Composite current collector, preparation method thereof, pole piece and battery

Abstract

The application provides a composite current collector and a preparation method thereof, a pole piece and a battery, and belongs to the technical field of composite current collector manufacturing. The preparation method of the composite current collector comprises the following steps: a cathode target material is used to form a first metal layer on the surface of a polymer layer and a second metal layer located on both sides of the first metal layer in a width direction of the first metal layer by a magnetron sputtering mode; wherein the cathode target material has a first section located in the middle and a second section located at both ends, the ionization rate of the first section is less than the ionization rate of the second section, so that the thickness of the first metal layer is less than the thickness of the second metal layer. The preparation method has the advantages of simple process, high production efficiency, low cost and easy implementation. In addition, the composite current collector prepared by the method also has the advantages of high bonding strength at the welding position, small direct current resistance and low perforation rate after welding.

Description

Technical Field

[0001] The present application relates to the technical field of composite current collector manufacturing, and specifically to a composite current collector and a preparation method thereof, a pole piece, and a battery. Background Art

[0002] Lithium batteries are widely used in various electronic devices due to their high energy density and long lifespan. With the advancement of technology, the energy density and safety requirements for lithium batteries are becoming increasingly stringent. Composite current collectors, in particular, have attracted widespread attention due to their potential to improve the energy density and safety of lithium batteries. Specifically, composite current collectors typically consist of a polymer layer and a metal layer disposed on one or both sides of the polymer layer. Typically, the polymer layer in the composite current collector itself is non-conductive, making welding a challenge at the application end.

[0003] Several solutions have been proposed for the welding of composite current collectors. For example, ultrasonic roll welding can be used to achieve transfer welding of composite current collectors. Specifically, ultrasonic roll welding converts ultrasonic energy into mechanical vibrations, generating friction and plastic deformation between the metal layer and the polymer layer, thereby achieving welding. This method is currently considered a reliable solution for achieving composite current collector welding. However, ultrasonic roll welding still presents some challenges in the application of transfer welding of composite current collectors, such as high DC resistance at the weld mark, insufficient weld strength, poor weld consistency, and even foil perforation and substrate exposure.

[0004] In order to solve the above problems, technicians have thought of optimizing the structure of the metal layer in the composite current collector. Specifically, the thickness of the metal layer in the welding area is controlled to be greater than the thickness in the active material coating area. However, the existing composite current collector preparation process has the problems of complex process, low production efficiency, high cost and inconvenient implementation. In addition, the composite current collector prepared by the existing process has problems such as low bonding strength at the weld after welding, large DC resistance and high perforation rate. Summary of the Invention

[0005] The purpose of the present application is to provide a composite current collector and its preparation method, a pole piece and a battery. The preparation method has the advantages of simple process, high production efficiency, low cost and easy implementation. In addition, the composite current collector prepared by this method has the advantages of high bonding strength at the weld, low DC resistance and low perforation rate after welding.

[0006] The embodiment of the present application is implemented as follows:

[0007] In the first aspect, an embodiment of the present application provides a method for preparing a composite current collector, comprising the following steps: a cathode target is formed on the surface of a polymer layer by magnetron sputtering to form a first metal layer and a second metal layer located on both sides of the first metal layer in a width direction; wherein the cathode target has a first section located in the middle and a second section located at both ends, and the ionization rate of the first section is less than the ionization rate of the second section, so that the thickness of the first metal layer is less than the thickness of the second metal layer.

[0008] In the prior art, for a composite current collector in which the metal layer is thin in the middle and thick at both ends, a metal layer of the same thickness is usually prepared first, and then the metal layer in the middle area is thinned (for example, by chemical liquid etching) or the metal layer at both ends is additionally thickened (for example, by water electroplating, vapor deposition or chemical plating, etc.). That is, a step-by-step preparation method is usually adopted. This preparation method has the problems of many process steps, low production efficiency, high cost and inconvenience in implementation. In addition, the composite current collector prepared by the step-by-step method also has the problems of low bonding strength at the weld after welding, large DC resistance and high perforation rate. In the present application, by adjusting the structure of the cathode target material, specifically, the cathode target material has a first section located in the middle and a second section located at both ends, the ionization rate of the first section is less than the ionization rate of the second section (the larger the ionization rate, the faster the deposition rate), that is, the deposition rate of the cathode target material in the first section is slower, and the deposition rate of the cathode target material in the second section is faster, so that under the same other process conditions, a composite current collector with a thin metal layer in the middle and thick at both ends can be prepared in one step by magnetron sputtering coating technology. The one-step preparation method has the advantages of simple process, high production efficiency, low cost and easy implementation; in addition, the one-step method is realized by magnetron sputtering coating technology, and the prepared metal layer and the polymer layer have the advantages of high bonding strength, relatively uniform thickness of the metal layer, relatively dense metal layer and high cleanliness of the metal layer. In addition, the metal layer is a unified whole (that is, there is no bonding interface inside the metal layer), so that the composite current collector prepared by this method has the advantages of high bonding strength at the weld, low DC resistance and low perforation rate after welding.

[0009] In some optional embodiments, in the cathode target material, the ionization rate of the first section is A1, the ionization rate of the second section is A2, and the ratio of A1 to A2 is 1:(1.1-2).

[0010] In the above technical solution, the ratio of the ionization rates of the first segment and the second segment is limited to the above range, so that the prepared first metal layer and the second metal layer have a more suitable thickness ratio, thereby facilitating the subsequent formation of the active material layer on the first metal layer and welding on the second metal layer.

[0011] In some alternative embodiments, A1 is 10-20%.

[0012] In the above technical solution, the ionization rate is in the range of 10-20%, so that the thickness of the prepared metal layer is in a more suitable range. At the same time, this ionization rate range is easier to achieve, thereby facilitating the specific implementation of the solution.

[0013] In some optional embodiments, in the cathode target material, the magnetic induction intensity of the first segment is B1, the magnetic induction intensity of the second segment is B2, and B1 < B2; or / and, in the cathode target material, the area of ​​the ionization region of the first segment is S1, the area of ​​the ionization region of the second segment is S2, and S1 < S2.

[0014] In the above technical solution, in order to make the ionization rate of the cathode target material in the first section greater than the ionization rate of the second section, it can be achieved by adjusting the magnetic induction intensity, specifically, setting the magnetic induction intensity B1 of the first section to be smaller than the magnetic induction intensity B2 of the second section, or by adjusting the area of ​​the ionization region, specifically, setting the ionization region area S1 of the first section to be smaller than the ionization region area S2 of the second section, or by simultaneously adjusting the magnetic induction intensity and the ionization region area. There are many feasible implementation options, which facilitates the promotion and application of the technical solution of this application; at the same time, the above adjustment method also has the advantage of being easy to implement.

[0015] In some optional embodiments, B1 is 400-600 Gs.

[0016] In the above technical solution, B1 is within the range of 400 to 600 Gs, so that the thickness of the prepared metal layer is within a more suitable range. At the same time, this magnetic induction intensity range is easier to achieve, thereby facilitating the specific implementation of the solution.

[0017] In some optional embodiments, the number of permanent magnets in the first section and the number of permanent magnets in the second section are adjusted to be different so that the ratio of S1 to S2 is 1:(1.1-2).

[0018] In the above technical solution, by adjusting the number of permanent magnets so that the ratio of S1 to S2 is 1:(1.1-2), it has the advantage of being easy to implement.

[0019] In some optional embodiments, the cathode target material includes an annular metal layer and a plurality of permanent magnets housed in the annular metal layer. In the cathode target material, the thickness of the annular metal layer at the first section is D1, the thickness of the annular metal layer at the second section is D2, and D1<D2.

[0020] In the above technical solution, on the basis that the ionization rate of the first section is smaller than the ionization rate of the second section, the thickness of the annular metal layer at the first section is set to be smaller than the thickness of the annular metal layer at the second section, that is, the annular metal layer is thin in the middle and thick at both ends, which helps to reduce the risk of the target material being punctured and, at the same time, helps to improve the uniformity of the coating.

[0021] In a second aspect, an embodiment of the present application provides a composite current collector, which is prepared using the preparation method of the composite current collector provided in the embodiment of the first aspect.

[0022] In the above technical scheme, the composite current collector is prepared by the preparation method of the composite current collector provided in the embodiment of the first aspect. Since the composite current collector has the advantages of high bonding strength between the metal layer and the polymer layer, relatively uniform thickness of the metal layer, relatively dense metal layer and high cleanliness of the metal layer, and the metal layer is a unified whole (that is, there is no bonding interface inside the metal layer), the composite current collector has the advantages of high bonding strength at the welding point, low DC resistance and low perforation rate after welding.

[0023] In a third aspect, an embodiment of the present application provides a pole piece, comprising a composite current collector and an active material layer as provided in the embodiment of the second aspect, wherein the active material layer is located on the surface of the first metal layer.

[0024] In a fourth aspect, an embodiment of the present application provides a battery, comprising a pole piece provided in the embodiment of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 A front view of a cathode target material provided in an embodiment of the present application;

[0027] Figure 2 A side view of a cathode target material provided in an embodiment of the present application;

[0028] Figure 3 A schematic diagram of film material transportation provided in an embodiment of the present application;

[0029] Figure 4 A schematic structural diagram of a composite current collector provided in an embodiment of the present application.

[0030] Icons: 10-cathode target; 10a-first section; 10b-second section; 11-annular metal layer; 12-permanent magnet; 20-unwinding roller; 30-conveying roller; 40-main cold roller; 50-winding roller; 60-composite current collector; 61-polymer layer; 62-metal layer; 62a-first metal layer; 62b-second metal layer. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0032] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without making any creative efforts shall fall within the scope of protection of the present application.

[0033] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0034] In the description of this application, it should be noted that the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0035] The following is a detailed description of a composite current collector, a preparation method thereof, a pole piece, and a battery provided in this application.

[0036] In the first aspect, an embodiment of the present application provides a method for preparing a composite current collector, comprising the following steps: a cathode target is formed on the surface of a polymer layer by magnetron sputtering to form a first metal layer and a second metal layer located on both sides of the first metal layer in a width direction; wherein the cathode target has a first section located in the middle and a second section located at both ends, and the ionization rate of the first section is less than the ionization rate of the second section, so that the thickness of the first metal layer is less than the thickness of the second metal layer.

[0037] In the prior art, for a composite current collector in which the metal layer is thin in the middle and thick at both ends, a metal layer of the same thickness is usually prepared first, and then the metal layer in the middle area is thinned (for example, by chemical liquid etching) or the metal layer at both ends is additionally thickened (for example, by water electroplating, vapor deposition or chemical plating, etc.). That is, a step-by-step preparation method is usually adopted. This preparation method has the problems of many process steps, low production efficiency, high cost and inconvenience in implementation. In addition, the composite current collector prepared by the step-by-step method also has the problems of low bonding strength at the weld after welding, large DC resistance and high perforation rate. In the present application, by adjusting the structure of the cathode target material, specifically, the cathode target material has a first section located in the middle and a second section located at both ends, the ionization rate of the first section is less than the ionization rate of the second section (the larger the ionization rate, the faster the deposition rate), that is, the deposition rate of the cathode target material in the first section is slower, and the deposition rate of the cathode target material in the second section is faster, so that under the same other process conditions, a composite current collector with a thin metal layer in the middle and thick at both ends can be prepared in one step by magnetron sputtering coating technology. The one-step preparation method has the advantages of simple process, high production efficiency, low cost and easy implementation; in addition, the one-step method is realized by magnetron sputtering coating technology, and the prepared metal layer and the polymer layer have the advantages of high bonding strength, relatively uniform thickness of the metal layer, relatively dense metal layer and high cleanliness of the metal layer. In addition, the metal layer is a unified whole (that is, there is no bonding interface inside the metal layer), so that the composite current collector prepared by this method has the advantages of high bonding strength at the weld, low DC resistance and low perforation rate after welding.

[0038] It should be noted that the material and size of the polymer layer are not limited and can be adaptively adjusted according to actual needs. For example, a polymer layer made of polyethylene terephthalate (PET) with a width of 70 cm and a thickness of 4.5 μm can be used.

[0039] It should be noted that the first segment in the cathode target is used to form a first metal layer, and the second segment in the cathode target is used to form a second metal layer. The axial dimensions of the first segment and the second segment in the cathode target are not limited and can be adaptively adjusted according to actual needs. For example, the size of the first segment is 50 to 70 cm, and the size of a single second segment is 1 to 5 cm, that is, the width of the first metal layer formed is 50 to 70 cm, and the width of the single second metal layer formed is 1 to 5 cm.

[0040] It should be noted that the relative size of the ionization rates of the first section and the second section is not limited and can be adaptively adjusted according to actual needs.

[0041] As an example, in the cathode target, the ionization rate of the first section is A1, the ionization rate of the second section is A2, and the ratio of A1 to A2 is 1:(1.1-2), for example, but not limited to, any one of 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 and 1:2, or a range value between any two of them.

[0042] In this embodiment, the ratio of the ionization rates of the first section and the second section is limited in the above range, so that the prepared first metal layer and the second metal layer have a more appropriate thickness ratio, thereby facilitating the subsequent formation of an active material layer on the first metal layer and welding on the second metal layer.

[0043] It should be noted that the size of the ionization rate A1 of the first section is not limited and can be adaptively adjusted according to actual needs.

[0044] As an example, A1 is 10-20%, for example, but not limited to, any one of 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% and 20%, or a range value between any two of them.

[0045] In this embodiment, the ionization rate is in the range of 10-20%, so that the thickness of the prepared metal layer is in a more appropriate range, and this ionization rate range is relatively easy to achieve, thereby facilitating the specific implementation of the scheme.

[0046] It should be noted that in order to make the ionization rate of the first section of the cathode target less than that of the second section, the specific implementation is not limited.

[0047] As an example, in the cathode target, the magnetic induction intensity of the first section is B1, the magnetic induction intensity of the second section is B2, and B1

[0048] In this embodiment, in order to make the ionization rate of the first section of the cathode target greater than that of the second section, it can be realized by adjusting the magnetic induction intensity, specifically, setting the magnetic induction intensity B1 of the first section less than the magnetic induction intensity B2 of the second section, or by adjusting the ionization area, specifically, setting the ionization area S1 of the first section less than the ionization area S2 of the second section, or by adjusting the magnetic induction intensity and the ionization area at the same time, which has more implementable schemes, thereby facilitating the popularization and application of the technical scheme of the present application; at the same time, the above adjustment method also has the advantage of easy implementation.

[0049] It should be noted that in the process of adjusting the ionization rate of the cathode target by changing the magnetic induction intensity, the specifications of the magnetic induction intensity of the permanent magnet used are not limited and can be adaptively adjusted according to actual needs.

[0050] As an example, B1 is 400-600Gs, for example but not limited to, B1 is any one point value of 400Gs, 450Gs, 500Gs, 550Gs and 600Gs or a range value between any two of them.

[0051] In this embodiment, B1 is within the range of 400 to 600 Gs, so that the thickness of the prepared metal layer is within a more suitable range. At the same time, this magnetic induction intensity range is easier to achieve, thereby facilitating the specific implementation of the solution.

[0052] It should be noted that there is no limitation on the method of changing the size of the ionization region, and adaptive adjustment can be made according to actual needs.

[0053] As an example, by adjusting the number of permanent magnets in the first section and the second section to be different, the ratio of S1 to S2 is 1:(1.1~2), for example, but not limited to, the ratio is any one of 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 and 1:2, or a range between any two of them.

[0054] In this embodiment, by adjusting the number of permanent magnets so that the ratio of S1 to S2 is 1:(1.1-2), it has the advantage of being easy to implement.

[0055] As an example, the cathode target includes an annular metal layer and multiple permanent magnets contained in the annular metal layer. In the cathode target, the thickness of the annular metal layer at the first section is D1, the thickness of the annular metal layer at the second section is D2, and D1<D2.

[0056] In this embodiment, on the basis that the ionization rate of the first segment is less than the ionization rate of the second segment, the thickness of the annular metal layer in the first segment is set to be less than the thickness of the annular metal layer in the second segment, that is, the annular metal layer is thin in the middle and thick at both ends, which helps to reduce the risk of the target material being punctured and at the same time helps to improve the uniformity of the coating.

[0057] It should be noted that the ratio of the thickness of the annular metal layer in the first section to the thickness of the annular metal layer in the second section is not limited and can be adaptively adjusted according to actual needs.

[0058] As an example, the ratio of the thickness of the annular metal layer in the first section to the thickness of the annular metal layer in the second section is 1:(1.25-3), such as but not limited to any one of 1:1.25, 1:1.5, 1:2, 1:2.5 and 1:3 point values or range values between any two of them.

[0059] As an example, the thickness of the annular metal layer in the first section is 0.5-2 μm, such as but not limited to any one of 0.5 μm, 1 μm, 1.5 μm and 2 μm point values or range values between any two of them.

[0060] For a better understanding of the technical solutions, the structure of the cathode target material is illustrated here, which can be specifically referred to Figure 1 and Figure 2 , Figure 1 is a front view of a cathode target material 10, specifically, the permanent magnet 12 is fixed, the annular metal layer 11 can rotate around the permanent magnet 12, the thickness of the annular metal layer 11 at the first section 10a is smaller than the thickness of the annular metal layer 11 at the second section 10b, that is, it presents a state of thin in the middle and thick at the edge, Figure 2 is a side view of a cathode target material 10, specifically, the annular metal layer 11 contains three permanent magnets 12 arranged in the circumferential direction (that is, the N and S poles of the permanent magnets 12 are arranged alternately), and the permanent magnets 12 are located on the side close to the polymer layer.

[0061] It should be noted that the preparation process of the composite current collector can be adaptively adjusted according to the configuration of the composite current collector, for example, for the scheme of forming a metal layer on one side of the polymer layer, only single-sided magnetron sputtering is needed, and for the scheme of forming a metal layer on both sides of the polymer layer, magnetron sputtering is sequentially performed on both sides.

[0062] For a better understanding of the technical solutions, a film material conveying schematic diagram is used here for auxiliary explanation, which can be specifically referred to Figure 3 , along the film material conveying direction, the polymer layer is released from the unwinding roller 20 and conveyed to the cathode target material 10 (wherein a plurality of cathode target materials 10 are distributed at intervals around the main cold roller 40) through the conveying roller 30, after forming a metal layer on one side of the polymer layer, it is conveyed to another cathode target material 10 (wherein a plurality of cathode target materials 10 are distributed at intervals around the main cold roller 40) through the conveying roller 30, after forming a metal layer on the other side of the polymer layer, it is conveyed to the winding roller 50 for winding through the conveying roller 30.

[0063] It should be noted that the processes or steps not specially mentioned or limited in the preparation process of the composite current collector can be set according to conventional selection in the art.

[0064] In a second aspect, an embodiment of the present application provides a composite current collector, which is prepared using the preparation method of the composite current collector provided in the embodiment of the first aspect.

[0065] In the present application, the composite current collector is prepared by the preparation method of the composite current collector provided in the embodiment of the first aspect. Since the composite current collector has the advantages of high bonding strength between the metal layer and the polymer layer, relatively uniform thickness of the metal layer, relatively dense metal layer and high cleanliness of the metal layer, and the metal layer is a unified whole (that is, there is no bonding interface inside the metal layer), the composite current collector has the advantages of high bonding strength at the welding point, low DC resistance and low perforation rate after welding.

[0066] In order to better understand the technical solution, a structural diagram of a composite current collector is used here for auxiliary explanation. Figure 4 The composite current collector 60 includes a polymer layer 61 and a metal layer 62 located on both sides of the polymer layer 61, and along the width direction, the metal layer 62 has a first metal layer 62a located in the middle and a second metal layer 62b located on both sides of the first metal layer 62a, wherein the first metal layer 62a is used for subsequent coating to form an active material layer, and the second metal layer 62b is used for subsequent welding.

[0067] In a third aspect, an embodiment of the present application provides a pole piece, comprising a composite current collector and an active material layer as provided in the embodiment of the second aspect, wherein the active material layer is located on the surface of the first metal layer.

[0068] It should be noted that the material of the active material layer is not limited and can be adaptively adjusted according to actual needs. For example, it can be a positive electrode active material, that is, corresponding to a positive electrode sheet, or a negative electrode active material, that is, corresponding to a negative electrode sheet.

[0069] In a fourth aspect, an embodiment of the present application provides a battery, comprising a pole piece provided in the embodiment of the third aspect.

[0070] It should be noted that the type of battery is not limited, for example, it can be a lithium-ion battery or a sodium-ion battery, and can be adaptively adjusted according to actual needs.

[0071] The solution of this application is further introduced below with reference to embodiments.

[0072] Example 1

[0073] The present invention provides a method for preparing a composite current collector, comprising the following steps:

[0074] A PET film with a width of 70 cm and a thickness of 4.5 μm was used as the polymer layer. Figure 3 The composite current collector is prepared by the film material delivery route shown in FIG. , wherein the structure of the cathode target material is as shown in FIG. Figure 1 and Figure 2 As shown, specifically, the material of the annular metal layer is copper, the magnetic induction intensity of the first section is 400Gs, the magnetic induction intensity of the second section is 800Gs, the axial dimension of the first section is 5cm, the axial dimension of the second section is 60cm, and the number of permanent magnets is 3, so that the ionization rate of the first section is 15% and the ionization rate of the second section is 25%; the thickness of the annular metal layer in the first section is 1cm, the thickness of the annular metal layer in the second section is 1.5cm, the distance between the outer wall of the annular metal layer and the surface of the polymer layer (i.e., the target-substrate distance) is 9cm, and the rotation speed of the annular metal layer is 10rpm. At the same time, the power of the magnetron sputtering is controlled to be 50KW, the vacuum degree in the coating chamber is 0.5Pa, and the film travel speed of the film material is 2m / min, so as to prepare a first metal layer with a width of 60cm and a thickness of 1μm and a second metal layer with a width of 5cm and a thickness of 1.5μm to obtain a composite current collector.

[0075] Example 2

[0076] An embodiment of the present application provides a method for preparing a composite current collector, which differs from Example 1 only in that: the magnetic induction intensities of the first section and the second section are both 400 Gs, the number of permanent magnets in the first section is still three, but the number of permanent magnets in the second section is 5, so that the ionization rate of the first section is 15% and the ionization rate of the second section is 25%, so as to prepare a first metal layer with a width of 60 cm and a thickness of 1 μm and a second metal layer with a width of 5 cm and a thickness of 1.5 μm, thereby obtaining a composite current collector.

[0077] Example 3

[0078] An embodiment of the present application provides a method for preparing a composite current collector, which differs from Example 1 only in that: the magnetic induction intensity of the first section is 600 Gs, the magnetic induction intensity of the second section is 800 Gs, the number of permanent magnets in the first section is three, and the number of permanent magnets in the second section is five, so that the ionization rate of the first section is 20%, and the ionization rate of the second section is 35%, and the film speed is increased to 4 m / min to prepare a first metal layer with a width of 60 cm and a thickness of 1 μm and a second metal layer with a width of 5 cm and a thickness of 1.5 μm to obtain a composite current collector.

[0079] It should be noted that, compared with Examples 1 to 2, Example 3 takes less time to prepare the same composite current collector, indicating that combining the method of changing the magnetic induction intensity and the method of changing the area of ​​the ionization region can further improve production efficiency.

[0080] Comparative Example 1

[0081] The comparative example of the present application provides a method for preparing a composite current collector, which differs from Example 1 only in that the magnetic induction intensities of the first section and the second section are both 400 Gs, and the thickness of the annular metal layer is 1 cm, so as to prepare a first metal layer and a second metal layer with a thickness of 1 μm.

[0082] Comparative Example 2

[0083] The comparative example of the present application provides a method for preparing a composite current collector, which differs from comparative example 1 only in that: the magnetic induction intensities of the first section and the second section are both 400 Gs, and the thickness of the annular metal layer is 1 cm, so as to prepare a first metal layer and a second metal layer with a thickness of 1 μm; and then a metal layer with a thickness of 0.5 μm is formed on the second metal layer by evaporation, so that the total thickness of the second metal layer is 1.5 μm.

[0084] Test example

[0085] The composite current collectors prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were numbered respectively, and then ultrasonic roll welding was performed at the second metal layer (i.e., the welding point) in the composite current collector. The straight pull force, DC resistance, perforation rate, and peel force of the welding point of each sample were tested, and the test results were statistically summarized in Table 1.

[0086] The test steps for straight pull force are as follows:

[0087] Cut the welded sample into 90mm long and 15mm wide specifications, clamp it vertically on the tensile testing machine, clamp the transfer-welded copper foil on the top and the composite current collector on the bottom. Select the tensile test mode, set the tensile gauge length to 50mm, and the tensile speed to 50mm / min. Record the maximum force at the tensile fracture. The DC resistance test steps are as follows:

[0088] Cut the welded foil into 15mm widths and use a DC resistance tester to measure the resistance by placing two probes 10mm to the left and right of the weld mark.

[0089] Place the weld mark under an optical microscope to observe the perforated area, find and mark it, scan a certain range of weld marks, count the perforation area and number, calculate the perforation area to the weld mark area, and calculate the perforation rate. The peel force test steps are as follows:

[0090] Cut the welded foil into 25mm widths, peel off the copper foil on both sides of the roll weld, clamp one layer of pure copper foil on the top of the tensile testing machine and another layer of pure copper foil on the bottom, select peeling as the test mode and 20mm / min as the peeling speed. After it is completely peeled off, output the maximum peeling value.

[0091] Table 1

[0092]

[0093]

[0094] Referring to Table 1, it can be seen from the test results of Examples 1 to 3 and Comparative Example 1 that increasing the thickness of the second metal layer (i.e., increasing the thickness of the metal layer in the welding area) can improve the welding quality of the composite current collector. Specifically, the thickened second metal layer increases the straight pull force and peel force of the weld after welding, and reduces the DC resistance and perforation rate of the weld.

[0095] It can be seen from the test results of Example 1 and Comparative Example 2 that the composite current collector in which the metal layer is thin in the middle and thick at both ends is prepared by the one-step method using magnetron sputtering coating technology. Compared with the composite current collector in which the metal layer is thin in the middle and thick at both ends prepared by the step-by-step method, the former has the advantages of simple process, high production efficiency, low cost and easy implementation; in addition, the one-step method is realized by magnetron sputtering coating technology, and it can also make the prepared metal layer and the polymer layer have the advantages of higher bonding strength, more uniform thickness of the metal layer, denser metal layer and higher cleanliness of the metal layer. In addition, the metal layer is a unified whole (that is, there is no bonding interface inside the metal layer), so that the composite current collector prepared by this method has the advantages of higher bonding strength at the welding point, smaller DC resistance and lower perforation rate after welding.

[0096] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for preparing a composite current collector, characterized in that: The following steps are involved: The cathode target forms a first metal layer and second metal layers on both sides of the first metal layer in a width direction on the surface of the polymer layer by magnetron sputtering; wherein the cathode target has a first section located in the middle and second sections located at both ends, and the ionization rate of the first section is lower than the ionization rate of the second section, so that the thickness of the first metal layer is lower than the thickness of the second metal layer; In the cathode target material, the ionization rate of the first section is A1, the ionization rate of the second section is A2, and the ratio of A1 to A2 is 1:(1.1~2); The A1 is 10~20%; The cathode target comprises an annular metal layer and a plurality of permanent magnets contained in the annular metal layer. In the cathode target, the thickness of the annular metal layer at the first section is D1, and the thickness of the annular metal layer at the second section is D2, wherein D1 is less than D2. Along the film conveying direction, the polymer layer is released from the unwinding roller and conveyed to the cathode target via the conveying roller, wherein multiple cathode targets at the cathode target are spaced around the main cold roller to form a metal layer on a single side of the polymer layer.

2. The method for preparing a composite current collector according to claim 1, wherein: In the cathode target material, the magnetic induction intensity of the first section is B1, the magnetic induction intensity of the second section is B2, and B1 is less than B2; or / and, In the cathode target, the area of ​​the ionization region of the first section is S1, the area of ​​the ionization region of the second section is S2, and S1 is less than S2.

3. The method for preparing a composite current collector according to claim 2, wherein: The B1 is 400~600 Gs.

4. The method for preparing a composite current collector according to claim 2, wherein: The number of permanent magnets in the first section and the number of permanent magnets in the second section are adjusted to be different so that the ratio of S1 to S2 is 1:(1.1-2).

5. A composite current collector, characterized in that: The composite current collector is prepared by the preparation method according to any one of claims 1 to 4.

6. A pole piece, characterized in that: The composite current collector according to claim 5 and an active material layer are provided, wherein the active material layer is located on the surface of the first metal layer.

7. A battery, characterized in that: Comprising the pole piece as claimed in claim 6.

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