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

Abstract

The invention provides a composite copper current collector and a preparation method thereof, and a lithium ion battery. The composite copper current collector comprises a polymer base membrane; the bonding layer is arranged on at least one surface of the polymer base film; the composite copper layer is arranged on the surface of one side, relatively far away from the polymer base film, of the bonding layer; and the composite copper layer is formed by alternately laminating amorphous copper layers and crystalline copper layers. According to the invention, by constructing a multi-layer structure in which the amorphous copper layers and the crystalline copper layers are alternately arranged, the amorphous copper layers are easy to generate cracks and rapidly spread to the periphery in a battery acupuncture experiment process, so that the adjacent crystalline copper layers are driven to be subjected to large-area fracture and fragmentation, thereby realizing separation of the composite copper layer and the steel needle; and a closed loop formed by conduction of the positive and negative current collectors and battery thermal runaway caused by the closed loop are avoided, so that the safety performance of the battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly 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 extensive attention and applications in the new energy industry. The preparation of such composite current collectors usually involves depositing a layer of metal on a polymer film (such as polyester, polyolefin, etc.) by physical vapor deposition (PVD) to prepare 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 applied in the battery.

[0003] The improvement of the safety performance of the composite current collector for the battery mainly relies on the insulation and flame retardancy of its base film, i.e., the polymer film layer. However, although this improves the safety performance of the battery to some extent, the improvement is limited. Especially for the composite copper current collector, due to the structure of the metal layer under the current process limitations, the improvement of its battery safety performance is not obvious.

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

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a composite copper current collector, a preparation method thereof, and a lithium-ion battery. By constructing a multi-layer structure in which an amorphous copper layer and a crystalline copper layer are alternately arranged, during the battery needle-punching experiment, cracks are easily generated in the amorphous copper layer and quickly spread to the surrounding area, thereby driving the adjacent crystalline copper layer to break and fragment over a large area, so as to achieve the separation of the composite copper layer from the steel needle, avoid the conduction of the positive and negative current collectors to form a closed circuit and the resulting battery thermal runaway, and thus improve the safety performance of the battery.

[0006] To achieve the purpose of this invention, the following technical solutions are adopted by the present invention:

[0007] In the first aspect, the present invention provides a composite copper current collector, which includes:

[0008] A polymer base film;

[0009] An adhesive layer provided on at least one surface of the polymer base film;

[0010] A composite copper layer disposed on the surface of the adhesive layer relatively far from the side of the polymer-based film, the composite copper layer being formed by alternately laminating an amorphous copper layer and a crystalline copper layer.

[0011] In the present invention, by constructing a multi-layer structure in which an amorphous copper layer and a crystalline copper layer are alternately arranged, cracks are easily generated in the amorphous copper layer during the battery acupuncture experiment and quickly spread to the surrounding area, thereby driving large-area fractures and fragmentation of the adjacent crystalline copper layer, so as to realize the separation of the composite copper layer from the steel needle, avoid the conduction of the positive and negative current collectors to form a closed circuit and the resulting thermal runaway of the battery, thereby improving the safety performance of the battery.

[0012] In the present invention, the function of the adhesive layer is to improve the adhesion between the polymer film and the composite copper layer.

[0013] As a preferred technical solution of the present invention, 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.

[0014] In the present invention, it is defined that the side of the composite copper layer close to the adhesive layer is an amorphous copper layer, and the side far from the adhesive layer is a crystalline copper layer. The purpose of such a design is to improve the adhesion between the adhesive layer and the copper layer, and the amorphous state is easy to fuse with the adhesive layer.

[0015] Preferably, the amorphous copper layer is composed of amorphous copper, and the crystalline copper layer is composed of crystalline copper.

[0016] It should be noted that amorphous refers to the structure of some non-fully crystalline amorphous regions (amorphous zones) or the composition mode of some amorphous solids (non-crystals). Crystalline refers to the dominant form in which atoms are arranged regularly in a solid object.

[0017] Preferably, the number of layers of both the amorphous copper layer and the crystalline copper layer is n layers, n≥2, for example, it can be 2, 4, 6, 8 or 10, etc.

[0018] Preferably, 2≤n≤10.

[0019] In the present invention, if n is too small, the effect of improving the safety of the battery by the prepared composite copper current collector will become worse; if n is too large, the efficiency of preparing the composite copper current collector will be too low.

[0020] As a preferred technical solution of the present invention, the thickness of the composite copper layer is 500-2000 nm, for example, it can be 500 nm, 1000 nm, 1500 nm or 2000 nm, etc., and preferably 800-1200 nm.

[0021] In the present invention, if the thickness of the composite copper layer is too thin, the conductivity is poor; if the thickness of the composite copper layer is too thick, the prepared composite copper current collector is too heavy, which is not conducive to improving the energy density of the battery. Considering the conductivity and taking into account the improvement of the energy density, the preferred thickness is 800 - 1200 nm.

[0022] Preferably, the thickness of the amorphous copper layer is 0 - 100 nm and not 0, for example, it can be 10 nm, 30 nm, 50 nm, 70 nm or 90 nm, etc., and preferably 20 - 80 nm.

[0023] In the present invention, if the thickness of the amorphous copper layer is too thin, the preparation efficiency is affected and the effect is not obvious; if the thickness of the amorphous copper layer is too thick, the amorphous copper will transform into crystalline copper during the preparation process, which is not conducive to improving the battery safety performance, and being too thick will affect the mechanical properties of the composite copper current collector, resulting in poor mechanical properties.

[0024] Preferably, the thickness of the crystalline copper layer is 0 - 300 nm and not 0, for example, it can be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm or 300 nm, etc., and preferably 50 - 200 nm.

[0025] In the present invention, if the thickness of the crystalline copper layer is too thin, the preparation efficiency is affected and the preparation difficulty is increased; 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 is blocked during the needle punching process.

[0026] As a preferred technical solution of the present invention, the material of the polymer-based film is any one or at least two combinations 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).

[0027] Preferably, the thickness of the polymer-based film is 1 - 10 μm, for example, it can be 1 μm, 3 μm, 5 μm, 7 μm or 9 μm, etc.

[0028] In the present invention, considering the application requirements of the composite copper current collector, and taking into account the preparation process difficulty and cost, the preferred thickness of the polymer-based film is 1 - 10 μm.

[0029] Preferably, the material of the bonding layer includes any one or at least two combinations 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.

[0030] Preferably, the thickness of the adhesive layer is 1 to 100 nm, for example, it can be 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, etc.

[0031] In the present invention, if the thickness of the adhesive layer is too thin, the improvement of the adhesion force of the composite copper current collector is not obvious; if the thickness of the adhesive layer is too thick, the adhesion force cannot be further improved, and the production efficiency is affected.

[0032] As a preferred technical solution of the present invention, a protective layer is further provided on the surface of the composite copper layer away from the polymer base film.

[0033] In the present invention, the purpose of setting the protective layer is to prevent the composite copper layer from being chemically corroded or physically damaged.

[0034] Preferably, 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.

[0035] Preferably, the thickness of the protective layer is 5 to 100 nm, for example, it can be 5 nm, 10 nm, 30 nm, 50 nm, 70 nm or 90 nm, etc., and preferably 20 to 80 nm.

[0036] Preferably, the thickness of the protective layer ≤ one tenth of the thickness of the composite copper layer.

[0037] In a second aspect, the present invention provides a method for preparing a composite copper current collector as described in the first aspect, and the preparation method includes the following steps:

[0038] An adhesive layer and a composite copper layer are sequentially prepared on at least one surface of the polymer base film, and the composite copper layer is prepared by alternately laminating an amorphous copper layer and a crystalline copper layer.

[0039] The preparation method provided by the present invention is simple and easy to implement, and is easy to scale up production.

[0040] As a preferred technical solution of the present invention, the preparation method of the amorphous copper layer includes evaporation coating method and / or magnetron sputtering method.

[0041] Preferably, the specific process parameters of the evaporation coating method include: the heating evaporation temperature is 1400 - 1600 °C, for example, it can be 1400 °C, 1500 °C or 1600 °C, etc.; the coating vacuum degree < 0.1 Pa, for example, it can be 0.08 Pa, 0.06 Pa or 0.04 Pa, etc.; the cooling temperature of the main coating roller is -30 - -10 °C, for example, it can be -30 °C, -20 °C or -10 °C, etc.; the coating time is 0.1 - 10 s, for example, it can be 0.1 s, 1 s, 5 s or 10 s, etc.

[0042] Preferably, the specific process parameters of the magnetron sputtering method include: the target power is 2 - 6 kW, for example, it can be 2 kW, 4 kW or 6 kW, etc.; the vacuum degree in the chamber during coating ≤ 0.1 Pa, for example, it can be 0.1 Pa, 0.08 Pa or 0.05 Pa, etc.; the flow rate of the gas source is 10 - 200 mL / min, for example, it can be 10 mL / min, 50 mL / min, 100 mL / min, 150 mL / min or 200 mL / min, etc.; the coating time is 0.1 - 60 s, for example, it can be 1 s, 5 s, 10 s, 30 s or 60 s, etc.; the cooling temperature of the main coating roller is -30 - 0 °C, for example, it can be -30 °C, -20 °C, -10 °C or 0 °C, etc.

[0043] As a preferred technical solution of the present invention, the preparation method of the crystalline copper layer includes the electroplating method.

[0044] Preferably, in the electroplating method, the components of the electroplating solution include copper sulfate, sulfuric acid, hydrochloric acid, brightening agent, leveling agent and wetting agent.

[0045] Preferably, the concentration of the copper sulfate is 80 - 130 g / L, for example, it can be 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L or 130 g / L, etc.; the concentration of the sulfuric acid is 80 - 160 g / L, for example, it can be 80 g / L, 100 g / L, 120 g / L, 140 g / L or 160 g / L, etc.; the concentration of the chloride ion is 20 - 80 mg / L, for example, it can be 20 mg / L, 40 mg / L, 60 mg / L or 80 mg / L, etc.; the concentration of the brightening agent is 5 - 20 ppm, for example, it can be 5 ppm, 10 ppm, 15 ppm or 20 ppm, etc.; the concentration of the leveling agent is 1 - 5 ppm, for example, it can be 1 ppm, 3 ppm or 5 ppm, etc.; the concentration of the wetting agent is 20 - 200 ppm, for example, it can be 20 ppm, 50 ppm, 100 ppm, 150 ppm or 200 ppm, etc.

[0046] Preferably, 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.

[0047] Preferably, the leveling agent includes any one or a combination of at least two of N,N-diethylthiourea, 2-mercaptopyridine, or Janus green.

[0048] Preferably, the wetting agent includes any one or a combination of at least two of polyethylene glycol, polypropylene glycol, or polyoxyethylene ether.

[0049] Preferably, the specific process parameters of the electroplating method include: the average cathode current density is 1 - 3 A / dm 2 , for example, it can be 1 A / dm 2 , 2 A / dm 2 or 3 A / dm 2 etc., the bath temperature is 15 - 35 °C, for example, it can be 15 °C, 20 °C, 25 °C, 30 °C or 35 °C etc., and the electroplating time is 1 - 90 s, for example, it can be 1 s, 10 s, 30 s, 60 s or 90 s etc.

[0050] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0051] (1) Prepare a polymer-based film with a thickness of 1 - 10 μm by the melt-extrusion-biaxial stretching method;

[0052] (2) Adopt magnetron sputtering, physical vapor deposition or coating method to deposit a bonding layer with a thickness of 1 - 100 nm on each side of the polymer to obtain a composite film with a bonding layer on the surface;

[0053] (3) Alternately deposit an amorphous copper layer and a crystalline copper layer on each side of the composite film, and the number of layers of both 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;

[0054] Among them, the amorphous copper layer is prepared by magnetron sputtering, and 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 coating is ≤ 0.1 Pa, the flow rate of the gas source is 10 - 200 mL / min, the coating time is 0.1 - 60 s, and the cooling temperature of the coating main roller is -30 - 0 °C; the crystalline copper layer is prepared by electroplating, and the preparation process parameters include: the average cathode current density is 1 - 3 A / dm 2 , the bath temperature is 15 - 35 °C, and the electroplating time is 1 - 90 s;

[0055] (4) A protective layer with a thickness of 5 - 100 nm is deposited on each of the two 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 method.

[0056] In a third aspect, the present invention provides a lithium-ion battery, and the negative electrode of the lithium-ion battery includes the composite copper current collector as described in the first aspect.

[0057] The numerical ranges described in the present invention not only include the above-listed point values, but also any point values between the above numerical ranges not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the ranges.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] (1) By constructing a multi-layer structure with an amorphous copper layer and a crystalline copper layer arranged alternately, in the battery needle-punching experiment, the amorphous copper layer is prone to generate cracks and quickly spread to the surrounding area, thereby driving the adjacent crystalline copper layer to break and fragment over a large area, so as to realize the separation of the composite copper layer from the steel needle, avoid the conduction of the positive and negative current collectors to form a closed loop and the resulting battery thermal runaway, and thus improve the safety performance of the battery.

[0060] (2) The preparation method provided by the present invention is simple and easy to implement, and is easy to scale up production. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is the X-ray diffraction pattern of the composite copper layer and the amorphous copper layer prepared in a specific embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0062] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0063] Example 1

[0064] This example provides a composite copper current collector, which includes:

[0065] A polymer-based film, made of PET, with a thickness of 4.5 μm;

[0066] Bonding layers provided on the two surfaces of the polymer-based film, made of nickel-chromium alloy, with a single-sided thickness of 5 nm, including a first bonding layer and a second bonding layer;

[0067] A composite copper layer is disposed on the surface of the adhesive layer that is relatively far from the polymer-based film side. The single-sided thickness is 750 nm and it includes a first composite copper layer and a second composite copper layer. The composite copper layer is formed by alternating amorphous copper layers and crystalline copper layers. 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. Among them, the number of amorphous copper layers is 5, and the thickness of each layer is 50 nm. The number of crystalline copper layers is 5, and the thickness of each layer is 100 nm;

[0068] A protective layer is disposed on the surface of the composite copper layer that is relatively far from the polymer-based film side. The material is carbon nanotubes, and the single-sided thickness is 12 nm, including a first protective layer and a second protective layer.

[0069] This embodiment also provides a preparation method of the above composite copper current collector. The preparation method includes the following steps:

[0070] (1) Prepare a PET film by the melt-extrusion-biaxial stretching method;

[0071] (2) Place the PET film in a magnetron sputtering machine and deposit an adhesive layer on each side of the PET film. The specific process conditions are: using a nickel-chromium target (purity: 99.99%) as the target, the target power is 5.0 kW, the argon flow rate is 50 mL / min, the coating vacuum degree is 0.08 Pa, the coating time is 1 s, and the temperature of the main roller during the coating process is 0 °C to obtain a PET composite film with an adhesive layer on the surface;

[0072] (3) Place the PET composite film with an adhesive layer on the surface in a magnetron sputtering machine and alternately deposit amorphous copper layers and crystalline copper layers on each side of the composite film to obtain a PET film containing a composite copper layer and an adhesive layer. Among them, ① for the amorphous copper layer with 5 layers, the preparation process conditions for each layer are: using a copper target (purity: 99.99%) as the target, the target power is 5 kW, the gas source is argon, the argon flow rate is 60 mL / min, the coating vacuum degree 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 for the crystalline copper layer with 5 layers, the preparation process conditions for each layer are: the electroplating solution components include 100 g / L copper sulfate, 120 g / L sulfuric acid, 50 mg / L chloride ions, 10 ppm sodium polydithiopropane sulfonate, 2 ppm N,N-diethylthiourea, and 100 ppm polyethylene oxide ether, the average cathode current density is 1.7 A / dm 2 , the plating solution temperature is 25 °C, and the electroplating time is 30 s;

[0073] (4) 1.5 g of carbon nanotubes were uniformly dispersed into 998.5 g of N-methylpyrrolidone (NMP) solution by ultrasonic dispersion method to prepare a coating solution with a solid content of 0.15 wt.%. Then, the coating solution was uniformly coated on the surface of the PET film containing the composite copper layer and the adhesive layer by die coating process, and finally dried at 100 °C to obtain a protective layer with a thickness of 12 nm, thus obtaining the composite copper current collector.

[0074] In addition, in order to prove that the composite copper layer in this embodiment is 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, namely: a layer of amorphous copper was prepared on the surface of the PET film according to the preparation method of amorphous copper in this embodiment, which is sample 1; a layer of crystalline copper was prepared on the surface of sample 1 according to the preparation method of crystalline copper in this embodiment, which is sample 2. Then, according to the requirements of the X-ray diffractometer, the samples were prepared and placed in the X-ray diffractometer (Bruker D8 ADVANCE), with copper as the target material, a scanning speed of 2.0000 deg / min, and a scanning range of 30° to 80°. The test results are as Figure 1 shown. It can be seen from the figure that no diffraction peak of copper was found in the diffraction pattern of sample 1, while diffraction peaks of crystal plane orientations such as (111), (200), and (220) of copper were found in sample 2. This indicates that an amorphous copper layer and a crystalline copper layer can be prepared according to the preparation method of this embodiment, that is, the composite copper layer prepared in this embodiment is a laminated structure of an amorphous copper layer and a crystalline copper layer.

[0075] Example 2

[0076] 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 for each layer are: using a copper target (purity: 99.99%) 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 degree 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.

[0077] The remaining preparation methods and parameters are the same as those in Example 1.

[0078] Example 3

[0079] 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 for each layer are: using a copper target (purity: 99.99%) 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 degree 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.

[0080] The remaining preparation methods and parameters are the same as those in Example 1.

[0081] Example 4

[0082] The difference between this example and Example 1 is that the thickness of the amorphous copper layer is 100 nm, and the preparation process conditions for each layer are as follows: using a copper target (purity: 99.99%) 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 degree 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.

[0083] The remaining preparation methods and parameters are the same as those in Example 1.

[0084] Example 5

[0085] The difference between this example and Example 1 is that the thickness of the crystalline copper layer is 50 nm, and the preparation process conditions for each layer are as follows: the electroplating solution components include 100 g / L copper sulfate, 120 g / L sulfuric acid, 50 mg / L chloride ions, 10 ppm sodium polydithiopropane sulfonate, 2 ppm N,N - diethylthiourea, and 100 ppm polyoxyethylene ether, the average cathode current density is 1.7 A / dm 2 , the bath temperature is 25 °C, and the electroplating time is 15 s;

[0086] The remaining preparation methods and parameters are the same as those in Example 1.

[0087] Example 6

[0088] The difference between this example and Example 1 is that the thickness of the crystalline copper layer is 200 nm, and the preparation process conditions for each layer are as follows: the electroplating solution components include 100 g / L copper sulfate, 120 g / L sulfuric acid, 50 mg / L chloride ions, 10 ppm sodium polydithiopropane sulfonate, 2 ppm N,N - diethylthiourea, and 100 ppm polyoxyethylene ether, the average cathode current density is 1.7 A / dm 2 , the bath temperature is 25 °C, and the electroplating time is 60 s;

[0089] The remaining preparation methods and parameters are the same as those in Example 1.

[0090] Example 7

[0091] The difference between this example and Example 1 is that the thickness of the crystalline copper layer is 300 nm, and the preparation process conditions for each layer are as follows: the electroplating solution components include 100 g / L copper sulfate, 120 g / L sulfuric acid, 50 mg / L chloride ions, 10 ppm sodium polydithiopropane sulfonate, 2 ppm N,N - diethylthiourea, and 100 ppm polyoxyethylene ether, the average cathode current density is 1.7 A / dm 2 , the bath temperature is 25 °C, and the electroplating time is 90 s;

[0092] The remaining preparation methods and parameters are the same as those in Example 1.

[0093] Example 8

[0094] The difference between this example and Example 7 is that the number of layers of both the amorphous copper layer and the crystalline copper layer is 2 layers.

[0095] The remaining preparation methods and parameters are the same as those in Example 7.

[0096] Example 9

[0097] The difference between this example and Example 1 is that the number of layers of both the amorphous copper layer and the crystalline copper layer is 10 layers.

[0098] The remaining preparation methods and parameters are the same as those in Example 1.

[0099] Example 10

[0100] The difference between this example and Example 1 is that the amorphous copper layer is prepared by evaporation plating. The preparation process conditions for each layer are as follows: using copper wire (purity 99.99%) as the copper source, the heating evaporation temperature is 1500°C, the coating vacuum is 0.05 Pa, the cooling temperature of the main coating roller is -30°C, and the coating time is 1.5 s.

[0101] The remaining preparation methods and parameters are the same as those in Example 1.

[0102] Example 11

[0103] The difference between this example and Example 1 is that the amorphous copper layer is prepared in two steps by magnetron sputtering and evaporation plating. The preparation process conditions for each layer are as follows: ① Magnetron sputtering to prepare 20 nm of amorphous copper: using a copper target (purity: 99.99%) 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 Evaporation plating to prepare 30 nm of amorphous copper: using copper wire (purity 99.99%) as the copper source, the heating evaporation temperature is 1500°C, the coating vacuum is 0.05 Pa, the cooling temperature of the main coating roller is -30°C, and the coating time is 0.9 s.

[0104] The remaining preparation methods and parameters are the same as those in Example 1.

[0105] Example 12

[0106] The differences between this embodiment and Embodiment 1 are as follows: both the amorphous copper layer and the crystalline copper layer have a layer number of 1, and the thickness of the amorphous copper layer in the conductive layer is 100 nm, while the thickness of the crystalline copper layer is 300 nm. The preparation process conditions of the amorphous copper layer are as follows: using a copper target (purity: 99.99%) 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 degree 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 components of the electroplating solution include 100 g / L copper sulfate, 120 g / L sulfuric acid, 50 mg / L chloride ions, 10 ppm sodium polydisulfide propane sulfonate, 2 ppm N,N-diethylthiourea, and 100 ppm polyoxyethylene ether, the average cathode current density is 1.7 A / dm2, the electroplating solution temperature is 25 °C, and the electroplating time is 90 s.

[0107] The remaining preparation methods and parameters are the same as those in Embodiment 1.

[0108] Embodiment 13

[0109] The differences between this embodiment and Embodiment 1 are as follows: the thickness of the amorphous copper layer is 120 nm, and the preparation process conditions for each layer are as follows: using a copper target (purity: 99.99%) 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 degree 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.

[0110] The remaining preparation methods and parameters are the same as those in Embodiment 1.

[0111] Embodiment 14

[0112] The differences between this embodiment and Embodiment 1 are as follows: the thickness of the crystalline copper layer is 320 nm, and the preparation process conditions for each layer are as follows: the components of the electroplating solution include 100 g / L copper sulfate, 120 g / L sulfuric acid, 50 mg / L chloride ions, 10 ppm sodium polydisulfide propane sulfonate, 2 ppm N,N-diethylthiourea, and 100 ppm polyoxyethylene ether, the average cathode current density is 1.7 A / dm 2 , the electroplating solution temperature is 25 °C, and the electroplating time is 96 s;

[0113] The remaining preparation methods and parameters are the same as those in Embodiment 1.

[0114] Comparative Example 1

[0115] The difference between this comparative example and Example 1 is that the composite copper layer is a single-layer copper layer. The specific preparation process is as follows: using a copper target (purity: 99.99%) as the target material, the target power is 12 kW, the argon gas flow rate is 50 mL / min, the coating vacuum degree is 0.08 Pa, the coating time is 100 s, and the temperature of the main roller during the coating process is 2 °C.

[0116] The remaining preparation methods and parameters are the same as those in Example 1.

[0117] Performance testing

[0118] (1) Tensile strength tests were carried out on the composite copper current collectors prepared in the above examples and comparative examples. The specific test method includes: sampling longitudinally along the prepared composite copper current collector, and then referring to the national standard GB / T 1040.3 - 2006 for tensile strength tests.

[0119] (2) The composite copper current collectors prepared in the above examples and comparative examples were assembled into lithium-ion batteries for safety performance testing.

[0120] Battery assembly: For the positive electrode, the positive current collector uses a traditional aluminum current collector (thickness: 13 μm), and the positive electrode material uses LiNi 0.6 Mn 0.2 Co 0.2 O2 (NCM622); for the negative electrode: the negative current collector uses the composite copper current collector prepared in the present invention, and the negative electrode material uses artificial graphite; for the separator, a polyethylene separator coated with aluminum oxide ceramic (thickness: 25 μm) is used; for the electrolyte, a 1 mol·L -1 LiPF6 carbonate solution is used. The carbonate solution is a mixed solution 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.

[0121] The safety performance of the battery was verified by a needle-punching experiment, which is as follows: 100 batteries prepared above were placed in a needle-punching experiment device. The diameter of the steel needle is 3 mm, and the needle-punching speed is 10 mm / s. If the battery does not explode, catch fire, or emit smoke during the needle-punching process, it is considered to pass; otherwise, it is considered to fail. Record the number of batteries that pass and fail to obtain the needle-punching pass rate of the battery, that is, the number of passing batteries / the total number of batteries × 100%.

[0122] The above test results are shown in Table 1.

[0123] Table 1

[0124]

[0125]

[0126] Analysis:

[0127] 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 by the present invention has improved tensile strength (mechanical properties), and the puncture pass 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.

[0128] It can be seen from Examples 1-4 and 13 that as the thickness of amorphous copper in the conductive layer increases, the tensile strength of the composite current collector increases first and then decreases. This is because the introduction of thinner amorphous copper can provide a buffer for the movement of crystalline copper during the stretching process, thereby improving the tensile strength of the composite current collector. If the thickness is too high, the thickness ratio of amorphous copper to crystalline copper is too high, and the conductive layer will show certain characteristics of amorphous copper, resulting in a decrease in tensile strength. With the increase in the thickness of amorphous copper in the conductive layer, the needle puncture pass rate of the battery based on the prepared composite current collector shows an increasing trend, while the thickness is too high and the needle puncture pass rate decreases. This is because the increase in the thickness of amorphous copper makes it easy for the amorphous copper layer to crack during needle puncture deformation, and the cracks generated are more likely to spread rapidly to the surrounding area, thereby more easily driving the adjacent crystalline copper layer to break over a large area, thereby improving the safety performance of the battery. When its thickness is too high, amorphous copper will transform into crystalline copper during the preparation process, and it is not easy to generate cracks during the needle puncture process and the cracks will not spread to the surrounding area, thereby reducing the safety performance of the battery.

[0129] 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 decreasing 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 increase in the grain size 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 a deterioration in safety performance.

[0130] It can be seen from Example 1, Example 8, Example 9 and Example 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.

[0131] It can be seen from Example 1, Example 10 and Example 11 that the composite copper current collector prepared by combining magnetron sputtering and evaporation to prepare the amorphous copper layer has a better effect on improving the safety performance of the battery.

[0132] The applicant declares that the present invention illustrates the process method of the present invention through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of the raw materials selected for the present invention, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A composite copper current collector, characterized in that, The composite copper current collector includes: 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 on the side relatively far from the polymer-based film, and the composite copper layer is formed by alternately 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; Preferably, the number of layers of both the amorphous copper layer and the crystalline copper layer is n layers, where n≥2; Preferably, 2≤n≤10.

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

4. The composite copper current collector according to any one of claims 1-3, characterized in that, The thickness of the polymer-based film is 1 - 10 μm; Preferably, 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; Preferably, the thickness of the adhesive layer is 1 - 100 nm.

5. The composite copper current collector according to any one of claims 1-3, characterized in that, A protective layer is further disposed on the surface of the composite copper layer along the side far from the polymer-based film; Preferably, 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; Preferably, the thickness of the protective layer is 5 - 100 nm, preferably 20 - 80 nm.

6. A method for preparing a composite copper current collector according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: An adhesive layer and a composite copper layer are sequentially prepared on at least one surface of the polymer-based film, and the composite copper layer is prepared by alternately laminating an amorphous copper layer and a crystalline copper layer.

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

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

9. The preparation method according to any one of claims 6-8, characterized in that, 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) Use magnetron sputtering, physical vapor deposition or coating method to deposit a bonding layer with a thickness of 1-100 nm on each side of the polymer 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 side of the composite film. 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 bath temperature is 15-35 °C, and the electroplating time is 1-90 s; (4) Use physical vapor deposition, chemical vapor deposition, in-situ forming or coating method to deposit a protective layer with a thickness of 5-100 nm on each side of the composite film containing a composite copper layer and a bonding layer.

10. A lithium-ion battery, characterized in that, The negative electrode of the lithium-ion battery includes the composite copper current collector according to any one of claims 1-5.

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