Composite foil current collector welding method

Abstract

The invention belongs to the field of secondary battery manufacturing, and particularly relates to a composite foil current collector welding method.The composite current collector comprises an upper aluminum conducting layer, a middle high-molecular polymer layer and a lower aluminum conducting layer, and the welding method comprises the following steps that S1, micropore machining is carried out on a tab area of the composite current collector, forming a through micropore array; s2, laying a first pure metal foil on the upper surface of the tab area, and laying a second pure metal foil on the lower surface of the tab area; and S3, welding the tab area on which the pure metal foil is laid, so that the first pure metal foil, the upper aluminum conductive layer, the lower aluminum conductive layer and the second pure metal foil form through metallurgical bonding at the position of the micropore. According to the composite foil current collector welding method, ultrasonic energy is highly concentrated on a metal interface at the edge of a micropore, local metallurgical connection is achieved, overall heat input is low, hot melting and carbonization of a middle high-molecular polymer layer are effectively avoided, and an ultrathin metal layer is protected against heat damage.

Description

Technical Field

[0001] This invention relates to the field of secondary battery manufacturing technology, specifically to a composite foil current collector welding method. Background Technology

[0002] To improve the energy density of lithium-ion batteries, composite current collectors with a "metal layer-polymer layer-metal layer" sandwich structure (such as aluminum / polymer / aluminum) have attracted widespread attention due to their lightweight advantages. However, the polymer layer in this structure makes the two ultra-thin metal conductive layers (typically only 1-2 μm thick) insulated from each other.

[0003] Currently, in existing technologies, during battery manufacturing, a low-resistance, high-reliability electrical connection between the upper and lower metal layers is required in a specific area of ​​the current collector (i.e., the tab area) to collect current. Traditional single-sided welding methods (such as resistance welding and laser welding) face significant challenges when applied to this structure: direct heat input easily leads to cracking and burn-through of the ultra-thin metal layer, while high temperatures can cause the intermediate polymer layer to melt, carbonize, or suffer thermal damage, compromising its insulation and support functions. This results in a narrow process window, poor connection consistency and reliability, low yield, and difficulty in meeting the manufacturing requirements of high-rate charge / discharge and long-life batteries. Therefore, we propose a composite foil current collector welding method. Summary of the Invention

[0004] The main objective of this invention is to provide a composite foil current collector welding method that can solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention proposes a composite foil current collector welding method, wherein the composite current collector comprises an upper aluminum conductive layer, a middle polymer layer, and a lower aluminum conductive layer, and the welding method includes the following steps: S1. Micropores are fabricated in the tab region of the composite current collector to form a through-hole array; S2. Lay a first pure metal foil on the upper surface of the electrode area and lay a second pure metal foil on the lower surface. S3. Weld the tab area where the pure metal foil has been laid, 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 metallurgical bond at the micropore position.

[0006] Preferably, the pore size of the micropore array is from 10 μm to 6000 μm, the porosity is from 10% to 65%, and the pore shape is any one of circular, elliptical, or oblong groove shape.

[0007] Preferably, the first and second pure metal foils are made of pure aluminum or aluminum alloy and have a thickness of 5 μm to 12 μm.

[0008] Preferably, the welding current in step S3 is 1.0-8.0kA, the welding pressure is 30-100N, and the welding time is 50-1000ms.

[0009] Preferably, the welding process in step S3 is carried out in an inert atmosphere (argon or nitrogen) or a reduced pressure environment to reduce aluminum surface oxidation and improve joint stability.

[0010] Preferably, in step S1, a laser is used to process micro-holes, and the hole walls are cleaned or deburred after processing.

[0011] Preferably, the middle polymer layer is selected from polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), and polyvinylidene fluoride (PVDF).

[0012] Preferably, the welding apparatus used in step S3 includes an ultrasonic welding head with a raised or ribbed pattern, and an anvil with a pressure relief groove or hole clearance structure.

[0013] A composite foil current collector tab structure, comprising: The composite current collector has a micropore array that extends through the upper and lower surfaces in its tab region; A first pure metal foil is applied to the upper surface of the tab region; A second pure metal foil is applied to the lower surface of the tab region; And, a through-weld core is formed at the position corresponding to the micropore; the through-weld core connects the upper aluminum conductive layer and the lower aluminum conductive layer of the composite current collector, and together with the first pure metal foil and the second pure metal foil, forms an overall conductive path.

[0014] An electrochemical battery includes a positive electrode tab, wherein the positive electrode tab is the composite foil current collector tab structure described in the claims.

[0015] This invention provides a method for welding composite foil current collectors. It has the following beneficial effects: (1) The ultrasonic energy of the composite foil current collector welding method is highly concentrated at the metal interface at the edge of the micropore, realizing local metallurgical connection, while the overall heat input is low, effectively avoiding the thermal melting, carbonization or performance degradation of the intermediate polymer layer, and protecting the ultrathin metal layer from thermal damage.

[0016] (2) The composite foil current collector welding method achieves low-resistance reliable connection between the upper and lower metal layers and the outer foil through multiple through weld nuggets formed by the micro-hole array, providing parallel conductive paths and mechanical anchors. Even if a single weld point fails, the overall connection remains effective, greatly improving the fatigue resistance and reliability of the tab connection.

[0017] (3) The upper and lower aluminum conductive layers of the composite foil current collector welding method are directly connected by a weld nugget to achieve low resistance metallurgical connection. Combined with the parallel conductivity of the upper and lower pure metal foils, the overall contact resistance of the tab area is significantly reduced, which meets the requirements of high-rate charging and discharging.

[0018] (4) The laser drilling and ultrasonic welding methods used in this composite foil current collector welding method are mature industrial technologies with a wide process window, easy integration into existing battery production lines, high yield, controllable production cycle, and good prospects for large-scale production. Furthermore, the pore size, density, arrangement of micropores and the pattern of welding head can be flexibly designed and optimized according to specific current density and mechanical strength requirements to meet different product needs. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1 This is a schematic cross-sectional view of the ultrasonic welding process used to form a through weld nugget according to the present invention. Figure 2 Schematic diagram of the micropore array in the tab region of this invention Figure 1 ; Figure 3 Schematic diagram of the micropore array in the tab region of this invention Figure 2 ; Figure 4 This is a partial cross-sectional view of the present invention.

[0021] Explanation of reference numerals in the attached figures: 1. Composite current collector; 1.1. Upper aluminum conductive layer; 1.2. Middle polymer layer; 1.3. Lower aluminum conductive layer; 2. First pure metal foil; 3. Second pure metal foil.

[0022] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0024] Please see Figure 1 - Figure 4 This invention proposes a welding method for a composite foil current collector. The composite current collector includes an upper aluminum conductive layer 1.1, a middle polymer layer 1.1, and a lower aluminum conductive layer 1.3. The welding method includes the following steps: S1. Micropores are fabricated in the tab region of the composite current collector to form a through-hole array; S2. Lay a first pure metal foil 2 on the upper surface of the electrode area and a second pure metal foil 3 on the lower surface. S3. Weld the tab area where the pure metal foil has been laid, so that the first pure metal foil 2, the upper aluminum conductive layer 1.1, the lower aluminum conductive layer 1.3 and the second pure metal foil form a through metallurgical bond at the micropore position.

[0025] In embodiments of the present invention, the pore size of the micropore array is 10 μm to 6000 μm, the opening rate is 10% to 65%, and the pore shape is any one of circular, elliptical, or oblong groove. The first pure metal foil 2 and the second pure metal foil 3 are made of pure aluminum or aluminum alloy, with a thickness of 5 μm to 12 μm. The pressure welding current in step S3 is 1.0-8.0 kA, the welding pressure is 30-100 N, and the welding time is 50-1000 ms. The welding process in step S3 is carried out in an inert atmosphere (argon or nitrogen) or a reduced pressure environment to reduce aluminum surface oxidation and improve joint stability.

[0026] Furthermore, in step S1, laser is used to process micro-holes, and the hole walls are cleaned or deburred after processing. The middle polymer layer 1.2 is selected from polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), and polyvinylidene fluoride (PVDF). The welding device used in step S3 includes an ultrasonic welding head with a raised dot or rib pattern, and an anvil with a pressure relief groove or hole avoidance structure.

[0027] A composite foil current collector tab structure, comprising: The composite current collector 1 has a micropore array extending through the upper and lower surfaces in its tab region; The first pure metal foil 2 is covered on the upper surface of the electrode area; The second pure metal foil 3 is covered on the lower surface of the electrode area; Furthermore, a through-hole weld nugget is formed at the corresponding position of the micro-hole; the through-hole weld nugget connects the upper aluminum conductive layer 1.1 and the lower aluminum conductive layer 1.3 of the composite current collector, and together with the first pure metal foil 2 and the second pure metal foil 3, forms an overall conductive path, achieving an electromechanical through-connection of the upper and lower aluminum layers of the composite current collector 1 in the tab region without significantly damaging the polymer layer. The upper and lower pure aluminum foils are fused together in the through hole and welded to the surfaces of the upper and lower aluminum layers of the composite current collector respectively, so that the upper and lower aluminum layers achieve electrical continuity and mechanical reinforcement through the metal bridge in the hole.

[0028] An electrochemical battery includes a positive electrode tab, wherein the positive electrode tab is the composite foil current collector tab structure of claim 9.

[0029] General conditions and test method settings in the embodiments Environment: Dry room (dew point ≤ −40℃), nitrogen purging or normal pressure air (as indicated in the label).

[0030] Cleaning: After hole machining, perform plasma cleaning (O2 or Ar, 30–120s) and wipe with anhydrous ethanol.

[0031] Welding control: energy or displacement closed loop, recording energy-time and displacement-time curves, and adopting an inflection point termination strategy.

[0032] Quality evaluation: DC contact resistance per unit width (four probes): mΩ·cm Peel strength (180° or 90°, tensile clamp): N / mm Sectional continuity (metallography / SEM / XCT): Continuity of through weld nugget % The change rate of appearance and resistivity ΔR% after thermal shock (−20℃↔60℃, 100 cycles) Example 1

[0033] Structure and Materials: The composite current collector substrate used in this embodiment has an "aluminum (1.5μm) / PET (12μm) / aluminum (1.5μm)" structure. The reinforcing layers laid on the upper and lower surfaces are two 15μm thick pure aluminum foils (aluminum content ≥99.3%).

[0034] Micro-hole fabrication: A nanosecond laser drilling system was used to fabricate a circular micro-hole array in the tab region. Specific parameters were: hole diameter (Φ) 100 μm, hole center-to-center spacing (pitch) 300 μm. The calculated open area ratio of this array was approximately 8.7%. After drilling, the sample was surface-cleaned using argon plasma for 60 seconds to thoroughly remove molten residue and burrs around the hole walls, ensuring the cleanliness of the subsequent welding interface.

[0035] Welding Process: The stacked components are placed in an ultrasonic welding machine. The welding anvil is designed with clearance grooves precisely aligned with the micropore array. Welding is performed under a nitrogen protective atmosphere to inhibit aluminum surface oxidation. The core ultrasonic welding parameters used are: frequency 35kHz, amplitude 35μm, welding pressure 0.6MPa, and welding time 400ms. Before starting the ultrasonic welding, a preheating platform of 100℃ is applied and the workpiece is pre-pressed for 1 second to initially bond the layers together.

[0036] Results and Analysis: After welding, the sample underwent cross-sectional analysis and metallographic preparation. Microscopic observation revealed a continuous and dense recrystallized metal structure (i.e., a through-weld nugget) within the micropores, successfully connecting the upper and lower pure aluminum foils with the upper and lower aluminum layers of the composite current collector into a single unit. Electrical performance testing employed the four-probe method, and the DC contact resistance per unit width of the tab region remained stable within the range of 2.5–3.5 mΩ·cm. A 180° peel test showed a peel strength of 1.0–1.4 N / mm. To assess reliability, the sample was subjected to 100 thermal shock cycles from -20°C to 60°C. After the test, the rate of change in contact resistance (ΔR) was ≤10%, indicating excellent environmental stability of the connection structure. Example 2

[0037] Structure and Materials: The substrate is a thinner composite current collector of aluminum (1.0μm) / PET (8μm) / aluminum (1.0μm). The upper and lower reinforcing layers are 10μm thick pure aluminum foil.

[0038] Micropore fabrication: High-precision laser processing is used to fabricate micropores with a diameter of 30 μm and a pitch of 120 μm, resulting in an open area ratio of approximately 6.1%. This small aperture design aims to further reduce mechanical damage to the polymer matrix.

[0039] Welding process: In this embodiment, ultrasonic welding was performed using energy control mode, with a target energy set at 120J and no preheating. The welding frequency was 40kHz, the amplitude was 18μm, and the pressure was 0.4MPa. The welding process was also completed under nitrogen protection.

[0040] Results and Analysis: This process successfully achieved reliable bonding of the ultrathin aluminum layer. The contact resistance was 3.2–4.0 mΩ·cm, and the peel strength was 0.8–1.1 N / mm. Macroscopic inspection showed no visible signs of thermal shrinkage or deformation on the PET polymer surface. After thermal shock testing, the resistance change rate ΔR ≤ 12%, meeting the reliability requirements of high-density batteries. Example 3

[0041] Structure and Materials: The substrate is “aluminum (2.0μm) / PP (10μm) / aluminum (2.0μm)”. Both the upper and lower reinforcing layers use 5μm thick pure aluminum foil.

[0042] Micro-hole fabrication: Elongated oval groove-shaped holes are used, with dimensions of 60μm (width) × 300μm (length). The long axis of the grooves is arranged along the main path of current transmission, with a row spacing of 250μm and an opening ratio of approximately 12%. This design is beneficial for forming a continuous conductive path and relieving stress.

[0043] Welding process: Welding was performed under argon protection. Parameters were: frequency 30kHz, amplitude 40μm, pressure 0.8MPa, and time 500ms. Pre-pressure was applied at 80℃ for 1.5 seconds before welding.

[0044] Results and Analysis: The slotted hole design delivers excellent electrical and mechanical properties. Contact resistance is as low as 2.2–3.0 mΩ·cm, and peel strength is as high as 1.2–1.6 N / mm. Cross-sectional analysis shows a weld nugget continuity of ≥92%. Post-thermal shock, ΔR ≤9%, demonstrating outstanding performance. Example 4

[0045] Structure and Materials: The substrate is "aluminum (1.0μm) / PI (8μm) / aluminum (1.0μm)". Polyimide (PI) is heat resistant but prone to browning. The upper and lower reinforcing layers are 7μm thick pure aluminum foil.

[0046] Micro-hole machining: Machining Φ80μm circular holes with a pitch of 240μm and an open area ratio of approximately 9.1%.

[0047] Welding process: Welding parameters with a lower frequency (20kHz) and a higher amplitude (50μm) were used, with a pressure of 0.7MPa and a time of 350ms. To avoid browning of PI at high temperatures, a higher pre-pressure temperature (160℃) was used, but the time was shortened (0.8s), and welding was carried out in a slightly depressurized environment (90kPa) to better expel any possible gases.

[0048] Results and Analysis: The contact resistance of the welded joints was 2.8–3.6 mΩ·cm, and the peel strength was 1.1–1.5 N / mm. Crucially, no browning was observed in the PI substrate during either macroscopic or microscopic inspection, demonstrating that the process successfully controlled the heat-affected zone. The thermal shock ΔR was ≤8%. Example 5

[0049] Structure and Materials: The substrate is “aluminum (2.0μm) / PP (3.4μm) / aluminum (2.0μm)”, with an extremely thin polymer layer. The upper and lower reinforcing layers are 10μm thick pure aluminum foil.

[0050] Micro-hole machining: A large-diameter design is used to machine circular holes with a diameter of 300μm and a pitch of 800μm, resulting in an open area ratio of approximately 11.0%. This design reduces the number of holes while ensuring the conductive area.

[0051] Welding process: A displacement closed-loop control mode is adopted, with the welding endpoint displacement set at -45μm. Parameters are: frequency 28kHz, amplitude 32μm, pressure 0.9MPa. Pre-pressure conditions are 60℃ for 2 seconds, and the environment is nitrogen.

[0052] Results and Analysis: Due to the large aperture, the resulting individual weld nuggets are relatively large and few in number. The contact resistance is low, ranging from 1.8 to 2.6 mΩ·cm, and the peel strength is 1.0 to 1.3 N / mm. After thermal shock, ΔR ≤ 10%, demonstrating that this process can achieve reliable bonding without damage, even for ultrathin polymer layers. Example 6

[0053] Structure and Materials: The substrate is “aluminum (1.5μm) / PET (12μm) / aluminum (1.5μm)”. The upper and lower reinforcing layers are 12μm thick pure aluminum foil.

[0054] Micropore fabrication: This embodiment employs a gradient porosity design. From the edge of the current collector inwards, the pore sizes of the micropores are mixed and arranged between 80-120 μm, causing the porosity to gradually decrease from 16% at the edge to 6% in the interior. This design aims to optimize the current density distribution and reduce edge effects.

[0055] Welding process: A two-step welding method is employed to improve consistency. First, spot tack welding (amplitude 25μm, pressure 0.5MPa, time 120ms) is performed to initially fix each layer. Then, full-coverage area welding is performed (amplitude 35μm, pressure 0.7MPa, time 300ms). The entire process is conducted under argon protection.

[0056] Results and Analysis: The gradient aperture design effectively balanced the current distribution. The contact resistance was 2.3–3.1 mΩ·cm. The rate of change of resistance after thermal shock was significantly reduced, ΔR ≤ 7%, and infrared thermal imaging showed that the heating in the tab area was more uniform, and the edge overheating phenomenon was effectively suppressed. Example 7

[0057] Structure and Materials: The substrate is “aluminum (1.2μm) / PET (10μm) / aluminum (1.2μm)”. The upper and lower reinforcing layers are 8μm thick pure aluminum foil.

[0058] Micro-hole machining: Machining Φ120μm circular holes with a pitch of 360μm and an open area ratio of approximately 8.7%.

[0059] Welding Equipment and Process: This embodiment simulates a mass production scenario, using a rotary continuous ultrasonic welding device. The welding head has a linear structure, the anvil is roller-type, and a tension closed-loop control system is used. The process parameters are: frequency 30kHz, linear velocity 2.0m / min, linear pressure 0.6MPa, and equivalent amplitude approximately 30μm. A 90℃ preheater is installed at the entrance of the welding area, and a nitrogen curtain is used for protection.

[0060] Results and Analysis: This process cycle is perfectly adapted to mass production lines. The resulting tab structure has a contact resistance of 2.6–3.4 mΩ·cm and a peel strength of 0.9–1.2 N / mm. After thermal shock, ΔR ≤ 12%, demonstrating the feasibility and stability of this invention under continuous high-speed production. Example 8

[0061] Structure and Materials: The substrate is “aluminum (1.5μm) / PP (12μm) / aluminum (1.5μm)”. The upper and lower reinforcing layers are made of 15μm thick Al-Mg alloy (grade 5052) to take advantage of its higher mechanical strength.

[0062] Micro-hole machining: Machining elliptical holes with a minor axis of 80μm and a major axis of 120μm, using a staggered arrangement, with an opening rate of approximately 10%.

[0063] Welding process: Ultrasonic welding was used, with the following parameters: frequency 35kHz, amplitude 38μm, pressure 0.85MPa, and time 420ms. No preheating was performed under nitrogen protection.

[0064] Results and Analysis: Due to the use of higher-strength aluminum alloy reinforcing foil, the mechanical properties of the welded joint were further improved, with a peel strength of 1.3–1.8 N / mm. The contact resistance was 2.7–3.3 mΩ·cm, and ΔR ≤ 10% after thermal shock. Example 9

[0065] Structure and Materials: The substrate is “aluminum (1.0μm) / PET (12μm) / aluminum (1.0μm)”. The upper and lower reinforcing layers are 10μm thick pure aluminum foil.

[0066] Pretreatment: Before laying the reinforcing foil, the surface to be welded is subjected to two pretreatments: first, the surface roughness (Ra) is reduced to about 0.6 μm by precision brushing; then, a low-power argon plasma activation treatment is performed for 60 seconds to completely remove the natural oxide film and improve the surface energy.

[0067] Micro-hole machining: Machining Φ60μm circular holes with a pitch of 200μm and an open area ratio of approximately 9.0%.

[0068] Welding process: Energy control mode (target energy 180J). Parameters: frequency 40kHz, amplitude 22μm, pressure 0.55MPa. Pre-compression conditions: 70℃, 1 second.

[0069] Results and Analysis: Surface activation treatment significantly improved the interfacial bonding quality. Contact resistance was reduced to 2.1–2.9 mΩ·cm, and the weld nugget cross-sectional continuity reached ≥93%. After thermal shock, ΔR ≤8%, demonstrating the positive effect of pretreatment on improving connection quality and stability. Example 10

[0070] Structure and Materials: The substrate is “aluminum (2.0μm) / PET (16μm) / aluminum (2.0μm)”. The upper and lower reinforcing layers are 15μm thick pure aluminum foil, and the upper pure aluminum foil and the external electrode strip are integrated into one structure, which simplifies the subsequent integration process.

[0071] Micro-hole machining: Machining circular holes with a diameter of 150 μm, a pitch of 450 μm, and an open area ratio of approximately 9.1%.

[0072] Welding process: Parameters are: frequency 28kHz, amplitude 34μm, pressure 1.0MPa, time 600ms. Pre-pressure conditions are 100℃ for 1.5 seconds, performed under argon protection.

[0073] Results and Analysis: This structure achieves extremely low contact resistance of 1.6–2.4 mΩ·cm and peel strength of 1.1–1.5 N / mm. In 2C rate discharge tests, the battery temperature rise using the tabs of this embodiment was significantly reduced compared to tabs using conventional connection methods, demonstrating the value of its low resistance advantage in high-rate applications. Example 11

[0074] Structure and Materials: The substrate is “aluminum (1.5μm) / PP (6.0μm) / aluminum (1.5μm)”, with a very thin PP layer. The upper and lower reinforcing layers are 15μm thick pure aluminum foil.

[0075] Micro-hole machining: Machining Φ90μm circular holes with a pitch of 270μm and an open area ratio of approximately 9.3%.

[0076] Welding process: Relatively mild welding parameters are used to protect the ultra-thin PP layer: frequency 35kHz, amplitude 20μm, pressure 0.5MPa, time 300ms. No preheating, nitrogen protection.

[0077] Results and Analysis: The process successfully achieved the connection, and the thermal impact on the adjacent positive electrode active material coating was negligible. The contact resistance was 3.0–3.8 mΩ·cm, and ΔR ≤ 12% after thermal shock. Example 12

[0078] Structure and materials: The substrate is “aluminum (1.2μm) / PET (10μm) / aluminum (1.2μm)”.

[0079] Foil-coated design: To save materials, instead of coating the entire tab area with foil, a 10μm thick aluminum foil is precisely cut by laser so that it only covers the microporous array area, with no reinforcing foil in other areas.

[0080] Micro-hole machining: Machining 100μm circular holes with a pitch of 300μm and an open area ratio of approximately 8.7%.

[0081] Welding process: Welding was performed in a normal air environment. Parameters: frequency 30kHz, amplitude 32μm, pressure 0.7MPa, time 350ms. Pre-pressure 80℃ for 1 second.

[0082] Results and Analysis: This selective foil-coating design successfully reduced the amount of pure metal foil used by 35%–50% while maintaining basic performance (contact resistance 2.7–3.5 mΩ·cm), demonstrating a significant cost advantage. The thermal shock ΔR ≤ 15%, which remains within an acceptable range.

[0083] Comparative Example 1 (without micropores) Structure and Lamination: The same "aluminum (1.5μm) / PET (12μm) / aluminum (1.5μm)" substrate and 15μm pure aluminum foil on both the top and bottom are used as in Example 1. The key difference is that no micropores are formed.

[0084] Welding process: Attempt to perform direct ultrasonic welding with the following parameters: 35kHz, amplitude 40μm, pressure 0.8MPa, and time 400ms.

[0085] Results and Analysis: Welding failed. Due to the insulation and barrier effect of the intermediate PET layer, ultrasonic energy could not be effectively transmitted to the lower interface, failing to form a continuous connection between the upper and lower layers. The contact resistance was extremely high (≥15mΩ·cm). Disassembly revealed that only the upper pure aluminum foil and the upper aluminum layer of the composite current collector had local connections, and the upper ultrathin aluminum layer showed multiple tearing damages. This comparison demonstrates the necessity of micropores for achieving a continuous connection between the upper and lower layers.

[0086] Comparative Example 2 (without pure aluminum foil reinforcement) Structure and Preparation: The same composite current collector substrate as in Example 1 was used, and the same micropore processing (Φ100μm, pitch 300μm) was performed. The key difference is that no upper or lower pure aluminum foil reinforcement layers were laid, and an attempt was made to directly weld the 1-2μm thick aluminum layer.

[0087] Welding process: Parameters are: 30kHz, amplitude 30μm, pressure 0.6MPa, time 300ms.

[0088] Results and Analysis: Poor welding performance. Due to the limited strength and energy carrying capacity of the ultrathin aluminum layer, it is extremely prone to cracking and excessive deformation under ultrasonic treatment, resulting in highly discontinuous and fragile weld nuggets. Peel strength is extremely low (≤0.3 N / mm), failing under slight stress. After thermal shock, the contact resistance changes drastically, ΔR≥30%. This comparison demonstrates the indispensability of a pure metal foil reinforcement layer for achieving stable and robust connections.

[0089] Comparative Example 3 (pure hot pressing / hot riveting, without ultrasound) Structure and stacking: The same “aluminum (1.5μm) / PET (12μm) / aluminum (1.5μm)” substrate and 15μm pure aluminum foil on the top and bottom were used as in Example 1, and the same micropore processing was performed.

[0090] Welding process: A pure hot-pressing process was used for connection, without the use of ultrasonic vibration. The parameters were: hot-pressing temperature 180℃, pressure 0.8MPa, and time 3s.

[0091] Results and Analysis: The welding effect was unsatisfactory. The pure hot-pressing process caused localized thermal collapse of the intermediate PET polymer layer and posed a risk of carbonization. The resulting interface quality was poor, with high contact resistance (8–12 mΩ·cm). After thermal shock testing, weld cracking significantly increased. This comparison demonstrates the crucial role of introducing ultrasonic vibration in avoiding polymer thermal damage and achieving low-resistance and high-reliability connections.

[0092]

[0093] It should be noted that the above electrical components are all existing technology products. Those skilled in the art should select, install and complete the circuit debugging work according to the needs of use to ensure that all electrical appliances can work normally. The components are all general standard parts or components known to those skilled in the art. Their structure and principle can be known by those skilled in the art through technical manuals or conventional experimental methods. No specific restrictions are made here.

[0094] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural transformations made using the contents of the specification and drawings of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of patent protection of the present invention.

Claims

1. A composite foil current collector welding method, the composite current collector (1) comprising an upper layer of aluminum conductive layer (1.1), a middle layer of polymer layer (1.2) and a lower layer of aluminum conductive layer (1.3), characterized in that, The welding method comprises the following steps: S1, micro-hole processing is performed on the tab area of the composite current collector (1) to form a through micro-hole array; S2, a first pure metal foil (2) is laid on the upper surface of the tab area, and a second pure metal foil (3) is laid on the lower surface; S3, the tab area with the laid pure metal foils is welded, so that the first pure metal foil (2), the upper aluminum conductive layer (1.1), the lower aluminum conductive layer (1.3), and the second pure metal foil (3) form a through metallurgical bond at the micro-hole positions.

2. The welding method according to claim 1, characterized in that, The micro-hole array has a pore size of 10 μm to 6000 μm, an opening rate of 10% to 65%, and a pore shape of any one of a circle, an ellipse, or a long circular groove.

3. The welding method of claim 1, wherein, The first pure metal foil (2) and the second pure metal foil (3) are made of pure aluminum or aluminum alloy and have a thickness of 5 μm to 12 μm.

4. The welding method of claim 1, wherein, The pressure fusion welding current in step S3 is 1.0-8.0 kA, the welding pressure is 30-100 N, and the welding time is 50-1000 ms.

5. The welding method of claim 1, wherein, The welding process in step S3 is performed in an inert atmosphere (argon or nitrogen) or a reduced pressure environment to reduce aluminum surface oxidation and improve joint stability.

6. The welding method of claim 1, wherein, Laser is used for micro-hole processing in step S1, and the hole wall is cleaned or deburred after processing.

7. The welding method of claim 1, wherein, The middle layer of high polymer layer (1.2) is selected from polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), and polyvinylidene fluoride (PVDF).

8. The welding method of claim 1, wherein, The welding device used in step S3 includes an ultrasonic welding head with a convex point or rib pattern, and an anvil provided with a pressure relief groove or hole position avoidance structure.

9. A composite foil current collector tab structure, characterized by, Comprise: A composite current collector (1) provided with a through micro-hole array on the tab area; A first pure metal foil (2) laid on the upper surface of the tab area; A second pure metal foil (3) laid on the lower surface of the tab area; And a through welding core formed at the corresponding position of the micro-hole; the through welding core connects the upper aluminum conductive layer (1.1) and the lower aluminum conductive layer (1.3) of the composite current collector, and together with the first pure metal foil (2) and the second pure metal foil (3) forms an integral conductive path.

10. An electrochemical cell comprising a positive electrode tab, characterized in that, The positive electrode tab is the composite foil current collector tab structure of claim 9.

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