Laser welding method, battery, welding system, and control device for multilayer 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, particularly to the field of lithium-ion batteries, and specifically to a method for welding a multilayer aluminum foil of a battery current collector onto a corresponding structure, a corresponding laser welding system, a corresponding control device for the laser welding system, and a corresponding computer program product.

[0002] Background Art In recent years, with the development of battery technology, the requirements for batteries have become increasingly strict from the perspectives of weight reduction and high performance. Currently, lithium-ion batteries are attracting great attention because they have excellent characteristics in many aspects, especially when compared with other types of batteries, and are being increasingly used in various fields.

[0003] In the case of lithium-ion batteries, multilayer aluminum foil or multilayer copper foil is typically used as the current collector. The current collector can collect the current generated by the active material coated on the aluminum foil or copper foil and form a higher current. In this case, the current formed by the current collector is output through the terminals of the battery. For this purpose, it is necessary to form an electrical connection between the current collector and the terminals. Specifically, in lithium-ion batteries, usually, multilayer aluminum foil is used as the positive current collector, and multilayer copper foil is used as the negative current collector.

[0004] The purpose of using multilayer aluminum foil in this case is to increase the surface area of the aluminum foil through more layers, and as a result, more active material can be coated on 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 of the current collector and the terminals. To achieve an effective electrical connection between the multilayer aluminum foil and the terminals, the currently common practice is to place a connection-fitting sheet between the multilayer aluminum foil and the terminals. Here, the multilayer aluminum foil is connected to the connection-fitting sheet by ultrasonic welding, and the connection-fitting sheet is connected to the terminals by laser welding, thereby achieving an indirect connection between the multilayer aluminum foil and the terminals. However, this not only negatively impacts the lightweight production of the battery but also increases current transmission resistance. In other words, it degrades the battery's performance.

[0006] Currently, a technical solution has been proposed in which the connection fitting sheet is removed and multi-layer aluminum foil is directly welded to the terminal by laser welding. However, cracks easily occur during the welding process, especially at the boundaries of the molten zone. These cracks significantly reduce the overcurrent (overcharge) capacity and the strength of the weld seam, severely affecting the battery performance. This is also due to the thinness of the aluminum foil used for the current collector, which causes the aluminum foil near the heat-affected zone of the molten pool to easily deform at high temperatures. Consequently, tensile stress is superimposed during deformation, reducing the fluidity of the molten aluminum. As a result, the tensile strength of the formed liquid film is weakened, and the film easily cracks under the action of tensile stress. In addition, the surface of the aluminum foil is usually covered with an Al2O3 oxide film, which has both a much higher melting point and hardness than pure aluminum substrates. Consequently, at least a portion of the oxide film cannot completely melt 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 temperature and material deformation caused by laser energy input during the welding process also increase the risk of cracking.

[0007] In particular, the molten pool of a continuous, elongated weld seam has a very steep edge profile, leaving the aluminum foil severely deformed at the edge of the molten pool. The resulting tensile stress easily causes continuous cracks in the melting line of the molten pool. Alternatively, continuous, elongated weld seams have a longer length, and therefore the input welding heat gradually accumulates along the direction of the laser beam supply, causing more severe deformation at the tailing portion of the weld seam, making cracks in the rear of the molten pool even more apparent.

[0008] Therefore, continuous improvement is required.

[0009] Summary of the Invention To overcome the aforementioned shortcomings and / or other possible shortcomings present in the prior art but not mentioned herein, the object of this disclosure is to provide an improved method for welding multilayer aluminum foil of a battery current collector 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, a method is provided for welding multilayer aluminum foil of a battery current collector onto a corresponding structure, the method comprising at least a laser welding operation, which includes at least a spot welding operation in which the multilayer aluminum foil and the corresponding structure located beneath the multilayer aluminum foil in the lamination direction of the multilayer aluminum foil are welded to each other by spot welding using laser pulses. This means that at least spot welding is used regardless of the connection method.

[0011] According to alternative embodiments 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 a battery.

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

[0014] According to alternative embodiments of the present disclosure, the laser welding operation further includes a continuous welding operation in which multilayer aluminum foil and corresponding structures are welded to each other by continuous laser welding. The continuous welding operation and spot welding operation can be flexibly combined as needed.

[0015] According to alternative embodiments of the present disclosure, spot welding and / or continuous welding operations are performed by BrightLine Weld technology 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 is controlled by adjusting the energy density transmitted by the core optical fiber and / or the ring-shaped optical fiber.

[0016] According to alternative embodiments of the present disclosure, 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 than the core optical fiber to form a relatively shallow and wide weld area around the irradiation 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 operation performed using a coaxial optical fiber.

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

[0019] A second aspect of the present disclosure provides a battery comprising a multilayer aluminum foil and a corresponding structure located beneath the multilayer aluminum foil in the lamination direction of the multilayer aluminum foil, wherein the multilayer aluminum foil is welded onto the corresponding structure by a method described in any one of the above embodiments.

[0020] A third aspect of the present disclosure provides 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 carry out the method described in any one of the above embodiments.

[0021] A fourth aspect of the present disclosure provides a control device for a laser welding system, the control device being configured to be adapted to carry out the method described in any one of the embodiments described above.

[0022] According to a fifth aspect of the present disclosure, a computer program product is provided which, when executed by a processor, includes or stores computer program instructions that implement the method described in any one of the embodiments described above.

[0023] According to some exemplary embodiments of this disclosure, cracks, particularly continuous cracks, can be reduced, providing high resistance to ultrasonic pre-welding processes for multilayer aluminum foil, and improving weld strength, etc.

[0024] The principles, characteristics, and advantages of this disclosure can be better understood by describing this disclosure in more detail with reference to the accompanying drawings. [Brief explanation of the drawing]

[0025] [Figure 1] This figure shows an example of a battery in a schematic partial cross-sectional view. [Figure 2] This diagram shows an exemplary embodiment of a laser welding system in a schematic perspective view. [Figure 3] This diagram schematically shows a continuous, elongated weld seam on a multilayer aluminum foil. [Figure 4] This diagram schematically shows the path of the laser beam during continuous laser welding in a top view of multilayer aluminum foil. [Figure 5]In a top view similar to FIG. 3, it is a diagram schematically showing a schematic view 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] It is a diagram schematically showing a cross-sectional view passing through a weld spot joint cut along the section line A-A of FIG. 5. [Figure 7] It is a diagram showing a combination of the layouts of a weld spot joint and a continuous weld seam according to different exemplary embodiments of the present disclosure. [Figure 8] It is a diagram showing a combination of the layouts of a weld spot joint and a continuous weld seam according to different exemplary embodiments of the present disclosure. [Figure 9] It is a diagram showing a combination of the layouts of a weld spot joint and a continuous weld seam according to different exemplary embodiments of the present disclosure.

[0026] Mode for Carrying Out the Invention In order to more clearly understand the technical problem to be solved, the technical solution, and the advantageous technical effects of the present disclosure, the present disclosure will be described in more detail below in conjunction with the drawings and a number of exemplary embodiments. It should be understood that the specific embodiments described in this specification are not intended to limit the protection scope of the present disclosure, but are merely for explaining the present disclosure.

[0027] Before starting the description, in the description of the embodiments, the orientation or positional relationship such as "upper" and "lower" is used with respect to the orientation or positional relationship shown in the drawings, and it does not indicate or imply that the mentioned device or element must have a specific orientation or must be configured and operated in a specific orientation. It should be noted first that it is only used for facilitating the explanation and simplifying the illustration, and thus, it cannot be simply and indifferently interpreted as a limitation to the present disclosure unless technically necessary.

[0028] Figure 1 shows an example of a battery in a schematic partial cross-sectional view. The battery is, in this example, a lithium-ion battery. However, those skilled in the art will understand that the technical idea of ​​this disclosure is not limited to lithium-ion batteries but is applicable to other types of batteries, such as sodium-ion batteries. Furthermore, the technical idea of ​​this disclosure is not limited to prismatic batteries but is applicable to pouch batteries, cylindrical batteries, or similar welded seam structures of batteries of other structures. The cells of a lithium-ion battery are formed by a multilayer laminate structure consisting, for example, aluminum foil-diaphragm-copper foil, with other materials necessary for the manufacture of the battery mixed in between. 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 made by rolling and are very thin. In the battery, the multilayer aluminum foil can protrude, for example, from one end of the cell and be pre-welded, for example, by ultrasound, to form a positive electrode current collector. The positive electrode current collector comprises any suitable number of multilayer aluminum foil layers 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 the positive terminal, and in some cases, it may also need to be connected to the positive tab or other components of the battery. Such connections are usually established by welding. Specifically, the multilayer aluminum foil 10 is welded by laser beam to a corresponding structure 20 (typically aluminum), such as the positive terminal, located beneath the multilayer aluminum foil 10 in the lamination direction of the multilayer aluminum foil 10, thereby forming a weld seam 30.

[0029] Figure 2 shows an exemplary embodiment of the laser welding system 40 in a schematic perspective view. The laser welding system 40 is used, for example, to weld the multilayer aluminum foil 10 of the positive electrode current collector of a battery shown in Figure 1 to a corresponding structure 20. The laser welding system 40 comprises, 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 (Schematicically shown as a plan in Figure 2) for supporting the workpiece to be welded (in this case, the multilayer aluminum foil 10 and the corresponding structure 20) and / or fixtures for clamping the workpiece to be welded. The bearing platform and / or fixtures may be fixed or movable. The control device 430 can also control the movement of the bearing platform and / or fixtures as needed. The laser device 420 may include, for example, a galvanometer scanner, and in particular, a Programming Focus Optical (PFO).

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

[0031] Figure 5 schematically shows, in a top view similar to Figure 3, 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 using a laser spot welding method, in which laser pulses are used to weld a spot joint 50, through which the multilayer aluminum foil 10 of the battery's current collector is connected to the corresponding structure 20. Figure 6 schematically shows a cross-sectional view through the spot joint 50 cut along the cross-sectional line AA of Figure 5.

[0033] As shown in Figure 6, it can be seen that in reality, the cracks 510 occur only at specific depths around each weld spot joint 50 on the outer circumference of the weld spot joint 50. This prevents the observation of continuous cracks in the stress direction of the peel test and increases the peel strength.

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

[0035] Furthermore, the spot welding method has high resistance to the ultrasonic pre-welding process of the multilayer aluminum foil 10. In other words, even if a large gap occurs during the ultrasonic pre-welding process, it does not significantly affect the welding 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 this disclosure are outlined above, those skilled in the art will understand that the actual advantages are not limited thereto. In any case, the spot welding method of this disclosure takes into full consideration the properties of the multilayer aluminum foil 10 and the properties of laser welding, and matches them, something that no one has ever achieved before.

[0038] As shown in Figure 5, several rows of weld spot joints 50 are shown, each of which is separated from one another without contact. Specifically, three horizontal rows of weld spot joints 50 are shown in Figure 5, and these weld spot joints 50 are distributed approximately evenly within the welding area 520. The welding area 520 is schematically shown in Figure 5 by dashed block 530. The "welding area" can be understood as the region defined by the outermost edge of each weld, such as each weld spot joint 50.

[0039] Similarly, Figure 5 is merely a schematic representation of one 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, if it is found that there is insufficient area for current to flow, 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 welding spot joints 50, the actual situation is not limited to this. For example, it is also possible to weld the multilayer aluminum foil 10 to the corresponding structure 20 using a combination of continuous laser welding (i.e., the continuous laser welding seams shown in Figures 3 and 4) and laser pulsed spot welding (Figure 5). In particular, if it is found that the area through which current flows is still insufficient after increasing the welding spot joints 50, auxiliary continuous laser welding work can be performed to meet that requirement.

[0041] Those skilled in the art will understand that even when spot welding is used on only one part of a welding area, and other parts are still welded by continuous welding or other types of welding (or other possible connections), existing problems of the prior art can be mitigated. Therefore, this disclosure does not limit the number of welded spot joints.

[0042] Figures 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 actual situations are 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 the laser source simultaneously directs the laser into a core optical fiber and a ring-shaped optical fiber arranged around the core optical fiber. Since the two laser beams act together within 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 outer ring (e.g., a circular ring) within the cross-section of the laser beam.

[0044] According to exemplary embodiments of the present disclosure, in 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, using a relatively low energy density, further forms 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 cracking caused by shrinkage of the aluminum foil after welding.

[0045] According to exemplary embodiments of the present disclosure, in BrightLine Welding technology, the ring-shaped optical fiber may be used first for pre-welding, followed by the formal welding operation, meaning that at least the core optical fiber is used for welding. Using the ring-shaped optical fiber for preheating before welding can reduce cracking.

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

[0047] In addition, the method of the present disclosure can be implemented, for example, using the control device 430 of Figure 2, which may include or store a corresponding computer program product that, when executed by a processor, controls the laser welding system 40 of Figure 2 to implement the method described above. The computer program product may also be a computer-readable program carrier.

[0048] While specific embodiments of this disclosure have been described in detail here, they are presented for illustrative purposes only and should not be construed as limiting the scope of this disclosure. Various substitutions, changes, and modifications can be devised without departing from the spirit and scope of this disclosure.

Claims

1. A method for welding a multilayer aluminum foil (10) of a battery current collector onto a corresponding structure (20), A laser welding operation comprising 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 lamination direction of the multilayer aluminum foil (10) are welded to each other by spot welding using laser pulses to form weld spots (50). It includes at least, The laser welding operation further includes a continuous welding operation in which the multilayer aluminum foil (10) and the corresponding structure (20) are welded to each other by continuous laser welding. The spot welding and / or continuous welding operations are performed by BrightLine Weld technology 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 is controlled by adjusting the energy density transmitted by the core optical fiber and / or the ring-shaped optical fiber. The core optical fiber is used to increase the depth of the molten pool, and the ring-shaped optical fiber uses a relatively lower energy density than the core optical fiber to form a relatively shallow and wide weld area around the irradiation area of ​​the core optical fiber. The current collector is formed by an ultrasonic pre-welding process preceding the laser welding operation. method.

2. The battery is a lithium-ion battery, and / or The corresponding structure (20) is the positive electrode of the battery, and / or The corresponding structure (20) is made of aluminum. The method according to claim 1.

3. The spot welding operation includes a preheating operation performed using the ring-shaped optical fiber and a subsequent laser spot welding operation performed using the coaxial optical fiber. The method according to claim 1 or 2.

4. The spot welding operation includes laser spot welding performed using the coaxial optical fiber and a subsequent slow cooling operation performed using the ring-shaped optical fiber. The method according to claim 1 or 2.

5. A laser welding system (40), A laser device (420) for generating a laser beam (410), At least a control device (430) for controlling the laser device (420) and Equipped with, The laser welding system (40) is configured to be adapted to carry out the method described in claim 1 or 2. Laser welding system (40).

6. A control device (430) for a laser welding system (40), The control device (430) is configured to be adapted to carry out the method described in claim 1 or 2. A control device (430) for a laser welding system (40).

7. A computer program product that, when executed by a processor, includes or stores computer program instructions that implement the method according to claim 1 or 2.

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