Manufacturing method for energy storage modules

Abstract

Providing a technology to improve the uniformity of welding depth in laser welding between busbars and electrode terminals. [Solution] The technology disclosed herein provides a method for manufacturing an energy storage module comprising a busbar and electrode terminals. This manufacturing method involves overlapping the busbar and electrode terminals and laser welding the two components. In the laser welding, a laser beam is irradiated onto the busbar, which is overlapped with the electrode terminals, along a predetermined welding pattern. The welding pattern includes a plurality of weld lines that are aligned in mutually different directions. The busbar has a build-up portion provided at the point where one of the plurality of weld lines intersects with another of the plurality of weld lines on the surface irradiated with the laser beam in the laser welding.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a power storage module.

Background Art

[0002] As an example of a power storage module, a power storage module including a secondary battery such as a lithium-ion secondary battery can be mentioned. In recent years, this type of power storage module has been suitably used, for example, as a power source for driving vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.

[0003] WO 2015 / 186168 discloses a laser welding method in which thin plate-like workpieces to be welded are overlapped and laser light is irradiated onto the overlapping portion between the workpieces to be welded to perform welding. In this method, while irradiating laser light along a preset multi-loop-shaped weld line, the laser light is moved, and at this time, the movement of the laser light along the outer loop-shaped weld line is performed prior to the movement of the laser light along the inner loop-shaped weld line. The publication describes that with such a configuration, even if there is a gap between the workpieces to be welded, the gap is gradually filled from the outer region toward the inner region, and at least in the inner region of the inner loop-shaped weld line, a reliable welded joint can be made.

[0004] The power storage device disclosed in WO 2019 / 082956 includes a plurality of power storage elements having external terminals, and a bus bar that connects the external terminals of different power storage elements in a conductive manner. The bus bar includes a pair of connection portions arranged so as to overlap the external terminals. In each of the pair of connection portions, a plurality of curved weld portions that are curved convexly toward the inside in the first direction in which the pair of connection portions are arranged are formed. The plurality of curved weld portions are formed so as to be arranged in the first direction. The publication describes that with such a configuration, it is possible to suppress the bus bar from peeling off from the external terminals of the power storage elements.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] International Publication No. 2015 / 186168 [Patent Document 2] International Publication No. 2019 / 082956 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The manufacturing process for energy storage modules includes, for example, laser welding of busbars and electrode terminals. In laser welding, the busbars and electrode terminals are welded together, for example, by irradiating a laser beam onto a predetermined welding pattern. After the laser beam is irradiated in the direction defined by one welding line in the welding pattern, the direction of the laser beam may be changed so that the laser beam is irradiated in the direction defined by another welding line. When the direction of the laser beam is changed from one direction to another, the laser beam may be irradiated for a longer time at the change point than at other points. As a result, the welding at the change point tends to be deeper than the welding at other points. This is undesirable because it can lead to damage to other components, welding defects, poor conductivity, etc.

[0007] Therefore, the present invention has been made in view of the above circumstances, and its object is to provide a technology to improve the uniformity of the welding depth in laser welding between a busbar and an electrode terminal. [Means for solving the problem]

[0008] The technology disclosed herein provides a method for manufacturing an energy storage module comprising a busbar and electrode terminals. This manufacturing method involves overlapping the busbar and electrode terminals and laser welding the two components. In the laser welding, a laser beam is irradiated onto the busbar, which is overlapped with the electrode terminals, along a predetermined welding pattern. The welding pattern includes a plurality of weld lines that are aligned in mutually different directions. On the surface of the busbar irradiated with the laser beam in the laser welding, a build-up portion is provided at the intersection of one of the plurality of weld lines and another of the plurality of weld lines. With this configuration, the uniformity of the welding depth in the laser welding of the busbar and electrode terminals can be improved. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a perspective view of the energy storage module 100. [Figure 2] Figure 2 is a cross-sectional view taken along line II-II in Figure 1. [Figure 3] Figure 3 is an explanatory diagram of the welding pattern WP1. [Figure 4] Figure 4 is a partial plan view of the busbar 14. [Figure 5] Figure 5 is a partial side view of the busbar 14. [Figure 6] Figure 6 is a graph showing the welding depth along the first weld line W11. [Figure 7] Figure 7 is a graph showing the welding depth along the third weld line W13. [Figure 8] Figure 8 is a graph showing the welding depth along the first weld line W11. [Figure 9] Figure 9 is a graph showing the welding depth along the third weld line W13. [Figure 10] Figure 10 is a partial plan view of the busbar 24. [Modes for carrying out the invention]

[0010] The following describes one embodiment of the energy storage device disclosed herein. The embodiment described herein is not limited to the technology disclosed herein. Unless otherwise specified, the technology disclosed herein is not limited to the embodiment described herein. The drawings are schematic and do not necessarily reflect the actual object. Components and parts that perform the same function are appropriately denoted by the same reference numeral, and redundant explanations may be omitted. In the drawings, the reference numerals "R", "L", "U", "D", "F", and "Rr" indicate "right", "left", "up", "down", "front", and "back", respectively. The notation "A~B" indicating a numerical range means "A or more and B or less" unless otherwise specified, and also includes the meaning of "greater than A and less than B".

[0011] In this specification, "energy storage device" refers to a device in which charging and discharging occur through the movement of a charge carrier between a pair of electrodes (positive and negative electrodes) via an electrolyte. Energy storage devices include secondary batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries; and capacitors such as lithium-ion capacitors and electric double-layer capacitors. An energy storage device may be, for example, a lithium-ion secondary battery.

[0012] Figure 1 is a perspective view of the energy storage module 100. The energy storage module 100 is the energy storage module to be manufactured by the manufacturing method disclosed herein. As shown in Figure 1, the energy storage module 100 comprises a plurality of energy storage devices 12 and a busbar 14. As shown in Figure 1, each energy storage device 12 is arranged so that its first surface 30a faces the other. Here, the plurality of energy storage devices 12 are arranged in a direction from one first surface 30a of each energy storage device 12 toward the other first surface 30a. The direction in which the plurality of energy storage devices 12 are arranged is the direction from the rear (Rr) side toward the front (F) side in Figure 1. Hereinafter, the arrangement in which the plurality of energy storage devices 12 are arranged will also be referred to as the "arrangement direction P".

[0013] In the configuration shown in Figure 1, the energy storage device 12 comprises a rectangular parallelepiped case 30, which has a pair of opposing first faces 30a, a pair of opposing second faces 30b, and a bottom face 30c. The first faces 30a are rectangular in shape and are the largest surface area of ​​the case 30. As shown in Figure 1, the pair of opposing first faces 30a are surfaces extending from a pair of opposing long sides of the bottom face 30c. The second faces 30b are rectangular in shape and are the surfaces sandwiched between the pair of opposing first faces 30a. As shown in Figure 1, the pair of opposing second faces 30b are surfaces extending from a pair of opposing short sides of the bottom face 30c.

[0014] The energy storage device 12 comprises, for example, a case 30, an electrode body (not shown) housed within the case 30, and an electrolyte (not shown). The case 30 comprises a main body 31 and a sealing plate 32, as shown in Figure 1. The main body 31 is, for example, a member that houses the electrode body and the electrolyte. The main body 31 here has a rectangular parallelepiped shape with one side open. In the configuration shown in Figure 1, the main body 31 has a pair of opposing first surfaces 30a, a pair of opposing second surfaces 30b, and a bottom surface 30c. Here, the bottom surface 30c and the opening are opposite each other. The sealing plate 32 is, for example, a member that closes the opening of the main body 31. The sealing plate 32 has a shape corresponding to the opening of the main body 31, and here it is rectangular (including substantially rectangular; the same applies hereinafter). The sealing plate 32 has a first through hole (not shown) and a second through hole 322 (see Figure 2). The first through hole is through which the positive electrode terminal 40 is inserted. The second through hole 322 is through which the negative electrode terminal 50 is inserted. The electrode body and electrolyte of the energy storage device 12 can be any electrode body and electrolyte of this type of energy storage device (for example, a lithium-ion secondary battery) without any particular limitations.

[0015] In this embodiment, the energy storage device 12 includes a positive terminal 40 and a negative terminal 50 in a case 30. In the configuration shown in Figures 1 and 2, the positive terminal 40 and the negative terminal 50 are attached to a sealing plate 32. The negative terminal 50 will be described first below.

[0016] Figure 2 is a sectional view taken along line II-II of Figure 1. In Figure 2, a cross-section near the connection portion between the bus bar 14 and the negative electrode terminal 50 is shown enlarged. As shown in Figure 2, the negative electrode terminal 50 has a negative electrode current collecting terminal 52 and a negative electrode external terminal 54. The negative electrode current collecting terminal 52 is, for example, a member connected to the negative electrode of an electrode body (not shown). In this embodiment, the negative electrode current collecting terminal 52 is in a flat plate shape. The negative electrode current collecting terminal 52 is arranged along the inner surface 32d of the sealing plate 32. The negative electrode current collecting terminal 52 is connected to the negative electrode of the electrode body through, for example, a current collecting plate (not shown). The negative electrode current collecting terminal 52 has a through hole 52h. In this embodiment, the negative electrode current collecting terminal 52 is connected to the negative electrode external terminal 54 by inserting a part of the negative electrode external terminal 54 into the through hole 52h. The negative electrode current collecting terminal 52 is preferably, for example, copper or a copper alloy (an alloy containing at least 70% by mass of copper among all components. The same shall apply hereinafter).

[0017] The negative electrode external terminal 54 is, for example, a part connected to the bus bar 14. In this embodiment, the negative electrode external terminal 54 has a part arranged inside the case 30 and a part arranged outside the case 30. As shown in Figure 2, the negative electrode external terminal 54 includes a first member 56 and a second member 58. The first member 56 is, for example, a part connected to the negative electrode current collecting terminal 52. In this embodiment, the first member 56 includes a connection portion 56a and a shaft portion 56b. The connection portion 56a is, for example, a part connected to the second member 58. In this embodiment, the connection portion 56a is in a disc shape. Here, the connection portion 56a is accommodated inside the recess 582 of the second member 58. The shaft portion 56b is, for example, a part connected to the negative electrode current collecting terminal 52. In this embodiment, the shaft portion 56b is in a cylindrical shape. The shaft portion 56b extends from the connection portion 56a. The shaft portion 56b is inserted through the through hole 52h of the negative electrode current collecting terminal 52.

[0018] The first member 56 is made of, for example, a first metal. The first metal may be, for example, aluminum, an aluminum alloy (an alloy containing at least 70% by mass of aluminum among all components; the same shall apply hereinafter), copper, or a copper alloy. Although not particularly limited, the first metal and the second metal described later may be the same or different from each other. When the first metal and the second metal are different metals from each other, the first metal is preferably copper or a copper alloy.

[0019] The second member 58 is, for example, a part where the bus bar 14 is welded. In this embodiment, the second member 58 is in a flat plate shape. The second member 58 is arranged along the outer surface 32u of the sealing plate 32. As shown in FIG. 2, the second member 58 has a non-through recess 582 on the first surface 581 in the thickness direction. The connecting portion 56a of the first member 56 is accommodated in the recess 582, and the peripheral portion thereof is caulked to the inner wall surface of the recess 582. Here, "the peripheral portion of the connecting portion 56a of the first member 56 is caulked to the inner wall surface of the recess 582" means, for example, a state in which the first member 56 is fixed to the second member 58 by pressure-welding the peripheral portion of the connecting portion 56a of the first member 56 to the inner wall surface of the insertion hole 582. The second surface 584 in the thickness direction of the second member 58 is a flat surface here. In this embodiment, the bus bar 14 is welded to the second surface 584.

[0020] The second member 58 is made of, for example, a second metal. The second metal may be, for example, aluminum, an aluminum alloy, copper, or an alloy mainly composed of copper. When the first metal and the second metal are different metals from each other, the second metal is preferably aluminum or an aluminum alloy.

[0021] The positive electrode terminal 40 may have, for example, the same structure as the negative electrode terminal 50. Therefore, the description of the structure of the positive electrode terminal 40 is omitted here. The positive electrode terminal 40 is preferably made of, for example, aluminum or an aluminum alloy.

[0022] As shown in Figure 2, the energy storage device 12 comprises a first insulating member 61 and a second insulating member 62. The first insulating member 61 is, for example, a member that insulates the negative electrode external terminal 54 from the sealing plate 32. In this embodiment, the first insulating member 61 is positioned between the negative electrode external terminal 54 and the outer surface 32u of the sealing plate 32, and between the negative electrode external terminal 54 and the second through hole 322. The second insulating member 62 is, for example, a member that insulates the sealing plate 32 from the negative electrode current collector terminal 52. In this embodiment, the second insulating member 62 is positioned between the inner surface 32d of the sealing plate 32 and the negative electrode current collector terminal 52. The materials constituting the first insulating member 61 and the second insulating member 62 can be any material used as an insulating member in this type of energy storage device (e.g., a lithium-ion secondary battery) without any particular limitations. Although not shown in the figures, the energy storage device 12 also has a similar insulating member on the positive electrode side.

[0023] A busbar 14 is, for example, a component that electrically connects two adjacent energy storage devices 12. As shown in Figure 1, the busbar 14 spans two adjacent energy storage devices 12 in the array direction P. In this embodiment, the busbar 14 spans the positive terminal 40 of one of the two adjacent energy storage devices 12 in the array direction P and the negative terminal 50 of the other energy storage device 12. The busbar 14 is laser-welded to the positive terminal 40 of one of the two adjacent energy storage devices 12 in the array direction P and the negative terminal 50 of the other energy storage device 12. The busbar 14 is made of, for example, aluminum or an aluminum alloy.

[0024] As shown in Figure 2, the busbar 14 is placed on the negative electrode external terminal 54 and welded to the negative electrode external terminal 54 (welded portion 14a). In the configuration shown in Figure 2, the busbar 14 is placed on the second surface 584 of the second member 58 and welded to the second member 58. In this embodiment, the upper surface 141 of the busbar 14 is the surface to which a laser beam is irradiated during the manufacturing process of the energy storage module 100. The lower surface 142 of the busbar 14 is the surface in contact with the negative electrode external terminal 54.

[0025] As shown in Figure 1, in the energy storage module 100, multiple energy storage devices 12 are constrained in the arrangement direction P. The energy storage module 100 comprises a spacer 11 and a pair of end plates 17. The spacer 11 is positioned between adjacent energy storage devices 12 in the arrangement direction P. The end plates 17 are positioned at both ends of the multiple energy storage devices 12 arranged in the arrangement direction P, constraining the multiple energy storage devices 12. The end plates 17 are bridged by metal restraint bands 18. The ends of the restraint bands 18 are fixed by screws 19.

[0026] The manufacturing method for the energy storage module 100 includes, for example, overlapping the busbar 14 and the negative electrode terminal 50 and laser welding the two components. In laser welding, a laser beam is irradiated onto the busbar 14, which is overlapped with the negative electrode terminal 50, along a predetermined welding pattern WP1 (see Figure 3). Prior to this, it is preferable to prepare a plurality of energy storage devices 12. The manufacturing method for the energy storage devices 12 is not particularly limited, and for example, conventionally known methods can be used.

[0027] Figure 3 is an explanatory diagram of the welding pattern WP1. Figure 3 shows the welding pattern when welding the busbar 14 and the negative electrode terminal 50. The welding pattern WP1 is, for example, the trajectory of the laser beam irradiated when welding the busbar 14 and the negative electrode terminal 50. In the configuration shown in Figure 3, the welding pattern WP1 is spiral-shaped. When welding the busbar 14 and the negative electrode terminal 50, for example, the laser beam is irradiated along the welding pattern WP1 from the inside to the outside, with the inner first end WS1 as the starting point and the outer second end WE1 as the ending point.

[0028] As shown in Figure 3, the welding pattern WP1 includes a first welding line W11, a second welding line W12, a third welding line W13, and a fourth welding line W14, all aligned in different directions. In this embodiment, the first welding line W11 is a welding line aligned in a first direction D1, where D1 is the direction from the right (R) side to the left (L) side. In the embodiment shown in Figure 3, the welding pattern WP1 has two first welding lines W11. The second welding line W12 is a welding line aligned in a second direction D2, where D2 is the direction from the rear (Rr) side to the front (F) side. In the embodiment shown in Figure 3, the welding pattern WP1 has two second welding lines W12. The third welding line W13 is a welding line aligned in a third direction D3, where D3 is the direction from the left (L) side to the right (R) side. In the configuration shown in Figure 3, the welding pattern WP1 has two third welding lines W13. The fourth welding line W14 is a welding line along the fourth direction D4. The fourth direction D4 here is the direction from the front (F) side to the back (Rr) side. In the configuration shown in Figure 3, the welding pattern WP1 has one fourth welding line W14.

[0029] The shape shown in welding pattern WP1 is formed by combining, for example, a first welding line W11, a second welding line W12, a third welding line W13, and a fourth welding line W14. In the configuration shown in Figure 3, the shape shown in welding pattern WP1 is formed by connecting the first welding line W11, the second welding line W12, the third welding line W13, the fourth welding line W14, the first welding line W11, the second welding line W12, and the third welding line W13 in this order. Note that the shape of welding pattern WP1 shown in Figure 3 is just one example. Therefore, in other embodiments, the number of turns of the spiral can be changed by increasing or decreasing the number of each welding line to form a desired shape. For example, in another embodiment, a unit formed by connecting a first weld line W11, a second weld line W12, a third weld line W13, and a fourth weld line W14 in that order from the first end WS1 to the second end WE1, is repeated a desired number of times, and the number of turns of the spiral can be changed to form a desired size and shape by adding or omitting weld lines constituting the unit as needed.

[0030] In the configuration shown in Figure 3, in the welding pattern WP1, each weld line intersects at an angle of 90° ± 10°. In this embodiment, the first weld line W11 and the second weld line W12 intersect at an angle of 90° ± 10°. The second weld line W12 and the third weld line W13 intersect at an angle of 90° ± 10°. The third weld line W13 and the fourth weld line W14 intersect at an angle of 90° ± 10°.

[0031] Incidentally, in the negative electrode terminal 50, there may be a gap between the connection portion 56a of the first member 56 and the bottom surface or inner wall surface of the recess 582 of the second member 58 in which gas (for example, air) can accumulate. When the negative electrode terminal 50 is heated by the irradiation of the laser beam during laser welding, for example, the gas in the gap may expand within the gap. As a result, for example, pressure is applied to the bottom surface of the recess 582 due to the gas that has expanded within the gap. On the other hand, for example, a part of the second member 58 is melted by the irradiation of the laser beam. Therefore, due to the pressure from the gas, for example, a part of the molten second member 58 may be scattered into the surroundings. This can cause welding defects between the busbar 14 and the negative electrode terminal 50, and consequently, can cause poor conductivity between the busbar 14 and the negative electrode terminal 50. The scattering of a portion of the molten second member 58 into the surroundings can occur, for example, when the second surface 584 of the busbar 14 is irradiated with a laser beam and the second member 58 melts to a deeper level.

[0032] As described above, the welding pattern WP1 includes a first welding line W11, a second welding line W12, a third welding line W13, and a fourth welding line W14, all aligned in different directions. At the intersections of these welding lines, the laser beam tends to irradiate for a longer time than in other areas. Therefore, at the intersections of the welding lines, for example, the second member 58 may melt to a deeper depth, increasing the risk of molten second member 58 scattering. The inventors considered that if the uniformity of the welding depth of both members could be improved during the welding of the busbar 14 and the negative electrode terminal 50, the risk of molten second member 58 scattering could be reduced, and therefore investigated the welding of the busbar 14 and the electrode terminal (in this case, the negative electrode terminal 50).

[0033] Figure 4 is a partial plan view of the busbar 14. The welding pattern WP1 is also shown in Figure 4. Figure 5 is a partial side view of the busbar 14. Figure 5 shows a partial side view of the long side of the busbar 14. The busbar 14 shown in Figures 4 and 5 is used in the manufacturing process of the energy storage module 100 and is before it is laser-welded to the electrode terminals. As shown in Figures 4 and 5, the busbar 14 has a build-up portion 145 on its upper surface 141. The build-up portion 145 may be formed, for example, by press working.

[0034] The build-up portion 145 is provided, for example, to correspond to the portion where one weld line included in the welding pattern WP1 intersects with another weld line. The build-up portion 145 is, for example, a portion that protrudes from the upper surface 141 of the busbar 14. The build-up portion 145 is, for example, a portion that has a height of 1 / 8 to 1 / 2 of the thickness of the busbar 14 when the thickness of the busbar 14 is 1. In the configuration shown in Figure 4, the build-up portion 145 is provided to correspond to the portion A1 where the first weld line W11 and the second weld line W12 intersect, the portion B1 where the second weld line W12 and the third weld line W13 intersect, the portion C1 where the third weld line W13 and the fourth weld line W14 intersect, and the portion D1 where the fourth weld line W14 and the first weld line W11 intersect.

[0035] In this embodiment, as described above, the welding pattern WP1 includes a plurality of points where one welding line intersects with another welding line. In the busbar 14, the build-up portion 145 is provided to include at least two of the plurality of intersecting points included in the welding pattern WP1. From the viewpoint of realizing the effects of the technology disclosed herein, the two adjacent intersecting points are, for example, two adjacent intersecting points in the short-side direction (front-back direction in Figure 4) of the welding pattern WP1. In the embodiment shown in Figure 4, point A1 where the first welding line W11 and the second welding line W12 intersect, and point B1 where the second welding line W12 and the third welding line W13 intersect, are adjacent in the short-side direction of the welding pattern WP1. Point C1 where the third welding line W13 and the fourth welding line W14 intersect, and point D1 where the fourth welding line W14 and the first welding line W11 intersect, are adjacent in the short-side direction of the welding pattern WP1.

[0036] On the other hand, from the viewpoint of suppressing welding defects, the build-up portion 145 is not provided so as to include two adjacent intersecting portions in the longitudinal direction (left-right direction in Figure 4) of the welding pattern WP1. In the configuration shown in Figure 4, the portion B1 where the second welding line W12 and the third welding line W13 intersect, and the portion C1 where the third welding line W13 and the fourth welding line W14 intersect, are adjacent in the longitudinal direction of the welding pattern WP1. The portion A1 where the first welding line W11 and the second welding line W12 intersect, and the portion D1 where the fourth welding line W14 and the first welding line W11 intersect, are adjacent in the longitudinal direction of the welding pattern WP1.

[0037] The conditions for laser welding are not particularly limited. Preferably, the output of the laser beam is constant from the first end WS1 to the second end WE1.

[0038] The connection between the busbar 14 and the positive terminal 40 may be the same as that between the negative terminal and the busbar 14. That is, the busbar 14 and the positive terminal 40 may be superimposed and laser-welded together using the same procedure as described above. The manufacturing method disclosed herein may include laser welding the busbar 14 to at least one of the positive terminal 40 and the negative terminal 50 using the same procedure as described above.

[0039] After connecting multiple energy storage devices 12 to each other via a busbar 14, the connected energy storage devices 12 are then constrained in the arrangement direction P using the aforementioned restraining member. This completes the production of the energy storage module 100.

[0040] As described above, this is a method for manufacturing an energy storage module comprising a busbar 14 and electrode terminals. This manufacturing method involves overlapping the busbar 14 and the negative electrode terminal 50 and laser welding the two components. In laser welding, a laser beam is irradiated onto the busbar 14, which is overlapped with the negative electrode terminal 50, along a predetermined welding pattern WP1. The welding pattern WP1 includes multiple welding lines (here, a first welding line W11, a second welding line W12, a third welding line W13, and a fourth welding line W14) that are aligned in mutually different directions. The busbar 14 is provided with build-up portions 145 on the surface (in this case, the upper surface 141) to which the laser beam is irradiated during laser welding, at the points where one of the multiple welding lines intersects with another of the multiple welding lines (in this case, the point where the first welding line W11 intersects with the second welding line W12, the point where the second welding line W12 intersects with the third welding line W13, the point where the third welding line W13 intersects with the fourth welding line W14, and the point where the fourth welding line W14 intersects with the first welding line W11).

[0041] When laser welding a busbar 14 to a negative electrode terminal 50, if the laser beam is irradiated along a welding pattern WP1 which includes multiple welding lines that are aligned in different directions, the welding at the point where one of the multiple welding lines intersects with another of the multiple welding lines tends to be deeper than the welding at other points. The busbar 14 used in the above manufacturing method has a build-up portion 145 provided on the surface irradiated with the laser beam (here, the upper surface 141) at the point where one of the multiple welding lines intersects with another of the multiple welding lines. By providing the build-up portion 145 on the busbar 14 in the relatively deeper welding portion of the welding pattern WP1, it is possible to suppress the localized deepening of the welding. This makes it possible to improve the uniformity of the welding depth in laser welding between the busbar 14 and the negative electrode terminal 50.

[0042] One weld line and another weld line may intersect at an angle of 100° or less. In this case, the laser beam irradiation time tends to be longer at the point where the two weld lines intersect. Therefore, the effects of the technology disclosed herein can be better realized when a welding pattern WP1 is set that includes a point where one weld line and another weld line intersect at an angle of 100° or less.

[0043] The welding pattern WP1 may be configured in a spiral shape using multiple welding lines (first welding line W11, second welding line W12, third welding line W13, and fourth welding line W14). By making the welding pattern WP1 spiral, the welding area between the busbar 14 and the negative electrode terminal 50 can be enlarged. This makes it possible to increase the welding strength between the busbar 14 and the negative electrode terminal 50.

[0044] The welding pattern WP1 may have multiple points where one welding line from a plurality of welding lines intersects with another welding line from a plurality of welding lines. The busbar 14 may be provided with build-up portions 145 that include at least two of the multiple intersecting points. This allows for a reduction in the number of build-up portions 145 to be formed, for example. This increases the productivity of the busbar 14, and consequently, the productivity of the energy storage module 100.

[0045] In the above-described embodiment, at least two intersecting portions may be aligned along the short direction of the welding pattern WP1. At least two intersecting portions aligned along the short direction are closer to each other than at least two intersecting portions aligned along the longitudinal direction. Therefore, by providing the build-up portion 145 to include such at least two intersecting portions, rather than providing the build-up portion 145 for each of the at least two intersecting portions aligned along the short direction, the uniformity of the welding depth in laser welding between the busbar 14 and the negative electrode terminal 50 can be improved more efficiently.

[0046] In the above-described embodiment, it is preferable to provide a build-up portion 145 at each of the at least two intersecting portions aligned along the longitudinal direction. This makes it possible to suppress a decrease in the uniformity of the welding depth in laser welding between the busbar 14 and the negative electrode terminal 50.

[0047] In laser welding, the output of the laser beam irradiated along the welding pattern WP1 may be constant. In other words, the output of the laser beam does not need to be changed when irradiating along the welding pattern WP1. Therefore, it is possible to more easily achieve the effect of improving the uniformity of the welding depth in laser welding between the busbar 14 and the negative electrode terminal 50.

[0048] The negative electrode terminal 50 may have a first member 56 made of a first metal and a second member 58 made of a second metal. The first surface 581 of the second member 58 may be provided with a recess 582 that accommodates a part of the first member 56 (in this case, a connecting portion 56a). Laser welding may be performed with the busbar 14 superimposed on the second surface 584 of the second member 58 opposite to the first surface 581. If the electrode terminal used for welding with the busbar 14 has the configuration of the negative electrode terminal 50 described above, it is possible to suppress localized deep melting of the second member 58 during laser welding. Therefore, it is possible to suppress the scattering of molten second member 58 into the surroundings.

[0049] In the above-described embodiment, the first metal and the second metal may be different metals. This allows the first member 56, which is a connecting member to the negative electrode current collector terminal 52 that collects current from the negative electrode of the electrode body, and the second member 58, which is a connecting member to the busbar 14, to be made of different metals. As a result, the conductivity between the electrode body, the negative electrode terminal 50, and the busbar 14 can be improved.

[0050] The energy storage module 100 can be used for various purposes, but it is particularly suitable for use as a power source (driving power supply) for motors mounted on vehicles such as passenger cars and trucks. The type of vehicle is not particularly limited, but preferred examples include plug-in hybrid vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs).

[0051] The following describes test examples related to the technology disclosed herein. However, there is no intention to limit the technology disclosed herein to those shown in the following test examples. The following test examples use the reference numerals shown in Figures 3 to 5 as appropriate.

[0052] <Examples> In this embodiment, a busbar 14 having the shape shown in Figures 4 and 5, and a negative electrode external terminal 54 having the shape shown in Figure 3 were prepared. The busbar 14 was made of aluminum. The thickness of the busbar 14 was 0.8 mm. The height H of the build-up portion 145 was 0.2 mm. In the build-up portion 145, the length L1 was 0.5 mm and the length L2 was 1 mm. Length L1 is the short side length of the outer build-up portion 145 along the short side direction of the welding pattern WP1. Length L2 is the short side length of the portion protruding inward from the outer build-up portion 145 along the short side direction of the welding pattern WP1. The negative electrode external terminal 54 prepared here was a negative electrode external terminal having a first member 56 made of copper and a second member 58 made of aluminum.

[0053] The busbar 14 was superimposed on the second surface 584 of the second member 58 of the negative electrode external terminal 54, and the busbar 14 and the negative electrode external terminal 54 were welded together by irradiating the upper surface 141 with a laser beam along the welding pattern WP1. Next, a cross-section of the weld with the negative electrode external terminal 54 (here, a cross-section along the overlapping direction of the two members) was cut out and observed under a microscope. The objects of observation were the cross-section of the weld along each first welding line W11 and the cross-section of the weld along each third welding line W13. The images obtained from the microscopic observation were analyzed using commercially available image analysis software, and the welding depth in the second member 58 was measured. The results are shown in Figures 6 to 9.

[0054] Figures 6 and 8 are graphs showing the welding depth along the first weld line W11. Figure 6 shows the welding depth of the weld along the first weld line W11, starting from the first end WS1. Figure 8 shows the welding depth of the weld along the outer first weld line W11. Figures 7 and 9 are graphs showing the welding depth along the third weld line W13. Figure 7 shows the welding depth of the weld along the inner third weld line W13. Figure 9 shows the welding depth of the weld along the outer third weld line W13, which is directed toward the second end WE1. The X-axis in Figures 6 to 9 indicates the position on the first weld line W11 or the third weld line W13. The left-right direction on the X-axis in Figures 6 to 9 coincides with the left-right direction in Figure 4. The notation "145" on the X-axis in Figures 6 to 9 indicates the position of the build-up portion 145. The Y-axis in Figures 6-9 indicates the welding depth. In Figures 6-9, the lower the Y-axis, the deeper the weld.

[0055] <Comparative Example> Instead of the busbar 14, a flat aluminum plate-shaped member without a build-up portion 145 was used. The dimensions of the flat plate-shaped member were the same as those of the busbar 14. Except for this, the same members and procedures as in the example were used to obtain a weld between the flat plate-shaped member and the negative electrode external terminal 54, and the weld depth was analyzed. The weld depths of the welds along each weld line in the comparative example are shown in Figures 6 to 9.

[0056] In the plotted areas of Figures 6 to 9, the difference (mm) in welding depth between the example and the comparative example is shown for the portion corresponding to the build-up portion 145 in the example. From the results shown in Figures 6 to 9, it was found that in the comparative example, the welding was locally deeper, and the uniformity of the welding depth was low. In the example, it was found that the welding was shallower in the portion corresponding to the portion where the welding was locally deeper in the comparative example (the portion where the build-up portion 145 was provided), and the uniformity of the welding depth was improved. As described above, the busbar 14 used in the example had a build-up portion 145 provided at the point where one of the multiple welding lines along mutually different directions in the welding pattern WP1 intersected with another welding line. From the results of this test example, it was found that this configuration can improve the uniformity of the welding depth between the busbar and the electrode terminal.

[0057] The embodiments of the technology disclosed herein have been described above, but these embodiments are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes, for example, various modifications and changes to the following specific examples.

[0058] Figure 10 is a partial plan view of the busbar 24. In addition to the busbar 24, Figure 10 also shows the welding pattern WP2. As shown in Figure 10, the welding pattern WP2 has a zigzag shape. The welding pattern WP2 here includes a first welding line W21 and a second welding line W22. In the embodiment shown in Figure 10, the shape shown in the welding pattern WP2 is formed by alternately connecting the first welding line W21 and the second welding line W22, starting from the first end WS2 and moving toward the second end WE1. Note that the shape of the welding pattern WP2 shown in Figure 10 is just one example. Therefore, in other embodiments, the number of each welding line can be increased or decreased to form a desired zigzag shape. Although not particularly limited, the first welding line W21 and the second welding line W22 should intersect at an angle of approximately 100° or less, for example, 30° to 90°, preferably 40° to 80°.

[0059] As shown in Figure 10, the busbar 24 has a build-up portion 245 on its upper surface 241. In this embodiment, the build-up portion 245 is provided at the point where the first weld line W21 and the second weld line W22 intersect.

[0060] The welding patterns described in the above embodiments were spiral or zigzag in shape. However, the shape of the welding pattern to be set is not particularly limited as long as it includes multiple weld lines that are aligned in mutually different directions. A build-up portion can be provided on the busbar to correspond to the point where one weld line intersects with another in such a welding pattern.

[0061] The technologies disclosed herein may include the technologies described in the following sections. Section 1: A method for manufacturing an energy storage module comprising a busbar and electrode terminals, The method involves overlapping the busbar and the electrode terminal and laser welding the two components together. In the aforementioned laser welding, a laser beam is irradiated onto the busbar, which is superimposed on the electrode terminal, along a predetermined welding pattern. The welding pattern includes multiple weld lines that are aligned in mutually different directions. A manufacturing method wherein the busbar has a build-up portion provided at the intersection of one of the plurality of welding lines and another of the plurality of welding lines on the surface irradiated by the laser beam in the laser welding. Section 2: The manufacturing method according to item 1, wherein the first weld line and the other weld line intersect at an angle of 100° or less. Section 3: The manufacturing method according to item 1 or 2, wherein the welding pattern is formed in a spiral shape by a plurality of welding lines. Section 4: The welding pattern has multiple points where one welding line among the plurality of welding lines intersects with another welding line among the plurality of welding lines. The manufacturing method according to any one of claims 1 to 3, wherein the bus bar is provided with built-up portions so as to include at least two of the multiple intersecting portions. Section 5: The manufacturing method according to any one of claims 1 to 4, wherein the at least two of the intersecting portions are aligned along the shorter direction of the welding pattern. Item 6: The manufacturing method according to any one of items 1 to 5, wherein the output of the laser beam irradiated along the welding pattern is constant in the laser welding. Section 7: The electrode terminal comprises a first member made of a first metal and a second member made of a second metal. The first surface of the second member is provided with a recess for accommodating a part of the first member. The manufacturing method according to any one of items 1 to 6, wherein the laser welding is performed with the busbar superimposed on the second surface of the second member opposite to the first surface. Section 8: The manufacturing method according to any one of items 1 to 7, wherein the first metal and the second metal are different metals from each other. [Explanation of Symbols]

[0062] 100 Energy Storage Modules 12 Energy Storage Devices 14,24 Bus Bar 145,245 Overlay part 30 cases 40 Positive terminal 50 Negative terminal 52 Negative current collection terminal 54 Negative external terminal 56 First Member 58 Second Member WP1 Welding Pattern W11 First Weld Line W12 Second Weld Line W13 Third Weld Line W14 4th weld line WP2 welding pattern W21 First Weld Line W22 Second Weld Line

Claims

1. A method for manufacturing an energy storage module comprising a busbar and electrode terminals, The method involves overlapping the busbar and the electrode terminal and laser welding the two components together. In the aforementioned laser welding, a laser beam is irradiated onto the busbar, which is superimposed on the electrode terminal, along a predetermined welding pattern. The welding pattern includes multiple weld lines that are aligned in mutually different directions. A manufacturing method wherein the busbar has a build-up portion provided at the intersection of one of the plurality of welding lines and another of the plurality of welding lines on the surface irradiated by the laser beam in the laser welding.

2. The manufacturing method according to claim 1, wherein the first weld line and the other weld line intersect at an angle of 100° or less.

3. The manufacturing method according to claim 1 or 2, wherein the welding pattern is formed in a spiral shape by a plurality of welding lines.

4. The welding pattern has multiple points where one welding line among the plurality of welding lines intersects with another welding line among the plurality of welding lines. The manufacturing method according to claim 1 or 2, wherein the busbar is provided with built-up portions so as to include at least two of the multiple intersecting portions.

5. The manufacturing method according to claim 4, wherein the at least two of the intersecting portions are aligned along the shorter direction of the welding pattern.

6. The manufacturing method according to claim 1 or 2, wherein the output of the laser beam irradiated along the welding pattern is constant in the laser welding.

7. The electrode terminal comprises a first member made of a first metal and a second member made of a second metal. The first surface of the second member is provided with a recess for accommodating a part of the first member. The manufacturing method according to claim 1 or 2, wherein the busbar is superimposed on the second surface of the second member opposite to the first surface, and the laser welding is performed in this state.

8. The manufacturing method according to claim 1 or 2, wherein the first metal and the second metal are different metals from each other.

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