Copper-lithium composite belt welding method

Abstract

The invention relates to a copper-lithium composite belt welding method which comprises the following steps: pretreating the surface of a copper material to remove a passivation layer on the surface of the copper material; the surface of the lithium material is pretreated, and the lithium material with the flat surface is obtained; the pretreated copper material, the pretreated lithium material and the protective layer are laminated and assembled to form a laminated body; welding and fixing the assembled laminated body; and removing the protective layer of the laminated body after welding is completed, and cutting the laminated body to a required size. According to the copper-lithium composite belt welding method, the surfaces of the copper material and the lithium material are pretreated and then laminated and assembled with the protective layer, the protective layer is arranged below the lithium material, the copper material is arranged on the upper surface of the edge of the lithium material, and during welding, welding equipment is in direct contact with the copper material, so that edge warping caused by uneven pressure on the edge of the lithium material is avoided; the welding consistency is improved; and through the welding method, the situation that the pole piece is welded through due to the viscosity and the softness temperature of the metal lithium is avoided, and the yield of the formed copper-lithium composite belt is increased.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method for welding copper-lithium composite strips. Background Art

[0002] Lithium metal batteries are considered to be an ideal candidate for the next generation of high-performance batteries due to their high energy density and long cycle life. In lithium battery manufacturing, lithium metal anodes are considered to be key materials for the next generation of high-energy-density batteries due to their high theoretical capacity (3860 mAh / g) and low electrochemical potential (-3.04 V vs. SHE).

[0003] However, lithium metal anodes are prone to dendrite growth and dissolution during charge and discharge, leading to battery capacity decay and reduced safety performance. Currently, various methods have been proposed to protect lithium metal battery anodes, such as: Constructing a protective film: A protective film is constructed on the surface of the lithium metal anode to inhibit the growth and dissolution of lithium dendrites. Optimizing the electrode structure: Optimizing the structure of the lithium metal anode can improve its ability to inhibit lithium dendrite growth.

[0004] However, in terms of the preparation process, the traditional roll welding method (resistance welding or ultrasonic welding) is used to weld the lithium ribbon and copper foil (as the tab). Since lithium metal is soft (Mohs hardness ≈ 0.6), during the welding process, due to the concentrated pressure (usually 50 to 200 MPa), the lithium ribbon is prone to plastic deformation or even fragmentation, resulting in poor contact or local fracture of the tab, resulting in poor welding consistency. In addition, the ductility of the lithium ribbon under pressure is poor, making it difficult to form a uniform metallurgical bond with the copper foil. Traditional roll welding relies on thermal-mechanical coupling, but the metallurgical compatibility of lithium and copper is poor, which can easily lead to electrode penetration during the welding process. Summary of the Invention

[0005] Based on this, it is necessary to provide a copper-lithium composite strip welding method to address the problem of poor welding consistency of the current copper-lithium composite strip.

[0006] A first aspect of the present application provides a copper-lithium composite strip welding method, comprising the following steps:

[0007] Pre-treating the copper surface to remove the passivation layer on the surface;

[0008] Pre-treating the surface of the lithium material to obtain a lithium material with a smooth surface;

[0009] assembling the pretreated copper material, lithium material and protective layer in multiple layers to form a laminate;

[0010] Welding and fixing the assembled laminated body;

[0011] The protective layer of the laminated body after welding is removed and the laminated body is cut into a desired size.

[0012] In one embodiment, the copper material surface is pretreated, including: the copper material is a copper foil, and the copper foil has a thickness of 4 to 8 μm. During the pretreatment, the copper foil surface is plasma cleaned to remove the CuO passivation layer of the copper foil.

[0013] In one embodiment, the surface of the lithium material is pretreated, including: the lithium material is a lithium strip or lithium sheet, and the thickness of the lithium strip or lithium sheet is 20 to 100 μm. During the pretreatment, the surface of the lithium strip or lithium sheet is rolled to be flat.

[0014] In one embodiment, the pressure of rolling the lithium ribbon or lithium sheet is 50-300 MPa.

[0015] In one embodiment, the laminate comprises the copper foil, the lithium sheet, and the protective layer stacked in sequence; or

[0016] The copper foil, the lithium sheet, the copper foil and the protective layer are stacked in sequence.

[0017] In one embodiment, when stacked, the copper foil is arranged at the edge of the lithium sheet, and there is an overlap of 5±0.5 mm with the edge of the lithium sheet.

[0018] In one embodiment, the protective layer is non-sticky, has a surface energy of less than 30 mN / m, and has a thickness of 25 to 100 μm.

[0019] In one embodiment, the protective layer forms an uncovered strip with a width of 5±0.5 mm on the welding-related side of the lithium ribbon in the width direction, and the protective layer coverage range of the remaining areas exceeds the edge of the lithium ribbon by at least 2 cm.

[0020] In one embodiment, the welding method used to fix the assembled stacked body is to use a roll welding machine for roll welding, the amplitude of the roll welding machine is 10-15%, the welding pressure is 0.04-0.1 MPa, the roll welding temperature is set to 25-35°C, the roll welding speed is set to 1-5 m / min, the weld mark depth is 0.01-0.05 mm, and the welding spacing is 0.1-0.6 mm.

[0021] In one embodiment, the seam welder performs welding in air, and during the seam welding, the roller of the seam welder needs to stay on the laminate for 0.5 to 2 seconds.

[0022] In the above-mentioned copper-lithium composite strip welding method, the surfaces of the copper and lithium materials are pre-treated and then stacked and assembled with a protective layer. The copper material, lithium strip / lithium sheet, copper material, and protective layer are stacked in sequence. The protective layer is placed under one of the copper materials, that is, at the bottom layer, and the other copper material is placed on the upper surface of the edge of the lithium strip / lithium sheet, that is, at the top layer. During welding, the welding equipment is in direct contact with the copper material to avoid uneven pressure on the edge of the lithium strip / lithium sheet and the resulting warping, thereby improving the consistency of welding.

[0023] Furthermore, in this lithium-copper composite ribbon welding method, the lithium ribbon / sheet is first plasma-cleaned to completely remove the CuO passivation layer, thereby promoting Cu-Li atomic diffusion and improving the yield rate of the copper-lithium composite ribbon after welding. The edge of the protective layer near the roll welder is spaced 5mm from the edge of the lithium ribbon / sheet, with a tolerance of ±10%, and aligned with the edge of the copper foil being roll welded. The low-surface-energy protective layer acts as a barrier, preventing adhesion between the lithium sheet and the roll welder's gears. Furthermore, the entire welding process can be performed directly in air, saving the cost of working in an inert gas environment.

[0024] Furthermore, the gears of the seam welder are in direct contact with the copper foil, preventing warping of the edges of the lithium ribbons or sheets and effectively improving welding consistency. Furthermore, by adjusting the gear shape and process parameters of the seam welder, it is possible to prevent electrode penetration during welding due to the stickiness and softness of metallic lithium. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the first copper-lithium composite strip welding method in the embodiment of the present application;

[0026] Figure 2 This is a structural diagram of the first copper-lithium composite belt in the embodiment of this application;

[0027] Figure 3 This is a structural diagram of the second copper-lithium composite belt in the embodiment of this application.

[0028] Description of reference numerals:

[0029] 1. Copper foil; 2. Lithium sheet; 3. Protective layer. DETAILED DESCRIPTION

[0030] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0031] In the description of this application, it should be understood that if the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. appear, the orientation or position relationship indicated by these terms is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0032] In addition, if the terms "first" or "second" appear, these terms are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of this application, if the term "plurality" appears, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0033] Currently, in lithium battery manufacturing, the traditional roll welding method is commonly used to weld lithium and copper materials. Due to the soft texture of lithium metal, the concentrated pressure during welding can easily cause the lithium material to undergo plastic deformation or even breakage. This can also easily lead to poor contact or localized fracture of the tabs, resulting in poor welding consistency. In addition, due to the poor ductility of lithium under pressure, it is difficult to form a uniform metallurgical bond with copper. Moreover, because traditional roll welding relies on thermal-mechanical coupling, the metallurgical compatibility of lithium and copper is poor, which can easily lead to electrode wear during the welding process.

[0034] like Figure 1 As shown, an embodiment of the present application provides a copper-lithium composite strip welding method, which includes the following steps:

[0035] Pre-treating the copper surface to remove the passivation layer on the surface;

[0036] Pre-treating the surface of the lithium material to obtain a lithium material with a smooth surface;

[0037] The pre-treated copper material, lithium material and protective layer 3 are stacked and assembled in multiple layers to form a laminate;

[0038] Welding and fixing the assembled laminated body;

[0039] The protective layer 3 of the laminated body after welding is removed and the laminated body is cut into a desired size.

[0040] In addition, after the cutting is completed, the welding integrity is checked to ensure that no other adverse conditions such as cracking occur. In this welding method, the copper material, the lithium material and the protective layer 3 are stacked in multiple layers, and the protective layer 3 is placed below the lithium material. The welding edge of the protective layer 3 is spaced apart from the edge of the lithium material by a set distance, and the copper material is placed on the upper surface of the lithium material. During welding, the welding equipment is in direct contact with the copper foil 1, thereby avoiding the occurrence of adverse conditions such as warping caused by uneven pressure on the lithium material, thereby improving the consistency of welding and ensuring the yield rate of the final product.

[0041] The copper material used in this copper-lithium composite strip welding method is copper foil 1, preferably 4 to 8 μm thick. The surface of copper foil 1 is pretreated by plasma cleaning to remove the CuO passivation layer on the surface. Plasma cleaning completely removes the CuO passivation layer, promoting interdiffusion of Cu and Li atoms and improving the bonding strength of the weld interface. Furthermore, the lithium material used is lithium ribbon or sheet 2, with a thickness of 20 to 100 μm. The surface of the lithium material is pretreated by rolling the surface of the lithium ribbon or sheet 2 to flatten it, using a pressure of 50 to 300 MPa. Using a high pressure of 50 to 300 MPa to roll the lithium sheet 2 eliminates surface wrinkles and pores, reduces thickness uniformity errors, and reduces void defects at the weld interface, thereby improving current carrying capacity.

[0042] In the following embodiments, the lithium material is set as the lithium sheet 2 for discussion.

[0043] In lithium battery design, optimizing the structure of the laminate is crucial to performance. Two examples of laminates are provided herein. By varying the arrangement of the copper foil 1, lithium sheet 2, and protective layer 3, multiple technical benefits can be achieved. The following details the structural forms and technical benefits of each of the two laminates:

[0044] like Figure 2 Specifically, the laminate consists of a copper foil 1, a lithium sheet 2, and a protective layer 3 stacked in order from top to bottom. The copper foil 1 on the top layer serves as the negative electrode current collector, primarily collecting electrons and transferring them to the external circuit. The lithium sheet 2 in the middle serves as the negative electrode active material, providing a source of lithium ions. The protective layer 3 at the bottom prevents adhesion between the roller and the lithium sheet 2 during the roll welding process, ensuring the integrity of the overall interface.

[0045] like Figure 3Specifically, the laminate comprises a copper foil 1, a lithium sheet 2, a copper foil 1, and a protective layer 3 stacked in order from top to bottom. Here, by placing copper foil 1 on both the upper and lower layers of the lithium sheet 2 to form a dual current collector structure, the upper and lower current collectors work together to reduce interfacial resistance and promote uniform deposition of lithium ions.

[0046] Furthermore, when stacked, the copper foil 1 is suitable for being placed at the edge of the lithium sheet 2, and there is an overlap of 5±0.5mm between the edges of the copper foil 1 and the lithium sheet 2. The setting of this overlapping portion can enhance the interface bonding strength. The non-overlapping design relies only on surface bonding, and this overlapping structure improves the copper-lithium peeling strength, avoiding the interruption of electron transmission caused by interface separation during battery cycling. In addition, the overlapping portion has an accuracy range of 5±0.5mm. Within this accuracy range, it is compatible with the alignment error of the welding equipment, which significantly improves the yield of the composite tape of the copper foil 1 and the lithium sheet 2 (up to 99.9%).

[0047] Furthermore, the protective layer 3 used in the laminate is non-sticky and has a surface energy of less than 30 mN / m. Surface energy is the energy state exhibited by molecules on a material's surface due to unbalanced forces, reflecting the tendency of the material's surface to interact with other substances (such as liquids or solids). In lithium battery manufacturing, surface energy directly impacts the performance of key processes such as coating, bonding, and welding. The thickness of the protective layer 3 ranges from 25 to 100 μm. Furthermore, the protective layer 3 forms an uncovered band of 5±0.5 mm wide on the widthwise side of the lithium sheet 2, where the weld is to be performed. The remaining areas of the protective layer 3 extend at least 2 cm beyond the edge of the lithium sheet 2. Thus, the protective layer 3, with a surface energy of less than 30 mN / m, covers the main body of the lithium sheet 2, leaving only a 5±0.5 mm wide weld zone exposed. This overlap and the 5±0.5 mm uncovered band of the protective layer 3 form a process buffer, preventing the protective layer 3 from being drawn into the weld zone. This ensures that the heat-affected zone during welding is strictly confined to the overlapped band, facilitating interference with the protective layer 3 design.

[0048] Specifically, the specific material of protective layer 3 is not limited herein; it only requires that the surface of protective layer 3 be non-sticky. For example, protective layer 3 can be made of a fluoropolymer modified membrane, a polytetrafluoroethylene (PTFE) membrane, a silicone membrane, a super-hydrophobic membrane, or the like. The non-stick surface of protective layer 3 prevents adhesion between the lithium sheet 2 and the roller or the laminate. Setting the thickness of protective layer 3 to 25 to 100 μm can provide a certain buffering effect during the welding process, reducing the possibility of scratches or deformation of the lithium sheet 2 during rolling or welding. Furthermore, the protective layer 3 can be peeled off without damage after welding.

[0049] More specifically, the assembled stack is secured using a seam welder, which performs the welding in air. This method eliminates the need for inert gas shielding and allows welding to be performed in air, significantly reducing equipment costs and process complexity.

[0050] In addition, when performing roll welding, the roller of the roll welding machine needs to stay on the laminate for 0.5 to 2 seconds. Furthermore, the process parameters of the roll welding machine need to be set. Specifically, the amplitude of the roll welding machine is 10 to 15%, the welding pressure is 0.04 to 0.1 MPa, the roll welding temperature is set to 25 to 35 ° C, the roll welding speed is set to 1 to 5 m / min, the weld print depth is 0.01 to 0.05 mm, and the welding spacing is 0.1 to 0.6 mm. Thus, the mutual diffusion of Cu-Li atoms in the copper-lithium composite strip can be promoted by the welding of the roll welding machine, and the sufficient diffusion of the interface of the copper-lithium composite strip can be ensured after the roll welding is performed according to the set process parameters.

[0051] Thus, through the lithium-copper composite strip welding method, the copper foil 1 is first plasma cleaned to completely remove the CuO passivation layer, thereby promoting the diffusion of Cu-Li atoms and improving the yield rate of the copper-lithium composite strip after welding. The copper foil 1, the lithium strip / lithium sheet 2, the copper foil 1, and the protective layer 3 are stacked in sequence, and the protective layer 3 is placed below the lithium strip / lithium sheet 2. The edge of the protective layer 3 close to the side of the roll welder is 5mm away from the edge of the lithium strip / lithium sheet 2, with a tolerance of ±10%. When only one piece of copper foil 1 is provided, it is preferably placed on the upper surface of the edge of the lithium strip / lithium sheet 2. A low surface energy protective layer is used as an isolation layer to avoid adhesion between the lithium sheet 2 and the gears of the roll welder, and the welding operation can be carried out directly in the air, saving the cost required for operation in an inert gas environment.

[0052] Furthermore, the gears of the seam welder are in direct contact with the copper foil 1, preventing uneven pressure on the lithium ribbon / sheet 2, which could cause warping and other undesirable conditions. This configuration also effectively improves welding consistency. Furthermore, by adjusting the gear shape and process parameters of the seam welder, it is possible to prevent electrode penetration during welding due to the stickiness and softness of metallic lithium.

[0053] Example 1. A copper-lithium composite tape welding method of the present application includes: plasma cleaning the surface of the copper foil 1 to remove the CuO passivation layer on the surface of the copper foil 1, and setting the thickness of the copper foil 1 to 5 μm; then, when rolling the surface of the lithium tape or lithium sheet 2 to be flat, setting the rolling pressure to 150 MPa, and setting the thickness of the lithium tape or lithium sheet 2 to 50 μm; stacking the copper foil 1, the lithium sheet 2, the copper foil 1, and the modified PET film, the modified PET film is non-sticky (its surface energy is <30 mN / m) to avoid adhesion with the lithium sheet 2, and the copper foil 1 is set at the edge of the lithium sheet 2, and there is a 5 mm overlap between the copper foil 1 and the edge of the lithium sheet 2. After the above materials are positioned, they are directly roll welded to fix them; using a roll welding machine to weld the laminated body after the laminated assembly is completed, the welding is performed directly in the air, and the roller used in the welding machine is set to square teeth to increase local pressure concentration, thereby promoting the mutual diffusion of Cu-Li atoms in the copper-lithium composite tape. After the roll welding machine performs roll welding according to the set process parameters, it is necessary to ensure that the roller stays on the copper-lithium composite strip for 0.8 seconds to ensure sufficient diffusion of the interface.

[0054] In addition, the preparation method of the modified PET film adopted in this embodiment 1 is: by having the material PTFE of low surface energy on the PET film surface coating one deck, PTFE has extremely low surface energy, can form a smooth, non-stick protective film on the PET film surface after coating, effectively reduce the friction and the adhesive force of PET film and other objects. Fluoropolymer can form the fluorine atom protective layer 3 of close arrangement on the PET film surface, due to the characteristic of fluorine atom, makes film surface have excellent water-repellent, oil-repellent and anti-sticking property. The thickness of this modified PET film after preparation is 50 μm, and this modified PET film is formed with the uncovered band that width is 5.5mm at the roll welding associated side of lithium sheet 2 width directions, and the coverage range of all the other areas all exceeds lithium sheet 2 edge 5cm.

[0055] Furthermore, with respect to the process parameters of the seam welding machine, in this embodiment, the amplitude of the seam welding machine is set to 11%, the welding pressure is 0.05 MPa; the seam welding temperature is set to 28°C; the roller speed is set to 3m / min; the weld depth is 0.02mm; and the weld spacing is 0.5mm. By setting the process parameters of the seam welding machine as described above, and performing the seam welding operation after the setting is completed, the protective layer 3 on the copper-lithium composite strip is removed after the seam welding is completed, and the finished product after welding is cut to a suitable size as needed, and then the welding integrity is checked and the finished copper-lithium composite strip is tested. After testing, the qualified rate of the copper-lithium composite strip obtained by the above method is 99.9%.

[0056] Comparative Example 1

[0057] Comparative Example 1 is substantially the same as the solution described in Example 1, except that in Comparative Example 1, the rollers of the roll welder used are set to traditional diamond-shaped teeth, and the qualified rate of the copper-lithium composite strip after roll welding using the roll welder with the diamond-shaped teeth is 50%. This shows that the roll welder with square teeth has a larger planar contact area, making the pressure distribution more uniform, effectively breaking the interface oxide layer and promoting atomic diffusion, while the diamond-shaped teeth may cause uneven pressure due to point contact, thereby leading to an insufficient interface structure, thereby affecting the qualified rate of the copper-lithium composite strip after roll welding.

[0058] Comparative Example 2

[0059] This comparative example 2 is basically the same as the scheme described in Example 1, except that: in this comparative example 2, the process parameters of the seam welding machine are adjusted, specifically, the amplitude of the seam welding machine is set to 30%. After this adjustment, the qualified rate of the copper-lithium composite strip is 78%.

[0060] It can be seen that in this comparative example 2, by adjusting the amplitude of the seam welder from 11% to 30%, the amplitude of 11% can provide moderate vibration to promote diffusion, while at an amplitude of 30%, severe vibration may be caused, resulting in local tearing of the lithium sheet 2 or the copper foil 1 or excessive deformation of the interface causing microcracks, and may cause the protective layer 3 to shift and fail. Therefore, controlling the amplitude of the seam welder within an appropriate range can avoid damage to the material structure due to excessive vibration, thereby improving the yield of the final product.

[0061] In this application, unless otherwise specified or limited, the terms "mounted," "connected," "connected," "fixed," etc., should be interpreted broadly. For example, these terms may refer to fixed connections, removable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediary; and internal communication between two components or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0062] In this application, unless otherwise expressly specified or limited, if a first feature is described as being "above" or "below" a second feature, or similar descriptions, this may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, when a first feature is described as being "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is described as being "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0063] It should be noted that if an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element. If an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. If any, the terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in this application are for illustrative purposes only and do not represent the only embodiment.

[0064] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0065] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A copper-lithium composite strip welding method, characterized in that: The following steps are involved: Pre-treating the copper surface to remove the passivation layer on the surface; Pre-treating the surface of the lithium material to obtain a lithium material with a smooth surface; The pretreated copper material, lithium material and protective layer are stacked and assembled in multiple layers to form a laminate; Welding and fixing the assembled laminated body; The protective layer of the laminated body after welding is removed and the laminated body is cut into a desired size.

2. The copper-lithium composite strip welding method according to claim 1, characterized in that: The copper material surface is pretreated, comprising: the copper material is a copper foil with a thickness of 4 to 8 μm; during the pretreatment, the copper foil surface is plasma cleaned to remove a CuO passivation layer on the copper foil surface.

3. The copper-lithium composite strip welding method according to claim 2, characterized in that: The surface of the lithium material is pretreated, comprising: the lithium material is a lithium strip or a lithium sheet, and the thickness of the lithium strip or the lithium sheet is 20 to 100 μm; during the pretreatment, the surface of the lithium strip or the lithium sheet is rolled to be flat.

4. The copper-lithium composite strip welding method according to claim 3, characterized in that: The pressure of rolling the lithium ribbon or lithium sheet is 50 to 300 MPa.

5. The copper-lithium composite strip welding method according to claim 3, characterized in that: The laminated body comprises the copper foil, the lithium sheet, and the protective layer stacked in sequence from top to bottom; or The copper foil, the lithium sheet, the copper foil and the protective layer are stacked in sequence from top to bottom.

6. The copper-lithium composite strip welding method according to claim 5, characterized in that: When stacked, the copper foil is arranged at the edge of the lithium sheet, and there is an overlapping portion of 5±0.5 mm with the edge of the lithium sheet.

7. The copper-lithium composite strip welding method according to claim 3, characterized in that: The protective layer is non-sticky, and its surface energy is less than 30 mN / m. The thickness of the protective layer is 25-100 μm.

8. The copper-lithium composite strip welding method according to claim 7, characterized in that: The protective layer forms an uncovered strip with a width of 5±0.5 mm on the welding-related side of the lithium strip in the width direction, and the protective layer coverage range of the remaining areas exceeds the edge of the lithium strip by at least 2 cm.

9. The copper-lithium composite strip welding method according to any one of claims 1 to 8, characterized in that: The welding method used to fix the assembled stacked body is to use a roll welding machine for roll welding. The amplitude of the roll welding machine is 10-15%, the welding pressure is 0.04-0.1 MPa, the roll welding temperature is set to 25-35 ° C, the roll welding speed is set to 1-5 m / min, the weld mark depth is 0.01-0.05 mm, and the welding spacing is 0.1-0.6 mm.

10. The copper-lithium composite strip welding method according to claim 9, characterized in that: The seam welding machine performs welding in the air, and during the seam welding, the roller of the seam welding machine needs to stay on the laminate for 0.5 to 2 seconds.

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