Battery pack

Abstract

Provided is a battery pack in which metal members that are overlapped and welded are appropriately connected by laser welding regardless of the presence or absence of a gap between the metal members, and even if the metal members are dissimilar metals. The battery pack has a battery module having a plurality of single cells each having a positive electrode tab and a negative electrode tab, and a bus bar welded to at least either of the positive electrode tab and the negative electrode tab. The material of either of the positive electrode tab and the negative electrode tab is different from the material of the bus bar. At least either of the positive electrode tab and the negative electrode tab and a welded portion (73) of the bus bar are connected by laser welding using a scanning laser (70). The track of the laser has a shape in which a first portion (71) in which the tracks overlap and a second portion (72) in which the tracks do not overlap are repeatedly generated. Furthermore, the connection strength of the welded portion is obtained at intervals at either of the first portion and the second portion.

Description

Technical Field

[0001] This invention relates to battery packs. Background Technology

[0002] The battery pack includes a battery module having multiple individual cells and multiple busbars. Each individual cell has a positive electrode tab and a negative electrode tab. Busbars are welded to at least one of the positive and negative electrode tabs. The positive electrode tab is, for example, formed of aluminum, and the negative electrode tab is, for example, formed of copper.

[0003] When single cells are connected in series, for example using aluminum busbars, the positive electrode tab and the busbar are made of the same material. Therefore, when the positive electrode tab and the busbar are overlapped and laser-welded, the weld quality, such as connection strength, can be adequately ensured. However, the negative electrode tab and the busbar are made of dissimilar materials. Therefore, even if the negative electrode tab and the busbar are overlapped and laser-welded, it is difficult to ensure the weld quality, such as connection strength.

[0004] Therefore, when connecting single cells in series, a busbar made of cladding material is used. This busbar has a first busbar section made of aluminum and a second busbar section made of copper. The first and second busbar sections are joined by crimping. The positive electrode tab is laser-welded to the first busbar section, and the negative electrode tab is laser-welded to the second busbar section. Although the positive and negative electrode tabs are made of dissimilar metals, the welding points with the busbar are made of the same metal. This ensures welding quality, including connection strength.

[0005] However, the cost of busbars made of cladding material is high, which is one of the reasons that hinders the reduction of battery pack costs.

[0006] As a technique for joining dissimilar materials together, the techniques disclosed in the following patent documents 1 and 2 are known.

[0007] Patent document 1 discloses a technique for welding dissimilar metals together. This technique involves repeatedly performing laser spot welding at intervals.

[0008] Patent document 2 discloses a technology for improving the adhesion between metal parts and resin parts. This technology adjusts the spacing between adjacent rough surfaces and the ratio of the depth to the width of the rough surfaces by using a laser to form rough surfaces arranged on the surface of the metal part.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Publication No. 2018-505058

[0012] Patent Document 2: Japanese Patent Application Publication No. 2014-117724 Summary of the Invention

[0013] The problem the invention aims to solve

[0014] In the technology disclosed in Patent Document 1, if there are gaps between the overlapping welded metal components, it is difficult to obtain sufficient connection strength.

[0015] The technology disclosed in Patent Document 2 relates to the roughening of metal parts and does not consider its application to laser welding of dissimilar metals.

[0016] The object of the present invention is to provide a battery pack in which the overlapping welded metal components are properly connected by laser welding, regardless of whether there are gaps between them, and even if they are dissimilar metals.

[0017] Solution for solving the problem

[0018] A battery pack according to one embodiment of the present invention for achieving the above-mentioned objective comprises: a battery module having a plurality of individual cells, each individual cell having a positive electrode tab and a negative electrode tab; and a busbar welded to at least one of the positive electrode tabs and the negative electrode tabs. The material of either the positive electrode tab or the negative electrode tab is different from the material of the busbar. At least one of the positive electrode tabs and the negative electrode tab is connected to the welded portion of the busbar by laser welding using a scanning laser, the laser trajectory having a shape that repeatedly produces a first portion of overlapping trajectories and a second portion of non-overlapping trajectories. Furthermore, the connection strength of the welded portion is obtained intermittently at either the first portion or the second portion.

[0019] Furthermore, another embodiment of the present invention for achieving the above-mentioned objective includes a battery module having a plurality of individual cells, each individual cell having a positive electrode tab and a negative electrode tab. The positive electrode tab of one individual cell is welded to the negative electrode tab of another individual cell. The positive electrode tab is made of a different material than the negative electrode tab. The welded portions of the positive and negative electrode tabs are connected by laser welding using a scanning laser, the laser trajectory having a shape that repeatedly produces a first portion with overlapping trajectories and a second portion with non-overlapping trajectories. Moreover, the connection strength of the welded portions is obtained intermittently at either the first or the second portion.

[0020] The effects of the invention

[0021] According to the present invention, the welding depth can be appropriately varied by oscillating the laser. The connection strength of the welded portion is obtained intermittently at either the first part or the second part. A battery pack can be provided that can be appropriately connected by laser welding regardless of whether gaps exist between the overlapping welded metal components, and even if they are dissimilar metals. Attached Figure Description

[0022] Figure 1 It is a 3D diagram showing the main parts of the battery pack.

[0023] Figure 2 It is a 3D diagram representing a single battery.

[0024] Figure 3 This is a side view showing the main parts of the implementation method, and a side view showing the state in which the positive electrode tab of one single cell and the negative electrode tab of another single cell are welded and connected to the busbar.

[0025] Figure 4 It is a three-dimensional diagram showing the connection of metal components to each other by overlapping welding based on laser welding.

[0026] Figure 5 It is a diagram representing the trajectory of a laser beam, and it is a diagram representing the shapes of the overlapping and non-overlapping parts of the repeatedly generated trajectories.

[0027] Figure 6 It is a cross-sectional view schematically showing the state in which the weld strength is obtained at intervals by the welding depth of the non-overlapping parts of the laser trajectory.

[0028] Figure 7 It is a cross-sectional view schematically showing the state in which the weld strength is obtained at intervals by the welding depth of the overlapping parts of the laser trajectory.

[0029] Figure 8 This is a side view showing the main part of the modified example, and a side view showing the state in which the positive electrode tab of one single cell is welded to the negative electrode tab of another single cell. Detailed Implementation

[0030] Hereinafter, with reference to the accompanying drawings, the methods for carrying out the present invention will be described in detail. The embodiments shown herein are illustrative of the technical concept of the present invention and are not intended to limit the present invention. Therefore, all other methods, embodiments, and application techniques that can be implemented by those skilled in the art without departing from the spirit of the present invention are included within the scope and spirit of the present invention, and are included within the scope of the invention as set forth in the claims and its equivalents.

[0031] In addition, for ease of illustration and understanding, the accompanying drawings may schematically represent scales, aspect ratios, shapes, etc., with appropriate changes relative to the actual object, but these are merely examples and are not intended to limit the interpretation of the present invention.

[0032] In addition, ordinal numbers such as "the first" and "the second" are sometimes used in this specification. However, unless otherwise specified, these ordinal numbers are used to identify the constituent elements for ease of explanation and do not indicate quantity or order.

[0033] <Implementation Method>

[0034] like Figure 1 and Figure 2 As shown, the battery pack 10 includes a battery module 30 having a plurality of individual cells 20 and a plurality of busbars 40. Each individual cell 20 has a positive electrode tab 21 and a negative electrode tab 22. The busbars 40 are welded to at least one of the positive electrode tab 21 and the negative electrode tab 22.

[0035] The battery module 30 has a stacked structure formed by stacking multiple individual cells 20. Each individual cell 20 has a flat shape and is held by spacers 31. Each individual cell 20 has a flat battery body 23 containing power generation elements and a positive electrode tab 21 and a negative electrode tab 22 extending from the battery body 23. The top ends 21a and 22a of the positive electrode tab 21 and the negative electrode tab 22 are bent along the direction of the stacked individual cells 20. The busbar 40 has a flat shape. The busbar 40 is welded to the top ends 21a and 22a in a state opposite to the top ends 21a and 22a of the positive electrode tab 21 and the negative electrode tab 22. Figure 1 The diagram shows a configuration where a busbar 40 connects to the positive tab 21 of each of the three individual cells 20 and to the negative tab 22 of each of the three individual cells 20. That is, two groups of individual cells 20 are connected in series via a busbar 40. Furthermore, to form a desired electrical path, the busbar 40 can be connected only to the positive tab 21 or only to the negative tab 22.

[0036] The positive electrode tab 21 is made of a different material than the negative electrode tab 22. Furthermore, the material of either the positive electrode tab 21 or the negative electrode tab 22 is different from the material of the busbar 40. Specifically, the positive electrode tab 21 is, for example, made of aluminum, the negative electrode tab 22 is, for example, made of copper, and the busbar 40 is, for example, made of aluminum.

[0037] like Figure 3As shown, the positive electrode tab 21 of one single cell 20 is connected to the welding portion 73 of the busbar 40 via overlapping welding using laser welding based on scanning laser 70. Similarly, the negative electrode tab 22 of another single cell 20 is also connected to the welding portion 73 of the busbar 40 via overlapping welding based on laser welding. In this embodiment, the welding of the positive electrode tab 21 to the busbar 40 is a welding of the same metal, while the welding of the negative electrode tab 22 to the busbar 40 is a welding of dissimilar metals. Figure 1 In the figure, the welded parts of the same metal are indicated by the line of reference numeral 51, and the welded parts of dissimilar metals are indicated by the line of reference numeral 52.

[0038] Figure 4 This indicates the case where metal components 61 and 62 are connected to each other by overlapping welding based on laser welding. Figure 5 This represents the trajectory 70a of laser 70.

[0039] like Figure 4 and Figure 5 As shown, in laser welding, the trajectory 70a of the laser 70 has a shape comprising a first portion 71 where trajectories 70a overlap, a second portion 72 where trajectories 70a do not overlap, and a portion 74 where no trajectories 70a exist. Like Figure 5 As shown by the trajectory 70a of the laser 70, the oscillating laser 70 has overlapping portions 71, non-overlapping portions 72, and portions 74 where the trajectory 70a does not exist, thereby allowing for appropriate variation in the welding depth. The weld strength of the welded portion 73 is obtained intermittently at either the first portion 71 or the second portion 72. Here, "obtaining weld strength intermittently" does not mean obtaining joint strength at all locations of the welded portion 73, but rather obtaining joint strength intermittently and locally at either the first portion 71 or the second portion 72.

[0040] Reference Figure 6 and Figure 7 To explain in more detail. Figure 6 The diagram shows the state in which the welded portion 73 is intermittently strengthened at point 72 in section 2. Figure 7 The diagram shows the state in which the welded portion 73 is intermittently strengthened at point 71 in section 1. (The text will continue...) Figure 4 , Figure 6 as well as Figure 7 Among the overlapping metal components 61 and 62, the upper metal component 61 is called the first metal component 61, and the lower metal component 62 is called the second metal component 62. Figure 6 This indicates a state where there is no gap S between the first metal member 61 and the second metal member 62. Figure 4 , Figure 7This indicates a state where a gap S exists between the first metal member 61 and the second metal member 62. Furthermore, in this specification, "a state where there is no gap S" means a state where the gap between the first metal member 61 and the second metal member 62, which overlap for welding, remains below the designed maximum gap. Below the maximum gap also includes situations where the first metal member 61 and the second metal member 62 are in contact or in close contact due to external pressure, etc. In this specification, "a state where there is a gap S" means a state where the gap between the first metal member 61 and the second metal member 62 remains larger than the designed maximum gap (a larger gap than "a state where there is no gap S"). The designed maximum gap is determined by considering the manufacturing tolerances of the positive electrode tab 21 and the negative electrode tab 22, the offset generated when the single cell 20 is set for laser welding, the surface roughness of the positive electrode tab 21 and the negative electrode tab 22, the amount of bending, etc.

[0041] A deeper weld depth can be formed at the first part 71 of the laser trajectory 70a, and a shallower weld depth can be formed at the second part 72 (see reference). Figure 4 Difference in weld depth () Figure 4 Reference numeral d) is set to a design maximum spacing greater than that between the first metal member 61 and the second metal member 62. In the embodiment, even if the objects to be overlapped for welding (same type of metal or different type of metal) change, the welding conditions (laser output, oscillation magnitude, scanning speed, etc.) remain constant. In cases where the required welding depth cannot be set due to changes in the objects to be overlapped for welding, the welding conditions can be changed for each change in objects.

[0042] This explains the function of the first metal component 61 as the busbar 40 and the second metal component 62 as the positive electrode tab 21. The welding of the positive electrode tab 21 and the busbar 40 is a welding of the same metal to each other.

[0043] like Figure 6As shown, when laser welding is performed with no gap S between the positive electrode tab 21 and the busbar 40, the positive electrode tab 21 and the busbar 40 come into contact at the second part 72. In this specification, "coming into contact" includes not only the state where the positive electrode tab 21 and the busbar 40 are in contact, but also the state where the gap between the positive electrode tab 21 and the busbar 40 is less than the maximum designed gap. While excessive welding depth at the first part 71 may result in hole defects, the welding depth at the second part 72 is a relatively shallow and appropriate depth. Therefore, the connection strength of the welded portion 73 between the positive electrode tab 21 and the busbar 40 is obtained intermittently based on the welding depth at the second part 72. Thus, when there is no gap S between the positive electrode tab 21 and the busbar 40, the positive electrode tab 21 and the busbar 40 can be properly connected by laser welding.

[0044] like Figure 7 As shown, when laser welding is performed with a gap S between the positive electrode tab 21 and the busbar 40, a residual gap S remains between the positive electrode tab 21 and the busbar 40 at the second part 72. In this state, the welding depth at the first part 71 becomes a relatively shallow and appropriate depth. Therefore, the connection strength of the welded portion 73 between the positive electrode tab 21 and the busbar 40 is obtained intermittently by the welding depth at the first part 71. Thus, even when a gap S exists between the positive electrode tab 21 and the busbar 40, the positive electrode tab 21 and the busbar 40 can be properly connected by laser welding.

[0045] Thus, whether there is no gap S between the overlapping welded positive electrode tab 21 and the busbar 40 or there is a gap S, the positive electrode tab 21 and the busbar 40 can be welded together without changing the welding conditions, ensuring the required welding quality.

[0046] This explains the function of the first metal component 61 as the busbar 40 and the second metal component 62 as the negative electrode tab 22. The welding of the negative electrode tab 22 and the busbar 40 is a welding of dissimilar metals.

[0047] like Figure 6 As shown, when laser welding is performed with no gap S between the negative electrode tab 22 and the busbar 40, the negative electrode tab 22 and the busbar 40 abut at the second part 72. While the welding depth at the first part 71 might be too deep and potentially cause hole defects, the welding depth at the second part 72 is a relatively shallow and appropriate depth. Therefore, the connection strength of the welded portion 73 between the negative electrode tab 22 and the busbar 40 is obtained intermittently by varying the welding depth at the second part 72. Thus, even without a gap S between the negative electrode tab 22 and the busbar 40, the negative electrode tab 22 and the busbar 40 can be properly connected by laser welding.

[0048] Welding of the same metals (positive electrode tab 21 and busbar 40) ensures sufficient weld quality, including connection strength. However, welding of dissimilar metals (negative electrode tab 22 and busbar 40) inevitably results in the formation of intermetallic compounds at the interface. This formation of intermetallic compounds reduces the connection strength. While the amount of intermetallic compound formation is greater at section 71, it does not occur at all locations within the welded section 73. Therefore, the negative electrode tab 22 and busbar 40 are connected with intermittent strength at section 72.

[0049] like Figure 7 As shown, when laser welding is performed with a gap S between the negative electrode tab 22 and the busbar 40, a residual gap S remains between the negative electrode tab 22 and the busbar 40 at the second part 72. In this state, the welding depth at the first part 71 becomes a relatively shallow and appropriate depth. Therefore, intermetallic compounds are not generated throughout the welded portion 73, but the connection strength of the welded portion 73 between the negative electrode tab 22 and the busbar 40 is obtained intermittently based on the welding depth at the first part 71. Thus, even when a gap S exists between the negative electrode tab 22 and the busbar 40, the negative electrode tab 22 and the busbar 40 can be properly connected by laser welding.

[0050] Thus, whether there is no gap S between the overlapped negative electrode tab 22 and the busbar 40 or there is a gap S, the negative electrode tab 22 and the busbar 40 can be welded together without changing the welding conditions, ensuring the required welding quality.

[0051] As described above, in this embodiment, the trajectory 70a of the laser 70 has a shape that repeatedly generates a first portion 71 where the trajectories 70a overlap and a second portion 72 where the trajectories 70a do not overlap. Furthermore, the connection strength of the welded portion 73 is obtained at intervals at either the first portion 71 or the second portion 72. With this configuration, regardless of whether a gap S exists between the overlapping welded metal components 61 and 62, and whether the overlapping welding is between the same type of metal (e.g., the positive electrode tab 21 and the busbar 40) or between dissimilar metals (e.g., the negative electrode tab 22 and the busbar 40), a battery pack 10 that is properly welded together by laser welding can be provided. Furthermore, even if the objects of the overlapping welding (the same type of metal or dissimilar metals) change, the required welding quality can be ensured without changing the welding conditions (laser output, oscillation magnitude, scanning speed, etc.). Therefore, laser welding can be performed efficiently, and a battery pack 10 that is cost-effective compared to the case where a busbar 40 using cladding material is used can be provided.

[0052] In this embodiment, to prevent the formation of a gap S between the overlapping welded metal components 61 and 62, the melting depth is varied by oscillating the laser 70 even when there is no gap S between the metal components 61 and 62. Even when there is no overall gap S between the metal components 61 and 62 (see...) Figure 6 Furthermore, it does not achieve bond strength at all locations within the molten portion, but rather at intervals (locally separated by gaps). In this respect, it differs from laser spot welding techniques that repeatedly perform laser spot welding at intervals.

[0053] (Variation example)

[0054] Figure 8 This is a side view showing the main parts of the modified example, indicating the state in which the positive electrode tab 21 of one single cell 20 is welded to the negative electrode tab 22 of another single cell 20. The modified battery pack 10 has a portion where the positive electrode tab 21 and the negative electrode tab 22, which are dissimilar metals, are welded together without passing through the busbar 40. Other structures are the same as those of the battery pack 10 in the embodiment.

[0055] like Figure 4 and Figure 5 As shown, similar to the embodiment, in laser welding, the trajectory 70a of the laser 70 has a shape that repeatedly produces a first portion 71 where the trajectories 70a overlap and a second portion 72 where the trajectories 70a do not overlap. Like Figure 5 As shown in the trajectory 70a of the laser 70, the welding depth can be appropriately varied by oscillating the laser 70. The connection strength of the welded portion 73 is obtained intermittently at either the first part 71 or the second part 72.

[0056] Reference Figure 6 and Figure 7 The modified examples are described in more detail. In the modified examples, in Figure 6 and Figure 7 In the overlapping metal components 61 and 62, the first metal component 61 is the positive electrode tab 21, and the second metal component 62 is the negative electrode tab 22. The welding of the positive electrode tab 21 and the negative electrode tab 22 is the welding of dissimilar metals.

[0057] like Figure 6As shown, when laser welding is performed without a gap S between the positive electrode tab 21 and the negative electrode tab 22, the positive electrode tab 21 and the negative electrode tab 22 abut at the second part 72. While the welding depth at the first part 71 might be too deep and potentially cause hole defects, the welding depth at the second part 72 is a relatively shallow and appropriate depth. Therefore, the connection strength of the welded portion 73 between the positive electrode tab 21 and the negative electrode tab 22 is obtained intermittently by varying the welding depth at the second part 72. Thus, even without a gap S between the positive electrode tab 21 and the negative electrode tab 22, the positive electrode tab 21 and the negative electrode tab 22 can be properly connected by laser welding.

[0058] In the welding connection of dissimilar metals (positive electrode tab 21 and negative electrode tab 22), intermetallic compounds inevitably form at the connection interface. The formation of intermetallic compounds leads to a decrease in connection strength. The amount of intermetallic compound formation is increased at the first part 71, but it does not form at all parts of the welded portion 73. Therefore, the positive electrode tab 21 and negative electrode tab 22 are connected with strength at intervals at the second part 72.

[0059] like Figure 7 As shown, when laser welding is performed with a gap S between the positive electrode tab 21 and the negative electrode tab 22, a gap S remains between the positive electrode tab 21 and the negative electrode tab 22 at the second part 72. In this state, the welding depth at the first part 71 becomes a relatively shallow and appropriate depth. Therefore, intermetallic compounds are not generated throughout the welded portion 73, but the connection strength of the welded portion 73 between the positive electrode tab 21 and the negative electrode tab 22 is obtained intermittently based on the welding depth at the first part 71. Thus, even when a gap S exists between the positive electrode tab 21 and the negative electrode tab 22, the positive electrode tab 21 and the negative electrode tab 22 can be properly connected by laser welding.

[0060] Thus, whether there is no gap S between the overlapping positive electrode tab 21 and the negative electrode tab 22 or there is a gap S, the positive electrode tab 21 and the negative electrode tab 22 can be welded together without changing the welding conditions, ensuring the required welding quality.

[0061] As described above, in the modified example, the trajectory 70a of the laser 70 has a shape that repeatedly produces a first portion 71 where the trajectories 70a overlap and a second portion 72 where the trajectories 70a do not overlap. Furthermore, the connection strength of the welded portion 73 is obtained intermittently at either the first portion 71 or the second portion 72. With this configuration, regardless of whether a gap S exists between the dissimilar metals being welded (positive electrode tab 21 and negative electrode tab 22), a battery pack 10 that is properly welded together by laser welding can be provided. Moreover, even if the objects being welded (same metals or dissimilar metals) change, the required weld quality can be ensured without changing the welding conditions (laser output, oscillation magnitude, scanning speed, etc.). Therefore, laser welding can be performed efficiently, and a battery pack 10 that is cost-effective compared to the case of using a busbar 40 with cladding material can be provided.

[0062] The above describes the embodiments and variations of the battery pack 10 of the present invention. However, the present invention is not limited to the structure described above and can be appropriately modified based on the claims.

[0063] This application is based on Japanese Patent Application No. 2024-063927, filed on April 11, 2024, and incorporates its disclosure in its entirety.

[0064] Explanation of reference numerals in the attached figures

[0065] 10. Battery pack; 20. Single cell; 21. Positive electrode tab; 21a. Top end; 22. Negative electrode tab; 22a. Top end; 23. Battery body; 30. Battery module; 31. Spacer; 40. Busbar; 61. First metal component; 62. Second metal component; 70. Laser; 70a. Trajectory; 71. First part of overlapping trajectories; 72. Second part of non-overlapping trajectories; 73. Welded part; 74. Part without trajectory; S. Gap.

Claims

1. A battery pack, wherein, This battery pack has the following features: A battery module having multiple individual cells, each individual cell having a positive electrode tab and a negative electrode tab; and A busbar, which is welded to at least one of the positive electrode tab and the negative electrode tab. The material of either the positive electrode tab or the negative electrode tab is different from the material of the busbar. At least one of the positive electrode tabs and the negative electrode tabs is connected to the welding portion of the busbar by laser welding using a scanning laser, wherein the laser trajectory has a shape that repeatedly produces a first portion of overlapping trajectories and a second portion of non-overlapping trajectories. The connection strength of the weld is obtained at intervals at either the first part or the second part.

2. The battery pack according to claim 1, wherein, At the second part, at least one of the positive electrode tab and the negative electrode tab abuts against the busbar, and the connection strength of the weld is obtained at intervals by the welding depth at the second part.

3. The battery pack according to claim 1, wherein, In the second part, there is a gap between at least one of the positive electrode tab and the negative electrode tab and the busbar, and the connection strength of the welded part is obtained intermittently by the welding depth in the first part.

4. A battery pack, wherein, The battery pack has a battery module, which has multiple individual cells, each individual cell having a positive electrode tab and a negative electrode tab. The positive electrode tab of one of the single cells is welded to the negative electrode tab of the other single cell. The positive electrode tab is made of a different material than the negative electrode tab. The positive electrode tab and the negative electrode tab are connected by laser welding using a scanning laser. The laser trajectory has a shape that repeatedly produces a first portion of overlapping trajectories and a second portion of non-overlapping trajectories. The connection strength of the weld is obtained at intervals at either the first part or the second part.

5. The battery pack according to claim 4, wherein, At the second part, the positive electrode tab abuts against the negative electrode tab, and the connection strength of the welded part is obtained intermittently by the welding depth at the second part.

6. The battery pack according to claim 4, wherein, In the second part, there is a gap between the positive electrode tab and the negative electrode tab, and the connection strength of the welded part is obtained intermittently by the welding depth in the first part.

Images