Terminal, secondary battery, and manufacturing method of terminal

Abstract

The present invention relates to a terminal, a secondary battery, and a manufacturing method of the terminal. The terminal member disclosed herein is provided with a first metal and a second metal overlapping the first metal. The first metal is plated with nickel at least at a boundary surface with the second metal. An interface portion by diffusion bonding of the metals is formed at a part of the boundary between the first metal and the second metal.

Description

Technical Field

[0001] This invention relates to terminals, secondary batteries, and methods for manufacturing terminals. Background Technology

[0002] There is a technique disclosed for plating a portion of a terminal component for the purpose of improving the weldability of the metal components constituting the terminal of a secondary battery.

[0003] Japanese Patent Application Publication No. 2014-17081 discloses a negative terminal component having a negative external terminal plate with a metal plating and a negative connection terminal. The negative external terminal plate is a component disposed on a battery cover and connected to a busbar. The negative external terminal plate has a through hole. The negative connection terminal passes through the through hole and is riveted together via the metal plating. According to this structure, the tightness of the negative terminal plate and the negative connection terminal can be improved, and the connection resistance can be reduced.

[0004] Japanese Patent Publication No. 2013-519213 discloses a pouch lithium battery tab material in which a nickel plating layer is deposited on one end of one side of a substrate, and a tin plating layer is also deposited on the nickel plating layer. This pouch lithium battery tab material has low production cost, good weldability, and suitable thermal conductivity.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-17081

[0006] Patent Document 2: Japanese Patent Publication No. 2013-519213

[0007] However, the inventors have investigated using terminal components made of different types of metals as external terminals for secondary batteries. When the secondary battery is used in a vehicle, the vehicle's driving vibrations are also transmitted to the external terminals of the secondary battery through the busbar. When the external terminals are made of multiple metals, vibrations are also transmitted to the inter-metal interfaces. The inventors aim to provide a terminal component with high durability that maintains the bonding state of the inter-metal interfaces even when external forces such as vibrations are transmitted. Summary of the Invention

[0008] The terminal component disclosed herein includes a first metal and a second metal overlapping the first metal. The first metal is nickel-plated at least at its boundary with the second metal. A joint is formed at a portion of the boundary between the first metal and the second metal, where the metals are joined by diffusion.

[0009] The terminal component has a joint with high bonding strength, which improves durability.

[0010] It can also be configured such that the joint is formed at the center position including the boundary surface.

[0011] Alternatively, it can be configured such that, in the first metal, the average thickness of the nickel plating at the joint is less than or equal to the average thickness of the nickel plating at the boundary surface.

[0012] Alternatively, the second metal may have a recess in the portion overlapping with the first metal that is wider inside than the opening. Alternatively, the first metal may have a portion that extends into the recess.

[0013] Alternatively, in a secondary battery comprising a battery case and electrode terminals mounted in the battery case, the electrode terminals may include portions formed by the aforementioned terminal components.

[0014] The method for manufacturing the terminal component disclosed herein includes a step of preparing a first metal, a step of preparing a second metal, and a step of applying an electric current to the first metal and the second metal to join a portion of the boundary between the first metal and the second metal. Nickel plating is performed on the boundary surface between the first metal and the second metal.

[0015] According to this manufacturing method, the bonding strength of the joint formed by diffusion bonding of metals can be improved.

[0016] It can also be configured such that a predetermined joining portion for joining with the second metal is provided in the first metal. It can also be configured such that the average thickness of the nickel plating in the predetermined joining portion is less than or equal to the average thickness of the nickel plating on the boundary surface.

[0017] It can also be configured such that the predetermined joint is set to include the center position of the boundary surface.

[0018] It can also be configured such that the process of preparing the first metal includes electrolytic plating of the first metal with nickel.

[0019] It can also be configured as follows: the process of preparing the first metal includes thinning the nickel plating locally by grinding or laser irradiation. Attached Figure Description

[0020] Figure 1 This is a partial cross-sectional view of the lithium-ion secondary battery 10.

[0021] Figure 2 It means Figure 1 Sectional view of section II-II.

[0022] Figure 3 yes Figure 2 Sectional view III-III.

[0023] Figure 4 This is a schematic cross-sectional view of the terminal component 200. Detailed Implementation

[0024] The following describes one embodiment of the terminal component and secondary battery disclosed herein. The embodiment described herein is not intended to specifically limit the invention. Unless otherwise specifically stated, the invention is not limited to the embodiment described herein. The figures are depicted schematically and do not necessarily reflect the actual object. Furthermore, components or parts that perform the same function are appropriately labeled with the same reference numerals, and repeated descriptions are omitted. Also, unless otherwise specifically stated, expressions indicating numerical ranges such as "A~B" mean "A or more, B or less". Furthermore, the dimensional relationships (length, width, thickness, etc.) in the figures do not reflect actual dimensional relationships.

[0025] In this specification, "secondary battery" generally refers to an energy storage device that generates a charging and discharging reaction by the movement of charge carriers between a pair of electrodes (positive and negative electrodes) via an electrolyte. This secondary battery includes not only so-called storage batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, but also capacitors such as electric double-layer capacitors. The following describes an embodiment using a lithium-ion secondary battery as an example.

[0026] <Lithium-ion secondary battery 10>

[0027] Figure 1 This is a partial cross-sectional view of the lithium-ion secondary battery 10. Figure 1 The image depicts a state in which the interior of the lithium-ion secondary battery 10 is exposed along a wide surface on one side of the roughly rectangular battery box 41. Figure 1 The lithium-ion secondary battery 10 shown is a so-called closed-type battery. Figure 2 It means Figure 1 A sectional view of section II-II. Figure 2 The image shows a partial cross-sectional view schematically depicting the state in which the interior of the lithium-ion secondary battery 10 is exposed along a narrow section along one side of the generally rectangular battery box 41.

[0028] like Figure 1 As shown, the lithium-ion secondary battery 10 includes an electrode body 20, a battery case 41, a positive terminal 42, and a negative terminal 43 (also referred to as electrode terminals 42 and 43).

[0029] <Electrode 20>

[0030] The electrode body 20 is housed in the battery case 41 while covered by an insulating film (not shown). The electrode body 20 includes a positive electrode plate 21 as a positive electrode element, a negative electrode plate 22 as a negative electrode element, and separator plates 31 and 32 as separators. The positive electrode plate 21, the first separator plate 31, the negative electrode plate 22, and the second separator plate 32 are all long strip-shaped components.

[0031] For the positive electrode 21, a positive electrode current collector foil 21a (e.g., aluminum foil) with a predetermined width and thickness is formed on both sides, except for an unformed portion 21a1 at one end in the width direction. This unformed portion contains a positive electrode active material layer 21b. The positive electrode active material is, for example, a material used in lithium-ion secondary batteries, such as a lithium transition metal composite material, capable of releasing lithium ions during charging and absorbing lithium ions during discharging. Various materials other than lithium transition metal composite materials are generally proposed for the positive electrode active material, and there is no particular limitation.

[0032] For the negative electrode 22, a negative electrode current collector foil 22a (here, a copper foil) of predetermined width and thickness has a negative electrode active material layer 22b formed on both sides, except for the unformed portion 22a1 at one end in the width direction. The negative electrode active material is, for example, a material like natural graphite used in lithium-ion secondary batteries, capable of absorbing lithium ions during charging and releasing them during discharge. Various materials other than natural graphite are commonly proposed for the negative electrode active material, and there is no particular limitation.

[0033] The separators 31 and 32 are, for example, porous resin sheets that allow electrolytes to pass through and have the required heat resistance. Various structures have been proposed for the separators 31 and 32, and there is no particular limitation.

[0034] Here, the width of the negative electrode active material layer 22b is, for example, wider than that of the positive electrode active material layer 21b. The widths of the separators 31 and 32 are wider than that of the negative electrode active material layer 22b. The unformed portions 21a1 of the positive electrode current collector foil 21a and 22a1 of the negative electrode current collector foil 22a face opposite directions in the width direction. Furthermore, the positive electrode sheet 21, the first separator 31, the negative electrode sheet 22, and the second separator 32 are wound in a sequentially overlapping manner with their orientation aligned in the length direction. The negative electrode active material layer 22b covers the positive electrode active material layer 21b with the separators 31 and 32 positioned between them. The negative electrode active material layer 22b is covered by the separators 31 and 32. The unformed portion 21a1 of the positive electrode current collector foil 21a extends from one side of the separators 31 and 32 in the width direction. The unformed portion 22a1 of the negative electrode current collector foil 22a extends from the separators 31 and 32 on the opposite side in the width direction.

[0035] like Figure 1 As shown, the electrode body 20 is flat along a plane including the winding axis so that it can be accommodated in the main body 41a of the battery case 41. Moreover, along the winding axis of the electrode body 20, an unformed portion 21a1 of the positive electrode current collector foil 21a is arranged on one side, and an unformed portion 22a1 of the negative electrode current collector foil 22a is arranged on the opposite side.

[0036] <Battery Box 41>

[0037] like Figure 1 As shown, the battery case 41 houses the electrode body 20. The battery case 41 has: a case body 41a, which is a generally rectangular shape with an opening on one side; and a cover 41b, which is fitted to the opening. In this embodiment, from the viewpoint of lightweighting and ensuring the required rigidity, the case body 41a and the cover 41b are respectively formed of aluminum or an aluminum alloy mainly composed of aluminum.

[0038] <Box body 41a>

[0039] The box body 41a has a generally rectangular shape with an opening on one side. The box body 41a has a generally rectangular base 61 and a pair of wide faces 62 and 63 (see reference). Figure 2 A pair of narrow faces 64 and 65 are formed on one side of the box body 41a. A pair of wide faces 62 and 63 stand out from the long side of the bottom face 61. A pair of narrow faces 64 and 65 stand out from the short side of the bottom face 61. An opening 41a1 is formed on one side of the box body 41a, which is surrounded by a pair of wide faces 62 and 63 and a pair of narrow faces 64 and 65.

[0040] Cover 41b

[0041] Cover 41b is fitted onto a pair of wide faces 62, 63 (see reference). Figure 2 The opening 41a1 of the box body 41a is surrounded by the long side of the lid 41b and the short sides of a pair of narrow facets 64 and 65. Furthermore, the periphery of the lid 41b joins the edge of the opening 41a1 of the box body 41a. This joining can also be achieved, for example, by a seamless, continuous weld. This weld can be achieved, for example, by laser welding.

[0042] In this embodiment, a positive terminal 42 and a negative terminal 43 are mounted on the cover 41b. The positive terminal 42 has an internal terminal 42a and an external terminal 42b. The negative terminal 43 has an internal terminal 43a and an external terminal 43b. The internal terminals 42a and 43a are mounted on the inner side of the cover 41b via an insulator 72. The external terminals 42b and 43b are mounted on the outer side of the cover 41b via washers 71. The internal terminals 42a and 43a extend into the interior of the housing body 41a. The internal terminal 42a of the positive terminal is connected to the unformed portion 21a1 of the positive current collector foil 21a. The internal terminal 43a of the negative terminal is connected to the unformed portion 22a1 of the negative current collector foil 22a.

[0043] like Figure 1As shown, the unformed portions 21a1 of the positive current collector foil 21a and the unformed portions 22a1 of the negative current collector foil 22a of the electrode body 20 are mounted on the internal terminals 42a and 43a respectively mounted on both sides of the cover 41b in the long side direction. The electrode body 20 is housed in the battery case 41 with the internal terminals 42a and 43a mounted on the cover 41b. Furthermore, a wound type electrode body 20 is illustrated here. The structure of the electrode body 20 is not limited to this form. For example, the electrode body 20 can also be constructed by alternating layers of separator sheets between the positive and negative electrode sheets. Additionally, multiple electrode bodies 20 may be housed within the battery case 41.

[0044] Alternatively, the battery box 41 can also contain an electrolyte (not shown) along with the electrode body 20. As the electrolyte, a non-aqueous electrolyte that dissolves the supporting salt in a non-aqueous solvent can be used. Examples of non-aqueous solvents include carbonate solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of supporting salts include fluorinated lithium salts such as LiPF6.

[0045] Figure 3 yes Figure 2 Sectional view III-III. Figure 3 The image shows a cross-section of the portion where the negative terminal 43 is mounted to the cover 41b. In this embodiment, the external terminal 43b of the negative electrode uses a component made by joining different types of metals. Figure 3 The structure of the different types of metals constituting the external terminal 43b and the interfaces of the different types of metals are not shown in the figure, but the cross-sectional shape of the external terminal 43b is schematically shown.

[0046] like Figure 3 As shown, the cover 41b has a mounting hole 41b1 for mounting the external terminal 43b of the negative electrode. The mounting hole 41b1 penetrates the cover 41b at a predetermined position. The internal terminal 43a and the external terminal 43b of the negative electrode are mounted in the mounting hole 41b1 of the cover 41b, with a washer 71 and an insulator 72 positioned between them. A step 41b2 for mounting the washer 71 is provided around the mounting hole 41b1 on the outside of the mounting hole 41b1. A seat surface 41b3 for mounting the washer 71 is provided on the step 41b2. A protrusion 41b4 for positioning the washer 71 is provided on the seat surface 41b3.

[0047] Here, as Figure 3As shown, the external terminal 43b of the negative electrode includes a head 43b1, a shaft portion 43b2, and a rivet tab 43b3. The head 43b1 is located on the outside of the cover 41b. The head 43b1 is a generally flat plate-shaped portion larger than the mounting hole 41b1. The shaft portion 43b2 is fitted into the mounting hole 41b1 via a washer 71. The shaft portion 43b2 protrudes downward from approximately the center of the head 43b1. Figure 3 As shown, the rivet 43b3 is located inside the cover 41b and is riveted to the internal terminal 43a of the negative electrode. The rivet 43b3 extends from the shaft portion 43b2 and bends after being inserted into the cover 41b to rivet to the internal terminal 43a of the negative electrode.

[0048] <Washer 71>

[0049] like Figure 3 As shown, washer 71 is a component that is mounted on the mounting hole 41b1 and the seat surface 41b3 of the cover 41b. In this embodiment, washer 71 includes a seat portion 71a, a protrusion 71b, and a sidewall 71c. The seat portion 71a is a portion that is fitted onto the seat surface 41b3, which is provided on the outer side of the mounting hole 41b1 of the cover 41b. The seat portion 71a has a generally flat surface corresponding to the seat surface 41b3. The seat portion 71a has a recess corresponding to the protrusion 41b4 of the seat surface 41b3. The protrusion 71b protrudes from the bottom surface of the seat portion 71a. The protrusion 71b has an outer shape that follows the inner side of the mounting hole 41b1 so as to be fitted onto the mounting hole 41b1 of the cover 41b. The inner side of the protrusion 71b becomes a mounting hole for mounting the shaft portion 43b2 of the external terminal 43b. The sidewall 71c rises upward from the periphery of the seat portion 71a. The head 43b1 of the external terminal 43b is fitted to the part surrounded by the side wall 71c of the washer 71.

[0050] Gasket 71 is disposed between cover 41b and external terminal 43b, ensuring insulation between the two terminals. Additionally, gasket 71 ensures the airtightness of the mounting hole 41b1 in cover 41b. From this perspective, it is preferable to use a material with excellent chemical resistance and durability. In this embodiment, gasket 71 is made of PFA. PFA is a copolymer of tetrafluoroethylene and perfluoroalkylvinylether. However, the material used for gasket 71 is not limited to PFA.

[0051] <Insulator 72>

[0052] The insulator 72 is a component fitted around the mounting hole 41b1 of the cover 41b and attached to the inside of the cover 41b. The insulator 72 includes a base portion 72a, a hole 72b, and a sidewall 72c. The base portion 72a is a portion disposed along the inner surface of the cover 41b. In this embodiment, the base portion 72a is a generally flat portion. The base portion 72a is disposed along the inner surface of the cover 41b and is sized to be housed within the housing body 41a without protruding from the cover 41b. The hole 72b is a hole corresponding to the inner surface of the protrusion 71b of the washer 71. In this embodiment, the hole 72b is located approximately at the center of the base portion 72a. On the side opposite to the inner surface of the cover 41b, a recessed step 72b1 is provided around the hole 72b. The front end of the protrusion 71b of the washer 71, fitted into the mounting hole 41b1, is housed therein without interfering with the step 72b1. The sidewall 72c rises downward from the periphery of the base portion 72a. The base portion 72a houses a base 43a1 at one end of the internal terminal 43a provided for the negative electrode. For the insulator 72, since it is disposed inside the battery case 41, it preferably possesses the required chemical resistance. In this embodiment, the insulator 72 uses PPS. PPS is polyphenylene sulfide resin. However, the material used for the insulator 72 is not limited to PPS.

[0053] The internal terminal 43a of the negative electrode has a base 43a1 and a connecting piece 43a2 (see reference). Figure 1 and Figure 2 The base 43a1 is the portion that is fitted onto the base portion 72a of the insulator 72. In this embodiment, the base 43a1 has a shape corresponding to the inner side of the sidewall 72c surrounding the base portion 72a of the insulator 72. The connecting piece 43a2 extends from one end of the base 43a1, extends within the housing body 41a, and connects to the unformed portion 22a1 of the negative electrode of the electrode body 20 (see reference). Figure 1 and Figure 2 ).

[0054] In this embodiment, a protrusion 71b is fitted into the mounting hole 41b1, and a washer 71 is fitted onto the outside of the cover 41b. An external terminal 43b is fitted onto the washer 71. At this time, the shaft portion 43b2 of the external terminal 43b is inserted through the protrusion 71b of the washer 71, and the head 43b1 of the external terminal 43b is positioned on the seat portion 71a of the washer 71. An insulator 72 and a negative terminal 43 are fitted onto the inside of the cover 41b. Furthermore, as... Figure 3 As shown, the rivet tab 43b3 of the external terminal 43b is bent to rivet the base 43a1 of the negative terminal 43. In order to improve conductivity, the rivet tab 43b3 of the external terminal 43b and the base 43a1 of the negative terminal 43 can also be joined locally by welding or metal bonding.

[0055] However, the required level of oxidation-reduction resistance in the internal terminal 42a of the positive electrode of the lithium-ion secondary battery 10 is no higher than that in the negative electrode. Furthermore, from the viewpoints of required oxidation-reduction resistance and lightweight design, the internal terminal 42a of the positive electrode ( Figure 1 (Referencing) Aluminum can be used. In contrast, the required level of oxidation-reduction resistance is higher for the internal terminal 43a of the negative electrode than for the positive electrode. From this point of view, copper can be used for the internal terminal 43a of the negative electrode. On the other hand, for the busbar connected to the external terminal 43b, from the viewpoint of lightweighting and cost reduction, aluminum or aluminum alloy can be used.

[0056] The inventors investigated using different types of metal at the connection points with the internal terminal 43a and with the busbar. Specifically, they investigated using metals with relatively high solderability at the connection points with the busbar and with the internal terminal 43a in the external terminal 43b. However, according to the inventors' understanding, the joining of different types of metals presents issues regarding conductivity and joint strength. The inventors investigated both mechanically fastening the metals and metallurgically joining them to ensure conductivity.

[0057] The terminal component 200 disclosed herein will be described below along with the manufacturing method of the terminal component 200. Here, the terminal component 200 is made of copper and aluminum. However, the metal constituting the external terminal 43b is not limited to copper and aluminum.

[0058] Terminal component 200

[0059] Figure 4 This is a schematic cross-sectional view of the terminal component 200. The terminal component 200 can serve as... Figure 3 The external terminal 43b of the negative electrode is shown for use. Figure 4 In the diagram, the structure of different types of metals and the interfaces between them are schematically shown for terminal component 200. Additionally, in... Figure 4 The diagram schematically illustrates the process of joining the first metal 201 and the second metal 202 that constitute the terminal component 200.

[0060] The terminal component 200 includes a first metal 201 and a second metal 202 overlapping the first metal 201. The first metal 201 is nickel-plated at least at its boundary with the second metal 202. A joint portion 203, formed by metal diffusion, is formed at a portion of the boundary between the first metal 201 and the second metal 202. In this embodiment, as... Figure 4As shown, the second metal 202 has a recess 202a at the location where it overlaps with the first metal 201. The interior of the recess 202a is wider than the opening 202a1. The first metal 201 has a portion that enters into the recess 202a. In this embodiment, nickel plating is applied to the surface of the portion that enters into the recess 202a (i.e., the end 201a1 where the flange portion 201b is provided and the outer edge 201b1 of the flange portion 201b). A joint 203 is formed at a portion of the boundary between the bottom 202a2 of the recess 202a of the first metal 201 and the second metal 202.

[0061] The method for manufacturing terminal component 200 includes the following steps (a) to (c):

[0062] (a) The process of preparing the first metal 201;

[0063] (b) The process of preparing the second metal 202; and

[0064] (c) A process of energizing the first metal 201 and the second metal 202 to join a portion of the boundary between the first metal 201 and the second metal 202.

[0065] Here, the first metal 201 is nickel plated at the interface 201a1, 201b1 with the second metal 202.

[0066] <Process (a): Process of preparing the first metal 201>

[0067] In step (a), the first metal 201 is prepared. This step may also include nickel plating on the first metal 201.

[0068] The first metal 201 constitutes a portion of the terminal component 200 that is disposed towards the interior of the battery compartment 41 and connected to the internal terminal 43a of the negative electrode. In this embodiment, the first metal 201 is made of copper that has been nickel-plated. For example, the material of the first metal 201 (copper in this embodiment) can be subjected to known metal processing, and then the processed first metal 201 can be nickel-plated to prepare the first metal 201. Metal processing can be performed, for example, by forging, machining, etc. Nickel plating can be performed, for example, by electroless plating, electrolytic plating, etc.

[0069] In this embodiment, the first metal 201 has a shaft portion 201a and a flange portion 201b extending outwardly from one end of the shaft portion 201a. The end portion 201a1 of the first metal 201 where the flange portion 201b is provided is approximately circular. The flange portion 201b is continuously formed in the circumferential direction of the shaft portion 201a. The outer edge 201b1 of the flange portion 201b is formed of a tapered surface that slopes gradually from the end face side of the first metal 201 including the flange portion 201b toward the other side side. In addition, on the shaft portion 201a, on the side opposite to the side where the flange portion 201b is provided, a portion 201c is provided for riveting a rivet piece 43b3 to the internal terminal 43a.

[0070] In this process, the first metal 201 prepared is nickel-plated at least on the surface of the portion 201d where it enters the recess 202a of the second metal 202. The thickness of the nickel plating at the end 201a1 is not particularly limited, but can be 1 μm or more, for example, 3 μm or more. The thickness of the nickel plating at the end 201a1 can be 20 μm or less, for example, 10 μm or less. The thickness of the nickel plating can be measured, for example, by SEM imaging or high-magnification (e.g., 500x or more) optical microscopy.

[0071] In this embodiment, a pre-engagement portion 201e for engaging with the second metal 202 is provided on the first metal 201. The pre-engagement portion 201e is positioned at the center of a surface (i.e., boundary surface 201a1) opposite to the bottom 202a2 of the second metal 202. The nickel plating thickness is thinner in the pre-engagement portion 201e compared to other portions of the portion 201d that extends into the recess 202a.

[0072] The thickness of the nickel plating on the pre-joined portion 201e should be less than or equal to the average thickness of the nickel plating on the boundary surfaces 201a1 and 201b1. While not particularly restrictive, the thickness of the nickel plating on the pre-joined portion 201e may also be less than 0.5 times the average thickness of the nickel plating on the boundary surfaces 201a1 and 201b1. Alternatively, the thickness of the nickel plating on the pre-joined portion 201e may be more than 0.1 times or more than 0.2 times the average thickness of the nickel plating on the boundary surfaces 201a1 and 201b1.

[0073] As described above, nickel plating of the first metal 201 can be performed by electroless plating, electrolytic plating, etc. The plating processing conditions are appropriately set according to the thickness of the nickel plating on the first metal 201. From the viewpoint of making the plating thickness of the first metal 201 uniform, electroless plating can also be performed, but electrolytic plating is preferred. When performing plating by electroless plating, it is necessary to perform processing to thin the plating thickness of the bonding predetermined portion 201e or to remove the plating. Although not limited to this, for example, the plating thickness can be adjusted by performing plating with the bonding predetermined portion 201e covered, or by performing processing to thin the plating thickness of the bonding predetermined portion 201e after plating. As a process to thin the thickness, examples include locally thinning the nickel plating by grinding, laser irradiation, etc. When adjusting the plating thickness by such methods, grinding marks may remain in the thinned portion. Electroplating allows for thicker plating at the edges and corners of the first metal 201 where resistance is high. Therefore, compared to the end 201a1 of the first metal 201, the plating thickness at the flange 201b and the portion near the flange 201b is thicker. In other words, the pre-joint portion 201e can be positioned near the center of the end 201a1 without thickness adjustment. Furthermore, the range of the pre-joint portion 201e can be adjusted by locally adjusting the plating thickness after electroplating.

[0074] Compared to copper and aluminum, nickel has a higher laser absorption rate near the wavelength of 1 μm. In this embodiment, nickel plating is performed not only on the portion 201d where the first metal 201 enters the recess 202a of the second metal 202, but also on the entire surface of the first metal 201. Therefore, the portion 201c of the rivet tab 43b3, which becomes the external terminal 43b, has good weldability with the internal terminal 43a. In addition, nickel has a higher resistance than copper and aluminum. The resistance of the thinner nickel-plated portion (the bonding predetermined portion 201e) is suppressed to be lower. From the viewpoint of improving weldability and concentrating the current in the bonding predetermined portion 201e in the later-described process (c), it is preferable to use nickel with higher purity.

[0075] <Process (b): Process for preparing the second metal 202>

[0076] In step (b), a second metal 202 is prepared. In this embodiment, the second metal 202 has a recess 202a that is wider inside than the opening 202a1. The second metal 202 constitutes a portion of the terminal component 200 that protrudes to the outside of the battery box 41 and is connected to external connecting components such as busbars.

[0077] In this embodiment, the second metal 202 is made of aluminum, which is ductile and has lower rigidity than the first metal 201. The second metal 202 has a recess 202a that covers the end portion 201a1 of the first metal 201, including the flange portion 201b. In this embodiment, the side surface of the recess 202a is a tapered surface that slopes gently from the opening 202a1 toward the bottom 202a2. For example, the second metal 202 can be prepared by performing known metalworking on the material of the second metal 202 (aluminum in this embodiment).

[0078] The bottom 202a2 of the recess 202a of the second metal 202 has a size corresponding to the outer diameter of the flange 201b of the first metal 201. Furthermore, as described above, the recess 202a slopes from the opening 202a1 toward the bottom 202a2. Therefore, the opening 202a1 of the recess 202a has an opening area narrower than the outer diameter of the flange 201b of the first metal 201.

[0079] <Process (c): The process of joining the first metal 201 and the second metal 202 by applying electricity>

[0080] In step (c), the first metal 201 and the second metal 202 are energized, and a portion of the boundary between the first metal 201 and the second metal 202 is joined by the diffusion of the metal.

[0081] In this embodiment, the first metal 201 and the second metal 202 are mechanically joined by causing a portion of the first metal 201 to enter the recess 202a of the second metal 202, and then the first metal 201 and the second metal 202 are joined by metal diffusion.

[0082] First, the first metal 201 is forced into the recess 202a by pressing the first metal 201 and the second metal 202 against each other. For example, with the second metal 202 overlapping the end 201a1 of the first metal 201, the required stamping pressure is applied using a stamping press or the like. As a result, the second metal 202 undergoes plastic deformation, and the portion of the first metal 201, including the flange portion 201b, enters the recess 202a. Figure 4 As shown, the end portion 201a1 of the first metal 201, including the flange portion 201b, is received in the recess 202a of the second metal 202. A so-called riveting structure is formed between the first metal 201 and the second metal 202. By mechanically fastening the first metal 201 and the second metal 202 in this way, a high bonding strength between the first metal 201 and the second metal 202 is achieved.

[0083] Next, in this embodiment, the first metal 201 and the second metal 202 are joined by so-called resistance welding. Electrodes 301 and 302 clamp the first metal 201 and the second metal 202, which were mechanically fastened in step (c), and energize them. The energizing conditions are not particularly limited, but for example, they can be set to a current value of 9kA to 12kA, a pressure of 50N to 500N, and an energizing time of approximately 20ms to 300ms.

[0084] Compared to other portions, the nickel plating on the pre-joint portion 201e of the first metal 201 is thinner. In this embodiment, the thickness of the nickel plating on the pre-joint portion 201e is less than or equal to the average thickness of the nickel plating on the boundary surfaces 201a1 and 201b1. When the first metal 201 and the second metal 202 are energized, the current concentrates on the pre-joint portion 201e, where the resistance is suppressed. Since the current is concentrated on the pre-joint portion 201e, the heat generated at this location increases. Nickel diffusion occurs in the pre-joint portion 201e where the heat generation increases. In this embodiment, the nickel diffuses towards the aluminum side (the second metal 202 side), where diffusion is more likely to occur. Thus, the first metal 201 and the second metal 202 are joined to form the joint portion 203.

[0085] In this way, terminal component 200 can be manufactured.

[0086] The terminal component 200 is joined at the junction 203 by a so-called solid-state bonding. As a result, the on-resistance between the first metal 201 and the second metal is reduced.

[0087] Although the specific details vary depending on the conditions of energization and plating, a bonding structure can be achieved at the joint 203 where nickel plating applied to the first metal 201 diffuses approximately 1 μm to 20 μm into the aluminum side constituting the second metal 202. That is, bonding is achieved by diffusing nickel plating from the copper-based first metal 201 into the aluminum-based second metal 202. Furthermore, the presence of nickel at the boundary suppresses copper diffusion into the aluminum. This prevents the formation of a weak intermetallic compound between the copper of the first metal 201 and the aluminum of the second metal 202. This bonding state can be confirmed, for example, by analyzing the cross-section of the joint using an electron probe microanalysis (EPMA) system, that nickel diffuses relative to aluminum at the atomic level.

[0088] The terminal component 200 described above has a joint portion 203 formed at the boundary between the first metal 201 and the second metal 202, which is joined by metal diffusion. By joining this joint portion 203 through metal diffusion, a low on-resistance is achieved despite the use of different types of metals. Furthermore, as described above, the formation of intermetallic compounds is suppressed, resulting in a stronger bond. Therefore, the durability of the joint portion 203 is improved.

[0089] In the above embodiment, the joint 203 of the terminal component 200 is formed at the center position including the boundary surface 201a1. By using the terminal component 200 with this structure as the external terminal 43b of the lithium-ion secondary battery 10, it becomes a structure in which electrolyte is difficult to penetrate to the interface between the first metal 201 and the second metal 202, thus making the joint 203 difficult to corrode. In addition, when a busbar is installed on the terminal component 200 used as the external terminal 43b and vibration is transmitted through the busbar, the joint 203 will not bear a large force because it is formed at the center position including the recess 202a.

[0090] exist Figure 1 The lithium-ion secondary battery 10 shown includes a battery case 41 and electrode terminals 42 and 43 mounted on the battery case 41. The electrode terminals 42 and 43 may also include the terminal component 200 described above (see reference). Figure 4 The parts that make up )

[0091] The terminal components and secondary batteries disclosed herein have been described in various ways. Unless otherwise specified, the embodiments of the terminal components and batteries described herein are not limited to the present invention. Furthermore, the batteries disclosed herein can be modified in various ways, and structural elements and processes mentioned herein can be appropriately omitted or combined without causing particular problems.

[0092] For example, in the above embodiment, a first metal 201 having a shaft portion 201a and a flange portion 201b extending outwardly from one end of the shaft portion 201a is overlapped by a second metal 202 whose interior is wider than the opening 202a1. However, the first metal is not limited to having a flange portion. For example, it may have a structure with a portion protruding from the shaft portion and the protruding portion entering the recess of the second metal. In addition, the portion of the first metal entering the recess of the second metal may be formed discontinuously or intermittently.

[0093] In the above embodiment, the recess 202a of the second metal 202 is a conical surface that slopes from the opening 202a1 toward the bottom 202a2. The flange 201b of the first metal 201 has a shape corresponding to the recess 202a. It is not limited to this shape; for example, the recess may also be a shape where the central portion of the side is wider.

[0094] Furthermore, in the above embodiment, the joint 203 is formed at the center of the recess 202a of the second metal 202, but the number and position of the joints are not particularly limited. Multiple joints may also be provided. The joints may also be provided on the side of the recess of the second metal. The number and position of the joints can be appropriately set according to the shapes of the first and second metals.

Claims

1. A terminal component, wherein, The terminal component includes: Copper is the first metal; and A second aluminum metal overlapping the first metal. The first metal is nickel-plated at least on its entire surface at the interface with the second metal. A joint is formed at the center of the boundary surface between the first metal and the second metal, where the metal is bonded by the diffusion of nickel. In the first metal, the average thickness of the nickel plating layer at the joint is less than or equal to the average thickness of the nickel plating layer at the boundary surface. The resistance of the joint is lower than the resistance of the portion of the boundary surface outside the joint.

2. The terminal component according to claim 1, wherein, The second metal has a recess in the portion where it overlaps with the first metal, the recess being wider than the opening. The first metal has a portion that enters into the recess.

3. A secondary battery, wherein, The secondary battery has the following features: Battery box; and The electrode terminals installed in the battery box, The electrode terminal includes a portion formed by the terminal component as described in claim 1 or 2.

4. A method for manufacturing a terminal component, wherein, The method for manufacturing the terminal component includes: The process of preparing the first metal, copper; The process of preparing a second metal, aluminum; and The process of applying an electric current to the first metal and the second metal to join a portion of the boundary surface between the first metal and the second metal. In the process of preparing the first metal, the entire surface of the first metal at the boundary with the second metal is nickel-plated. A predetermined joining portion for bonding with the second metal is provided on the first metal, wherein the average thickness of the nickel plating layer of the predetermined joining portion is less than or equal to the average thickness of the nickel plating layer on the boundary surface. In the process of joining a portion of the boundary between the first metal and the second metal, when the first metal and the second metal are energized, the current is concentrated in the pre-joint portion where the resistance is suppressed, and nickel diffusion occurs in the pre-joint portion where the heat generation increases, thereby forming the joint.

5. The method for manufacturing a terminal component according to claim 4, wherein, The predetermined joint is set to include the center position of the boundary surface.

6. The method for manufacturing a terminal component according to claim 4 or 5, wherein, The process of preparing the first metal includes electroplating the first metal with nickel.

7. The method for manufacturing a terminal component according to claim 4 or 5, wherein, The process of preparing the first metal includes locally thinning the nickel plating layer by grinding or laser irradiation.

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