Battery pack and manufacturing method thereof

Abstract

To obtain a manufacturing method for a battery pack having a structure capable of properly connecting a bus bar to a negative terminal even when the negative terminal is formed from a dissimilar metal.SOLUTION: In a manufacturing method for a battery pack 100 including a first battery 11 and a second battery 12, the first battery 11 includes a negative terminal 50, and the negative terminal 50 includes a first metal portion 51 and a second metal portion 52 made of a metal different from the first metal portion 51, the second metal portion 52 is joined to the first metal portion 51 with dissimilar metals, a joint surface 53 and a concave portion 54 are formed on the second metal portion 52, and the manufacturing method for the battery pack 100 includes the steps of inserting a welding auxiliary member 60 into the concave portion 54, placing a bus bar 70 on the joint surface 53 of the negative terminal 50 with the welding auxiliary member 60 inserted into the concave portion 54, and joining the bus bar 70 onto the joint surface 53 of the negative terminal 50 by laser welding.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a battery pack and a manufacturing method thereof. [Background technology]

[0002] As disclosed in the following Patent Documents 1 and 2, a battery pack is constructed by stacking a plurality of secondary batteries and electrically connecting adjacent secondary batteries. For example, the positive and negative terminals of adjacent secondary batteries are electrically connected by a bus bar (metal plate) to connect the plurality of secondary batteries in series.

[0003] The positive electrode terminal and the negative electrode terminal may be made of different metals, that is, different types of metals from each other. For example, the positive electrode terminal may be made of an aluminum alloy, and the negative electrode terminal may be made of a copper alloy.

[0004] For example, assume that the bus bar is made of an aluminum alloy and is connected to a positive terminal and a negative terminal by welding. In this case, the welding between the bus bar and the positive terminal is welding between metals of the same kind, and the welding between the bus bar and the negative terminal is welding between metals of different kinds. When welding between metals of different kinds, it is more difficult to obtain a sufficient connection strength than when welding between metals of the same kind. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-192322 A [Patent Document 2] JP 2020-191230 A Summary of the Invention [Problem to be solved by the invention]

[0006] One method for improving the connection strength between the busbar and the negative electrode terminal is to form the negative electrode terminal from two dissimilar metals (e.g., a copper alloy and an aluminum alloy). For example, the lower part of the negative electrode terminal is formed from a copper alloy, and the upper part of the negative electrode terminal is formed from an aluminum alloy. The copper alloy and the aluminum alloy are joined in advance to form the negative electrode terminal. A busbar made of an aluminum alloy is joined to the negative electrode terminal thus obtained (specifically, the aluminum alloy of the negative electrode terminal). This makes it possible to firmly join the aluminum alloy portion of the negative electrode terminal to the aluminum alloy busbar.

[0007] However, when the negative electrode terminal is made of two dissimilar metals (e.g., copper alloy and aluminum alloy), it is necessary to appropriately join the two dissimilar metals to form the negative electrode terminal so that it can withstand long-term use. When the two dissimilar metals are joined by ultrasonic welding, resistance welding, friction stir spot welding, or the like, the thickness of the negative electrode terminal becomes thin at the welded portion, and a concave portion is formed. The concave portion is formed, for example, in the aluminum alloy joined to the upper part of the copper alloy.

[0008] When laser welding a busbar to a negative electrode terminal having a concave portion, the laser irradiation position may deviate from the desired position due to misalignment that may occur when assembling each component, or manufacturing tolerances that may occur in the busbar, terminal, and cell. If misalignment occurs and the laser hits the concave portion, the concave portion is thin, so heat is likely to reach the joint surface between dissimilar metals in the negative electrode terminal. If a lot of heat is supplied to the joint surface between dissimilar metals in the negative electrode terminal, an intermetallic compound is formed between the dissimilar metals, and as a result, the joint strength of the joint surface between the dissimilar metals may decrease.

[0009] An object of the present disclosure is to provide a battery assembly having a configuration that enables a bus bar to be appropriately connected to a negative terminal even when the negative terminal is formed from dissimilar metals joined to each other, and a method for manufacturing such a battery assembly. [Means for solving the problem]

[0010] A manufacturing method for a battery assembly based on the present disclosure is a manufacturing method for a battery assembly including a first battery and a second battery, wherein the first battery includes a negative electrode terminal, the negative electrode terminal has a first metal portion and a second metal portion formed from a metal different from the first metal portion, the second metal portion is joined to an upper portion of the first metal portion by dissimilar metal joining, and an upper surface of the second metal portion is formed with a joint surface and a concave portion having a shape recessed relative to the joint surface, the second battery includes a positive electrode terminal electrically connected to the negative electrode terminal via a bus bar, and the manufacturing method for the battery assembly includes the steps of inserting a welding auxiliary member into the concave portion, and positioning the bus bar on the joint surface of the negative electrode terminal with the welding auxiliary member inserted into the concave portion, and joining the bus bar to the joint surface of the negative electrode terminal by laser welding.

[0011] In the method for manufacturing the battery pack, the welding auxiliary member may be made of the same metal as the second metal portion of the negative electrode terminal.

[0012] In the manufacturing method of the battery pack, the concave portion may be formed by dissimilar metal joining the second metal portion to the upper part of the first metal portion, so as to have a recessed shape with respect to the joining surface.

[0013] In the method for manufacturing the battery pack, the second metal portion may be dissimilarly metal-joined to an upper portion of the first metal portion by friction stir spot welding, ultrasonic welding, or resistance welding.

[0014] A battery pack according to the present disclosure is a battery pack including a first battery, a second battery, and a bus bar, wherein the first battery includes a negative electrode terminal, the negative electrode terminal having a first metal portion and a second metal portion formed from a metal different from the first metal portion, the second metal portion being joined to an upper portion of the first metal portion by dissimilar metal joining, and an upper surface of the second metal portion being formed with a joining surface and a concave portion having a shape recessed relative to the joining surface, the second battery includes a positive electrode terminal electrically connected to the negative electrode terminal via the bus bar, a welding auxiliary member is inserted into the concave portion, the bus bar is positioned on the joining surface of the negative electrode terminal with the welding auxiliary member inserted into the concave portion, and the bus bar is joined onto the joining surface of the negative electrode terminal by laser welding.

[0015] In the battery pack, the welding auxiliary member may be made of the same metal as the second metal portion of the negative electrode terminal. Effect of the Invention

[0016] According to the present disclosure, it is possible to obtain a battery pack having a configuration that enables a bus bar to be appropriately connected to a negative electrode terminal even when the negative electrode terminal is formed from dissimilar metals joined to each other, and a method for manufacturing such a battery pack. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a perspective view showing a battery pack 100. [Diagram 2] 2 is a cross-sectional view showing the internal structure of a secondary battery 11. FIG. [Diagram 3] FIG. 1 is a cross-sectional view showing a state in which a second metal part 52 is joined to an upper part of a first metal part 51 by dissimilar metal joining using a friction stir spot welding technique. [Figure 4] FIG. 1 is a cross-sectional view showing a state in which a second metal part 52 is dissimilarly joined to an upper part of a first metal part 51 by friction stir spot welding. [Diagram 5] 13 is a cross-sectional view showing a state in which a welding auxiliary member 60 is inserted into a recessed portion 54 provided in a second metal portion 52. FIG. [Figure 6] 10 is a cross-sectional view showing a state in which a welding auxiliary member 60 is inserted into a recessed portion 54 provided in a second metal portion 52. FIG. [Figure 7] 11 is a cross-sectional view showing a state in which a bus bar 70 is joined onto a joining surface 53 of a negative terminal 50 (a second metal portion 52) by laser welding. [Figure 8] 13 is a cross-sectional view showing a state in which a bus bar 70 is joined onto a joining surface 53 of a negative terminal 50 (second metal portion 52) by laser welding in the case of Comparative Example 1. FIG. [Figure 9] 13 is a cross-sectional view showing a state in which a bus bar 70 is joined onto a joining surface 53 of a negative terminal 50 (second metal portion 52) by laser welding in the case of Comparative Example 2. FIG. [Figure 10] FIG. 11 is a cross-sectional view showing a state in which second metal part 52 is joined to an upper part of first metal part 51 by ultrasonic welding, in accordance with a first modification of the embodiment. [Figure 11] FIG. 11 is a cross-sectional view showing a state in which second metal part 52 is joined to an upper part of first metal part 51 by resistance welding, in accordance with a second modified example of the embodiment. [Figure 12] 11 is a cross-sectional view showing a state in which a welding auxiliary member 60 is inserted into a recessed portion 54 provided in a second metal portion 52, in accordance with a third modified example of the embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] [Embodiment Mode] The battery pack 100 and its manufacturing method in the embodiment will be described below with reference to the drawings. When referring to the number, amount, material, and the like, the scope of the present disclosure is not necessarily limited to the number, amount, material, and the like, unless otherwise specified. The same reference numbers are given to the same parts and corresponding parts, and duplicate descriptions may not be repeated. It is originally intended that the configurations in the embodiment will be used in appropriate combinations. The dimensional relationships of the length, width, thickness, depth, and the like have been appropriately changed to clarify and simplify the drawings, and do not represent the actual dimensional relationships.

[0019] (Battery pack 100) 1 is a perspective view showing a battery pack 100. The battery pack 100 includes a secondary battery 11 as a first battery, a secondary battery 12 as a second battery, a bus bar 70, and end plates 18 and 19.

[0020] In the battery pack 100, a plurality of secondary batteries including secondary batteries 11 and 12 are stacked in one direction, with end plates 18 and 19 disposed at both ends in the stacking direction. The stacked state is maintained by a restraining member (not shown) to constitute one battery pack 100. The secondary batteries 11 and 12 are disposed adjacent to each other. The battery pack 100 is mounted, for example, in a hybrid vehicle, a plug-in hybrid vehicle, a fuel cell vehicle, or an electric vehicle, and is used as a power source for these vehicles.

[0021] Each of the multiple secondary batteries included in the battery pack 100 is a nonaqueous electrolytic secondary battery such as a lithium ion secondary battery. Each of the multiple secondary batteries includes a positive terminal and a negative terminal, and among the mutually adjacent secondary batteries, the negative terminal 50 of one secondary battery 11 and the positive terminal 80 of the other secondary battery 12 are electrically connected via a bus bar 70. The technical idea of ​​the present disclosure is not limited to a battery pack including multiple nonaqueous electrolytic secondary batteries, but can also be applied to battery packs including other secondary batteries and manufacturing methods thereof, and the use of the battery pack is not limited to automobiles, but can be applied to a variety of technical fields.

[0022] (Secondary battery 11) 2 is a cross-sectional view showing the internal structure of the secondary battery 11. The secondary battery 11 includes an electrode body 20, an electrolyte 22, a case 30, a gasket 40, a negative electrode terminal 50, a positive electrode terminal (not shown), and a welding auxiliary member 60.

[0023] The electrode assembly 20 is constructed by stacking or winding a positive electrode, a negative electrode, and a separator, and functions as a power generating element. Inside the case 30, the electrode assembly 20 is impregnated with an electrolyte solution 22.

[0024] The housing 30 has a case member 31 and a lid member 32. The case member 31 has an opening 31H, and is formed in an overall rectangular shape. The case member 31 accommodates the electrode body 20 and the electrolyte 22 therein. The lid member 32 has a flat plate shape, and the lid member 32 has an outer shape (e.g., a rectangular shape) that corresponds to the opening 31H of the case member 31.

[0025] Lid member 32 is joined to case member 31 by welding, and is disposed so as to close opening 31H of case member 31. Fig. 2 illustrates a state in which lid member 32 is joined to the portion of opening 31H in case member 31, and lid member 32 and case member 31 are integrated together.

[0026] The negative electrode terminal 50 is electrically connected to the electrode body 20 arranged inside the case member 31 by a conductive structure (not shown). A gasket 40 is arranged between the cover member 32 of the housing 30 and the negative electrode terminal 50. The gasket 40 electrically insulates the negative electrode terminal 50 from the cover member 32. Although a detailed description will be omitted, the positive electrode terminal (not shown in FIG. 2) is also electrically connected to the electrode body 20, and employs a conductive structure similar to that of the negative electrode terminal 50. The positive electrode terminal (not shown) is formed of, for example, an aluminum alloy.

[0027] The negative electrode terminal 50 has a first metal portion 51 and a second metal portion 52 formed from a metal different from the first metal portion 51. The first metal portion 51 constitutes the lower portion of the negative electrode terminal 50, i.e., the portion of the negative electrode terminal 50 that is closer to the electrode body 20. The second metal portion 52 constitutes the upper portion of the negative electrode terminal 50, i.e., the portion of the negative electrode terminal 50 that is farther from the electrode body 20.

[0028] The first metal portion 51 is formed of, for example, a copper alloy, and the second metal portion 52 is formed of, for example, an aluminum alloy. The second metal portion 52 is joined by dissimilar metal bonding to the upper portion of the first metal portion 51. The manufacturing method of the battery pack 100 may include a step of joining the second metal portion 52 by dissimilar metal bonding to the upper portion of the first metal portion 51.

[0029] On the upper surface of second metal part 52, there are formed a bonding surface 53 and a concave portion 54 having a shape recessed with respect to bonding surface 53. Concave portion 54 is formed so as to have a shape recessed with respect to bonding surface 53, for example, by bonding second metal part 52 to the upper part of first metal part 51 by dissimilar metal bonding. This will be described in more detail below.

[0030] (Manufacturing method) The manufacturing method of battery pack 100 may include a step of dissimilar metal joining second metal part 52 to the upper part of first metal part 51 by, for example, friction stir spot welding, ultrasonic welding, or resistance welding. Fig. 3 is a cross-sectional view showing the state when second metal part 52 is dissimilar metal joined to the upper part of first metal part 51 by a technique of friction stir spot welding.

[0031] 3, in the case of friction stir spot welding, the second metal part 52 is joined to the first metal part 51 using an FSW stick 91 (FSW: Friction Stir Welding). An effective connection part 98 having a joint strength equal to or greater than a predetermined value is formed on the joint surface between the second metal part 52 and the first metal part 51. Before the second metal part 52 is joined to the first metal part 51, the concave part 54 is not formed on the joint surface 53, and the joint surface 53 has an overall flat surface shape.

[0032] Fig. 4 is a cross-sectional view showing a state in which a second metal part 52 is dissimilarly metal-joined to an upper part of a first metal part 51 by a friction stir spot welding technique. By performing friction stir spot welding, as shown in Fig. 4, the second metal part 52 is dissimilarly metal-joined to an upper part of the first metal part 51, thereby forming a negative electrode terminal 50. The concave part 54 is formed to have a shape recessed with respect to the joining surface 53 by dissimilarly metal-joining the second metal part 52 to the upper part of the first metal part 51.

[0033] Fig. 5 is a cross-sectional view showing a state in which welding auxiliary member 60 is inserted into concave portion 54 provided in second metal part 52. Fig. 6 is a cross-sectional view showing a state in which welding auxiliary member 60 has been inserted into concave portion 54 provided in second metal part 52. As shown in Figs. 5 and 6, welding auxiliary member 60 is inserted into concave portion 54. The manufacturing method of battery pack 100 includes the step of inserting welding auxiliary member 60 into concave portion 54.

[0034] The welding auxiliary member 60 is formed, for example, from a metal. The welding auxiliary member 60 is formed, for example, from the same metal as the second metal portion 52 of the negative terminal 50, and here, as an example, the welding auxiliary member 60 is formed from an aluminum alloy. The welding auxiliary member 60 is not limited to being formed from the same metal as the second metal portion 52, and may be formed from a member that melts at the same or a similar melting point as the second metal portion 52 during laser welding.

[0035] The welding auxiliary member 60 is inserted into the inside of the concave portion 54 from its bottom side. The welding auxiliary member 60 may have a width W2, diameter, or bottom area larger than the width W1, hole diameter, or area of ​​the opening of the concave portion 54. The welding auxiliary member 60 can be firmly fixed to the inside of the concave portion 54 by press-fitting or fitting (interference fit).

[0036] 7 is a cross-sectional view showing a state in which the bus bar 70 is joined onto the joining surface 53 of the negative electrode terminal 50 (second metal part 52) ​​by laser welding. The joining surface 53 of the second metal part 52 constitutes a part of the negative electrode terminal 50 that protrudes towards the outside of the secondary battery 11. The bus bar 70 is electrically connected onto the joining surface 53.

[0037] The manufacturing method of the battery pack 100 includes the steps of placing the bus bar 70 on the joint surface 53 of the negative terminal 50 with the welding auxiliary member 60 inserted into the concave portion 54, and joining the bus bar 70 to the joint surface 53 of the negative terminal 50 by laser welding using irradiation with a laser L (FIG. 7). The bus bar 70 and the negative terminal 50 function as a current path and are used to extract power stored in the electrode body 20 to the outside and to take in power from the outside to the electrode body 20.

[0038] (Action and Effects) The operation and effects of the present embodiment will be described in comparison with Comparative Example 1 (FIG. 8) and Comparative Example 2 (FIG. 9). FIG. 8 is a cross-sectional view showing a state in which bus bar 70 is joined onto joining surface 53 of negative terminal 50 (second metal portion 52) by laser welding in the case of Comparative Example 1.

[0039] Comparative Example 1 As shown in Fig. 8, in the case of Comparative Example 1, the welding auxiliary member 60 is not inserted into the concave portion 54. When the bus bar 70 is laser-welded to the negative terminal 50, a positional deviation occurs in the irradiation position of the laser L, and the laser L may hit the concave portion 54 (the state shown in Fig. 8). The portion of the negative terminal 50 (second metal portion 52) where the concave portion 54 is formed is thinner than the portion of the negative terminal 50 (second metal portion 52) where the concave portion 54 is not formed.

[0040] As described at the beginning of this specification, heat is likely to reach the joint surface between dissimilar metals in the negative electrode terminal 50 (in other words, the effective connection portion 98 where the first metal portion 51 and the second metal portion 52 are joined to each other). If a large amount of heat is supplied to the joint surface between dissimilar metals in the negative electrode terminal 50, an intermetallic compound 85 is formed between the dissimilar metals, and as a result, there is a risk that the joint strength of the joint surface between the dissimilar metals, particularly the joint strength at the effective connection portion 98, will decrease. In addition, when the laser L hits the concave portion 54, sparks may be generated and fumes (unwanted matter) may be formed.

[0041] In contrast to the comparative example 1, the above-described embodiment (see FIG. 7) can provide the following functions and effects [1] to [5].

[0042] [1] Because the welding auxiliary member 60 is present inside the concave portion 54, even if the irradiation position of the laser beam L is misaligned, the laser beam L will seldom or never hit the concave portion 54, and therefore there will be little or no sparks and fumes formed.

[0043] [2] Because the welding auxiliary member 60 is present inside the concave portion 54, even if the irradiation position of the laser L is misaligned, the heat is effectively prevented from reaching the joint surface between the dissimilar metals in the negative terminal 50 (in other words, the effective connection portion 98 where the first metal portion 51 and the second metal portion 52 are joined to each other). As a result, intermetallic compounds 85 are hardly formed between the dissimilar metals. As a result, the joint strength of the joint surface between the dissimilar metals, particularly the joint strength at the effective connection portion 98, is hardly reduced.

[0044] [3] Since the welding auxiliary member 60 is present inside the concave portion 54, even if a positional shift occurs in the irradiation position of the laser L and the laser L hits the welding auxiliary member 60, it is possible to perform welding of the bus bar 70 and / or to continue welding, which makes it possible to reduce the welding defect rate and ultimately improve the manufacturing yield.

[0045] [4] Welding marks on the dissimilar metal processed surface between first metal portion 51 and second metal portion 52 are likely to become the starting point of cracks that may occur over time. However, in the case of the embodiment, welding auxiliary member 60 melts and fills in the welding marks, making it possible to prevent the above-mentioned cracks from occurring.

[0046] [5] By filling the concave portion 54 with the welding auxiliary member 60, it is possible to prevent moisture from condensing within the concave portion 54 and to prevent dust from accumulating within the concave portion 54, thereby improving the corrosion resistance of the negative terminal 50.

[0047] In addition, in the above-described embodiment, by configuring the welding auxiliary member 60 and the second metal portion 52 of the negative electrode terminal 50 to melt at the same melting point, for example by forming the welding auxiliary member 60 and the second metal portion 52 of the negative electrode terminal 50 from the same metal, laser welding can be easily performed.

[0048] Comparative Example 2 9 is a cross-sectional view showing a state in which bus bar 70 is joined onto joining surface 53 of negative terminal 50 (second metal part 52) ​​by laser welding in the case of Comparative Example 2. In the case of Comparative Example 2, second metal part 52 is formed thicker than in Comparative Example 1. As a result, even if a positional shift occurs in the irradiation position of laser L and laser L hits the concave portion, heat is prevented from reaching the joining surface between dissimilar metals in negative terminal 50 (in other words, the portion where first metal part 51 and second metal part 52 are joined to each other).

[0049] In the case of Comparative Example 2, it is possible to prevent intermetallic compound 85 (FIG. 8) from being formed between dissimilar metals, resulting in a decrease in the bonding strength of the bonding surface between the dissimilar metals. However, in order to bond second metal part 52 having such a large thickness to first metal part 51, it may be necessary to adopt a limited method, such as providing a mechanical fitting structure at the interface therebetween or using a method called friction welding (solid-state bonding) using the action of rotation and pressure welding.

[0050] That is, when joining second metal part 52 having such a large thickness to first metal part 51, it becomes difficult to adopt techniques such as ultrasonic welding, resistance welding, or friction stir spot welding, and it becomes difficult to improve the degree of freedom in manufacturing. In addition, the entire device may become bulky by the amount that second metal part 52 is made thick.

[0051] In contrast to Comparative Example 2, in the case of the above-described embodiment, the second metal part 52 can be joined to the first metal part 51 by performing friction stir spot welding using, for example, an FSW stick 91 (FIG. 3), and there are almost no restrictions on manufacturing. Compared to Comparative Example 2, the entire device does not become bulky due to the thickness of the second metal part 52.

[0052] (Variation 1) 10 is a cross-sectional view showing dissimilar metal joining of second metal part 52 to an upper part of first metal part 51 by ultrasonic welding in the first modified example of the embodiment. The joining is not limited to friction stir spot welding in the above-mentioned embodiment, and first metal part 51 may be joined to second metal part 52 by ultrasonic welding using horn 92 and anvil 93. Even when this configuration is adopted, by forming concave part 54 (see FIG. 4) and inserting welding auxiliary member 60 (see FIG. 6) into concave part 54, it is possible to obtain the same action and effect as the above-mentioned embodiment.

[0053] (Variation 2) 11 is a cross-sectional view showing a state in which second metal part 52 is dissimilarly joined to an upper part of first metal part 51 by resistance welding in the second modification of the embodiment. The joining is not limited to friction stir spot welding in the above-described embodiment or ultrasonic welding in the first modification, but first metal part 51 may be joined to second metal part 52 by resistance welding. Even when this configuration is adopted, by forming concave part 54 (see FIG. 4) and inserting welding auxiliary member 60 (see FIG. 6) into concave part 54, it is possible to obtain the same action and effect as the above-described embodiment.

[0054] (Variation 3) 12 is a cross-sectional view showing a state where a welding auxiliary member 60 is inserted into a concave portion 54 provided in a second metal part 52, in the third modified example of the embodiment. The welding auxiliary member 60 shown in FIG. 12 is inserted into the inside of the concave portion 54 from its bottom side, similarly to the case shown in FIG. 5. The welding auxiliary member 60 may have a tapered shape (or a wedge shape) narrower on the bottom side than the concave portion 54. The press-fit or fitting (interference fit) structure allows the welding auxiliary member 60 to be firmly fixed to the inside of the concave portion 54.

[0055] Although the embodiment based on the present disclosure has been described above, the contents disclosed herein are illustrative and not restrictive in all respects. The technical scope of the present invention is defined by the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0056] 11 secondary battery (first battery), 12 secondary battery (second battery), 18, 19 end plate, 20 electrode body, 22 electrolyte, 30 housing, 31 case member, 31H opening, 32 cover member, 40 gasket, 50 negative terminal, 51 first metal part, 52 second metal part, 53 joining surface, 54 concave portion, 60 welding auxiliary member, 70 bus bar, 80 positive terminal, 85 intermetallic compound, 91 stick, 92 horn, 93 anvil, 98 effective connection portion, 100 battery pack, L laser, W1, W2 width.

Claims

1. A method for manufacturing a battery pack including a first battery and a second battery, comprising: the first battery includes a negative electrode terminal, the negative electrode terminal having a first metal portion and a second metal portion formed from a metal different from the first metal portion, the second metal portion being joined to an upper portion of the first metal portion by dissimilar metal joining, and a joining surface and a concave portion having a shape recessed relative to the joining surface are formed on an upper surface of the second metal portion, the second battery includes a positive terminal electrically connected to the negative terminal via a bus bar; The method for manufacturing the battery pack includes: inserting a welding auxiliary member into the concave portion; placing the bus bar on the joint surface of the negative terminal with the welding auxiliary member inserted into the concave portion, and joining the bus bar to the joint surface of the negative terminal by laser welding. A method for manufacturing a battery pack.

2. The welding auxiliary member is formed from the same metal as the second metal portion of the negative electrode terminal. A method for manufacturing the battery pack according to claim 1 .

3. the concave portion is formed by dissimilar metal bonding of the second metal portion to an upper portion of the first metal portion, so as to have a shape recessed with respect to the bonding surface; A method for producing the battery pack according to claim 1 or 2.

4. The second metal portion is dissimilarly metal-joined to an upper portion of the first metal portion by friction stir spot welding, ultrasonic welding, or resistance welding; A method for producing the battery pack according to claim 3.

5. A battery pack including a first battery, a second battery, and a bus bar, the first battery includes a negative electrode terminal, the negative electrode terminal having a first metal portion and a second metal portion formed from a metal different from the first metal portion, the second metal portion being joined to an upper portion of the first metal portion by dissimilar metal joining, and a joining surface and a concave portion having a shape recessed relative to the joining surface are formed on an upper surface of the second metal portion, the second battery includes a positive terminal electrically connected to the negative terminal via the bus bar; A welding auxiliary member is inserted into the concave portion, the bus bar is disposed on the joint surface of the negative terminal with the welding auxiliary member inserted into the concave portion, and the bus bar is joined onto the joint surface of the negative terminal by laser welding. Battery pack.

6. The welding auxiliary member is formed from the same metal as the second metal portion of the negative electrode terminal. The battery pack according to claim 5 .

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