Electrode composition, electrode, and battery

Abstract

A battery composition according to the present disclosure contains a polymer (A). The polymer (A) contains a structural unit (a). The structural unit (a) has a five-membered or six-membered nitrogen-containing heterocyclic structure. The nitrogen-containing heterocyclic structure is derived from a compound containing an unsaturated bond. The ratio of the structural unit (a) in the polymer (A) to the total of all structural units constituting the polymer (A) exceeds 50 mol%.

Description

Electrode composition, electrode, and battery

[0001] The present disclosure relates to an electrode composition, an electrode, and a battery.

[0002] Lithium-ion secondary batteries have been attracting attention as batteries with high energy density.

[0003] Patent Document 1 discloses a coating liquid used in manufacturing battery electrodes. The coating liquid disclosed in Patent Document 1 contains a solvent, a binder, a carbon-based substance, and a polymer having a nitrogen-containing five-membered ring structure. The content of the polymer is 1 ppm or more and 10,000 ppm or less relative to the total mass of the coating liquid. Patent Document 1 specifically discloses a copolymer of polyvinylpyrrolidone and polyvinylimidazole (monomer ratio 50:50) as the polymer. The coating liquid disclosed in Patent Document 1 is used as a raw material for a battery electrode material layer.

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-63423

[0005] Batteries are required to have an electrode composition that can suppress an increase in resistance (hereinafter also referred to as "resistance after high-temperature storage") after long-term storage (e.g., 28 days) in a high-temperature environment (e.g., 60°C).

[0006] In view of the above circumstances, an object of the present disclosure is to provide an electrode composition, an electrode, and a battery that can suppress an increase in resistance after high-temperature storage of a battery.

[0007] Means for solving the above problems include the following aspects. <1> An electrode composition comprising a polymer (A), wherein the polymer (A) has a five- or six-membered nitrogen-containing heterocyclic structure and comprises a structural unit (a) derived from a compound in which the nitrogen-containing heterocyclic structure contains an unsaturated bond, and the proportion of the structural unit (a) in the polymer (A) relative to the total of all structural units constituting the polymer (A) is greater than 50 mol %. <2> The electrode composition according to <1>, wherein the proportion of the structural unit (a) is 60 mol % or more. <3> The electrode composition according to <1> or <2>, wherein the structural unit (a) comprises a structural unit derived from vinylimidazole. <4> The electrode composition according to any one of <1> to <3>, further comprising an active material (B) and a binder (C). <5> The electrode composition according to <4>, wherein the active material (B) comprises a carbon-based compound. <6> The composition for an electrode according to any one of <1> to <5>, wherein the content of the polymer (A) relative to the solid content of the composition for an electrode is 0.01% by mass to 1.0% by mass. <7> An electrode comprising: a current collector; and a solid material of the composition for an electrode according to any one of <1> to <6>. <8> A battery comprising the electrode according to <7>.

[0008] According to the present disclosure, there are provided an electrode composition, an electrode, and a battery that can suppress an increase in resistance after high-temperature storage of a battery.

[0009] FIG. 1 is a schematic cross-sectional view showing a laminated battery, which is an example of a battery according to the present disclosure.

[0010] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, when a composition contains multiple substances corresponding to each component, the amount of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified. In this specification, "(meth)acrylate" refers to acrylate or methacrylate.

[0011] (1) Electrode Composition The electrode composition of the present disclosure (hereinafter also simply referred to as the "electrode composition") contains a polymer (A). The polymer (A) includes a structural unit (a). The structural unit (a) has a five- or six-membered nitrogen-containing heterocyclic structure, and is derived from a compound (hereinafter also referred to as the "monomer (a)") in which the nitrogen-containing heterocyclic structure contains an unsaturated bond. The proportion of the structural unit (a) in the polymer (A) relative to the total of all structural units constituting the polymer (A) (hereinafter also simply referred to as the "proportion of structural unit (a)") is greater than 50 mol%.

[0012] An "unsaturated bond" refers to a double bond or a triple bond. A "heterocyclic structure" refers to a cyclic structure composed of carbon atoms and heteroatoms (e.g., nitrogen, oxygen, sulfur, etc.). In the present disclosure, the terms "content" and "addition amount" are considered to be substantially the same.

[0013] The electrode composition of the present disclosure has the above-described configuration, and therefore can suppress an increase in resistance after high-temperature storage of a battery.

[0014] The electrode composition of the present disclosure is used as a raw material for electrodes, the details of which will be described later.

[0015] (1.1) Polymer (A) The electrode composition contains a polymer (A). When the electrode composition contains an active material (B), the polymer (A) adsorbs onto and / or coats the surface of the active material (B), thereby suppressing the progress of the decomposition reaction of the electrolyte on the surface of the active material (B) when the electrode composition is made into a battery. As a result, the electrode composition can suppress an increase in the resistance of the battery after high-temperature storage.

[0016] The weight average molecular weight of the polymer (A) is not particularly limited, and is preferably 1,000 or more, more preferably 5,000 or more, and even more preferably 10,000 or more. The weight average molecular weight of the polymer (A) is preferably 1,000,000 or less, more preferably 800,000 or less, and even more preferably 500,000 or less. The weight average molecular weight can be measured, for example, using a gel permeation chromatograph, Alliance GPC-2000 model, manufactured by Waters Corporation.

[0017] The content of the polymer (A) relative to the solid content of the electrode composition (hereinafter also referred to as the "content of polymer (A)") is not particularly limited, but is preferably 0.01% by mass to 1.0% by mass. This enables the electrode composition to further suppress an increase in the resistance of the battery after high-temperature storage. From the viewpoint of further suppressing an increase in the resistance of the battery after high-temperature storage, the content of polymer (A) is more preferably 0.05% by mass to 0.8% by mass, even more preferably 0.1% by mass to 0.6% by mass, and particularly preferably 0.2% by mass to 0.4% by mass.

[0018] The "solid content of the electrode composition" refers to the total mass of the electrode composition excluding the solvent (D) when the electrode composition contains the solvent (D) described below, and refers to the total mass of the electrode composition when the electrode composition does not contain the solvent (D).

[0019] (1.1.1) Structural Unit (a) The polymer (A) contains a structural unit (a). The structural unit (a) is derived from a monomer (a).

[0020] Among the monomers (a), examples of compounds having a five-membered nitrogen-containing heterocyclic structure containing an unsaturated bond include vinylimidazole, vinylpyrrole, vinylindole, vinylpyrazole, vinylbenzimidazole, vinyl-1H-indazole, vinylpyrroline, vinylpyrazoline, vinyltriazole, vinyltetrazole, vinyloxazole, vinyloxazoline, vinylisoxazole, vinylisoxazoline, vinylthiazole, and vinylthiazoline. Among the monomers (a), examples of compounds having a six-membered nitrogen-containing heterocyclic structure containing an unsaturated bond include vinylquinoline, vinylpyridine, vinylquinoline, and vinyltriazine. The monomers (a) may be used alone or in combination of two or more.

[0021] In particular, the structural unit (a) preferably contains a structural unit derived from vinylimidazole, and more preferably is a structural unit derived from vinylimidazole, which allows the electrode composition to further suppress an increase in resistance after high-temperature storage of the battery.

[0022] (1.1.2) Structural unit (b) The polymer (A) may or may not contain the structural unit (b). The structural unit (b) is derived from a compound copolymerizable with the monomer (a) (excluding the monomer (a)) (hereinafter also referred to as "monomer (b)"). When the polymer (A) does not contain the structural unit (b), the polymer (A) may be a homopolymer of the monomer (a) (proportion of the structural unit (a): 100 mol%). When the polymer (A) contains the structural unit (b), the polymer (A) may be a copolymer of the monomer (a) and the monomer (b).

[0023] When the polymer (A) contains the structural unit (b), when the electrode composition contains an active material (B), the polymer (A) adsorbs and / or coats the surface of the active material (B), thereby suppressing the progress of the decomposition reaction of the electrolyte on the surface of the active material (B) when the electrode composition is made into a battery. As a result, the electrode composition tends to be able to further suppress an increase in the resistance of the battery after high-temperature storage. This is presumably because the polymer (A) further containing the structural unit (b) is more likely to adsorb to the surface of the active material (B) and function as a protective coating layer than when the polymer (A) does not contain the structural unit (b).

[0024] Monomer (b) is not particularly limited as long as it is a compound copolymerizable with monomer (a). Examples of monomer (b) include unsaturated monomers having a carboxyl group and their salts, (meth)acrylic acid alkyl esters, unsaturated monomers having an acidic phosphate ester group, (meth)acrylamide and its derivatives, ether sulfate-type ammonium salts, and unsaturated monomers having a carbonyl group. Examples of unsaturated monomers having a carboxyl group and their salts include (meth)acrylic acid, maleic acid, maleic anhydride, itaconic acid, fumaric acid, crotonic acid, and acrylamidoglycolic acid. Examples of salts include alkali metal salts (e.g., sodium or potassium), alkaline earth metal salts (e.g., calcium or magnesium), ammonium salts, and organic amine salts (e.g., monoethanolamine or triethanolamine). Examples of (meth)acrylic acid alkyl esters include hydroxyethyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, and aminoethyl (meth)acrylate. Examples of unsaturated monomers having an acidic phosphate group include 2-(meth)acryloyloxyethyl acid phosphate, 2-(meth)acryloyloxypropyl acid phosphate, 2-(meth)acryloyloxy-3-chloropropyl acid phosphate, and 2-(meth)acryloyloxyethylphenyl phosphate. Examples of (meth)acrylamide and derivatives thereof include (meth)acrylamide, methylenebis(meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, and N,N-dimethyl(meth)acrylamide. The ether sulfate-type ammonium salt may be a commercially available product. Commercially available ether sulfate ammonium salts include products from ADEKA Corporation (for example, "SR-10," "SR-020," "SR-1025," or "SR-3025").Examples of the unsaturated monomer having a carbonyl group include vinylpyrrolidone, acrolein, diacetone (meth)acrylamide, vinyl methyl ketone, vinyl ethyl ketone, and vinyl butyl ketone.

[0025] The proportion of the structural unit (a) is greater than 50 mol%. The proportion of the structural unit (a) is preferably 60 mol% or greater. The proportion of the structural unit (a) is more preferably 60 mol% to 100 mol%, even more preferably 70 mol% or greater but less than 100 mol%, particularly preferably 80 mol% or greater but less than 100 mol%, more preferably 80 mol% to 99 mol%, and even more preferably 85 mol% to 99 mol%. When the proportion of the structural unit (a) is within the above range, the electrode composition can suppress an increase in resistance after high-temperature storage of a battery compared to when the proportion of the structural unit (a) is not within the above range.

[0026] When the polymer (A) does not contain the structural unit (b), the proportion of the structural unit (a) may be 100 mol %.

[0027] When the polymer (A) contains the structural unit (b), the proportion of the structural unit (a) and the proportion of the structural unit (b) in the polymer (A) relative to the total of all structural units constituting the polymer (A) (hereinafter also referred to as the "proportion of structural unit (b)") are preferably within the following ranges. From the viewpoint of further suppressing an increase in the resistance of a battery after high-temperature storage with the electrode composition, the proportion of the structural unit (a) is preferably 60 mol% or more and less than 100 mol%, more preferably 70 mol% or more and less than 100 mol%, even more preferably 80 mol% or more and less than 100 mol%, particularly preferably 80 mol% to 99 mol%, and more preferably 85 mol% to 99 mol%. The proportion of the structural unit (b) is appropriately selected depending on the type of structural unit (b) (i.e., the type of monomer (b)), etc. The proportion of the structural unit (b) is preferably greater than 0 mol%. From the viewpoint of further suppressing an increase in the resistance of the electrode composition after high-temperature storage of the battery, the content is preferably more than 0 mol% and not more than 40 mol%, more preferably more than 0 mol% and not more than 30 mol%, even more preferably more than 0 mol% and not more than 20 mol%, particularly preferably 1 mol% to 20 mol%, and more preferably 1 mol% to 15 mol%.

[0028] (1.2) Active material (B) The electrode composition may contain an active material (B). This allows the solid of the electrode composition to function as an electrode mixture layer. The "electrode mixture layer" refers to at least one of a negative electrode mixture layer and a positive electrode mixture layer.

[0029] The active material (B) may be either a negative electrode active material (B1) or a positive electrode active material (B2).

[0030] The shape of the active material (B) is not particularly limited, and examples thereof include fibrous, spherical, and flake-like shapes. When the active material (B) is particulate, the particle size of the active material (B) is not particularly limited. The particle size of the negative electrode active material (B1) is preferably 5 μm to 20 μm. The particle size of the positive electrode active material (B2) is preferably 5 μm to 15 μm. The primary particle size of the particles of the positive electrode active material (B2) is preferably 2.0 μm or less, more preferably 0.2 μm to 1.0 μm. The particle size of the active material (B) is the particle size (particle size distribution D50, median diameter) corresponding to the cumulative 50% by volume from the smallest particle size side in the volume-based particle size distribution measured using a particle size distribution measuring device based on a laser light diffraction scattering method.

[0031] When the electrode composition contains the active material (B), the content of the active material (B) is not particularly limited and is preferably 10% by mass to 99.9% by mass, more preferably 30% by mass to 99% by mass, even more preferably 50% by mass to 99% by mass, and particularly preferably 70% by mass to 99% by mass, relative to the solid content of the electrode composition.

[0032] The active material (B) is appropriately selected depending on the type of battery and the intended use of the electrode composition, and may be a known active material.

[0033] Hereinafter, the active material (B) will be described when the battery is a lithium ion secondary battery and the solid of the electrode composition is used in the electrode mixture layer.

[0034] (1.2.1) Negative Electrode Active Material (B1) There are no particular limitations on the negative electrode active material (B1) as long as it is a material capable of absorbing and releasing lithium ions. Examples of the negative electrode active material (B1) include carbonaceous compounds, silicon oxides, metals (e.g., silicon, tin, lithium, etc.), alloys (e.g., silicon alloys, tin alloys, lithium alloys, etc.), and lithium titanate.

[0035] The term "carbonaceous compound" refers to a carbonaceous material having a volume resistivity at 20°C of less than 40 Ω cm, preferably less than 3 Ω cm. The term "silicon oxide" refers to a compound represented by the following formula (1): Formula (1): SiO Ｘ [In formula (1), X represents 0.5 or more and less than 1.6.]

[0036] Examples of carbon-based compounds include graphite and amorphous carbon materials. Examples of graphite include artificial graphite and natural graphite (e.g., flake graphite, lump graphite, or amorphous graphite). Examples of amorphous carbon materials include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500°C or less, and mesophase pitch carbon fiber (MCF). The silicon oxide may be coated with amorphous carbon. The silicon oxide may be a known compound. For silicon oxide, reference may be made to International Publication No. 2013 / 094668, Japanese Patent Application Laid-Open No. 2016-143642, etc., as appropriate. The negative electrode active material (B1) may be used alone or in combination of two or more.

[0037] In particular, the negative electrode active material (B1) preferably contains a carbon-based compound, and more preferably is a carbon-based compound, which allows the battery to achieve both a high energy density and a high charge-discharge cycle durability, compared to a case in which the negative electrode active material (B1) does not contain a carbon-based compound.

[0038] (1.2.2) Positive Electrode Active Material (B2) The positive electrode active material (B2) is not particularly limited as long as it is a material capable of absorbing and releasing lithium ions, and can be adjusted appropriately depending on the application of the lithium ion secondary battery.

[0039] Examples of the positive electrode active material (B2) include a first oxide and a second oxide. The first oxide contains lithium (Li) and nickel (Ni) as constituent metal elements. The second oxide contains Li, Ni, and at least one metal element other than Li and Ni as constituent metal elements. Examples of metal elements other than Li and Ni include transition metal elements and typical metal elements. The second oxide preferably contains the metal elements other than Li and Ni in an amount equivalent to or less than Ni in atomic number terms. The metal elements other than Li and Ni may be, for example, at least one selected from the group consisting of Co, Mn, Al, Cr, Fe, V, Mg, Ca, Na, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. The positive electrode active material (B2) may be used alone or in combination of two or more.

[0040] The positive electrode active material (B2) preferably contains a lithium-containing composite oxide (hereinafter, sometimes referred to as "NCM") represented by the following formula (X): The lithium-containing composite oxide (X) has the advantages of high energy density per unit volume and excellent thermal stability.

[0041] LiNi ａ Co ｂ Mn ｃ O ２ ... Formula (X)

[0042] In formula (X), a, b, and c each independently represent a number greater than 0 and less than 1, and the sum of a, b, and c is 0.99 to 1.00.

[0043] Specific examples of NCM include LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ , LiNi ０．５ Co ０．３ Mn ０．２ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２, or LiNi ０．８ Co ０．１ Mn ０．１ O ２ Examples include:

[0044] The positive electrode active material (B2) may contain a lithium-containing composite oxide (hereinafter, sometimes referred to as "NCA") represented by the following formula (Y).

[0045] Li ｔ Ni １－ｘ－ｙ Co ｘ Al ｙ O ２ ... Formula (Y)

[0046] In formula (Y), t is 0.95 to 1.15, x is 0 to 0.3, y is 0.01 to 0.2, and the sum of x and y is less than 0.5.

[0047] Specific examples of NCA include LiNi ０．８ Co ０．１５ Al ０．０５ O ２ Examples include:

[0048] (1.3) Binder (C) The electrode composition may contain a binder (C). Thereby, when the electrode composition contains an active material (B) and forms an electrode mixture layer on a current collector, the binder (C) can bind the active material (B) to the electrode current collector.

[0049] Examples of the binder (C) include carboxymethyl cellulose (CMC), polyvinyl acetate, polymethyl methacrylate, nitrocellulose, fluororesin, and rubber particles. Examples of the fluororesin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and vinylidene fluoride-hexafluoropropylene copolymer. Examples of the rubber particles include styrene butadiene rubber (SBR) particles and acrylonitrile rubber particles. The binder (C) may be used alone or in combination of two or more.

[0050] When the electrode composition contains the binder (C), the content of the binder (C) is not particularly limited, and is preferably 0.1% by mass to 4% by mass relative to the solid content of the battery composition.

[0051] (1.4) Solvent (D) The electrode composition may contain a solvent (D).

[0052] Examples of the solvent (D) include water and liquid media compatible with water. When the solvent (D) contained in the electrode composition includes a liquid medium compatible with water, the coatability of the electrode composition onto an electrode current collector is improved. Examples of liquid media compatible with water include alcohols, glycols, cellosolves, aminoalcohols, amines, ketones, amides (e.g., N-methylpyrrolidone), carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, phosphoric acid esters, ethers, and nitriles. When the electrode composition includes a positive electrode active material (B2) and a solvent (D), it is preferable to use N-methylpyrrolidone as the solvent (D).

[0053] When the composition for an electrode contains a solvent (D), the ratio of the total amount of solids to the total amount of the composition for an electrode (hereinafter also referred to as "solids concentration") is not particularly limited and is preferably 30% by mass or more, more preferably 35% by mass or more, and even more preferably 40% by mass or more. The solids concentration is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and particularly preferably 70% by mass or less.

[0054] (1.5) Conductive Aid (E) The electrode composition may contain a conductive aid (E).

[0055] The conductive additive (E) may be a known conductive additive. A conductive carbon material is preferred as the known conductive additive. Examples of the conductive carbon material include carbon black, conductive carbon fiber, and fullerene. Examples of the conductive carbon fiber include carbon nanotubes, carbon nanofibers, and carbon fiber. Examples of natural graphite include flake graphite, lump graphite, and amorphous graphite. The conductive additive (E) may be used alone or in combination of two or more.

[0056] The conductive additive (E) may be a commercially available product. Examples of commercially available carbon black include "Super P" (manufactured by TIMCAL). Examples of commercially available flake graphite include "KS-6" (manufactured by TIMREX).

[0057] The content of the conductive auxiliary (E) is not particularly limited, and is preferably 0.05% by mass to 5% by mass relative to the solid content of the electrode composition.

[0058] (1.6) Additive (F) The electrode composition may contain an additive (F). This allows the electrode composition to be endowed with various functions depending on the type of additive (F). Examples of the additive (F) include a thickener, a surfactant, a dispersant, a wetting agent, and an antifoaming agent.

[0059] (1.7) Preferred Composition The electrode composition preferably contains, in addition to the polymer (A), an active material (B) and a binder (C). This allows the solid content of the electrode composition to function as an electrode mixture layer of a battery.

[0060] When the electrode composition further contains an active material (B) and a binder (C), the active material (B) preferably contains a carbon-based compound, more preferably is a carbon-based compound. By including the carbon-based compound in the active material (B), the battery can achieve both a high energy density and a high charge-discharge cycle durability compared to when the active material (B) does not contain a carbon-based compound.

[0061] (2) Electrode The electrode of the present disclosure includes a current collector and a solid material of the electrode composition of the present disclosure.

[0062] The term "electrode" refers to at least one of the positive electrode and negative electrode of a battery. When the electrode composition contains a solvent (D), the term "solid electrode composition" refers to a composition that is in a solid state at room temperature (23°C) and from which the solvent (D) has been removed. When the electrode composition does not contain a solvent (D), the term "solid electrode composition" refers to a composition that is in a solid state at room temperature (23°C) and is made of the electrode composition. When the electrode composition contains a solvent (D), the solid electrode composition is formed, for example, by applying the electrode composition to a current collector and drying it. When the electrode composition does not contain a solvent (D), the solid electrode composition is formed, for example, by applying a molten electrode composition to a current collector and cooling it.

[0063] The electrode of the present disclosure has the above-described configuration, and therefore can suppress an increase in resistance after high-temperature storage of the battery.

[0064] The solid electrode layer composition may be formed on at least one main surface of the current collector.

[0065] The function of the solid electrode composition depends on the raw materials of the electrode composition. When the electrode composition contains the active material (B), the solid electrode composition may function as an electrode mixture layer. When the electrode composition does not contain the active material (B), the solid electrode composition may function as an undercoat layer interposed between the current collector and the electrode mixture layer. Below, the case where the solid electrode composition functions as an electrode mixture layer will be described.

[0066] (2.1) Negative Electrode The negative electrode includes a current collector (hereinafter also referred to as "negative electrode current collector") and a negative electrode mixture layer. The negative electrode mixture layer is formed on at least one main surface of the negative electrode current collector.

[0067] Examples of the material for the negative electrode current collector include copper, aluminum, nickel, stainless steel (SUS), and nickel-plated steel.

[0068] The negative electrode mixture layer is a solid material of the electrode composition of the present disclosure. Specifically, the negative electrode mixture layer preferably contains a polymer (A), a negative electrode active material (B1), and a binder (C). The negative electrode mixture layer may further contain at least one of a conductive auxiliary (E) and an additive (F) as needed.

[0069] (2.2) Positive Electrode The positive electrode includes a current collector (hereinafter also referred to as a "positive electrode current collector") and a positive electrode mixture layer. The positive electrode mixture layer is formed on at least one main surface of the positive electrode current collector.

[0070] Examples of the material of the positive electrode current collector include aluminum, nickel, stainless steel (SUS), copper, etc. "Aluminum" includes pure aluminum and aluminum alloys.

[0071] The positive electrode mixture layer is a solid material of the electrode composition of the present disclosure. Specifically, the positive electrode mixture layer preferably contains a polymer (A), a positive electrode active material (B2), and a binder (C). The positive electrode mixture layer may further contain at least one of a conductive auxiliary (E) and an additive (F) as needed.

[0072] (3) Battery The battery of the present disclosure includes the electrode of the present disclosure.

[0073] The battery of the present disclosure has the above-described configuration, and therefore, an increase in resistance after high-temperature storage is suppressed.

[0074] In the battery of the present disclosure, the electrode of the present disclosure is at least one of a positive electrode and a negative electrode. The type of battery is not particularly limited and is appropriately selected depending on the application of the battery. Examples of the type of battery include a lithium-ion secondary battery, a manganese battery, a nickel-metal hydride battery, a nickel-cadmium battery, a nickel-zinc battery, a sodium-sulfur battery, a zinc-halide battery, and a redox flow battery.

[0075] Hereinafter, a lithium ion secondary battery will be described as an example of the battery of the present disclosure.

[0076] (3.1) Lithium-ion secondary battery A lithium-ion secondary battery comprises the electrode of the present disclosure.

[0077] A lithium-ion secondary battery generally includes an outer casing, a positive electrode, a negative electrode, a separator, and an electrolyte. The outer casing accommodates the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte. The separator separates the positive electrode from the negative electrode.

[0078] In the lithium ion secondary battery of the present disclosure, at least one of the positive electrode and the negative electrode is the electrode of the present disclosure. When one of the positive electrode and the negative electrode of the lithium ion secondary battery of the present disclosure is the electrode of the present disclosure, the other of the positive electrode and the negative electrode may be a known electrode used in lithium ion secondary batteries.

[0079] Hereinafter, a case where the positive electrode and the negative electrode are the electrodes of the present disclosure will be described.

[0080] (3.1.1) Exterior Body The shape of the exterior body is not particularly limited and may be appropriately selected depending on the application of the lithium-ion secondary battery, etc. Examples of the exterior body include an exterior body including a laminate film, and an exterior body consisting of a battery can and a battery can lid.

[0081] (3.1.2) Positive Electrode and Negative Electrode The positive electrode is the positive electrode of the present disclosure. The negative electrode is the negative electrode of the present disclosure.

[0082] (3.1.3) Separator An example of the separator is a porous resin flat plate. Examples of materials for the porous resin flat plate include resins and nonwoven fabrics containing such resins. Examples of resins include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyester, cellulose, and polyamide. Among these, the separator is preferably a porous resin sheet having a single layer or multilayer structure. The material of the porous resin sheet is mainly composed of one or more polyolefin resins. The thickness of the separator is preferably 5 μm to 30 μm. The separator is preferably disposed between the positive electrode and the negative electrode.

[0083] (3.1.4) Nonaqueous Electrolyte The nonaqueous electrolyte contains an electrolyte and a nonaqueous solvent.

[0084] (3.1.4.1) Electrolyte The electrolyte preferably contains at least one of a fluorine-containing lithium salt (hereinafter sometimes referred to as a "fluorine-containing lithium salt") and a fluorine-free lithium salt.

[0085] Examples of the fluorine-containing lithium salt include inorganic acid anion salts and organic acid anion salts. Examples of the inorganic acid anion salt include lithium hexafluorophosphate (LiPF ６ ), lithium tetrafluoroborate (LiBF ４ ), lithium hexafluoroarsenate (LiAsF ６ ), or lithium hexafluorotantalate (LiTaF ６ Examples of organic acid anion salts include lithium trifluoromethanesulfonate (LiCF ３ SO ３ Among them, the fluorine-containing lithium salt is LiPF ６ is particularly preferred. As the fluorine-free lithium salt, lithium perchlorate (LiClO ４ ), lithium aluminum tetrachloride (LiAlCl ４ ), or lithium decachlorodecaborate (Li ２ B １０ Cl １０ ) etc.

[0086] When the electrolyte contains a fluorine-containing lithium salt, the content of the fluorine-containing lithium salt is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and even more preferably 80% by mass to 100% by mass, based on the total amount of the electrolyte.

[0087] The fluorine-containing lithium salt is lithium hexafluorophosphate (LiPF ６ ), lithium hexafluorophosphate (LiPF ６ The content of the component (a) is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and even more preferably 80% by mass to 100% by mass, based on the total amount of the electrolyte.

[0088] When the non-aqueous electrolyte solution contains an electrolyte, the concentration of the electrolyte in the non-aqueous electrolyte solution is preferably 0.1 mol / L to 3 mol / L, and more preferably 0.5 mol / L to 2 mol / L.

[0089] The non-aqueous electrolyte is lithium hexafluorophosphate (LiPF ６ ), the non-aqueous electrolyte contains lithium hexafluorophosphate (LiPF ６ The concentration of the HCl HCl solution is preferably 0.1 mol / L to 3 mol / L, more preferably 0.5 mol / L to 2 mol / L.

[0090] (3.1.4.2) Non-aqueous Solvent The non-aqueous electrolyte generally contains a non-aqueous solvent.

[0091] Examples of non-aqueous solvents include cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, fluorine-containing chain carbonates, aliphatic carboxylic acid esters, fluorine-containing aliphatic carboxylic acid esters, γ-lactones, fluorine-containing γ-lactones, cyclic ethers, fluorine-containing cyclic ethers, chain ethers, fluorine-containing chain ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, dimethyl sulfoxide phosphate, etc. The non-aqueous solvents may be used singly or in combination of two or more.

[0092] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of fluorine-containing cyclic carbonates include fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and trifluoropropylene carbonate. Examples of chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and dipropyl carbonate (DPC). Examples of fluorine-containing chain carbonates include methyl 2,2,2-trifluoroethyl carbonate. Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylbutyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, ethyl isobutyrate, and ethyl trimethylbutyrate. Examples of fluorine-containing aliphatic carboxylic acid esters include methyl difluoroacetate, methyl 3,3,3-trifluoropropionate, ethyl difluoroacetate, and 2,2,2-trifluoroethyl acetate. Examples of γ-lactones include γ-butyrolactone and γ-valerolactone. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, and 1,4-dioxane. Examples of the chain ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane. Examples of the fluorine-containing chain ethers include HCF ２ CF ２ CH ２ OCF ２ CF ２ H, C.F. ３ CF ２ CH ２ OCF２ CF ２ H, HCF ２ CF ２ CH ２ OCF ２ CFHCF ３ , C.F. ３ CF ２ CH ２ OCF ２ CFHCF ３ , C ６ F １３ OCH ３ , C ６ F １３ O.C. ２ H ５ , C ８ F １７ OCH ３ , C ８ F １７ O.C. ２ H ５ , C.F. ３ CFHCF ２ CH (CH ３ ) OCF ２ CFHCF ３ , HCF ２ CF ２ OCH (C ２ H ５ ) ２ , HCF ２ CF ２ O.C. ４ H ９ , HCF ２ CF ２ OCH ２ CH(C ２ H ５ ) ２ , or HCF ２ CF ２ OCH ２ CH (CH ３ ) ２ Examples of nitriles include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, and 3-methoxypropionitrile. Examples of amides include N,N-dimethylformamide. Examples of lactams include N-methylpyrrolidinone, N-methyloxazolidinone, and N,N'-dimethylimidazolidinone.

[0093] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates. In this case, the total proportion of the cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and even more preferably 80% by mass to 100% by mass, based on the total amount of the non-aqueous solvent.

[0094] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates and chain carbonates. In this case, the total amount of the cyclic carbonates and chain carbonates in the non-aqueous solvent is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and even more preferably 80% by mass to 100% by mass, based on the total amount of the non-aqueous solvent.

[0095] The content of the nonaqueous solvent is preferably 99% by mass or less, more preferably 97% by mass or less, and more preferably 90% by mass or less, based on the total amount of the nonaqueous electrolyte. The content of the nonaqueous solvent is preferably 60% by mass or more, and more preferably 70% by mass or more, based on the total amount of the nonaqueous electrolyte.

[0096] The intrinsic viscosity of the non-aqueous solvent is preferably 10.0 mPa·s or less at 25° C., from the viewpoint of further improving the dissociation property of the electrolyte and the mobility of ions.

[0097] (3.1.4.3) Electrolyte Additives The non-aqueous solvent may contain an electrolyte additive. This can make it difficult for side reactions that are not the original battery reaction to proceed during the charge / discharge cycle of the lithium-ion secondary battery. The battery reaction is a reaction in which lithium ions enter and exit (intercalate) the positive electrode and the negative electrode. Side reactions include a reductive decomposition reaction of the non-aqueous electrolyte by the negative electrode, an oxidative decomposition reaction of the non-aqueous electrolyte by the positive electrode, and elution of metal elements in the positive electrode active material. There are no particular limitations on the electrolyte additive, and any known additive can be used. For example, the additives described in JP 2019-153443 A can be used.

[0098] (3.2) Example of Lithium-ion Secondary Battery An example of a lithium-ion secondary battery according to an embodiment of the present disclosure will be specifically described with reference to Fig. 1. Fig. 1 is a cross-sectional view of a lithium-ion secondary battery 1 according to an embodiment of the present disclosure.

[0099] A lithium-ion secondary battery 1 according to an embodiment of the present disclosure is a laminated type. As shown in FIG. 1 , the lithium-ion secondary battery 1 includes a battery element 10, a positive electrode lead 21, a negative electrode lead 22, and an exterior body 30. The battery element 10 is enclosed inside the exterior body 30. The exterior body 30 is formed of a laminate film. The positive electrode lead 21 and the negative electrode lead 22 are attached to the battery element 10. The positive electrode lead 21 and the negative electrode lead 22 are led out in opposite directions, from the inside to the outside of the exterior body 30.

[0100] 1, the battery element 10 is formed by laminating a positive electrode 11, a separator 13, and a negative electrode 12. The positive electrode 11 is formed by forming a positive electrode composite layer 11B on both main surfaces of a positive electrode current collector 11A. The negative electrode 12 is formed by forming a negative electrode composite layer 12B on both main surfaces of a negative electrode current collector 12A.

[0101] As shown in FIG. 1 , a positive electrode composite layer 11B formed on one main surface of a positive electrode current collector 11A of a positive electrode 11 and a negative electrode composite layer 12B formed on one main surface of a negative electrode current collector 12A of a negative electrode 12 adjacent to the positive electrode 11 face each other via a separator 13.

[0102] A non-aqueous electrolyte solution is poured into the interior of exterior body 30. The non-aqueous electrolyte solution permeates positive electrode composite layer 11B, separator 13, and negative electrode composite layer 12B. In lithium-ion secondary battery 1, one cell layer 14 is formed by adjacent positive electrode composite layer 11B, separator 13, and negative electrode composite layer 12B.

[0103] In the present embodiment, the lithium ion secondary battery 1 is a stacked type, but the present disclosure is not limited thereto. The lithium ion secondary battery 1 may be, for example, a wound type. The wound type is formed by stacking a positive electrode, a separator, a negative electrode, and a separator in this order and winding them into layers. The wound type includes a cylindrical type and a rectangular type. In the present embodiment, as shown in FIG. 1 , the directions in which the positive electrode lead 21 and the negative electrode lead 22 protrude from the inside of the exterior body 30 to the outside are opposite directions relative to the exterior body 30, but the present disclosure is not limited thereto. For example, the directions in which the positive electrode lead and the negative electrode lead protrude from the inside of the exterior body 30 to the outside may be the same direction relative to the exterior body 30.

[0104] Examples of the present disclosure will be described below, but the present disclosure is not limited to the following examples. In the following, "addition amount" means the content relative to the total amount of the non-aqueous electrolyte solution finally obtained, and "wt %" means mass %.

[0105] [1] Polymerization Examples [1.1] Polymerization Example 1 (Polyvinylpyrrolidone Homopolymer) A reaction vessel equipped with a stirrer, reflux condenser, dropping device, and thermometer was prepared. 75 parts by mass of 1-vinylpyrrolidone as monomer (x) and 75 parts by mass of distilled water were mixed to prepare an aqueous monomer solution. 309.5 parts by mass of distilled water was charged into the reaction vessel, and the temperature was raised to 80°C while stirring and purging with nitrogen. While maintaining the internal temperature at 80°C, 1.3 parts by mass of 4,4'-azobis(4-cyanovaleric acid) was added as a polymerization initiator, and the aqueous monomer solution was continuously added dropwise to the reactor over 2 hours. After completion of the dropwise addition, the mixture was aged for 6 hours. The resulting aqueous solution was cooled to room temperature, and distilled water was added to obtain an aqueous polymer solution. The solids concentration of the aqueous polymer solution was 14.8% by weight. The aqueous polymer solution of Polymerization Example 1 contained polyvinylpyrrolidone homopolymer. 1-Vinylpyrrolidone, which is the monomer (b) of the polyvinylpyrrolidone homopolymer, does not have a five- or six-membered nitrogen-containing heterocyclic structure containing an unsaturated bond.

[0106] [1.2] Polymerization Example 2 (Polyvinylimidazole Homopolymer) An aqueous polymer solution was obtained in the same manner as in Polymerization Example 1, except that 1-vinylpyrrolidone was replaced with 1-vinylimidazole as the monomer (a). The aqueous polymer solution of Polymerization Example 2 contained a polyvinylimidazole homopolymer as the polymer (A). 1-Vinylimidazole, which is the monomer (a) of the polyvinylimidazole homopolymer, has a five-membered nitrogen-containing heterocyclic structure containing an unsaturated bond. Therefore, the polyvinylimidazole homopolymer of Polymerization Example 2 has the structural unit (a).

[0107] [1.3] Polymerization Example 3 (Polyvinylimidazole Homopolymer) A reaction vessel equipped with a stirrer, reflux condenser, dropping device, and thermometer was prepared. 75 parts by mass of 1-vinylimidazole as monomer (a) and 75 parts by mass of distilled water were mixed to prepare an aqueous monomer solution. 279.5 parts by mass of distilled water and 2.5 parts by mass of a 35% aqueous hydrochloric acid solution were charged into the reaction vessel, and the temperature was raised to 80°C while stirring and purging with nitrogen. While maintaining the internal temperature at 80°C, 1.3 parts by mass of 4,4'-azobis(4-cyanovaleric acid) was added as a polymerization initiator, and the aqueous monomer solution was continuously added dropwise to the reactor over 2 hours. After completion of the dropwise addition, the mixture was aged for 6 hours. The resulting aqueous solution was cooled to room temperature, and then distilled water was added to obtain an aqueous polymer solution. The solids concentration of the aqueous polymer solution was 14.8% by weight. The aqueous polymer solution of Polymerization Example 3 contained a polyvinylimidazole homopolymer as the polymer (A). Therefore, the polyvinylimidazole homopolymer of Polymerization Example 3 has the structural unit (a).

[0108] [1.4] Polymerization Example 4 (Polyvinylimidazole Copolymer) A reaction vessel equipped with a stirrer, reflux condenser, dropping device, and thermometer was prepared. 67.5 parts by mass of 1-vinylimidazole as monomer (a), 7.5 parts by mass of 2-hydroxyethyl methacrylate as monomer (b), and 75 parts by mass of distilled water were mixed to prepare an aqueous monomer solution. 309.5 parts by mass of distilled water was charged into the reaction vessel, and the temperature was raised to 80°C while stirring and purging with nitrogen. While maintaining the internal temperature at 80°C, 1.3 parts by mass of 4,4'-azobis(4-cyanovaleric acid) was added as a polymerization initiator, and the aqueous monomer solution was continuously added dropwise to the reactor over 2 hours. After completion of the dropwise addition, the mixture was aged for 6 hours. The resulting aqueous solution was cooled to room temperature, and then distilled water was added to obtain an aqueous polymer solution. The solids concentration of the aqueous polymer solution was 14.8% by weight. The aqueous polymer solution of Polymerization Example 3 contained a polyvinylimidazole copolymer as the polymer (A). 1-Vinylimidazole, which is the monomer (a) of the polyvinylimidazole copolymer, has a five-membered nitrogen-containing heterocyclic structure containing an unsaturated bond. Therefore, the polyvinylimidazole copolymer of Polymerization Example 4 has the structural unit (a).

[0109] [1.5] Polymerization Examples 5 to 12 (Polyvinylimidazole Copolymer) Water-soluble polymers were obtained in the same manner as in Polymerization Example 4, except that 2-hydroxyethyl methacrylate as monomer (b) was replaced with the monomer (b) shown in Table 1, and the ratio of monomer (a) to monomer (b) was changed to the ratio shown in Table 1. The aqueous polymer solution in Polymerization Example 5 contained a polyvinylimidazole copolymer. 1-Vinylimidazole, the monomer (a) of the polyvinylimidazole copolymer, has a five-membered, nitrogen-containing heterocyclic structure containing an unsaturated bond, but the proportion of monomer (a) did not exceed 50%. The aqueous polymer solutions in Polymerization Examples 6 to 12 contained a polyvinylimidazole copolymer as polymer (A). 1-Vinylimidazole, the monomer (a) of the polyvinylimidazole copolymer, has a five-membered, nitrogen-containing heterocyclic structure containing an unsaturated bond. Therefore, the polyvinylimidazole copolymers in Polymerization Examples 5 to 12 have the structural unit (a).

[0110] [2] Example 1 [2.1] Electrode Composition A 5 L planetary dispenser was used to prepare the slurry.

[0111] 960 parts by mass of natural graphite as the negative electrode active material (B1) and “Super-P” (material: conductive carbon, BET specific surface area: 62 m) as the conductive additive (E) were used. ２ To 10 parts by mass of the carboxymethyl cellulose (CMC) solution, 450 parts by mass of a "1% CMC aqueous solution" serving as a binder (C) and a solvent (D) was added, and the mixture was mixed for 30 minutes to obtain a mixture. The "1% by mass aqueous solution of carboxymethyl cellulose (CMC)" refers to an aqueous solution in which the mass ratio of CMC serving as a binder (C) to the total amount of the aqueous solution is 1% by mass. 300 parts by mass of a 1% CMC aqueous solution was added to the obtained mixture, and the mixture was kneaded for 30 minutes, and then 250 parts by mass of a 1% CMC aqueous solution was added and kneaded for 30 minutes. 200 parts by mass of the aqueous polymer solution of Polymerization Example 2 serving as a polymer (A) and a solvent (D) was added to the obtained mixture, and the mixture was kneaded for 30 minutes. 50 parts by mass of styrene butadiene rubber (SBR) (40% emulsion) serving as a binder (C) was added to the obtained kneaded mixture, and the mixture was mixed for 30 minutes, followed by vacuum degassing for 30 minutes. This yielded a negative electrode mixture slurry (i.e., an electrode composition). The solid content of the negative electrode mixture slurry was 44%.

[0112] [2.2] Lithium-ion secondary battery (laminated battery) As a lithium-ion secondary battery, a laminated battery for evaluating heat generation rate was fabricated as follows.

[0113] [2.2.1] Negative electrode A die coater was used to apply the slurry. The applied mass after drying was 11.0 mg / cm ２ The negative electrode mixture slurry was applied to a portion of one surface of a copper foil (thickness: 10 μm) serving as a negative electrode current collector, and then dried. Next, a coating mass of 11.0 mg / cm was applied to a portion of the opposite surface (uncoated surface) of the copper foil. ２ The negative electrode composite slurry was applied and dried so that the double-sided coated copper foil (the total coating amount on both sides was 22.0 mg / cm ２ ) was dried in a vacuum drying oven at 120°C for 12 hours.

[0114] The double-sided coated copper foil after drying was pressed in a small press to a density of 1.45±0.05 g / cm ３ The electrode was pressed to a size of 31 mm x 42 mm. The electrode was slit to obtain an electrode coating area (31 mm x 42 mm) and a tab welding margin. The double-sided coated copper foil after the pressing was slit to obtain a coated area (42 mm x 31 mm) and a tab welding margin. This gave a negative electrode.

[0115] [2.2.2] Positive electrode: A 5 L planetary dispersion was used to prepare the slurry. NMC532 (i.e., LiNi) was used as the positive electrode active material. ０．５ Mn ０．３ Co ０．２ O ２ 920 parts by mass of "Super-P" (conductive carbon manufactured by TIMCAL) as a conductive additive, 20 parts by mass of "KS-6" (flake graphite manufactured by TIMREX) as a conductive additive were mixed for 10 minutes, and then 100 parts by mass of N-methylpyrrolidone (NMP) was added thereto, and the mixture was further mixed for 20 minutes.

[0116] Next, 150 parts by mass of "8%-PVDF solution" (PVDF W#7200 manufactured by Kureha Corporation dissolved in NMP) was added and kneaded for 30 minutes, and then 150 parts by mass of the 8%-PVDF solution was added and kneaded for 30 minutes. "8%-PVDF solution" refers to a solution in which the mass ratio of PVDF (PVDF "W#7200" manufactured by Kureha Corporation) to the total amount of PVDF solution (solution: NMP) is 8%. Then, 200 parts by mass of the 8%-PVDF solution was added and kneaded for 30 minutes. Next, 80 parts by mass of the solution dissolved in NMP was added and kneaded for 30 minutes. Thereafter, 27 parts by mass of NMP was added to adjust the viscosity, and the mixture was mixed for 30 minutes, followed by vacuum degassing for 30 minutes. As a result, a positive electrode composite slurry with a solids concentration of 60% was obtained.

[0117] A die coater was used to apply the slurry. The applied mass after drying was 19.0 mg / cm ２ The positive electrode composite slurry was applied to a portion of one side of an aluminum foil (thickness: 20 μm, width: 200 mm) serving as a positive electrode current collector, and then dried. Next, a coating mass of 19.0 mg / cm was similarly applied to a portion of the opposite side (uncoated side). ２The positive electrode composite slurry was applied to an aluminum foil and dried so that the total coating amount of the double-sided coated aluminum foil obtained in this manner (coating amount on both sides was 38.0 mg / cm ２ ) was dried in a vacuum drying oven at 130°C for 12 hours.

[0118] The double-sided coated aluminum foil after drying was pressed in a 35-ton press to a press density of 2.9±0.05 g / cm ３ The double-sided coated aluminum foil after pressing was slit to obtain a coated portion (40 mm x 29 mm) and a tab welding margin, thereby obtaining a positive electrode.

[0119] [2.2.3] Non-aqueous electrolyte solution Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:70 to obtain a non-aqueous mixed solvent. ６ The above was dissolved in the non-aqueous electrolyte solution to a concentration of 1 mol / L (hereinafter also referred to as "1M"). Next, vinylene carbonate (VC) was dissolved as an additive in a content of 0.5 mass% relative to the non-aqueous electrolyte solution to be finally obtained. This resulted in a non-aqueous electrolyte solution.

[0120] [2.2.4] Laminated Battery Precursor A polyethylene porous membrane (50 mm x 50 mm) with a porosity of 45% and a thickness of 25 μm was prepared as a separator. The negative electrode (front surface), separator, positive electrode (back surface / front surface), separator, and negative electrode (front surface) were stacked and fixed in order to obtain a laminate having five layers of positive electrodes and six layers of negative electrodes. An aluminum tab was bonded to the margin of the positive electrode of the obtained laminate using an ultrasonic bonding machine as a positive electrode tab, and a nickel tab was bonded to the margin of the negative electrode using an ultrasonic bonding machine as a negative electrode tab. The laminate with the bonded positive and negative electrode tabs was sandwiched between laminate sheets and three sides were heat-sealed to obtain a laminated laminated battery precursor. The battery capacity of the battery precursor was 350 mAh in terms of discharge capacity.

[0121] The interior of the laminate obtained above was dried under reduced pressure for 12 hours in a vacuum dryer at 70° C. After the reduced pressure drying, 1.20±0.05 parts by mass of the nonaqueous electrolyte solution was injected into the remaining side of the laminate that had not been heat-sealed, and then the remaining side was heat-sealed while drawing a vacuum to obtain a stacked battery precursor (i.e., a stacked battery before being charged and discharged).

[0122] [2.2.5] Stacked Battery The stacked battery precursor was kept in the atmosphere at 25°C for 24 hours, then charged at a constant current of 0.1C (0.1C-CC) for 3 hours, and then left to rest at 25°C for 12 hours.

[0123] Next, the rested stacked battery precursor was charged at a constant current and constant voltage (0.1C-CCCV) at 0.1C up to 4.2V (SOC 100%), rested for 30 minutes, and then discharged at a constant current (0.1C-CC) at 0.1C down to 2.8V to obtain a stacked battery.

[0124] [2.3] Evaluation [2.3.1] Battery Resistance (Relative Value) After High-Temperature Storage The following battery resistance evaluation was performed on the laminated battery. The battery was charged to a constant voltage of 4.2 V at room temperature and then discharged at a constant current of 0.1 C at room temperature, and the first potential drop was measured for 10 seconds from the start of discharge. Similarly, the battery after activation treatment was charged to a constant voltage of 4.2 V at room temperature and then discharged at a constant current of 0.2 C at room temperature, and the second potential drop was measured for 10 seconds from the start of discharge. The battery after activation treatment was charged to a constant voltage of 4.2 V at room temperature and then discharged at a constant current of 0.5 C at room temperature, and the third potential drop was measured for 10 seconds from the start of discharge. The battery after activation treatment was charged to a constant voltage of 4.2 V at room temperature and then discharged at a constant current of 1.0 C at room temperature, and the fourth potential drop was measured for 10 seconds from the start of discharge. The battery resistance (direct current resistance; DC-IR) at the beginning of discharge was calculated from the first to fourth potential drop amounts when discharged at each current rate.

[0125] The stacked battery was evaluated as follows: The battery was charged to a constant voltage of 4.2 V at room temperature and stored in a thermo-hygrostat at 60° C. for 28 days. After storage, the battery was removed and allowed to stand at room temperature for 2 hours, after which the battery resistance (direct current resistance; DC-IR) was evaluated.

[0126] The battery resistance increase rate was calculated from the battery resistance before and after storage. The resistance increase rate of Example 1 was calculated based on the resistance increase rate of Comparative Example 1 obtained below, which was set to 100, and this was used as the resistance increase rate after storage (relative value). An acceptable resistance increase rate after storage (relative value) is less than 100.

[0127] [2.3.2] Nail Penetration Test (Relative Value) The following nail penetration test was conducted on the stacked battery to evaluate the internal heat generation rate during a short circuit. The stacked battery fabricated above was charged at 0.1 C to 4.2 V (100% SOC) at a constant current and constant voltage (0.1 C-CCCV) and a nail penetration test was conducted. A nail with a diameter of 3 mm, length of 15 mm, tip angle of 30°, and a hole with a bottom of 0.6 mm was covered with Macol (registered trademark). Next, a sheathed type K thermocouple (product number: IP10-K-0.5-200) with a sheath diameter of 0.5 mm and a sheath length of 200 mm was inserted to a position near the tip of the nail to obtain a nail penetration test device. The nail test tool and the stacked battery were fixed to a nail penetration test device (TYS-94DM45 manufactured by Toyo Systems), and the nail was inserted into the center of the battery (cell) at a speed of 1 mm / sec, short-circuiting the positive and negative electrodes inside the battery container. The temperature inside the battery measured by the nail penetration test tool and the surface temperature obtained from a thermocouple attached to the surface of the battery were measured over time.

[0128] The heat generation rate of the battery was calculated as follows from the measurement results of the nail penetration test. The time when the internal temperature of the battery rose by 0.2°C after short-circuiting was defined as the heat generation start time T0 (seconds), and 1 second after T0 was defined as T1 (seconds). The internal temperature of the battery at T0 was defined as H0 (°C), and the internal temperature of the battery at T1 was defined as H1 (°C), and the heat generation rate immediately after short-circuiting was calculated using the following formula: Heat generation rate = (H1 - H0) / (T1 - T0)

[0129] The heat release rate of Example 1 was calculated based on the heat release rate of Comparative Example 1 obtained below, which was set to 100, and this was used as a nail penetration test value (relative value).

[0130] [3] Examples 2 to 11 and Comparative Examples 1 to 4 Evaluations were made in the same manner as in Example 1, except that the type and amount of polymer added were changed as shown in Table 1. Note that for Comparative Examples 2 to 3 and Examples 2 to 3, and 5 to 11, the nail penetration test was not performed.

[0131]

[0132] In Table 1, "ether sulfate type ammonium salt" refers to Rearsoap "SR-10" manufactured by Adeka Corporation. "Addition amount" refers to the mass ratio of the polymer (A) to the solid content of the negative electrode mixture slurry (i.e., the electrode composition).

[0133] The electrode compositions of Comparative Examples 1 to 3 did not contain the polymer (A). In Comparative Example 4, the proportion of the structural unit (a) did not exceed 50 mol%. Therefore, the post-storage resistance increase rates (relative values) of Comparative Examples 1 to 4 were not less than 100. As a result, it was found that the electrode compositions of Comparative Examples 1 to 4 were not electrode compositions capable of suppressing an increase in resistance after high-temperature storage of a battery.

[0134] The electrode compositions of Examples 1 to 11 contained polymer (A). The proportion of polymer (A) was more than 50 mol %. Therefore, the resistance increase rate (relative value) after storage of Examples 1 to 11 was less than 100. As a result, it was found that the electrode compositions of Examples 1 to 11 are electrode compositions that can suppress an increase in resistance after high-temperature storage of a battery.

[0135] The disclosure of Japanese Patent Application No. 2023-122890, filed on July 27, 2023, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A composition for an electrode comprising a polymer (A), the polymer (A) having a five- or six-membered nitrogen-containing heterocyclic structure and including a structural unit (a) derived from a compound containing an unsaturated bond, and the proportion of the structural unit (a) in the polymer (A) relative to the total of all structural units constituting the polymer (A) is greater than 50 mol %.

2. The electrode composition according to claim 1, wherein the proportion of the structural unit (a) is 60 mol % or more.

3. The electrode composition according to claim 1 or 2, wherein the structural unit (a) includes a structural unit derived from vinylimidazole.

4. The electrode composition according to any one of claims 1 to 3, further comprising an active material (B) and a binder (C).

5. The electrode composition according to claim 4, wherein the active material (B) comprises a carbon-based compound.

6. An electrode composition according to any one of claims 1 to 5, wherein the content of the polymer (A) relative to the solid content of the electrode composition is 0.01 mass % to 1.0 mass %.

7. An electrode comprising: a current collector; and a solid material of the electrode composition according to any one of claims 1 to 6.

8. A battery comprising the electrode according to claim 7.

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