Ion-conducting layer for power storage devices

Abstract

To provide an ion-conducting layer for a power storage devices having high ionic conductivity.SOLUTION: An ion-conducting layer according to an embodiment of the present disclosure disposed between a positive electrode and a negative electrode of an electricity storage device contains an acrylic polymer, and the acrylic polymer includes a structural unit (A) derived from a compound represented by the following formula (I) and a structural unit (B) derived from a compound represented by the following formula (II).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an ion conductive layer for an electricity storage device. [Background technology]

[0002] The demand for energy storage devices has been growing in recent years due to factors such as the widespread use of smartphones, zero-emission regulations in the automotive market, and the expanded use of natural energy. Therefore, energy storage devices are expected to be small, lightweight, and have large capacities, and there is a growing demand for higher output and energy density in automobiles and other applications. To meet these demands, the development of energy storage devices such as lithium-ion secondary batteries, alkali-ion secondary batteries, electric double-layer capacitors, lithium-ion capacitors, and all-solid-state batteries is progressing.

[0003] Such energy storage devices generally include electrodes in which a composite layer containing an active material is applied to a metal foil, and an electrolyte that allows ions to move between the electrodes is filled. This electrolyte can be liquid, semi-solid, or solid, depending on the purpose. It is known that in the case of liquids, a solvent containing metal ions is used, in the case of semi-solids, a gel containing the liquid is used, and in the case of solids, a solid with ion conductivity is used. Storage batteries that primarily use liquid or semi-solid electrolytes have separators between the electrodes to prevent short circuits between the electrodes. On the other hand, in the case of storage batteries that use solid electrolytes, a mixed membrane of solid electrolyte and resin is used to prevent peeling, as the solid electrolyte alone is prone to peeling.

[0004] In addition, because pouch-type batteries have a large range of movement, electrode and separator misalignment occurs, which reduces durability, and adhesive layers are provided to prevent this. It is also known that surface protective films are provided on the surfaces of the positive and negative electrodes to prevent metal deposition due to local reactions and the formation of highly ion-resistant adhesive films due to electrolyte denaturation.

[0005] For example, separator adhesive layers and electrode surface protective films have been proposed (Patent Documents 1 and 2). Patent Document 1 discloses a composition for an electrochemical device functional layer, which comprises a polymer A and a solvent, wherein the polymer A contains alkylene oxide structure-containing monomer units and (meth)acrylic acid ester monomer units. In the examples of this document, the polymer A is a polymer having structural units derived from methoxypolyethylene glycol acrylate and structural units derived from 2-ethylhexyl acrylate, a polymer having structural units derived from ethoxydiethylene glycol acrylate and structural units derived from 2-ethylhexyl acrylate, or a polymer having structural units derived from methoxypolyethylene glycol acrylate and structural units derived from stearyl acrylate. Patent Document 2 discloses a resin composition for use in electrodes of electrical storage devices, which comprises polymer particles containing a structural unit A consisting of a compound of a specific structure having a CH2=CC=O structural unit and having an -O- or -NH- bond, and a structural unit B derived from at least one compound selected from a compound of a specific structure having a CH2=CC=O structural unit and having an -OM bond (M is a hydrogen atom or a cation), a compound having a CH2=CC=O structural unit and having a functional group of a specific structure bonded via an -O- or -NH- bonding group, and an unsaturated dibasic acid. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] WO2019 / 044912 issue [Patent Document 2] Japanese Patent Application Publication No. 2018-32623 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in order to meet the recent demands for miniaturization, higher capacity, and higher output, it is necessary to improve the ionic conductivity of resins used in electrolytes, separators, solid electrolyte mixed membranes, adhesive layers, surface protection layers, etc., and proposals for resin layers with higher ionic conductivity are being sought. By improving the ionic conductivity of the resin layer, for example, it is possible to improve the durability of the resin layer while suppressing an increase in the internal resistance of the battery.

[0008] Further improvement in ionic conductivity is desired for resin layers produced using polymer A disclosed in Patent Document 1 and polymer particles disclosed in Patent Document 2. In addition, the polymer particles disclosed in Patent Document 2 have been found to pose a problem in improving cycle durability in terms of adhesion in separators having an ion-conductive layer.

[0009] In one aspect, the present disclosure provides an ion-conductive layer for an electricity storage device, which can provide an electrode or separator having high ionic conductivity and high cycle durability. [Means for solving the problem]

[0010] In one aspect, the present disclosure relates to an ion-conducting layer for an electricity storage device, which is disposed between a positive electrode and a negative electrode of the electricity storage device, the ion-conducting layer containing an acrylic polymer, the acrylic polymer including a structural unit (A) derived from a compound represented by the following formula (I) and a structural unit (B) derived from a compound represented by the following formula (II): [ka] In formula (I), R 1 represents a hydrogen atom or a methyl group. 2 represents a linear or branched alkyl group having 1 to 4 carbon atoms. 1 represents —O— or —NH—. [ka] In formula (II), R 3 represents a hydrogen atom or a methyl group, and X 2is -O- or -N(R 5 )- indicates X 2 When is -O-, R 4 is a structure having an alkylene oxide (wherein the average number of moles of alkylene oxide added is 2 to 50), or -R 6 N + (R 7 )(R 8 )(R 9 )·Y - It has the structure: R 6 represents a linear or branched alkylene group having 1 to 3 carbon atoms; R 7 , R 8 , R 9 are the same or different and represent a linear or branched alkyl group having 1 to 3 carbon atoms. Y - indicates an anion. 2 -N(R 5 )-, R 4 and R 5 are the same or different and represent a straight-chain or branched-chain alkyl group having 1 to 3 carbon atoms.

[0011] In one aspect, the present disclosure relates to a method of improving ionic conductivity comprising forming an ion-conducting layer comprising the acrylic polymer of the present disclosure.

[0012] In one aspect, the present disclosure relates to a member for an electricity storage device containing the ion conductive layer of the present disclosure.

[0013] In one aspect, the present disclosure relates to an electricity storage device having the electricity storage device member of the present disclosure.

[0014] In one aspect, the present disclosure relates to a method for forming an ion-conducting layer for an electricity storage device, the method comprising the steps of applying a slurry containing an acrylic polymer composition to a surface of a substrate and drying the applied slurry to form an ion-conducting layer, wherein the acrylic polymer composition contains acrylic polymer particles, and the acrylic polymer contains a structural unit (A) derived from a compound represented by the following formula (I) and a structural unit (B) derived from a compound represented by the following formula (II): [ka] In formula (I), R 1 represents a hydrogen atom or a methyl group. 2 represents a linear or branched alkyl group having 1 to 4 carbon atoms. 1 represents —O— or —NH—. [ka] In formula (II), R 3 represents a hydrogen atom or a methyl group, and X 2 is -O- or -N(R 5 )- indicates X 2 When is -O-, R 4 is a structure having an alkylene oxide (wherein the average number of moles of alkylene oxide added is 2 to 50), or -R 6 N + (R 7 )(R 8 )(R 9 )·Y - It has the structure: R 6 represents a linear or branched alkylene group having 1 to 3 carbon atoms; R 7 , R 8 , R 9 are the same or different and represent a linear or branched alkyl group having 1 to 3 carbon atoms. Y - indicates an anion. 2 -N(R 5 )-, R 4 and R 5 are the same or different and represent a straight-chain or branched-chain alkyl group having 1 to 3 carbon atoms. [Effects of the Invention]

[0015] According to the present disclosure, an ion-conducting layer for an electricity storage device having high ion conductivity can be provided. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of a bipolar battery. DETAILED DESCRIPTION OF THE INVENTION

[0017] [Ion-conducting layers for power storage devices] In one aspect, the present disclosure is based on the finding that ion conductivity can be improved by forming an ion conductive layer for an electricity storage device from a specific acrylic polymer.

[0018] That is, in one aspect, the present disclosure relates to an ion-conducting layer for an electricity storage device (hereinafter also referred to as the "ion-conducting layer of the present disclosure") that is disposed between a positive electrode and a negative electrode of an electricity storage device, the ion-conducting layer containing an acrylic polymer (hereinafter also referred to as the "acrylic polymer of the present disclosure"), and the acrylic polymer containing a structural unit (A) derived from the compound represented by formula (I) above and a structural unit (B) derived from the compound represented by formula (II) above.

[0019] The present disclosure provides an ion-conducting layer for an electricity storage device having high ion conductivity. By using the ion-conducting layer of the present disclosure in an electrolyte, separator, solid electrolyte mixed membrane, adhesive layer between electrodes and separators, surface protective layer, or the like of an electricity storage device, an electricity storage device with excellent battery characteristics can be obtained.

[0020] Although the details of the mechanism by which the effects of the present disclosure are manifested are not clear, the following is presumed. Polymers (e.g., SBR, PVDF) typically used in lithium-ion batteries are thought to hinder the movement of lithium ions within the battery, resulting in resistance. However, the acrylic polymer of the present disclosure contained in the ion-conductive layer of the present disclosure has high affinity with the electrolyte, allowing the electrolyte to be contained in the ion-conductive layer containing the polymer. This allows lithium ions to move quickly through the electrolyte in the ion-conductive layer, potentially reducing resistance. As a result, battery characteristics such as capacity retention and cycle durability are thought to be excellent. Furthermore, the acrylic polymer of the present disclosure contains structural unit (B), which improves emulsion stability and is thought to enhance the adhesion of the ion-conductive layer to electrodes and separators. This ultimately improves the durability of the energy storage device and improves its cycle characteristics. However, these are speculations, and the present disclosure may not be interpreted as being limited to these mechanisms.

[0021] The ion conduction layer of the present disclosure is an ion conduction layer disposed between the positive and negative electrodes of an electricity storage device in which ions are exchanged between the positive and negative electrodes. In one or more embodiments, the ion conduction layer of the present disclosure is an ion-conductive resin-containing layer intended for the purposes of protecting or adhering the electrodes or for the safety and durability of the electricity storage device. The ion conduction layer of the present disclosure may be disposed anywhere between the positive and negative electrodes. Examples of locations where the ion conduction layer of the present disclosure may be disposed include the negative electrode surface (e.g., a negative electrode protective layer), the electrolyte layer, the separator surface (e.g., an adhesive layer), the separator itself, and the positive electrode surface (e.g., a positive electrode protective layer). By disposing the ion conduction layer of the present disclosure in at least one of these locations, the battery characteristics of the electricity storage device can be improved.

[0022] In one or more embodiments, the ion conduction layer of the present disclosure is formed from the acrylic polymer of the present disclosure. In one or more embodiments, the ion conduction layer of the present disclosure has high ion conductivity due to its ability to transmit ions. Therefore, the ion conduction layer of the present disclosure exhibits high ion conductivity, for example, in the measurement method described below, and is thought to be effective in reducing the ionic resistance of an electricity storage device. Therefore, in one aspect, the present disclosure relates to a method for improving ion conductivity, which includes forming an ion conduction layer containing the acrylic polymer of the present disclosure. The method for forming the ion conduction layer is described below.

[0023] [Acrylic polymer] The ion conduction layer of the present disclosure contains the acrylic polymer of the present disclosure. From the viewpoints of performance and production of the electricity storage device, the content of the acrylic polymer of the present disclosure in the ion conduction layer of the present disclosure is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, even more preferably 5% by mass or more, and preferably 100% by mass or less. The ion conduction layer of the present disclosure may contain a polymer other than the acrylic polymer of the present disclosure, but from the viewpoint of the performance and manufacturing of the electricity storage device, the content of the acrylic polymer of the present disclosure in the polymer of the ion conduction layer of the present disclosure is preferably 75% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and preferably 100% by mass or less. Examples of polymers other than the acrylic polymer of the present disclosure include acrylic polymers other than the acrylic polymer of the present disclosure, styrene-based polymers, fluorine-based polymers, and cellulose-based polymers.

[0024] The acrylic polymer of the present disclosure contains the structural unit (A) and the structural unit (B) described below. The structural units (A) and (B) are each structural units derived from a monofunctional monomer of the compound described below. The monofunctional monomer refers to a monomer having one unsaturated bond. In one or more embodiments, the acrylic polymer of the present disclosure may further contain a structural unit (C) described below. In one or more embodiments, the acrylic polymer of the present disclosure may be at least one selected from a copolymer containing the structural unit (A) described below and the structural unit (B) described below, and a copolymer containing the structural unit (A) described below, the structural unit (B) described below, and the structural unit (C) described below. The acrylic polymer may be one type, or a combination of two or more types.

[0025] <Constituent unit (A)> The structural unit (A) is a structural unit derived from a compound represented by the following formula (I) (hereinafter also referred to as "monomer (A)"). The monomer (A) may be used alone or in combination of two or more types. [ka]

[0026] In formula (I), R 1 represents a hydrogen atom or a methyl group, and from the viewpoint of ease of synthesis, a hydrogen atom is preferred. 2 represents a linear or branched alkyl group having 1 to 4 carbon atoms, and from the viewpoint of affinity to metal ions and the electrolyte, a linear alkyl group having 1 to 4 carbon atoms is preferred. 1 represents -O- or -NH-, and from the viewpoint of ease of synthesis, -O- is preferred.

[0027] Examples of the monomer (A) include one or a combination of two or more selected from the group consisting of alkyl ester (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, normal propyl (meth)acrylate, isopropyl (meth)acrylate, and butyl (meth)acrylate; and monofunctional (meth)acrylamides such as methyl (meth)acrylamide, ethyl (meth)acrylamide, normal propyl (meth)acrylamide, and isopropyl (meth)acrylamide. Among these, from the viewpoint of affinity for metal ions and the electrolyte, one or a combination of two or more selected from methyl methacrylate (MMA), ethyl acrylate (EA), and butyl acrylate (BA) is preferred, with ethyl acrylate (EA) being more preferred. In the present disclosure, (meth)acrylate refers to methacrylate or acrylate, and (meth)acrylamide refers to methacrylamide or acrylamide.

[0028] The content of the structural unit (A) in all structural units of the acrylic polymer of the present disclosure is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, from the viewpoint of affinity with the electrolyte solution. Furthermore, the content of the structural unit (A) in all structural units of the acrylic polymer of the present disclosure is preferably 99% by mass or less, from the viewpoint of affinity with metal ions. The content of the structural unit (A) can be determined by a known analytical method or analytical device. When the structural unit (A) is composed of structural units derived from two or more types of monomers (A), the content of the structural unit (A) refers to the total content thereof.

[0029] <Constituent Unit (B)> The structural unit (B) is a structural unit derived from a compound represented by the following formula (II) (hereinafter also referred to as "monomer (B)"). The monomer (B) may be used alone or in combination of two or more types. [ka]

[0030] In formula (II), R 3 represents a hydrogen atom or a methyl group, and X 2 is -O- or -N(R 5 )- indicates. X 2 When is -O-, R 4 is a structure having an alkylene oxide (wherein the average number of moles of alkylene oxide added is 2 to 50), or -R 6 N + (R 7 )(R 8 )(R 9 )·Y - It has the structure: R 6 represents a linear or branched alkylene group having 1 to 3 carbon atoms; R 7 , R 8 , R 9 are the same or different and represent a linear or branched alkyl group having 1 to 3 carbon atoms. Y - represents an anion. Y - represents an anion. Examples of the anion include halide ions such as chloride ion, bromide ion, and fluoride ion; sulfate ion; and phosphate ion. In one or more embodiments, the structure having an alkylene oxide is represented by -(AO)mR 10 (wherein AO represents an alkylene oxide group, m represents the average number of moles of alkylene oxide added and represents 2 to 50, and R 10 represents a hydrogen atom or a straight-chain or branched-chain alkyl group having from 1 to 4 carbon atoms.) Examples of the alkylene oxide group include an ethylene oxide group and / or a propylene oxide group. From the viewpoints of affinity with the electrolyte solution and dispersion stability of the polymer, m is preferably 2 or more, more preferably 3 or more, even more preferably 6 or more, still more preferably 9 or more, and is preferably 50 or less, more preferably 40 or less, even more preferably 30 or less, and still more preferably 25 or less. X 2 -N(R 5 )-, R 4 and R 5 are the same or different and represent a straight-chain or branched-chain alkyl group having 1 to 3 carbon atoms.

[0031] The content of the structural unit (B) in all structural units of the acrylic polymer of the present disclosure is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of dispersion stability of the polymer, and is preferably 50% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, even more preferably 15% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of affinity with the electrolyte solution. The content of the structural unit (B) can be determined using a known analytical method or analytical device. When the structural unit (B) is composed of structural units derived from two or more types of monomer (B), the content of the structural unit (B) refers to the total content thereof.

[0032] The ratio (A / B) of the content of the structural unit (A) to the content of the structural unit (B) in the acrylic polymer of the present disclosure is preferably 99 or less, more preferably 75 or less, and even more preferably 50 or less, from the viewpoint of dispersion stability, and is preferably 1 or more, more preferably 3 or more, even more preferably 5 or more, and even more preferably 10 or more, from the viewpoint of affinity to the electrolyte solution.

[0033] <Constituent Unit (C)> From the viewpoints of ion conductivity and dispersion stability of the polymer, the acrylic polymer of the present disclosure preferably further contains a structural unit (C). The structural unit (C) is a structural unit derived from a crosslinkable monomer (hereinafter also referred to as "monomer (C)"). In one or more embodiments, the crosslinkable monomer is a monomer having two or more functional groups, and examples of the functional groups include a double bond, a hydroxyl group, and an amino group. The monomer (C) may be at least one selected from polyfunctional (meth)acrylates (hereinafter also referred to as "monomer (C1)") and N-methylolamide group-containing monomers (hereinafter also referred to as "monomer (C2)"). The monomer (C) may be used alone or in combination of two or more. The polyfunctional (meth)acrylate may be, for example, an ester of a dihydric or higher alcohol with two or more (meth)acrylic acids.

[0034] Examples of the monomer (C1) include compounds represented by the following formula (III). [ka]

[0035] In the formula (III), R 11 and R 12 are each independently preferably a hydrogen atom or a methyl group from the viewpoint of ease of synthesis. 3 and X 4 are each independently preferably -O- or -NH- from the viewpoints of ease of synthesis and affinity to the electrolyte solution, and n is preferably an integer of 1 or more and 20 or less from the viewpoints of ease of synthesis and affinity to the electrolyte solution.

[0036] Examples of the compound represented by formula (III) include at least one selected from ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, decaethylene glycol di(meth)acrylate, and pentadecaethylene glycol di(meth)acrylate.

[0037] Examples of the other monomer (C1) include at least one selected from 1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, glycerin di(meth)acrylate, allyl (meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, diethylene glycol phthalate di(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate, caprolactone-modified hydroxypivalic acid ester neopentyl glycol di(meth)acrylate, and polyester (meth)acrylate.

[0038] The N-methylolamide group-containing monomer (C2) is at least one selected from N-methylol acrylamide and N-methylol methacrylamide.

[0039] When the acrylic polymer of the present disclosure contains a structural unit (C), the content of the structural unit (C) of the acrylic polymer of the present disclosure is, from the viewpoints of ease of synthesis and affinity with the electrolyte solution, preferably 0.001 mol% or more, more preferably 0.01 mol% or more, and even more preferably 0.05 mol% or more, relative to the total number of moles of structural units other than the structural unit (C). From the same viewpoint, it is preferably 5 mol% or less, more preferably 3 mol% or less, and even more preferably 1 mol% or less. When the structural unit (C) is composed of structural units derived from two or more types of monomer (C), the content of the structural unit (C) refers to the total content thereof.

[0040] The acrylic polymer of the present disclosure may contain other structural units in addition to the structural unit (A), the structural unit (B), and the structural unit (C), as long as the effects of the present disclosure are not impaired. The other structural units may be structural units derived from monomers copolymerizable with the monomers (A), (B), and (C). Examples of monomers copolymerizable with the monomers (A), (B), and (C) include (meth)acrylonitrile, styrene, methylstyrene, alkyl (meth)acrylates having a linear or branched alkyl group with 4 or more carbon atoms, aromatic-containing (meth)acrylates, alkyl vinyl ethers, alkyl vinyl esters, and alkenyl-group-containing monomers. The monomers copolymerizable with the monomers (A), (B), and (C) may be used singly or in combination of two or more.

[0041] The total content of the structural units (A) and (B) in all structural units of the acrylic polymer of the present disclosure is 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more, from the viewpoint of affinity to metal ions and the electrolyte solution.

[0042] <Method of manufacturing acrylic polymer> The acrylic polymer of the present disclosure can be produced, for example, by copolymerizing monomer (A) and monomer (B), and, if necessary, monomer (C). That is, in one aspect, the present disclosure includes a polymerization step of polymerizing a monomer mixture containing monomer (A) and monomer (B), and, if necessary, monomer (C). Examples of the polymerization method include known polymerization methods such as emulsion polymerization, solution polymerization, suspension polymerization, and bulk polymerization, and from the viewpoint of ease of polymer production, emulsion polymerization is preferred.

[0043] In the present disclosure, the content of the structural unit (A) in all structural units of an acrylic polymer can be considered as the ratio of the amount of monomer (A) used to the total amount of monomers used in polymerization. The content of the structural unit (B) in all structural units of a polymer particle can be considered as the ratio of the amount of monomer (B) used to the total amount of monomers used in polymerization. The ratio (A / B) of the content of the structural unit (A) to the content of the structural unit (B) can be considered as the ratio of the amount of monomer (A) used to the amount of monomer (B) used in the total amount of monomers used in polymerization. The total content of the structural unit (A) and the structural unit (B) in all structural units of a polymer particle can be considered as the ratio of the total amount of monomer (A) and monomer (B) used to the total amount of monomers used in polymerization. The content of the structural unit (C) in a polymer particle can be considered as the ratio of the amount of monomer (C) used to the total number of moles of monomers other than monomer (C) used in polymerization (for example, when the polymer particle contains structural units (A) to (C), to the total number of moles of monomers (A) and (B)).

[0044] Examples of emulsion polymerization methods include known methods that use an emulsifier and methods that do not substantially use an emulsifier, so-called soap-free emulsion polymerization methods, and from the viewpoint of battery performance, soap-free emulsion polymerization methods are preferred. Examples of the acrylic polymer of the present disclosure include a polymer obtained by emulsion polymerization, preferably soap-free emulsion polymerization, of a monomer mixture containing monomer (A) and monomer (B), and optionally monomer (C).

[0045] From the viewpoint of suppressing a decrease in binding strength, the amount of emulsifier used in the emulsion polymerization is preferably 0.05% by mass or less, more preferably 0.02% by mass or less, even more preferably 0.01% by mass or less, and even more preferably substantially 0% by mass, relative to the total amount of monomers used in the emulsion polymerization. In the present disclosure, the amount of emulsifier used in the emulsion polymerization can be the amount of surfactant used in the polymerization step. In one or more embodiments, the acrylic polymer of the present disclosure is obtained by emulsion polymerizing a monomer mixture containing monomer (A) and monomer (B), and the amount of emulsifier contained in the ion conduction layer of the present disclosure is preferably 0% by mass or more and 0.05% by mass or less, more preferably 0% by mass or more and 0.02% by mass or less, even more preferably 0% by mass or more and 0.01% by mass or less, and even more preferably substantially 0% by mass, relative to the acrylic polymer.

[0046] The ion-conducting layer of the present disclosure may contain optional components other than the acrylic polymer, such as adhesives, resin modifiers, metal salts, inorganic oxides, and solid electrolytes.

[0047] The metal salt is preferably an alkali metal salt used in a supporting electrolyte of a battery, more preferably a lithium salt used in a lithium ion battery, such as LiPF, LiAsF, LiBF, LiSbF, LiAlCl, LiClO, CFSOLi, CFS0Li, CCFCoLi, (CFCO)NLi, (CFSO)NLi, (CFS0)NLi, or (CFS0)NLi.

[0048] Inorganic oxides can be used to improve the safety and strength of the electricity storage device, as long as the effects of the present disclosure are not impaired. Examples of inorganic oxides include alumina (aluminum oxide), magnesia (magnesium oxide), calcium oxide, titania (titanium oxide), zirconia (zirconium oxide), talc, and silica stone.

[0049] The solid electrolyte may be an inorganic compound having ion conductivity (e.g., lithium ion conductivity). The type of solid electrolyte is not particularly limited, and both inorganic and organic solid electrolytes may be used, but inorganic solid electrolytes are preferred from the viewpoint of flame retardancy. Known materials may be used as the inorganic solid electrolyte, such as sulfide-based solid electrolytes and oxide-based solid electrolytes. The oxide-based solid electrolyte may also serve as any of the inorganic oxides described above.

[0050] The ions that are conducted within the ion conduction layer of the present disclosure are preferably metal ions, more preferably alkali metal ions, and even more preferably lithium ions.

[0051] The ion conductive layer of the present disclosure preferably retains an organic solvent within the electricity storage device. The organic solvent is preferably a solvent that solubilizes ions, and more preferably an electrolyte solution. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and derivatives thereof; chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), and derivatives thereof; aliphatic carboxylic acid esters such as methyl formate, methyl acetate, ethyl propionate, and derivatives thereof; and γ-lactones such as γ-butyrolactone and derivatives thereof. Among these, cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, and γ-lactones are preferred, with cyclic carbonates and chain carbonates being more preferred, and EC, PC, DMC, DEC, and EMC being even more preferred. The organic solvent may be used alone or in combination of two or more kinds. The amount of organic solvent retained in the ion conduction layer in the electricity storage device is, from the viewpoint of ion conductivity, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 1% by mass or more, even more preferably 10% by mass or more, and particularly preferably 50% by mass or more, relative to the ion conduction layer, and from the viewpoint of battery durability, is preferably 10,000% by mass or less, more preferably 5,000% by mass or less, even more preferably 2,000% by mass or less, even more preferably 1,000% by mass or less, and particularly preferably 500% by mass or less.

[0052] [Acrylic polymer composition] In one aspect, the present disclosure relates to an acrylic polymer composition for forming an ion-conducting layer (hereinafter also referred to as the "acrylic polymer composition of the present disclosure"), which comprises the acrylic polymer of the present disclosure.

[0053] The acrylic polymer contained in the acrylic polymer composition of the present disclosure is preferably in the form of particles. From the viewpoints of polymer production and the performance of the electricity storage device, the content of the acrylic polymer of the present disclosure in the acrylic polymer composition of the present disclosure is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0054] In one or more embodiments, the acrylic polymer composition of the present disclosure contains a polar medium. The polar medium may be any liquid capable of dissolving or dispersing the acrylic polymer. From the viewpoints of production of the acrylic polymer and dispersion stability, the polar medium is preferably at least one organic solvent selected from methanol, ethanol, isopropanol, acetone, tetrahydrofuran, and dioxane, an aqueous medium containing such an organic solvent and water, or water, more preferably an aqueous medium and water, and even more preferably water. Examples of water include ion-exchanged water.

[0055] [Method for forming ion-conducting layer] In one or more embodiments, a method for forming an ion conduction layer according to the present disclosure includes a method for forming an ion conduction layer (hereinafter also referred to as the "method for forming an ion conduction layer according to the present disclosure"), which includes a step (application step) of applying a slurry containing the acrylic polymer composition according to the present disclosure (hereinafter also referred to as the "slurry for an ion conduction layer according to the present disclosure") to the surface of a substrate (e.g., a separator, an electrode, a release film, etc.), and a step (drying step) of drying the applied slurry to form an ion conduction layer.

[0056] The acrylic polymer contained in the slurry for the ion conduction layer of the present disclosure has a particulate shape. From the viewpoints of affinity with the electrolyte and productivity, the average particle size of the acrylic polymer particles is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. From the viewpoints of productivity and slurry stability, it is preferably 1 μm or less, more preferably 0.8 μm or less, even more preferably 0.6 μm or less, even more preferably 0.5 μm or less, and even more preferably 0.45 μm or less. In the present disclosure, the average particle size refers to the volume-average particle size (D50) measured by a laser diffraction / scattering method, and refers to the particle size at the point where the cumulative volume is 50% on a cumulative volume distribution curve where the total volume of the particle size distribution calculated on a volume basis is 100%. The volume-average particle size (D50) can be measured using a laser diffraction / scattering particle size distribution analyzer, specifically, by the method described in the Examples.

[0057] The acrylic polymer contained in the slurry for the ion conduction layer of the present disclosure may be in the form of a powder, or may be a polymer particle dispersion (also referred to as a polymer dispersion) in which polymer particles are dispersed in a medium. The medium may be a medium used in emulsion polymerization, preferably a polar medium, more preferably an aqueous medium, and even more preferably water. In one or more embodiments, the slurry for the ion conduction layer of the present disclosure may be a polymer dispersion in which the acrylic polymer of the present disclosure is dispersed in a medium.

[0058] From the viewpoint of producing an electricity storage device, the content of the acrylic polymer in the slurry for the ion conduction layer of the present disclosure is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0059] The slurry for the ion conduction layer of the present disclosure may further contain a thickener, an antifoaming agent, a neutralizing agent, etc. in addition to the optional components of the ion conduction layer of the present disclosure described above (adhesive, resin modifier, metal salt, inorganic oxide, solid electrolyte, etc.), as long as the effects of the present disclosure are not impaired. Examples of thickeners include thickening polysaccharides, alginic acid, carboxymethyl cellulose, starch, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, etc. Among these, carboxymethyl cellulose (CMC) is preferred from the viewpoint of assisting the binder action of the polymer particles.

[0060] In one or more embodiments, the method for producing a slurry for an ion conduction layer according to the present disclosure may include a polymerization step of polymerizing a monomer mixture containing monomer (A) and monomer (B), and, if necessary, monomer (C), to obtain polymer particles. The polymerization method, types of components that can be used in the polymerization, and amounts used thereof in the polymerization step of the method for producing a slurry according to the present disclosure may be the same as those in the polymerization step of the above-described method for producing an acrylic polymer.

[0061] In the coating step of the method for forming an ion conduction layer according to the present disclosure, the method for coating the slurry for the ion conduction layer according to the present disclosure is not particularly limited, and examples thereof include a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a die coater method, and a brush coating method.

[0062] In the drying step of the method for forming an ion conduction layer according to the present disclosure, examples of the drying method include drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams, etc. The drying time is typically 5 to 30 minutes, and the drying temperature is typically 40 to 180°C.

[0063] In one or more embodiments, the ion conduction layer of the present disclosure is formed by preparing a film containing an acrylic polymer. Examples of methods for preparing a film containing an acrylic polymer include the ion conduction layer formation method of the present disclosure described above. Other methods for preparing a film containing an acrylic polymer include, for example, applying or immersing a substrate such as a separator or electrode in a solution or dispersion (slurry) containing an acrylic polymer and drying the resulting solution or dispersion. Alternatively, a method is used in which a solution or slurry containing an acrylic polymer is applied to a release film substrate, drying the solution or slurry, and then forming a film, and transferring the resulting film to a predetermined location.

[0064] The thickness of the ion conduction layer of the present disclosure can be set according to the purpose, and from the viewpoints of ease of production of the electricity storage device and battery characteristics, it is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 5 μm or more, and from the same viewpoints, it is preferably 500 μm or less, more preferably 100 μm or less, even more preferably 70 μm or less, and even more preferably 50 μm or less.

[0065] (Electricity storage device components) In one or more embodiments, the ion conductive layer of the present disclosure can be used in electricity storage device components such as electrolytes, separators, surface protection layers for electrodes, solid electrolyte mixed membranes, and resin layers. That is, in one aspect, the present disclosure relates to an electricity storage device member (hereinafter also referred to as "electricity storage device member of the present disclosure") containing the ion conductive layer of the present disclosure. In one or more embodiments, the electricity storage device member of the present disclosure is at least one selected from an electrolyte layer having the ion conductive layer of the present disclosure, an electrode having the ion conductive layer of the present disclosure, and a separator having the ion conductive layer of the present disclosure.

[0066] In one or more embodiments, a separator having an ion-conductive layer according to the present disclosure (hereinafter also referred to as a "separator with an ion-conductive layer according to the present disclosure") can be obtained by forming an ion-conductive layer according to the present disclosure on one or both sides of a separator. The method for producing a separator with an ion-conductive layer according to the present disclosure can be the same as the above-described method for forming an ion-conductive layer according to the present disclosure, for example. The separator is a porous film, and examples thereof include a porous polyolefin film, a porous polyolefin terephthalate film, a porous polyimide film, a porous polyester film, a porous cellulose film, a porous Teflon (registered trademark) film, a nonwoven fabric, and paper.

[0067] In one or more embodiments, an electrode having an ion conduction layer according to the present disclosure (hereinafter also referred to as an "electrode with an ion conduction layer according to the present disclosure") can be obtained by forming an ion conduction layer according to the present disclosure on the surface of an electrode. The electrodes are the positive and negative electrodes of an electricity storage device, and typically comprise an electrode active material layer formed on one or both sides of a metal foil called a current collector. An electrode having electrode active material layers formed on both sides (a double-sided electrode) may have both sides as positive electrodes, both sides as negative electrodes, or one side as a positive electrode and the other side as a negative electrode (a bipolar electrode). The electrode active material layer contains an active material, a binder, and, if necessary, components such as a conductive material. An electrode having an ion conduction layer is an electrode in which the ion conduction layer according to the present disclosure is provided on the surface of an electrode active material layer. When both surfaces are positive electrodes or negative electrodes, at least one of the surfaces may have the ion-conducting layer of the present disclosure. In the case of a bipolar electrode, at least one of the negative electrode surface and the positive electrode surface may have the ion-conducting layer of the present disclosure. The electrode with an ion-conductive layer of the present disclosure can be produced, for example, in the same manner as the above-described method for forming an ion-conductive layer of the present disclosure.

[0068] [Energy storage devices] In one aspect, the present disclosure relates to an electricity storage device (hereinafter also referred to as "the electricity storage device of the present disclosure") that includes a member for an electricity storage device of the present disclosure. In one or more embodiments, the electricity storage device of the present disclosure may be an electricity storage device having at least one positive electrode, at least one negative electrode, and, if necessary, a bipolar electrode, in which at least one selected from the positive electrode, the negative electrode, and the bipolar electrode has the ion conduction layer of the present disclosure.

[0069] In one or more embodiments, the power storage device of the present disclosure may be a bipolar battery. In one or more embodiments, the bipolar battery of the present disclosure is a battery in which a positive electrode having a positive electrode active material layer on at least one surface and a negative electrode having a negative electrode active material layer on at least one surface are provided as outermost layers, at least one bipolar electrode is stacked between the positive electrode and the negative electrode with a separator and an electrolyte interposed therebetween so that the negative electrode faces the positive electrode, the positive electrode and the negative electrode are arranged in series within the battery, and an ion conductive layer of the present disclosure is formed in at least one location between the positive electrode and the negative electrode facing each other within the battery.

[0070] In one or more embodiments, an electrolytic solution can be held in the ion conductive layer in the power storage device of the present disclosure. The electrolytic solution can be, for example, at least one selected from cyclic and chain carbonates.

[0071] The thickness of the ion conduction layer in the electricity storage device of the present disclosure is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 5 μm or more, from the viewpoints of durability and battery characteristics of the electricity storage device, and from the same viewpoints, is preferably 500 μm or less, more preferably 100 μm or less, even more preferably 70 μm or less, and even more preferably 50 μm or less. [Example]

[0072] Hereinafter, the present disclosure will be described with reference to examples, but the present disclosure is not limited thereto.

[0073] 1. Preparation of Polymer Dispersions (Examples 1 to 11 and Comparative Examples 1 to 4) The following raw materials were used to prepare the polymer dispersions of Examples 1 to 11 and Comparative Examples 1 to 4 shown in Table 1. The abbreviations for the raw materials used in Table 1 and the following examples are as follows.

[0074] <Monomer (A)> (see below R 1 , R 2 and X 1 means the symbol in formula (I) MMA: Methyl methacrylate (Wako Pure Chemical Industries, Ltd.) 1 :CH3, R 2 :CH3, X 1 :O) EA: Ethyl acrylate (Wako Pure Chemical Industries, Ltd.) (R 1 :H,R 2 :C2H5,X 1 :O) BA: Butyl acrylate (Wako Pure Chemical Industries, Ltd.) (R 1 :H,R 2 :C4H9,X 1 :O) <Monomer (B)> (see below R 3 , R 4 and X 2 means the symbol in formula (II) M-90G (Shin Nakamura Chemical) (R 3 :CH3, X 2 :O,R 4 :(CH2CH2O)9CH3) M-230G (Shin Nakamura Chemical) (R 3 :CH3, X 2 :O,R 4 :(CH2CH2O) 23 CH3) AM-230G (Shin Nakamura Chemical) (R 3 :H,X 2 :O,R 4 :(CH2CH2O) 23 CH3) DMAA: Dimethylacrylamide (Wako Pure Chemical Industries, Ltd.): (R 3 :H,X 2 :N(CH3), R 4 :CH3) QDM: Methacryloyloxyethyl trimethylammonium chloride (Kao): (R 3 :CH3, X 2 :O,R 4 :C2H4N + (CH2)3Cl ― ) <Monomer (C)> (see below R 11 , R 12 , X 3 and X 4 means the symbol in formula (III) EGDMA: Ethylene glycol dimethacrylate (Wako Pure Chemical Industries, Ltd.) (R 11 and R 12 :CH3, X 3 and X 4 :O) <Monomer (D)> 2-EHA: 2-ethylhexyl acrylate (Wako Pure Chemical Industries, Ltd.) <Polymer> SBR: Styrene butadiene rubber (manufactured by Nippon Zeon, "BM-400B", solid content 40% by mass) PVDF-HFP: Poly(vinylidene fluoride-co-hexafluoropropylene) (Sigma-Aldrich, average Mw ~455,000, average Mn ~110,000, pellets) <Polymerization initiator> APS: ammonium persulfate (Sigma-Aldrich) V-50: 2,2'-azobis(2-methylpropionamidine) dihydrochloride (Wako Pure Chemical Industries, Ltd.) <Solvent> NMP: N-methylpyrrolidone (Wako Pure Chemical Industries, Ltd.)

[0075] (Acrylic polymer dispersion of Example 1) 196 g of EA as monomer (A), 4 g of M-90G as monomer (B), 3.90 g of EGDMA as monomer (C) [1 mol% relative to the total moles of monomers (A) and (B)], and 340 g of ion-exchanged water were placed in a 1 L four-neck glass separable flask and stirred for a certain period (0.5 hours) under a nitrogen atmosphere. The reaction solution in the flask was then heated to approximately 70°C, after which a polymerization initiator solution consisting of 1 g of APS dissolved in 10 g of ion-exchanged water was added to the flask. The reaction solution in the flask was maintained at approximately 70-75°C for 6 hours for polymerization and aging, yielding an acrylic polymer dispersion. The acrylic polymer dispersion in the flask was then cooled to room temperature, after which aggregates were removed using a 200-mesh filter cloth. The acrylic polymer dispersion was diluted with ion-exchanged water to a concentration of 30% by mass, yielding the acrylic polymer dispersion of Example 1. The amounts and types of each component used in preparing the acrylic polymer dispersion of Example 1 are shown in Tables 1 to 3. Furthermore, the stability of the polymer dispersion of Example 1 (emulsion stability) confirmed by the amount of the aggregates and the measurement results of the average particle size of the polymer particles of Example 1 are shown in Tables 1 to 3.

[0076] (Acrylic polymer dispersions of Examples 2 to 5, 7 to 11, and Comparative Examples 1 and 2) Acrylic polymer dispersions of Examples 2 to 5, 7 to 11 and Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the monomer types were changed to give the structural units shown in Tables 1 to 3. The amount and type of each component used in preparing the acrylic polymer dispersions obtained here are shown in Tables 1 to 3.

[0077] (Acrylic polymer dispersion of Example 6) An acrylic polymer dispersion of Example 6 was obtained in the same manner as in Example 1, except that the monomer type was changed to obtain the structural units shown in Tables 1 to 3 and that APS was replaced with V-50. The amount and type of each component used in preparing the acrylic polymer dispersion obtained here are shown in Tables 1 to 3.

[0078] (Polymer dispersion of Comparative Example 3) As the polymer dispersion in Comparative Example 3, SBR was used.

[0079] (Polymer dispersion of Comparative Example 4) PVDF-HFP was used as the polymer in Comparative Example 4. The polymer dispersion in Comparative Example 4 was prepared by dissolving PVDF-HFP in NMP to a concentration of 10% by mass.

[0080] [Measurement of average particle size of polymer particles] The average particle size of the polymer particles was measured using a laser diffraction particle size analyzer (LA-920 manufactured by Horiba, Ltd.) at room temperature by diluting with a dispersion medium (water) until the particle size was within the specified light intensity range of the device. The results are shown in Tables 1 to 3. Polymers that were not measured are indicated by "-" in the tables.

[0081] [Measurement of solids concentration of polymer dispersion] The solid content concentration of the polymer dispersion was calculated by measuring the weight loss after drying at 105° C. for 24 hours. The results are shown in Tables 1 to 3.

[0082] [Measurement of ionic conductivity] The polymer dispersion was applied to an aluminum foil so that the thickness after drying would be 20 μm, and then dried for 8 hours at 40° C. After punching out a piece with a diameter of 16 mm, it was further dried at 50° C. under reduced pressure for another 8 hours to obtain a film for measuring ion conductivity (ion-conducting layer). The film for measuring ionic conductivity was placed on a two-electrode coin cell (Hosen Corporation's "HS Flat Cell"), and then a 1 M LiPF solution (solvent: EC / DEC mixed solvent (volume ratio 3 / 7)) was poured into the cell as a non-aqueous electrolyte, and the cell was sealed to assemble the cell for measuring ionic conductivity. The AC impedance (10 mV, frequency 0.05 Hz to 100 kHz) of the ion conductivity measurement cell obtained in the above process was measured using a Solartron Impedance Gain Analyzer (FRA) "1260A." The resistance value was calculated from the arc width of the obtained Cole-Cole plot, and the ion conductivity (mS / cm) was calculated from this. The results are shown in Tables 1 to 3. The higher the ion conductivity, the better the ion-conducting layer.

[0083] [Emulsion stability] In the agglomerate removal step in the production of the acrylic polymer dispersion, the agglomerates remaining on the 200-mesh filter cloth and the agglomerates adhering to the inside of the reaction vessel were collected and dried at 105°C for 24 hours to calculate the dry weight of all agglomerates. The dry weight of the agglomerates relative to the obtained polymer (solid content) was calculated as A if it was less than 0.5%, B if it was 0.5 to 1.5%, and C if it was 1.5% or more, and these are shown in Tables 1 to 3.

[0084] 2. Production of electricity storage devices using the polymer dispersions of Examples 1 to 11 and Comparative Examples 1 to 4 A lithium ion secondary battery, which is a type of electricity storage device, was fabricated as follows.

[0085] [Preparation of negative electrode] The materials used for the negative electrode paste are as follows: Negative electrode active material: graphite, Showa Denko "AF-C" Negative electrode conductive material: Carbon fiber, manufactured by Showa Denko, "VGCF-H" Negative electrode binder: SBR Anode thickener: Sodium carboxymethyl cellulose (CMC), Daicel, #2200

[0086] First, 288 g of negative electrode active material, 3 g of negative electrode conductive material, and 3 g of negative electrode thickener were mixed, and then distilled water was gradually added in an amount necessary to achieve a final solids concentration of 50 to 55% by mass, and the mixture was kneaded using a disperser. 6 g of negative electrode binder was then added as polymer solids to the kneaded mixture, and the mixture was further kneaded using a disperser. The mixture was then defoamed using a stirring defoamer (Thinky Corporation's "Awatori Rentaro"), and coarse particles were removed using a 150-mesh filter cloth to obtain a negative electrode paste. The resulting negative electrode paste was applied to a copper foil current collector at a density of 80 g / m after drying. 2 The thickness was adjusted so that the coating was applied using a bar coater. The coating was dried at 80°C for 5 minutes using a blower dryer, and then further dried at 150°C for 10 minutes. After that, the electrode density was adjusted to 1.3 to 1.4 g / cm using a roll press. 3 The mixture was left in a dry room overnight or longer to prepare a negative electrode having a negative electrode mixture layer.

[0087] [Preparation of negative electrode A with ion-conducting layer] A 1.5 mass % aqueous solution of CMC (sodium carboxymethylcellulose, manufactured by Daicel Corporation, #2200) was mixed with the polymer dispersions of Examples 1 to 5, 7 to 10 and Comparative Examples 1 to 3 so that the solid mass ratio of the polymer dispersion / CMC aqueous solution was 9 / 1, and then the mixture was diluted with ion-exchanged water so that the total solid concentration was 10 mass %, thereby obtaining a slurry for the ion-conducting layer. The polymer dispersions of Example 6 and Comparative Example 4 were used as they were as slurries for the ion-conducting layer. The slurry for the ion conduction layer was applied to the surface of the composite layer of the negative electrode using an applicator so that the thickness after drying would be 20 μm, dried at 60° C. for 10 minutes, and then left in a dry room overnight or more to obtain a negative electrode A (Table 1) having an ion conduction layer.

[0088] [Preparation of separator A with ion-conductive layer] A 1.5 mass % CMC aqueous solution was mixed with the polymer dispersions obtained in Examples 1 to 4, 7 to 11 and Comparative Examples 1 to 3 so that the solid mass ratio of polymer dispersion / CMC aqueous solution was 9 / 1, and then the mixture was diluted with ion-exchanged water so that the total solid concentration was 10 mass %, thereby obtaining a slurry for the ion conduction layer. The polymer dispersions of Example 6 and Comparative Example 4 were used as they were as slurries for the ion-conducting layer. The slurry for the ion-conducting layer was applied to one side of a separator (porous polyethylene) using an applicator so that the thickness after drying would be 20 μm, and the coating was dried at 60°C for 10 minutes and then left in a dry room overnight or more to obtain separator A (Table 2) having an ion-conducting layer.

[0089] [Preparation of separator B with ion-conductive layer] The polymer dispersions obtained in Examples 1 to 5, 7 to 10 and Comparative Examples 1 to 3 were mixed with a 1.5 mass % CMC aqueous solution and alumina filler (aluminum oxide, alpha-phase, 99%, metal basis, manufactured by Alfer Aesar) so that the solids mass ratio of polymer dispersion / CMC aqueous solution / alumina filler was 9 / 1 / 90, and then diluted with ion-exchanged water to a total solids concentration of 40 mass %, thereby obtaining a slurry for the ion conduction layer. The polymer dispersion of Example 6 was prepared by mixing alumina filler to a solids mass ratio of 10 / 90, and then diluting with ion-exchanged water to a total solids concentration of 40 mass % to obtain a slurry for the ion-conducting layer. The polymer dispersion of Comparative Example 4 was prepared by mixing alumina filler to a solids mass ratio of 10 / 90, and then diluting with NMP to a total solids concentration of 40 mass % to obtain a slurry for an ion conduction layer. The slurry for the ion-conducting layer was applied to one side of a separator (porous polyethylene) using an applicator so that the thickness after drying would be 20 μm, and the coating was dried at 60°C for 10 minutes and then left in a dry room overnight or more to obtain separator B (Table 3) having an ion-conducting layer.

[0090] [Average Thickness of Ion Conduction Layer] The difference between the average thickness of the negative electrode before the ion-conductive layer was applied and the average thickness of the negative electrode A obtained by the above method was defined as the average thickness of the ion-conductive adhesive layer (the set average thickness of the ion-conductive layer). The average thickness was measured using a high-precision film thickness meter (Tosei Engineering) and was taken as the average of five measurements. The results are shown in Tables 1 to 3.

[0091] [Preparation of Lithium-Ion Secondary Battery Evaluation Cell Having Negative Electrode A with Ion Conductive Layer] Leaving a terminal attachment area, the negative electrode A with an ion-conducting layer was punched out to 45 mm × 45 mm, and the lithium foil was punched out to 40 mm × 40 mm, and a terminal was attached to each. A separator punched out to 50 mm × 50 mm was placed on the active material layer side of the negative electrode, and the lithium foil was then placed on top of it. These were sandwiched between aluminum packaging laminate films, and three sides excluding the side facing the terminal were sealed by heat sealing. The following electrolyte solution was injected through the opening on the terminal side, the inside was evacuated, and the terminal side was also heat-sealed to seal the cell, producing a lithium-ion secondary battery. The electrolyte solution used was a 1M LiPF6 solution (solvent: EC / DEC mixed solvent (volume ratio 3 / 7)) to which 1% by mass of vinylene carbonate (VC) was added. In this manner, a lithium ion secondary battery evaluation cell was produced, which had an ion-conductive layer-attached negative electrode A in which the ion-conductive layer was present only on the surface of the negative electrode active material layer. The negative electrode A with an ion-conductive layer prepared using the polymer dispersion of Comparative Example 4 could not be evaluated because the ion-conductive layer peeled off during punching.

[0092] [Preparation of lithium-ion secondary battery evaluation cells having separator A with ion-conducting layer] A lithium ion secondary battery evaluation cell having separator A with an ion conductive layer, in which the ion conductive layer was located on only one side of the separator, was produced in the same manner as the lithium ion secondary battery evaluation cell having negative electrode A with an ion conductive layer, except that negative electrode A with an ion conductive layer was used as the negative electrode, separator A with an ion conductive layer was used as the separator, and the side of separator A without the ion conductive layer was overlaid on the negative electrode composite layer. The separator A with an ion-conductive layer produced using the polymer dispersion of Comparative Example 4 could not be evaluated because the ion-conductive layer peeled off during punching.

[0093] [Preparation of lithium-ion secondary battery evaluation cells having separator B with ion-conducting layer] A lithium ion secondary battery evaluation cell having a separator B with an ion conductive layer, in which the ion conductive layer was located on only one side of the separator, was produced in the same manner as the lithium ion secondary battery evaluation cell having the separator A with an ion conductive layer, except that separator A with an ion conductive layer was replaced with separator B with an ion conductive layer. Separator B with an ion-conductive layer, which was produced using the polymer dispersion of Comparative Example 4, could not be evaluated because the ion-conductive layer peeled off during punching.

[0094] <Capacity maintenance rate> The fabricated lithium ion secondary battery (lithium ion secondary battery having negative electrode A with an ion conductive layer, separator A with an ion conductive layer, or separator B with an ion conductive layer) evaluation cell was charged at a constant current of 0.2 C to a voltage of 0 V in an environment of 25°C, then charged at a constant voltage (CC / CV) to 0.05 C at a constant 0 V, and subsequently discharged at a constant current of 0.2 C to a voltage of 3.0 V. This charge / discharge cycle was repeated three times to complete conditioning, after which the following battery evaluation was performed. In an environment with a temperature of 25°C, the battery was charged at a constant current of 0.2 C to a voltage of 0 V, and the charge capacity at this time was defined as C0. Subsequently, the battery was similarly charged at a constant current of 0.2 C using CC-CV charging, and then discharged at a constant current of 0.2 C to a voltage of 3.0 V. The battery was then charged at a constant current of 3.0 C to 0 V, and the charge capacity at this time was defined as C1. The capacity retention rate (%) was then calculated as C = (C1 / C0) × 100 (%) to determine the rate characteristics. The larger the capacity retention rate C, the better the battery characteristics. The results are shown in Tables 1 to 3.

[0095] <Cycle durability> After the conditioning was completed, the lithium ion secondary battery evaluation cells having the ion-conducting layer-attached negative electrode A of Examples 1 to 10 and Comparative Examples 1 to 4 were charged at a constant current of 0.2 C to a voltage of 0 V in an environment of 25°C, and then charged at a constant voltage of 0.05 C while maintaining the voltage at 0 V. Discharge was performed at a constant current of 0.2 C to a voltage of 3.0 V. This charge / discharge cycle was repeated 100 times. Cycle durability was evaluated by the ratio of the charge capacity C0 after 100 cycles to the charge capacity C0 at the first cycle. 100 The ratio (cycle capacity retention rate) of the above values ​​was calculated. The results are shown in Table 1. In Table 1, a capacity retention rate of 80% or more is indicated as A, 60% or more as B, and less than 60% as C.

[0096] [Table 1]

[0097] As shown in Table 1, the ion-conducting layers using the polymer dispersions of Examples 1 to 10 were found to have superior ion conductivity compared to those of Comparative Examples 1 to 4. Excellent ion conductivity can suppress an increase in the internal resistance of the battery. As shown in Table 1, the lithium ion secondary batteries having the ion-conductive layer-equipped negative electrodes A prepared using the polymer dispersions of Examples 1 to 10 had the same capacity retention rate or a reduced decrease in capacity retention rate compared to the lithium ion secondary batteries having the ion-conductive layer-equipped negative electrodes A prepared using the polymer dispersions of Comparative Examples 1 to 4, demonstrating improved battery characteristics. Furthermore, it was found that the lithium ion secondary batteries having the ion-conductive layer-attached negative electrodes A prepared using the polymer dispersions of Examples 1 to 10 had cycle durability equivalent to or superior to that of Comparative Examples 1 to 4.

[0098] [Table 2]

[0099] As shown in Table 2, the lithium ion secondary batteries having separators A with ion conductive layers prepared using the polymer dispersions of Examples 1 to 4 and 6 to 11 showed a suppressed decrease in capacity retention rate and improved battery characteristics compared to the lithium ion secondary batteries having separators A with ion conductive layers prepared using the polymer dispersions of Comparative Examples 1 to 4.

[0100] [Table 3]

[0101] As shown in Table 3, the lithium ion secondary batteries having separators B with ion-conductive layers prepared using the polymer dispersions of Examples 1 to 10 showed a suppressed decrease in capacity retention rate compared to the lithium ion secondary batteries having separators B with ion-conductive layers prepared using the polymer dispersions of Comparative Examples 1 to 4, demonstrating improved battery characteristics.

[0102] [Example of bipolar battery construction] Using the polymer dispersion of Example 1, a bipolar battery shown in FIG. 1 was fabricated by the following method.

[0103] (Preparation of positive electrode) The abbreviations for the materials used in the positive electrode paste are as follows: ·Cathode active material: NMC111 (manufactured by Nihon Kagaku Kogyo), composition: LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 (D50: 6.5μm, BET specific surface area: 0.7m 2 / g) Positive electrode conductive material: Acetylene black (manufactured by Denki Kagaku Kogyo, product name: Denka Black HS-100) Positive electrode binder: Polyvinylidene fluoride (PVDF) (Kureha, 8% NMP solution)

[0104] First, 282 g of positive electrode active material, 9 g of positive electrode conductive material, and 9 g of positive electrode binder were mixed using NMP as a non-aqueous solvent to prepare a positive electrode paste. Here, the mass ratio of the positive electrode active material, positive electrode conductive material, and positive electrode binder was 94:3:3 (solid content equivalent). The above mixing was performed by kneading using a disper. The prepared positive electrode paste was applied to an aluminum foil current collector at a concentration of 125 g / m after drying. 2 The thickness was adjusted so that the coating was applied using a bar coater. The coating was dried at 100°C for 5 minutes using a blower dryer, and then further dried at 150°C for 10 minutes. After that, the electrode density was adjusted to 2.8 to 3.2 g / cm using a roll press. 3 The mixture was left in a dry room overnight or longer to prepare a positive electrode having a positive electrode mixture layer.

[0105] (Fabrication of negative electrodes and bipolar electrodes with ion-conducting layers) A negative electrode was produced in the same manner as in the negative electrode of the lithium ion battery. A negative electrode paste obtained by the same method as the negative electrode paste used in the preparation of the lithium ion battery was applied to one side of a stainless steel foil current collector in an amount of 80 g / m after drying. 2The thickness was adjusted to 125 g / m2, and the coating was applied using a bar coater. The coating was dried at 80°C for 5 minutes using a blower dryer, and then further dried at 150°C for 10 minutes. Next, the positive electrode paste was applied to the other side of the foil at a thickness of 125 g / m2 after drying. 2 The coating was applied using a bar coater, adjusting the thickness so that the coating was 100°C for 5 minutes using a blower dryer, to obtain a bipolar electrode. An oxide-based solid electrolyte (LiO-AlO-SiO-PO-TiO, manufactured by OHARA, trade name LICGC powder) was mixed with the polymer dispersion of Example 1 to a solids weight ratio of 10 / 90, and then the mixture was diluted with ethanol to a total solids concentration of 30 mass % and mixed uniformly to obtain a slurry for the ion conduction layer. The above-mentioned slurry for the ion conduction layer was applied onto the negative electrode and the negative electrode of the bipolar electrode so as to have a thickness of 40 μm after drying, dried at 60° C. for 10 minutes, and then left in a dry room overnight or more to obtain a negative electrode C and a bipolar electrode C having an ion conduction layer C.

[0106] (Fabrication of bipolar battery) The negative electrode C and positive electrode were punched out to 40 mm x 40 mm, leaving the terminal attachment area, and terminals were attached to each. Two 40 mm x 40 mm bipolar electrode C sheets were punched out, with the negative electrode C and positive electrode as the outermost layers. Two bipolar electrodes C were stacked between them, with the negative and positive electrodes facing each other, to produce a laminated electrode. The laminated electrode was pressed under vacuum to eliminate any remaining voids between the layers, and then immersed in electrolyte for 8 hours to thoroughly impregnate the electrodes and ion-conducting layers. The surface of the removed laminated electrode was wiped clean, sandwiched between aluminum laminate film, and three sides, excluding the side facing the terminal, were heat-sealed. The interior was evacuated and the terminal side was also heat-sealed to seal the cell, producing the bipolar lithium-ion secondary battery shown in Figure 1. The electrolyte used was a 1M LiPF6 solution (solvent: EC / DEC mixed solvent (volume ratio 3 / 7)) to which 1 mass % vinylene carbonate (VC) was added. [Industrial Applicability]

[0107] As described above, the ion conductive layer of the present disclosure, which has high ionic conductivity, is useful in lithium ion batteries, lithium ion capacitors, and other electricity storage devices. [Explanation of symbols]

[0108] 1 negative electrode current collector, 2 negative electrode active material, 3 ion conductive layer C, 4 positive electrode active material, 5 bipolar electrode current collector, 6 positive electrode current collector, 7 negative electrode C, 8 positive electrode, 9 bipolar electrode C, 10 current collecting tab, 11 aluminum packaging laminate film, 12 laminated portion

Claims

1. An ion-conducting layer disposed between a positive electrode and a negative electrode of an electricity storage device, the ion-conducting layer contains an acrylic polymer, The acrylic polymer comprises a structural unit (A) derived from a compound represented by the following formula (I) and a structural unit (B) derived from a compound represented by the following formula (II): 【Chemistry 1】 In formula (I), R １ represents a hydrogen atom or a methyl group. ２ represents a linear or branched alkyl group having 1 to 4 carbon atoms. １ represents —O— or —NH—. 【Chemistry 2】 In formula (II), R ３ represents a hydrogen atom or a methyl group, and X ２ is -O- or -N(R ５ )-. X ２ When is -O-, R ４ represents a structure having an alkylene oxide (wherein the average number of moles of alkylene oxide added is 2 to 50), or -R ６ N ＋ (R ７ ) (R ８ ) (R ９ ) Y － It has the structure: ６ represents a linear or branched alkylene group having 1 to 3 carbon atoms; R ７ , R ８ , R ９ are the same or different and represent a linear or branched alkyl group having 1 to 3 carbon atoms. － represents an anion. ２ -N (R ５ )-, then R ４ and R ５ are the same or different and represent a straight-chain or branched-chain alkyl group having 1 to 3 carbon atoms.

2. 2. The ion conductive layer for an electricity storage device according to claim 1, wherein the content of the structural unit (A) is 50% by mass or more and the content of the structural unit (B) is 0.5% by mass or more, based on all structural units of the acrylic polymer.

3. The acrylic polymer further contains a structural unit (C) derived from a crosslinkable monomer, 3. The ion conductive layer for an electricity storage device according to claim 1, wherein the content of the structural unit (C) is from 0.001 mol % to 5 mol % based on the total number of moles of structural units other than the structural unit (C).

4. 4. The ion-conductive layer for an electricity storage device according to claim 3, wherein the crosslinkable monomer is at least one selected from the group consisting of polyfunctional (meth)acrylates and N-methylolamide group-containing monomers.

5. A method for improving ionic conductivity comprising forming an ion-conducting layer comprising the acrylic polymer defined in any one of claims 1 to 4.

6. A member for an electricity storage device, comprising the ion conductive layer according to claim 1 .

7. 7. The electricity storage device member according to claim 6, wherein the electricity storage device member is at least one member selected from the group consisting of an electrolyte layer having an ion conductive layer, an electrode having an ion conductive layer, and a separator having an ion conductive layer on at least one surface thereof.

8. An electricity storage device comprising the electricity storage device member according to claim 6 or 7.

9. 1. A method for forming an ion-conducting layer for an electricity storage device, comprising: applying a slurry containing an acrylic polymer composition to a surface of a substrate; and drying the applied slurry to form an ion-conducting layer. the acrylic polymer composition contains particles of an acrylic polymer; The acrylic polymer comprises a structural unit (A) derived from a compound represented by the following formula (I) and a structural unit (B) derived from a compound represented by the following formula (II): 【Transformation 3】 In formula (I), R １ represents a hydrogen atom or a methyl group. ２ represents a linear or branched alkyl group having 1 to 4 carbon atoms. １ represents —O— or —NH—. 【Chemistry 4】 In formula (II), R ３ represents a hydrogen atom or a methyl group, and X ２ is -O- or -N(R ５ )-. X ２ When is -O-, R ４ represents a structure having an alkylene oxide (wherein the average number of moles of alkylene oxide added is 2 to 50), or -R ６ N ＋ (R ７ ) (R ８ ) (R ９ ) Y － It has the structure: ６ represents a linear or branched alkylene group having 1 to 3 carbon atoms; R ７ , R ８ , R ９ are the same or different and represent a linear or branched alkyl group having 1 to 3 carbon atoms. － represents an anion. ２ -N (R ５ )-, then R ４ and R ５ are the same or different and represent a straight-chain or branched-chain alkyl group having 1 to 3 carbon atoms.

10. 10. The method for forming an ion-conducting layer according to claim 9, wherein the thickness of the ion-conducting layer is from 1 μm to 500 μm.

Images