Method for manufacturing current-carrying component for secondary batteries, and current-carrying component for secondary batteries

Abstract

The present invention relates to: a method for manufacturing a current-carrying component for secondary batteries, with which it is possible, especially even in cases where a metal plate material with a lower melting point than a metal foil material are to be combined with the metal foil material, to efficiently weld the materials to each other while ensuring the plate thickness of the metal plate material; and a current-carrying component for secondary batteries. The present invention specifically provides a manufacturing method that includes: a first welding step in which a plurality of metal foil materials 11-15 are stacked in the thickness direction and a rotating friction stir welding tool 50 is inserted into the stack in the thickness direction downward from above a metal foil material 11 that is positioned on the outermost surface; and a second welding step in which, after the first welding step, the plurality of metal foil materials 11-15 are superposed above a metal plate material 20, and the rotating friction stir welding tool 50 is inserted again in the thickness direction downward from above the metal foil material 11 that is positioned on the outermost surface. The present invention also specifically provides a current-carrying component for secondary batteries.

Description

Method for manufacturing current-carrying component for secondary battery, and current-carrying component for secondary battery

[0001] The present invention relates to a method for manufacturing an electric current-carrying part for secondary batteries mounted mainly on automobiles, etc., and to an electric current-carrying part for secondary batteries.

[0002] Current-carrying components formed from two or more sheets or foils, particularly current-carrying components for secondary batteries in automobiles, are also called bus bars, and Patent Document 1 discloses a technique for forming current-carrying components from highly conductive materials such as aluminum alloys and copper alloys. Patent Document 2 also discloses a method for manufacturing current-carrying components using friction stir spot joining technology as one method for joining two or more laminated foils and sheets.

[0003] Japanese Patent No. 6971990 Japanese Patent No. 6516408

[0004] However, when joining a metal foil material and a metal plate material using the friction stir spot joining method, since the thicknesses of these materials are different, for example, if the metal foil material is laminated on top of a plate material and then joined, a part of the metal foil material is pressed into the metal plate material, resulting in a poor joining of the metal foil material and the metal plate material.

[0005] Furthermore, when joining laminated metal foil material and a metal plate material with a lower melting point (than the metal foil material), when a rotating friction stir joining tool is inserted from the side where the metal foil material is laminated, the metal plate material softens first due to frictional heat, and part of the metal foil material is easily pushed into the metal plate material, resulting in the problem that the laminated metal foil materials do not join together.

[0006] Furthermore, when a rotating friction stir welding tool is inserted into the metal plate material with a low melting point to avoid the above-mentioned poor joining, the thickness of the metal plate material is reduced, and there is a problem that the part with reduced thickness generates heat when a large current is passed through it.

[0007] An object of the present invention is to provide a method for manufacturing an electrical component for a secondary battery that can efficiently join metal foil material and metal plate material of different materials and thicknesses using a friction stir spot joining method while ensuring the thickness of the metal plate material, especially when the metal plate material has a lower melting point than the metal foil material.

[0008] Therefore, the manufacturing method for a secondary battery current-carrying part of the present invention is a manufacturing method for a secondary battery current-carrying part formed from a plurality of metal foil materials and a metal plate material of a different material, and includes a first joining process in which a friction stir welding tool rotated from above to below the metal foil material located on the top surface is inserted along the thickness direction while the plurality of metal foil materials are stacked in the thickness direction, and a second joining process in which, after the first joining process, the plurality of metal foil materials joined in the first joining process are placed above the metal plate material, and the plurality of metal foil materials joined in the first joining process are stacked above the metal plate material, and a friction stir welding tool rotated from above to below the metal foil material located on the top surface is inserted along the thickness direction to join the metal foil material joined in the first joining process and the metal plate material.

[0009] In this case, the deepest position into which the tip of the second friction stir welding tool is inserted in the second joining step is set above the metal foil material located in the lowest layer. The metal foil material may be made of either copper or a copper alloy, and the metal plate material may be made of either aluminum or an aluminum alloy. Furthermore, the friction stir welding tools used in the first and second joining steps may differ in specifications such as tool diameter, shape, and material. The number of metal foil materials may be five or more, and the thickness of each sheet may be 0.21 mm or less.

[0010] The conductive component for a secondary battery of the present invention is a conductive component for a secondary battery formed from a plurality of sheets of metal foil material and a metal plate material of a different material from the metal foil material, wherein the melting point of the metal plate material is lower than the melting point of the metal foil material, the plurality of sheets of metal foil material are stacked above the metal plate material, and the metal foil material and the metal plate material are joined together, and in the cross section of the joint between the plurality of sheets of metal foil material and the metal plate material, no boundary lines between the plurality of sheets of metal foil material are observed.

[0011] In this case, in the current-carrying component for secondary batteries of the present invention, the thickness of the metal plate material directly below the joint between the multiple metal foil materials and the metal plate material is 60% or more of the thickness of the metal plate material before joining. Also, in the current-carrying component for secondary batteries of the present invention, the position of the cut cross section of the joint between the multiple metal foil materials and the metal plate material is the position of the rotation center of the friction stir welding tool used for joining. Also, in the current-carrying component for secondary batteries of the present invention, the deepest position where the tip of the friction stir welding tool used to join the multiple metal foil materials and the metal plate material is inserted is above the metal foil material located in the lowest layer.

[0012] The method for manufacturing an electrical component for a secondary battery of the present invention has the advantage that, when laminated metal foil materials are joined to the metal foil material using a friction stir spot joining method, efficient joining can be achieved while maintaining the thickness of the metal plate material, especially even when the metal plate material has a lower melting point than the metal foil material (the melting point of the metal plate material is lower than that of the metal foil material).

[0013] 5 is a schematic cross-sectional view of a current-carrying component for a secondary battery in a first joining step of the present invention; FIG. 6 is a schematic cross-sectional view of a current-carrying component 1 for a secondary battery in a second joining step of the present invention; FIG. 7 is a cross-sectional photograph of the vicinity of a joint of the current-carrying component for a secondary battery of the present invention; FIG. 8 is a cross-sectional photograph of the vicinity of a joint of a current-carrying component for a secondary battery of a comparative material; FIG. 9 is an enlarged cross-sectional photograph of the boundary between the aluminum alloy plate and the copper foil shown in FIG. 3;

[0014] 1 shows a schematic cross-sectional view of multiple metal foil materials 11-15 during a first joining step in the manufacturing method of a secondary battery current-carrying component of the present invention, and FIG. 2 shows a schematic cross-sectional view of a secondary battery current-carrying component 1 during a second joining step in the manufacturing method of a secondary battery current-carrying component of the present invention. The five metal foil materials 11-15 that form the secondary battery current-carrying component of the present invention are formed in a form in which multiple metal foil materials 10 (11, 12, 13, 14, 15) are stacked in the thickness direction, as shown in FIG. 1. A clamp (jig) 70 is used to press and fix these metal foil materials 10 (11, 12, 13, 14, 15) from above the metal foil material 11 that is the uppermost layer.

[0015] Thereafter, the rotating friction stir welding tool 50 is inserted from above into the metal foil materials 10 (11, 12, 13, 14, 15) in the thickness direction (of the metal foil materials), and a recess 80 is formed following the trace of the tip shape of the friction stir welding tool 50. At this time, these metal foil materials 10 (11, 12, 13, 14, 15) are morphologically integrated by the solid-state welding portion 30 located immediately below the recess 80, as shown in FIG.

[0016] Next, the multiple metal foil materials 11-15 joined in the first joining step are placed above the metal plate material 20, and then a clamp (jig) 70 is used to simultaneously press and fix the metal foil materials 11-15 and the metal plate material 20 from above the metal foil materials 11-15, as shown in Figure 2. Thereafter, a rotating friction stir welding tool 50 is inserted from above the metal foil materials 11-15 into the recesses formed in the first joining step.

[0017] At this time, the deepest position into which the tip of the friction stir welding tool 50 is inserted in the second joining step is set to be above the metal foil material 15 located in the lowest layer. Ultimately, a new recess 81 is formed in the metal foil materials 11 to 15 and the metal plate material 20 as shown in Figure 2, and a new solid-state weld 31 is formed directly below the recess 81.

[0018] The manufacturing method of this embodiment solid-state bonds (structurally and morphologically integrated) multiple sheets of metal foil material, and also solid-state bonds with a metal plate material that is different in thickness from the metal foil material and is located in the lowest layer. This makes it possible to provide an electrically conductive component for a secondary battery that can efficiently bond metal materials of different materials and thicknesses and ensure electrical conductivity (minimize electrical resistance).

[0019] If the metal foil material is aluminum or an aluminum alloy, the thickness may be 0.2 mm or less (JIS H4160, H4170), and if the metal foil material is copper or a copper alloy, the thickness may be 0.21 mm or less (JIS C6515).

[0020] The results of a joining test (hereinafter referred to as the "test") for the above-described embodiment of the present invention will be described with reference to the drawings. In the test, copper foil was used as the metallic foil material, and an aluminum alloy plate was used as the metallic plate material, and these foil and plate materials were joined by friction stir spot joining.

[0021] Specifically, the inventive material was prepared by carrying out a first bonding step in which only 40 copper foils were temporarily bonded together, followed by a second bonding step in which the integrated 40 copper foils were directly bonded to one aluminum alloy plate, i.e., a two-stage bonding step. In contrast, the comparative material was prepared by directly bonding 40 copper foils to one aluminum alloy plate without temporary bonding. For both the inventive material and the comparative material, the copper foil thickness before the test was 0.1 mm, and the aluminum alloy plate thickness was 1 mm.

[0022] The joining conditions for the inventive material were as follows: in the first joining step, a friction stir welding tool rotating at 5000 rpm was used to weld 40 sheets of copper foil with a plunge depth of 0.25 mm, thereby integrating only the copper foil. Subsequently, in the second joining step, a friction stir welding tool rotating at 5000 rpm was used to weld 40 sheets of copper foil and aluminum alloy sheet with a plunge depth of 0.30 mm, thereby joining together the 40 sheets of copper foil and aluminum alloy sheet. In contrast, for the comparative material, a friction stir welding tool rotating at 3000 rpm was used to directly weld the copper foil and aluminum alloy sheet with a plunge depth of 0.30 mm.

[0023] After joining the inventive material and the comparative material, the vicinity of the joint (at or near the center of rotation of the friction stir welding tool 50) was cut and the cross section was photographed. A cross-sectional photograph (before etching: 20x magnification) of the vicinity of the joint of the inventive material in this test is shown in Figure 3, a cross-sectional photograph (before etching: 20x magnification) of the vicinity of the joint of the comparative material in this test is shown in Figure 4, an enlarged cross-sectional photograph (after etching: 100x magnification) of the boundary between the copper foil and the aluminum alloy plate in Figure 3 is shown in Figure 5, and an enlarged cross-sectional photograph (after etching: 100x magnification) of the boundary between the copper foil and the aluminum alloy plate in Figure 4 is shown in Figure 6. (Note that for the convenience of filing, the image data of the photographs in Figures 3 to 6 have been converted to black and white and are shown as Figures 7 to 10, respectively.)

[0024] As a result of observing the cross sections of the inventive material and the comparative material after bonding, it was found that the copper foil of the inventive material was integrated as shown in Figures 3 and 5, and the thickness of the aluminum alloy plate directly below the bonded portion (the thickness at the thinnest position) was measured to be 0.735 mm. Since the thickness of the aluminum alloy plate before the test was 1 mm, this means that the plate thickness was maintained at 70% or more of the plate thickness (1 mm) before bonding.

[0025] In contrast, the thickness of the aluminum alloy plate of the comparative material (thickness at the thinnest point) was 0.576 mm, which was thinner than the thickness of the inventive material, and the boundary between the copper foil and the aluminum alloy plate was clearly observed. This indicates that the comparative material did not achieve complete integration of the copper foil due to the omission of the first joining step, and therefore the joining strength and electrical resistance were inferior. Since the thickness of the aluminum alloy plate before the test was 1 mm, it means that the plate thickness was not maintained at 60% of the plate thickness (1 mm) before joining.

[0026] Furthermore, observations after etching confirmed that the copper foil of the inventive material had no visible boundaries between the laminated foils, and was completely integrated (the laminated foils were integrated to the very bottom). In contrast, in the comparative material, boundaries between the laminated foils were visible in the copper foil in contact with the aluminum alloy plate and in the copper foil above it (boundaries at the very bottom and near the very bottom of the laminated foils remained, and they were not integrated). This indicates that the copper foil in the comparative material was insufficiently stirred, resulting in weak strength in the crimped state and high electrical resistance. Furthermore, despite the deepest insertion point of the tip of the friction stir welding tool used to join the foil and plate materials being above the foil in the lowest layer, the foil and plate materials were integrated, which is advantageous in terms of both manufacturing and product usage.

[0027] Therefore, by using the two-step joining process (first and second joining processes) of the method of the present invention, the laminated copper foil is integrated and then joined to the aluminum alloy sheet, making it possible to obtain a joint with high strength and low electrical resistance.

[0028] 1 Current-carrying part for secondary battery 10 (11 to 15) Metal foil material 20 Metal plate material 30, 31 Solid-state welding part 50 Friction stir welding tool 70 Clamp 80, 81 Recess

Claims

1. A method for manufacturing a conductive component for a secondary battery, comprising: a first joining step of joining the multiple metal foils to each other by inserting a friction agitation joining tool, which rotates downward from above the metal foil located on the outermost surface, along the thickness direction, while the multiple metal foils are stacked in the thickness direction; and a second joining step of joining the metal foils joined in the first joining step to the metal plate, after the first joining step, by placing the multiple metal foils joined in the first joining step above the metal plate, and inserting the friction agitation joining tool, which rotates from the metal foil side, while the multiple metal foils joined in the first joining step are stacked above the metal plate, thereby joining the metal foils joined in the first joining step to the metal plate.

2. The method for manufacturing a conductive component for a secondary battery according to claim 1, characterized in that, in the second joining step, the deepest position into which the tip of the friction agitation joining tool is inserted is above the lowest layer of the metal foil material.

3. The method for manufacturing a conductive component for a secondary battery according to claim 2, characterized in that the melting point of the metal plate is lower than the melting point of the metal foil.

4. The method for manufacturing a power-carrying component for a secondary battery according to claim 3, characterized in that the metal foil material is made of copper or a copper alloy, and the metal plate material is made of aluminum or an aluminum alloy.

5. The method for manufacturing a conductive component for a secondary battery according to any one of claims 1 to 4, characterized in that the number of metal foil materials is five or more, and the thickness of each foil is 0.21 mm or less.

6. A conductive component for a secondary battery, formed from multiple metal foil materials and a metal plate material of a different material from the said metal foil materials, The melting point of the metal plate is lower than that of the metal foil. The plurality of metal foil materials are stacked on top of the metal plate material, and the metal foil materials and the metal plate material are joined together. The deepest point into which the tip of the friction agitation bonding tool used to join the multiple metal foil materials and the metal plate material is inserted is above the lowest layer of the metal foil material. A conductive component for a secondary battery, characterized in that no boundary lines between the multiple metal foil materials are observed in the cross-section of the joint between the multiple metal foil materials and the metal plate material.

7. The current-carrying component for a secondary battery according to claim 6, characterized in that the thickness of the metal plate material directly below the joint between the plurality of metal foil materials and the metal plate material is 60% or more of the thickness of the metal plate material before joining.

8. The conductive component for a secondary battery according to claim 6 or 7, characterized in that the position of the cut surface of the joint between the plurality of metal foil materials and the metal plate material is the position of the rotation center of the friction agitation joining tool used for joining.