An electrode assembly and a tab welding method

Abstract

This application discloses a battery cell unit and a tab welding method, which can reduce process steps and improve current carrying capacity. The battery cell unit provided by this application includes a battery cell and tabs directly welded to the battery cell. The solder mark between the tab and the battery cell extends along a first direction, and the solder mark includes multiple solder lines spaced apart along the first direction, each of the solder lines extending along a second direction.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a battery cell and a method for welding tabs. Background Technology

[0002] Please refer to Figure 9 , Figure 9 This is a schematic diagram of a structure for welding electrodes and battery cells.

[0003] The battery cell unit includes battery cell 01 and electrode 02. Electrode 02 needs to be connected to the positive or negative terminal of battery cell 01. Figure 9 In the process, tab 02 is connected to battery cell 01 via connecting piece 03. During manufacturing, tab 02 and connecting piece 03 are first welded together, for example, using ultrasonic welding. Then, connecting piece 03 is welded to battery cell 01, which can be done via laser welding. Specifically, it can be welded to the top cover 011 of battery cell 01. Figure 9 The middle arrow indicates the current path. This connection method between the tab 02 and the cell 01 requires the addition of a connecting piece 03, which makes the welding process more complex. Moreover, the connecting piece 03 also increases resistance, which is not conducive to improving the overcurrent capacity. Summary of the Invention

[0004] The purpose of this application is to provide a battery cell unit and a tab welding method that can reduce process steps and improve current carrying capacity.

[0005] To solve the above-mentioned technical problems, this application provides a battery cell unit, including a battery cell and a tab directly soldered to the battery cell. The solder mark between the tab and the battery cell extends along a first direction, and the solder mark includes multiple solder lines spaced apart along the first direction, each of the solder lines extending along a second direction.

[0006] Optionally, the first direction and the second direction are perpendicular.

[0007] This application also provides a method for welding tabs, which directly welds the tabs and the battery cell. During welding, multiple welding passes are performed along a first direction to form multiple spaced welding lines, and each welding line extends along a second direction.

[0008] Optionally, the first direction and the second direction are perpendicular.

[0009] Optionally, each of the weld lines includes two end weld lines distributed along the second direction and a middle weld line segment located between the two end weld lines, wherein the welding energy corresponding to the end weld lines is less than the welding energy corresponding to the middle weld line segment.

[0010] Optionally, the welding energy corresponding to the end welding segments increases in the direction closer to the middle welding segment.

[0011] Optionally, the welding energy corresponding to the end of the end weld segment that is far from the middle weld segment is 25% to 35% of the welding energy corresponding to the middle weld segment, and the welding energy corresponding to the end of the end weld segment that connects to the middle weld segment is 75% to 85% of the welding energy corresponding to the middle weld segment.

[0012] Optionally, the weld wire is a straight weld wire extending along the second direction.

[0013] Optionally, the tabs and the battery cell are laser-welded using a ring-spot laser.

[0014] Optionally, multiple metal layers stacked along a third direction are prepared, and the multiple metal layers are partially welded together to obtain the electrode tab; the third direction is perpendicular to the first direction and the second direction.

[0015] Wherein, the thickness of the welded portion of the multi-layer metal layer in the third direction before welding is the first thickness, and the thickness of the welded portion of the multi-layer metal layer in the third direction after welding is the second thickness. The first thickness is greater than the second thickness. A preset ratio of the first thickness and a preset ratio of the second thickness are set, and the second preset ratio of the second thickness is less than the first preset ratio of the first thickness.

[0016] The ratio of the second thickness to the first thickness is controlled to be no greater than a preset ratio of the first thickness and no less than a preset ratio of the second thickness.

[0017] Optionally, the first preset thickness ratio is 75%~85%, and the second preset thickness ratio is 35%~45%.

[0018] Alternatively, ultrasonic welding can be performed by applying pressure to the multiple metal layers using tooling.

[0019] Optionally, the welded multilayer metal layers are cut to obtain the tabs.

[0020] The battery cell unit of this application has the tabs directly soldered to the cell, which can reduce the number of process steps. Moreover, the multiple solder lines are distributed at intervals along the first direction and the adjacent solder lines do not overlap, which can reduce the heat accumulation on both sides of the solder line, thereby improving the cracks on both sides of the solder line. This results in more stable current carrying capacity, stronger mechanical stability, and better appearance. It can be applied to mass production of battery cell products with higher rate and higher energy density.

[0021] The tab welding method of this application allows for direct welding of the tabs to the battery cell, eliminating the need for indirect welding via connecting pieces as in the prior art. This simplifies the process by eliminating the welding step of connecting pieces. Furthermore, the direct connection between the tabs and the battery cell reduces resistance, thereby improving the utilization of internal space and current carrying capacity within the battery cell. This, in turn, facilitates innovations in battery cell performance, such as high energy density and ultra-fast charging, while also resulting in lower costs and better stability. In addition, the tab welding method in this application forms multiple weld lines spaced apart along a first direction, with adjacent weld lines not overlapping. This reduces heat accumulation on both sides of the solder joint, improving crack formation and resulting in more stable current carrying capacity, stronger mechanical stability, and a better appearance. This method can be applied to mass production of battery cells with higher rate and higher energy density. Attached Figure Description

[0022] Figure 1 This is a partial location diagram of a battery cell unit in one embodiment of this application, illustrating the connection position between the battery cell and the electrode.

[0023] Figure 2 for Figure 1 Structural principle diagram of the solder joint;

[0024] Figure 3 This is a schematic diagram of the structural principle of a Z-shaped solder mark;

[0025] Figure 4 This is a schematic diagram of the structural principle of a spiral solder joint.

[0026] Figure 5 Metallographic image of cracks after the electrode tab is directly welded to the battery cell using conventional welding methods;

[0027] Figure 6 for Figure 1 Metallographic image of the crack in the weld bead;

[0028] Figure 7 This is a schematic diagram showing the distribution of welding energy corresponding to the solder marks in the embodiments of this application;

[0029] Figure 8 This is a comparative schematic diagram of the multilayer metal layers of the electrode tab before and after welding in an embodiment of this application.

[0030] Figure 9 This is a schematic diagram of a structure for welding electrodes and battery cells.

[0031] The annotations in the attached figures are explained as follows:

[0032] 10 - Battery cell; 101 - Top cover;

[0033] 20 - tab; 201 - metal layer; 20A - solder mark; 20A1 - solder line; 20A11 - middle solder line segment; 20A12 - end solder line segment; 20B - welding area; 20C - solid part; 0L - crack;

[0034] X - First direction; Y - Second direction; Z - Third direction;

[0035] 20A'-Z-shaped solder mark; 20A''-spiral solder mark; 20C'-solid part; 0L'-crack;

[0036] 01-Battery cell; 011-Top cover; 02-Electrical tab; 03-Connecting piece. Detailed Implementation

[0037] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] The ordinal numbers used in this article, such as first and second, are used to distinguish different parts with the same name and do not indicate a specific order or primary / secondary relationship.

[0039] like Figure 1 As shown, Figure 1 This is a partial location diagram of a battery cell unit in one embodiment of this application, illustrating the connection position between the battery cell and the electrode.

[0040] The battery cell unit includes a battery cell 10. The battery cell 10 may include a housing with an opening on one side and a top cover 101 that seals the opening. The battery cell 10 may also include internal structures such as positive and negative electrodes, a separator, and an electrolyte. These internal structures can be installed inside the housing of the battery cell 10 and then sealed by the top cover 101. In this embodiment, the battery cell unit also includes tabs 20, which are used to connect to the positive or negative electrode inside the battery cell 10 as external electrical connectors. As an example, when the tab 20 is used as the positive electrode, a metal foil with an aluminum content of 99% or higher can be selected; when the tab 20 is used as the negative electrode, a metal foil with a copper content of 99% or higher can be selected.

[0041] It is worth noting that in this embodiment, the tab 20 is directly soldered to the battery cell 10, specifically, it is directly soldered to the top cover 101 of the battery cell 10. Since the tab 20 and the battery cell 10 are directly soldered, the indirect soldering method using connecting tabs as described in the prior art is no longer used. This eliminates the soldering step of the connecting tabs, thus simplifying the process. Furthermore, the direct connection of the tab 20 to the battery cell 10 reduces resistance, thereby improving the internal space utilization and current carrying capacity of the battery cell 10. Figure 1 The arrows in the middle indicate the current path, which helps to improve the high energy ratio and ultra-fast charging performance of the battery cell 10, while also reducing costs and improving stability.

[0042] When the tab 20 and the cell 10 are soldered, a solder mark 20A will be formed. It should be noted that the tab 20 is not completely fused to the cell 10; rather, a portion of the tab 20 is soldered to the cell 10 to form solder mark 20A. Solder mark 20A is shown as... Figure 1 The black area shown in the image.

[0043] You can continue to refer to this. Figure 2 understand, Figure 2 for Figure 1 Structural schematic diagram of the Zhongshan 20A soldering pad.

[0044] The solder mark 20A formed by welding the tab 20 and the cell 10 appears to be continuous to the naked eye, but in actual welding, it is formed through multiple welding passes. That is, the solder mark 20A actually includes multiple spaced welding lines 20A1. The welding lines 20A1 are the structures formed by the melting and solidification of parts of the tab 20 during the welding process. Figure 2 The solder mark 20A shown in the diagram includes multiple straight solder lines 20A1. During soldering, multiple A1 soldering passes are performed along the first direction X to form multiple solder lines 20A1. Each solder line 20A1 extends along the second direction Y. The first direction X and the second direction Y can be perpendicular to each other or not, but perpendicularity makes soldering control easier. The solder lines 20A1 described here extend along the second direction Y, but this is not a limitation. Figure 2 The straight line shown can be formed as long as it extends along the second direction Y, such as a wavy weld line extending along the second direction Y. Obviously, a straight weld line 20A1 is easier to operate. During the welding process, the welding head of the welding equipment (not shown in the figure) travels a certain distance along the second direction Y to form a weld line 20A1. Then the welding head is moved a certain distance along the first direction X, and continues to travel along the second direction Y and output welding energy to form another weld line 20A1. This process is repeated until the number of weld lines 20A1 is sufficient to reliably weld the tab 20 and the cell 10. Finally, multiple weld lines 20A1 distributed along the first direction X are formed to form a weld mark 20A.

[0045] Comparable Figure 3 and Figure 4 understand, Figure 3 This is a schematic diagram of a Z-shaped solder mark 20A'. Figure 4 This is a schematic diagram of a spiral solder mark 20A''.

[0046] During welding, Z-shaped weld marks 20A' and spiral weld marks 20A'' are relatively common. The welding head forming a Z-shaped weld mark 20A' continuously outputs welding energy during welding, thus generally forming a weld mark extending along the first direction X. Although the welding head moves back and forth roughly along the second direction Y during welding, the resulting weld lines are continuous. The welding head forming a spiral weld mark 20A' is similar to a circular welding motion, with overlapping weld lines in some areas. The spiral weld mark 20A' also extends along the first direction X. Conventional welding processes use... Figure 3 , 4 The welding method aims to strengthen the connection between weld lines to improve the welding effect, but it does not consider that when the welding head reciprocates along the second direction Y, heat is prone to accumulate at the end or edge of the weld mark along the second direction Y. Specifically, with... Figure 3 For example, when the welding head moves from left to right to position A, it needs to move to the left again from position A. This increases the time spent at position A, causing heat to accumulate at the end of the Z-shaped weld mark 20A'. Now let's look at... Figure 4 In addition to the heat buildup at position B on the end of the welding head due to the increased dwell time, there is also overlap of the weld lines at position C, meaning that the same position is welded twice. This will cause heat buildup on both sides of the weld mark, and the overlapping position is also prone to problems such as blasting and explosion.

[0047] Conventional welding does not consider the impact of heat accumulation, or rather, heat accumulation does not have an adverse effect in general welding scenarios. However, the inventors discovered that if the tab 20 and the battery cell 10 are directly welded, given the material characteristics of the tab 20—its relatively low melting point and excellent thermal conductivity, especially since the material composition of 20 is mainly aluminum—the tab 20 will rapidly melt and then solidify when absorbing large welding energy. The higher the temperature change, the linearly greater the thermal shrinkage rate of the tab 20. As mentioned above, using conventional welding methods, heat will accumulate on both sides of the part of the tab 20 used for welding to the battery cell 10. This causes the surrounding matrix to be unable to fill in time during the melting and solidification process on both sides of the welded part of the tab 20, resulting in a break along the fusion line, i.e., cracks. (See reference...) Figure 5 understand, Figure 5 The image shows a metallographic image of the crack after the electrode tab is directly welded to the battery cell using conventional welding methods. The metallographic image is shown along the third direction Z (indicated on the...). Figure 8 The cross-sectional view of the third direction Z is perpendicular to the first direction X and the second direction Y. The weld mark is the above-mentioned Z-shaped weld mark 20A' or spiral weld mark 20A''. There is a wide crack 0L' between the weld mark and the unmelted solid part 20C' of the surrounding electrode tab.

[0048] In this embodiment, the welding head moves intermittently, forming multiple weld lines 20A1 extending along the second direction Y. The welding head does not move continuously, and adjacent weld lines 20A1 do not overlap. This reduces heat accumulation on both sides of the solder mark 20A, thereby improving the crack OL on both sides of the solder mark 20A. (See reference...) Figure 6 understand, Figure 6 for Figure 1 The metallographic image of the crack in weldment 20A is also a cross-sectional view of weldment 20A along the third direction Z. Figure 5 Understanding, it is obvious Figure 6 The crack OL between the central solder mark 20A and the solid portion 20C of the surrounding tab 20 narrows, allowing for a tighter bond. Therefore, the cell unit with the soldered tab 20 exhibits more stable current carrying capacity, stronger mechanical stability, and a better appearance. This demonstrates that the soldering method in this embodiment represents a significant optimization in the process, enabling mass production of cell products with higher rate and higher energy density.

[0049] Please look again. Figure 7 , Figure 7 This is a schematic diagram of the welding energy distribution corresponding to solder mark 20A in the embodiments of this application.

[0050] Each solder line 20A1 includes two end solder line segments 20A12 distributed along the second direction Y and a middle solder line segment 20A11 located between the two end solder line segments 20A12. The soldering energy corresponding to the end solder line segment 20A12 is less than the soldering energy corresponding to the middle solder line segment 20A11. The parameters of the soldering energy include, for example, power, i.e., high power is used in the main soldering area and low power is used in the edge part. The welding wire 20A1 is in a liquid state when it melts along both sides of the second direction Y. It is in contact with the other unmelted solid parts 20C of the electrode 20. During the melting and solidification process, it does not receive filling from the surrounding matrix (i.e., solid parts 20C), which causes cracks 0L. However, the position of the middle welding wire segment 20A11 can be filled by the liquid material at the end welding wire segment 20A12, making it less prone to cracking. Therefore, in this embodiment, when welding along the second direction Y, the welding energy can be reduced when the welding head is located at the end of the welding wire 20A1, and increased when it is located at the middle welding wire segment 20A11. That is, in the welding stroke of each welding wire 20A1, the welding energy is output in a low-high-low manner, thereby ensuring welding quality and reducing the generation of cracks.

[0051] In some embodiments, the welding energy corresponding to the end welding segment 20A12 can increase gradually towards the direction of the middle welding segment 20A11. This increase can be linear or gradient, with gradient increase being more conducive to control. That is, as the welding head moves from one end to the middle, the welding energy can increase gradually, and as the welding head moves from the middle to the other end, the welding energy can decrease gradually. This makes the change in welding energy relatively uniform, which is more conducive to ensuring the welding effect.

[0052] Specifically, the welding energy corresponding to the end weld segment 20A12 can be increased or decreased according to a certain proportion of the welding energy corresponding to the middle weld segment 20A11. For example, the welding energy corresponding to the end of the end weld segment 20A12 away from the middle weld segment 20A11 can be 25% to 35% of the welding energy corresponding to the middle weld segment 20A11, and the welding energy corresponding to the end of the end weld segment 20A11 and the middle weld segment 20A11 that are connected can be 75% to 85% of the welding energy corresponding to the middle weld segment.

[0053] For example, the welding energy trend for the end welding segment 20A12 can be 30% to 80% of the welding energy corresponding to the middle welding segment 20A11. Figure 7 As shown, taking one end weld segment 20A12 as an example, the end of end weld segment 20A12 furthest from the middle weld segment 20A11 is position E, and the other end connected to the middle weld segment 20A11 is position D. Let Q be the welding energy corresponding to the middle weld segment 20A11. Then, the welding energy at position E is 30%Q, and the welding energy at position D is 80%Q. From E to D, the welding energy gradually increases from 30%Q to 80%Q, or from D to E, the welding energy gradually decreases from 80%Q to 30%Q. Of course, 30%~80% is merely an example; the range of welding energy variation can be determined based on actual needs and experimental methods to balance welding effect and reduce heat buildup.

[0054] In this embodiment, the tab 20 and the battery cell 10 can be laser-welded using a ring-spot laser. The welding energy parameters mentioned above include the laser's emission power; higher power results in higher welding energy, and lower power results in lower welding energy. A common laser welding device is a single-film laser. The ring-spot laser selected in this embodiment has better heat dissipation performance compared to a single-film laser and has a modifying effect on the molten pool morphology of the weld bead 20A. Of course, the tab 20 and the battery cell 10 can also be welded using other welding methods. This embodiment also optimizes laser selection and cross-validates related parameters to reduce defects during the welding process.

[0055] You can continue to refer to this. Figure 8 , Figure 8This is a comparative schematic diagram of the multilayer metal layer 201 of the tab 20 in this embodiment before and after welding.

[0056] In this embodiment, the electrode 20 includes multiple metal layers 201. When welding the electrode 20 and the battery cell 10, multiple metal layers 201 stacked along the third direction Z are prepared first. In this embodiment, the third direction Z is perpendicular to both the first direction X and the second direction Y. Figure 8 From the perspective of Z, the third direction is vertical, and the first direction X and the second direction Y lie on a plane perpendicular to the third direction Z. The multi-layered metal layers 201 can be partially welded together to obtain the tab 20. Figure 1 The diagram shows the welding area 20B, which is a pre-welding area. Its size can be determined according to the welding area requirements of the battery cell 10.

[0057] In this design, the thickness of the welded portion of the multilayer metal layer 201 along the Z-direction at the welding front is defined as a first thickness T1. After welding, the thickness of the welded portion of the multilayer metal layer 201 along the Z-direction is defined as a second thickness T2. The first thickness T1 is greater than the second thickness T2, meaning the thickness of the welded area 20B becomes thinner to the second thickness T2. The thickness of other areas of the multilayer metal layer 201 outside the welded portion remains the first thickness T1. Simultaneously, a preset ratio for the first thickness is set to control the ratio of the second thickness T2 to the first thickness T1 to be no greater than this preset ratio, thus controlling the compaction rate of the multilayer metal layer 201 at the pre-welding position. This preset ratio for the first thickness is determined based on welding requirements. As described above, in this embodiment, the tab 20 needs to be directly welded to the battery cell 10 to improve the internal space utilization of the battery cell 10 and increase the current carrying capacity. However, there are gaps between the multiple metal layers 201 of the tab 20. If the tab 20 is directly connected to the battery cell 10, the presence of these gaps will exacerbate crack formation and also easily generate bubbles. Therefore, in this embodiment, when welding the multiple metal layers 201, the gaps between the multiple metal layers 201 are controlled to mitigate the impact of these gaps on cracks generated during welding with the battery cell 10 and to reduce bubble formation. It can be seen that the first thickness preset ratio can be determined based on actual welding requirements, experiments, and other factors. Specifically, in this embodiment, the first thickness preset ratio can be 75% to 85%, and more specifically, it can be 80%.

[0058] A second preset thickness ratio can also be set, which is less than the first preset thickness ratio. T2 / T1 should not be less than the second preset thickness ratio, meaning T2 should not be too small, to avoid excessive thinning after compaction, which could lead to high brittleness of the tab 20. For example, if the tab 20 is mainly made of aluminum, its surface has a layer of alumina. If compaction is too thin, the alumina will be too dense, resulting in excessive brittleness. The second preset thickness ratio is, for example, 35%~45%, more specifically, 40%. The second preset thickness ratio can also be determined based on actual needs, experiments, and other factors. In this embodiment, T2 / T1 can be controlled between 40% and 80%, which can further reduce cracks and bubbles. This ensures consistency of incoming materials before welding and maintains a certain level of hardness. Excessive hardness will lead to brittle samples, while excessive softness will lead to welding misalignment.

[0059] In some embodiments, ultrasonic welding can be performed by applying pressure to local locations of the multilayer metal layer 201 using a tooling. Ultrasonic welding is reliable, and applying pressure to the multilayer metal layer 201 during ultrasonic welding can reduce the second thickness T2, facilitating better control of T2 / T1.

[0060] In some embodiments, the welded multilayer metal layer 201 can be cut to obtain the tab 20. The cutting direction can be the third direction Z. As mentioned above, pressure is applied to the multilayer metal layer 201 during welding. To facilitate the implementation of pressure, the area of ​​the metal layer 201 can be appropriately increased. During the pressure process, the area of ​​the metal layer 201 will also increase to a certain extent. When matching the corresponding battery cell 10, there may be excess parts. Therefore, according to the actual size requirements of the battery cell 10, the multilayer metal layer 201 can be cut after ultrasonic welding to obtain the required tab 20.

[0061] In this embodiment, the electrode 20 and the battery cell 10 are welded together using the above welding method to form a sample. The solder mark 20A of the sample includes multiple spaced solder lines 20A1. The energy distribution at both ends and the middle of the solder lines 20A1 is different during welding. After testing the sample, it has the advantage of high reliability and can meet the relevant requirements such as overcurrent and tensile testing. The test results can be understood by referring to Table 1 below. The sample disassembled after testing has a good appearance and no abnormalities.

[0062] Table 1

[0063]

[0064] Table 1 shows the cell state BOL (Beginning of Life) test, which is a comprehensive check of the cell at the beginning of its lifespan; the cell state EOL (End of Life) test, which is the final test of the cell; and the cell SOC (State of Charge), which refers to the percentage of the cell's remaining charge relative to its rated capacity. The above welding method, which welds the tab 20 and cell 10 to form a sample, undergoes metallographic disassembly, visual inspection, and tensile testing. The resulting molten pool exhibits fewer bubbles, narrower cracks, a superior appearance, and greater mechanical reliability, improving current carrying capacity. It also forms a stable connection, resulting in a longer service life. Furthermore, the processing is simple and suitable for large-scale application.

[0065] In this embodiment, during the process of welding the tab 20 to the cell 10, corresponding dust removal equipment, water cooling equipment, etc. can be turned on to prevent the generation of welding slag and ensure good heat dissipation of the welding equipment.

[0066] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A battery cell unit, characterized in that, The device includes a battery cell (10) and a tab (20) directly soldered to the battery cell (10). A solder mark (20A) between the tab (20) and the battery cell (10) extends along a first direction. The solder mark (20A) includes multiple solder lines (20A1) spaced apart along the first direction. Each solder line (20A1) extends along a second direction.

2. The battery cell unit according to claim 1, characterized in that, The first direction and the second direction are perpendicular.

3. A method for welding electrode tabs, characterized in that, The tab (20) and the cell (10) are directly welded together. During welding, multiple welding passes are performed along the first direction to form multiple spaced welding lines (20A1), each of which extends along the second direction.

4. The battery cell unit according to claim 3, characterized in that, The first direction and the second direction are perpendicular.

5. The electrode tab welding method according to claim 3, characterized in that, Each of the aforementioned weld lines (20A1) includes two end weld line segments (20A12) distributed along the second direction and a middle weld line segment (20A11) located between the two end weld line segments (20A12), wherein the welding energy corresponding to the end weld line segment (20A12) is less than the welding energy corresponding to the middle weld line segment (20A11).

6. The electrode tab welding method according to claim 5, characterized in that, The welding energy corresponding to the end welding segment (20A12) increases in the direction closer to the middle welding segment (20A11).

7. The electrode tab welding method according to claim 6, characterized in that, The welding energy corresponding to the end of the end weld segment (20A12) away from the middle weld segment (20A11) is 25% to 35% of the welding energy corresponding to the middle weld segment (20A11); the welding energy corresponding to the end of the end weld segment (20A12) and the middle weld segment (20A11) that are connected is 75% to 85% of the welding energy corresponding to the middle weld segment (20A11).

8. The electrode tab (20) welding method according to any one of claims 5-7, characterized in that, The weld line (20A1) is a straight weld line extending along the second direction.

9. The electrode tab welding method according to any one of claims 5-7, characterized in that, The tab (20) and the battery cell (10) are laser welded using a ring-shaped laser.

10. The electrode tab welding method according to any one of claims 5-7, characterized in that, Prepare multiple layers of metal (201) stacked along a third direction, and weld the multiple layers of metal (201) together to obtain the tab (20); the third direction is perpendicular to the first direction and the second direction. Wherein, the thickness of the welded portion of the multilayer metal layer (201) in the third direction before welding is the first thickness, and the thickness of the welded portion of the multilayer metal layer (201) in the third direction after welding is the second thickness. The first thickness is greater than the second thickness. A first thickness preset ratio and a second preset thickness ratio are set, and the second preset thickness ratio is less than the first preset thickness ratio. The ratio of the second thickness to the first thickness is controlled to be no greater than a preset ratio of the first thickness and no less than a preset ratio of the second thickness.

11. The electrode tab welding method according to claim 10, characterized in that, The first preset thickness ratio is 75%~85%, and the second preset thickness ratio is 35%~45%.

12. The electrode tab welding method according to claim 10, characterized in that, Ultrasonic welding is performed by applying pressure to the multiple metal layers (201) using a tooling.

13. The electrode tab welding method according to claim 10, characterized in that, The welded multilayer metal layers (201) are cut to obtain the tabs (20).

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