Method for manufacturing a battery pack

Abstract

The present invention provides a method for manufacturing a battery pack, wherein the battery pack comprises a plurality of stacked battery cells, wherein electrodes of adjacent battery cells are connected by a busbar, wherein the busbar has two holes smaller than the electrodes and is arranged so that each hole overlaps with each electrode. The method comprises: welding the busbar to one of the electrodes; then, welding the busbar to the other electrode in a middle region between the two holes of the busbar; and finally, welding the busbar to the other electrode in an end region of the busbar adjacent to the middle region.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a method for manufacturing a battery pack. A battery pack is a device formed by stacking a plurality of battery cells, with electrodes of adjacent battery cells connected by bus bars. Background Art

[0002] An example of a battery pack is disclosed in International Publication No. 2017 / 130705. A battery pack is a device composed of multiple stacked battery cells. In a battery pack, the electrodes of adjacent battery cells are connected by busbars. Busbars connect multiple battery cells electrically in series or in parallel. In the battery pack of International Publication No. 2017 / 130705, the busbars and electrodes are laser welded. A "busbar" is a component made of conductive metal sheets with low internal resistance suitable for power transmission. Summary of the Invention

[0003] If the weld strength between the busbar and the electrode is weak, the busbar can easily detach from the electrode. Improving weld strength can generate significant stress in the busbar during welding. Alternatively, increasing weld strength can damage the battery cell due to the heat of welding. This manual provides techniques for properly welding busbars to electrodes.

[0004] The first technical solution disclosed in this specification involves a method for manufacturing a battery pack, which is a method for manufacturing a battery pack in which a plurality of battery cells are stacked, and the electrodes of adjacent battery cells of the battery cells are connected by a bus bar, wherein the bus bar has two holes smaller than the electrodes and is configured so that each of the holes overlaps with each of the electrodes. The method for manufacturing the battery pack includes: welding the bus bar to one of the electrodes; then, welding the bus bar to the other electrode in the middle area between the two holes of the bus bar; and then, welding the bus bar to the other electrode in the end area of the bus bar adjacent to the middle area.

[0005] If the busbar and electrode are welded at the end regions and then at the middle region, high stress will be generated in the middle region of the busbar. This is because the busbar and electrode are welded in the region between the two constrained points (i.e., the middle region) while being constrained at two points (the weld between the busbar and one electrode and the weld between the busbar and the other electrode at the end region). Further welding between these two constrained points leaves no room for deformation in the busbar, resulting in high stress within the busbar.

[0006] If the busbar is welded to the other electrode outside the constrained parts (i.e., the end areas) after the other two points (the welding part with one electrode and the welding part between the busbar and the other electrode in the middle area) are constrained, there is room for the busbar to deform during the final welding, so the stress generated in the busbar is small.

[0007] The manufacturing method disclosed in this specification may also have the following features: The bus bar may have two holes that are smaller than the electrodes, and the holes may be arranged so that each hole overlaps with each electrode.

[0008] In the manufacturing method according to the above-mentioned aspect, the bus bar may be irradiated with laser light at a position away from the edge of the hole, or the laser irradiation may be stopped when the bus bar melts to the edge.

[0009] In the manufacturing method according to the above technical solution, during welding in the middle region, the bus bar may be irradiated with laser light at a position away from the edge of the hole, or the laser irradiation may be stopped when the bus bar melts to the edge.

[0010] The second technical solution of the present invention involves a method for manufacturing a battery pack, which is a method for manufacturing a battery pack in which a plurality of battery cells are stacked, and the electrodes of adjacent battery cells are connected by a bus bar, wherein the bus bar has two holes smaller than the electrodes and is configured so that each of the holes overlaps with each of the electrodes. The method for manufacturing the battery pack includes: irradiating the bus bar with a laser at a position away from the edge of the hole, and stopping the laser irradiation when the bus bar melts to the edge.

[0011] If you simply irradiate the laser at a location away from the edge of the hole, the electrode and the welding piece will not be welded to the edge of the hole, and high welding strength cannot be achieved. If the laser is directly irradiated at the edge of the busbar, a large amount of heat may transfer to the electrode and damage the battery cell. By irradiating the busbar with a laser at a location away from the edge of the hole and stopping the laser irradiation when the busbar melts to the edge, the edge of the busbar can be welded to the electrode without damaging the battery cell. By welding the electrode to the edge of the busbar, high welding strength can be achieved. In addition, at this time, the busbar and the electrode are in a so-called fillet weld state. Excellent results can also be achieved by fillet welding alone.

[0012] In the following “Detailed Description of the Invention”, details and further improvements of the technology disclosed in this specification are described. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like reference numerals represent like components, and wherein:

[0014] Figure 1 It is a top view of the battery pack.

[0015] Figure 2 is a side view of the battery pack.

[0016] Figure 3 It is a three-dimensional diagram of the battery pack.

[0017] Figure 4 This is an enlarged top view of the busbar area.

[0018] Figure 5 It is along Figure 4 A cross-sectional view along the dotted line V.

[0019] Figure 6 This is an enlarged top view of the busbar area.

[0020] Figure 7A It is along Figure 6 The first sectional view along line VII-VII.

[0021] Figure 7B It is along Figure 6 The second sectional view along line VII-VII.

[0022] Figure 7C It is along Figure 6 The third sectional view along line VII-VII. DETAILED DESCRIPTION

[0023] Before describing the manufacturing method of the embodiment, the battery pack 2 is described. Figure 1 FIG shows a top view of the battery pack 2. Figure 2 A side view of the battery pack 2 is shown in FIG.

[0024] The battery pack 2 is a power source in which a plurality of battery cells 10 are stacked. The battery cells 10 are flat and arranged with the wide faces of adjacent battery cells 10 facing each other. Isolators 3 are arranged between adjacent battery cells 10. The plurality of battery cells 10 and the plurality of separators 3 are stacked one on top of another in an alternating manner. End plates 4 are arranged at both ends of the stack of battery cells 10 and separators 3. The separators 3 and end plates 4 protect the battery cells 10. The stack of battery cells 10, separators 3, and end plates 4 is constrained by a frame 5.

[0025] Two electrodes 12 are arranged on one narrow surface of each battery cell 10. For ease of explanation, the surface provided with electrodes 12 is referred to as top surface 11. From the stacking direction, the two electrodes 12 are arranged at both ends of top surface 11 (one electrode 12 at each end). The X direction of the coordinate system in the figure corresponds to the stacking direction.

[0026] The electrodes 12 of adjacent battery cells 10 are connected by bus bars 20. The positive electrode 12 of one battery cell 10 is connected to the negative electrode 12 of another battery cell 10 by a bus bar 20. The positive electrode 12 of another battery cell 10 is connected to the negative electrode 12 of another adjacent battery cell 10 by another bus bar 20. All battery cells 10 are connected in series via a plurality of bus bars 20.

[0027] exist Figure 3 A perspective view of the battery pack 2 is shown in FIG. Figure 3 This is a partial enlarged view of the vicinity of several bus bars 20. Figure 3 In FIG, for the sake of convenience, the central bus bar 20 is depicted as being separated from the electrode 12. Figure 4 FIG shows an enlarged top view of the bus bar 20 and its surroundings. Figure 3 、 Figure 4 In the figure, the gray hatched area is the location where the bus bar 20 and the electrode 12 are welded, indicating the location where the bus bar and the electrode are temporarily melted by the heat of welding. In the following, for convenience of explanation, the gray hatched area is referred to as the "melting area."

[0028] As described above, the battery cell 10 has an electrode 12 on its upper surface 11. The electrode 12 is a protrusion protruding from the upper surface 11, and its top surface is flat. A small protrusion 13 is also provided on the top surface of the electrode 12.

[0029] The bus bar 20 is a metal plate having a U shape. For the sake of convenience, the bus bar 20 is divided into a pair of end portions 21a and 21b extending in parallel and a connecting portion 22 connecting the pair of end portions 21a and 21b. Figure 4 In the figure, two adjacent battery cells 10 are referred to as battery cells 10a and 10b, the electrode 12 of battery cell 10a is referred to as electrode 12a, and the electrode 12 of battery cell 10b is referred to as electrode 12b. The end 21a of the bus bar 20 is welded to electrode 12a, and the end 21b is welded to electrode 12b. Furthermore, when battery cells 10a and 10b are not distinguished from each other, they are referred to as battery cell 10. Similarly, when end 21a and 21b (electrodes 12a and 12b) are not distinguished from each other, they are referred to as end 21 (electrode 12).

[0030] (First embodiment)

[0031] A method for manufacturing the battery pack 2 in the first embodiment will be described. In particular, a process for welding the bus bar 20 to the electrodes 12a and 12b of the adjacent battery cells 10a and 10b will be described.

[0032] A hole 23a is provided at the end 21a, and a hole 23b is provided at the end 21b. Sometimes, holes 23a and 23b are not distinguished and are recorded as holes 23. Hole 23 expands in the center. The size of hole 23 is smaller than the area of the top surface of electrode 12 when viewed from above. In addition, the center of hole 23 is larger than the area of the top surface of small protrusion 13 when viewed from above. Busbar 20 is placed on adjacent electrodes 12 so that each hole 23 overlaps with each electrode 12 and small protrusion 13 is located in the center of each hole 23. Then, end 21a is welded to electrode 12a, and end 21b is welded to electrode 12b.

[0033] Each end portion 21 of the bus bar 20 and each electrode 12 are welded at both sides of the hole 23 (melting points 31, 32). Figure 4 The cross section of the dotted line V is shown in Figure 5 . For ease of explanation, the area between the two holes 23 along the busbar 20 is referred to as the middle area of the busbar 20, and the area outside the middle area along the length direction of the busbar 20 is referred to as the end area. The busbar 20 and the electrode 12a (12b) are welded on both sides of the hole 23a (23b). The melting part 31 belongs to the middle area, and the melting part 32 belongs to the end area. The end area can also be expressed as the area between the hole 23 and the end of the busbar. Figure 4 , the welded portions 31 and 32 are shown in gray. Furthermore, the welded portions 31a and 31b are collectively referred to as the melted portion 31, and the melted portions 32a and 32b are collectively referred to as the melted portion 32.

[0034] In the manufacturing method of the first embodiment, after welding bus bar 20 to one electrode (e.g., electrode 12a), when welding bus bar 20 to the other electrode (e.g., electrode 12b), bus bar 20 and electrode 12b are first welded at molten zone 31b, and then welded to electrode 12b at molten zone 32b. In other words, after welding bus bar 20 to one electrode (electrode 12a), bus bar 20 and the other electrode (electrode 12b) are welded at the middle region (molten zone 31b) between the two holes 23 of bus bar 20, and then welded to the other electrode (electrode 12b) at the end region (molten zone 32b) adjacent to the middle region of bus bar 20. Welding laser light is irradiated onto bus bar 20 to weld bus bar 20 to the electrodes.

[0035] Reference Figure 5The advantages of the above-mentioned welding sequence are explained. If, after welding the busbar 20 to the electrode 12a, the busbar 20 to the electrode 12b is welded at the end region (melting portion 32b), then the busbar 20 to the electrode 12b is welded at the middle region (melting portion 31b). When welding at the melting portion 31b, the busbar 20 thermally expands due to the heat of welding. At this time, both sides of the melting portion 31b (one side of the electrode 12a and one side of the melting portion 32b) are constrained. On both sides of the melting portion 31b, the busbar 20 cannot deform freely, and high stress is generated. This high stress may cause cracks in the busbar 20 or remain as residual stress.

[0036] In the manufacturing method disclosed in this specification, after the bus bar 20 is welded to one electrode 12 (for example, electrode 12a), the bus bar 20 is welded to the other electrode 12 (for example, electrode 12b) in the middle area (melting area 31b), and then the bus bar 20 is welded to the other electrode (electrode 12b) in the end area (melting area 32b) adjacent to the middle area.

[0037] When welding is performed on the molten portion 32b, one side of the molten portion (the side of the hole 23b) is constrained, but the opposite side is not constrained. Therefore, when welding heat is applied to the bus bar 20, the non-constrained side (the side of the hole 23b) is constrained. Figure 5 (The figure in the middle shows the right end of bus bar 20), leaving room for bus bar 20 to deform. Since bus bar 20 deforms unconstrained, the stress generated in bus bar 20 near the molten area is reduced. By welding bus bar 20 to electrode 12b in the middle region and then welding them to the end regions, stress generated in bus bar 20 can be suppressed. As a result, cracks in bus bar 20 and increases in residual stress can be suppressed.

[0038] The same applies when the bus bar 20 is first welded to the electrode 12b and then to the electrode 12a. That is, after welding the bus bar 20 to the electrode 12b, the bus bar 20 and the electrode 12a are welded at the molten portion 31a in the middle region, and then the bus bar 20 and the electrode 12a are welded at the molten portion 32a in the end region adjacent to the middle region.

[0039] The hole 23 is located between the center and the end of the busbar 20 along the length of the busbar. The area between the center of the busbar and the hole 23 can also be referred to as the middle area, and the area between the hole 23 and the end of the busbar can be referred to as the end area. The busbar 20 and the electrode 12 are welded on both sides of the hole 23. In the manufacturing method of the first embodiment, after the busbar 20 is welded to one electrode (electrode 12a), the busbar 20 is welded to the other electrode (electrode 12b) in the middle area using a laser, and then the busbar 20 is welded to the other electrode (electrode 12b) in the end area using a laser.

[0040] (Second embodiment)

[0041] Reference Figure 6 、 Figure 7A -7C describes the manufacturing method of the second embodiment. Figure 6 FIG is a top view of the bus bar 20 and its surroundings. Figure 6 An enlarged view of the dotted line range is shown below. Figure 7A -7C is along Figure 6 Cross-sectional view along line VII-VII. Figure 7A This is a picture when the irradiation of the welding laser LB is started. Figure 7B This is a diagram obtained when a certain amount of time has passed since the irradiation of the laser beam LB. Figure 7C This is a diagram when the laser LB is stopped.

[0042] The shapes of the battery cells 10a, 10b and bus bar 20 are the same as those in the first embodiment. Bus bar 20 has two holes 23 that are smaller than electrodes 12. Bus bar 20 is arranged so that each hole 23 overlaps with each electrode 12. The manufacturing method of the second embodiment differs from that of the first embodiment in the method of applying laser light to the melted portion 33.

[0043] To help understand, Figure 6 Gray hatching is added to the melted areas 32 and 33. As described above, the "melted area" is a region where the metal is temporarily melted by the heat of welding (heat of the laser), and when it cools and solidifies again, the bus bar and the terminal are joined. Figure 6 The dotted line TR in the lower figure represents the trajectory of the welding laser. That is, although the melted portion 33 reaches the edge 25 of the hole 23, the welding laser is irradiated onto the bus bar 20 at a position away from the edge 25. In other words, the laser light (dashed line TR) does not reach the edge 25 of the hole 23, but the melted portion 33 does reach the edge 25 of the hole 23.

[0044] In the manufacturing method of the second embodiment, the laser beam LB is irradiated to the bus bar 20 at a position away from the edge 25 of the hole 23, and the irradiation of the laser beam LB is stopped when the bus bar 20 is melted to the edge 25. Figure 7AAs shown, in the short time immediately after the laser LB is irradiated, the melting portion 33 (1) is small, and only the front surface of the bus bar 20 is melted, and the melting range does not reach the back surface of the bus bar 20. Here, the back surface of the bus bar 20 refers to the surface facing the electrode 12.

[0045] When the irradiation of the laser beam LB is further continued, the melted portion 33 ( 2 ) expands. Figure 7B The figure shows the state where the melted portion 33 (2) reaches the back of the bus bar 20. When the laser LB is further irradiated, the melted portion 33 (2) reaches the edge 25 of the hole 23. At this time, the inner side surface 26 of the hole 23 melts from the edge 25 on the front side of the bus bar 20 to the edge on the back side. In addition, the surface of the electrode 12 under the bus bar 20 also melts. The back of the bus bar 20 and the surface of the electrode 12 melt, and the two are joined. When Figure 7C When the laser LB is stopped in the state of , the molten portion 33 ( 3 ) spreads from the edge 25 on the front side of the bus bar 20 to the edge on the back side. Figure 7C The state represents the structure (shape) of so-called fillet welding, which can obtain high welding strength.

[0046] Furthermore, in the manufacturing method of the second embodiment, the irradiation point of laser light LB is away from the edge 25 of hole 23. Therefore, even if the irradiation point of laser light LB is slightly deviated, laser light LB will not directly irradiate electrode 12. Therefore, the transfer of welding heat to battery cell 10 is suppressed, and damage to battery cell 10 caused by welding heat can be suppressed.

[0047] In the second embodiment, in the end region, the melted portion 32 does not reach the edge of the hole 23. In the end region, as in the melted portion 33, the welding range can be extended to the edge 25. However, the laser beam LB is continuously irradiated to a position away from the edge 25.

[0048] The following describes the points to note regarding the technology described in the embodiments. The melting point 33 of the second embodiment can be expressed as follows. For ease of explanation, the two holes provided in the bus bar 20 are referred to as the first hole 23a and the second hole 23b. The bus bar 20 and the electrode 12 are welded on both sides of the first hole 23a. On the side close to the second hole 23b, the bus bar 20 and the electrode 12 are welded (melting point 33) to the edge of the first hole 23a. On the side away from the second hole 23b, the melting point 32 is away from the edge of the first hole 23a.

[0049] The same is true near the second hole 23b. On the side closer to the first hole 23a, the busbar 20 and electrode 12 are welded (melt portion 33) to the edge of the second hole 23b. On the side farther from the first hole 23a, a melt portion 32 separates from the edge of the second hole 23b. Melt portion 33 belongs to the middle region of the first embodiment, while melt portion 32 belongs to the end region of the first embodiment.

[0050] A technique that combines the manufacturing method of the first embodiment with the manufacturing method of the second embodiment is also suitable. That is, after welding the busbar 20 to one electrode (e.g., electrode 12a), the busbar 20 is welded to the other electrode (e.g., electrode 12b) in the middle region between the two holes 23 of the busbar 20. Then, the busbar 20 is welded to the other electrode (electrode 12b) in the end region of the busbar 20 adjacent to the middle region. During welding in the middle region, the busbar 20 is irradiated with laser LB at a position away from the edge of the hole 23, and the irradiation of laser LB is stopped when the busbar 20 melts to the edge 25. In the end region, the busbar 20 is welded to the electrode 12 in such a manner that the molten portion 32 does not reach the edge 25 of the hole 23.

[0051] While the specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The techniques described in the claims include technical solutions obtained by various modifications and alterations to the specific examples illustrated above. The technical elements described in this specification or the drawings are practical individually or in various combinations and are not limited to the combinations described in the technical solutions at the time of application. In addition, the techniques illustrated in this specification or the drawings can achieve multiple objectives simultaneously, and achieving one of the objectives itself is practical.

Claims

1. A method for manufacturing a battery pack, wherein the battery pack comprises a plurality of stacked battery cells, wherein electrodes of adjacent battery cells are connected by bus bars, The bus bar has two holes that are smaller than the electrodes and is arranged so that each hole overlaps with each electrode. The method for manufacturing a battery pack is characterized by comprising: Welding the bus bar to one of the electrodes; Then, welding the bus bar to the other electrode at a middle area between the two holes of the bus bar; Next, the bus bar and the other electrode are welded at an end region of the bus bar adjacent to the middle region.

2. The method for manufacturing a battery pack according to claim 1, wherein: The bus bar is irradiated with laser light at a position away from the edge of the hole, and the laser irradiation is stopped when the bus bar is melted to the edge.

3. The method for manufacturing a battery pack according to claim 1, wherein: In the welding at the intermediate region, the bus bar is irradiated with laser light at a position away from the edge of the hole, and the laser irradiation is stopped when the bus bar melts to the edge.

4. A method for manufacturing a battery pack, wherein the battery pack comprises a plurality of stacked battery cells, wherein electrodes of adjacent battery cells are connected by bus bars, The bus bar has two holes that are smaller than the electrodes and is arranged so that each hole overlaps with each electrode. The method for manufacturing a battery pack is characterized by comprising: The bus bar is irradiated with laser light at a position away from the edge of the hole, and the laser irradiation is stopped when the bus bar is melted to the edge.

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