Welding method and welded structure

Abstract

The invention provides a welding method and a welding structure. In the welding method of the present disclosure, a first metal layer and a second metal layer are a first metal material of the same kind, a third metal layer is a second metal material different from the first metal material, and when the first metal layer and the second metal layer are joined by laser welding by irradiating and scanning a laser from the side where the first metal layer is located, the first metal layer and the second metal layer are bonded by laser welding. The scanning of the laser light includes a first scanning step and a subsequent second scanning step, the first scanning step includes a step in which the irradiation of the laser light penetrates the second metal layer, and the second scanning step includes a step in which the irradiation of the laser light does not penetrate the second metal layer.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a welding method and a welded structure. BACKGROUND

[0002] In Japanese Patent Application Publication No. 2003-094184, a welding method that reduces the generation of molten metal spatter and welding defects is disclosed. Specifically, after preheating by a first laser beam that precedes, a second laser beam that follows performs the actual welding, thereby reducing the generation of molten metal spatter and welding defects.

[0003] In a battery pack, a bus bar is fixed to an electrode terminal provided to a battery cell by welding. For the electrode terminal, a terminal of a double-layer structure can be used, and in order to be well welded with a bus bar using aluminum, an upper layer uses aluminum, and in order to be well connected to a battery element of the battery cell, a lower layer uses copper.

[0004] Thus, when welding a bus bar to an electrode terminal having a double-layer structure, the bus bar is welded to the aluminum of the upper layer. At the time of welding, air present in a gap between the upper layer and the lower layer of the electrode terminal is heated and thermally expands due to the heat of the laser used for welding. Also, organic substances present in the gap are similarly heated and gasified due to the heat of the laser used for welding. As a result, the gap between the upper layer and the lower layer is filled with the expanded air and the gasified gas.

[0005] If the operation of welding the bus bar to the electrode terminal is continued while maintaining this state, at the instant when the molten pool at the time of welding reaches the region between the upper layer and the lower layer (the region filled with gas), the expanded air and the gasified gas are ejected to the outside, and it can not be possible to connect the bus bar and the electrode terminal well. SUMMARY

[0006] The present disclosure was achieved to solve the above-described problem, and aims to provide a welding method and a welded structure that can well weld a bus bar to an electrode terminal provided to a battery cell used in a battery pack. [1]

[0008] The welding structure of the present disclosure is configured in order from the upper side with a first metal layer, a second metal layer, and a third metal layer, and the first metal layer and the second metal layer are joined by laser welding, wherein the first metal layer and the second metal layer are the same first metal material, the third metal layer is a second metal material different from the first metal material, when the first metal layer and the second metal layer are joined by laser welding by irradiating and scanning laser from the side where the first metal layer is located, the scanning of the laser includes a first scanning process and a second scanning process thereafter, the first scanning process has a process in which the irradiation of the laser penetrates the second metal layer, and the second scanning process has a process in which the irradiation of the laser does not penetrate the second metal layer. [2]

[0010] In the welding method described in [1], the output of the laser in the first scanning process is greater than the output of the laser in the second scanning process. [3]

[0012] In the welding method described in [1], the irradiation time of the laser in the first scanning process is longer than the irradiation time of the laser in the second scanning process. [4]

[0014] In any one of the welding methods described in [1] to [3], the first metal material is aluminum, and the second metal material is copper. [5]

[0016] In any one of the welding methods described in [1] to [4], the first metal layer is a bus bar for a battery pack, the second metal layer and the third metal layer are electrode terminals that constitute the battery pack, and the bus bar is welded to the electrode terminals using the laser. [6]

[0018] The welding structure of the present disclosure is configured in order from the upper side with a first metal layer, a second metal layer, and a third metal layer, and the first metal layer and the second metal layer are joined by laser welding, wherein the first metal layer and the second metal layer are the same first metal material, the third metal layer is a second metal material different from the first metal material, the laser is irradiated and scanned from the side where the first metal layer is located, thereby joining the first metal layer and the second metal layer by laser welding, and when the welded portion of the first metal layer and the second metal layer is observed in a cross section along the irradiation direction of the laser after the laser welding, the welding depth of the welded portion of the first metal layer and the second metal layer is set to be shallower in the center than on the outside, and the welding depth on the outside penetrates the second metal layer. [7]

[0020] In the welding structure described in [6], the first metal material is aluminum and the second metal material is copper. [8]

[0022] In the welding structure described in any one of [6] or [7], the first metal layer is a bus bar for a battery pack, and the second metal layer and the third metal layer are electrode terminals constituting the battery pack.

[0023] The above and other objects, features, aspects, and advantages of the present invention will become apparent from the following detailed description of the present invention understood in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a diagram showing the basic structure of a battery pack.

[0025] Figure 2 It is showing Figure 1 a diagram of a battery cell and an end plate in the battery pack shown.

[0026] Figure 3 It is showing Figure 1 a diagram of a battery cell in the battery pack shown.

[0027] Figure 4 It is a diagram showing the arrangement of bus bars in a battery pack.

[0028] Figure 5 It is Figure 4 a partial cross-sectional view in the direction of arrow V in.

[0029] Figure 6 It is a first schematic diagram showing a welding method of an electrode terminal and a bus bar.

[0030] Figure 7 It is a second schematic diagram showing a welding method of an electrode terminal and a bus bar.

[0031] Figure 8 It is in the related art and corresponds to Figure 4 the first cross-sectional view in the direction of arrow V in.

[0032] Figure 9 It is in the related art and corresponds to Figure 4 the second cross-sectional view in the direction of arrow V in. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] Hereinafter, embodiments of the present technology will be described. The same or corresponding parts may be denoted by the same reference numerals and will not be described repeatedly.

[0034] In the embodiments described below, when numbers, quantities, etc., are mentioned, the scope of this technology is not necessarily limited to those numbers, quantities, etc., unless specifically stated otherwise. In the embodiments described below, each constituent element is not necessarily essential to this technology unless specifically stated otherwise. This technology is not limited to performing all the effects mentioned in this embodiment.

[0035] In this specification, the terms "comprise," "include," and "have" are open-ended. That is, when a structure is included, other structures besides that structure may also be included, or none may be included.

[0036] In this specification, when using geometric terms and terms indicating positional or directional relationships, such as "parallel," "orthogonal," "45° oblique," "coaxial," and "along," these terms allow for errors or slight variations. In this specification, when using terms indicating relative positional relationships such as "upper side" and "lower side," these terms are used to indicate the relative positional relationship in a single state, and the relative positional relationship can be reversed or rotated to any angle depending on the orientation of each mechanism (e.g., reversing the overall vertical orientation of the mechanism).

[0037] The battery pack 1 shown below can be installed in electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and hybrid electric vehicles (HEVs). However, the application of battery pack 1 is not limited to vehicle use.

[0038] (Battery Pack 1)

[0039] Figure 1 This is a diagram showing the basic structure of battery pack 1. Figure 2 This is a diagram showing the battery cells 100 and end plates 200 contained in battery pack 1. Figure 3 This is a diagram showing the individual battery cell 100 in battery pack 1.

[0040] like Figure 1 , Figure 2 As shown, a battery pack 1, which is an example of an "energy storage module", includes a battery cell 100, an end plate 200, and a constraint component 300.

[0041] As an example, battery cell 100 is a lithium-ion battery, but battery cell 100 can also be other batteries such as nickel-metal hydride batteries.

[0042] Multiple battery cells 100 are arranged in a manner that runs along the Y-axis (arrangement direction). Each battery cell 100 includes electrode terminals 110. Separators (not shown) may also be clamped between the multiple battery cells 100. The multiple battery cells 100, held by two end plates 200, are pressed together by the end plates 200 and thus constrained between the two end plates 200.

[0043] End plates 200 are disposed at both ends of the battery pack 1 in the Y-axis direction (arrangement direction). End plates 200 are fixed to a base such as a housing that houses the battery pack 1.

[0044] The constraint component 300 connects the two end plates 200 to each other. The constraint component 300 is mounted on the two end plates 200.

[0045] By applying a compressive force in the Y-axis direction to the stack of multiple battery cells 100 and end plates 200, the constraint member 300 is engaged with the end plates 200. After releasing the compressive force, a tensile force is applied to the constraint member 300 connecting the two end plates 200. In response, the constraint member 300 presses the two end plates 200 together in a direction that brings them closer together.

[0046] like Figure 3 As shown, the battery cell 100 is formed into a flat, rectangular parallelepiped shape. The electrode terminals 110 include a positive terminal 111 and a negative terminal 112. The electrode terminals 110 are formed on the upper surface of a square frame 120. Electrode bodies (not shown) and electrolyte are housed in the frame 120. For ease of explanation of the shape of the battery cell 100, in the following description, the X direction will sometimes be referred to as the width direction, the Y direction as the thickness direction, and the Z direction as the height direction.

[0047] Figure 4 This diagram shows the configuration of the busbar 400 in battery pack 1. Figure 4 In the example, the positive terminal 111 and negative terminal 112 of adjacent battery cells 100 are electrically connected through busbar 400, so that multiple battery cells 100 are electrically connected in series.

[0048] That is, the battery pack 1 includes a plurality of battery cells 100, each having an electrode terminal 110 and arranged in a predetermined direction, and a busbar 400 connecting the electrode terminals 110 of the plurality of battery cells 100 to each other.

[0049] (Welding methods and welding structures)

[0050] Next, refer to Figures 5-7 The welding method and welding structure between the electrode terminal 110 and the busbar 400 will be described. As an example of the electrode terminal 110, the case of welding the negative terminal 112 to the busbar 400 will be described.

[0051] The busbar 400 (first metal layer) is made of aluminum. The negative terminal 112 has a first electrode component 112a connected to a battery element (not shown) disposed inside the battery cell 100, and a second electrode component 112b disposed in a manner that covers the first electrode component 112a and is integral with the first electrode component 112a. Since the busbar 400 is fixed to the second electrode component 112b by welding, the second electrode component 112b is made of aluminum (second metal layer). In order to improve the electrical connection with the battery element (not shown) disposed inside the battery cell 100, the first electrode component 112a is made of copper (third metal layer).

[0052] As described above, the negative terminal 112 is provided in such a way that the first electrode component 112a and the second electrode component 112b are integrated, but a plurality of air layers A are formed between the first electrode component 112a and the second electrode component 112b. Furthermore, organic matter P inevitably exists in these air layers A. For ease of explanation, the air layers A and the organic matter P are shown in scaled-up, regardless of their actual size.

[0053] Busbar 400 and negative terminal 112 are sequentially provided with a first metal layer, a second metal layer, and a third metal layer from top to bottom. The first metal layer and the second metal layer are joined by laser welding. The first metal layer and the second metal layer are made of the same first metal material (aluminum), and the third metal layer is made of a different second metal material (copper).

[0054] like Figure 6 As shown, the busbar 400 and the second electrode component 112b are fixed by welding using laser L11. In this embodiment, the scanning process of laser welding, which involves irradiating the busbar 400 side with laser L11 to join the busbar 400 and the second electrode component 112b by laser welding, includes a first scanning process LS1 and a subsequent second scanning process LS2. The first scanning process LS1 involves irradiating the second electrode component 112b with laser L11, and the subsequent second scanning process LS2 involves irradiating the second electrode component 112b with laser but penetrating it.

[0055] Here, the process of penetrating the second electrode component 112b by irradiation of the laser L11 in the first scanning process LS1 refers to a process that includes penetrating the second electrode component 112b by intentionally controlling the irradiation of the laser L11. Therefore, before and after the process of penetrating the second electrode component 112b, there may sometimes be processes that do not penetrate the second electrode component 112b.

[0056] Furthermore, the so-called process in which the irradiation of the laser L11 in the second scanning process LS2 does not penetrate the second electrode component 112b refers to a process in which the irradiation of the laser L11 is intentionally controlled to prevent penetration of the second electrode component 112b. Therefore, before and after the process in which the laser L11 does not penetrate the second electrode component 112b, there may sometimes be processes in which the laser L1111b is unintentionally (unavoidably) penetrated.

[0057] like Figure 6 As shown, in the first scanning process LS1, there is a process of controlling the irradiation of the laser to penetrate the second electrode component 112b. In this way, by forming the molten pool W during welding in a manner that penetrates the second electrode component 112b in the initial stage, the molten pool W reaches the air layer A formed between the first electrode component 112a and the second electrode component 112b.

[0058] At this time, in the case of air that has expanded due to the heat of the laser and gas that has vaporized organic matter P, the expanded air and gas can be released to the outside from the gap of the molten pool in advance (arrow R in the figure).

[0059] After that, Figure 7 In the second scanning process LS2 shown, the irradiation of laser L11 is controlled to perform a welding process that does not penetrate the second electrode component 112b.

[0060] In the irradiation control of laser L11 in the first scanning step LS1 and the second scanning step LS2, various control methods can be considered. For example, a method can be given to make the output of laser L11 in the first scanning step greater than the output of laser L11 in the second scanning step.

[0061] For example, as one example, the thickness of the busbar 400 is about 0.5 to 1 mm, the thickness of the first electrode component 112a is about 0.5 to 1 mm, the thickness of the second electrode component 112b is about 1 to 2 mm, in the first scanning process LS1, the output of the laser L11 is 1800 W, the scanning speed is 400 mm / s, and the irradiation time is 10 msec, and in the second scanning process LS2, the output of the laser L11 is 1500 W, the scanning speed is 400 mm / s, and the irradiation time is 10 msec.

[0062] Furthermore, as another control method, one example is to make the irradiation time of laser L11 in the first scanning step LS1 longer than the irradiation time of laser in the second scanning step KS2.

[0063] For example, as one example, the thickness of the busbar 400 is about 0.5 to 1 mm, the thickness of the first electrode component 112a is about 0.5 to 1 mm, the thickness of the second electrode component 112b is about 1 to 2 mm, in the first scanning process LS1, the output of the laser L11 is 1500 W, the scanning speed is 200 mm / s, and the irradiation time is 10 msec, and in the second scanning process LS2, the output of the laser L11 is 1500 W, the scanning speed is 400 mm / s, and the irradiation time is 20 msec.

[0064] By employing the above welding method, in the welded structure, such as Figure 7 As shown, when viewed in a cross-section along the irradiation direction of laser L11 after laser welding, the welding depth of the welded portion between the busbar 400 and the second electrode component 112b is set to be shallower in the center than on the outside, and the welding depth on the outside becomes a cross-sectional structure that penetrates the second electrode component 112b.

[0065] Furthermore, as a construction of the related technology, refer to Figure 8 and Figure 9 Explanation will be provided. In Figure 8 and Figure 9 The diagram shows the case where the output and scanning speed of the laser L11 are constant when the busbar 400 is welded and fixed to the second electrode component 112b. The output of the laser L11 is controlled to not penetrate the second electrode component 112b, but it is heated by the heat of the laser, and heat gradually accumulates, causing the welding depth of the weld between the busbar 400 and the second electrode component 112b to gradually increase.

[0066] As a result, the weld reaches air layer A midway through the laser L11 scan. Consequently, in air layer A, the pressure of the initially expanded air and vaporized gas from the welding process increases, and at the instant the weld reaches air layer A, the expanded air and vaporized gas are ejected outward (arrow E in the figure).

[0067] Thus, according to the welding method in this embodiment, the expanded air and vaporized gas present in the air layer A can be released to the outside in the initial stage, and the ejection of the expanded air and vaporized gas to the outside can be suppressed.

[0068] As a result, the busbar 400 can be well welded to the electrode terminals 110 of the battery cell 100 used in the battery pack 1.

[0069] Furthermore, the above description describes the case where the busbar 400 is welded to the electrode terminal 110 provided on the battery cell 100, but it is not limited to this application example and can be applied to connection parts with the same structure.

[0070] Embodiments of the present invention have been described, but the embodiments disclosed herein should be considered as illustrative in all respects and not restrictive. The scope of the invention is set forth in the claims and is intended to include all modifications of the same meaning and scope as the claims.

Claims

1. A welding method comprising a first metal layer, a second metal layer, and a third metal layer sequentially disposed from top to bottom, wherein the first metal layer and the second metal layer are joined by laser welding. The welding method is characterized in that... The first metal layer and the second metal layer are made of the same first metal material. The third metal layer is a second metal material that is different from the first metal material. When the first metal layer and the second metal layer are joined by laser welding by irradiating and scanning a laser from the side where the first metal layer is located, The laser scanning process includes a first scanning step and a subsequent second scanning step. The first scanning process includes the step of the laser irradiating through the second metal layer. The second scanning process includes a process in which the laser irradiation does not penetrate the second metal layer.

2. The welding method according to claim 1, characterized in that, The laser output in the first scanning step is greater than the laser output in the second scanning step.

3. The welding method according to claim 1, characterized in that, The laser irradiation time in the first scanning process is longer than the laser irradiation time in the second scanning process.

4. The welding method according to claim 1, characterized in that, The first metallic material is aluminum. The second metallic material is copper.

5. The welding method according to claim 1, characterized in that, The first metal layer is used for the busbar of the battery pack. The second and third metal layers are electrode terminals constituting the battery pack, and the busbar is welded to the electrode terminals using the laser.

6. A welding structure comprising a first metal layer, a second metal layer, and a third metal layer sequentially disposed from top, wherein the first metal layer and the second metal layer are joined by laser welding. The welded structure is characterized in that... The first metal layer and the second metal layer are made of the same first metal material. The third metal layer is a second metal material that is different from the first metal material. A laser is irradiated and scanned from the side containing the first metal layer, thereby joining the first metal layer and the second metal layer by laser welding. When observing a cross-section along the direction of laser irradiation after laser welding, The welding depth of the weld between the first metal layer and the second metal layer is set such that the center is shallower than the outer side, and The welding depth on the outer side extends through the second metal layer.

7. The welded structure according to claim 6, characterized in that, The first metallic material is aluminum. The second metallic material is copper.

8. The welded structure according to claim 6, characterized in that, The first metal layer is used for the busbar of the battery pack. The second metal layer and the third metal layer are the electrode terminals constituting the battery pack.

Images