Energy storage module

Abstract

To stabilize bonding strength between a bus bar and an external terminal, at both ends of a laser irradiation area in a longitudinal direction.SOLUTION: In a power storage module 1 based on the present disclosure, a bus bar 20 includes: an annular welding line 30 formed by being irradiated with laser to be bonded to an external terminal 11; and a laser irradiation area 40 that is an area inside an outer peripheral edge 30E of the welding line 30. The laser irradiation area 40 extends in a first direction DR1 and has a first end portion 41 located at one end in the first direction DR1, a second end portion 42 located at the other end in the first direction DR1, and a central portion 43 located at the center in the first direction DR1. Each of a first width dimension D1 that is a dimension of the first end portion 41 in a second direction DR2 orthogonal to the first direction DR1 and a second width dimension D2 that is a dimension of the second end portion 42 in the second direction DR2 is longer than a central width dimension DC that is a dimension of the central portion 43 in the second direction DR2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an energy storage module. [Background technology]

[0002] Conventionally, an energy storage module includes a plurality of energy storage cells. The energy storage cells have external terminals. The external terminals of the plurality of energy storage cells are connected to one another by bus bars. The external terminals and the bus bars are joined to one another by laser welding. Japanese Patent Laid-Open Publication No. 2016-196034 (Patent Document 1) discloses a technology related to laser welding. The welded structure disclosed in Patent Document 1 includes a first member and a second member joined to the first member by laser welding, and having a welded portion with at least one weld line formed thereon. Each end of the weld line is positioned away from a single periphery line that surrounds the welded portion at the shortest length. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-196034 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, when the region defined by the outer periphery is viewed as the laser irradiation region, the weld line is significantly curved at both longitudinal ends of the laser irradiation region. Irradiating the laser so as to significantly curve the weld line may result in a decrease in the output of the laser irradiator, the laser trajectory passing on the inner side of the intended path, or fluctuations in the laser scanning speed. This results in unstable joint strength at both longitudinal ends of the laser irradiation region.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide an energy storage module that can stabilize the bonding strength between the bus bar and the external terminal at both longitudinal ends of the laser irradiation area. [Means for solving the problem]

[0006] The energy storage module according to the present disclosure includes an energy storage cell and a bus bar. The energy storage cell has an external terminal. The bus bar is disposed on an upper surface of the external terminal and is joined to the external terminal by laser welding from above. The bus bar has an annular weld line formed by irradiating the bus bar with a laser for joining to the external terminal, and a laser irradiation area that is an area inside the outer periphery of the weld line. The laser irradiation area extends in a first direction and has a first end located at one end in the first direction, a second end located at the other end in the first direction, and a central portion located at the center of the first direction. A first width dimension that is the dimension of the first end in a second direction perpendicular to the first direction, and a second width dimension that is the dimension of the second end in the second direction, are each longer than a central width dimension that is the dimension of the central portion in the second direction.

[0007] According to the above configuration, since the first width dimension and the second width dimension are longer than the central width dimension, the joint length in the second direction between the bus bar and the external terminal is longer at the first end portion and the second end portion. This relatively reduces the influence of instability in joint strength caused by a large bend in the weld line. Therefore, the joint strength between the bus bar and the external terminal at both longitudinal ends of the laser irradiation area can be stabilized.

[0008] In the above-described energy storage module, the central width dimension may be equal to or greater than the thickness dimension of a portion of the bus bar that is located on the upper surface of the external terminal.

[0009] According to the above configuration, a desired bonding strength can be ensured in the center of the laser irradiated region.

[0010] In the above-described power storage module, a pair of holes may be formed on the upper surface of the external terminal, positioned on both sides of the laser irradiation region in the first direction when viewed from above and below.

[0011] According to the above configuration, during laser irradiation, molten pools formed at and near the first and second ends of the laser irradiation area flow into each hole. The molten pools solidify to form welds. The portions of the welds located at the opening edges of the holes have relatively low strength. When excessive external force acts on the bus bar and external terminal in the first direction, the bus bar is likely to break from the welds on the opening edges. In other words, it is easy to control the location of the bus bar breakage when excessive external force acts on both longitudinal sides of the laser irradiation area, thereby stabilizing the bond between the bus bar and the external terminal. [Effects of the Invention]

[0012] According to the present disclosure, it is possible to stabilize the bonding strength between the bus bar and the external terminal at both longitudinal ends of the laser irradiated region. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a partial perspective view schematically illustrating an electricity storage module according to a first embodiment of the present disclosure. [Figure 2] 1 is a plan view showing the vicinity of an external terminal of an electricity storage module according to a first embodiment of the present disclosure. [Figure 3] FIG. 2 is a plan view showing an external terminal according to the first embodiment of the present disclosure. [Figure 4] FIG. 2 is a plan view schematically showing a weld line and a laser irradiation region according to the first embodiment of the present disclosure. [Figure 5] FIG. 10 is a plan view showing an external terminal according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a description will be given of an energy storage module according to each embodiment of the present disclosure with reference to the drawings. In the following description of the embodiments, the same or corresponding parts in the drawings will be denoted by the same reference numerals, and description thereof will not be repeated.

[0015] (Embodiment 1) Fig. 1 is a partial perspective view schematically illustrating an energy storage module according to a first embodiment of the present disclosure. As shown in Fig. 1, the energy storage module 1 includes a (first) energy storage cell 10, a second energy storage cell 10a, and a bus bar 20. The energy storage module 1 is mounted on, for example, a hybrid vehicle that can run using power from at least one of a motor and an engine, or an electric vehicle that runs using driving power obtained from electric energy.

[0016] The energy storage cell 10 is, for example, a secondary battery such as a nickel-metal hydride battery or a lithium-ion battery. The energy storage cell 10 has a (first) external terminal 11 and a cell case 15. The external terminal 11 is fixed to the upper surface of the cell case 15. An electrode assembly (not shown) is housed in the cell case 15. The external terminal 11 is electrically connected to the positive electrode or the negative electrode of the electrode assembly. The second energy storage cell 10a has a similar configuration to the energy storage cell 10. The second energy storage cell 10a has a second external terminal 11a having a similar configuration to the external terminal 11.

[0017] The external terminal 11 is formed in a substantially rectangular parallelepiped shape and is made of a metal such as aluminum or an aluminum alloy.

[0018] Fig. 2 is a plan view showing the vicinity of the external terminals of the energy storage module according to the first embodiment of the present disclosure. As shown in Figs. 1 and 2, the bus bar 20 is disposed on the upper surface 111 of the external terminal 11 and on the upper surface 111a of the second external terminal 11a. The bus bar 20 is joined to each of the external terminal 11 and the second external terminal 11a by laser welding from above. This electrically connects the external terminal 11 and the second external terminal 11a to each other. The bus bar 20 is made of a metal such as aluminum, aluminum, or an aluminum alloy.

[0019] A through hole 22 is formed in a portion 21 of the bus bar 20 located on the upper surface 111 of the external terminal 11. Note that the through hole 22 does not necessarily have to be formed.

[0020] Fig. 3 is a plan view showing an external terminal according to the first embodiment of the present disclosure. As shown in Figs. 2 and 3, the bus bar 20 has an annular (first) welding line 30 and a laser irradiation area 40. Note that Fig. 3 shows the annular welding line 30 and the laser irradiation area 40 in a schematic manner for ease of understanding. In this embodiment, the bus bar 20 has a pair of welding lines 30 and a pair of laser irradiation areas 40 located on both sides of the through hole 22 when viewed from above. These may have the same configuration. Below, one welding line 30 and the corresponding laser irradiation area 40 will be described.

[0021] The annular weld line 30 is formed by irradiating a laser for joining to the external terminal 11. More specifically, when a laser is irradiated from above the bus bar 20 arranged on the upper surface 111 of the external terminal 11 toward the bus bar 20 while the irradiation position is moved, the weld line 30 is formed along the trajectory of the irradiation position.

[0022] The shape of the annular weld line 30 will now be described. Fig. 4 is a plan view schematically showing the weld line and laser irradiation area according to the first embodiment of the present disclosure. As shown in Fig. 4, the annular weld line 30 has a substantially rectangular ring-shaped outer shape. The weld line 30 has a pair of short sides 31 and a pair of long sides 32.

[0023] The pair of short sides 31 are portions of the weld line 30 located at both ends in the first direction DR1. The pair of short sides 31 extend in the second direction DR2. The second direction DR2 is a direction perpendicular to the first direction DR1. In this embodiment, the first direction DR1 and the second direction DR2 are both directions that are approximately perpendicular to the up-down direction, but the first direction DR1 and the second direction DR2 may both be inclined with respect to the up-down direction.

[0024] The pair of long sides 32 are portions of the welding line 30 that connect one end of the pair of short sides 31 to the other end of the pair of short sides 31. The pair of long sides 32 generally extend along the first direction DR1. The pair of long sides 32 are located inside both ends of the pair of short sides 31 when viewed from the first direction DR1.

[0025] The bus bar 20 further has a second welding line 35. The second welding line 35 also extends in an annular shape. The second welding line 35 is also formed by irradiating a laser for joining to the external terminal 11. A portion of the second welding line 35 overlaps with the welding line 30 (specifically, one of the short side portions 31). The second welding line 35 also extends along the second welding line 35 on the inner circumferential side of the welding line 30.

[0026] In this embodiment, the weld line 30 and the second weld line 35 are formed by a single laser irradiation. In FIG. 4 , the laser irradiation path is schematically indicated by white arrows on the weld line 30 and the second weld line 35. First, the weld line 30 is irradiated to a portion corresponding to one end of one short side portion 31. Then, the laser irradiation position is moved, thereby forming one short side portion 31, one long side portion 32, the other short side portion 31, and the other long side portion 32 in this order. Then, the laser irradiation position is moved from one end of the one short side portion 31 inside the weld line 30, thereby forming the second weld line 35. Thereafter, the laser irradiation position returns to one end of the one short side portion 31, thereby forming the second weld line 35. In this way, one end of the one short side portion 31 serves as the starting point and the ending point of the laser irradiation path. Note that the laser irradiation path is not limited to the above.

[0027] 2 to 4, the laser irradiation area 40 is defined as the area inside the outer peripheral edge 30E of the weld line 30 (the area indicated by the two-dot chain line in FIG. 4). A weld 50 extends into and outside the laser irradiation area 40. The weld 50 is a portion where the molten pool has solidified. The molten pool is formed when the busbar 20 and the external terminal 11 are melted by the heat of the laser irradiation during laser irradiation.

[0028] The laser irradiation area 40 extends in the first direction DR1. The laser irradiation area 40 has a first end 41, a second end 42, and a central portion 43. The first end 41 is located at one end in the first direction DR1. In this embodiment, the first end 41 corresponds to one short side portion 31 of the welding line 30. The second end 42 is located at the other end in the first direction DR1. In this embodiment, the second end 42 corresponds to the other short side portion 31 of the welding line 30. The central portion 43 is located in the center of the first direction DR1.

[0029] In this embodiment, the first width dimension D1, which is the dimension of the first end 41 in the second direction DR2 perpendicular to the first direction DR1, and the second width dimension D2, which is the dimension of the second end 42 in the second direction DR2, are each longer than the central width dimension DC, which is the dimension of the central portion 43 in the second direction DR2.

[0030] According to the above configuration, the first width dimension D1 and the second width dimension D2 are longer than the central width dimension DC, so that the joint length in the second direction DR2 between the busbar 20 and the external terminal 11 is longer at the first end 41 and the second end 42. This makes it possible to relatively reduce the influence of instability in joint strength caused by a large bend in the weld line 30. This makes it possible to stabilize the joint strength between the busbar 20 and the external terminal 11 at both longitudinal ends of the laser irradiation region 40.

[0031] Furthermore, in this embodiment, the central width dimension DC is equal to or greater than the thickness dimension DT (see FIG. 1) of the portion 21 of the bus bar 20 located on the top surface 111 of the external terminal 11.

[0032] According to the above configuration, a desired bonding strength can be ensured in the central portion 43 of the laser irradiation region 40.

[0033] (Embodiment 2) The following describes an energy storage module according to a second embodiment of the present disclosure. The energy storage module according to the second embodiment of the present disclosure differs from the energy storage module according to the second embodiment of the present disclosure in the configuration of its external terminals. Therefore, the description of the same configuration and effects as those of the energy storage module according to the first embodiment of the present disclosure will not be repeated.

[0034] Fig. 5 is a plan view showing an external terminal according to the second embodiment of the present disclosure. In Fig. 5, the annular weld line 30 and the laser irradiation region 40 are shown schematically for ease of understanding.

[0035] As shown in Figure 5, in embodiment 2 of the present disclosure, a pair of holes 12 are formed on the upper surface 111S of the external terminal 11S, located on both sides of the laser irradiation area 40 in the first direction DR1 when viewed from the top and bottom.

[0036] According to the above configuration, during laser irradiation, molten pools formed at and near the first end 41 and second end 42 of the laser irradiation region 40 flow into each hole 12. The molten pools solidify to form welds 50. The portions of the welds 50 located at the opening edges 121 of the holes 12 have relatively low strength. When excessive external force acts on the busbar 20 and the external terminal 11S in the first direction DR1, the busbar 20 is likely to break from the welds 50 on the opening edges 121. That is, on both sides of the longitudinal direction (first direction DR1) of the laser irradiation region 40, it is easy to control the location of breakage of the busbar 20 when excessive external force acts, thereby stabilizing the joining state between the busbar 20 and the external terminal 11S.

[0037] As described above, the hole 12 has the opening edge 121. The opening edge 121 has a circular outer shape, but the shape of the opening edge 121 is not limited to a circular shape.

[0038] In the above-described embodiments, configurations that can be combined may be combined with each other.

[0039] It should be noted that the embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims rather than the description of the above embodiments, and further includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0040] 1 energy storage module, 10 energy storage cell, 10a second energy storage cell, 11, 11S external terminal, 11a second external terminal, 12 hole portion, 121 opening edge, 15 cell case, 20 bus bar, 22 through hole, 30 welding line, 30E outer peripheral edge, 31 short side portion, 32 long side portion, 35 second welding line, 40 laser irradiation area, 41 first end portion, 42 second end portion, 43 central portion, 50 welding portion.

Claims

1. a storage cell having an external terminal; a bus bar disposed on an upper surface of the external terminal and joined to the external terminal by laser welding from above, the bus bar has an annular weld line formed by irradiating a laser for joining to the external terminal, and a laser irradiated region that is a region inside an outer periphery of the weld line, the laser irradiation region extends in a first direction which is a longitudinal direction, and has a first end portion located at one end in the first direction, a second end portion located at the other end in the first direction, and a central portion located at a center in the first direction, a first width dimension, which is the dimension of the first end in a second direction that is the direction of a short side perpendicular to the first direction, and a second width dimension, which is the dimension of the second end in the second direction, are each longer than a central width dimension, which is the dimension of the central portion in the second direction.

2. The energy storage module according to claim 1 , wherein the central width dimension is equal to or greater than a thickness dimension of a portion of the bus bar that is located on the upper surface of the external terminal.

3. The energy storage module according to claim 1 , wherein the upper surface of the external terminal has a pair of holes formed therein, the holes being located on both sides of the laser irradiation area in the first direction when viewed from above and below.

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