Improvement method, welding method, processing system, control device, program product

Abstract

The present invention relates to an improvement method for improving a weld seam, where the weld seam is formed by welding a multi-layer aluminum foil of a current collector of a battery to a corresponding component of the battery. Among them, the improvement method at least includes a remelting step. In the remelting step, the weld seam edge on the surface of the multi-layer aluminum foil is remelted at least once by using a laser beam with a heat input smaller than the heat input for welding the weld seam. The present invention also relates to a corresponding welding method, a laser processing system, a control device, and a computer program product. The advantages of the present invention are as follows: By remelting the fusion line of the initial weld seam with low power, the internal stress in the fusion line area of the newly formed weld seam during solidification can be reduced, thereby reducing cracks in the fusion line area; by repeating the remelting, the length of the cracks can be reduced and made discontinuous based on the continuously decreasing welding energy.

Description

Technical Field

[0001] The present invention relates to an improvement method for improving a weld, a welding method for welding a multilayer aluminum foil of a current collector of a battery to a counterpart of the battery, a laser processing system, a control device for the laser processing system, and a computer program product. The present invention particularly relates to the field of lithium-ion batteries and laser welding. Background Art

[0002] Due to the superiority of lithium-ion batteries in various aspects compared with other batteries, lithium-ion batteries are increasingly used in various fields.

[0003] In lithium-ion batteries, the positive electrode includes 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 includes a current collecting electrode composed of graphitized carbon material and copper foil. Aluminum foil is also used as a current collector for the positive electrode. Multilayer aluminum foil is used here to obtain a larger aluminum foil surface through more layers and thereby coat more active materials on the surface of the aluminum foil. In order to make a battery, the multilayer aluminum foil needs to be effectively connected to the pole. Since the aluminum foil is very thin, ultrasonic welding is usually preferred. However, the shape of the pole is usually irregular, so the usual practice is to add a transition piece between the aluminum foil and the pole, wherein the multilayer aluminum foil and the transition piece are first connected by ultrasonic welding, and then the transition piece that is not easy to form welding cracks is connected to the pole by laser welding.

[0004] However, in order to make the battery cell lightweight and superchargeable, the current demand is to eliminate the adapter, which requires direct welding of the multi-layer aluminum foil to the pole. However, thin aluminum foil is very prone to cracking during welding, especially at the interface edge of the molten area. This is mainly because: the surface of the aluminum foil is often covered with an Al2O3 oxide layer, which has a melting point and hardness much higher than that of the parent material pure aluminum, so that part of the oxide layer does not have time to completely melt during welding and gathers at the edge of the weld, which significantly increases the hardness of the weld edge and makes it easy to crack; the thickness of 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 temperature. The tensile stress generated in this process will also increase the risk of cracking in the molten pool; the uneven heat and cold and material deformation caused by the laser energy input during welding will also increase the risk of cracking.

[0005] In addition, since the weld is long along the feed direction, the molten pool of the weld is U-shaped in the cross section perpendicular to the feed direction, that is, the edge profile of the molten pool is very steep. As a result, the aluminum foil at the edge of the molten pool is severely deformed, and the tensile stress generated makes it very easy to produce continuous cracks on the fusion line of the molten pool. Summary of the invention

[0006] The object of the present invention is to provide an improvement method for improving a weld seam, so as to reduce cracks and provide a high-strength and high-quality weld seam when welding multi-layer aluminum foils.

[0007] According to a first aspect of the present invention, there is provided an improvement method for improving a weld seam, where the weld seam is a weld seam formed by welding a multi-layer aluminum foil of a current collector of a battery with a corresponding component of the battery. Among them, the improvement method at least includes a remelting step. In the remelting step, the weld seam edge on the surface of the multi-layer aluminum foil is remelted at least once by using a laser beam with a heat input smaller than the heat input for welding the weld seam.

[0008] Herein, the "corresponding component" should be particularly understood as any component of the battery to be welded with the multi-layer aluminum foil. The "weld seam" should be particularly understood as any form of weld seam formed by welding the multi-layer aluminum foil with the corresponding component by a laser beam, especially the initial weld seam formed in a traditional manner. It is conceivable that the weld seam is a weld seam formed by a linear trajectory, a zigzag trajectory, or other trajectories on the multi-layer aluminum foil by a laser beam. The "weld seam edge on the surface of the multi-layer aluminum foil of the weld seam" is particularly understood as: the contour line of the weld seam on the surface of the multi-layer aluminum foil, that is, the boundary line between the weld seam and the aluminum foil base material, or the weld toe of the weld seam. The weld seam edge particularly limits the width of the weld seam. The "width of the weld seam" is particularly understood as the width of the weld seam transverse to the feeding direction of the laser beam. After each remelting, especially a new weld seam edge of the weld seam is generated on the surface of the multi-layer aluminum foil. Herein, the "weld seam edge" always particularly refers to two lines at the boundary between the weld seam and the aluminum foil base material, and does not represent the lines generated due to remelting within the weld seam. "Remelting the weld seam edge on the surface of the multi-layer aluminum foil of the weld seam" particularly covers: remelting at least a part of the two weld seam edges of the weld seam, especially remelting both weld seam edges completely. It should be understood that when remelting the weld seam edge, the molten pool generated by the laser beam is, for example, wider than the weld seam edge, so the area near the weld seam edge is also melted simultaneously. In addition, it should be understood that after remelting, solidification of the melted area will also occur and thus new weld seam edges will be formed.

[0009] According to an optional embodiment of the present invention, in the remelting step, the weld seam edge on the surface of the multi-layer aluminum foil of the weld seam is remelted multiple times by using a laser beam. Among them, the heat input used for the first remelting is smaller than the heat input for welding the weld seam, and the heat input used for each remelting after the first remelting is reduced compared with the previous remelting, and in each remelting, the weld seam edge formed by the previous remelting is remelted. "Multiple times" is particularly understood as more than two times. Each remelting particularly involves the two weld seam edges of the weld seam on the surface of the multi-layer aluminum foil.

[0010] According to an alternative embodiment of the present invention, in the remelting step, the laser beam is moved relative to the multi-layer aluminum foil along the weld edge or moved parallel to the weld edge near the weld edge. Obviously, it is not mandatory for the focal spot of the laser beam to be along the weld edge, but it is sufficient that the weld edge is within the molten pool of the laser beam.

[0011] According to an alternative embodiment of the present invention, a reduction in the heat input in the remelting step is achieved by reducing the laser power of the laser beam compared to welding the weld and / or by increasing the moving speed of the laser beam relative to the multi-layer aluminum foil compared to welding the weld.

[0012] According to an alternative embodiment of the present invention, the weld edge formed by each remelting is offset in a direction away from the weld relative to the weld edge formed by the previous remelting.

[0013] According to an alternative embodiment of the present invention, the lengths of the weld edges formed by each remelting are equal to each other. Herein, "equal" should be understood to cover both absolute equality and approximate equality, and "approximate equality" is especially understood to mean a deviation within ±10%, especially within ±5%.

[0014] According to an alternative embodiment of the present invention, the depth of the molten pool during each remelting decreases successively and is less than the thickness of the multi-layer aluminum foil.

[0015] According to an alternative embodiment of the present invention, the number of remeltings is selected such that the weld meets the requirements in terms of cracks.

[0016] According to an alternative embodiment of the present invention, the battery is a lithium-ion battery.

[0017] According to an alternative embodiment of the present invention, the corresponding part is the positive pole post of the battery.

[0018] According to a second aspect of the present invention, there is provided a welding method for welding a multi-layer aluminum foil of a current collector of a battery to a corresponding part of the battery, wherein the welding method includes: an initial welding step, in which the multi-layer aluminum foil and the corresponding part are welded by a laser beam to form a weld; an improvement step, in which the aforementioned improvement method for improving the weld is performed on the weld.

[0019] According to an alternative embodiment of the present invention, in the initial welding step, the weld is formed with a linear or curved trajectory of the laser beam on the surface of the multi-layer aluminum foil.

[0020] According to an alternative embodiment of the present invention, the welding method is performed with a scanning galvanometer or a stationary welding head. The stationary welding head particularly refers to a welding head where the laser beam does not move relative to the welding head.

[0021] According to an alternative embodiment of the present invention, before the welding method, the multi-layer aluminum foils have been pre-welded together by ultrasonic waves.

[0022] According to a third aspect of the present invention, there is provided a laser processing system, at least comprising: a laser device for generating a laser beam; a control device for at least controlling the laser device; wherein, the laser processing system is configured to be adapted to perform the foregoing improvement method or the foregoing welding method.

[0023] According to a fourth aspect of the present invention, there is provided a control device for a laser processing system, wherein the control device is configured to be adapted to perform the foregoing improvement method or the foregoing welding method.

[0024] According to a fifth aspect of the present invention, there is provided a computer program product, wherein the computer program product includes computer program instructions, and the computer program instructions, when executed by a processor, implement the foregoing improvement method or the foregoing welding method.

[0025] The positive effects of the present invention are as follows: By remelting the fusion line of the initial weld with a small power, the internal stress in the fusion line region of the newly formed weld during solidification can be reduced, thereby reducing cracks in the fusion line region; By repeating the remelting, the length of the crack can be reduced and made discontinuous based on the continuously decreasing welding energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Hereinafter, the present invention will be described in more detail by referring to the drawings, and the principles, features, and advantages of the present invention can be better understood. 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 processing system is schematically shown in a perspective view.

[0029] Figure 3 An example of a weld and a region prone to cracking on the weld are shown in a schematic top view.

[0030] Figure 4 Is shown schematically Figure 3 The cross-section of the molten pool of the weld in.

[0031] Figure 5 An example of a weld and an improvement of the weld according to the present invention are shown in a schematic top view.

[0032] Figure 6 is schematically shown Figure 5 a cross-section of the weld pool of the weld in DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and beneficial technical effects to be solved by the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the drawings and a plurality of exemplary embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the protection scope of the present invention.

[0034] First of all, it should be pointed out that for the sake of clarity and brevity of the drawings, only one of the features such as the weld edge, crack, and weld edge formed by remelting of the weld is labeled.

[0035] Figure 1 An example of a battery is schematically shown in a partial cross-sectional view. The battery is, by way of example, a lithium-ion battery. However, it is obvious that the idea of the present invention can also be applied to other types of batteries, such as sodium-ion batteries, rather than being limited only to lithium-ion batteries. In addition, the idea of the present invention is not limited to square-shell batteries, and is equally applicable to similar weld forms of soft-pack batteries, cylindrical batteries or batteries with other structures. The battery cell of the lithium-ion battery is formed, for example, by a multi-layer stacked structure of aluminum foil - separator - copper foil, and other substances required for manufacturing the battery are interposed between these stacked structures, which are well known to those skilled in the art and will not be described in detail herein. These aluminum foil layers protrude, for example, at one end of the battery cell and form a positive current collector through ultrasonic pre-welding. The positive current collector includes, for example, multiple layers of aluminum foil 10 ranging from 20 to 130 layers. The positive electrode of the battery also includes, for example, a positive electrode terminal and a positive electrode tab, etc. The positive current collector generally needs to be connected to the positive electrode terminal, and may also need to be connected to the positive electrode tab or other components of the battery in some cases. Such a connection is usually completed by welding. Among them, for example, a laser beam 430 is required to weld the multiple layers of aluminum foil 10 and a corresponding member 20, such as a positive electrode terminal, located under the lowermost aluminum foil of the multiple layers of aluminum foil 10 to form a weld 30.

[0036] Figure 2 An example of a laser processing system 40 is schematically shown. The laser processing system 40 is used, for example, for welding Figure 1 the welds and / or improving Figure 1 the welds of Figure 2shown schematically in a plane) and / or a fixture for clamping an object to be welded, etc. The placement table and / or the fixture may be fixed or movable. The control device 420 can also control the movement of the placement table and / or the fixture when necessary. The laser device 410 may include, for example, a scanning galvanometer or a fixed welding head.

[0037] During welding Figure 1 the multilayer aluminum foil 10 of the current collector of the battery shown, a weld seam 30 as shown in Figure 3 is generally used. The weld seam 30 is shown here in a schematic top view. The length-width ratio here is only for clarity, and in reality the width may be much smaller than the length. The length of the weld seam 30 is, for example, 20 millimeters to 60 millimeters, and the width is, for example, 2 millimeters to 6 millimeters. The weld seam 30 is, for example, elongated here. To form such a weld seam 30, generally the laser beam 430 is made to travel a straight path relative to the multilayer aluminum foil 10. However, it is also conceivable here that depending on the shape and size of the weldable area, other paths may be used, for example the laser beam 430 may perform a narrow amplitude oscillating movement transverse to the feed direction in addition to the straight feed movement along the feed direction. In Figure 3 the feed direction of the laser beam 430 is marked with an arrow and the symbol V. In Figure 3 the area 340 prone to cracking on the weld seam 30, that is, the area near the initial weld edge 300, is also marked with oblique hatching. The weld seam 30 has two initial weld edges 300, but only one of them is marked for clarity and brevity of the drawing. In Figure 4 a schematic view shows Figure 3 the cross-section of the molten pool of the weld seam 30 in Figure 3 and the area 340 prone to cracking is also marked with oblique hatching here. In Figure 4 the cross-section of

[0038] Figure 5 A schematic top view shows the weld seam 30 and an example of improving the weld seam 30 according to the present invention. Here, for example, by Figure 2The laser processing system 40 performs an improvement method for improving the weld seam 30. The improvement method for improving the weld seam 30 at least includes a remelting step. In the remelting step, the weld seam 30 is remelted at least once at the weld edge on the surface of the multi-layer aluminum foil 10 by using a laser beam 430 with a heat input smaller than the heat input for welding the weld seam 30. The weld seam 30 can also be completed by the laser processing system 40 for improvement. In this case, the laser processing system 40 performs a welding method for welding the multi-layer aluminum foil 10 of the current collector of the battery to the corresponding part 20 of the battery. The welding method includes an initial welding step and an improvement step. First, in the initial welding step, the multi-layer aluminum foil 10 and the corresponding part 20 are welded by the laser beam 430 to form the weld seam 30. Figure 5 The initial weld seam 30 in Figure 3 and 4 The description of the weld seam 30 can be particularly referred to. Then, in the improvement step, the aforementioned improvement method for improving the weld seam 30 is performed. Here, for example, the welding method is performed by a scanning galvanometer or a fixed welding head. However, the initial welding step and the improvement step can also be completed by different laser processing systems 40. In this case, these two laser processing systems 40 may be in different factories.

[0039] Here, for example, with Figure 2 The control device 420 implements the improvement method or the welding method of the present invention. In the control device 420, for example, there is a corresponding computer program product, and the computer program product includes computer program instructions. When the computer program instructions are executed by a processor, they will control Figure 2 The laser processing system 40 implements the improvement method or the welding method.

[0040] According to an alternative embodiment of the present invention, the reduction of the heat input in the remelting step is achieved by reducing the laser power of the laser beam 430 compared with welding the weld seam 30 and / or by increasing the moving speed of the laser beam 430 relative to the multi-layer aluminum foil 10 compared with welding the weld seam 30.

[0041] According to an exemplary embodiment of the present invention, the laser power used for remelting is between 5% and 50% of the laser power used for welding. Compared with welding, during remelting, other parameters of the laser beam 430, such as the focal spot diameter, feed speed, etc., can remain unchanged, but can also change. In addition, during each remelting, the parameters of the laser beam 430 can also be changed. For example, the rear section of the weld seam 30 along the length direction may have more cracks due to the heat accumulation effect. Therefore, during each remelting, different laser beam parameters can be used for the rear section of the weld edge compared with the front section.

[0042] According to an exemplary embodiment of the present invention, in the remelting step, the weld edges of the weld 30 on the surface of the multilayer aluminum foil 10 are remelted multiple times by a laser beam 430. Among them, the heat input used for the first remelting is smaller than the heat input for welding the weld 30, and the heat input used for each remelting after the first remelting is reduced compared with the previous remelting, and in each remelting, the weld edges formed by the previous remelting are remelted. Each remelting is especially carried out at least after the molten pool formed by the previous remelting solidifies. In Figure 5 it shows that the weld edges are remelted twice. Here, the initial weld 30 is represented by a thick black solid line, the first remelting is represented by a slightly thinner dotted line, and the second remelting is represented by an even thinner dotted line. Here, the initial weld edges 300, the weld edges 311 formed by the first remelting, and the weld edges 322 formed by the second remelting are marked. In Figure 6 it schematically shows in Figure 5 a cross-section of the molten pool of the weld 30 of Figure 5 which is schematically shown by a dotted line in

[0043] According to an exemplary embodiment of the present invention, in the remelting step, the laser beam 430 is moved relative to the multilayer aluminum foil 10 along the weld edge or moved parallel to the weld edge near the weld edge. However, other trajectories of the laser beam 430 on the surface of the multilayer aluminum foil 10 during remelting can also be envisaged, for example, having a transverse oscillating motion in addition to the feeding motion, and so on.

[0044] According to an exemplary embodiment of the present invention, the weld edges formed by each remelting are offset in a direction away from the weld 30 relative to the weld edges formed by the previous remelting. As Figure 5 shown, the weld edges 322 formed by the second remelting are offset in a direction away from the weld 30 relative to the weld edges 311 formed by the first remelting. This can also be regarded as the continuous widening of the weld 30. However, it can also be envisaged that the weld edges formed by remelting coincide with the initial weld edges 300 of the weld 30, that is, the width of the weld 30 remains unchanged.

[0045] According to an exemplary embodiment of the present invention, the lengths of the weld edges formed by each remelting are equal to each other. However, it can also be envisaged that the weld edges formed by each remelting are slightly shorter (see Figure 5 ) or slightly longer compared with the previous one, and so on.

[0046] According to an exemplary embodiment of the present invention, asFigure 6 As shown, the depth of the molten pool during each remelting decreases successively and is less than the thickness of the multi-layer aluminum foil 10.

[0047] According to an exemplary embodiment of the present invention, the number of remelting times is selected such that the weld 30 meets the requirements in terms of cracks.

[0048] Although specific embodiments of the present invention have been described in detail herein, they are given for illustrative purposes only and should not be considered as limiting the scope of the present invention. Various substitutions, alterations, and modifications can be conceived without departing from the spirit and scope of the present invention.

Claims

1. An improvement method for improving a weld, wherein the weld (30) is a weld (30) formed by welding a multi-layer aluminum foil (10) of a current collector of a battery to a corresponding part (20) of the battery, where The improvement method at least includes the following steps: a remelting step, in which the weld edge of the weld (30) on the surface of the multi-layer aluminum foil (10) is remelted at least once by a laser beam (430) with a heat input smaller than the heat input for welding the weld (30). In the remelting step, the weld edge of the weld (30) on the surface of the multi-layer aluminum foil (10) is remelted multiple times by the laser beam (430). Among them, the heat input used in the first remelting is smaller than the heat input for welding the weld (30), and the heat input used in each remelting after the first remelting is reduced compared with the previous remelting. And in each remelting, the weld edge formed by the previous remelting is remelted, and the weld edge formed by each remelting is offset in a direction away from the weld (30) relative to the weld edge formed by the previous remelting.

2. The improvement method according to claim 1, wherein, In the remelting step, the laser beam (430) is moved relative to the multi-layer aluminum foil (10) along the weld edge or moved parallel to the weld edge near the weld edge; and / or the reduction of the heat input in the remelting step is achieved by reducing the laser power of the laser beam (430) compared with welding the weld (30) and / or by increasing the moving speed of the laser beam (430) relative to the multi-layer aluminum foil (10) compared with welding the weld (30); and / or the surface is the upper surface of the multi-layer aluminum foil (10) facing the laser beam (430), and the corresponding part (20) is below the lower surface of the multi-layer aluminum foil (10) away from the laser beam (430).

3. The improvement method according to claim 2, wherein, The lengths of the weld edges formed by each remelting are equal to each other; and / or the molten pool depth during each remelting decreases successively and is less than the thickness of the multi-layer aluminum foil (10); and / or the number of remeltings is selected such that the weld (30) meets the requirements in terms of cracks.

4. The improvement method according to any one of claims 1 to 3, wherein, The battery is a lithium-ion battery; and / or the corresponding part (20) is the positive pole post of the battery.

5. A welding method for welding a multi-layer aluminum foil of a current collector of a battery to a corresponding part of the battery, wherein, The welding method includes the following steps: an initial welding step, in which the multi-layer aluminum foil (10) and the corresponding part (20) are welded by a laser beam (430) to form a weld (30); an improvement step, in which the improvement method for improving the weld (30) according to any one of claims 1 to 4 is performed on the weld (30).

6. The welding method according to claim 5, wherein, In the initial welding step, the weld (30) is formed by a linear or curved trajectory of the laser beam (430) on the surface of the multi-layer aluminum foil (10).

7. The welding method according to claim 5 or 6, wherein The welding method is performed by a scanning galvanometer or a fixed welding head; and / or before the welding method, the multi-layer aluminum foils (10) have been pre-welded together by ultrasonic waves.

8. A laser processing system, at least comprising: A laser device (410) for generating a laser beam (430); a control device (420) for at least controlling the laser device (410); wherein the laser processing system (40) is configured to perform the improvement method according to any one of claims 1 to 4 or the welding method according to any one of claims 5 to 7.

9. A control device for a laser processing system, wherein, The control device (420) is configured to perform the improvement method according to any one of claims 1 to 4 or the welding method according to any one of claims 5 to 7.

10. A computer program product, wherein, The computer program product includes computer program instructions which, when executed by a processor, implement the improvement method according to any one of claims 1 to 4 or the welding method according to any one of claims 5 to 7.

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