The present application claims priority from Japanese Patent Application No. 2021-039714 filed on Mar. 11, 2021, which is incorporated by reference herein in its entirety.
The present disclosure relates to a terminal component and an electricity storage device.
JP 2016-018675 A discloses an invention related to a secondary battery. The secondary battery disclosed in the publication includes positive and negative electrode external terminals. The batteries are connected in series by a bus bar made of the same kind of material as that of one of the positive and negative electrode external terminals. The secondary battery includes a metal member that is made of a material having excellent weldability to the material of one of the external terminals and is ultrasonic pressure-welded to the other one of the positive and negative electrode external terminals. The metal member has a bus bar joint face to which the bus bar is to be welded.
When such a secondary battery is used for in-vehicle applications, vehicle vibration during travelling may be transmitted to the external terminals of the secondary battery through the bus bar. When the external terminal is provided with a structure having a dissimilar metal joint, the vibration is transmitted to the dissimilar metal joint. The present inventors understand that dissimilar metal joint parts joined by a joining method such as ultrasonic pressure-welding tend to result in large variations in joining strength between the individual joined parts during the mass production process. The present inventors are also considering, not merely ultrasonic pressure-welding of dissimilar metals, but a combination of ultrasonic pressure-welding of dissimilar metals with press-fitting one of the metals with the other one of the metals. However, when ultrasonic pressure-welding is to be carried out after one of the metals is press-fitted to the other one, it is difficult to apply the ultrasonic vibration required for ultrasonic pressure-welding to the metals because the two metals are press-fitted to each other. On the other hand, when the metals are press-fitted together after ultrasonic pressure-welding is carried out, it is feared that the strain resulting from the press-fitting process may adversely affect the portion that has undergone ultrasonic pressure-welding and deteriorate the quality of the portion that has been joined by ultrasonic pressure-welding.
In accordance with the present disclosure, a terminal component includes a first metal and a second metal overlapped with the first metal. A boundary between the first metal and the second metal includes: a press-fit portion in which one of the first metal and the second metal is press-fitted to the other one; a joined portion disposed at a location different from the press-fit portion, in which the first metal and the second metal are overlapped and joined together; and a gap formed around the joined portion. Because the just-described terminal component includes the gap around the joined portion, quality of joining is improved at the joined portion.
The first metal and the second metal may be made of dissimilar metals. The gap may be continuously present around the joined portion. Because the gap is present continuously around the joined portion, quality of joining is significantly improved at the joined portion.
The first metal may include a shaft portion and a flange portion extending radially outward from one end of the shaft portion. The second metal may have malleability and have lower rigidity than the first metal. The second metal may be overlapped on an end of the first metal including the flange portion, and may be press-fitted to a circumferential edge of the flange portion.
In a location where the first metal and the second metal are overlapped with each other, at least one of the first metal and the second metal may include a protrusion, and the other one may include a recess in which the protrusion is accommodated. The first metal and the second metal may be joined together at a location where a tip of the protrusion is in contact with a bottom portion of the recess, and a circumferentially continuous gap may be formed around the protrusion.
The first metal may include a first protrusion protruding toward the second metal, the first protrusion disposed at an end thereof including the flange portion. In this case, the second metal may include a second protrusion disposed at a location overlapped on the end of the first metal having the flange portion, the second protrusion protruding toward the first metal and being joined to the first protrusion.
In another embodiment, an electricity storage device may include a battery case and an electrode terminal attached to the battery case, wherein the electrode terminal includes a part including the above-described terminal component.
Hereinbelow, embodiments of a terminal component and an electricity storage device according to the present disclosure are described. It should be noted, however, that the disclosed embodiments are, of course, not intended to limit the invention. The present invention is not limited to the embodiments described herein unless specifically stated otherwise. The drawings are depicted schematically and do not necessarily reflect actual objects. The features and components that exhibit the same effects are designated by the same reference symbols as appropriate, and the description thereof will not be repeated.
In the present description, the term “electricity storage device” refers to a device that is capable of charging and discharging. The electricity storage device may include lithium polymer battery and lithium-ion capacitor, in addition to a variety of batteries generally referred to as lithium-ion battery and lithium secondary battery. The secondary battery refers to a battery that is capable of charging and discharging repeatedly in association with transfer of charge carriers between positive and negative electrodes. Herein, a lithium-ion secondary battery is illustrated as an example of one embodiment of the electricity storage device.
As illustrated in
The electrode assembly 20 is covered with an insulating film (not shown) and is enclosed in the battery case 41. The electrode assembly 20 includes a positive electrode sheet 21 serving as a positive electrode element, a negative electrode sheet 22 serving as a negative electrode element, and separator sheets 31 and 32 serving as separators. Each of the positive electrode sheet 21, the first separator sheet 31, the negative electrode sheet 22, and the second separator sheet 32 is a long strip-shaped member.
The positive electrode sheet 21 includes a positive electrode current collector foil 21a (for example, an aluminum foil) having a predetermined width and a predetermined thickness, a positive electrode active material layer 21b containing a positive electrode active material, and an uncoated portion 21a1 defined along one lateral edge of the positive electrode current collector foil 21a with a constant width. The positive electrode active material layer 21b is formed on both faces of the positive electrode current collector foil 21a, except for the uncoated portion 21a1. In a lithium-ion secondary battery, for example, the positive electrode active material is a material that is capable of releasing lithium ions during charge and absorbing lithium ions during discharge, such as lithium-transition metal composite material. Generally, other than the lithium-transition metal composite material, various materials have been proposed for use as the positive electrode active material, and the positive electrode active material is not limited to any particular material.
The negative electrode sheet 22 includes a negative electrode current collector foil 22a (copper foil herein) having a predetermined width and a predetermined thickness, a negative electrode active material layer 22b containing a negative electrode active material, and an uncoated portion 22a1 defined along one lateral edge of the negative electrode current collector foil 22a with a constant width. The negative electrode active material layer 22b is formed on both faces of the negative electrode current collector foil 22a, except for the uncoated portion 22a1. In a lithium-ion secondary battery, for example, the negative electrode active material is a material that is capable of absorbing lithium ions during charge and releasing the absorbed lithium ions during discharge, such as graphite. Generally, other than graphite, various materials have been proposed for use as the negative electrode active material, and the negative electrode active material is not limited to any particular material.
Each of the separator sheets 31 and 32 may be formed of, for example, an electrolyte permeable porous resin sheet with required heat resistance. Various proposals have been made about the separator sheets 31 and 32, and there is no particular restriction on the separator sheets 31 and 32.
Here, the negative electrode active material layer 22b is formed, for example, so as to be wider than the positive electrode active material layer 21b. The width of the separator sheets 31 and 32 is wider than the width of the negative electrode active material layer 22b. The uncoated portion 21a1 of the positive electrode current collector foil 21a and the uncoated portion 22a1 of the negative electrode current collector foil 22a are arranged at laterally opposite ends. The positive electrode sheet 21, the first separator sheet 31, the negative electrode sheet 22, and the second separator sheet 32 are aligned longitudinally, stacked one on another, and wound together. The negative electrode active material layer 22b covers the positive electrode active material layer 21b with the separator sheets 31 and 32 interposed therebetween. The negative electrode active material layer 22b is covered with the separator sheets 31 and 32. The uncoated portion 21a1 of the positive electrode current collector foil 21a protrudes from one of the lateral edges of the separator sheets 31 and 32. The uncoated portion 22a1 of the negative electrode current collector foil 22a protrudes from the other one of the lateral edges of the separator sheets 31 and 32.
As illustrated in
As illustrated in
As illustrated in
The lid 41b is fitted to the open end 41a1 of the case main body 41a, which is surrounded by the longer sides of the pair of wider side surface portions 62 and 63 and the shorter sides of the pair of narrower side surface portions 64 and 65. The peripheral edge portion of the lid 41b is joined to the edge of the open end 41a1 of the case main body 41a. The joining may be achieved by, for example, continuous welding, with no gaps. Such welding may be carried out by, for example, laser welding.
In this embodiment, the positive electrode terminal 42 and the negative electrode terminal 43 are fitted to the lid 41b. The positive electrode terminal 42 includes an internal terminal 42a and an external terminal 42b. The negative electrode terminal 43 includes an internal terminal 43a and an external terminal 43b. Each of the internal terminals 42a and 43a is fitted to the inside of the lid 41b with an insulator 72 interposed. Each of the external terminal 42b and 43b is fitted to the outside of the lid 41b with a gasket 71 interposed. Each of the internal terminals 42a and 43a extends inward of the case main body 41a. The internal terminal 42a of the positive electrode is connected to the uncoated portion 21a1 of the positive electrode current collector foil 21a. The internal terminal 43a of the negative electrode is connected to the uncoated portion 22a1 of the negative electrode current collector foil 22a.
As illustrated in
As illustrated in
Herein, as illustrated in
The gasket 71 is a member that is attached to the mounting hole 41b1 and the seating surface 41b3 of the lid 41b, as illustrated in
The gasket 71 is disposed between the lid 41b and the external terminal 43b to ensure electrical insulation between the lid 41b and the external terminal 43b. The gasket 71 also ensures hermeticity of the mounting hole 41b1 of the lid 41b. From such viewpoints, it is possible to use a material that is excellent in chemical resistance and weather resistance for the gasket 71. In this embodiment, the gasket 71 uses PFA. PFA is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. It should be noted that the material that may be used for the gasket 71 is not limited to PFA.
The insulator 72 is a member to be fitted inside the lid 41b, around the mounting hole 41b1 of the lid 41b. The insulator 72 includes a base portion 72a, a hole 72b, and a side wall 72c. The base portion 72a is a portion disposed along the inner surface of the lid 41b. In this embodiment, the base portion 72a is a substantially flat-plate shaped portion. The base portion 72a is disposed along the inner surface of the lid 41b. The base portion 72a has a size such that it does not jut out from the lid 41b so as to be contained within the case main body 41a. The hole 72b is formed correspondingly to the mounting hole 41b1. In this embodiment, the hole 72b is formed at a substantially central portion of the base portion 72a. In the surface of the insulator 72 that faces the inner surface of the lid 41b, a recessed stepped portion 72b1 is provided around the hole 72b. The stepped portion 72b1 accommodates the tip of the boss portion 71b of the gasket 71, which is fitted to the mounting hole 41b1. The side wall 72c extends downward from the peripheral edge of the base portion 72a. The base portion 72a accommodates a base portion 43a1, which is provided at one end of the negative electrode internal terminal 43a. Because the insulator 72 is disposed inside the battery case 41, the insulator 72 may be provided with required chemical resistance. In this embodiment, the insulator 72 uses PPS. PPS means a polyphenylene sulfide resin. It should be noted that the material that may be used for the insulator 72 is not limited to PPS.
The negative electrode internal terminal 43a includes a base portion 43a1 and a connecting piece 43a2 (see
In this embodiment, while the boss portion 71b is fitted into the mounting hole 41b1, the gasket 71 is attached to the outside of the lid 41b. The external terminal 43b is fitted to the gasket 71. At that time, the shaft portion 43b2 of the external terminal 43b is inserted through the boss portion 71b of the gasket 71, and the head portion 43b1 of the external terminal 43b is placed on the seat portion 71a of the gasket 71. The insulator 72 and the negative electrode terminal 43 are attached to the inside of the lid 41b. Then, as illustrated in
The required level of resistance to oxidation and reduction that is required by the positive electrode internal terminal 42a of the lithium-ion secondary battery 10 is not as high as that is required by the negative electrode. From the viewpoint of required resistance to oxidation and reduction and weight reduction, aluminum may be used the positive electrode internal terminal 42a. However, the required level of resistance to oxidation and reduction that is required by the negative electrode internal terminal 43a is higher than that is required by the positive electrode. From this viewpoint, copper may be used for the negative electrode internal terminal 43a. On the other hand, aluminum or aluminum alloy may be used for the bus bar to which the external terminal 43b is connected, from the viewpoint of weight reduction and cost reduction.
The present inventors are considering the use of copper for a portion of the external terminal 43b to which the internal terminal 43a is joined, and the use of aluminum or aluminum alloy for a portion of the external terminal 43b to which a bus bar is connected. In order to accomplish such a structure, a member in which copper and aluminum are joined by a dissimilar metal joint is used for the external terminal 43b in this embodiment. Generally, it is difficult for dissimilar metal joining to ensure sufficient joining strength. For this reason, the present inventors are considering additionally adopting a mechanical fitting structure of copper and aluminum. Note that an example illustrated herein adopts a member in which copper and aluminum are joined together for the external terminal 43b, taking the lithium-ion secondary battery 10 as an example. The two metals that constitute the external terminal 43b are not limited to copper and aluminum. Hereinafter, the structure of a terminal component 200 that constitutes the negative electrode external terminal 43b is described.
As illustrated in
In this embodiment, the first metal 201 includes a shaft portion 201a and a flange portion 201b extending radially outward from one end of the shaft portion 201a. An outer edge 201b1 of the flange portion 201b is provided with a press-fitted portion to which the second metal 202 is to be press-fitted. In this embodiment, the outer edge 201b1 of the flange portion 201b, to which the second metal 202 is press-fitted, includes a sloping surface that slopes in such a manner that its outer diameter gradually decreases from one end surface of the first metal 201 including the flange portion 201b toward the other end surface thereof. On one end of the first metal 201 where the flange portion 201b is provided, a protrusion 201a1 is provided at an end of the shaft portion 201a. On the other end of the first metal 201 that is opposite to the end where the flange portion 201b is provided, the shaft portion 201a is further provided with a portion 201c that later forms the press-fit piece 43b3 that is to be press-fitted to the internal terminal 43a.
Herein, the first metal 201 is disposed facing the inside of the battery case 41 so as to constitute a portion of the terminal component 200 that is to be joined to the negative electrode internal terminal 43a. In this embodiment, the first metal 201 is composed of copper. A nickel coating film may be formed, when necessary, on at least a part of the terminal component 200 where a portion composed of copper is exposed. When the nickel coating film is formed, damages originating from copper are prevented appropriately. The nickel coating film may be formed by, for example, plating.
The second metal 202 uses a metal that has malleability and a lower rigidity than the first metal 201. In this embodiment, the second metal 202 is composed of aluminum or an aluminum alloy. The second metal 202 includes a recessed portion 202a such as to cover an end of the first metal 201 including the flange portion 201b. In this embodiment, a recess 202a1 that accommodates the protrusion 201a1 of the first metal 201 is formed at the bottom of the recessed portion 202a. The outer diameter of the recess 202a1 is a size larger than the protrusion 201a1 of the first metal 201, and the depth of the recess 202a1 is approximately the same as the height of the protrusion 201a1.
The second metal 202 is overlapped with the end of the first metal 201 where the flange portion 201b is formed. In this case, the end of the first metal 201 where the flange portion 201b is formed is placed in the recessed portion 202a of the second metal 202. In addition, the protrusion 201a1 provided on the end of the first metal 201 where the flange portion 201b is formed is placed in the recess 202a1 provided in the recessed portion 202a of the second metal 202. In this case, the bottom of the recess 202a1 and the top portion of the protrusion 201a1 face each other in such a state as to be in contact with each other or adjacent to each other. In this way, the height of the protrusion 201a1 and the depth of the recess 202a1 may be determined in advance.
It should be noted that the joined portion 212 may be joined by resistance welding. When resistance welding is employed, resistance welding electrodes are pressed against the first metal 201 and the second metal 202 and energized, in place of the horn 302 and the anvil 301. In this case as well, because the gap 213 exists around the joined portion 212, electric current is applied intensively to the bottom of the recess 202a1 and the top portion of the protrusion 201a1 so that the interface between the bottom of the recess 202a1 and the top portion of the protrusion 201a1 can be heated and joined together. As a result, the joined portion 212 is resistance welded with good quality. Because so-called solid phase bonding is formed in the joined portion 212 that is joined in this way, the electrical resistance between the first metal 201 and the second metal 202 is reduced.
The terminal component 200 includes the press-fit portion 211, in which the second metal 202 is press-fitted with the first metal 201. In this embodiment, the second metal 202 is press-fitted onto the outer edge 201b1 of the flange portion 201b of the first metal 201. In this embodiment, the flange portion 201b of the first metal 201 is placed in the recessed portion 202a of the second metal 202. The outer edge 201b1 of the flange portion 201b of the first metal 201 includes a sloping surface such that its diameter gradually decreases from the bottom end of the recessed portion 202a toward the open end thereof. The inner surface of the recessed portion 202a of the second metal 202 is deformed along the sloping surface. For example, the first metal 201 and the second metal 202 are ultrasonic welded with the flange portion 201b of the first metal 201 being placed in the recessed portion 202a of the second metal 202 and clamped by the horn 302 and the anvil 301, and a side edge face 202b of the second metal 202 is hammered simultaneously. Thereby, as illustrated in
Thus, the first metal 201 and the second metal 202 includes the press-fit portion 211 that is mechanically press-fitted together, in addition to the joined portion 212 joined by solid-state welding such as metal joining, or by welding. Therefore, the press-fit portion 211 serves to provide mechanical bonding strength, and also the joined portion 212 serves to provide electrical conductivity due to the low electrical resistance resulting from solid-state welding. The shaft portion 201a of the first metal 201 of the terminal component 200 constitutes the shaft portion 43b2 that is inserted into the mounting hole 41b1 of the lid 41b, as illustrated in
The terminal component 200 shown in
Thus, the terminal component 200 proposed herein includes the press-fit portion 211, the joined portion 212, and the gap 213 that are disposed at a boundary of the first metal 201 and the second metal 202. The press-fit portion 211 is a portion in which one of the first metal 201 and the second metal 202 is press-fitted to the other one. The joined portion 212 is a portion that is provided at a different location from the press-fit portion 211 and in which the first metal 201 and the second metal 202 are overlapped and joined together. The gap 213 is formed around the joined portion 212. For the joined portion 212, it is possible to adopt, for example, ultrasonic welding in which joining is achieved by applying vibration to the first metal 201 and the second metal 202 while press-contacting the interface between the first metal 201 and the second metal 202, and resistance welding in which electric current is applied to the first metal 201 and the second metal 202 while press-contacting the interface between the first metal 201 and the second metal 202. In this case, because the gap 213 is provided around the joined portion 212, it is easy to apply vibration in ultrasonic welding and electric current in resistance welding intensively to the joined portion 212. Therefore, quality of ultrasonic welding and resistance welding is improved in the joined portion 212.
The first metal 201 and the second metal 202 may be composed of dissimilar metals. The gap 213 may be continuously present around the joined portion 212. The gap 213 may be provided at least one location in a circumferential periphery of the joined portion 212. However, when the gap 213 is continuously present around the joined portion 212, vibration or electric current may be more reliably applied intensively to the joined portion 212 in ultrasonic welding or resistance welding. Therefore, quality of ultrasonic welding and resistance welding is significantly improved in the joined portion 212.
As described previously, the first metal 201 may include a shaft portion 201a and a flange portion 201b extending radially outward from one end of the shaft portion 201a. The second metal 202 may exhibit malleability and have lower rigidity than the first metal 201. The second metal 202 may be overlapped on an end of the first metal 201 including the flange portion 201b. The second metal 202 may be press-fitted to a circumferential edge of the flange portion 201b. In the embodiment shown in
For example, as illustrated in the embodiment shown in
The above-described terminal component 200A includes the gap 213 provided around the joined portion 212. This allows vibration to be applied intensively to the joined portion 212 when the joined portion 212 is ultrasonic welded. As a result, the joined portion 212 is ultrasonic welded with good quality. In addition, the joined portion 212 may be joined by resistance welding by using electrodes for resistance welding in place of the horn 302 and the anvil 301. In the case where the joined portion 212 is resistance welded as well, the terminal component 200A enables electric current to be applied intensively to the joined portion 212 because the gap 213 is provided around the joined portion 212. As a result, the joined portion 212 is resistance welded with good quality. In addition, the first metal 201 and the second metal 202 are provided with the press-fit portion 211 at a position different from the joined portion 212. Therefore, required mechanical joining strength is ensured for the first metal 201 and the second metal 202. As in the embodiment shown in
In the embodiment shown in
In the embodiment shown in
In the embodiment shown in
Various embodiments of the terminal component and the electricity storage device according to the present disclosure have been described hereinabove according to the present disclosure. Unless specifically stated otherwise, the embodiments of the terminal component, the electricity storage device, and the like described herein do not limit the scope of the present invention. It should be noted that various other modifications and alterations may be possible in the embodiments of the electricity storage device disclosed herein. In addition, the features, structures, or steps described herein may be omitted as appropriate, or may be combined in any suitable combinations, unless specifically stated otherwise.
For example, the foregoing embodiments illustrate an example in which the second metal 202 is overlapped on the first metal 201 that includes the shaft portion 201a and the flange portion 201b extending radially outward from one end of the shaft portion 201a. The second metal 202 may have malleability and have lower rigidity than the first metal 201. The second metal 202 may be overlapped on an end of the first metal 201 including the flange portion 201b. The second metal 202 may be press-fitted to a circumferential edge (outer edge 201b1) of the flange portion 201b. The terminal component 200 is not limited to the embodiments that include such a flange portion 201b. The boundary between the first metal 201 and the second metal 202 overlapped on the first metal 201 may include a press-fit portion in which one of the first metal 201 and the second metal 202 is press-fitted to the other one. The terminal component 200 may include a joined portion 212 disposed at a different location from the press-fit portion 211, wherein the first metal 201 and the second metal 202 are overlapped and joined together, and a gap 213 may be formed around the joined portion 212. From such a viewpoint, the presence or absence of the part corresponding to the flange portion 201b, the position of the press-fit portion 211 at which the first metal 201 and the second metal 202 are press-fitted together, and so forth are not limited unless specifically stated otherwise. For example, the flange portion 201b is not limited to one that is provided to have a uniform circumferential width. The flange portion 201b may be provided partially or intermittently along the circumferential direction. The portion to which the second metal 202 is press-fitted is not limited to the peripheral edge of the flange portion 201b, but may be provided at any appropriate location. Furthermore, it is also possible to change the shape of the peripheral edge of the flange portion 201b to which the second metal 202 is press-fitted, as appropriate.
Number | Date | Country | Kind |
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2021-039714 | Mar 2021 | JP | national |