups, a tetrafluoroborate anion, a (perfluoroalkyl)fluoroborate anion in which some fluorine atoms of the tetrafluoroborate anion are substituted with perfluoroalkyl groups, and an N-(perfluoroalkylsulfonyl)perfluorocarboxylic acid amide anion, or a tricyanomethanide anion, a tetracyanoborate anion, a tricyanomethoxyborate anion, a tricyanoisopropoxyborate anion, a tricyano(pentafluorophenoxy)borate anion, a tricyano(trimethylsiloxy)borate anion, The modifier according to any one of [1] to [4], wherein the imide anion is an anion containing a cyano group selected from the group consisting of a tricyano(hexafluoroisopropoxy)borate anion, a tricyanomethylthioborate anion, a dicyanodimethoxyborate anion, and a cyanotrimethoxyborate anion. [6] The imide anion is represented by the formula (A):

[0014]

[0015] [In formula (A), m and n each independently represent an integer of 0 or more.], a bis(perfluoroalkylsulfonyl)imide anion, a bis(fluorosulfonyl)imide anion, and an N-(fluorosulfonyl)-N-(perfluoroalkylsulfonyl)imide anion represented by formula (B):

[0016]

[0017] and a cyclohexafluoropropane-1,3-bis(sulfonyl)imide anion represented by formula (C):

[0018]

[0019] and a cyclotetrafluoroethane-1,3-bis(sulfonyl)imide anion represented by formula (D):

[0020]

[0021] [In formula (D), q is an integer of 1 or more.] The (perfluoroalkyl)fluoroborate anion is a tris(fluoroalkyl)trifluorophosphate anion represented by formula (E):

[0022]

[0023] [In formula (E), r is an integer of 1 or more, and s is an integer of 0 or more.] The anion is selected from the group consisting of mono(fluoroalkyl)trifluoroborate anions and bis(fluoroalkyl)fluoroborate anions represented by formula (F):

[0024]

[0025] [In formula (F), j and k are each independently an integer of 1 or greater.] The modifier according to [5] above, which is an anion represented by the formula: [In formula (F), j and k are each independently an integer of 1 or greater.] [7] The modifier according to any one of [1] to [6] above, which further contains a polymerization initiator. [8] An electricity storage device comprising: a membrane formed from the modifier according to any one of [1] to [7] above; a solid electrolyte; and two electrodes facing each other with the solid electrolyte sandwiched therebetween, wherein the membrane is present between the solid electrolyte and at least one of the two electrodes. [9] The electricity storage device according to [8] above, wherein at least one of the two electrodes is a polarizable electrode having an active material layer made of a porous material and a current collector.

[0026] The modifier for a solid electrolyte of the present invention can be used to form a membrane that is in contact with a solid electrolyte, has excellent adaptability to volume changes of the solid electrolyte, and exhibits high ionic conductivity.

[0027] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and various modifications (such as modifications to the modifier composition and the battery composition) are possible. The present invention includes configurations that are substantially identical to the configurations of the following embodiments (for example, configurations with the same function, method, and result, or configurations with the same purpose and effect). The present invention also includes configurations in which non-essential parts of the configurations of the following embodiments are replaced with other configurations. Furthermore, the present invention also includes configurations that achieve the same effects or purposes as the configurations of the following embodiments. Furthermore, the present invention also includes configurations in which publicly known technology is added to the configurations of the following embodiments.

[0028] The descriptions in this specification can be combined with each other unless it is clear that they cannot be combined.

[0029] <Modifier for Solid Electrolyte> The modifier for solid electrolyte of the present invention (hereinafter may be abbreviated as "modifier of the present invention") comprises: an ionic compound (hereinafter may be abbreviated as "ionic compound") consisting of an anion containing a fluorine atom or a cyano group and a pyrrolidinium cation; a borate ester having a polymerizable functional group; and a lithium salt.

[0030] The modifier of the present invention is preferably a coating material for a solid electrolyte. Here, the term "coating material for a solid electrolyte" refers to a material used to form a film that coats a part or the entire surface of a solid electrolyte.

[0031] The modifier of the present invention may contain only one component or two or more components in combination. Each component will be described below in order.

[0032] <Ionic Compound> The ionic compound used in the present invention comprises an anion containing a fluorine atom or a cyano group and a pyrrolidinium cation. These will be described in order below.

[0033] The anion containing a fluorine atom or a cyano group is preferably (i) NH ２ － An imide anion in which two hydrogen atoms of the anion are each independently substituted with a perfluoroalkylsulfonyl group or a fluorosulfonyl group (the above-mentioned NH ２ － When two hydrogen atoms of the anion are each independently substituted with the perfluoroalkylsulfonyl group, the two perfluoroalkyl groups contained therein may be linked together), (ii) tris(trifluoromethanesulfonyl)methanide anion, (iii) hexafluorophosphate anion (PF ６ － (iv) a (perfluoroalkyl)fluorophosphate anion in which some of the fluorine atoms in the hexafluorophosphate anion are substituted with perfluoroalkyl groups; (v) a tetrafluoroborate anion (BF ４ － (vi) a (perfluoroalkyl)fluoroborate anion in which some of the fluorine atoms in a tetrafluoroborate anion are substituted with perfluoroalkyl groups, and (vii) an N-(perfluoroalkylsulfonyl)perfluorocarboxylic acid amide anion, or (viii) a tricyanomethanide anion, (ix) a tetracyanoborate anion, (x) a tricyanomethoxyborate anion, (xi) a tricyanoisopropoxyborate anion, (xii) a tricyano(pentafluorophenoxy)borate anion, (xiii) a tricyano(trimethylsiloxy)borate anion, (xiv) a tricyano(hexafluoroisopropoxy)borate anion, (xv) a tricyanomethylthioborate anion, (xvi) a dicyanodimethoxyborate anion, and (xvii) a cyanotrimethoxyborate anion. is an anion containing a cyano group selected from the group consisting of:

[0034] The anion containing a fluorine atom or a cyano group is more preferably an anion containing a fluorine atom selected from the group consisting of (i) to (vii) above.

[0035] The imide anion (i) is preferably represented by the formula (A):

[0036]

[0037] [in formula (A), m and n each independently represent an integer of 0 or greater], a bis(perfluoroalkylsulfonyl)imide anion (i.e., an anion in formula (A), in which m and n each independently represent an integer of 1 or greater), a bis(fluorosulfonyl)imide anion (i.e., an anion in formula (A), in which m and n are both 0), and an N-(fluorosulfonyl)-N-(perfluoroalkylsulfonyl)imide anion (i.e., an anion in formula (A), in which m is an integer of 1 or greater and n is 0), a compound represented by formula (B):

[0038]

[0039] and a cyclohexafluoropropane-1,3-bis(sulfonyl)imide anion represented by formula (C):

[0040]

[0041] and cyclotetrafluoroethane-1,3-bis(sulfonyl)imide anions represented by the formula:

[0042] When n in formula (A) is 0, C in formula (A) ｎ F ２ｎ＋１ means that n is 1 or more. ｎ F ２ｎ＋１ means a perfluoroalkyl group. ｎ F ２ｎ＋１ " and the same symbol "C ｎ F ２ｎ＋１ The perfluoroalkyl group may be linear or branched.

[0043] In the bis(perfluoroalkylsulfonyl)imide anion represented by formula (A), m and n are preferably each independently an integer of 1 or more and 5 or less, and more preferably each independently an integer of 1 or more and 3 or less.

[0044] In the N-(fluorosulfonyl)-N-(perfluoroalkylsulfonyl)imide anion represented by formula (A), m is preferably an integer of 1 or more and 5 or less, and more preferably an integer of 1 or more and 3 or less.

[0045] Examples of the bis(perfluoroalkylsulfonyl)imide anion include bis(trifluoromethanesulfonyl)imide anion (an anion in which m and n are both 1 in formula (A)) and bis(pentafluoroethylsulfonyl)imide anion (an anion in which m and n are both 2 in formula (A)).

[0046] The tris(trifluoromethanesulfonyl)methanide anion (ii) is represented by the following formula (G):

[0047]

[0048] The (perfluoroalkyl)fluorophosphate anion (iv) is preferably represented by formula (D):

[0049]

[0050] [In formula (D), q is an integer of 1 or more.] In formula (D), q is preferably an integer of 1 or more and 5 or less, more preferably an integer of 1 or more and 3 or less.

[0051] Examples of tris(fluoroalkyl)trifluorophosphate anions include tris(pentafluoroethyl)trifluorophosphate anions (ie, anions in which q in formula (D) is 2).

[0052] The (perfluoroalkyl)fluoroborate anion (vi) is preferably represented by the formula (E):

[0053]

[0054] [In formula (E), r is an integer of 1 or more, and s is an integer of 0 or more.] The anion is selected from the group consisting of mono(fluoroalkyl)trifluoroborate anions (i.e., anions in which r in formula (E) is an integer of 1 or more, and s is 0) and bis(fluoroalkyl)fluoroborate anions (i.e., anions in formula (E) where r and s are each independently an integer of 1 or more).

[0055] In formula (E), r is preferably an integer of 1 or more and 5 or less, more preferably an integer of 1 or more and 3 or less. In the mono(fluoroalkyl)trifluoroborate anion represented by formula (E), s is preferably an integer of 0 or more and 5 or less, more preferably an integer of 0 or more and 3 or less. In the bis(fluoroalkyl)fluoroborate anion represented by formula (E), s is preferably an integer of 1 or more and 5 or less, more preferably an integer of 1 or more and 3 or less.

[0056] The N-(perfluoroalkylsulfonyl)perfluorocarboxylic acid amide anion (vii) is preferably represented by the formula (F):

[0057]

[0058] [In formula (F), j and k each independently represent an integer of 1 or greater.] In formula (F), j and k each independently represent an integer of 1 or greater and 5 or less, and more preferably, each independently represent an integer of 1 or greater and 3 or less.

[0059] An example of the N-(perfluoroalkylsulfonyl)perfluorocarboxylic acid amide anion is 2,2,2-trifluoro-N-(trifluoromethylsulfonyl)acetamide anion (that is, an anion in which j and k in formula (F) are both 1).

[0060] Among the above-mentioned anions containing a fluorine atom, the imide anion of (i) is preferred, which is widely used as an electrolyte material for battery device materials such as lithium salts, and from the viewpoints of its proven use and ease of availability; a bis(perfluoroalkylsulfonyl)imide anion in which m and n in formula (A) are each independently an integer of 1 or more and 3 or less, a bis(fluorosulfonyl)imide anion in which m and n in formula (A) are both 0, and an N-(fluorosulfonyl)-N-(perfluoroalkylsulfonyl)imide anion in which n in formula (A) is 0 and m is an integer of 1 or more and 3 or less are more preferred; and a bis(fluorosulfonyl)imide anion is even more preferred.

[0061] The pyrrolidinium cation constituting the ionic compound is preferably represented by the formula (2):

[0062]

[0063] [In formula (2), R １ and R ２ are each independently a methyl group, an ethyl group, a propyl group, an isopropyl group, a methoxymethyl group, or a methoxyethyl group.

[0064] The pyrrolidinium cation represented by formula (2) is, for example, an N-ethyl-N-methylpyrrolidinium cation (i.e., R １ is a methyl group, and R ２ is an ethyl group), N-isopropyl-N-methylpyrrolidinium cation (i.e., R １ is a methyl group, and R ２ is an isopropyl group), N,N-diethylpyrrolidinium cation (i.e., R １ and R ２ and (cations in which both are ethyl groups) are preferred. Among these, the N,N-ethylpyrrolidinium cation is preferred from the viewpoint of lithium ion conductivity.

[0065] From the viewpoint of ionic conductivity, the content of the ionic compound in the modifier of the present invention is preferably 10 to 90 mass %, more preferably 20 to 80 mass %, and even more preferably 50 to 75 mass %, based on the total of the ionic compound, the borate ester having a polymerizable functional group, and the lithium salt.

[0066] The ionic compound can be produced by a known method (for example, the method described in Patent Document 1) using commercially available starting materials.

[0067] <Borate ester having polymerizable functional group> The polymerizable functional group of the borate ester used in the present invention is preferably a functional group having an ethylenic carbon-carbon double bond, more preferably an acryloyl group or a methacryloyl group, and even more preferably a methacryloyl group. The borate ester used in the present invention may have only one type of polymerizable functional group, or may have two or more types of polymerizable functional groups.

[0068] The boric acid ester having a polymerizable functional group is preferably represented by formula (1):

[0069]

[0070] [In formula (1), Y １ ~Y ３ are each independently an acryloyl group, a methacryloyl group, or an alkyl group having 1 to 4 carbon atoms, and at least one of them is an acryloyl group or a methacryloyl group; A １ O-A ３ O are each independently an oxyalkylene group having 2 to 4 carbon atoms, and p1 to p3 are each independently a number from 1 to 600.

[0071] Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group.

[0072] Y １ ~Y ３are preferably each independently an acryloyl group or a methacryloyl group, and more preferably both are methacryloyl groups, from the viewpoint of thermal stability of the borate ester having a polymerizable functional group when processed into an electricity storage device or the like.

[0073] Examples of the oxyalkylene group having 2 to 4 carbon atoms include an oxyethylene group, an oxypropylene group, an oxytrimethylene group, an oxybutylene group, an oxytetramethylene group, etc. Among these, from the viewpoint of compatibility between the borate ester having a polymerizable functional group and the ionic compound and the lithium salt, an oxyethylene group and an oxypropylene group are preferred, and an oxyethylene group is more preferred.

[0074] p1 to p3 are the A in the molecule, respectively. １ O-A ３ p1 represents the number of O. In other words, p1 to p3 are the average number of moles of alkylene oxide added per mole of the starting compound of boric acid ester (1). Since p1 to p3 are actually average numbers, they may be decimals. From the viewpoint of the ionic conductivity of the membrane produced from the modifier of the present invention, p1 to p3 are preferably each independently 1 to 80, more preferably each independently 1 to 50.

[0075] (A １ O) ｐ１ ~ (A ３ O) ｐ３ may each independently be formed of only one type of oxyalkylene group having 2 to 4 carbon atoms, or may be formed of two or more types thereof. １ O) ｐ１ ~ (A ３ O) ｐ３ The polymerization method may be random polymerization, block polymerization, alternating polymerization, or a combination thereof.

[0076] (A １ O) ｐ１ ~ (A ３ O) ｐ３ may be the same or different from each other, but are preferably the same from the viewpoint of ease of production of the boric acid ester (1).

[0077] The boric acid ester having a polymerizable functional group (for example, boric acid ester (1)) can be produced by a known method (for example, the method described in JP-A-2004-2342).

[0078] From the viewpoint of the compressive shrinkage property of the film obtained from the modifier of the present invention, the content of the borate ester having a polymerizable functional group in the modifier of the present invention is preferably 1 to 20 mass %, more preferably 3 to 20 mass %, and even more preferably 5 to 15 mass %, based on the total of the ionic compound, the borate ester having a polymerizable functional group, and the lithium salt.

[0079] <Lithium Salt> Examples of lithium salts include Li(CF ３ SO ２ ) ２ N (abbreviation: LiTFSI), Li(FSO ２ ) ２ N (abbreviation: LiFSI), Li(C ２ F ５ SO ２ ) ２ N, LiPF ６ , LiBF ４ , LiAsF ６ , LiTaF ６ , LiClO ４ , LiCF ３ SO ３ The lithium salt is preferably lithium bis(fluorosulfonyl)imide (Li(FSO ２ ) ２ N).

[0080] From the viewpoint of compatibility between the lithium salt and the borate ester having a polymerizable functional group and the ionic compound, the content of the lithium salt in the modifier of the present invention is preferably 5 to 70 mass %, more preferably 8 to 60 mass %, and even more preferably 10 to 40 mass %, based on the total of the ionic compound, the borate ester having a polymerizable functional group, and the lithium salt.

[0081] <Other Components> The modifier of the present invention may contain other components other than the ionic compound, the boric acid ester having a polymerizable functional group, or the lithium salt, as long as the effects of the present invention are not impaired. Examples of other components include a polymerization initiator, a solvent, a reactive diluent, etc. Each of the other components may be used alone or in combination of two or more.

[0082] The polymerization initiator is not particularly limited, and known initiators can be used. Examples of the polymerization initiator include ammonium persulfate, benzoyl peroxide, azobisisobutyronitrile, 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-methylpropionate)dimethyl, 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis[N-(2-hydroxyethyl)-2-methylpropanamide], 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine], 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxycyclohexylphenylketone, and 2-hydroxy-2-methyl-1-phenylpropane. 2-(4-(4-morpholinyl)phenyl)-1-butanone, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, methyl benzoylformate, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, and derivatives thereof. The polymerization initiator may be a mixture (for example, a mixture of benzoyl peroxide and its derivatives).

[0083] When a polymerization initiator is used, its content in the modifier of the present invention is preferably 0.0001 to 0.1 mol%, more preferably 0.0001 to 0.05 mol%, and even more preferably 0.0001 to 0.01 mol%, relative to the boric acid ester having a polymerizable functional group, from the viewpoint of polymerization time. Note that, in this specification, the "content (mol %) of B relative to A" means "100 × amount (mol) of B / amount (mol) of A."

[0084] Examples of the solvent include hydrocarbons such as pentane, ethers such as tetrahydrofuran, esters such as ethyl formate, ketones such as acetone, alcohols such as methanol, and nitriles such as acetonitrile. Of these, nitriles are preferred.

[0085] From the viewpoint of processability of the modifier of the present invention, the content of the solvent in the modifier of the present invention is preferably 0 to 30% by mass, more preferably 0 to 25% by mass, and even more preferably 0 to 10% by mass, based on the total of the ionic compound, the borate ester having a polymerizable functional group, and the lithium salt. Note that, in this specification, the "content (mass%) of B relative to A" means "100 × amount of B (g) / amount of A (g)."

[0086] In the present invention, a reactive diluent may be used. Here, the term "reactive diluent" refers to a compound that has a reactive functional group (e.g., a functional group having an ethylenic carbon-carbon double bond) and is liquid at room temperature. Examples of reactive diluents include acrylonitrile and methacrylonitrile. Among these, acrylonitrile is preferred.

[0087] When a reactive diluent is used, the content thereof in the modifier of the present invention is, from the viewpoint of processability of the modifier of the present invention, preferably 0.1 to 10 mass %, more preferably 0.1 to 8 mass %, and even more preferably 0.1 to 5 mass %, based on the total of the ionic compound, the boric acid ester having a polymerizable functional group, and the lithium salt.

[0088] <Method for Producing Modifier> The modifier of the present invention can be produced by mixing an ionic compound, a borate ester having a polymerizable functional group, and a lithium salt, as well as other components (e.g., a polymerization initiator, a solvent, a reactive diluent) as needed. There are no particular limitations on the mixing method, and the components can be mixed using known tools or devices.

[0089] <Electricity Storage Device> The present invention provides an electricity storage device comprising a membrane formed from the modifier of the present invention (hereinafter sometimes abbreviated as "the membrane of the present invention"), a solid electrolyte, and two electrodes facing each other with the solid electrolyte sandwiched therebetween, the membrane being present between the solid electrolyte and at least one of the two electrodes. One membrane may be present between the solid electrolyte and one of the two electrodes, or one membrane may be present between the solid electrolyte and one of the two electrodes and one membrane may be present between the solid electrolyte and the other of the two electrodes (two membranes in total). The electricity storage device of the present invention is preferably a secondary battery, more preferably an all-solid-state secondary battery.

[0090] The membrane of the present invention can be produced, for example, by applying the modifier of the present invention to a solid electrolyte and heating it. Alternatively, the modifier of the present invention may be applied to a support other than the solid electrolyte and heated to form the membrane of the present invention, and the solid electrolyte, the membrane, and at least one of the electrodes may be laminated together.

[0091] The heating temperature for forming the film of the present invention is preferably 50 to 150° C., more preferably 50 to 90° C., and the heating time is preferably 0.5 to 3 hours, more preferably 0.5 to 1 hour.

[0092] The thickness of the membrane of the present invention is preferably 0.1 to 10 μm, more preferably 0.1 to 5 μm, from the viewpoint of the solid electrolyte behavior required for the electricity storage device.

[0093] As the solid electrolyte, any of sulfide-based solid electrolytes, oxide-based solid electrolytes, and plastic crystal-based solid electrolytes can be used, of which sulfide-based solid electrolytes and oxide-based solid electrolytes are preferred.

[0094] The light of the sky is the light of the moon. ２ 3-0 ２ ﳳ ５ 、i ２ 3-0 ２ ﳳ ５ -iCl、ｬi ２ 3-0 ２ ﳳ ５ -8 ２ ｳ、ii ２ 3-0 ２ ﳳ ５ -8 ２ 3-LiCl、ii ２ 3-:i9-P ２ ﳳ ５ 、i ２ 3-LiI-i ２ 9-0 ２ ﳳ ５ 、i ２ 3_i｢rmｰ ２ ﳳ ５ 、i ２ S-i ２ 9-0 ２ ﳳ ５ 、i ２ S-i ３ PO ４ -P ２ ﳳ ５ 、i ２ 3-0 ２ ﳳ ５ -P ２ 9 ５ 、i ２ 3-0 ２ ﳳ ５ -3iｳ ２ 、i ２ 3-0 ２ ﳳ ５ -3iｳ ２ -iCl、ｬi ２ 3-0 ２ ﳳ ５ -3n、Li ２ 3-0 ２ ﳳ ５ -2l ２ ﳳ ３ 、i ２ 3-11⁄3 ２ 、i ２ 3-11⁄3 ２ -Zn、Li ２ 3-1a ２ ﳳ３ , Li ２ S-GeS ２ -Ga ２ S ３ , Li ２ S-GeS ２ -P ２ S ５ , Li ２ S-GeS ２ -Sb ２ S ５ , Li ２ S-GeS ２ -Al ２ S ３ , Li ２ S-SiS ２ , Li ２ S-Al ２ S ３ , Li ２ S-SiS ２ -Al ２ S ３ , Li ２ S-SiS ２ -P ２ S ５ , Li ２ S-SiS ２ -P ２ S ５ - LiI, Li ２ S-SiS ２ - LiI, Li ２ S-SiS ２ -Li ４ SiO ４ , Li ２ S-SiS ２ -Li ３ P.O. ４ , Li １０ GeP ２ S １２、 Li ６ P.S. ５ Among these, from the viewpoint of practicality for all-solid-state batteries, Li, which is an LGPS-type crystal, is preferred. １０ GeP ２ S １２ and argyrodite-type crystals, Li ６ P.S. ５ Br is preferred, Li ６ P.S. ５ Br is more preferred.

[0095] Examples of oxide-based solid electrolytes include Li ｘａ La ｙａ TiO ３ (wherein 0.3≦xa≦0.7, 0.3≦ya≦0.7) (LLT), Li ｘｂ La ｙｂ Zr ｚｂ Mbb ｍｂ O ｎｂ (wherein Mbb is at least one element selected from the group consisting of Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, and 5≦xb≦10, 1≦yb≦4, 1≦zb≦4, 0≦mb≦2, 5≦nb≦20), Li ｘｃ B ｙｃ Mcc ｚｃ O ｎｃ (wherein Mcc is at least one element selected from C, S, Al, Si, Ga, Ge, In, and Sn, and 0≦xc≦5, 0≦yc≦1, 0≦zc≦1, 0≦nc≦6), Li ｘｄ (Al, Ga) ｙｄ (Ti, Ge) ｚｄ Si ａｄ P ｍｄ O ｎｄ (wherein (Al, Ga) is Al or Ga, (Ti, Ge) is Ti or Ge, and 1≦xd≦3, 0≦yd≦1, 0≦zd≦2, 0≦ad≦1, 1≦md≦7, 3≦nd≦13), Li （３－２ｘｅ） Mee ｘｅ DeeO (wherein 0≦xe≦0.1, Mee is a divalent metal atom, and Dee is a halogen atom or a combination of two or more halogen atoms), Li ｘｆ Si ｙｆ O ｚｆ (wherein 1≦xf≦5, 0<yf≦3, 1≦zf≦10), Li ｘｇ S ｙｇ O ｚｇ (wherein 1≦xg≦3, 0<yg≦2, 1≦zg≦10), Li ３ BO ３ -Li ２ SO ４ , Li ２ Alumni ２ O ３ -P ２ O ５ , Li２ O—SiO ２ , Li ６ BaLa ２ Ta ２ O １２ , Li ３ P.O. （４－３／２ｗ） N ｗ (wherein w<1), Li having a LISICON (lithium super ionic conductor) type crystal structure ３ . ５ Zn ０ . ２５ GeO ４ , La having a perovskite crystal structure ０．５５ Li ０．３５ TiO ３ , LiTi having a NASICON (sodium super ionic conductor) type crystal structure ２ P ３ O １２ , Li １＋ｘｈ＋ｙｈ (Al, Ga) ｘｈ (Ti, Ge) ２－ｘｈ Si ｙｈ P ３－ｙｈ O １２ (wherein (Al, Ga) is Al or Ga, (Ti, Ge) is Ti or Ge, and 0≦xh≦1, 0≦yh≦1), Li having a garnet-type crystal structure ７ La ３ Zr ２ O １２ (LLZ), etc. Phosphorus compounds containing Li, P, and O are also desirable. For example, lithium phosphate (Li ３ P.O. ４ LiPOD1 (where D1 is at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, and Au) and LiPON (wherein D1 is at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, and Au) are examples of lithium phosphates. LiAlON (where A1 is at least one element selected from Si, B, Ge, Al, C, Ga, and the like) and the like are also preferably used. Among these, from the viewpoint of practicality in all-solid-state batteries, LaAlON having a perovskite-type crystal structure is preferred. ０．５５ Li ０．３５ TiO３ , LiTi having a NASICON type crystal structure ２ P ３ O １２ , Li １＋ｘｈ＋ｙｈ (Al, Ga) ｘｈ (Ti, Ge) ２－ｘｈ Si ｙｈ P ３－ｙｈ O １２ (wherein (Al, Ga) is Al or Ga, (Ti, Ge) is Ti or Ge, and 0≦xh≦1, 0≦yh≦1), and Li ７ La ３ Zr ２ O １２ (LLZ) is preferred, and Li １＋ｘｈ＋ｙｈ (Al, Ga) ｘｈ (Ti, Ge) ２－ｘｈ Si ｙｈ P ３－ｙｈ O １２ (In the above formula, (Al, Ga) is Al or Ga, (Ti, Ge) is Ti or Ge, and 0≦xh≦1, 0≦yh≦1) (for example, Li １．４ Al ０．４ Ti １．６ (P.O. ４ ) ３ ) is more preferred.

[0096] As the plastic crystalline solid electrolyte, for example, the one described in Patent Document 1 can be used.

[0097] A separator may be disposed between the positive and negative electrodes to prevent contact between the positive and negative electrodes and to maintain the shape of the solid electrolyte. However, if the solid electrolyte has a thickness sufficient to prevent contact between the positive and negative electrodes and is hard enough to maintain its shape by itself, the separator may be unnecessary.

[0098] The positive and negative electrodes of an electric double layer capacitor, a type of electricity storage device, are constructed by forming an active material layer on a current collector. The current collector can be made of aluminum foil, platinum, gold, nickel, titanium, steel, carbon, or the like. The current collector can have any shape, such as a film, foil, plate, mesh, expanded metal, or cylinder. The surface of the current collector may be textured by etching or may be plain. Furthermore, surface treatment may be performed to deposit phosphorus on the surface of the current collector.

[0099] At least one of the electrodes is a polarizable electrode having an active material layer preferably made of a porous material and a current collector. Examples of the porous material include a porous carbon material. The other of the positive and negative electrodes may have an active material layer containing metal compound particles or a carbon material that causes a Faraday reaction.

[0100] The carbon material in the polarizable electrode is, for example, mixed with a conductive additive and a binder and applied to a current collector by a doctor blade method or the like. The mixture of the carbon material, conductive additive, and binder may be formed into a sheet and then pressed onto the current collector. Here, the pores of the porous structure are formed by gaps between primary particles and secondary particles when the carbon material has a particulate shape, or by gaps between fibers when the carbon material is fibrous.

[0101] Examples of carbon materials for the active material layer in the polarizable electrode include natural plant tissues such as coconut husks, synthetic resins such as phenols, activated carbons derived from fossil fuels such as coal, coke, and pitch, carbon blacks such as ketjen black, acetylene black, and channel black, carbon nanohorns, amorphous carbon, natural graphite, artificial graphite, graphitized ketjen black, mesoporous carbon, carbon nanotubes, and carbon nanofibers. The specific surface area of ​​these carbon materials may be improved by activation treatment such as steam activation, alkali activation, zinc chloride activation, or electric field activation, as well as by aperture treatment.

[0102] Examples of binders include rubbers such as fluorine-based rubber, diene-based rubber, and styrene-based rubber (for example, styrene-butadiene copolymer), fluorine-containing polymers such as polytetrafluoroethylene and polyvinylidene fluoride, celluloses such as carboxymethyl cellulose and nitrocellulose, and also polyolefin resins, polyimide resins, acrylic resins, nitrile resins, polyester resins, phenolic resins, polyvinyl acetate resins, polyvinyl alcohol resins, and epoxy resins. These binders may be used alone or in combination of two or more.

[0103] Examples of the conductive additive that can be used include ketjen black, acetylene black, natural / artificial graphite, and fibrous carbon. Examples of the fibrous carbon include carbon nanotubes and carbon nanofibers. The carbon nanotubes may be single-walled carbon nanotubes (SWCNTs) each having one graphene sheet, or multi-walled carbon nanotubes (MWCNTs) each having two or more graphene sheets rolled coaxially to form multiple tube walls, or a mixture of these.

[0104] A carbon coating layer containing a conductive agent such as graphite may be provided between the current collector and the active material layer. The carbon coating layer can be formed by applying a slurry containing a conductive agent such as graphite, a binder, etc. to the surface of the current collector and drying the slurry.

[0105] The positive and negative electrodes of a lithium-ion secondary battery, a type of power storage device, are constructed by forming an active material layer on a current collector. Examples of current collectors that can be used include metals such as aluminum foil, platinum, gold, nickel, titanium, and steel; conductive polymer materials such as carbon, polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole; and resins containing non-conductive polymer materials filled with conductive fillers. The current collectors can be in any shape, such as a film, foil, plate, mesh, expanded metal, or cylinder.

[0106] The active material is mixed with a binder, for example, and applied to the current collector by a doctor blade method or the like. The mixture of the carbon material and the binder may be formed into a sheet and then pressed onto the current collector. Conductive carbon such as carbon black, acetylene black, ketjen black, or graphite may be added to the active material layer as a conductive additive. The active material and the binder may be added, kneaded, and then applied or pressed onto the current collector.

[0107] As the positive electrode active material, metal compound particles capable of absorbing and releasing lithium ions can be used. For example, layered rock salt LiMO ２ , layered Li ２ MnO ３ -LiMO ２ Solid solutions and spinel-type LiM ２ O ４ (wherein M represents Mn, Fe, Co, Ni or a combination thereof). Specific examples thereof include LiCoO ２ , LiNiO ２ , LiNi ４／５ Co １／５ O ２ , LiNi １／３ Co １／３ Mn １／３ O ２ , LiNi ４／５ Co １／１０ Mn １／１０ O ２ , LiNi 1／2 Co 1／5 Mn 3／１０ O ２ , LiNi １／２ Mn １／２ O ２ , LiFeO ２ , LiMnO ２ , Li ２ MnO ３ -LiCoO ２ , Li ２ MnO ３ -LiNiO ２ , Li ２ MnO ３ -LiNi １／３ Co １／３ Mn １／３ O ２, Li ２ MnO ３ -LiNi １／２ Mn １／２ O ２ , Li ２ MnO ３ -LiNi １／２ Mn １／２ O ２ -LiNi １／３ Co １／３ Mn １／３ O ２ , LiMn ２ O ４ , LiMn ３／２ Ni １／２ O ４ The metal compound particles include sulfur and Li ２ S, TiS ２ , MoS ２ , FeS ２ , V.S. ２ , Cr １／２ V １／２ S ２ Sulfides such as NbSe ３ , VSe ２ , NbSe ３ Selenides such as Cr ２ O ５ , Cr ３ O ８ , V.O. ２ , V ３ O ８ , V ２ O ５ , V ６ O １３ In addition to oxides such as LiNi ０．８ Co ０．１５ A ｌ０．０５ O ２ , LiVOPO ４ , LiV ３ O ５ , LiV ３ O ８ , MoV ２ O ８ , Li ２ FeSiO ４ , Li ２ MnSiO ４ , LiFePO ４ , LiFe １／２ Mn １／２ P.O. ４, LiMnPO ４ , Li ３ V ２ (P.O. ４ ) ３ Examples of the composite oxides include:

[0108] As the negative electrode active material, metal compound particles capable of absorbing and releasing lithium ions can be used. For example, FeO, Fe ２ O ３ , Fe ３ O ４ , MnO, MnO ２ , Mn ２ O ３ , Mn ３ O ４ , CoO, Co ３ O ４ , NiO, Ni ２ O ３ , TiO, TiO ２ , TiO ２ (B), CuO, NiO, SnO, SnO ２ , SiO ２ , RuO ２ , WO, WO ２ , WO3, MoO ３ , oxides such as ZnO, metals such as Sn, Si, Al, and Zn, LiVO ２ , Li ３ VO ４ , Li ４ Ti ５ O １２ , Sc ２ TiO ５ , Fe ２ TiO ５ composite oxides such as Li ２．６ Co ０．４ N, Ge ３ N ４ , Zn ３ N ２ , Cu ３ Nitrides such as N, Y ２ Ti ２ O ５ S ２ , MoS ２ Examples include:

[0109] When a separator is used in an electricity storage device, examples of the separator include cellulose papers such as kraft, Manila hemp, esparto, hemp, and rayon, and mixed papers thereof, polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof, polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins, polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides, polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, and acrylic resins. These may be used alone or in combination of two or more.

[0110] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope that can comply with the above and below aims, and all such modifications are included in the technical scope of the present invention.

[0111] (Example 1) Preparation of modifier and film A modifier for the solid electrolyte of Example 1 was prepared using an ionic compound, a boric acid ester having a polymerizable functional group, and a lithium salt, and the modifier was formed into a film under conditions for coating the solid electrolyte.

[0112] For the solid electrolyte of Example 1, a bis(fluorosulfonyl)imide anion (i.e., an anion in which n and m in the above formula (A) are both 0; hereinafter, referred to as an “FSI anion”) was used as the anion constituting the ionic compound.

[0113] As the cation constituting the ionic compound, N,N-ethylpyrrolidinium cation (i.e., R １ and R ２ and P22 are both ethyl groups, hereinafter referred to as "cation P22").

[0114] As the borate ester having a polymerizable functional group, tris(diethylene glycol monomethacrylate) borate ester (Y in the above formula (1)) １ ~Y ３are both methacryloyl groups, and A １ O-A ３ A compound in which each O is an oxyethylene group and p1 to p3 are each an average of 2 (hereinafter referred to as "PE-90 Borate") was used.

[0115] As the lithium salt, lithium bis(fluorosulfonyl)imide (hereinafter referred to as "LiFSI") manufactured by Tokyo Chemical Industry Co., Ltd. was used.

[0116] Specifically, an ionic compound composed of FSI anion and P22 cation (hereinafter referred to as "[P22][FSI]") was added to a vial. In this example, [P22][FSI] was synthesized by ion exchange.

[0117] To adjust the viscosity of the modifier, about 3 mass % of acrylonitrile (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the total of the ionic compound, boric acid ester having a polymerizable functional group, and lithium salt.

[0118] A benzoyl peroxide-based polymerization initiator (NOF Corporation's "Niper BMT-K40") was added to the vial so that the amount was 0.0003 mol % relative to the boric acid ester having a polymerizable functional group, to prepare a modifier.

[0119] The content of each component in the modifier of Example 1 (standard: total of ionic compound, boric acid ester having a polymerizable functional group, and lithium salt) is as follows: Ionic compound: 70% by mass, Boric acid ester having a polymerizable functional group: 12% by mass, Lithium salt: 18% by mass

[0120] The obtained modifier was dropped onto a SUN316 plate for measuring ionic conductivity, and polymerized for 1 hour at 80°C, which was the same condition as when coating the solid electrolyte, to obtain a membrane of Example 1 (thickness: 0.5 mm).

[0121] (Comparative Examples 1 and 2) Preparation of Modified Material and Membrane Modified materials and membranes of Comparative Examples 1 and 2, which are to be compared with the membrane of Example 1, were also prepared.

[0122] The modifier of Comparative Example 1 is similar to the modifier of Example 1 in that it contains an ionic compound and a lithium salt, but differs in that it does not contain a boric acid ester having a polymerizable functional group or a polymerization initiator.

[0123] The content of each component in the modifier of Comparative Example 1 (standard: total of ionic compound and lithium salt) is as follows: Ionic compound: 85% by mass Lithium salt: 15% by mass

[0124] The modifier of Comparative Example 2 is similar to the modifier of Example 1 in that it contains a borate ester having a polymerizable functional group and a lithium salt, but differs in that it does not contain an ionic compound.

[0125] The content of each component in the modifier of Comparative Example 2 (standard: total of borate ester having a polymerizable functional group and lithium salt) is as follows: borate ester having a polymerizable functional group: 75% by mass, lithium salt: 25% by mass

[0126] The membrane of Comparative Example 1 or 2 (thickness: 0.5 mm) was produced from the modified material of Comparative Example 1 or 2 in the same manner as in Example 1.

[0127] (Test Example 1) Evaluation of Membrane Characteristics The ionic conductivity of the membranes obtained in Example 1, Comparative Example 1, and Comparative Example 2 was measured. Specifically, the obtained membrane was sandwiched between two SUS316 plates and opposed by an electrode press, to assemble a two-electrode sealed cell (manufactured by Toyo Systems Co., Ltd.), and impedance measurement was performed. Furthermore, to confirm whether the membrane could follow the expansion and contraction of the solid electrolyte, pressure was applied to the SUS316 plates from above and below, and the ionic conductivity of the membrane was also measured when pressure was applied and after pressure was released. The ionic conductivity was calculated from the impedance measurement results and the membrane thickness. The measurement results are shown in Table 1. Note that "1.01E-03" and the like in Table 1 represent "1.01 x 10 －３ " etc.

[0128] The thickness of the resulting film was measured for thickness reduction due to pressure and recovery after pressure was released. The measurement results are shown in Table 1. The ambient temperature at the time of each measurement is also shown in Table 1.

[0129]

[0130] As shown in Table 1, the membrane obtained in Example 1, which used an ionic compound, a borate ester having a polymerizable functional group, and a lithium salt, had an ionic conductivity that was 22 to 36 times higher than the membrane obtained in Comparative Example 1, which did not use a borate ester having a polymerizable functional group. Furthermore, the membrane of Example 1 showed less thickness loss due to pressure application and was also excellent in recovering its thickness after pressure was released, compared to the membrane of Comparative Example 1.

[0131] Furthermore, the membrane obtained in Example 1 had an ionic conductivity that was improved by 216 to 543 times compared to the membrane obtained in Comparative Example 2, which did not use an ionic compound. Furthermore, the membrane of Example 1 recovered its thickness after the pressure was released, confirming that it had high adaptability to shape changes.

[0132] From the above results, it was confirmed that a membrane formed from a solid electrolyte modifier containing an ionic compound, a borate ester with a polymerizable functional group, and a lithium salt can adapt to changes such as volume expansion and contraction of the solid electrolyte and exhibits high ionic conductivity.

[0133] Test Example 2: Reduction of interfacial resistance between positive electrode and solid electrolyte by a film formed from the modifier of Example 1 It was confirmed that the interfacial resistance between the positive electrode and the solid electrolyte was reduced by forming a film between the positive electrode and the oxide-based solid electrolyte or between the positive electrode and the sulfide-based solid electrolyte using the modifier of Example 1.

[0134] As the positive electrode active material, LiNi ０．８ Co ０．１ Mn ０．１ O ２ (Abbreviation indicating the composition of the positive electrode active material: NMC811) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used. １．４ Al ０．４ Ti １．６ (P.O. ４ ) ３ (abbreviation: LATP) (manufactured by Sumita Optical Glass Co., Ltd.) was used. ６ P.S. ５ Br (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used.

[0135] A cell (symmetric cell) was fabricated in which an oxide-based solid electrolyte or a sulfide-based solid electrolyte was used as an intermediate layer and a positive electrode was disposed on both sides of the intermediate layer. The modifier of Example 1 was polymerized between the solid electrolyte and the positive electrode at 80°C for 1 hour to fabricate a membrane. Next, the interface resistance between the positive electrode and the solid electrolyte was measured by AC impedance measurement without applying pressure or crimping. The measurement results are shown in Table 2.

[0136]

[0137] As shown in Table 2, it was confirmed that the interfacial resistance between the positive electrode and the sulfide-based solid electrolyte was significantly reduced without pressure or crimping by forming the film of Example 1 between them. It was also confirmed that the interfacial resistance between the positive electrode and the oxide-based solid electrolyte was significantly reduced by forming the film of Example 1 between them.

[0138] (Test Example 3) Preparation and Evaluation of Composite Film of Solid Electrolyte A fine powder of oxide-based solid electrolyte was mixed with the modifier of Example 1, and the resulting mixture was heated on a PET film at a temperature of 80°C for 1 hour to prepare a composite film of oxide-based solid electrolyte. In addition, without using the modifier of Example 1, a slurry of fine powder of oxide-based solid electrolyte was used to form the fine powder of solid electrolyte into a film. As the oxide-based solid electrolyte, Li １．４ Al ０．４ Ti １．６ (P.O. ４ ) ３ (abbreviation: LATP) (manufactured by Sumita Optical Glass) was used.

[0139] The prepared composite membrane or the oxide-based solid electrolyte formed into a membrane was compressed at 500 MPa, and the thickness and ions were measured thereafter. The ionic conductivity was measured by AC impedance measurement. Table 3 shows the amount of the modifier of Example 1 added to the entire composite membrane, as well as the thickness and ionic conductivity of the composite membrane or the oxide-based solid electrolyte formed into a membrane after compression at 500 MPa. Note that "2.00E-07" and the like in Table 3 represent "2.00 x 10 －７ " etc.

[0140]

[0141] Because the oxide-based solid electrolyte has a large interparticle resistance, when only the oxide-based solid electrolyte was used (i.e., the modifier of Example 1 was 0 mass %), a value close to insulation was obtained even when pressure was applied. By forming a composite film using the modifier of Example 1 and the oxide-based solid electrolyte (i.e., by covering the oxide-based solid electrolyte with a film formed from the modifier of Example 1), it became possible to bond the interparticle interfaces, and ionic conductivity was confirmed without sintering the oxide-based solid electrolyte.

[0142] (Comparative Example 3) Preparation of all-solid-state secondary battery <Preparation of positive electrode slurry> LiNi was used as the positive electrode active material. 1／2 Co 1／5 Mn 3／１０ O ２ (Abbreviation indicating the composition of the positive electrode active material: NMC523) (average particle diameter: 10 μm, manufactured by Toshima Manufacturing Co., Ltd.) 70 parts by mass, and Li as a solid electrolyte ２ S and P ２ S ５ Sulfide glass (Li ２ S / P ２ S ５ = 75 mol % / 25 mol %, average particle size 5 μm (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 28 parts by mass of acetylene black as a conductive additive, and 1.2 parts by mass of polyvinylidene fluoride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a binder were mixed, and xylene was further added as a liquid medium to adjust the solid content concentration to 75 mass %, and the mixture was mixed for 30 minutes in a planetary centrifugal mixer (manufactured by THINKY Corporation, Awatori Rentaro ARV-310) to prepare a positive electrode slurry.

[0143] <Preparation of slurry for solid electrolyte layer> Li was used as the solid electrolyte. ２ S and P ２ S ５ Sulfide glass (Li ２ S / P ２ S ５= 75 mol % / 25 mol %, average particle size 5 μm) and 2 parts by mass of polyvinylidene fluoride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a binder were mixed, and xylene was further added as a liquid medium to adjust the solid content concentration to 55 mass %, and the mixture was mixed for 30 minutes in a planetary centrifugal mixer ("Awatori Rentaro ARV-310" manufactured by THINKY Corporation) to prepare a slurry for the solid electrolyte layer.

[0144] <Preparation of negative electrode slurry> A negative electrode slurry was prepared by dissolving artificial graphite (average particle size: 20 μm, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (65 parts by mass) as a negative electrode active material and Li ２ S and P ２ S ５ Sulfide glass (Li ２ S / P ２ S ５ = 75 mol % / 25 mol %, average particle size 5 μm, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 2 parts by mass of styrene-butadiene copolymer (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a binder were mixed, and xylene was further added as a liquid medium to adjust the solid content concentration to 65 mass %, and then the mixture was mixed for 10 minutes with a planetary centrifugal mixer ("Awatori Rentaro ARV-310" manufactured by THINKY Corporation) to prepare a negative electrode slurry.

[0145] <Preparation of Positive Electrode> The positive electrode slurry prepared above was applied onto aluminum foil by a doctor blade method, and the coated aluminum foil was dried at 120°C under reduced pressure for 3 hours to remove the xylene, thereby preparing a positive electrode on which a positive electrode active material layer having a thickness of 0.1 mm was formed.

[0146] <Preparation of Solid Electrolyte Layer> The slurry for the solid electrolyte layer prepared above was applied onto a release PET film by a doctor blade method, and the film was dried at 120°C under reduced pressure for 3 hours to remove xylene, thereby preparing a solid electrolyte layer having a thickness of 0.1 mm.

[0147] <Preparation of Negative Electrode> The negative electrode slurry prepared above was applied onto a stainless steel foil by a doctor blade method, and the foil was dried at 120°C under reduced pressure for 3 hours to remove the xylene, thereby preparing a negative electrode on which a negative electrode active material layer having a thickness of 0.1 mm was formed.

[0148] <Fabrication of All-Solid-State Secondary Battery> The positive electrode fabricated as described above was cut into a disk with a diameter of 13 mm, and the negative electrode and the solid electrolyte layer peeled from the release PET film were cut into a disk with a diameter of 15 mm. Next, the cut positive electrode was attached to one side of the cut solid electrolyte layer so that the surface of the positive electrode active material layer of the positive electrode was in contact with the solid electrolyte layer. Next, the cut negative electrode was attached to the other side of the cut solid electrolyte layer so that the surface of the negative electrode active material layer of the negative electrode was in contact with the solid electrolyte layer. Using a heat press, the laminate was heated (90°C) and pressed (500 MPa, 2 minutes) to fabricate an all-solid-state secondary battery laminate having a laminate structure of aluminum foil / positive electrode active material layer / solid electrolyte layer / negative electrode active material layer / stainless steel foil. Next, the all-solid-state secondary battery laminate fabricated in this manner was placed in a stainless steel 2032-type coin case incorporating a spacer and a washer, and the 2032-type coin case was crimped to fabricate an all-solid-state secondary battery.

[0149] Example 2: Preparation of an All-Solid-State Secondary Battery (Positive Electrode Interface Treatment) The positive electrode prepared in Comparative Example 3 was cut into a 14 mm × 20 mm shape. The negative electrode and solid electrolyte layer were cut into a 19 mm × 24 mm shape. The solid electrolyte layer, negative electrode active material layer, and stainless steel foil were laminated in this order and heated (90°C) and pressed (490 MPa, 2 minutes) using a heat press to prepare a solid electrolyte layer / negative electrode active material layer / stainless steel foil laminate structure. Next, the modifier of Example 1 was applied to the surface of the positive electrode active material layer, and the laminate was bonded to the solid electrolyte layer of the solid electrolyte layer / negative electrode active material layer / stainless steel foil laminate structure so that it was in contact with the solid electrolyte layer. The modifier was then heated (80°C) and pressed (3 MPa, 1 minute) using a heat press to prepare a laminate for an all-solid-state secondary battery having a laminate structure of aluminum foil / positive electrode active material layer / membrane formed from the modifier / solid electrolyte layer / negative electrode active material layer / stainless steel foil. Next, the laminate for an all-solid-state secondary battery thus produced was placed in an aluminum pouch and compressed to produce an all-solid-state secondary battery (positive electrode interface treatment).

[0150] Example 3: Preparation of an All-Solid-State Secondary Battery (Both Interfaces Treated) The positive electrode, negative electrode, and solid electrolyte layer prepared in Comparative Example 3 were separately cut into 14 mm x 20 mm shapes. The modifier of Example 1 was applied to the surface of the positive electrode active material layer of the positive electrode and the surface of the negative electrode active material layer of the negative electrode, and the two were bonded together so as to contact the solid electrolyte layer. The resulting laminate was heated (80°C) and pressed (3 MPa, 1 minute) using a heat press to prepare an all-solid-state secondary battery laminate having a laminate structure of aluminum foil / positive electrode active material layer / membrane formed from the modifier / solid electrolyte layer / membrane formed from the modifier / negative electrode active material layer / stainless steel foil. The all-solid-state secondary battery laminate thus prepared was then placed in an aluminum pouch and compressed to prepare an all-solid-state secondary battery (both interfaces treated).

[0151] Test Example 4: Measurement of DC Internal Resistance (DCR) of All-Solid State Secondary Battery A DC internal resistance (DCR) test was carried out in an environment of 25°C using the all-solid state secondary battery of Comparative Example 3 and the all-solid state secondary battery of Example 2 (positive electrode interface treatment). Charging was performed by increasing the voltage to a cut-off voltage of 3.7 V over 120 minutes, followed by a 10-minute pause, followed by discharging to a cut-off voltage of 1.9 V over 120 minutes, followed by a 10-minute pause. This cycle was repeated, and the DC internal resistance (DCR) was measured from the voltage change according to Ohm's law. The results are shown in Table 4. In Table 4 below, "DCR (10 min)" means the DC internal resistance value obtained by pausing charging at a charging rate (SOC) of 90%, and then dividing the difference between the voltage 10 minutes later and the voltage before the pause by the current value at a constant current; "DCR (1 sec)" means the DC internal resistance value obtained by pausing charging at a charging rate (SOC) of 90%, and then dividing the difference between the voltage 1 second later and the voltage before the pause by the current value at a constant current; and "DCR (1 sec-10 min)" means the difference between DCR (10 min) and DCR (1 sec).

[0152]

[0153] Test Example 5 Evaluation of Initial Charge / Discharge Characteristics of Solid-State Secondary Battery An initial charge / discharge test (3 cycles) was performed in an environment of 25°C using the all-solid-state secondary battery of Comparative Example 3, the all-solid-state secondary battery of Example 2 (positive electrode interface treatment), and the all-solid-state secondary battery of Example 3 (both interface treatments). Charging was performed by increasing the voltage to a cut-off voltage of 3.7 V over 120 minutes, followed by a 10-minute pause, followed by decreasing the voltage to a cut-off voltage of 1.9 V over 120 minutes, followed by a 10-minute pause. This cycle was repeated for a total of 3 cycles, and the charge capacity and discharge capacity of each cycle were measured, and the Ah efficiency (= 100 × discharge capacity / charge capacity) was calculated. The results are shown in Tables 5 to 7.

[0154]

[0155]

[0156]

[0157] <Evaluation Results> From the results shown in Tables 4, 6, and 7, it was confirmed that the all-solid-state secondary battery of Example 2 (positive electrode interface treatment) and the all-solid-state secondary battery of Example 3 (both interface treatments) had performance comparable to that of the all-solid-state battery of Comparative Example 3. In particular, in Example 3, an all-solid-state secondary battery having performance comparable to that of the all-solid-state secondary battery of Comparative Example 3, which was produced through a step of applying high pressure (500 MPa, 2 minutes), could be easily produced without performing the step of applying high pressure.

[0158] The solid electrolyte modifier of the present invention can be used to form a membrane that is in contact with a solid electrolyte, has excellent adaptability to volume changes of the solid electrolyte, and exhibits high ionic conductivity. A solid electrolyte having such a membrane is useful for electricity storage devices such as secondary batteries and electric double layer capacitors.

[0159] This application is based on Japanese Patent Application No. 2023-139368, the contents of which are incorporated in their entirety herein.

Claims

1. A modifier for a solid electrolyte comprising an ionic compound consisting of an anion containing a fluorine atom or a cyano group and a pyrrolidinium cation, a borate ester having a polymerizable functional group, and a lithium salt.

2. The solid electrolyte modifier according to claim 1, wherein the content of the ionic compound is 10 to 90 mass %, the content of the borate ester having a polymerizable functional group is 1 to 20 mass %, and the content of the lithium salt is 5 to 70 mass %, based on the total of the ionic compound, the borate ester having a polymerizable functional group, and the lithium salt.

3. The boric acid ester having a polymerizable functional group is represented by the formula (1): [In formula (1), Y １ ~Y ３ are each independently an acryloyl group, a methacryloyl group, or an alkyl group having 1 to 4 carbon atoms, and at least one of them is an acryloyl group or a methacryloyl group; １ O-A ３ O is each independently an oxyalkylene group having 2 to 4 carbon atoms, and p1 to p3 are each independently a number from 1 to 600.

4. The pyrrolidinium cation has the formula (2): [In formula (2), R １ and R ２ and each independently represents a methyl group, an ethyl group, a propyl group, an isopropyl group, a methoxymethyl group, or a methoxyethyl group.

5. The anion containing a fluorine atom or a cyano group is NH ２ － An imide anion in which two hydrogen atoms of the anion are each independently substituted with a perfluoroalkylsulfonyl group or a fluorosulfonyl group (the above-mentioned NH ２ － when two hydrogen atoms of the anion are each independently substituted with the perfluoroalkylsulfonyl group, the two perfluoroalkyl groups contained therein may be linked together), an anion containing a fluorine atom selected from the group consisting of a tris(trifluoromethanesulfonyl)methanide anion, a hexafluorophosphate anion, a (perfluoroalkyl)fluorophosphate anion in which some fluorine atoms of the hexafluorophosphate anion are substituted with perfluoroalkyl groups, a tetrafluoroborate anion, a (perfluoroalkyl)fluoroborate anion in which some fluorine atoms of the tetrafluoroborate anion are substituted with perfluoroalkyl groups, and an N-(perfluoroalkylsulfonyl)perfluorocarboxylic acid amide anion, or a tricyanomethanide anion, a tetracyanoborate anion, a tricyanomethoxyborate anion, a tricyanoisopropoxyborate anion, a tricyano(pentafluorophenoxy)borate anion, a tricyano(trimethylsiloxy)borate anion, The modifier according to claim 4, which is an anion containing a cyano group selected from the group consisting of tricyano(hexafluoroisopropoxy)borate anion, tricyanomethylthioborate anion, dicyanodimethoxyborate anion, and cyanotrimethoxyborate anion.

6. The imide anion has the formula (A): [In formula (A), m and n each independently represent an integer of 0 or more.] A bis(perfluoroalkylsulfonyl)imide anion, a bis(fluorosulfonyl)imide anion, and an N-(fluorosulfonyl)-N-(perfluoroalkylsulfonyl)imide anion represented by formula (B): and a cyclohexafluoropropane-1,3-bis(sulfonyl)imide anion represented by formula (C): and a cyclotetrafluoroethane-1,3-bis(sulfonyl)imide anion represented by formula (D): [In formula (D), q is an integer of 1 or more.] The (perfluoroalkyl)fluoroborate anion is a tris(fluoroalkyl)trifluorophosphate anion represented by formula (E): [In formula (E), r is an integer of 1 or more, and s is an integer of 0 or more.] and a mono(fluoroalkyl)trifluoroborate anion represented by the formula (E) and a bis(fluoroalkyl)fluoroborate anion represented by the formula (F): The modifier according to claim 5 , which is an anion represented by the following formula (F): [in which j and k each independently represent an integer of 1 or more.] 7. The modifier according to claim 1, further comprising a polymerization initiator.

8. An electricity storage device comprising: a membrane formed from the modifier according to any one of claims 1 to 7; a solid electrolyte; and two electrodes facing each other with the solid electrolyte sandwiched therebetween, wherein the membrane is present between the solid electrolyte and at least one of the two electrodes.

9. The electricity storage device according to claim 8, wherein at least one of the electrodes is a polarizable electrode having an active material layer made of a porous material and a current collector.

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