Laser welding method, welding system, control device, program product and battery

Abstract

The application proposes a method for welding a multilayer aluminum foil of a current collector of a battery on a corresponding part, wherein the method comprises at least the following steps: a welding step, in which the multilayer aluminum foil and the corresponding part under the multilayer aluminum foil along the stacking direction of the multilayer aluminum foil are welded by a laser beam to form a weld seam, wherein the length of the weld seam along the feeding direction when the weld seam is formed is less than the width of the weld seam transverse to the feeding direction. The application also relates to a laser welding system, a control device, a computer program product, and a battery. The advantage of the application is that by changing the welding feeding direction from the longitudinal direction of the conventional weld seam to the short direction of the special welding track, the energy at the connection between the weld seam and the foil can be conveniently controlled by setting the energy slow rise and slow fall at the light emitting and light receiving positions of the laser, so as to reduce the cracks on the fusion line.

Description

Technical Field

[0001] This invention relates to a method for welding multilayer aluminum foil current collectors of a battery onto corresponding components, a laser welding system, a control device for the laser welding system, a computer program product, and a battery. The invention particularly relates to lithium-ion batteries and the field of laser welding. Background Technology

[0002] Due to the superior performance of lithium-ion batteries compared to other batteries in various aspects, their application in various fields is becoming increasingly widespread.

[0003] In lithium-ion batteries, the positive electrode consists of a current-collecting electrode composed of lithium cobalt oxide (or lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium iron phosphate, etc.) and aluminum foil, while the negative electrode consists of a current-collecting electrode composed of graphitized carbon material and copper foil. Aluminum foil is also used as the current collector for the positive electrode. Multilayer aluminum foil is used here to obtain a larger aluminum foil surface area through more layers, thereby allowing for the coating of more active material onto the aluminum foil surface. To manufacture the battery, the multilayer aluminum foil needs to be effectively connected to the terminals. Because the aluminum foil is very thin, ultrasonic welding is usually preferred. However, the shape of the terminals is often irregular, so a common practice is to add an adapter plate between the aluminum foil and the terminals. First, the multilayer aluminum foil and the adapter plate are connected by ultrasonic welding, and then the adapter plate, which is less prone to welding cracks, is connected to the terminals by laser welding.

[0004] However, for the sake of lightweight battery cells and supercharging, the current requirement is to eliminate the adapter plate, which necessitates directly welding multiple layers of aluminum foil to the terminals. But thin aluminum foil is very prone to cracking during welding, especially at the interface edges of the molten zone. This is mainly because: the aluminum foil surface is often covered with an Al2O3 oxide layer, whose melting point and hardness are much higher than the base material, pure aluminum. This causes some of the oxide layer to not completely melt during welding and accumulate at the weld edge, significantly increasing the hardness of the weld edge and making it prone to cracking; the aluminum foil is very thin, and the aluminum foil near the heat-affected zone of the molten pool is prone to huge deformation under high temperatures, and the tensile stress generated during this process also increases the risk of cracking in the molten pool; uneven heating and cooling and material deformation caused by laser energy input during welding also increase the risk of cracking.

[0005] Furthermore, because the weld seam is elongated along the feed direction, the molten pool is U-shaped in the cross-section perpendicular to the feed direction, meaning the edge profile of the molten pool is very steep. This results in severe deformation of the aluminum foil at the edge of the molten pool, and the resulting tensile stress makes the fusion line of the molten pool extremely prone to continuous cracking. On the other hand, the relatively long length of the weld seam along the feed direction causes the welding heat input to accumulate continuously along the feed direction of the laser beam, resulting in increasingly greater deformation in the later section of the weld seam, thus making cracking of the molten pool in the later section more pronounced. Summary of the Invention

[0006] The purpose of this invention is to provide a method for welding a multilayer aluminum foil current collector of a battery onto a corresponding component, thereby reducing cracking and providing a high-strength, high-quality weld when welding multilayer aluminum foil.

[0007] According to a first aspect of the present invention, a method is provided for welding a multilayer aluminum foil current collector of a battery onto a corresponding component, wherein the method comprises at least the following steps:

[0008] The welding step involves welding the multilayer aluminum foil and a corresponding component located beneath the multilayer aluminum foil along its stacking direction using a laser beam to form a weld. The length of the weld along the feed direction during weld formation is less than the width of the weld transverse to the feed direction. Here, "corresponding component" should be understood in particular as any component of the battery to be welded to the multilayer aluminum foil. "Stacking direction" is specifically understood as a direction perpendicular to the plane of extension of the multilayer aluminum foil, along which the multilayer aluminum foil is stacked. "Corresponding component located beneath the multilayer aluminum foil along its stacking direction" is specifically understood as the corresponding component located below the lowest layer of the multilayer aluminum foil. "Weld" should be specifically understood as the entire area of ​​the object to be welded where solid-liquid and liquid-solid transitions occur due to welding, rather than the trajectory of the laser beam across the multilayer aluminum foil. "Feed direction during weld formation" should be specifically understood as the feed direction of the laser beam relative to the object to be welded, particularly the multilayer aluminum foil and the corresponding component, during weld formation. The feeding of the laser beam relative to the object to be welded can be accomplished by the movement of the laser beam along the feed direction while the object remains stationary, or by a combined feeding motion of the object and the laser beam, or even by the movement of the object along the feed direction while the laser beam remains stationary. "Feed" should be understood in particular as being independent of the oscillation of the laser beam.

[0009] According to an optional embodiment of the invention, the weld is elongated when viewed along its width. "Elongated" is understood, for example, as a shape with an aspect ratio of 4:1 or greater.

[0010] According to an alternative embodiment of the invention, the laser beam travels along a zigzag path relative to the surface of the multilayer aluminum foil to form the weld.

[0011] According to an alternative embodiment of the invention, the weld is formed by a combination of scanning along the feed direction and oscillations of the laser beam transverse to the feed direction. The oscillations are particularly perpendicular to the feed direction.

[0012] According to an optional embodiment of the present invention, the battery is a lithium-ion battery.

[0013] According to an optional embodiment of the present invention, the corresponding component is the positive terminal of the battery.

[0014] According to an optional embodiment of the invention, the length of the weld is 2 mm to 6 mm.

[0015] According to an optional embodiment of the invention, the width of the weld is 20 mm to 60 mm.

[0016] According to an optional embodiment of the present invention, the average moving speed of the focal spot of the laser beam on the multilayer aluminum foil is more than 2 meters per second.

[0017] According to an optional embodiment of the invention, the power of the laser beam is lower at both ends of the weld than at the middle of the weld, in terms of the length of the weld. Here, "both ends" is understood, for example, as regions occupying, for example, 1 / 3 or 1 / 4 of the length of the weld, starting from the outermost endpoint of the weld's length.

[0018] According to an optional embodiment of the invention, the power of the laser beam decreases linearly towards the endpoints of the weld at both ends.

[0019] According to an optional embodiment of the present invention, the welding step is performed by laser high-frequency oscillation continuous scanning.

[0020] According to an optional embodiment of the invention, the welding step is performed using a scanning galvanometer.

[0021] According to a second aspect of the present invention, a laser welding system is provided, comprising at least: a laser device for generating a laser beam; and at least a control device for controlling the laser device; wherein the laser welding system is configured to perform the aforementioned method.

[0022] According to a third aspect of the invention, a control device for a laser welding system is provided, wherein the control device is configured to perform the aforementioned method.

[0023] According to a fourth aspect of the present invention, a computer program product is provided, wherein the computer program product includes computer program instructions that, when executed by a processor, implement the aforementioned method.

[0024] According to a fifth aspect of the invention, a battery is provided, wherein the multiple layers of aluminum foil for the current collector of the battery are welded by the aforementioned method.

[0025] The positive effects of this invention are as follows: By employing a special welding trajectory that changes the laser beam welding feed direction from the longitudinal direction of the traditional weld to a narrow and short direction, the energy at the weld and foil connection can be easily controlled by setting the gradual increase and decrease of energy at the laser initiation and termination points, thereby reducing cracks on the fusion line. This welding trajectory can ultimately optimize the shape of the molten pool from a "U" shape to a "V" shape, releasing the stress in the heat-affected zone of the weld. At the same time, the larger opening at the top of the molten pool facilitates gas escape, reducing porosity. Attached Figure Description

[0026] The invention will now be described in more detail with reference to the accompanying drawings, which will provide a better understanding of its principles, features, and advantages. The drawings include:

[0027] Figure 1 An example of a battery is shown in a schematic partial cross-sectional view.

[0028] Figure 2 An example of a laser welding system is illustrated schematically.

[0029] Figure 3 The schematic diagram illustrates the overall shape of the weld.

[0030] Figure 4 The laser beam trajectory according to the conventional method is schematically shown from a top-down view of a multilayer aluminum foil.

[0031] Figure 5 An example of a laser beam trajectory according to the method of the present invention is schematically shown from a top-down view of a multilayer aluminum foil.

[0032] Figure 6 The illustration shows the press Figure 5 The trajectory shown represents the shape of the weld pool in the cross-section.

[0033] Figure 7 The illustration shows another example of the laser beam trajectory and weld shape.

[0034] Figure 8 This schematically illustrates yet another example of a laser beam trajectory.

[0035] Figure 9 This schematically illustrates an example of the correspondence between the power distribution of a laser beam and its trajectory.

[0036] Figure 10 The enlarged diagram shows Figure 9 The curve graph. Detailed Implementation

[0037] To make the technical problems to be solved, the technical solutions, and the beneficial technical effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and several exemplary embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0038] Figure 1 An example of a battery is shown in a schematic partial cross-sectional view. The battery described here is exemplarily a lithium-ion battery. However, it is clear that the ideas of the invention can also be applied to other types of batteries, such as sodium-ion batteries, and are not limited to lithium-ion batteries. Furthermore, the ideas of the invention are not limited to prismatic batteries, but are equally applicable to similar weld forms in pouch batteries, cylindrical batteries, or other battery structures. The cell of the lithium-ion battery is formed, for example, from a multi-layered structure of aluminum foil-separator-copper foil, with other materials required for battery manufacturing sandwiched between these layers, which are well known to those skilled in the art and will not be described in detail. These aluminum foil layers protrude, for example, from one end of the cell and are formed by ultrasonic pre-welding to form a positive current collector. The positive current collector comprises, for example, 20 to 130 layers of multilayer aluminum foil 10. The positive electrode of the battery also includes, for example, a positive electrode post and a positive electrode tab. The positive current collector generally needs to be connected to the positive electrode post, and in some cases may also need to be connected to the positive electrode tab or other components of the battery. Such connections are typically made by welding, where, for example, a laser beam 430 is used to weld the multilayer aluminum foil 10 and the corresponding component 20, such as a positive electrode post, located under the multilayer aluminum foil 10 along the stacking direction of the multilayer aluminum foil 10 to form a weld 30.

[0039] Figure 2 An example of a laser welding system 40 is illustrated schematically. The laser welding system 40 is used, for example, for welding... Figure 1 The battery shown is a multilayer aluminum foil 10 as the positive current collector. The laser welding system 40 includes, for example, a laser device 410 for generating a laser beam 430; and at least a control device 420 for controlling the laser device 410. The laser welding system 40 may also include a support platform (in a...) for holding the objects to be welded (i.e., the multilayer aluminum foil 10 and the corresponding component 20). Figure 2 The support stage (shown schematically in plan view) and / or fixtures for holding the object to be welded. The support stage and / or the fixtures can be fixed or movable. The control device 420 can also control the movement of the support stage and / or the fixtures if necessary. The laser device 410 may include, for example, a scanning galvanometer, and in particular, a PFO (Programming Focus Optical System).

[0040] In welding Figure 1When the current collector of the battery shown is a multilayer aluminum foil 10, it is usually made of materials such as aluminum foil 10. Figure 3 The weld 30 shown is for clarity only; in reality, the width may be much smaller than the length. To form such a weld 30, the laser beam 430 is typically positioned relative to the multilayer aluminum foil 10 as follows: Figure 4 The trajectory shown is a straight line, 340. Figure 3 and 4 For example, this is a top view of the multilayer aluminum foil 10. In Figure 4 In the process of forming weld 30, the feed direction 310 is, for example, from left to right as indicated by the arrow. Because the width of weld 30 transverse to the feed direction 310 is very narrow, the resulting molten pool is approximately U-shaped in cross-section, for example... Figure 1 As shown. The cross-section of the molten pool here refers to the cross-section perpendicular to the feed direction 310 of the weld 30. Figure 4 The cross-section is schematically shown in the diagram with dotted lines. Since the thickness of common aluminum foil is between 8 and 13 micrometers, cracks can easily occur at both ends of weld 30 in the width direction.

[0041] Figure 5 The illustration schematically shows an example of the trajectory 340 of the laser beam 430 across the surface of the multilayer aluminum foil 10 in the method of the present invention for welding a multilayer aluminum foil 10, a current collector for a battery, to a corresponding component 20. Clearly, Figure 5 For example, this is also a top view of the multilayer aluminum foil 10. In Figure 5 In this example, the feed direction 310 during weld formation is, for example, from bottom to top as indicated by the arrow, while the width direction of weld 30 and the oscillation direction of laser beam 430 are in the left-right direction. It can be seen that the length 320 of the weld 30 along the feed direction 310 during weld formation is less than the width 330 of the weld 30 transverse to the feed direction 310. The length 320 can be greater than that of a conventional weld, for example... Figure 4 The width of the weld along the vertical direction is large, for example, approximately twice its original width.

[0042] For example, here Figure 2 The method of the present invention is implemented by a control device 420, in which, for example, a corresponding computer program product is provided, the computer program product including computer program instructions, which, when executed by a processor, control... Figure 2 The laser welding system 40 implements the method.

[0043] Figure 6 The illustration shows the press Figure 5 The shape of the weld pool in the cross-section of the weld 30 formed by the trajectory 340 shown. This cross-section... Figure 5The diagram is also schematically shown with dashed lines. The molten pool is approximately V-shaped in cross-section, with the two sides of the V forming an obtuse angle. This provides sufficient areas at both ends of the weld 30 along its length for power modulation of the laser beam 430, reducing cracking at the ends. Simultaneously, the opening at the top of the molten pool widens, facilitating gas escape, and because the length 320 of the weld 30 is very short, the difference in heat input along its length is minimal, further reducing cracking.

[0044] According to an exemplary embodiment of the present invention, the weld 30 is elongated in shape when viewed along its width. The elongated shape can be rectangular (e.g., ...). Figure 5 As shown), oblong, oblong (as shown) Figure 7 (as shown). Any other possible shapes can also be imagined here.

[0045] According to an exemplary embodiment of the present invention, such as Figure 5 As shown, the laser beam 430 travels along a zigzag trajectory 340 relative to the surface of the multilayer aluminum foil 10 to form the weld 30. However, a spiral-shaped trajectory 340 is also conceivable (e.g., Figure 8 (as shown) or other suitable trajectories.

[0046] According to an exemplary embodiment of the present invention, the weld 30 is formed by a combination of scanning along the feed direction 310 and oscillation of the laser beam 430 transverse to the feed direction 310. Here, the scanning along the feed direction 310 and the oscillation of the laser beam 430 are performed, for example, solely by moving the laser beam 430. However, it is also conceivable that the scanning and oscillation of the laser beam 430 relative to the multilayer aluminum foil 10 are accomplished by a combined movement of the laser beam 430 and the object to be welded. The movement of the object to be welded is achieved, for example, by the movement of the worktable and / or fixture. For example, the scanning along the feed direction 310 can be achieved entirely by the movement of the object to be welded.

[0047] According to an exemplary embodiment of the present invention, the welding step is performed using a laser high-frequency oscillation continuous scanning method. Here, the velocity component of the laser beam 430 for the oscillation is significantly higher than the velocity component for the scan.

[0048] According to an exemplary embodiment of the present invention, the welding step is performed using a scanning galvanometer. Thus, the scanning and the oscillation are achieved solely by moving the laser beam 430 using the scanning galvanometer.

[0049] According to an exemplary embodiment of the present invention, the length 320 of the weld 30 is 2 mm to 6 mm; and / or, the width 330 of the weld 30 is 20 mm to 60 mm. However, it is obvious that, depending on the actual requirements of the battery and the actual situation of the space available for welding, other suitable values ​​can be selected for the length 320 and the width 330 of the weld 30.

[0050] According to an exemplary embodiment of the present invention, the average moving speed of the focal spot of the laser beam 430 on the multilayer aluminum foil 10 is 2 m / s or more. This significantly reduces the linear energy heat input and the overall heat input, thereby effectively reducing cracking. However, other average moving speeds are also conceivable, such as 0.5 m / s to 1 m / s.

[0051] Figure 9 The diagram schematically illustrates an example of the correspondence between the power distribution of the laser beam and the trajectory 340 of the laser beam 430, wherein, in Figure 10 The enlarged diagram is shown in the middle. Figure 9 The graph shows the laser power on the vertical axis. According to an exemplary embodiment of the present invention, the power of the laser beam 430 is lower at both ends of the weld 30 (i.e., the regions from 0 to L1 and L2 to L3) than in the middle of the weld 30 (i.e., the region from L1 to L2) in terms of the length direction of the weld 30.

[0052] According to an exemplary embodiment of the present invention, the power of the laser beam 430 decreases linearly towards the endpoints of the weld 30 at both ends. It is conceivable that the power slope is gentler at the starting point of the laser beam 430 (e.g., 0 to L1) and steeper at the ending point of the laser beam 430 (e.g., L2 to L3). However, this is not limited to a linear decrease; other forms of decrease can be employed as needed.

[0053] Although specific embodiments of the invention have been described in detail herein, they are given for illustrative purposes only and should not be construed as limiting the scope of the invention. Various substitutions, alterations, and modifications can be conceived without departing from the spirit and scope of the invention.

Claims

1. A method for welding a multilayer aluminum foil (10) for current collectors of a battery onto a corresponding component (20), wherein, The method includes at least the following steps: In the welding step, a weld (30) is formed by welding the multilayer aluminum foil (10) and the corresponding part (20) located under the multilayer aluminum foil (10) along the stacking direction of the multilayer aluminum foil (10) using a laser beam (430). The weld (30) is formed by a combination of scanning along the feed direction (310) and oscillation of the laser beam (430) transverse to the feed direction (310). The length (320) of the weld (30) along the feed direction (310) when the weld (30) is formed is less than the width (330) of the weld (30) transverse to the feed direction (310). In terms of the length direction of the weld (30), the power of the laser beam (430) is lower at both ends of the weld (30) than at the middle of the weld (30).

2. The method according to claim 1, wherein, The weld (30) is elongated when viewed along its width; and / or The laser beam (430) travels along a zigzag path (340) relative to the surface of the multilayer aluminum foil (10) to form the weld (30).

3. The method according to claim 1 or 2, wherein, The battery is a lithium-ion battery; and / or The corresponding component (20) is the positive terminal of the battery.

4. The method according to claim 1 or 2, wherein, The length (320) of the weld (30) is 2 mm to 6 mm. The width (330) of the weld (30) is 20 mm to 60 mm.

5. The method according to claim 1 or 2, wherein, The average moving speed of the focal spot of the laser beam (430) on the multilayer aluminum foil (10) is more than 2 meters per second.

6. The method according to claim 1 or 2, wherein, The power of the laser beam (430) decreases linearly towards the endpoints of the weld (30) at both ends.

7. The method according to claim 1 or 2, wherein, The welding process is performed using a laser high-frequency oscillation continuous scanning method.

8. The method according to claim 1 or 2, wherein, The welding step is performed using a scanning galvanometer.

9. A laser welding system (40), comprising at least: Laser device (410) for generating laser beam (430); At least a control device (420) for controlling the laser device (410); The laser welding system (40) is configured to perform the method according to any one of claims 1 to 8.

10. A control device (420) for a laser welding system (40), wherein, The control device (420) is configured to perform the method according to any one of claims 1 to 8.

11. A computer program product, wherein, The computer program product includes computer program instructions that, when executed by a processor, implement the method according to any one of claims 1 to 8.

12. A battery, wherein, The multilayer aluminum foil (10) of the current collector of the battery is welded by the method according to any one of claims 1 to 8.

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