Clad material for laser welding, joint structure using the same, and battery manufacturing method

Abstract

To provide a clad material for laser welding which enables downsizing of a joint structure involving joint between dissimilar metals, enables reduction of a space in which the joint structure is disposed, and is suitable for laser welding.SOLUTION: A clad material 1 for laser welding comprises: an Al layer 1a formed of pure aluminum or aluminum alloy; and an Fe layer 1b joined to the Al layer 1a by rolling and formed of iron-based alloy. A thickness of the Al layer 1a ranges from 20 μm to 140 μm. The clad material 1 for laser welding is laser-welded to another member by laser radiation from the Al layer 1a side.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a clad material for laser welding, a joint structure using the clad material for laser welding, and a method for manufacturing a battery. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in the field of battery packs for vehicle applications and the like that require impact resistance, battery packs that are made up of a plurality of batteries with a structure in which bus bars are joined to terminals have been known (see, for example, Patent Document 1).

[0003] The above-mentioned Patent Document 1 discloses an assembled battery (battery pack) made up of multiple batteries and suitable for in-vehicle use. In Patent Document 1, multiple batteries are arranged side by side, and adjacent batteries are connected by bus bars (lead plates). The bus bars are also welded to the terminals of the batteries.

[0004] Although not disclosed in Patent Document 1, there are cases where the battery terminal is made of an iron-based alloy and the bus bar is made of pure aluminum or an aluminum alloy. A battery terminal made of an iron-based alloy and a bus bar made of pure aluminum or an aluminum alloy have a disadvantage in that a brittle intermetallic compound is formed at the joint between the battery terminal and the bus bar, reducing the joint strength, due to the welding of dissimilar metals.

[0005] Therefore, it has been proposed to place a clad insert material between the bus bar and the battery terminal (see, for example, Patent Document 2).

[0006] Patent Document 2 discloses a clad insert material suitable for resistance welding, in which steel and aluminum are overlapped and joined. In Patent Document 2, a steel layer of the clad insert material, which is an iron-based alloy, is resistance welded to a surface-treated steel plate, and an aluminum layer of the clad insert material is resistance welded to an aluminum plate. Specifically, the surface-treated steel plate, the clad insert material, and the aluminum plate are overlapped in this order, and then sandwiched between a pair of electrodes for resistance welding to perform resistance welding. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2008-66001 A [Patent Document 2] Japanese Patent Application Publication No. 7-155964 Summary of the Invention [Problem to be solved by the invention]

[0008] Resistance welding is a welding method that uses Joule heat generated at the welded area due to the contact resistance between the metals to be welded or Joule heat generated due to the resistance of the metals to be welded themselves to melt and weld the welded area. Resistance welding involves a significant energy loss in welding a narrow area because the generated heat is easily lost by being conducted to the metals to be welded and the electrodes. For this reason, it is considered that the thickness of the aluminum layer that is easily melted with a smaller amount of heat is specified to be more than 0.2 mm (claim 1) in the clad insert material disclosed in the above Patent Document 2. Therefore, it is considered that the clad insert material used in a welding method that melts and joins the joints, such as resistance welding, needs to ensure (sufficiently large) the thickness of the aluminum layer with a low melting point.

[0009] In addition, when the clad insert material disclosed in the above Patent Document 2 is used for resistance welding, it is necessary to arrange a pair of electrodes that sandwich the clad insert material. However, depending on the structure of the assembled battery, the space may be small and it may be difficult to arrange electrodes for each battery. In such cases, laser welding, which does not require electrodes as in resistance welding and is advantageous in saving space, has been proposed. Note that, when using a clad insert material for laser welding, which melts and joins the welded parts by irradiating a laser, it is also considered necessary to ensure a sufficient thickness (sufficiently large) of the aluminum layer, which has a low melting point.

[0010] In recent years, the use of electric vehicles has rapidly increased, driven by environmental issues such as global warming, and this has led to a strong demand for improved performance and downsizing (miniaturization) of on-board battery packs. Therefore, there is an urgent need to improve the performance of battery packs and to downsize the numerous joint structures that make up the battery packs. However, the clad insert material disclosed in the above Patent Document 2 has a problem in that it is difficult to downsize it because the thickness of the aluminum layer needs to be sufficiently large.

[0011] The present invention has been made to solve the problem of downsizing the joint structure that constitutes the above-mentioned assembled battery, and one object of the present invention is to provide a clad material for laser welding that enables downsizing of a joint structure involving joining dissimilar metals and is suitable for laser welding that can reduce the space required to arrange the joint structure, a joint structure using a clad material for laser welding, and a method for manufacturing a battery. [Means for solving the problem]

[0012] In order to achieve the above object, the inventors of the present application have focused on the configuration of the aluminum layer (Al layer) of the clad insert material disclosed in the above Patent Document 2, and have conducted extensive research to develop a clad material (clad insert material) suitable for laser welding, and have found the following configuration: That is, the clad material for laser welding according to a first aspect of the present invention is a clad material for laser welding to be laser welded to another member made of an iron-based alloy, and is composed of an Al layer made of pure aluminum or an aluminum alloy, and an Fe layer made of an iron-based alloy and roll-bonded to the Al layer, the thickness of the Al layer being 20 μm or more and 140 μm or less, and the Fe layer is laser welded to the other member by laser irradiation from the Al layer side.

[0013] As described above, the laser welding clad material according to the first aspect of the present invention is composed of an Al layer made of pure aluminum or an aluminum alloy, and an Fe layer made of an iron-based alloy and roll-bonded to the Al layer, and the thickness of the Al layer is 20 μm or more and 140 μm or less, and is laser-welded to another member by laser irradiation from the Al layer side. Since the thickness of the Al layer is 20 μm or more, the Al layer, which has a melting point sufficiently lower than that of the Fe layer, is quickly melted by laser irradiation from the Al layer side, so that heat is quickly transferred from the molten Al layer to the Fe layer, and the laser welding clad material can be quickly melted in the thickness direction. As a result, it is possible to provide a laser welding clad material to which general laser welding, which does not involve a large energy loss like resistance welding, can be applied when joining the laser welding clad material to another member made of an iron-based alloy.

[0014] Furthermore, since the thickness of the Al layer is 140 μm or less, an amount of Al suitable for laser welding (thickness of the Al layer) is ensured, while the absence of an excessive amount of Al (thickness of the Al layer) prevents the thickness of the clad material for laser welding from becoming excessively large. As a result, the entire clad material for laser welding can be made thinner, and therefore it is possible to downsize a joining structure in which dissimilar metals are joined using the clad material for laser welding.

[0015] In addition, by making the thickness of the Al layer 20 μm or more and 140 μm or less, the protruding height of the protruding portion formed on the laser irradiated side of the Al layer due to the volume change when the Al layer melted by the laser irradiation is solidified can be reduced. As a result, the protruding height of the protruding portion formed on the exposed surface of the Al layer due to the laser welding is small, and the entire clad material for laser welding can be thinned, so that the joint structure in which dissimilar metals are joined together using the clad material for laser welding can be downsized. The inventors of the present application have found through experiments (examples) described below that the above effect can be obtained by making the thickness of the Al layer 20 μm or more and 140 μm or less. In addition, by making it possible to downsize the joint structure, the space in which the joint structure is arranged can be reduced. As a result of these, the joint structure involving the joining of dissimilar metals can be downsized, and the space in which the joint structure is arranged can be reduced.

[0016] In the cladding material for laser welding according to the first aspect, the thickness of the Al layer is preferably 40 μm or more and 140 μm or less. With this configuration, the proportion of the volume change that occurs when the Al layer melted by laser irradiation solidifies is contained within the Al layer, and it has been found through an experiment described later that the protruding height of the protrusion formed on the exposed surface of the Al layer on the laser irradiation side can be made smaller.

[0017] A joint structure using a clad material for laser welding according to a second aspect of the present invention includes an Al layer made of pure aluminum or an aluminum alloy, an Fe layer made of an iron-based alloy and roll-bonded to the Al layer, the Al layer having a thickness of 20 μm or more and 140 μm or less, and another member made of an iron-based alloy and laser-welded to the Fe layer, and the Fe layer is laser-welded to the other member by laser irradiation from the Al layer side.

[0018] In the joining structure using the clad material for laser welding according to the second aspect of the present invention, as described above, the Al layer is made of pure aluminum or an aluminum alloy, and the Fe layer is roll-joined to the Al layer and made of an iron-based alloy, and the thickness of the Al layer is 20 μm or more and 140 μm or less, and the Al layer is laser-welded to another member by laser irradiation from the Al layer side. Since the thickness of the Al layer is 20 μm or more, the Al layer, which has a sufficiently lower melting point than the Fe layer, is quickly melted by laser irradiation from the Al layer side, so that heat transfer from the molten Al layer to the Fe layer is quickly performed, and the clad material for laser welding can be quickly melted in the thickness direction. As a result, since general laser welding can be applied as described above, a joining structure involving joining by laser welding of dissimilar metals using the clad material for laser welding can be provided.

[0019] In addition, since the thickness of the Al layer is 140 μm or less, an amount of Al suitable for laser welding (thickness of the Al layer) is ensured, while an excessive amount of Al (thickness of the Al layer) is not present, and therefore the thickness of the clad material for laser welding can be prevented from becoming excessively large. As a result, as described above, it is possible to downsize the joining structure in which dissimilar metals are joined using the clad material for laser welding.

[0020] In addition, by making the thickness of the Al layer 20 μm or more and 140 μm or less, the protruding height of the protruding portion formed on the laser irradiated side of the Al layer due to the volume change when the Al layer melted by the laser irradiation is solidified can be reduced. As a result, as described above, the joint structure in which dissimilar metals are joined using the clad material for laser welding can be downsized. The inventors of the present application have found through experiments (examples) described below that the above effects can be obtained by making the thickness of the Al layer 20 μm or more and 140 μm or less. In addition, by making it possible to downsize the joint structure, the space in which the joint structure is arranged can be reduced. As a result of these, the joint structure involving the joining of dissimilar metals can be downsized, and the space in which the joint structure is arranged can be reduced.

[0021] In the joint structure using the clad material for laser welding according to the second aspect, the length in the direction of extension of the molten portion formed on the joint surface by laser welding between the Fe layer and another member is preferably 40 μm or more. With this configuration, the joint strength between the clad material for laser welding and the other member can be appropriately increased. The inventors of the present application have found through experiments (examples) described below that the above effect can be obtained by setting the length in the direction of extension of the molten portion on the joint surface to 40 μm or more.

[0022] In the joining structure using the clad material for laser welding according to the second aspect, preferably, the protrusion height of the protrusion formed on the exposed surface of the Al layer opposite to the surface where the Fe layer is roll-joined by the laser irradiation from the Al layer side is 20 μm or less. With this configuration, the protrusion height is sufficiently small, so that the protrusion can be prevented from contacting members other than the clad material for laser welding. As a result, the risk that the protrusion will be damaged by contact with members other than the clad material for laser welding and that the operation of the joining structure and the assembled battery will become unstable due to fragments of the damaged protrusion can be reduced.

[0023] In this case, preferably, the thickness of the Al layer is 40 μm or more and 140 μm or less, and the protrusion height of the protrusion formed on the exposed surface of the Al layer opposite to the surface where the Fe layer is roll-bonded by irradiating the laser from the Al layer side to the Fe layer side is 15 μm or less. With this configuration, the protrusion height of the protrusion is 15 μm or less, so that the protrusion can be further prevented from contacting members other than the clad material for laser welding. As a result, the risk of the joint structure and the operation of the battery pack becoming unstable due to the protrusion contacting members other than the clad material for laser welding can be further reduced. Note that the inventors of the present application have found through experiments described below that the protrusion height of the protrusion can be 15 μm or less by setting the thickness of the Al layer to 40 μm or more and 140 μm or less.

[0024] A battery manufacturing method according to a third aspect of the present invention includes the steps of: preparing a clad material for laser welding by roll-bonding an Al plate material made of pure aluminum or an aluminum alloy and an Fe plate material made of an iron-based alloy, the clad material being composed of an Al layer and an Fe layer, the Al layer having a thickness of 20 μm or more and 140 μm or less; bonding a battery terminal member made of an iron-based alloy to the Fe layer; bonding one end of an Al-based wire for bonding to the Al layer by wire bonding; and bonding the other end of the Al-based wire to a bus bar made of pure aluminum or an aluminum alloy.

[0025] The method for manufacturing a battery according to the third aspect of the present invention includes the step of preparing a clad material for laser welding, which is composed of an Al layer and an Fe layer, and has a thickness of 20 μm to 140 μm, by rolling and bonding an Al plate material made of pure aluminum or an aluminum alloy and an Fe plate material made of an iron-based alloy, as described above. Since the thickness of the Al layer is 20 μm or more, the Al layer, which has a melting point sufficiently lower than that of the Fe layer, is quickly melted by laser irradiation from the Al layer side, so that heat is quickly transferred from the molten Al layer to the Fe layer, and the clad material for laser welding can be quickly melted in the thickness direction. As a result, a battery can be manufactured by applying general laser welding as described above.

[0026] In addition, since the thickness of the Al layer is 140 μm or less, an amount of Al (thickness of the Al layer) suitable for laser welding is ensured, while an excessive amount of Al (thickness of the Al layer) is not present, and therefore the thickness of the clad material for laser welding can be prevented from becoming excessively large. As a result, as described above, this is advantageous for downsizing the joint structure in which dissimilar metals are joined using the clad material for laser welding, and therefore a battery that can be downsized appropriately can be manufactured. In addition, since the joint structure can be downsized, the space for arranging the joint structure can be reduced, and therefore a battery that can be downsized can be manufactured.

[0027] In addition, by making the thickness of the Al layer 20 μm or more and 140 μm or less, the protruding height of the protrusion formed on the laser irradiated side of the Al layer due to the volume change when the Al layer melted by the laser irradiation is solidified can be reduced. As a result, as described above, it is advantageous for downsizing the joint structure in which dissimilar metals are joined using the clad material for laser welding, so that a battery that can be appropriately downsized can be manufactured. Note that the inventors of the present application have found through experiments (examples) described below that the above effects can be obtained by making the thickness of the Al layer 20 μm or more and 140 μm or less. As a result, it is possible to downsize the joint structure involving the joining of dissimilar metals, and to reduce the space in which the joint structure is arranged. Effect of the Invention

[0028] According to the present invention, it is possible to provide a clad material for laser welding, a joint structure using a clad material for laser welding, and a method for manufacturing a battery, which are suitable for laser welding that enables downsizing of a joint structure involving joining of different metals and reduces the space required for arranging the joint structure. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a diagram showing a battery pack according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing an example of a clad material for laser welding according to the present embodiment. [Diagram 3] FIG. 2 is a diagram showing a state in which a clad material for laser welding according to the present embodiment and a lid material are joined together. [Figure 4] 1 is a diagram showing a laser irradiation position on a laser welding clad material when the laser welding clad material according to the present embodiment is laser welded to a battery terminal. FIG. [Diagram 5] FIG. 1 is a cross-sectional view showing a part of a joint structure using a clad material for laser welding, in a state where the clad material for laser welding is laser welded to a lid material. [Figure 6]FIG. 2 is a diagram showing an example of a unit cell according to the present embodiment. [Figure 7] 1A to 1C are diagrams illustrating a method for manufacturing a clad material for laser welding according to an embodiment of the present invention. [Figure 8] 1A to 1C are diagrams for explaining a method of joining the laser welding clad material according to the present embodiment to a battery terminal. [Figure 9] 1A to 1C are diagrams for explaining a wire bonding method according to an embodiment of the present invention. [Figure 10] 1 is a graph showing the relationship between the thickness of an Al layer of a laser welding clad material and the joint strength, fusion width, penetration depth, and protrusion height. [Figure 11] FIG. 13 is a diagram showing a battery pack according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0031] As shown in FIG. 1, a clad material 1 for laser welding according to an embodiment of the present invention is used in a battery pack 100. The battery pack 100 is configured by electrically connecting a plurality of lithium ion secondary batteries 10 by a bus bar 20. Note that, although the battery pack 100 is illustrated in a simplified manner in FIG. 1, the number of lithium ion secondary batteries 10 constituting the battery pack 100 for vehicle use or the like is greater than that shown in FIG. 1. The battery pack 100 for vehicle use is a large battery system mounted in an electric vehicle (EV) or a hybrid electric vehicle (HEV). Note that the battery pack 100 is an example of a "battery" as described in the claims.

[0032] As shown in Fig. 2, the laser welding clad material 1 is composed of an Al layer 1a and an Fe layer 1b. In Fig. 2, the laser welding clad material 1 has a circular shape, but the shape of the laser welding clad material 1 is not limited to this.

[0033] The Al layer 1a is made of pure aluminum or an aluminum alloy. The pure aluminum has an aluminum content of 99% or more and 100% or less, such as the A1000 series of JIS standards including A1050. The aluminum alloy is an alloy in which other elements such as Mn or Mg are added to Al, such as the A3000 series of JIS standards including A3003 and the A5000 series of JIS standards including A5052.

[0034] The Fe layer 1b is made of an iron-based alloy. The iron-based alloy is an alloy in which Fe is the largest among the constituent metal elements. Among the iron-based alloys, those containing about 10 mass% or more of Cr are called stainless steel. The iron-based alloy constituting the Fe layer 1b is preferably a stainless steel that is an iron-based alloy containing 10 mass% or more of Cr from the viewpoint of durability. Furthermore, the iron-based alloy constituting the Fe layer 1b is preferably a ferritic stainless steel that is a stainless steel that does not contain Ni in order to reduce the difference in hardness with the Al layer 1a. The ferritic stainless steel is a stainless steel that contains 16 mass% to 18 mass% of Cr and has a main metal structure of a ferrite phase with a body-centered cubic lattice structure even at room temperature, such as SUS430.

[0035] As shown in Fig. 2 and Fig. 5, the total thickness t1 of the laser welding clad material 1 is 200 μm or more and 400 μm or less. The thickness t2 of the Al layer 1a is 20 μm or more and 140 μm or less. The thickness t2 of the Al layer 1a is set to 20 μm or more in order to quickly melt the Al layer 1a, which has a melting point sufficiently lower than that of the Fe layer 1b, by laser irradiation from the Al layer 1a side, quickly transfer heat from the Al layer 1a to the Fe layer 1b, and quickly melt toward the Z2 side in the thickness direction (Z direction) of the laser welding clad material 1. The thickness t2 of the Al layer 1a is set to 140 μm or less in order to prevent the total thickness t1 of the laser welding clad material 1 from becoming excessively large by preventing the presence of an excessive amount of Al while ensuring an amount of Al suitable for laser welding. In addition, the thickness t2 of the Al layer 1a is set to be 20 μm or more and 140 μm or less in order to reduce the protrusion height x3 of the protrusion 1d formed on the laser irradiated side of the Al layer 1a due to the volume change when the Al layer melted by laser irradiation solidifies.

[0036] In order to prevent a part of the Al layer 1a from peeling off by setting the protruding height x3 of the protruding portion 1d formed on the exposed surface 1c (Z1 side surface) of the Al layer 1a, which is the surface of the Al layer 1a opposite to the surface bonded to the Fe layer 1b, to 20 μm or less, the thickness t2 of the Al layer 1a is set to 20 μm or more. In order to further prevent a part of the Al layer 1a from peeling off by setting the protruding height x3 of the protruding portion 1d formed on the exposed surface 1c (Z1 side surface) of the Al layer 1a to 15 μm or less, the thickness t2 of the Al layer 1a is preferably set to 40 μm or more and 140 μm or less.

[0037] As shown in FIG. 3, a terminal (negative terminal or positive terminal) made of an iron-based alloy of a lithium-ion secondary battery 10 is joined to the Fe layer 1b of the laser welding clad material 1. FIG. 3 shows a configuration example in which a lid material 12 made of an iron-based alloy, which is a positive terminal, is joined to the Fe layer 1b. The joining method is laser welding. By irradiating the Al layer 1a with a laser from the Z1 side, the Al layer 1a and the Fe layer 1b melt in the Z direction and a part of the lid material 12 melts, and the laser welding clad material 1 and the lid material 12 are joined. The type of laser may be selected according to various conditions such as the joining structure, and is not limited. The lid material 12 is an example of the "other member" and the "electronic terminal member" described in the claims.

[0038] For example, when the clad material 1 for laser welding has a circular shape, the Al layer 1a can be irradiated with a laser in a circular shape within the region where the clad material 1 for laser welding and the lid material 12 overlap, as shown by the dashed line in Fig. 4 which shows the laser irradiation position on the clad material 1 for laser welding. For example, when the diameter of the clad material 1 for laser welding and the lid material 12 is about 23 mm, the laser can be irradiated in a circular shape with a diameter of about 20 mm or less (for example, 15 mm).

[0039] For example, when the laser is irradiated from the Z1 side of the Al layer 1a to laser weld the clad material 1 for laser welding to the lid material 12, the clad material 1 for laser welding melts by the laser irradiation and melts into the lid material 12 side, as shown by the two-dot chain line in FIG. 5 showing a part of the joint structure. At this time, the length (melting width) x1 of the melted portion formed on the joint surface 1e by laser welding between the Fe layer 1b of the clad material 1 for laser welding and the lid material 12 in the extending direction (X direction) of the joint surface 1e is preferably 40 μm or more. Note that FIG. 5 shows an XZ cross section, but the joint surface 1e of the melted portion is parallel to the XY plane. Also, in FIG. 5, the extending direction of the joint surface 1e of the melted portion is the X direction, but the extending direction of the joint surface 1e may be the Y direction.

[0040] The penetration depth x2 shown in Fig. 5 may be 50 µm or more and 130 µm or less. With this configuration, the lid material 12 can be thinned while being bonded to the laser welding clad material 1 with an appropriate bonding strength. As a result, the bonding structure between dissimilar metals using the laser welding clad material 1 can be downsized. The penetration depth refers to the amount (length) of the lid material 12 melted in the Z direction by laser irradiation, based on the bonding surface 1e of the melted portion.

[0041] On the exposed surface 1c of the Al layer 1a, due to a volume change when the Al layer 1a melted by the laser irradiation solidifies, a protrusion 1d is formed on the opposite side (Z1 side) from the lid member 12 (Fe layer 1b) as shown in Fig. 5. The protrusion height x3 of the protrusion 1d is preferably 20 µm or less in order to suppress damage to the protrusion 1d. Moreover, the protrusion height x3 of the protrusion 1d is more preferably 15 µm or less in order to further suppress damage to the protrusion 1d.

[0042] A bus bar 20 is bonded to the exposed surface 1c of the Al layer 1a. For bonding to the bus bar 20, for example, wire bonding is used. Specifically, as shown in Fig. 9, one end of an Al-based wire 2 for bonding is bonded to the Al layer 1a by wire bonding, and the other end of the Al-based wire 2 for bonding is bonded to a recess 20a of the bus bar 20 by wire bonding. The Al-based wire 2 is made of pure aluminum or an aluminum alloy.

[0043] (Lithium-ion secondary battery) 6, lithium ion secondary battery 10 includes cylindrical housing 11, a cover member 12 that seals an opening of housing 11, and an electricity storage element 13 disposed within housing 11. Housing 11 is made of Ni-plated steel sheet, and also serves as the negative terminal of lithium ion secondary battery 10.

[0044] The housing 11 contains an electricity storage element 13 and an electrolyte (not shown). The cover member 12 is made of an iron-based alloy and also serves as the positive electrode terminal of the lithium-ion secondary battery 10. The electricity storage element 13 is formed by winding a positive electrode 14, a negative electrode 15, and an insulating separator 16 disposed between the positive electrode 14 and the negative electrode 15. The positive electrode 14 includes a positive electrode current collector (not shown) made of aluminum foil, and a positive electrode active material layer (not shown) disposed on the surface of the positive electrode current collector. The positive electrode active material layer has a positive electrode active material such as lithium manganate, and a binder made of a resin material.

[0045] The lithium ion secondary battery 10 further includes a positive electrode lead material 17 for connecting the positive electrode 14 and the positive electrode terminal (lid material 12), and a negative electrode lead material 18 for connecting the negative electrode 15 and the negative electrode terminal (casing 11). The positive electrode lead material 17 is made of aluminum foil, and is joined to the positive electrode current collector of the positive electrode 14 and the lid material 12 by resistance welding or the like. The negative electrode lead material 18 is made of copper foil, and is joined to the negative electrode current collector of the negative electrode 15 and the casing 11 by resistance welding or the like.

[0046] As shown in FIG. 1, the busbar 20 is made of pure aluminum or an aluminum alloy. The busbar 20 electrically connects between terminals (negative electrode terminal, positive electrode terminal) of the lithium ion secondary battery 10. In this embodiment, the busbar 20 has a plate shape and electrically connects between the positive electrode terminals of a plurality of single cells (lithium ion secondary batteries 10). In this embodiment, the laser welding clad material 1 is disposed between the busbar 20 and the positive electrode terminal of the lithium ion secondary battery 10. Also, as shown in FIG. 1, a recess 20a is provided in a portion of the busbar 20 to which the Al-based wire 2 is joined. Note that, while FIG. 1 shows an example in which the recess 20a is provided on one side (X1 side) in the short direction, the recess 20a may be provided on one side (X1 side) and the other side (X2 side) in the short direction. The busbar 20 can simultaneously connect a plurality of terminals with one busbar 20. Although not shown in FIG. 1, the negative electrode terminals are also connected to each other with another busbar. The negative electrode terminal is joined to another bus bar by laser welding, spot welding, or the like. The battery pack 100 shown in FIG. 1 is intended to show an example of the configuration of the portion connecting the positive electrode terminals to each other with the bus bar 20, and other connection portions and the like are omitted. The battery pack may be configured to connect the positive electrode terminal and the negative electrode terminal with a bus bar. The battery pack may be configured by combining a configuration in which the positive electrode terminals are connected to each other with a bus bar and the negative electrode terminals are connected to each other with a bus bar, with a configuration in which the positive electrode terminal and the negative electrode terminal are connected to each other with a bus bar.

[0047] (Battery manufacturing method) As shown in FIG. 7, an Al plate material 50a and an Fe plate material 50b are roll-bonded to prepare a clad material 1 for laser welding, which is composed of an Al layer 1a and an Fe layer 1b, and the thickness of the Al layer 1a is 20 μm or more and 140 μm or less. The Al plate material 50a is a plate material composed of the same pure aluminum or aluminum alloy as the Al layer 1a. The Fe plate material 50b is a plate material composed of the same iron-based alloy as the Fe layer 1b. In the roll-bonding, the rolling ratio (degree of processing) is set so that the thicknesses of the Al plate material 50a and the Fe plate material 50b before rolling are the same as the thicknesses of the Al layer 1a and the Fe layer 1b after rolling. Although not shown in FIG. 7, diffusion annealing may be performed after the roll-bonding of the Al plate material 50a and the Fe plate material 50b. In addition, softening annealing may be performed before the roll-bonding of the Al plate material 50a and the Fe plate material 50b. In addition, after the Al plate material 50a and the Fe plate material 50b are roll-bonded, further rolling may be performed to obtain a desired thickness for the Al layer 1a and a desired thickness for the Fe layer 1b. In addition, softening annealing may be performed before further rolling. The produced clad material 1 for laser welding is then processed into, for example, a circular shape. The method of processing into a circular shape may be performed by punching the clad material 1 for laser welding. The diameter of the clad material 1 for laser welding formed into a circular shape is set to be suitable for the diameter of the terminal to be joined.

[0048] When constructing the battery pack 100 shown in FIG. 1, as shown in FIG. 8, the Fe layer 1b of the laser welding clad material 1 is joined to the battery terminal member. In FIG. 8, the battery terminal member is the cover material 12 (positive terminal). Depending on the configuration of the battery pack, the negative terminal (outer bottom surface of the housing 11) can also be joined to the Fe layer 1b of the laser welding clad material 1. The method for joining the Fe layer 1b of the laser welding clad material 1 to the battery terminal member is laser welding. In laser welding, the laser irradiation unit 40 is disposed on the Al layer 1a side (Z1 side) and laser irradiation is performed. For example, the laser irradiation is performed so as to form a circular trajectory along the outer periphery of the circular laser welding clad material 1 as shown by the dashed line in FIG. 4. As a result, a joining structure involving joining of dissimilar metals constituted by the laser welding clad material 1 and the cover material 12 is formed.

[0049] 9, after the laser welding clad material 1 is joined to the battery terminal member, the bus bar 20 is joined to the Al layer 1a. The method of joining the bus bar 20 to the Al layer 1a includes joining one end of an Al-based wire 2 for joining to the Al layer 1a by wire bonding, and joining the other end of the Al-based wire 2 to the recess 20a of the bus bar 20 by wire bonding.

[0050] Wire bonding can be performed in two ways: one in which one end and the other end of the Al-based wire 2 are melted to form a ball-shaped joint, and the other in which a ball-shaped joint is not formed. Methods for bonding one end and the other end of the Al-based wire 2 to the Al layer 1a and the bus bar 20, respectively, include a method using heat, a method using pressure, a method using ultrasonic waves, or a method using a suitable combination of heat, pressure, ultrasonic waves, etc. When ultrasonic waves are used, for example, ultrasonic vibration is applied while one end of the wire is pressed against the Al layer 1a of the laser welding clad material 1 by a tool 50 to generate heat inside, and one end of the wire and the vicinity of the surface of the Al layer 1a are melted and bonded.

[0051] <Effects of this embodiment> In this embodiment, the following effects can be obtained.

[0052] In this embodiment, the clad material 1 for laser welding is composed of an Al layer 1a made of pure aluminum or an aluminum alloy, and an Fe layer 1b made of an iron-based alloy and roll-bonded to the Al layer 1a. The thickness of the Al layer 1a is 20 μm or more and 140 μm or less, and the Al layer 1a is laser-welded to another member by laser irradiation from the Al layer 1a side. Since the thickness of the Al layer 1a is 20 μm or more, the Al layer 1a, which has a melting point sufficiently lower than that of the Fe layer 1b, is quickly melted by laser irradiation from the Al layer 1a side, so that heat transfer from the molten Al layer 1a to the Fe layer 1b is quickly performed, and the clad material 1 for laser welding can be quickly melted in the thickness direction (Z direction). As a result, when the clad material 1 for laser welding is bonded to another member (lid material 12) made of an iron-based alloy, a clad material 1 for laser welding can be provided that can be applied with general laser welding that does not involve large energy loss like resistance welding. Moreover, since the thickness of the Al layer 1a is 140 μm or less, an amount of Al suitable for laser welding is ensured, while there is no excessive amount of Al, so that the thickness of the clad material 1 for laser welding can be prevented from becoming excessively large. As a result, the entire clad material 1 for laser welding can be thinned, so that the joint structure in which dissimilar metals are joined using the clad material 1 for laser welding can be downsized. Furthermore, since the thickness of the Al layer 1a is 20 μm or more and 140 μm or less, the protruding height of the protruding portion 1d formed on the laser irradiated side (Z1 side) of the Al layer 1a due to the volume change when the Al layer 1a melted by laser irradiation solidifies can be reduced. As a result, the protruding height of the protruding portion 1d formed on the exposed surface 1c of the Al layer 1a due to laser welding is small, and the entire clad material 1 for laser welding can be thinned, which is advantageous for downsizing the joint structure in which dissimilar metals are joined using the clad material 1 for laser welding. The inventors of the present application have found through experiments (Examples) described below that the above effects can be obtained by making the thickness of the Al layer 1a 20 μm or more and 140 μm or less. In addition, the junction structure can be downsized, so that the space required for arranging the junction structure can be reduced.As a result, it is possible to downsize a joint structure involving the joining of dissimilar metals, and also to reduce the space required for arranging the joint structure.

[0053] In this embodiment, the thickness of the Al layer 1a is 40 μm or more and 140 μm or less. This increases the proportion of the volume change that occurs when the Al layer 1a melted by laser irradiation solidifies within the Al layer 1a, and it has been found through experiments described later that the protruding height of the protruding portion 1d formed on the exposed surface 1c on the laser irradiation side (Z1 side) of the Al layer 1a can be made smaller.

[0054] In addition, the joining structure using the clad material 1 for laser welding according to the present embodiment is composed of the Al layer 1a made of pure aluminum or aluminum alloy and the Fe layer 1b made of an iron-based alloy and roll-joined to the Al layer 1a, as described above, and the thickness t2 of the Al layer 1a is 20 μm or more and 140 μm or less, and is laser-welded to the lid material 12 by laser irradiation from the Al layer 1a side. As a result, since the thickness of the Al layer 1a is 20 μm or more, the Al layer 1a, which has a sufficiently lower melting point than the Fe layer 1b, is quickly melted by laser irradiation from the Al layer 1a side (Z1 side), so that heat transfer from the molten Al layer 1a to the Fe layer 1b is quickly performed, and the clad material 1 for laser welding can be quickly melted in the thickness direction (Z direction). As a result, since general laser welding can be applied as described above, a welded structure involving joining by laser welding of dissimilar metals using the clad material 1 for laser welding can be provided. Moreover, since the thickness of the Al layer 1a is 140 μm or less, an amount of Al suitable for laser welding is ensured, while there is no excessive amount of Al, so that the thickness of the clad material 1 for laser welding can be suppressed from becoming excessively large. As a result, as described above, the clad material 1 for laser welding can be used to downsize a joint structure involving joining dissimilar metals by laser welding. Furthermore, since the thickness of the Al layer 1a is 20 μm or more and 140 μm or less, the protruding height of the protruding portion 1d formed on the laser irradiated side (Z1 side) of the Al layer 1a due to the volume change when the Al layer 1a melted by laser irradiation solidifies can be reduced. As a result, as described above, the clad material 1 for laser welding can be used to downsize a joint structure involving joining dissimilar metals by laser welding. The inventors of the present application have found through experiments (examples) described below that the above effects can be obtained by setting the thickness of the Al layer 1a to 20 μm or more and 140 μm or less. In addition, the joining structure can be downsized, which reduces the space required to place the joining structure. As a result, the joining structure involving the joining of dissimilar metals can be downsized, and the space required to place the joining structure can be reduced.

[0055] In this embodiment, the length of the molten portion formed on the joining surface 1e by laser welding between the Fe layer 1b and another member in the extending direction of the joining surface is 40 μm or more. This allows the joining strength between the laser welding clad material 1 and the other member (the lid material 12) to be appropriately increased. The inventors of the present application have found through experiments (examples) described below that the above-mentioned effects can be obtained by setting the length of the joining surface 1e of the molten portion in the extending direction (X direction) to 40 μm or more.

[0056] In addition, in this embodiment, as described above, the protrusion height of the protrusion 1d formed on the exposed surface 1c of the Al layer 1a opposite to the surface to which the Fe layer 1b of the Al layer 1a is roll-bonded by laser irradiation from the Al layer 1a side is 20 μm or less. This makes it possible to prevent the protrusion 1d from contacting members other than the laser welding clad material 1, since the protrusion height of the protrusion 1d is sufficiently small. As a result, it is possible to provide a joining structure that can prevent the risk of the protrusion 1d being damaged by contact with members other than the laser welding clad material 1, and the operation of the joining structure and the battery pack becoming unstable due to fragments of the damaged protrusion 1d.

[0057] In this embodiment, the thickness of the Al layer 1a is preferably 40 μm or more and 140 μm or less, and the protrusion height of the protrusion 1d formed on the exposed surface 1c of the Al layer 1a opposite to the surface where the Fe layer 1b of the Al layer 1a is roll-bonded by irradiating the laser from the Al layer 1a side (Z1 side) to the Fe layer 1b side is 15 μm or less. This can further prevent the protrusion 1d from contacting members other than the clad material 1 for laser welding. As a result, the risk of the joint structure and the operation of the battery pack becoming unstable due to the protrusion 1d contacting members other than the clad material 1 for laser welding can be further reduced. The inventor of the present application has found through an experiment described later that the protrusion height x3 of the protrusion 1d can be made 15 μm or less by setting the thickness of the Al layer 1a to 40 μm or more and 140 μm or less.

[0058] In addition, the manufacturing method of the battery of the present embodiment includes a step of preparing a laser welding clad material 1, which is composed of an Al layer 1a and an Fe layer 1b, and a thickness of the Al layer 1a is 20 μm or more and 140 μm or less, by rolling and joining an Al plate material 50a made of pure aluminum or an aluminum alloy and an Fe plate material 50b made of an iron-based alloy, as described above. Since the thickness of the Al layer 1a is 20 μm or more, the Al layer 1a, which has a melting point sufficiently lower than that of the Fe layer 1b, is melted quickly by laser irradiation from the Al layer 1a side (Z1 side), and heat transfer from the molten Al layer 1a to the Fe layer 1b is quickly performed, and the laser welding clad material 1 can be quickly melted in the thickness direction (Z direction). As a result, as described above, a battery can be manufactured by applying general laser welding. Furthermore, since the thickness of the Al layer 1a is 140 μm or less, an amount of Al suitable for laser welding is ensured, while an excessive amount of Al is not present, and therefore the thickness of the laser welding clad material 1 can be prevented from becoming excessively large. As a result, as described above, the laser welding clad material 1 is advantageous for downsizing the joint structure in which dissimilar metals are joined by laser welding, so that a battery capable of being appropriately downsized can be manufactured. In addition, since the thickness of the Al layer 1a is 20 μm or more and 140 μm or less, the protruding height of the protruding portion 1d formed on the laser irradiated side of the Al layer 1a due to the volume change when the Al layer 1a melted by laser irradiation is solidified can be reduced. As a result, as described above, the laser welding clad material 1 is advantageous for downsizing the joint structure involving laser welding of dissimilar metals, so that a battery capable of being appropriately downsized can be manufactured. The inventors of the present application have found through experiments (examples) described later that the above effects can be obtained by making the thickness of the Al layer 1a 20 μm or more and 140 μm or less. As a result, the joint structure involving the joining of dissimilar metals can be downsized, and the space for arranging the joint structure can be reduced.

[0059] [Example] We will explain an experiment (example) in which the joint strength, fusion width x1, penetration depth x2, and protrusion height x3 of protrusion 1d of the laser weld formed by laser welding as shown in Figure 5 were measured and evaluated for a joint structure in which a test piece, a clad material for laser welding 1, was joined to another member made of an iron-based alloy by laser welding.

[0060] First, as test specimens having an Al layer 1a, six types of clad materials 1 for laser welding (Examples 1 to 5 and Comparative Example 2) were prepared, each having a total thickness t1 of 300 μm, an Al layer 1a made of A1050, and an Fe layer 1b made of SUS430, and the thickness t2 of the Al layer 1a being different. In addition, as a test specimen without an Al layer, a SUS430 single plate (Comparative Example 1) made of ferritic stainless steel and having a thickness of 300 μm was prepared. In addition, as another member made of an iron-based alloy, a SUS430 single plate having a thickness of 300 μm was prepared. The thicknesses t2 of the Al layer 1a of the six types of clad materials 1 for laser welding, which were test specimens, were 10 μm (Comparative Example 2), 20 μm (Example 1), 40 μm (Example 2), 60 μm (Example 3), 90 μm (Example 4), and 140 μm (Example 5).

[0061] Next, the Al layer 1a of the specimens of Examples 1 to 5 and Comparative Example 2 was partially joined to another member by laser welding to prepare a joint structure including a dissimilar metal joint between Al050 and SUS430. The specimen of Comparative Example 1 was also partially joined to another member by laser welding to prepare a joint structure including a homogeneous metal joint between SUS430 and SUS430. In each joint structure, the laser welding was performed by irradiating the laser with a laser output of 300 W and a laser irradiation speed of 500 mm / s to draw a circle with a diameter of 15 mm on the surface of the Z1 side of the Al layer 1a.

[0062] A joint strength evaluation test was performed on the laser welded portions of the joint structures of Examples 1 to 5 and Comparative Examples 1 and 2. Specifically, a tensile test was performed on the joint structures of Examples 1 to 5 and Comparative Examples 1 and 2, in which the test specimen and the other member were pulled in opposite directions so that a load in the shear direction was applied to the laser welded portion. In addition, the laser welded interface (joint surface 1e) was observed with an electron microscope.

[0063] Table 1 shows the measured values ​​(joint strength, fusion width x1, penetration depth x2, and protruding height of protrusion 1d) of the joint structures of Examples 1 to 5, Comparative Example 1, and Comparative Example 2 relative to the thickness t2 of the Al layer 1a. Table 2 also shows the ratios (hereinafter referred to as "comparison values") of the measured values ​​of the joint structures of Examples 1 to 5 and Comparative Example 2 to the measured values ​​of the joint structure of Comparative Example 1 (thickness of the Al layer is 0 μm). Furthermore, FIG. 10 shows a graph in which the thickness t2 of the Al layer 1a is plotted on the horizontal axis and the joint strength, fusion width x1, penetration depth x2, and protruding height x3 of the laser welded portion of each joint structure are plotted on the vertical axis using the values ​​shown in Table 1. The dotted line shown in FIG. 10 is a polynomial approximation (cubic) curve of the thickness t2 of the Al layer 1a and each measured value.

[0064] [Table 1] TIFF2024168866000002.tif56170

[0065] [Table 2] TIFF2024168866000003.tif59170

[0066] In the joint structure using the SUS430 single plate of Comparative Example 1 (Al layer thickness: 0 μm), as shown in Table 1, the joint strength was 1999 N, the fusion width x1 was 54 μm, the penetration depth x2 was 123 μm, and the protrusion height x3 of the protrusion 1d was 30 μm.

[0067] In the welded structure using the laser welding clad material 1 in which the thickness t2 of the Al layer 1a of Comparative Example 2 is 10 μm, the joint strength was 1859 N, the fusion width x1 was 54 μm, the penetration depth x2 was 133 μm, and the protrusion height x3 of the protrusion 1d was 30 μm, as shown in Table 1. In addition, as shown in Table 2, the comparison values ​​with Comparative Example 1 were the joint strength of 0.93, the fusion width x1 of 1.00, the penetration depth x2 of 1.08, and the protrusion height x3 of the protrusion 1d of 1.00.

[0068] In the welded structure using the laser welding clad material 1 in Example 1, in which the thickness t2 of the Al layer 1a is 20 μm, the joint strength was 2066 N, the fusion width x1 was 54 μm, the penetration depth x2 was 123 μm, and the protrusion height x3 of the protrusion 1d was 20 μm, as shown in Table 1. In addition, as shown in Table 2, the comparison values ​​with Comparative Example 1 were the joint strength of 1.03, the fusion width x1 of 1.00, the penetration depth x2 of 1.00, and the protrusion height x3 of the protrusion 1d of 0.67.

[0069] In the welded structure using the laser welding clad material 1 in which the thickness t2 of the Al layer 1a of Example 2 is 40 μm, the joint strength was 1865 N, the fusion width x1 was 49 μm, the penetration depth x2 was 99 μm, and the protrusion height x3 of the protrusion 1d was 15 μm, as shown in Table 1. In addition, as shown in Table 2, the comparison values ​​with Comparative Example 1 were the joint strength of 0.93, the fusion width x1 of 0.91, the penetration depth x2 of 0.80, and the protrusion height x3 of the protrusion 1d of 0.50.

[0070] In the welded structure using the laser welding clad material 1 in which the thickness t2 of the Al layer 1a of Example 3 is 60 μm, the joint strength was 2054 N, the fusion width x1 was 50 μm, the penetration depth x2 was 73 μm, and the protrusion height x3 of the protrusion 1d was 5 μm, as shown in Table 1. In addition, as shown in Table 2, the comparison values ​​with Comparative Example 1 were the joint strength of 1.03, the fusion width x1 of 0.93, the penetration depth x2 of 0.59, and the protrusion height x3 of the protrusion 1d of 0.17.

[0071] In the welded structure using the laser welding clad material 1 in which the thickness t2 of the Al layer 1a of Example 4 is 90 μm, the joint strength was 1961 N, the fusion width x1 was 55 μm, the penetration depth x2 was 61 μm, and the protrusion height x3 of the protrusion 1d was 10 μm, as shown in Table 1. In addition, as shown in Table 2, the comparison values ​​with Comparative Example 1 were the joint strength of 0.98, the fusion width x1 of 1.02, the penetration depth x2 of 0.50, and the protrusion height x3 of the protrusion 1d of 0.33.

[0072] In the welded structure using the laser welding clad material 1 of Example 5 in which the thickness t2 of the Al layer 1a was 140 μm, the joint strength was 1921 N, the fusion width x1 was 54 μm, the penetration depth x2 was 78 μm, and the protrusion height x3 of the protrusion 1d was 10 μm, as shown in Table 1. In addition, as shown in Table 2, the comparison values ​​with Comparative Example 1 were the joint strength of 0.96, the fusion width x1 of 1.00, the penetration depth x2 of 0.63, and the protrusion height x3 of the protrusion 1d of 0.33.

[0073] As described above, the joint strength of the laser welded portion of the joint structure is slightly larger when the thickness t2 of the Al layer 1a is 20 μm (Example 1) and 60 μm (Example 3) compared to Comparative Example 1 not having an Al layer, and is slightly smaller when the thickness t2 of the Al layer 1a is 10 μm (Comparative Example 2), 40 μm (Example 2), 90 μm (Example 4) and 140 μm (Example 5). This shows that the joint strength of the laser welded portion of the joint structure varies regardless of the thickness t2 of the Al layer 1a. This phenomenon in which the joint strength varies regardless of the thickness t2 of the Al layer 1a can also be confirmed from the plot of the joint strength and its approximation curve shown in FIG. 10. In addition, the degree of variation in the joint strength is considered to be about 10%, since the comparison value in the case of having the Al layer 1a shown in Table 2 is 0.93 (minimum value) to 1.03 (maximum value), and the fluctuation range is 0.10 (-3% to +7%). From the above, it was found that the joint strength of the laser welded part of the joint structure having the Al layer 1a is substantially equivalent to that of the laser welded part of the joint structure not having the Al layer, although there is a possibility of a variation of about 10%, and is at a sufficiently practical level. Therefore, it was found that the laser welding clad material 1 having the Al layer 1a is suitable for laser welding with other members made of iron-based alloys from the viewpoint of the joint strength of the laser welded part of the joint structure using it.

[0074] As described above, the fusion width x1 of the laser welded portion of the joint structure was equivalent when the thickness t2 of the Al layer 1a was 10 μm (Comparative Example 2), 20 μm (Example 1), and 140 μm (Example 5) compared to Comparative Example 1 without the Al layer, but was slightly larger at 90 μm (Example 4) and slightly smaller at 40 μm (Example 2) and 60 μm (Example 3). This shows that the fusion width x1 of the laser welded portion of the joint structure varies regardless of the thickness t2 of the Al layer 1a. The phenomenon in which the fusion width x1 varies regardless of the thickness t2 of the Al layer 1a can also be confirmed from the plot of the fusion width x1 shown in FIG. 10 and its approximation curve. In addition, the degree of variation of the fusion width x1 is considered to be about 10% since the comparison value in the case of having the Al layer 1a shown in Table 2 is 0.91 (minimum value) to 1.02 (maximum value), and the fluctuation range is 0.11 (-9% to +2%). From the above, it was found that the fusion width x1 of the laser welded part of the joint structure having the Al layer 1a may vary by about 10%, but is substantially equivalent to the laser welded part of the joint structure not having the Al layer and is sufficiently practical. Therefore, it was found that the clad material 1 for laser welding having the Al layer 1a is suitable for laser welding with other members made of iron-based alloys from the viewpoint of the fusion width x1 of the laser welded part of the joint structure using the clad material.

[0075] As described above, the penetration depth x2 of the laser welded portion of the joint structure was equivalent when the thickness t2 of the Al layer 1a was 20 μm (Example 1) compared to Comparative Example 1 not having an Al layer, but was larger when it was 10 μm (Comparative Example 2) and smaller when it was 40 μm (Example 2) to 140 μm (Example 5). In addition, looking at the comparison values ​​with Comparative Example 1 shown in Table 2, it can be confirmed that the penetration depth x2 tends to decrease as the thickness t2 of the Al layer 1a increases from 10 μm to 90 μm. This shows that the penetration depth x2 of the laser welded portion of the joint structure is affected by the thickness t2 of the Al layer 1a. The phenomenon in which the penetration depth x2 is affected by the thickness t2 of the Al layer 1a can also be confirmed from the plot of the penetration depth x2 shown in FIG. 10 and its approximation curve. From the above, it was found that the penetration depth x2 of the laser welded portion of the joint structure having the Al layer 1a is affected by the thickness t2 of the Al layer 1a, and is equal to or smaller than that of the joint structure not having the Al layer (Comparative Example 1) in the joint structure (Examples 1 to 5) in which the thickness t2 of the Al layer 1a is 20 μm or more and 140 μm or less, and is smaller in the joint structure (Examples 2 to 5) in which the thickness t2 of the Al layer 1a is 40 μm or more and 140 μm or less. Therefore, it was found that the laser welding clad material 1 in which the thickness t2 of the Al layer 1a is 20 μm or more and 140 μm or less (preferably 40 μm or more and 140 μm or less) is suitable for laser welding with other members made of iron-based alloys in terms of the penetration depth x2 of the laser welded portion of the joint structure using it.

[0076] Here, in a joint structure in which the penetration depth x2 of the laser welded portion is large, the melt of the clad material 1 for laser welding may reach the vicinity of the surface opposite to the surface of the laser-welded other member (positive terminal) to which the clad material 1 for laser welding is welded and solidify. In that case, problems such as the other member having a reduced mechanical strength and being easily cracked due to this may occur, so it is necessary to make the thickness of the other member extra large. However, in the joint structure in which the thickness t2 of the Al layer 1a is 20 μm or more and 140 μm or less (Examples 1 to 5), the penetration depth x2 is equal to or less than that of the joint structure without the Al layer (Comparative Example 1), so there is no need to make the thickness of the other member to be laser welded extra large. In particular, in the joint structure in which the thickness t2 of the Al layer 1a is 40 μm or more and 140 μm or less (Examples 2 to 5), the penetration depth x2 is sufficiently smaller than that of the joint structure without the Al layer (Comparative Example 1), so the thickness of the other member to be laser welded can be made thinner. In addition, looking at the approximation curve of the penetration depth x2 shown in Fig. 10, there is a tendency for the penetration depth x2 to increase as the thickness t2 of the Al layer 1a increases from 90 µm toward 140 µm, so it is considered undesirable for the thickness t2 of the Al layer 1a to exceed 140 µm. From this perspective, the laser welding clad material 1 in which the thickness t2 of the Al layer 1a is 140 µm or less is not excessively thick and can reduce the space required for placement, making it possible to downsize the joint structure using this.

[0077] As described above, the protruding height x3 of the protruding portion 1d of the joint structure was 30 μm when the thickness t2 of the Al layer 1a was 10 μm (Comparative Example 2) compared to Comparative Example 1 not having an Al layer, but was small, 20 μm or less, when the thickness t2 of the Al layer 1a was 20 μm (Example 1) to 140 μm (Example 5). In addition, looking at the comparison value with Comparative Example 1 shown in Table 2, it can be confirmed that the protruding height x3 tends to decrease as the thickness t2 of the Al layer 1a increases from 10 μm to 140 μm. This shows that the protruding height x3 of the protruding portion 1d of the joint structure is affected by the thickness t2 of the Al layer 1a. The phenomenon that the protruding height x3 is affected by the thickness t2 of the Al layer 1a can also be confirmed from the plot of the protruding height x3 shown in FIG. 10 and its approximate curve. From the above, it was found that the protruding height x3 of the protruding portion 1d of the joint structure having the Al layer 1a is influenced by the thickness t2 of the Al layer 1a, and can be made smaller, for example, 20 μm or less in the joint structure (Examples 1 to 5) in which the thickness t2 of the Al layer 1a is 20 μm or more and 140 μm or less than that of the joint structure (Comparative Example 1) that does not have the Al layer, and can be made smaller, 15 μm or less, in the joint structure (Examples 2 to 5) in which the thickness t2 of the Al layer 1a is 40 μm or more and 140 μm or less. Therefore, it was found that the laser welding clad material 1 in which the thickness t2 of the Al layer 1a is 20 μm or more and 140 μm or less (preferably 40 μm or more and 140 μm or less) is suitable for laser welding with other members made of iron-based alloys in terms of the protruding height x3 of the protruding portion 1d of the laser welded part of the joint structure using it.

[0078] Here, if the protruding height x3 of the protruding portion 1d of the joint structure using the laser welding clad material 1 is small, the thickness is not excessively large, so that the arrangement space can be reduced, and the protruding portion 1d is less likely to come into contact with members other than the laser welding clad material and be damaged, so that the risk of the joint structure and the operation of the battery pack becoming unstable due to damage to the protruding portion 1d can be suppressed. From this perspective, the laser welding clad material 1 in which the thickness t2 of the Al layer 1a in which the protruding height x3 of the protruding portion 1d of the joint structure is 20 μm or less and 140 μm or less, preferably the thickness t2 of the Al layer 1a in which the protruding height x3 of the protruding portion 1d of the joint structure is 40 μm or more and 140 μm or less in which the protruding height x3 of the protruding portion 1d is 15 μm or less, is suitable for laser welding with other members made of iron-based alloys, and is also advantageous for downsizing the joint structure using this.

[0079] From the above, based on the evaluation results of the joining strength, fusion width x1, penetration depth x2, and protrusion height x3 of the protrusion 1d of the laser welded portion of the joining structure in which the clad material 1 for laser welding and another member are joined by laser welding, the inventors of the present application have found that the clad material 1 for laser welding in which the thickness t2 of the Al layer 1a is 20 μm or more and 140 μm or less can be placed in a small space, is suitable for laser welding involving joining of dissimilar metals with another member made of an iron-based alloy, and that it is possible to downsize the joining structure using the clad material.

[0080] [Variations] The embodiments and examples disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the description of the embodiments and examples described above, and further includes all modifications (variations) within the meaning and scope of the claims.

[0081] For example, in the present embodiment, a configuration example in which the clad material 1 for laser welding is used in the assembled battery 100 has been shown, but the present invention is not limited to this. In the present invention, for example, the clad material 1 for laser welding may be used in other than the assembled battery 100, and may be used in, for example, electric / electronic circuit boards for in-vehicle use, etc.

[0082] In the present embodiment, the clad material 1 for laser welding is bonded to the bus bar 20 by wire bonding, but the present invention is not limited to this. In the present invention, the clad material 1 for laser welding may be bonded to the bus bar 20 by laser welding or the like.

[0083] In the present embodiment, the clad material 1 for laser welding has a configuration example in which the thickness t2 of the Al layer 1a is smaller than the thickness t3 of the Fe layer 1b shown in Fig. 2, but the present invention is not limited to this. In the present invention, the clad material 1 for laser welding may have a thickness t2 of the Al layer 1a that is equal to or larger than the thickness t3 of the Fe layer 1b, for example.

[0084] In the present embodiment, the clad material 1 for laser welding is used in a cylindrical lithium ion secondary battery 10 as shown in Fig. 6, but the present invention is not limited to this. In the present invention, the clad material 1 for laser welding may be used in a prismatic lithium ion secondary battery 10 as shown in Fig. 11.

[0085] In the present embodiment, the Fe layer 1b of the laser-welded clad material 1 is laser-welded to the cover material 12 (battery terminal member) made of an iron-based alloy, which is the positive electrode terminal, but the present invention is not limited to this. In the present invention, the Fe layer 1b of the laser-welded clad material 1 may be laser-welded to a case that also serves as a negative electrode terminal, for example.

[0086] In the present embodiment, the Fe layer 1b of the clad material 1 for laser welding is directly laser welded to the lid material 12 (terminal member for battery), but the present invention is not limited to this. In the present invention, another component may be provided between the Fe layer 1b of the clad material 1 for laser welding and the lid material 12. In this case, the other component provided between the Fe layer 1b of the clad material 1 for laser welding and the lid material 12 becomes the terminal member for battery. [Explanation of symbols]

[0087] 1 Clad materials for laser welding 1a Al layer 1b Fe layer 1c Exposed surface 1d protrusion 1e Joint surface 12 Lid materials (other parts, battery terminal parts) 20 Busbar 50a: Al plate material 50b:Fe plate material 100 battery pack (battery)

Claims

1. A clad material for laser welding to be laser welded to another member made of an iron-based alloy, An Al layer made of pure aluminum or an aluminum alloy; an Fe layer made of an iron-based alloy and roll-bonded to the Al layer; The thickness of the Al layer is 20 μm or more and 140 μm or less, The Fe layer is laser-welded to the other member by laser irradiation from the Al layer side.

2. The clad material for laser welding according to claim 1 , wherein the thickness of the Al layer is 40 μm or more and 140 μm or less.

3. A laser welding clad material including an Al layer made of pure aluminum or an aluminum alloy, and an Fe layer made of an iron-based alloy and roll-bonded to the Al layer, the Al layer having a thickness of 20 μm or more and 140 μm or less; and another member made of an iron-based alloy and laser-welded to the Fe layer; A joint structure using a clad material for laser welding, in which the Fe layer is laser-welded to the other member by laser irradiation from the Al layer side.

4. A joint structure using a clad material for laser welding as described in claim 3, wherein a length of a molten portion formed on a joint surface by laser welding between the Fe layer and the other member in a direction extending from the joint surface is 40 μm or more and 140 μm or less.

5. A joining structure using the clad material for laser welding according to claim 3, wherein a protrusion height formed on an exposed surface of the Al layer opposite to the surface where the Fe layer is roll-joined by laser irradiation from the Al layer side is 20 μm or less.

6. The thickness of the Al layer is 40 μm or more and 140 μm or less, A joining structure using the clad material for laser welding described in claim 5, wherein a protrusion height formed on an exposed surface of the Al layer opposite to the surface where the Fe layer is roll-joined by irradiating a laser from the Al layer side to the Fe layer side is 15 μm or less.

7. A step of preparing a clad material for laser welding, the clad material being composed of an Al layer and an Fe layer by rolling and bonding an Al plate material made of pure aluminum or an aluminum alloy and an Fe plate material made of an iron-based alloy, the Al layer having a thickness of 20 μm or more and 140 μm or less; a step of joining a battery terminal member made of an iron-based alloy to the Fe layer by irradiating a laser from the Al layer side toward the Fe layer side; and joining a bus bar made of pure aluminum or an aluminum alloy to the Al layer.

Images