Composite current collector with thickness capable of elastic deformation, preparation method thereof and lithium ion battery

Abstract

The application discloses a composite current collector with elastically deformable thickness, which comprises a five-layer composite structure of copper layer, polymer film layer, nanofiber film layer, polymer film layer and copper layer arranged in sequence, wherein the thickness of the copper layer is 0.2-5 mu m, the thickness of the polymer film layer is 0.2-10 mu m, the fiber diameter of the nanofiber film layer is 50-2000 nm, and the thickness of the nanofiber film layer is 5-100 mu m. The application further discloses a preparation method of the composite current collector with elastically deformable thickness. The application further discloses a lithium ion battery. The composite current collector has the characteristic of changing thickness with pressure, can effectively avoid performance degradation of high specific energy batteries caused by volume expansion of high capacity anodes, keep the pressure between the pole pieces relatively balanced, moderately keep good contact, and thus improve the volume expansion and cycle life attenuation of the battery in the charging and discharging process.

Description

Technical Field

[0001] This invention relates to the field of lithium batteries, and more particularly to a composite current collector with elastically deformable thickness, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the continuous advancement of modern technology, lithium-ion batteries have been widely used in numerous fields such as electronic products and electric vehicles due to their advantages such as high energy density, long cycle life, and no memory effect. However, as energy density requirements continue to increase, traditional lithium-ion batteries using graphite as the anode have reached their energy limit. Therefore, developing novel anodes with higher specific capacity (such as silicon-based anodes and lithium metal anodes) is particularly important. Consequently, high-specific-capacity anodes, as a type of anode material with higher energy density, have become one of the current research hotspots in the field of lithium-ion batteries.

[0003] However, both silicon-based and lithium metal anodes suffer from severe volume expansion during charge and discharge, affecting the cycle life and volume expansion of high-energy-density batteries using them as anodes. The problem of low cycle life due to volume expansion is prevalent in high-energy-density lithium-ion battery systems, severely limiting the commercialization of high-capacity silicon-based and lithium metal anode batteries.

[0004] To address these issues, existing technologies have improved the structural stability of the electrodes by modifying the binder or by designing silicon-carbon materials to provide a stable void structure and allow space for volume expansion. While these methods can improve the cycle life of the battery to some extent, they still cannot solve the problem of battery volume expansion. Summary of the Invention

[0005] The purpose of this invention is to provide a composite current collector with elastically deformable thickness.

[0006] The present invention also provides a method for preparing a composite current collector with elastic deformation of thickness.

[0007] The present invention also provides a lithium-ion battery.

[0008] The innovation of this invention lies in the fact that the composite current collector with elastically deformable thickness has the characteristic of changing its thickness with the pressure. This can effectively avoid the performance degradation of high-specific-energy batteries caused by volume expansion of high-capacity negative electrodes, especially the reduction in cycle life. By introducing a porous nanofiber membrane with variable thickness into the current collector, the composite current collector can be compressed under pressure, thereby reducing its thickness. When the pressure decreases, it can expand, avoiding drastic changes in internal battery pressure, maintaining a relatively balanced pressure between the electrodes, and maintaining good contact. This improves the battery volume expansion and cycle life degradation during charging and discharging.

[0009] To achieve the above-mentioned objectives, the technical solution of this invention is as follows:

[0010] A composite current collector with elastically deformable thickness comprises a five-layer composite structure consisting of a copper layer, a polymer film layer, a nanofiber film layer, another polymer film layer, and a copper layer arranged sequentially. The copper layer has a thickness of 0.2–5 μm, the polymer film layer has a thickness of 0.2–10 μm, the nanofiber film layer has a fiber diameter of 50–2000 nm, and the nanofiber film layer has a thickness of 5–100 μm.

[0011] Furthermore, the polymer film is polyimide, and the nanofiber film is organic nanofiber or organic / composite nanofiber.

[0012] Furthermore, the compressive deformation of the composite current collector is between 10% and 90%.

[0013] Furthermore, the organic nanofiber is at least one of polyacrylonitrile, polyimide, polyetherimide, PVDF, PTFE, and aramid; the organic / composite nanofiber is composed of at least one of polyacrylonitrile, polyimide, polyetherimide, PVDF, PTFE, and aramid combined with inorganic or metallic materials.

[0014] Furthermore, the polyimide in the polymer film contains at least one of hydroxyl and carboxyl groups.

[0015] Further, the polyimide in the polymer film is obtained by cyclizing polyamic acid, which is formed by the condensation polymerization of diacid anhydride and diamine; the diamine is composed of functional and non-functional diamines selected from those containing hydroxyl and carboxyl groups, wherein the functional diamine accounts for 5-80% of the total molar ratio of all diamines; the hydroxyl-containing functional diamine is one or more of 5,5'-diamino-2,2'-hydroxy-biphenyl (p-HAB), 2,2'-bis(3-amino-4-hydroxyphenyl)propane (BAHPP), and 3,3'-diamino-4,4'-dihydroxybiphenyl (DADHBP); the carboxyl-containing functional diamine is one or more of 3,5-diaminobenzoic acid (DABA) and 3,5-bis(4-aminophenoxy)benzoic acid (BAPBA).

[0016] A method for preparing a composite current collector with elastically deformable thickness includes the following steps:

[0017] (1) Synthesis of polyamide solution: Select any one or more of the dicarboxylic acid anhydrides, any one or more of the functional diamines, or any one or more of the non-functional diamines as raw materials, dissolve them in organic solvent A, and then polymerize them by condensation to form a polyimide precursor - polyamic acid solution. Then add silver precursor solution to obtain a polyamic acid solution containing silver salt. Dilute the polyamic acid solution containing silver salt with organic solvent A to the required solid content, coat it into a polyamic acid / silver salt film containing functional groups, and dry it for 1 to 24 hours to obtain a dried film.

[0018] (2) Polyamic acid spinning solution is obtained by condensation polymerization of diamine monomer and dianhydride monomer;

[0019] (3) The polyamic acid spinning solution is deposited on one surface of the dried film obtained in step (1) by electrospinning to obtain a composite film with nanofibers on one side.

[0020] (4) The two composite films obtained in step (3) are pressed together with the nanofiber membrane side, pressure is applied, and they are heated to 300-450°C in a reducing or inert atmosphere for cyclization and reduction. The temperature is maintained for 0.1-5h to obtain a composite structure of polymer film layer / nanofiber film layer / polymer film layer with silver on the surface, realizing the first surface metallization of polyimide film surface, forming a seed layer, and then cleaning with deionized water to obtain metallized composite film;

[0021] (5) After surface treatment of the silver-plated composite film obtained in step (4), it is immersed in a water-soluble copper salt solution and electro-reduced to achieve secondary surface copper plating of the film surface, and finally a five-layer composite structure of copper layer / polymer film layer / nanofiber film layer / polymer film layer / copper layer is formed.

[0022] Further, in step (2), the diamine monomer and dianhydride monomer are condensed and polymerized to obtain an initial solution. Inorganic particles or metal salts are added to the initial solution and stirred evenly to obtain polyamic acid spinning solution.

[0023] Further, the silver salt in step (1) is one or a mixture of two or more of silver nitrate, silver fluoride, silver fluoroborate, silver acetate, silver trifluoroacetylacetone, and silver acetylacetone; the aqueous copper salt in step (5) is copper chloride, copper sulfate, or copper nitrate; the molar ratio of Ag in the silver precursor solution to the molar ratio of the dicarboxylic acid anhydride synthesized from the polyamic acid solution in step (1) is 0.04–0.75:1, the required solid content is 5–20 wt%, and the thickness of the dried film is 1–100 μm; the pressure applied in step (4) The pressure is 0.01-5 MPa; the surface treatment in step (5) is carried out in three steps: organic solvent B → dilute acid activation → deionized water rinsing; the organic solvent B is at least one of acetone, ethanol, and methanol; the copper ion concentration in the aqueous copper salt is 150-300 g / L, and the electroreduction time is 1-50 min; the organic solvent A is one or more of N-dimethylformamide (DMF), N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), or N-methylpyrrolidone (NMP).

[0024] A lithium-ion battery comprising a composite current collector with elastically deformable thickness as the negative electrode current collector.

[0025] The beneficial effects of this invention are:

[0026] 1. The characteristic of the composite current collector thickness changing with pressure in this invention can effectively suppress battery volume expansion, thereby improving battery cycle life and other electrical performance.

[0027] 2. This invention uses a high-temperature resistant polymer to prepare the intermediate nanofiber membrane layer. Since the nanofiber membrane has high porosity and good elastic deformation, it is the main part of the thickness variation of the entire composite current collector, building a stable internal support structure and significantly improving the elastic deformation of the composite current collector. This makes it possible for the thickness of the entire composite current collector to be variable. The variable thickness structure of the composite current collector can prevent problems such as changes in electrode contact caused by volume changes in the cell during charging and discharging, thereby ensuring the integrity and stability of the battery structure and extending the cycle life of the battery. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will now be clearly and completely described in conjunction with the accompanying drawings.

[0030] Example 1: A composite current collector with elastic deformation of thickness, comprising a five-layer composite structure consisting of a copper layer, a polymer film layer, a nanofiber film layer, a polymer film layer, and a copper layer arranged sequentially. The copper layer has a thickness of 0.2 μm, the polymer film layer has a thickness of 0.2 μm, the nanofiber film layer has a fiber diameter of 50 nm, and the nanofiber film layer has a thickness of 5 μm.

[0031] The composite current collector has a compression deformation of 10%.

[0032] The polymer film layer is polyimide, the nanofiber film layer is organic nanofibers, and the organic nanofibers are polyacrylonitrile;

[0033] The polyimide in the polymer film contains at least one of hydroxyl and carboxyl groups.

[0034] The polyimide in the polymer film is obtained by cyclizing polyamic acid, which is formed by the condensation polymerization of diacid anhydride and diamine. The diamine is composed of functional and non-functional diamines selected from those containing hydroxyl and carboxyl groups, wherein the functional diamine accounts for 5% of all diamines in molar ratio. The hydroxyl-containing functional diamine is 5,5'-diamino-2,2'-hydroxy-bisphenyl (p-HAB), and the carboxyl-containing functional diamine is 3,5-diaminobenzoic acid (DABA).

[0035] Example 2: A composite current collector with elastic deformation of thickness, comprising a five-layer composite structure consisting of a copper layer, a polymer film layer, a nanofiber film layer, a polymer film layer, and a copper layer arranged sequentially. The copper layer has a thickness of 3 μm, the polymer film layer has a thickness of 5 μm, the nanofiber film layer has a fiber diameter of 1000 nm, and the nanofiber film layer has a thickness of 50 μm.

[0036] The composite current collector has a compression deformation of 50%.

[0037] The polymer film is made of polyimide, and the nanofiber film is made of organic nanofibers, which are made of polyimide.

[0038] The polyimide in the polymer film contains at least one of hydroxyl and carboxyl groups.

[0039] The polyimide in the polymer film is obtained by cyclizing polyamic acid, which is formed by the condensation polymerization of diacid anhydride and diamine. The diamine is composed of functional and non-functional diamines selected from those containing hydroxyl and carboxyl groups, wherein the functional diamine accounts for 40% of the total molar ratio of all diamines. The hydroxyl-containing functional diamine is 2,2'-bis(3-amino-4-hydroxyphenyl)propane (BAHPP), and the carboxyl-containing functional diamine is 3,5-bis(4-aminophenoxy)benzoic acid (BAPBA).

[0040] Example 3: A composite current collector with elastic deformation of thickness, comprising a five-layer composite structure consisting of a copper layer, a polymer film layer, a nanofiber film layer, a polymer film layer, and a copper layer arranged sequentially. The copper layer has a thickness of 5 μm, the polymer film layer has a thickness of 10 μm, the nanofiber film layer has a fiber diameter of 2000 nm, and the nanofiber film layer has a thickness of 100 μm.

[0041] The composite current collector has a compression deformation of 90%.

[0042] The polymer membrane is made of polyimide, and the nanofiber membrane is made of organic / composite nanofibers; the organic / composite nanofibers are composed of polyacrylonitrile and inorganic materials.

[0043] The polyimide in the polymer film contains at least one of hydroxyl and carboxyl groups.

[0044] The polyimide in the polymer film is obtained by cyclizing polyamic acid, which is formed by the condensation polymerization of diacid anhydride and diamine. The diamine is composed of functional and non-functional diamines selected from those containing hydroxyl and carboxyl groups, wherein the functional diamine accounts for 80% of the total molar ratio of all diamines. The hydroxyl-containing functional diamine is 3,3'-diamino-4,4'-dihydroxybiphenyl (DADHBP), and the carboxyl-containing functional diamine is 3,5-diaminobenzoic acid (DABA).

[0045] Example 4: Referring to Example 1, the nanofiber membrane is an organic nanofiber or an organic / composite nanofiber. The organic nanofiber is polyacrylonitrile, polyimide, polyetherimide, PVDF, PTFE, or aramid. The organic / composite nanofiber is composed of at least one of polyacrylonitrile, polyimide, polyetherimide, PVDF, PTFE, or aramid, combined with an inorganic material or a metallic material.

[0046] The hydroxyl-containing functional diamine is one or more of 5,5'-diamino-2,2'-hydroxy-biphenyl (p-HAB), 2,2'-bis(3-amino-4-hydroxyphenyl)propane (BAHPP), and 3,3'-diamino-4,4'-dihydroxybiphenyl (DADHBP); the carboxyl-containing functional diamine is one or more of 3,5-diaminobenzoic acid (DABA) and 3,5-bis(4-aminophenoxy)benzoic acid (BAPBA).

[0047] Example 5: A method for preparing a composite current collector with elastically deformable thickness, comprising the following steps:

[0048] (1) Synthesis of polyamide solution: The diacid anhydride, functional diamine, and non-functional diamine from Example 1 were selected as raw materials and dissolved in organic solvent A. After dissolution, they were polymerized by condensation to form a polyimide precursor—polyamic acid solution. Then, a silver precursor solution was added to obtain a polyamic acid solution containing silver salt, which was silver nitrate. The polyamic acid solution containing silver salt was diluted with organic solvent A to a solid content of 5 wt%, and coated into a polyamic acid / silver salt film containing functional groups. The film was dried for 1 hour to obtain a dried film. The molar ratio of Ag in the silver precursor solution to the molar ratio of diacid anhydride in the polyamic acid solution during synthesis was 0.04:1. The thickness of the dried film was 1 μm. Organic solvent A was N-dimethylformamide (DMF).

[0049] (2) Polyamic acid spinning solution is obtained by condensation polymerization of diamine monomer and dianhydride monomer;

[0050] (3) The polyamic acid spinning solution is deposited on one surface of the dried film obtained in step (1) by electrospinning to obtain a composite film with nanofibers on one side.

[0051] (4) The two composite films obtained in step (3) are pressed together with the nanofiber membrane side, and pressure is applied. The pressure is 0.01 MPa. They are heated to 300℃ in a reducing atmosphere for cyclization and reduction, and kept at the temperature for 0.1 h to obtain a composite structure of polymer film layer / nanofiber film layer / polymer film layer with silver on the surface. This achieves the first surface metallization of the polyimide film surface, forming a seed layer. Then, it is cleaned with deionized water to obtain the metallized composite film.

[0052] (5) After surface treatment of the silver-plated composite film obtained in step (4), it is immersed in a water-soluble copper salt solution and electro-reduced for 1 min to achieve secondary surface copper plating of the film surface, and finally form a five-layer composite structure of copper layer / polymer film layer / nanofiber film layer / polymer film layer / copper layer; the copper salt in the aqueous solution is copper chloride, and the copper ion concentration in the aqueous solution is 150 g / L. The surface treatment is carried out in three steps: organic solvent B → dilute acid activation → deionized water rinsing; organic solvent B is acetone.

[0053] Example 6: A method for preparing a composite current collector with elastically deformable thickness, comprising the following steps:

[0054] (1) Synthesis of polyamide solution: The diacid anhydride, functional diamine, and non-functional diamine from Example 2 were selected as raw materials. After being dissolved in organic solvent A, they were polymerized by condensation to form a polyimide precursor—polyamic acid solution. Then, a silver precursor solution was added to obtain a polyamic acid solution containing silver salt, which is silver fluoride. The polyamic acid solution containing silver salt was diluted with organic solvent A to a solid content of 10 wt%, and coated into a polyamic acid / silver salt film containing functional groups. The film was dried for 10 h to obtain a dried film. The molar ratio of Ag in the silver precursor solution to the molar ratio of diacid anhydride in the polyamic acid solution during synthesis was 0.3:1. The thickness of the dried film was 50 μm. Organic solvent A was N-dimethylacetamide (DMAc).

[0055] (2) The diamine monomer and dianhydride monomer are condensed and polymerized to obtain an initial solution. Inorganic particles are added to the initial solution and stirred evenly to obtain polyamic acid spinning solution.

[0056] (3) The polyamic acid spinning solution is deposited on one surface of the dried film obtained in step (1) by electrospinning to obtain a composite film with nanofibers on one side.

[0057] (4) The two composite films obtained in step (3) are pressed together with the side containing the nanofiber membrane, and pressure is applied at a pressure of 2 MPa; they are heated to 400℃ in an inert atmosphere for cyclization and reduction, and kept at the temperature for 2 hours to obtain a composite structure of polymer film layer / nanofiber film layer / polymer film layer with silver on the surface, realizing the first surface metallization of the polyimide film surface, forming a seed layer, and then cleaned with deionized water to obtain the metallized composite film;

[0058] (5) After surface treatment, the silver-plated composite film obtained in step (4) is immersed in a water-soluble copper salt solution and electro-reduced for 30 minutes to achieve secondary surface copper plating of the film surface, and finally form a five-layer composite structure of copper layer / polymer film layer / nanofiber film layer / polymer film layer / copper layer; the copper salt in the aqueous solution is copper sulfate, and the copper ion concentration in the aqueous solution is 200g / L. The surface treatment is carried out in three steps: organic solvent B → dilute acid activation → deionized water rinsing; organic solvent B is ethanol.

[0059] Example 7: A method for preparing a composite current collector with elastic thickness deformation, comprising the following steps:

[0060] (1) Synthesis of polyamide solution: The diacid anhydride, functional diamine, and non-functional diamine from Example 3 were selected as raw materials. After being dissolved in organic solvent A, they were polymerized by condensation to form a polyimide precursor - polyamic acid solution. Then, a silver precursor solution was added to obtain a polyamic acid solution containing silver salt, which was silver fluoroborate. The polyamic acid solution containing silver salt was diluted with organic solvent A to a solid content of 20 wt%, and coated into a polyamic acid / silver salt film containing functional groups. The film was dried for 24 h to obtain a dried film. The molar ratio of Ag in the silver precursor solution to the molar ratio of diacid anhydride in the polyamic acid solution during synthesis was 0.75:1. The thickness of the dried film was 100 μm. Organic solvent A was dimethyl sulfoxide (DMSO).

[0061] (2) The diamine monomer and the dianhydride monomer are condensed and polymerized to obtain an initial solution. A metal salt is added to the initial solution and stirred evenly to obtain a polyamic acid spinning solution.

[0062] (3) The polyamic acid spinning solution is deposited on one surface of the dried film obtained in step (1) by electrospinning to obtain a composite film with nanofibers on one side.

[0063] (4) The two composite films obtained in step (3) are pressed together with the side containing the nanofiber membrane, and pressure is applied at a pressure of 5 MPa. They are then heated to 450°C in a reducing atmosphere for cyclization and reduction, and kept at that temperature for 5 hours to obtain a composite structure of polymer film layer / nanofiber film layer / polymer film layer with silver on the surface. This achieves the first surface metallization of the polyimide film surface, forming a seed layer. The film is then cleaned with deionized water to obtain the metallized composite film.

[0064] (5) After surface treatment, the silver-plated composite film obtained in step (4) is immersed in a water-soluble copper salt solution and electro-reduced for 50 min to achieve secondary surface copper plating of the film surface, and finally form a five-layer composite structure of copper layer / polymer film layer / nanofiber film layer / polymer film layer / copper layer; the copper salt in the aqueous solution is copper nitrate, and the copper ion concentration in the aqueous solution is 300 g / L. The surface treatment is carried out in three steps: organic solvent B → dilute acid activation → deionized water rinsing; organic solvent B is methanol.

[0065] Example 8: Refer to Example 5,

[0066] The silver salt is one or a mixture of two or more of silver nitrate, silver fluoride, silver fluoroborate, silver acetate, silver trifluoroacetylacetone, and silver acetylacetone; organic solvent A is one or more of N-dimethylformamide (DMF), N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP); organic solvent B is at least one of acetone, ethanol, and methanol.

[0067] Example 9: A lithium-ion battery containing a composite current collector with elastically deformable thickness as the negative electrode current collector.

[0068] Comparative Example 1: Steps (2) and (3) of Example 5 were removed, and the dried film was directly pressed together and pressure was applied, while other conditions remained unchanged.

[0069] Comparative Example 2: Step (1) of Example 5 was performed without adding silver salt, while other conditions remained unchanged.

[0070] Comparative Example 3: The functional diamine in step (1) of Example 5 was not modified by adding a functional diamine containing a carboxyl group, but by adding a functional diamine containing a hydroxyl group, while keeping other conditions unchanged.

[0071] Using the negative electrode current collectors of Examples 5, 6, and 7, and Comparative Examples 1, 2, and 3, a 10-positive, 11-negative pouch cell was assembled. Electrolyte was injected, and the initial formation charge was performed at 0.1C, with a charging cutoff voltage of 4.3V. Then, constant voltage charging was applied until the current decreased to 0.05C. After standing for 30 minutes, a 0.1C discharge cutoff voltage of 2.5V was applied. After capacitation, the battery capacity was 3.8Ah. Cycling was performed at 1MPa pressure using 1C / 1C cycles, with a voltage range of 2.8–4.3V. The test temperature was room temperature. After 1000 cycles, the battery capacity retention rate and the thickness-direction expansion rate were measured.

[0072] The experimental results are shown in Table 1.

[0073] Table 1

[0074]

[0075]

[0076] The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a composite current collector with elastically deformable thickness, characterized in that, Includes the following steps: (1) Synthesis of polyamic acid solution: Select any one or more of the dicarboxylic acid anhydrides, any one or more of the functional diamines containing hydroxyl groups, any one or more of the functional diamines containing carboxyl groups, and any one or more of the non-functional diamines as raw materials. Dissolve them in organic solvent A and then polymerize them by condensation to form a polyamic acid solution that is a precursor of polyimide. Then add a silver precursor solution to obtain a polyamic acid solution containing silver salt. Dilute the polyamic acid solution containing silver salt with organic solvent A to the required solid content, coat it into a polyamic acid / silver salt film containing functional groups, and dry it for 1~24h to obtain a dried film. The molar ratio of functional diamines containing hydroxyl groups and functional diamines containing carboxyl groups to all diamines is 5~80%. The functional diamines containing hydroxyl groups are 5,5'-diamino-2,2'-hydroxy-diphenyl (p-HAB), 2,2'-bis(3-amino-4-hydroxyphenyl)propane (BAHPP), 3 The organic solvent A is one or more of 3'-diamino-4,4'-dihydroxybiphenyl (DADHBP); the functional diamine containing a carboxyl group is one or more of 3,5-diaminobenzoic acid (DABA) and 3,5-bis(4-aminophenoxy)benzoic acid (BAPBA); the organic solvent A is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) or N-methylpyrrolidone (NMP); (2) The polyamic acid spinning solution is obtained by condensation polymerization of diamine monomer and dianhydride monomer; (3) The polyamic acid spinning solution is deposited on one surface of the dried film obtained in step (1) by electrospinning to obtain a composite film with nanofibers on one side. (4) The two composite films obtained in step (3) are pressed together with the nanofiber membrane side, pressure is applied, and they are heated to 300~450℃ in a reducing or inert atmosphere for cyclization and reduction. The temperature is maintained for 0.1~5h to obtain a composite structure of polymer film layer / nanofiber film layer / polymer film layer with silver on the surface, realizing the first surface metallization of polyimide film surface, forming a seed layer, and then cleaning with deionized water to obtain metallized composite film; (5) After surface treatment of the silver-plated composite film obtained in step (4), it is immersed in a water-soluble copper salt solution and electro-reduced to achieve secondary surface copper plating of the film surface, and finally a five-layer composite structure of copper layer / polymer film layer / nanofiber film layer / polymer film layer / copper layer is formed.

2. The method for preparing the composite current collector with elastic thickness deformation according to claim 1, characterized in that, In step (2), the diamine monomer and dianhydride monomer are condensed and polymerized to obtain an initial solution. Inorganic particles or metal salts are added to the initial solution and stirred evenly to obtain polyamic acid spinning solution.

3. The method for preparing the composite current collector with elastic thickness deformation according to claim 1, characterized in that, The silver salt in step (1) is one or a mixture of two or more of silver nitrate, silver fluoride, silver fluoroborate, silver acetate, silver trifluoroacetylacetone, and silver acetylacetone; the aqueous copper salt in step (5) is copper chloride, copper sulfate, or copper nitrate; the molar ratio of Ag in the silver precursor solution and the molar ratio of the dicarboxylic acid anhydride synthesized in the polyamic acid solution in step (1) is 0.04~0.75:1, the required solid content is 5~20wt%, and the thickness of the dried film is 1~100μm; the pressure applied in step (4) is 0.01~5MPa; the surface treatment in step (5) is carried out in three steps: organic solvent B → dilute acid activation → deionized water rinsing; the organic solvent B is at least one of acetone, ethanol, and methanol; the copper ion concentration in the aqueous copper salt is 150~300g / L, and the electroreduction time is 1~50min.

4. A composite current collector with elastically deformable thickness prepared by the method for preparing a composite current collector with elastically deformable thickness as described in any one of claims 1 to 3, characterized in that, It comprises a five-layer composite structure consisting of a copper layer, a polymer film layer, a nanofiber film layer, a polymer film layer, and a copper layer arranged sequentially. The copper layer has a thickness of 0.2~5μm, the polymer film layer has a thickness of 0.2~10μm, the nanofiber film layer has a fiber diameter of 50~2000nm, and the nanofiber film layer has a thickness of 5~100μm.

5. The composite current collector with elastically deformable thickness according to claim 4, characterized in that, The polymer membrane is polyimide, and the nanofiber membrane is polyimide.

6. The composite current collector with elastically deformable thickness according to claim 4, characterized in that, The composite current collector has a compression deformation of 10-90%.

7. A lithium-ion battery, characterized in that, The composite current collector with elastically deformable thickness as described in claim 4 is used as the negative electrode current collector.

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