A method of welding a battery current collector

Abstract

The application discloses a battery current collector welding method, which comprises the following steps: exposing positive and negative pole lug of an electric core to compact positive and negative end surfaces; tightly adhering a current collector to the positive and negative end surfaces by using an adhering tool; setting a welding groove on the current collector; identifying the welding groove by using a visual identification device; projecting laser on the welding surface by using a vibrating mirror device in cooperation with a laser; adjusting the defocusing amount of the vibrating mirror device; setting the defocusing amount when welding the current collector; setting suitable laser parameters; setting the welding track of the vibrating mirror device in the welding groove of the current collector; directing the outlet of the protection gas flow channel of the adhering tool to the positive and negative welding surfaces; and introducing inert protection gas into the protection gas flow channel; and emitting light by using the laser, forming different shapes of welding lines in the welding groove of the current collector according to the welding track by using a continuous welding mode, and firmly welding the current collector on the pole lug surface. The battery current collector welding method can improve the welding strength.

Description

Technical Field

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

[0002] Lithium-ion batteries possess advantages such as high energy density, safety and pollution-free operation, long lifespan, and no memory effect, and are widely used in electric vehicles, energy storage, and portable electronic products. In the field of power batteries, cylindrical lithium batteries are a common type and have received considerable attention.

[0003] Laser welding plays a crucial role in the battery cell manufacturing process. Due to its advantages such as high welding strength, high energy, fast speed, large depth, and minimal deformation, laser welding is used in many processes. In the current collector welding process of cylindrical batteries, laser welding is required to weld the tabs to the cover plate. Because cylindrical batteries have multiple tabs, the welding difficulty is significantly increased. Excessive laser power can burn through the separator and copper foil, causing a short circuit in the battery cell.

[0004] Existing technology, specifically invention patent CN114976494A, describes a current collector for a cylindrical battery. The current collector includes an upper component, a lower component, and a connecting post. The upper and lower components are rotatably connected via the connecting post. Both the upper and lower components include a disk body and several blades, with gaps between adjacent blades. During current collector assembly, the tabs are cut to the appropriate size according to the current collector's structure. The tabs extend between the upper and lower components, and the lower component is fixed. Rotating the upper component causes the tabs to fold, and the pressure between the upper and lower components presses the tabs together. After assembly, welding is performed. However, this existing technology uses spot welding, resulting in low weld strength. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the issue of low welding strength when spot welding is used for welding the current collector of the all-hole tab.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A method for welding a battery current collector includes the following steps: S100: After flattening the positive and negative tabs of the battery cell, the dense positive and negative terminal surfaces are exposed. S200, the fitting fixture tightly fits the positive collector plate to the positive end face and the negative collector plate to the negative end face; S300, both the positive collector plate and the negative collector plate are provided with welding grooves, and the visual recognition device identifies the welding grooves; S400, the galvanometer device is equipped with a laser to project the laser onto the positive electrode welding surface of the positive current collector and the positive terminal face, as well as the negative electrode welding surface of the negative current collector and the negative terminal face; S500, adjust the defocus amount of the galvanometer device, and set the positive electrode defocus amount when welding the positive electrode welding surface and the negative electrode defocus amount when welding the negative electrode welding surface respectively; S600, set laser parameters suitable for the positive and negative end faces; S700, welding tracks are set on the galvanometer device in the welding grooves of the positive current collector and the negative current collector; S800, the outlet of the protective airflow channel of the fitting fixture is aligned with the positive electrode welding surface and the negative electrode welding surface, and inert protective gas is introduced into the protective airflow channel; S900, the laser emits light, heats the collector plate, melts the tabs on the positive and negative end surfaces that are in close contact with it, and forms weld patterns of different shapes in the welding groove of the collector plate according to the welding trajectory, so that the collector plate is firmly welded to the surface of the tabs.

[0008] Advantages: The current collector is welded to the electrode surface using a continuous welding method, which is fast and greatly improves the welding rate. At the same time, it avoids the burning through of foil and separator while increasing the welding strength, reducing the short circuit rate and the rate of poor soldering. Therefore, it greatly improves the cell yield, reduces material waste, and lowers costs.

[0009] In one embodiment of the present invention, the positive current collector is made of aluminum, and the surface of the positive current collector is roughened by physical sandblasting; and the welding power density of the positive current collector is 6300w / mm²~8100w / mm².

[0010] In one embodiment of the present invention, the negative current collector is made of copper, and the surface of the negative current collector is nickel-plated; and the welding power density of the negative current collector is 15800w / mm²~22700w / mm².

[0011] In one embodiment of the present invention, the fiber core diameter of the laser is 100~200um, and the spot diameter at its focal point is 200~600um.

[0012] In one embodiment of the present invention, the positive electrode defocusing amount is +24mm to +28mm, and the negative electrode defocusing amount is +4mm to +20mm.

[0013] In one embodiment of the present invention, the laser parameters suitable for the positive and negative extreme surfaces include: the focal length of the galvanometer of the galvanometer device is 80-140mm, and the focal length of the focusing lens of the galvanometer device is 200-400mm; the working field of the galvanometer device is 110mm×110mm or 220mm×220mm; the working focal distance of the galvanometer device is 200-300mm; and at the focal point, the magnification of the laser light from the laser by the galvanometer device is 2-3 times.

[0014] In one embodiment of the present invention, when the laser is welding the positive electrode welding surface, its welding power is 1800w~2300w and the welding speed is 20~100mm / s; when the laser is welding the negative electrode welding surface, its welding power is 2600w~3200w and the welding speed is 40~120mm / s.

[0015] In one embodiment of the present invention, when welding the positive electrode welding surface, welding is performed without oscillation along the welding trajectory in a straight line; when welding the negative electrode welding surface, welding is performed with oscillation along the welding trajectory in the form of a sine curve. The oscillation parameters of the laser are: amplitude of 0.6mm~0.8mm and frequency of 40~60Hz.

[0016] In one embodiment of the present invention, the diameter of the laser spot projected by the laser into the welding groove of the positive current collector is 0.6mm~0.7mm, and the diameter of the laser spot projected by the laser into the welding groove of the negative current collector is 0.4mm~0.5mm.

[0017] In one embodiment of the present invention, the pressure of the inert protective gas needs to be ≥0.5MPa, and the flow rate of the inert protective gas is 15L / min~20L / min.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses a continuous laser welding method to weld the current collector onto the electrode surface. The processing speed is fast, and it only takes 0.12 seconds to complete the welding of one current collector. Compared with the traditional YAG laser welding speed, it is 5 times faster. When combined with an automated production line, it can achieve a production efficiency of 80PPM.

[0019] 2. Compared with traditional spot welding, the welding method of the present invention increases the bonding area by 1 times and the current carrying capacity by 1.45 times, effectively improving the internal current carrying capacity of the battery cell and making it more suitable for high-current or ultra-high-current charging and discharging.

[0020] 3. The welding strength of the welding method of the present invention is increased by 50% compared with the traditional spot welding method, effectively avoiding the risk of the manifold falling off during transportation on the automated production line or during the next processing step.

[0021] 4. This invention utilizes the control of defocusing amount and the differentiation of laser process parameters between the positive and negative extreme surfaces and the collector plate to precisely control power density, thereby avoiding the heat generated during welding from burning the internal diaphragm of the core and effectively controlling micro-short circuits in the battery cell.

[0022] 5. This invention is the first to introduce inert gas to protect the welding position during the welding process. The plasma shielding generated during welding is dispersed by the protective gas, ensuring that the laser power continuously and stably affects the weld, and greatly reducing the incidence of incomplete welds.

[0023] 6. This invention offers a simple production and maintenance method, reducing maintenance frequency. The welding process eliminates the need for frequent replacement of protective lenses, reducing costs and avoiding downtime for maintenance that could decrease line efficiency. The use of a fiber laser results in a compact, maintenance-free design. Furthermore, it effectively reduces the incidence of high reflections, protecting the galvanometer and laser. Attached Figure Description Figure 1 This is a flowchart of a welding method for a battery current collector according to the present invention.

[0024] Figure 2 This is a diagram showing the effect after the positive current collector plate of the present invention has been welded.

[0025] Figure 3 This is a diagram showing the effect after the negative current collector of the present invention has been welded. Detailed Implementation

[0026] To facilitate understanding of the technical solution of the present invention by those skilled in the art, the technical solution of the present invention will now be further described in conjunction with the accompanying drawings.

[0027] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0028] Please see Figure 1 As shown, the present invention provides a welding method for a battery current collector, comprising the following steps: S100 involves flattening the positive and negative tabs of the battery cell to expose the dense positive and negative terminal surfaces.

[0029] In this embodiment, the positive and negative tabs of the battery cell are ultrasonically and mechanically flattened to expose dense positive and negative end faces. The tabs are multi-tabs.

[0030] S200, the fitting fixture tightly fits the positive collector plate to the positive end face and the negative collector plate to the negative end face.

[0031] The positive current collector is made of aluminum, the negative current collector is made of copper, and the materials of the tabs on the positive and negative ends of the battery cell are different. Therefore, different welding laser parameters are required to meet the welding effect and strength requirements. In this embodiment, through experiments and calculations, the welding power density of the positive current collector is 6300w / mm²~8100w / mm², and the welding power density of the negative current collector is 15800w / mm²~22700w / mm². This ensures both welding strength and adhesion area, while preventing laser welding from burning the core diaphragm inside the tab.

[0032] During the welding process, due to the use of laser welding, copper and aluminum materials have high laser reflection, which not only affects the welding effect, but also the laser reflected back to the optical path will affect the normal operation of the internal components of the galvanometer device and cause high laser reflection. Therefore, it is necessary to perform nickel plating on the surface of the negative current collector and use physical sandblasting process to roughen the surface of the positive current collector to prevent high laser reflection.

[0033] S300, both the positive current collector and the negative current collector are provided with welding grooves, and the visual recognition device identifies the welding grooves.

[0034] The laser trajectory is located within the welding groove. The visual recognition device uses a CCD camera to take pictures, and the recognition algorithm automatically identifies the laser.

[0035] S400, the galvanometer device is equipped with a laser to project the laser onto the positive electrode welding surface of the positive current collector and the positive terminal face, as well as the negative electrode welding surface of the negative current collector and the negative terminal face.

[0036] In one embodiment of the invention, the galvanometer device is an IPG 2D high-power galvanometer. The fiber core diameter of the laser is 100~200um, and the spot diameter at its focal point is 200~600um. Specifically, the laser is a YSL-4000-U or a YSL-4000-AMB.

[0037] To further improve the high laser reflection phenomenon and enhance welding quality, the laser can be replaced with a continuous multimode fiber laser with a "ring spot" emission mode or a green continuous laser with a wavelength of 600nm~700nm. Welding with a dedicated green laser galvanometer device can effectively improve the laser absorption rate.

[0038] S500, adjust the defocus amount of the galvanometer device, and set the positive defocus amount when welding the positive electrode welding surface and the negative defocus amount when welding the negative electrode welding surface.

[0039] The positive electrode defocusing amount is +24mm to +28mm, and the negative electrode defocusing amount is +4mm to +20mm. When welding the positive electrode welding surface and the negative electrode welding surface, if the same optical configuration of the galvanometer device and laser is used, different defocusing amounts need to be set.

[0040] S600, set laser parameters suitable for the positive and negative end faces.

[0041] In one embodiment of the present invention, the laser parameters suitable for the positive and negative electrode surfaces include: the galvanometer diameter and focal length of the galvanometer device are 80-140mm, and the focal length of the focusing lens is 200-400mm. The working field of the galvanometer device is 110mm×110mm or 220mm×220mm. The working focal distance of the galvanometer device is 200-300mm. Furthermore, at the focal point, the galvanometer device amplifies the laser beam by 2-3 times. When welding the positive electrode welding surface, the laser has a welding power of 1800W-2300W and a welding speed of 20-100mm / s. When welding the negative electrode welding surface, the laser has a welding power of 2600W-3200W and a welding speed of 40-120mm / s.

[0042] S700, welding tracks are set on the galvanometer device within the welding grooves of the positive and negative current collectors.

[0043] The welding trajectory paths for the positive and negative current collectors are set in the optical path editing software of the galvanometer device. When welding the positive electrode welding surface, because aluminum material requires a relatively low power density, the laser spot diameter projected into the welding groove of the positive current collector is relatively large, ranging from 0.6mm to 0.7mm. Linear laser welding can achieve the required adhesion area and avoid heat accumulation that could burn the inner core diaphragm of the electrode tab. Therefore, when welding the positive current collector, a straight, non-oscillating welding method is used along the welding trajectory.

[0044] When welding the negative electrode welding surface, because copper material requires a high power density, the diameter of the laser spot projected by the laser into the welding groove of the negative current collector is small, with a laser spot diameter of 0.4mm~0.5mm. Laser linear welding cannot achieve the required adhesion area. Therefore, laser oscillation welding is used to meet the adhesion area requirement. During welding, the laser oscillation welding is performed along the welding trajectory in the form of a sine curve. The laser oscillation curve type is a sine curve, the oscillation amplitude is 0.6mm~0.8mm, and the oscillation frequency is 40~60Hz. After testing, these parameters can avoid burning the inner core diaphragm of the electrode tab.

[0045] During the welding process, the current collector plate is located at the center of the welding area of the galvanometer device, and its relative position with the galvanometer device remains fixed. The laser beam is moved by the rotation of two sets of reflecting mirrors driven by the motor inside the galvanometer device.

[0046] S800, align the outlet of the protective gas flow channel of the bonding tooling with the positive welding surface and the negative welding surface, and introduce an inert protective gas into the protective gas flow channel.

[0047] During the welding process, a large amount of plasma is generated, which shields the laser energy, resulting in a laser energy density lower than the required value and causing false welding. Therefore, an inert protective gas must be introduced at the welding position throughout the welding process to remove the influence of plasma shielding. Among them, the pressure of the inert protective gas should be ≥0.5MPa, the flow rate of the inert protective gas is 15L / min - 20L / min, and the type of inert protective gas should be selected as one or a mixture of multiple gases among the inert gases. Among them, helium is the best because helium can effectively protect the welding position, form a stable atmosphere, does not react with the welding metal, and because it is not easily ionized itself, it can effectively disperse the plasma. Specifically, the inert protective gas includes, but is not limited to, one or a mixture of N2, He, Ne, Ar, Kr, Xe, Rn.

[0048] S900, the laser emits light to heat the current collector plate and melt the tabs on the positive and negative end faces in close contact with it. According to the welding trajectory, a continuous welding method is used to form weld beads of different shapes in the welding groove of the current collector plate, so that the current collector plate is firmly welded to the tab surface.

[0049] Please refer to Figures 1 to 3 As shown, in an embodiment of the present invention, after welding, a welding strength tensile test and a short - circuit test of the completed battery cell are carried out along the wire. The specific implementation method is as follows: after welding, the mechanical gripper automatically clamps the position where the current collector plate connects to the battery cell top cover, and applies a tensile force of 150N to the current collector plate and the wound core. If the current collector plate does not fall off, it is judged as qualified; if the current collector plate falls off, it is judged as unqualified. After completing the welding strength tensile test, a precision short - circuit test instrument is connected to the completed - welded current collector plate and the battery cell. If no short - circuit current is detected, it is judged as qualified; otherwise, it is unqualified.

[0050] Verification of comparative examples Please refer to Figure 1As shown, in one embodiment of the present invention, the visual recognition device uses a CCD camera to take pictures, and the galvanometer device uses an IPG 2D high-power galvanometer, paired with a YSL-4000-AMB multimode continuous ring-shaped fiber laser. After the laser is focused by the galvanometer device, the diameter of the spot at the focal point is 375µm. The defocusing distance of the positive electrode is 26mm, and the defocusing distance of the negative electrode is 4mm. At this point, the defocusing distance of the positive electrode exceeds the Rayleigh length of the laser beam, while the defocusing distance of the negative electrode does not exceed the Rayleigh length of the laser beam. Therefore, the heat conduction capacity is strong for the penetration of the negative current collector, while the positive current collector will not cause the internal diaphragm to shrink due to excessive laser energy, resulting in a short circuit in the battery. The galvanometer device has a galvanometer diameter and focal length of 140mm, and a focusing lens focal length of 400mm. When the laser is welding the positive electrode welding surface, the welding power is 1800W, the welding speed is 60mm / s, and the laser's oscillation function is turned off. When welding the negative electrode surface, the laser power was 2800W, the welding speed was 80mm / s, the laser's oscillation function was activated, the oscillation amplitude was 0.6mm, the oscillation frequency was 45Hz, and the inert shielding gas flow rate was 15L / min. After welding, each manifold took 1.2s to complete, and the average test connection strength was approximately 100N.

[0051] The comparative example follows the same steps S100 to S300 of this invention. A YAG laser is used with a collimated welding head. A three-axis servo motor and a guide rail are used to move the welding head to pre-set welding points. The motor then restarts, moving the welding head to the next point for further welding, continuing this process until all points are welded. The motor remains stationary during the welding process to ensure optimal welding quality. In the comparative example, the motor displacement speed is 80 mm / s, the laser power is 1200 W, and the single-point welding time is 50 ms. No protective gas is needed to protect the welding surface. Welding one manifold takes 2 minutes, and the average connection strength is 50 N.

[0052] Compared to the comparative example, this application increases the current collector adhesion area by 50% and the post-weld current collector connection strength by 100%. The processing time is only 1% of the comparative example, while efficiency is increased by 100 times. The internal resistance is reduced by 30% compared to the comparative example. Long-term production testing shows that the average post-weld short-circuit pass rate of the battery current collector in this application is 99.47%, while the average post-weld short-circuit pass rate of the comparative example battery current collector is 98.87%, representing an improvement of 0.6%.

[0053] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0054] The above embodiments are merely examples of implementation methods of the invention. The scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A welding method for a battery current collector, characterized in that, Applicable to cylindrical batteries, the power density is controlled by adjusting the defocusing amount of the galvanometer device and distinguishing the positive and negative terminal surfaces from the current collector laser process parameters. This prevents the heat generated during welding from burning the internal separator of the core. The steps include: S100: After flattening the positive and negative tabs of the battery cell, the dense positive and negative terminal surfaces are exposed. S200, the fitting fixture tightly fits the aluminum positive current collector to the positive end face and the copper negative current collector to the negative end face, and the welding power density of the positive current collector is 6300w / mm²~8100w / mm², and the welding power density of the negative current collector is 15800w / mm²~22700w / mm². S300, both the positive collector plate and the negative collector plate are provided with welding grooves, and the visual recognition device identifies the welding grooves; S400, the galvanometer device is equipped with a laser to project the laser onto the positive electrode welding surface of the positive current collector and the positive terminal face, as well as the negative electrode welding surface of the negative current collector and the negative terminal face; S500, adjust the defocus amount, and set the positive electrode defocus amount when welding the positive electrode welding surface and the negative electrode defocus amount when welding the negative electrode welding surface; wherein, the positive electrode defocus amount is +24mm~+28mm, the negative electrode defocus amount is +4mm~+20mm, and the distance of the positive electrode defocus amount exceeds the Rayleigh length of the laser beam, while the negative electrode defocus amount does not exceed the Rayleigh length of the laser beam; S600, set laser parameters suitable for the positive and negative end faces; S700, welding paths are set on the welding grooves of the positive current collector and the negative current collector on the galvanometer device; when welding the positive electrode welding surface, welding is performed in a straight line along the welding path without oscillation, and the diameter of the laser spot projected by the laser into the welding groove of the positive current collector is 0.6mm~0.7mm; when welding the negative electrode welding surface, welding is performed in an oscillating curve along the welding path, and the diameter of the laser spot projected by the laser into the welding groove of the negative current collector is 0.4mm~0.5mm; S800, the outlet of the protective airflow channel of the fitting fixture is aligned with the positive electrode welding surface and the negative electrode welding surface, and inert protective gas is introduced into the protective airflow channel; S900, the laser emits light, heats the collector plate, melts the tabs on the positive and negative end surfaces that are in close contact with it, and forms weld patterns of different shapes in the welding groove of the collector plate according to the welding trajectory, so that the collector plate is firmly welded to the surface of the tabs.

2. The welding method for the battery current collector according to claim 1, characterized in that, The positive collector is made of aluminum, and its surface is roughened by physical sandblasting.

3. The welding method for the battery current collector according to claim 2, characterized in that, The negative current collector is made of copper, and its surface is nickel-plated.

4. The welding method for the battery current collector according to claim 1, characterized in that, The laser has an optical fiber core diameter of 100~200um and a spot diameter of 200~600um at its focal point.

5. The welding method for the battery current collector according to claim 1, characterized in that, When the laser is used to weld the positive electrode welding surface, its welding power is 1800w~2300w and the welding speed is 20~100mm / s; when the laser is used to weld the negative electrode welding surface, its welding power is 2600w~3200w and the welding speed is 40~120mm / s.

6. The welding method for the battery current collector according to claim 1, characterized in that, The oscillation parameters of the laser are: amplitude of 0.6mm~0.8mm and frequency of 40~60Hz.

7. The welding method for the battery current collector according to claim 1, characterized in that, The pressure of the inert protective gas must be ≥0.5MPa, and the flow rate of the inert protective gas must be 15L / min~20L / min.

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