Current collector, method for producing same, electrode, and battery

Abstract

The present invention addresses the problem of providing a current collector in which cracks and the like do not readily occur in a composite material layer during electrode production. The current collector for solving the technical problem comprises: a base material containing a metal; and a coating layer disposed on at least one surface of the substrate, the coating layer containing a conductive auxiliary agent, a vinylidene fluoride copolymer, and a dispersant, the vinylidene fluoride copolymer containing a structural unit derived from vinylidene fluoride and a structural unit derived from a compound having a carboxyl group, the amount of the conductive auxiliary agent is from 45% by mass to 80% by mass (inclusive) with respect to the total mass of the coating layer.

Description

Technical Field

[0001] This invention relates to current collectors and their manufacturing methods, electrodes, and batteries. Background Technology

[0002] Lithium-ion rechargeable batteries are widely used in various electronic devices, electric vehicles, and other applications. The electrodes of a lithium-ion rechargeable battery typically have a current collector and a composite material layer containing active materials and a binder disposed on the current collector.

[0003] In recent years, there has been a demand to increase the capacity of lithium-ion secondary batteries, for example, by attempting to increase the capacity of lithium-ion secondary batteries through high-voltage charging. Therefore, it is considered to reduce the resistance at the interface between the current collector and the composite material layer by constructing a current collector consisting of a substrate and a conductive layer (hereinafter also referred to as a "coating") disposed on the substrate. Patent Document 1 describes a current collector composed of an aluminum foil and a coating containing acrylic-modified polyvinylidene fluoride and a conductor.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Chinese Patent Application Publication No. 113725398 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, through in-depth research, the inventors discovered that when a composite material layer is formed on the coating of the current collector described in Patent Document 1, cracks are prone to appear in the composite material layer.

[0009] The purpose of this invention is to provide a current collector that is less prone to cracking during electrode fabrication, its manufacturing method, an electrode using the current collector, and a battery.

[0010] Solution for solving the problem

[0011] [1] The present invention provides a current collector, wherein the current collector has: a substrate comprising a metal; and a coating disposed on at least one side of the substrate, the coating comprising a conductive additive, a vinylidene fluoride copolymer and a dispersant, the vinylidene fluoride copolymer comprising structural units derived from vinylidene fluoride and structural units derived from compounds having carboxyl groups, the amount of the conductive additive being 45% by mass or more and 80% by mass or less relative to the total mass of the coating.

[0012] [2] The present invention provides a current collector according to [1], wherein the compound having a carboxyl group is a compound represented by the following general formula (1).

[0013] [Chemical Formula 1]

[0014]

[0015] (In general formula (1), R) 1 It represents an alkyl group with 1 or more but less than 5 carbon atoms, or -C(=O)-OC. n H 2n+1 (n is 1 or more and 5 or less), R 2 and R 3 Each of the following can be independently represented as either a hydrogen atom or an alkyl group having 1 or more but less than 5 carbon atoms: X 1 This refers to a divalent group with 1 or more atoms in the single bond or main chain and a molecular weight of 500 or less.

[0016] [3] The present invention provides a current collector according to [1] or [2], wherein the coating of the vinylidene fluoride copolymer comprises structural units derived from vinylidene fluoride, and structural units derived from acrylic acid and / or structural units derived from monomethyl maleate.

[0017] [4] The present invention provides a current collector according to any one of [1] to [3], wherein the dispersant is at least one compound selected from the group consisting of polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, hydroxypropyl methylcellulose, and N-methylethanolamine.

[0018] [5] The present invention provides a current collector according to any one of [1] to [4], wherein the amount of the dispersant is 0.2% by mass or more relative to the total mass of the coating.

[0019] [6] The present invention provides an electrode having: a current collector according to any one of [1] to [5]; and a composite material layer disposed on a coating of the current collector, the composite material layer comprising an active substance and an adhesive.

[0020] [7] The present invention provides an electrode according to [6], wherein the adhesive comprises structural units derived from vinylidene fluoride.

[0021] [8] The present invention provides a battery, wherein the battery has electrodes according to [6] above.

[0022] Furthermore, the present invention provides an electrode having the current collector and a composite material layer disposed on a coating of the current collector, the composite material layer comprising an active substance and a binder.

[0023] [9] The present invention provides a method for manufacturing a current collector, wherein the method includes a step of coating at least one side of a substrate comprising a metal substrate with a coating liquid comprising a conductive additive, a vinylidene fluoride copolymer, a dispersant and a solvent, wherein the vinylidene fluoride copolymer comprises structural units derived from vinylidene fluoride and structural units derived from compounds having carboxyl groups, and the amount of the conductive additive is 45% by mass or more and 80% by mass or less relative to the total amount of solid components of the coating liquid.

[0024]

[10] The present invention provides a method for manufacturing a current collector according to [9], wherein the compound having a carboxyl group is a compound represented by the following general formula (1).

[0025] [Chemical Formula 2]

[0026]

[0027] (In general formula (1),

[0028] R 1 It represents an alkyl group with 1 or more but less than 5 carbon atoms, or -C(=O)-OC. n H 2n+1 (where n is 1 or more and 5 or less),

[0029] R 2 and R 3 Each can be independently represented by either a hydrogen atom or an alkyl group having 1 or more but less than 5 carbon atoms.

[0030] X 1 This refers to a divalent group with 1 or more atoms in the single bond or main chain and a molecular weight of 500 or less.

[0031] Invention Effects

[0032] Even when a composite material layer is formed on the current collector of the present invention, the composite material layer is not prone to cracking. Therefore, the current collector and the electrodes using the current collector are suitable as components of various lithium-ion secondary batteries. Detailed Implementation

[0033] 1. Current collector

[0034] The current collector of the present invention is a current collector for lithium-ion secondary batteries, etc., having a substrate comprising a metal and a coating of a predetermined composition disposed on at least one surface of the substrate. Typically, a composite material layer is formed on the coating of the current collector for use.

[0035] As described above, in the current collector of Patent Document 1, that is, in a current collector having a substrate and a coating disposed on the substrate containing acrylic-modified polyvinylidene fluoride (a copolymer of acrylic acid and vinylidene fluoride) and a small amount of conductor, when a composite material layer is formed on the coating, cracks easily appear on the surface of the composite material layer. The reason is not clear, but it can be inferred as follows.

[0036] The vinylidene fluoride copolymer, obtained by copolymerizing acrylic acid and vinylidene fluoride used in the above coating, is very prone to agglomeration when mixed with a conductor, making it difficult to form a uniform coating. This agglomeration is believed to be due to the close alignment of structural units derived from vinylidene fluoride with carboxyl groups derived from acrylic acid.

[0037] On the other hand, the composite material layer disposed on this coating typically contains vinylidene fluoride (VDF) polymers. Therefore, the composite slurry used to form this composite material layer usually contains a good solvent with high affinity for the VDF copolymer in the coating. When such a composite slurry is applied to the coating, the VDF copolymer in the coating dissolves into the good solvent in the composite slurry. Furthermore, when the dissolved VDF copolymer cures again, shrinkage of the coating occurs, accompanied by crystallization of the VDF copolymer. As a result, strain is easily generated within the composite material layer disposed on the coating, and cracks appear on the surface of the composite material layer.

[0038] In contrast, although the coating of the present invention comprises a vinylidene fluoride copolymer containing structural units derived from vinylidene fluoride and structural units derived from compounds having carboxyl groups (such as compounds represented by general formula (1) described later), the amount of conductive additive is 45% by mass or more and 80% by mass or less relative to the total mass of the coating. Therefore, when the composite slurry is applied to the coating, even if the aforementioned vinylidene fluoride copolymer dissolves into a good solvent in the composite slurry, the conductive additive physically inhibits the movement of the vinylidene fluoride copolymer, and strain is less likely to occur within the composite layer. Furthermore, by adding a dispersant, the aggregation of the aforementioned conductive additive and the vinylidene fluoride copolymer can be suppressed. Therefore, it is considered that uneven portions are less likely to occur within the coating formed on the substrate, and strain in the coating itself is also suppressed. As a result, the composite layer formed on the coating of this current collector is less prone to strain and less prone to cracking.

[0039] The structure of the current collector of the present invention will be described in detail below.

[0040] (1) Substrate

[0041] The substrate is a base material that forms a current collector, provided that the substrate has sufficient conductivity and contains a metal. The substrate may contain only metal, or it may contain materials other than metal (e.g., resin, ceramics, etc.). More preferably, the substrate is composed only of metal. Here, the type of metal contained in the substrate is appropriately selected based on the type and shape of the current collector (or even the battery). The substrate may contain only one type of metal, or it may contain two or more types of metal. Examples of metals contained in the substrate include aluminum, copper, iron, stainless steel, steel, nickel, titanium, etc.

[0042] Furthermore, the shape of the substrate is appropriately selected according to the type and size of the current collector (and even the battery). The substrate can be, for example, a foil or metal mesh of the aforementioned metal. Alternatively, the substrate can be a material formed by laminating the aforementioned metal foil or metal mesh onto the surface of a material other than metal.

[0043] (2) Coating

[0044] The coating only needs to contain at least a specified amount of conductive additives, a specified structure of vinylidene fluoride copolymer, and a dispersant, and may also contain other components as needed.

[0045] Conductive additives

[0046] The conductive additive enables electrical conduction between the substrate and the active material in the composite layer. Known conductive additives can be used as this conductive additive. Specific examples of conductive additives include acetylene black, Ketjen black, carbon black, graphite powder, graphene, carbon nanofibers, carbon nanotubes, carbon fibers, and metal powders. The coating may contain only one of these conductive additives or may contain two or more.

[0047] The amount of conductive additive in the coating only needs to be 45.0% by mass or more and 80.0% by mass or less relative to the total mass of the coating, preferably 47.0% by mass or more and 75.0% by mass or less, and more preferably 49.5% by mass or more and 65.0% by mass or less. As described above, when the amount of conductive additive in the coating is 45% by mass or more, the composite material layer formed on the current collector (coating) is less prone to cracking. On the other hand, when the amount of conductive additive in the coating is 80% by mass or less, the adhesion strength between the current collector and the composite material layer is easily improved.

[0048] • Vinylidene fluoride copolymer

[0049] Vinylidene fluoride copolymers comprise structural units derived from vinylidene fluoride and structural units derived from compounds having carboxyl groups. A coating may contain only one type of vinylidene fluoride copolymer, or it may contain two or more types.

[0050] The amount of vinylidene fluoride-derived structural units in the vinylidene fluoride copolymer, relative to the total amount (moles) of all structural units constituting the vinylidene fluoride copolymer, is preferably 90.0 mol% or more and 99.99 mol% or less, more preferably 93.0 mol% or more and 99.98 mol% or less, and particularly preferably 96.0 mol% or more and 99.97 mol% or less. When the amount of vinylidene fluoride-derived structural units is 90.0 mol% or more, properties derived from vinylidene fluoride, such as electrochemical stability, are readily obtained in the coating. The amount of vinylidene fluoride-derived structural units in the vinylidene fluoride copolymer can be determined by… 19 F-NMR confirmed.

[0051] Furthermore, there are no particular limitations on compounds containing carboxyl groups; for example, compounds represented by the following general formula (1) can be listed. Hereinafter, we will use compounds represented by this general formula (1) as examples, but the structures of compounds containing carboxyl groups are not limited thereto. Polymers based on vinylidene fluoride may contain only one structural unit derived from a compound represented by the following general formula (1), or they may contain two or more structural units.

[0052] [Chemical Formula 3]

[0053]

[0054] In the above general formula (1), R 1 It represents an alkyl group with 1 or more but less than 5 carbon atoms, or -C(=O)-OC. n H 2n+1 (n is 1 or more and 5 or less). From the perspective of polymerization reactivity, R... 1 Preferably, it contains hydrogen atoms, methyl groups, or -C(=O)-OCH3.

[0055] R 2 and R 3 Each of the substituents can be independently represented by a hydrogen atom or an alkyl group having 1 or more but less than 5 carbon atoms. From the viewpoint of polymerization reactivity, substituents with low steric hindrance are preferred, and hydrogen or an alkyl group having 1 or more but less than 3 carbon atoms is preferred, as is hydrogen or methyl.

[0056] X 1 This refers to a divalent atomic group with 1 or more but less than 20 atoms in the single bond or main chain, and a molecular weight of less than 500. X 1 The number of atoms in the main chain is the number of atoms in the shortest chain that forms the carboxyl group and carbon-carbon double bond at the connection end in the above general formula (1). More preferably, the number of atoms in the main chain is 15 or less.

[0057] From the above X 1The atomic groups represented here have no particular restrictions on their structure as long as their molecular weight is less than 500 and they meet the above-mentioned number of atoms in the main chain. They can be linear, branched, or contain ring structures. Examples of structures constituting the above-mentioned atomic groups include alkylene groups, carbonyl groups (-C(=O)-), ether bonds (-O-), aromatic rings, and alicyclic structures.

[0058] Specific examples of compounds represented by the general formula (1) above include: monomethyl maleate (MMM), acrylic acid (AA), methacrylic acid, carboxymethyl acrylate, carboxymethyl methacrylate, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, acryloyloxyethyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate, methacryloyloxyethyl phthalate, acryloyloxypropyl succinate, methacryloyloxypropyl succinate, etc. Among these, acrylic acid or monomethyl maleate is preferred.

[0059] The amount of structural units derived from carboxyl-containing compounds (e.g., compounds represented by general formula (1)) in the aforementioned vinylidene fluoride copolymer is preferably 0.01 mol% or more and 10.0 mol% or less, more preferably 0.02 mol% or more and 7.0 mol% or less, and particularly preferably 0.03 mol% or more and 4.0 mol% or less, relative to the total amount (moles) of all structural units constituting the vinylidene fluoride copolymer. It should be noted that when the amount of structural units derived from carboxyl-containing compounds (e.g., compounds represented by general formula (1)) is 0.01 mol% or more, the adhesion between the coating and the composite material layer and the substrate is easily further improved. On the other hand, when these amounts are 10.0 mol% or less, the amount of structural units derived from vinylidene fluoride is relatively increased, and the electrochemical stability of the vinylidene fluoride copolymer, and consequently the electrochemical stability of the coating, is easily improved. The amount of structural units derived from carboxyl-containing compounds (e.g., compounds represented by general formula (1)) can be adjusted by... 19 F-NMR, 1 We used methods such as H-NMR for analysis.

[0060] Furthermore, the vinylidene fluoride copolymer may also contain structural units derived from compounds other than those derived from vinylidene fluoride and compounds having carboxyl groups (e.g., compounds represented by general formula (1)) (hereinafter also referred to as "other compounds"), to a extent that does not impair the purpose and effect of the present invention. The amount (total amount) of structural units derived from other compounds is preferably 10.0 mol% or less, more preferably 4.0 mol% or less, relative to the total number of structural units (moles) of the vinylidene fluoride copolymer. When the amount of structural units derived from other compounds in the vinylidene fluoride copolymer is 10.0 mol% or less, the electrochemical stability of the coating becomes better, and the adhesion strength between the coating and the substrate is easily improved. The amount of structural units derived from other compounds can be adjusted by... 19F-NMR, 1 We used methods such as H-NMR for analysis.

[0061] Other examples of compounds include fluorinated compounds other than vinylidene fluoride, such as fluoroethylene, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, hexafluoroethylene, fluoroalkyl vinyl ethers, and perfluoromethyl vinyl ethers.

[0062] Here, the specific logarithmic viscosity of the vinylidene fluoride copolymer is preferably 1.0 or higher, more preferably 1.3 dL / g or higher, and even more preferably 2.0 dL / g or higher. When the specific logarithmic viscosity is as described above, the adhesion strength between the coating and the substrate, and the adhesion strength between the coating and the composite material layer formed on the coating, are easily improved. The specific logarithmic viscosity can be determined by the following method. First, 80 mg of the vinylidene fluoride copolymer is dissolved in 20 mL of N,N-dimethylformamide, and the viscosity is measured using an Ubbelohde viscometer in a constant temperature bath at 30°C. Then, based on the obtained value, the specific logarithmic viscosity (η) of the vinylidene fluoride copolymer is calculated using the following formula. i ).

[0063] η i = (1 / C)·ln(η / η0)

[0064] It should be noted that in the above formula, η is the solution viscosity, η0 is the viscosity of N,N-dimethylformamide as a solvent, and C is the concentration of vinylidene fluoride copolymer, i.e., 0.4 g / dL.

[0065] There are no particular limitations on the preparation method of the above-mentioned vinylidene fluoride copolymer. It is possible to polymerize vinylidene fluoride, structural units derived from compounds having carboxyl groups (e.g., compounds represented by general formula (1)), and other compounds as needed using known methods. Examples of polymerization methods include suspension polymerization, emulsion polymerization, solution polymerization, etc.

[0066] The amount of vinylidene fluoride copolymer in the coating is preferably 10.0% by mass or more and 54.8% by mass or less relative to the total mass of the coating, more preferably 15.0% by mass or more and 52.8% by mass or less, and even more preferably 25.0% by mass or more and 50.3% by mass or less. If the amount of vinylidene fluoride copolymer is within this range, the electrochemical stability of the coating is easily improved, and consequently, the adhesion between the coating and the substrate, and the adhesion between the current collector and the composite material layer, are easily improved. Furthermore, relative to 100 parts by mass of the conductive additive, the amount of vinylidene fluoride copolymer is preferably 25 parts by mass or more and 122 parts by mass or less, more preferably 53.8 parts by mass or more and 102 parts by mass or less. If the ratio of the amount of conductive additive to the amount of vinylidene fluoride copolymer is within this range, the composite material layer formed on the current collector layer is further less prone to cracking. Furthermore, if the ratio of the amount of conductive additive to the amount of vinylidene fluoride copolymer is within the above range, the adhesion between the current collector and the composite material layer is also easily improved.

[0067] Dispersant

[0068] The dispersant used in this specification can be any compound capable of inhibiting the aggregation of the aforementioned vinylidene fluoride copolymer and conductive additives; examples include vinyl copolymers, cellulose compounds, and alkanolamines. As described above, by including a dispersant in the coating, the composite material layer formed on the current collector (coating) is less prone to cracking, and the adhesion between the coating and the composite material layer becomes better. The coating may contain only one dispersant or may contain two or more dispersants.

[0069] Specific examples of the aforementioned vinyl copolymers include polyvinylpyrrolidone and polyvinyl alcohol. Furthermore, examples of the aforementioned cellulose compounds include methylcellulose and hydroxypropyl methylcellulose. Moreover, any amine can be a compound in which one or more alkyl alcohols are bonded to the nitrogen atom of an amine; examples include N-methylethanolamine. That is, preferred examples of the aforementioned dispersants include polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, hydroxypropyl methylcellulose, and N-methylethanolamine.

[0070] The dispersant can be liquid or solid at room temperature, but a dispersant with good compatibility with N-methyl-2-pyrrolidone is preferred.

[0071] The amount of dispersant relative to the total mass of the coating is preferably 0.2% by mass or more and 10.0% by mass or less, more preferably 0.4% by mass or more and 10.0% by mass or less. If the amount of dispersant is within this range, the composite material layer formed on the current collector layer (coating) is less prone to cracking.

[0072] ·other

[0073] In addition to the conductive additives, vinylidene fluoride copolymers, and dispersants mentioned above, the coating may also contain other components without impairing the purpose and effects of the present invention. Examples include: nitrogen compounds such as phosphorus compounds, sulfur compounds, organic acids, amine compounds, and ammonium compounds; coupling agents such as organic esters, silane-based, titanium-based, and aluminum-based agents; and resins such as polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and polyacrylonitrile (PAN). The amount of these other components relative to the total mass of the coating is preferably 10% by mass or less, more preferably 5% by mass or less.

[0074] • Physical properties of the coating

[0075] Furthermore, the coating can be applied to only one surface of the substrate, or it can be formed on both surfaces. Additionally, the coating can be patterned on one surface of the substrate, but from the viewpoint of suppressing cracks in the composite layer or reducing the electrical resistance between the composite layer and the substrate, it is preferable to apply the coating in a manner that fully covers one or both surfaces of the substrate.

[0076] The thickness of the coating on at least one side of the substrate is preferably 0.5 μm or more and 10 μm or less, more preferably 0.8 μm or more and 5 μm or less. When the coating thickness is 0.5 μm or more, the adhesion strength between the coating and the composite material layer tends to be good. On the other hand, by setting the coating thickness to 10 μm or less, the energy density of the battery using the current collector can be increased.

[0077] (3) Method for manufacturing current collectors

[0078] The method for manufacturing the current collector of the present invention is not particularly limited as long as it is a method capable of forming a coating on the aforementioned substrate, but preferably includes a step of applying a coating liquid to at least one side of the aforementioned substrate (hereinafter also referred to as the "coating step") and a step of drying the coating liquid (hereinafter also referred to as the "drying step"). Hereinafter, each step will be described.

[0079] Coating process

[0080] The coating liquid used in the coating process only needs to contain at least the aforementioned conductive additives, vinylidene fluoride copolymers, dispersants, and organic solvents; other components may also be included as needed. The conductive additives, vinylidene fluoride copolymers, dispersants, and other components are as described above.

[0081] On the other hand, the organic solvent contained in the coating solution only needs to be sufficient to uniformly disperse or dissolve the aforementioned conductive additives, vinylidene fluoride copolymers, and dispersants. Examples of such organic solvents include amide compounds such as dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; alcohols such as methanol, ethanol, isopropanol, 2-ethyl-1-hexanol, 1-nonanol, lauryl alcohol, and tripropylene glycol; amine compounds such as o-toluidine, m-toluidine, and p-toluidine; 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; lactones such as γ-butyrolactone and δ-butyrolactone; and sulfoxide / sulfone compounds such as dimethyl sulfoxide and sulfolane. The coating solution may contain only one organic solvent or two or more. Among these, N-methylpyrrolidone is preferred from the viewpoint that it can easily dissolve the aforementioned vinylidene fluoride copolymers.

[0082] The amount of the organic solvent is appropriately selected according to the type of organic solvent and the desired viscosity of the coating liquid. It is usually 100 parts by mass relative to the total mass of the conductive additive and the vinylidene fluoride copolymer, preferably 1,000 parts by mass or more and 10,000 parts by mass or less, more preferably 3,000 parts by mass or more and 7,000 parts by mass or less.

[0083] There are no particular restrictions on the method of applying the coating liquid to the substrate. Methods such as doctor blade method, reverse roller method, comma roller method, gravure printing method, air knife method, mold coating method, and dip coating method can be used.

[0084] Drying process

[0085] After applying the coating liquid, the mixture is heated at any temperature to evaporate the organic solvent and obtain a coating layer. There are no particular limitations on the heating temperature; in one example, 60°C or higher is preferred, and 80°C or higher is more preferred. The upper limit is appropriately selected depending on the type of coating liquid. Heating can be performed multiple times at different temperatures. Furthermore, the drying process can be carried out under atmospheric pressure, pressurized conditions, or reduced pressure.

[0086] 2. Electrodes

[0087] The electrode of the present invention has the aforementioned current collector and a composite material layer comprising an active material and a binder disposed on the current collector. The composite material layer may contain any active material and a binder, and their types are not particularly limited. Preferably, the binder comprises a vinylidene fluoride homopolymer, or a vinylidene fluoride-based polymer comprising structural units derived from vinylidene fluoride, structural units derived from hexafluoropropylene, and / or structural units derived from compounds represented by general formula (2) described later. The various components of this electrode will be described below.

[0088] • Active substances

[0089] The active material contained in the composite material layer can be either a positive electrode active material or a negative electrode active material, and the appropriate material should be selected according to its intended use.

[0090] Examples of negative electrode active materials include: artificial graphite, natural graphite, difficult-to-graphitize carbon, easily-graphitize carbon, activated carbon, or carbon materials such as phenolic resin and asphalt obtained by calcination and carbonization; metal / alloy materials such as Cu, Li, Mg, B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Cd, Ag, Zn, Hf, Zr, and Y; and metal / alloy materials such as SiO, SiO2, GeO, GeO2, SnO, SnO2, PbO, PbO2, and Li4Ti5O. 12 Metal oxides such as LTO. Furthermore, the negative electrode active material can be a substance coated on these surfaces, and can contain only one type or two or more. It should be noted that the negative electrode active material can be a commercially available product.

[0091] On the other hand, examples of positive electrode active materials include lithium-based positive electrode active materials, such as lithium metal oxides represented by the following general formula (a), and materials on which a coating treatment has been applied.

[0092] LiM x O2……(a)

[0093] In general formula (a), M represents at least one metallic element containing Ni. The metallic element other than Ni is preferably selected from the group consisting of Co, Al, Fe, Mn, Cr, and V. More preferably, in addition to Ni, it further contains one or more metals selected from the group consisting of Co, Mn, and Al. Furthermore, in the lithium metal oxide represented by the above formula (a), when the total amount of the metallic elements constituting M is 100 mol%, it preferably contains 55 mol% or more of Ni, and more preferably 70% or more of Ni.

[0094] In the above general formula (a), 0.5≤x≤1.5, and more preferably 0.7≤x≤1.3.

[0095] Examples of the composition of lithium-based cathode active materials represented by the above general formula (a), and other lithium-based cathode active materials include Li 1.0 Ni 0.8 Co 0.2 O2, Li 1.0 Ni 0.5 Mn 0.5 O2, Li 1.00 Ni 0.35 Co 0.34 Mn 0.34 O2(NCM111), Li 1.00 Ni0.52 Co 0.20 Mn 0.30 O2 (NCM523), Li 1.00 Ni 0.50 Co 0.30 Mn 0.20 O2 (NCM532), Li 1.00 Ni 0.6 Co 0.2 Mn 0.2 O2 (NCM622), Li 1.00 Ni 0.83 Co 0.12 Mn 0.05 O2 (NCM811), Li 1.00 Ni 0.85 Co 0.15 Al 0.05 O2(NCA811), LiCoO2(LCO), LiMn2O4(LMO), LiFePO4(LFP), and LiMnPO4(LMP), LiMn 1-x Fe x PO4 (LFMP), etc. Furthermore, the positive electrode active material can be a substance that has undergone coating treatment on these surfaces; it can contain only one type or two or more. It should be noted that the positive electrode active material can be a commercially available product.

[0096] The amount of active material contained in the composite material layer is appropriately selected based on its type, electrode function, battery type, etc., and there are no particular restrictions. However, in one example, it is preferably 50.0% by mass or more and 99.9% by mass or less relative to the total amount of the composite material layer. If the amount of active material is within this range, for example, sufficient charge and discharge capacity can be obtained, and the battery performance is likely to be good.

[0097] Adhesives

[0098] The adhesive contained in the composite material layer is not particularly limited as long as it can bond the aforementioned active substances, but as mentioned above, it is preferable to contain a vinylidene fluoride homopolymer, or a vinylidene fluoride copolymer containing structural units derived from vinylidene fluoride and structural units derived from hexafluoropropylene and / or structural units derived from the compound represented by general formula (2) described later (hereinafter also referred to as "vinylidene fluoride polymer A"). The adhesive may contain only a vinylidene fluoride homopolymer, only vinylidene fluoride polymer A, or both. When the adhesive contains vinylidene fluoride polymer A, the adhesive may contain only one type of vinylidene fluoride polymer A, or it may contain two or more types.

[0099] The vinylidene fluoride homopolymer that can be used as an adhesive is the same as known vinylidene fluoride homopolymers. There are no particular limitations on the preparation method of this vinylidene fluoride homopolymer; vinylidene fluoride can be polymerized using known methods. Examples of polymerization methods include suspension polymerization, emulsion polymerization, and solution polymerization.

[0100] On the other hand, the vinylidene fluoride polymer A can be any polymer that contains structural units derived from vinylidene fluoride, structural units derived from hexafluoropropylene, and / or structural units derived from compounds represented by general formula (2). For example, the vinylidene fluoride polymer A can be a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and a compound represented by general formula (2), or a copolymer of vinylidene fluoride, hexafluoropropylene, and a compound represented by general formula (2). Furthermore, the vinylidene fluoride polymer A may contain other copolymer components without prejudice to the purpose and effects of the present invention.

[0101] Relative to the total amount (moles) of all structural units constituting the vinylidene fluoride polymer A, the amount of vinylidene fluoride-derived structural units in the vinylidene fluoride polymer A is preferably 50 mol% or more, more preferably 60 mol% or more, and particularly preferably 80 mol% or more. When the amount of vinylidene fluoride-derived structural units is 50 mol% or more, it is easy to obtain vinylidene fluoride-derived properties, such as electrochemical stability. The amount of vinylidene fluoride-derived structural units in the vinylidene fluoride polymer A can be adjusted by... 19 Determined by F-NMR.

[0102] On the other hand, relative to the total amount (moles) of all structural units constituting vinylidene fluoride polymer A, the amount of hexafluoropropylene-derived structural units in vinylidene fluoride polymer A is more preferably 10 mol% or less. When the amount of hexafluoropropylene-derived structural units is within the above range, the melting point of vinylidene fluoride polymer A tends to fall within the desired range, and the adhesive strength between vinylidene fluoride polymer A and the aforementioned active substances is improved. The amount of hexafluoropropylene-derived structural units in vinylidene fluoride polymer A can be adjusted by... 19 Determined by F-NMR.

[0103] Next, general formula (2) is shown below. Polymer A of vinylidene fluoride may contain only one structural unit derived from a compound represented by general formula (2) below, or it may contain two or more structural units.

[0104] [Chemical Formula 4]

[0105]

[0106] In the above general formula (2), R 4 This indicates hydrogen atoms, alkyl groups with 1 or more but less than 5 carbon atoms, or -C(=O)-OC. n H2n+1 (n is 1 or more and 5 or less). From the perspective of polymerization reactivity, R... 4 Preferably, it contains hydrogen atoms, methyl groups, or -C(=O)-OCH3.

[0107] In addition, R 5 and R 6 Each of the substituents can be independently represented as either a hydrogen atom or an alkyl group having 1 or more but less than 5 carbon atoms. From the viewpoint of polymerization reactivity, substituents with low steric hindrance are preferred, as are alkyl groups having 1 or more but less than 3 carbon atoms, and hydrogen or methyl groups.

[0108] Moreover, X in the above general formula (2) 2 This refers to a divalent atomic group with 1 or more but less than 20 atoms in the single bond or main chain and a molecular weight of less than 500. X 2 The number of atoms in the main chain is the number of atoms in the shortest chain that forms the connection between the terminal carboxyl group and the carbon-carbon double bond in the above general formula (2). More preferably, the number of atoms in the main chain is 15 or less.

[0109] From the above X 2 The atomic groups represented here have no particular restrictions on their structure as long as their molecular weight is less than 500 and they meet the above-mentioned number of atoms in the main chain. They can be linear, branched, or contain ring structures. Examples of structures constituting the above-mentioned atomic groups include alkylene groups, carbonyl groups (-C(=O)-), ether bonds (-O-), aromatic rings, and alicyclic structures.

[0110] Specific examples of compounds represented by the above general formula (2) include: monomethyl maleate (MMM), acrylic acid (AA), methacrylic acid, carboxymethyl acrylate, carboxymethyl methacrylate, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, acryloyloxyethyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate, methacryloyloxyethyl phthalate, acryloyloxypropyl succinate, methacryloyloxypropyl succinate, etc.

[0111] Relative to the total amount (moles) of all structural units constituting vinylidene fluoride polymer A, the amount of structural units derived from the compound represented by the above general formula (2) is preferably 0.01 mol% or more and 10 mol% or less, more preferably 0.02 mol% or more and 7 mol% or less, and particularly preferably 0.03 mol% or more and 4 mol% or less. When the amount of structural units derived from the compound represented by general formula (2) is 0.01 mol% or more, the adhesive strength between the adhesive and the active material, and the adhesive strength between the composite material layer and the coating are improved. On the other hand, when the amount of structural units derived from the compound represented by general formula (2) is 10 mol% or less, the amount of structural units derived from vinylidene fluoride is relatively increased, and the electrochemical stability of the composite material layer is more likely to improve. The amount of structural units derived from the compound represented by the above general formula (2) in vinylidene fluoride polymer A can be adjusted by... 19 F-NMR, 1 We used methods such as H-NMR for analysis.

[0112] Furthermore, as described above, the vinylidene fluoride polymer A may also partially contain structural units derived from compounds other than vinylidene fluoride, hexafluoropropylene, and compounds represented by general formula (2) (hereinafter also referred to as "other compounds"), to the extent that it does not impair the purpose and effect of the present invention. Specific examples of other compounds include those listed in the description of the vinylidene fluoride copolymer of the coating described above. The amount of structural units derived from other compounds is preferably 10 mol% or less relative to the total amount (moles) of all structural units constituting the vinylidene fluoride polymer A. When the amount of structural units derived from other compounds in the vinylidene fluoride polymer A is 10 mol% or less, the electrochemical stability of the composite layer is easily improved, and the adhesive strength between the composite layer and the coating is easily improved. The amount of structural units derived from other compounds can be adjusted by... 19 F-NMR, 1 We used methods such as H-NMR for analysis.

[0113] There are no particular limitations on the preparation method of the above-mentioned vinylidene fluoride polymer A. It is possible to polymerize vinylidene fluoride, hexafluoropropylene, and / or the compound represented by the above general formula (2) with other compounds as needed using known methods. Examples of polymerization methods include suspension polymerization, emulsion polymerization, solution polymerization, etc.

[0114] Furthermore, the amount of binder in the composite material layer is appropriately selected based on the composition of the binder, the function of the electrode, the type of battery, etc., and is not particularly limited. However, in one example, it is preferably 0.1% by mass or more and 50% by mass or less relative to the total amount of the composite material layer. When the amount of binder is within this range, the adhesive strength between the composite material layer and the coating is good. In addition, since the amount of active material becomes relatively sufficient, sufficient charge and discharge capacity can be obtained, and the battery performance is easily improved.

[0115] ·other

[0116] The composite material layer may also contain known dispersants, adhesives, tackifiers, etc., without impairing the purpose and effect of the present invention. Furthermore, it may further contain: nitrogen compounds such as phosphorus compounds, sulfur compounds, organic acids, amine compounds, and ammonium compounds; organic esters, various silane-based, titanium-based, and aluminum-based coupling agents; and resins such as polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and polyacrylonitrile (PAN). The total amount of these components is preferably 15% by mass or less relative to the total amount of the composite material layer.

[0117] Methods for forming composite material layers

[0118] The composite material layer can be formed by applying a composite material slurry containing the aforementioned active material, binder, and other components as needed, as well as an organic solvent, onto the coating of the current collector using a known method, and then drying it using a known method. The organic solvent contained in the composite material slurry is the same as the organic solvent used in the aforementioned coating liquid.

[0119] 3. Battery

[0120] The aforementioned current collectors and electrodes can be used in various lithium-ion secondary batteries, but they can also be used for other purposes.

[0121] Example

[0122] Hereinafter, specific embodiments and comparative examples of the present invention will be described together, but the present invention is not limited thereto.

[0123] 1. Preparation of materials

[0124] Prepare the following conductive additives, vinylidene fluoride copolymers, and dispersants respectively.

[0125] (Conductive additive)

[0126] ·Timcal Japan Co., Ltd. produces Super-P.

[0127] (vinylidene fluoride copolymer)

[0128] • VDF / AA1: Vinylidene fluoride acrylic acid copolymer (prepared in Preparation Example 1 below).

[0129] • VDF / AA2: Vinylidene fluoride acrylic acid copolymer (prepared in Preparation Example 2 below).

[0130] • VDF / MMM: Polyvinylidene fluoride monomethyl maleate copolymer (prepared in Preparation Example 3 below).

[0131] • VDF / AES: Vinylidene fluoride / acryloyloxyethyl succinate (prepared in Preparation Example 4 below).

[0132] •PVDF: Polyvinylidene fluoride homopolymer (prepared in Preparation Example 5 below).

[0133] [Preparation Example 1]

[0134] In a 2-liter autoclave, 900 g of deionized water, 0.4 g of hydroxypropyl methylcellulose, 3.1 g of tert-butyl peroxypentanoate, 396 g of vinylidene fluoride, and an initial addition of 0.2 g of acrylic acid were added, and the mixture was heated to 50°C. Under constant pressure during polymerization, a 0.7 wt% aqueous solution of acrylic acid containing acrylic acid was continuously fed into the reaction vessel. The resulting polymer slurry was dehydrated and dried to obtain a vinylidene fluoride copolymer (VDF / AA1). The total amount of acrylic acid added, including the initial addition, was 3.52 g. The specific logarithmic viscosity, determined by the method described later, was 2.5 dl / g.

[0135] [Preparation Example 2]

[0136] In a 2-liter autoclave, 900 g of deionized water, 0.4 g of hydroxypropyl methylcellulose, 2.0 g of tert-butyl peroxypentanoate, 396 g of vinylidene fluoride, and an initial addition of 0.2 g of acrylic acid were added, and the mixture was heated to 50°C. Under constant pressure during polymerization, a 0.7 wt% aqueous solution of acrylic acid containing acrylic acid was continuously fed into the reaction vessel. The resulting polymer slurry was dehydrated and dried to obtain a vinylidene fluoride copolymer (VDF / AA2). The total amount of acrylic acid added, including the initial addition, was 3.08 g. The specific logarithmic viscosity, determined by the method described later, was 3.1 dl / g.

[0137] [Preparation Example 3]

[0138] In a 2-liter autoclave, 1084 g of deionized water, 0.63 g of Metrolose SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.), 3.81 g of 500 wt% diisopropyl peroxide-HFe-347 pc-f solution, 414 g of vinylidene fluoride (VDF), and 4.2 g of monomethyl maleate (MMM) were added, and the mixture was heated to 29°C over 1 hour. Polymerization was then carried out at 29°C. The resulting polymer slurry was dehydrated and dried to obtain a vinylidene fluoride copolymer (VDF / MMM). The specific logarithmic viscosity, determined by the method described later, was 2.1 dl / g.

[0139] [Preparation Example 4]

[0140] In a 2-liter autoclave, 1092 g of deionized water, 0.2 g of Metrolose 90SH-100 (manufactured by Shin-Etsu Chemical Co., Ltd.), 3.6 g of 50% (w / w) diisopropyl peroxide dicarbonate-HFE-347pc-f solution, 5.3 g of ethyl acetate, 423 g of vinylidene fluoride, and an initial addition of 0.2 g of acryloyloxyethyl succinate (AES) were added. The mixture was heated to 26°C over 1 hour. Then, while maintaining the temperature at 26°C, a 5% (w / w) aqueous solution of acryloyloxyethyl succinate was slowly added at a rate of 0.6 g / min. The resulting polymer slurry was dehydrated and dried to obtain vinylidene fluoride copolymer (VDF / AES). The total amount of acryloyloxyethyl succinate added, including the initial addition, was 4.2 g. The specific logarithmic viscosity, determined by the method described later, was 1.8 dl / g.

[0141] [Preparation Example 5]

[0142] In a 2-liter autoclave, 1085 g of deionized water, 0.2 g of Metrolose SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.), 1.3 g of 50 wt% diisopropyl peroxide-HFE-347pc-f solution, 2.1 g of ethyl acetate, and 424 g of vinylidene fluoride (VDF) were added, and the mixture was heated to 26°C over 1 hour. Polymerization was then carried out at 26°C. The resulting polymer slurry was dehydrated and dried to obtain vinylidene fluoride homopolymer (PVDF). The specific logarithmic viscosity, determined by the method described later, was 3.1 dl / g.

[0143] (Dispersant)

[0144] •PVP: Polyvinylpyrrolidone.

[0145] PVA: Polyvinyl alcohol.

[0146] Methylcellulose.

[0147] HPMC: Hydroxypropyl methylcellulose.

[0148] ·N-Methylethanolamine.

[0149] 2. Electrode fabrication (Example 1)

[0150] • Coating preparation

[0151] The vinylidene fluoride copolymer (VDF / AA1) prepared in Adjustment Example 1 was dissolved in N-methyl-2-pyrrolidone (hereinafter also referred to as "NMP") to prepare a polymer solution containing 6% by mass of the vinylidene fluoride copolymer (VDF / AA1). Then, a conductive additive (Super-P manufactured by Timcal Japan Co., Ltd.), a dispersant (PVP), and NMP were added to this polymer solution to adjust the solid content concentration to 4%. The mass ratio of the conductive additive (Super-P) to the vinylidene fluoride copolymer (VDF / AA1) in the coating solution was set to 50:50. Furthermore, the amount of dispersant (PVP) was set to 1% by mass relative to the total mass of the vinylidene fluoride copolymer and the conductive additive. The resulting coating solution was coated onto an aluminum foil (substrate) with a thickness of 15 μm, serving as the current collector, using a TH-C type coating machine manufactured by THANK METAL Co., Ltd., and dried to form a surface area weight of approximately 0.7 g / m². 2 The coating.

[0152] • Fabrication of composite material layers

[0153] The vinylidene fluoride homopolymer (PVDF) prepared in Preparation Example 5 was dissolved in NMP to prepare a polymer solution containing 6% by mass of the vinylidene fluoride homopolymer. Then, a dispersion of conductive additive CNTs (carbon nanotubes) (containing tubes with a diameter of 7 nm and a specific surface area of ​​300 m²) was added to this polymer solution. 2 The mixture was prepared by mixing MWCNTs (multi-walled carbon nanotubes) with 4.3% NMP solution (by mass) and NMP. Then, the positive electrode active material LFP (lithium iron phosphate: primary particle size: D50: 2μm, specific surface area: 19.9m²) was added. 2 The solid content was adjusted to 55% by mass. Then, it was mixed to prepare a composite slurry. The mass ratio of the positive electrode active material (LFP), conductive additive (CNT), and vinylidene fluoride homopolymer in the composite slurry was set to 100:2:2 in this order. The obtained composite slurry was coated onto the above-mentioned coating using a TH-C type coating machine manufactured by THANK METAL Co., Ltd., and allowed to dry, forming a unit area weight of approximately 150 g / m². 2 The composite material layer has a unit area weight of approximately 150 g / m². 2 .

[0154] (Examples 2-11 and Comparative Examples 1-6)

[0155] The electrodes were fabricated in the same manner as in Example 1, except that the type and amount of vinylidene fluoride (co)polymer in the coating solution used to form the coating were changed as shown in Table 1.

[0156] 3. Evaluation

[0157] The determination and evaluation of various physical properties are carried out as follows.

[0158] Method for determining the specific concentration logarithmic viscosity of vinylidene fluoride (copolymer)

[0159] The specific logarithmic viscosity of the above-mentioned vinylidene fluoride (co)polymer was determined as follows. First, 80 mg of the vinylidene fluoride (co)polymer was dissolved in 20 mL of N,N-dimethylformamide, and the viscosity was measured using an Ubbelohde viscometer in a constant temperature bath at 30°C. Then, based on the obtained value, the specific logarithmic viscosity (η) of the vinylidene fluoride (co)polymer was calculated using the following formula. i ).

[0160] η i = (1 / C)·ln(η / η0)

[0161] It should be noted that in the above formula, η is the viscosity of the solution, η0 is the viscosity of the solvent N,N-dimethylformamide alone, and C is the concentration of the vinylidene fluoride polymer, i.e., 0.4 g / dL.

[0162] • Electrode state

[0163] After the composite material layer is formed, it is visually inspected. Layers with cracks are rated C, those with minor cracks are rated B, and those without cracks are rated A. The electrodes are then pressed using rollers to adjust the electrode density to 2.3 g / cm³. 3 In the case of a composite layer rated B, the cracks were repaired and no longer observed. On the other hand, the cracks in the composite layer rated C were not repaired even after the same rolling process.

[0164] Peel strength test

[0165] After rolling, the peel strength of the composite layer and coating was measured on electrodes for which no cracks were observed (electrodes rated A and B). Electrodes were cut to a length of 50 mm and a width of 20 mm, and a 90-degree peel test was performed using a tensile testing machine (A&D "STB-1225S") at a clamping speed of 10 mm / min, according to JIS K6854-1, to determine the peel strength (gf / mm). It should be noted that the peeling of the current collector from the composite layer before the test is referred to as "peeling".

[0166] [Table 1]

[0167]

[0168]

[0169] As shown in Table 1 above, cracks appeared on the surface of the composite layer when the coating did not contain a dispersant and the amount of conductive additive in the coating was too small (less than 45% by mass relative to the total mass of the coating) (Comparative Examples 1, 2, 4, and 5). This is believed to be because, during the formation of the composite layer, a portion of the coating dissolved due to the good solvent in the composite slurry, and the coating shrank during re-curing.

[0170] On the other hand, when the vinylidene fluoride polymer is a vinylidene fluoride homopolymer, although cracks are less likely to appear on the surface of the composite layer, delamination is prone to occur at the interface between the current collector and the coating (Comparative Example 3). This is believed to be because, when the coating is a vinylidene fluoride homopolymer, the adhesion between the components in the coating and the current collector is weak. Furthermore, when the amount of conductive additive in the coating is excessive (exceeding 80% by mass relative to the total mass of the coating), cracks are also less likely to appear on the surface of the composite layer, but the composite layer is prone to delamination (Comparative Example 6). This is believed to be because the resin content in the coating is low, making it difficult for the coating (current collector) to adhere tightly to the composite layer.

[0171] On the other hand, when the coating comprises a conductive additive, a vinylidene fluoride copolymer derived from the structural units of the aforementioned carboxyl-containing compounds (represented by general formula (1)), and a dispersant, and the amount of the conductive additive is 45% by mass or more and 80% by mass or less relative to the total mass of the coating (Examples 1-11), the composite material layer is less prone to cracking, and the composite material layer adheres well to the coating (current collector). It is believed that by including a conductive additive within a specified range, and further including a dispersant, the aggregation of the aforementioned vinylidene fluoride copolymer can be suppressed. Furthermore, it is believed that by setting the amount of the conductive additive to 80% by mass or less, the coating (current collector) adheres well to the composite material layer.

[0172] This application claims priority based on Japanese Patent Application No. 2023-055710, filed on March 30, 2023. The entire contents of that application are incorporated herein by reference.

[0173] Industrial availability

[0174] When a composite material layer is formed on the current collector of the present invention and an electrode is fabricated, cracks are less likely to appear on the electrode surface, enabling the manufacture of high-quality electrodes and batteries. Therefore, it is very useful in the manufacture of lithium-ion secondary batteries and the like.

Claims

1. A current collector, wherein, The current collector has: Substrates containing metals; and A coating disposed on at least one side of the substrate, The coating comprises conductive additives, vinylidene fluoride copolymer, and dispersant. The vinylidene fluoride copolymer comprises structural units derived from vinylidene fluoride and structural units derived from compounds having carboxyl groups. The amount of the conductive additive is more than 45% by mass and less than 80% by mass relative to the total mass of the coating.

2. The current collector according to claim 1, wherein, The compound having a carboxyl group is a compound represented by the following general formula (1). [Chemical Formula 1] In general formula (1), R 1 It represents an alkyl group with 1 or more but less than 5 carbon atoms, or -C(=O)-OC. n H 2n+1 Where n is greater than 1 and less than 5, R 2 and R 3 Each can be independently represented by either a hydrogen atom or an alkyl group having 1 or more but less than 5 carbon atoms. X 1 This refers to a divalent group with 1 or more but less than 20 atoms in the single bond or main chain and a molecular weight of less than 500.

3. The current collector according to claim 1, wherein, The coating's vinylidene fluoride copolymer comprises structural units derived from vinylidene fluoride, as well as structural units derived from acrylic acid and / or structural units derived from monomethyl maleate.

4. The current collector according to any one of claims 1 to 3, wherein, The dispersant is at least one compound selected from the group consisting of polyvinylpyrrolidone, polyvinyl alcohol, methylcellulose, hydroxypropyl methylcellulose, and N-methylethanolamine.

5. The current collector according to any one of claims 1 to 3, wherein, The amount of the dispersant is 0.2% by mass or more relative to the total mass of the coating.

6. An electrode, wherein, The electrode has: The current collector according to any one of claims 1 to 3; and A composite material layer disposed on the coating of the current collector, The composite material layer contains active substances and adhesives.

7. The electrode according to claim 6, wherein, The adhesive contains structural units derived from vinylidene fluoride.

8. A battery, wherein, The battery has the electrodes according to claim 6.

9. A method for manufacturing a current collector, wherein, The method for manufacturing the current collector includes a step of coating at least one side of a metal-containing substrate with a coating liquid comprising a conductive additive, a vinylidene fluoride copolymer, a dispersant, and a solvent. The vinylidene fluoride copolymer comprises structural units derived from vinylidene fluoride and structural units derived from compounds having carboxyl groups. The amount of the conductive additive is 45% by mass or more and 80% by mass or less relative to the total amount of solid components in the coating liquid.

10. The method for manufacturing a current collector according to claim 9, wherein, The compound having a carboxyl group is a compound represented by the following general formula (1). [Chemical Formula 2] In general formula (1), R 1 It represents an alkyl group with 1 or more but less than 5 carbon atoms, or -C(=O)-OC. n H 2n+1 Where n is greater than 1 and less than 5, R 2 and R 3 Each can be independently represented by either a hydrogen atom or an alkyl group having 1 or more but less than 5 carbon atoms. X 1 This refers to a divalent group with 1 or more but less than 20 atoms in the single bond or main chain and a molecular weight of less than 500.

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