Double-layer carbon-coated current collector and preparation method therefor, electrode sheet, and battery

Abstract

A double-layer carbon-coated current collector and a preparation method therefor, an electrode sheet, and a battery. The double-layer carbon-coated current collector comprises a foil, a carbon-coated layer, and a gallium-indium alloy coating, wherein at least one surface of the foil is coated with the carbon-coated layer, and a surface of the carbon-coated layer is coated with the gallium-indium alloy coating. In the double-layer carbon-coated current collector, the carbon-coated layer on the surface of the foil improves the current collection intensity of the current collector for active material, improves the rate capability, and reduces the resistance; and the provision of the gallium-indium alloy coating can enhance the electron transport capability of the current collector, effectively suppress the thermal runaway reaction at high temperature, and improve the safety performance of the battery.

Description

Double-layer carbon-coated current collector, preparation method thereof, pole piece, and battery Technical Field

[0001] The present application belongs to the field of battery technology and relates to a double-layer carbon-coated current collector, a preparation method thereof, a pole piece, and a battery. Background Art

[0002] During the manufacturing process of lithium-ion batteries and sodium-ion batteries, in order to improve the current collection intensity of the current collector for the active material and the adhesion performance of the active material to the electrode, a conductive material is coated on the surface of the current collector, and then the active material is directly coated on the surface of the current collector with the conductive material when manufacturing the electrode.

[0003] CN 116230947A discloses a high-safety current collector, comprising a current collector layer and a heat-conducting, flame-retardant polymer layer disposed on the current collector layer. The heat-conducting, flame-retardant polymer layer is provided with hollowing, thereby achieving the purpose of differentially isolating the current collector layer. The high-safety current collector can effectively separate the active material slurry, thereby effectively differentially isolating the electrode sheets, controlling the risk of local overheating or short circuit of the electrode sheets during operation within a certain range, and preventing single-point overheating and short circuit from spreading to the entire electrode sheet. The heat-conducting, flame-retardant polymer layer of the high-safety current collector also has the function of flame retardancy and heat dissipation, further preventing thermal runaway of the battery and improving battery safety. In addition, the preparation method has the advantages of simple operation and low cost, is suitable for large-scale production and application, and has broad application prospects.

[0004] CN 116111104A relates to a composite current collector and its preparation method, belonging to the field of secondary battery technology. The disclosed composite current collector comprises a shape-memory polymer support layer having a pointed cone-shaped original structure, with the openings of the support layer filled with a foaming agent and a foaming aid. The disclosed composite current collector can reduce weight and increase the energy density of the battery. Furthermore, the disclosed composite current collector has a thermally sensitive function. Firstly, it has a self-blocking design that can interrupt the electrochemical reaction within the secondary battery after thermal runaway or external impact. Secondarily, it can reduce heat generation in the secondary battery at high temperatures, providing a triple guarantee for battery safety.

[0005] Existing current collectors are unable to cut off the electron collection and transmission function of active material at high temperatures, and are unable to curb the internal reactions of the battery caused by high temperatures, leading to thermal runaway and causing battery explosion and combustion.

[0006] Therefore, how to design a new current collector structure to improve battery safety performance is a technical problem that needs to be solved urgently.

[0007] Summary of the Invention

[0008] 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.

[0009] The present application provides a double-layer carbon-coated current collector, a preparation method thereof, an electrode, and a battery. The double-layer carbon-coated current collector provided by the present application has a carbon coating layer on the surface of the foil material that improves the current collection intensity of the current collector for the active material, improves the rate performance and reduces the resistance; providing a gallium-indium alloy coating can enhance the electron transmission ability of the current collector, effectively curb the thermal runaway reaction at high temperature, and improve the safety performance of the battery.

[0010] To achieve this goal, this application adopts the following technical solutions:

[0011] In a first aspect, the present application provides a double-layer carbon-coated current collector, which includes a foil, a carbon-coated layer and a gallium-indium alloy coating, wherein the carbon-coated layer is coated on at least one surface of the foil, and the gallium-indium alloy coating is coated on the surface of the carbon-coated layer.

[0012] The double-layer carbon-coated current collector provided in this application has a carbon-coated layer on the surface of the foil that improves the current collection intensity of the current collector for the active material, improves the rate performance and reduces the resistance; the provision of a gallium-indium alloy coating can enhance the electron transmission ability of the current collector, effectively curb the thermal runaway reaction at high temperature, and improve the safety performance of the battery.

[0013] Gallium-indium alloy is liquid metal at room temperature and belongs to semiconductor with certain conductivity. The resistivity of gallium-indium alloy at room temperature is about 10 -3 ~10 -4 Ω·cm, oxidized at high temperature to form gallium oxide and indium oxide, the resistivity of gallium oxide is about 10 4 ~10 8 Ω·cm, the resistivity of indium oxide is about 10 3 ~10 5 Ω·cm; therefore, due to the sharp increase in resistance, the electron transport of the active material can be blocked, preventing the battery from further reacting and thermal runaway, leading to combustion and explosion.

[0014] In one embodiment, the carbon coating layer includes a conductive carbon material and a binder.

[0015] In one embodiment, the conductive carbon material includes any one or a combination of at least two of conductive carbon black, conductive graphite, carbon nanotubes, carbon nanofibers or graphene. Typical but non-limiting combinations include a combination of conductive carbon black and conductive graphite, a combination of conductive graphite and carbon nanotubes, a combination of carbon nanotubes and carbon nanofibers, a combination of carbon nanofibers and graphene, a combination of conductive carbon black, conductive graphite and carbon nanotubes, a combination of conductive graphite, carbon nanotubes and carbon nanofibers, and a combination of carbon nanotubes, carbon nanofibers and graphene.

[0016] In one embodiment, the binder comprises an acrylic resin.

[0017] In one embodiment, the single-sided thickness of the carbon coating layer is ≤1 μm, for example, 1 μm, 0.8 μm, 0.6 μm, 0.4 μm, 0.2 μm or 0.1 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] In one embodiment, the melting point of the gallium-indium alloy in the gallium-indium alloy coating is -19 to 16°C, for example, it can be -19°C, -15°C, -5°C, 0°C, 5°C, 10°C or 15°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] In one embodiment, the thickness of the gallium-indium alloy coating is 0.5 to 1 μm, for example, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] In one embodiment, the single-sided loading of the gallium-indium alloy coating is 1 to 3 mg / cm 2 , for example, it can be 1 mg / cm 2 , 1.5mg / cm 2 , 2mg / cm 2 , 2.5mg / cm 2 or 3 mg / cm 2 , but not limited to the listed values, other unlisted values ​​within the numerical range are also applicable.

[0021] This application ensures that the thickness selection and loading selection of the gallium-indium alloy coating promote its function. If the thickness or single-sided loading is too small, the temperature control effect is not obvious and the safety performance requirements cannot be met. If the thickness or single-sided loading is too large, the resistance at room temperature is too large and the electrochemical performance requirements cannot be met.

[0022] In one embodiment, the mass percentage of gallium in the gallium-indium alloy coating is 30-90 wt%, for example, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt% or 90 wt%, with the remainder being indium.

[0023] The corresponding table of gallium-indium alloy melting points is as follows:

[0024] The content of gallium and indium in the gallium-indium alloy coating of the present application will affect the melting point of the gallium-indium alloy. If the gallium content in the gallium-indium alloy is too high and the indium content is too low, the increase in thermal resistance at high temperature is low, that is, the temperature control effect is not obvious. If the gallium content is too low and the indium content is too high, the melting point of the alloy is too high and it cannot be used at room temperature.

[0025] The gallium-indium alloy in this application has the characteristics of low melting point, high electrical conductivity, good fluidity, and high chemical stability. As a current collector alloy coating, it can enhance the electron transmission capacity of the current collector. In addition, because the positive electrode material releases oxygen during the charging and discharging process, the gallium-indium alloy basically does not undergo oxidation reaction at room temperature. Only when it is above room temperature will gallium be partially oxidized. When it exceeds 100°C, indium will oxidize to form gallium oxide and indium oxide. The resistance increases from a few milliohms to hundreds of milliohms, which hinders electron transmission, effectively curbs further thermal runaway reactions at high temperatures, and improves the safety performance of the battery.

[0026] In one embodiment, the foil material includes aluminum foil and / or composite aluminum foil.

[0027] Further research found that the wettability of the double-layer carbon-coated current collector of the present application to the electrolyte is greatly improved, that is, the electrolyte can completely wet the double-layer carbon-coated current collector, and its contact angle is 0°, thereby promoting the contact between the electrolyte and the electrode, increasing the contact area, reducing the interface resistance, improving the electrode stability, and increasing the lithium ion diffusion rate in the electrolyte, thereby improving the performance of the battery.

[0028] In a second aspect, the present application provides a method for preparing the double-layer carbon-coated current collector according to the first aspect, the preparation method comprising:

[0029] (1) preparing a carbon coating slurry, applying the obtained carbon coating slurry on the surface of the foil, drying and rolling it to obtain a carbon coating layer;

[0030] (2) Coating gallium-indium alloy liquid metal on the surface of the carbon-coated layer to obtain the double-layer carbon-coated current collector.

[0031] In one embodiment, the carbon coating layer slurry in step (1) includes, by mass percentage: 4 to 12 parts of conductive carbon material, for example, 4 parts, 6 parts, 8 parts, 10 parts or 12 parts, 10 to 60 parts of binder, for example, 10 parts, 20 parts, 30 parts, 40 parts, 50 parts or 60 parts, 3 to 20 parts of wetting agent, for example, 3 parts, 5 parts, 10 parts, 15 parts or 20 parts, and the balance is solvent.

[0032] In one embodiment, the solid content of the carbon coating slurry in step (1) is 8 to 16%, for example, it can be 8%, 10%, 12%, 14% or 16%, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0033] In one embodiment, the pH of the carbon coating slurry in step (1) is 4 to 9, for example, 4, 5, 6, 7, 8 or 9, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] In one embodiment, the conductive carbon material includes any one or a combination of at least two of conductive carbon black, conductive graphite, carbon nanotubes, carbon nanofibers or graphene. Typical but non-limiting combinations include a combination of conductive carbon black and conductive graphite, a combination of conductive graphite and carbon nanotubes, a combination of carbon nanotubes and carbon nanofibers, a combination of carbon nanofibers and graphene, a combination of conductive carbon black, conductive graphite and carbon nanotubes, a combination of conductive graphite, carbon nanotubes and carbon nanofibers, and a combination of carbon nanotubes, carbon nanofibers and graphene.

[0035] In one embodiment, the binder comprises an acrylic resin.

[0036] In one embodiment, the wetting agent includes any one of isopropyl alcohol, propylene glycol, n-octanol, polyethylene glycol or polyoxyethylene ether, or a combination of at least two thereof. Typical non-limiting combinations include a combination of isopropyl alcohol and propylene glycol, a combination of propylene glycol and n-octanol, a combination of n-octanol and polyethylene glycol, a combination of polyethylene glycol and polyoxyethylene ether, a combination of isopropyl alcohol, propylene glycol and n-octanol, a combination of propylene glycol, n-octanol and polyethylene glycol, and a combination of n-octanol, polyethylene glycol and polyoxyethylene ether.

[0037] In one embodiment, the solvent comprises deionized water.

[0038] In one embodiment, the method for preparing the carbon coating layer slurry in step (1) comprises:

[0039] (a) mixing a binder and a solvent, and stirring to obtain a binder solution;

[0040] (b) mixing the conductive carbon material and the obtained binder solution, and stirring to obtain a conductive solution;

[0041] (c) mixing the wetting agent and the obtained conductive solution, and stirring to obtain a mixed solution;

[0042] (d) performing particle size treatment and vacuuming on the obtained mixed solution to obtain the carbon coating layer slurry.

[0043] In one embodiment, the stirring rates in step (a), step (b) and step (c) are independently 10 to 6000 rpm, for example, 10 rpm, 100 rpm, 500 rpm, 1000 rpm, 3000 rpm, 5000 rpm or 6000 rpm, the temperatures are independently 15 to 30° C., for example, 15° C., 20° C., 25° C. or 30° C., and the times are independently 15 to 90 min, for example, 15 min, 30 min, 50 min, 70 min or 90 min, but are not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0044] In one embodiment, after the particle size treatment in step (d), D50<2μm and D90<5μm in the solution, D50<2μm can be, for example, 0.1μm, 0.5μm, 1μm, 1.5μm or 2μm, and D90<5μm can be, for example, 1μm, 2μm, 3μm, 4μm or 4.5μm, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] In one embodiment, the vacuum treatment in step (d) also includes stirring, and the specific steps include: tumbling stirring under double planetary stirring at a speed of 8 to 12 rpm, for example, 8 rpm, 9 rpm, 10 rpm, 11 rpm or 12 rpm, the vacuum degree is <-0.07 KPa, for example, -5 KPa, -1 KPa, -0.5 KPa, -0.1 KPa or -0.08 KPa, the temperature is 15 to 30 ° C, for example, 15 ° C, 18 ° C, 20 ° C, 25 ° C or 30 ° C, and the time is 30 to 60 min, for example, 30 min, 35 min, 40 min, 50 min or 60 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0046] In one embodiment, the coating in step (1) is performed in a coating machine.

[0047] In one embodiment, the coating speed in step (1) is 40 to 120 m / min, for example, 40 m / min, 60 m / min, 80 m / min, 100 m / min or 120 m / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0048] In one embodiment, the drying temperature in step (1) is 75-120°C, for example, 75°C, 90°C, 100°C, 110°C or 120°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0049] In one embodiment, the coating method in step (2) includes using any one or a combination of at least two of a brush, a rubber brush or a scraper for coating. Typical non-limiting combinations include a combination of a brush and a rubber brush, a combination of a rubber brush and a scraper, and a combination of a brush and a scraper.

[0050] In a third aspect, the present application provides a pole piece, which contains the double-layer carbon-coated current collector as described in the first aspect.

[0051] In a fourth aspect, the present application provides a battery, wherein the battery contains the double-layer carbon-coated current collector as described in the first aspect or the pole piece as described in the third aspect.

[0052] According to the above technical solution, the beneficial effects of this application are as follows:

[0053] The double-layer carbon-coated current collector provided in this application has a carbon-coated layer on the surface of the foil that improves the current collection intensity of the current collector for the active material, improves the rate performance and reduces the resistance; the provision of a gallium-indium alloy coating can enhance the electron transmission ability of the current collector, effectively curb the thermal runaway reaction at high temperature, and improve the safety performance of the battery.

[0054] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] 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 on the technical solution of this article.

[0056] FIG1 is a schematic structural diagram of the double-layer carbon-coated current collector described in Example 1.

[0057] FIG2 is a schematic structural diagram of the double-layer carbon-coated current collector described in Example 2.

[0058] FIG3 is a schematic diagram of the contact angle of the double-layer carbon-coated current collector described in Example 1 after being wetted by the electrolyte.

[0059] FIG4 is a schematic diagram of the contact angle of the carbon-coated current collector in Comparative Example 1 after being wetted with the electrolyte.

[0060] Among them: 1-foil, 2-carbon coating layer, 3-gallium-indium alloy coating. DETAILED DESCRIPTION

[0061] The technical solution of the present application will be further described below with reference to the accompanying drawings and through specific implementation methods. Those skilled in the art should understand that the embodiments are only for the purpose of helping to understand the present application and should not be regarded as specific limitations of the present application.

[0062] Example 1

[0063] This embodiment provides a double-layer carbon-coated current collector (as shown in FIG1 ), which includes a foil 1 , a carbon-coated layer 2 , and a gallium-indium alloy coating 3 .

[0064] The foil material 1 is aluminum foil with a thickness of 13 μm.

[0065] The carbon coating layer 2 is coated on both surfaces of the foil 1 . The thickness of the carbon coating layer 2 on one side is 0.7 μm. The carbon coating layer 2 includes SP-Li, acrylic resin and isopropyl alcohol.

[0066] The gallium-indium alloy coating 3 is coated on the surface of the carbon coating layer 2, wherein the gallium-indium alloy has a melting point of 15.7°C and contains 65 wt% gallium and 35 wt% indium. The single-sided thickness of the gallium-indium alloy coating 3 is 0.5 μm, and the single-sided loading is 2 mg / cm 2 .

[0067] The preparation method of the double-layer carbon-coated current collector comprises:

[0068] (1) A carbon coating slurry is prepared. The carbon coating slurry comprises, by weight percentage, 5 wt% of a conductive carbon material SP-Li, 20 wt% of a binder acrylic resin, 15 wt% of isopropyl alcohol, and the balance is deionized water. The solid content of the carbon coating slurry is 8.9% and the pH is 6.3. The preparation method is as follows:

[0069] a. Mix the acrylic resin and deionized water according to the formula at a stirring speed of 2000 rpm, a temperature of 25 ± 5 ℃, and a time of 15 min to obtain a binder solution;

[0070] b. The SP-Li conductive carbon material was divided into two equal portions and sequentially added to the resulting binder solution and stirred at a stirring speed of 4000 rpm, a temperature of 25 ± 5 ° C, and a total stirring time of 30 min to obtain a conductive solution;

[0071] c. Mix isopropyl alcohol and the resulting conductive solution with a stirring speed of 4000 rpm and a temperature of 25±5°C for 30 min to obtain a mixed solution;

[0072] d. The obtained mixed solution was processed by a homogenizer for particle size treatment. After treatment, D50 = 0.989 μm, D90 = 4.12 μm, and a dispersed mixed solution was obtained. The solution was then vacuumed while stirring in a double planetary mixer at a stirring speed of 10 rpm, a vacuum degree of <-0.07 KPa, a temperature of 25 ± 5 ° C, and a time of 30 min to obtain the carbon coating slurry;

[0073] (2) coating the obtained carbon coating slurry on the surface of the foil 1 at a speed of 80 m / min. The foil 1 is an aluminum foil pretreated by a corona machine, and then drying at 85°C and rolling up to obtain the carbon coating layer 2;

[0074] (3) Gallium-indium alloy liquid metal is coated on the surface of the carbon-coated layer 2 with a brush to obtain the double-layer carbon-coated current collector.

[0075] Example 2

[0076] This embodiment provides a double-layer carbon-coated current collector (as shown in FIG2 ). The difference from Example 1 is that the carbon-coated layer 2 is coated on one surface of the foil 1, and the thickness of the carbon-coated layer 2 on one side is 1 μm. The gallium-indium alloy coating 3 is coated on the surface of the carbon-coated layer 2, and the loading of the gallium-indium alloy coating on one side is 1 mg / cm 2 , the rest are the same as in Example 1.

[0077] Example 3

[0078] This embodiment provides a double-layer carbon-coated current collector. The difference from embodiment 1 is that the thickness of the gallium-indium alloy coating on one side is 1 μm, and the loading on one side is 3 mg / cm 2 , the rest are the same as in Example 1.

[0079] Example 4

[0080] This embodiment provides a double-layer carbon-coated current collector, which differs from Example 1 in that the thickness of the gallium-indium alloy coating on one side is 0.3 μm, and the rest is the same as Example 1.

[0081] Example 5

[0082] This embodiment provides a double-layer carbon-coated current collector, which differs from Example 1 in that the thickness of the gallium-indium alloy coating on one side is 1.5 μm, and the rest is the same as Example 1.

[0083] Example 6

[0084] This embodiment provides a double-layer carbon-coated current collector, which differs from embodiment 1 in that the single-sided loading of the gallium-indium alloy coating is 0.5 mg / cm 2 , the rest are the same as in Example 1.

[0085] Example 7

[0086] This embodiment provides a double-layer carbon-coated current collector. The difference from Example 1 is that the single-sided loading of the gallium-indium alloy coating is 3.5 mg / cm 2 , the rest are the same as in Example 1.

[0087] Example 8

[0088] This embodiment provides a double-layer carbon-coated current collector, which differs from Example 1 in that the gallium-indium alloy has a melting point of 15.1° C. and contains 90 wt % gallium and 10 wt % indium. The rest is the same as Example 1.

[0089] Example 9

[0090] This embodiment provides a double-layer carbon-coated current collector, which differs from Example 1 in that the gallium-indium alloy has a melting point of 10.5° C. and contains 30 wt % gallium and 70 wt % indium. The rest is the same as Example 1.

[0091] Comparative Example 1

[0092] This comparative example provides a carbon-coated current collector, which differs from Example 1 in that it does not contain a gallium-indium alloy coating, and is otherwise the same as Example 1.

[0093] Comparative Example 2

[0094] This comparative example provides a current collector, which differs from Example 1 in that it does not contain a carbon coating layer, and the surface of the foil is coated with a gallium-indium alloy coating. The rest is the same as Example 1.

[0095] The square resistance of the current collector obtained above was tested at room temperature and high temperature using a four-probe resistance tester. The test results are shown in Table 1.

[0096] Table 1

[0097] (1) It can be seen from the examples and comparative examples that the thicker the gallium-indium alloy coating and the greater the density, the more rapidly the square resistance increases with increasing temperature; it can be seen from Examples 1 and 4-7 that the thickness and single-sided loading of the gallium-indium alloy coating will affect the square resistance of the current collector, and when the thickness and loading are within a specific range, it can ensure that the current collector has a lower square resistance at low temperatures and a higher square resistance at high temperatures; it can be seen from Examples 1 and 8-9 that the content of gallium and indium in the gallium-indium alloy will also affect the square resistance of the current collector; it can be seen from Example 1 and comparative examples 1-2 that comparative example 1 does not contain a gallium-indium alloy coating, and the square resistance is small at high temperatures, which cannot guarantee the safety performance of the battery, and although comparative example 2 also shows the result of increased square resistance at high temperatures, the square resistance is large at 25°C, which is not conducive to electrochemical performance.

[0098] (2) After being wetted with the electrolyte, the contact angles of Example 1 and Comparative Example 1 are shown in Figures 3 and 4. It can be seen that the wettability of the double-layer carbon-coated current collector of the present application to the electrolyte is greatly improved, that is, the electrolyte can completely wet the double-layer carbon-coated current collector, and its contact angle is 0°, thereby promoting the contact between the electrolyte and the electrode, increasing the contact area, reducing the interface resistance, improving the electrode stability, and increasing the lithium ion diffusion rate in the electrolyte, thereby improving the performance of the battery.

[0099] In summary, the double-layer carbon-coated current collector provided in this application has a carbon-coated layer on the surface of the foil that improves the current collection intensity of the current collector for the active material, improves the rate performance and reduces the resistance; providing a gallium-indium alloy coating can enhance the electron transmission ability of the current collector, effectively curb the thermal runaway reaction at high temperature, and improve the safety performance of the battery.

[0100] The present application uses the above-mentioned embodiments to illustrate the detailed structural features of the present application. However, the present application is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present application must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements of selected components of the present application, addition of auxiliary components, selection of specific methods, etc., all fall within the scope of protection and disclosure of the present application.

Claims

1. A double-layer carbon-coated current collector, comprising a foil, a carbon-coated layer and a gallium-indium alloy coating, wherein the carbon-coated layer is coated on at least one surface of the foil, and the gallium-indium alloy coating is coated on the surface of the carbon-coated layer.

2. The double-layer carbon-coated current collector according to claim 1, wherein: The carbon coating layer includes a conductive carbon material and a binder.

3. The double-layer carbon-coated current collector according to claim 1 or 2, wherein: The conductive carbon material includes any one of conductive carbon black, conductive graphite, carbon nanotubes, carbon nanofibers or graphene, or a combination of at least two of them.

4. The double-layer carbon-coated current collector according to any one of claims 1 to 3, wherein: The binder includes acrylic resin.

5. The double-layer carbon-coated current collector according to any one of claims 1 to 4, wherein: The single-side thickness of the carbon coating layer is ≤1 μm.

6. The double-layer carbon-coated current collector according to any one of claims 1 to 5, wherein: The melting point of the gallium-indium alloy in the gallium-indium alloy coating is -19 to 16°C; Optionally, the gallium-indium alloy coating has a thickness of 0.5 to 1 μm; Optionally, the single-sided loading of the gallium-indium alloy coating is 1 to 3 mg / cm 2 ; Optionally, the mass percentage of gallium in the gallium-indium alloy coating is 30-90wt%, and the balance is indium; Optionally, the foil material includes aluminum foil and / or composite aluminum foil.

7. A method for preparing the double-layer carbon-coated current collector according to any one of claims 1 to 6, the method comprising: (1) preparing a carbon coating slurry, applying the obtained carbon coating slurry on the surface of the foil, drying and rolling up to obtain a carbon coating layer; (2) Coating gallium-indium alloy liquid metal on the surface of the carbon-coated layer to obtain the double-layer carbon-coated current collector.

8. The preparation method according to claim 7, wherein: The carbon coating slurry of step (1) comprises, by weight percentage: 4 to 12 parts of conductive carbon material, 10 to 60 parts of binder, 3 to 20 parts of wetting agent, and the balance is solvent; Optionally, the solid content of the carbon coating slurry in step (1) is 8 to 16%; Optionally, the pH of the carbon coating slurry in step (1) is 4 to 9; Optionally, the conductive carbon material includes any one or a combination of at least two of conductive carbon black, conductive graphite, carbon nanotubes, carbon nanofibers or graphene; Optionally, the binder includes acrylic resin; Optionally, the wetting agent includes any one or a combination of at least two of isopropyl alcohol, propylene glycol, n-octanol, polyethylene glycol or polyoxyethylene ether; Optionally, the solvent comprises deionized water.

9. The preparation method according to claim 7 or 8, wherein: The method for preparing the carbon coating slurry in step (1) comprises: (a) mixing a binder and a solvent, and stirring to obtain a binder solution; (b) mixing the conductive carbon material and the obtained binder solution, and stirring to obtain a conductive solution; (c) mixing the wetting agent and the obtained conductive solution, and stirring to obtain a mixed solution; (d) subjecting the obtained mixed solution to particle size treatment and vacuuming to obtain the carbon coating layer slurry.

10. The preparation method according to claim 9, wherein: The stirring rates of step (a), step (b) and step (c) are independently 10 to 6000 rpm, the temperatures are independently 15 to 30° C., and the times are independently 15 to 90 min; Optionally, in step (d), after the particle size treatment, D50 in the solution is less than 2 μm and D90 is less than 5 μm; Optionally, the vacuum treatment in step (d) also includes stirring, and the specific steps include: flip stirring under double planetary stirring, the speed is 8 to 12 rpm, the vacuum degree is <-0.07 KPa, the temperature is 15 to 30°C, and the time is 30 to 60 min.

11. The preparation method according to any one of claims 7 to 10, wherein: The coating in step (1) is carried out in a coating machine; Optionally, the coating speed in step (1) is 40 to 120 m / min; Optionally, the drying temperature in step (1) is 75-120° C. Optionally, the coating method in step (2) includes coating with a brush, a rubber brush or a scraper.

12. A pole piece, comprising the double-layer carbon-coated current collector according to any one of claims 1 to 6.

13. A battery, comprising the double-layer carbon-coated current collector according to any one of claims 1 to 6 or the pole piece according to claim 12.

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