Composite current collector, manufacturing method therefor and use thereof

Abstract

Provided in the present application are a composite current collector, a manufacturing method therefor and the use thereof. The composite current collector comprises a polymer base film, and a bonding layer and a composite conductive layer which are sequentially stacked on at least one side surface of the polymer base film, the composite conductive layer comprising a carbon layer. The present application develops a novel composite current collector, that is, a carbon layer is introduced into the composite conductive layer, and due to the unique conductive layer structure, the defect rate of the composite current collector can be reduced, thereby improving the structure and performance stability of the composite current collector, and enhancing the stability thereof during battery processing and cycling. The manufacturing method is simple and feasible, and can be used for large-scale production.

Description

Composite current collector and its preparation method and application Technical Field

[0001] The present application belongs to the field of battery material technology, and specifically relates to a composite current collector and its preparation method and application. Background Art

[0002] At present, composite copper current collectors based on polymer films have received widespread attention and application in the new energy industry. The preparation process of this composite copper current collector is usually divided into two steps: first, a layer of copper is deposited on a polymer film (such as polypropylene, polyethylene or polyester) by magnetron sputtering to prepare a composite copper current collector semi-finished product with a certain conductivity; then, the composite copper current collector semi-finished product is further processed by electroplating to thicken the conductive copper layer, thereby preparing a composite copper current collector with good conductivity. Compared with traditional current collectors (copper foil), composite copper 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] However, the current preparation of composite copper current collectors has the following problems: when a copper layer is deposited on a polymer film using a winding magnetron sputtering device to prepare a composite copper current collector semi-finished product, the film surfaces that are in contact with each other will adhere to each other during the winding process, resulting in the bonded film surfaces being torn during the unwinding process of the subsequent process (electroplating), and the microscopic copper layer on the film surface falling off, resulting in microscopic defects. During the electroplating process, copper cannot be deposited near the defect point due to the lack of conductivity, which ultimately causes microscopic defects in the prepared composite copper current collector, affecting the performance and application of the composite current collector.

[0004] Therefore, in order to address the above problems, it is necessary to develop a low-defect composite current collector so as to improve the stability of the structure and performance of the composite current collector and promote the promotion and application of the composite current collector.

[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 prior art, the present application aims to provide a composite current collector, its preparation method, and its application. This application develops a new composite current collector, namely, a carbon layer is introduced into the composite conductive layer. Due to its unique conductive layer structure, the defect rate of the composite current collector can be reduced, thereby improving the stability of the structure and performance of the composite current collector, promoting its stability during battery processing and cycling. The preparation method is simple and easy to implement, and can be easily scaled up for production.

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

[0009] In a first aspect, the present application provides a composite current collector, comprising a polymer base film, and an adhesive layer and a composite conductive layer sequentially stacked on at least one side surface of the polymer base film;

[0010] The composite conductive layer includes a carbon layer.

[0011] This application develops a new composite current collector, that is, introducing a carbon layer into the composite conductive layer. Due to its unique conductive layer structure, the defect rate of the composite current collector can be reduced, thereby improving the stability of the structure and performance of the composite current collector, promoting its stability during battery processing and cycling, and the preparation method is simple and easy to scale up production.

[0012] In this application, the presence of the carbon layer has the following advantages: ① It can inhibit the adhesion between layers and prevent defects caused by film surface adhesion during the electroplating unwinding process; ② The carbon layer is conductive and will not affect the conductive properties of the composite current collector semi-finished product; ③ It has strong stability and will not introduce new impurities into the electroplating solution, nor will it affect the protection effect.

[0013] In the present application, the purpose of providing the adhesive layer is to enhance the adhesive force between the polymer base film and the composite conductive layer.

[0014] As an optional technical solution of the present application, the composite conductive layer further includes a seed layer and a thickening layer.

[0015] In this application, the role of the seed layer is to provide a certain degree of conductivity and to provide a basis for the preparation of the thickening layer.

[0016] In the present application, the function of the thickened layer is to provide conductivity for the composite current collector.

[0017] In one embodiment, along a direction away from the polymer-based film, the composite conductive layer includes a seed layer, a carbon layer and a thickening layer in sequence.

[0018] In the present application, the carbon layer is arranged between the seed layer and the thickening layer, which not only can inhibit the adhesion between the copper layers of the composite current collector semi-finished product and prevent defects caused by film surface adhesion during the unwinding process of the thickening layer, but also has a conductive layer, which will not affect the conductive properties of the composite current collector semi-finished product prepared by magnetron sputtering, thereby affecting the electroplating effect; in addition, the carbon layer has strong stability and will not react with the electroplating solution after entering the electroplating process, which can avoid introducing new impurities into the electroplating solution and affecting the electroplating effect; finally, the carbon layer is amorphous, which can improve the adhesion with the seed layer and the thickening layer, and promote the stability of the composite current collector structure.

[0019] It should be noted that during the winding process of the composite copper current collector semi-finished product, the film surfaces that come into contact with each other will adhere to each other, causing the bonded film surfaces to tear during the unwinding process of the subsequent process (electroplating), causing the microscopic copper layer on the film surface to fall off, resulting in microscopic defects. During the electroplating process, copper cannot be deposited near the defect point due to the lack of conductivity, ultimately causing microscopic defects in the prepared composite copper current collector, affecting the performance and application of the composite current collector. Therefore, providing a carbon layer on the surface of the seed layer can prevent the seed layers on the surface of the composite current collector semi-finished product from contacting each other and causing defects, thereby ensuring the generation of a thickened layer with a lower defect rate.

[0020] In one embodiment, the carbon layer is an amorphous carbon layer.

[0021] In the present application, the carbon layer is in an amorphous state, which can promote the stability of the composite current collector structure.

[0022] In one embodiment, the material of the seed layer includes metallic copper and / or copper alloy, and can be metallic copper.

[0023] In one embodiment, the seed layer is further doped with carbon, and the content of the carbon element accounts for 0.1-5% of the total mass of the seed layer, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 4% or 5%.

[0024] In the present application, the seed layer is doped with a certain amount of carbon element, which helps to improve the adhesion between the seed layer and the carbon layer, thereby improving the structural stability of the prepared composite current collector.

[0025] In one embodiment, the material of the thickening layer includes metallic copper and / or copper alloy, and can be metallic copper.

[0026] In one embodiment, the thickening layer is further doped with carbon element, and the content of the carbon element accounts for 0.1-5% of the total mass of the thickening layer, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 4% or 5%.

[0027] In the present application, a certain amount of carbon element is doped into the thickening layer, which helps to improve the bonding force between the thickening layer and the carbon layer, thereby improving the structural stability of the prepared composite current collector.

[0028] As an optional technical solution of the present application, the thickness of the seed layer is 40-100 nm, for example, it can be 40 nm, 60 nm, 80 nm or 100 nm.

[0029] In this application, if the thickness of the seed layer is too low, the stable preparation of the thickening layer cannot be guaranteed; if the thickness of the seed layer is too high, the stable preparation of the thickening layer cannot be further promoted, and the energy consumption during the preparation process is high, which will affect the mechanical properties of the composite current collector.

[0030] In one embodiment, the thickness of the carbon layer is ≥1 nm, for example, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm or 30 nm, etc., and can be optionally 5-20 nm.

[0031] In this application, if the thickness of the carbon layer is too low, the conductivity is too poor; if the thickness of the carbon layer is too high, the stable preparation of the thickened layer cannot be guaranteed, and after the thickness reaches a certain value, the finished product defect rate caused by the adhesion between the seed layer and the thickened layer in the composite current collector semi-finished product is reduced to 0, and further increasing the thickness cannot improve the effect, which is a waste of cost.

[0032] In one embodiment, the thickness of the thickened layer is 500-2000 nm, for example, 500 nm, 1000 nm, 1500 nm or 2000 nm, etc., and can be optionally 800-1200 nm.

[0033] In this application, if the thickness of the thickening layer is too low, the conductivity is poor; if the thickness of the thickening layer is too high, the prepared composite 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 improvement, the thickness can be selected to be 800-1200nm.

[0034] As an optional technical solution of the present application, the material of the polymer base film is any one 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), or a combination of at least two thereof.

[0035] As an optional technical solution of the present application, the thickness of the polymer base film is 1-10 μm, for example, it can be 1 μm, 3 μm, 5 μm, 7 μm or 9 μm.

[0036] In this application, considering the application requirements of the composite copper current collector and the difficulty and cost of the preparation process, the thickness of the optional polymer base film is 1-10 μm.

[0037] 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.

[0038] In one embodiment, the thickness of the bonding layer is 1-10 nm, for example, 1 nm, 3 nm, 5 nm, 7 nm, or 9 nm.

[0039] In one embodiment, a protective layer is provided on the surface of the composite conductive layer away from the polymer base film.

[0040] 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.

[0041] 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.

[0042] In one embodiment, the thickness of the protective layer is 5-100 nm, for example, 5 nm, 10 nm, 30 nm, 50 nm, 70 nm or 90 nm, etc., and can be optionally 10-80 nm.

[0043] 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.

[0044] In a second aspect, the present application provides a method for preparing the composite current collector as described in the first aspect, the preparation method comprising the following steps:

[0045] sequentially preparing an adhesive layer and a composite conductive layer on at least one surface of the polymer base film;

[0046] The composite conductive layer includes a carbon layer.

[0047] The preparation method provided in this application is simple and easy to implement, and can be easily scaled up for production.

[0048] As an optional technical solution of the present application, along the direction away from the polymer base film, the composite conductive layer includes a seed layer, a carbon layer and a thickening layer in sequence.

[0049] In one embodiment, the carbon layer is prepared by a method comprising magnetron sputtering and / or chemical vapor deposition, and the magnetron sputtering method can be selected.

[0050] In one embodiment, the specific process parameters of the magnetron sputtering method include:

[0051] The target power is 2-10kW, for example, 2kW, 4kW, 6kW, 8kW or 10kW, etc. The gas source flow rate is 30-200mL / min, for example, 30mL / min, 50mL / min, 100mL / min, 150mL / min or 200mL / min, etc. The vacuum degree is ≤1Pa, for example, 1Pa, 0.8Pa or 0.5Pa, etc.

[0052] In one embodiment, the gas source comprises nitrogen.

[0053] As an optional technical solution of the present application, the preparation method of the seed layer is physical vapor deposition.

[0054] In one embodiment, the physical vapor deposition method includes magnetron sputtering and / or evaporation.

[0055] In one embodiment, the preparation method of the thickened layer includes electroplating.

[0056] In one embodiment, in the electroplating method, components of the electroplating solution include copper sulfate, sulfuric acid, HCl, a brightener, a leveler, and a wetting agent.

[0057] In one embodiment, the concentration of the copper sulfate is 80-130 g / L, for example, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L or 130 g / L, and 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 HCl 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 brightener is 0.5-20 ppm, for example, it can be 0.5 ppm, 5 ppm, 10 ppm, 15 ppm or 20 ppm, etc. The concentration of the leveler is 0.5-5 ppm, for example, it can be 0.5 ppm, 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] In one embodiment, the specific process parameters of the electroplating method include:

[0062] The average cathode current density is 0.5-5A / dm 2 , for example, it can be 0.5A / dm 2 , 1A / dm 2 , 2A / dm 2 、3A / dm 2 , 4A / dm 2 or 5A / 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 electroplating time is 1-20 minutes, for example, 1 minute, 5 minutes, 10 minutes, 15 minutes or 20 minutes.

[0063] As an optional technical solution of the present application, the preparation method of the bonding layer includes physical vapor deposition and / or coating method.

[0064] As an optional technical solution of the present application, the preparation method comprises the following steps:

[0065] (1) preparing a polymer base film with a thickness of 1-10 μm by a melt-extrusion-biaxial stretching method;

[0066] (2) depositing a bonding layer with a thickness of 1-10 nm on each side of the polymer base film by magnetron sputtering, physical vapor deposition or coating to obtain a composite film having a bonding layer on the surface;

[0067] (3) using physical vapor deposition to deposit a seed layer with a thickness of 40-100 nm on each side of the composite film having the bonding layer on the surface, then using magnetron sputtering and / or chemical vapor deposition to deposit a carbon layer with a thickness of 1 nm or more on each side of the composite film including the seed layer, and then using electroplating to deposit a thickening layer with a thickness of 500-2000 nm on the surface of the carbon layer to obtain a composite film having a composite conductive layer on the surface;

[0068] (4) A protective layer with a thickness of 5-100 nm is deposited on both sides of the composite film having a composite conductive layer on the surface by physical vapor deposition, chemical vapor deposition, in-situ forming or coating.

[0069] In a second aspect, the present application provides a lithium-ion battery, wherein the negative electrode of the lithium-ion battery includes the composite current collector as described in the first aspect.

[0070] 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.

[0071] Compared with the prior art, this application has the following beneficial effects:

[0072] (1) This application develops a new composite current collector, namely, a carbon layer is introduced into the composite conductive layer. Due to its unique conductive layer structure, the defect rate of the composite current collector can be reduced, thereby improving the stability of the structure and performance of the composite current collector, and promoting its stability during battery processing and cycling.

[0073] (2) In the present application, the presence of the carbon layer has the following advantages: ① It can inhibit the adhesion between the layers and prevent defects caused by film surface adhesion during the electroplating unwinding process; ② The carbon layer is conductive and will not affect the conductive properties of the composite current collector semi-finished product; ③ It has strong stability and will not introduce new impurities or affect the protection effect; ④ The carbon layer is amorphous and can promote the stability of the composite current collector structure.

[0074] (3) The preparation method provided in this application is simple and easy to implement, and can be easily scaled up for production.

[0075] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0076] 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.

[0077] Example 1

[0078] This embodiment provides a composite current collector, comprising a polymer base film, and an adhesive layer, a composite conductive layer, and a protective layer sequentially stacked on both sides of the polymer base film.

[0079] Along the direction away from the polymer base film, the composite conductive layer includes a seed layer, a carbon layer and a thickening layer in sequence;

[0080] The seed layer is a copper layer with a thickness of 50 nm, the thickening layer is a copper layer with a thickness of 1100 nm, the carbon layer has a thickness of 1 nm, the polymer base film is a PET film with a thickness of 4.5 μm, the bonding layer is a nickel-chromium alloy layer with a thickness of 5 nm, and the protective layer is graphene with a thickness of 10 nm.

[0081] This embodiment also provides a method for preparing the composite current collector, which comprises the following steps:

[0082] (1) PET film was prepared by melt-extrusion-biaxial stretching method;

[0083] (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;

[0084] (3) Preparation of composite conductive layer:

[0085] ① Preparation of seed layer: The PET composite film with the adhesive layer prepared above was placed in a magnetron sputtering machine. Using a copper target (purity: 99.99%) as the target material, a 50 nm thick copper layer was deposited on each side of the composite film. The specific process conditions were: target power of 12 kW, argon flow rate of 50 mL / min, coating vacuum of 0.08 Pa, coating time of 5 s, and the main roller temperature of 2°C during the coating process.

[0086] ② Preparation of carbon layer: Using a graphite target (purity: 99.99%) as the target material, a 1 nm thick carbon layer was deposited on both sides of the composite film containing the seed layer. The specific process conditions were: target power of 3 kW, argon flow rate of 100 mL / min, coating vacuum of 0.5 Pa, coating time of 0.5 s, and the temperature of the main roller during the coating process was 0°C.

[0087] ③ Preparation of thickening layer: The composite film with a carbon layer on the surface prepared above was placed in an electroplating device, and a thickening layer with a thickness of 1100 nm was prepared on each surface of the composite film. The specific process conditions were: the electroplating solution components included 120 g / L copper sulfate, 110 g / L sulfuric acid, 50 mg / L HCl, 10 ppm sodium N,N-dimethyldithiocarboxamide propane sulfonate, 2 ppm 2-mercaptopyridine and 80 ppm polyoxyethylene ether, and the average cathode current density was 2 A / dm 2 , the plating solution temperature is 25℃, and the electroplating time is 6min;

[0088] (4) Preparation of protective layer: 1 g of graphene was uniformly dispersed in 999 g of nitrogen methyl pyrrolidone (NMP) solution by ultrasonic dispersion to prepare a coating solution with a solid content of 0.1 wt.%, and then the coating solution was uniformly applied to the surface of the thickened layer prepared above by die coating. Finally, it was dried at 70°C to obtain a protective layer with a thickness of 10 nm, thereby obtaining the composite current collector.

[0089] Example 2

[0090] The difference between this embodiment and Example 1 is that the thickness of the carbon layer is 5 nm, and the specific process conditions are: target power is 6 kW, argon flow rate is 100 mL / min, coating vacuum is 0.5 Pa, coating time is 1 s, and the temperature of the main roller during the coating process is 0°C.

[0091] The rest of the preparation methods and parameters remained the same as in Example 1.

[0092] Example 3

[0093] The difference between this embodiment and Example 1 is that the thickness of the carbon layer is 10 nm, and the specific process conditions are: target power is 6 kW, argon flow rate is 100 mL / min, coating vacuum is 0.5 Pa, coating time is 2 s, and the temperature of the main roller during the coating process is 0°C.

[0094] The rest of the preparation methods and parameters remained the same as in Example 1.

[0095] Example 4

[0096] The difference between this embodiment and Example 1 is that the thickness of the carbon layer is 20 nm, and the specific process conditions are: target power is 6 kW, argon flow rate is 100 mL / min, coating vacuum is 0.5 Pa, coating time is 4 s, and the temperature of the main roller during the coating process is 0°C.

[0097] The rest of the preparation methods and parameters remained the same as in Example 1.

[0098] Example 5

[0099] This embodiment differs from embodiment 1 in that a composite conductive layer containing a carbon layer is deposited on one side of the PET film, and a composite conductive layer without a carbon layer is deposited on the other side of the PET film. The remaining preparation methods and parameters remain the same as those in embodiment 1.

[0100] Example 6

[0101] The difference between this embodiment and Example 3 is that the thickness of the seed layer is 40 nm, and the specific process conditions are: target power is 12 kW, argon flow rate is 50 mL / min, coating vacuum is 0.08 Pa, coating time is 4 s, and the temperature of the main roller during the coating process is 2°C.

[0102] The rest of the preparation methods and parameters remained the same as in Example 3.

[0103] Example 7

[0104] The difference between this embodiment and embodiment 3 is that the thickness of the seed layer is 80nm, and the specific process conditions are: target power is 12kW, argon flow rate is 50mL / min, coating vacuum is 0.08Pa, coating time is 8s, and the temperature of the main roller during the coating process is 2°C.

[0105] The rest of the preparation methods and parameters remained the same as in Example 3.

[0106] Example 8

[0107] The difference between this embodiment and embodiment 3 is that the polymer base film is a PP film.

[0108] The rest of the preparation methods and parameters remained the same as in Example 3.

[0109] Example 9

[0110] The difference between this embodiment and Example 1 is that the thickness of the carbon layer is 0.5 nm, and the specific process conditions are: target power is 3 kW, argon flow rate is 100 mL / min, coating vacuum is 0.5 Pa, coating time is 0.25 s, and the temperature of the main roller during the coating process is 0°C.

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

[0112] Example 10

[0113] The difference between this embodiment and Example 1 is that the thickness of the carbon layer is 25 nm, and the specific process conditions are: target power is 6 kW, argon flow rate is 100 mL / min, coating vacuum is 0.5 Pa, coating time is 5 s, and the temperature of the main roller during the coating process is 0°C.

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

[0115] Comparative Example 1

[0116] The difference between this comparative example and Example 1 is that no carbon layer is prepared on both sides of the polymer base film.

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

[0118] Comparative Example 2

[0119] The difference between this comparative example and Example 1 is that no carbon layer is provided in the composite conductive layer, but the carbon layer is provided between the bonding layer and the composite conductive layer, that is, the carbon layer is prepared first, and then the seed layer and the thickening layer are prepared.

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

[0121] Comparative Example 3

[0122] The difference between this comparative example and Example 1 is that no carbon layer is provided in the composite conductive layer, but the carbon layer is provided between the composite conductive layer and the protective layer, that is, the seed layer and the thickening layer are prepared first, and then the carbon layer is prepared.

[0123] The rest of the preparation methods and parameters remained the same as in Example 1.

[0124] Performance Testing

[0125] The sheet resistance, defect rate, and adhesion between the polymer base film and the composite conductive layer of the composite current collector prepared in the above examples and comparative examples were tested. The specific testing method is as follows:

[0126] 1) Sheet resistance: Place the flat composite current collector product on the sample table and use a four-probe sheet resistance meter to test the sheet resistance of the sample;

[0127] 2) Defect rate: Place the finished composite copper current collector with an area of ​​A0 in a surface quality inspection system (micro-visual charge-coupled device CCD) and scan its surface. The optical signal is then converted into an electrical signal and transmitted to a computer. The defect area of ​​the finished product is counted and recorded as A1. The defect rate is (A0 / A1)×100%;

[0128] 3) Adhesion between polymer base film and composite conductive layer: A layer of Permacel P-94 double-sided tape was adhered to a 1 mm thick aluminum foil, the composite current collector was adhered on top of the double-sided tape, and a layer of ethylene acrylic acid copolymer film (DuPont Nurcel0903, thickness of 50 μm) was covered on the top of the finished product; then, a layer of Permacel P-94 double-sided tape was adhered to the composite current collector on top of the double-sided tape. 5 N / m 2 , hot pressing at 120℃ for 10s, cooling to room temperature, and then cutting into small strips of 150mm×15mm; finally, the finished strips of ethylene acrylic acid copolymer film are fixed on the upper fixture of the tensile machine, and the rest are fixed on the lower fixture. After fixation, the two are peeled off at an angle of 180o and a speed of 100mm / min to test the peeling force, that is, the bonding force between the polymer base film and the composite conductive layer is obtained.

[0129] The above test results are shown in Table 1.

[0130] Table 1

[0131] analyze:

[0132] As can be seen from the above table, the composite current collector developed in this application can achieve improved mechanical properties of the composite current collector due to its unique conductive layer structure, effectively promoting its stability during battery processing and cycling.

[0133] It can be seen from Examples 1-8 and Comparative Examples 1-3 that by introducing a carbon layer between the seed layer and the thickening layer, the defect rate of the prepared composite current collector is reduced, thereby causing the square resistance to be reduced, that is, the conductivity to be improved, and the adhesion between the polymer base film and the composite conductive layer in the composite current collector to be improved.

[0134] It can be seen from Examples 1-4 and Examples 9-10 that by increasing the thickness of the carbon layer, the defects of the prepared composite current collector are first reduced to 0 and then remain unchanged, causing the square resistance to first decrease and then remain unchanged, and the adhesion between the polymer base film and the composite conductive layer in the composite current collector is first increased and then remains unchanged. However, if the thickness of the carbon layer is too low, the defect rate of the prepared composite current collector will increase. If the thickness of the carbon layer is too high, the effect cannot be further improved, but it will bring about the problem of increased energy consumption and raw material consumption, resulting in cost waste.

[0135] It can be seen from Example 1, Example 5 and Comparative Example 1 that the composite current collector with a single-sided carbon layer can still achieve good results, but the performance of the composite current collector with a double-sided carbon layer is better than that of the composite current collector with a single-sided carbon layer.

[0136] It can be seen from Examples 3, 6, 7 and 8 that when the thickness of the seed layer changes or the polymer base film changes, the composite current collector can still achieve good results due to the presence of the carbon layer.

[0137] It can be seen from Example 1 and Comparative Examples 2-3 that if the carbon layer is set between the bonding layer and the composite conductive layer, or if the carbon layer is set between the composite conductive layer and the protective layer, it will not be effective. That is, due to the lack of the carbon layer on the surface of the seed layer, it is impossible to prevent the defects caused by the contact and adhesion of the seed layers on the surface of the composite current collector semi-finished product, which in turn leads to the generation of a thickened copper layer with a higher defect rate by electroplating, affecting the conductivity and structural stability of the composite current collector.

[0138] 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 current collector comprising a polymer base film, and an adhesive layer and a composite conductive layer sequentially stacked on at least one surface of the polymer base film; The composite conductive layer includes a carbon layer.

2. The composite current collector according to claim 1, wherein The composite conductive layer also includes a seed layer and a thickening layer; Optionally, along a direction away from the polymer-based film, the composite conductive layer includes a seed layer, a carbon layer and a thickening layer in sequence; Optionally, the carbon layer is an amorphous carbon layer; Optionally, the material of the seed layer includes metallic copper and / or copper alloy, and may further be metallic copper; Optionally, the seed layer is further doped with carbon, and the content of the carbon element accounts for 0.1-5% of the total mass of the seed layer; Optionally, the material of the thickening layer includes metallic copper and / or copper alloy, and may further be metallic copper; Optionally, the thickened layer is further doped with carbon element, and the content of the carbon element accounts for 0.1-5% of the total mass of the thickened layer.

3. The composite current collector according to claim 2, wherein: The thickness of the seed layer is 40-100 nm; Optionally, the thickness of the carbon layer is ≥1 nm, and further optionally 5-20 nm; Optionally, the thickness of the thickened layer is 500-2000 nm, further optionally 800-1200 nm.

4. The composite current collector according to any one of claims 1 to 3, wherein: The thickness of the polymer base film is 1-10 μm; Optionally, 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; Optionally, the thickness of the bonding layer is 1-10 nm; Optionally, a protective layer is provided on the surface of the composite conductive layer away from the polymer base film; Optionally, the material of the protective layer includes any one or a combination of at least two 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; Optionally, the thickness of the protective layer is 5-100 nm, and further optionally 10-80 nm.

5. A method for preparing the composite current collector according to any one of claims 1 to 4, comprising the following steps: sequentially preparing an adhesive layer and a composite conductive layer on at least one surface of the polymer base film; The composite conductive layer includes a carbon layer.

6. The preparation method according to claim 5, wherein Along the direction away from the polymer base film, the composite conductive layer includes a seed layer, a carbon layer and a thickening layer in sequence; Optionally, the carbon layer is prepared by a method comprising magnetron sputtering and / or chemical vapor deposition, and further optionally by magnetron sputtering; Optionally, the specific process parameters of the magnetron sputtering method include: The target power is 2-10kW, the gas flow rate is 30-200mL / min, and the vacuum degree is ≤1Pa.

7. The preparation method according to claim 6, wherein The preparation method of the seed layer is physical vapor deposition; Optionally, the preparation method of the thickened layer includes electroplating; Optionally, in the electroplating method, the components of the electroplating solution include copper sulfate, sulfuric acid, HCl, a brightener, a leveler, and a wetting agent; Optionally, the specific process parameters of the electroplating method include: The average cathode current density is 0.5-5A / dm 2 , the plating solution temperature is 15-35℃, and the electroplating time is 1-20min.

8. The preparation method according to any one of claims 5 to 7, wherein The preparation method of the bonding layer includes physical vapor deposition and / or coating method.

9. The preparation method according to any one of claims 5 to 8, wherein The preparation method comprises the following steps: (1) preparing a polymer base film with a thickness of 1-10 μm by a melt-extrusion-biaxial stretching method; (2) depositing a bonding layer with a thickness of 1-10 nm on each side of the polymer base film by magnetron sputtering, physical vapor deposition or coating to obtain a composite film having a bonding layer on the surface; (3) using physical vapor deposition to deposit a seed layer with a thickness of 40-100 nm on each side of the composite film having the bonding layer on the surface, then using magnetron sputtering and / or chemical vapor deposition to deposit a carbon layer with a thickness of 1 nm or more on each side of the composite film including the seed layer, and then using electroplating to deposit a thickening layer with a thickness of 500-2000 nm on the surface of the carbon layer to obtain a composite film having a composite conductive layer on the surface; (4) A protective layer with a thickness of 5-100 nm is deposited on both sides of the composite film having a composite conductive layer on the surface by physical vapor deposition, chemical vapor deposition, in-situ forming or coating.

10. A lithium ion battery, wherein: The negative electrode of the lithium-ion battery includes the composite current collector according to any one of claims 1 to 4 or the composite current collector prepared by the preparation method of the composite current collector according to any one of claims 5 to 9.

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