A method for connecting a carbon fiber cloth flexible current collector and a metal electrode

Abstract

This invention belongs to the technical field of electrochemical energy storage device manufacturing, specifically relating to a method for connecting a flexible carbon fiber current collector to a metal electrode. The method includes coating the area of ​​the carbon fiber cloth to be welded with a highly conductive metal slurry, allowing it to fully penetrate the fiber network, and then pre-curing it to form a fiber-metal composite transition layer; folding the metal electrode in half and stacking it with the treated carbon fiber cloth to form a three-layer assembly of metal electrode-carbon fiber cloth-metal electrode; applying static pressure and high-frequency vibration in an ultrasonic welding device to achieve a strong interface connection through a metallurgical-mechanical composite action. The method utilizes a synergistic mechanism of slurry penetration into the transition layer and ultrasonic solid-state welding to achieve a high-quality connection.

Description

Technical Field

[0001] This invention relates to the technical field of manufacturing electrochemical energy storage devices, and specifically to a method for connecting a flexible carbon fiber current collector to a metal electrode. Background Technology

[0002] In the manufacturing of energy storage devices such as batteries and supercapacitors, the connection quality between the current collector and the electrode directly affects the device's internal resistance, power performance, and long-term reliability. Carbon fiber cloth, due to its high conductivity, good chemical stability, and porous structure, has been widely studied and used as a high-performance current collector material. However, achieving a low-resistance, high-strength, and durable connection between this fibrous, porous carbon cloth and typically dense metal electrodes (such as tabs) is a key technological challenge in practical production.

[0003] Traditional bonding methods face significant limitations in this application. Conventional welding techniques (such as spot welding) applied to carbon fiber cloth are prone to fiber damage due to concentrated heat input, compromising structural integrity and even causing localized burn-through. Furthermore, it is difficult to form an effective alloy bond between carbon and metal, often resulting in insufficient mechanical strength at the joint. While conductive adhesive bonding is simple, it generally suffers from high interfacial resistance, the potential introduction of impurities into the adhesive, or performance degradation under high and low temperature environments, leading to decreased connection reliability. Mechanical pressing, although avoiding thermal damage, typically cannot achieve sufficiently uniform and sustained contact pressure under lightweight and thin-film requirements, easily resulting in unstable contact resistance.

[0004] Therefore, existing technologies struggle to construct a connection interface between carbon fiber cloth and metal electrodes that combines low interfacial resistance, high connection strength, and long-term stability while ensuring efficient production. This urgently necessitates the development of a new connection strategy to resolve the fundamental contradiction between material compatibility and process reliability. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of high interfacial resistance, insufficient bonding strength, and poor long-term stability in the connection of carbon fiber flexible current collectors and metal electrodes in existing technologies. Instead, it provides a simple, reliable, and high-performance method for connecting carbon fiber flexible current collectors and metal electrodes. This method achieves high-strength, low-impedance connection between the carbon fiber flexible current collector and the metal electrode, and can be widely used in the manufacture of electrode components for flexible lithium-ion batteries, flexible supercapacitors, and various wearable / deformable electronic devices.

[0006] High-quality joints are achieved through a synergistic mechanism of slurry penetration into the transition layer and ultrasonic solid-state welding. Specifically, this includes: A highly conductive metal slurry is coated onto the area of ​​the carbon fiber cloth to be welded, and then fully penetrated into the fiber network through vacuum, centrifugation or pressure, and a fiber-metal composite transition layer is formed after pre-curing.

[0007] The metal electrode is folded in half and then stacked with the treated carbon fiber cloth to form a three-layer assembly of metal electrode-carbon fiber cloth-metal electrode.

[0008] Static pressure and high-frequency vibration are applied in ultrasonic welding equipment to achieve a firm interface connection through metallurgical-mechanical composite action. Finally, the welded joint is subjected to post-treatment such as heat treatment.

[0009] The core innovation of this invention lies in the synergistic effect of slurry penetration and ultrasonic welding. The metal slurry constructs a highly conductive and malleable transition layer inside the fiber, fundamentally improving surface weldability and electrical continuity; ultrasonic welding, at low temperatures, achieves three-dimensional metallurgical bonding and mechanical interlocking between the transition layer and the metal electrode through vibration energy, simultaneously optimizing the interface conductivity and mechanical properties.

[0010] The technical solution of this invention is as follows: A method for connecting a flexible carbon fiber cloth current collector to a metal electrode includes the following steps: (1) Prepare conductive metal paste, coat the prepared conductive metal paste on the area to be welded of carbon fiber cloth, and ensure that the conductive metal paste penetrates into the fiber network of carbon fiber cloth; arrange the carbon fibers penetrated with conductive metal paste and heat them at 80-160℃ for 5-30 minutes to allow the organic solvent to evaporate and the binder to partially crosslink, forming a prepared fiber-metal composite transition layer on the carbon fiber cloth.

[0011] The conductive metal paste, by weight percentage, comprises 60%-90% conductive metal powder, 5%-20% organic binder, and 5%-20% organic solvent. The organic binder can be any one of thermoplastic resin or thermosetting resin.

[0012] The conductive metal slurry is prepared by the following steps: conductive metal powder, organic binder and organic solvent are mixed in proportion and stirred with a planetary mixer at a speed of 500-2000 rpm for 1-4 hours until a uniform slurry is formed.

[0013] The conductive metal is selected from at least one of silver, copper, or nickel. The conductive metal powder can be at least one of micron-sized silver powder, micron-sized copper powder, nano-silver wire, nano-copper wire, flake silver powder, flake copper powder, nickel powder, silver-plated copper powder, or silver-coated copper powder.

[0014] The coating method can be any one of screen printing, blade coating, spraying, dipping, or dispensing.

[0015] (2) First, fold the metal electrode in half to form upper and lower double-layer metal electrodes; Then, the carbon fiber with the fiber-metal composite transition layer prepared in step (1) is arranged between the double-layer metal electrodes, so that the fiber-metal composite transition layer on the carbon fiber cloth completely covers the preset overlap area of ​​the upper and lower double-layer metal electrodes, forming a stacked assembly of metal electrode-carbon fiber cloth-metal electrode. The edges of the three-layer structure of the stacked assembly should be aligned or the edge of the metal electrode should slightly extend beyond the edge of the carbon fiber cloth.

[0016] (3) Place the laminated assembly obtained in step (2) between the welding head and the bottom anvil of the ultrasonic welding equipment and apply a preset static pressure; wherein the static pressure is controlled at 100-800N.

[0017] (4) Start the ultrasonic welding equipment and apply ultrasonic vibration for welding, controlling the welding energy between 200-3000J. High-frequency vibration energy generates frictional heat and plastic deformation at the laminate interface, forming a composite connection of metallurgical bonding and mechanical interlocking. The welding energy is adjusted by controlling the welding power and welding time. There are interdependent relationships among the ultrasonic welding parameters (frequency, amplitude, power, and time). For example, when a higher working frequency (e.g., 40kHz) is used, the upper limit of the achievable stable amplitude is usually no more than 20μm; when a larger power and longer welding time are used, the total energy is higher. Matching should be done according to the actual material and equipment conditions to ensure welding quality. If the welding energy is too low, an effective metallurgical bond cannot be formed, but if it is too high, it may damage the carbon fiber cloth.

[0018] During the welding process, a buffer pad can be placed between the welding head and the laminated assembly, or between the metal electrode and the anvil. The buffer pad can be made of polyurethane, silicone, or copper foil, and is used to protect the electrode surface and optimize pressure distribution. The thickness of the buffer pad is preferably 0.05mm-0.5mm.

[0019] After welding is completed, the welded joint is heat-treated at 80-180℃ for 10-60 minutes to further solidify the resin binder phase in the slurry, promote interfacial diffusion, and remove residual stress.

[0020] Finally, any excess slurry overflowing around the weld joint is physically cleaned or chemically cleaned.

[0021] In this invention, the method for connecting the flexible carbon fiber cloth current collector to the metal electrode, wherein the areal density of the carbon fiber cloth in step (1) is 50-200 g / m³. 2 The thickness is 0.1-0.5mm. The carbon fiber cloth can be any type, such as polyacrylonitrile-based carbon fiber cloth or pitch-based carbon fiber cloth.

[0022] The carbon fiber cloth described herein may be pretreated on its surface. The pretreatment methods include any one of plasma treatment, ultraviolet ozone treatment, or dilute acid cleaning, in order to improve the wettability and adhesion of the slurry.

[0023] The conductive metal powder is in the form of particles with a particle size of 0.05μm-10μm or nanowires with a diameter of 20-200nm and a length of 5-50μm.

[0024] The organic binder is selected from at least one of polyvinyl butyral, polyurethane, epoxy resin, phenolic resin or acrylic resin.

[0025] The organic solvent is selected from at least one of terpineol, butylcarbidol, ethanol, N-methylpyrrolidone, or deionized water.

[0026] In this invention, the method for connecting the flexible carbon fiber cloth current collector to the metal electrode has a solid content of 80wt%-95wt% in the conductive metal slurry in step (1) and a viscosity of 5000-30000cP at 25℃.

[0027] In this invention, the connection method between the flexible carbon fiber cloth current collector and the metal electrode, in step (1), the thickness of the conductive metal paste coated on the carbon fiber cloth is controlled to be 10-100 μm.

[0028] In this invention, the method for connecting the flexible carbon fiber current collector to the metal electrode, in step (1), to ensure that the conductive metal slurry penetrates into the fiber network of the carbon fiber cloth, the coated carbon fiber cloth is treated according to any of the methods in ac: a. Vacuum treatment: The vacuum level is controlled between -0.1MPa and -0.05MPa, and the holding time is 1-10min; b. Centrifugation: The centrifugation speed is controlled at 1000-5000 rpm, and the processing time is controlled at 30-180 seconds; c. Apply a uniform pressure of 5-50 kPa during the coating process and maintain it for 10-60 seconds.

[0029] In this invention, the method for connecting the carbon fiber cloth flexible current collector and the metal electrode, in step (2), the material of the metal electrode is selected from any one of pure aluminum, aluminum alloy, pure copper, copper alloy, pure nickel or nickel alloy; the thickness of the metal electrode is 0.05-0.5mm.

[0030] In this invention, the method for connecting the flexible carbon fiber current collector to the metal electrode includes a roughening treatment in step (2) of the surface where the metal electrode contacts the carbon fiber cloth, controlling the surface roughness Ra to be between 0.8 μm and 3.2 μm. The roughening treatment methods include sanding, laser roughening, or chemical etching, to increase the mechanical interlocking effect.

[0031] In this invention, the connection method between the carbon fiber cloth flexible current collector and the metal electrode, wherein the working frequency of the ultrasonic welding equipment in steps (3) and (4) is controlled at 20-40kHz.

[0032] In this invention, the connection method between the carbon fiber cloth flexible current collector and the metal electrode, in step (4), the amplitude of ultrasonic vibration is controlled at 10-50 μm.

[0033] In the present invention, the method for connecting the carbon fiber cloth flexible current collector and the metal electrode, in step (4), the welding power is controlled at 1000-2000W; and the welding time is controlled at 0.2-1.5s.

[0034] The beneficial effects of this invention are as follows: This invention provides a highly efficient and reliable solid-state bonding method for carbon fiber cloth / metal electrode: First, a specially formulated metal slurry is used to functionalize and infiltrate the carbon fiber cloth, constructing a highly conductive and plastically flexible composite transition layer within it, fundamentally improving surface weldability; then, ultrasonic welding is used at low temperatures through high-frequency vibration energy to simultaneously achieve high-strength metallurgical bonding and mechanical anchoring between the metal electrode and the transition layer, as well as between the metal phase within the transition layer and the carbon fiber, forming a three-dimensional interlocking and stable interface. This method effectively avoids thermal damage to the fibers at high temperatures, overcomes the inherent defects of poor direct weldability of carbon fiber cloth and high and unstable conductive adhesive resistance, and achieves a unity of low interface resistance, high mechanical strength, and long-term stability in the joint. Simultaneously, the process is simple, highly adaptable, and easily integrated into large-scale production.

[0035] This method significantly reduces interface resistance, improves connection strength and long-term stability, and has a simple and reliable process. It is suitable for high-performance connection of carbon fiber current collectors and metal electrodes in fields such as flexible electronics and new energy batteries. This method is particularly suitable for the manufacture of wearable devices, flexible energy storage devices and high-performance power batteries that have high requirements for connection reliability and conductivity. Attached Figure Description

[0036] Figure 1 This is a schematic diagram illustrating the operation of the connection method between the carbon fiber cloth flexible current collector and the metal electrode described in this invention.

[0037] Figure 2This is a schematic diagram of the structure of the fiber-metal composite transition layer formed on the carbon fiber cloth in the connection method between the flexible carbon fiber cloth current collector and the metal electrode described in this invention.

[0038] Figure 3 This is a schematic diagram of the structure of the metal electrode-carbon fiber cloth-metal electrode laminated assembly formed in the connection method of the carbon fiber cloth flexible current collector and the metal electrode described in this invention.

[0039] Figure 4 This is a cross-sectional view of the ultrasonic welding of the carbon fiber cloth and metal electrode laminate assembly in the connection method of the carbon fiber cloth flexible current collector and the metal electrode described in this invention.

[0040] Among them, 1 is an ultrasonic controller, 2 is an ultrasonic transducer, 3 is an ultrasonic welding head, 4 is an ultrasonic welding anvil, 5 is a metal electrode, 6 is a carbon fiber cloth, and 7 is a fiber-metal composite transition layer formed on the carbon fiber cloth. Detailed Implementation

[0041] The present invention will be described in detail below through embodiments.

[0042] Example 1 In this embodiment, the objects to be connected are polyacrylonitrile-based carbon fiber cloth and pure aluminum electrodes.

[0043] The carbon fiber cloth has a size of 30mm × 50mm and an areal density of 100g / m³. 2 The thickness is 0.2mm. The metal electrode dimensions are 35mm × 55mm, and the thickness is 0.2mm.

[0044] The specific steps of the method for connecting the flexible carbon fiber current collector to the metal electrode are as follows: (1) Preparation of conductive metal paste: First, micron-sized silver powder with an average particle size of 2 μm and flake-shaped copper powder with a flake size of 6 μm were mixed at a mass ratio of 7:3 to form the conductive metal powder. The conductive metal powder accounted for 75% of the mass of the conductive metal paste.

[0045] Epoxy resin was selected as the organic binder, and its mass percentage in the conductive metal paste was 15%. This epoxy resin is a commercially available product.

[0046] A mixture of terpineol and anhydrous ethanol (volume ratio 4:1) was selected as the organic solvent, and its mass percentage in the conductive metal paste was 10%.

[0047] The above raw materials were placed in a planetary mixer and stirred at 1500 rpm for 3 hours to obtain a uniform metal slurry with a solid content of 85% and a viscosity of 18000 cP (25℃).

[0048] Before coating, the carbon fiber cloth to be joined area (20mm×40mm rectangular area) was subjected to plasma treatment (100W power, 60 seconds) to improve its surface wettability.

[0049] The prepared conductive metal paste was coated onto the treated area using screen printing, with the wet film thickness controlled at 50 μm.

[0050] Subsequently, the coated carbon fibers were arranged in a vacuum chamber and treated for 5 minutes under an absolute pressure of 50 Pa to allow the slurry to fully penetrate into the fiber network.

[0051] After infiltration, it is placed on a hot table at 120°C and heated for 15 minutes for pre-curing to form a stable fiber-metal composite transition layer.

[0052] (2) First, a 1060 pure aluminum plate with a thickness of 0.2 mm is selected as the metal electrode.

[0053] The surface of the electrode in contact with the carbon fiber cloth was uniformly polished using 400-grit sandpaper to increase its surface roughness Ra to 1.5 μm.

[0054] Place the pre-cured carbon fiber cloth (coated side up) from step (1) flat in the center of the lower aluminum electrode, and then cover it with the upper aluminum electrode to ensure that the coating area of ​​the carbon fiber cloth is completely covered by the two aluminum electrodes and forms a 2.5mm wide overlap area; finally, align the edges of the upper and lower aluminum electrodes and slightly extend them beyond the edge of the carbon fiber cloth; and obtain a stacked assembly of metal electrode-carbon fiber cloth-metal electrode.

[0055] (3) Select an ultrasonic metal spot welding machine with a working frequency of 20kHz.

[0056] A 0.1mm thick polyurethane buffer pad is placed between the welding head and the upper aluminum electrode.

[0057] Position the stacked assembly directly beneath the welding head, ensuring the welding head coverage area is within the pre-defined overlap zone. Activate the pressure device to apply a static pressure of 500 N.

[0058] (4) Start the ultrasonic generator, set the vibration amplitude to 35μm, the welding power to 2000W, the welding time to 0.5s, and the corresponding welding energy to 1000J.

[0059] During welding, high-frequency vibration can generate frictional heat and plastic deformation at the interface, thus achieving a connection.

[0060] After welding, place the welded joint in an oven at 150°C for 30 minutes to further cure the epoxy resin and relieve stress.

[0061] After cooling, use anhydrous ethanol swabs to clean the small amount of slurry overflowing from the edge of the joint, and finally obtain a firmly connected aluminum electrode-carbon fiber cloth-aluminum electrode composite joint.

[0062] Example 2 In this embodiment, the objects to be connected are high-modulus pitch-based carbon fiber cloth and pure copper electrodes.

[0063] The carbon fiber cloth has a size of 25mm × 40mm and an areal density of 150g / m³. 2 The thickness is 0.15mm. The metal electrode dimensions are 30mm × 45mm, and the thickness is 0.3mm.

[0064] The specific steps of the method for connecting the flexible carbon fiber current collector to the metal electrode are as follows: (1) Preparation of conductive metal paste: First, silver nanowires with a diameter of 80 nm and a length of 20 μm were mixed with silver-plated copper powder with a particle size of 3 μm and a conductivity greater than 80% IACS at a mass ratio of 1:1 to prepare the conductive metal powder. The conductive metal powder accounted for 85% of the mass of the conductive metal slurry.

[0065] Thermoplastic polyurethane resin was selected as the organic binder, and its mass percentage in the conductive metal paste was 10%.

[0066] N-methylpyrrolidone (NMP) was selected as the organic solvent, and its mass percentage in the conductive metal paste was 5%.

[0067] The above raw materials were placed in a planetary mixer and stirred at 2000 rpm for 2.5 hours to obtain a uniform metal slurry with a solid content of 90% and a viscosity of 10000 cP (25℃).

[0068] Before coating, the carbon fiber cloth to be joined is treated with ultraviolet ozone for 15 minutes.

[0069] The slurry was uniformly coated onto the treatment area using a spraying method, and the wet film thickness was controlled at 30 μm.

[0070] The coated parts were then immediately placed in a centrifuge and processed at 3000 rpm for 60 seconds to force the slurry to penetrate deeply into the dense fiber bundles.

[0071] After infiltration is complete, pre-curing is performed at 90°C for 20 minutes to form a stable fiber-metal composite transition layer.

[0072] (2) First, a T2 pure copper plate with a thickness of 0.3 mm is selected as the metal electrode.

[0073] Laser texturing is performed on the electrode contact surface to form a periodic array of micropits with a diameter of 50 μm, a depth of 10 μm, and a spacing of 100 μm, in order to enhance mechanical locking.

[0074] Carbon fibers are arranged between two layers of copper electrodes, ensuring that the coating area is aligned and that the copper electrodes extend 2 mm beyond the carbon fiber cloth around their perimeter, resulting in a laminated assembly of metal electrode-carbon fiber cloth-metal electrode.

[0075] (3) Select an ultrasonic welding machine with a working frequency of 30kHz.

[0076] A 0.05mm thick annealed copper foil is placed between the upper and lower electrodes and the welding head / anvil as a buffer / force transmission pad.

[0077] Position the stacked assembly directly beneath the welding head, ensuring the welding head coverage area is within the pre-defined overlap zone. Activate the pressure device to apply a static pressure of 300 N.

[0078] (4) Start the ultrasonic generator, set the vibration amplitude to 25μm, the welding power to 1200W, the welding time to 1.2s, and the corresponding welding energy to 1440J.

[0079] During welding, high-frequency vibration can generate frictional heat and plastic deformation at the interface, thus achieving a connection.

[0080] After welding, the welded joint is placed in an oven at 120°C for 45 minutes to allow the polyurethane binder phase to soften and reform, thus strengthening the interfacial bond.

[0081] Finally, clean the edges with acetone.

[0082] In this embodiment, the conductive phase first uses high aspect ratio silver nanowires and fully coated silver-plated copper powder to form a more efficient three-dimensional conductive network. Moreover, the copper core and silver shell structure controls the cost while ensuring high conductivity.

[0083] Secondly, for pitch-based carbon fiber cloth with higher modulus and denser structure, centrifugal infiltration was used instead of vacuum infiltration, which solved the technical difficulty of the slurry penetrating into the fiber bundle.

[0084] Furthermore, pure copper electrodes and laser-textured surfaces are selected, as their hardness and thermal conductivity differ from aluminum. Therefore, a lower welding amplitude, a longer welding time, and a copper foil buffer are used to prevent excessive metal lattice distortion and optimize energy transfer.

[0085] The solution described in this embodiment is particularly suitable for electrochemical devices or high-current transmission scenarios with extremely stringent requirements for interface resistance and current carrying capacity.

[0086] Example 3 In this embodiment, the objects to be connected are general-purpose polyacrylonitrile-based carbon fiber cloth and aluminum alloy electrodes.

[0087] The carbon fiber cloth has a size of 100mm × 150mm and an areal density of 80g / m³. 2 The thickness is 0.25mm; the metal electrode size is 105mm×155mm, and the thickness is 0.15mm.

[0088] The specific steps of the method for connecting the flexible carbon fiber current collector to the metal electrode are as follows: (1) Preparation of conductive metal paste: First, low-cost micron-sized copper powder with a particle size of 8 μm was selected as the main conductive phase, accounting for 70% by mass. To improve oxidation resistance and ensure connection reliability, 5% by mass of flake-shaped silver powder with a flake diameter of 4 μm was added as an auxiliary phase. The conductive metal powder accounted for 75% by mass of the conductive metal paste.

[0089] Phenolic resin was selected as the organic binder, and its mass percentage in the conductive metal paste was 15%.

[0090] A mixture of deionized water and anhydrous ethanol at a volume ratio of 2:1 was selected as the organic solvent, and its mass percentage in the conductive metal paste was 10%.

[0091] The above raw materials were placed in a planetary mixer and stirred at 800 rpm for 2.0 hours to obtain a uniform metal slurry with a solid content of 90% and a viscosity of 25000 cP (25℃).

[0092] Before coating, the carbon fiber cloth was immersed and cleaned in dilute nitric acid (5% by volume) at room temperature for 1 minute and then dried.

[0093] The coating process is carried out by impregnation-rolling: after the carbon fiber cloth to be joined is impregnated with slurry, it is quickly passed through a pair of rollers with a gap of 100μm to squeeze out the excess slurry and at the same time apply a pressure of 20kPa to achieve rapid coating and pressure penetration of the slurry.

[0094] After infiltration is complete, pre-curing is performed at 140°C for 10 minutes to form a stable fiber-metal composite transition layer.

[0095] (2) First, a 3003 aluminum alloy plate with a thickness of 0.15mm is selected as the metal electrode.

[0096] The electrode surface was simply cleaned with acetone without any additional roughening treatment.

[0097] Carbon fibers are arranged between two layers of copper electrodes, ensuring that the coating areas are aligned, to obtain a laminated assembly of metal electrode-carbon fiber cloth-metal electrode.

[0098] (3) Select an ultrasonic welding machine with a working frequency of 35kHz. No additional buffer pads are used.

[0099] Position the stacked assembly directly beneath the welding head, ensuring the welding head coverage area is within the pre-defined overlap zone. Activate the pressure device to apply a static pressure of 650 N.

[0100] (4) Start the ultrasonic generator, set the vibration amplitude to 45μm, the welding power to 2000W, the welding time to 0.42s, and the corresponding welding energy to 840J.

[0101] During welding, high-frequency vibration can generate frictional heat and plastic deformation at the interface, thus achieving a connection.

[0102] After welding, place the welded joint in a 180℃ oven and keep it at that temperature for 10 minutes to rapidly cure the phenolic resin. Any excess resin is cleaned up by mechanical scraping.

[0103] In this embodiment, the core conductive phase uses inexpensive micron-sized copper powder, with only a small amount of silver powder used to improve performance; the binder is fast-curing phenolic resin; and the solvent is a water-ethanol system, which is environmentally friendly and low-cost.

[0104] In terms of process, it pioneered a one-step immersion-rolling method, replacing screen printing and separate penetration steps, greatly improving coating efficiency and making it suitable for continuous production. Surface treatment is simplified, eliminating the need for plasma or complex texturing processes. The welding parameters adopt a "high power-short time" mode, resulting in a faster welding cycle. Post-processing time is also significantly reduced.

[0105] This embodiment significantly reduces material and manufacturing costs and increases production speed while ensuring connection reliability. It is suitable for cost-sensitive consumer electronics or lightweight energy storage devices that require large-scale manufacturing.

[0106] Comparative Example 1 The difference from Example 1 is that this comparative example has no transition layer, that is, it does not perform step (1) in Example 1, does not perform any slurry penetration treatment on the carbon fiber cloth, and directly performs ultrasonic welding on the original carbon fiber cloth and the metal electrode.

[0107] The specific steps for connecting the figures are as follows: (1) First, a 1060 pure aluminum plate with a thickness of 0.2 mm is selected as the metal electrode.

[0108] The surface of the electrode in contact with the carbon fiber cloth was uniformly polished using 400-grit sandpaper to increase its surface roughness Ra to 1.5 μm.

[0109] The original carbon fiber cloth is laid flat in the center of the lower aluminum electrode, and then the upper aluminum electrode is placed on top of it, so that the edges of the upper and lower aluminum electrodes are aligned and slightly extend beyond the edge of the carbon fiber cloth; thus obtaining a stacked assembly of metal electrode-carbon fiber cloth-metal electrode.

[0110] (3) Select an ultrasonic metal spot welding machine with a working frequency of 20kHz.

[0111] A 0.1mm thick polyurethane buffer pad is placed between the welding head and the upper aluminum electrode.

[0112] Position the stacked assembly directly beneath the welding head, ensuring the welding head coverage area is within the pre-defined overlap zone. Activate the pressure device to apply a static pressure of 500 N.

[0113] (4) Start the ultrasonic generator, set the vibration amplitude to 35μm, the welding power to 2000W, the welding time to 0.5s, and the corresponding welding energy to 1000J.

[0114] After welding, place the welded joint in an oven at 150°C for 30 minutes to further cure the epoxy resin and relieve stress.

[0115] After cooling, use anhydrous ethanol swabs to clean the small amount of slurry overflowing from the edge of the joint, and finally obtain a firmly connected aluminum electrode-carbon fiber cloth-aluminum electrode composite joint.

[0116] The others are the same as in Example 1.

[0117] Comparative Example 2 The difference from Example 1 is that the solid content of the conductive metal paste in step (1) is 65wt%.

[0118] The others are the same as in Example 1.

[0119] Comparative Example 3 The difference from Example 1 is that the welding energy in step (4) is 50J (power 200W, time 0.25 seconds).

[0120] The others are the same as in Example 1.

[0121] Comparative Example 4 The difference from Example 1 is that the welding energy in step (4) is 4000J (welding power 2000W, welding time 2.0 seconds).

[0122] The others are the same as in Example 1.

[0123] Comparative Example 5 The difference from Example 1 is that the static pressure applied in step (3) is 1000N.

[0124] The others are the same as in Example 1.

[0125] Performance testing The following performance tests were conducted on the connectors obtained in Examples 1-3 and Comparative Examples 1-5, and the results are shown in Table 1.

[0126] Among them, the interface contact resistance is measured using a four-probe resistance tester to measure the total DC resistance of the weld joint from the metal electrode to the carbon fiber cloth to the metal electrode, in mΩ.

[0127] Connection mechanical strength: A 90° peel test was performed using a universal testing machine, and the average peel force per unit width (1 mm) was recorded, in N / mm.

[0128] Table 1

[0129] The data analysis in Table 1 shows that: (1) In Comparative Example 1, the original carbon fiber cloth was directly ultrasonically welded to the aluminum electrode. The test results showed that the interfacial contact resistance was as high as 15.6 mΩ and the peel strength was only 0.12 N / mm. The resistance was much higher than that of Example 1 (0.85 mΩ) and the peel strength was much lower than that of Example 1 (1.62 N / mm).

[0130] As can be seen, the surface of untreated carbon fiber cloth is composed of a large number of discrete carbon fiber monofilaments, with gaps between the fibers. The contact with the metal electrode is discrete point contact, with very few conductive paths. At the same time, carbon fibers and aluminum cannot form an effective metallurgical bond. Ultrasonic vibration can only produce weak mechanical interlocking and cannot form a continuous and dense connection interface.

[0131] (2) In Comparative Example 2, the solid content of the slurry was reduced to 65% (85% in Example 1), which is equivalent to increasing the solvent ratio. The test results showed that the interfacial contact resistance increased to 3.85mΩ and the peel strength decreased to 0.58N / mm, both of which were significantly worse than those in Example 1.

[0132] It is evident that a low solids content in the conductive metal paste indicates a relatively reduced proportion of conductive metal powder and a relatively increased proportion of organic binder and solvent. After pre-curing, solvent evaporation leads to a decrease in the volume fraction of the metal phase in the transition layer, increased porosity, and discontinuity in the conductive network, resulting in increased resistance. Simultaneously, excessive binder forms a thick resin layer after curing, weakening the mechanical interlock between the metal phase and carbon fibers. Furthermore, during ultrasonic welding, an excessively thick resin layer hinders the sintering and fusion of metal particles, thereby reducing the connection strength. Therefore, an appropriate solids content in the conductive metal paste is crucial.

[0133] (3) In Comparative Example 3, the welding energy was reduced to 50J (1000J in Example 1). The test results showed that the interfacial contact resistance was as high as 8.20mΩ and the peel strength was only 0.21N / mm, making it almost impossible to form an effective connection.

[0134] Comparative Example 4 increased the welding energy to 4000J (1000J in Example 1) using a power of 2000W and a time of 2.0 seconds. The test results showed that the interfacial contact resistance increased to 12.5mΩ and the peel strength decreased to 0.15N / mm, both significantly worse than in Example 1.

[0135] Therefore, when the energy input of ultrasonic welding is too low, the frictional heat generated by the high-frequency vibration is insufficient to cause sufficient plastic deformation and surface melting of the metal particles in the transition layer, nor can it drive the diffusion of metal atoms at the interface. As a result, a continuous metallurgical bond cannot be formed inside the transition layer or between the transition layer and the metal electrode. The connection strength is extremely low due to weak mechanical interlocking, and there are a large number of voids at the interface, resulting in extremely high resistance.

[0136] When ultrasonic welding energy is too high, intense frictional heat is generated at the interface, and the local temperature can rapidly exceed the oxidation temperature of carbon fiber (approximately 400°C in air) or even the graphitization transition temperature (approximately 800°C in an oxygen-free environment). During the 2.0-second welding process, severe thermal oxidation and ablation occur in the area of ​​the carbon fiber cloth to be welded, causing the fibers to become brittle, break, and pulverize, completely losing structural integrity. Simultaneously, metal particles in the transition layer overmelt, forming irregular molten pools or spatter, failing to maintain a continuous conductive path and instead introducing high-resistivity oxides and voids. The surface of the metal electrode may also form a thick, loose oxide layer due to overheating, further deteriorating the contact. Ultimately, the welded joint is held together by only a small amount of residual adhesion and can barely withstand peel loads. This result demonstrates that higher welding energy is not always better; otherwise, thermal damage can lead to complete joint failure.

[0137] In summary, appropriate ultrasonic energy is required to activate the metallurgical-mechanical composite connection mechanism and achieve high-quality joints.

[0138] (4) Comparative Example 5 increased the static pressure to 1000N (500N in Example 1). The test results showed that the interfacial contact resistance increased to 2.10mΩ and the peel strength decreased to 0.95N / mm. Although this was better than the case without a transition layer or with too low energy, it was still significantly worse than Example 1.

[0139] Therefore, while excessive static pressure can promote tight interfacial contact, for porous and brittle carbon fiber cloth, excessive pressure can cause crushing, breakage, or even overall structural damage to the fiber filaments. Damage to the fiber structure reduces the anchoring effect between the transition layer and the carbon cloth. Furthermore, the crushed area may create localized short circuits or stress concentrations, leading to increased interfacial resistance and decreased mechanical strength. In addition, excessive pressure can cause excessive plastic deformation of the metal electrode, affecting the flatness and consistency of the weld joint. Therefore, controlling the static pressure within the range of 100-800N ensures sufficient interfacial contact while avoiding irreversible damage to the carbon fiber cloth.

[0140] In summary, this demonstrates the necessity and rationality of the process parameter ranges declared in this invention. Only when each step works in concert and the parameters are controlled within the preferred range can a reliable connection with low interface resistance and high peel strength be achieved. This fully reflects the inventiveness and industrial applicability of the technical solution of this invention.

Claims

1. A method for connecting a carbon fiber sheet flexible current collector and a metal electrode, characterized by, Includes the following steps: (1) Prepare conductive metal paste, coat the prepared conductive metal paste onto the area to be welded of carbon fiber cloth, and ensure that the conductive metal paste penetrates into the fiber network of carbon fiber cloth; arrange the carbon fibers penetrated with conductive metal paste and heat them at 80-160℃ for 5-30 minutes to form a prepared fiber-metal composite transition layer on the carbon fiber cloth. The conductive metal paste, by mass percentage, comprises 60%-90% conductive metal powder, 5%-20% organic binder, and 5%-20% organic solvent. The conductive metal is selected from at least one of silver, copper, or nickel; (2) First, fold the metal electrode in half to form upper and lower double-layer metal electrodes; Then, the carbon fiber with fiber-metal composite transition layer prepared in step (1) is arranged between the double metal electrodes so that the fiber-metal composite transition layer on the carbon fiber cloth completely covers the preset overlap area of ​​the upper and lower double metal electrodes, forming a stacked assembly of metal electrode-carbon fiber cloth-metal electrode. (3) Place the laminated assembly obtained in step (2) between the welding head and the bottom anvil of the ultrasonic welding equipment and apply a preset static pressure; wherein the static pressure is controlled at 100-800N; (4) Start the ultrasonic welding equipment, apply ultrasonic vibration to perform welding, and control the welding energy at 200-3000J; After welding is completed, the welded joint is heat-treated at 80-180℃ for 10-60 minutes.

2. The method of connecting a carbon-fiber-sheet flexible current collector to a metal electrode according to claim 1, characterized by, The areal density of the carbon fiber cloth in the step (1) is 50-200 g / m 2 , and the thickness is 0.1-0.5 mm. The conductive metal powder is in the form of particles with a particle size of 0.05μm-10μm or nanowires with a diameter of 20-200nm and a length of 5-50μm. The organic binder is selected from at least one of polyvinyl butyral, polyurethane, epoxy resin, phenolic resin or acrylic resin; The organic solvent is selected from at least one of terpineol, butylcarbidol, ethanol, N-methylpyrrolidone, or deionized water.

3. The method of connecting a carbon-fiber-sheet flexible current collector to a metal electrode according to claim 1, characterized by, The solid content of the conductive metal paste in step (1) is 80wt%-95wt%, and the viscosity at 25℃ is 5000-30000cP.

4. The method for connecting the carbon fiber cloth flexible current collector and the metal electrode according to claim 1, characterized in that, In step (1), the thickness of the conductive metal paste coated on the carbon fiber cloth is controlled to be 10-100 μm.

5. The method for connecting the carbon fiber cloth flexible current collector and the metal electrode according to claim 1, characterized in that, In step (1), to ensure that the conductive metal paste penetrates into the fiber network of the carbon fiber cloth, the coated carbon fiber cloth is treated according to any of the methods in ac: a. Vacuum treatment: The vacuum level is controlled between -0.1MPa and -0.05MPa, and the holding time is 1-10min; b. Centrifugation: The centrifugation speed is controlled at 1000-5000 rpm, and the processing time is controlled at 30-180 seconds; c. Apply a uniform pressure of 5-50 kPa during the coating process and maintain it for 10-60 seconds.

6. The method for connecting the carbon fiber cloth flexible current collector and the metal electrode according to claim 1, characterized in that, In step (2), the material of the metal electrode is selected from any one of pure aluminum, aluminum alloy, pure copper, copper alloy, pure nickel or nickel alloy; the thickness of the metal electrode is 0.05-0.5mm.

7. The method for connecting the carbon fiber cloth flexible current collector and the metal electrode according to claim 1, characterized in that, In step (2), the surface of the metal electrode in contact with the carbon fiber cloth is roughened to control the surface roughness Ra between 0.8 μm and 3.2 μm.

8. The method for connecting the carbon fiber cloth flexible current collector and the metal electrode according to claim 1, characterized in that, In steps (3) and (4), the operating frequency of the ultrasonic welding equipment is controlled at 20-40kHz.

9. The method for connecting the carbon fiber cloth flexible current collector and the metal electrode according to claim 1, characterized in that, In step (4), the amplitude of ultrasonic vibration is controlled between 10-50 μm.

10. The method for connecting the carbon fiber cloth flexible current collector and the metal electrode according to claim 1, characterized in that, In step (4), the welding power is controlled at 1000-2000W and the welding time is controlled at 0.2-1.5s.

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