Current collector, method for manufacturing current collector, and power storage element

Abstract

To provide a current collector which has high durability and can obtain high reliability as a secondary battery, a method for manufacturing a current collector, and a power storage element including the current collector.SOLUTION: A current collector includes a resin film having a resin layer A containing a nitrogen-containing heterocyclic compound on at least one surface, and a layer of metal and / or a metal compound contacting the resin A.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a current collector, a method for manufacturing a current collector, and an energy storage element. [Background technology]

[0002] Reducing carbon dioxide emissions is urgently needed to protect the environment, and the automotive industry is looking forward to the introduction and expansion of electric vehicles (EVs) and hybrid electric vehicles (HEVs). In addition to automobiles, next-generation mobility technologies such as drones, flying cars, and flying communication base stations are also being developed, requiring lightweight, high-energy-density secondary batteries. Against this backdrop, rapid progress is being made in the development of various next-generation batteries, including lithium-ion batteries, which can achieve high energy density and high power density, lithium-ion batteries using metallic lithium anodes, all-solid-state batteries, and air-air batteries.

[0003] Secondary batteries such as lithium-ion batteries are equipped with a current collector that connects the tab lead to the electrode layer to extract the generated electricity. Traditionally, metal foil (metal current collector foil) has been used as the current collector, but in recent years, film current collector foil made of resin film has been proposed as an alternative to metal foil. Resin film current collectors are lighter than metal current collector foils, and are expected to improve the output per unit weight of the battery.

[0004] For example, Patent Documents 1 and 2 disclose inventions related to resin current collectors. Patent Document 1 discloses a resin current collector that increases the electrical resistance in the planar direction to suppress performance degradation when defects occur inside the battery, while Patent Document 2 discloses a resin current collector that uses a specific inorganic metal compound as a filler. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-33066 [Patent Document 2] Japanese Patent Publication No. 2022-153250 Summary of the Invention [Problem to be solved by the invention]

[0006] However, although the resin current collectors in Patent Documents 1 and 2 are devised to improve the electrical conductivity of the resin, durability tests showed a decline in battery characteristics that was thought to be caused by deterioration of the laminate, and it was found that they have problems with withstanding long-term use as secondary batteries.

[0007] An object of the present invention is to provide a current collector that is highly durable and can provide high reliability as a secondary battery, a method for producing the current collector, and an electricity storage element including the current collector. [Means for solving the problem]

[0008] A preferred embodiment of the present invention is as follows. (1) A current collector comprising a resin film having a resin layer A containing a nitrogen-containing heterocyclic compound on at least one surface thereof, and a layer of a metal and / or metal compound in contact with the resin layer A. (2) The current collector according to (1), wherein the metal and / or metal compound layer contains copper. (3) The current collector according to (1) or (2), wherein the thickness of the metal and / or metal compound layer is 0.2 μm or more and 20 μm or less. (4) The current collector according to any one of (1) to (3), wherein the nitrogen-containing heterocyclic compound has an alkoxysilyl group. (5) The current collector according to any one of (1) to (4), wherein the resin film is a polyester-based resin or a polyolefin-based resin. (6) The current collector according to any one of (1) to (5), wherein the resin film includes a resin layer that is not in contact with the metal and / or metal compound layer, and a resin layer A. (7) The current collector according to any one of (1) to (6), wherein the resin film has a layer made of a metal and / or a metal compound on both surfaces thereof. (8) The current collector according to any one of (1) to (7), wherein the adhesive strength between the surface of the resin film and the layer made of metal and / or metal compound is 2 N / 10 mm or more. (9) A method for producing a current collector comprising a resin film having a resin layer A containing a nitrogen-containing heterocyclic compound on at least one surface thereof, and a metal and / or metal compound layer in contact with the resin layer A, wherein the metal and / or metal compound layer is formed by vacuum deposition, sputtering, or plating. (10) An electric storage element comprising the current collector according to any one of (1) to (8). [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a current collector that enables a highly durable and reliable secondary battery to be obtained, a method for producing the current collector, and an electricity storage element including the current collector. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional schematic view showing an example of the configuration of a current collector of the present invention. [Figure 2] 1 is a cross-sectional schematic view showing an example of the configuration of a current collector of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] A preferred embodiment of the current collector and the method for producing the current collector of the present invention will be described in more detail below.

[0012] The resin film of the present invention can be made from known resins, such as polyester-based resins, polyolefin-based resins, cyclic polyolefin-based resins, polyarylene sulfide-based resins, polyamide resins, polyimide-based resins, polyether-based resins, polyesteramide-based resins, polyetherester-based resins, acrylic resins, polyurethane-based resins, polycarbonate-based resins, fluorine-based resins, polyvinyl chloride-based resins, epoxy-based resins, silicone-based resins, or mixtures thereof. The term "major component" refers to a component that accounts for more than 50% by mass of the total components (100% by mass). Among these resins, polyester-based resins, polyolefin-based resins, and polyarylene sulfide-based resins are preferred from the viewpoints of electrical stability, strength, and chemical resistance. Polyester-based resins are obtained by polycondensation of a dicarboxylic acid component and a diol component, and may contain two or more dicarboxylic acid components and diol components. Examples of polyester-based resins include polyethylene terephthalate, polyethylene-2,6-naphthalate, polypropylene terephthalate, and polybutylene terephthalate. Polyolefin resins are primarily composed of resins whose main structural unit is an olefin hydrocarbon. The term "main structural unit" refers to the monomer unit contained in the resin that is most abundant (in terms of number). Examples of polyolefin resins include polymers and copolymers of α-olefins having alkyl groups in their side chains, such as ethylene, propylene, and 4-methyl-1-pentene; copolymers obtained by copolymerizing α-olefins with acrylic acid, C=C bond-containing carboxylic acids, C=C bond-containing carboxylates, or C=C bond-containing carboxylic acid alkyl esters; and polymers of norbornene and cyclodiene. Among these, polyethylene or polypropylene is preferred because of its relatively low cost, and polypropylene is even more preferred in terms of its heat resistance.The polyarylene sulfide resin is a homopolymer or copolymer having a repeating unit of -(Ar-S)-, and examples thereof include polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfide ketone, random copolymers thereof, block copolymers thereof, and mixtures thereof.

[0013] The resin film of the present invention may be unstretched or stretched, but is preferably biaxially stretched. Biaxial stretching improves the mechanical strength of the film, thereby suppressing wrinkles and curls and film breakage during processing. Furthermore, applying a uniform stretching stress during the stretching process makes it possible to make the film uniform in thickness in the width direction and length direction, thereby suppressing variations in electrical properties due to thickness unevenness when used as a current collector.

[0014] The thickness of the resin film of the present invention is preferably 1 μm or more and 30 μm or less. The lower limit of the thickness is more preferably 3 μm or more, and even more preferably 3.5 μm or more. By making the film thickness 1 μm or more, it is possible to suppress tearing during processing. The upper limit of the thickness is more preferably 20 μm or less, and even more preferably 15 μm or less. By making the film thickness 30 μm or less, it is possible to minimize increases in the weight and thickness of the battery itself when used as a battery component.

[0015] A preferred embodiment of the resin film of the present invention has a resin layer A containing a nitrogen-containing heterocyclic compound on at least one surface. The resin film may have a single-layer structure consisting of only resin layer A, or a laminate structure of two or more layers having resin layer A on the surface. However, a laminate structure is preferred because the nitrogen-containing heterocyclic compound can be efficiently disposed at the location in contact with the metal layer. In the case of a single-layer structure, the entire resin film corresponds to resin layer A, and the resin film itself contains the nitrogen-containing heterocyclic compound. Such a resin film can be obtained by adding a nitrogen-containing heterocyclic compound to the raw materials of the resin film and forming the film. In the case of a laminate structure, the main component of resin layer A may be the same as or different from the other layers constituting the resin film. The method for laminating the resin layer A is not particularly limited, and examples thereof include a method of applying a nitrogen-containing heterocyclic compound to the surface of a film, a co-extrusion method in which the resins of each layer are laminated and extruded in a molten state, and a method (melt lamination method) in which a resin layer raw material to which a nitrogen-containing heterocyclic compound has been added is melt-extruded from an extruder onto a film in the middle of film formation to laminate it.

[0016] When a nitrogen-containing heterocyclic compound is applied and laminated, a binder resin may or may not be used, and when a binder resin is used, its composition may be the same as that of the film to be applied or a different resin. The binder resin is not particularly limited as long as it can be mixed with the nitrogen-containing heterocyclic compound, such as an acrylic resin, an epoxy resin, a urethane resin, a polyester resin, or a polyimide resin, but is preferably an acrylic resin, an epoxy resin, or a polyester resin in terms of mixability with the compound, stability of the coating liquid, coatability, durability during post-processing such as metal lamination, etc.

[0017] The coating step may be performed during the resin film formation process or as a separate step after film formation. The resin layer A obtained by coating is preferred because it can efficiently impart functionality, allowing the nitrogen-containing heterocyclic compound to be present at a high concentration in the surface layer of the resin film, and its thickness in the resin film can be reduced, thereby reducing interlayer stress and making the resin film less prone to curling.

[0018] When laminating resin layer A using a co-extrusion method, a film can be formed by extruding raw materials mixed with a nitrogen-containing heterocyclic compound. That is, an extruder is used for each constituent layer, and the raw materials for each layer are melted. These are then laminated in the molten state in a confluence device installed between the extrusion device and the die, and then introduced into the die and extruded onto a casting drum to be processed into a sheet, thereby obtaining an unstretched film. Subsequently, if necessary, stretching can be performed to obtain a resin film having resin layer A on its surface. This method is preferred because it provides excellent lamination uniformity, is less susceptible to foreign matter entering between the layers, and ensures strong interlayer adhesion.

[0019] The nitrogen-containing heterocyclic compound of the present invention is a type of compound having a cyclic structure, containing carbon atoms and one or more nitrogen atoms, and also includes derivatives thereof. The nitrogen-containing heterocyclic compound may be a monocyclic compound containing only one ring, or a polycyclic compound containing two or more rings, but preferably contains a highly stable five- or six-membered ring. The resin layer A may contain one or a mixture of two or more of these. Nitrogen-containing heterocyclic compounds are preferably stable and have aromatic properties, such as imidazole, triazole, tetrazole, benzimidazole, benzotriazole, and triazine. Examples of the nitrogen-containing heterocyclic compound containing a triazole structure include monocyclic compounds such as 3-amino-1,2,4-triazole, as well as known polycyclic compounds such as 1,2,3-benzotriazole, 1-methyl-1H-benzotriazole, tolyltriazoles such as 4-methyl-1H-benzotriazole and 5-methyl-1H-benzotriazole, nitrobenzotriazoles such as 4-nitrobenzotriazole and 5-nitrobenzotriazole, carboxybenzotriazoles such as 1H-benzotriazole-5-carboxylic acid, 1-(2,3-dicarboxypropyl)benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]methylbenzotriazole, N-methylbenzotriazole-1-methylamine, and 5,5′-bi-1H-tetrazole.Examples of nitrogen-containing heterocyclic compounds containing a triazine structure include known compounds such as 2,4,6-trihydroxy-1,3,5-triazine, 2,4,6-triamino-1,3,5-triazine, 2,4-diamino-6-phenyl-1,3,5-triazine, 2,4,6-triphenyl-1,3,5-triazine, 2,4,6-tris[bis(methoxymethyl)amino]-1,3,5-triazine, 1,3,5-triazine-2,4,6-trithiol, 6-dibutylamino-2,4-dimethylthio-1,3,5-triazine, 6-dibutylamino-2,4-dithiol-1,3,5-triazine, 6-monobutylamino-2,4-dithiol-1,3,5-triazine, and 6-phenylamino-2,4-dithiol-1,3,5-triazine.

[0020] The nitrogen-containing heterocyclic compound of the present invention may have a hydroxy group, a thiol group, or an alkoxysilyl group attached to the cyclic structure via an alkyl chain. Among these, an alkoxysilyl group is preferred because it allows the nitrogen-containing heterocyclic compound to be firmly fixed in the resin layer A by reaction with another functional group or polycondensation. That is, the structure may be imidazole silane, triazole silane, or tetrazole silane. Specific examples include known compounds such as trimethoxy[3-(1H-imidazol-1-yl)propyl]silane, triethoxy[3-(1H-imidazol-1-yl)propyl]silane, N-(3-trimethoxysilanylpropyl)-[1,3,5]triazine-2,4,6-triamine, triethoxysilylpropylamino-1,3,5-triazine-2,4-dithiol, 6-(3-triethoxysilylpropylamino)-1,3,5-triazine-2,4-dithiol monosodium salt, 1-(3-propyltrimethoxysilyl)benzotriazole, and 1-(6-hexyltrimethoxysilyl)benzotriazole. The presence of these nitrogen-containing heterocyclic compounds can be confirmed by analyzing them with a time-of-flight secondary ion mass spectrometer (TOF-SIMS) and detecting their fragments.

[0021] The metal and / or metal compound layer constituting the current collector of the present invention is preferably in contact with resin layer A. Generally, when a resin and a metal are in contact with each other, a phenomenon known as metal damage occurs, in which the resin is oxidized and deteriorates due to hydrogen abstraction by ionized metals. This deterioration is particularly likely to occur when the resin is in contact with copper, and is sometimes referred to as copper damage. Meanwhile, nitrogen-containing heterocyclic compounds contained in resin layer A, such as triazine rings and triazole rings, are known to have high complex-forming properties. When resin layer A is present on the surface of a resin film and in contact with a metal or metal compound layer, the triazine ring or triazole ring forms a complex with the metal or metal compound in contact. This can suppress resin deterioration and migration due to metal ions and improve the durability of the battery. To fully achieve these effects, it is important that the nitrogen-containing heterocyclic compound is present on the surface of the resin film. When the resin layer A does not contain a binder, a sufficient amount is present in the surface layer, but when a binder resin is used, the amount of the nitrogen-containing heterocyclic compound added is preferably 0.5% by mass to 10% by mass, and more preferably 1% by mass to 5% by mass, based on the resin solid content. Adding 0.5% by mass or more is effective, while adding 10% by mass or less is preferable because it prevents difficulty in mixing and precipitation and maintains the properties of the binder resin.

[0022] The resin layer A of the present invention preferably further contains an antioxidant. Resin degradation due to metals, such as copper, is caused by radicals generated by hydrogen abstraction in the resin. Oxygen reacts with these radicals to form peroxides, which then decompose to generate radicals, resulting in a chain reaction that degrades the resin. Therefore, the coexistence of an antioxidant is effective in preventing this chain reaction. Known antioxidants, such as hindered phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, and lactone-based antioxidants, can be used, and two or more types may be mixed and used. Among these, from the viewpoint of bleed-out, it is preferable to include a phenol-based antioxidant with a high molecular weight and a molecular weight of 500 or more, which is highly sterically hindered. Examples include 2,6-di-t-butyl-p-cresol (BHT), 1,3,5-trimethyl-2,4,6-tris(3',5'-di-t-butyl-4'-hydroxybenzyl)benzene (e.g., "Irganox" (registered trademark) 1330 manufactured by BASF), and tetrakis[methylene-3(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane (e.g., "Irganox" (registered trademark) 1010 manufactured by BASF).

[0023] In addition, the resin film of the present invention may contain various additives such as a heat stabilizer, an antistatic agent, an ultraviolet absorber, an antiblocking agent, and a filler, as long as the effects of the present invention are not impaired.

[0024] The current collector of the present invention includes a metal and / or metal compound layer in contact with resin layer A. Examples of metal elements constituting the metal and / or metal compound layer include gold, silver, copper, zinc, lead, nickel, iron, aluminum, titanium, cobalt, manganese, cadmium, and palladium. The metal and / or metal compound layer may be a metal layer of any of the above metal elements, or a metal compound layer containing any of the above metal elements mixed with oxygen, nitrogen, fluorine, carbon, boron, chlorine, sulfur, or phosphorus. Furthermore, when metal and / or metal compound layers are provided on both sides of the resin film, the metal elements may be the same or different on both sides. When the current collector of the present invention is used for a lithium-ion battery, the metal element constituting the metal and / or metal compound layer preferably includes copper or aluminum. When used for a negative electrode, the metal and / or metal compound layer preferably includes copper.

[0025] The thickness of the layer containing a metal and / or metal compound is preferably 0.2 μm or more and 20 μm or less. The lower limit of the thickness is more preferably 0.3 μm or more. By making the thickness of the layer containing a metal or metal compound 0.1 μm or more, it is possible to minimize the deterioration of electrical properties due to uneven thickness of the metal layer. The upper limit of the thickness is more preferably 10 μm or less, and even more preferably 5 μm or less. By setting the upper limit of the thickness within these ranges, it is possible to minimize the increase in battery weight.

[0026] The method for providing the layer containing the metal and / or metal compound of the present invention is not particularly limited, and known methods can be used, such as vapor phase film formation methods typified by vacuum deposition, sputtering, and electroplating, plating methods in which a metal layer is provided by an electrochemical reaction using a solution containing a metal salt, and a method of laminating a metal or metal compound foil. Among these, vacuum deposition, sputtering, and plating methods are preferred, as they can be used to process the resin layer A and the layer containing the metal and / or metal compound into a contact state with a roll with good productivity.

[0027] Vacuum deposition methods include induction heating deposition, resistance heating deposition, laser beam deposition, and electron beam deposition. Among these, electron beam deposition, laser beam deposition, and induction heating deposition are preferably used because they have a high heat generation rate of the deposition source and a high film formation rate.

[0028] From the viewpoint of productivity, roll-to-roll processing is preferably used for vapor deposition on a film. A film roll is placed in advance in a vacuum chamber, and a metal or metal compound layer is formed on the surface of the film that is in close contact with a chill roll, and then the film is wound up as a film roll. Since the film is exposed to heat during vapor deposition, it is preferable to cool the film evenly from the back side of the vapor deposition surface by intimately contacting the chill roll to prevent thermal damage that could reduce the mechanical properties of the resin film or cause the resin film to melt.

[0029] In the case of sputtering, roll-to-roll processing is also preferred from the viewpoint of productivity. Sputtering may use any of DC, AC, and pulsed power supplies, and may utilize a magnetic field by placing a magnet inside the apparatus, or an ion beam. Examples of techniques include radio-frequency sputtering, magnetron sputtering, dual magnetron sputtering, ion beam sputtering, DC sputtering, and reactive sputtering. Among these, radio-frequency sputtering is preferred because the apparatus is simple and the damage to the sample is relatively small.

[0030] As a vapor phase film formation method, it is also possible to use a combination of sputtering and vacuum deposition. For example, two or more steps can be performed consecutively, such as forming a layer containing a first metal and / or metal compound by sputtering and then forming a layer containing a second metal and / or metal compound by vacuum deposition.

[0031] In order to achieve the desired metal layer thickness, the layer made of the metal and / or metal compound of the present invention is preferably formed in one pass (one pass is defined as a set of unwinding, film formation, and winding) from the viewpoints of productivity, resistance characteristics, and grade and quality, but it is also possible to repeat the thin film formation multiple times to stack the film to the desired thickness.

[0032] Although known plating methods such as electrolytic plating and electroless plating can be used, electrolytic plating is preferred from the viewpoint of obtaining the target thickness with good productivity. However, since the resin film is not conductive, it is preferable to first provide a conductive layer by electroless plating or vapor phase deposition, and then laminate a layer made of a metal and / or metal compound by electrolytic plating.

[0033] The current collector of the present invention preferably has a layer of metal and / or metal compound on both surfaces of the resin film, since the layer containing metal and / or metal compound on both surfaces functions as a substitute for metal foil.

[0034] The adhesive strength between the resin film and the layer made of metal and / or metal compound is preferably 2 N / 10 mm or more. An adhesive strength of 2 N / 10 mm is preferable because it makes it less likely for delamination to occur during post-processing or use, resulting in stable properties. The layer made of metal and / or metal compound is in contact with resin layer A. The nitrogen-containing heterocyclic compound contained in resin layer A can donate electrons to metal atoms contained in the metal or metal compound layer, strengthening the adhesive strength between the layers. A detailed method for measuring adhesive strength will be described later in the Examples.

[0035] The energy storage element of the present invention comprises an electrode assembly including a positive electrode and a negative electrode, and may include a battery case that houses the electrode assembly. When the energy storage element contains an electrolytic solution, it is preferable to include a separator between the positive electrode and the negative electrode. Energy storage elements that do not contain an electrolytic solution and are made of a solid electrolyte are also preferred. Examples of energy storage elements that can be used include primary batteries, secondary batteries, electric double layer capacitors, and aluminum electrolytic capacitors, and the present invention will particularly focus on secondary batteries.

[0036] Specific examples of secondary batteries include lithium secondary batteries, lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-iron batteries, silver oxide-zinc batteries, manganese dioxide-lithium secondary batteries, lithium cobalt oxide-carbonate secondary batteries, vanadium-lithium secondary batteries, etc. Among these, lithium secondary batteries are preferred because they can be used for a long period of time and have a high energy density.

[0037] The battery case for housing the electrode assembly may be, for example, an aluminum case, an iron case with a nickel-plated inner surface, or a case made of aluminum laminate film. Examples of the shape of the battery case include a pouch type, a cylindrical type, a square type, and a coin type. Among these, the pouch type is preferred because it can achieve a high energy density and can be freely designed into a shape at low cost.

[0038] The positive electrode of the energy storage element is a current collector laminated with a positive electrode material consisting of an active material, a binder resin, and a conductive additive. Examples of active materials include layered lithium-containing transition metal oxides such as LiCoO2, LiNiO2, and Li(NiCoMn)O2, spinel-type manganese oxides such as LiMn2O4, and iron-based compounds such as LiFePO4. The binder resin may be a resin with high oxidation resistance, specifically, fluororesin, acrylic resin, and styrene-butadiene resin. Examples of conductive additives include carbon materials such as carbon black and graphite. Metal foils such as aluminum foil and collectors with aluminum metal layers are suitable as current collectors, and the current collector of the present invention is particularly preferred due to its improved safety.

[0039] The negative electrode of a storage battery is made by laminating a negative electrode material consisting of an active material and a binder resin on a current collector. Active materials include carbon materials such as artificial graphite, natural graphite, hard carbon, and soft carbon, lithium alloy materials such as tin and silicon, metal materials such as lithium, and lithium titanate (Li4Ti5O 12) and the like. Examples of binder resins include fluororesins, acrylic resins, and styrene-butadiene resins. As the current collector, metal foils such as copper foils and current collectors with copper metal layers are suitable, and the current collector of the present invention is particularly preferred because it can improve safety.

[0040] When the energy storage element of the present invention contains an electrolyte, the electrolyte serves as a medium for ion transfer between the positive and negative electrodes of an electrochemical element such as a secondary battery, and is configured by dissolving the electrolyte in an organic solvent. Examples of the electrolyte include LiPF, LiBF, and LiClO, with LiPF being preferred from the viewpoints of solubility in organic solvents and ionic conductivity. Examples of the organic solvent include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and two or more of these organic solvents may be mixed and used.

[0041] A method for producing a lithium secondary battery, which is preferably used among the energy storage elements, will be described below.

[0042] The method for producing a lithium secondary battery involves first dispersing an active material and a conductive additive in a binder resin solution to prepare an electrode coating solution, then coating the coating solution on a current collector and drying the solvent to obtain a positive electrode and a negative electrode. The thickness of the coating film after drying is preferably 50 μm to 500 μm. Furthermore, it is preferable to apply pressure to the active material layer formed on the current collector, preferably by a roll press method, to densify it and thin the current collector.

[0043] A lithium secondary battery separator is placed between the obtained positive electrode and negative electrode so as to be in contact with the active material layer of each electrode, and the resulting battery is enclosed in an exterior material such as an aluminum laminate film. After injecting an electrolyte, a negative electrode lead and a safety valve are installed, and the exterior material is sealed.

[0044] The lithium secondary battery thus obtained has high adhesion to the electrode, excellent battery characteristics and life, and can be produced at low cost. [Example]

[0045] The present invention will be described below based on examples. However, the present invention is not limited to these examples, and these examples can be modified or changed based on the spirit of the present invention, and such modifications are not excluded from the scope of the invention.

[0046] [Evaluation method] (1) Thickness of the resin film, metal and / or metal compound layer The thickness of the resin film and metal and / or metal compound layer was measured by cutting the current collector in the thickness direction with a microtome and observing the cross section of the current collector with a Schottky field emission scanning electron microscope (SEM) JSM-7600F manufactured by JEOL Ltd. Three images were taken at a magnification of 50,000x when the thickness of the object to be measured was less than 1 μm, 10,000x when it was 1 μm or more but less than 5 μm, 5,000x when it was 5 μm or more but less than 10 μm, and 2,000x when it was 10 μm or more. The thickness of the resin film and metal and / or metal compound layer was measured for each of the three images obtained, and the arithmetic mean of these measurements was recorded as the thickness.

[0047] (2) Metal species of the metal and / or metal compound layer The metals contained in the metal and / or metal compound layer were subjected to elemental analysis using the SEM described in (1) and an energy dispersive X-ray spectroscopy (EDX) detector, AZtecLiv Standard UltimMax 65, manufactured by Oxford University Press, Oxford, UK. The accelerating voltage was varied from 0.5 kV to 30 kV.

[0048] (3) Adhesion The thickness of the metal and / or metal compound layer of the current collector was standardized to 5 μm, and adhesion was measured. If the metal layer thickness was less than 5 μm, it was increased by known methods such as plating. If it exceeded 5 μm, the thickness was adjusted by etching or polishing. The surface of the metal and / or metal compound layer was coated with an adhesive, and a polyethylene terephthalate film (Toray Industries, Inc., biaxially oriented polyester film "Lumirror" (registered trademark) #25-S10) was laminated. The adhesive was a 10:1:30 (mass ratio) mixture of DIC Graphics Corporation's adhesive DIC Dry LX-500 (main adhesive), KW-75 (curing agent), and ethyl acetate solvent, mixed at room temperature with stirring. The mixture was applied to the vapor-deposited surface of the current collector with a bar coater to a thickness of 2 μm and dried for 30 seconds in a hot air oven set at 85°C. This laminate was aged for 48 hours at 40°C, then cut into 10 mm wide samples. Measurements were performed under the following conditions to obtain adhesion profiles. For the measurements, the sample was attached to a 1.5 mm thick SUS plate with double-sided tape (Nitto Denko Corporation double-sided tape No. 532, tape thickness 0.08 mm) with the current collector side attached and secured with an air chuck. The attached PET film was then secured with the other air chuck, and the PET film side was pulled for measurement. Note that during peeling, the surface layer of the resin film may adhere to the surface of the metal and / or metal compound layer, and in this case, the metal and / or metal compound layer was also considered to have peeled off. Three measurements were taken for each specimen, and the arithmetic average value was used to determine the adhesion strength.

[0049] Measurement equipment: A&D Co., Ltd. Tensilon universal material testing machine RTG-1210 Load cell: 50N Peeling angle: 180° Peeling speed: 50mm / min Measurement environment: room temperature 23℃, humidity 50%. The resulting adhesion was evaluated as follows. A: Adhesion strength is 5N / 10mm or more B: Adhesion strength is 2N / 10mm or more and less than 5N / 10mm C: Adhesion strength is less than 2N / 10mm.

[0050] (4) Heat-resistant adhesion The laminate prepared in the same manner as in (3) was attached to a SUS tray, and then placed in a thermo-hygrostat (Espec Corporation, LH-114 thermo-hygrostat) set at 60°C and 90% RH with the current collector facing downwards to prevent water droplets from adhering, and treated for 120 hours. After treatment, the adhesion strength was measured in the same manner as in (3), and this was taken as the heat-resistant adhesion strength. The adhesion retention rate (%) was calculated by dividing the heat-resistant adhesion strength by the adhesion strength measured in (3) × 100, and evaluated as follows. A: Adhesion retention rate is 90% or more B: Adhesion retention rate is 50% or more but less than 90% C: Adhesion maintenance rate is less than 50%.

[0051] (5) Battery characteristic evaluation (5-1) Battery construction The positive electrode sheet contains Li(Ni 5 / 10 Mn 2 / 10 Co 3 / 10 A positive electrode slurry was prepared by dispersing 96 parts by mass of 1.0 mass parts of acetylene black and 1.0 mass parts of graphite as a positive electrode conductive additive in N-methyl-2-pyrrolidone using a planetary mixer, and the slurry was then applied to a positive electrode current collector, dried, and rolled to prepare a positive electrode (coating weight: 10.0 mg / cm). 2 ). This positive electrode sheet was cut into a piece of 40 mm x 40 mm. At this time, the current collecting tab adhesive portion, which was not attached to the active material layer, was cut out to a size of 5 mm x 5 mm on the outside of the active material surface. An aluminum tab having a width of 5 mm and a thickness of 0.1 mm was ultrasonically welded to the tab adhesive portion. The negative electrode sheet was prepared by dispersing 98 parts by mass of natural graphite as the negative electrode active material, 1 part by mass of carboxymethyl cellulose as a thickener, and 1 part by mass of styrene-butadiene copolymer as a negative electrode binder in water using a planetary mixer, and then coating, drying, and rolling the resulting negative electrode slurry onto a negative electrode current collector (coating weight: 6.6 mg / cm). 2This negative electrode sheet was cut into a piece of 45 mm x 45 mm. At this time, the current collecting tab adhesive portion, which was not attached to the active material layer, was cut out to a size of 5 mm x 5 mm outside the active material surface. A copper tab of the same size as the positive electrode tab was ultrasonically welded to the tab adhesive portion.

[0052] Next, the porous film was cut into a 55mm x 55mm piece. The positive and negative electrodes were placed on both sides of the porous film, with the active material layer separating the porous film. The positive electrode and negative electrode were then placed facing the negative electrode. The electrode assembly was then heat-pressed at 70°C / 5 MPa / 10 seconds to bond the positive electrode, porous film, and negative electrode. The positive electrode, porous film, and negative electrode were sandwiched between a 90mm x 200mm aluminum laminate film, the long edge of the aluminum laminate film folded, and the two long edges of the aluminum laminate film were heat-sealed to form a bag. An electrolyte solution was prepared by dissolving LiPF6 as a solute in a 3:7 (volume ratio) mixed solvent of ethylene carbonate and ethyl methyl carbonate to a concentration of 1 mol / L. 1.5 g of the electrolyte solution was poured into the bag-shaped aluminum laminate film, and the short sides of the aluminum laminate film were heat-sealed while the electrolyte solution was being impregnated under reduced pressure to form a laminated battery.

[0053] (5-2) Life characteristics The life characteristics were tested according to the following procedure and evaluated in terms of discharge capacity retention rate. <1st to 1,000th cycle> One cycle of charge and discharge was defined as a constant current charge of 2C and 4.3V, and a constant current discharge of 2C and 2.7V. The charge and discharge cycle was repeated 1,000 times at 25°C. <Calculation of discharge capacity retention rate> The discharge capacity retention rate was calculated as (discharge capacity at the 1,000th cycle) / (discharge capacity at the 1st cycle) × 100. Five laminated batteries were produced, and the results with the highest and lowest discharge capacity retention rates were removed. The average of the measurement results for three batteries was taken as the capacity retention rate and evaluated as follows: A: Discharge capacity retention rate is 70% or more B: Discharge capacity retention rate is 50% or more and less than 70% C: Discharge capacity retention rate is less than 50%.

[0054] [Example 1] A coating liquid prepared by dissolving a triazine derivative (VD-5 manufactured by Shikoku Chemical Industry Co., Ltd.) having an alkoxysilyl group as a nitrogen-containing heterocyclic compound in methanol was applied to both sides of a 6 μm-thick biaxially stretched PET film (polyester film "Lumirror" (registered trademark) model number #6-CF53 manufactured by Toray Industries, Inc.), to obtain a resin film having a resin layer A on its surface. Copper was deposited to a thickness of 2 μm by vacuum deposition on the resin layer A on each of the surfaces of the resin film, to obtain a negative electrode current collector.

[0055] [Example 2] 100 parts by mass of trimethylolpropane triacrylate (NK Ester A-TMPT manufactured by Shin-Nakamura Chemical Co., Ltd.) and 5 parts by mass of 1-hydroxycyclohexyl phenyl ketone (Omnirad184 manufactured by IGM Resins BV) were dissolved in ethyl acetate to a solid content of 10% by mass. Furthermore, a triazine derivative having an alkoxysilyl group (VD-5 manufactured by Shikoku Chemicals Corporation) was mixed as a nitrogen-containing heterocyclic compound at a resin ratio of 3% by mass to prepare a coating liquid. The obtained coating liquid was applied and dried at 120°C, and then subjected to an integrated light intensity of 500 mJ / cm. 2 A current collector was obtained in the same manner as in Example 1, except that the resin layer A was cured by irradiating it with ultraviolet light of 1000 nm to form a layer with a thickness of 500 nm.

[0056] Example 3 A current collector was obtained in the same manner as in Example 2, except that the amount of the triazine derivative having an alkoxysilyl group added was 0.8 mass %.

[0057] [Example 4] A current collector was obtained in the same manner as in Example 2, except that the thickness of the copper was set to 0.2 µm.

[0058] [Example 5] A current collector was obtained in the same manner as in Example 2, except that a 100 nm thick copper layer was laminated on each of the resin layers A on both surfaces of the resin film by magnetron sputtering, and then electrolytic plating was performed to laminate copper to a total thickness of 3 μm.

[0059] [Example 6] A current collector was obtained in the same manner as in Example 2, except that copper was laminated by electroless plating and electrolytic plating on each of the resin layers A on both surfaces of the resin film.

[0060] [Example 7] A current collector was obtained in the same manner as in Example 2, except that a triazine derivative having an alkoxysilyl group, 6-(3-triethoxysilylpropylamino)-1,3,5-triazine-2,4-dithiol, was used as the nitrogen-containing heterocyclic compound.

[0061] Example 8 A current collector was obtained in the same manner as in Example 2, except that the triazine derivative having an alkoxysilyl group was changed to 1,2,3-benzotriazole (BT-120SG, manufactured by Johoku Chemical Industry Co., Ltd.).

[0062] [Example 9] A current collector was obtained in the same manner as in Example 2, except that the triazine derivative having an alkoxysilyl group was changed to a benzotriazole derivative having an alkoxysilyl group (silane coupling agent X-12-1214A manufactured by Shin-Etsu Chemical Co., Ltd.).

[0063] [Example 10] A polyester resin containing 5% by mass of a triazine derivative having an alkoxysilyl group (VD-5 manufactured by Shikoku Chemical Industry Co., Ltd.) was fed to extruder A, and a polyester resin not containing a triazine derivative having an alkoxysilyl group was fed to extruder B. They were melt-extruded to form an A / B / A structure, yielding a resin film having a resin layer A on its surface. Copper was laminated onto the obtained resin film in the same manner as in Example 1, yielding a current collector.

[0064] [Example 11] A current collector was obtained in the same manner as in Example 10, except that a single-layer resin film was obtained using a polyester resin containing 5% by mass of a triazine derivative having an alkoxysilyl group (VD-5 manufactured by Shikoku Chemical Industry Co., Ltd.) that was supplied to extruder A in Example 10.

[0065] [Example 12] A current collector was obtained in the same manner as in Example 2, except that the biaxially stretched PET film was replaced with a biaxially stretched polypropylene film containing tetrakis[methylene-3(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane (BASF "Irganox" (registered trademark) 1010) as an antioxidant.

[0066] [Example 13] A current collector was obtained in the same manner as in Example 12, except that a 100 nm thick copper layer was laminated on each of the resin layers A on both surfaces of the resin film by magnetron sputtering, and then electrolytic plating was performed to laminate copper to a total thickness of 3 μm.

[0067] [Example 14] A current collector was obtained in the same manner as in Example 12, except that copper was laminated on each of the two surfaces of the resin layer A by electroless plating and electrolytic plating.

[0068] [Example 15] A current collector was obtained in the same manner as in Example 12, except that a 12 μm thick electrolytic copper foil (electrolytic copper foil CF-T4M-HD-12 manufactured by Fukuda Metal Foil & Powder Co., Ltd.) was thermally laminated as a metal-containing layer to each of the resin layers A on both surfaces of the resin film.

[0069] [Example 16] A current collector was obtained in the same manner as in Example 12, except that the triazine derivative having an alkoxysilyl group was changed to a benzotriazole derivative having an alkoxysilyl group (silane coupling agent X-12-1214A manufactured by Shin-Etsu Chemical Co., Ltd.).

[0070] [Example 17] A polypropylene resin containing 5% by weight of a triazine derivative having an alkoxysilyl group (VD-5 manufactured by Shikoku Chemical Industry Co., Ltd.) was supplied to extruder A, and a polypropylene resin not containing a triazine derivative having an alkoxysilyl group was supplied to extruder B. They were melt-extruded to form an A / B / A structure, to obtain a resin film having a resin layer A on its surface. A current collector was obtained in the same manner as in Example 12, except that no coating liquid was applied.

[0071] [Example 18] A current collector was obtained in the same manner as in Example 2, except that the biaxially stretched PET film was changed to a biaxially stretched polyphenylene sulfide film having a thickness of 4 µm.

[0072] Comparative Example 1 A current collector was obtained in the same manner as in Example 1, except that the coating liquid was not applied and the resin layer A was not provided.

[0073] Comparative Example 2 A current collector was obtained in the same manner as in Example 12, except that the coating liquid was not applied and the resin layer A was not provided.

[0074] Comparative Example 3 A current collector was obtained in the same manner as in Example 10, except that the resins supplied to extruder A and extruder B were reversed when obtaining a biaxially stretched PET film having a laminated structure.

[0075] In the battery evaluation described in evaluation item (5), the current collectors obtained in the examples and comparative examples were used as negative electrode current collectors, and aluminum foil was used as positive electrode current collectors.

[0076] [Table 1]

[0077] [Table 2] [Explanation of symbols]

[0078] 1. Layer containing metal and / or metal compound 2 Resin layer A 3. Resin layer not in contact with metal and / or metal compound layer

Claims

1. A current collector comprising: a resin film having a resin layer A containing a nitrogen-containing heterocyclic compound on at least one surface thereof; and a layer of a metal and / or metal compound in contact with the resin layer A.

2. 2. The current collector of claim 1, wherein the metal and / or metal compound layer comprises copper.

3. 2. The current collector according to claim 1, wherein the thickness of the metal and / or metal compound layer is 0.2 μm or more and 20 μm or less.

4. 3. The current collector according to claim 1, wherein the nitrogen-containing heterocyclic compound has an alkoxysilyl group.

5. 3. The current collector according to claim 1, wherein the resin film is a polyester resin or a polyolefin resin.

6. 3. The current collector according to claim 1, wherein the resin film comprises a resin layer not in contact with the metal and / or metal compound layer, and a resin layer A.

7. 3. The current collector according to claim 1, wherein the resin film has a layer made of a metal and / or a metal compound on both surfaces thereof.

8. 3. The current collector according to claim 1, wherein the adhesive strength between the surface of the resin film and the layer made of metal and / or metal compound is 2 N / 10 mm or more.

9. A method for producing a current collector comprising a resin film having, on at least one surface thereof, a resin layer A containing a nitrogen-containing heterocyclic compound, and a layer of metal and / or metal compound in contact with the resin layer A, wherein the layer of metal and / or metal compound is formed by any of vacuum deposition, sputtering, and plating.

10. An electric storage element comprising the current collector according to claim 1 or 2.

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