Shaped rechargeable battery electronic interconnect

Abstract

The apparatus and methods disclosed herein relate to forming superior mechanical and electrical connections between foil stacks, such as those used in electrochemical cells. The connections described herein use multiple weld types and material selections to facilitate electrical and mechanical connections using individual weld types.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 044,326, filed June 25, 2020, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This technology relates generally to methods for welding stacks of metal foil layers together using penetration welds, and to stacks made using such methods. These methods include stacking metal foil layers, extruding or compressing metal foil layers between end plates, and welding the end plates and the compressed metal foil stack together. Background Technology

[0004] This disclosure relates to a method of bonding thin metal foil layers together to form a conductive bonded stack, such as a stack of conductive contacts for electrodes in an electrochemical cell.

[0005] Stacked electrochemical cells comprise layers of metal foil or coated metal foil stacked on top of each other. Typically, such stacks of metal foil have tabs that are joined together at common locations to form electrical contacts. Welding the stacks of metal foil tabs together using penetration or edge welding techniques requires securing the individual layers tightly together with no gaps between any layers. If such gaps exist between these layers, the welding can cause individual layers to burn or fail to completely melt through, resulting in interconnects.

[0006] Existing metal foil stacks can suffer from a variety of failure modes. For example, one failure mode of stacked metal foils is insufficient electrical connectivity between the foils, or a decline in the level of electrical connectivity over time. In addition, stacks of metal foils may mechanically separate from each other, for example, at solder joints. Summary of the Invention

[0007] This disclosure discloses a method for welding a stack of metal foil layers together. In one embodiment, the method includes: stacking a plurality of metal foil layers to form a metal foil stack having a width, a length, and metal foil stack edges; clamping the metal foil stack between a top end plate and a bottom end plate; aligning the edges of the top and bottom end plates with the edges of the metal foil stack and pressing or compressing the metal foils together between the top and bottom end plates; and welding the metal foil stack to the top and bottom end plates.

[0008] Stacks of metal foil layers can be welded together using a variety of weld joint designs.

[0009] The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the technologies described in this disclosure will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a cross-sectional view of an electrode stack.

[0011] Figure 2 is a cross-sectional view of an electrode stack of Figure 1 with tabs of the electrodes gathered.

[0012] Figure 3 is a perspective view of an electrochemical cell according to one embodiment.

[0013] Figure 4 is a cross-sectional view of an electrode stack of Figure 3 with tabs of the electrodes gathered.

[0014] Figure 5 is a simplified schematic plan view of a gathered and welded stack of metal foils according to one embodiment.

[0015] Figure 6 is a flowchart of a method for forming mechanical and electrical connections between foils of an electrochemical cell according to one embodiment. DETAILED DESCRIPTION

[0016] Embodiments herein include electrochemical stacks, welded portions thereof, and methods of forming such stacks. Electrochemical stacks are used in a variety of devices, including but not limited to implanted medical devices. In the context of an implantable medical device such as an implantable pulse generator or an implantable cardioverter defibrillator, power from the implanted medical device provides electrical stimulation to the patient’s tissue. To provide the required level of power when electrical stimulation is needed, a capacitor can be charged using the battery of the implanted medical device, which in turn releases the electrical stimulation to the patient’s tissue.

[0017] An electrode stack is generally a repeating series of an anode plate, a cathode plate, and an insulating or dielectric separator therebetween. A single tab extends from each anode plate and cathode plate. A set of tabs extending from the anode plates are welded to form an anode, while the tabs from the cathode plates are welded together to form a cathode.

[0018] Figure 1One such electrode stack 1 is shown in cross-section according to one embodiment. The electrode stack 1 includes individual electrodes 2a and 2b, which can include a combination of negative (anode) electrodes 2a and positive (cathode) electrodes 2b, which are assembled in overlapping fashion to form the stack 1. For example, the electrodes 2a and 2b can be assembled in overlapping fashion in an alternating fashion, but separated by a dielectric layer 5.

[0019] Each electrode 2a and 2b includes a layer of conductive material 3a, such as a metal foil. Optionally, the electrodes can also include a conductive coating 3b on one or both sides of the conductive layer 3a, thereby increasing the relative thickness of the electrodes 2a or 2b within the stack 1. Each electrode 2a and 2b also includes a pair of opposing surfaces 4 that interface with the dielectric layer 5 (e.g., the interface between the conductive coating 3b and the dielectric layer 5). Each conductive (e.g., metal foil) layer 3a includes a tab portion or tail 6 that extends from the body of the stack 1, such that the tail 6 protrudes from the stack 1 beyond one or more sides of the stack 1. No dielectric layer 5 is included between the tails 6.

[0020] Typically, each electrode 2a and 2b in the electrode stack 1 has portions that are intended to be substantially the same in position, length, width, and thickness, such that the individual tabs align when the individual electrodes are stacked to form a metal foil layer stack 7. The stack 7 also includes the tails 6, which are portions of the conductive material layer 3a that are not separated by the dielectric layer 5 as described above, and which are intended to be pulled together, as shown and described with respect to Figures 2 to 5 to form an anode or cathode.

[0021] Figure 1 The cross-sectional view of FIG. 1 shows that in a typical electrochemical cell, there can be both anode-type electrodes 2a and cathode-type electrodes 2b incorporated into a common stack 1.

[0022] In embodiments, the anode-type electrodes 2a and cathode-type electrodes 2b can be interleaved (e.g., alternating), or a portion of the stack 1 (e.g., an upper portion with respect to the direction of the stack) can be dedicated to electrodes of one polarity (e.g., anode-type electrodes 2a), while a second portion of the stack 1 (e.g., a lower portion) can be dedicated to electrodes of a second polarity (e.g., cathode-type electrodes 2b), or can be incorporated in some combination thereof. The electrode stack 1 can also have additional separator layers or separators (not shown) appropriately placed between the electrode layers, for example, around the cathode material. In embodiments, the separator layers can be in the form of a sheet, wrap, pouch, or the like.

[0023] In some embodiments, the outermost electrodes in the stack 1 can be anode-type electrodes 2a or cathode-type electrodes 2b that include a conductive coating 3b on one side of the conductive material layer 3a. Such a conductive coating 3b can be on the side of the conductive layer 3a that faces the center of the stack 1, as shown inFigure 1 The outer side of the outermost electrode 2a or 2b can be covered by a dielectric layer 5 to aid in the electrical insulation and protection of the stack 1.

[0024] Once the electrodes 2a and 2b are stacked, the tails 6 of the metal foil layers are gathered together by pressing or compressing the tabs of the metal foil layers 3a together, and then sandwiched between a first end plate 20 and a second end plate 21 as shown in Figure 2 to form a compressed foil layer stack 22. After the end plates are pressed or compressed together to form the compressed metal foil layer stack 22, the extra foil extending beyond the end plates is trimmed to be flush with the edges of the end plates, the end plates 20 and 21 are welded to the compressed metal foil layer stack 22 and to each other. Once welded, the stack is electrically conductive.

[0025] Figure 2 The cross-section shown is taken through the center of the metal foil layer stack 22. In embodiments, the first end plate 20 and the second end plate 21 can have various geometries that hold the metal foil layer stack 22 together. For example, as shown in Figure 3 the first end plate 20 and the second end plate 21 can be shaped as halves of a bracket that includes rectangular holes. The effect of this design of the first end plate 20 and the second end plate 21 is to form mortise holes through which the metal foil layer stack 22 can pass, effectively forming a corresponding tenon. The size of the "mortise" holes formed in the first end plate 20 and the second end plate 21 can be set to correspond to the expected width, thickness, and number of foils that make up the metal foil layer stack 22.

[0026] The metal foil layers can be made of any electrically conductive and weldable material. Examples of such materials are copper, aluminum, nickel, titanium, or alloys of these metals or alloys containing any of these metals. The thickness of the metal foil layers is in the range of 5 microns to 40 microns, in other embodiments, in the range of 10 microns to 20 microns. The range of 5 microns to 40 microns is intended to include any range or value within the range of 5 microns to 40 microns.

[0027] Figure 3 is a perspective view of an electrochemical stack 30 according to an embodiment. As shown in Figure 3 the anode 31 and the cathode 32 are each made up of a stack of foils as previously described with respect to Figure 2 The anode 31 is electrically coupled to a first plurality of foils, while the cathode 32 is electrically coupled to a second plurality of foils. While the anode 31 and the cathode 32 are shown as being collected on the same side of the stack 30, in other examples, the anode and the cathode can be on different sides of the stack 30.

[0028] Anodes 31 and cathodes 32 can be connected to a battery or other power source to charge electrochemical stacks 30, as described above, or stacks 30 can be discharged to provide a desired power output, such as a medical therapy. Figure 4 A detailed view of an anode 40 is shown, which includes first end plates 41, second end plates 42, and interconnecting holes 43 and 44, which can be used to provide mechanical coupling to other structures that are powered by or power the respective electrochemical stack. As Figure 4 As will be apparent, coupling first end plates 41 to second end plates 42 around compressed tails 45 can provide an interference fit to compressively retain those tails 45 and facilitate electrical connections between the end plates (41, 42) and all of the tails (45).

[0029] However, merely coupling first end plates 41 to second end plates 42 can not be sufficient to prevent gaps between some of the tails 45, which can lead to the failure modes described above. Thus, it can be desirable to form weld joints that include the tails 45 themselves to prevent relative movement or delamination.

[0030] It has been found that the type of weld between various components of anode 40 has different requirements. In particular, it is important that the tails 45 be well electrically connected to one another to ensure the electrical performance of the electrode. At the same time, it is important that the end plates 41 and 42 be well mechanically connected to one another to prevent loss of good interference fit with the tails 45 and to protect the joint between the tails and the end plates.

[0031] Thus, it has been found that two separate types of welds can be used to enhance the electrical interconnection between the tails 45 and the mechanical connection between the end plates 41 and 42. In one embodiment, a spot weld (Ti-Ti) can be used to couple the end plates 41 and 42 together. At the same time, a seam weld (e.g., Al-Ti) can be used to join the tails 45 together, which promotes a higher level of electrical interconnection between them. It will be appreciated that the expression "Ti-Ti weld" herein can be a weld between titanium or titanium alloys, in an embodiment. Likewise, an "Al-Ti" weld is formed between titanium and aluminum, or alloys of titanium and / or aluminum. "Ti" shall include titanium alloys, such as Ti6Al4V (Grade 5 titanium), Ti6Al4V ELI (Grade 23 titanium), or Ti3Al2V (Grade 9 titanium). Likewise, "Al" shall include aluminum alloys, such as 1N30, KS81, or 1235D.

[0032] Figure 5 A schematic top view of a connector 50 (which can be an anode or a cathode, for example) is shown, which depicts two different welds to achieve enhanced electrical and mechanical connectivity between multiple tails 51 of an electrochemical stack. As Figure 5As shown, the connector 50 includes a tail 51 and a clamping structure 52, which can be made up of two or more end plates, as described above with respect to Figures 2 to 4 The tail 51 forms a through dowel 53 that extends partially beyond the clamping structure 52.

[0033] Optional holes 54, 55 are formed in the connector 50, as shown in dashed lines. The shape and size of the holes 54 and 55 can vary depending on the connection to other components that supply power to or receive power from the connector 50. For example, in Figure 5 the first hole 54 is elliptical and substantially larger than the smaller, more circular hole 55. In some embodiments, no holes 54, 55 are needed.

[0034] In Figure 5 A first weld, made up of two portions 56a and 56b, is formed at the clamping structure 52 in the illustrated figure. In one embodiment, the first weld (56a and 56b) can be a fusion weld. A fusion weld is a weld that fuses through the entire thickness of the welded part. In one such embodiment, a laser fusion welding process is used. Ideally, the top end plate has a low electrical resistivity in order to provide sufficient coupling of the laser energy. For example, a top end plate made of or including nickel can be used to weld a metal foil layer stack made of a copper metal foil layer. The bottom plate can also have a low electrical resistivity, but there is no requirement for the bottom end plate. Otherwise, the requirements for the bottom end plate are the same as for the top end plate. In alternative embodiments, spot welds can be used at one or more locations to form a mechanical connection at the clamping structure.

[0035] As Figure 5 shown, it has been found advantageous for a portion of the first weld (56a and 56b) to be formed at the portion of the clamping structure 52 where the top and bottom are in direct contact (i.e., where the tail 51 is not located in between). By providing a spot weld at such a location, the difference in material between the tail 51 and the clamping structure 52 can be exploited.

[0036] In one embodiment, for example, the tail 51 can be made of aluminum, while the clamping structure 52 is made of two pieces (top and bottom, as shown above), each of which is titanium or a titanium alloy, such as Ti6Al4V (Grade 5 titanium), Ti6Al4V ELI (Grade 23 titanium), and Ti3Al2V (Grade 9 titanium). Because the first weld (56a and 56b) extends over portions of the top and bottom of the clamping structure 52 that are not separated by the tail 51, this connection is a Ti-Ti weld. The Ti-Ti weld at these portions provides a certain amount of clamping force on the tail 51 that enhances the electrical connection, but more importantly, is a very strong mechanical connection that prevents relative displacement between the component parts of the connector 50.

[0037] At the same time, a second weld 57 is formed on the exposed tenon portions 53 of the tails 51, which are aluminum. In practice, the tails 51 are trimmed to be flush with the edges of the end plate prior to the formation of the second weld 57. The provision of a separate Al-Ti weld in this location enhances the mechanical connection to some extent, but more importantly, provides excellent electrical coupling between the tails 51.

[0038] As such, the two types of welds provide mechanical strength beyond conventional systems (due to the first welds 56a and 56b) and electrical connectivity beyond conventional systems (due to the second weld 57). Although Ti-Ti and Al-Ti welds are described herein, it should be understood that in embodiments, the materials of the foils, connectors, and weld materials can be selected to have desired properties of weld strength and electrical connectivity.

[0039] It should be understood that various aspects disclosed herein can be combined in different combinations than the combinations expressly presented in the description and accompanying drawings. It should also be understood that, depending on the example, certain acts or events of any of the processes described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the techniques). In addition, while certain aspects of this disclosure are described as being performed by a single module or unit for purposes of clarity, it should be understood that the techniques of this disclosure can be performed by a combination of units or modules associated with, for example, a medical device.

Claims

1. An electrochemical cell, comprising: a stack (30) comprising a plurality of foils (3a, 22); a plurality of tails (45, 51), each of the plurality of tails corresponding to one of the plurality of foils; a connector (40, 50) having a first end plate (20, 41) and a second end plate (21, 42) and defining a gap therebetween, wherein the plurality of tails are arranged to pass through the gap to form a through dowel (53); a first weld (56a, 56b) having a first weld type that mechanically couples the first end plate to the second end plate; a second weld (57) having a second weld type that mechanically and electrically couples the plurality of foils at the plurality of tails, the second weld type being different than the first weld type.

2. The electrochemical cell of claim 1, wherein the connector defines at least one interconnection hole.

3. The electrochemical cell of claim 2, wherein the at least one interconnection hole comprises a plurality of interconnection holes.

4. The electrochemical cell of claim 3, wherein the plurality of interconnection holes comprise holes having different sizes from one another.

5. The electrochemical cell of any one of claims 1-4, wherein the plurality of foils and their plurality of tails comprise aluminum.

6. The electrochemical cell of any one of claims 1-4, wherein the first weld is a Ti-Ti weld and the second weld is a Ti-Al weld.

7. The electrochemical cell of claim 1, wherein the stack comprises both an anode and a cathode, and the connector corresponds to one of the anode or the cathode.

8. The electrochemical cell of claim 7, further comprising a second connector corresponding to the other of the anode or the cathode.

9. The electrochemical cell of any one of claims 1-4, wherein the plurality of foils are separated from one another at a stacked portion of the electrochemical cell by a dielectric material.

10. An anode structure or a cathode structure of an electrochemical cell, the anode or cathode structure comprising: a connector (40, 50) having a first end plate (20, 41) and a second end plate (21, 42) and defining a mortise therebetween; a plurality of foils (3a, 22) forming a dowel (53) through the mortise defined by the connector from a first end to a second end; a first weld (56a, 56b) having a first weld type that mechanically connects the first end plate to the second end plate; a second weld (57) having a second weld type that mechanically and electrically connects the plurality of foils at one of the first end or the second end, wherein the second weld type is different than the first weld type.

11. The anode structure or cathode structure of claim 10, wherein the connector defines at least one interconnection hole.

12. The anode structure or cathode structure of claim 11, wherein the at least one interconnection hole comprises a plurality of holes.

13. The anode structure or cathode structure of claim 12, wherein the plurality of holes comprises holes having different sizes from one another.

14. The anode structure or cathode structure of any one of claims 10 to 13, wherein the plurality of foils comprises aluminum or an aluminum alloy.

15. The anode structure or cathode structure of any one of claims 10 to 13, wherein the first weld is a Ti-Ti weld and the second weld is a Ti-Al weld.

16. A method of forming a welded metal foil stack for an electrochemical cell, the method comprising: gathering a plurality of foils (3a, 22) in a mortise between first and second end plates (20, 41, 21, 42) of a connector (40, 50); mechanically coupling the first and second end plates of the connector with first welds (56a, 56b) having a first weld type; and mechanically and electrically coupling the plurality of foils with second welds (57) having a second weld type, wherein the second weld type is different than the first weld type.

17. The method of claim 16, wherein the first weld type is a fusion weld.

18. The method of claim 16, wherein the first weld type is a spot weld.

19. The method of any one of claims 16 to 18, wherein the plurality of foils comprises aluminum.

20. The method of any one of claims 16 to 18, wherein the first weld is a Ti-Ti weld and the second weld is a Ti-Al weld.

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