Composite copper current collector, preparation method thereof, electrode sheet and electrochemical device

Abstract

This invention provides a composite copper current collector, its preparation method, electrode sheet, and electrochemical device, relating to the technical field of lithium-ion batteries. The composite copper current collector comprises a first copper plating layer, a polymer substrate, and a second copper plating layer sequentially arranged. Both the first and second copper plating layers have welding areas for tab welding. The copper surface of the welding area includes a double-layer rough structure, comprising a micron-level uneven substrate and nano-level protrusions. This invention achieves precise control of the copper roughness in the welding area, improving welding bonding strength and stability, adapting to the actual needs of different welding processes, while reducing copper powder shedding and electrolyte contamination, thus improving the overall reliability of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a composite copper current collector and its preparation method, electrode sheet and electrochemical device. Background Technology

[0002] Composite copper current collectors typically employ a sandwich structure consisting of a polymer substrate and an ultra-thin copper plating layer. They offer advantages such as lightweight design, high safety, and high energy density, making them a core component of next-generation lithium-ion batteries. The welding quality between the tabs and the composite copper current collector directly affects the battery's conductivity, cycle stability, and safety performance. The surface roughness of the copper in the welding area is a key factor influencing the welding bond strength.

[0003] In existing technologies, chemical micro-etching and mechanical grinding are commonly used to improve the surface roughness of copper to enhance welding bonding. However, these technologies still have significant drawbacks, failing to meet the demands of large-scale production and high reliability. The core issue lies in insufficient welding bonding strength. Specifically, existing roughening processes are mostly single-dimensional operations, failing to fully adapt to the characteristics of the ultra-thin copper layer in composite current collectors, and lacking targeted design to meet the needs of different welding processes. This makes it difficult to form an effective mechanical interlocking structure, leading to easy detachment of the tabs from the composite current collector after welding. Furthermore, the copper surface is prone to oxidation after roughening and easily retains impurities, further weakening the welding bonding strength, affecting welding stability, and ultimately reducing the reliability of battery products. In addition, existing roughening processes are mostly full-area treatments; excessive roughness in non-welding areas can easily lead to copper powder shedding, contaminating the electrolyte, and affecting battery cycle life.

[0004] Therefore, there is an urgent need for a method to control the surface roughness of the copper in the welding zone that is adapted to the characteristics of composite current collectors, in order to solve the core problem of insufficient welding bonding force caused by unreasonable roughness control in the existing technology, and to meet the actual needs of large-scale production of lithium-ion batteries.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a composite copper current collector, its preparation method, electrode plates, and an electrochemical device. This invention aims to overcome the shortcomings of existing composite current collectors where the copper surface roughness in the welding area is not properly controlled, leading to insufficient welding bonding strength. It provides a composite copper current collector and its preparation method that achieves precise and controllable control of the copper roughness in the welding area, improving welding bonding strength and welding stability, and adapting to the actual needs of different welding processes (after improving the roughness of the welding area, the welding area and the adapter plate rub against each other during ultrasonic welding, improving the welding effect and efficiency). Simultaneously, it reduces copper powder shedding and electrolyte contamination, improving the overall reliability of the battery.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a composite copper current collector, the composite copper current collector comprising a first copper plating layer, a polymer substrate and a second copper plating layer disposed sequentially, wherein the first copper plating layer and the second copper plating layer are each provided with a welding area for electrode tab welding. The copper surface of the welding area includes a double-layer rough structure, which comprises a micron-level uneven substrate and nano-level protrusions.

[0008] Furthermore, the size ratio between a single micron-sized structure in the micron-sized uneven substrate and a single nano-sized structure in the nano-sized protrusion is (10~20):1.

[0009] Furthermore, the present invention provides a composite current collector, the composite copper current collector comprising a first copper plating layer, a polymer substrate, and a second copper plating layer arranged sequentially, wherein the first copper plating layer and / or the second copper plating layer are provided with a welding area for tab welding, and the roughness of the area where the composite current collector is welded to the tab is controlled, while the non-welding area retains its original smooth surface; specifically, a composite process combining plasma micro-etching and chemical modification is used to grade the roughness of the copper surface in the welding area, forming a double-layer rough structure composed of a micron-level uneven substrate and a nano-level dense protrusion, wherein the size ratio of the micron-level structure to the nano-level structure is controlled at (10~20):1, ensuring a balance between mechanical interlocking effect and surface density.

[0010] Furthermore, the micron-level uneven substrate includes micron-level pits or micron-level grooves.

[0011] Furthermore, when the composite copper current collector is adapted to the ultrasonic welding control mode, the diameter of a single micron-sized pit is 1~3 μm; the depth of a single micron-sized pit is 0.2~0.5 μm; and the distribution density of the micron-sized pits is 500~800 / mm. 2 .

[0012] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the width of a single micron-sized groove is 2~4 μm; the depth of a single micron-sized groove is 0.5~1.0 μm; and the micron-sized grooves are distributed in a grid pattern with a grid spacing of 5~8 μm. The intersections of the micron-sized grooves are rounded with a radius of 0.5~1.0 μm.

[0013] Furthermore, the nanoscale protrusions are disposed on the surface of the micron-scale uneven substrate.

[0014] Furthermore, the nanoscale protrusions cover more than 95% of the surface of the micron-scale uneven substrate.

[0015] Furthermore, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the height of a single nanoscale protrusion is 50~100 nm; the diameter of a single nanoscale protrusion is 50~100 nm; and the surface roughness Ra of the copper in the welding area is 1.0~1.5 μm.

[0016] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the height of a single nanoscale protrusion is 80~150 nm; the diameter of a single nanoscale protrusion is 80~150 nm; and the surface roughness Ra of the copper in the welding area is 8.0~12.5 μm.

[0017] Furthermore, the copper surface of the welding area is also provided with an anti-oxidation modification layer.

[0018] Furthermore, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the thickness of the antioxidant modification layer is 5~10 nm.

[0019] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the thickness of the antioxidant modification layer is 8~12 nm.

[0020] Furthermore, the antioxidant modification layer has a gradient structure, including a composite layer of metallic copper and cuprous oxide near the substrate and an organic-inorganic hybrid passivation layer away from the substrate.

[0021] Furthermore, the organic-inorganic hybrid passivation layer comprises an organic phase and an inorganic phase; wherein the organic phase comprises a coordination complex formed by a surfactant and copper ions; and the inorganic phase comprises copper oxide.

[0022] Furthermore, the surfactant includes sodium dodecylbenzenesulfonate.

[0023] In a second aspect, the present invention provides a method for preparing a composite copper current collector as described in the first aspect, the method comprising: The welding area of ​​the composite copper current collector is positioned and pretreated; Micron-level uneven substrates and nano-level protrusions are sequentially prepared in the positioned welding area to obtain the composite copper current collector.

[0024] Furthermore, the positioning includes: using laser positioning to position the welding area of ​​the composite copper current collector.

[0025] Furthermore, the positioning marking accuracy is ±0.1 mm, the area of ​​the welding area is 1.2 to 1.5 times the welding area of ​​the electrode tab, and the distance between the edge of the welding area and the edge of the electrode tab is 0.3 to 0.5 mm.

[0026] Furthermore, the pretreatment includes plasma cleaning of the marked welding area.

[0027] Furthermore, the plasma cleaning employs a low-frequency plasma generator.

[0028] Furthermore, the process parameters for plasma cleaning include: temperature of 25~45℃; power of 80~120 W; cleaning time of 10~30 s; cleaning gas is a mixture of argon and oxygen with a volume ratio of (8~9):(1~2); and conveying speed of 0.5~1 m / min.

[0029] Furthermore, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the preparation of the micron-scale uneven substrate and nano-scale protrusions specifically includes the following steps: The welding area is micro-etched using a plasma micro-etching process to form a micron-level uneven substrate, resulting in a micro-etched welding area. The micro-etched welding area is immersed in a chemical modification solution for chemical modification, forming nano-scale protrusions on the surface of the micron-scale uneven substrate and forming an antioxidant modification layer, thus obtaining the modified welding area.

[0030] Furthermore, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the parameters of the plasma micro-etching process include: micro-etching power of 50~80 W; micro-etching time of 5~15 s; argon as the protective gas used for micro-etching; and a flow rate of 10~20 sccm for the protective gas.

[0031] Furthermore, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the surface roughness Ra of the copper in the welded area after micro-etching is 0.8~1.2 μm.

[0032] Furthermore, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the chemical modification solution comprises, by molar concentration meter: 0.5~1.5 mol / L copper sulfate, 0.1~0.3 mol / L sulfuric acid, 0.05~0.1 mol / L surfactant, and 0.01~0.03 mol / L accelerator.

[0033] Furthermore, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the surfactant includes sodium dodecylbenzenesulfonate.

[0034] Furthermore, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the accelerator includes sodium chloride.

[0035] Furthermore, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the chemical modification time is 3-8 minutes.

[0036] Furthermore, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the chemical modification is carried out under stirring conditions, and the stirring speed is 50~100 r / min.

[0037] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the preparation of the micron-scale uneven substrate and nano-scale protrusions specifically includes the following steps: A grid-like anti-plasma etching mask is prepared on the surface of the welding area by roll-to-roll flexible printing process and then cured. Plasma micro-etching process is used to perform plasma-directed etching on the areas of the welding area not covered by the mask to form a micron-level uneven substrate. The mask is then removed to obtain the micro-etched welding area. The micro-etched welding area is immersed in a chemical modification solution for chemical modification, forming nano-scale protrusions on the surface of the micron-scale uneven substrate and forming an antioxidant modification layer, thus obtaining the modified welding area.

[0038] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the grid-like anti-plasma etching mask has a grid linewidth of 2~4 μm, a grid spacing of 5~8 μm, and rounded corners at the intersections of the mask with a radius of 0.5~1.0 μm.

[0039] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the mask is a positive photoresist mask.

[0040] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the parameters of the plasma micro-etching process include: micro-etching power of 100~150 W; micro-etching time of 15~25 s; the protective gas used for micro-etching is a mixture of argon and nitrogen with a volume ratio of (7~8):(2~3); and the flow rate of the protective gas is 20~30 sccm.

[0041] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the surface roughness Ra of the copper in the welded area after micro-etching is 6.3~8.0 μm.

[0042] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the chemical modification solution comprises, by molar concentration meter: 0.5~1.5 mol / L copper sulfate, 0.1~0.3 mol / L sulfuric acid, 0.05~0.1 mol / L surfactant, and 0.01~0.03 mol / L accelerator.

[0043] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the surfactant includes sodium dodecylbenzenesulfonate.

[0044] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the accelerator includes sodium chloride.

[0045] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the chemical modification time is 5~10 min.

[0046] Furthermore, when the composite copper current collector is adapted to the control mode of laser welding, the chemical modification is carried out under stirring conditions, and the stirring speed is 5~10 r / min; wherein, the time of a single stirring is 30~60 s, and the interval between each stirring is 60~120 s.

[0047] Thirdly, the present invention provides an electrode sheet, the electrode sheet comprising the composite copper current collector as described in the first aspect, or the composite copper current collector prepared by the preparation method described in the second aspect.

[0048] Fourthly, the present invention provides an electrochemical device comprising the electrode plates described in the third aspect.

[0049] Compared with the prior art, the present invention has the following beneficial effects: (1) The composite copper current collector of the present invention can significantly improve the welding bonding force. Through the mechanical interlocking effect of the double-layer rough structure, the welding bonding force is improved by more than 50% compared with the prior art. It can effectively solve the core problems of easy detachment of the electrode tab and low peel strength. At the same time, the bonding force has good uniformity and reduces batch-to-batch differences. (2) The composite copper current collector described in this invention can reduce contact resistance and improve welding consistency. While precisely controlling the roughness, it forms a dense anti-oxidation layer through chemical modification, reduces contact resistance, controls resistance fluctuation in the welding area, improves the welding qualification rate, and reduces the generation of defective welds. (3) The composite copper current collector described in this invention can protect the copper layer and improve reliability. Low-temperature plasma micro-etching can avoid damage to the ultra-thin copper layer. The chemical modification layer can effectively prevent copper surface oxidation. At the same time, the adhesion of the copper layer is ensured by bending test, which can extend the service life of the composite current collector, improve the battery cycle stability, and reduce electrolyte pollution. (4) The preparation method of the composite copper current collector described in this invention is suitable for large-scale production. The process steps are simple, highly controllable, and have high laser positioning accuracy. It is compatible with existing composite current collector production lines and does not require large-scale equipment modification. At the same time, by optimizing process parameters, the processing cycle is shortened, which helps to reduce production costs. (5) The preparation method of the composite copper current collector described in this invention has a wide range of applications and can be adapted to various welding processes such as ultrasonic welding and laser welding. In particular, the control of two different roughness levels can be combined with ultrasonic welding to increase the bonding force between the composite copper current collector and the electrical connector during ultrasonic welding, thereby effectively improving the welding efficiency. It can meet the welding requirements of composite current collectors for different types of lithium-ion batteries, while taking into account multiple dimensions such as lightweight and mechanical performance, and adapting to the battery usage requirements of different scenarios such as power and consumer batteries. Attached Figure Description

[0050] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0051] Figure 1 This is a schematic diagram of the layered structure of the composite copper current collector described in this invention.

[0052] Figure 2 This is a schematic diagram of the cross-sectional structure of the composite copper current collector described in this invention.

[0053] Wherein, 1 is the first copper plating layer, 2 is the polymer substrate, 3 is the second copper plating layer, 4 is the welding area, and 5 is the non-welding area. Detailed Implementation

[0054] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0055] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] In a first aspect, the present invention provides a composite copper current collector, such as... Figure 1 and Figure 2As shown, the composite copper current collector includes a first copper plating layer 1, a polymer substrate 2, and a second copper plating layer 3 arranged sequentially. Both the first copper plating layer and the second copper plating layer are provided with welding areas 4 for electrode tab welding. The copper surface of the welding area includes a double-layer rough structure, which comprises a micron-level uneven substrate and nano-level protrusions.

[0057] It should be noted that the copper surface of the welding area includes a double-layer roughening structure, which addresses relevant issues in the welding process. The combination of the two layers achieves dual optimization. The first-level micron-scale uneven substrate primarily solves the core problem of insufficient welding bonding caused by the inability of existing single roughening treatments to form effective mechanical interlocking. Micron-scale pits or grid-like grooves formed by plasma micro-etching significantly increase the effective contact area of ​​the welding area, constructing a basic mechanical interlocking structure and fundamentally improving the issue of easy tab detachment. The second-level nano-scale protrusions primarily address the problems of easy oxidation, residual impurities, and poor welding stability of the copper surface after micron-scale roughening. The dense nano-scale protrusions and anti-oxidation modification layer formed through chemical modification further enhance the mechanical interlocking effect and prevent copper oxidation and impurity residue, ensuring welding stability. The combination of the two layers achieves simultaneous improvement in welding bonding strength and welding stability, while adapting to the needs of different welding processes, avoiding the shortcomings of a single structure that cannot simultaneously address both bonding strength and stability.

[0058] As an optional implementation, the size ratio between a single micron-scale structure in the micron-scale uneven substrate and a single nano-scale structure in the nano-scale protrusion is (10~20):1, for example, it can be 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, etc.

[0059] It should be noted that this invention performs graded roughness control on the copper surface of the welding area, forming a double-layer rough structure consisting of a micron-level uneven substrate and a nano-level dense protrusion. The size ratio of the micron-level structure to the nano-level structure is controlled at (10~20):1. The size ratio is defined as the ratio of the diameter of the micron-level pit or the width of the groove to the diameter of the nano-level protrusion. When the size ratio is lower than 10:1, the nano-protrusion size is too large, which easily leads to agglomeration and collapse, and cannot be uniformly distributed on the surface of the micron-level structure. When the size ratio is higher than 20:1, the nano-protrusion size is too small, and cannot form an effective secondary mechanical interlock, resulting in limited enhancement effect. (10~20):1 is the optimal critical range that balances the mechanical interlock effect and surface density to ensure a balance between the two.

[0060] As an optional implementation, the micron-level uneven substrate includes micron-level pits or micron-level grooves.

[0061] As an optional implementation, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the micron-level uneven substrate includes micron-level pits; when the composite copper current collector is adapted to the control mode of laser welding, the micron-level uneven substrate includes micron-level grooves.

[0062] As an optional implementation, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the diameter of a single micron-sized pit is 1~3 μm, for example, it can be 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, etc.

[0063] As an optional implementation, when the composite copper current collector is adapted to the ultrasonic welding control mode, the depth of a single micron-sized pit is 0.2~0.5 μm, for example, it can be 0.2 μm, 0.22 μm, 0.24 μm, 0.26 μm, 0.28 μm, 0.3 μm, 0.32 μm, 0.34 μm, 0.36 μm, 0.38 μm, 0.4 μm, 0.42 μm, 0.44 μm, 0.46 μm, 0.48 μm, 0.5 μm, etc.

[0064] As an optional implementation, when the composite copper current collector is adapted to the ultrasonic welding control mode, the distribution density of the micron-sized pits is 500~800 / mm. 2 For example, it could be 500 pieces / mm 2 520 pieces / mm 2 540 pieces / mm 2 550 pieces / mm 2 560 pieces / mm 2 580 pieces / mm 2 600 pieces / mm 2 620 pieces / mm 2 640 pieces / mm 2 650 pieces / mm 2 660 pieces / mm 2 680 pieces / mm 2 700 pieces / mm 2 750 pieces / mm 2 800 pieces / mm 2 wait.

[0065] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the width of a single micron-sized groove is 2~4 μm, for example, it can be 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4 μm, etc.

[0066] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the depth of a single micron-sized groove is 0.5~1.0 μm, for example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, etc.

[0067] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the micron-sized grooves are distributed in a grid pattern.

[0068] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the grid spacing in the micron-level grooves distributed in a grid pattern is 5~8 μm, for example, it can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, etc.

[0069] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the intersection of the micron-level groove is rounded, and the radius of the rounded corner is 0.5~1.0 μm, for example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, etc.

[0070] As an optional implementation, the nanoscale protrusions are disposed on the surface of the micron-scale uneven substrate.

[0071] As an optional implementation, the nanoscale protrusions have a spherical single-crystal structure.

[0072] As an optional implementation, the nanoscale protrusions grow perpendicular to the copper substrate surface of the welding area and are distributed on the inner wall and bottom of the micron-scale pits or grooves.

[0073] As an optional implementation, the aspect ratio of a single nanoscale protrusion is (0.8~1.2):1, for example, it can be 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1, 1.15:1, 1.2, etc.

[0074] As an optional implementation, the nanoscale protrusions cover more than 95% of the surface of the micron-scale uneven substrate, for example, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, 100%, etc.

[0075] It should be noted that the nanoscale protrusions have a spherical single crystal structure, grow perpendicular to the surface of the copper substrate, and are uniformly distributed on the inner wall and bottom of the micron-level pits or grooves. The aspect ratio of a single protrusion is controlled at (0.8~1.2):1. The structure is stable and does not collapse. There is no overlap or agglomeration between individual protrusions. The coverage of the micron-level structure surface is ≥95%, and there is no exposed copper substrate area.

[0076] As an optional implementation, the nanoscale protrusion has a face-centered cubic structure of a single copper crystal, which grows in lattice matching with the base copper layer, with the (111) crystal plane as the main crystal orientation.

[0077] It should be noted that this crystal plane exhibits the densest copper atom arrangement, superior oxidation resistance, and strongest adhesion to the substrate, with no grain boundary defects, thus avoiding the problems of easy oxidation and detachment of polycrystalline structures. Furthermore, the bonding between the nanoscale protrusions and the micron-scale uneven substrate is a metallurgical bond, not a physical adsorption; during the chemical modification process, elemental copper nucleates and grows in situ at the substrate lattice defects, forming a continuous crystalline transition with the substrate copper layer, resulting in high bonding strength and preventing protrusion detachment during subsequent welding and bending.

[0078] As an optional implementation, when the composite copper current collector is adapted to the control mode of ultrasonic welding, a nano-scale dense protrusion is formed on the surface of the micron-scale pit. The height of a single nano-scale protrusion is 50~100 nm, for example, it can be 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, etc.

[0079] As an optional implementation, when the composite copper current collector is adapted to the control mode of ultrasonic welding, a nano-scale dense protrusion is formed on the surface of the micron-scale pit. The diameter of a single nano-scale protrusion is 50~100 nm, for example, it can be 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, etc.

[0080] As an optional implementation, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the surface roughness Ra of the copper in the welding area is 1.0~1.5 μm, for example, it can be 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, etc.

[0081] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, nanoscale dense protrusions are formed on the inner wall and surface of the groove. The height of a single nanoscale protrusion is 80~150 nm, for example, it can be 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, etc.

[0082] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, nanoscale dense protrusions are formed on the inner wall and surface of the groove. The diameter of a single nanoscale protrusion is 80~150 nm, for example, it can be 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, etc.

[0083] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the surface roughness Ra of the copper in the welding area is 8.0~12.5 μm, for example, it can be 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, 12.5 μm, etc.

[0084] As an optional implementation, the copper surface of the welding area is also provided with an anti-oxidation modification layer, which can effectively isolate the contact between air and the copper layer.

[0085] As an optional implementation, when the composite copper current collector is adapted to the ultrasonic welding control mode, the thickness of the anti-oxidation modification layer is 5~10 nm, for example, it can be 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, etc.

[0086] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the thickness of the anti-oxidation modification layer is 8~12 nm, for example, it can be 8 nm, 8.5 nm, 9 nm, 9.5 nm, 10 nm, 10.5 nm, 11.5 nm, 12 nm, etc.

[0087] As an optional implementation, the antioxidant modification layer has a gradient structure, including a composite layer of metallic copper and cuprous oxide near the substrate and an organic-inorganic hybrid passivation layer away from the substrate.

[0088] As an optional implementation, the organic-inorganic hybrid passivation layer includes an organic phase and an inorganic phase; wherein the organic phase includes a coordination complex formed by a surfactant and copper ions; and the inorganic phase includes copper oxide.

[0089] As an optional implementation, the organic-inorganic hybrid passivation layer includes an organic phase and an inorganic phase; wherein the organic phase includes a coordination complex formed by sodium dodecylbenzenesulfonate and copper ions; and the inorganic phase includes copper oxide.

[0090] It should be noted that the antioxidant modification layer has a gradient structure. The side closest to the copper substrate is a composite layer of metallic copper and cuprous oxide (Cu / Cu₂O), while the side furthest from the substrate (closer to air) is an organic-inorganic hybrid passivation layer. The inorganic phase is copper oxide (CuO), and the organic phase is a coordination complex formed by a surfactant (e.g., sodium dodecylbenzenesulfonate) and copper ions. The entire layer is chromium- and nickel-free. Furthermore, the antioxidant modification layer is a continuous, pinhole-free, dense film with a thickness uniformity deviation of ≤±1 nm. It conformally grows with the surface of the nanoprotrusions, completely covering the exposed areas of the nanoprotrusions and the micron-sized substrate. The modification layer has high density and low porosity, effectively isolating oxygen and water molecules from contact with the copper substrate. Specifically, the inner Cu / Cu2O composite layer of the antioxidant modification layer matches the lattice of the copper substrate, resulting in low internal stress and avoiding the problems of cracking and peeling of traditional passivation layers. It also prevents oxygen atoms from diffusing into the copper substrate. Meanwhile, the organic-inorganic hybrid layer on the outer layer of the antioxidant modification layer isolates water and corrosive ions in the electrolyte through the hydrophobic effect of the organic ligands, while the inorganic phase further enhances the antioxidant performance. Furthermore, the modification layer has semiconductor properties, with a resistivity much lower than that of traditional chromate passivation layers. It does not significantly increase the contact resistance of the welding area and can be rapidly decomposed under welding heat input without affecting atomic fusion during the welding process, thus solving the problem of traditional anti-oxidation layers easily leading to poor soldering.

[0091] As an optional implementation, the polymer substrate may be made of any one or a combination of at least two of PET, PP, and PI.

[0092] As an optional implementation, the thickness of the polymer substrate is 8~15 μm, for example, it can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc.

[0093] As an optional implementation, the thickness of the first copper plating layer and the second copper plating layer are each independently 1~2 μm, for example, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, etc.

[0094] In a second aspect, the present invention provides a method for preparing a composite copper current collector as described in the first aspect, the method comprising: The welding area of ​​the composite copper current collector is positioned and pretreated; Micron-level uneven substrates and nano-level protrusions are sequentially prepared in the positioned welding area to obtain the composite copper current collector.

[0095] As an optional implementation, the positioning includes: using laser positioning to position the welding area of ​​the composite copper current collector.

[0096] As an optional implementation, the positioning marking accuracy is ±0.1 mm, the area of ​​the welding area is 1.2 to 1.5 times the welding area of ​​the electrode tab, for example, it can be 1.2 times, 1.25 times, 1.3 times, 1.35 times, 1.4 times, 1.45 times, 1.5 times, etc., and the distance between the edge of the welding area and the edge of the electrode tab is 0.3 to 0.5 mm, for example, it can be 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, etc.

[0097] It should be noted that this invention first uses laser positioning technology to accurately mark the welding area on the composite current collector, with a marking accuracy of ±0.1mm. The area of ​​the welding area is 1.2 to 1.5 times the welding area of ​​the electrode tab, and the distance between the edge of the welding area and the edge of the electrode tab is controlled at 0.3 to 0.5 mm to avoid energy diffusion to the non-welding area during welding. At the same time, the non-welding area is fully protected by a high-temperature resistant PI mask. The mask is resistant to plasma etching and acidic chemical modification solution corrosion, and can completely isolate the non-welding area from the subsequent processing medium, ensuring that the non-welding area always maintains its original smooth surface without any etching damage.

[0098] As an optional implementation, the pretreatment includes plasma cleaning of the marked welding area.

[0099] As an optional implementation, the plasma cleaning uses a low-frequency plasma generator.

[0100] As an optional implementation, the process parameters of the plasma cleaning include: a temperature of 25~45℃, such as 25℃, 30℃, 35℃, 40℃, 45℃, etc.; a power of 80~120 W, such as 80 W, 85 W, 90 W, 95 W, 100 W, 110 W, 115 W, 120 W, etc.; a cleaning time of 10~30 s, such as 10 s, 12 s, 14 s, 16 s, 18 s, 20 s, 22 s, 24 s, 26 s, 28 s, 30 s, etc.; a cleaning gas mixture of argon and oxygen with a volume ratio of (8~9):(1~2); and a conveying speed of 0.5~1 m / min, such as 0.5 m / min, 0.6 m / min, 0.7 m / min, 0.8 m / min, 0.9 m / min, 1 m / min, etc.

[0101] As an optional implementation, the volume ratio of argon to oxygen during the plasma cleaning process is (8~9):(1~2), for example, it can be 8:2, 8.2:1.8, 8.4:1.6, 8.5:1.5, 8.6:1.4, 8.8:1.2, or 9:1.

[0102] It should be noted that the marked welding area is then subjected to plasma cleaning to remove surface oil, oxide layer and impurities. The plasma cleaning uses a low-frequency plasma generator with power controlled at 80~120W and cleaning time of 10~30s. The cleaning gas is a mixture of argon and oxygen in a certain volume ratio. During the cleaning process, the conveying speed of the composite current collector is controlled at 0.5~1 m / min to avoid local over-cleaning or insufficient cleaning. After cleaning, the thickness of the oxide layer on the copper surface of the welding area does not exceed 5nm and the surface cleanliness is not lower than Class 100.

[0103] As an optional implementation, when the composite copper current collector is adapted to the ultrasonic welding control mode, the preparation of the micron-scale uneven substrate and nano-scale protrusions specifically includes the following steps: The welding area is micro-etched using a plasma micro-etching process to form a micron-level uneven substrate, resulting in a micro-etched welding area. The micro-etched welding area is immersed in a chemical modification solution for chemical modification, forming nano-scale protrusions on the surface of the micron-scale uneven substrate and forming an antioxidant modification layer, thus obtaining the modified welding area.

[0104] As an optional implementation, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the parameters of the plasma micro-etching process include: micro-etching power of 50~80 W, for example, 50 W, 55 W, 60 W, 65 W, 70 W, 75 W, 80 W, etc.; micro-etching time of 5~15 s, for example, 5 s, 6 s, 8 s, 10 s, 12 s, 14 s, 15 s, etc.; the protective gas used for micro-etching is argon; the flow rate of the protective gas is 10~20 sccm, for example, 10 sccm, 11 sccm, 12 sccm, 13 sccm, 14 sccm, 15 sccm, 16 sccm, 17 sccm, 18 sccm, 19 sccm, 20 sccm, etc.

[0105] As an optional implementation, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the surface roughness Ra of the copper in the welded area after micro-etching is 0.8~1.2 μm, for example, it can be 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, etc.

[0106] As an optional implementation, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the chemical modification solution comprises, by molar concentration meter: copper sulfate 0.5~1.5 mol / L (e.g., 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, etc.), sulfuric acid 0.1~0.3 mol / L (e.g., 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, etc.), surfactant 0.05~0.1 mol / L (e.g., 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, etc.), and accelerator 0.01~0.03 mol / L. mol / L (e.g., 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, etc.).

[0107] As an optional implementation, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the surfactant includes sodium dodecylbenzenesulfonate.

[0108] As an optional implementation, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the accelerator includes sodium chloride.

[0109] As an optional implementation, when the composite copper current collector is adapted to the ultrasonic welding control mode, the chemical modification time is 3 to 8 minutes, for example, 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, 5 minutes, 5.5 minutes, 6 minutes, 6.5 minutes, 7 minutes, 7.5 minutes, 8 minutes, etc.

[0110] As an optional implementation, when the composite copper current collector is adapted to the control mode of ultrasonic welding, the chemical modification is carried out under stirring conditions, and the stirring speed is 50~100 r / min, for example, it can be 50 r / min, 60 r / min, 70 r / min, 80 r / min, 90 r / min, 100 r / min, etc.

[0111] It should be noted that when the composite copper current collector is adapted to the control mode of ultrasonic welding, the first stage is the preparation of a micron-level substrate using a low-temperature plasma micro-etching process. The micro-etching power is controlled at 50~80W, the micro-etching time is 5~15s, and argon is used as a protective gas during the micro-etching process with a gas flow rate of 10~20 sccm to avoid excessive oxidation of the copper layer and to form uniformly distributed micron-level pits on the copper surface. At this time, the surface roughness Ra of the copper can reach 0.8~1.2 μm, and the copper layer thickness loss does not exceed 10 nm. The second stage involves the preparation of nanoscale protrusions. The micro-etched welding area is immersed in a chemical modification solution, with low-speed stirring during immersion to ensure full contact between the modification solution and the copper surface. The chemical modification process achieves the controllable growth of nanoprotrusions based on the micro-etching-disproportionation redeposition equilibrium of copper in an acidic chloride-containing system. The specific reaction mechanisms involved are as follows: Micro-etching process: Sulfuric acid slightly corrodes the active sites on the copper surface after plasma micro-etching, generating cuprous ions; Disproportionation nucleation: Cuprous ions undergo disproportionation reactions at lattice defects on the copper surface, generating elemental copper and copper ions. Elemental copper nucleates in situ at the active sites; Controllable growth: Sodium chloride in the system provides chloride ions, which form a soluble complex [CuCl2] with cuprous ions. - The overpotential of the disproportionation reaction is reduced, and the nucleation rate is regulated. Sodium dodecylbenzenesulfonate is adsorbed on the surface of copper crystal nuclei, inhibiting the aggregation and directional growth of crystal nuclei, and finally forming uniform, non-agglomerated nanoscale copper protrusions on the surface of the micron-scale structure.

[0112] It should be noted that the second stage involves the preparation of nanoscale protrusions. The micro-etched welding area is immersed in a chemical modification solution at room temperature for 3-8 minutes. During the immersion process, low-speed stirring is used, with a stirring speed of 50-100 r / min, to ensure that the modification solution is in full contact with the copper surface. The chemical modification solution consists of 0.5-1.5 mol / L copper sulfate solution, 0.1-0.3 mol / L sulfuric acid solution, and 0.05-0.1 mol / L surfactant. Sodium dodecylbenzenesulfonate is selected as the surfactant. 0.01-0.03 mol / L sodium chloride can also be added as an accelerator to accelerate the growth rate of the nanoprotrusions.

[0113] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the preparation of the micron-scale uneven substrate and nano-scale protrusions specifically includes the following steps: A grid-like anti-plasma etching mask is prepared on the surface of the welding area by roll-to-roll flexible printing process and then cured. Plasma micro-etching process is used to perform plasma-directed etching on the areas of the welding area not covered by the mask to form a micron-level uneven substrate. The mask is then removed to obtain the micro-etched welding area. The micro-etched welding area is immersed in a chemical modification solution for chemical modification, forming nano-scale protrusions on the surface of the micron-scale uneven substrate and forming an antioxidant modification layer, thus obtaining the modified welding area.

[0114] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the grid linewidth of the mesh-like anti-plasma etching mask is 2~4 μm, for example, it can be 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4 μm, etc.; the grid spacing is 5~8 μm, for example, it can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, etc.; the intersections of the mask are rounded with a radius of 0.5~1.0 μm, for example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, etc.

[0115] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the mask is a positive photoresist mask.

[0116] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the parameters of the plasma micro-etching process include: micro-etching power of 100~150 W, for example, 100 W, 105 W, 110 W, 115 W, 120 W, 125 W, 130 W, 135 W, 140 W, 145 W, 150 W, etc.; micro-etching time of 15~25 s, for example, 15 s, 16 s, 18 s, 20 s, 22 s, 24 s, 25 s, etc.; the protective gas used for micro-etching is a mixture of argon and nitrogen with a volume ratio of (7~8):(2~3); the flow rate of the protective gas is 20~30 sccm, for example, 20 sccm, 22 sccm, 24 sccm, 25 sccm, 26 sccm, 28 sccm, 30 sccm, etc.

[0117] As an optional implementation, the volume ratio of argon to nitrogen during the plasma micro-etching process is (7~8):(2~3), for example, it can be 7:3, 7.2:2.8, 7.4:2.6, 7.5:2.5, 7.6:2.4, 7.8:2.2, 8:2, etc. As an optional implementation, when the composite copper current collector is adapted to the laser welding control mode, the surface roughness Ra of the copper in the welded area after micro-etching is 6.3~8.0 μm, for example, it can be 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.8 μm, 7.0 μm, 7.2 μm, 7.4 μm, 7.6 μm, 7.8 μm, 8.0 μm, etc.

[0118] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the chemical modification solution comprises, by molar concentration meter: copper sulfate 0.5~1.5 mol / L (e.g., 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, etc.), sulfuric acid 0.1~0.3 mol / L (e.g., 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, etc.), surfactant 0.05~0.1 mol / L (e.g., 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, etc.), and accelerator 0.01~0.03 mol / L. mol / L (e.g., 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.025 mol / L, 0.03 mol / L, etc.).

[0119] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the surfactant includes sodium dodecylbenzenesulfonate.

[0120] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the accelerator includes sodium chloride.

[0121] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the chemical modification time is 5 to 10 minutes, for example, it can be 5 minutes, 5.5 minutes, 6 minutes, 6.5 minutes, 7 minutes, 7.5 minutes, 8 minutes, 8.5 minutes, 9 minutes, 9.5 minutes, 10 minutes, etc.

[0122] As an optional implementation, when the composite copper current collector is adapted to the control mode of laser welding, the chemical modification is carried out under stirring conditions. The stirring speed is 5~10 r / min, for example, 5 r / min, 6 r / min, 7 r / min, 8 r / min, 9 r / min, 10 r / min, etc.; wherein, the time of a single stirring is 30~60 s, for example, 30 s, 35 s, 40 s, 45 s, 50 s, 55 s, 60 s, etc., and the interval between each stirring is 60~120 s, for example, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s, 120 s, etc.

[0123] It should be noted that when the composite copper current collector is adapted to the control mode of laser welding, the first stage involves the preparation of a micron-level substrate. First, a grid-like anti-plasma etching mask is prepared on the surface of the welding area using a roll-to-roll flexible printing process. The mask grid linewidth is 2-4 μm, the grid spacing is 5-8 μm, and the intersections of the mask are rounded with a radius of 0.5-1.0 μm. After the mask is cured, a plasma micro-etching process is used, with the micro-etching power controlled at 100-150W and the micro-etching time at 15-25s. During the micro-etching process, a mixture of argon and nitrogen is used as the protective gas, with a volume ratio of 8:2 and a gas flow rate of 20-30 sccm. Areas not covered by the mask are directionally etched by plasma to avoid stress concentration that could damage the copper layer. After micro-etching, the mask is removed using a low-concentration sodium hydroxide solution and then cleaned with anhydrous ethanol. At this point, the surface roughness Ra of the copper can reach 6.3-8.0 μm, and the copper layer thickness loss does not exceed 15 μm. nm; The second stage is the preparation of nanoscale protrusions. The welded area after micro-etching is immersed in the above chemical modification solution and soaked at room temperature for 5~10 min. During the soaking process, intermittent stirring is used, with a stirring time of 30 s and an interval of 1 min to reduce the agglomeration of nanoscale protrusions.

[0124] As an optional implementation, the preparation method of the composite copper current collector further includes post-processing.

[0125] As an optional implementation, the post-processing includes the following steps: vacuum drying the composite copper current collector obtained by graded roughness control, and then cooling it after drying.

[0126] It should be noted that the purpose of vacuum drying is to remove residual chemical modification liquid from the surface to avoid the residual liquid affecting the subsequent welding quality.

[0127] As an optional implementation, the drying temperature is controlled at 60~80℃, the drying time is 15~20 min, and the vacuum degree is controlled at -0.08~-0.1 MPa.

[0128] As an optional implementation, the cooling is performed using inert gas protective cooling to cool to room temperature.

[0129] As an optional implementation, the preparation method of the composite copper current collector further includes detection.

[0130] As an optional implementation, the testing items include: roughness, weld bonding strength, contact resistance, copper layer integrity, oxidation resistance, and surface cleanliness.

[0131] The specific testing standards are as follows: Ultrasonic welding adapter type: Ra is 1.0~1.5 μm, roughness uniformity deviation does not exceed ±0.1 μm, welding bonding force is not less than 15 N / cm, bonding force variation coefficient does not exceed 5%, contact resistance does not exceed 5 mΩ, and resistance fluctuation does not exceed ±0.5 mΩ. Laser welding compatible type: Ra is 8.0~12.5 μm, roughness uniformity deviation does not exceed ±0.5 μm, welding bonding force is not less than 20 N / cm, bonding force variation coefficient does not exceed 4%, contact resistance does not exceed 3 mΩ, and resistance fluctuation does not exceed ±0.3 mΩ; The copper layer is free from damage and peeling, and the thickness loss of the copper layer does not exceed 10% of the initial thickness. There are no impurities remaining in the soldering area, and the surface cleanliness is not lower than Class 100. The thickness of the anti-oxidation layer is not less than 10 nm. After being placed in an environment of 25℃ and 60% humidity for 72 h, the oxide layer thickness does not increase significantly, and there are no obvious oxidation spots on the copper surface. Additional bending test: The composite current collector is bent 180° along the vertical direction of the welding area. After repeating this 10 times, the copper layer in the welding area shows no peeling or cracking, and the roughness change does not exceed 0.2 μm, ensuring the reliability of subsequent processing.

[0132] Thirdly, the present invention provides an electrode sheet, the electrode sheet comprising the composite copper current collector as described in the first aspect, or the composite copper current collector prepared by the preparation method described in the second aspect.

[0133] Fourthly, the present invention provides an electrochemical device comprising the electrode plates described in the third aspect.

[0134] The present invention will be further illustrated below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0135] Example 1 This embodiment provides a composite copper current collector, which includes a first copper plating layer, a polymer substrate, and a second copper plating layer sequentially disposed thereon. The polymer substrate is a PET substrate with a thickness of 12 μm. The first and second copper plating layers are both 1.5 μm thick and are prepared using a magnetron sputtering process. The areal density of the composite current collector is 4 g / m³. 2 The tensile strength is 18 MPa, and the elongation at break is 12%. The weld area is 1.3 times the weld area of ​​the electrode tab, and the distance between the edge of the weld area and the edge of the electrode tab is 0.4 mm. The composite copper current collector has a composite copper current collector weld area adapted for ultrasonic welding.

[0136] The composite copper current collector is prepared by the following steps: S1. Welding zone positioning and pretreatment: The welding area is marked using a laser positioning device with a marking accuracy of ±0.1 mm; at the same time, the non-welding area is fully covered and protected with a high-temperature resistant PI mask with a bonding accuracy of ±0.05 mm. Plasma cleaning was then performed using a low-frequency plasma generator with a cleaning power of 100 W and a cleaning time of 20 s. The volume ratio of argon to oxygen was 9:1, the gas flow rate was 15 sccm, and the composite current collector conveying speed was 0.8 m / min. After cleaning, the oxide layer thickness on the copper surface of the welding area was 3 nm, and the surface cleanliness was Class 50.

[0137] S2, graded roughness control: S2-1, First-stage micro-etching: The weld area was micro-etched using a plasma micro-etching process to form a micron-level uneven substrate, resulting in the micro-etched weld area. The plasma micro-etching power was 60 W, the time was 10 s, and argon gas was used as the protective gas at a flow rate of 15 sccm. This process created uniform pits with a diameter of 2 μm and a depth of 0.3 μm on the copper surface, with a pit density of 650 pits / mm. 2 At this point, Ra is 1.0 μm, and the copper layer thickness loss is 8 nm; S2-2, Secondary Chemical Modification: The micro-etched weld area was immersed in a chemical modification solution for chemical modification, forming nanoscale protrusions on the surface of the micron-scale uneven substrate and creating an antioxidant modification layer, resulting in the modified weld area. The chemical modification solution, measured by molar concentration, consisted of 1.0 mol / L copper sulfate, 0.2 mol / L sulfuric acid, 0.08 mol / L sodium dodecylbenzenesulfonate, and 0.02 mol / L sodium chloride, with deionized water as the solvent. Immersion at room temperature for 5 min was performed under stirring at 80 r / min, resulting in nanoscale protrusions 70 nm high and 80 nm in diameter on the pit surface without agglomeration. The final Ra was 1.2 μm. The thickness of the antioxidant modification layer was 8 μm. nm, the antioxidant modification layer has a gradient structure, including a composite layer of metallic copper and cuprous oxide near the substrate, and an organic-inorganic hybrid passivation layer away from the substrate. The organic-inorganic hybrid passivation layer includes an organic phase and an inorganic phase; wherein, the organic phase includes a coordination complex formed by a surfactant and copper ions; and the inorganic phase includes copper oxide.

[0138] S3. Post-processing and inspection: The composite copper current collector obtained by graded roughness control was vacuum dried at a temperature of 70℃ for 18 min and a vacuum degree of -0.09 MPa. After drying, it was cooled to room temperature under nitrogen protection.

[0139] The nickel sheet was welded to the welding area of ​​the composite copper current collector using ultrasonic welding. The welding parameters were: welding pressure of 0.35 MPa, welding time of 0.3 s, and welding amplitude of 25 μm. The cooling method after welding was natural cooling at room temperature for 60 s.

[0140] The composite copper current collector was tested before and after welding. The test results showed that Ra was 1.2 μm, the roughness uniformity deviation was ±0.08 μm, the welding bond strength was 18 N / cm, the bond strength variation coefficient was 4%, the contact resistance was 4 mΩ, and the resistance fluctuation was ±0.4 mΩ. The copper layer was undamaged, the copper layer thickness loss was 8 nm, and the surface cleanliness was Class 50. The anti-oxidation layer thickness was 8 nm, and the oxide layer thickness did not increase significantly after 72 h, with no oxidation spots. After bending 180° repeatedly 10 times, the copper layer in the welding area did not peel off or crack, and the roughness change was 0.1 μm.

[0141] Example 2 This embodiment provides a composite copper current collector, which differs from Embodiment 1 only in that the plasma micro-etching process in S2-1 is adjusted to ensure that the size ratio of the micron-scale structure to the nano-scale structure is controlled at 10:1. The other steps are the same as in Embodiment 1.

[0142] Example 3 This embodiment provides a composite copper current collector, which differs from Embodiment 1 only in that the plasma micro-etching process in S2-1 is adjusted to ensure that the size ratio of the micron-scale structure to the nano-scale structure is controlled at 20:1. The other steps are the same as in Embodiment 1.

[0143] Example 4 This embodiment provides a composite copper current collector, which differs from Embodiment 1 only in that the plasma micro-etching process in S2-1 is adjusted to ensure that the size ratio of the micron-scale structure to the nano-scale structure is controlled at 5:1. The other steps are the same as in Embodiment 1.

[0144] Example 5 This embodiment provides a composite copper current collector, which differs from Embodiment 1 only in that the plasma micro-etching process in S2-1 is adjusted to ensure that the size ratio of the micron-scale structure to the nano-scale structure is controlled at 25:1. The other steps are the same as in Embodiment 1.

[0145] Example 6 This embodiment provides a composite copper current collector, which differs from Embodiment 1 only in that the plasma micro-etching process in S2-1 is adjusted to ensure that the size ratio of the micron-scale structure to the nano-scale structure is controlled at 20:1. The other steps are the same as in Embodiment 1.

[0146] Example 7 This embodiment provides a composite copper current collector, which differs from Example 1 only in that the chemical modification solution in S2-2 includes, by molar concentration meter: 1.0 mol / L copper chloride, 0.2 mol / L hydrochloric acid, and 0.08 mol / L sodium dodecyl sulfate. The other steps are the same as in Example 1.

[0147] Comparative Example 1 The roughness of the composite current collector welding area in Example 1 was controlled using an existing single chemical micro-etching method. The micro-etching solution consisted of 1.0 mol / L sulfuric acid and 0.5 mol / L hydrogen peroxide. The micro-etching time was 10 min, and the final Ra was 0.9 μm with a roughness uniformity deviation of ±0.2 μm.

[0148] Post-welding inspection showed that the bonding force was 10 N / cm, the coefficient of variation of bonding force was 8%, the contact resistance was 13 mΩ, and the resistance fluctuation was ±2 mΩ; the copper layer showed local damage, with a copper layer thickness loss of 20 nm, and the surface cleanliness was Class 300; after 72 hours, the oxide layer thickness increased to 25 nm, and obvious oxide spots appeared; after bending 180° repeatedly 10 times, the copper layer in the welded area showed peeling and cracks, and the roughness changed by 0.5 μm; the welding qualification rate was 92%.

[0149] Comparative Example 2 This comparative example provides a composite copper current collector, which differs from Example 1 only in that the second-stage chemical modification of S2-2 is not performed, and the post-processing is performed directly after the first-stage micro-etching of S2-1. The other steps are the same as those in Example 1.

[0150] Comparative Example 3 This comparative example provides a composite copper current collector, which differs from Example 1 only in that the first-stage micro-etching of S2-1 is not performed, and the second-stage chemical modification of S2-2 is performed directly after pretreatment. The other steps are the same as in Example 1.

[0151] Comparative Example 4 This comparative example provides a composite copper current collector, which differs from Example 1 only in that the second-stage chemical modification of S2-2 is not performed, and the post-processing is performed directly after the first-stage micro-etching of S2-1. The other steps are the same as those in Example 1.

[0152] Test case Test samples: Composite copper current collectors provided in Examples 1-7 and Comparative Examples 1-4.

[0153] The test items include: surface roughness, weld bond strength, contact resistance, copper layer integrity, oxidation resistance, and surface cleanliness. The specific test methods are as follows: Surface roughness (Ra) test: The test was conducted using a white light interferometer under normal room temperature and pressure conditions. Five test points were randomly selected from the welding area of ​​each sample, and the arithmetic mean was taken as the test result. Weld bond strength test: The test was conducted using an electronic universal tensile testing machine at a tensile speed of 50 mm / min. The maximum tensile force at which the tabs detached was recorded, and the weld bond strength and the coefficient of variation of the bond strength were calculated. Contact resistance test: A four-probe resistance tester was used to test the resistance at room temperature and normal pressure. Three measuring points were selected in the welding area, and the average value was taken as the contact resistance. The resistance fluctuation value was recorded. Copper layer integrity testing: The morphology of the copper layer was observed using a scanning electron microscope (SEM), and the thickness of the copper layer was measured at room temperature using a profilometer. The copper layer thickness loss was calculated. Antioxidant performance test: The oxide layer thickness was tested by placing the sample in a constant temperature and humidity chamber at 25℃ and 60% humidity for 72 hours and then measuring the thickness before and after placement using X-ray photoelectron spectroscopy (XPS). The thickness change before and after placement was compared. Surface cleanliness test: The cleanliness level is determined by counting the number of particles ≥0.5μm in a clean environment using a particle counter in accordance with ISO 14644-1 standard. Bending test: Using a bending tester at a bending speed of 10 times / min, the copper layer is bent 10 times at a 180° angle perpendicular to the welding area. The roughness change is measured using a white light interferometer to observe the state of the copper layer.

[0154] The specific test results are shown in Tables 1 and 2 below: Table 1

[0155] Table 2

[0156] As shown in Table 1, the copper surface of the welding area of ​​the composite copper current collector of the present invention has a double-layer rough structure composed of a micron-level uneven substrate and a nano-level dense protrusion. The surface roughness Ra of the copper surface in the non-welding area can reach below 1.4 μm, and the surface is smooth and free of scratches. The bonding force between the welding area and the electrode tab after welding can be improved by more than 80% compared with the prior art, the contact resistance can be reduced by more than 60%, and the welding qualification rate can reach more than 95.8%, which can meet the requirements of lightweight and high reliability of lithium-ion batteries. In summary, the comparison shows that the control method of the present invention is superior to the prior art in terms of welding bonding force, contact resistance, copper layer protection, oxidation resistance, welding qualification rate, and mechanical reliability.

[0157] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite copper current collector, characterized in that, The composite copper current collector includes a first copper plating layer, a polymer substrate, and a second copper plating layer arranged sequentially. Both the first copper plating layer and the second copper plating layer are provided with welding areas for electrode tab welding. The copper surface of the welding area includes a double-layer rough structure, which comprises a micron-level uneven substrate and nano-level protrusions.

2. The composite copper current collector according to claim 1, characterized in that, The size ratio between a single micron-sized structure in the micron-sized uneven substrate and a single nano-sized structure in the nano-sized protrusion is (10~20):

1.

3. The composite copper current collector according to claim 1 or 2, characterized in that, The micron-level uneven substrate includes micron-level pits or micron-level grooves; Preferably, when the composite copper current collector is adapted to the ultrasonic welding control mode, the diameter of a single micron-sized pit is 1~3 μm; the depth of a single micron-sized pit is 0.2~0.5 μm; and the distribution density of the micron-sized pits is 500~800 / mm. 2 ; Preferably, when the composite copper current collector is adapted to the control mode of laser welding, the width of a single micron-sized groove is 2~4 μm; the depth of a single micron-sized groove is 0.5~1.0 μm; and the micron-sized grooves are distributed in a grid pattern with a grid spacing of 5~8 μm, and the intersections of the micron-sized grooves are rounded with a radius of 0.5~1.0 μm.

4. The composite copper current collector according to claim 1 or 2, characterized in that, The nanoscale protrusions are disposed on the surface of the micron-scale uneven substrate; Preferably, the nanoscale protrusions cover more than 95% of the surface of the micron-scale uneven substrate; Preferably, when the composite copper current collector is adapted to the ultrasonic welding control mode, the height of a single nanoscale protrusion is 50~100 nm; the diameter of a single nanoscale protrusion is 50~100 nm; and the surface roughness Ra of the copper in the welding area is 1.0~1.5 μm. Preferably, when the composite copper current collector is adapted to the control mode of laser welding, the height of a single nanoscale protrusion is 80~150 nm; the diameter of a single nanoscale protrusion is 80~150 nm; and the surface roughness Ra of the copper in the welding area is 8.0~12.5 μm. Preferably, the copper surface of the welding area is further provided with an anti-oxidation modification layer; Preferably, when the composite copper current collector is adapted to the ultrasonic welding control mode, the thickness of the antioxidant modification layer is 5~10 nm; Preferably, when the composite copper current collector is adapted to the control mode of laser welding, the thickness of the antioxidant modification layer is 8~12 nm; Preferably, the antioxidant modification layer has a gradient structure, including a composite layer of metallic copper and cuprous oxide near the substrate and an organic-inorganic hybrid passivation layer away from the substrate. Preferably, the organic-inorganic hybrid passivation layer comprises an organic phase and an inorganic phase; wherein the organic phase comprises a coordination complex formed by a surfactant and copper ions; and the inorganic phase comprises copper oxide. Preferably, the surfactant comprises sodium dodecylbenzenesulfonate.

5. A method for preparing a composite copper current collector according to any one of claims 1 to 4, characterized in that, The preparation method includes: The welding area of ​​the composite copper current collector is positioned and pretreated; Micron-level uneven substrates and nano-level protrusions are sequentially prepared in the positioned welding area to obtain the composite copper current collector.

6. The method for preparing the composite copper current collector according to claim 5, characterized in that, The positioning includes: using laser positioning to position the welding area of ​​the composite copper current collector; Preferably, the positioning marking accuracy is ±0.1 mm, the area of ​​the welding area is 1.2 to 1.5 times the welding area of ​​the electrode tab, and the distance between the edge of the welding area and the edge of the electrode tab is 0.3 to 0.5 mm. Preferably, the pretreatment includes: plasma cleaning of the marked welding area; Preferably, the plasma cleaning employs a low-frequency plasma generator; Preferably, the process parameters for plasma cleaning include: temperature of 25~45℃; power of 80~120 W; cleaning time of 10~30 s; cleaning gas is a mixture of argon and oxygen with a volume ratio of (8~9):(1~2); and conveying speed of 0.5~1 m / min.

7. The method for preparing the composite copper current collector according to claim 5, characterized in that, When the composite copper current collector is adapted to the ultrasonic welding control mode, the preparation of the micron-scale uneven substrate and nano-scale protrusions specifically includes the following steps: The welding area is micro-etched using a plasma micro-etching process to form a micron-level uneven substrate, resulting in a micro-etched welding area. The micro-etched welding area is immersed in a chemical modification solution for chemical modification, forming nano-scale protrusions on the surface of the micron-scale uneven substrate and forming an antioxidant modification layer, thus obtaining the modified welding area. Preferably, the parameters of the plasma micro-etching process include: micro-etching power of 50~80 W; micro-etching time of 5~15 s; argon as the protective gas used for micro-etching; and a flow rate of 10~20 sccm for the protective gas. Preferably, the surface roughness Ra of the copper in the welded area after micro-etching is 0.8~1.2 μm; Preferably, the chemically modified solution comprises, by molar concentration meter: 0.5~1.5 mol / L copper sulfate, 0.1~0.3 mol / L sulfuric acid, 0.05~0.1 mol / L surfactant, and 0.01~0.03 mol / L accelerator; Preferably, the surfactant comprises sodium dodecylbenzenesulfonate; Preferably, the accelerator comprises sodium chloride; Preferably, the chemical modification takes place for 3 to 8 minutes; Preferably, the chemical modification is carried out under stirring conditions, and the stirring speed is 50~100 r / min.

8. The method for preparing the composite copper current collector according to claim 5, characterized in that, When the composite copper current collector is adapted to the control mode of laser welding, the preparation of micron-scale uneven substrate and nano-scale protrusions specifically includes the following steps: A grid-like anti-plasma etching mask is prepared on the surface of the welding area by roll-to-roll flexible printing process and then cured. Plasma micro-etching process is used to perform plasma-directed etching on the areas of the welding area not covered by the mask to form a micron-level uneven substrate. The mask is then removed to obtain the micro-etched welding area. The micro-etched welding area is immersed in a chemical modification solution for chemical modification, forming nano-scale protrusions on the surface of the micron-scale uneven substrate and forming an antioxidant modification layer, thus obtaining the modified welding area. Preferably, the grid-like anti-plasma etching mask has a grid linewidth of 2~4 μm and a grid spacing of 5~8 μm; the intersections of the mask are rounded with a radius of 0.5~1.0 μm. Preferably, the parameters of the plasma micro-etching process include: micro-etching power of 100~150 W; micro-etching time of 15~25 s; the protective gas used for micro-etching is a mixture of argon and nitrogen with a volume ratio of (7~8):(2~3); and the flow rate of the protective gas is 20~30 sccm. Preferably, the surface roughness Ra of the copper in the welded area after micro-etching is 6.3~8.0 μm; Preferably, the chemically modified solution comprises, by molar concentration meter: 0.5~1.5 mol / L copper sulfate, 0.1~0.3 mol / L sulfuric acid, 0.05~0.1 mol / L surfactant, and 0.01~0.03 mol / L accelerator; Preferably, the surfactant comprises sodium dodecylbenzenesulfonate; Preferably, the accelerator comprises sodium chloride; Preferably, the chemical modification takes 5-10 minutes; Preferably, the chemical modification is carried out under stirring conditions, and the stirring speed is 5~10 r / min; wherein the time for a single stirring is 30~60 s, and the interval between each stirring is 60~120 s.

9. An electrode sheet, characterized in that, The electrode sheet comprises the composite copper current collector according to any one of claims 1 to 4, or the composite copper current collector prepared by the preparation method according to any one of claims 5 to 8.

10. An electrochemical device, characterized in that, The electrochemical device includes the electrode plates as described in claim 9.

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