Battery pack manufacturing method

Abstract

To provide a technology for appropriately welding a busbar and an electrode in a battery pack in which the electrodes of adjacent battery cells are connected by a busbar.SOLUTION: In a battery pack 2, electrodes 12 of adjacent battery cells 10 are connected by a busbar 20. The bus bar 20 has two holes smaller than the electrodes 12, and is arranged such that the holes respectively overlap the electrodes 12. In a battery pack manufacturing method, the busbar 20 and one electrode 12 are welded, the busbar 20 and the other electrode 12 are welded in the middle region between the two holes of the busbar 20, and then the busbar 20 and the other electrode 12 are welded together in the end region adjacent to the middle region of the busbar 20.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a battery pack. A battery pack is a device in which a plurality of battery cells are stacked, and electrodes of adjacent battery cells are connected by bus bars. [Background technology]

[0002] An example of a battery pack is disclosed in Patent Document 1. A battery pack is a device in which multiple battery cells are stacked. In a battery pack, the electrodes of adjacent battery cells are connected by bus bars. The bus bars electrically connect the multiple battery cells in series or parallel. In the battery pack in Patent Document 1, the bus bars and electrodes are welded with a laser. A "bus bar" is a component made of conductive metal pieces that has low internal resistance and is suitable for transmitting power. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 130705 Summary of the Invention [Problem to be solved by the invention]

[0004] If the welding strength between the bus bar and the electrode is low, the bus bar will easily come off the electrode. Attempting to increase the welding strength may result in large stress being generated in the bus bar during welding. Alternatively, attempting to increase the welding strength may result in the heat of welding damaging the battery cells. This specification provides a technology for appropriately welding the bus bar and the electrode. [Means for solving the problem]

[0005] The manufacturing method disclosed in this specification targets the following battery pack. In the battery pack, the electrodes of adjacent battery cells are connected by a bus bar. The bus bar has two holes that are smaller than the electrodes, and the holes are arranged so that they overlap with each other. In the manufacturing method disclosed in this specification, after welding the bus bar to one electrode, the bus bar is welded to the other electrode in a middle region between the two holes of the bus bar, and then the bus bar is welded to the other electrode in an end region adjacent to the middle region of the bus bar.

[0006] If the busbar and electrode are welded in the middle region after being welded in the end region, high stress will occur in the middle region of the busbar. This is because the busbar and electrode are welded in the region between the two restrained points (the weld between the busbar and one electrode, and the weld between the busbar and the other electrode in the end region) while the two points are constrained. If further welding is performed between the two constrained points, there will be no room for the busbar to deform, and high stress will occur inside the busbar.

[0007] If two other points (the welding point with one electrode and the welding point between the bus bar and the other electrode in the middle region) are restrained and then the bus bar is welded to the other electrode outside the two restraint points (i.e., the end region), there will be room for the bus bar to deform during the final welding, and the stress generated in the bus bar will be reduced.

[0008] The manufacturing method disclosed in this specification may have the following features. The bus bar has two holes smaller than the electrodes, and the holes are positioned so that they overlap with the respective electrodes. A welding laser is irradiated onto the bus bar at a position away from the edge of the holes, and the laser irradiation is stopped when the bus bar melts down to the edge. Simply applying the laser to a point away from the edge of the holes does not weld the electrode and the weld piece down to the edge of the holes, and high weld strength is not achieved. If the laser is irradiated directly onto the edge of the bus bar, a large amount of heat may be transferred to the electrode, which may damage the battery cell. By irradiating the bus bar with a laser at a position away from the edge of the holes and stopping the laser irradiation when the bus bar melts down to the edge, the edge of the bus bar and the electrode can be welded without damaging the battery cell. Welding the electrode to the bus bar up to the edge of the bus bar achieves high weld strength. Note that at this time, the bus bar and the electrode are in a so-called fillet weld state. Excellent results can be achieved even with fillet welding alone.

[0009] Details and further improvements of the technology disclosed in this specification are described in the following "Description of Embodiments of the Invention." [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a plan view of the battery pack. [Figure 2] FIG. 2 is a side view of the battery pack. [Figure 3] FIG. [Figure 4] FIG. [Figure 5] FIG. 5 is a cross-sectional view taken along dashed line V in FIG. [Figure 6] FIG. [Figure 7A] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. 6 (1). [Figure 7B] FIG. 7 is a cross-sectional view (2) taken along line VII-VII in FIG. [Figure 7C] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. 6 (3). DETAILED DESCRIPTION OF THE INVENTION

[0011] Prior to describing the manufacturing method of the embodiment, the battery pack 2 will be described. FIG. 1 shows a plan view of the battery pack 2, and FIG.

[0012] The battery pack 2 is a power source made up of multiple stacked battery cells 10. The battery cells 10 have a flat shape and are arranged so that the wide surfaces of adjacent battery cells 10 face each other. Spacers 3 are placed between adjacent battery cells 10. The multiple battery cells 10 and multiple spacers 3 are stacked one by one in an alternating pattern. End plates 4 are placed on both ends of the stack of battery cells 10 and spacers 3. The spacers 3 and end plates 4 protect the battery cells 10. The stack of battery cells 10, spacers 3, and end plates 4 is bound together by a frame 5.

[0013] Two electrodes 12 are arranged on one narrow surface of each battery cell 10. For ease of explanation, the surface on which the electrodes 12 are provided is referred to as the top surface 11. The two electrodes 12 are provided on both ends of the top surface 11 when viewed from the stacking direction. The X direction of the coordinate system in the drawing corresponds to the stacking direction.

[0014] 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 of another battery cell 10 is connected to the negative electrode 12 of another adjacent battery cell 10 by a bus bar 20. All of the battery cells 10 are connected in series by the multiple bus bars 20.

[0015] FIG. 3 shows a perspective view of the battery pack 2. FIG. 3 is a partially enlarged view of the vicinity of several bus bars 20. For ease of explanation, the central bus bar 20 is depicted separated from the electrode 12 in FIG. 3. FIG. 4 shows an enlarged plan view of the periphery of the bus bar 20. In FIGS. 3 and 4, the gray-hatched areas indicate the locations where the bus bars 20 and the electrodes 12 are welded, and where the bus bars and the electrodes are temporarily melted by the heat of welding. Hereinafter, for convenience, the gray-hatched areas will be referred to as "melted locations."

[0016] As described above, the battery cell 10 has an electrode 12 on its top surface 11. The electrode 12 is a protrusion that protrudes from the top surface 11, and its top surface is flat. A small protrusion 13 is further provided on the top surface of the electrode 12.

[0017] The bus bar 20 is a U-shaped metal plate. For ease of explanation, the bus bar 20 is divided into a pair of end portions 21a, 21b extending parallel to one another and a connecting portion 22 connecting the pair of end portions 21a, 21b. For ease of explanation, two adjacent battery cells 10 in FIG. 4 may be referred to as battery cells 10a, 10b, the electrode 12 of the battery cell 10a as electrode 12a, and the electrode 12 of the battery cell 10b as electrode 12b. The end portion 21a of the bus bar 20 is welded to the electrode 12a, and the end portion 21b is welded to the electrode 12b. When the battery cells 10a, 10b are not to be distinguished from one another, they are referred to as battery cells 10. Similarly, when the end portions 21a, 21b (electrodes 12a, 12b) are not to be distinguished from one another, they are referred to as end portion 21 (electrode 12).

[0018] (First embodiment) A method for manufacturing a battery pack 2 will be described. In particular, a process for welding the bus bar 20 to the electrodes 12a, 12b of adjacent battery cells 10a, 10b will be described.

[0019] A hole 23a is provided in the end 21a, and a hole 23b is provided in the end 21b. When holes 23a and 23b are not to be distinguished, they may be referred to as hole 23. Hole 23 is widened at the center. The size of hole 23 is smaller than the area of ​​the top surface of electrode 12 when viewed in a plan view. The center of hole 23 is larger than the area of ​​the top surface of small protrusion 13 when viewed in a plan view. Busbar 20 is placed on adjacent electrodes 12 so that each hole 23 overlaps with each electrode 12 and the 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.

[0020] Each end 21 of the busbar 20 and each electrode 12 are welded on both sides of the hole 23 (fusion points 31, 32). A cross section taken along dashed line V in FIG. 4 is shown in FIG. 5. For ease of explanation, the region between the two holes 23 along the busbar 20 is referred to as the middle region of the busbar 20, and the regions outside the middle region along the longitudinal direction of the busbar 20 are referred to as the end regions. The busbar 20 and the electrode 12a (12b) are welded on both sides of the hole 23a (23b). The fusion point 31 belongs to the middle region, and the fusion point 32 belongs to the end region. The end region may also be expressed as the region between the hole 23 and the busbar end. In FIG. 4, the weld welds 31, 32 are shown in gray. The weld welds 31a, 31b are collectively referred to as the fusion point 31, and the weld welds 32a, 32b are collectively referred to as the fusion point 32.

[0021] In the manufacturing method of the first embodiment, after welding the bus bar 20 to one electrode (e.g., electrode 12a), when welding the bus bar 20 to the other electrode (e.g., electrode 12b), the bus bar 20 and electrode 12b are first welded by welding fusion 31b, and then the bus bar 20 and electrode 12b are welded by welding fusion 32b. In other words, after welding the bus bar 20 to one electrode (e.g., electrode 12a), the bus bar 20 and the other electrode (electrode 12b) are welded in an intermediate region (weld fusion point 31b) between two holes 23 of the bus bar 20, and then the bus bar 20 and the other electrode (electrode 12b) are welded in an end region (melt point 32b) adjacent to the intermediate region of the bus bar 20. A welding laser beam is irradiated onto the bus bar 20 to weld the bus bar 20 to the electrode.

[0022] The advantages of the above welding order will be explained with reference to FIG. 5. Suppose that after welding the bus bar 20 to the electrode 12a, the bus bar 20 is welded to the electrode 12b in the end region (melting point 32b), and then the bus bar 20 is welded to the electrode 12b in the middle region (melting point 31b). When welding is performed at the melting point 31b, the bus bar 20 thermally expands due to the heat of welding. At this time, both sides of the melting point 31b (the side of the electrode 12a and the side of the melting point 32b) are constrained. The bus bar 20 cannot deform freely on both sides of the melting point 31b, and high stress is generated. This high stress can cause cracks in the bus bar 20 or remain as residual stress.

[0023] In the manufacturing method disclosed in this specification, after welding the bus bar 20 to one electrode 12 (e.g., electrode 12a), the bus bar 20 is welded to the other electrode 12 (e.g., electrode 12b) in the middle region (melting point 31b), and then the bus bar 20 is welded to the other electrode (electrode 12b) in the end region (melting point 32b) adjacent to the middle region.

[0024] When welding is performed at the fusion point 32b, one side of the fusion point (the side of the hole 23b) is constrained, but the other side is not. Therefore, when welding heat is applied to the bus bar 20, there is room for the bus bar 20 to deform on the unconstrained side (the right end of the bus bar 20 in FIG. 5). The bus bar 20 deforms without being constrained, reducing the stress generated in the bus bar 20 near the fusion point. By welding the bus bar 20 to the electrode 12b in the middle region and then welding the bus bar 20 to the electrode 12b in the end region, the stress generated in the bus bar 20 can be reduced. As a result, the occurrence of cracks in the bus bar 20 and the increase in residual stress are suppressed.

[0025] The same applies to the case where bus bar 20 and electrode 12b are welded first, and then bus bar 20 and electrode 12a are welded. That is, after bus bar 20 and electrode 12b are welded, bus bar 20 and electrode 12a are welded at melting point 31a belonging to the intermediate region, and then bus bar 20 and electrode 12a are welded at melting point 32a belonging to the end region adjacent to the intermediate region.

[0026] A hole 23 is located between the center and end of the busbar 20 along the longitudinal direction of the busbar. The area between the center of the busbar and the hole 23 may be referred to as the middle region, and the area between the hole 23 and the end of the busbar may be referred to as the end region. 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 welding the busbar 20 to one electrode (electrode 12a), the busbar 20 and the other electrode (electrode 12b) are welded in the middle region with a laser, and then the busbar 20 and the other electrode (electrode 12b) are welded in the end region with a laser.

[0027] Second Embodiment A manufacturing method of a second embodiment will be described with reference to Fig. 6 and Figs. 7A-7C. Fig. 6 is a plan view of the periphery of bus bar 20. An enlarged view of the dashed line area is shown at the bottom of Fig. 6. Figs. 7A-7C are cross-sectional views taken along line VII-VII in Fig. 6. Fig. 7A is a view when irradiation of welding laser LB begins, and Fig. 7B is a view a short time after irradiation of laser LB. Fig. 7C is a view when laser LB is stopped.

[0028] The shapes of the battery cells 10a, 10b and the bus bar 20 are the same as in the first embodiment. The bus bar 20 has two holes 23 that are smaller than the electrodes 12. The bus bar 20 is arranged so that the holes 23 overlap with the respective electrodes 12. In the manufacturing method of the second embodiment, the method of applying the laser to the melting point 33 differs from that of the first embodiment.

[0029] To facilitate understanding, melted areas 32 and 33 are hatched gray in Figure 6. As mentioned above, the "melted area" is the area where the metal is temporarily melted by the heat of welding (laser heat), and when it cools and re-solidifies, the bus bar and terminal are joined. The dashed line TR in the lower diagram of Figure 6 represents the trajectory of the welding laser. That is, although melted area 33 reaches edge 25 of hole 23, the welding laser is irradiated onto bus bar 20 at a position away from edge 25. In other words, the laser (dashed line TR) does not reach edge 25 of hole 23, but melted area 33 does reach edge 25 of hole 23.

[0030] In the manufacturing method of the second embodiment, the bus bar 20 is irradiated with a laser beam LB 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 up to the edge 25. As shown in FIG. 7A, for a while after the irradiation of the laser beam LB starts, the melted area 33(1) is small, and only the front surface of the bus bar 20 is melted, and the melted range does not reach the back surface of the bus bar 20. Here, the back surface of the bus bar 20 means the surface facing the electrode 12.

[0031] As the laser beam LB continues to be applied, the melted portion 33(2) expands. FIG. 7(B) shows the state where the melted portion 33(2) has reached the back surface of the busbar 20. As the laser beam LB continues to be applied, the melted portion 33(3) reaches the edge 25 of the hole 23. At this time, the inner surface 26 of the hole 23 melts from the edge 25 on the front surface side of the busbar 20 to the edge on the back surface side. The surface of the electrode 12 below the busbar 20 also melts. The back surface of the busbar 20 and the surface of the electrode 12 melt and are joined together. When the laser beam LB is stopped in the state shown in FIG. 7(C), the melted portion 33(3) expands from the edge 25 on the front surface side of the busbar 20 to the edge on the back surface side. The state shown in FIG. 7(C) is a so-called fillet weld, and high weld strength is obtained.

[0032] Furthermore, in the manufacturing method of the second embodiment, the irradiation point of the laser LB is away from the edge 25 of the hole 23. Therefore, even if the irradiation point of the laser LB is slightly shifted, the laser LB does not directly strike the electrode 12. This reduces the amount of welding heat transferred to the battery cell 10, and reduces damage to the battery cell 10 caused by the welding heat.

[0033] In the second embodiment, in the end region, the melted point 32 does not reach the edge of the hole 23. In the end region, the welding range may be expanded to the edge 25, similar to the melted point 33. However, the laser LB continues to irradiate a position away from the edge 25.

[0034] Points to note regarding the technology described in the embodiments will be described below. The melting point 33 in the second embodiment can be expressed as follows. For ease of explanation, the two holes provided in the bus bar 20 will be 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 closer to the second hole 23b, the bus bar 20 and the electrode 12 are welded up to the edge of the first hole 23a (melting point 33). On the side farther from the second hole 23b, the melting point 32 is away from the edge of the first hole 23a.

[0035] The same is true in the vicinity of second hole 23b. On the side closer to first hole 23a, bus bar 20 and electrode 12 are welded up to the edge of second hole 23b (melted point 33). On the side farther from first hole 23a, melted point 32 is away from the edge of second hole 23b. Melted point 33 belongs to the middle region of the first embodiment, and melted point 32 belongs to the end region of the first embodiment.

[0036] A technique that combines the manufacturing methods of the first and second embodiments is also suitable. That is, after welding the bus bar 20 to one electrode (e.g., electrode 12a), the bus bar 20 is welded to the other electrode (e.g., electrode 12b) in the intermediate region between the two holes 23 of the bus bar 20, and then the bus bar 20 is welded to the other electrode (electrode 12b) in the end region adjacent to the intermediate region of the bus bar 20. In the welding in the intermediate region, the bus bar 20 is irradiated with a laser LB at a position away from the edge of the hole 23, and the irradiation of the laser LB is stopped when the bus bar 20 is melted up to the edge 25. In the end region, the bus bar 20 is welded to the electrode 12 so that the melted point 32 does not reach the edge 25 of the hole 23.

[0037] Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives alone is technically useful. [Explanation of symbols]

[0038] 2: Battery pack 3: Spacer 4: End plate 5: Frame 10, 10a, 10b: Battery cell 11: Top surface 12, 12a, 12b: Electrode 13: Small protrusion 20: Bus bar 21, 21a, 21b: End 22: Connection part 23, 23a, 23b: Hole 25: Edge 26: Inner surface 31, 31a, 31b, 32, 32a, 32b, 33: Melted part

Claims

1. A method for manufacturing a battery pack in which a plurality of battery cells are stacked, and electrodes of adjacent battery cells are connected by bus bars, the bus bar has two holes smaller than the electrodes, and is arranged so that the holes overlap with the electrodes, respectively; a first electrode and a second electrode, respectively, and a second electrode and a third electrode, respectively, connected to the first electrode and the second electrode, and connected to the second electrode and the third electrode, respectively, at an end region of the bus bar adjacent to the intermediate region of the bus bar.

2. The manufacturing method according to claim 1 , wherein the welding in the intermediate region includes irradiating the bus bar with a laser at a position away from an edge of the hole, and stopping the irradiation of the laser when the bus bar is melted up to the edge.

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