Composite copper current collector and preparation method therefor, and lithium ion battery

Abstract

A composite copper current collector and a preparation method therefor, and a lithium ion battery. The composite copper current collector comprises: a polymer base film; a bonding layer provided on at least one surface of the polymer base film; and a composite copper layer provided on the surface of the side of the bonding layer relatively distant from the polymer base film, wherein the composite copper layer is formed by alternately laminating amorphous copper layers and crystalline copper layers. By constructing a multi-layer structure in which the amorphous copper layers and the crystalline copper layers are alternately arranged, during a battery nail penetration test, the amorphous copper layers are prone to forming cracks that rapidly spread to the periphery, thereby causing extensive fracture and fragmentation of adjacent crystalline copper layers. Therefore, separation of the composite copper layer and a steel nail is achieved, the formation of a closed loop due to conduction between positive and negative current collectors and battery thermal runaway caused thereby are avoided, thereby improving the safety performance of the battery.

Description

Composite copper current collector, preparation method thereof, and lithium ion battery Technical Field

[0001] The present application belongs to the technical field of battery materials, and specifically relates to a composite copper current collector, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] At present, composite current collectors based on polymer films have received widespread attention and application in the new energy industry. The preparation of this composite current collector usually adopts the physical vapor deposition (PVD) method to deposit a layer of metal on a polymer film (such as polyester, polyolefin, etc.), thereby preparing a composite current collector with good conductivity. Compared with traditional current collectors, composite current collectors based on polymer films have the characteristics of low cost, light weight, and good internal insulation. These characteristics enable the composite current collector to reduce the cost of the battery and improve the energy density and safety of the battery when used in the battery.

[0003] Composite current collectors improve battery safety primarily through the insulation and flame retardancy of their base polymer membranes. However, while this improvement is modest, it's limited. Composite copper current collectors, in particular, offer limited improvements in battery safety due to the structure of the metal layer in current processes.

[0004] Therefore, in order to further improve the safety performance of batteries based on composite copper current collectors, it is necessary to develop a new composite copper current collector to promote the application and promotion of composite copper current collectors in batteries.

[0005] Summary of the Invention

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0007] In response to the shortcomings of the existing technology, the purpose of this application is to provide a composite copper current collector, a preparation method thereof, and a lithium-ion battery. This application constructs a multilayer structure with alternating amorphous copper layers and crystalline copper layers. During the battery needle penetration test, the amorphous copper layer is prone to cracking and quickly spreads to the surrounding area, thereby causing the adjacent crystalline copper layer to break over a large area and fragment. This allows the composite copper layer to be separated from the steel needle, avoiding the formation of a closed circuit by the positive and negative current collectors and the resulting thermal runaway of the battery, thereby improving the safety performance of the battery.

[0008] To achieve this goal, this application adopts the following technical solutions:

[0009] In a first aspect, the present application provides a composite copper current collector, comprising:

[0010] polymer-based films;

[0011] an adhesive layer disposed on at least one surface of the polymer base film;

[0012] The composite copper layer is arranged on the surface of the bonding layer on a side relatively far away from the polymer base film, and the composite copper layer is formed by alternately stacking amorphous copper layers and crystalline copper layers.

[0013] This application constructs a multilayer structure with alternating amorphous copper layers and crystalline copper layers. During the battery puncture test, the amorphous copper layer is prone to cracks and quickly spreads to the surrounding area, thereby causing the adjacent crystalline copper layer to break over a large area and fragment. This achieves separation of the composite copper layer from the steel needle, avoiding the formation of a closed circuit by the positive and negative current collectors and the resulting thermal runaway of the battery, thereby improving the safety performance of the battery.

[0014] In the present application, the role of the bonding layer is to enhance the bonding force between the polymer film and the composite copper layer.

[0015] As an optional technical solution of the present application, the side of the composite copper layer close to the bonding layer is an amorphous copper layer, and the side of the composite copper layer away from the bonding layer is a crystalline copper layer.

[0016] In this application, the side of the composite copper layer close to the bonding layer is defined as an amorphous copper layer, and the side away from the bonding layer is defined as a crystalline copper layer. The purpose of this design is to enhance the bonding force between the bonding layer and the copper layer, and the amorphous state is easily fused with the bonding layer.

[0017] In one embodiment, the amorphous copper layer consists of amorphous copper, and the crystalline copper layer consists of crystalline copper.

[0018] It should be noted that amorphous refers to the structure of some non-completely crystalline amorphous regions (non-crystalline regions) or the composition of some amorphous solids (non-crystals). Crystalline refers to the dominant form of solid objects in which atoms are arranged in a regular pattern.

[0019] In one embodiment, the number of layers of the amorphous copper layer and the crystalline copper layer is n, where n≥2, for example, 2, 4, 6, 8 or 10.

[0020] In one embodiment, 2≤n≤10.

[0021] In the present application, if n is too small, the effect of the prepared composite copper current collector on improving battery safety will be reduced; if n is too large, the efficiency of preparing the composite copper current collector will be too low.

[0022] As an optional technical solution of the present application, the thickness of the composite copper layer is 500 to 2000 nm, for example, it can be 500 nm, 1000 nm, 1500 nm or 2000 nm, and can further be 800 to 1200 nm.

[0023] In this application, if the composite copper layer is too thin, the conductivity is poor; if the composite copper layer is too thick, the prepared composite copper current collector is too thick and heavy, which is not conducive to improving the energy density of the battery. Considering both conductivity and energy density, the thickness can be further selected to be 800-1200nm.

[0024] In one embodiment, the thickness of the amorphous copper layer is 0-100 nm, and is not 0, for example, it can be 10 nm, 30 nm, 50 nm, 70 nm or 90 nm, and can further be 20-80 nm.

[0025] In this application, if the thickness of the amorphous copper layer is too thin, the preparation efficiency will be affected and the effect will not be obvious; if the thickness of the amorphous copper layer is too thick, the amorphous copper will be transformed into crystalline copper during the preparation process, which is not conducive to improving the safety performance of the battery, and too thick will affect the mechanical properties of the composite copper current collector, resulting in poor mechanical properties.

[0026] In one embodiment, the thickness of the crystalline copper layer is 0 to 300 nm, and is not 0, for example, it can be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm or 300 nm, and can further be 50 to 200 nm.

[0027] In this application, if the thickness of the crystalline copper layer is too thin, it will affect the preparation efficiency and increase the difficulty of preparation; if the thickness of the crystalline copper layer is too thick, the length of the columnar crystals in the layer will be too long, and the crack propagation during the needle puncture process will be hindered.

[0028] As an optional technical solution of the present application, the material of the polymer base film is any one or a combination of at least two of polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethylene (PE), polypropylene, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polystyrene (PS) or polyimide (PI).

[0029] In one embodiment, the polymer base film has a thickness of 1 to 10 μm, for example, 1 μm, 3 μm, 5 μm, 7 μm, or 9 μm.

[0030] In the present application, considering the application requirements of the composite copper current collector and the difficulty and cost of the preparation process, the thickness of the polymer base film can be further selected to be 1 to 10 μm.

[0031] In one embodiment, the material of the bonding layer includes any one or a combination of at least two of aluminum oxide, silicon oxide, titanium oxide, nickel, chromium, titanium, nickel-chromium alloy, nickel-chromium-copper alloy, silicon-aluminum alloy, polyacrylic acid, polyacrylate, polyacrylamide or polyurethane.

[0032] In one embodiment, the thickness of the bonding layer is 1 to 100 nm, for example, 1 nm, 3 nm, 5 nm, 7 nm, 9 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm.

[0033] In the present application, if the thickness of the adhesive layer is too thin, the improvement of the adhesive force of the composite copper current collector is not obvious; if the thickness of the adhesive layer is too thick, the adhesive force cannot be further improved and the production efficiency is affected.

[0034] As an optional technical solution of the present application, a protective layer is further provided on the surface of the composite copper layer along the side away from the polymer base film.

[0035] In the present application, the purpose of providing the protective layer is to prevent the composite copper layer from being chemically corroded or physically damaged.

[0036] In one embodiment, the material of the protective layer includes any one of nickel, chromium, nickel-chromium alloy, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper-chromium oxide, graphite, carbon black, carbon nano-quantum dots, carbon nanotubes, carbon nanofibers, graphene or graphene oxide, or a combination of at least two thereof.

[0037] In one embodiment, the thickness of the protective layer is 5 to 100 nm, for example, 5 nm, 10 nm, 30 nm, 50 nm, 70 nm or 90 nm, and can further be 20 to 80 nm.

[0038] In one embodiment, the thickness of the protective layer is less than or equal to one tenth of the thickness of the composite copper layer.

[0039] In a second aspect, the present application provides a method for preparing the composite copper current collector as described in the first aspect, the preparation method comprising the following steps:

[0040] An adhesive layer and a composite copper layer are sequentially prepared on at least one surface of a polymer base film, wherein the composite copper layer is prepared by alternately stacking an amorphous copper layer and a crystalline copper layer.

[0041] The preparation method provided in this application is simple and easy to implement and can be easily scaled up for production.

[0042] As an optional technical solution of the present application, the preparation method of the amorphous copper layer includes evaporation and / or magnetron sputtering.

[0043] In one embodiment, the specific process parameters of the vapor deposition method include: a heating evaporation temperature of 1400 to 1600°C, for example, 1400°C, 1500°C or 1600°C, etc., a coating vacuum degree of <0.1Pa, for example, 0.08Pa, 0.06Pa or 0.04Pa, etc., a coating main roller cooling temperature of -30 to -10°C, for example, -30°C, -20°C or -10°C, etc., a coating time of 0.1 to 10s, for example, 0.1s, 1s, 5s or 10s, etc.

[0044] In one embodiment, the specific process parameters of the magnetron sputtering method include: target power of 2 to 6 kW, for example, 2 kW, 4 kW or 6 kW, etc., the vacuum degree in the chamber during coating is ≤ 0.1 Pa, for example, 0.1 Pa, 0.08 Pa or 0.05 Pa, etc., the flow rate of the gas source is 10 to 200 mL / min, for example, 10 mL / min, 50 mL / min, 100 mL / min, 150 mL / min or 200 mL / min, etc., the coating time is 0.1 to 60 s, for example, 1 s, 5 s, 10 s, 30 s or 60 s, etc., the cooling temperature of the coating main roller is -30 to 0°C, for example, -30°C, -20°C, -10°C or 0°C, etc.

[0045] As an optional technical solution of the present application, the method for preparing the crystalline copper layer includes an electroplating method.

[0046] In one embodiment, in the electroplating method, the components of the electroplating solution include copper sulfate, sulfuric acid, hydrochloric acid, a brightener, a leveler, and a wetting agent.

[0047] In one embodiment, the concentration of the copper sulfate is 80 to 130 g / L, for example, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L or 130 g / L, the concentration of the sulfuric acid is 80 to 160 g / L, for example, 80 g / L, 100 g / L, 120 g / L, 140 g / L or 160 g / L, and the concentration of the chloride ion is 20 to 80 mg / L, for example, 20 mg / L, 40mg / L, 60mg / L or 80mg / L, etc., the concentration of the brightener is 5-20ppm, for example, 5ppm, 10ppm, 15ppm or 20ppm, etc., the concentration of the leveler is 1-5ppm, for example, 1ppm, 3ppm or 5ppm, etc., the concentration of the wetting agent is 20-200ppm, for example, 20ppm, 50ppm, 100ppm, 150ppm or 200ppm, etc.

[0048] In one embodiment, the brightener includes any one of sodium polydisulfide propane sulfonate, sodium 3-mercapto-1-propane sulfonate, or sodium N,N-dimethyldithiocarboxamide propane sulfonate, or a combination of at least two thereof.

[0049] In one embodiment, the leveler includes any one of N,N-diethylthiourea, 2-mercaptopyridine, or Janus Green, or a combination of at least two thereof.

[0050] In one embodiment, the wetting agent includes any one of polyethylene glycol, polypropylene glycol, or polyoxyethylene ether, or a combination of at least two thereof.

[0051] In one embodiment, the specific process parameters of the electroplating method include: an average cathode current density of 1 to 3 A / dm 2 , for example, it can be 1A / dm 2 , 2A / dm 2 or 3A / dm 2 The plating solution temperature is 15-35°C, for example, 15°C, 20°C, 25°C, 30°C or 35°C, and the plating time is 1-90s, for example, 1s, 10s, 30s, 60s or 90s.

[0052] As an optional technical solution of the present application, the preparation method comprises the following steps:

[0053] (1) preparing a polymer base film with a thickness of 1 to 10 μm by a melt-extrusion-biaxial stretching method;

[0054] (2) depositing a bonding layer with a thickness of 1 to 100 nm on each side of the polymer by magnetron sputtering, physical vapor deposition or coating to obtain a composite film having a bonding layer on the surface;

[0055] (3) alternately depositing an amorphous copper layer and a crystalline copper layer on both sides of the composite film, wherein the number of layers of the amorphous copper layer and the crystalline copper layer is ≥2, to obtain a composite film containing a composite copper layer and an adhesive layer;

[0056] Among them, the amorphous copper layer is prepared by magnetron sputtering, and the preparation process parameters include: using copper target as target material, target power of 2-6kW, vacuum degree in the chamber during coating ≤0.1Pa, gas flow rate of 10-200mL / min, coating time of 0.1-60s, and cooling temperature of the coating main roller of -30-0℃; the crystalline copper layer is prepared by electroplating, and the preparation process parameters include: average cathode current density of 1-3A / dm 2 , the plating solution temperature is 15-35°C, and the plating time is 1-90s;

[0057] (4) A protective layer with a thickness of 5 to 100 nm is deposited on both sides of the composite film containing the composite copper layer and the bonding layer by physical vapor deposition, chemical vapor deposition, in-situ forming or coating.

[0058] In a third aspect, the present application provides a lithium-ion battery, wherein the negative electrode of the lithium-ion battery comprises the composite copper current collector as described in the first aspect.

[0059] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to limited space and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0060] Compared with the prior art, this application has the following beneficial effects:

[0061] (1) The present application constructs a multilayer structure in which amorphous copper layers and crystalline copper layers are arranged alternately. During the battery puncture test, the amorphous copper layer is prone to cracks and quickly spreads to the surrounding area, thereby causing the adjacent crystalline copper layer to break over a large area and fragment. This allows the composite copper layer to be separated from the steel needle, avoiding the formation of a closed circuit by the positive and negative current collectors and the resulting thermal runaway of the battery, thereby improving the safety performance of the battery.

[0062] (2) The preparation method provided in this application is simple and easy to implement and can be easily scaled up for production.

[0063] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation to the technical solution of this article.

[0065] FIG1 is an X-ray diffraction pattern of a composite copper layer and an amorphous copper layer prepared in a specific embodiment of the present application. DETAILED DESCRIPTION

[0066] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0067] Example 1

[0068] This embodiment provides a composite copper current collector, comprising:

[0069] Polymer base film, made of PET, with a thickness of 4.5 μm;

[0070] The bonding layers provided on both surfaces of the polymer base film are made of nickel-chromium alloy, have a thickness of 5 nm on a single side, and include a first bonding layer and a second bonding layer;

[0071] a composite copper layer disposed on a surface of the bonding layer on a side relatively far from the polymer base film, having a single-side thickness of 750 nm and comprising a first composite copper layer and a second composite copper layer, wherein the composite copper layer is formed by alternating amorphous copper layers and crystalline copper layers, wherein the side of the composite copper layer close to the bonding layer is the amorphous copper layer, and the side of the composite copper layer away from the bonding layer is the crystalline copper layer, wherein the number of amorphous copper layers is 5, each layer having a thickness of 50 nm, and the number of crystalline copper layers is 5, each layer having a thickness of 100 nm;

[0072] The protective layer disposed on the surface of the composite copper layer on the side relatively far from the polymer base film is made of carbon nanotubes, has a single-side thickness of 12 nm, and includes a first protective layer and a second protective layer.

[0073] This embodiment also provides a method for preparing the composite copper current collector, which comprises the following steps:

[0074] (1) PET film was prepared by melt-extrusion-biaxial stretching method;

[0075] (2) placing the PET film in a magnetron sputtering machine, and depositing a bonding layer on each side of the PET film. The specific process conditions are: using a nickel-chromium target (purity: 99.99%) as the target material, a target power of 5.0 kW, an argon flow rate of 50 mL / min, a coating vacuum of 0.08 Pa, a coating time of 1 s, and a main roller temperature of 0° C. during the coating process, to obtain a PET composite film having a bonding layer on the surface;

[0076] (3) The PET composite film containing the bonding layer on the surface is placed in a magnetron sputtering machine, and amorphous copper layers and crystalline copper layers are alternately deposited on both sides of the composite film to obtain a PET film containing a composite copper layer and a bonding layer; wherein, ① the number of amorphous copper layers is 5, and the preparation process conditions of each layer are as follows: a copper target (purity: 99.99%) is used as the target material, the target power is 5 kW, the gas source is argon, the argon flow rate is 60 mL / min, the coating vacuum is 0.09 Pa, the coating time is 15 s, and the cooling temperature of the main roller during the coating process is -30°C; ② the number of crystalline copper layers is 5, and the preparation process conditions of each layer are as follows: the electroplating solution components include 100 g / L copper sulfate, 120 g / L sulfuric acid, 50 mg / L chloride ion, 10 ppm sodium polydisulfide dipropane sulfonate, 2 ppm N,N-diethylthiourea and 100 ppm polyoxyethylene ether, and the average cathode current density is 1.7 A / dm 2 , the plating solution temperature is 25℃, and the plating time is 30s;

[0077] (4) 1.5 g of carbon nanotubes were uniformly dispersed in 998.5 g of nitrogen methyl pyrrolidone (NMP) solution by ultrasonic dispersion to prepare a coating solution with a solid content of 0.15 wt.%, and then the coating solution was uniformly coated on the surface of the PET film containing the composite copper layer and the adhesive layer by a die coating process. Finally, the film was dried at 100° C. to obtain a protective layer with a thickness of 12 nm, thereby obtaining the composite copper current collector.

[0078] Furthermore, to demonstrate that the composite copper layer of this embodiment comprises a laminated structure of an amorphous copper layer and a crystalline copper layer, two samples were first prepared according to the preparation method of this embodiment: a layer of amorphous copper was deposited on the surface of a PET film according to the preparation method for amorphous copper in this embodiment, namely, Sample 1; and a layer of crystalline copper was deposited on the surface of Sample 1 according to the preparation method for crystalline copper in this embodiment, namely, Sample 2. The samples were then prepared according to the requirements of an X-ray diffractometer and placed in an X-ray diffractometer (Bruker D8 ADVANCE) using copper as the target, with a scanning speed of 2.0000 deg / min and a scanning range of 30° to 80°. The test results are shown in Figure 1. As can be seen from the figure, no diffraction peak of copper was found in the diffraction pattern of sample 1, while diffraction peaks of copper crystal plane orientations such as (111), (200), and (220) were found in sample 2. This shows that amorphous copper layers and crystalline copper layers can be prepared according to the preparation method of this embodiment, that is, the composite copper layer prepared in this embodiment is a stacked structure of amorphous copper layers and crystalline copper layers.

[0079] Example 2

[0080] The difference between this embodiment and Example 1 is that the thickness of the amorphous copper layer is 20 nm, and the preparation process conditions of each layer are: a copper target (purity: 99.99%) is used as the target material, the target power is 5 kW, the gas source is argon, the argon flow rate is 60 mL / min, the coating vacuum is 0.09 Pa, the coating time is 6 s, and the cooling temperature of the main roller during the coating process is -30°C.

[0081] The rest of the preparation methods and parameters remained the same as in Example 1.

[0082] Example 3

[0083] The difference between this embodiment and Example 1 is that the thickness of the amorphous copper layer is 80 nm, and the preparation process conditions of each layer are: a copper target (purity: 99.99%) is used as the target material, the target power is 5 kW, the gas source is argon, the argon flow rate is 60 mL / min, the coating vacuum is 0.09 Pa, the coating time is 24 s, and the cooling temperature of the main roller during the coating process is -30°C.

[0084] The rest of the preparation methods and parameters remained the same as in Example 1.

[0085] Example 4

[0086] The difference between this embodiment and Example 1 is that the thickness of the amorphous copper layer is 100 nm, and the preparation process conditions of each layer are: a copper target (purity: 99.99%) is used as the target material, the target power is 5 kW, the gas source is argon, the argon flow rate is 60 mL / min, the coating vacuum is 0.09 Pa, the coating time is 30 s, and the cooling temperature of the main roller during the coating process is -30°C.

[0087] The rest of the preparation methods and parameters remained the same as in Example 1.

[0088] Example 5

[0089] The difference between this embodiment and embodiment 1 is that the thickness of the crystalline copper layer is 50 nm. The preparation process conditions of each layer are as follows: the electroplating solution components include 100 g / L copper sulfate, 120 g / L sulfuric acid, 50 mg / L chloride ion, 10 ppm sodium polydisulfide dipropane sulfonate, 2 ppm N,N-diethylthiourea and 100 ppm polyoxyethylene ether, and the average cathode current density is 1.7 A / dm 2 , the plating solution temperature is 25℃, and the plating time is 15s;

[0090] The rest of the preparation methods and parameters remained the same as in Example 1.

[0091] Example 6

[0092] The difference between this embodiment and embodiment 1 is that the thickness of the crystalline copper layer is 200 nm. The preparation process conditions of each layer are as follows: the electroplating solution components include 100 g / L copper sulfate, 120 g / L sulfuric acid, 50 mg / L chloride ion, 10 ppm sodium polydisulfide dipropane sulfonate, 2 ppm N,N-diethylthiourea and 100 ppm polyoxyethylene ether, and the average cathode current density is 1.7 A / dm 2 , the plating solution temperature is 25℃, and the plating time is 60s;

[0093] The rest of the preparation methods and parameters remained the same as in Example 1.

[0094] Example 7

[0095] The difference between this embodiment and embodiment 1 is that the thickness of the crystalline copper layer is 300 nm. The preparation process conditions of each layer are as follows: the electroplating solution components include 100 g / L copper sulfate, 120 g / L sulfuric acid, 50 mg / L chloride ion, 10 ppm sodium polydisulfide dipropane sulfonate, 2 ppm N,N-diethylthiourea and 100 ppm polyoxyethylene ether, and the average cathode current density is 1.7 A / dm 2 , the plating solution temperature is 25℃, and the plating time is 90s;

[0096] The rest of the preparation methods and parameters remained the same as in Example 1.

[0097] Example 8

[0098] The difference between this embodiment and embodiment 7 is that the number of layers of the amorphous copper layer and the crystalline copper layer are both 2.

[0099] The rest of the preparation methods and parameters remained the same as in Example 7.

[0100] Example 9

[0101] The difference between this embodiment and embodiment 1 is that the number of layers of the amorphous copper layer and the crystalline copper layer are both 10.

[0102] The rest of the preparation methods and parameters remained the same as in Example 1.

[0103] Example 10

[0104] The difference between this embodiment and Example 1 is that the amorphous copper layer is prepared by evaporation, and the preparation process conditions of each layer are: copper wire (purity 99.99%) is used as the copper source, the heating evaporation temperature is 1500°C, the coating vacuum is 0.05 Pa, the cooling temperature of the coating main roller is -30°C, and the coating time is 1.5s.

[0105] The rest of the preparation methods and parameters remained the same as in Example 1.

[0106] Example 11

[0107] The difference between this embodiment and Example 1 is that the amorphous copper layer is prepared in two steps of magnetron sputtering and evaporation, and the preparation process conditions of each layer are as follows: ① Preparation of 20 nm amorphous copper by magnetron sputtering: a copper target (purity: 99.99%) is used as the target material, the target power is 5 kW, the gas source is argon, the argon flow rate is 60 mL / min, the coating vacuum is 0.09 Pa, the coating time is 6 s, and the temperature of the main roller during the coating process is -30°C; ② Preparation of 30 nm amorphous copper by evaporation: a copper wire (purity 99.99%) is used as the copper source, the heating evaporation temperature is 1500°C, the coating vacuum is 0.05 Pa, the coating main roller cooling temperature is -30°C, and the coating time is 0.9 s.

[0108] The rest of the preparation methods and parameters remained the same as in Example 1.

[0109] Example 12

[0110] The difference between this embodiment and embodiment 1 is that the number of layers of the amorphous copper layer and the crystalline copper layer is 1, and the thickness of the amorphous copper layer in the conductive layer is 100 nm, and the thickness of the crystalline copper layer is 300 nm. The preparation process conditions of the amorphous copper layer are as follows: a copper target (purity: 99.99%) is used as the target material, the target power is 5 kW, the gas source is argon gas, the argon gas flow rate is 60 mL / min, the coating vacuum is 0.09 Pa, the coating time is 30 s, and the cooling temperature of the main roller during the coating process is -30°C; the preparation process conditions of the crystalline copper layer are as follows: the electroplating solution composition includes 100 g / L copper sulfate, 120 g / L sulfuric acid, 50 mg / L chloride ion, 10 ppm sodium polydisulfide dipropane sulfonate, 2 ppm N,N-diethylthiourea and 100 ppm polyoxyethylene ether, the average cathode current density is 1.7 A / dm2, the plating solution temperature is 25°C, and the electroplating time is 90 s.

[0111] The rest of the preparation methods and parameters remained the same as in Example 1.

[0112] Example 13

[0113] The difference between this embodiment and Example 1 is that the thickness of the amorphous copper layer is 120 nm, and the preparation process conditions of each layer are: a copper target (purity: 99.99%) is used as the target material, the target power is 5 kW, the gas source is argon, the argon flow rate is 60 mL / min, the coating vacuum is 0.09 Pa, the coating time is 36 s, and the cooling temperature of the main roller during the coating process is -30°C.

[0114] The rest of the preparation methods and parameters remained the same as in Example 1.

[0115] Example 14

[0116] The difference between this embodiment and embodiment 1 is that the thickness of the crystalline copper layer is 320 nm. The preparation process conditions of each layer are as follows: the electroplating solution composition includes 100 g / L copper sulfate, 120 g / L sulfuric acid, 50 mg / L chloride ion, 10 ppm sodium polydisulfide propane sulfonate, 2 ppm N,N-diethylthiourea and 100 ppm polyoxyethylene ether, and the average cathode current density is 1.7 A / dm 2 , the bath temperature is 25°C, and the plating time is 96s;

[0117] The rest of the preparation methods and parameters remained the same as in Example 1.

[0118] Comparative Example 1

[0119] The difference between this comparative example and Example 1 is that the composite copper layer is a single-layer copper layer, and the specific preparation process is: using a copper target (purity: 99.99%) as the target material, the target power is 12 kW, the argon flow rate is 50 mL / min, the coating vacuum is 0.08 Pa, the coating time is 100 s, and the temperature of the main roller during the coating process is 2°C.

[0120] The rest of the preparation methods and parameters remained the same as in Example 1.

[0121] Performance Testing

[0122] (1) The composite copper current collectors prepared in the above examples and comparative examples were tested for tensile strength. The specific testing method included taking samples along the longitudinal direction of the prepared composite copper current collector and then performing a tensile strength test in accordance with the national standard GB / T1040.3-2006.

[0123] (2) The composite copper current collectors prepared in the above examples and comparative examples were assembled into lithium-ion batteries and safety performance tests were performed.

[0124] Battery assembly: For the positive electrode, the positive electrode current collector uses a traditional aluminum current collector (thickness is 13μm), and the positive electrode material uses LiNi 0.6 Mn 0.2 Co 0.2 O2 (NCM622); for the negative electrode: the negative electrode current collector adopts the composite copper current collector prepared in this application, and the negative electrode material adopts artificial graphite; for the diaphragm, a polyethylene diaphragm coated with alumina ceramic (thickness 25μm) is adopted; for the electrolyte, 1mol·L -1 A carbonate solution of LiPF6, wherein the carbonate solution is a mixture of propylene carbonate, ethylene carbonate and ethyl methyl carbonate, and the mass ratio of the three is 1:1:1; a lithium-ion battery is assembled using the above materials.

[0125] A needle penetration test was used to verify the safety performance of the battery, as follows: 100 batteries prepared as described above were placed in a needle penetration test apparatus, wherein the diameter of the steel needle was 3 mm and the penetration speed was 10 mm / s. If the battery did not explode, catch fire, or emit smoke during the penetration, it passed; otherwise, it failed. The number of batteries that passed and failed was recorded, and the battery penetration pass rate was calculated as the number of batteries that passed / the total number of batteries × 100%.

[0126] The above test results are shown in Table 1.

[0127] Table 1

[0128] analyze:

[0129] It can be seen from Examples 1-14 and Comparative Example 1 that, compared with the traditional composite copper current collector, the composite copper current collector prepared in the present application has improved tensile strength (mechanical properties), and the needle penetration rate of the battery based on the prepared composite current collector is improved, that is, the safety performance is improved, which is due to the stacked structure of amorphous copper and crystalline copper in the conductive layer.

[0130] From Examples 1-4 and 13, it can be seen that as the thickness of the amorphous copper in the conductive layer increases, the tensile strength of the composite current collector first increases and then decreases. This is because the introduction of thinner amorphous copper can provide a buffer for the movement of the crystalline copper during the stretching process, thereby improving the tensile strength of the composite current collector. However, if the thickness is too high and the thickness ratio of the amorphous copper to the crystalline copper is too high, the conductive layer will show certain characteristics of amorphous copper, resulting in a decrease in tensile strength. As the thickness of the amorphous copper in the conductive layer increases, the needle penetration rate of the battery based on the prepared composite current collector shows an upward trend, while if the thickness is too high, the needle penetration rate decreases. This is because as the thickness of the amorphous copper increases, the amorphous copper layer is prone to cracking during needle penetration deformation, and the cracks generated are more likely to spread rapidly to the surrounding area, thereby more likely to cause large-scale fractures in the adjacent crystalline copper layer, improving the safety performance of the battery. When its thickness is too high, the amorphous copper will transform into crystalline copper during the preparation process, making it less likely to crack during the needle penetration process and the cracks will not spread to the surrounding area, thereby reducing the safety performance of the battery.

[0131] It can be seen from Example 1, Examples 5-7 and Example 14 that as the thickness of the crystalline copper in the conductive layer increases, the tensile strength of the composite copper current collector and the needle penetration rate of the battery based on the composite copper current collector both show a downward trend. This is because with the increase in the thickness of the crystalline copper, the size of the copper grains along the thickness square becomes larger, resulting in a decrease in the tensile strength of the composite copper current collector, and the grain size becomes larger, which is not conducive to the amorphous copper driving the crystalline copper to produce large-area cracks, resulting in a decrease in the needle penetration rate and poor safety performance.

[0132] It can be seen from Examples 1, 8, 9 and 12 that with the increase in the number of amorphous copper and crystalline copper layers in the conductive layer, the tensile strength of the prepared composite current collector first increases and then decreases, while the needle penetration rate of the battery based on the composite copper current collector shows an increasing trend. This is because the increase in the number of layers can promote the generation of cracks in the conductive layer during the needle penetration process and quickly spread to the surrounding area, thereby improving the safety performance of the battery.

[0133] It can be seen from Example 1, Example 10 and Example 11 that the composite copper current collector prepared by the amorphous copper layer prepared by the combination of magnetron sputtering and evaporation has a better effect on improving the safety performance of the battery.

[0134] The applicant declares that while the above-mentioned embodiments are used to illustrate the process of the present application, the present application is not limited to the above-mentioned process steps, which does not mean that the present application must rely on the above-mentioned process steps in order to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements for the raw materials used in the present application, addition of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present application.

Claims

1. A composite copper current collector, comprising: A polymer-based film; An adhesive layer disposed on at least one surface of the polymer-based film; A composite copper layer disposed on the surface of the adhesive layer relatively far from the polymer-based film, the composite copper layer being formed by alternatingly laminating an amorphous copper layer and a crystalline copper layer.

2. The composite copper current collector according to claim 1, wherein, The side of the composite copper layer close to the adhesive layer is an amorphous copper layer, and the side of the composite copper layer far from the adhesive layer is a crystalline copper layer; Optionally, the number of layers of both the amorphous copper layer and the crystalline copper layer is n layers, where n≥2; Optionally, 2≤n≤10.

3. The composite copper current collector according to claim 1 or 2, wherein, The thickness of the composite copper layer is 500 - 2000 nm, and further optionally 800 - 1200 nm; Optionally, the thickness of the amorphous copper layer is 0 - 100 nm and not 0, and further optionally 20 - 80 nm; Optionally, the thickness of the crystalline copper layer is 0 - 300 nm and not 0, and further optionally 50 - 200 nm.

4. The composite copper current collector according to any one of claims 1-3, wherein, The thickness of the polymer-based film is 1 - 10 μm; Optionally, the material of the adhesive layer includes any one or a combination of at least two of alumina, silica, titanium oxide, nickel, chromium, titanium, nickel-chromium alloy, nickel-chromium-copper alloy, silicon-aluminum alloy, polyacrylic acid, polyacrylate, polyacrylamide, or polyurethane; Optionally, the thickness of the adhesive layer is 1 - 100 nm.

5. The composite copper current collector according to any one of claims 1-3, wherein, A protective layer is further disposed on the surface of the composite copper layer along the side far from the polymer-based film; Optionally, the material of the protective layer includes any one or a combination of at least two of nickel, chromium, nickel-chromium alloy, alumina, nickel oxide, chromium oxide, cobalt oxide, copper-chromium oxide, graphite, carbon black, carbon nano quantum dots, carbon nanotubes, carbon nanofibers, graphene, or graphene oxide; Optionally, the thickness of the protective layer is 5 - 100 nm, and further optionally 20 - 80 nm.

6. A method for preparing a composite copper current collector according to any one of claims 1 - 5, comprising the following steps: Sequentially prepare an adhesive layer and a composite copper layer on at least one surface of a polymer-based film, the composite copper layer being prepared by alternatingly laminating an amorphous copper layer and a crystalline copper layer.

7. The preparation method according to claim 6, wherein, The method for preparing the amorphous copper layer includes evaporation coating method and / or magnetron sputtering method; Optionally, the specific process parameters of the evaporation coating method include: heating evaporation temperature of 1400 - 1600 °C, coating vacuum degree <0.1 Pa, coating main roller cooling temperature of -30 - -10 °C, and coating time of 0.1 - 10 s; Optionally, the specific process parameters of the magnetron sputtering method include: target power of 2 - 6 kW, coating chamber vacuum degree ≤0.1 Pa during coating, gas source flow rate of 10 - 200 mL / min, coating time of 0.1 - 60 s, and coating main roller cooling temperature of -30 - 0 °C.

8. The preparation method according to claim 6 or 7, wherein, The method for preparing the crystalline copper layer includes electroplating method; Optionally, in the electroplating method, the components of the electroplating solution include copper sulfate, sulfuric acid, hydrochloric acid, brightening agent, leveling agent, and wetting agent; Optionally, the brightening agent includes any one or a combination of at least two of sodium polydithiopropane sulfonate, sodium 3-mercapto-1-propanesulfonate, or sodium N,N-dimethyldithiocarbamoylpropane sulfonate; Optionally, the leveling agent includes any one or a combination of at least two of N,N-diethylthiourea, 2-mercaptopyridine, or Janus green; Optionally, the sizing agent includes any one or a combination of at least two of polyethylene glycol, polypropylene glycol, or polyoxyethylene ether; Optionally, the specific process parameters of the electroplating method include: an average cathode current density of 1 to 3 A / dm 2 , a plating solution temperature of 15 to 35 °C, and an electroplating time of 1 to 90 s.

9. The preparation method according to any one of claims 6-8, wherein, The preparation method includes the following steps: (1) Prepare a polymer-based film with a thickness of 1-10 μm by a melt-extrusion-biaxial stretching method; (2) Deposit a bonding layer with a thickness of 1-100 nm on each of the two sides of the polymer by magnetron sputtering, physical vapor deposition, or coating method to obtain a composite film with a bonding layer on the surface; (3) Alternately deposit an amorphous copper layer and a crystalline copper layer on each of the two sides of the composite film, and the number of layers of the amorphous copper layer and the crystalline copper layer is ≥2 layers to obtain a composite film containing a composite copper layer and a bonding layer; Among them, the amorphous copper layer is prepared by magnetron sputtering. The preparation process parameters include: using a copper target as the target, the target power is 2-6 kW, the vacuum degree in the chamber during film coating is ≤0.1 Pa, the gas source flow rate is 10-200 mL / min, the film coating time is 0.1-60 s, and the cooling temperature of the main film coating roller is -30-0 °C; the crystalline copper layer is prepared by electroplating. The preparation process parameters include: the average cathode current density is 1-3 A / dm 2 , the plating solution temperature is 15-35 °C, and the electroplating time is 1-90 s; (4) Deposit a protective layer with a thickness of 5-100 nm on each of the two sides of the composite film containing a composite copper layer and a bonding layer by physical vapor deposition, chemical vapor deposition, in-situ forming, or coating method.

10. A lithium-ion battery including the composite copper current collector according to any one of claims 1-5.

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