Method of welding electrode tabs and welded assembly resulting therefrom

Abstract

This invention provides a method for welding electrode sheets and a welded assembly obtained therefrom, relating to the technical field of lithium-ion batteries. The welding method for the electrode sheets includes: locally heating a predetermined welding area of ​​a composite current collector, raising the temperature of the polymer material layer within that area to above its softening point and / or melting point, forming a molten and / or highly elastic polymer material; applying mechanical pressure to the heated predetermined welding area to expel at least partially the molten and / or highly elastic polymer material from between a first metal layer and a second metal layer; and welding a conductive element to at least a portion of the predetermined welding area of ​​the treated composite current collector, forming a metallurgical bond between the conductive element and the first and / or second metal layers, thereby obtaining the welded composite current collector. This welding method features high welding strength and excellent conductivity, and is simple to operate.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a welding method for electrode sheets and a welded assembly obtained therefrom. Background Technology

[0002] In the lithium-ion battery production process, conductive components are connected using a welding process, the core of which lies in the synergistic effect of precise pressure control and high-frequency vibration. This process mainly comprises three key stages: First, in the energy conversion stage, an ultrasonic generator converts 50 / 60 Hz input electrical energy into 20 / 40 kHz high-frequency mechanical vibration energy; second, in the film-breaking and bonding stage, the welding head applies 0.1~0.5 MPa pressure and performs high-frequency vibration to ensure effective removal and initial bonding of the oxide film on the surfaces of the conductive component and the current collector; finally, through continuous pressure and vibration, the interface metal undergoes plastic deformation and forms a stable metallurgical bond, thereby achieving a reliable connection between the conductive component and the current collector.

[0003] In the lithium-ion battery manufacturing process, the welding process between conductive components and current collectors plays a decisive role in battery performance. Composite current collectors (such as composite copper foil and composite aluminum foil) employ a sandwich structure design of a metal layer-polymer layer-metal layer, which can significantly improve battery safety and energy density. However, the polymer intermediate layer in this structure (mainly composed of PP, PET, etc.) has insulating properties and a significantly lower melting point than the metal layer. In traditional ultrasonic welding processes, the energy generated by ultrasonic vibration cannot completely break down or remove the polymer material, leading to a series of technical challenges: Composite current collectors present significant technical challenges in conventional ultrasonic welding processes due to their metal-polymer-metal sandwich structure. Specifically, the intermediate polymer substrate effectively blocks ultrasonic vibration energy, hindering its complete penetration and application to the interface. This prevents the polymer material from fully breaking down, resulting in a substantial reduction in fresh contact area between the metal layers. This physical barrier directly weakens molecular diffusion and fusion between the two metals under high-frequency vibration, leading to inadequate metallurgical bonding and consequently reducing weld strength. Furthermore, the insulating properties of the polymer substrate further exacerbate weld quality issues. Even if the metal plating achieves partial physical contact through welding, the substrate's isolation effect still results in discontinuous conductive paths in the weld, manifesting as a significant increase in contact resistance. Under high-current conditions, high-resistance areas are prone to localized overheating, affecting not only the conductivity stability of the current collector but also potentially posing safety hazards.

[0004] CN113523531A discloses a method for welding a special current collector to an external electrode in a lithium-ion battery, relating to the field of new energy batteries. The method includes three steps: replacing the circular welding head; adjusting the ultrasonic welding equipment parameters, namely, adjusting the welding pressure, energy, amplitude, and time; placing the special current collector above the welding base, placing the external electrode above the special current collector, and then pressing the ultrasonic welding switch to perform the welding. While using a circular welding head and a metal ring / thermal conductive gel to assist welding, and optimizing ultrasonic parameters to solve welding problems, it is essentially still a single ultrasonic welding process. It fails to overcome the blocking effect of the polymer layer on ultrasonic energy, making it difficult to form an effective metallurgical bond between the metal layers, and it does not solve the problem of discontinuous conductive paths in the weld.

[0005] CN120674760A discloses a tab welding structure and welding method, and a secondary battery. The tab welding structure has at least one through hole at the stacked position of the metal tab, and at the stacked position, the first metal layer and the second metal layer are broken and electrically contact each other. The polymer layer in the composite current collector partially melts and penetrates into the through hole. The core is to pre-process the through hole on the metal tab, and during welding, the molten polymer material is squeezed into the hole, thereby achieving direct contact between the upper and lower metal layers. This is a method to improve welding through structural design.

[0006] CN121355550A discloses a welding method for composite foil current collectors. The welding method includes the following steps: S1, micro-hole processing is performed in the tab region of the composite current collector to form a through-hole array; S2, a first pure metal foil is laid on the upper surface of the tab region, and a second pure metal foil is laid on the lower surface; S3, the tab region with the laid pure metal foil is welded, so that the first pure metal foil, the upper aluminum conductive layer, the lower aluminum conductive layer, and the second pure metal foil form a through-hole metallurgical bond at the micro-hole location. The core lies in processing micro-holes in the tab region of the composite current collector itself and covering the upper and lower surfaces with pure metal foil for welding to form a through-hole "weld nugget," which is also a combination of structural design and welding process.

[0007] In summary, existing technologies suffer from three main problems: First, insufficient welding strength: the residual polymer layer hinders direct contact and metallurgical bonding between the upper and lower metal layers, resulting in low weld strength and a tendency for incomplete welds. Second, poor conductivity: the physical barrier formed by the polymer layer causes discontinuous conductive paths at the weld, leading to higher contact resistance. This makes the battery prone to overheating during high-current charging and discharging, thus affecting rate performance and safety. Third, narrow process window: existing technologies require optimizing the welding head shape, adjusting welding parameters, or pre-fabricating micropores and filling them with metal layers on the tabs and current collectors to achieve electrical conductivity, which increases the complexity of the structural design.

[0008] In view of this, the present invention is hereby proposed. Summary of the Invention

[0009] The purpose of this invention is to provide a welding method for electrode sheets and the resulting composite current collector, aiming to solve the problems in existing composite current collectors where, due to the presence of a polymer in the middle, a metal sheet needs to be welded to each of the upper and lower metal layers via an adapter welding process to achieve electrical conductivity. This welding process is complex and often suffers from over-welding, causing the polymer layer to crack, resulting in light transmission, low welding strength, and high contact resistance. Specifically, this invention provides a composite current collector welding method that eliminates the need for an adapter welding process, achieving high welding strength, good conductivity, and a simple process. During welding, the organic polymer material in the composite fluid is melted by a wire, and then metallurgical bonding is achieved through metal vibration friction. The core idea is to precisely remove the polymer layer in the welding area before welding via a separate step.

[0010] 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 method for welding an electrode sheet, the electrode sheet comprising a composite current collector, the composite current collector comprising a first metal layer, a polymer material layer, and a second metal layer stacked sequentially, the method for welding the electrode sheet comprising: S1. Local heating softening / melting: Local heating is applied to the preset welding area of ​​the composite current collector, so that the temperature of the polymer material layer inside the area rises to above its softening point and / or melting point, forming a molten and / or highly elastic polymer material. S2, Extrusion Discharge: Apply mechanical pressure to the pre-designed welding area after heating to extrude at least partially the molten and / or highly elastic polymer material from between the first and second metal layers; S3. Metal welding: Welding the conductive element to at least a portion of the preset welding area of ​​the treated composite current collector, so that the conductive element forms a metallurgical bond with the first metal layer and / or the second metal layer, to obtain the welded composite current collector.

[0011] Furthermore, the local heating method is laser heating.

[0012] Furthermore, the laser heating device includes a CO2 laser and / or a quantum cascade laser.

[0013] Furthermore, the laser heating employs a pulsed mode, with a pulse width of 10 ms to 100 ms and a power density of 10. 4 W / cm 2 ~10 5 W / cm 2 The wavelength of the laser heating is 9 μm to 11 μm.

[0014] Furthermore, the preset welding area is located at the edge of the composite current collector and is situated within the uncoated blank area on the composite current collector where no active material layer is applied.

[0015] Furthermore, the width of the preset welding area is 3 mm to 8 mm.

[0016] Furthermore, a transition region is provided between the preset welding area and the coating area on the composite current collector where the electrode active material is coated, and the width of the transition region is <0.2 mm.

[0017] Furthermore, the mechanical pressure is applied by a pressing tool, the cutting head of which has a rounded corner structure.

[0018] Furthermore, the fillet radius of the cutter head is 0.05 mm to 0.5 mm; Furthermore, the extrusion tool includes a heating element, and the heating element is used to control the temperature of the extrusion tool within a range of 10°C to 20°C above the melting point of the polymer material.

[0019] Furthermore, the mechanical pressure is applied by an extrusion tool, which applies mechanical pressure to the pre-heated welding area at an angle of attack of 15° to 60°; wherein, the angle of attack is the angle between the working surface of the extrusion tool and the surface of the composite current collector.

[0020] Furthermore, the parameters for the extrusion discharge include: extrusion pressure of 0.1 MPa to 5 MPa; unit linear pressure of the cutter head of 0.5 N / mm to 10 N / mm; static pressure holding time of 0.05 s to 1 s; and extrusion speed of 1 mm / s to 50 mm / s.

[0021] Furthermore, the process of applying mechanical pressure and / or squeezing out is carried out under the protection of an inert gas.

[0022] Furthermore, the inert gas includes any one or a combination of at least two of nitrogen, helium, and argon.

[0023] Furthermore, the welding is ultrasonic spot welding.

[0024] Furthermore, the parameters of the ultrasonic spot welding include: welding power of 200 W to 800 W, working air pressure of 2 bar to 5 bar, welding frequency of 10 kHz to 30 kHz, and single spot welding time of 0.5 s to 2 s.

[0025] Furthermore, the conductive element is made of any one or a combination of at least two of the following materials: aluminum, copper, nickel, and nickel-plated copper.

[0026] Furthermore, the materials of the first metal layer and the second metal layer include aluminum and / or copper.

[0027] Furthermore, the polymer material layer is made of polypropylene and / or polyethylene terephthalate.

[0028] Furthermore, the thickness of the conductive element is 0.05 mm to 0.2 mm.

[0029] Furthermore, the thickness of the first metal layer is 0.5 μm to 2 μm, the thickness of the polymer material layer is 3 μm to 10 μm, and the thickness of the second metal layer is 0.5 μm to 2 μm.

[0030] Furthermore, the welding area of ​​the conductive element is provided with micropores, and the diameter of the micropores is 0.2 mm to 2 mm.

[0031] In a second aspect, the present invention provides a welding assembly comprising a conductive element and an electrode plate; wherein the conductive element is welded to the electrode plate by the welding method for the electrode plate as described in the first aspect.

[0032] Compared with the prior art, the present invention has the following beneficial effects: (1) Significantly improved welding strength: The welding method described in this invention effectively eliminates welding interface barriers through the innovative process of pre-extruding polymer layers, enabling the conductive element and the current collector metal layer to form a direct and sufficient metallurgical bond, and the peel strength and tensile strength are simultaneously and significantly improved, fundamentally solving the problem of insufficient bonding strength in traditional welding.

[0033] (2) Excellent conductivity: The welding method described in this invention can form a pure metal-metal connection structure in the welding area, with extremely low contact resistance and good long-term stability, which can significantly improve the rate performance of the battery and reduce heat generation.

[0034] (3) Optimization of process reliability and economy: The welding method described in this invention reduces the process burden of a single ultrasonic welding process, allowing subsequent metal welding to be carried out under milder parameter conditions, significantly reducing the risk of damage to ultra-thin metal layers (such as perforation, coating peeling and other defects); at the same time, it has strong compatibility with automated production, and is especially suitable for welding scenarios of multi-layer conductive components (such as stacked batteries), effectively solving the industry problem of complex processes and weak welding when multiple layers are stacked.

[0035] (4) Improved molding quality and scope of application: The welding method described in this invention ensures that the weld marks in the welding area are flat and burr-free, and that the metal layer at the contact surface with the welding head is free from penetration and cracks, and the molding quality meets the precision manufacturing standards. It is particularly suitable for one-step welding process of multilayer composite current collectors and conductive components, and the welding yield is much higher than that of traditional composite current collector welding molding technology, providing a reliable guarantee for the large-scale production of high energy density batteries. Attached Figure Description

[0036] 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.

[0037] Figure 1 A schematic flowchart of the welding method for the electrode sheet provided by the present invention; Wherein, 1 is the laser heating device, 2 is the extrusion tool, 3 is the ultrasonic spot welding device; 10 is the welding area, 20 is the transition area, 30 is the coating area; 100 is the first metal layer, 200 is the polymer material layer, 300 is the second metal layer, and 400 is the conductive element. Detailed Implementation

[0038] 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.

[0039] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance. The terms "horizontal," "vertical," and "suspended," etc., do not indicate that the component must be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0040] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0041] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0042] 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.

[0043] In a first aspect, the present invention provides a method for welding electrode sheets, such as... Figure 1As shown, the composite current collector comprises a first metal layer 100, a polymer material layer 200, and a second metal layer 300 stacked sequentially; the welding method of the electrode sheet includes: S1. Local heating softening / melting: Local heating is applied to the preset welding area 10 of the composite current collector, so that the temperature of the polymer material layer 200 inside the area rises to above its softening point and / or melting point, forming a molten and / or highly elastic polymer material. S2, Extrusion Discharge: Apply mechanical pressure to the pre-welded area 10 after heating to extrude at least partially the molten and / or highly elastic polymer material from between the first metal layer 100 and the second metal layer 300; S3. Metal welding: The conductive element 400 is welded to at least a portion of the preset welding area 10 of the composite current collector after being processed in sequence by S1 and S2, so that the conductive element 400 forms a metallurgical bond with the first metal layer 100 and / or the second metal layer 300, and the welded composite current collector is obtained.

[0044] It should be noted that the welding method described in this invention first selectively softens / melts the polymer layer, then actively removes it through directional mechanical extrusion, and finally completes metallurgical bonding at a pure metal interface, thereby achieving highly reliable, low-impedance, and process-robust composite current collector welding. This welding method fundamentally eliminates the obstruction of atomic diffusion, surface contact, and electronic conduction by the insulating polymer, transforming welding from "restricted fusion" to "near-pure metal foil welding," thereby simultaneously improving bonding strength, conductivity continuity, and long-term stability. Furthermore, because the heat-sensitive barrier layer has been removed before welding, subsequent ultrasonic energy can be precisely used for metal plastic deformation and interface diffusion, avoiding plating damage, oxidation, or substrate cracking caused by overheating, significantly widening process tolerances, and making it particularly suitable for ultra-thin, multi-layer, and high-consistency batch manufacturing requirements.

[0045] As an optional implementation, the present invention can clean the metal surface to remove the oxide layer before welding, and then use local heating to bring the polymer material between the composite metal layers to a molten state; and / or, inert gas can be added to the heating zone to prevent thin metal coating, easy damage to polymer substrate, and easy oxidation / impurity at the welding interface; and / or, the molten polymer material in this area can be separated from the metal layer by oblique extrusion at a certain angle; and / or, metal welding can be performed by ultrasonic waves.

[0046] It should be noted that the method proposed in this invention effectively solves key technical problems such as insufficient atomic diffusion efficiency, incomplete oxide film removal, and insufficient micro-melting of polymer materials under low-temperature conditions through an innovative technical approach. Practical verification has shown that this method can significantly improve the bonding strength, electrical conductivity, and long-term operational stability of welded joints, while simultaneously reducing welding energy requirements and greatly decreasing the probability of process defects such as substrate perforation and coating peeling, thus providing technical support for high-quality welding in related fields.

[0047] As an optional implementation, the local heating method is laser heating.

[0048] It should be noted that the polymer material layer (such as PP, PET) and the first metal layer and / or the second metal layer (such as copper, aluminum) have different heat absorption methods and thermal conductivity characteristics. The metal layer (such as copper, aluminum) is a good conductor of heat, and heat will diffuse rapidly; while the polymer material layer (such as PP, PET) is an insulator, and heat will easily accumulate. Therefore, in order to melt and flow out the polymer material layer while keeping the metal layer in its original state and preventing oxidation, the local heating method described in step S1 is laser heating. In addition, the laser can achieve efficient absorption of the polymer material and high reflection of the metal surface through spectral matching of specific wavelengths, so that the heat energy is almost specifically deposited in the target layer. At the same time, this targeted excitation mechanism ensures that the polymer layer softens and melts to facilitate subsequent discharge, while keeping the metal layer in a low-temperature and clean state, avoiding oxidation and structural degradation, thus creating the preconditions for high-quality metallurgical bonding.

[0049] As an optional implementation, the laser heating device includes a CO2 laser and / or a quantum cascade laser.

[0050] It should be noted that by using CO2 lasers and / or quantum cascade lasers, the strong absorption peaks of polymer materials such as PP and PET in the mid-infrared band can be precisely matched, enabling energy to be absorbed efficiently and selectively by the polymer layer, while the metal layer hardly heats up due to its high reflectivity. Both support pulsed output and precise power control, taking into account both sufficient melting and suppression of the heat-affected zone, ensuring a clean welding interface and an intact metal coating, and significantly improving process stability and weld reliability.

[0051] As an optional implementation, the laser heating adopts a pulse mode.

[0052] It should be noted that during the laser heating process, a pulse mode is adopted, preferably a microsecond-level pulse, which can precisely control the time scale of heat input, so that the energy is terminated before the polymer layer completes the melting phase transition, avoiding the continuous conduction of heat to the metal layer, which would cause it to overheat, oxidize or deform. At the same time, it suppresses heat diffusion, strictly confines the temperature field to the target area, significantly reduces the heat-affected zone, and protects the adjacent active coating. The instantaneous high power density of the pulse is more conducive to overcoming the thermal inertia of the polymer material, achieving rapid and uniform softening, and improving process repeatability and welding consistency.

[0053] As an optional implementation, the pulse width of the laser heating is 10 ms to 100 ms, for example, it can be 10 ms, 20 ms, 30 ms, 40 ms, 50 ms, 60 ms, 70 ms, 80 ms, 90 ms, 100 ms, etc.

[0054] It should be noted that the pulse width is set in the range of 10 ms to 100 ms to take into account both the phase change kinetics of polymer materials and the thermal response characteristics of metal layers: to ensure sufficient heat conduction in the preset welding area, while preventing heat conduction to non-welding areas.

[0055] As an optional implementation, the power density of the laser heating is 10. 4 W / cm 2 ~10 5 W / cm 2 For example, it could be 1×10 4 W / cm 2 2×10 4 W / cm 2 3×10 4 W / cm 2 4×10 4 W / cm 2 5×10 4 W / cm 2 6×10 4 W / cm 2 7×10 4 W / cm 2 8×10 4 W / cm 2 9×10 4 W / cm 2 1×10 5 W / cm 2 wait.

[0056] It should be noted that the power density is set at 10. 4 W / cm 2 ~10 5 W / cm 2The specified range is a key parameter window for achieving selective heating: below this range, the energy is insufficient to overcome the thermal dissipation of the metal layer, and heat will be conducted away through the metal layer, making it difficult to fully heat the polymer layer, or resulting in slow and uneven heating, leading to heating failure; above this range, local overheating is likely to occur, potentially causing the metal layer to melt directly, even if the polymer layer does not have time to transfer heat to the metal before the melting process is complete. Therefore, this range ensures that laser energy is efficiently absorbed by the polymer and rapidly converted into a molten state, while the metal layer, due to its high reflectivity, only experiences a slight temperature rise, thus balancing sufficient melting, interface cleanliness, and structural integrity.

[0057] As an optional implementation, the wavelength of the laser heating is 9 μm to 11 μm, for example, it can be 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, etc.

[0058] It should be noted that in step S1 of this invention, the laser of a specific wavelength exhibits significant material-selective absorption characteristics. Polymer materials (such as PET, polypropylene, etc.) have extremely high energy absorption efficiency for mid-infrared lasers (typically CO2 pulsed laser beams with wavelengths of 9 μm to 11 μm), while metallic materials (including commonly used substrates such as copper and aluminum) have extremely high reflectivity (>95%) for this wavelength of laser. This differential absorption characteristic allows laser energy to be directly absorbed by the polymer layer and rapidly converted into heat energy, prompting the material to undergo a melting phase transition within millisecond timescales. Simultaneously, due to the efficient reflection of laser energy, the temperature rise of the first and second metal layers does not exceed 20% of their melting points, effectively avoiding thermal damage to the metal substrate and providing important technical support for high-precision material processing.

[0059] As an optional implementation method, such as Figure 1 As shown, the preset welding area 10 is located at the edge of the composite current collector and is situated within the uncoated blank area on the composite current collector where no active material layer is coated.

[0060] As an optional implementation method, such as Figure 1 As shown, the width of the preset welding area 10 is 3 mm to 8 mm, for example, it can be 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, etc.

[0061] As an optional implementation method, such as Figure 1As shown, a transition region 20 is provided between the preset welding area 10 and the coating area 30 on the composite current collector where the electrode active material is coated. The width of the transition region 20 is ≤0.2 mm, and can be, for example, 0.2 mm, 0.18 mm, 0.16 mm, 0.15 mm, 0.14 mm, 0.12 mm, 0.10 mm, 0.08 mm, 0.05 mm, 0.02 mm, etc.

[0062] It should be noted that the transition area set in this invention can effectively isolate the welding heat-affected zone from the electrode active material coating area, avoiding the impact of heat, stress or mechanical disturbance during laser heating and subsequent extrusion on the active layer, and preventing coating cracking, peeling or interface side reactions; and the width of the transition area should not be too wide, while taking into account the feasibility of process implementation. If it is too narrow, the equipment precision requirements will be too high and there is still a risk of burning the active material in the coating area. If it is too wide, it will encroach on the effective welding area.

[0063] As an optional implementation, the mechanical pressure is applied by a pressing tool, the cutting head of which has a rounded corner structure.

[0064] As an optional implementation, the fillet radius of the cutter head is 0.05 mm to 0.5 mm, for example, it can be 0.05 mm, 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm, etc.

[0065] It should be noted that the mechanical pressure mentioned in step S2 is provided by an extrusion tool with a specific angle and shape. The blade of the extrusion tool has a rounded corner with a radius of 0.05 mm to 0.5 mm. Sharp blades can easily scratch the ultra-thin metal layer, while a tool with rounded corners can ensure the integrity of the metal layer while extruding the melt.

[0066] As an optional implementation, the extrusion tool includes a heating element, and the heating element is used to control the temperature of the extrusion tool within a range of 10°C to 20°C above the melting point of the polymer material (e.g., 10°C, 11°C, 12°C, 13°C, 14°C, 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, etc.).

[0067] It should be noted that the extrusion tool in step S2 has a built-in heating function, which keeps the tool temperature 10°C to 20°C above the melting point of the polymer, allowing the melt to remain in a low viscosity state during the extrusion process and be fully extruded.

[0068] As an optional implementation, the mechanical pressure is applied by an extrusion tool, which extrudes obliquely at an angle of attack of 15° to 60° (e.g., 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, etc.) to apply mechanical pressure to the pre-set welding area after heating; wherein, the angle of attack is the angle between the working surface of the extrusion tool and the surface of the composite current collector.

[0069] In a preferred embodiment, the mechanical pressure is applied by an extrusion tool, which applies mechanical pressure to the pre-heated welding area at an angle of attack of 20° to 45°; wherein, the angle of attack is the angle between the working surface of the extrusion tool and the surface of the composite current collector.

[0070] It should be noted that the extrusion tool, with its oblique extrusion pressure, is more conducive to extracting the molten material from between layers. Specific parameters are as follows: Extrusion angle of attack (the angle between the working surface of the extrusion head and the surface of the composite current collector): 15°~60°, preferably 20°~45°. If the angle is too small, the molten material may be pressed under the pressurized extrusion head and cannot be extracted. If the angle is too large, the extrusion head may directly pierce the metal layer or push the molten material to the front end of the extrusion direction and accumulate instead of being extracted from the side. Within the angle range of 30°-45°, the tool can generate better vertical force (maintaining close contact) and better horizontal force (propelling the melt flow), achieving the best extrusion effect.

[0071] As an optional implementation, the extrusion head of the extrusion tool is made of a high-temperature resistant and non-conductive wedge-shaped ceramic cutter head, which presses against the surface of the composite current collector in the preset welding area with a set pressure and moves forward to push (scrape) the molten material directly out of the composite current collector.

[0072] As an optional implementation, the parameters for the extrusion discharge include: extrusion pressure of 0.1 MPa to 5 MPa, for example, 0.1 MPa, 0.5 MPa, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, etc.

[0073] It should be noted that this extrusion pressure is much lower than the static pressure of conventional ultrasonic welding. This is because the polymer is already in a molten state at this point, with good fluidity, and it can be extruded without much force. If the pressure is too low, the polymer will not peel off completely; if the pressure is too high (exceeding 5 MPa), it may crush the metal layer (1~2 μm) or excessively press the metal layer into the support structure, causing damage.

[0074] As an optional implementation, the parameters for the extrusion discharge include: the unit linear pressure of the cutter head is 0.5 N / mm to 10 N / mm, for example, it can be 0.5 N / mm, 1 N / mm, 1.5 N / mm, 2 N / mm, 2.5 N / mm, 3 N / mm, 3.5 N / mm, 4 N / mm, 4.5 N / mm, 5 N / mm, 5.5 N / mm, 6 N / mm, 6.5 N / mm, 7 N / mm, 7.5 N / mm, 8 N / mm, 8.5 N / mm, 9 N / mm, 9.5 N / mm, 10 N / mm, etc.

[0075] As an optional implementation, the parameters for the extrusion discharge include: a static pressure holding time of 0.05 s to 1 s, for example, 0.05 s, 0.1 s, 0.2 s, 0.3 s, 0.4 s, 0.5 s, 0.6 s, 0.7 s, 0.8 s, 0.9 s, 1 s, etc.

[0076] It should be noted that the static pressure holding time ensures that the molten polymer has sufficient time to undergo viscous flow and be fully discharged under pressure, avoiding residue due to insufficient time; at the same time, it prevents heat loss, melt cooling and thickening, or plastic creep deformation of the metal layer caused by excessive time.

[0077] As an optional implementation, the parameters for the extrusion discharge include: an extrusion speed of 1 mm / s to 50 mm / s, for example, 1 mm / s, 5 mm / s, 10 mm / s, 15 mm / s, 20 mm / s, 25 mm / s, 30 mm / s, 35 mm / s, 40 mm / s, 45 mm / s, 50 mm / s, etc.

[0078] It should be noted that this range ensures that the melt maintains a stable and continuous flow under shear action, achieving uniform and thorough interlayer removal, while taking into account both melt rheological behavior and process efficiency. If the speed is too fast, the molten polymer will exhibit viscoelastic fracture and will not be able to flow out continuously, possibly remaining at the interface; if the speed is too slow, heat will be lost, the melt viscosity will increase, and the melt flow resistance will increase.

[0079] As an optional implementation, the process of applying mechanical pressure and / or squeezing out is carried out under inert gas protection.

[0080] It should be noted that the process is carried out under inert gas protection to prevent oxidation of the metal layer surface at high temperatures. At high temperatures, the exposed copper or aluminum in the pre-welded area is extremely prone to oxidation. Once oxidized, subsequent welding will also fail. During heating, the pre-welded area must be circulated with inert gas. An air curtain nozzle can be installed on the extrusion head to provide real-time protection to the pre-welded area.

[0081] As an optional implementation, the inert gas includes any one or a combination of at least two of nitrogen, helium, and argon.

[0082] As an optional implementation, the welding is ultrasonic spot welding.

[0083] It should be noted that the welding is ultrasonic spot welding. Since the polymer layer has been pre-extruded, the welding interface is closer to that of pure metal foil welding, which allows the conductive element to directly contact and weld with the upper and lower metal layers, omitting the transfer welding step of the composite current collector (the transfer welding process is prone to problems such as over-welding and poor welding strength). The conductive element is used to conduct external circuit systems.

[0084] As an optional implementation, the parameters of the ultrasonic spot welding include: working pressure of 2 bar to 5 bar, for example, 2 bar, 2.5 bar, 3 bar, 3.5 bar, 4 bar, 4.5 bar, 5 bar, etc.

[0085] It should be noted that the working pressure is set at 2 bar to 5 bar. Within this pressure range, a tight interface adhesion is ensured, promoting atomic diffusion. This allows for sufficient and uniform physical contact between the conductive element and the metal layer of the composite current collector, providing the necessary interfacial pressure for the mutual diffusion of metal atoms under ultrasonic vibration, ensuring a continuous and dense metallurgical bond. Simultaneously, it avoids damage to the ultra-thin metal layer. The thickness of the first and second metal layers of the composite current collector is only 0.5 μm to 2 μm. Too low a pressure (<2 bar) can lead to insufficient contact and poor soldering; too high a pressure (>5 bar) may break the ultra-thin metal layer or cause excessive deformation. The 2 bar to 5 bar pressure window effectively protects the structural integrity of the metal layer while ensuring welding quality. Furthermore, it is adaptable to multi-layer tab welding scenarios. In the welding of multi-layer tabs such as stacked batteries, appropriately increasing the pressure (close to 5 bar) can ensure good bonding at each interface within the multi-layer structure, avoiding uneven welding caused by poor interlayer contact.

[0086] As an optional implementation, the parameters of the ultrasonic spot welding include: welding power of 200 W to 800 W, for example, 200 W, 300 W, 400 W, 500 W, 600 W, 700 W, 750 W, 800 W, etc.

[0087] It should be noted that the welding energy is set to 200 W~800 W. The ultrasonic power is converted into high-frequency mechanical vibration, generating frictional heat and plastic deformation at the metal interface, achieving interfacial metallurgical bonding. A power range of 200 W~800 W is sufficient to cause microscopic melting and diffusion on the metal surface, forming a strong metallurgical bond and avoiding metal spatter or an excessively large heat-affected zone caused by excessive power. Conversely, insufficient power is inadequate to activate atomic diffusion and interfacial metallurgical bonding, easily leading to incomplete welds and weak bonds.

[0088] As an optional implementation, the parameters of the ultrasonic spot welding include: a welding frequency of 10 kHz to 30 kHz, such as 10 kHz, 12.5 kHz, 15 kHz, 17.5 kHz, 20 kHz, 22.5 kHz, 25 kHz, 27.5 kHz, 30 kHz, etc.

[0089] It should be noted that the welding frequency is 10 kHz to 30 kHz. Welding frequencies within this range allow metal atoms to acquire sufficient diffusion energy. The welding frequency determines the rate of frictional heat generation. Due to the extremely thin metal layer (0.5 μm to 2 μm), excessively high welding frequencies (>30 kHz) will generate enormous shear stress, directly tearing the metal layer.

[0090] As an optional implementation, the parameters of the ultrasonic spot welding include: the time for a single weld point is 0.5 s to 2 s, for example, 0.5 s, 0.6 s, 0.8 s, 1 s, 1.2 s, 1.5 s, 1.8 s, 2 s, etc.

[0091] As an optional implementation, the conductive element may be made of any one or a combination of at least two of the following materials: aluminum, copper, nickel, and nickel-plated copper.

[0092] As an optional implementation, the material of the first metal layer includes aluminum and / or copper.

[0093] As an optional implementation, the material of the second metal layer includes aluminum and / or copper.

[0094] As an optional implementation, the polymer material layer may be made of polypropylene (PP) and / or polyethylene terephthalate (PET).

[0095] It should be noted that the melting point of polypropylene (PP) material is 150℃~200℃; the melting point of polyethylene terephthalate (PET) material is 240℃~260℃.

[0096] As an optional implementation, the thickness of the conductive element is 0.05 mm to 0.2 mm, for example, it can be 0.05 mm, 0.06 mm, 0.08 mm, 0.1 mm, 0.12 mm, 0.14 mm, 0.15 mm, 0.16 mm, 0.18 mm, 0.2 mm, etc.

[0097] As an optional implementation, the thickness of the first metal layer is 0.5 μm to 2 μm, for example, it can be 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, etc.

[0098] As an optional implementation, the thickness of the polymer material layer is 3 μm to 10 μm, for example, it can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc.

[0099] As an optional implementation, the thickness of the second metal layer is 0.5 μm to 2 μm, for example, it can be 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, etc.

[0100] As an optional implementation, the welding area of ​​the conductive element is provided with micropores, and the diameter of the micropores is 0.2 mm to 2 mm, for example, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1 mm, 1.2 mm, 1.4 mm, 1.6 mm, 1.8 mm, 2 mm, etc.

[0101] It should be noted that micropores with a diameter of 0.2 mm to 2 mm can be provided in the welding area of ​​the conductive element. During welding, the conductive element is pressed down, and any trace amounts of residual polymer can be squeezed into these micropores, preventing contamination of the final welding interface. (The metal conductive element has at least one through-hole with a diameter of 0.2 to 2 mm in the welding area where it is stacked with the composite current collector, for accommodating trace amounts of polymer material that were not completely discharged in step S2.)

[0102] In a second aspect, the present invention provides a welded composite current collector, the welded composite current collector comprising a conductive element; wherein the conductive element is welded to the electrode sheet by the electrode sheet welding method described in the first aspect.

[0103] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0104] Example 1 This embodiment provides a method for welding electrode sheets, the method comprising: S1, Localized heating to soften / melt: The pre-set welding area of ​​the composite current collector is locally heated so that the temperature of the polymer material layer inside the area rises to 10°C above its melting point, forming a molten polymer material. The composite current collector comprises a first metal layer, a polymer material layer, and a second metal layer stacked sequentially; the first and second metal layers are made of aluminum, and the polymer material layer is made of polypropylene (PP) (molecular weight Mw of 150,000 g / mol, melting point of 160℃); the thickness of the first metal layer is 0.5 μm, the thickness of the polymer material layer is 3 μm, and the thickness of the second metal layer is 0.5 μm. The width of the preset welding area is 5 mm; and a transition area with a width of 0.15 mm is provided between the preset welding area and the coating area on the composite current collector where the electrode active material is coated. The localized heating method is laser heating; the laser heating device includes a CO2 laser, employing a pulsed mode, and the laser heating parameters include: a pulse width of 50 ms and a power density of 5 × 10⁻⁶. 4 W / cm 2 The wavelength is 10 μm.

[0105] S2, Extrusion discharge: Mechanical pressure is applied to the pre-designed welding area after heating to expel the molten polymer material from between the first metal layer and the second metal layer; The mechanical pressure is applied by an extrusion tool, the extrusion tool having a rounded blade with a radius of 0.25 mm; and the extrusion tool includes a heating element, which is used to control the temperature of the extrusion tool at 15°C above the melting point of the polymer material. The mechanical pressure is applied by an extrusion tool, which applies mechanical pressure to the pre-heated welding area at a 30° angle of attack. The angle of attack is the angle between the working surface of the extrusion tool and the surface of the composite current collector. The extrusion head of the extrusion tool is a high-temperature resistant and non-conductive wedge-shaped ceramic cutter head, which presses against the surface of the composite current collector in the pre-welded area with a set pressure and moves forward to directly push (scrape) the molten material out of the composite current collector. The parameters for the extrusion discharge include: extrusion pressure of 2.5 MPa, unit linear pressure of the cutter head of 5 N / mm, static pressure holding time of 0.5 s, and extrusion speed of 25 mm / s. The process of applying mechanical pressure and squeezing out the material is carried out under the protection of argon gas.

[0106] S3, Metal Welding: The conductive element is welded to the welding area of ​​the composite current collector after being treated by S1 and S2 in sequence, so that the conductive element, the first metal layer, and the second metal layer form a three-layer metallurgical bond, and the welded electrode sheet is obtained. The conductive element is made of aluminum and has a thickness of 0.12 mm; the welding area of ​​the conductive element is provided with micropores, and the diameter of the micropores is 1 mm. The welding is ultrasonic spot welding, and the parameters of ultrasonic spot welding include: welding power of 200 W, working air pressure of 2 bar, welding frequency of 10 kHz, and single weld time of 0.5 s.

[0107] Example 2 This embodiment provides a method for welding electrode sheets, the method comprising: S1, Localized heating to soften / melt: The pre-set welding area of ​​the composite current collector is locally heated so that the temperature of the polymer material layer inside the area rises to 10°C above its melting point, forming a molten polymer material. The composite current collector comprises a first metal layer, a polymer material layer, and a second metal layer stacked sequentially; the first and second metal layers are made of aluminum, and the polymer material layer is made of polypropylene (PP) (molecular weight of 250,000 g / mol, melting point of 170 °C); the thickness of the first metal layer is 1 μm, the thickness of the polymer material layer is 6 μm, and the thickness of the second metal layer is 1 μm. The width of the preset welding area is 3 mm; and a transition area with a width of 0.1 mm is provided between the preset welding area and the coating area on the composite current collector where the electrode active material is coated. The localized heating method is laser heating; the laser heating device includes a CO2 laser, employing a pulsed mode, and the laser heating parameters include: a pulse width of 10 ms and a power density of 1×10⁻⁶. 4 W / cm 2 The wavelength is 9 μm.

[0108] S2, Extrusion discharge: Mechanical pressure is applied to the pre-designed welding area after heating to expel the molten polymer material from between the first metal layer and the second metal layer; The mechanical pressure is applied by an extrusion tool, the extrusion tool having a rounded blade with a radius of 0.05 mm; and the extrusion tool includes a heating element, which is used to control the temperature of the extrusion tool at 10°C above the melting point of the polymer material. The mechanical pressure is applied by an extrusion tool, which applies mechanical pressure to the pre-heated welding area at a 20° angle of attack. The angle of attack is the angle between the working surface of the extrusion tool and the surface of the composite current collector. The extrusion head of the extrusion tool is a high-temperature resistant and non-conductive wedge-shaped ceramic cutter head, which presses against the surface of the composite current collector in the pre-welded area with a set pressure and moves forward to directly push (scrape) the molten material out of the composite current collector. The parameters for the extrusion discharge include: extrusion pressure of 0.1 MPa, unit linear pressure of the cutter head of 0.5 N / mm, static pressure holding time of 0.05 s, and extrusion speed of 1 mm / s. The process of applying mechanical pressure and squeezing out the material is carried out under the protection of argon gas.

[0109] S3, Metal Welding: The conductive element is welded to the welding area of ​​the composite current collector after being treated by S1 and S2 in sequence, so that the conductive element, the first metal layer, and the second metal layer form a three-layer metallurgical bond, and the welded electrode sheet is obtained. The conductive element is made of aluminum and has a thickness of 0.05 mm; the welding area of ​​the conductive element is provided with micropores and the pore diameter of the micropores is 0.2 mm. The welding is ultrasonic spot welding, and the parameters of the ultrasonic spot welding include: welding power of 500 W, working air pressure of 3.5 bar, welding frequency of 20 kHz, and single spot welding time of 1 s.

[0110] Example 3 This embodiment provides a method for welding electrode sheets, the method comprising: S1, Localized heating to soften / melt: The pre-set welding area of ​​the composite current collector is locally heated so that the temperature of the polymer material layer inside the area rises to 20°C above its melting point, forming a molten polymer material. The composite current collector comprises a first metal layer, a polymer material layer, and a second metal layer stacked sequentially; the first and second metal layers are made of aluminum, and the polymer material layer is made of polypropylene (PP) (molecular weight of 400,000 g / mol, melting point of 180℃); the thickness of the first metal layer is 2 μm, the thickness of the polymer material layer is 10 μm, and the thickness of the second metal layer is 2 μm. The width of the preset welding area is 8 mm; and a transition area with a width of 0.2 mm is provided between the preset welding area and the coating area on the composite current collector where the electrode active material is coated. The localized heating method is laser heating; the laser heating device includes a CO2 laser, employing a pulsed mode, and the laser heating parameters include: a pulse width of 100 ms and a power density of 1×10⁻⁶. 5 W / cm 2 The wavelength is 11μm.

[0111] S2, Extrusion discharge: Mechanical pressure is applied to the pre-designed welding area after heating to expel the molten polymer material from between the first metal layer and the second metal layer; The mechanical pressure is applied by an extrusion tool, the extrusion tool having a rounded blade with a radius of 0.5 mm; and the extrusion tool includes a heating element, which is used to control the temperature of the extrusion tool at 20°C above the melting point of the polymer material. The mechanical pressure is applied by an extrusion tool, which applies mechanical pressure to the pre-heated welding area at a 45° angle of attack. The angle of attack is the angle between the working surface of the extrusion tool and the surface of the composite current collector. The extrusion head of the extrusion tool is a high-temperature resistant and non-conductive wedge-shaped ceramic cutter head, which presses against the surface of the composite current collector in the pre-welded area with a set pressure and moves forward to directly push (scrape) the molten material out of the composite current collector. The parameters for the extrusion discharge include: extrusion pressure of 5 MPa, unit linear pressure of the cutter head of 10 N / mm, static pressure holding time of 1 s, and extrusion speed of 50 mm / s. The process of applying mechanical pressure and squeezing out the material is carried out under the protection of argon gas.

[0112] S3, Metal Welding: The conductive element is welded to the welding area of ​​the composite current collector after being treated by S1 and S2 in sequence, so that the conductive element, the first metal layer, and the second metal layer form a three-layer metallurgical bond, and the welded electrode sheet is obtained. The conductive element is made of aluminum and has a thickness of 0.2 mm; the welding area of ​​the conductive element is provided with micropores, and the pore diameter of the micropores is 2 mm. The welding is ultrasonic spot welding, and the parameters of the ultrasonic spot welding include: welding power of 800 W, working air pressure of 5 bar, welding frequency of 30 kHz, and single spot welding time of 2 s.

[0113] Example 4 This embodiment provides a welding method for electrode sheets. The difference from Embodiment 1 is that the first metal layer and the second metal layer are made of copper, and the conductive element is made of copper. Other settings are the same as in Embodiment 1.

[0114] Example 5 This embodiment provides a welding method for electrode sheets. The difference from Embodiment 1 is that the polymer material layer is polyethylene terephthalate (PET) material (molecular weight of 50,000 g / mol, melting point of 255°C), and the other settings are the same as in Embodiment 1.

[0115] Example 6 This embodiment provides a welding method for electrode sheets. The difference from Embodiment 1 is that in step S1, the pulse width is 5 ms and the power density is 9×10⁻⁶. 3 W / cm 2 The wavelength is 12 μm, and other settings are the same as in Example 1.

[0116] Example 7 This embodiment provides a welding method for electrode sheets. The difference from Embodiment 1 is that in step S1, the pulse width is 55 ms and the power density is 2×10⁻⁶. 5 W / cm 2 The wavelength is 8 μm, and other settings are the same as in Example 1.

[0117] Example 8 This embodiment provides a welding method for electrode sheets. The difference from Embodiment 1 is that in step S1, instead of laser heating, heat conduction is used for heating. The parameters include: heating head temperature of 250°C, heating time of 2s, heating pressure of 0.2 MPa, and other settings are the same as in Embodiment 1.

[0118] Example 9 This embodiment provides a welding method for electrode sheets. The difference from Embodiment 1 is that in step S2, the extrusion tool applies mechanical pressure to the pre-heated welding area at a 15° angle of attack. Other settings are the same as in Embodiment 1.

[0119] Example 10 This embodiment provides a welding method for electrode sheets. The difference from Embodiment 1 is that in step S2, the extrusion tool applies mechanical pressure to the pre-heated welding area at a 60° angle of attack. Other settings are the same as in Embodiment 1.

[0120] Example 11 This embodiment provides a welding method for electrode sheets. The difference from Embodiment 1 is that in step S2, the parameters for extrusion discharge include: extrusion pressure of 0.05 MPa, unit linear pressure of the cutting head of 0.4 N / mm, static pressure holding time of 0.04 s, extrusion speed of 0.9 mm / s, and other settings are the same as in Embodiment 1.

[0121] Example 12 This embodiment provides a welding method for electrode sheets. The difference from Embodiment 1 is that in step S2, the parameters for extrusion discharge include: extrusion pressure of 6 MPa, unit linear pressure of the cutting head of 12 N / mm, static pressure holding time of 1.2 s, extrusion speed of 60 mm / s, and other settings are the same as in Embodiment 1.

[0122] Test case Test samples: Welded electrode sheets provided in Examples 1-12.

[0123] Test method: (1) Welding peel force: Cut the welded electrode sample into a specimen with a width of 20 mm, ensuring that the welded area is located in the middle of the specimen; use a universal testing machine to fix the conductive element end to the upper clamp and the composite current collector end to the lower clamp, with the clamp spacing initially set to 50 mm; set the peel angle to 180° and the tensile speed to 50 mm / min; start the testing machine, record the force change during the peeling process, and take the average value of the peeling force stable segment as the welding peel force (unit: N / mm).

[0124] (2) Contact solder joint resistance: The resistance is tested using the four-probe method or a micro-ohmmeter; the welded electrode sample is placed on an insulation test platform, and the test probes are respectively in contact with the conductive element and the two sides of the composite current collector metal layer to ensure that the probes and the metal layers on both sides of the solder joint form good electrical contact; a constant current (such as 1 A) is applied, the voltage drop across the solder joint is measured, and the contact resistance (unit: mΩ) is calculated according to Ohm's law.

[0125] (3) Cycle performance (rate performance of the battery): The welded electrode sheets were assembled into button batteries, and after liquid injection, sealing, and standing, formation was carried out; the button batteries were charged and discharged using a button battery charge and discharge tester (Wuhan Landian, CT2001A) to test their cycle performance: voltage range 2.8-4.2V, number of cycles 200, discharge current 1C, and capacity retention rate was tested; the obtained data are shown in the table below: The specific test results are shown in Table 1: Table 1

[0126] As shown in Table 1, the welding method of this invention effectively eliminates welding obstacles by pre-extruding a polymer material layer, achieving direct and sufficient metallurgical bonding between the conductive element and the current collector metal layer. The peel strength and tensile strength are significantly superior to existing technologies. Furthermore, the welded area forms a pure metal-metal connection with extremely low contact resistance and excellent long-term stability, significantly improving battery rate performance and reducing heat generation. This process features large-area continuous metal bonding, significantly improved peel strength, near-zero resistance solder joint resistance, smooth and burr-free solder marks, and no penetration or cracks in the metal layer at the solder head contact surface. It is particularly suitable for one-step welding of multilayer composite current collectors and conductive elements, with a welding yield far exceeding that of traditional composite current collector welding processes.

[0127] 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 welding method of an electrode tab including a composite current collector including a first metal layer, a polymer material layer, and a second metal layer which are sequentially stacked, characterized by, The welding method includes: The pre-set welding area of ​​the composite current collector is locally heated so that the temperature of the polymer material layer inside the area rises above its softening point and / or melting point, forming a molten and / or highly elastic polymer material. Mechanical pressure is applied to the pre-designed welding area after heating to expel at least partially the molten and / or highly elastic polymer material from between the first and second metal layers; The conductive element is welded to at least a portion of the pre-defined welding area of ​​the treated composite current collector, so that the conductive element forms a metallurgical bond with the first metal layer and / or the second metal layer, thereby obtaining the welded composite current collector.

2. The method of welding an electrode segment as defined in claim 1, wherein, The local heating method is laser heating; Preferably, the laser heating device includes a CO2 laser and / or a quantum cascade laser; Preferably, the laser heating is in a pulse mode, a pulse width of the laser heating is 10 ms~100 ms, a power density of the laser heating is 10 4 W / cm 2 ~10 5 W / cm 2 , and a wavelength of the laser heating is 9 μm~11 μm.

3. The method of welding an electrode segment as defined in claim 1, wherein The preset welding area is located at the edge of the composite current collector and is situated within the uncoated blank area on the composite current collector where no active material layer is applied. Preferably, the width of the preset welding area is 3 mm to 8 mm; Preferably, a transition region is provided between the preset welding area and the coating area on the composite current collector where the electrode active material is coated, and the width of the transition region is ≤0.2 mm.

4. The method of welding an electrode segment as defined in claim 1, wherein The mechanical pressure is applied by a pressing tool, the cutting head of which has a rounded corner structure; Preferably, the fillet radius of the cutter head is 0.05 mm to 0.5 mm; Preferably, the extrusion tool includes a heating element, and the heating element is used to control the temperature of the extrusion tool within a range of 10°C to 20°C above the melting point of the polymer material.

5. The method of welding electrode segments as claimed in claim 1 or 4, characterized in that The mechanical pressure is applied by an extrusion tool, which extrudes at an angle of attack of 15° to 60° to apply mechanical pressure to the pre-heated welding area; wherein, the angle of attack is the angle between the working surface of the extrusion tool and the surface of the composite current collector.

6. The method of welding an electrode segment as defined in claim 1, wherein The parameters for the extrusion discharge include: extrusion pressure of 0.1 MPa to 5 MPa; unit linear pressure of the cutter head of 0.5 N / mm to 10 N / mm; static pressure holding time of 0.05 s to 1 s; and extrusion speed of 1 mm / s to 50 mm / s. Preferably, the process of applying mechanical pressure and / or squeezing out is carried out under the protection of an inert gas; wherein the inert gas includes any one or a combination of at least two of nitrogen, helium, and argon.

7. The method of welding an electrode segment as defined in claim 1, wherein The welding is ultrasonic spot welding; Preferably, the parameters of the ultrasonic spot welding include: welding power of 200 W to 800 W, working air pressure of 2 bar to 5 bar, welding frequency of 10 kHz to 30 kHz, and single spot welding time of 0.5 s to 2 s.

8. The welding method for electrode sheets according to claim 1, characterized in that, The conductive element is made of any one or a combination of at least two of the following materials: aluminum, copper, nickel, and nickel-plated copper. Preferably, the materials of the first metal layer and the second metal layer include aluminum and / or copper; Preferably, the polymer material layer is made of polypropylene and / or polyethylene terephthalate; Preferably, the thickness of the conductive element is 0.05 mm to 0.2 mm; The thickness of the first metal layer is 0.5 μm to 2 μm, the thickness of the polymer material layer is 3 μm to 10 μm, and the thickness of the second metal layer is 0.5 μm to 2 μm.

9. The welding method for electrode sheets according to claim 1 or 8, characterized in that, The preset welding area is provided with micropores, and the diameter of the micropores is 0.2 mm to 2 mm.

10. A welding assembly, characterized in that, It includes a conductive element and an electrode plate; wherein the conductive element is welded onto the electrode plate by the welding method of any one of claims 1 to 9.

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