Method for welding a cell contacting system to a battery cell and welding system

Abstract

A method for welding a cell contacting system to a battery cell is described, wherein the cell contacting system has a cell connector, wherein the cell connector is pre-tensioned to an electrode of the battery cell by means of a hold-down device, creating a zero gap, in a further step at least one sacrificial weld is applied to temporarily fix the cell connector to the electrode in an overlap area not covered by the hold-down device, in a further step the hold-down device is removed and in a further step a main weld is applied.

Description

[0001] A method for welding a cell contacting system to a battery cell and a welding system are described.

[0002] Methods for welding a cell contacting system to a battery cell and welding systems of the type mentioned above are known in the prior art.

[0003] To manufacture traction batteries for motor vehicles, a large number of battery cells must be permanently connected to create the necessary series and parallel circuits required to supply the drive energy for an electric motor. For this purpose, the battery cells are typically welded together at the electrodes using cell contacting systems to establish the required connections. The quality of the contact must be high, as poor connections can lead to a defective traction battery, increase resistance, cause sparking, and other problems.

[0004] Furthermore, it is known that there is a need to make traction batteries lighter and more robust, and to maximize energy density (power per volume). This requires, on the one hand, that the battery cells be packed as densely as possible, which in turn necessitates that the cell contacting systems be as compact as possible, and on the other hand, that the cell contacting systems be able to withstand both static and dynamic loads. For this reason, the cell contacting systems must also be able to withstand alternating dynamic forces over the long term. Therefore, the welded joints must be as large and durable as possible.

[0005] It is also known that cell contacting systems have a cell connector shaped like a tab, which must be welded to an electrode of a battery cell. Furthermore, it is known that welding with a clamp requires a zero gap between the electrode and the cell connector to produce a clean weld, especially in non-fat welding processes. Known clamps have a free interior area within which a weld can be applied. The problem with this is that the resulting available welding area is relatively small, usually less than 10 mm². 2 .

[0006] From DE 10 2022 000 181 A1, electrical contacting of components by means of a welded joint is known, the primary path of which has two ends. The electrical contacting is characterized in that a termination contour of the welded joint is arranged at each of the ends of the primary path, which has a curved profile.

[0007] From DE 10 2004 015 250 A1, a clamping device for machining, in particular for welding, workpieces is known, comprising at least one first clamping element and at least one second clamping element, between which at least one workpiece is held, wherein a tool is movable relative to the workpiece, the first clamping element is designed as a clamping finger and engages the workpiece on the side where the tool acts on the workpiece, and furthermore, the second clamping element is designed as a clamping roller and rests against a workpiece on the side facing away from the tool.

[0008] DE 10 2015 204 844 A1 relates to a method for connecting battery cells, comprising terminals, characterized by providing a continuous material, assembling a cell connector from the continuous material, and attaching the continuous material or the cell connector to the terminals, a device, and a battery pack, a battery module, a battery and a vehicle.

[0009] DE 10 2020 006 154 A1 describes a device and a method for joining cell arresters and cell connectors of an electric battery with a cell block comprising several individual cells and their cell frames by means of laser welding with at least one hold-down device for applying pressure to at least two superimposed cell arresters and at least one cell connector with a hold-down force and at least one laser welding device for generating a welded connection between the cell arresters and the cell connector.The at least one hold-down device is flexibly mounted and is arranged on the cell block below the at least two cell arresters on a bearing area of ​​the same contours, wherein the contours are raised above their surroundings, sections of the contours forming the bearing area extend in the direction of the cell arresters, and when the hold-down force is applied, at least in the area to be welded, a corresponding bending of the cell arresters takes place and the at least two cell arresters lie on top of each other over their entire surface in this area.

[0010] WO 2022 / 248609 A1 discloses a busbar for contacting preferably cylindrical battery cells held in a cell holder to form a battery module of a high-voltage battery, preferably a traction battery for a vehicle, comprising a base body extending in a main direction of extension and at least one contact connection formed integrally with the base body for contacting a cell contact of one of the battery cells, wherein the contact connection extends in a connection direction which includes a connection angle between 0° and less than 90° with the main direction of extension; furthermore, a battery module arrangement with such a busbar and a method for connecting a busbar to a cell contact.

[0011] The task therefore is to further develop methods for welding a cell contacting system to a battery cell, as well as welding systems of the type mentioned above, in such a way that a larger weld seam can be applied between a cell connector and a battery cell than with conventional methods.

[0012] The problem is solved by a method for welding a cell contacting system to a battery cell according to claim 1 and a welding system according to dependent claim 9. Further embodiments and developments are the subject of the dependent claims.

[0013] A method for welding a cell contacting system to a battery cell is described, wherein the cell contacting system has a cell connector, wherein the cell connector is pre-tensioned to an electrode of the battery cell by means of a hold-down device, creating a zero gap, in a further step at least one sacrificial weld is applied to temporarily fix the cell connector to the electrode in an overlap area not covered by the hold-down device, in a further step the hold-down device is removed and in a further step a main weld is applied.

[0014] In this process, the battery cell and cell contacting system are first positioned relative to each other. Then, the cell connector is pressed against the battery cell electrode using the hold-down clamp to create a zero gap. A sacrificial weld can then be applied, temporarily bonding the cell connector to the electrode. This allows the hold-down clamp to be removed, providing a significantly larger welding surface that would otherwise be partially inaccessible due to the clamp. Finally, the weld that permanently bonds the cell connector and electrode can be applied.

[0015] Using the method described here, it is possible to achieve large-area and mechanically robust welded connections between the cell contacting system and the battery cell, even with compact cell contacting systems. This allows for increases in the available welding area of ​​20% or more with the same cell contacting system size, for example, by approximately 9 mm. 2 to 12 mm 2 with cell connectors of the same size. This significantly increases the stability of the connection while maintaining the same compactness, which improves both the mechanical load-bearing capacity and minimizes the electrical contact resistance between the cell connector and the electrode.

[0016] Furthermore, with defined required connection cross-sections, more compact and lighter cell contacting systems can be used, and adjacent battery cells can be positioned closer together than with conventional methods, which increases the storage density and reduces the weight.

[0017] According to a first further development, it is provided that the sacrificial weld is made in the form of one or more welding points.

[0018] Spot welds generate less heat than longer weld seams, allowing for a faster transition to the next process step. Furthermore, applying multiple spot welds ensures that the cell connector makes full contact with the electrode for the subsequent main weld.

[0019] In a further embodiment, it is provided that the hold-down has a pressure piece with a free inner area, wherein the overlap area is determined by the free inner area, and wherein at least one sacrificial weld is applied in the free inner area.

[0020] The pressure piece with a free interior area can ensure a flat contact of the cell connector with the electrode in the interior, making it possible to produce one or more stable sacrificial welds.

[0021] In a further refinement, it is provided that several sacrificial welds are applied distributed across the free interior area.

[0022] In a further embodiment, it is provided that the pressure piece has an insulating collar that surrounds the free inner area, wherein at least one sacrificial weld is applied within the insulating collar at a minimum distance to the insulating collar.

[0023] Such an insulating collar can act as a barrier against weld spatter, thus preventing the weld spatter that sometimes occurs from contaminating other components of an arrangement of battery cells or the welding equipment used, which would necessitate costly cleaning.

[0024] In a further refinement, it is provided that the sacrificial weld is applied using laser welding or resistance spot welding.

[0025] These methods are fast and can be used without the need for additional welding material. They are particularly suitable for joining two components over a large area and can be applied from one side.

[0026] In a further, more advanced embodiment, it is provided that the main weld seam is applied using laser welding or resistance spot welding.

[0027] These processes are fast and can be used without the need for additional welding material. They are particularly suitable for joining two components over a large area and, unlike certain other welding processes, can be applied from a single side.

[0028] In a further refined embodiment, it is provided that a shield is positioned around the electrode and the battery cell before the main weld is applied, the shield having a larger open area than the free interior area of ​​the hold-down device.

[0029] Such a shield can form a barrier against weld spatter and thus prevent such weld spatter, which sometimes occurs, from contaminating other components of an arrangement of battery cells or the welding device.

[0030] A first independent subject relates to a welding device for welding a cell contacting system to a battery cell comprising a welding system, a hold-down device and a positioning device for positioning the battery cell and electrode, wherein the welding device is configured to carry out the method of the type described above.

[0031] According to a first further embodiment, it is provided that a shield is provided which has a larger open area than the free interior area of ​​the hold-down device.

[0032] Further advantages, features, and details will become apparent from the following description, in which – possibly with reference to the drawing – at least one embodiment is described in detail. Identical, similar, and / or functionally equivalent parts are identified by the same reference numerals.

[0033] They show schematically: Fig. 1 to Fig. 5. A top view of a cell contacting system and a battery cell during various work steps for welding the cell contacting system to the battery cell, as well as Fig. 6 to Fig. 9 A side view of a welding device during various processing steps to produce a welded connection between the cell contacting system and the battery cell.

[0034] Fig. Figure 1 shows a top view of a cell contacting system 2 and a battery cell 4.

[0035] The cell contacting system 2 is to be fixed to the battery cell 4 by means of laser welding. For this purpose, a cell connector 6 of the cell contacting system 2 is inserted into the Fig. 1 shown correct alignment relative to an electrode 8 of the battery cell 4, in which the cell connector 6 overlaps with the electrode 8.

[0036] In Fig. Figure 2 shows the next step of the process. A hold-down device 10, which has a pressure piece 12, is pressed onto the cell connector 6 so that it makes contact with the electrode 8 over its entire surface, thus creating a zero gap between the cell connector 6 and the electrode 8.

[0037] The pressure piece 12 has an insulating collar 14 which is aligned in the plane of the sheet. Inside the insulating collar 14, a free inner area 16 is formed, which provides space for a welding head of a device inserted into the Fig. The laser welding device described in more detail in section 6 ff. is accessible.

[0038] As in Fig. 3 shown, in the free interior area 16, a series of spot-shaped sacrificial welds 18 are placed distributed over the surface, by means of which the cell connector 6 is temporarily held on the electrode 8 and a permanent zero gap is maintained.

[0039] Then, as in Fig. As can be seen in Figure 4, the hold-down device 10 is removed. Cell connector 6 and electrode 8 maintain their relative position due to the sacrificial welds 18.

[0040] The connection between cell connector 6 and electrode 8 is not yet sufficiently robust for permanent use and cannot absorb the required mechanical loads, exhibiting a higher contact resistance than specified.

[0041] In Fig. Figure 5 shows the final welding step. Cell connector 6 and electrode 8 are permanently welded together by a main weld seam 20 (dashed line).

[0042] The connection between cell connector 6 and electrode 8 is operationally stable after this step and after cell connector 6 and electrode 8 have cooled down.

[0043] Fig. Figure 6 shows a welding system 30 for producing a welded connection between the cell contacting system 2 and the battery cell 4 in order to connect the battery cells 4, 4' together. The in Fig. The work step shown in step 6 corresponds to the processing step from Fig. 3.

[0044] The welding system 30 has a movable laser welding head 32 which produces several sacrificial welds using a laser beam 34 within the free interior area 16 of the pressure piece 12 of the hold-down clamp 10 with the insulating collar 14 arranged on the pressure piece 12. A shield 36 is positioned in a waiting position next to the hold-down clamp 10. The shield 36 has an open area 38 that is larger than the free interior area 16.

[0045] Once the sacrificial weld or welds 18 have been applied, as described in Fig. 7 and Fig. 8 shown, the retainer 10 removed and the shield 36 positioned over the cell connector 6 and the electrode 8.

[0046] Fig. Figure 9 shows the step of producing the main weld 20 using the laser welding head 32, in which the main weld is applied to cell connector 6 and electrode 8 by means of the laser beam 34 under the protection of the shield. This step corresponds to the one in Fig. Step 5 as shown. Reference symbol list 2 cell contacting system 4.4' battery cell 6 cell connectors 8 electrode 10 hold-down devices 12 printed piece 14 insulating collars 16 free indoor areas 18 sacrificial weld 20 Main weld 30 welding systems 32 Laser welding head 34 Laser beam 36 Shielding 38 open area

Claims

[1] Method for welding a cell contact system (2) to a battery cell (4, 4'), wherein the cell contact system (2) has a cell connector (6), characterized by that the cell connector (6) is prestressed by means of a hold-down device (10) to an electrode (8) of the battery cell (4, 4') to produce a zero gap, in a further step at least one sacrificial weld seam (18) for provisionally fixing the cell connector (6) to the electrode (8) is applied in an overlap region uncovered by the hold-down device (10), in a further step the hold-down device (10) is removed and in a further step a main weld seam (20) is set. [2] Method according to claim 1, characterized by that the sacrificial weld seam (18) is set in the form of one or more welding points. [3] Method according to claim 1 or 2, characterized byin that the hold-down device (10) has a pressure piece (12) with a free inner region (16), wherein the overlap region is determined by the free inner region (16), wherein the at least one sacrificial weld seam (18) is applied in the free inner region (16). [4] Method according to claim 3, characterized by that several sacrificial welds (18) are distributed over the free inner area (16). [5] Method according to claim 3 or 4, characterized by in that the pressure piece (12) has an insulating collar (14) which surrounds the free inner region (16), wherein the at least one sacrificial weld seam (18) is applied within the insulating collar (14) with a minimum distance from the insulating collar (14). [6] Method according to one of the preceding claims, characterized by that the sacrificial weld seam (18) is applied using a laser welding process or resistance spot welding process. [7] Method according to one of the preceding claims, characterized by that the main weld seam (20) is applied using the laser welding process or resistance spot welding process. [8] Method according to claim 3, 4 or 5, characterized by that before the main weld seam (20) is applied, a shield (36) is positioned around the electrode (8) and the battery cell (4, 4'), wherein the shield (36) has a larger open area (38) than the free inner area (16) of the hold-down device (10). [9] Welding device for welding a cell contact system (2) to a battery cell (4, 4') with a welding system (30), a hold-down device (10) and a positioning device for positioning the battery cell (4, 4') and electrode (8), wherein the welding device is configured to carry out the method according to one of the preceding claims. [10] Welding device according to claim 9, characterized bythat a shield (36) is provided which has a larger open area (38) than the free inner area (16) of the hold-down device (10).

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