Laser welding method, battery, welding system, and control device for multi-layer aluminum foil

Abstract

The present disclosure provides a method for welding a multilayer aluminum foil (10) of a battery current collector onto a corresponding structure (20), the method including at least a laser welding operation, which includes at least a spot welding operation using laser pulses to weld the multilayer aluminum foil (10) and a corresponding structure (20) located below the multilayer aluminum foil (10) in the stacking direction of the multilayer aluminum foil (10). Additionally, a corresponding battery, a corresponding laser welding system (40), a corresponding control device (430) for the laser welding system (40), and a corresponding computer program product are also disclosed. According to some exemplary embodiments of the present disclosure, cracks, especially continuous cracks, can be reduced, the multilayer aluminum foil is provided with high resistance to ultrasonic pre-welding processes, and weld strength and the like can be improved.

Description

[Technical Field]

[0001] The present disclosure relates to the field of batteries, in particular to the field of lithium-ion batteries, and in particular to a method for welding a multilayer aluminum foil of a current collector of a battery onto a corresponding structure, a corresponding laser welding system, a corresponding control device for a laser welding system, and a corresponding computer program product.

[0002] Background technology In recent years, with the development of battery technology, the demands on batteries have become increasingly stringent in terms of weight reduction and performance improvement. Currently, lithium-ion batteries have attracted much attention due to their many superior properties compared to other types of batteries, and are increasingly being used in various fields.

[0003] In lithium-ion batteries, multilayer aluminum foil or multilayer copper foil is typically used as a current collector. The current collector collects the current generated by the active material coated on the aluminum foil or copper foil, allowing for higher currents to be generated. In this case, the current generated by the current collector is output through the battery's terminals. For this purpose, an electrical connection must be formed between the current collector and the terminals. Specifically, in lithium-ion batteries, multilayer aluminum foil is typically used as the positive electrode current collector, and multilayer copper foil is typically used as the negative electrode current collector.

[0004] The purpose of using multi-layer aluminum foil in this case is to increase the surface area of ​​the aluminum foil through more layers, so that more active material can be coated onto the surface of the aluminum foil.

[0005] Due to the special structure of the terminals, ultrasonic welding cannot be performed on the multilayer aluminum foil current collector and the terminal. To achieve an effective electrical connection between the multilayer aluminum foil and the terminal, the current-connection technique commonly used is to place a connection-matching sheet between the multilayer aluminum foil and the terminal. Here, the multilayer aluminum foil is connected to the connection-matching sheet by ultrasonic welding, and the connection-matching sheet is then connected to the terminal by laser welding, thereby achieving an indirect connection between the multilayer aluminum foil and the terminal. However, this not only negatively impacts the lightweight production of the battery, but also increases current transmission resistance, thereby degrading battery performance.

[0006] Currently, a technical solution has been proposed that involves removing the connection compatibility sheet and directly welding multilayer aluminum foil to the terminals using laser welding. However, cracks easily occur during the welding process, especially at the boundary of the fusion zone. These cracks significantly reduce the overcurrent (overcharging) capacity and the strength of the weld seam, severely affecting battery performance. This is also due to the thin thickness of the aluminum foil used for current collectors. This means that the aluminum foil near the heat-affected zone of the molten pool is easily deformed at high temperatures. This creates tensile stress during deformation, resulting in poor fluidity of the molten aluminum. As a result, the tensile strength of the resulting liquid film is weakened, making the film prone to cracking. In addition, the surface of aluminum foil is usually covered with an Al2O3 oxide film, which has both a much higher melting point and hardness than pure aluminum substrates. As a result, at least a portion of the oxide film cannot be completely melted during the welding process and accumulates at the edges of the weld seam, significantly increasing the hardness of the weld seam edges and making them more susceptible to cracking. Uneven temperatures and material deformation caused by laser energy input during the welding process also increase the risk of cracking.

[0007] In particular, the weld pool of a continuous, elongated weld seam has a very steep edge profile, which leaves the aluminum foil at the edge of the weld pool severely deformed, and the resulting tensile stress easily causes continuous cracks in the fusion line of the weld pool. Another thing is that a continuous, elongated weld seam has a longer length, so the input welding heat gradually accumulates along the supply direction of the laser beam, causing more severe deformation at the tailing part of the weld seam, so the cracks in the rear part of the weld pool are more obvious.

[0008] Therefore, continuous improvement is required.

[0009] Summary of the Invention In order to overcome one of the aforementioned drawbacks and / or other possible drawbacks present in the prior art but not mentioned herein, it is an object of the present disclosure to provide an improved method for welding a multi-layer aluminum foil of a current collector of a battery onto a corresponding structure, a corresponding laser welding system, a corresponding control device for the laser welding system, and a corresponding computer program product.

[0010] According to a first aspect of the present disclosure, there is provided a method for welding a multilayer aluminum foil of a battery current collector onto a corresponding structure, the method including at least a laser welding operation, which includes at least a spot welding operation for welding the multilayer aluminum foil and the corresponding structure located below the multilayer aluminum foil in the stacking direction of the multilayer aluminum foil together by spot welding using laser pulses. This means that at least spot welding is used regardless of the connection method.

[0011] According to an alternative embodiment of the present disclosure, the battery is a lithium ion battery.

[0012] According to an alternative embodiment of the present disclosure, the corresponding structure is the positive terminal of the battery.

[0013] According to an alternative embodiment of the present disclosure, the corresponding structure is made of aluminum.

[0014] According to an alternative embodiment of the present disclosure, the laser welding operation further includes a continuous welding operation, in which the multi-layer aluminum foil and the corresponding structure are welded together by continuous laser welding. The continuous welding operation and the spot welding operation can be flexibly combined as needed.

[0015] According to an alternative embodiment of the present disclosure, spot welding operations and / or continuous welding operations are performed by BrightLine Weld technology using a coaxial optical fiber, which comprises a core optical fiber and a ring-shaped optical fiber arranged around the core optical fiber, allowing control of the laser welding operation by adjusting the density of energy transmitted by the core optical fiber and / or the ring-shaped optical fiber.

[0016] According to an alternative embodiment of the present disclosure, a core optical fiber is used to increase the depth of the molten pool, and a ring-shaped optical fiber uses a lower energy density relative to the core optical fiber to form a relatively shallow and wide weld area around the irradiated area of ​​the core optical fiber.

[0017] According to an alternative embodiment of the present disclosure, the spot welding operation includes a preheating operation performed using a ring-shaped optical fiber and a subsequent laser spot welding performed using a coaxial optical fiber.

[0018] According to an alternative embodiment of the present disclosure, the spot welding operation includes a laser spot welding performed using a coaxial optical fiber and a subsequent annealing operation performed using a ring-shaped optical fiber.

[0019] According to a second aspect of the present disclosure, there is provided a battery comprising a multilayer aluminum foil and a corresponding structure located below the multilayer aluminum foil in the stacking direction of the multilayer aluminum foil, wherein the multilayer aluminum foil is welded onto the corresponding structure by the method according to any one of the preceding embodiments.

[0020] According to a third aspect of the present disclosure, there is provided a laser welding system comprising: a laser device for generating a laser beam; and a control device for controlling at least the laser device, wherein the laser welding system is configured to be adapted to perform a method according to any one of the preceding embodiments.

[0021] According to a fourth aspect of the present disclosure, there is provided a controller for a laser welding system, wherein the controller is configured to be adapted to perform a method according to any one of the preceding embodiments.

[0022] According to a fifth aspect of the present disclosure, there is provided a computer program product including or having stored thereon computer program instructions which, when executed by a processor, implements a method according to any one of the preceding embodiments.

[0023] According to some exemplary embodiments of the present disclosure, cracks, especially continuous cracks, can be reduced, and high resistance to ultrasonic pre-welding processes of multi-layer aluminum foils is provided, improving weld strength, etc.

[0024] The principles, features, and advantages of the present disclosure may be better understood by describing the disclosure in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 shows an example of a battery in a schematic partial cross-sectional view. [Figure 2] FIG. 1 illustrates an exemplary embodiment of a laser welding system in a schematic perspective view. [Figure 3] FIG. 1 shows a schematic diagram of a continuous elongated weld seam on a multi-layer aluminum foil. [Figure 4] FIG. 1 shows a schematic diagram of the path of the laser beam during continuous laser welding in a top view of a multi-layer aluminum foil. [Figure 5]FIG. 4 is a top view similar to FIG. 3, illustrating a schematic diagram of a method for welding a multilayer aluminum foil of a current collector of a battery onto a corresponding structure according to an exemplary embodiment of the present disclosure. [Figure 6] 6 shows a schematic cross-sectional view through the weld spot joint taken along section line AA in FIG. 5. FIG. [Figure 7] 10A-10C illustrate combined weld spot joint and continuous weld seam layouts according to different exemplary embodiments of the present disclosure. [Figure 8] 10A-10C illustrate combined weld spot joint and continuous weld seam layouts according to different exemplary embodiments of the present disclosure. [Figure 9] 10A-10C illustrate combined weld spot joint and continuous weld seam layouts according to different exemplary embodiments of the present disclosure.

[0026] MODE FOR CARRYING OUT THE INVENTION In order to make the technical problems, technical solutions, and advantageous technical effects of the present disclosure more clearly understandable, the present disclosure will be described in more detail below in conjunction with drawings and a number of exemplary embodiments. It should be understood that the specific embodiments described herein do not limit the protection scope of the present disclosure, but are merely for illustrating the present disclosure.

[0027] Before starting the description, it should be noted at the outset that in describing the embodiments, orientations or positional relationships such as "upper" and "lower" are used with respect to orientations or positional relationships shown in the drawings, and do not indicate or imply that the referred-to devices or elements must have a particular orientation or be configured and operated in a particular orientation, but are used only to facilitate explanation and simplify illustration, and therefore cannot be simply and indiscriminately construed as limitations on the present disclosure unless technically necessary.

[0028] FIG. 1 shows an example of a battery in a schematic, partial cross-sectional view. The battery shown here is a lithium-ion battery. However, those skilled in the art will understand that the technical concept of the present disclosure is not limited to lithium-ion batteries but is also applicable to other types of batteries, such as sodium-ion batteries. Furthermore, the technical concept of the present disclosure is not limited to prismatic batteries but is also applicable to similar welded seam structures in pouch batteries, cylindrical batteries, or batteries of other structures. A lithium-ion battery cell is formed, for example, by a multilayer laminate structure consisting of aluminum foil, a separator, and copper foil, with other materials necessary for battery manufacturing intermixed therein. These are well known to those skilled in the art and are not the focus of this disclosure, so they will not be described in further detail here. These aluminum foil layers are typically produced by rolling and are very thin. In a battery, the multilayer aluminum foil may protrude from one end of the cell and be pre-welded, for example, ultrasonically, to form a positive current collector. The positive current collector comprises any suitable number of layers of multilayer aluminum foil 10, such as 20 to 130 layers. The positive electrode of the battery further comprises, for example, a positive terminal and a positive tab. The positive electrode current collector generally needs to be connected to a positive terminal, and in some cases may also need to be connected to a positive tab or other component of the battery. Such connection is usually established by welding. Specifically, the multilayer aluminum foil 10 is welded by a laser beam to a corresponding structure 20 (typically aluminum), such as a positive terminal, located below the multilayer aluminum foil 10 in the stacking direction of the multilayer aluminum foil 10, thereby forming a weld seam 30.

[0029] FIG. 2 shows an exemplary embodiment of a laser welding system 40 in a schematic perspective view. The laser welding system 40 may be used, for example, to weld the multilayer aluminum foil 10 of the positive current collector of the battery shown in FIG. 1 to a corresponding structure 20. The laser welding system 40 may include, for example, a laser device 420 for generating a laser beam 410 and a control device 430 for controlling at least the laser device 420. The laser welding system 40 may further include a bearing platform (schematically shown as a plane in FIG. 2) for supporting the object to be welded (in this case, the multilayer aluminum foil 10 and the corresponding structure 20) and / or a fixture for clamping the object to be welded. The bearing platform and / or fixture may be fixed or movable. The control device 430 may also control the movement of the bearing platform and / or fixture as needed. The laser device 420 may include, for example, a galvanometer scanner, particularly a PFO (Programmed Focus Optical).

[0030] Currently, when welding the multilayer aluminum foil 10 of the battery current collector shown in FIG. 1 to a corresponding structure 20, typically only a weld seam 30 such as that shown in FIG. 3 is used, with its length-to-width ratio set for clarity, and the actual width being much smaller than the length. To form such a weld seam 30, a laser beam 410 is typically moved relative to the multilayer aluminum foil 10 along a linear path 310 as shown in FIG. 4. Here, FIGS. 3 and 4 are top views of the multilayer aluminum foil 10, for example. Corresponding structures 20 located below the multilayer aluminum foil 10 and that may protrude beyond the edge of the multilayer aluminum foil 10 are omitted for clarity. In FIG. 4, when the weld seam 30 is being formed, the feed direction 320 (i.e., the general direction of movement of the laser head relative to the workpiece) is, for example, from left to right, as indicated by the arrow. Because the width of the weld seam 30 across the feed direction 320 is narrow, the cross section of the resulting weld pool is roughly U-shaped, as shown in FIG. 1, for example. Here, the cross section of the weld pool refers to the cross section of the weld seam 30 perpendicular to the feed direction 320, and the plane on which the cross section lies is shown schematically by the dotted line in Figure 4. Since aluminum foil typically has a thickness of 8 to 13 microns, it can be seen, in combination with the explanation in the Background Art section, that cracks may appear at both ends of the weld seam 30 in the width direction.

[0031] FIG. 5 shows, in a top view similar to FIG. 3, a schematic diagram of a method for welding a multilayer aluminum foil 10 of a battery current collector onto a corresponding structure 20 according to an exemplary embodiment of the present disclosure.

[0032] As shown in Figure 5, the welding is performed in the form of laser spot welding, in which laser pulses are used for welding to form a weld spot joint 50 through which the multilayer aluminum foil 10 of the battery current collector is connected to the corresponding structure 20. Figure 6 shows a schematic cross-sectional view through the weld spot joint 50 cut along the section line AA in Figure 5.

[0033] As shown in Figure 6, it can be seen that cracks 510 actually occur only at a specific depth of each weld spot joint 50 around the circumference of the weld spot joint 50. This prevents continuous cracks from being observed in the stress direction of the peel test, increasing the peel strength.

[0034] Those skilled in the art will also understand that, compared to a weld seam 30 that is only a continuous strip, as shown in Figures 3 and 4, the use of spot welding can increase the stress area per unit weld area, thereby further improving peel strength. Furthermore, as shown in Figures 3 and 4, if the weld seam 30 is only a continuous strip, when a crack occurs at the outer edge of the weld seam, all of the aluminum foil layers will easily peel off, making the entire peeling process quick and difficult to complete. However, with spot welding, the weld strength of each weld spot joint is independent, effectively improving weld strength.

[0035] Furthermore, the spot welding method has high resistance to the ultrasonic pre-welding process of the multi-layer aluminum foil 10. In other words, even if a large gap occurs during the ultrasonic pre-welding process, it does not have a significant effect on the weld strength of the subsequent weld.

[0036] In addition, compared to continuous laser welding, welding using laser pulses can also significantly reduce the overall heat input, thereby reducing deformation of the aluminum foil at high temperatures and further reducing the formation of cracks, especially continuous cracks.

[0037] While the advantages of using spot welding in the present disclosure have been outlined above, those skilled in the art will understand that the actual advantages may not be limited to these. In any case, the spot welding method of the present disclosure fully considers and matches the characteristics of the multi-layer aluminum foil 10 and the characteristics of laser welding, something that has never been achieved before.

[0038] As shown in Figure 5, several rows of weld spot joints 50 are shown, with each of the weld spot joints 50 separated from one another without touching. Specifically, three horizontal rows of weld spot joints 50 are shown in Figure 5, with the weld spot joints 50 being approximately evenly distributed within a weld area 520. The weld area 520 is indicated schematically in Figure 5 by a dashed block 530. A "weld area" can be understood as the area defined by the outermost edges of each weld site, such as each weld spot joint 50.

[0039] 5 merely shows a schematic example of the layout of the weld spot joints 50, and in practice the layout of the weld spot joints 50 can be designed according to specific conditions such as the welding area. For example, in practice, if it is found that the area through which current flows is insufficient, it is possible to increase the number, i.e., density, of the weld spot joints in the determined welding area to meet that requirement.

[0040] Furthermore, those skilled in the art will understand that although the welding area in Figure 5 is welded only through the weld spot joints 50, the actual situation is not limited to this. For example, it is also possible to weld the multi-layer aluminum foil 10 to the corresponding structure 20 using a combination of continuous laser welding (i.e., the continuous laser weld seam shown in Figures 3 and 4) and laser pulse spot welding (Figure 5). In particular, if it is found that the area through which current flows is still insufficient after increasing the weld spot joints 50, an auxiliary continuous laser welding operation can be performed to meet the requirement.

[0041] Those skilled in the art can understand that the existing problems of the prior art can also be alleviated even if spot welding is used only in one portion within the welding area, and other portions are still welded by continuous welding or other types of welding (or other possible connections). Therefore, the present disclosure does not limit the number of weld spot joints.

[0042] 7, 8 and 9 show combined layouts of weld spot joints 50 and continuous weld seams 30 according to different exemplary embodiments of the present disclosure, but the actual situation is not limited thereto.

[0043] The applicant's BrightLine Welding technology can be used for welding, particularly spot welding. This technology is protected by the applicant's related patents. BrightLine Welding employs a "2-in-1" optical fiber, in which a laser source simultaneously directs laser light to a core optical fiber and a ring-shaped optical fiber arranged around the core optical fiber. Since the two laser beams act together in the processing area, the energy density can be adjusted within the cross section of the laser beam, for example, it is possible to adjust the energy density of the core and the outer ring (e.g., a circular ring) within the cross section of the laser beam.

[0044] According to an exemplary embodiment of the present disclosure, in the BrightLine Welding technology, the core optical fiber can play a role in increasing the depth of the molten pool, while the ring-shaped optical fiber uses a relatively low energy density to further form a shallow and wide weld area around the irradiated area of ​​the core optical fiber, thereby achieving equal preheating and slow cooling to further reduce cracks caused by shrinkage of the aluminum foil after welding.

[0045] According to an exemplary embodiment of the present disclosure, in the BrightLine Welding technique, the ring-shaped optical fiber may be first used for pre-welding, followed by the actual welding operation, which means that at least the core optical fiber is used for welding. Using the ring-shaped optical fiber for pre-heating before welding can reduce cracks.

[0046] According to an exemplary embodiment of the present disclosure, BrightLine Welding technology also allows for rewelding using a ring-shaped optical fiber after the proper welding, thereby enabling a slow cooling process after welding and reducing cracking.

[0047] Additionally, the methods of the present disclosure can be implemented using, for example, the controller 430 of Figure 2, which can include or store a corresponding computer program product including computer program instructions that, when executed by, for example, a processor, control the laser welding system 40 of Figure 2 to implement the methods described above. The computer program product can be on a computer-readable program carrier.

[0048] While particular embodiments of the present disclosure have been described in detail herein, they have been presented for purposes of illustration and should not be construed as limiting the scope of the disclosure. Various substitutions, changes, and modifications can be devised without departing from the spirit and scope of the disclosure.

Claims

1. A method for welding a multilayer aluminum foil (10) of a battery current collector onto a corresponding structure (20), comprising: a laser welding operation including at least a spot welding operation in which the multilayer aluminum foil (10) and the corresponding structure (20) located below the multilayer aluminum foil (10) in the stacking direction of the multilayer aluminum foil (10) are welded together by spot welding using laser pulses. The method includes at least

2. the battery is a lithium ion battery, and / or said corresponding structure (20) being the positive terminal of said battery; and / or said corresponding structure (20) being made of aluminium; The method of claim 1.

3. The laser welding operation further comprises a continuous welding operation in which the multilayer aluminum foil (10) and the corresponding structure (20) are welded together by continuous laser welding.

3. The method according to claim 1 or 2.

4. the spot welding operation and / or the continuous welding operation is performed by a BrightLine Weld technique using a coaxial optical fiber, the coaxial optical fiber comprising a core optical fiber and a ring-shaped optical fiber arranged around the core optical fiber, and the laser welding operation can be controlled by adjusting the density of energy transmitted by the core optical fiber and / or the ring-shaped optical fiber.

4. The method according to any one of claims 1 to 3.

5. The core optical fiber is used to increase the depth of the molten pool, and the ring-shaped optical fiber uses a lower energy density on the core optical fiber to form a relatively shallow and wide weld area around the irradiation area of ​​the core optical fiber. The method of claim 4.

6. the spot welding operation includes a preheating operation performed using the ring-shaped optical fiber and a subsequent laser spot welding performed using the coaxial optical fiber; The method of claim 4.

7. the spot welding operation includes laser spot welding performed using the coaxial optical fiber and a subsequent annealing operation performed using the ring-shaped optical fiber; The method of claim 4.

8. A multilayer aluminum foil (10), a corresponding structure (20) located under the multilayer aluminum foil (10) in the stacking direction of the multilayer aluminum foil (10); Equipped with The multilayer aluminum foil (10) is welded onto the corresponding structure (20) by a method according to any one of claims 1 to 7. battery.

9. A laser welding system (40) comprising: a laser device (420) for generating a laser beam (410); a control device (430) for controlling at least the laser device (420); Equipped with The laser welding system (40) is configured to be adapted to perform the method according to any one of claims 1 to 7. A laser welding system (40).

10. A control device (430) for a laser welding system (40), comprising: The control device (430) is configured to be adapted to perform the method according to any one of claims 1 to 7. A controller (430) for a laser welding system (40).

11. A computer program product comprising or storing computer program instructions which, when executed by a processor, implements the method of any one of claims 1 to 7.

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