battery pack

Abstract

Provided is a battery pack that can suppress deterioration of a battery by suppressing heat generation due to a current flowing through a bus bar, and can improve battery performance by weight reduction.　A battery pack 10 has: a first battery 1 to a fourth battery 4 stacked on each other and provided with a positive electrode external terminal 12 and a negative electrode external terminal 13 that has high electroconductivity; and, a busbar 6 for electrically connecting the positive electrode external terminal 12 of the second battery 2 on one side and the negative electrode external terminal 13 of the third battery 3 on the other side, which are arranged side by side adjacent to each other. The bus bar 6 has: a first electroconductive section 6a connected to the positive electrode external terminal 12 of the second battery 2 on the one side; a second electroconductive section 6b connected to the negative electrode external terminal 13 of the third battery 3 on the other side and having a high electroconductivity and a high specific gravity; and, a coupling section 6c for coupling the first electroconductive section 6a and the second electroconductive section 6b. The coupling section 6c is disposed in either a first region that opposes the second battery 2 on the one side or a second region that opposes the third battery 3 on the other side.

Description

[Technical Field]

[0001] The present invention relates to a battery pack including a plurality of stacked batteries and a bus bar. [Background technology]

[0002] One such battery pack has been disclosed that includes cells each having a battery body and an electrode tab extending from the battery body, and a flat bus bar that stacks the cells in the thickness direction and electrically connects the electrode tabs of the cells together (see Patent Document 1).Another battery pack has been disclosed that includes a plurality of cells and a bus bar, the bus bar having a pair of flat and bent portions that connect the cells together, and a joint of a clad material made by joining dissimilar metals together, located on one flat portion and the other flat portion (see Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-84468 [Patent Document 2] International Publication No. 2018 / 155090 Summary of the Invention [Problem to be solved by the invention]

[0004] The battery packs described in Patent Documents 1 and 2 have the problem that when multiple cells are connected in parallel, a relatively large current flows through the bus bar, and this current may generate heat in the battery pack including the bus bar. The generated heat accelerates the deterioration of the cells, resulting in a decrease in the performance of the battery pack. Furthermore, if copper, which has a high electrical conductivity (S / m, hereinafter referred to as "conductivity"), is used as the bus bar material, copper has a higher specific gravity than aluminum, which increases the weight of the entire battery pack and may result in poor fuel economy for an in-vehicle battery.

[0005] The present invention has been made to solve such problems, and an object of the present invention is to provide a battery pack that can suppress heat generation due to current flowing through the bus bar, suppress battery deterioration, and improve battery performance by reducing weight. [Means for solving the problem]

[0006] (1) The battery pack according to the present invention is a plurality of stacked batteries each including a positive electrode external terminal and a negative electrode external terminal having a higher electrical conductivity than the positive electrode external terminal; a bus bar that electrically connects a positive external terminal of one battery and a negative external terminal of another battery that are arranged side by side among the plurality of batteries, the bus bar comprising: a first conductive part connected to the positive external terminal of the one battery; a second conductive part connected to the negative external terminal of the other battery and having a higher conductivity and a higher specific gravity than the first conductive part; a connecting portion that connects the first conductive portion and the second conductive portion, The connecting portion is characterized in that it is disposed in either a first region facing one of the batteries or a second region facing the other of the batteries.

[0007] According to the battery pack described in (1), for example, when the connecting portion is disposed in the first region facing one of the batteries, the second conductive portion, which has a relatively high conductivity, has a larger area through which current flows than the first conductive portion. This facilitates current flow from one battery to the other, suppressing heat generation in the bus bar and reducing deterioration of the unit cells due to heat. On the other hand, when the connecting portion is disposed in the second region facing the other battery, the second conductive portion, which has a high specific gravity, is smaller than the first conductive portion. This reduces the weight of the entire battery pack, thereby achieving a lightweight battery pack.

[0008] (2) The battery pack according to the present invention is the battery pack according to (1), the plurality of batteries includes at least a first battery, a second battery, a third battery, and a fourth battery; the first battery and the second battery are arranged side by side with the positive electrode external terminals adjacent to each other and the negative electrode external terminals adjacent to each other in the stacking direction of the plurality of batteries, the third battery and the fourth battery are arranged side by side with the positive electrode external terminals adjacent to each other and the negative electrode external terminals adjacent to each other in the stacking direction of the plurality of batteries, the first battery and the second battery and the third battery and the fourth battery are arranged side by side in a stacking direction of the plurality of batteries, with the positive external terminals of the first battery and the second battery and the negative external terminals of the third battery and the fourth battery being adjacent to each other; the bus bar extends along the stacking direction of the plurality of batteries and is disposed at a position facing the positive external terminals of the first battery and the second battery and the negative external terminals of the third battery and the fourth battery; The first conductive portion is joined to the positive external terminals of the first battery and the second battery, the second conductive portion is joined to the negative external terminals of the third battery and the fourth battery, and the connecting portion is disposed in either the first region facing at least one of the first battery and the second battery, or the second region facing at least one of the third battery and the fourth battery.

[0009] According to the battery pack described in (2), for example, when the connecting portion is disposed in the first region facing at least one of the first and second batteries, the second conductive portion, which has a relatively high conductivity, has a larger area through which current flows than the first conductive portion. This facilitates current flow between the first and second batteries and the third and fourth batteries, suppressing heat generation in the bus bar and reducing deterioration of the cells due to heat. On the other hand, when the connecting portion is disposed in the second region facing at least one of the third and fourth batteries, the second conductive portion, which has a high specific gravity, is smaller in size than the first conductive portion. This reduces the weight of the entire battery pack, thereby achieving a lightweight battery pack.

[0010] (3) The battery pack according to the present invention is the battery pack according to (2), The second conductive portion extends from a position facing the third battery and the fourth battery to a position facing the second battery, or extends from a position facing the third battery and the fourth battery to a position facing the second battery and the first battery.

[0011] According to the invention described in (3), the second conductive portion extends from a position facing the third and fourth batteries toward the second battery, and faces either the second battery or the second and first batteries. Therefore, the second conductive portion, which has a relatively high conductivity, has a wider area through which current flows than the first conductive portion. This makes it easier for current to flow between the first and second batteries and the third and fourth batteries, suppressing heat generation in the busbar and reducing deterioration of the cells due to heat generation.

[0012] (4) The battery pack according to the present invention is the battery pack according to (3), The connecting portion is characterized in that it is arranged from one end to the other end in a width direction perpendicular to the extending direction of the bus bar.

[0013] (5) The battery pack according to the present invention is the battery pack according to (3), The connecting portion is disposed across the bus bar from one end to the other end in the width direction thereof, obliquely intersecting the extending direction of the bus bar.

[0014] (6) The battery pack according to the present invention is the battery pack according to (3), The connecting portion is characterized in that it is arranged in a position facing the second battery between the edge of the second battery facing the third battery and the positive external terminal of the second battery in the first region.

[0015] (7) The battery pack according to the present invention is the battery pack according to (3), The connecting portion is disposed in a position in the first region that faces the positive external terminal of the second battery.

[0016] (8) The battery pack according to the present invention is the battery pack according to (3), The connecting portion has a generally L-shape that extends from one end of the first region in a width direction perpendicular to the stacking direction of the batteries to the other end at a position facing the positive external terminal of the second battery, is bent toward the stacking direction, and extends to a position facing the positive external terminal of the first battery.

[0017] (9) The battery pack according to the present invention is the battery pack according to (5), The connecting portion is characterized in that, in the first region, an end portion on one side in the width direction of the bus bar is positioned facing the second battery between the edge of the second battery facing the third battery and the center of the positive external terminal of the second battery in the stacking direction of the multiple batteries, and an end portion on the other side in the width direction of the bus bar is positioned facing the first battery between the side of the positive external terminal of the first battery facing the second battery and the center of the positive external terminal of the second battery in the stacking direction of the multiple batteries.

[0018] (10) The battery pack according to the present invention is the battery pack according to (5), The connecting portion is characterized in that, in the first region, an end portion on one side of the width direction of the bus bar is positioned facing the second battery between an edge of the second battery on the side facing the third battery and a side of the positive external terminal of the second battery facing the third battery, and an end portion on the other side of the width direction of the bus bar is positioned facing the first battery between an edge of the first battery on the side facing away from the second battery and a side of the positive external terminal of the first battery facing the second battery.

[0019] (11) The battery pack according to the present invention is the battery pack according to (1), the bus bar includes a plurality of flat regions arranged in a row facing the positive electrode external terminal and the negative electrode external terminal, respectively, and a curved region interposed between the plurality of flat regions, protruding and curved in a direction perpendicular to a surface of the flat regions, and connecting adjacent flat regions to each other; At least a part of the connecting portion is located within the flat region.

[0020] (12) The battery pack according to the present invention is the battery pack according to (1), The bus bar has a flat plate shape that extends along the stacking direction of the plurality of batteries and faces the positive electrode external terminal and the negative electrode external terminal.

[0021] (13) The battery pack according to the present invention is the battery pack according to (2), The first conductive portion is characterized in that it extends from a position facing the first battery and the second battery to a position facing the third battery, or extends from a position facing the first battery and the second battery to a position facing the third battery and the fourth battery.

[0022] (14) The battery pack according to the present invention is the battery pack according to (1), The bus bar is a facing surface facing the positive external terminal and a facing surface facing the negative external terminal, The positive electrode external terminal and the negative electrode external terminal are characterized in that a facing region of the facing surface facing one of the terminals made of a material different from the bus bar has a non-contact region where a step is formed to separate the terminal, or a contact region where a plating layer is formed in the facing region and the terminals come into contact with each other via the plating layer.

[0023] According to the invention described in (14), the occurrence of corrosion due to direct contact between the bus bar and the terminal made of a different metal is prevented. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide a battery pack that can suppress heat generation due to current flowing through the bus bars, suppress battery deterioration, and improve battery performance by reducing weight.

[0025] Further features related to the present invention will become apparent from the description of the present specification and the accompanying drawings. In addition, problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a perspective view of a battery pack according to a first embodiment. [Figure 2] FIG. 2 is an exploded perspective view of the battery pack according to the first embodiment. [Figure 3] FIG. 2 is a perspective view of a bus bar according to the first embodiment. [Figure 4] FIG. 2 is a partial plan view showing a part of the battery pack according to the first embodiment. [Figure 5] 5 is a cross-sectional view showing the cross section AA shown in FIG. 4. [Figure 6] FIG. 10 is a partial plan view showing a part of a battery pack according to a second embodiment. [Figure 7] FIG. 7 is a cross-sectional view showing the cross section BB shown in FIG. 6. [Figure 8] FIG. 11 is a partial plan view showing a part of a battery pack according to a third embodiment. [Figure 9] 9 is a cross-sectional view showing the CC cross section shown in FIG. 8. [Figure 10] FIG. 10 is a perspective view of a bus bar according to a fourth embodiment. [Figure 11] FIG. 10 is a partial plan view showing a part of a battery pack according to a fourth embodiment. [Figure 12] FIG. 11 is a perspective view of a bus bar according to a fifth embodiment. [Figure 13] FIG. 11 is a partial plan view showing a part of a battery pack according to a fifth embodiment. [Figure 14] FIG. 13 is a perspective view of a bus bar according to a sixth embodiment. [Figure 15] FIG. 13 is a partial plan view showing a part of a battery pack according to a sixth embodiment. [Figure 16] FIG. 13 is a perspective view of a bus bar according to a seventh embodiment. [Figure 17] FIG. 13 is a partial plan view showing a part of a battery pack according to a seventh embodiment. [Figure 18] FIG. 13 is a partial plan view showing a part of a battery pack according to an eighth embodiment. [Figure 19] FIG. 13 is a partial plan view showing a part of a battery pack according to a ninth embodiment. [Figure 20] FIG. 23 is a partial plan view showing a part of a battery pack according to a tenth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, battery packs 10 to 10I according to first to tenth embodiments to which the battery pack according to the present invention is applied will be described with reference to the drawings.

[0028] (First embodiment) 1 and 2, the battery pack 10 according to the first embodiment includes a first battery 1, a second battery 2, a third battery 3, a fourth battery 4, a cell holder 5, and a bus bar 6. The first battery 1, the second battery 2, the third battery 3, and the fourth battery 4 are stacked in the X direction shown in FIG. 1, i.e., in the thickness direction.

[0029] The first battery 1 and the second battery 2 are electrically connected in parallel via the bus bar 6, and the third battery 3 and the fourth battery 4 are electrically connected in parallel via the bus bar 6. The first battery 1 and the second battery 2 connected in parallel and the third battery 3 and the fourth battery 4 connected in parallel are electrically connected in series via the bus bar 6.

[0030] Although the battery pack 10 according to the first embodiment has four stacked cells, the first cell 1 to the fourth cell 4, the number of cells may be other than four. For example, two cells or a plurality of cells, such as five or more cells, may be stacked.

[0031] 2, the first battery 1 includes a battery container 11, a positive electrode external terminal 12, a negative electrode external terminal 13, insulators 14 and 15, a gas release valve 16, and a liquid filling plug 22a. The battery container 11 is composed of a battery can 31 and a battery lid 22, and the battery can 31 and the battery lid 22 are made of a metal material such as aluminum or an aluminum alloy.

[0032] The battery can 31 is a flat rectangular box with one end opened in the Z direction, and is formed by a processing method such as deep drawing. The battery lid 22 is a rectangular flat plate, and is formed in the same shape as the opening of the battery can 31 so as to close the opening. The battery lid 22 is joined to the opening of the battery can 31 by a joining method such as laser welding, and seals the opening of the battery can 31. A positive electrode external terminal 12, a negative electrode external terminal 13, and a gas release valve 16 are attached to the battery lid 22.

[0033] 2, the positive electrode external terminal 12 has a flat joint surface at its end face in the Z direction that abuts and is joined to the bus bar 6, and is made of aluminum (Al) or an aluminum alloy. The positive electrode external terminal 12 is attached to one end of the battery lid 22 in the longitudinal direction, i.e., in the Y direction, via an insulator 14. The width of the positive electrode external terminal 12 in the short direction, i.e., in the X direction, is narrower than the width of the battery lid 22, and the battery lid 22 is exposed by a predetermined width from the positive electrode external terminal 12 in the direction away from each other along the X direction.

[0034] Like the positive external terminal 12, the negative external terminal 13 has a flat joint surface at its end surface in the Z direction that abuts and is joined to the bus bar 6, and is made of copper (Cu) or a copper alloy. The negative external terminal 13 is attached to the other end of the battery lid 22 of the battery container 11 in the Y direction via an insulator 15. The negative external terminal 13 has a shape in which the width in the X direction of the battery lid 22 is narrower than the width of the battery lid 22, and is structured so that the battery lid 22 is exposed by a predetermined width from the negative external terminal 13 in a direction separating them from each other along the X direction. In other words, a portion where the battery lid 22 is exposed is provided between the edge of the battery lid 22 extending in the Y direction and the negative external terminal 13.

[0035] 2, the positive electrode external terminal 12 and the negative electrode external terminal 13 are arranged at positions spaced apart from each other in the longitudinal direction of the battery lid 22. The positive electrode external terminal 12 and the negative electrode external terminal 13 have their respective joint surfaces set at the same height from the battery lid 22.

[0036] The first battery 1 and the second battery 2 are arranged so that their positive external terminals 12 and their negative external terminals 13 are adjacent to each other in the X direction, which is the stacking direction. The third battery 3 and the fourth battery 4 are also arranged so that their positive external terminals 12 and their negative external terminals 13 are adjacent to each other in the X direction, which is the stacking direction. The first battery 1 and the second battery 2 and the third battery 3 and the fourth battery 4 are arranged so that their positive external terminals 12 and their negative external terminals 13 are adjacent to each other in the X direction, which is the stacking direction.

[0037] As shown in Fig. 2, the second battery 2, the third battery 3, and the fourth battery 4 are configured in the same manner as the first battery 1. After the first battery 1, the second battery 2, the third battery 3, and the fourth battery 4 are stacked, both ends of each cell in the Y direction are held by four cell holders 5, respectively, to maintain the stacked state.

[0038] 3, 4, and 5, the busbar 6 has a single structure in which a first conductive portion 6a, a second conductive portion 6b, and a connecting portion 6c that electrically connects the first conductive portion 6a and the second conductive portion 6b are integrally joined together. The connecting portion 6c indicates the boundary between the first conductive portion 6a and the second conductive portion 6b. The busbar 6 has a plurality of flat regions that are aligned facing the positive electrode external terminal 12 and the negative electrode external terminal 13, respectively, and curved regions that are interposed between the plurality of flat regions and that protrude and curve in a direction perpendicular to the planes of the flat regions to connect adjacent flat regions.

[0039] As shown in FIGS. 3 , 4 , and 5 , when the busbar 6 is arranged extending in the stacking direction of the first battery 1, the second battery 2, the third battery 3, and the fourth battery 4, the busbar 6 has flat regions H1, H2, H3, and H4 that face the joint surfaces of the positive electrode external terminal 12 and the negative electrode external terminal 13. The busbar 6 also has a curved region W1 that is curved between the flat regions H1 and H2 and protrudes in a direction perpendicular to the planes of the flat regions H1 and H2. Similarly to the curved region W1, the busbar 6 also has a curved region W2 that is formed between the flat regions H2 and H3, and a curved region W3 that is formed between the flat regions H3 and H4. The curved regions W1, W2, and W3 function to absorb shocks such as vibrations acting on the battery pack 10 and to reduce stresses that occur at the joints between the positive electrode external terminal 12 and the negative electrode external terminal 13.

[0040] The first conductive portion 6a is made of a metal material primarily composed of aluminum, and is joined to the positive electrode external terminals 12 of the first battery 1 and the second battery 2, which are made of aluminum or an aluminum alloy, at the flat regions H1 and H2 by spot joining or surface joining using joining means such as laser welding. The first conductive portion 6a has a lower electrical conductivity and a smaller specific gravity than the second conductive portion 6b.

[0041] The second conductive portion 6b is made of a metal material primarily composed of copper, and is joined to the negative electrode external terminals 13 of the third battery 3 and the fourth battery 4, which are made of copper or a copper alloy, at the flat regions H3 and H4 by spot joining or surface joining using joining means such as laser welding. The second conductive portion 6b has a higher electrical conductivity and a larger specific gravity than the first conductive portion 6a.

[0042] The busbar 6 is formed so that the second conductive portion 6b is longer in the extension direction than the first conductive portion 6a. When the flat regions H1 and H2 are arranged to overlap the joint surfaces of the positive external terminals 12 of the first battery 1 and the second battery 2, and the flat regions H3 and H4 are arranged to overlap the joint surfaces of the negative external terminals 13 of the third battery 3 and the fourth battery 4, as shown in Fig. 5, for example, the busbar 6 is configured so that the second conductive portion 6b faces the third battery 3 and the fourth battery 4, respectively, and further has a length that extends to a position where an end of the second conductive portion 6b faces the second battery 2, and the connecting portion 6c is positioned to face the battery lid 22 of the second battery 2.

[0043] The bus bar 6 connects the first conductive portion 6a and the second conductive portion 6b via the connecting portion 6c, and is made of a clad material made of aluminum and copper. The clad material is made by rolling and joining dissimilar metals together, and is characterized by its resistance to peeling despite the absence of adhesive.

[0044] As shown in FIG. 4 , the connecting portion 6c is disposed from one end Ta to the other end Tb in the width direction of the busbar 6, which is perpendicular to the extension direction of the busbar 6. The connecting portion 6c is formed across the entire width of the busbar 6, dividing one end and the other end in the extension direction of the busbar 6 into a first conductive portion 6a and a second conductive portion 6b. The connecting portion 6c is entirely formed in the first region of the busbar 6 that faces the second battery 2 and the first battery 1. In the first embodiment, the connecting portion 6c is formed in the flat region H2 and is provided along the width direction of the busbar 6 near the boundary between the flat region H2 and the curved region W2, as shown in FIG. 5 . When the busbar 6 is attached as shown in FIG. 5 , the connecting portion 6c is positioned facing the battery lid 22 of the second battery 2 between the edge of the battery lid 22 and the positive external terminal 12. The edge of the battery cover 22 of this second battery 2 corresponds to the edge of the second battery facing the third battery in claim 6 of the claims.

[0045] In the battery pack 10 according to the first embodiment, the first battery 1 and the second battery 2 are connected in parallel, the third battery 3 and the fourth battery 4 are connected in parallel, and the parallel-connected first battery 1 and the second battery 2 are connected in series with the parallel-connected third battery 3 and the fourth battery 4. Therefore, when current flows from the first battery 1 and the second battery 2 to the third battery 3 and the fourth battery 4, the same amount of current flows through the first battery 1, the second battery 2, the third battery 3, and the fourth battery 4.

[0046] Both the currents from the first battery 1 and the second battery 2 flow between the point where the busbar 6 is joined to the positive external terminal 12 of the second battery 2 and the point where it is joined to the negative external terminal 13 of the third battery 3, resulting in a relatively large current.

[0047] The effects of the battery pack 10 according to the first embodiment will be described. The battery pack 10 according to the first embodiment includes a first battery 1 to a fourth battery 4 stacked one on top of the other, each battery including a positive external terminal 12 and a negative external terminal 13 having a higher electrical conductivity than the positive external terminal 12, and a bus bar 6 that electrically connects the positive external terminal 12 of one of the first batteries 1 to the fourth battery 4, a second battery 2, which is arranged adjacent to one another, with the negative external terminal 13 of the other of the first batteries 1 to the fourth battery 4. The bus bar 6 has a first conductive part 6a connected to the positive external terminal 12, a second conductive part 6b connected to the negative external terminal 13 and having a higher electrical conductivity and specific gravity than the first conductive part 6a, and a connecting part 6c that connects the first conductive part 6a and the second conductive part 6b, and the connecting part 6c is positioned facing one of the second batteries 2.

[0048] More specifically, the battery pack 10 includes a first battery 1, a second battery 2, a third battery 3, and a fourth battery 4 as multiple batteries, and the first battery 1 and the second battery 2 are arranged side by side with their positive external terminals 12 and their negative external terminals 13 adjacent to each other in the stacking direction of the first batteries 1 to 4, and the third battery 3 and the fourth battery 4 are arranged side by side with their positive external terminals 12 and their negative external terminals 13 adjacent to each other in the stacking direction of the first batteries 1 to 4. The positive external terminals 12 of the first battery 1 and the second battery 2 and the negative external terminals 13 of the third battery 3 and the fourth battery 4 are arranged side by side in a row adjacent to each other in the stacking direction of the first batteries 1 to 4. The busbar 6 extends in the stacking direction of the first battery 1 to the fourth battery 4, and is positioned to face the positive external terminals 12 of the first battery 1 and the second battery 2 and the negative external terminals 13 of the third battery 3 and the fourth battery 4. The first conductive portion 6a is joined to the positive external terminals 12 of the first battery 1 and the second battery 2, the second conductive portion 6b is joined to the negative external terminals 13 of the third battery 3 and the fourth battery 4, and the connecting portion 6c is positioned in a first region facing at least one of the first battery 1 and the second battery.

[0049] In the battery pack 10 of the first embodiment, the end of the second conductive portion 6b has a length that extends from a position facing the third battery 3 and the fourth battery 4 to a position facing the second battery 2, and the connecting portion 6c is configured to be positioned facing the battery cover 22 of the second battery 2. Therefore, the second conductive portion 6b, which has a relatively high conductivity, has a wider area through which current flows than the first conductive portion 6a. This makes it easier for current to flow between the first battery 1 and the second battery 2 and the third battery 3 and the fourth battery 4, suppressing heat generation in the bus bar 6 and ultimately suppressing accelerated deterioration of the cells due to heat generation, thereby improving the performance of the battery pack 10.

[0050] In the battery pack 10 according to the first embodiment, the bus bar 6 has flat regions H1, H2, H3, and H4 that face the cells in parallel along the stacking direction of the cells, and curved regions W1, W2, and W3 that are perpendicular to the stacking direction of the cells and protrude in a direction away from the battery lid 22 to face the battery lid 22. With this configuration, the bus bar 6 can be electrically connected to the positive electrode external terminal 12 and the negative electrode external terminal 13 at the flat regions H1, H2, H3, and H4. Furthermore, since the bus bar 6 has the curved regions W1, W2, and W3, shocks such as vibrations acting on the battery pack 10 can be absorbed by the curved regions, and stresses generated in the connecting portions 6c can be reduced, resulting in improved durability of the battery pack.

[0051] The battery pack 10 according to the first embodiment has been described as having the connecting portion 6c of the bus bar 6 formed in the flat region H2 along the curved region W2 near the boundary between the flat region H2 and the curved region W2. In the battery pack according to the present invention, the connecting portion of the bus bar may be configured with a structure other than the connecting portion 6c of the bus bar 6. Hereinafter, battery packs 10A according to the second embodiment to battery packs 10I according to the tenth embodiment, in which the connecting portion of the bus bar is configured with a structure other than the connecting portion 6c of the bus bar 6, will be described with reference to the drawings. Note that the same components as those in the battery pack 10 according to the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

[0052] (Second embodiment) The battery pack 10A according to the second embodiment includes a first battery 1, a second battery 2, a third battery 3, a fourth battery 4, a cell holder 5, and a bus bar 6A.

[0053] 6 and 7, the busbar 6A has a single structure in which a first conductive portion 6Aa, a second conductive portion 6Ab, and a connecting portion 6Ac that electrically connects the first conductive portion 6Aa and the second conductive portion 6Ab are integrally joined. Similar to the connecting portion 6c in the first embodiment, the connecting portion 6Ac indicates the boundary between the first conductive portion 6Aa and the second conductive portion 6Ab. The busbar 6A has flat regions H1, H2, H3, and H4 that face each battery in parallel along the stacking direction of the first, second, third, and fourth batteries 1, 2, 3, and 4.

[0054] Furthermore, the bus bar 6A has the same curved regions W1, W2, and W3 as in the first embodiment, and the curved regions W1, W2, and W3 function in the same way as in the first embodiment.

[0055] The first conductive portion 6Aa is made of a metal material primarily composed of aluminum, and is joined to the positive electrode external terminals 12, which are made of aluminum or an aluminum alloy, of the first battery 1 and the second battery 2, at the flat regions H1 and H2 by spot joining or surface joining using joining means such as laser welding. The first conductive portion 6Aa has a lower electrical conductivity and a smaller specific gravity than the second conductive portion 6Ab.

[0056] Like the busbar 6 of the first embodiment, the second conductive portion 6Ab is made of a metal material primarily composed of copper, and is joined to the negative electrode external terminals 13 of the third battery 3 and the fourth battery 4, which are made of copper or a copper alloy, at the flat regions H3 and H4 by spot joining or surface joining using joining means such as laser welding. The second conductive portion 6Ab has a higher electrical conductivity and a larger specific gravity than the first conductive portion 6Aa. The second conductive portion 6Ab extends from a position facing the third battery 3 and the fourth battery 4 to a position facing the second battery 2.

[0057] Similar to the busbar 6 of the first embodiment, the connecting portion 6Ac connects the first conductive portion 6Aa and the second conductive portion 6Ab, and therefore the busbar 6A is made of an aluminum-copper clad material. As shown in FIG. 6 , the connecting portion 6Ac is disposed from one end TAa to the other end TAb in the width direction of the busbar 6A, which is perpendicular to the extension direction of the busbar 6A. The connecting portion 6Ac is formed across the entire width of the busbar 6A, dividing the one and the other sides of the extension direction of the busbar 6A into the first conductive portion 6Aa and the second conductive portion 6Ab. The connecting portion 6Ac is entirely formed in the first region of the busbar 6A facing the second battery 2 and the first battery 1. In the second embodiment, the connecting portion 6Ac is formed in the flat region H2 and is positioned opposite the center of the positive external terminal 12 of the second battery 2 when the busbar 6A is attached to each battery.

[0058] The first conductive portion 6Aa and the positive external terminal 12 in the flat region H2 are made of the same material, aluminum, and are therefore joined to each other in the region of the first conductive portion 6Aa in the flat region H2. Meanwhile, in the region of the flat region H2 between the connecting portion 6Ac and the curved region W2, the second conductive portion 6Ab is made of copper and the positive external terminal 12 is made of aluminum, which may cause corrosion due to contact between dissimilar metals. The busbar 6A is provided with a corrosion prevention structure that prevents this corrosion.

[0059] Examples of the corrosion prevention structure include a non-contact region in which a step is formed to separate the terminals from the facing region of the facing surface of the busbar 6A, facing either the positive external terminal 12 or the negative external terminal 13, whichever is made of a different material from the busbar 6A, or a contact region in which a plating layer is formed in the facing region and the terminals come into contact with each other via the plating layer. Examples of the corrosion prevention structure include a structure in which a step is formed in the region in the flat region H2 between the connecting portion 6Ac and the curved region W2 to prevent contact with each other, or a structure in which surface treatment such as plating that does not cause corrosion is performed.

[0060] The connections of the cells and the currents flowing through the cells in the battery pack 10A according to the second embodiment are similar to those in the battery pack 10 according to the first embodiment, and therefore will not be described here.

[0061] Between the point where the busbar 6A is joined to the positive external terminal 12 of the second battery 2 and the point where it is joined to the negative external terminal 13 of the third battery 3, a current flows between the first and second batteries and the third and fourth batteries, resulting in a relatively large current.

[0062] The effects of the battery pack 10A according to the second embodiment will be described. The battery pack 10A according to the second embodiment includes a positive external terminal 12 and a negative external terminal 13 having a higher conductivity than the positive external terminal 12, and is stacked in the order of a first battery 1, a second battery 2, a third battery 3, and a fourth battery 4, and includes a bus bar 6A composed of a first conductive portion 6Aa, a second conductive portion 6Ab having a higher conductivity and a larger specific gravity than the first conductive portion 6Aa, and a connecting portion 6Ac.

[0063] The first conductive portion 6Aa is joined to the positive external terminals 12 of the first battery 1 and the second battery 2, and the second conductive portion 6Ab is joined to the negative external terminals 13 of the third battery 3 and the fourth battery 4. The connecting portion 6Ac is formed in parallel to the curved region W2 in the center of the flat region H2 in the X direction. The second conductive portion 6Ab extends from a position facing the third battery 3 and the fourth battery 4 to a position facing the second battery 2, and the connecting portion 6Ac is located in a region facing the positive external terminal 12 of the second battery 2.

[0064] In the battery pack 10A of the second embodiment, the end of the second conductive part 6Ab has a length that extends from a position facing the third battery 3 and the fourth battery 4 to a position facing the second battery 2, and the connecting part 6Ac is configured to be positioned facing the positive external terminal 12 of the second battery 2. Therefore, the second conductive part 6Ab, which has a relatively high conductivity, has a wider area through which current flows than the first conductive part 6Aa. Therefore, current flows more easily between the first battery 1 and the second battery 2 and the third battery 3 and the fourth battery 4, suppressing heat generation in the bus bar 6A and preventing accelerated deterioration of the cells due to heat generation, thereby improving the performance of the battery pack 10A.

[0065] (Third embodiment) The battery pack 10B according to the third embodiment includes a first battery 1, a second battery 2, a third battery 3, a fourth battery 4, a cell holder 5, and a bus bar 6B.

[0066] 8 and 9, like the busbar 6 of the first embodiment, the busbar 6B has a single structure in which a first conductive portion 6Ba, a second conductive portion 6Bb, and a connecting portion 6Bc that electrically connects the first conductive portion 6Ba and the second conductive portion 6Bb are integrally joined together. Like the connecting portion 6c of the first embodiment, the connecting portion 6Bc indicates the boundary between the first conductive portion 6Ba and the second conductive portion 6Bb. Like the busbar 6 of the first embodiment, the busbar 6B has flat regions H1, H2, H3, and H4 that face each battery in parallel along the stacking direction of the first, second, third, and fourth batteries 1, 2, and 3.

[0067] Furthermore, the bus bar 6B has the same curved regions W1, W2, and W3 as in the first embodiment, and the curved regions W1, W2, and W3 function in the same way as in the first embodiment.

[0068] Like the busbar 6 of the first embodiment, the first conductive portion 6Ba is made of a metal material primarily composed of aluminum, and is joined to the positive electrode external terminals 12 of the first battery 1 and the second battery 2, which are made of aluminum or an aluminum alloy, at the flat regions H1 and H2 by spot joining or surface joining using joining means such as laser welding. The first conductive portion 6Ba has a lower electrical conductivity and a smaller specific gravity than the second conductive portion 6Bb.

[0069] Like the busbar 6 of the first embodiment, the second conductive portion 6Bb is made of a metal material primarily composed of copper, and is joined to the negative electrode external terminals 13 of the third battery 3 and the fourth battery 4, which are made of copper or a copper alloy, at the flat regions H3 and H4 by spot joining or surface joining using joining means such as laser welding. The second conductive portion 6Bb has a higher electrical conductivity and a larger specific gravity than the first conductive portion 6Ba. A portion of the second conductive portion 6Bb extends from a position facing the third battery 3 and the fourth battery 4 to a position facing the second battery 2 and the first battery 1.

[0070] The second conductive part 6Bb faces a portion of the positive external terminal 12 of the second battery 2 and a portion of the positive external terminal 12 of the first battery 1, and the first conductive part 6Ba is disposed at a position facing another portion of the positive external terminal 12 of the second battery 2 and another portion of the positive external terminal 12 of the first battery 1. In the third embodiment, the first conductive part 6Ba faces approximately one-quarter of the positive external terminal 12 of the second battery 2 and has a size that faces approximately one-half of the positive external terminal 12 of the first battery 1. The second conductive part 6Bb faces approximately three-quarters of the positive external terminal 12 of the second battery 2 and has a size that faces approximately one-half of the positive external terminal 12 of the first battery 1.

[0071] Similar to the bus bar 6 of the first embodiment, the connecting portion 6Bc connects the first conductive portion 6Ba and the second conductive portion 6Bb, and therefore the bus bar 6B is made of an aluminum-copper clad material. Also, as shown in Figures 8 and 9, the connecting portion 6Bc is formed in a substantially L-shape so as to extend from an edge TBa of the flat region H2 to a center TBb in the Y direction at the center of the flat region H2 in the X direction, and to extend across W1 from an edge TBc of the flat region H1 in the X direction to the center TBb of the flat region H2 in the X direction at the center TBb of the flat regions H1 and H2 in the Y direction.

[0072] The first conductive portion 6Ba and the positive external terminal 12 in the flat regions H1 and H2 are made of the same material, aluminum, and are therefore joined to each other in the region of the first conductive portion 6Ba in the flat regions H1 and H2, i.e., the inner region of the L-shape. On the other hand, in the region outside the L-shape in the flat regions H1 and H2, the second conductive portion 6Bb is made of copper and the positive external terminal 12 is made of aluminum, so there is a risk of corrosion occurring due to contact between dissimilar metals. The busbar 6B is formed with a corrosion prevention structure that prevents this corrosion.

[0073] As an anti-corrosion structure, similar to the busbar 6A of the second embodiment, the busbar 6B may have a non-contact region in the opposing surface facing the positive external terminal 12 or the negative external terminal 13, whichever is made of a different material from the busbar 6B, by forming a step to separate the terminal, or a contact region in which a plating layer is formed in the opposing region and the terminals come into contact with each other via the plating layer.

[0074] The connections of the cells and the currents flowing through the cells in the battery pack 10B according to the third embodiment are similar to those in the battery pack 10 according to the first embodiment, and therefore will not be described here.

[0075] A current flows between the point of the busbar 6B joined to the positive external terminal 12 of the second battery 2 and the point of the busbar 6B joined to the negative external terminal 13 of the third battery 3, between the first and second batteries and the third and fourth batteries, resulting in a relatively large current.

[0076] The effects of the battery pack 10B according to the third embodiment will be described. The battery pack 10B according to the third embodiment includes a positive electrode external terminal 12 and a negative electrode external terminal 13 having a higher conductivity than the positive electrode external terminal 12, and includes a bus bar 6B stacked in the order of a first battery 1, a second battery 2, a third battery 3, and a fourth battery 4, and including a first conductive portion 6Ba, a second conductive portion 6Bb having a higher conductivity and a larger specific gravity than the first conductive portion 6Ba, and a connecting portion 6Bc.

[0077] The first conductive portion 6Ba is joined to the positive external terminals 12 of the first battery 1 and the second battery 2, the second conductive portion 6Bb is joined to the negative external terminals 13 of the third battery 3 and the fourth battery 4, and the connecting portion 6Bc has a generally L-shaped configuration that extends from the end of the busbar on one side in the width direction perpendicular to the stacking direction of the batteries at a position facing the positive external terminal 12 of the second battery 2 in the first region toward the other side, is bent toward the stacking direction of the batteries, and extends to a position facing the positive external terminal 12 of the first battery 1.

[0078] In the battery pack 10B of the third embodiment, the busbar 6B has a length such that an end of the second conductive portion 6Bb extends from a position facing the third battery 3 and the fourth battery 4 to a position facing a part of the second battery 2 and a part of the first battery 1. The connecting portion 6Bc has a generally L-shaped configuration that extends from one busbar end on one side in the width direction perpendicular to the stacking direction of the batteries at a position facing the positive external terminal 12 of the second battery 2 to the other side, bends toward the stacking direction of the batteries, and extends to a position facing the positive external terminal 12 of the first battery 1. The first conductive portion 6Ba faces a quarter of the positive external terminal 12 of the second battery 2 and faces a half of the positive external terminal 12 of the first battery 1. The second conductive portion 6Bb faces three-quarters of the positive external terminal of the second battery 2 and half of the positive external terminal 12 of the first battery 1. Therefore, the second conductive portion 6Bb, which has a relatively high conductivity, has a wider area through which current flows than the first conductive portion 6Ba. Furthermore, the first conductive portion 6Ba and the second conductive portion 6Bb are adjacent to each other via a connecting portion 6Bc extending in the X direction, which is the extension direction of the bus bar 6B. This facilitates current flow from the first conductive portion 6Ba to the second conductive portion 6Bb. This facilitates current flow between the first and second batteries 1 and 2 and the third and fourth batteries 3 and 4, suppressing heat generation in the bus bar 6 and accelerating cell deterioration due to heat generation, thereby improving the performance of the battery pack 10B.

[0079] (Fourth embodiment) The battery pack 10C according to the fourth embodiment includes a first battery 1, a second battery 2, a third battery 3, a fourth battery 4, a cell holder 5, and a bus bar 6C.

[0080] 10 and 11, like the busbar 6 of the first embodiment, the busbar 6C has a single structure in which a first conductive portion 6Ca, a second conductive portion 6Cb, and a connecting portion 6Cc that electrically connects the first conductive portion 6Ca and the second conductive portion 6Cb are integrally joined together. Like the connecting portion 6c of the first embodiment, the connecting portion 6Cc indicates the boundary between the first conductive portion 6Ca and the second conductive portion 6Cb. Like the busbar 6 of the first embodiment, the busbar 6C has flat regions H1, H2, H3, and H4 that face each battery in parallel with the first battery 1, second battery 2, third battery 3, and fourth battery 4 in the stacking direction.

[0081] Furthermore, the bus bar 6C has the same curved regions W1, W2, and W3 as in the first embodiment, and the curved regions W1, W2, and W3 function in the same way as in the first embodiment.

[0082] Like the busbar 6 of the first embodiment, the first conductive portion 6Ca is made of a metal material primarily composed of aluminum, and is joined to the positive electrode external terminals 12 of the first battery 1 and the second battery 2, which are made of aluminum or an aluminum alloy, at the flat regions H1 and H2 by spot joining or surface joining using joining means such as laser welding. The first conductive portion 6Ca has a lower electrical conductivity and a smaller specific gravity than the second conductive portion 6Cb.

[0083] Like the busbar 6 of the first embodiment, the second conductive portion 6Cb is made of a metal material primarily composed of copper, and is joined to the negative electrode external terminals 13 of the third battery 3 and the fourth battery 4, which are made of copper or a copper alloy, at the flat regions H3 and H4 by spot joining or surface joining using joining means such as laser welding. The second conductive portion 6Cb has a higher electrical conductivity and a larger specific gravity than the first conductive portion 6Ca.

[0084] Similar to the busbar 6 of the first embodiment, the connecting portion 6Cc connects the first conductive portion 6Ca and the second conductive portion 6Cb, and therefore the busbar 6C is made of an aluminum-copper clad material. As shown in FIG. 11 , the connecting portion 6Cc is disposed obliquely across the extension direction of the busbar 6C, from the end TCa on one side to the end TCb on the other side in the width direction of the busbar 6C. The connecting portion 6Cc is formed across the entire width direction of the busbar 6C, dividing the one and the other sides in the extension direction of the busbar 6C into the first conductive portion 6Ca and the second conductive portion 6Cb. The connecting portion 6Cc is entirely formed in the first region of the busbar 6C facing the second battery 2 and the first battery 1. The connecting portion 6Cc extends obliquely across the curved region W1 between the flat region H1 and the flat region H2 in the extension direction (X direction) of the busbar 6C.

[0085] As shown in Figures 10 and 11, the connecting portion 6Cc is arranged in the first region such that the end TCa on one width side of the busbar 6C is positioned facing the second battery 2 between the edge of the second battery 2 facing the third battery 3 (the edge of the battery lid 22 of the second battery 2) and the side of the positive external terminal 12 of the second battery 2 facing the third battery 3, and the end TCb on the other width side of the busbar 6C is positioned facing the first battery 1 between the edge of the first battery 1 on the side facing away from the second battery 2 and the side of the positive external terminal 12 of the first battery 1 facing the second battery.

[0086] The first conductive portion 6Ca and the positive external terminal 12 in the flat region H2 are made of the same material, aluminum, and are therefore joined to each other in the region of the first conductive portion 6Ca in the flat region H2. Meanwhile, in the region of the flat region H2 between the connecting portion 6Cc and the curved region W2, the second conductive portion 6Cb is made of copper and the positive external terminal 12 is made of aluminum, which may cause corrosion due to contact between dissimilar metals. The busbar 6C is provided with a corrosion prevention structure that prevents this corrosion.

[0087] As an example of a corrosion prevention structure, similar to the busbar 6A of the second embodiment, the busbar 6C may have a non-contact area or a contact area similar to that of the busbar 6A in the opposing area of ​​the opposing surface facing the positive external terminal 12 or the negative external terminal 13, whichever is made of a different material from that of the busbar 6C.

[0088] The connections of the cells and the currents flowing through the cells in the battery pack 10C according to the fourth embodiment are similar to those in the battery pack 10 according to the first embodiment, and therefore will not be described here.

[0089] Between the point where the busbar 6C is joined to the positive external terminal 12 of the second battery 2 and the point where it is joined to the negative external terminal 13 of the third battery 3, a current flows between the first and second batteries and the third and fourth batteries, resulting in a relatively large current.

[0090] The effects of the battery pack 10C according to the fourth embodiment will be described. The battery pack 10C of the fourth embodiment includes a positive electrode external terminal 12 and a negative electrode external terminal 13 having a higher conductivity than the positive electrode external terminal 12, and includes a bus bar 6C stacked in the order of a first battery 1, a second battery 2, a third battery 3, and a fourth battery 4, and including a first conductive portion 6Ca, a second conductive portion 6Cb having a higher conductivity and a larger specific gravity than the first conductive portion 6Ca, and a connecting portion 6Cc.

[0091] The first conductive portion 6Ca is joined to the positive external terminals 12 of the first battery 1 and the second battery 2, and the second conductive portion 6Cb is joined to the negative external terminals 13 of the third battery 3 and the fourth battery 4. The connecting portion 6Cc is configured to extend in a straight line from one end to the other end of the busbar 6C in the width direction, diagonally intersecting the extension direction of the busbar 6C. One end of the connecting portion 6Cc in the width direction of the busbar 6C is located at a position facing the edge of the second battery 2 facing the third battery 3 and the positive external terminal 12 of the second battery 2, and the other end of the busbar 6C is located at a position facing the edge of the first battery 1 facing the second battery 2 and the positive external terminal 12 of the first battery 1.

[0092] In the battery pack 10C of the fourth embodiment, the end of the second conductive portion 6Cb has a length that extends from a position facing the third battery 3 and the fourth battery 4 to a position facing the first battery 1 and the second battery 2, and the connecting portion 6Cc is configured to extend in a straight line from one end of the bus bar 6C to the other end in the width direction, diagonally intersecting the extension direction of the bus bar 6C. Therefore, the second conductive portion 6Cb, which has a relatively high conductivity, has a wider area through which current flows than the first conductive portion 6Ca. This makes it easier for current to flow between the first battery 1 and the second battery 2 and the third battery 3 and the fourth battery 4, suppresses heat generation in the bus bar 6C, and suppresses accelerated deterioration of the cells due to heat generation, thereby improving the performance of the battery pack 10C.

[0093] In the battery pack 10C according to the fourth embodiment, the second conductive portion 6Cb of the bus bar 6C faces the second battery 2, and the entire area of ​​the connecting portion 6Cc is located somewhere between the positive external terminal 12 of the second battery 2 and the first battery 1. With this configuration, the first conductive portion 6Ca, which has a small specific gravity but low electrical conductivity, and the second conductive portion 6Cb, which has a large specific gravity but high electrical conductivity, achieve a good balance between reducing the weight of the battery pack 10C and suppressing deterioration of the cells due to heat generation.

[0094] (Fifth embodiment) The battery pack 10D according to the fifth embodiment includes a first battery 1, a second battery 2, a third battery 3, a fourth battery 4, a cell holder 5, and a bus bar 6D.

[0095] 12 and 13, like the busbar 6 of the first embodiment, the busbar 6D has a single structure in which a first conductive portion 6Da, a second conductive portion 6Db, and a connecting portion 6Dc that electrically connects the first conductive portion 6Da and the second conductive portion 6Db are integrally joined together. Like the connecting portion 6c of the first embodiment, the connecting portion 6Dc indicates the boundary between the first conductive portion 6Da and the second conductive portion 6Db. Like the busbar 6 of the first embodiment, the busbar 6D has flat regions H1, H2, H3, and H4 that face each battery in parallel along the stacking direction of the first, second, third, and fourth batteries 1, 2, and 3.

[0096] Furthermore, the bus bar 6D has the same curved regions W1, W2, and W3 as in the first embodiment, and the curved regions W1, W2, and W3 function in the same way as in the first embodiment.

[0097] Like the busbar 6 of the first embodiment, the first conductive portion 6Da is made of a metal material primarily composed of aluminum, and is joined to the positive electrode external terminals 12 of the first battery 1 and the second battery 2, which are made of aluminum or an aluminum alloy, at the flat regions H1 and H2 by spot joining or surface joining using joining means such as laser welding. The first conductive portion 6Da has a lower electrical conductivity and a smaller specific gravity than the second conductive portion 6Db.

[0098] Like the busbar 6 of the first embodiment, the second conductive portion 6Db is made of a metal material primarily composed of copper, and is joined to the negative electrode external terminals 13 of the third battery 3 and the fourth battery 4, which are made of copper or a copper alloy, at the flat regions H3 and H4 by spot joining or surface joining using joining means such as laser welding. The second conductive portion 6Db has a higher electrical conductivity and a larger specific gravity than the first conductive portion 6Da.

[0099] Similar to the busbar 6 of the first embodiment, the connecting portion 6Dc connects the first conductive portion 6Da and the second conductive portion 6Db, and therefore the busbar 6D is made of an aluminum-copper clad material. As shown in FIG. 13 , the connecting portion 6Dc is disposed obliquely across the extension direction of the busbar 6D, from one end TDa to the other end TDb in the width direction of the busbar 6D. The connecting portion 6Dc is formed across the entire width of the busbar 6D, dividing one end and the other end of the extension direction of the busbar 6D into the first conductive portion 6Da and the second conductive portion 6Db. The connecting portion 6Dc is entirely formed in the first region of the busbar 6D that faces the second battery 2 and the first battery 1. The connecting portion 6Dc extends obliquely across the curved region W1 between the flat region H1 and the flat region H2 in the extension direction (X direction) of the busbar 6D.

[0100] As shown in Figures 12 and 13, the connecting portion 6Dc is arranged in the first region such that the end TDa on one width side of the busbar 6D is positioned facing the second battery 2 between the edge of the second battery 2 facing the third battery 3 and the side of the positive external terminal 12 of the second battery 2 facing the third battery 3, and the end TDb on the other width side of the busbar 6D is positioned facing the first battery 1 between the edge of the first battery 1 facing away from the second battery 2 (the edge of the battery lid 22 of the first battery 1) and the side of the positive external terminal 12 of the first battery 1 facing away from the second battery 2.

[0101] The first conductive portion 6Da and the positive electrode external terminal 12 in the flat regions H1 and H2 are made of the same material, aluminum, and are therefore joined to each other in the area of ​​the first conductive portion 6Da in the flat regions H1 and H2. Meanwhile, in the area between the connecting portion 6Dc and the curved regions W1 and W2 in the flat regions H1 and H2, the second conductive portion 6Db is made of copper and the positive electrode external terminal 12 is made of aluminum, which may cause corrosion due to contact between dissimilar metals. The busbar 6D has a corrosion prevention structure to prevent this corrosion.

[0102] As an example of a corrosion prevention structure, similar to the busbar 6A of the second embodiment, the busbar 6D may have a non-contact area or a contact area similar to that of the busbar 6A in the opposing area of ​​the opposing surface facing the positive external terminal 12 or the negative external terminal 13, whichever is made of a different material from that of the busbar 6D.

[0103] The connections of the cells and the currents flowing through the cells in the battery pack 10D according to the fifth embodiment are similar to those in the battery pack 10 according to the first embodiment, and therefore will not be described here.

[0104] Between the point of the busbar 6D joined to the positive external terminal 12 of the second battery 2 and the point of the busbar 6D joined to the negative external terminal 13 of the third battery 3, a current flows between the first and second batteries and the third and fourth batteries, resulting in a relatively large current.

[0105] The effects of the battery pack 10D according to the fifth embodiment will be described. The battery pack 10D of the fifth embodiment includes a positive electrode external terminal 12 and a negative electrode external terminal 13 having a higher conductivity than the positive electrode external terminal 12, and is stacked in the order of a first battery 1, a second battery 2, a third battery 3, and a fourth battery 4, and has a bus bar 6D composed of a first conductive part 6Da, a second conductive part 6Db having a higher conductivity and a larger specific gravity than the first conductive part 6Da, and a connecting part 6Dc.

[0106] The first conductive portion 6Da is joined to the positive external terminals 12 of the first battery 1 and the second battery 2, and the second conductive portion 6Db is joined to the negative external terminals 13 of the third battery 3 and the fourth battery 4. The connecting portion 6Dc is configured to extend in a straight line from one end to the other end of the busbar 6D in the width direction, diagonally intersecting the extension direction of the busbar 6D. One end of the connecting portion 6Dc in the width direction of the busbar 6D is located between the edge of the second battery 2 facing the third battery 3 and the positive external terminal 12 of the second battery 2, and the other end of the busbar 6D is located between the edge of the first battery 1 facing away from the second battery 2 and the positive external terminal 12 of the first battery 1.

[0107] In the battery pack 10D of the fifth embodiment, the second conductive portion 6Db has a length that extends from a position facing the third battery 3 and the fourth battery 4 to a position facing the first battery 1 and the second battery 2, and the connecting portion 6Dc is configured to diagonally intersect the extension direction of the busbar 6D and extend in a straight line from one end of the busbar 6D in the width direction to the end of the busbar 6D on the first battery 1 side in the extension direction of the busbar 6D. Therefore, the second conductive portion 6Db, which has a relatively high conductivity, has a wider area through which current flows than the first conductive portion 6Da. This makes it easier for current to flow between the first battery 1 and the second battery 2 and the third battery 3 and the fourth battery 4, suppressing heat generation in the busbar 6D and accelerating deterioration of the cells due to heat generation, thereby improving the performance of the battery pack 10D.

[0108] In the battery pack 10D according to the fifth embodiment, the second conductive portion 6Db of the bus bar 6D faces the second battery 2, and the entire area of ​​the connecting portion 6Dc is located somewhere between the positive external terminal 12 of the second battery 2 and the first battery 1. With this configuration, the first conductive portion 6Da, which has a small specific gravity but low electrical conductivity, and the second conductive portion 6Db, which has a large specific gravity but high electrical conductivity, achieve a good balance between reducing the weight of the battery pack 10D and suppressing deterioration of the cells due to heat generation.

[0109] (Sixth embodiment) The battery pack 10E according to the sixth embodiment includes a first battery 1, a second battery 2, a third battery 3, a fourth battery 4, a cell holder 5, and a bus bar 6E.

[0110] 14 and 15, like the busbar 6 of the first embodiment, the busbar 6E has a single structure in which a first conductive portion 6Ea, a second conductive portion 6Eb, and a connecting portion 6Ec that electrically connects the first conductive portion 6Ea and the second conductive portion 6Eb are integrally joined together. Note that, like the connecting portion 6c of the first embodiment, the connecting portion 6Ec indicates the boundary portion between the first conductive portion 6Ea and the second conductive portion 6Eb. The busbar 6E has a flat plate shape formed only by flat regions.

[0111] Like the busbar 6 of the first embodiment, the first conductive portion 6Ea is made of a metal material primarily composed of aluminum, and is joined to the positive electrode external terminals 12 of the first battery 1 and the second battery 2, which are made of aluminum or an aluminum alloy, by spot joining or surface joining using joining means such as laser welding. The first conductive portion 6Ea has lower conductivity and a smaller specific gravity than the second conductive portion 6Eb.

[0112] Like the busbar 6 of the first embodiment, the second conductive portion 6Eb is made of a metal material primarily composed of copper, and is joined to the negative electrode external terminals 13 of the third battery 3 and the fourth battery 4, which are made of copper or a copper alloy, by spot joining or surface joining using joining means such as laser welding. The second conductive portion 6Eb has a higher electrical conductivity and a larger specific gravity than the first conductive portion 6Ea.

[0113] Similar to the busbar 6 of the first embodiment, the connecting portion 6Ec connects the first conductive portion 6Ea and the second conductive portion 6Eb, and therefore the busbar 6E is made of an aluminum-copper clad material. As shown in FIG. 14 , the connecting portion 6Ec is disposed diagonally across the extension direction of the busbar 6E, from the end TEa on one side to the end TEb on the other side in the width direction of the busbar 6E. The connecting portion 6Ec is formed across the entire width direction of the busbar 6E, dividing the one and the other sides in the extension direction of the busbar 6E into the first conductive portion 6Ea and the second conductive portion 6Eb. The connecting portion 6Ec is entirely formed in the first region of the busbar 6E facing the second battery 2 and the first battery 1.

[0114] The connecting portion 6Ec is arranged such that an end portion TEa on one width side of the busbar 6E faces the second battery 2 between the edge of the second battery 2 facing the third battery 3 and the center of the positive external terminal 12 of the second battery 2 in the stacking direction of the multiple batteries, and an end portion TEb on the other width side of the busbar 6E faces the first battery 1 between the edge of the first battery 1 facing the second battery 2 and the side of the positive external terminal of the first battery 1 that faces away from the second battery.

[0115] The first conductive portion 6Ea and the positive external terminal 12 are both made of aluminum, and therefore the busbar 6E and the positive external terminal 12 are joined in the region of the first conductive portion 6Ea of the busbar 6E. On the other hand, in the region where the second conductive portion 6Eb of the busbar 6E and the positive external terminal 12 come into contact, the second conductive portion 6Eb is made of copper and the positive external terminal 12 is made of aluminum, so there is a risk of corrosion occurring due to contact between dissimilar metals. The busbar 6E is formed with a corrosion prevention structure that prevents this corrosion.

[0116] As an example of a corrosion prevention structure, similar to the busbar 6A of the second embodiment, the busbar 6E may have a non-contact area or a contact area similar to that of the busbar 6A in the opposing area of ​​the opposing surface facing the positive external terminal 12 or the negative external terminal 13, whichever is made of a different material from that of the busbar 6E.

[0117] The connections of the cells and the currents flowing through the cells in the battery pack 10E according to the sixth embodiment are similar to those in the battery pack 10 according to the first embodiment, and therefore will not be described here.

[0118] Between the point of the busbar 6E joined to the positive external terminal 12 of the second battery 2 and the point of the busbar 6E joined to the negative external terminal 13 of the third battery 3, a current flows between the first and second batteries and the third and fourth batteries, resulting in a relatively large current.

[0119] The effects of the battery pack 10E according to the sixth embodiment will be described. The battery pack 10E according to the sixth embodiment includes a positive external terminal 12 and a negative external terminal 13 having a higher conductivity than the positive external terminal 12, and includes a bus bar 6E stacked in the order of a first battery 1, a second battery 2, a third battery 3, and a fourth battery 4, and including a first conductive portion 6Ea, a second conductive portion 6Eb having a higher conductivity and a larger specific gravity than the first conductive portion 6Ea, and a connecting portion 6Ec.

[0120] The first conductive portion 6Ea is joined to the positive external terminals 12 of the first battery 1 and the second battery 2, and the second conductive portion 6Eb is joined to the negative external terminals 13 of the third battery 3 and the fourth battery 4. The connecting portion 6Ec is configured to extend in a straight line from one end to the other end of the busbar 6E in the width direction, diagonally intersecting the extension direction of the busbar 6E. One end of the connecting portion 6Ec in the width direction of the busbar 6E is located at a position facing the edge of the second battery 2 facing the third battery 3 and the positive external terminal 12 of the second battery 2, and the other end of the busbar 6E is located at a position facing the edge of the first battery 1 facing the second battery 2 and the positive external terminal 12 of the first battery 1.

[0121] In the battery pack 10E of the sixth embodiment, the end of the second conductive portion 6Eb has a length that extends from a position facing the third battery 3 and the fourth battery 4 to a position facing the second battery 2 and the first battery 1, and the connecting portion 6Ec is configured to extend in a straight line from one end of the bus bar 6E to the other end in the width direction, diagonally intersecting the extension direction of the bus bar 6E. Therefore, the second conductive portion 6Eb, which has a relatively high conductivity, has a wider area through which current flows than the first conductive portion 6Ea. This makes it easier for current to flow between the first battery 1 and the second battery 2 and the third battery 3 and the fourth battery 4, suppresses heat generation in the bus bar 6E, and inhibits accelerated deterioration of the cells due to heat generation, thereby improving the performance of the battery pack 10E.

[0122] In the battery pack 10E according to the sixth embodiment, the second conductive portion 6Eb of the bus bar 6E faces the second battery 2, and the entire area of ​​the connecting portion 6Ec is located somewhere between the positive external terminal 12 of the second battery 2 and the first battery 1. With this configuration, the first conductive portion 6Ea, which has a small specific gravity but low electrical conductivity, and the second conductive portion 6Eb, which has a large specific gravity but high electrical conductivity, achieve a good balance between reducing the weight of the battery pack 10E and suppressing deterioration of the cells due to heat generation.

[0123] (Seventh embodiment) The battery pack 10F according to the seventh embodiment includes a first battery 1, a second battery 2, a third battery 3, a fourth battery 4, a cell holder 5, and a bus bar 6F.

[0124] 16 and 17, like the busbar 6 of the first embodiment, the busbar 6F has a single structure in which a first conductive portion 6Fa, a second conductive portion 6Fb, and a connecting portion 6Fc that electrically connects the first conductive portion 6Fa and the second conductive portion 6Fb are integrally joined together. Like the connecting portion 6c of the first embodiment, the connecting portion 6Fc indicates the boundary between the first conductive portion 6Fa and the second conductive portion 6Fb. Like the busbar 6 of the first embodiment, the busbar 6F has flat regions H1, H2, H3, and H4 that face each battery in parallel along the stacking direction of the first, second, third, and fourth batteries 1, 2, 3, and 4.

[0125] Furthermore, the bus bar 6F has the same curved regions W1, W2, and W3 as in the first embodiment, and the curved regions W1, W2, and W3 function in the same way as in the first embodiment.

[0126] Like the busbar 6 of the first embodiment, the first conductive portion 6Fa is made of a metal material primarily composed of aluminum, and is joined to the positive electrode external terminals 12 of the first battery 1 and the second battery 2, which are made of aluminum or an aluminum alloy, at the flat regions H1 and H2 by spot joining or surface joining using joining means such as laser welding. The first conductive portion 6Fa has a lower electrical conductivity and a smaller specific gravity than the second conductive portion 6Fb.

[0127] Like the busbar 6 of the first embodiment, the second conductive portion 6Fb is made of a metal material primarily composed of copper, and is joined to the negative electrode external terminals 13 of the third battery 3 and the fourth battery 4, which are made of copper or a copper alloy, at the flat regions H3 and H4 by spot joining or surface joining using joining means such as laser welding. The second conductive portion 6Fb has a higher electrical conductivity and a larger specific gravity than the first conductive portion 6Fa.

[0128] Similar to the busbar 6 of the first embodiment, the connecting portion 6Fc connects the first conductive portion 6Fa and the second conductive portion 6Fb, and therefore the busbar 6F is made of an aluminum-copper clad material. As shown in FIG. 17 , the connecting portion 6Fc is disposed obliquely across the extension direction of the busbar 6F, from the end TFa on one side to the end TFb on the other side in the width direction of the busbar 6F. The connecting portion 6Fc is formed across the entire width direction of the busbar 6F, dividing the one and the other sides in the extension direction of the busbar 6F into the first conductive portion 6Fa and the second conductive portion 6Fb. The connecting portion 6Fc is entirely formed in the second region of the busbar 6F facing the third battery 3 and the fourth battery 4. The connecting portion 6Fc extends obliquely across the curved region W3 between the flat region H3 and the flat region H4 in the extension direction (X direction) of the busbar 6F.

[0129] As shown in Figures 16 and 17, in the second region, the connecting portion 6Fc is arranged such that the end TFa on one width side of the busbar 6F is positioned opposite the edge of the fourth battery 4 facing the third battery 3 (the edge of the battery lid 22 of the fourth battery 4) and the negative external terminal 13 of the fourth battery 4, and the end TFb on the other width side of the busbar 6F is positioned opposite the edge of the third battery 3 facing the second battery 2 (the edge of the battery lid 22 of the third battery 3) and the negative external terminal 13 of the third battery 3.

[0130] The second conductive portion 6Fb and the negative external terminal 13 in the flat regions H3 and H4 are formed from the same copper, and therefore the second conductive portion 6Fb and the negative external terminal 13 are joined in the region of the second conductive portion 6Fb in the flat regions H3 and H4.

[0131] On the other hand, in the flat regions H3 and H4, in the region between the connecting portion 6Fc and the curved regions W3 and W2, the first conductive portion 6Fa is made of aluminum and the negative electrode external terminal 13 is made of copper, so there is a risk of corrosion due to contact between dissimilar metals. The busbar 6F is provided with a corrosion prevention structure to prevent this corrosion.

[0132] As an example of a corrosion prevention structure, similar to the busbar 6A of the second embodiment, the busbar 6F may have a non-contact area or a contact area similar to that of the busbar 6A in the opposing area of ​​the opposing surface facing the positive external terminal 12 or the negative external terminal 13, whichever is made of a different material from that of the busbar 6F.

[0133] The connections of the cells and the currents flowing through the cells in the battery pack 10F according to the seventh embodiment are similar to those in the battery pack 10 according to the first embodiment, and therefore will not be described here.

[0134] Between the point of the busbar 6F joined to the positive external terminal 12 of the second battery 2 and the point of the busbar 6F joined to the negative external terminal 13 of the third battery 3, a current flows between the first and second batteries and the third and fourth batteries, resulting in a relatively large current.

[0135] The effects of the battery pack 10F according to the seventh embodiment will be described. The battery pack 10F of the seventh embodiment includes a positive electrode external terminal 12 and a negative electrode external terminal 13 having a higher conductivity than the positive electrode external terminal 12, and is stacked in the order of a first battery 1, a second battery 2, a third battery 3, and a fourth battery 4, and has a bus bar 6F composed of a first conductive portion 6Fa, a second conductive portion 6Fb having a higher conductivity and a larger specific gravity than the first conductive portion 6Fa, and a connecting portion 6Fc.

[0136] The first conductive portion 6Fa is joined to the positive external terminals 12 of the first battery 1 and the second battery 2, and the second conductive portion 6Fb is joined to the negative external terminals 13 of the third battery 3 and the fourth battery 4. The connecting portion 6Fc is configured to extend in a straight line from one end to the other end of the busbar 6F in the width direction, diagonally intersecting the extension direction of the busbar 6F. One end TFa of the connecting portion 6Fc in the width direction of the busbar 6F is located between the edge of the fourth battery 4 facing the third battery 3 and the negative external terminal 13 of the fourth battery 4, and the other end TFb of the busbar 6F in the width direction is located between the edge of the third battery 3 facing the second battery 2 and the negative external terminal 13 of the third battery 3.

[0137] In the battery pack 10F of the seventh embodiment, the end of the first conductive portion 6Fa has a length that extends from a position facing the first battery 1 and the second battery 2 to a position facing the third battery 3 and the fourth battery 4, and the connecting portion 6Fc is configured to extend in a straight line from one end of the bus bar 6F to the other end in the width direction, diagonally intersecting the extension direction of the bus bar 6F. Therefore, the first conductive portion 6Fa, which has a smaller specific gravity, is longer and has a larger volume than the second conductive portion 6Fb. Therefore, the main effect achieved is that the weight of the battery pack 10F can be reduced.

[0138] (Eighth embodiment) The battery pack 10G according to the eighth embodiment includes a first battery 1, a third battery 3, two cell holders 5 that hold both ends of each battery, and a bus bar 6G. The first battery 1 and the third battery 3 are connected in series via the bus bar 6G.

[0139] 18, the busbar 6G has a single structure in which a first conductive portion 6Ga, a second conductive portion 6Gb, and a connecting portion 6Gc that electrically connects the first conductive portion 6Ga and the second conductive portion 6Gb are integrally joined. Similar to the connecting portion 6c in the first embodiment, the connecting portion 6Gc indicates the boundary between the first conductive portion 6Ga and the second conductive portion 6Gb. The busbar 6G has flat regions H1 and H2 that face each other in parallel with the first and third batteries 1 and 3 along the stacking direction of the batteries.

[0140] Moreover, the bus bar 6G has the same curved region W1 as in the first embodiment, and the curved region W1 functions in the same way as in the first embodiment.

[0141] The first conductive portion 6Ga is made of a metal material primarily composed of aluminum, and is joined to the positive electrode external terminal 12, which is made of aluminum or an aluminum alloy, of the first battery 1 at the flat region H1 by spot joining or surface joining using joining means such as laser welding. The first conductive portion 6Ga has a lower electrical conductivity and a smaller specific gravity than the second conductive portion 6Gb.

[0142] The second conductive portion 6Gb is made of a metal material primarily composed of copper, and is joined to the negative electrode external terminal 13 of the third battery 3, which is made of copper or a copper alloy, in the flat region H2 by spot joining or surface joining using joining means such as laser welding. The second conductive portion 6Gb has a higher electrical conductivity and a larger specific gravity than the first conductive portion 6Ga.

[0143] The connecting portion 6Gc connects the first conductive portion 6Ga and the second conductive portion 6Gb, and therefore the busbar 6G is made of an aluminum-copper clad material. As shown in FIG. 18 , the connecting portion 6Gc is disposed from an end TGa on one side to an end TGb on the other side in the width direction (Y direction) of the busbar 6G, which is perpendicular to the extension direction (X direction) of the busbar 6G. The connecting portion 6Gc is formed across the entire width direction of the busbar 6G, dividing one side and the other side in the extension direction of the busbar 6G into the first conductive portion 6Ga and the second conductive portion 6Gb. The connecting portion 6Gc is entirely formed in the first region of the busbar 6G facing the first battery 1. In the eighth embodiment, the connecting portion 6Gc is formed in the flat region H1 and is provided along the width direction of the busbar 6G near the boundary between the flat region H1 and the curved region W1. When the bus bar 6G is attached as shown in FIG. 18, the connecting portion 6Gc is positioned opposite the battery lid 22 of the first battery 1 between the edge of the battery lid 22 of the first battery 1 and the positive external terminal 12.

[0144] The effects of the battery pack 10G according to the eighth embodiment will be described. The battery pack 10G according to the eighth embodiment includes a positive external terminal 12 and a negative external terminal 13 having a higher conductivity than the positive external terminal 12, a first battery 1 and a third battery 3 connected in series, and a busbar 6G including a first conductive part 6Ga, a second conductive part 6Gb having a higher conductivity and a larger specific gravity than the first conductive part 6Ga, and a connecting part 6Gc. The busbar 6G includes the first conductive part 6Ga connected to the positive external terminal 12, the second conductive part 6Gb connected to the negative external terminal 13 having a higher conductivity and a larger specific gravity than the first conductive part 6Ga, and a connecting part 6Gc connecting the first conductive part 6Ga and the second conductive part 6Gb, and the connecting part 6Gc is disposed in a position facing one of the first batteries 1.

[0145] More specifically, the battery pack 10G includes a first battery 1 and a third battery 3 as multiple batteries, and the first battery 1 and the third battery 3 are arranged side by side in the stacking direction of the batteries, with the positive external terminal 12 of the first battery 1 and the negative external terminal 13 of the third battery 3 adjacent to each other. The bus bar 6G extends along the stacking direction of the batteries and is positioned opposite the positive external terminal 12 of the first battery 1 and the negative external terminal 13 of the third battery 3. The first conductive portion 6Ga is joined to the positive external terminal 12 of the first battery 1, the second conductive portion 6Gb is joined to the negative external terminal 13 of the third battery 3, and the connecting portion 6Gc is arranged in a first region facing the first battery 1.

[0146] In the battery pack 10G of the eighth embodiment, the end of the second conductive part 6Gb has a length that extends from a position facing the third battery 3 to a position facing the first battery 1, and the connecting part 6Gc is configured to be positioned facing the battery lid 22 of the first battery 1. Therefore, the second conductive part 6Gb, which has a relatively high conductivity, has a wider area through which current flows than the first conductive part 6Ga. Therefore, current flows more easily between the first battery 1 and the third battery 3, heat generation in the bus bar 6G is suppressed, and accelerated deterioration of the unit cells due to heat generation is suppressed, resulting in the effect of improving the performance of the battery pack 10G.

[0147] In the battery pack 10G of the eighth embodiment, the second conductive portion 6Gb of the bus bar 6G faces the third battery 3, and the entire area of ​​the connecting portion 6Gc is positioned to face the area between the edge of the first battery 1 facing the third battery 3 and the positive external terminal 12 of the first battery 1. With this configuration, the first conductive portion 6Ga, which has a small specific gravity but low electrical conductivity, and the second conductive portion 6Gb, which has a large specific gravity but high electrical conductivity, achieve a good balance between reducing the weight of the battery pack 10G and suppressing deterioration of the cells due to heat generation.

[0148] (Ninth embodiment) The battery pack 10H according to the ninth embodiment includes a first battery 1, a third battery 3, two cell holders 5 that hold both ends of each battery, and a bus bar 6H. The first battery 1 and the third battery 3 are connected in series via the bus bar 6H.

[0149] As shown in Fig. 19, the busbar 6H has a single structure in which a first conductive portion 6Ha, a second conductive portion 6Hb, and a connecting portion 6Hc that electrically connects the first conductive portion 6Ha and the second conductive portion 6Hb are integrally joined together. Similar to the connecting portion 6c in the first embodiment, the connecting portion 6Hc indicates the boundary between the first conductive portion 6Ha and the second conductive portion 6Hb. The busbar 6H has flat regions H1 and H2 that face each other in parallel with the first and third batteries 1 and 3 along the stacking direction.

[0150] Furthermore, the bus bar 6H has the same curved region W1 as in the first embodiment, and the curved region W1 functions in the same way as in the first embodiment.

[0151] The first conductive portion 6Ha is made of a metal material primarily composed of aluminum, and is joined to the positive electrode external terminal 12, which is made of aluminum or an aluminum alloy, of the first battery 1 in the flat region H1 by spot joining or surface joining using joining means such as laser welding. The first conductive portion 6Ha has a lower electrical conductivity and a smaller specific gravity than the second conductive portion 6Hb.

[0152] The second conductive portion 6Hb is made of a metal material primarily composed of copper, and is joined to the negative electrode external terminal 13, which is made of copper or a copper alloy, of the third battery 3 in the flat region H2 by spot joining or surface joining using joining means such as laser welding. The second conductive portion 6Hb has a higher electrical conductivity and a larger specific gravity than the first conductive portion 6Ha.

[0153] The connecting portion 6Hc connects the first conductive portion 6Ha and the second conductive portion 6Hb, and the busbar 6H is made of an aluminum-copper clad material. As shown in FIG. 19, the connecting portion 6Hc is disposed diagonally across the extension direction (X direction) of the busbar 6H, from one end THa to the other end THb in the width direction of the busbar 6H. The connecting portion 6Hc is formed across the entire width of the busbar 6H, dividing one end and the other end in the extension direction of the busbar 6H into the first conductive portion 6Ha and the second conductive portion 6Hb. The connecting portion 6Hc is entirely formed in a first region of the busbar 6H that faces the first battery 1.

[0154] 19 , in the first region, the connecting portion 6Hc is arranged such that one widthwise end THa of the busbar 6H faces the edge of the first battery 1 facing the third battery 3 (the edge of the battery lid 22 of the first battery 1) and the edge of the positive external terminal 12 of the first battery 1 facing the third battery 3, and the other widthwise end THb of the busbar 6H faces the positive external terminal 12 of the first battery 1 on the inner side in the longitudinal direction of the battery lid 22. In the ninth embodiment, the other widthwise end THb of the busbar 6H is arranged at the center of the positive external terminal 12 of the first battery 1 in the battery stacking direction.

[0155] The first conductive portion 6Ha and the positive electrode external terminal 12 in the flat region H1 are both made of aluminum, and therefore the first conductive portion 6Ha and the positive electrode external terminal 12 are joined in the region of the first conductive portion 6Ha in the flat region H1. On the other hand, in the region in the flat region H1 between the connecting portion 6Hc and the curved region W1, the second conductive portion 6Hb is made of copper and the positive electrode external terminal 12 is made of aluminum, so there is a risk of corrosion occurring due to contact between dissimilar metals. The busbar 6H has a corrosion prevention structure formed therein to prevent this corrosion.

[0156] As an example of a corrosion prevention structure, similar to the busbar 6A of the second embodiment, the busbar 6H may have a non-contact area or a contact area similar to that of the busbar 6A in the opposing area of ​​the opposing surface facing the positive external terminal 12 or the negative external terminal 13, whichever is made of a different material from that of the busbar 6H.

[0157] The effects of the battery pack 10H according to the ninth embodiment will be described. The battery pack 10H of the ninth embodiment includes a positive external terminal 12 and a negative external terminal 13 having a higher conductivity than the positive external terminal 12, a first battery 1 and a third battery 3 connected in series, and a bus bar 6H composed of a first conductive part 6Ha, a second conductive part 6Hb having a higher conductivity and a larger specific gravity than the first conductive part 6Ha, and a connecting part 6Hc.

[0158] The first conductive portion 6Ha is joined to the positive external terminal 12 of the first battery 1, and the second conductive portion 6Hb is connected to the negative external terminal 13 of the third battery 3. The connecting portion 6Hc is configured to extend in a straight line from one end to the other end of the busbar 6H in the width direction, diagonally intersecting the extension direction of the busbar 6H. One end of the connecting portion 6H in the width direction is located between the edge of the positive external terminal 12 of the first battery 1 that faces the third battery 3 and the edge of the positive external terminal 12 of the first battery 1 opposite the edge that faces the third battery 3, and the other end of the busbar 6H in the width direction is located between the edge of the positive external terminal 12 of the first battery 1 that faces the third battery 3 and the edge of the positive external terminal 12 of the first battery 1 opposite the edge that faces the third battery 3.

[0159] In the battery pack 10H of the ninth embodiment, the end of the second conductive portion 6Hb has a length that extends from a position facing the third battery 3 to a position facing the first battery 1, and the connecting portion 6Hc is configured to extend in a straight line from one end of the bus bar 6H to the other end in the width direction, diagonally intersecting the extension direction of the bus bar 6H. Therefore, the second conductive portion 6Hb, which has a relatively high conductivity, has a wider area through which current flows than the first conductive portion 6Ha. Therefore, current flows more easily between the first battery 1 and the third battery 3, heat generation in the bus bar 6H is suppressed, and accelerated deterioration of the cells due to heat generation is suppressed, resulting in an effect of improving the performance of the battery pack 10H.

[0160] (Tenth embodiment) The battery pack 10I according to the tenth embodiment includes a first battery 1, a third battery 3, two cell holders 5 that hold both ends of each battery, and a bus bar 6I. The first battery 1 and the third battery 3 are connected in series via the bus bar 6I.

[0161] As shown in Fig. 20, the busbar 6I has a single structure in which a first conductive portion 6Ia, a second conductive portion 6Ib, and a connecting portion 6Ic that electrically connects the first conductive portion 6Ia and the second conductive portion 6Ib are integrally joined together. Note that, like the connecting portion 6c in the first embodiment, the connecting portion 6Ic indicates the boundary between the first conductive portion 6Ia and the second conductive portion 6Ib. The busbar 6I has flat regions H1 and H2 that face each other in parallel with the first battery 1 and the third battery 3 along the stacking direction.

[0162] Furthermore, the bus bar 6I has the same curved region W1 as in the first embodiment, and the curved region W1 functions in the same way as in the first embodiment.

[0163] The first conductive portion 6Ia is made of a metal material primarily composed of aluminum, and is joined to the positive external terminal 12 of the first battery 1, which is made of aluminum or an aluminum alloy, by spot joining or surface joining using joining means such as laser welding, in the flat region H1. The first conductive portion 6Ia has a lower electrical conductivity and a smaller specific gravity than the second conductive portion 6Ib.

[0164] The second conductive portion 6Ib is made of a metal material primarily composed of copper, and is joined to the negative electrode external terminal 13 of the third battery 3, which is made of copper or a copper alloy, in the flat region H2 by spot joining or surface joining using joining means such as laser welding. The second conductive portion 6Ib has a higher electrical conductivity and a larger specific gravity than the first conductive portion 6Ia.

[0165] The connecting portion 6Ic connects the first conductive portion 6Ia and the second conductive portion 6Ib, and the busbar 6I is made of an aluminum-copper clad material. As shown in FIG. 20, the connecting portion 6Ic is disposed diagonally across the extension direction (X direction) of the busbar 6I, from an end TIa on one side in the width direction of the busbar 6I to an end TIb in the extension direction. The connecting portion 6Ic divides one side and the other side in the extension direction of the busbar 6I into a first conductive portion 6Ia and a second conductive portion 6Ib. The connecting portion 6Ic is entirely formed in a first region of the busbar 6I that faces the first battery 1.

[0166] As shown in Figure 20, in the first region, the connecting portion 6Ic is arranged such that the end TIa on one side of the width of the busbar 6I is positioned opposite the edge of the first battery 1 facing the third battery 3 (the edge of the battery lid 22 of the first battery 1) and the positive external terminal 12 of the first battery 1, and the end TIb in the extension direction of the busbar 6I is positioned opposite the positive external terminal 12 of the first battery 1 and at the center position of the positive external terminal 12 in the width direction perpendicular to the stacking direction of the batteries.

[0167] The first conductive portion 6Ia and the positive external terminal 12 in the flat region H1 are both made of aluminum, and therefore the first conductive portion 6Ia and the positive external terminal 12 are joined in the region of the first conductive portion 6Ia in the flat region H1. On the other hand, in the region in the flat region H1 between the connecting portion 6Ic and the curved region W1, the second conductive portion 6Ib is made of copper and the positive external terminal 12 is made of aluminum, so there is a risk of corrosion occurring due to contact between dissimilar metals. The busbar 6H is formed with a corrosion prevention structure that prevents this corrosion.

[0168] As an example of a corrosion prevention structure, similar to the busbar 6A of the second embodiment, the busbar 6I may have a non-contact area or a contact area similar to that of the busbar 6A in the opposing area of ​​the opposing surface facing the positive external terminal 12 or the negative external terminal 13, whichever is made of a different material from that of the busbar 6I.

[0169] The effects of the battery pack 10I according to the tenth embodiment will be described. The battery pack 10I of the tenth embodiment includes a positive electrode external terminal 12 and a negative electrode external terminal 13 having a higher conductivity than the positive electrode external terminal 12, a first battery 1 and a third battery 3 connected in series, and a bus bar 6I composed of a first conductive part 6Ia, a second conductive part 6Ib having a higher conductivity and a larger specific gravity than the first conductive part 6Ia, and a connecting part 6Ic.

[0170] The first conductive part 6Ia is joined to the positive external terminal 12 of the first battery 1, and the second conductive part 6Ib is connected to the negative external terminal 13 of the third battery 3. The connecting part 6Ic is configured to extend in a straight line from one end of the busbar 6I in the width direction to the other end in the extension direction, diagonally intersecting the extension direction of the busbar 6I. The connecting part 6Ic is arranged such that one end of the busbar 6I in the width direction faces the edge of the first battery 1 facing the third battery 3 and the positive external terminal 12 of the first battery 1, and the end of the busbar 6I in the extension direction faces the positive external terminal 12 of the first battery 1 and is located in the center of the positive external terminal 12 in the width direction perpendicular to the stacking direction of the batteries.

[0171] In the battery pack 10I of the tenth embodiment, the end of the second conductive part 6Ib has a length that extends from a position facing the third battery 3 to a position facing the first battery 1, and the connecting part 6Ic is configured to diagonally intersect the extension direction of the busbar 6I and extend in a straight line from one end of the busbar 6I in the width direction to a position facing the positive external terminal 12 of the first battery 1 and to the center of the positive external terminal 12 in the width direction perpendicular to the battery stacking direction. Therefore, the second conductive part 6Ib, which has a relatively high conductivity, has a wider area through which current flows than the first conductive part 6Ia. This makes it easier for current to flow between the first battery 1 and the third battery 3, suppresses heat generation in the busbar 6I, and suppresses accelerated cell deterioration due to heat generation, thereby improving the performance of the battery pack 10I.

[0172] In the above embodiment, a bus bar that connects a positive external terminal and a negative external terminal to each other has been described, but it goes without saying that the present invention can also be applied to a bus bar that connects an electrode external terminal at the end of a battery group to an external terminal for supplying power to the outside. As such, the present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as defined in the claims. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0173] 1...1st battery, 2...2nd battery, 3...3rd battery, 4...4th battery, 5...cell holder, 6, 6A, 6B, 6C, 6D, 6E, 6F, 6G, 6H, 6I...bus bar, 6a, 6Aa, 6Ba, 6Ca, 6Da, 6Ea, 6Fa, 6Ga, 6Ha, 6Ia...first conductivity Part, 6b, 6Ab, 6Bb, 6Cb, 6Db, 6Eb, 6Fb, 6Gb, 6Hb, 6Ib...Second conductive part, 6c, 6Ac, 6Bc, 6Cc , 6Dc, 6Ec, 6Fc, 6Gc, 6Hc, 6Ic...Connection part, 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 1 0H, 10I: assembled battery, 11: battery container, 12: external positive electrode terminal, 13: external negative electrode terminal, 14, 15: insulator, 16: gas release valve, 21: battery can, 22: battery lid, 22a: liquid filling plug, H1, H2, H3, H4: flat region, Ta, TAa, TCa, TDa, TEa, TFa, TGa, THa, TIa: end on one side, Tb, TAb, TCb, TDb, TEb, TFb, TGb, THb: end on the other side, TBa, TBc: edge, TBb: center, TIb: end in the extension direction, W1, W2, W3: curved region.

Claims

1. a plurality of stacked batteries each including a positive electrode external terminal and a negative electrode external terminal having a higher electrical conductivity than the positive electrode external terminal; a bus bar that electrically connects the positive external terminal of one battery and the negative external terminal of the other battery, the positive external terminal and the negative external terminal of the other battery being arranged side by side adjacent to each other among the plurality of batteries, the plurality of batteries includes at least a first battery, a second battery, a third battery, and a fourth battery; the first battery and the second battery are arranged side by side with the positive electrode external terminals adjacent to each other and the negative electrode external terminals adjacent to each other in the stacking direction of the plurality of batteries, the third battery and the fourth battery are arranged side by side with the positive electrode external terminals adjacent to each other and the negative electrode external terminals adjacent to each other in the stacking direction of the plurality of batteries, the first battery and the second battery and the third battery and the fourth battery are arranged side by side in a stacking direction of the plurality of batteries, with the positive external terminals of the first battery and the second battery and the negative external terminals of the third battery and the fourth battery being adjacent to each other; the bus bar includes: a plurality of flat regions extending along the stacking direction of the plurality of batteries, and aligned in a row facing the positive electrode external terminal and the negative electrode external terminal, respectively; and curved regions interposed between the plurality of flat regions, protruding in a direction perpendicular to the plane of the flat regions, and curved to connect adjacent flat regions; the bus bar has a first conductive portion joined to the positive external terminals of the first battery and the second battery, and a second conductive portion joined to the negative external terminals of the third battery and the fourth battery, the second conductive portion having a higher conductivity and a higher specific gravity than the first conductive portion, and a connecting portion connecting the first conductive portion and the second conductive portion; the connecting portion is disposed in either a first region facing at least one of the first battery and the second battery, or a second region facing at least one of the third battery and the fourth battery, Moreover, the connecting portion is disposed from one end to the other end in a width direction perpendicular to the extending direction of the bus bar.

2. A plurality of stacked batteries each including a positive electrode external terminal and a negative electrode external terminal having a higher electrical conductivity than the positive electrode external terminal; a bus bar that electrically connects the positive external terminal of one battery and the negative external terminal of the other battery, the positive external terminal and the negative external terminal of the other battery being arranged side by side adjacent to each other among the plurality of batteries, the plurality of batteries includes at least a first battery, a second battery, a third battery, and a fourth battery; the first battery and the second battery are arranged side by side with the positive electrode external terminals adjacent to each other and the negative electrode external terminals adjacent to each other in the stacking direction of the plurality of batteries, the third battery and the fourth battery are arranged side by side with the positive electrode external terminals adjacent to each other and the negative electrode external terminals adjacent to each other in the stacking direction of the plurality of batteries, the first battery and the second battery and the third battery and the fourth battery are arranged side by side in a stacking direction of the plurality of batteries, with the positive external terminals of the first battery and the second battery and the negative external terminals of the third battery and the fourth battery being adjacent to each other; the bus bar extends along the stacking direction of the plurality of batteries and is disposed at a position facing the positive external terminals of the first battery and the second battery and the negative external terminals of the third battery and the fourth battery; the bus bar has a first conductive portion joined to the positive external terminals of the first battery and the second battery, and a second conductive portion joined to the negative external terminals of the third battery and the fourth battery, the second conductive portion having a higher conductivity and a higher specific gravity than the first conductive portion, and a connecting portion connecting the first conductive portion and the second conductive portion; the connecting portion is disposed in either a first region facing at least one of the first battery and the second battery, or a second region facing at least one of the third battery and the fourth battery, Moreover, the connecting portion is disposed so as to extend from one end to the other end of the bus bar in the width direction, obliquely intersecting the extending direction of the bus bar.

3. A plurality of stacked batteries each including a positive electrode external terminal and a negative electrode external terminal having a higher electrical conductivity than the positive electrode external terminal; a bus bar that electrically connects the positive external terminal of one battery and the negative external terminal of the other battery, the positive external terminal and the negative external terminal of the other battery being arranged side by side adjacent to each other among the plurality of batteries, the plurality of batteries includes at least a first battery, a second battery, a third battery, and a fourth battery; the first battery and the second battery are arranged side by side with the positive electrode external terminals adjacent to each other and the negative electrode external terminals adjacent to each other in the stacking direction of the plurality of batteries, the third battery and the fourth battery are arranged side by side with the positive electrode external terminals adjacent to each other and the negative electrode external terminals adjacent to each other in the stacking direction of the plurality of batteries, the first battery and the second battery and the third battery and the fourth battery are arranged side by side in a stacking direction of the plurality of batteries, with the positive external terminals of the first battery and the second battery and the negative external terminals of the third battery and the fourth battery being adjacent to each other; the bus bar extends along the stacking direction of the plurality of batteries and is disposed at a position facing the positive external terminals of the first battery and the second battery and the negative external terminals of the third battery and the fourth battery; the bus bar has a first conductive portion joined to the positive external terminals of the first battery and the second battery, and a second conductive portion joined to the negative external terminals of the third battery and the fourth battery, the second conductive portion having a higher conductivity and a higher specific gravity than the first conductive portion, and a connecting portion connecting the first conductive portion and the second conductive portion; The connecting portion is disposed in either a first region facing at least one of the first battery and the second battery, or a second region facing at least one of the third battery and the fourth battery. Moreover, the connecting portion is disposed in a position in the first region that faces the positive external terminal of the second battery.

4. A plurality of batteries each including a positive electrode external terminal and a negative electrode external terminal having a higher electrical conductivity than the positive electrode external terminal, the batteries being stacked on top of each other; a bus bar that electrically connects the positive external terminal of one battery and the negative external terminal of the other battery, the positive external terminal and the negative external terminal of the other battery being arranged side by side adjacent to each other among the plurality of batteries, the plurality of batteries includes at least a first battery, a second battery, a third battery, and a fourth battery; the first battery and the second battery are arranged side by side with the positive electrode external terminals adjacent to each other and the negative electrode external terminals adjacent to each other in the stacking direction of the plurality of batteries, the third battery and the fourth battery are arranged side by side with the positive electrode external terminals adjacent to each other and the negative electrode external terminals adjacent to each other in the stacking direction of the plurality of batteries, the first battery and the second battery and the third battery and the fourth battery are arranged side by side in a stacking direction of the plurality of batteries, with the positive external terminals of the first battery and the second battery and the negative external terminals of the third battery and the fourth battery being adjacent to each other; the bus bar extends along the stacking direction of the plurality of batteries and is disposed at a position facing the positive external terminals of the first battery and the second battery and the negative external terminals of the third battery and the fourth battery; the bus bar has a first conductive portion joined to the positive external terminals of the first battery and the second battery, and a second conductive portion joined to the negative external terminals of the third battery and the fourth battery, the second conductive portion having a higher conductivity and a higher specific gravity than the first conductive portion, and a connecting portion connecting the first conductive portion and the second conductive portion; the connecting portion is disposed in either a first region facing at least one of the first battery and the second battery, or a second region facing at least one of the third battery and the fourth battery, the connecting portion has an L-shape that extends from one end of the first region in a width direction perpendicular to the stacking direction of the plurality of batteries to the other end at a position facing the positive external terminal of the second battery, and is bent toward the stacking direction to extend to a position facing the positive external terminal of the first battery.

5. The battery pack described in Claim 2, characterized in that the connecting portion is arranged in the first region such that one end of the bus bar in the width direction is positioned facing the second battery between the edge of the second battery on the side facing the third battery and the center of the positive external terminal of the second battery in the stacking direction of the multiple batteries, and the other end of the bus bar in the width direction is positioned facing the first battery between the side of the positive external terminal of the first battery facing the second battery and the center of the positive external terminal of the second battery in the stacking direction of the multiple batteries.

6. The battery pack described in Claim 2, characterized in that the connecting portion is arranged in the first region such that one end of the bus bar in the width direction is positioned facing the second battery between the edge of the second battery on the side facing the third battery and the side of the positive external terminal of the second battery facing the third battery, and the other end of the bus bar in the width direction is positioned facing the first battery between the edge of the first battery on the side facing away from the second battery and the side of the positive external terminal of the first battery facing the second battery.

7. The bus bar includes a plurality of flat regions arranged in a row facing the positive electrode external terminal and the negative electrode external terminal, respectively, and curved regions interposed between the plurality of flat regions, protruding and curved in a direction perpendicular to the plane of the flat regions, and connecting adjacent flat regions, 5. The battery pack according to claim 2, wherein at least a portion of the connecting portion is located within the flat region.

8. A plurality of batteries each including a positive electrode external terminal and a negative electrode external terminal having a higher electrical conductivity than the positive electrode external terminal, the batteries being stacked on top of each other; a bus bar that electrically connects the positive external terminal of one battery and the negative external terminal of the other battery, the positive external terminal and the negative external terminal of the other battery being arranged side by side adjacent to each other among the plurality of batteries, The bus bar is a first conductive part connected to the positive electrode external terminal of the one battery; a second conductive portion connected to the negative electrode external terminal of the other battery and having a higher conductivity and a higher specific gravity than the first conductive portion; a connecting portion that connects the first conductive portion and the second conductive portion, The connecting portion is disposed in either a first region facing the one battery or a second region facing the other battery. Along with the bus bar has a flat plate shape that extends in a stacking direction of the plurality of batteries and faces the positive electrode external terminal and the negative electrode external terminal.

9. The plurality of batteries includes at least a first battery, a second battery, a third battery, and a fourth battery; The second conductive portion extends from a position facing the third battery and the fourth battery to a position facing the second battery, or extends from a position facing the third battery and the fourth battery to a position facing the second battery and the first battery.

9. The battery pack according to claim 8.

10. The connecting portion is disposed from one end to the other end in a width direction perpendicular to the extending direction of the bus bar. The battery pack according to claim 9 .

11. A plurality of stacked batteries each including a positive electrode external terminal and a negative electrode external terminal having a higher electrical conductivity than the positive electrode external terminal; a bus bar that electrically connects the positive external terminal of one battery and the negative external terminal of the other battery, the positive external terminal and the negative external terminal of the other battery being arranged side by side adjacent to each other among the plurality of batteries, the plurality of batteries includes at least a first battery, a second battery, a third battery, and a fourth battery; the first battery and the second battery are arranged side by side with the positive electrode external terminals adjacent to each other and the negative electrode external terminals adjacent to each other in the stacking direction of the plurality of batteries, the third battery and the fourth battery are arranged side by side with the positive electrode external terminals adjacent to each other and the negative electrode external terminals adjacent to each other in the stacking direction of the plurality of batteries, the first battery and the second battery and the third battery and the fourth battery are arranged side by side in a stacking direction of the plurality of batteries, with the positive external terminals of the first battery and the second battery and the negative external terminals of the third battery and the fourth battery being adjacent to each other; the bus bar extends along the stacking direction of the plurality of batteries and is disposed at a position facing the positive external terminals of the first battery and the second battery and the negative external terminals of the third battery and the fourth battery; the bus bar has a first conductive portion joined to the positive external terminals of the first battery and the second battery, and a second conductive portion joined to the negative external terminals of the third battery and the fourth battery, the second conductive portion having a higher conductivity and a higher specific gravity than the first conductive portion, and a connecting portion connecting the first conductive portion and the second conductive portion; the connecting portion is disposed in either a first region facing at least one of the first battery and the second battery, or a second region facing at least one of the third battery and the fourth battery, a first conductive portion extending from a position facing the first battery and the second battery to a position facing the third battery, or extending from a position facing the third battery and the fourth battery to a position facing the second battery.

12. A plurality of stacked batteries each including a positive electrode external terminal and a negative electrode external terminal having a higher electrical conductivity than the positive electrode external terminal; a bus bar that electrically connects the positive external terminal of one battery and the negative external terminal of the other battery, the positive external terminal and the negative external terminal of the other battery being arranged side by side adjacent to each other among the plurality of batteries, The bus bar is a first conductive part connected to the positive electrode external terminal of the one battery; a second conductive portion connected to the negative electrode external terminal of the other battery and having a higher conductivity and a higher specific gravity than the first conductive portion; a connecting portion that connects the first conductive portion and the second conductive portion, The connecting portion is disposed in either a first region facing the one battery or a second region facing the other battery, Furthermore, the bus bar a facing surface facing the positive external terminal and a facing surface facing the negative external terminal, a non-contact region in which a step is formed to separate the positive electrode external terminal and the negative electrode external terminal from one of the terminals, the positive electrode external terminal and the negative electrode external terminal, in a facing region of the facing surface that faces the terminal made of a different material from the bus bar, or a contact region in which a plating layer is formed in the facing region and the terminals come into contact with each other via the plating layer.

Images