A composite current collector membrane and its preparation method

Abstract

This invention provides a composite current collector membrane and its preparation method, relating to the field of batteries. The composite current collector membrane and its preparation method include a second metal layer, a thin film layer, and a coating layer; the coating layer is located on both sides of the thin film layer, and the second metal layer is connected to the thin film layer through the coating layer. This method eliminates the need for magnetron sputtering in the preparation of the composite current collector, reducing the heat generated by magnetron sputtering that could cause deformation and perforation of the polymer film; it also improves the formation efficiency. The metal layer, thickened by water plating or chemical plating, contains a large amount of surfactants. These surfactants are approximately one micrometer in size. During long-term immersion of the metal in the electrolyte, these surfactants dissolve and are removed from the metal layer. Heat treatment removes the surfactant residue, improving the electrolyte resistance of the metal layer. Removing surfactants introduced during water plating or chemical plating improves the conductivity of the composite current collector, as well as the adhesion between the polymer film and the metal layer, or the adhesion between the negative electrode material and metallic copper.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a composite current collector membrane and its preparation method. Background Technology

[0002] Currently, current collectors are one of the most important components in lithium-ion batteries. Their role is twofold: firstly, to carry the active materials of both the positive and negative electrodes; and secondly, to collect electrons generated by the electrochemical reaction and conduct them to the external circuit, thus converting chemical energy into electrical energy. An ideal current collector should possess high conductivity, high stability, high strength, flexibility, and thinness. In lithium-ion batteries, the negative electrode current collector is copper foil, and the positive electrode current collector is aluminum foil. With the development of lithium battery technology, high energy density, lightweight design, and flexibility have become increasingly important. Reducing the thickness of the copper / aluminum foil (the total mass of the positive and negative electrode current collectors accounts for approximately 14%-18% of the total battery mass) can achieve lightweighting, increased energy density, and reduced costs in lithium-ion batteries. However, due to limitations in manufacturing technology, it is difficult to further reduce the thickness of the copper / aluminum foil (currently, copper foil can be mass-produced down to 4.5μm, and aluminum foil down to 8μm). Furthermore, thinning the copper / aluminum foil reduces its mechanical strength, leading to decreased processing performance.

[0003] Composite current collectors have a "sandwich" structure, with an inner polymer layer (such as PET, PP, or PI) and two outer conductive metal layers (such as Al or Cu). Currently, industrially produced composite current collectors using copper foil employ 4.5µm OPP (polypropylene) as the substrate. A 50nm copper layer is first magnetron sputtered onto both sides of the substrate, followed by electroplating to thicken the copper layer to approximately 1µm. Composite aluminum foil typically uses 6µm PET (polyethylene terephthalate) as the substrate, with a 1µm aluminum layer vapor-deposited on both sides. The advantages of composite current collectors lie in their high energy density and good cycle life, while also providing sufficient overcharge protection, stable high-current discharge capability, and excellent safety performance. They can be widely used in high-performance battery fields such as solar cells and lithium-ion batteries. Compared to traditional aluminum or copper foil, composite current collectors can reduce battery costs, improve energy density, and enhance safety performance, thus being considered one of the best solutions for achieving high-energy-density batteries. Metal layers used as current collectors in lithium-ion batteries exhibit poor toughness, mechanical properties, and other mechanical characteristics during use. Metal layers, as current collectors in lithium-ion batteries, are particularly prone to short-circuit related problems, which can sometimes lead to uncontrolled (runaway) combustion and fire as described above. Therefore, the ability to implement appropriate measures to prevent short-circuit-related runaway events is crucial. Using composite current collectors allows for further reductions in current collector thickness, weight, and cost.

[0004] However, most current current collectors that include polymer layers are prepared by vacuum evaporation using expensive vacuum deposition magnetron sputtering equipment, or by magnetron sputtering followed by water plating. The composite current collectors prepared by these methods have a loose surface structure with poor density and uniformity, resulting in a high sheet resistance. When used in lithium-ion batteries, this increases the internal resistance of the battery and degrades the electrochemical performance of the lithium-ion battery. In addition, vacuum evaporation requires a relatively thick polymer layer in the middle of the current collector before aluminum foil can be deposited on the polymer surface. The resulting current collector is relatively thick, which is not conducive to achieving a high energy density in the battery.

[0005] The one-step vacuum copper plating method for preparing composite current collectors results in a metal layer on the thin film surface existing in the form of copper particles. This leads to a loose surface structure with poor density and uniformity. The high copper plating temperature easily causes thermal deformation, perforation, and breakage of the thinner central layer, requiring repeated plating processes, which severely impacts the plating speed and reduces production efficiency. The two-step method for preparing composite copper foil current collectors, using magnetron sputtering, suffers from some of the same problems as the one-step method. To maintain the properties of the prepared metal layer, such as brightness and smoothness, the copper plating solution in the two-step water plating method contains a large amount of surfactants. These surfactants become part of the metal layer along with the deposited metal. A metal layer containing a large amount of surfactants can easily lead to metal dissolution during electrolysis in the electrolyte, affecting the long-term stability of the metal composite current collector. Simultaneously, the surfactants in the metal layer affect the adhesion of the negative electrode material to the metal.

[0006] Currently, the method involves first magnetron sputtering a thin conductive metal layer onto the polymer film to make it conductive, followed by water plating to thicken it. However, magnetron sputtering of polymer films requires high temperatures, the polymer film is easily deformed, the thickness of a single deposition is low, and multiple depositions are required, resulting in low efficiency, poor yield, and high cost. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] To address the shortcomings of existing technologies, this invention provides a composite current collector film and its preparation method. It solves the problems of existing methods for preparing composite current collectors, which require magnetron sputtering, which easily generates heat leading to polymer film deformation and perforation, resulting in low formation efficiency, high consumption, and poor electrolytic resistance of the conductive metal layer. This invention also solves the problem of the presence of organic components, such as surfactants and cellulose, in the metal layer prepared by water plating or chemical plating, thereby improving the performance of the metal layer.

[0009] (II) Technical Solution

[0010] To achieve the above objectives, the present invention provides the following technical solution: According to one aspect of the present invention, a method for preparing a composite current collector membrane is provided. The composite current collector membrane includes a second metal layer, a thin film layer, and a coating layer. The coating layer is located on both sides of the thin film layer. The second metal layer is connected to the thin film layer through the coating layer. The second metal layer is copper, nickel, zinc, or an alloy thereof. The thickness of the thin film layer is 2-12 micrometers. The thin film layer is a PET, nylon, polyimide, PP, PE, polysulfone, or polyetheretherketone film. The specific preparation steps are as follows:

[0011] S1: Directly deposit metal on one or both sides of the first metal layer, using either water plating or chemical plating. The first metal layer is made of aluminum foil, zinc foil, nickel foil, magnesium foil, copper foil, or tin. The thickness of the first metal layer is 2-36 micrometers. Once the metal plating reaches a certain thickness, stop plating to obtain the second metal layer, which has a thickness of 0.5-2 micrometers. Then, wash and dry the second metal layer for later use.

[0012] S2: The composite metal layer obtained in S1 is subjected to high-temperature heat treatment at 300-800 degrees Celsius to reduce the adhesion between the first metal layer and the second metal layer, while removing the organic surfactant in the second metal layer, and cleaning and drying the surface of the composite metal layer.

[0013] S3: Coat both sides of the film layer with adhesive, dry it, and hot-press it with one side of the second metal layer to form a composite. The adhesive is a carboxylic acid modified polyolefin, ethylene acrylate copolymer or acrylic acid-acrylonitrile copolymer resin.

[0014] S4: Use an acidic or alkaline solution that can react with the first metal layer to remove the first metal layer, and then wash and dry it for later use. The alkali is one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide, and the acid is one or more of sulfuric acid, hydrochloric acid, nitric acid, acetic acid, lactic acid, and oxalic acid.

[0015] S5: Passivate the other side of the second metal layer to obtain the composite current collector membrane described in this invention.

[0016] Preferably, a conductive thin film can be used to replace the first metal layer, and the specific steps are as follows:

[0017] B1: Perform single-sided metal plating on the conductive thin film layer. Once the metal plating layer reaches a certain thickness, stop the metal plating, then wash with water, dry, and passivate for later use.

[0018] B2: Coat both sides of the film with adhesive, dry it, and then hot-press it with the metal surface of B1 to form a composite.

[0019] B3: Removing the conductive film, washing with water, drying, and passivation treatment can also yield a composite current collector.

[0020] According to another aspect of the present invention, a method for preparing a composite current collector membrane is also provided. The composite current collector membrane includes a second metal layer, a thin film layer, and an adhesive layer. The adhesive layer is located on both sides of the thin film layer. The second metal layer is connected to the thin film layer through the adhesive layer. The thickness of the second metal layer is 0.3-3 micrometers, and the second metal layer is copper, nickel, zinc, or an alloy thereof. The thickness of the thin film layer is 2-12 micrometers, and the thin film layer is a PET, nylon, polyimide, PP, PE, polysulfone, or polyetheretherketone film. The specific steps are as follows:

[0021] A1: A protective layer is coated on the surface of the first metal layer. Metal is then plated by water plating or chemical plating. Once the metal plating reaches a certain thickness, the plating is stopped to obtain the second metal layer. The second metal layer is then washed with water and dried for later use. The protective layer is an interface layer composed of one or more of the following: release agent, polymer, slurry formed by polymer and conductive particles, zinc plating, nickel plating, nitrogen-containing organic compound, sulfur-containing organic compound, and carboxylic acid. The dry film thickness of the protective layer is 20 nanometers to 2 micrometers.

[0022] A2: The composite metal layer obtained in A1 is subjected to high-temperature heat treatment. The protective layer is degraded or carbonized by high temperature, which reduces the adhesion between the second metal layer and the first metal layer. At the same time, the organic surfactant in the second metal layer is removed. After the treatment is completed, the layer is cooled, cleaned, and dried. The second metal layer is then passivated and ready for use.

[0023] A3: Coat both sides of the thin film layer with adhesive, dry it, and then hot-press it with the second metal layer of A2 to form a composite;

[0024] A4: Peel the second metal layer from the adhesive film, remove the first metal layer, clean, dry, and passivate to obtain the composite current collector membrane described in this invention.

[0025] (III) Beneficial Effects

[0026] This invention provides a composite current collector membrane and its preparation method. It has the following beneficial effects:

[0027] The high-temperature processing technology used in this invention replaces the existing polymer thin film magnetron sputtering process, eliminating the need to prepare composite current collectors through magnetron sputtering, and reducing the deformation and perforation of polymer films caused by the heat generated by magnetron sputtering.

[0028] Improve generation efficiency; furthermore, the metal layer thickened by water plating or chemical plating contains a large amount of surfactants. These surfactants are about one micrometer in size. During long-term immersion in the electrolyte, the metal layer dissolves in the electrolyte and becomes visible. Heat treatment can reduce surfactant residue and improve the electrolytic resistance of the metal layer.

[0029] The high-temperature treatment process can remove surfactants introduced during water plating or chemical treatment, improve the conductivity of the composite current collector, as well as the adhesion between the polymer film and the metal layer, or the adhesion between the negative electrode material and the metallic copper. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of a composite current collector membrane in one embodiment of the present invention;

[0031] Figure 2 This is a flowchart illustrating a method for preparing a composite current collector membrane according to one embodiment of the present invention;

[0032] Figure 3 This is a flowchart illustrating a method for preparing a composite current collector membrane according to another embodiment of the present invention.

[0033] Among them, 2 is the second metal layer; 3 is the thin film layer; and 4 is the adhesive layer. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1:

[0036] Referring to the accompanying drawings, embodiments of the present invention provide a composite current collector membrane and its preparation method, comprising a second metal layer 2, a thin film layer 3, and a coating layer 4;

[0037] The adhesive layer 4 is distributed on both sides of the thin film layer 3;

[0038] Furthermore, the first metal layer is aluminum foil, zinc foil, nickel foil, magnesium foil, tin, or copper foil;

[0039] Preferably, the thickness of the first metal layer is 2-36 micrometers, and the first metal layer can be aluminum foil, zinc foil, nickel foil, magnesium foil, tin, copper foil or a metal alloy layer of two or more of them.

[0040] Preferably, the thickness of the second metal layer 2 is 0.3-3 micrometers, more preferably 0.5-2 micrometers, and the second metal layer 2 is copper, nickel, zinc or their alloy, and the second metal layer 2 is coated on the first metal layer by either water plating or chemical plating.

[0041] Preferably, the thickness of the thin film layer 3 is 2-12 micrometers, and the thin film layer 3 is a commonly used film such as PET, nylon, polyimide, PP, PE, polysulfone or polyetheretherketone;

[0042] Preferably, the adhesive layer 4 is a polyurethane prepared from carboxylic acid modified polyolefin, ethylene acrylate copolymer, acrylic acid-acrylonitrile copolymer resin, nitrile rubber, hydrogenated nitrile rubber, or hydroxyl-terminated butadiene rubber. It can be water-based, solvent-based, or a solid resin. The thickness of the adhesive layer 4 is 20 nanometers to 2 micrometers, and the thickness of the second metal layer 2 is 0.3 to 3 micrometers, preferably 0.5 to 2 micrometers. The protective layer is an interface layer composed of one or more of the following: release agent, polymer, nitrogen-containing organic compound, sulfur-containing organic compound, and carboxylic acid; or a slurry formed by conductive polymer and conductive particles. The thickness of the adhesive layer 4 is 20 nanometers to 2 micrometers, and the thickness of the second metal layer 2 is 0.3 to 3 micrometers, preferably 0.5 to 2 micrometers. The second metal layer 2 is copper, nickel, zinc, or an alloy thereof, and is coated onto the first metal layer by either water plating or chemical plating.

[0043] Example 2:

[0044] A method for preparing a composite current collector membrane includes the following steps:

[0045] Step 1: First, clean the 6-micron thick aluminum foil with acetone solvent, air dry it, and then clean it again with 0.1 mol sodium carbonate solution for 10 minutes. After cleaning, zinc is deposited on the surface to obtain aluminum foil with zinc deposited on the surface.

[0046] Step 2: Place the passivated aluminum into an electrolyte solution composed of sulfuric acid (100 g / L), copper sulfate pentahydrate (280 g / L), hydroxyethyl cellulose (70 mg / L), polyethyleneimine (20 mg / L), and sodium 3-mercapto-1-propanesulfonate for electroplating.

[0047] Step 3: Electrolysis was performed at an electrolytic current density of 35 A / dm² and an electrolyte temperature of 40°C to obtain a carrier copper foil with a thickness of 0.5 micrometers, which was then wound up. The carrier copper foil was placed in a muffle furnace, purged with nitrogen, and treated at 300°C for 60 minutes, followed by annealing and cooling.

[0048] Step 4: Coat both sides of a 4.5-micron thick PET sheet with TOYO-TACPMA adhesive, with a dry adhesive thickness of 0.5 microns;

[0049] Step 5: Hot-press the PET coated with adhesive to the carrier copper foil at 110°C and 0.3MPa for 3-5 seconds;

[0050] Step 6: Immerse the composite membrane in a 10% sodium hydroxide aqueous solution for 60 minutes to dissolve the aluminum foil. After dissolution, passivate the copper layer to obtain the composite copper foil current collector.

[0051] Example 3: Following the method in Example 2, except that the thickness of the copper foil in the carrier copper foil is 1 micrometer.

[0052] Example 4: Following the method in Example 2, except that the thickness of the copper foil in the carrier copper foil is 2 micrometers.

[0053] Example 5: Following the method in Example 3, except that the carrier copper foil is placed in a muffle furnace, filled with nitrogen, treated at 500°C for 60 minutes, annealed, and cooled.

[0054] Example 6: The method in Example 3 is followed, except that the aluminum foil is replaced with nickel foil, nitrogen gas is introduced, the 10% sodium hydroxide aqueous solution is replaced with a 10% hydrochloric acid solution, the temperature is treated at 800 degrees Celsius for 1 minute, annealed, and then cooled.

[0055] Example 7:

[0056] A method for preparing a composite current collector membrane includes the following steps:

[0057] Step 1: First, clean the 6-micron thick aluminum foil with acetone solvent, air dry it, and then clean it again with 0.1 mol sodium carbonate solution for 10 min. After cleaning, coat the aluminum foil with a conductive water-based polyester polyurethane graphene coating with a dry adhesive thickness of 1 micron to obtain coated aluminum foil.

[0058] Step 2: The coated aluminum foil is placed in an electrolyte solution consisting of sulfuric acid (100 g / L), copper sulfate pentahydrate (280 g / L), hydroxyethyl cellulose (70 mg / L), polyethyleneimine (20 mg / L), and sodium 3-mercapto-1-propanesulfonate for electroplating.

[0059] Step 3: Electrolysis was performed at an electrolytic current density of 35 A / dm² and an electrolyte temperature of 40°C to obtain a carrier copper foil with a thickness of 0.5 micrometers, which was then wound up. The carrier copper foil was placed in a muffle furnace, purged with nitrogen, and treated at 500°C for 2 minutes, followed by annealing and cooling.

[0060] Step 4: Coat both sides of a 4.5-micron thick PET sheet with TOYO-TACPMA adhesive, with a dry adhesive thickness of 0.5 microns.

[0061] Step 5: Apply adhesive-coated PET and carrier copper foil to a hot press at 110°C and 0.3MPa for 3-5 seconds, remove aluminum foil, clean, passivate copper foil, and obtain composite current collector.

[0062] Example 8:

[0063] A method for preparing a composite current collector membrane includes the following steps:

[0064] Step 1: First, mix water-based polyester and graphene solid-solid in a 1:1 ratio, coat the mixture onto a 36-micron PET release film, and obtain a conductive polyester film with a dry film thickness of 12 microns.

[0065] Step 2: Electroplating is performed by immersing the conductive polyester film in an electrolyte solution composed of sulfuric acid (100 g / L), copper sulfate pentahydrate (280 g / L), hydroxyethyl cellulose (70 mg / L), polyethyleneimine (20 mg / L), and sodium 3-mercapto-1-propanesulfonate.

[0066] Step 3: Electrolysis was performed at an electrolytic current density of 35 A / dm² and an electrolyte temperature of 40°C to obtain a carrier copper foil with a thickness of 1 micrometer. The release film was removed, and the foil was wound up. The carrier copper foil was placed in a muffle furnace, purged with nitrogen, and treated at 500°C for 2 minutes, followed by annealing and cooling.

[0067] Step 4: Coat both sides of a 4.5-micron thick PET sheet with TOYO-TACPMA adhesive, with a dry adhesive thickness of 0.5 microns. Then, hot-press the adhesive-coated PET sheet to the carrier copper foil at 110°C and 0.3 MPa for 3-5 seconds.

[0068] Step 5: Dissolve the conductive polyester film in a 10% sodium hydroxide aqueous solution for 60 minutes. After passivation treatment of the copper foil, a composite copper foil current collector is obtained.

[0069] Example 9:

[0070] A method for preparing a composite current collector membrane includes the following steps:

[0071] Step 1: First, clean the 6-micron thick aluminum foil with acetone solvent, air dry it, and then clean it again with 0.1 mol sodium carbonate solution for 10 min. After cleaning, coat the aluminum foil with a conductive water-based polyester polyurethane graphene coating with a dry adhesive thickness of 1 micron to obtain coated aluminum foil.

[0072] Step 2: Placing the coated aluminum foil into an electrolyte solution consisting of sulfuric acid (100 g / L), copper sulfate pentahydrate (280 g / L), hydroxyethyl cellulose (70 mg / L), polyethyleneimine (20 mg / L), and sodium 3-mercapto-1-propanesulfonate for electroplating.

[0073] Step 3: Electrolysis was performed at an electrolytic current density of 35 A / dm² and an electrolyte temperature of 40°C to obtain a carrier copper foil with a thickness of 0.5 micrometers, which was then wound up. The carrier copper foil was placed in a muffle furnace, purged with nitrogen, and treated at 500°C for 2 minutes, followed by annealing and cooling.

[0074] Step 4: Continue chemical copper plating as described in Step 3. The copper ion concentration is 10 g / L, N,N,N,N'-tetra(2-hydroxypropyl)ethylenediamine is 20 g / L, citric acid is 20 g / L, polyethylene glycol is 50 mg / L, sodium hypophosphite is 20 g / L, glyoxalic acid is 5 g / L, sodium borohydride is 5 g / L, etc. The plating was carried out at room temperature and pH 10.5, with a copper plating thickness of 0.2 micrometers, followed by heat treatment at 400℃ for 10 minutes.

[0075] Step 5: Coat both sides of a 4.5-micron thick PET sheet with TOYO-TACPMA adhesive, with a dry adhesive thickness of 0.5 microns;

[0076] Step 6: Apply adhesive-coated PET and carrier copper foil to a hot press at 110°C and 0.3MPa for 3-5 seconds, remove aluminum foil, clean, passivate, and obtain composite current collector.

[0077] Comparative Example 1

[0078] A method for preparing a composite current collector membrane includes the following steps:

[0079] Step 1: First, a PET film with a thickness of 4.5 micrometers is deposited with nickel (5 micrometers), chromium (5 micrometers), and copper (20 micrometers) by magnetron sputtering.

[0080] Step 2: The PET film with a thickness of 4.5 micrometers is thickened to 1 micrometer by chemical copper plating, and then passivated.

[0081] Comparative Example 2

[0082] The method of Example 3 differs from that of Example 3 in that the carrier copper foil is not subjected to heat treatment.

[0083] Comparative Example 3

[0084] The method of Example 3 differs from that of Example 3 in that the carrier copper foil is heat-treated at 200°C.

[0085] Comparative Example 4

[0086] First, a PET film with a thickness of 4.5 micrometers is deposited with nickel (5 micrometers), chromium (5 micrometers), and copper (1 micrometer) by magnetron sputtering.

[0087] To further illustrate the performance of the composite current collectors prepared using the methods given in different embodiments and comparative examples, Table 1 is provided:

[0088] Table 1. Copper dissolution phenomenon after immersion in electrolyte:

[0089] Examples 1-8 and Comparative Examples 1-4 show that copper treated at high temperatures has better electrolyte resistance than traditional magnetron sputtering, water-based copper plating, or vacuum sputtering copper plating. It is less prone to large-scale copper dissolution in the electrolyte and is more resistant to electrolyte.

[0090] Table 2 Electrolyte Immersion Sheet Resistance

[0091] Examples 1-8 and Comparative Examples 1-4 show that copper treated at high temperatures has a more stable sheet resistance in the long term and is more resistant to electrolytes. The higher the treatment temperature of the copper, the better its resistance to electrolytes.

[0092] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite current collector membrane, characterized in that, The composite current collector membrane includes a second metal layer, a thin film layer, and an adhesive layer. The adhesive layer is located on both sides of the thin film layer. The second metal layer is connected to the thin film layer through the adhesive layer. The second metal layer is copper, nickel, zinc, or an alloy thereof. The thickness of the thin film layer is 2-12 micrometers. The thin film layer is made of PET, nylon, polyimide, PP, PE, polysulfone, or polyetheretherketone film. The specific preparation steps are as follows: S1: Directly deposit metal on one or both sides of the first metal layer, using either water plating or chemical plating. The first metal layer is made of aluminum foil, zinc foil, nickel foil, magnesium foil, copper foil, or tin. The thickness of the first metal layer is 2-36 micrometers. Once the metal plating reaches a certain thickness, stop plating to obtain the second metal layer, which has a thickness of 0.5-2 micrometers. Then, wash and dry the second metal layer for later use. S2: The composite metal layer obtained in S1 is subjected to high-temperature heat treatment at 300-800 degrees Celsius to reduce the adhesion between the first metal layer and the second metal layer, while removing the organic surfactant in the second metal layer, and cleaning and drying the surface of the composite metal layer. S3: Coat both sides of the film layer with adhesive, dry it, and hot-press it with one side of the second metal layer to form a composite. The adhesive is a carboxylic acid modified polyolefin, ethylene acrylate copolymer or acrylic acid-acrylonitrile copolymer resin. S4: Use an acidic or alkaline solution that can react with the first metal layer to remove the first metal layer, and then wash and dry it for later use. The alkali is one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide, and the acid is one or more of sulfuric acid, hydrochloric acid, nitric acid, acetic acid, lactic acid, and oxalic acid. S5: Passivate the other side of the second metal layer to obtain the composite current collector film.

2. The method for preparing a composite current collector membrane according to claim 1, characterized in that: The first metal layer is further replaced by a conductive thin film, and the specific steps are as follows: B1: Perform single-sided metal plating on the conductive thin film layer. Once the metal plating layer reaches a certain thickness, stop the metal plating, then wash with water, dry, and passivate for later use. B2: Coat both sides of the thin film layer with adhesive, dry it, and then hot-press it with the metal surface of B1 to form a composite. B3: Remove the conductive film, wash with water, dry, and passivate to obtain a composite current collector membrane.

3. A method for preparing a composite current collector membrane, characterized in that, The composite current collector membrane includes a second metal layer, a thin film layer, and an adhesive layer. The adhesive layer is located on both sides of the thin film layer. The second metal layer is connected to the thin film layer through the adhesive layer. The thickness of the second metal layer is 0.3-3 micrometers, and the second metal layer is copper, nickel, zinc, or their alloy. The thickness of the thin film layer is 2-12 micrometers, and the thin film layer is a PET, nylon, polyimide, PP, PE, polysulfone, or polyetheretherketone film. The specific preparation steps are as follows: A1: A protective layer is coated on the surface of the first metal layer. Metal is then plated by water plating or chemical plating. Once the metal plating reaches a certain thickness, the plating is stopped to obtain the second metal layer. The second metal layer is then washed with water and dried for later use. The protective layer is an interface layer composed of one or more of the following: release agent, polymer, slurry formed by polymer and conductive particles, zinc plating, nickel plating, nitrogen-containing organic compound, sulfur-containing organic compound, and carboxylic acid. The dry film thickness of the protective layer is 20 nanometers to 2 micrometers. A2: The composite metal layer obtained in A1 is subjected to high-temperature heat treatment. The protective layer is degraded or carbonized by high temperature, which reduces the adhesion between the second metal layer and the first metal layer. At the same time, the organic surfactant in the second metal layer is removed. After the treatment is completed, the layer is cooled, cleaned, and dried. The second metal layer is then passivated and ready for use. A3: Coat both sides of the thin film layer with adhesive, dry it, and then hot-press it with the second metal layer of A2 to form a composite; A4: Peel the second metal layer from the adhesive film, remove the first metal layer, clean, dry, and passivate to obtain the composite current collector membrane.

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