Ion conductive layer for energy storage devices

Abstract

One embodiment of the present disclosure provides an ion conductive layer for electricity storage devices, said ion conductive layer being capable of improving the battery characteristics of electricity storage devices.　One embodiment of the present disclosure relates to an ion conductive layer for electricity storage devices, said ion conductive layer being arranged between the positive electrode and the negative electrode of an electricity storage device. This ion conductive layer for electricity storage devices contains an acrylic polymer; the acrylic polymer contains a constituent unit (A) that is derived from a compound represented by formula (I); the content of the constituent unit (A) in all constituent units of the acrylic polymer is from 88% by mass to 100% by mass; and the thickness of this ion conductive layer is more than 1 μm but not more than 500 μm.

Description

[Technical Field]

[0001] This disclosure relates to an ion-conducting layer for energy storage devices. [Background technology]

[0002] In recent years, the demand for energy storage devices has been growing due to the widespread adoption of smartphones, zero-emission regulations in the automotive market, and the expansion of renewable energy use. Therefore, there is a growing demand for smaller, lighter, and larger capacity energy storage devices, and for automobiles and other applications, there is an increasing need for even higher output and higher energy density. In response to these demands, development of energy storage devices such as lithium-ion secondary batteries, alkaline-ion secondary batteries, electric double-layer capacitors, lithium-ion capacitors, and all-solid-state batteries is progressing.

[0003] Such energy storage devices generally have electrodes in which a composite layer containing an active material is coated on a metal foil, and an electrolyte that facilitates ion movement is filled between the electrodes. Depending on the purpose, liquid, semi-solid, or solid electrolytes are used. In the case of liquids, solvents containing metal ions are used; in the case of semi-solids, gels containing the aforementioned liquid are used; and in the case of solids, solids with ion conductivity are used. In the case of batteries that mainly use liquid or semi-solid electrolytes, separators are provided between the electrodes to prevent short circuits. On the other hand, in the case of batteries that use solid electrolytes, a mixed film of solid electrolyte and resin is used to prevent delamination, as solid electrolytes alone are prone to delamination.

[0004] Furthermore, because pouch-type batteries have a large range of motion, electrode and separator misalignment can occur, which reduces durability. To prevent this misalignment, an adhesive layer is provided. It is also known that surface protective films are provided on the surfaces of the positive and negative electrodes to suppress the formation of highly ion-resistant fixed films due to localized reactions such as metal deposition and electrolyte modification.

[0005] However, in order to meet the recent requirements for miniaturization, high capacity, and high output, it is necessary to improve the ionic conductivity of the resins used in electrolytes, separators, solid electrolyte mixed membranes, adhesive layers, surface protection layers, etc., and there is a demand for the proposal of a resin layer having high ionic conductivity.

[0006] To solve such problems, adhesive layers for separators and electrode surface protection films have been proposed (Patent Documents 1 and 2).

[0007] WO2014 / 081035 (Patent Document 1) discloses a method for manufacturing an electrode / separator laminate, characterized in that the adhesive layer contains a particulate polymer A having a glass transition temperature of -50 to 5°C and a particulate polymer B having a glass transition temperature of 50 to 120°C, the average thickness of the adhesive layer is 0.2 to 1.0 μm, and the thermocompression bonding is performed at 50 to 100°C. In the examples, a particulate polymer A composed of 86.8 parts of ethyl acrylate, 10 parts of acrylonitrile, 2 parts of methacrylic acid, and 1.2 parts of N-methylolacrylamide and a particulate polymer B composed of 18 parts of butyl acrylate, 80 parts of styrene, 2 parts of acrylonitrile, 2 parts of methacrylic acid, and 1.2 parts of acrylamide are mixed so that the solid content weight ratio (particulate polymer A / particulate polymer B) is 15 / 85 to obtain an aqueous dispersion slurry for the adhesive layer.

[0008] WO2009 / 123168 (Patent Document 2) discloses a porous membrane containing a water-soluble polymer, an inorganic filler, and a water-insoluble particulate polymer containing 0.5 to 40% by mass of a monomer unit containing a hydrophilic group selected from the group consisting of a carboxylic acid group, a hydroxyl group, and a sulfonic acid group. In the examples, a particulate polymer composed of 80 parts of ethyl acrylate, 15 parts of acrylonitrile, and 5 parts of itaconic acid is obtained.

[0009] WO2018 / 021552 (Patent Document 3) discloses a binder for a power storage device electrode, which contains polymer particles having ion permeability and a specific elastic change rate. In the examples, polymer particles composed of 97% by mass of ethyl acrylate and 3% by mass of acrylic acid are disclosed.

Summary of the Invention

[0010] In one aspect, the present disclosure relates to an ion-conducting layer disposed between the positive and negative electrodes of a power storage device. The ion-conducting layer contains an acrylic polymer, and the acrylic polymer contains a structural unit (A) derived from a compound represented by the following formula (I). The content of the structural unit (A) in all the structural units of the acrylic polymer is 88% by mass or more and 100% by mass or less, and the thickness of the ion-conducting layer is more than 1 μm and 500 μm or less. The present disclosure relates to an ion-conducting layer for a power storage device.

Chemical Formula

[0011] In one aspect, the present disclosure relates to an acrylic polymer composition for forming the ion-conducting layer of the present disclosure.

[0012] In one aspect, the present disclosure relates to a member for a power storage device containing the ion-conducting layer of the present disclosure, wherein the thickness of the ion-conducting layer is more than 1 μm and 500 μm or less.

[0013] In one aspect, the present disclosure relates to a power storage device having the member for a power storage device of the present disclosure.

[0014] This disclosure relates to a method for forming an ion-conducting layer for an energy storage device, comprising the steps of: applying a slurry containing an acrylic polymer composition to a substrate surface such that the thickness of the ion-conducting layer is greater than 1 μm and 500 μm or less; and drying the applied slurry to form an ion-conducting layer, wherein the acrylic polymer composition contains particles of an acrylic polymer, the acrylic polymer contains a constituent unit (A) derived from a compound represented by the following formula (I), and the content of constituent unit (A) in the total constituent units of the acrylic polymer is 88% by mass or more and 100% by mass or less. [ka] In formula (I), R 1 R represents a hydrogen atom or a methyl group. 2 represents a linear or branched alkyl group having 1 to 3 carbon atoms. X represents -O- or -NH-. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a schematic diagram of a bipolar battery. [Modes for carrying out the invention]

[0016] Patent Document 1 discloses that the adhesive layer itself has poor ionic conductivity, and that if its thickness exceeds 1 μm, it clogs the pores of the porous polyolefin film, impairing ionic conductivity. However, it does not mention the ionic conductivity of the particulate polymer itself, and therefore, the electrode battery characteristics sufficient to meet the above requirements cannot be obtained. The porous membrane disclosed in Patent Document 2 states that, due to the poor ionic conductivity of the polymer, if the content of water-soluble polymers and particulate polymers is high relative to the inorganic filler, the pores are covered and the movement of Li is inhibited. However, the ionic conductivity of the polymer itself is not mentioned, and the electrode battery characteristics sufficient to meet the above requirements cannot be obtained. The polymer particles described in Patent Document 3 are used as an electrode binder, and there is no mention of their use in forming an ion-conducting layer.

[0017] In one embodiment, this disclosure provides an ion-conducting layer for an energy storage device that can improve the battery characteristics of the energy storage device.

[0018] This disclosure is based on the finding that the battery characteristics of an energy storage device can be improved by forming an ion-conducting layer for the energy storage device with a predetermined acrylic polymer.

[0019] In other words, the present disclosure relates to an ion conductive layer for an energy storage device (hereinafter also referred to as "the ion conductive layer of the present disclosure"), wherein the ion conductive layer contains an acrylic polymer (hereinafter also referred to as "the acrylic polymer of the present disclosure"), the acrylic polymer contains a constituent unit (A) derived from a compound represented by the above formula (I), the content of constituent unit (A) in the total constituent units of the acrylic polymer is 88% by mass or more and 100% by mass or less, and the thickness of the ion conductive layer is greater than 1 μm and 500 μm or less. This disclosure provides an ion-conducting layer for energy storage devices that can improve the battery characteristics of the energy storage device. By using the ion-conducting layer of this disclosure in the electrolyte, separator, solid electrolyte mixed film, adhesive layer for electrodes and separators, surface protective layer, etc. of an energy storage device, an energy storage device with excellent battery characteristics can be obtained.

[0020] Although the detailed mechanism of how the effects of this disclosure are realized is not clear, the following can be inferred. In this disclosure, the acrylic polymer contained in the ion-conducting layer for energy storage devices is thought to have a high affinity for metal ions and electrolytes used in energy storage devices, and to not hinder the movement of metal ions, by having a constituent unit (A) derived from a (meth)acrylic acid ester (compound represented by formula (I)) having a linear or branched alkyl group with 1 to 3 carbon atoms. Furthermore, it is thought that a high proportion of constituent unit (A) in the total constituent units of the acrylic polymer contained in the ion-conducting layer will suppress the internal resistance of the battery and improve the battery characteristics of energy storage devices made using the ion-conducting layer of this disclosure. However, these are presumptions, and this disclosure does not have to be interpreted as being limited to these mechanisms.

[0021] The ion-conducting layer of this disclosure is an ion-conducting layer disposed between the positive and negative electrodes of an energy storage device that exchanges ions between the positive and negative electrodes. In one or more embodiments, the ion-conducting layer of this disclosure is an ion-conducting resin-containing layer for purposes such as electrode protection and adhesion, or for the safety and durability of the energy storage device. The ion-conducting layer of this disclosure may be disposed at any location between the positive and negative electrodes. Examples of locations where the ion-conducting layer of this disclosure may be disposed include the negative electrode surface (such as a negative electrode protective layer), the electrolyte layer, the separator surface (such as an adhesive layer), the separator itself, and the positive electrode surface (such as a positive electrode protective layer). By distributing the ion-conducting layer of this disclosure at least at one of these locations, the battery characteristics of the energy storage device can be improved.

[0022] [Acrylic polymer] The ion-conducting layer of the present disclosure comprises the acrylic polymer of the present disclosure. From the viewpoint of the performance and manufacture of the energy storage device, the content of the acrylic polymer of the present disclosure in the ion-conducting 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. Furthermore, the ion-conducting layer of this disclosure may contain polymers other than the acrylic polymer of this disclosure. From the viewpoint of the performance and manufacture of the energy storage device, the content of the acrylic polymer of this disclosure in the polymer of the ion-conducting layer of this 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 this disclosure include acrylic polymers, styrene polymers, fluorine polymers, cellulose polymers, etc., in which the content of constituent unit (A) in the total constituent units is less than 88% by mass.

[0023] The acrylic polymers of this disclosure include a constituent unit (A) described later. Constituent unit (A) is a constituent unit derived from a monofunctional monomer of the compound described later. A monofunctional monomer is a monomer having one unsaturated bond. In one or more embodiments, the acrylic polymers of this disclosure may further contain the constituent unit (B) and / or the constituent unit (C) described later. In one or more embodiments, the acrylic polymers of this disclosure include, but are not limited to, homopolymers consisting of a constituent unit (A) described later, copolymers containing a constituent unit (A) and a constituent unit (B) described later, copolymers containing a constituent unit (A) and a constituent unit (C) described later, and at least one selected from copolymers containing a constituent unit (A), a constituent unit (B), and a constituent unit (C) described later. The acrylic polymer may be a single type or a combination of two or more types.

[0024] <Constituent Unit (A)> The constituent unit (A) is a constituent unit derived from the compound represented by the following formula (I) (hereinafter also referred to as "monomer (A)"). Monomer (A) may be used alone or in combination of two or more types.

[0025] [ka]

[0026] In formula (I), R 1 From the viewpoint of ease of synthesis, it represents a hydrogen atom or a methyl group, with a hydrogen atom being more preferred. 2 From the viewpoint of affinity to metal ions and electrolytes, R represents a linear or branched alkyl group having 1 to 3 carbon atoms, with alkyl groups having 1 to 2 carbon atoms being more preferred, and alkyl groups having 2 carbon atoms being even more preferred. X represents -O- or -NH-. In this disclosure, R in formula (I) above, formula (II) described later, and formula (III) above. 1 They are all independent of each other.

[0027] Examples of monomer (A) include alkyl ester (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate; and monofunctional (meth)acrylamides such as methyl (meth)acrylamide, ethyl (meth)acrylamide, n-propyl (meth)acrylamide, and isopropyl (meth)acrylamide; one or more combinations of these. Among these, one or more combinations of methyl methacrylate (MMA), methyl acrylate (MA), ethyl methacrylate (EMA), and ethyl acrylate (EA) are preferred from the viewpoint of affinity for metal ions and electrolytes. In this disclosure, (meth)acrylate means methacrylate or acrylate, and (meth)acrylamide means methacrylamide or acrylamide.

[0028] From the perspective of the affinity to the electrolytic solution, the content of the constitutional unit (A) in all the constitutional units of the acrylic polymer of the present disclosure is 88% by mass or more, preferably 90% by mass or more, more preferably 92% by mass or more, still more preferably 94% by mass or more, and even more preferably 96% by mass or more. And from the perspective of the affinity to metal ions, it is 100% by mass or less, preferably 99.9% by mass or less, more preferably 99.5% by mass or less, and still more preferably 99% by mass or less. The content of the constitutional unit (A) can be determined by known analysis methods or analyzers. When the constitutional unit (A) consists of constitutional units derived from two or more monomers (A), the content of the constitutional unit (A) refers to their total content.

[0029] From the perspective of the affinity to the electrolytic solution, the constitutional unit (A) contained in the acrylic polymer of the present disclosure is R in the formula (I). 1 is a hydrogen atom, and R 2 is a constitutional unit derived from a compound in which is a linear or branched alkyl group having 1 to 3 carbon atoms (hereinafter, also referred to as "constitutional unit (A1)"), or R in the formula (I) 1 is a hydrogen atom or a methyl group, and R 2 is preferably a constitutional unit derived from a compound in which is an alkyl group having 1 to 2 carbon atoms (hereinafter, also referred to as "constitutional unit (A2)"). When the constitutional unit (A) contains the constitutional unit (A1), from the perspective of the affinity to the electrolytic solution, the content of the constitutional unit (A1) in all the constitutional units of the acrylic polymer of the present disclosure is preferably 70% by mass or more, more preferably 85% by mass or more, still more preferably 90% by mass or more, even more preferably 94% by mass or more, and particularly preferably 96% by mass or more. When the constitutional unit (A) contains the constitutional unit (A2), from the perspective of the affinity to the electrolytic solution, the content of the constitutional unit (A2) in all the constitutional units of the acrylic polymer of the present disclosure is preferably 70% by mass or more, more preferably 85% by mass or more, still more preferably 90% by mass or more, even more preferably 94% by mass or more, and particularly preferably 96% by mass or more.

[0030] <Constitutional unit (B)> The constituent unit (B) is a constituent unit derived from at least one compound selected from the compound represented by the following formula (II) (hereinafter also referred to as "monomer (B1)"), the compound represented by the following formula (III) (hereinafter also referred to as "monomer (B2)"), and an unsaturated dibasic acid (hereinafter also referred to as "monomer (B3)"). From the viewpoint of affinity for metal ions, the constituent unit (B) is preferably a constituent unit derived from monomer (B1). Monomer (B) may be used alone or in combination of two or more.

[0031] [ka]

[0032] In the above equation (II), R 1 From the viewpoint of ease of synthesis, is a hydrogen atom or a methyl group. From the viewpoint of affinity to metal ions, M is a hydrogen atom or a cation, and a cation is preferred. As for the cation, from the viewpoint of improving battery characteristics, at least one of alkali metal ions and ammonium ions is preferred, at least one selected from ammonium ions, lithium ions, sodium ions and potassium ions is more preferred, and at least one of lithium ions and sodium ions is even more preferred.

[0033] When M in formula (II) is a cation, monomer (B1) may be, for example, a monomer in which M is a hydrogen atom that has been neutralized with an alkali (ammonia, sodium hydroxide, lithium hydroxide, potassium hydroxide, etc.), or it may be a polymer obtained by polymerizing a monomer in which M is a hydrogen atom and then neutralizing it with an alkali. Alternatively, a polymer obtained by polymerizing a monomer in which M is a hydrogen atom may have its hydrogen atoms substituted by metal ions contained in the electrolyte inside the energy storage device. From the viewpoint of polymerization reaction control and dispersion stability, it is preferable that the polymer is neutralized with an alkali after polymerization to form the constituent units. In one or more embodiments, the monomer (B1) may be partially neutralized or completely neutralized. In one or more embodiments, M in formula (II) is preferably at least one selected from lithium ions and hydrogen atoms.

[0034] Examples of monomers (B1) include one or more selected from acrylic acid (AA), methacrylic acid (MAA), and their salts. Examples of salts include at least one selected from ammonium salts, sodium salts, lithium salts, and potassium salts.

[0035] [ka]

[0036] In the above equation (III), R 1 represents a hydrogen atom or a methyl group, and X represents -O- or -NH-. 4 is, -(CH2) n Ure 3 , -R 5 SO3M, -R 6 N(R 7 )(R 8 ) and -R 6 N + (R 7 )(R 8 )(R 9 )·Y - It shows at least one selected from the following. n represents the average number of moles added, and is between 1 and 4. 3 R represents a hydrogen atom or a methyl group. 5 represents a linear or branched alkylene group having 1 to 3 carbon atoms. M represents a hydrogen atom or a cation. Examples of cations include the same cations as M in formula (II) described above. In this disclosure, M in formula (II) and formula (III) are independent of each other. 6 R represents a linear or branched alkylene group with 1 to 3 carbon atoms. 7 and R 8R represents a linear or branched alkyl group having 1 to 3 carbon atoms, which may be identical or different. 9 This represents a linear or branched alkyl group having 1 to 3 carbon atoms. - This indicates anion. Examples of anions include halide ions such as chloride ions, bromide ions, and fluoride ions; sulfate ions; phosphate ions; and others.

[0037] When M in formula (III) is a cation, monomer (B2) may be, for example, a monomer in which M is a hydrogen atom that has been neutralized with an alkali, or it may be a polymer obtained by polymerizing a monomer in which M is a hydrogen atom and then neutralizing it with an alkali. Alternatively, a polymer obtained by polymerizing a monomer in which M is a hydrogen atom may have hydrogen atoms substituted by metal ions contained in the electrolyte inside the energy storage device. From the viewpoint of polymerization reaction control and dispersion stability, it is preferable that the polymer is neutralized with an alkali after polymerization to form the constituent units. In one or more embodiments, the monomer (B2) may be partially neutralized or completely neutralized. In one or more embodiments, M in formula (III) is preferably at least one selected from lithium ions and hydrogen atoms.

[0038] As monomer (B2), from the viewpoint of ease of synthesis, at least one selected from hydroxyl group-containing ester (meth)acrylates such as hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate; and nitrogen atom-containing ester (meth)acrylates such as dimethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, and trimethylammoniumethyl (meth)acrylate; is preferred, with at least one selected from hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate being more preferred, and at least one of hydroxyethyl methacrylate and hydroxyethyl acrylate being more preferred.

[0039] The monomer (B3) is an unsaturated dibasic acid, and from the viewpoint of ease of synthesis, for example, at least one selected from unsaturated dibasic acids having 4 to 12 carbon atoms and their salts, with a preferred carbon number of 4 to 8 carbon atoms, and a more preferred carbon number of 4 to 6 carbon atoms.

[0040] Examples of monomers (B3) from the viewpoint of ease of synthesis include maleic acid, fumaric acid, citraconic acid, mesaconic acid, itaconic acid, 2-pentenioic acid, 3-hexenioic acid, and their salts. At least one selected from maleic acid, fumaric acid, itaconic acid, and their salts is preferred, and at least one of maleic acid and its salts is more preferred.

[0041] When monomer (B3) is a salt of an unsaturated dibasic acid, the salt is preferably at least one selected from ammonium salts, lithium salts, sodium salts, and potassium salts, with at least one of lithium salts and sodium salts being more preferred, from the viewpoint of affinity to metal ions and dispersion stability.

[0042] The unsaturated dibasic acid salt of monomer (B3) may be obtained by neutralizing the unsaturated dibasic acid with an alkali, or by using the unsaturated dibasic acid to polymerize and then neutralizing with an alkali. Alternatively, the polymer polymerized using the unsaturated dibasic acid may have hydrogen atoms substituted by metal ions contained in the electrolyte inside the energy storage device. From the viewpoint of polymerization reaction control and dispersion stability, it is preferable that the polymer is neutralized with an alkali after it has become a constituent unit of the polymer following polymerization.

[0043] If the acrylic polymer of this disclosure contains constituent unit (B), the content of constituent unit (B) in the total constituent units of the acrylic polymer of this disclosure is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and from the viewpoint of affinity to metal ions and dispersion stability, preferably 12% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, even more preferably 6% by mass or less, and even more preferably 4% by mass or less. The content of constituent unit (B) can be determined by known analytical methods or analytical instruments. If constituent unit (B) consists of constituent units derived from two or more monomers (B), the content of constituent unit (B) refers to their total content.

[0044] If the acrylic polymer of this disclosure contains constituent unit (B), the mass ratio (A / B) of the content of constituent unit (A) to the content of constituent unit (B) in the acrylic polymer of this disclosure is preferably 5000 or less, more preferably 500 or less, even more preferably 200 or less, and from the viewpoint of affinity to metal ions and electrolytes, and dispersion stability, preferably 8 or more, more preferably 15 or more, even more preferably 20 or more, and even more preferably 25 or more.

[0045] <Component Unit (C)> The constituent unit (C) is a constituent unit derived from a crosslinkable monomer (hereinafter also referred to as "monomer (C)"). Examples of monomer (C) include 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)"). Monomer (C) may be used alone or in combination of two or more.

[0046] Examples of monomers (C1) include compounds represented by the following formula (IV). [ka]

[0047] In the above equation (IV), R 10 From the viewpoint of ease of synthesis, a hydrogen atom or a methyl group is preferred for X. From the viewpoint of ease of synthesis and affinity to the electrolyte, -O- or -NH- is preferred for X. From the viewpoint of ease of synthesis and affinity to the electrolyte, an integer between 1 and 20 is preferred for n. In this disclosure, X in formulas (III) and (IV) are independent of each other.

[0048] Specific examples of compounds represented by formula (IV) above include, for example, 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.

[0049] Other monomers (C1) include, for example, 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 hydroxypivalate neopentyl glycol di(meth)acrylate, and polyester(meth)acrylate.

[0050] The monomer (C2) containing an N-methylolamide group can be at least one selected from N-methylolacrylamide and N-methylolmethacrylamide.

[0051] If the acrylic polymer of this disclosure contains a constituent unit (C), the content of the constituent unit (C) of the acrylic polymer of this disclosure is 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 constituent units other than the constituent unit (C), and similarly, preferably 5 mol% or less, more preferably 3 mol% or less, even more preferably 1 mol% or less, and even more preferably 0.8 mol% or less, relative to the total number of moles of constituent units other than the constituent unit (C). If the constituent unit (C) consists of constituent units derived from two or more monomers (C), the content of the constituent unit (C) refers to their total content.

[0052] The acrylic polymers of this disclosure may contain other structural units other than structural units (A), structural unit (B), and structural unit (C) as long as they do not impair the effects of this disclosure. Other structural units may be structural units derived from monomers copolymerizable with monomers (A), (B), and (C) (hereinafter also referred to as "monomer (D)"). Examples of monomer (D) include (meth)acrylonitrile, styrene, methylstyrene, alkyl (meth)acrylates having linear or branched alkyl groups with 4 or more carbon atoms, aromatic (meth)acrylates, alkyl vinyl ethers, alkyl vinyl esters, alkenyl group-containing monomers, etc. Monomer (D) may be used alone or in combination of two or more.

[0053] The total content of constituent units (A) and (B) in all constituent units of the acrylic polymer of this disclosure is 88% by mass or more, preferably 90% by mass or more, more preferably 92% by mass or more, even more preferably 94% by mass or more, even more preferably 96% by mass or more, and particularly preferably 98% by mass or more, from the viewpoint of affinity to metal ions and electrolytes.

[0054] [Method for manufacturing acrylic polymers] The acrylic polymers of this disclosure can be produced, for example, by polymerizing monomer (A) and optionally at least one monomer from monomers (B) to (D). That is, in one embodiment, this disclosure includes a polymerization step of polymerizing a monomer mixture containing monomer (A) and optionally at least one monomer from monomers (B) to (D). Examples of polymerization methods include known polymerization methods such as emulsion polymerization, solution polymerization, suspension polymerization, and bulk polymerization, and emulsion polymerization is preferred from the viewpoint of ease of polymer production.

[0055] In this disclosure, the content (mass%) of component (A) in all component units of the acrylic polymer can be considered as the amount (mass%) of monomer (A) used relative to the total amount of monomer used in polymerization. The content (mass%) of component (B) in all component units of the polymer particles can be considered as the amount (mass%) of monomer (B) used relative to the total amount of monomer used in polymerization. The mass ratio (A / B) of the content of component (A) to component (B) can be considered as the mass ratio of the amount of monomer (A) used relative to the amount of monomer (B) used in the total amount of monomer used in polymerization. The total content (mass%) of component (A) and component (B) in all component units of the polymer particles can be considered as the total amount (mass%) of monomer (A) and monomer (B) used relative to the total amount of monomer used in polymerization. The content (mol%) of constituent unit (C) in polymer particles can be considered as the amount (mol%) of monomer (C) used relative to the total number of moles of monomers other than monomer (C) used in polymerization (for example, if the polymer particles contain constituent units (A) to (C), relative to the total number of moles of monomers (A) and (B)).

[0056] Examples of emulsion polymerization methods include known methods using emulsifiers and methods that substantially do not use emulsifiers, so-called soap-free emulsion polymerization methods, and from the viewpoint of battery performance, soap-free emulsion polymerization methods are preferred. Examples of acrylic polymers in this disclosure include polymers obtained by emulsion polymerization, preferably soap-free emulsion polymerization, of a monomer mixture containing monomer (A) and optionally at least one monomer from monomers (B) to (D).

[0057] From the viewpoint of suppressing a decrease in binding properties, the amount of emulsifier used in 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 monomer used in emulsion polymerization. In this disclosure, the amount of emulsifier used in emulsion polymerization can be the amount of surfactant used in the polymerization step. In one or more embodiments, the acrylic polymer of this disclosure is obtained by emulsion polymerization of a monomer mixture containing monomer (A), and the amount of emulsifier contained in the ion-conducting layer of this 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 even more preferably substantially 0% by mass, relative to the acrylic polymer.

[0058] [Acrylic polymer composition] In one embodiment, this disclosure relates to an acrylic polymer composition for forming the ion-conducting layer of this disclosure (hereinafter also referred to as "the acrylic polymer composition of this disclosure").

[0059] The acrylic polymer compositions of the present disclosure include, in one or more embodiments, the acrylic polymers of the present disclosure described above. The acrylic polymers contained in the acrylic polymer compositions of the present disclosure are preferably in the form of particles. The content of the acrylic polymer in the acrylic polymer compositions of the present disclosure is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less, from the viewpoint of polymer production and the performance of energy storage devices.

[0060] The acrylic polymer compositions of this disclosure include a polar medium in one or more embodiments. The polar medium may be any liquid capable of dissolving or dispersing the acrylic polymer. From the viewpoint of production and dispersion stability of the acrylic polymer, the polar medium is preferably at least one organic solvent selected from methanol, ethanol, isopropanol, acetone, tetrahydrofuran, and dioxane, an aqueous medium containing these organic solvents and water, or water, more preferably an aqueous medium and water, and even more preferably water. Examples of water include deionized water.

[0061] [Method for forming an ion-conducting layer] One or more embodiments of a method for forming an ion-conducting layer of the present disclosure includes a step of applying a slurry containing the acrylic polymer composition of the present disclosure (hereinafter also referred to as the "ion-conducting layer slurry of the present disclosure") to the surface of a substrate (e.g., a separator, electrode, release film, etc.) such that the thickness of the ion-conducting layer is greater than 1 μm and less than or equal to 500 μm (coating step), and a step of drying the applied slurry to form an ion-conducting layer (drying step). In one or more embodiments, the substrate to which the ion-conducting layer slurry of the present disclosure is applied includes a porous film or an electrode active material layer containing an electrode active material and a binder.

[0062] The acrylic polymer contained in the ion-conducting layer slurry of this disclosure has a particle shape. From the viewpoint of affinity to the electrolyte and productivity, the average particle diameter of the acrylic polymer particles is preferably 0.1 μm or more, more preferably 0.2 μm or more, and from the viewpoint of productivity and slurry stability, 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 particularly preferably 0.4 μm or less. In this disclosure, the average particle size is the volume-average particle size (D50) measured by laser diffraction scattering, and refers to the particle size at the point where the cumulative volume is 50% in the cumulative volume distribution curve, where the total volume of the particle size distribution determined on a volume basis is 100%. The volume-average particle size (D50) can be measured using a laser diffraction / scattering particle size distribution analyzer, and specifically can be measured by the method described in the examples.

[0063] The acrylic polymer contained in the slurry for the ion-conducting layer of this disclosure may be in the form of a powder or a polymer particle 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.

[0064] From the viewpoint of manufacturing energy storage devices, the content of the acrylic polymer in the slurry for the ion conducting layer of this disclosure is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0065] In one or more embodiments, the method for producing a slurry for an ion-conducting layer of the present disclosure may include a polymerization step to obtain polymer particles by polymerizing a monomer mixture containing monomer (A) and, optionally, at least one monomer from monomers (B) to (D). The polymerization method, the types of components that can be used for polymerization, and the amounts used in the polymerization step of the slurry production method of the present disclosure may be the same as those in the polymerization step of the acrylic polymer production method described above.

[0066] In the coating step of the ion-conducting layer formation method of this disclosure, the coating method for the slurry for the ion-conducting layer of this disclosure is not particularly limited and includes, for example, the doctor blade method, the dip method, the reverse roll method, the direct roll method, the gravure method, the extrusion method, and the brush coating method.

[0067] In the drying step of the ion-conducting layer formation method of this disclosure, drying methods include, for example, drying with hot air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying time is usually 5 to 30 minutes, and the drying temperature is usually 40 to 180°C.

[0068] [Ion Conduction Layer] In one or more embodiments, the ion-conducting layer of the present disclosure is formed of the acrylic polymer of the present disclosure. In one or more embodiments, the ion-conducting layer of the present disclosure has ion conductivity through its ability to permeate ions. Therefore, the ion-conducting layer of the present disclosure exhibits ion permeability in the measurement method described later, for example, and exhibits the effect of reducing the ion resistance of an energy storage device.

[0069] In one or more embodiments, the formation of the ion-conducting layer of this disclosure is carried out by preparing a film containing an acrylic polymer. An example of a method for preparing a film containing an acrylic polymer is the ion-conducting layer formation method of this disclosure described above. Other methods for preparing a film containing an acrylic polymer include, for example, a method of applying or immersing a solution or dispersion (slurry) containing an acrylic polymer to a substrate such as a separator or electrode and drying it, or a method of applying, drying, and forming a film on a release film substrate with an acrylic polymer and transferring the resulting film to a predetermined location.

[0070] A solution or slurry containing an acrylic polymer in which the content of constituent unit (A) in the total constituent units is 88% by mass or more, used in the ion-conducting layer of this disclosure, has high surface tension, which may cause the liquid to repel when applied to a substrate, resulting in an impairment of the uniformity of the thickness of the resulting film. The thickness of the ion-conducting layer of this disclosure can be set according to the purpose, and from the viewpoint of ease of manufacturing of the energy storage device, battery characteristics, and thickness uniformity, it is preferably greater than 1 μm, more preferably 2 μm or more, even more preferably 3 μm or more, and even more preferably 5 μm or more. Similarly, from the viewpoint of this, 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.

[0071] The ions conducting within the ion-conducting layer of this disclosure are preferably metal ions, more preferably alkali metal ions, and even more preferably lithium ions.

[0072] The ion-conducting layer of this disclosure preferably holds an organic solvent within the energy storage device. The organic solvent is preferably a solvent that solubilizes ions, and more preferably an electrolyte. Examples include cyclic carbonates: ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and their derivatives; linear carbonates: dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), and their derivatives; aliphatic carboxylic acid esters: methyl formate, methyl acetate, ethyl propionate, and their derivatives; γ-lactones: γ-butyrolactone, and their derivatives. Among these, cyclic carbonates, linear carbonates, aliphatic carboxylic acid esters, and γ-lactones are preferred, cyclic carbonates and linear carbonates are more preferred, and EC, PC, DMC, DEC, and EMC are even more preferred. Organic solvents may be used individually or in combination of two or more. From the viewpoint of ionic conductivity, the amount of organic solvent held in the ion-conducting layer within the energy storage device is 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-conducting layer. Furthermore, from the viewpoint of battery durability, it 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.

[0073] The ion-conducting layer of this disclosure may contain optional components in addition to the acrylic polymer described above. Examples of optional components include adhesives, resin modifiers, metal salts, inorganic oxides, and solid electrolytes.

[0074] The metal salt is preferably an alkali metal salt used as the support electrolyte in the battery, and more preferably a lithium salt used in lithium-ion batteries. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)2NLi.

[0075] Inorganic oxides can be used to enhance the safety and strength of energy storage devices, to the extent that they do not impair the effects of the present disclosure. Examples of inorganic oxides include alumina (aluminum oxide), magnesia (magnesium oxide), calcium oxide, titania (titanium oxide), zirconia (zirconium oxide), talc, and silica. In one or more embodiments, the ion-conducting layer of the present disclosure may be free of inorganic oxides.

[0076] The solid electrolyte can be an inorganic compound having ionic conductivity (e.g., lithium ion conductivity). The type of solid electrolyte is not particularly limited; both inorganic and organic solid electrolytes can be used, but inorganic solid electrolytes are preferred from the viewpoint of flame retardancy. Known materials can be used as inorganic solid electrolytes, such as sulfide-based solid electrolytes and oxide-based solid electrolytes. Oxide-based solid electrolytes may also be the inorganic oxides described above.

[0077] From the viewpoint of ionic conductivity, the content of the acrylic polymer in the ion-conducting layer of this disclosure is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 100% by mass or less.

[0078] (Components for energy storage devices) The ion-conducting layer of this disclosure can be used in one or more embodiments as a component for an energy storage device, such as an electrolyte, separator, electrode surface protective layer, solid electrolyte mixed film, or resin layer. In other words, the present disclosure relates, in one embodiment, to an energy storage device component (hereinafter also referred to as "the energy storage device component of the present disclosure") which contains the ion conducting layer of the present disclosure and the thickness of the ion conducting layer is greater than 1 μm and less than or equal to 500 μm. In one or more embodiments, the energy storage device component of the present disclosure is at least one selected from an electrolyte layer having the ion conducting layer of the present disclosure, an electrode having the ion conducting layer of the present disclosure, and a separator having the ion conducting layer of the present disclosure.

[0079] A separator having the ion-conducting layer of the present disclosure (hereinafter also referred to as "separator with ion-conducting layer of the present disclosure") can be obtained in one or more embodiments by forming the ion-conducting layer of the present disclosure on one or both sides of a separator. The method for manufacturing the ion-conducting layer separator of this disclosure can be, for example, similar to the ion-conducting layer formation method of this disclosure described above. The separator is a porous film, and examples include porous polyolefin film, porous polyolefin terephthalate film, porous polyimide film, porous polyester film, porous cellulose film, porous Teflon® film, nonwoven fabric, paper, etc.

[0080] An electrode having the ion-conducting layer of this disclosure (hereinafter also referred to as "electrode with ion-conducting layer of this disclosure") can be obtained in one or more embodiments by forming the ion-conducting layer of this disclosure on the surface of an electrode. The electrode is the positive electrode and negative electrode in an energy storage device, and is usually formed by forming an electrode active material layer (electrode composite layer) on one or both sides of a metal foil called a current collector. An electrode having electrode active material layers on both sides (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 (bipolar electrode). The electrode active material layer contains an electrode active material, a binder, and optionally components such as a conductive material, and an electrode having an ion-conducting layer is an electrode having the ion-conducting layer of this disclosure on the surface of the electrode active material layer. If both sides are positive or negative electrodes, at least one of the two sides may have the ion conductive layer of this disclosure. In the case of a bipolar electrode, the ion conductive layer of this disclosure may be provided on at least one of the negative electrode surface and the positive electrode surface. The method for manufacturing the electrode with the ion-conducting layer according to this disclosure can be, for example, the same as the method for forming the ion-conducting layer according to this disclosure described above.

[0081] [Energy storage devices] This disclosure relates, in one embodiment, to an energy storage device (hereinafter also referred to as "the energy storage device of this disclosure") having the energy storage device component of this disclosure. In one or more embodiments, the energy storage device of the present disclosure is an energy storage device having at least one positive electrode, at least one negative electrode, and optionally a bipolar electrode, wherein at least one selected from the positive electrode, negative electrode, and bipolar electrode has the ion conducting layer of the present disclosure.

[0082] The energy 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, in one or more embodiments, 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 the outermost layer, and at least one bipolar electrode is stacked between the positive electrode and the negative electrode via a separator or electrolyte such that the opposite side of the positive electrode becomes the negative electrode, and the positive electrode and the negative electrode are arranged in series within the battery, and the ion conducting layer of the present disclosure is formed at at least one location between the positive electrode and the negative electrode facing each other within the battery.

[0083] In one or more embodiments, an electrolyte can be retained in the ion-conducting layer within the energy storage device of the present disclosure. Examples of the electrolyte include at least one selected from cyclic and linear carbonates.

[0084] The thickness of the ion-conducting layer in the energy storage device of this disclosure is, from the viewpoint of durability and battery characteristics of the energy storage device, and thickness uniformity, greater than 1 μm, preferably 2 μm or more, more preferably 3 μm or more, and more preferably 5 μm or more. Similarly, from the viewpoint of 500 μm or less, preferably 100 μm or less, more preferably 70 μm or less, and even more preferably 50 μm or less.

[0085] This disclosure further relates to one or more embodiments described below. <1> An electrode having an ion-conducting layer, The ion-conducting layer contains an acrylic polymer, The acrylic polymer includes a constituent unit (A) derived from the compound represented by formula (I), The aforementioned constituent unit (A) is R in formula (I) 1 is a hydrogen atom, and R 2 It contains a constituent unit (A1) derived from a compound in which C1 is a linear or branched alkyl group having 1 to 3 carbon atoms, The content of component (A) in the total constituent units of the acrylic polymer is 88% by mass or more and 100% by mass or less, and the content of component (A1) in the total constituent units of the acrylic polymer is 70% by mass or more. An electrode having an ion-conducting layer, wherein the thickness of the ion-conducting layer is greater than 1 μm and less than or equal to 500 μm. <2> A separator having an ion-conducting layer placed between the positive and negative electrodes of an energy storage device, The ion-conducting layer contains an acrylic polymer, The acrylic polymer includes a constituent unit (A) derived from the compound represented by formula (I), The aforementioned constituent unit (A) is R in formula (I) 1 is a hydrogen atom or a methyl group, R 2 It contains a constituent unit (A2) derived from a compound in which C1-C2 alkyl groups, The content of component (A) in the total constituent units of the acrylic polymer is 88% by mass or more and 100% by mass or less, and the content of component (A2) in the total constituent units of the acrylic polymer is 70% by mass or more. A separator having an ion-conducting layer, wherein the thickness of the ion-conducting layer is greater than 1 μm and less than or equal to 500 μm. <3> A component for an energy storage device that holds an electrolyte in an ion conducting layer, The ion-conducting layer contains an acrylic polymer, The acrylic polymer includes a constituent unit (A) derived from the compound represented by formula (I), The content of component (A) in the total constituent units of the acrylic polymer is 88% by mass or more and 100% by mass or less. The electrolyte is at least one selected from cyclic and linear carbonates. A component for an energy storage device, wherein the thickness of the ion conductive layer is greater than 1 μm and less than or equal to 500 μm. <4> An energy storage device having a positive electrode, a negative electrode, and at least one bipolar electrode disposed between the positive electrode and the negative electrode, At least one selected from the positive electrode, negative electrode, and bipolar electrode has an ion-conducting layer. The ion-conducting layer contains an acrylic polymer, The acrylic polymer includes a constituent unit (A) derived from the compound represented by formula (I), The content of component (A) in the total constituent units of the acrylic polymer is 88% by mass or more and 100% by mass or less. An energy storage device in which the thickness of the ion-conducting layer is greater than 1 μm and less than or equal to 500 μm. The ion-conducting layer and the acrylic polymer in these embodiments may be the ion-conducting layer and the acrylic polymer of the present disclosure described above, respectively. [Examples]

[0086] The present disclosure will be explained below with reference to examples, but the disclosure is not limited thereto.

[0087] 1. Preparation of polymer dispersions (Examples 1-14 and Comparative Examples 1-7) The polymer dispersions for Examples 1-14 and Comparative Examples 1-7 shown in Table 1 were prepared using the following raw materials. The abbreviations for the raw materials used in Table 1 and the following examples are as follows:

[0088] <Monomer (A)> (See R below) 1 , R 2 (and X represents the symbols in equation (I)) MMA: Methyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.) 1 :CH3, R 2 :CH3, X:O) EMA: Ethyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.) 1 :CH3, R 2 :C2H5, X:O) EA: Ethyl acrylate (manufactured by Wako Pure Chemical Industries, Ltd.) (R 1 :H, R 2 :C2H5, X:O) <Monomer (B)> (See R below) 1 (and M refers to the symbols in equation (II)) MAA: Methacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd.) (R 1 :CH3, M:H) AA: Acrylic acid (manufactured by Wako Pure Chemical Industries) (R 1 :H, M:H) ITA: Itaconic acid (manufactured by Wako Pure Chemical Industries, Ltd.) (unsaturated dibasic acid) <Monomer (C)> (See R below) 10 (and X represents the symbols in equation (IV)) NMAM: N-methylolacrylamide (manufactured by Wako Pure Chemical Industries, Ltd.) EGDMA: Ethylene glycol dimethacrylate (manufactured by Wako Pure Chemical Industries, Ltd.) (R 10 :CH3, X:O) <Monomer (D)> BA: Butyl acrylate (manufactured by Wako Pure Chemical Industries, Ltd.) AN: Acrylonitrile (manufactured by Wako Pure Chemical Industries, Ltd.) <polymer> SBR: Styrene-butadiene rubber (manufactured by Nippon Zeon, "BM-400B", solids content 40% by mass) PVDF-HFP: Poly(vinylidene fluoride-co-hexafluoropropylene) (manufactured by Sigma-Aldrich, average Mw ~455,000, average Mn ~110,000, pellets) <Polymerization initiator> APS: Ammonium persulfate <Neutralizing salt> Li: Lithium <Solvent> NMP: N-methylpyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.)

[0089] (Acrylic polymer dispersion of Example 1) 194 g of EA as monomer (A), 6 g of AA as monomer (B), 0.20 g of EGDMA as monomer (C) [0.1 mol% of the total number of moles of monomers (A) and (B)], and 340 g of deionized water were placed in a 1 L glass four-neck separable flask and stirred for a set time (0.5 hours) under a nitrogen atmosphere. Then, the reaction solution in the flask was heated to around 70°C, and a polymerization initiator solution prepared by dissolving 1 g of APS in 10 g of deionized water was added to the flask. Polymerization and maturation were carried out by holding the reaction solution in the flask at around 70-75°C for 6 hours to obtain an acrylic polymer dispersion. Subsequently, the acrylic polymer dispersion in the flask was cooled to room temperature, neutralized by adding 29.14 g of 1 N LiOH aqueous solution, aggregates were removed using a 200 mesh filter cloth, and the mixture was concentrated to a concentration of 30% by mass to obtain the acrylic polymer dispersion of Example 1. Table 1 shows the amounts and types of each component used in the preparation of the acrylic polymer dispersion in Example 1. Furthermore, Table 1 shows the stability (emulsion stability) of the polymer dispersion in Example 1, as confirmed by the amount of aggregates, and the measurement results of the average particle size of the polymer particles in Example 1.

[0090] (Acrylic polymer dispersions of Examples 2-11) The acrylic polymer dispersions of Examples 2 to 11 were obtained in the same manner as in Example 1, except that the monomer species or the amount of monomer components were changed to form the constituent units shown in Table 1. The amount and type of each component used in the preparation of the acrylic polymer dispersions of Examples 2 to 11 are shown in Table 1. Furthermore, the results of the emulsion stability and average particle size measurements for Examples 2 to 11 are shown in Table 1.

[0091] (Acrylic polymer dispersions of Examples 12-14 and Comparative Example 7) The acrylic polymer dispersions used in Examples 12-14 and Comparative Example 7 were the same as those used in Example 1.

[0092] (Acrylic polymer dispersions of Comparative Examples 1-4) Acrylic polymer dispersions of Comparative Examples 1 to 4 were obtained in the same manner as in Example 1, except that the monomer species were changed to form the constituent units shown in Table 1. The amounts and types of each component used in the preparation of the acrylic polymer dispersions of Comparative Examples 1 to 4 are shown in Table 1. Furthermore, the measurement results of the average particle size of the polymer particles of Comparative Examples 1 to 4 are shown in Table 1.

[0093] (Polymer dispersion of Comparative Example 5) SBR was used as the polymer dispersion in Comparative Example 5. Table 1 shows the measurement results of the average particle size of the polymer particles in Comparative Example 5.

[0094] (Polymer dispersion of Comparative Example 6) PVDF-HFP was used as the polymer in Comparative Example 6. The polymer dispersion for Comparative Example 6 was prepared by dissolving PVDF-HEP in NMP at a concentration of 10% by mass.

[0095] [Measurement of average particle size of polymer particles] The average particle size of polymer particles was measured using a laser diffraction particle size analyzer (LA-920, Horiba, Ltd.) at room temperature, after diluting the sample with a dispersion medium (water) until the light intensity reached the instrument's specified range. The results are shown in Table 1.

[0096] [Measurement of solid content concentration in polymer dispersions] The solid content concentration of the polymer dispersion was calculated by drying at 105°C for 24 hours and measuring the weight loss. The results are shown in Table 1.

[0097] [Measurement of glass transition temperature (Tg)] The glass transition temperature (Tg) was calculated from the Tgn of the homopolymer of each monomer constituting the polymer, according to the Fox equation [TGFox, Bull. Am. Physics Soc., Vol. 1, No. 3, p. 123 (1956)], using the following equation (I). The results are shown in Table 1. 1 / Tg = Σ(Wn / Tgn) (I) In equation (I), Tgn represents the Tg of each monomer component expressed as absolute temperature, and Wn represents the mass fraction of each monomer component.

[0098] [Measurement of ion permeability] We prepared two solutions: EC / DEC mixed solvent I (volume ratio 3 / 7) which does not contain lithium (Li) salts, and lithium-containing solvent II (1 mol / L: LiClO4) which was prepared by dissolving lithium perchlorate in the EC / DEC mixed solvent (volume ratio 3 / 7). A polymer dispersion was poured into a tray equipped with a Teflon® sheet in an amount that would result in a dry thickness of 0.7 mm, and a polymer film was prepared by drying at 105°C for 24 hours. One side of the polymer film was in contact with EC / DEC mixed solvent I, and the other side was in contact with lithium-containing solvent II, and the film was left for 6 hours. Subsequently, the amount of Li (ppm) in EC / DEC mixed solvent I was confirmed using an inductively coupled plasma mass spectrometer (ICP-MS). The results are shown in Table 1.

[0099] [Measuring Adhesion] A polymer dispersion was coated onto copper foil to a thickness of 20 μm after drying. The sample was then dried overnight at room temperature, followed by 8 hours of drying at 40°C, and finally 8 hours of reduced-pressure drying at 50°C to prepare the sample. The measurement involved setting a polymer coating on copper foil in a tack tester (TAC1000; manufactured by Resca Co., Ltd.), pressing a jig against the polymer on the copper foil with a force of 150 gf, holding for 1 second, and then pulling it away at a speed of 10 mm / s to record the maximum adhesive force (gf). The results are shown in Table 1.

[0100] [Measurement of ionic conductivity] A polymer dispersion was coated onto aluminum foil to a thickness of 20 μm after drying, and dried at 40°C for 8 hours. After punching out a 16 mm diameter die, it was dried again at 50°C under reduced pressure for another 8 hours to obtain a film for ionic conductivity measurement. The aforementioned ionic conductivity measurement film was placed on a two-electrode coin cell (Hosen Co., Ltd. "HS Flat Cell"). Next, a 1M LiPF6 solution (solvent: EC / DEC mixed solvent (volume ratio 3 / 7)) was poured in as a non-aqueous electrolyte, the cell was sealed, and the ionic conductivity measurement cell was assembled. The ion conductivity measurement cell obtained in the above process was subjected to AC impedance measurement (10mV, frequency 0.05Hz~100KHz) 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 there. The results are shown in Table 1. A higher ion conductivity indicates a superior ion-conducting layer.

[0101] [Emulsion stability] In the agglutination removal step in the production of the aforementioned acrylic polymer dispersion, the agglutinants remaining on the 200-mesh filter cloth and those adhering to the reaction vessel were collected and dried at 105°C for 24 hours to calculate the dry weight of the total agglutinants. Based on the obtained polymer (solid content), if the agglutinants were less than 0.5%, they were classified as A; if they were 0.5% or more but less than 1.5%, they were classified as B; and if they were 1.5% or more, they were classified as C.

[0102] 2. Fabrication of energy storage devices (Examples 1-14 and Comparative Examples 1-7) A lithium-ion secondary battery, a type of energy storage device, was fabricated as follows.

[0103] [Fabrication of the negative electrode] The materials used in the negative electrode paste are as follows: • Negative electrode active material: Graphite, manufactured by Showa Denko, "AF-C" • Negative electrode conductive material: Carbon fiber, manufactured by Showa Denko, "VGCF-H" • Negative electrode binder: SBR • Negative electrode thickener: Sodium carboxymethylcellulose (CMC), manufactured by Daicel, "#2200"

[0104] First, 288g of negative electrode active material, 3g of negative electrode conductive material, and 3g of negative electrode thickener were mixed. Then, the mixture was kneaded using a disperser, with the amount of distilled water required to achieve a final solid content concentration of 50-55% by mass being added gradually. Next, 6g of negative electrode binder as polymer solids was added to the mixture, and it was kneaded further with the disperser. After that, the mixture was defoamed using a stirring and defoaming machine (Thinky Co., Ltd. "Awatori Rentaro"), and coarse particles were removed using a 150-mesh filter cloth to obtain a negative electrode paste. The obtained negative electrode paste was dried onto copper foil, which serves as the current collector, at a density of 80g / m². 2 The thickness was adjusted and the coating was applied using a bar coater. The coating film was dried in a forced-air dryer at 80°C for 5 minutes, and then at 150°C for 10 minutes. After that, the electrode density was reduced to 1.3-1.4 g / cm³ using a roll press. 3 The material was adjusted and left in a dry room for at least one night to produce a negative electrode with a negative electrode composite layer.

[0105] [Fabrication of negative electrode A with ion conduction layer] The polymer dispersions of Examples 1-11 and Comparative Examples 1-5 were mixed with a 1.5% by mass aqueous solution of CMC (carboxymethylcellulose sodium, manufactured by Daicel, #2200) so that the solid content mass ratio of the polymer dispersion to the CMC aqueous solution was 9 / 1. Then, the mixture was diluted with deionized water to obtain a slurry for the ion conduction layer to a total solid content concentration of 10% by mass. The polymer dispersion of Comparative Example 6 was used as is as a slurry for the ion-conducting layer. The ion-conducting layer slurry was applied to the surface of the composite layer of the negative electrode using an applicator so that its thickness after drying was 20 μm, dried at 60°C for 10 minutes, and then left in a dry room for at least one night to obtain a negative electrode A having an ion-conducting layer. The preparation of the ion-conducting negative electrode A using the polymer dispersion of Example 12 was carried out in the same manner as the preparation example using the polymer dispersion of Example 1, except that the coating was applied so that the thickness after drying was 45 μm. The preparation of the ion-conducting negative electrode A using the polymer dispersion of Example 13 was carried out in the same manner as the preparation example using the polymer dispersion of Example 1, except that the polymer dispersion was appropriately diluted with deionized water and then coated so that the thickness after drying was 5 μm. The preparation of the ion-conducting layer-equipped negative electrode A using the polymer dispersion of Example 14 was carried out in the same manner as the preparation example using the polymer dispersion of Example 1, except that the polymer dispersion was appropriately diluted with deionized water and then coated so that the thickness after drying was 2 μm. The preparation of the ion-conducting negative electrode A using the polymer dispersion of Comparative Example 7 was carried out in the same manner as the preparation example using the polymer dispersion of Example 1, except that the polymer dispersion was appropriately diluted with deionized water and then coated so that the thickness after drying was 0.8 μm.

[0106] [Fabrication of separator A with ion conduction layer] The polymer dispersions obtained in Examples 1-11 and Comparative Examples 1-5 were mixed with a 1.5% by mass CMC aqueous solution so that the solid content mass ratio of the polymer dispersion to the CMC aqueous solution was 9 / 1. Then, the mixture was diluted with deionized water to obtain a slurry for the ion conduction layer, resulting in a total solid content concentration of 10% by mass. The polymer dispersion of Comparative Example 6 was used as is as a slurry 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 was 20 μm. It was dried at 60°C for 10 minutes, and then left in a dry room for at least one night to obtain a separator A having an ion-conducting layer. The preparation of the ion-conducting layer separator A using the polymer dispersion of Example 12 was carried out in the same manner as the preparation example using the polymer dispersion of Example 1, except that the coating was applied so that the thickness after drying was 45 μm. The preparation of the ion-conducting layer separator A using the polymer dispersion of Example 13 was carried out in the same manner as the preparation example using the polymer dispersion of Example 1, except that the polymer dispersion was appropriately diluted with deionized water and then coated so that the thickness after drying was 5 μm. The preparation of the ion-conducting layer separator A using the polymer dispersion of Example 14 was carried out in the same manner as the preparation example using the polymer dispersion of Example 1, except that the polymer dispersion was appropriately diluted with deionized water and then coated so that the thickness after drying was 2 μm. The preparation of the ion-conducting layer separator A using the polymer dispersion of Comparative Example 7 was carried out in the same manner as the preparation example using the polymer dispersion of Example 1, except that the polymer dispersion was appropriately diluted with deionized water and then coated so that the thickness after drying was 0.8 μm.

[0107] [Fabrication of separator B with ion conduction layer] The polymer dispersions obtained in Examples 1-11 and Comparative Examples 1-5 were mixed with a 1.5% by mass CMC aqueous solution and an alumina filler (Alfer Aesar aluminum oxide, alpha-phase, 99% metal basis) so that the solid content mass ratio of the polymer dispersion / CMC aqueous solution / alumina filler was 9 / 1 / 90. The mixture was then diluted with deionized water to obtain a slurry for the ion conduction layer, resulting in a total solid content concentration of 40% by mass. In Comparative Example 6, the polymer dispersion was prepared by mixing alumina filler with a solid content mass ratio of 10 / 90, and then diluting it with NMP to obtain a slurry for the ion conductive layer with a total solid content concentration of 40% by mass. 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 was 20 μm. It was dried at 60°C for 10 minutes, and then left in a dry room overnight or longer to obtain a separator B having an ion-conducting layer.

[0108] [Average thickness of the ion-conducting layer] The average thickness of the ion-conducting adhesive layer was defined as the difference between the average thickness of the negative electrode and separator before the application of the ion-conducting layer and the average thickness of negative electrode A and separators A and B obtained by the method described above. The average thickness was measured for both the porous polyolefin film and the separator with the ion-conducting layer using a high-precision film thickness gauge (Tosei Engineering), and the average of five measurements was used. In the case where the ion-conducting layer was formed on both sides of the porous polyolefin film, the average thickness was calculated by dividing the average value of each side by two. The results are shown in Table 1.

[0109] [Fabrication of a lithium-ion secondary battery evaluation cell having an ion-conducting negative electrode A] Leaving the terminal mounting area intact, the ion-conducting layer-equipped negative electrode A was punched out to 45mm x 45mm, and the lithium foil to 40mm x 40mm, and terminals were attached to each. A separator punched out to 50mm x 50mm was placed on the active material layer side of the negative electrode, and the lithium foil was then placed on top of that. These were sandwiched between aluminum packaging laminate film, and the three sides excluding the terminal side were sealed by heat fusion. A lithium-ion secondary battery was fabricated by injecting the following electrolyte solution through the terminal opening, creating a vacuum inside, and then sealing the cell by heat-sealing the terminal side. The electrolyte solution used was a 1M LiPF6 solution (solvent: EC / DEC mixed solvent (volume ratio 3 / 7)) with 1% by mass of vinylene carbonate (VC) added. As described above, a lithium-ion secondary battery evaluation cell having a negative electrode A with an ion-conducting layer, in which the ion-conducting layer is located only on the surface of the negative electrode active material layer, was fabricated. Furthermore, the negative electrode A with an ion-conducting layer using the polymer dispersion in Comparative Example 6 could not be evaluated because the ion-conducting layer peeled off during punching.

[0110] [Fabrication of a lithium-ion secondary battery evaluation cell with an ion-conducting layer separator A] A lithium-ion secondary battery evaluation cell having an ion-conducting layer-equipped separator A was fabricated in the same manner as the lithium-ion secondary battery evaluation cell having an ion-conducting layer-equipped separator A, except that the ion-conducting layer-equipped separator A was used as the negative electrode, the separator was used as the separator, and the side of the separator A without the ion-conducting layer was superimposed on the negative electrode composite layer, in which the ion-conducting layer was located only on one side of the separator. Furthermore, the ion-conducting layer-equipped separator A prepared using the polymer dispersion of Comparative Example 6 could not be evaluated because the ion-conducting layer peeled off during punching.

[0111] [Fabrication of a lithium-ion secondary battery evaluation cell with an ion-conducting layer separator B] A lithium-ion secondary battery evaluation cell was fabricated in the same manner as the lithium-ion secondary battery evaluation cell having the ion-conducting layer separator B, except that the ion-conducting layer separator A was replaced with an ion-conducting layer separator B, in which the ion-conducting layer is located only on one side of the separator. Furthermore, the ion-conducting layer-equipped separator B prepared using the polymer dispersion of Comparative Example 6 could not be evaluated because the ion-conducting layer peeled off during punching.

[0112] <Charging capacity> Using the fabricated lithium-ion secondary battery (a lithium-ion secondary battery having an ion-conducting negative electrode A, an ion-conducting separator A, or an ion-conducting separator B), the evaluation cell was charged at a constant current of 0.2C to 0V in an environment of 25°C, then charged at a constant voltage (CC / CV) until the voltage reached 0.05C while maintaining a constant voltage of 0V, and subsequently discharged at a constant current of 0.2C to 3.0V. After repeating this charge-discharge cycle three times to complete the conditioning, the following battery evaluation was performed. Under conditions of 25°C, constant current charging at 0.2C was performed until the voltage reached 0V, and the charging capacity at this time was defined as C0. Subsequently, CC-CV charging was performed similarly with a constant current of 0.2C, followed by constant current discharge at a current of 0.2C until the voltage reached 3.0V, and then charging was performed with a constant current of 3.0C until the voltage reached 0V, and the charging capacity at this time was defined as C1. The capacity retention rate (%), expressed as C = (C1 / C0) × 100 (%), was then calculated as a rate characteristic. A larger value of this capacity retention rate C indicates superior battery characteristics. The results are shown in Tables 1-3.

[0113] <Charge-discharge cycle characteristics> Using the lithium-ion secondary battery evaluation cells having an ion-conducting layer-equipped negative electrode A of Examples 1-12 and Comparative Examples 1-5, after completing the conditioning, constant current charging was performed at a current of 0.2C until the voltage reached 0V in an environment of 25°C, and then constant voltage charging was performed at a fixed voltage of 0V until the voltage reached 0.05C. Discharge was performed at a constant current of 0.2C until the voltage reached 3.0V. This charge-discharge cycle was repeated 100 times, with one cycle being defined as the charge capacity C0 at the first cycle. Cycle durability was defined as the charge capacity C0 at the end of 100 cycles. 100 The ratio (cycle capacity retention rate) was calculated. The results are shown in Table 1. In Table 1, a capacity retention rate of 80% or more is denoted as A, 60% or more as B, and less than 60% as C.

[0114] [Table 1]

[0115] As shown in Table 1, the lithium-ion secondary batteries having an ion-conducting layer anode A prepared using the polymer dispersions of Examples 1 to 12 showed a suppressed decrease in capacity retention rate and improved battery characteristics compared to the lithium-ion secondary batteries having an ion-conducting layer anode A prepared using the polymer dispersions of Comparative Examples 1 to 5. Furthermore, it was found that lithium-ion secondary batteries having an ion-conducting negative electrode A prepared using the polymer dispersions of Examples 1 to 12 exhibited superior charge-discharge cycle characteristics compared to Comparative Examples 1 to 5.

[0116] [Table 2]

[0117] As shown in Table 2, the lithium-ion secondary batteries having ion-conducting layer separator A prepared using the polymer dispersions of Examples 1 to 11 showed a suppressed decrease in capacity retention rate and improved battery characteristics compared to the lithium-ion secondary batteries having ion-conducting layer separator A prepared using the polymer dispersions of Comparative Examples 1 to 5.

[0118] [Table 3]

[0119] As shown in Table 3, the lithium-ion secondary batteries having ion-conducting layer separator B prepared using the polymer dispersions of Examples 1 to 11 showed a suppression of capacity retention rate degradation and improved battery characteristics compared to the lithium-ion secondary batteries having ion-conducting layer separator B prepared using the polymer dispersions of Comparative Examples 1 to 5.

[0120] <Uniformity of the ion-conducting layer (coating film)> For the ion-conducting layer-equipped negative electrode A or separator A using the polymer dispersions of Examples 1, 12-14 and Comparative Example 7, the ion-conducting layer (coating film) was visually inspected, and the uniformity of the coating film was evaluated based on whether or not exposure of the negative electrode (or separator) surface occurred due to repulsion. The results are shown in Table 4. In Table 4, if no exposure of the negative electrode (or separator) surface due to repulsion was observed and the thickness of the coating film was almost uniform, it was indicated as A; if no exposure of the negative electrode (or separator) surface due to repulsion was observed but the thickness of the coating film was slightly uneven, it was indicated as B; and if exposure of the negative electrode (or separator) surface due to repulsion was observed and the thickness of the coating film was uneven, it was indicated as C.

[0121] [Table 4]

[0122] As shown in Table 4, in the ion-conducting layers of Examples 1, 12, and 13, no exposure of the negative electrode (or separator) surface was observed, and the thickness was almost uniform. In the ion-conducting layer of Example 14, no exposure of the negative electrode (or separator) surface was observed, but the thickness was somewhat uneven. In the ion-conducting layer of Comparative Example 7, exposure of the negative electrode (or separator) surface was observed, and the thickness was non-uniform.

[0123] [Example of a bipolar battery] A bipolar battery, as shown in Figure 1, was fabricated using the polymer dispersion from Example 1 by the following method.

[0124] (Fabrication of the 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) (manufactured by Kureha Corporation, L#7208; 8% NMP solution)

[0125] 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 positive electrode active material, positive electrode conductive material, and positive electrode binder was 94:3:3 (on a solid content basis). The mixing was performed using a disperser. The prepared positive electrode paste was dried onto aluminum foil, which serves as the current collector, at a density of 125 g / m². 2 The thickness was adjusted and the coating was applied using a bar coater. The coating film was dried in a forced-air dryer at 100°C for 5 minutes, and then at 150°C for 10 minutes. After that, the electrode density was reduced to 2.8~3.2 g / cm³ using a roll press. 3 The mixture was adjusted and left in a dry room for at least one night to produce a positive electrode with a positive electrode composite layer.

[0126] (Fabrication of negative electrodes and bipolar electrodes with ion-conducting layers) The negative electrode was fabricated using the same method as that used for the negative electrode of the lithium-ion battery described above. The negative electrode paste, obtained by the same method as the negative electrode paste used in the production of the lithium-ion battery, was dried and applied to one side of the stainless steel foil current collector at a density of 80 g / m². 2The thickness was adjusted to achieve the desired result, and the coating was applied using a bar coater. The coating film was dried in a forced-air dryer at 80°C for 5 minutes, and then at 150°C for 10 minutes. Next, the positive electrode paste was applied to the other side of the foil at a rate of 125 g / m² after drying. 2 The thickness was adjusted to achieve the desired result, and the coating was applied using a bar coater. The coating film was dried at 100°C for 5 minutes using a forced-air dryer to obtain a bipolar electrode. In the polymer dispersion of Example 1, an oxide-based solid electrolyte (Ohara, Li2O-Al2O3-SiO2-P2O5-TiO2, trade name LICGC powder) was mixed to a solid content weight ratio of 10 / 90. Then, the mixture was diluted with ethanol to a total solid content concentration of 30% by mass and uniformly mixed to obtain a slurry for the ion conductive layer. The above-mentioned ion-conducting layer slurry was coated onto the negative electrode and the negative electrode of the bipolar electrode to a thickness of 40 μm after drying, dried at 60°C for 10 minutes, and then left in a dry room overnight or longer to obtain a negative electrode C and a bipolar electrode C having an ion-conducting layer C.

[0127] (Fabrication of bipolar batteries) Leaving the terminal mounting area intact, the negative electrode C and positive electrode were punched out to 40mm x 40mm, and terminals were attached to each. Two bipolar electrodes C were punched out to 40mm x 40mm, with the outermost layers being the negative electrode C and positive electrode. Two bipolar electrodes C were then stacked between them, with the negative and positive electrodes facing each other, to create a laminated electrode. To eliminate any remaining air gaps between the layers, the laminated electrode was pressed under vacuum, then immersed in electrolyte for 8 hours to allow the electrolyte to thoroughly penetrate the electrodes and ion-conducting layers. The surface of the removed laminated electrode was wiped clean, and it was sandwiched between aluminum packaging laminate film. The three sides, excluding the terminal side, were sealed by heat fusion. The inside was then vacuumed and the terminal side was also heat-fused to seal the cell, thus creating the bipolar lithium-ion secondary battery shown in Figure 1. The electrolyte used was a 1 M LiPF6 solution (solvent: EC / DEC mixed solvent (volume ratio 3 / 7)) to which 1% by mass of vinylene carbonate (VC) was added. [Industrial applicability]

[0128] As described above, the ion-conducting layer of this disclosure, which has excellent battery characteristics, is useful in lithium-ion batteries, lithium-ion capacitors, and other energy storage devices. [Explanation of Symbols]

[0129] 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 collector tab, 11. Aluminum packaging laminate film, 12. Laminated section

Claims

1. An ion-conducting layer disposed between the positive and negative electrodes of an energy storage device, The ion-conducting layer contains an acrylic polymer, The aforementioned acrylic polymer is obtained by emulsion polymerization of a monomer mixture containing a compound represented by the following formula (I), The amount of emulsifier contained in the ion conducting layer is 0% by mass or more and 0.05% by mass or less relative to the acrylic polymer. The acrylic polymer includes a constituent unit (A) derived from a compound represented by the following formula (I) and a constituent unit (B) which includes a constituent unit derived from a compound represented by the following formula (II). 【Chemistry 1】 (In formula (I), R1 represents a hydrogen atom or a methyl group. R2 represents a linear or branched alkyl group having 1 to 3 carbon atoms. X represents -O- or -NH-.) 【Chemistry 2】 (In formula (II), R1 represents a hydrogen atom or a methyl group, and M represents a hydrogen atom or a cation.) The aforementioned component unit (A) includes component unit (A1), The aforementioned structural unit (A1) is a structural unit derived from a compound in which R1 in the above formula (I) is a hydrogen atom, R2 is a linear or branched alkyl group having 1 to 3 carbon atoms, and X is -O- or -NH-. The content of constituent unit (A1) in the total constituent units of the acrylic polymer is 70% by mass or more. The content of constituent unit (A) in the total constituent units of the acrylic polymer is 88% by mass or more and 99.9% by mass or less. An ion-conducting layer for an energy storage device, wherein the thickness of the ion-conducting layer is greater than 1 μm and less than or equal to 500 μm.

2. The ion-conducting layer for an energy storage device according to claim 1, wherein the acrylic polymer further comprises constituent units derived from at least one compound selected from a compound represented by the following formula (III) and an unsaturated dibasic acid. 【Transformation 3】 In formula (III), Rrepresents a hydrogen atom or a methyl group, and X represents -O- or -NH-. R 4 represents at least one selected from - (CH 2 ) n OR 3 , -R 5 SO 3 M, -R 6 N(R 7 )(R 8 ), and -R 6 N + (R 7 )(R 8 )(R 9 ).Y - n is 1 or more and 4 or less. R 3 represents a hydrogen atom or a methyl group. R 5 represents a linear or branched alkylene group having 1 to 3 carbon atoms. M represents a hydrogen atom or a cation. R 6 represents a linear or branched alkylene group having 1 to 3 carbon atoms. R 7 and R 8 are the same or different and represent a linear or branched alkyl group having 1 to 3 carbon atoms. R 9 represents a linear or branched alkyl group having 1 to 3 carbon atoms. Y -

1. represents an anion.​

3. The ion-conducting layer for an energy storage device according to claim 1 or 2, wherein M in formula (II) and / or formula (III) is at least one selected from lithium ions and hydrogen atoms.

4. The acrylic polymer further comprises a structural unit (C) derived from a crosslinkable monomer, The ion conductive layer for an energy storage device according to any one of claims 1 to 3, wherein the content of the constituent unit (C) of the acrylic polymer is 0.001 mol% or more and 5 mol% or less with respect to the total number of moles of constituent units other than the constituent unit (C).

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

6. An ion-conducting layer for an energy storage device according to any one of claims 1 to 5, which does not contain inorganic oxides.

7. A component for an energy storage device, comprising an ion-conducting layer according to any one of claims 1 to 6, wherein the thickness of the ion-conducting layer is greater than 1 μm and less than or equal to 500 μm.

8. A component for an energy storage device according to claim 7, comprising a solid electrolyte in an ion conducting layer.

9. A component for an energy storage device according to claim 7 or 8, comprising an inorganic oxide in the ion conducting layer.

10. The energy storage device component according to any one of claims 7 to 9, wherein the energy storage device component is at least one selected from 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.

11. A power storage device having a power storage device component according to any one of claims 7 to 10.

12. The energy storage device according to claim 11, wherein an electrolyte is held in an ion conducting layer.

13. A method for forming an ion-conducting layer for an energy storage device, A step of applying a slurry containing an acrylic polymer composition to the surface of a substrate so that the thickness of the ion-conducting layer is greater than 1 μm and less than or equal to 500 μm, The process includes the step of drying the coated slurry to form an ion-conducting layer, A certain acrylic polymer composition contains acrylic polymer particles, The aforementioned acrylic polymer is obtained by emulsion polymerization of a monomer mixture containing a compound represented by the following formula (I), The amount of emulsifier contained in the ion conducting layer is 0% by mass or more and 0.05% by mass or less relative to the acrylic polymer. The acrylic polymer includes a constituent unit (A) derived from a compound represented by the following formula (I) and a constituent unit (B) which includes a constituent unit derived from a compound represented by the following formula (II). 【Chemistry 4】 (In formula (I), R1 represents a hydrogen atom or a methyl group. R2 represents a linear or branched alkyl group having 1 to 3 carbon atoms. X represents -O- or -NH-.) 【Transformation 5】 (In formula (II), R1 represents a hydrogen atom or a methyl group, and M represents a hydrogen atom or a cation.) The aforementioned component unit (A) includes component unit (A1), The aforementioned structural unit (A1) is a structural unit derived from a compound in which R1 in the above formula (I) is a hydrogen atom, R2 is a linear or branched alkyl group having 1 to 3 carbon atoms, and X is -O- or -NH-. The content of constituent unit (A1) in the total constituent units of the acrylic polymer is 70% by mass or more. A method for forming an ion-conducting layer, wherein the content of constituent unit (A) in the total constituent units of the acrylic polymer is 88% by mass or more and 99.9% by mass or less.

14. The method for forming an ion conductive layer according to claim 13, wherein the substrate to which the slurry is applied is a porous film or an electrode active material layer containing an electrode active material and a binder.

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