Battery pack

Abstract

To provide a highly reliable bus bar for connecting positive and negative electrodes in a battery pack in which rectangular parallelepiped cells are arranged.SOLUTION: There is provided a battery pack in which: a positive terminal of a first cell and a negative terminal of a second cell are arranged adjacent to each other; a bus bar 10 connects the positive and negative terminals; a first conductive member 11 of the bus bar includes a first joint 111 that joins with the positive terminal and a first extension 112 that extends in a first direction; a second conductive member 12 of the bus bar includes a second joint 121 that joins with the negative terminal and a second extension 122 that extends in the first direction; the first conductive member and the second conductive member are connected at a third joint 131; an end of the first extension and an end of the second extension are spaced apart in the first direction from a line connecting the first joint and the second joint; and the third joint is near either the first joint or the second joint and is formed at an overlapping portion between the first extension and the second extension.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a bus bar for a battery pack and a battery pack. [Background technology]

[0002] In a battery pack containing multiple secondary batteries such as lithium-ion secondary batteries, the positive and negative electrodes of adjacent secondary batteries are connected by a metal connecting member called a bus bar. A bus bar is a flat plate-shaped member made of metal such as aluminum, copper, or iron, and is attached to the positive and negative electrodes of the secondary batteries by joining such as laser welding or ultrasonic welding, or by using fastening members.

[0003] The relative distance between the secondary battery cells that make up the battery pack may change to an undesired positional relationship during assembly or due to vibrations during transportation. The relative distance between the secondary batteries may also change due to current flow or battery expansion and contraction. This creates stress in the busbar or the positive and negative electrodes of the secondary batteries, raising concerns that this could lead to fatigue failure.

[0004] To relieve stress generated in a busbar or a secondary battery, a known method is to form a U-shaped protruding stress relief portion at the midpoint of the busbar's length by bending a flat plate perpendicular to the thickness direction using a press. This structure is believed to reduce the load transmitted to the positive and negative electrodes of the secondary battery by deforming the stress relief portion when the busbar thermally expands. In some such structures, the U-shaped stress relief portion is formed as a twisted portion twisted approximately 90 degrees relative to the thickness direction of the flat plate (see, for example, Patent Document 1). However, this structure has almost no effect on stress relief against loads applied perpendicular to the thickness direction. Even when the stress relief portion is formed as a twisted portion twisted approximately 90 degrees relative to the thickness direction of the flat plate, the twisted portion has high rigidity, so it is basically the same as a busbar without a twisted portion, and no stress relief effect can be expected against loads applied perpendicular to the thickness direction.

[0005] In contrast, Patent Document 2 discloses a bus bar for a battery pack that exhibits a stress relaxation effect, in which first mounting surface 11 and second mounting surface 12 are arranged parallel to the XY plane, first rising surface 13 and second rising surface 14 are arranged parallel to or inclined toward the YZ plane, connecting surface 15 is arranged parallel to or inclined toward the XZ plane, the second rising surface is arranged parallel to or inclined toward the YZ plane from a side of the second mounting surface on the same side in the X direction as the first mounting surface, the connecting surface has a recess with a U-shaped cross section bent in a direction intersecting the Y direction, a first curved portion or inclined portion is formed between the first mounting surface and the first rising surface, and a second curved portion or inclined portion is formed between the second mounting surface and the second rising surface. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-73266 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-73398 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention relates to a busbar manufactured using USW, a joining method in which multiple metal plates are stacked and joined in the thickness direction of the plates, and a battery pack using the busbar. USW does not require large-scale equipment, so USW-jointed busbars can be obtained more inexpensively than pressure welding or FSW joining. However, as mentioned above, these joining methods require the joint to be located within the overlapping area of multiple plates, which creates a problem in that the upper limit of the joint strength is determined by the overlapping area in the planar direction of the plates.

[0008] The bus bar is arranged to bridge the positive and negative electrode terminals of adjacent batteries. Generally, the shape of a bus bar is roughly flat, connecting the positive and negative electrode terminals, but when USW bus bars are made roughly flat, especially when the linear distance between the terminals is short, the overlapping area in the planar direction between the plates is small, which can easily cause problems with the joint strength. [Means for solving the problem]

[0009] To solve the above problems, the present invention uses a bus bar with a shape that increases the overlap area on one side of the metal plates to be joined. According to a first aspect of the present invention, a method for ensuring the joint strength of the joining surface while providing a three-dimensional structure that relieves stress is achieved by overlapping a first member and a second member and joining the overlapping portion using ultrasonic welding, thereby increasing the joint area and increasing the likelihood of joint strength. This reduces the risk of fatigue failure of the bus bar arranged in the battery pack.

[0010] Specifically, the present invention provides a battery comprising a plurality of stacked unit cells each including a positive terminal and a negative terminal, and a bus bar connecting the positive terminal of a first unit cell and the negative terminal of a second unit cell, the bus bar having a positive electrode side conductive member joined to the positive terminal of the first unit cell and a negative electrode side conductive member joined to the negative electrode terminal of a second unit cell positioned adjacent to the first unit cell, the positive electrode terminal and the positive electrode side conductive member being made of a different material from the negative electrode terminal and the negative electrode side conductive member, the positive electrode side conductive member having a first joint portion joined to the positive electrode terminal and a first extension portion extending from the first joint portion, the negative electrode side conductive member having a second joint portion joined to the negative electrode terminal and a second extension portion extending from the first joint portion, a second extending portion extending from a second joint and extending to the same side as the first extending portion with respect to an imaginary line passing through the first joint and the second joint, and a third joint at which the first extending portion and the second extending portion are joined, wherein, when viewed from the direction in which the bus bar and the single cells overlap, an end of the positive electrode side conductive member is positioned away from an end of the negative electrode side conductive member facing the positive electrode side conductive member on the imaginary line connecting the first joint and the second joint, and the third joint is in a region where one of the distances from the first joint or the second joint to the third joint is shorter than the other, and the third joint is formed at an overlapping portion where the first extending portion and the second extending portion are overlapped. [Effects of the Invention]

[0011] The bus bar of the present invention can be deformed in different directions in three dimensions, providing a stress relief effect against loads from any direction, and the large joint area in the planar direction of the overlapping plates ensures sufficient strength of the joint surface against stress, resulting in a battery pack with a low risk of fatigue failure of the bus bar. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an exploded perspective view of a battery pack according to the present invention; [Figure 2] FIG. 1 is a perspective view of a bus bar according to a first embodiment. [Figure 3]FIG. 2 is an exploded perspective view of the bus bar according to the first embodiment. [Figure 4] FIG. 10 is a perspective view of a bus bar according to a comparative example. [Figure 5] FIG. 10 is a perspective view of a bus bar according to a second embodiment. [Figure 6] FIG. 10 is an exploded perspective view of a bus bar according to a second embodiment. [Figure 7] FIG. 10 is a perspective view of a bus bar according to a third embodiment. [Figure 8] FIG. 10 is an exploded perspective view of a bus bar according to a third embodiment. [Figure 9] FIG. 10 is a perspective view of a bus bar according to a fourth embodiment. [Figure 10] FIG. 10 is a perspective view of a bus bar according to a fifth embodiment. [Figure 11] FIG. 13 is a perspective view of a bus bar according to a sixth embodiment. [Figure 12] FIG. 13 is a perspective view of a bus bar according to a seventh embodiment. [Figure 13] FIG. 13 is a perspective view of a bus bar according to an eighth embodiment. [Figure 14] FIG. 13 is a perspective view of a bus bar according to a ninth embodiment. [Figure 15] FIG. 23 is a perspective view of a bus bar according to a tenth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Examples of a battery pack bus bar and a battery pack according to the present invention will be described below with reference to the drawings. FIG. 1 is an exploded perspective view showing an example of a battery pack to which the present invention is applied. As shown in FIG. 1, the battery pack 1 has a structure in which a number of unit cells 2 are fixed by a pair of end plates 4 and a pair of side plates 5. The unit cells 2 are, for example, prismatic secondary batteries such as lithium-ion secondary batteries.

[0014] Each rectangular cell 2 has a rectangular parallelepiped shape with an upper surface, a lower surface, a pair of large flat surfaces, and a pair of small side surfaces. The dimensions of a cell 2 are, for example, 12 cm in length, 1.2 cm in width, and 6.5 cm in height, but this is merely an example and cells can be of various sizes. The cells 2 are arranged in a row with their large flat surfaces facing each other, and holders 3 are installed between each cell 2, in front of the first cell 2 in the row, and behind the last cell 2 in the row.

[0015] The cells 2 each have a positive electrode 2a and a negative electrode 2b on their upper sides, and all have the same size, shape, and structure. Adjacent cells 2 are arranged with their positive electrodes 2a and negative electrodes 2b facing each other, in other words, with their front and back surfaces alternately inverted. The positive electrodes 2a are made of an aluminum-based metal such as aluminum or an aluminum alloy, and the negative electrodes 2b are made of a copper-based metal such as copper or a copper alloy.

[0016] End plates 4 are arranged in front of the first holder 3 in the row and behind the last holder 3 in the row. The pair of end plates 4 are made of metal and have a substantially rectangular shape, with openings 4a at the four corners through which bolts 6 are inserted. A pair of side plates 5 are arranged on the sides of the cells 2 arranged in a row. Each side plate 5 is a rectangular frame body having spanning sections spaced apart above and below and connecting sections that connect these spanning sections. Openings 5a are formed at each corner of the frame body to correspond to the openings 4a of the end plates 4.

[0017] The battery pack 1 is formed by placing the end plate 4 at the front of the row and the end plate 4 at the rear of the row inside the front and rear connecting portions of each side plate 5, and fastening them together with bolts 6 inserted through openings 5a in the side plates 5 and openings 4a in the end plates 4. The bolts 6 are threaded into threaded holes (not shown) formed in the holder 3, or fastened together with nuts (not shown) placed on the backside of the end plates 4. Fastening with bolts 6 may also be done with rivets.

[0018] An insulating cover 7 is arranged above each cell 2 so as to surround the positive and negative electrodes 2a, 2b of the cells 2 arranged in a row. The positive electrodes 2a and negative electrodes 2b of adjacent cells 2 are connected by a bus bar 10. All cells 2 are connected in series by the bus bar 10. An end bus bar 8 is connected to the positive electrode 2a1 of the first cell 2 in the row and the negative electrode 2b1 of the last cell 2 in the row. The bus bar 10 or the end bus bar 8 is joined to the positive and negative electrodes 2a, 2b by welding such as laser welding or ultrasonic welding. Instead of welding, a structure in which the connections are made by screw fastening may also be used.

[0019] The bus bars 10 arranged on one side of the continuous insulating cover 7 have substantially the same shape and structure. The bus bars 10 arranged on the other side of the continuous insulating cover 7 have a shape that is substantially a mirror image of the bus bars 10 arranged on one side of the insulating cover 7. The end bus bars 8 have an attachment surface that connects to one of the positive and negative electrodes 2a, 2b of the cells 2, and the end opposite the attachment surface is provided with through holes for screw fastening. The present invention is characterized by the structure of the bus bars 10, and one embodiment of the bus bar 10 will be described below. [Example]

[0020] Fig. 2 is an external perspective view of the battery pack bus bar 10 according to the first embodiment shown in Fig. 1, and Fig. 3 is an exploded perspective view. The bus bar 10 includes a first plate 11 formed by pressing a single sheet of metal made of an aluminum-based metal such as aluminum or an aluminum alloy, a copper-based metal such as copper or a copper alloy, or a metal such as iron, and a second plate 12 formed by pressing a single sheet of metal made of a different material from the first plate 11, such as an aluminum-based metal such as aluminum or an aluminum alloy, a copper-based metal such as copper or a copper alloy, or a metal such as iron. In the following description, the X direction, the Y direction perpendicular to the X direction, and the Z direction perpendicular to the X and Y directions are as shown in Fig. 3.

[0021] The busbar 10 is composed of a first plate 11, which is a positive electrode side conductive member that is joined to the positive electrode terminal 2a of the first cell, and a second plate 12, which is a negative electrode side conductive member that is joined to the negative electrode terminal 2b of the second cell located adjacent to the first cell. The first plate 11, which is a positive electrode side conductive member, has a first joint portion 111 that is joined to the positive electrode terminal 2a and a first extension portion 112 that extends from the first joint portion 111.

[0022] On the other hand, the second plate 12, which is the negative electrode side conductive member, has a second joint 121 joined to the negative electrode terminal 2b and a second extension 122 extending from the second joint 121 and extending to the same side as the first extension 112 with respect to a virtual line passing through the first joint 111 and the second joint 121.

[0023] In addition, the busbar 10 has a third extension portion 13 extending from at least one of the first extension portion 111 and the second extension portion 121, from an end face of the extension portion 112 or 122. The third extension portion 13 extends substantially parallel to the overlapping direction of the cells 2, and at least a portion of the surface of the third extension portion 13 and the other extension portion 112 or 122 forms a third joint portion 131 joined by ultrasonic welding. The third joint portion 13 is located at a position perpendicular to an imaginary line connecting the first joint portion 111 and the second joint portion 121. Furthermore, the end of the first plate 11, which is the positive electrode side conductive member, and the end of the second plate 12, which is the negative electrode side conductive member, are located at a distance from each other. In other words, the ends are not butted together. Furthermore, the third joint portion 131 is configured such that the distance between the first joint portion 111 and the second joint portion 121 is shorter than the distance between the third joint portion 131 and the other.

[0024] The reason for using the busbar 10 having such a shape is that the portion of the busbar 10 that is located above the terminal is required to be flat. In other words, if the portion of the busbar that is located above the terminal is not flat, there is a possibility that a problem will occur in the clamping force during joining when the terminal and the busbar are joined in a subsequent process, or that a poor joint is likely to occur. Meanwhile, ultrasonic welding (USW) joining leaves marks that are unique to USW joining. As a result, there is a problem that the upper and lower surfaces of the busbar become uneven. In contrast, the busbar 10 of the present invention has the advantage of being able to secure a large area for joining the first plate 11 and the second plate 12 while maintaining the flatness of the upper portion of the terminal. Therefore, the joining strength between the first plate 11 and the second plate 12 can be increased.

[0025] That is, in a simple overlapping structure, when third bonding portions are used above and below the surface connecting the positive and negative terminals, the flatness required is such that the bonding area must be small. However, this problem can be solved by using the busbar 10 of the present invention. By using the busbar 10 of the present invention, no bonding marks are left on the upper surface of the terminals of the busbar 10, so the bonding area can be made larger.

[0026] A specific calculation of the joining area that can be adopted is as follows. Here, the area in the planar direction of the plates is described. That is, the width of the first plate 11 is A, the width of the second plate 12 is B, the distance between the first plate 11 and the second plate 12 is C, and the width of the third extension portion is D. In this case, the maximum area S1 that can be ultrasonically joined for the bus bar of the present invention can be expressed as S1 = (A + B + C) × D. Examples of A, B, C, and D are A = 1 cm, B = 1 cm, C = 5 mm, and D = 2 mm to 10 mm. In addition, the plate thickness of the first plate 11 and the second plate 12 is, for example, 0.5 mm to 1.5 mm, and more preferably, approximately 0.6 mm to 0.8 mm.

[0027] However, the above dimensions are examples, and there are no particular restrictions on the widths of A, B, C, and D, and they may be any size as long as they can be installed inside a module or pack. Furthermore, the effects of the present invention can be obtained regardless of the area and location of the joining surface, as long as it is in the area where the extension part and the other plate overlap.

[0028] In this case, the third extension portion 13 or the fourth extension portion may be provided extending from the end face of both the first extension portion 112 and the second extension portion 122, and in this case, the maximum area S1 also becomes as shown in Fig. 2. Note that a voltage detection wire can be attached to the first extension portion 112, the third extension portion 131, and the second extension portion 122 of the busbar 10 at a location where no USW joint is provided.

[0029] The surface of at least one of the first plate 11 and the second plate 12 in the busbar 10 where the first plate 11 and the second plate 12 are physically connected to each other may be nickel-plated. Nickel plating may also be applied to both the first plate 11 and the second plate 12. The nickel-plated surface may be only a part of the surface where the first plate 11 and the second plate 12 are physically connected to each other, or may be the entire surface. Furthermore, the nickel-plated surface may be only the surface where the first plate 11 and the second plate 12 are physically connected to each other, or may also be nickel-plated to other surfaces of the plates.

[0030] By applying nickel plating to the surfaces where the first and second plates 11 and 12 are physically connected to each other, the process margin for joining aluminum-based metals and copper-based metals can be increased, resulting in increased joint strength at the joining surfaces. This can also be expected to have the effect of suppressing corrosion of the aluminum-based metal. The thickness of the applied nickel plating is preferably 1 μm to 100 μm, more preferably 3 μm to 50 μm, and most preferably 4 μm to 10 μm. Increasing the thickness of this nickel plating can also increase the process margin for USW joining. Nickel plating can be matte, semi-bright, or bright, and any gloss level can be selected depending on the joining conditions.

[0031] Glossiness can be measured using a gloss meter. Specifically, when measuring with a gloss meter, the intensity of incident light from directly above the plate surface, I in and the intensity of the reflected light reflected at a 45-degree angle to the incident light, I out The logarithm of the reciprocal of the ratio of log(I in / I out ) is defined as gloss, the gloss is preferably 0.2 or more and 2.5 or less, more preferably 0.3 or more and 2.5 or less, and most preferably 0.6 or more and 2.5 or less. By keeping the gloss in this range, the process margin of USW joining can also be increased.

[0032] A specific example of the combination of this embodiment 1 is shown below. The first plate 11 can be made of pure aluminum, the second plate 12 can be made of oxygen-free copper, and the surface of the second plate 12 can be nickel-plated. The nickel plating thickness can be 5 μm, and the gloss can be 2.0. Nickel plating methods include electroplating and electroless plating. Either method can be used as long as USW bonding is possible, but electroplating is preferred.

[0033] FIG. 4 is a perspective view showing a comparative example of busbar 10. In FIG. 4, a flat first plate 11 and a flat second plate 12 are butt-jointed at their end faces. Hereinafter, this configuration will be referred to as a flat clad material. In FIG. 4, first plate 11 and second plate 12 are joined at joining surface 30. A mixed region 31 of the material constituting first plate 11 and the material constituting second plate 12 is formed over a width w in the planar direction of the plates, centered on joining surface 30. Width w is, for example, 1 mm. The configuration shown in FIG. 4 does not have any indentations due to USW, so the reliability of the connection at the positive electrode or negative electrode can be ensured. However, flat clad material such as that shown in FIG. 4 has the problem of being expensive. [Example]

[0034] FIG. 5 is a perspective view showing Example 2. In Example 2, in contrast to Embodiment 1, in addition to the third extension portion 13, a protrusion 113 for attaching a voltage detection wire is provided on the end face of the extension portion 112 extending from the first plate 11. FIG. 6 is an exploded perspective view of FIG. 5. The rest of the configuration is the same as that of Example 1. Although not shown here, a protrusion 113 for attaching a voltage detection wire may be provided on the extension portion 122 extending from the second plate 12. In this case, too, the maximum area S2 in the planar direction of the plate that can be ultrasonically bonded in the bus bar of the present invention is S2 = (A + B + C) × D, and the bonding area can still be increased. [Example]

[0035] FIG. 7 is a perspective view showing Example 3. In FIG. 7, the first and second extension portions 112 and 122 of the first and second plates 11 and 12 are bent, and a third extension portion 13 extends from both of the extension portions 112 and 122. FIG. 8 is an exploded perspective view of FIG. 7. The rest of the configuration is the same as that of Example 1. The busbar 10 of Example 3 also has a large maximum area S3 in the planar direction of the plate that can be ultrasonically bonded, which is S3 = (A + B + C) × D. In this case, the bending angle can be any angle as long as it allows installation within a module or pack. In this embodiment, a 45-degree angle is shown, but even if it is 90 degrees, the maximum area that can be ultrasonically bonded remains the same. Note that voltage detection wires can be attached to the first extension portion 112 and the second extension portion 122 of the busbar 10 at locations where no USW joint is provided. [Example]

[0036] Fig. 9 is a perspective view showing Example 4. Fig. 9 shows a configuration in which a protrusion 114 for attaching a voltage detection line is added to the first plate 11 in the opposite direction to the first extension portion in the configuration of Example 3. The other configurations are the same as those of Example 3. In Example 4 as well, the maximum area S4 in the planar direction of the plate that can be ultrasonically bonded with the bus bar of the present invention can be expressed as S4 = (A + B + C) × D, and the bonding area can be made large. [Example]

[0037] FIG. 10 is a perspective view of Example 5. FIG. 10 shows a configuration in which, in Example 3, first extension portion 112 and second extension portion 122 present on first plate 11 and second plate 12 are bent, third extension portion 13 extends from one of extension portions 112 or 122, and third extension portion 13 is provided with scaled structure 14 for stress relief. In Example 5, the bending angle of the third extension portion relative to the first extension portion and second extension portion is 90 degrees, but similar effects can be obtained with other angles. The other configurations are the same as those of Example 3. In this case, if the length of scaled structure 14 is E, the maximum area S5 in the planar direction of the plate that can be ultrasonically bonded with busbar 10 of the present invention can be expressed as S5 = (A + CE) × D or S5 = (B + CE) × D, allowing for a large bonding area. [Example]

[0038] Fig. 11 is a perspective view showing Example 6. Fig. 11 shows a configuration in which, in plan view, the configuration of Example 1 has a third extension portion 13 extending in the second direction from one of the first extension portion 112 or the second extension portion 122 present on the first plate 11 and the second plate 12. The other configurations are the same as those of Example 1. In Example 6 as well, the maximum area S6 in the planar direction of the plates that can be ultrasonically bonded in the busbar 10 can be expressed as S6 = A × D or S6 = B × D, and the bonding area can be made large. [Example]

[0039] Fig. 12 is a perspective view showing Example 7. Fig. 12 shows a configuration in which, in the configuration of Example 1, first extension portion 112 and second extension portion 122 present on first plate 11 and second plate 12 are bent, a third extension portion 13 extends from one of the extension portions, and a scale structure 14 is provided on a part of third extension portion 13. The rest of the configuration is the same as Example 1. In this case, the maximum area S7 in the planar direction of the plate that can be ultrasonically bonded with the bus bar of the present invention can be expressed as S7 = (A + CE) × D or S7 = (B + CE) × D, and the bonding area can be made large. [Example]

[0040] FIG. 13 is a perspective view showing Example 8. FIG. 13 shows a configuration in which the first extension portion 112 and the second extension portion 122 present on the first plate 11 and the second plate 12 in Example 3 are bent, and a third extension portion 13 is provided extending from one of the extension portions. In Example 8, the bending angle is set to 90 degrees, but similar effects can be obtained with other angles. The other configurations are the same as those of Example 3. In this case, too, the maximum area S8 in the planar direction of the plate that can be ultrasonically bonded in the busbar 10 in Example 8 can be expressed as S8 = A × D or S8 = B × D, and the bonding area can be made large. [Example]

[0041] FIG. 14 is a perspective view showing Example 9. In FIG. 14, protrusions 114 for attaching a voltage detector are provided on one of first plate 11 and second plate 12, but the other configuration is the same as Example 5. In Example 9, the bending angle of third extension portion 13 relative to first extension portion 112 or second extension portion 122 is set to 90 degrees, but similar effects can be obtained with other angles. In this case, if the length of scale structure 14 is E, the maximum area S9 in the planar direction of the plate that can be ultrasonically bonded with the bus bar of the present invention can be expressed as S9 = (A + CE) × D or S9 = (B + CE) × D, and the bonding area can be made large. [Example]

[0042] FIG. 15 is a perspective view showing Example 10. In FIG. 15, the first extension portion 112 and the second extension portion 122 present on the first plate 11 and the second plate 12 are bent, and a third extension portion 13 extends from either the extension portion 112 or the second plate 122. The relationship of the extension portion 13 is reversed from that of Example 8. The orientation of the horn and anvil of the USW may be such that the horn faces the first plate 11 and the anvil faces the second plate 12, or such that the horn faces the second plate 12 and the anvil faces the first plate 11. In either case, the effects of the present invention can be achieved. In Example 10, the bending angle is 90 degrees, but similar effects can be achieved with other angles. The rest of the configuration is the same as Example 3. In the busbar 10 of Example 10, the maximum area S3 in the planar direction of the plates that can be ultrasonically welded can also be expressed as S3 = (A + B + C) × D, allowing for a large welding area.

[0043] The above-described embodiments are merely examples. For example, the effects of the present invention can be achieved even when the thicknesses of the first plate 11 and the second plate 12 are changed. The position and area of the connecting surface of the busbar 10 can be varied in accordance with the length of each extension portion 3. Furthermore, curved portions, bent portions, or inclined portions may be added to the flat portions of each extension portion, as appropriate, or steps may be added. Furthermore, the structures shown in the above-described embodiments may be combined.

[0044] The method of attaching the bus bar and voltage detection wire in the present invention is not particularly limited, but examples include ultrasonic bonding, laser welding, screw fastening, crimping, etc. Furthermore, the structure on the bus bar for extracting the voltage detection wire can be provided at any desired location on the bus bar as long as it does not interfere with other components of the battery pack. The shape of the structure may also vary.

[0045] For example, as shown in the embodiment, the protrusions may be provided as extensions parallel to the bus bar surface, or as protrusions perpendicular to the bus bar surface. The protrusions may be flat or may have complex three-dimensional structures. A press-fit connector may be attached to the protrusions to attach a voltage detection line. The protrusions may be three-dimensionally configured to suit the size of the press-fit connector and the layout of the connector within the battery pack.

[0046] The present invention is not limited to busbar 10 for connecting lithium-ion secondary batteries, but can also be applied to busbars for connecting secondary batteries that use a water-soluble electrolyte, such as nickel-metal hydride batteries, nickel-cadmium batteries, and lead-acid batteries.The present invention can also be applied to busbars for connecting storage elements, such as lithium-ion capacitors and electrolytic double-layer capacitors.

[0047] In addition, the bus bar 10 for the battery pack of the present invention can be modified and applied in various ways. [Explanation of symbols]

[0048] 1...battery assembly, 2...cell, 2a...positive electrode, 2b...negative electrode, 3...holder, 4...end plate, 4a...opening, 5...side plate, 5b...opening, 6...bolt, 7...insulating cover, 8...end bus bar, 10...bus bar, 10...display panel, 11...first plate (positive electrode side conductive member), 12...second plate (negative electrode side conductive member), 13...third extension portion, 14...scaled structure, 20...end of electrode terminal, 30...joint surface, 31...mixed region, 111...first joint portion, 112...first extension portion, 113...first protrusion, 114...second protrusion, 121...second joint portion, 122...second extension portion, 131...third joint portion.

Claims

1. a first battery having a first positive electrode terminal and a first negative electrode terminal arranged at a first interval in a first direction, and a second battery having a second positive electrode terminal and a second negative electrode terminal arranged at a second interval in the first direction, the first battery being arranged in a second direction intersecting the first direction; a battery pack in which the first positive electrode terminal and the second negative electrode terminal are arranged adjacent to each other in the second direction, and a bus bar connects the first positive electrode terminal and the second negative electrode terminal, the first conductive member of the bus bar has a first joint portion joined to the first positive terminal and a first extension portion extending from the first joint portion in the first direction, the second conductive member of the bus bar has a second joint portion joined to the second negative electrode terminal and a second extension portion extending from the second joint portion in the first direction, the first conductive member and the second conductive member are made of different materials, the first conductive member and the second conductive member are connected at a third joint; an end of the first extension portion and an end of the second extension portion are spaced apart from a line connecting the first joint portion and the second joint portion in the first direction; the third joint portion is formed at an overlapping portion of the first extension portion and the second extension portion, with one of the third joint portion and the first joint portion being closer to the first joint portion or the second joint portion than the other.

2. the first extension portion further includes a third extension portion extending in the second direction, 2. The battery pack according to claim 1, wherein the third joint portion is present in an overlapping portion of the second extension portion and the third extension portion.

3. the second extension portion further includes a fourth extension portion extending in the second direction, 2. The battery pack according to claim 1, wherein the third joint portion is present in an overlapping portion of the first extension portion and the fourth extension portion.

4. the second extension portion further includes a fourth extension portion extending in the second direction, 3. The battery pack according to claim 2, wherein the third joint portion is present in an overlapping portion of the third extension portion and the fourth extension portion.

5. 2. The battery pack according to claim 1, wherein the first conductive member or the second conductive member has a protrusion for voltage detection in the first direction in a plan view.

6. 5. The battery pack according to claim 2, wherein a surface on which the third joint portion is formed is angled with respect to a surface on which the first joint portion and the second joint portion are formed.

7. The battery pack according to claim 1 , wherein the first extension portion and the second extension portion are joined via nickel or a nickel alloy.

8. 3. The battery pack according to claim 2, wherein the third extension portion has a scaled structure in a region other than the region where the third joint portion is formed.

9. 4. The battery pack according to claim 3, wherein the fourth extension portion has a scaled structure in a region other than the region where the third joint portion is formed.

10. 5. The battery pack according to claim 4, wherein the third extension portion or the fourth extension portion has a scaled structure in a region other than the region where the third joint portion is formed.

11. 2. The battery pack according to claim 1, wherein the first battery and the second battery are rectangular parallelepipeds, the first positive terminal and the first negative terminal of the first battery are formed on the same surface of the rectangular parallelepiped, and the second positive terminal and the second negative terminal of the second battery are formed on the same surface of the rectangular parallelepiped.

12. 2. The battery pack according to claim 1, wherein a plurality of sets of the first battery and the second battery are arranged in the second direction.

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