Composite copper foil, method for producing the same, current collector, electrode sheet, secondary battery, and electric device

Abstract

The application relates to a composite copper foil and a preparation method thereof, a current collector, an electrode sheet, a secondary battery and an electric device. The preparation method comprises the following steps: sputtering on the surface of a base material by a pulse direct-current power supply to prepare a copper alloy plating layer; sputtering on the surface of the copper alloy plating layer by a direct-current power supply to prepare a pure copper plating layer; wherein the total current of the direct-current power supply is 300 A to 400 A, and the voltage is 400 V to 550 V; the thickness of the pure copper plating layer is 950 nm to 1000 nm; and sputtering on the surface of the pure copper plating layer by a direct-current power supply to prepare a copper-nickel plating layer. The preparation method of the composite copper foil is prepared by a sputtering plating film method in one step, avoids a traditional water electroplating process, is simple in preparation process, and is green and environment-friendly. The composite copper foil prepared by the preparation method has good surface adhesion, oxidation resistance and low square resistance, and is especially suitable for preparing a battery current collector.

Description

Technical Field

[0001] This application relates to the field of new material preparation technology, specifically to a composite copper foil and its preparation method, a current collector, an electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] Composite copper foil is a material with a "copper-polymer material-copper" sandwich structure, which can be used as a current collector in secondary batteries. Specifically, composite copper foil uses materials such as polymer insulating resin as the "core" layer, and metallic copper is deposited on the surface. Compared with traditional copper foil, composite copper foil can improve the energy density of secondary batteries and reduce costs.

[0003] However, traditional composite copper foil is usually prepared by a two-step process. First, an ultra-thin copper film is prepared on the substrate surface by vacuum deposition, and then the copper layer is thickened by electroplating. The process is relatively complicated and the electroplating process is more polluting. Summary of the Invention

[0004] Therefore, it is necessary to provide a composite copper foil with a simple preparation process and an environmentally friendly preparation method.

[0005] In addition, current collectors, electrode sheets, secondary batteries and electrical devices containing the aforementioned composite copper foil are also provided.

[0006] One aspect of this application provides a method for preparing composite copper foil, comprising the following steps:

[0007] A copper alloy target is sputtered using a pulsed DC power supply to deposit a copper alloy coating on the surface of the substrate.

[0008] A pure copper plating layer is deposited on the surface of the copper alloy plating layer by sputtering a pure copper target using a first DC power supply; wherein the total current of the first DC power supply is 300A to 400A and the voltage is 400V to 550V; and the thickness of the pure copper plating layer is 950nm to 1000nm.

[0009] A copper-nickel alloy target is sputtered using a second DC power supply to deposit a copper-nickel plating layer on the surface of the pure copper plating layer.

[0010] The method for preparing composite copper foil provided in this application involves sequentially preparing a copper alloy plating layer, a pure copper plating layer, and a copper-nickel plating layer on a substrate surface to obtain the composite copper foil. The copper alloy plating layer prepared by pulsed DC power sputtering exhibits good overall density, which can improve the adhesion between the plating layer and the substrate. A pure copper plating layer with a thickness of 950nm to 1000nm is prepared by high-power DC power sputtering, resulting in good density and adhesion. Then, a copper-nickel plating layer is prepared by DC power sputtering, which has good oxidation resistance and avoids adverse chemical reactions with battery materials. The above-mentioned method for preparing composite copper foil is a one-step sputtering deposition method, avoiding the electroplating process of traditional composite copper foil preparation methods. The preparation process is simple and environmentally friendly. The composite copper foil prepared by the above method has good surface adhesion, oxidation resistance, and low sheet resistance, making it particularly suitable for preparing battery current collectors.

[0011] In some embodiments, the cooling temperature in the preparation method is 10°C to 20°C.

[0012] In some embodiments, the pulsed DC power supply has a current of 10A to 15A, a voltage of 350V to 450V, and a duty cycle of 40% to 70%.

[0013] In some embodiments, the second DC power supply has a current of 5A to 15A and a voltage of 360V to 430V.

[0014] In some embodiments, the thickness of the copper alloy plating is 10 nm to 15 nm.

[0015] In some embodiments, the copper alloy target material includes one of copper-nickel alloy, copper-zinc alloy, and copper-silver alloy;

[0016] Optionally, the copper alloy target is a copper-nickel alloy, wherein the mass content of nickel in the copper-nickel alloy is 5% to 15%.

[0017] In some embodiments, the thickness of the copper-nickel plating is 15 nm to 20 nm.

[0018] In some embodiments, the nickel content in the copper-nickel plating is 5% to 15% by mass.

[0019] In some embodiments, the substrate satisfies at least one of the conditions (1) to (2):

[0020] (1) The thickness of the substrate is 3μm to 6μm;

[0021] (2) The material of the substrate includes at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene and polyethylene.

[0022] Secondly, this application also provides a composite copper foil, which is prepared according to the above-described method for preparing composite copper foil.

[0023] Thirdly, this application also provides a current collector comprising the composite copper foil described in the second aspect above.

[0024] Fourthly, this application also provides an electrode sheet comprising the current collector described in the third aspect above.

[0025] Fifthly, this application also provides a secondary battery, including the electrode sheet described in the fourth aspect above.

[0026] Sixthly, this application also provides an electrical device, including the secondary battery described in the fifth aspect above. Detailed Implementation

[0027] To facilitate understanding of this application, a more complete description will be provided below. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0028] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0029] In this application, the selection range of "and / or", "or / and", and "and / or" includes any one of two or more related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or", "or / and", and "and / or", it should be understood that the technical solution undoubtedly includes technical solutions connected by "logical AND", and also undoubtedly includes technical solutions connected by "logical OR". For example, "A and / or B" includes three parallel solutions: A, B, and A+B. For example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, a technical solution that is connected by "logical OR"), as well as any and all combinations of A, B, C, and D, that is, combinations of any two or three of A, B, C, and D, and also combinations of all four of A, B, C, and D (that is, a technical solution that is connected by "logical AND").

[0030] In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more.

[0031] In this application, the terms "combinations thereof", "any combination thereof", and "any combination thereof" include all suitable combinations of any two or more of the listed items.

[0032] In this application, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0033] In this application, terms such as "preferred," "better," "more suitable," and "ideal" are used only to describe implementation methods or embodiments with better effects, and should be understood not to constitute a limitation on the scope of protection of this application.

[0034] In this application, terms such as "further," "even further," and "particularly" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0035] In this application, the terms "optionally," "optionally," and "optional" refer to options that are optional, meaning they can be selected from either "with" or "without." If multiple "optional" options appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" option is independent.

[0036] In this application, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only a non-exhaustive enumeration purpose and should be understood not to constitute a closed limitation on quantity.

[0037] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0038] In this application, numerical intervals (i.e., numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the aforementioned numerical intervals are considered continuous and include the two endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. In this document, this is equivalent to directly listing every integer. For example, if t is an integer selected from 1 to 10, it means that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Furthermore, when multiple ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0039] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0040] In this application, percentage content refers to mass percentage for solid-liquid mixtures and solid-phase-solid mixtures, and volume percentage for liquid-phase-liquid mixtures, unless otherwise specified.

[0041] In this application, unless otherwise specified, percentage concentrations refer to final concentrations. The final concentration refers to the percentage of the added component in the system after its addition.

[0042] In this application, % (w / w) and wt% both represent weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass-volume percentage.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] One embodiment of this application provides a method for preparing composite copper foil, including the following steps S110, S120 and S130.

[0045] Step S110: A copper alloy target is sputtered using a pulsed DC power supply to deposit a copper alloy coating on the surface of the substrate. The copper alloy coating prepared by pulsed DC power supply sputtering has good overall density, which can improve the adhesion between the coating and the substrate.

[0046] In some embodiments, the pulsed DC power supply has a current of 10A to 15A, a voltage of 350V to 450V, and a duty cycle of 40% to 70%. The pulsed DC power supply meets these conditions, has relatively low energy, does not damage the surface of the substrate, and produces a dense coating. Optionally, the pulsed DC power supply current is within the range of 10A, 11A, 12A, 13A, 14A, 15A, or any combination thereof. The pulsed DC power supply voltage is within the range of 350V, 360V, 380V, 390V, 400V, 420V, 440V, 450V, or any combination thereof. The pulsed DC power supply duty cycle is within the range of 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any combination thereof.

[0047] In some embodiments, the thickness of the copper alloy coating is 10 nm to 15 nm. A thickness within this range can effectively increase the adhesion between the coating and the substrate. Optionally, the thickness of the copper alloy coating is within the range of 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, or any combination thereof.

[0048] In some embodiments, the copper alloy target material includes one of copper-nickel alloy, copper-zinc alloy, and copper-silver alloy.

[0049] In some embodiments, the copper alloy target is a copper-nickel alloy. The nickel content in the copper-nickel alloy is 5% to 15% by mass. When the nickel content of the copper-nickel alloy is within the above range, the resulting copper alloy coating exhibits both good conductivity and toughness. Optionally, the nickel content in the copper-nickel alloy is within the range of 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any combination thereof.

[0050] Step S120: A pure copper plating layer is deposited on the surface of the copper alloy coating by sputtering a pure copper target using a first DC power supply. The total current of the first DC power supply is 300A–400A, and the voltage is 400V–550V; the thickness of the pure copper plating layer is 950nm–1000nm. The pure copper plating layer with a thickness of 950nm–1000nm is prepared by sputtering with a high-power DC power supply, resulting in good density and adhesion.

[0051] Optionally, in step S120, the current of the first DC power supply is within the range of any combination of 300A, 320A, 340A, 360A, 380A, 400A, or higher. The voltage is within the range of any combination of 400V, 420V, 440V, 460V, 480V, 500V, 520V, 550V, or higher. Optionally, the thickness of the pure copper plating layer is within the range of any combination of 950nm, 960nm, 970nm, 980nm, 990nm, 1000nm, or higher.

[0052] Step S130: A copper-nickel alloy target is sputtered using a second DC power supply to deposit a copper-nickel coating on the surface of the pure copper coating. The copper-nickel coating is prepared by DC power supply sputtering, and it exhibits good oxidation resistance, avoiding adverse chemical reactions with the battery materials.

[0053] In some embodiments, in step S130, the current of the second DC power supply is 5A to 15A, and the voltage is 360V to 430V. Optionally, the current of the second DC power supply in step S130 is within the range of 5A, 7A, 9A, 11A, 13A, 15A, or any combination thereof. Optionally, the voltage of the DC power supply in step S130 is within the range of 360V, 380V, 400V, 410V, 420V, 430V, or any combination thereof.

[0054] In some embodiments, the thickness of the copper-nickel plating is 15 nm to 20 nm. When the thickness of the copper-nickel plating is within this range, the composite copper foil exhibits better oxidation resistance, lower sheet resistance, and better uniformity. Optionally, the thickness of the copper-nickel plating is within the range of 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, or any combination thereof.

[0055] In some embodiments, the nickel content in the copper-nickel plating is 5% to 15% by mass. When the nickel content in the copper-nickel plating is within this range, the copper-nickel plating exhibits superior oxidation resistance, as well as excellent electrical conductivity and toughness. Optionally, the nickel content in the copper-nickel plating is within the range of 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any combination thereof.

[0056] The composite copper foil preparation method provided in this application is a one-step sputtering deposition method. A copper alloy plating layer, a pure copper plating layer, and a copper-nickel plating layer are sequentially prepared on the surface of a substrate to obtain the composite copper foil. This method avoids the electroplating process of traditional composite copper foil preparation methods, making the preparation process simple and environmentally friendly. The composite copper foil prepared by the above method has good surface adhesion, oxidation resistance, and low sheet resistance, making it particularly suitable for preparing battery current collectors.

[0057] In some embodiments, the cooling temperature in steps S110 to S130 is 10°C to 20°C. Controlling the cooling temperature within this range is beneficial for the sputtering target to deposit a coating on the substrate surface.

[0058] In some embodiments, in steps S110 to S130, cooling is performed on the back side of the sputtered substrate by a cooling roller.

[0059] In some embodiments, the thickness of the substrate is 3 μm to 6 μm. Optionally, the thickness of the substrate is within the range of 3 μm, 4 μm, 5 μm, 6 μm, or any combination thereof.

[0060] In some embodiments, the substrate material includes, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0061] Secondly, this application also provides a composite copper foil, which is prepared according to the above-described method for preparing composite copper foil.

[0062] In some embodiments, the sheet resistance of the composite copper foil is ≤25mΩ.

[0063] Thirdly, this application also provides a current collector comprising the composite copper foil described in the second aspect above.

[0064] The aforementioned current collector includes the aforementioned composite copper foil. The current collector has good adhesion, oxidation resistance, and good conductivity.

[0065] Fourthly, this application also provides an electrode sheet comprising the current collector described in the third aspect above.

[0066] In some embodiments, the electrode sheet includes the aforementioned current collector and an active material layer disposed on at least one surface of the current collector.

[0067] Fifthly, this application also provides a secondary battery, including the electrode sheet described in the fourth aspect above.

[0068] Sixthly, this application also provides an electrical device, including the secondary battery described in the fifth aspect above.

[0069] To make the objectives, technical solutions, and advantages of this application clearer and more concise, the following specific embodiments are used for illustration, but this application is by no means limited to these embodiments. The embodiments described below are merely preferred embodiments of this application and can be used to describe this application, but should not be construed as limiting the scope of this application. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

[0070] To better illustrate this application, the following description, in conjunction with specific embodiments, further explains its content. The following are specific embodiments.

[0071] Example 1

[0072] The method for preparing the composite copper foil in this embodiment includes the following steps:

[0073] (1) Use a PET film with a thickness of 5μm as the substrate.

[0074] (2) Using a copper-nickel alloy (nickel content 10%) as the target material, a copper alloy coating is deposited on the substrate surface by pulsed DC power supply sputtering. The thickness of the copper alloy coating is 10 nm. The pulsed DC power supply has a current of 10 A, a voltage of 350 V, and a duty cycle of 40%.

[0075] (3) Using metallic copper as the target material, a pure copper coating is prepared by sputtering on the surface of the copper alloy coating with a DC power supply. The thickness of the pure copper coating is 950 nm. The total current of the DC power supply is 350 A and the voltage is 460 V.

[0076] (4) Using a copper-nickel alloy (nickel content 10%) as the target material, a copper-nickel coating is deposited on the surface of a pure copper coating by pulsed DC power supply. The thickness of the copper-nickel coating is 15nm. The DC power supply has a current of 7A and a voltage of 370V.

[0077] In steps (2) to (4), the cooling temperature is 20°C.

[0078] The film adhesion of the composite copper foil obtained in step (4) was 5B, the sheet resistance of the composite copper foil was ≤22mΩ, the sheet resistance uniformity was ±5%, and the sheet resistance change rate was 10% after baking at 140℃ for 1 hour.

[0079] Example 2

[0080] The method for preparing the composite copper foil in this embodiment includes the following steps:

[0081] (1) Use a PET film with a thickness of 5μm as the substrate.

[0082] (2) Using a copper-nickel alloy (nickel content 10%) as the target material, a copper alloy coating is deposited on the substrate surface by pulsed DC power supply sputtering. The thickness of the copper alloy coating is 10 nm. The pulsed DC power supply has a current of 10 A, a voltage of 350 V, and a duty cycle of 40%.

[0083] (3) Using metallic copper as the target material, a pure copper coating is prepared by sputtering on the surface of the copper alloy coating with a DC power supply. The thickness of the pure copper coating is 980 nm. The total current of the DC power supply is 355 A and the voltage is 467 V.

[0084] (4) Using a copper-nickel alloy (nickel content 10%) as the target material, a copper-nickel coating is deposited on the surface of a pure copper coating by pulsed DC power supply. The thickness of the copper-nickel coating is 15nm. The DC power supply has a current of 7A and a voltage of 370V.

[0085] In steps (2) to (4), the cooling temperature is 20°C.

[0086] The film adhesion of the composite copper foil obtained in step (4) was 5B, the sheet resistance of the composite copper foil was ≤21mΩ, the sheet resistance uniformity was ±5%, and the sheet resistance change rate was 10% after baking at 140℃ for 1 hour.

[0087] Example 3

[0088] The method for preparing the composite copper foil in this embodiment includes the following steps:

[0089] (1) Use a PET film with a thickness of 5μm as the substrate.

[0090] (2) Using a copper-nickel alloy (nickel content 10%) as the target material, a copper alloy coating is deposited on the substrate surface by pulsed DC power supply sputtering. The thickness of the copper alloy coating is 10 nm. The pulsed DC power supply has a current of 10 A, a voltage of 350 V, and a duty cycle of 40%.

[0091] (3) Using metallic copper as the target material, a pure copper coating is prepared by sputtering on the surface of the copper alloy coating with a DC power supply. The thickness of the pure copper coating is 1000 nm. The total current of the DC power supply is 358 A and the voltage is 473 V.

[0092] (4) Using a copper-nickel alloy (nickel content 10%) as the target material, a copper-nickel coating is deposited on the surface of a pure copper coating by pulsed DC power supply. The thickness of the copper-nickel coating is 15nm. The DC power supply has a current of 7A and a voltage of 370V.

[0093] In steps (2) to (4), the cooling temperature is 20°C.

[0094] The film adhesion of the composite copper foil obtained in step (4) was 5B, the sheet resistance of the composite copper foil was ≤21mΩ, the sheet resistance uniformity was ±5%, and the sheet resistance change rate was 10% after baking at 140℃ for 1 hour.

[0095] Comparative Example 1

[0096] The method for preparing the copper foil in this comparative example includes the following steps:

[0097] (1) Use a PET film with a thickness of 5μm as the substrate.

[0098] (2) Using metallic copper as the target material, a pure copper coating is prepared by sputtering on the surface of the substrate with a DC power supply. The thickness of the pure copper coating is 40 nm. The DC power supply has a current of 17 A and a voltage of 407 V.

[0099] (3) Electroplating: The copper foil obtained in step (2) is immersed in the electroplating solution and a copper layer is deposited on the surface by electroplating. The thickness of the copper layer is 1 μm. The electroplating solution consists of 210 g / L copper sulfate solution, and the electroplating current is 5 A and the voltage is 12 V.

[0100] Tests showed that the ultrathin copper foil obtained in step (2) had a film adhesion of 4B, a sheet resistance of ≤1300mΩ after coating, a sheet resistance uniformity of ±7%, and a sheet resistance change rate of 40% after baking at 140℃ for 1 hour. The copper foil obtained after electroplating in step (3) had a film adhesion of 3B, a sheet resistance of ≤22mΩ, uneven thickness, and poor oxidation resistance.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 1 is that in step (3), the total current of the DC power supply is 230A and the voltage is 440V. The thickness of the pure copper coating obtained is 600nm.

[0103] Tests showed that the composite copper foil prepared in this comparative example had a film adhesion of 4B, a sheet resistance of ≤43mΩ, a sheet resistance uniformity of ±6%, and a sheet resistance change rate of 15% after baking at 140℃ for 1 hour. This is because the DC power supply has relatively low power, resulting in poor density and adhesion of the coating when preparing a thick pure copper plating layer, leading to poor uniformity of the composite copper foil.

[0104] The preparation process parameters and performance parameters of the composite copper foils of Examples 1-3 and Comparative Examples 1-2 are recorded in Table 1.

[0105] Table 1

[0106]

[0107]

[0108] As can be seen from the data in Table 1, the composite copper foils prepared in Examples 1-3 all have an adhesion of 5B, a sheet resistance ≤22mΩ, a sheet resistance uniformity ≤±5%, and a sheet resistance change rate ≤10% after baking at 140℃ for 1 hour. Compared with Comparative Examples 1-2, it can be seen that the composite copper foils prepared by the methods in Examples 1-3 have higher adhesion, lower sheet resistance, higher sheet resistance uniformity, and a smaller sheet resistance change rate after baking for 1 hour. This indicates that the composite copper foils prepared by the methods in Examples 1-3 have better coating density and adhesion, better oxidation resistance, and a smaller sheet resistance change rate after baking.

[0109] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0110] The embodiments described above merely illustrate several implementation methods of this application to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing composite copper foil, characterized in that, Includes the following steps: A copper alloy target is sputtered using a pulsed DC power supply to deposit a copper alloy coating on the surface of a substrate. The pulsed DC power supply has a current of 10A~15A, a voltage of 350V~450V, and a duty cycle of 40%~70%. The thickness of the copper alloy coating is 10 nm~15 nm. A pure copper plating layer is deposited on the surface of the copper alloy plating layer by sputtering a pure copper target using a first DC power supply; wherein the total current of the first DC power supply is 300 A~400 A and the voltage is 400 V~550 V; and the thickness of the pure copper plating layer is 950 nm~1000 nm. A copper-nickel alloy target is sputtered using a second DC power supply to deposit a copper-nickel coating on the surface of the pure copper coating. The thickness of the copper-nickel coating is 15 nm to 20 nm. The sheet resistance of the composite copper foil is ≤25 mΩ.

2. The method for preparing composite copper foil according to claim 1, characterized in that, In the preparation method, the cooling temperature is 10℃~20℃.

3. The method for preparing composite copper foil according to claim 1, characterized in that, The second DC power supply has a current of 5A~15A and a voltage of 360V~430V.

4. The method for preparing composite copper foil according to claim 1, characterized in that, The copper alloy target material includes one of copper-nickel alloy, copper-zinc alloy, and copper-silver alloy.

5. The method for preparing composite copper foil according to claim 1, characterized in that, The copper alloy target is a copper-nickel alloy, in which the mass content of nickel is 5% to 15%.

6. The method for preparing composite copper foil according to claim 1, characterized in that, The nickel content in the copper-nickel plating is 5% to 15% by mass.

7. The method for preparing composite copper foil according to any one of claims 1 to 6, characterized in that, The substrate satisfies at least one of the conditions in (1) to (2): (1) The thickness of the substrate is 3 μm to 6 μm; (2) The material of the substrate includes at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene and polyethylene.

8. A composite copper foil, characterized in that, The composite copper foil is prepared according to any one of claims 1 to 7.

9. A current collector, characterized in that, Includes the composite copper foil as described in claim 8.

10. An electrode sheet, characterized in that, Includes the current collector as described in claim 9.

11. A secondary battery, characterized in that, Includes the electrode sheet as described in claim 10.

12. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 11.

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