Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K15/00—Electron-beam welding or cutting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/20—Bonding
  • B23K26/21—Bonding by welding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/20—Bonding
  • B23K26/32—Bonding taking account of the properties of the material involved
  • B23K26/322—Bonding taking account of the properties of the material involved involving coated metal parts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/20—Bonding
  • B23K26/32—Bonding taking account of the properties of the material involved
  • B23K26/323—Bonding taking account of the properties of the material involved involving parts made of dissimilar metallic material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K9/00—Arc welding or cutting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K9/00—Arc welding or cutting
  • B23K9/23—Arc welding or cutting taking account of the properties of the materials to be welded
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/50—Current conducting connections for cells or batteries
  • H01M50/502—Interconnectors for connecting terminals of adjacent batteries; Interconnectors for connecting cells outside a battery casing
  • H01M50/505—Interconnectors for connecting terminals of adjacent batteries; Interconnectors for connecting cells outside a battery casing comprising a single busbar
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/50—Current conducting connections for cells or batteries
  • H01M50/502—Interconnectors for connecting terminals of adjacent batteries; Interconnectors for connecting cells outside a battery casing
  • H01M50/521—Interconnectors for connecting terminals of adjacent batteries; Interconnectors for connecting cells outside a battery casing characterised by the material
  • H01M50/522—Inorganic material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/50—Current conducting connections for cells or batteries
  • H01M50/502—Interconnectors for connecting terminals of adjacent batteries; Interconnectors for connecting cells outside a battery casing
  • H01M50/521—Interconnectors for connecting terminals of adjacent batteries; Interconnectors for connecting cells outside a battery casing characterised by the material
  • H01M50/526—Interconnectors for connecting terminals of adjacent batteries; Interconnectors for connecting cells outside a battery casing characterised by the material having a layered structure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/50—Current conducting connections for cells or batteries
  • H01M50/543—Terminals
  • H01M50/562—Terminals characterised by the material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/50—Current conducting connections for cells or batteries
  • H01M50/569—Constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to a dissimilar metal bonded structure in which metals of different materials are bonded, and to a battery pack that uses the same.
• Figure 39 shows a cross section of a lap joint (hereinafter also referred to as a dissimilar metal joint structure) in which an aluminum-based member 1 is arranged on the upper side (the side where heat is input by the laser beam) and a copper-based member 2 is arranged on the lower side, where the molten metal portion 3 formed by applying thermal energy from a laser beam or the like from above has penetrated the upper aluminum-based member 1 and melted into the lower copper-based member 2.
• a dissimilar metal joint structure in which an aluminum-based member 1 is arranged on the upper side (the side where heat is input by the laser beam) and a copper-based member 2 is arranged on the lower side, where the molten metal portion 3 formed by applying thermal energy from a laser beam or the like from above has penetrated the upper aluminum-based member 1 and melted into the lower copper-based member 2.
• the metal structure of the molten metal portion 3 is a metallic compound consisting of a mixture of aluminum-based and copper-based metals.
• an intermetallic compound that becomes an embrittlement phase is formed, when an external force is applied to the lap joint, the fusion boundary 5 at the lap interface 4, where stress is concentrated, becomes the starting point for fracture.
• Patent Document 1 proposes the bonding method shown in Figures 42 and 43.
• the dimensional specifications of the molten metal portion 3 that penetrates the aluminum-based member 1 and melts into the copper-based member 2 are such that the melt width dimension W1 at the lap interface 4 in the longitudinal direction of the lap joint is 10 to 50 ⁇ m, and the depth dimension D1 is 5 to 30 ⁇ m.
• the molten metal structure near the lap interface 4 which is the starting point for fracture of the lap joint in the molten metal portion 3 in Figure 42, is a mixture of copper-based material and aluminum-based material, regardless of how small the molten ratio of the copper-based material to the aluminum-based material is, so there is a need to reduce the risk of metallurgical brittle fracture.
• the object of the present invention is to solve at least one or more of the problems with the prior art described above, and in particular to provide a new dissimilar metal bonded structure and battery assembly that, when subjected to an external force, undergoes ductile fracture in the base material rather than brittle fracture in the molten metal portion.
• the present invention relates to a dissimilar metal joint structure having a first member made of a metallic material, a second member made of a metallic material different from the first member, an overlapping portion formed by the second member overlapping the first member on the heat input side, and a molten metal portion formed in the overlapping portion where the first member and the second member are melted and solidified, wherein the molten metal portion has the following characteristics: (1) the depth of the molten metal portion melting from the overlapping interface of the overlapping portion into the second member is 0.1 mm or more, (2) the depth of the molten metal portion melting from the overlapping interface of the first member and the second member is 0.1 mm or more, (3) The cross-sectional area of the molten metal at the interface between the first and second members is greater than the cross-sectional area formed by the length along the outer edge of the molten metal at the interface and the thickness of the second member.
• the present invention also provides a dissimilar metal bonded structure having a first member made of a metallic material, a second member made of a metallic material different from the first member, an overlapping portion formed by the second member overlapping the first member on the heat-input side, and a molten metal portion formed in the overlapping portion and formed by melting and solidifying the first member and the second member, wherein (1) the depth of the molten metal portion melting from the overlapping interface of the overlapping portion into the second member is 0.1 mm or more, (2) the depth of the molten metal portion melting from the overlapping interface of the overlapping portion into the second member is 0.1 mm or more,
• the molten metal width dimension at the interface in the longitudinal direction of the first and second members is at least 1.2 times the thickness of the member with the shorter thickness if the first and second members have different thicknesses, or at least 1.2 times the thickness of either member if the first and second members have the same thickness; and (3) the cross-sectional area of the molten metal portion at the overlapping interface between
• the present invention also provides a dissimilar metal bonded structure having a first member made of a metallic material, a second member made of a metallic material different from the first member, an overlapping portion formed by the second member overlapping the first member on the heat-input side, and a molten metal portion formed in the overlapping portion and formed by melting and solidifying the first member and the second member, wherein a narrow portion is formed in the plate width direction by a notch penetrating in the plate thickness direction in the first member or the second member in the overlapping portion, and the molten metal portion is: (1) a molten metal portion that melts into the second member from the overlapping interface of the overlapping portion The depth of the gap is 0.1 mm or more; (2) the molten width of the molten metal at the overlapping interface between the first and second members in the longitudinal direction of the first and second members is 1.2 times or more the thickness of the member with the shorter thickness if the first and second members have different thicknesses, or 1.2 times or more the thickness of either member if
• the present invention also provides a dissimilar metal joint structure having a first member made of a metallic material, a second member made of a metallic material different from the first member, an overlapping portion formed by the second member overlapping the first member on the heat-input side, and a molten metal portion formed in the overlapping portion where the first member and the second member are melted and solidified, wherein a thinned portion having a short length in the plate thickness direction is formed in the first member or the second member in the overlapping portion by a concave groove formed in the plate thickness direction, and the molten metal
• the metal part is characterized by satisfying the following conditions: (1) the depth of the molten metal part that melts from the overlapping interface of the overlapping part into the second member is 0.1 mm or more; (2) the melting width dimension of the molten metal in the longitudinal direction of the first member and the second member at the overlapping interface between the first member and the second member is 1.2 times or more the plate thickness of the thinned portion of the first member or the second member
• ductile fracture occurs not in the molten metal portion of the overlapping portion, but in the base material portion of the plate members that make up the dissimilar metal bonded structure. This prevents destabilization of fatigue strength due to brittle fracture at the overlapping interface of the molten metal portions of the dissimilar metals, and allows for the production of a dissimilar metal bonded structure with stable strength reliability.
• FIG. 1 is a cross-sectional view showing the penetration depth, fusion width, fusion area, and plate thickness of the plate members constituting the lap joint of a molten metal portion formed in a lap joint in which one heat-input side is an aluminum-based plate member and the other side is a copper-based plate member, according to an embodiment of the present invention.
• FIG. 2 is a diagram showing the lap joint of FIG. 1 as viewed from the heat input side (laser beam irradiation side), illustrating the melting area at the overlapping interface of the lapped portion and the total length of the molten metal portion at the overlapping interface.
• FIG. 1 is a cross-sectional view showing a cross section in which the penetration depth of the molten metal portion formed in a lap joint made of dissimilar metals according to an embodiment of the present invention penetrates the plate member on the opposite side from the heat input side.
• FIG. 10 is an explanatory diagram illustrating a technique in which a laser beam is moved repeatedly at high speed within a predetermined region in the melting direction.
• FIG. 1 is a schematic diagram showing a lap joint with a molten bead shape that is an annular ellipse, viewed from the heat input side (the side irradiated with the laser beam), illustrating the molten area at the overlapping interface of the lapped portion and the total length of the molten metal at the overlapping interface.
• FIG. 1 is an explanatory diagram illustrating the relationship between specific values of the fusion width and fusion area and the fracture mode according to the present invention.
• FIG. 1 is an explanatory diagram showing a load-displacement curve due to ductile fracture occurring in a lap joint according to an embodiment of the present invention.
• 10 is a cross-sectional view illustrating a state in which base material fracture occurs in a plate member having low strength when a tensile force acts in the longitudinal direction of a lap joint.
• FIG. 10 is a cross-sectional view illustrating a state in which base material fracture occurs in a plate member having low strength when a tensile force acts in a direction perpendicular to the longitudinal direction of the lap joint.
• FIG. 10 is a cross-sectional view illustrating a state in which base material fracture occurs in a plate member having a small plate thickness when a tensile force acts in the longitudinal direction of a lap joint.
• FIG. 10 is an explanatory diagram illustrating a state in which base material fracture occurs in a plate member having a small plate thickness when a tensile force acts in a direction perpendicular to the longitudinal direction of the lap joint.
• FIG. 10 is a diagram showing the lap joint as viewed from the heat input side (laser beam irradiation side), and shows the melting area at the overlapping interface of the overlapping portion and the plate width of the overlapping portion.
• 10 is a cross-sectional view showing a configuration in which the plate width in the short direction of the plate member on the heat input side of the overlapping portion is locally reduced according to an embodiment of the present invention.
• FIG. This is a diagram showing the lap joint of Figure 14 as seen from the heat input side (laser beam irradiation side), and shows the melting area at the overlapping interface of the overlapping part and the shape of the part where the plate width is locally reduced.
• 16 is a cross-sectional view illustrating base material fracture at a portion where the plate thickness in FIG.
• FIG. 10 is a cross-sectional view showing a configuration in which a thin-walled portion consisting of a recess is formed in the short side direction of the plate member on the heat-input side of the overlapping portion according to an embodiment of the present invention.
• FIG. 18 is a cross-sectional view illustrating the destruction of the base material at the thin-walled portion in FIG. 17.
• 10 is a cross-sectional view showing a configuration in which a thin-walled portion consisting of a recess is formed in the short direction of the plate member on the side opposite to the heat input side of the overlapping portion according to an embodiment of the present invention.
• FIG. 20 is a cross-sectional view illustrating the destruction of the base material at the thin-walled portion in FIG.
• FIG. 1 is a cross-sectional view showing the penetration depth, fusion width, fusion area, and plate thickness of the plate members constituting the lap joint of a molten metal portion formed in a lap joint in which one heat-input side is a copper-based plate member and the other side is an aluminum-based plate member, according to an embodiment of the present invention.
• FIG. 22 is a diagram showing the lap joint of FIG. 21 as viewed from the heat input side (laser beam irradiation side), illustrating the melting area at the overlapping interface of the overlapping portion and the total length of the molten metal portion at the overlapping interface.
• FIG. 1 is a cross-sectional view showing the penetration depth, molten width, molten area, and plate thickness of the plate members constituting the lap joint of an embodiment of the present invention, of a molten metal portion formed in a lap joint in which one heat-input side is an aluminum-based plate member and the other side is a copper-based plate member having a plating layer.
• FIG. 24 is a diagram showing the lap joint of FIG. 23 as viewed from the heat input side (laser beam irradiation side), illustrating the melting area at the overlapping interface of the overlapping portion and the total length of the molten metal portion at the overlapping interface.
• FIG. 10 is a cross-sectional view showing an example of using a lap joint, in which one heat-input side is an aluminum-based plate member and the other side is a copper-based plate member with a plated layer, as a bus bar, according to an embodiment of the present invention.
• FIG. 26 is a diagram showing the bus bar of FIG. 25 as viewed from the heat input side (laser beam irradiation side), illustrating the melted area at the overlapping interface of the overlapping portion and the total length of the molten metal portion at the overlapping interface.
• FIG. 10 is a cross-sectional view showing an example of a lap joint in which one heat-input side is a copper-based plate member with a plated layer and the other side is an aluminum-based plate member, and which is used as a bus bar, according to an embodiment of the present invention.
• FIG. 26 is a cross-sectional view showing an example of a modification of FIG. 25 in which the shape of the bus bar is inverted and a lap joint is used as the bus bar, with one side to which heat is input being an aluminum-based plate member and the other side being a copper-based plate member with a plated layer.
• FIG. 26 is a diagram showing an example of a usage form of the present invention, illustrating a configuration when terminals of two adjacent cells are connected via the bus bar shown in FIG.
• FIG. 10 is a diagram showing an example of an application form of the present invention, illustrating a configuration in which electrode terminals made of dissimilar metals of two adjacent unit cells are connected to a bus bar made of an aluminum-based member.
• 31 is a diagram showing the configuration when viewed from the side in the direction A in FIG. 30.
• FIG. 31 is a diagram showing the configuration when viewed from the side in the direction B in FIG. 30.
• FIG. 31 is a diagram showing the configuration of the bus bar in FIG. 30 when viewed from the heat input side in a state where the bus bar, the positive electrode terminal, and the negative electrode terminal are laser beam welded together.
• FIG. 34 is a cross-sectional view showing the AA cross section in FIG. 33.
• FIG. 34 is a diagram showing the configuration of the bus bar and the negative electrode terminal in FIG. 33 when viewed from the heat input side after laser beam welding.
• FIG. FIG. 10 is a diagram showing an example of an application form of the present invention, illustrating the configuration when viewed from the heat input side in a state where a bus bar and a voltage detection line terminal are laser beam welded.
• 37 is a cross-sectional view showing the cross section BB in FIG. 36.
• 37 is a diagram showing the configuration of the bus bar and the voltage detection terminal in FIG. 36 when laser beam welded together, as viewed from the heat input side.
• FIG. FIG. 1 is a cross-sectional view showing the configuration of a molten metal portion in a conventional lap joint using dissimilar metals.
• FIG. 40 is a cross-sectional view showing a state in which brittle fracture has occurred in the lap joint shown in FIG. 39 in the direction of the lap interface of the welded metal portion.
• FIG. 41 is an explanatory diagram showing an example of a load-displacement curve in brittle fracture occurring at the overlapping interface of the molten metal portion shown in FIG. 40.
• 1 is a cross-sectional view showing a cross section of a molten metal portion in which penetration into a lower member is controlled to be small in Patent Document 1.
• FIG. 1 is a cross-sectional view showing a molten metal portion in which the penetration into the lower member is controlled to be small, when the number of fusion lines is increased to increase the molten area of the molten metal portion in Patent Document 1.
• the basic concept of the present invention is to propose a dissimilar metal bonded structure with a different configuration from that of Patent Document 1, which is capable of undergoing ductile fracture in the base material rather than the molten metal portion when an external force is applied.
• Figures 1 and 2 show a lap joint (dissimilar metal joint structure) made of an elongated, flat, rectangular aluminum-based member (plate member) 1 and an elongated, flat, rectangular copper-based member (plate member) 2.
• the side irradiated with the laser beam (the side where heat is input) is the aluminum-based member 1, and the opposite side is the copper-based member 2.
• the side irradiated with the laser beam (the side where heat is input) may be referred to as the upper member or the first member, and the opposite side as the lower member or the second member, depending on the depiction in the drawings.
• the aluminum-based material may also be referred to as the first metal
• the copper-based material may also be referred to as the second metal.
• the ends of the aluminum-based member 1, which is a plate member made of a first metal, and the copper-based member 2, which is a plate member made of a second metal, are overlapped at an overlapping portion Ov along the longitudinal direction Ld.
• the widths (lengths in the direction perpendicular to the longitudinal direction) L1 of the aluminum-based member 1 and the copper-based member 2 are set to the same length, and when overlapped, the side surfaces of the aluminum-based member 1 and the copper-based member 2 in the longitudinal direction are dimensionally consistent.
• the plate thickness of the aluminum-based member 1 and the copper-based member 2 is set to a range of 0.2 to 4 mm.
• the plate thickness of the aluminum-based member 1 and the copper-based member 2 is set to be the same, or one of them is set to be shorter. For example, it is expected that the plate thickness of the copper-based member 2 will be shorter due to strength considerations. This will allow the strength of the aluminum-based member 1 and the copper-based member 2 to be closer.
• a molten metal portion 3 is formed at the overlapping portion Ov of the aluminum-based member 1 and the copper-based member 2, for example, by irradiation with a laser beam.
• This molten metal portion 3 is a metal compound in which the metals of the aluminum-based member 1 and the copper-based member 2 have melted into each other.
• the molten metal portion 3 is formed near the center of the overlapping portion Ov in the longitudinal direction.
• the molten metal portion 3 penetrates the aluminum-based member 1 and melts into the copper-based member 2 to near the center in the plate thickness direction.
• the penetration depth D of this molten metal portion 3 can be controlled by the output and scanning speed of the laser beam.
• the inventors have found that the following dimensional relationship for the molten metal portion 3 is effective as a configuration that allows ductile fracture to occur in the base material portion rather than the molten metal portion when an external force is applied.
• the penetration depth D of the molten metal portion 3 is set to a depth of 0.1 mm or more on the copper-based member 2 side, based on the overlapping interface 4 where the aluminum-based member 1 and copper-based member 2 come into contact, while taking into consideration variations in the flatness and surface roughness of each plate member. It has been found that if the penetration depth D is less than 0.1 mm, it is not possible to ensure sufficient fusion between the aluminum-based member 1 and copper-based member 2.
• the penetration depth D into the copper-based member 2 covers the surface of the copper-based member 2 opposite the overlapping interface 4, and therefore the penetration depth D into the copper-based member 2 has the relationship "0.1 mm ⁇ D ⁇ T2.”
• the thickness Tmin the thickness of the molten metal portion 3 in the longitudinal direction of the aluminum-based member 1 and the copper-based member 2 at the overlapping interface 4 between the aluminum-based member 1 and the copper-based member 2 and the thickness Tmin satisfy the relationship "(1.2 x Tmin) ⁇ W ⁇ L2.”
• L2 is the longitudinal length of the overlapping portion Ov shown in Figures 1 and 2.
• a laser beam that can achieve the above-mentioned melt width W for one bead (single bead) can be obtained by optimizing the output, focal position, scanning speed, etc., using a multi-mode oscillation mode that is often used in welding work, and a beam with a beam spot diameter of 100 ⁇ m or more.
• the penetration depth D of the copper-based member 2 in the molten metal portion 3 may reach the thickness T2, causing the molten metal portion 3 to penetrate through, as shown in Figure 3.
• FIG. 4 shows the ray trajectory 8 of a laser beam 6 that moves in the melting direction while tracing a minute arc 7 at high speed, and the molten bead surface 9.
• This repeated high-speed movement of the laser beam 6 can be in the shape of a polygon, a cycloid curve, or two-dimensional movement such as a double swing, in addition to a minute arc.
• the metal fusion zone 3 is formed as a single bead with no partial overlap in the direction of the weld width W of the overlapping interface 4.
• Patent Document 1 when a laser beam is irradiated multiple times to overlap multiple beads, this increases the construction time and the total heat input, which can result in reduced production efficiency and concerns about adverse effects on product performance, such as deformation of the lap joint due to excessive heat input and thermal degradation of the resin part.
• using a single bead avoids these problems.
• the laser beam 6 used it is effective for the laser beam 6 used to have a small beam diameter, for example a single-mode or multi-mode oscillation mode with a beam spot diameter of 80 ⁇ m or less.
• a small beam diameter for example a single-mode or multi-mode oscillation mode with a beam spot diameter of 80 ⁇ m or less.
• ductile fracture means fracture that occurs while stretching and plastically deforming at the time of fracture.
• the total length AL of the periphery of the molten metal portion 3 at the overlap interface 4 refers to the length of the fracture initiation point when an external force is applied.
• the shape of the molten metal portion 3 at the overlap interface 4 is an annular ellipse as shown in Figure 5
• fracture will occur mainly on the outer diameter side of the molten metal portion 3 when stress is applied, so the length on the outer diameter side should be taken as the total length AL so as to satisfy the above relationship.
• the molten width W is calculated by adding the width Wc of the annular portion of the annular molten metal portion 3.
• the fusion width and fusion area are ensured to satisfy the above relationship so that the strength is greater than the base material strength, avoiding the fracture path that would lead to brittle fracture, then overall the fracture will be induced to occur on the weaker side of either the aluminum or copper base material, i.e., ductile fracture.
• Figure 7 illustrates the region of fracture morphology when an external force is applied, based on the relationship between the molten width W and molten area S described above obtained by the inventors, with the molten width correlation ratio [W/Tmin] between the molten width W of the molten metal portion 3 at the lap interface 4 and the plate thickness Tmin on the horizontal axis, and the molten area correlation ratio [S/(AL x Tmin)] between the molten area S at the lap interface 4 and the total length AL of the periphery of the molten metal portion and Tmin on the vertical axis.
• melt width correlation ratio [W/Tmin] is "1.2 or greater” and the melt area correlation ratio [S/(L1 x Tmin)] is “1 or greater”
• base material failure ductile failure
• interfacial failure brittle failure
• the interface fracture region is the region where brittle fracture occurs as shown in Figure 41, where there is almost no plastic deformation of the material at the time of fracture and the fracture occurs instantaneously.
• ductile fracture occurs where the fracture progresses gradually while accompanied by plastic deformation of the base material.
• the thickness of the plate members (aluminum-based and copper-based members) used in the relationship between the melt width W and melt area S described above is the thickness Tmin of the shorter plate member, but even if the plate members (aluminum-based and copper-based members) are set to the same thickness, a similar relationship can be applied.
• Figures 9 and 10 show the state of base material failure when aluminum-based member 1 and copper-based member 2 are used and the plate thickness is the same. In this case, since the plate thickness is the same, the strength of the base material itself is smaller in aluminum-based member 1.
• Figure 9 shows the case where a tensile force (external force) acts in the longitudinal direction of a lap joint, with base material failure 10 occurring in the aluminum-based member 1, which has lower base material strength.
• base material failure occurs on the tension side, not the compression side.
• Figure 10 shows the case where a tensile force (external force) is applied in a direction perpendicular to the longitudinal direction of the lap joint (vertical direction in the drawing), and base material failure 10 occurs in the aluminum-based member 1, which has lower base material strength.
• the aluminum-based member 1 is pulled apart, and base material failure 10 occurs around the entire circumference of the molten metal portion 3.
• Figures 11 and 12 show the state of base material failure when aluminum-based member 1 and copper-based member 2 are used, and the plate thickness of copper-based member 2 is shortened. In this case, because the plate thickness of copper-based member 2 is thinner than that of aluminum-based member 1, the strength of the base material itself is smaller for copper-based member 2.
• Figure 11 shows the case where a tensile force (external force) acts in the longitudinal direction of a lap joint, with base material failure 10 occurring in the copper-based member 2, which has lower base material strength.
• a tensile force exital force
• base material failure 10 occurs in the copper-based member 2, which has lower base material strength.
• Figure 12 shows the case where a tensile force (external force) is applied in a direction perpendicular to the longitudinal direction of the lap joint (vertical direction in the drawing), and base material failure 10 occurs in the copper-based member 2, which has lower base material strength.
• the copper-based member 2 is pulled apart, and base material failure 10 occurs around the entire circumference of the molten metal portion 3.
• the type of fracture that occurs will vary depending on how the load is applied, the thickness of each plate member, the material and physical properties, etc., but in any case, it will result in ductile fracture accompanied by plastic deformation as shown in Figure 8, eliminating the risk of brittle fracture.
• the penetration depth D of the molten metal portion to "0.1 mm ⁇ D ⁇ T2”
• the molten width W of the molten metal portion 3 to "(1.2 x Tmin) ⁇ W ⁇ L2”
• the molten area S of the molten metal portion 3 to "(AL x Tmin) ⁇ S ⁇ SAL”
• a laser beam is used as the heat source for forming the molten metal portion, but electron beam welding, arc welding, etc. can also be used.
• Electron beam welding achieves the same effect as laser beam welding by increasing the beam's convergence and moving it in the melting direction while oscillating at high speed, making it possible to form a molten metal area with a large melt width in a single bead.
• Arc welding, while inferior in convergence, can also form a molten metal area with a large melt width in a single bead by melting while slightly oscillating the electrode.
• the penetration depth D of the molten metal portion 3 into the copper-based member 2 and the longitudinal molten width W of the molten metal portion 3 have the same relationship as in the first embodiment.
• Base material fracture in this structure is in the same form as base material fracture 10 shown in Figures 9 to 12, and is a ductile fracture accompanied by plastic deformation as in the first embodiment, eliminating the risk of brittle fracture.
• the upper aluminum-based member 1 has a locally narrow portion 11 (hereinafter referred to as a narrow portion).
• This narrow portion 11 is adjacent to the molten metal portion 3 of the aluminum-based member 1 and is formed within the overlapping portion Ov. Furthermore, this narrow portion 11 extends inward from both side surfaces of the aluminum-based member 1 and is formed by a notch 11n that penetrates the aluminum-based member 1 in the thickness direction. Therefore, the narrow portion 11 is weaker in strength.
• the narrow width portion 11 is formed on the side where a tensile force acts on the molten metal portion 3 (the left side of the molten metal portion 3 of the aluminum-based member 1 in Figure 14).
• the side opposite the side where the tensile force acts is subject to a compressive force, making it less likely for fracture to occur.
• the melt width W at the overlapping interface 4 and the thickness T1 are determined to have the relationship "(1.2 x T1) ⁇ W ⁇ L2".
• the melting area S at the overlapping interface 4 and the plate width Lmin are determined to have the relationship "(Lmin x T1) ⁇ S ⁇ SAL.”
• a narrow width portion 11 with a locally narrow plate width is provided in the upper aluminum-based member 1, and an example is shown in which base material fracture occurs in the aluminum-based member 1 when an external force is applied.
• the same effect can be achieved by forming a similar narrow width portion 11 in the lower copper-based member 2 instead.
• the penetration depth D of the molten metal portion to "0.1 mm ⁇ D ⁇ T2”
• the molten width W of the molten metal portion 3 to "(1.2 x T1) ⁇ W ⁇ L2”
• the molten area S of the molten metal portion 3 to "(Lmin x T1) ⁇ S ⁇ SAL”
• the base material strength is naturally high, and when it is difficult to ensure a molten width W and molten area S of the molten metal portion 3 that exceeds the base material strength, or to avoid the risk of fracture at the overlapping interface and to increase the likelihood of base material fracture, a short (thin) portion of the base material is locally formed.
• the penetration depth D of the molten metal portion 3 into the copper-based member 2 has the same relationship as in the first embodiment.
• the upper aluminum-based member 1 has a locally thin portion (hereinafter referred to as a thinned portion) 12.
• This thinned portion 12 is adjacent to the molten metal portion 3 of the aluminum-based member 1 and is formed within the overlapping portion Ov.
• This thinned portion 12 extends inward in the thickness direction from the heat-input surface of the aluminum-based member 1, and is formed by a concave groove 12g that extends in the width direction of the aluminum-based member 1. Therefore, this thinned portion 12 is weaker in strength.
• the groove 12g is formed across the entire width of the aluminum-based member 1, but it may also be formed as a groove 12g of a predetermined length across only a portion of the width of the aluminum-based member 1, rather than across the entire width of the plate.
• the thinned portion 12 is formed on the side where a tensile force acts on the molten metal portion 3 (the left side of the molten metal 3 in the aluminum-based member 1 in Figure 17).
• the side opposite the side where the tensile force acts is subject to a compressive force, making it less likely to break.
• the melt width W at the overlap interface 4 and the plate thickness Tgrv are determined to have the relationship "(1.2 x Tgrv) ⁇ W ⁇ L2.”
• the melting area S and plate thickness Tgrv at the overlapping interface 4 are determined to have the relationship "(L1 x Tgrv) ⁇ S ⁇ SAL".
• the penetration depth D of the molten metal portion to "0.1 mm ⁇ D ⁇ T2”
• the molten width W of the molten metal portion 3 to "(1.2 x Ttgv) ⁇ W ⁇ L2”
• the molten area S of the molten metal portion 3 to "(L1 x Tgrv) ⁇ S ⁇ SAL”
• a locally thinned portion 12 is provided in the upper aluminum-based member 1, which induces base material fracture in the aluminum-based member 1 when an external force is applied. Conversely, the same effect can be achieved by forming a similar thinned portion 12 in the lower copper-based member 2.
• a brief explanation is provided below using Figures 19 and 20.
• the copper-based member 2 below the overlapping interface 4 has a locally thin portion 12 (hereinafter referred to as a thinned portion).
• This thinned portion 12 is adjacent to the molten metal portion 3 of the copper-based member 2 and is formed within the overlapping portion Ov. Furthermore, this thinned portion 12 extends inward in the thickness direction from the surface on the overlapping interface 4 side, and is formed by a concave groove 12g that extends in the width direction of the copper-based member 2. Therefore, this thinned portion 12 is weaker in strength.
• the thinned portion 12 is formed on the side where tensile force acts on the molten metal portion 3 (to the right of the molten metal 3 of the copper-based member 2 in Figure 19).
• the side opposite the side where tensile force acts is subject to compressive force, making it less likely for fracture to occur.
• the melt width W at the overlap interface 4 and the thickness Tgrv are determined to have the relationship "(1.2 x Tgrv) ⁇ W ⁇ L2.”
• the melting area S and plate thickness Tgrv at the overlapping interface 4 are determined to have the relationship "(L1 x Tgrv) ⁇ S ⁇ SAL".
• the groove 12g is formed on the side of the overlapping interface 4, but it can also be formed on the surface opposite the overlapping interface 4 (the lower side in the figure), as shown in Figure 17. Even in this case, the same effects and advantages as those shown in Figure 18 can be achieved.
• the grooves 12g can be formed by mechanical thinning methods such as plastic processing or cutting, thermal thinning methods such as electric discharge machining or laser irradiation, or chemical thinning methods such as local etching or reactive liquids.
• Figures 21 and 22 show a lap joint consisting of a long, thin, flat, rectangular copper-based member (plate member) 2 and a long, thin, flat, rectangular aluminum-based member (plate member) 1.
• the side irradiated with the laser beam is the copper-based member 2, and the opposite side is the aluminum-based member 1.
• the respective ends of the copper-based member 2 and aluminum-based member 1, which serve as plate members, are overlapped at an overlapping portion Ov along the longitudinal direction Ld.
• the widths L1 (lengths perpendicular to the longitudinal direction) of the copper-based member 2 and aluminum-based member 1 are set to the same length, and when overlapped, the side surfaces of the copper-based member 1 and aluminum-based member 1 in the longitudinal direction are dimensionally consistent.
• the plate thickness of the copper-based member 2 and the aluminum-based member 1 is set to a range of 0.2 to 4 mm.
• the plate thickness of the copper-based member 2 and the aluminum-based member 1 is set to be the same, or one of them is set to be shorter. For example, it is expected that the plate thickness of the copper-based member 2 will be shortened due to tensile strength relationships. This will allow the strength of the aluminum-based member 1 and the copper-based member 2 to be closer.
• a molten metal portion 3 is formed at the overlapping portion Ov of the copper-based member 2 and the aluminum-based member 1, for example, by irradiation with a laser beam.
• This molten metal portion 3 is a metal compound in which the metals of the copper-based member 2 and the aluminum-based member 1 have melted into each other.
• the molten metal portion 3 is formed near the center of the overlapping portion 3 in the longitudinal direction. The molten metal portion 3 penetrates the copper-based member 2 and melts into the aluminum-based member 1 up to near the center in the plate thickness direction.
• a configuration is achieved that allows ductile fracture to occur in the base material rather than the molten metal portion when an external force is applied. This is achieved by setting the penetration depth D of the molten metal portion 3 to "0.1 mm ⁇ D ⁇ T2", the molten width W of the molten metal portion 3 to "(1.2 x Tmin) ⁇ W ⁇ L2", and the molten area S of the molten metal portion 3 to "(AL x Tmin) ⁇ S ⁇ SAL", so that when an external force is applied, ductile fracture will occur in the base material rather than brittle fracture in the molten metal portion 3.
• this embodiment also suppresses the destabilization of fatigue strength due to brittle fracture at the overlapping interface of the molten metal portions made of dissimilar metals, thereby obtaining a dissimilar metal bonded structure with stable strength reliability. It goes without saying that the same can be applied to some of the embodiments described above.
• the aluminum-based member 1 and the copper-based member 2 have different physical properties, such as melting point, thermal conductivity, and light absorption rate, so the penetration behavior differs when the light is irradiated on the surface of the aluminum-based member 1 and when the light is irradiated on the surface of the copper-based member 2.
• the strength per unit area of the weld metal portion 3 may be higher than the strength of either base material at the upper limit of the range, as shown in Figure 6.
• the penetration depth D of the molten metal portion is set to "0.1 mm ⁇ D ⁇ T2”
• the molten width W of the molten metal portion 3 is set to "(1.2 x Tmin) ⁇ W ⁇ L2”
• the molten area S of the molten metal portion 3 is set to "(AL x Tmin) ⁇ S ⁇ SAL”. This makes it possible to induce ductile fracture in the base material rather than brittle fracture in the molten metal portion 3 when an external force is applied.
• the plate thickness includes the thickness of the plating layer 13.
• the molten metal portion 3 contains plating components (nickel and tin) in addition to aluminum and copper-based metal materials, making the component composition of the molten metal structure more complex.
• plating components nickel and tin
• the strength properties of the molten metal structure still tend to be higher than the strength of the base material, as described in embodiment 1.
• the penetration depth D of the molten metal portion, the molten width W of the molten metal portion 3, and the molten area S of the molten metal portion 3 satisfy the above-mentioned relationship, so that when an external force is applied, ductile fracture occurs in the narrow width portion 11 of the base material, rather than brittle fracture in the molten metal portion 3. Therefore, it is possible to suppress destabilization of fatigue strength due to brittle fracture at the overlapping interface of the molten metal portions of dissimilar metals, and to obtain a dissimilar metal bonded structure with stable strength reliability.
• Figure 23 shows a configuration in which a plating layer is formed on the copper-based member 2, it is also possible to form a plating layer on the aluminum-based member 1, or on both the aluminum-based member 1 and the copper-based member 2, and the above-mentioned effects can also be achieved by melting the plating layer.
• This dissimilar metal bonded structure is the dissimilar metal bonded structure with a plated layer formed thereon, as described in the sixth embodiment (Example 6).
• This embodiment is an example in which it is applied to a bus bar that connects the electrode terminals of cells in a battery pack.
• the penetration depth D, fusion width W, and fusion area S can be any of those described in the above-described embodiments.
• Figures 25 and 26 show a longitudinal cross section of the busbar as viewed from the side.
• the busbar 14 is made from a dissimilar metal joint structure as described in Examples 1 to 6.
• the upper heat input side is made of an aluminum-based member 1
• the lower side is made of a copper-based member 2 on which a plating layer 13 is formed.
• the joint between the aluminum-based member 1 and the copper-based member 2 (the portion including the molten metal portion 3) has a stepped shape (a shape that protrudes upward in the drawings) consisting of a curved portion 15 that absorbs and alleviates external forces such as vibration and expansion of the battery pack.
• a lap joint is then formed on the protruding flat portion, and a laser beam is irradiated onto the surface of the upper aluminum-based member 1 to form a molten metal portion 3.
• the penetration depth D, molten width W, and molten area S are as described in the respective embodiments above.
• Figure 27 shows a modified example of the busbar 14.
• the busbar 14 is made from a dissimilar metal joint structure, with the upper heat input side being made of a copper-based member 2 with a plating layer 13 formed thereon, and the lower side being made of an aluminum-based member 1.
• the joint (molten metal portion 3) between the copper-based member 2 and the aluminum-based member 1 has a stepped shape (a shape that protrudes upward in the drawing) consisting of a curved portion 15 to absorb and mitigate external forces such as vibration and expansion of the battery pack.
• a lap joint is then formed on the protruding flat portion, and a laser beam is irradiated onto the surface of the upper copper-based member 2 to form a molten metal portion 3.
• the penetration depth D, molten width W, and molten area S are as described in the respective embodiments above.
• Figure 28 shows a further modified example of the busbar 14.
• the busbar 14 is made from a dissimilar metal joint structure, with the upper heat input side being made of an aluminum-based member 1 and the lower side being made of a copper-based member 2 on which a plating layer 13 is formed.
• the joint (molten metal portion 3) between the aluminum-based member 1 and the copper-based member 2 has a stepped shape (a shape that protrudes downward in the drawing) consisting of a curved portion 15 to absorb and mitigate external forces such as vibration and expansion of the battery pack.
• a lap joint is formed on the flat portion protruding downward, and a laser beam is irradiated onto the surface of the upper aluminum-based member 1 to form a molten metal portion 3.
• the penetration depth D, molten width W, and molten area S are as described in the respective embodiments above.
• bus bar 14 described above can be used, for example, as a bus bar to electrically connect the electrode terminals of different cells.
• Figure 29 shows an example of a battery pack made up of adjacent cells combined together.
• a battery pack 22 is formed by combining multiple cells 16.
• Each cell 16 has a battery can and a battery lid.
• the battery can contains a wound electrode body as a "storage element" that outputs stored electricity, and the opening of the battery can is sealed by the battery lid.
• the battery can also contains an electrolyte, and the wound electrode body is immersed in the electrolyte. Note that electrolytes other than liquid electrolytes, such as solid electrolytes, may also be used.
• the battery lid is provided with a positive electrode terminal 17 and a negative electrode terminal 18.
• the single cell 16 charges the wound electrode body via the positive electrode terminal 17 and negative electrode terminal 18, and also supplies power to an external load.
• a predetermined number of these cells 16 are stacked to form a battery pack, and the electrode terminals of adjacent cells 16 are connected by a bus bar.
• the bus bar electrically connects the positive electrode terminal 17 and negative electrode terminal 18 of adjacent cells 16, and the cells 16 are connected in series.
• each cell 16 has a pair of positive and negative electrode terminals 17 and 18.
• the positive and negative electrode terminals 17 and 18 of adjacent cells 16 are connected.
• the aluminum-based member 1 of the busbar 14 is connected to the positive electrode terminal 17 of the cell 16, which is made of an aluminum-based material
• the copper-based member 2 of the busbar 14, which has a nickel- or tin-plated plating layer 13 is connected to the negative electrode terminal 18 of the cell 16, which is also made of a copper-based material.
• busbar 14 that utilizes the dissimilar metal bonded structure described in the first to sixth embodiments, even if a mechanical external force due to a temperature rise in the battery pack 22 acts on the busbar, it is possible to lead to ductile fracture in the base material rather than brittle fracture in the molten metal portion 3. Therefore, it is possible to suppress destabilization of fatigue strength due to brittle fracture at the overlapping interface of the molten metal portions of dissimilar metals, resulting in a busbar with stable strength reliability.
• the molten metal part as a single bead when heat is input using a laser beam or other method, there is no increase in construction time or total heat input, which in turn suppresses declines in production efficiency and avoids adverse effects on product performance, such as deformation of lap joints and thermal degradation of resin parts due to excessive heat input.
• Figure 31 shows a side view as viewed from direction A shown in Figure 30
• Figure 32 shows a side view as viewed from direction B shown in Figure 30.
• Figures 30 to 32 show the joints between the electrode terminals 17, 18 and bus bar 19 of two adjacent cells 16A, 16B that make up the battery pack.
• Cell 16A has a positive electrode terminal 17A made of an aluminum-based material and a negative electrode terminal 18A made of a copper-based material
• cell 16B has a positive electrode terminal 17B made of an aluminum-based material and a negative electrode terminal 18B made of a copper-based material. Note that the symbols in parentheses after the reference numbers in the drawings indicate the materials.
• bus bars 19-1 and 19-2 shown in Figures 30 and 31 are the first member made of a first metal, and negative electrode terminal 18B of cell 16B and negative electrode terminal 18A of cell 16A, made of a second metal different from the first metal, are the second member.
• This combination forms a dissimilar metal bonded structure corresponding to Examples 1 to 6.
• the positive electrode terminal 17A, made of an aluminum-based material, and the negative electrode terminal 18B, made of a copper-based material, are electrically connected by a bus bar 19-1 made entirely of an aluminum-based material.
• the negative electrode terminal 18A, made of a copper-based material is electrically connected by a bus bar 19-2 made entirely of an aluminum-based material, and similarly, the positive electrode terminal 17B, made of an aluminum-based material, is electrically connected by a bus bar 19-3 made entirely of an aluminum-based material.
• the dissimilar metals that are the subject of this invention are the joining area between the negative electrode terminal 18B of the cell 16B and the bus bar 19-1, and the joining area between the negative electrode terminal 18A of the cell 16A and the bus bar 19-2. Furthermore, in these two joining areas, a molten metal portion 3 is formed using any of the methods described in the first to sixth embodiments above.
• the positive electrode terminal 17A of the cell 16A and the bus bar 19-1, and the positive electrode terminal 17B of the cell 16B and the bus bar 19-3 are both joined using an aluminum-based material, so no intermetallic compounds are formed and there is little risk of embrittlement.
• Figure 33 shows an extracted portion where the positive electrode terminal 17A, made of an aluminum-based material, and the negative electrode terminal 18B, made of a copper-based material, are electrically connected by a bus bar 19-1 made entirely of an aluminum-based material.
• a molten metal portion 20 is formed at the joint between the positive electrode terminal 17A, which is made of an aluminum-based material, and the bus bar 19-1, which is also made of an aluminum-based material. As described above, this molten metal portion 20 is made of the same type of aluminum-based metal. Note that while the cross-sectional shape of the molten metal portion 20 along the overlapping interface is shown as a horizontal "U" in the figure, the bead shape itself is arbitrary.
• a molten metal portion 3 is formed at the joint between the negative electrode terminal 18B, made of a copper-based material, and the bus bar 19-1, made of an aluminum-based material. As described above, this molten metal portion 3 is a joint made of dissimilar metals, aluminum and copper. Note that while the cross-sectional shape of the molten metal portion 3 along the overlapping interface is shown as a horizontal "U" in the figure, the bead shape itself is arbitrary.
• Figure 34 shows the A-A cross section of Figure 33, and similar to the embodiment shown in Figure 1, a molten metal portion 3 is formed penetrating the bus bar 19-1 toward the negative electrode terminal 18B made of a copper-based material.
• the penetration depth D of this molten metal portion 3 has the relationship shown in the above-mentioned embodiment.
• Figure 35 also shows the molten width W and molten area S of the molten metal portion 3, which also have the relationship shown in the above-mentioned embodiment.
• the penetration depth D of the molten metal portion 3, the molten width W of the molten metal portion 3, and the molten area S of the molten metal portion 3 formed in the joint area between the negative electrode terminal 18B of the cell 16B and the bus bar 19-1, and in the joint area between the negative electrode terminal 18A of the cell 16A and the bus bar 19-2, are as described in the respective embodiments above.
• a flat terminal portion 23 formed on a bus bar 19 made of an aluminum-based material and connected to the electrode terminal of the cells that make up the battery pack is overlaid on a flat voltage detection terminal 21 made of a copper-based material, and a laser beam is irradiated onto the surface of this voltage detection terminal 21 to form a molten metal portion 3.
• a lead wire 24 is electrically connected to the voltage detection terminal 21, and is connected to control means (not shown).
• the terminal portion 23 of the bus bar 19 shown in Figure 36 is the first member made of a first metal, and the voltage detection terminal 21 made of a second metal different from the first metal is the second member.
• This combination forms a dissimilar metal bonded structure corresponding to Examples 1 to 6.
• the voltage detection terminal 21 is made of a copper-based material such as phosphor bronze, or a material such as nickel. If a copper-based material is used, it may be nickel-plated, tin-plated, or both.
• the voltage detection terminal 21 can be placed on the back side of the busbar 19, i.e., on the side where the busbar 19 is joined to the electrode terminal of the cell, and the laser beam can be irradiated onto the voltage detection terminal 21.
• Figure 37 is the B-B cross section shown in Figure 36
• Figure 38 shows the cross-sectional shape of the molten metal portion 3 at the overlapping interface between the voltage detection terminal 21 and the terminal portion 23 of the busbar 19.
• the molten metal portion 3 formed in the joint area between the terminal portion 23 of the bus bar 19 and the voltage detection terminal 21 has the penetration depth D of the molten metal portion, the molten width W of the molten metal portion 3, and the molten area S of the molten metal portion 3 that satisfy the relationships described in the above-mentioned embodiment, so that when an external force is applied, it can lead to ductile fracture in the base material rather than brittle fracture in the molten metal portion 3. Therefore, it is possible to suppress destabilization of fatigue strength due to brittle fracture at the overlapping interface of the molten metal portions made of dissimilar metals, and to provide a battery pack with stable strength reliability.
• the molten metal part as a single bead when applying heat using a laser beam or other method, there is no increase in construction time or total heat input, which in turn suppresses declines in production efficiency and avoids adverse effects on product performance, such as deformation of the lap joint or thermal degradation of the resin part due to excessive heat input.
• the voltage detection terminal 21 is made of a copper-based material, the functions and effects described in the above-mentioned embodiment can be obtained.
• the voltage detection terminal 21 is made of a material that is not copper-based but contains nickel, the strength is greater than that of aluminum base material or nickel-based terminal base material due to the properties of the aluminum-nickel compound phase, and the same functions and effects described in the embodiment can be obtained.
• the present invention is not limited to the several embodiments described above, and includes various modifications.
• the above embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those that include all of the configurations described.
• it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace other configurations with respect to the configuration of each embodiment.

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