CONNECTING CONTACT LEADS TO LITHIUM-BASED ELECTRODES

Abstract

There is disclosed a method of connecting a lithium electrode to a contact lead in a rechargeable battery. The electrode comprises a sheet or foil of lithium or lithium alloy with a tab protruding from an edge of the sheet or foil. The contact lead comprises an electrically conductive lead with an end portion made of a second metal that does not alloy with lithium and has a plurality of through holes. The end portion of the contact lead and the tab of the electrode are positioned so that there is substantial overlap between the end portion and the tab. The metal of the tab is then caused, for example by pressing and welding, to penetrate through the through holes of the end portion so as to join the electrode to the contact lead. A combination electrode/contact lead assembly made by this method is also disclosed.

Claims

1. A method of forming a lithium-sulphur battery, the lithium-sulphur battery comprising a stack of electrodes, wherein each electrode of the stack of electrodes comprises a lithium or lithium alloy sheet formed with a tab protruding from each sheet in substantially the same location, so that the tabs of the stack of electrodes are substantially aligned when the electrodes are aligned with each other and arranged as an electrode stack, wherein each tab has a dimension perpendicular to the direction in which it protrudes from the sheet that is smaller than that of the corresponding dimension of that sheet, wherein each stack of electrodes defines an electrochemically active area and comprises a separator, and wherein each tab protrudes from a respective electrochemically active area and beyond the edge of a respective separator, the method comprising: i) obtaining a contact lead, wherein the contact lead comprises an electrically conductive lead with an end portion, and wherein the end portion is composed of a metal that does not form an alloy with lithium; ii) positioning the end portion of the contact lead a) on top of the tabs of the electrode stack, b) underneath the tabs of the electrode stack, or c) at an intermediate position between the top and the bottom of the electrode stack; and iii) ultrasonically welding at least one of the tabs to the end portion to form a bond between at least one electrode and the contact lead, wherein the ultrasonic welding further includes forming a lithium to lithium or a lithium alloy to lithium alloy weld between at least two tabs of the electrode stack, wherein an area of the weld is less than 10% of the surface area of the lithium or lithium alloy sheet; wherein the ultrasonic welding step is carried out at a frequency between 20 kHz to 60 kHz

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

[0070] FIGS. 1a to 1c shows a battery stack with anodes, cathodes and tabs, and three alternative positionings for a contact lead;

[0071] FIGS. 2a to 2e show possible designs for the contact lead;

[0072] FIG. 3 shows the contact lead being ultrasonically welded to the tabs; and

[0073] FIGS. 4a to 4d show an apparatus suitable for use in forming an ultrasonic weld in use.

DETAILED DESCRIPTION

[0074] A battery can be formed by an alternating stack of numerous cathodes and anodes. Each of these layers is divided by a separator. An ionic pathway is maintained by the presence, between each electrode, of an electrolyte. Each electrode 1 features a tab 2 protruding from its electrochemically active area and beyond the edge of the separator. These tabs 2 provide the first surface through which the stack 3 of lithium anodes will be welded to each other and joined to a contact lead 4. The tabs 2 are first folded and/or formed by pressing. A contact lead 4 is then positioned at the top (FIG. 1a) or bottom (FIG. 1b) of the stack 5 of tabs 2, or it may be positioned between any two lithium tabs 2 (FIG. 1c).

[0075] The contact leads 4 may take a number of forms (FIGS. 2a to 2e). The body 6 is composed of a conductive metal ribbon, typically nickel, copper, stainless steel or some composite conductor. The end portion 7 (the area to be welded) may be perforated, meshed or punched. Alternatively, the end portion 7 may be devoid of any through-holes (not shown). The end portion 7 may be an integral part of the metal ribbon 6, or it may be a separate piece welded to the ribbon 6. Where the end portion 7 is a separate piece welded to the ribbon 6, it may be made of a different metal to that of the ribbon 6. The contact may be linear, “T” or “L” shaped. The perforations, when present, may be rhombic, circular, square, rounded, polygonal or any other suitable shape.

[0076] The tabs 2 and the contact lead 4 are then positioned between the two weld fixtures 8 of an ultrasonic welder (FIG. 3). The ultrasonic welder then simultaneously applies pressure and an ultrasonic wave to the weld area. This causes the numerous lithium layers 2 to fuse together to form a lithium-lithium weld. Further, where the contact lead 4 includes through holes, the softened lithium percolates through the perforated or meshed area 7 of the contact lead 4. The contact lead 4 is hence joined to the lithium 2 as the mesh 7 is intimately surrounded by lithium. The high surface area contact between the mesh 7 of the contact lead 4 and the lithium electrode 1 produces a low resistance and a mechanically strong electrical contact. When the ultrasonic wave ceases and the pressure is released, the contact lead 4 will be joined to the lithium anodes 1.

[0077] FIGS. 4a to 4e depict an apparatus that may be used for forming an ultrasonic weld. The apparatus comprises a first clamping portion 12 and a second clamping portion 14 that are movable from a first spaced apart position to a second position where the portions 12, 14 are closer to one another. The apparatus also includes a positioning jig 16 for supporting the parts 18 to be welded in position. The second clamping portion 14 is configured to vibrate at ultrasonic frequencies.

[0078] As best seen in FIG. 4a, the parts 18 to be welded are placed on top of the first clamping portion 12 while the clamping portions are in their first spaced apart position. The second clamping portion 14 is then moved relatively towards the first clamping portion 12 to apply a clamping pressure between the parts 18 to be welded. The second clamping portion 14 is then vibrated at ultrasonic frequency (FIG. 4b). This pre-shapes and rubs the parts 18 together, so that their surfaces are prepared for weld formation. In the main welding phase, the parts 18 are joined together (see FIG. 4c). The first and second clamping portions 12, 14 are then moved apart to allow the welded parts 18 to be removed from the apparatus (see FIG. 4d).

Example 1

[0079] A linear nickel contact lead, composed of 50 μm thick nickel ribbon, was used. The endmost 5 mm of the contact lead was expanded to form a mesh. A battery with 60 lithium anodes, each of 78 μm thickness, was assembled. A stack of lithium contact tabs protruded from the battery. The lithium contact tabs were formed and trimmed to produce a flat welding area and to ensure that each of the tabs, regardless of its position, in the stack used the minimum quantity of lithium. The formed stack of lithium tabs was then positioned between the welding fixtures of an ultrasonic welder. The contact lead was then positioned on top of the stack of lithium tabs, such that the meshed region overlapped with the flat lithium welding zone. The welding conditions listed in Table 1 were then entered into an AmTech 900B 40 kHz ultrasonic welder. A single weld was then performed. Each of the 60 lithium layers were welded firmly to each other. A strong join was produced between the lithium and the contact lead. This join had been created by the softened lithium penetrating through the mesh of the contact lead.

TABLE-US-00001 TABLE 1 The welder setting used in Example 1. Energy/J Amplitude/μm Trigger Pressure/Psi Pressure/Psi 180 5 20 20

Example 2

[0080] A “T” shaped contact lead was made by welding a piece of nickel ribbon (50 μm thick) to a piece of copper mesh. The mesh opening was approximately 200×700 μm, with a bar width of 100 μm. The mesh was thrice as long as the nickel ribbon was wide. The mesh was 5 mm wide; the same as the welding zone. The mesh was positioned centrally to form the cross of the “T” and welded into position by an ultrasonic welder using the conditions given in Table 2, weld A. The contact lead was positioned between the welding fixtures of an ultrasonic welder such that the meshed region fell into the welding zone.

[0081] A battery with 20 lithium anodes, each of 78 μm thickness, was assembled. A stack of lithium contact tabs protruded from the battery. The stack of lithium contact tabs was formed and trimmed to produce a flat welding area and to ensure that each of the contact tabs, regardless of its position, in the stack used the minimum quantity of lithium.

[0082] The stack of lithium contact tabs was then positioned on top of the contact lead, between the welding fixtures of an ultrasonic welder. The copper mesh “arms” of the “T” shaped contact lead were then folded around the stack of lithium contact tabs. The welding conditions listed in Table 2, weld B were then entered into an AmTech 900B 40 kHz ultrasonic welder. A single weld was then performed. Each of the 20 lithium layers were welded firmly to each other. A strong join was produced between the lithium and the contact lead. This join had been created by the softened lithium penetrating through the mesh of the contact lead.

TABLE-US-00002 TABLE 2 The welder settings used in Example 2 Weld Energy/J Amplitude/μm Trigger Pressure/Psi Pressure/Psi A 70 80 80 5 B 10 5 20 20

Example 3

[0083] An “L” shaped contact lead was manufactured by photochemical etching from a sheet of 100 μm thick stainless steel. The upright section of the “L” is continuous steel foil. The base of the “L” was etched with a mesh pattern. The mesh opening was 500×500 μm and the bar width was 10 μm. The base of the “L” was twice the width of the upright section. The width of the base section was 5 mm, the same as the weld zone.

[0084] A battery with 20 lithium anodes, each of 78 μm thickness, was assembled. A stack of lithium contact tabs protruded from the battery. The contact lead was positioned between the top face to the lowermost lithium contact tab and the bottom face of the remainder of the stack. The remainder of the stack of lithium contact tabs was pushed down onto the meshed region of the contact lead. The protruding meshed section of the contact lead was folded over the stack of contact tabs. The contact assembly was positioned between the welding fixtures of an ultrasonic welder such that the meshed regions fell into the welding zone.

[0085] The welding conditions listed in Table 3 were then entered into an AmTech 900B 40 kHz ultrasonic welder. A single weld was then performed. Each of the 20 lithium layers were welded firmly to each other. A strong join was produced between the lithium and the contact lead. This join had been created by the softened lithium penetrating through the mesh of the contact lead.

TABLE-US-00003 TABLE 3 The welder settings used in Example 3 Energy/J Amplitude/μm Trigger Pressure/Psi Pressure/Psi 40 5 20 20

Example 4 (Nickel)

[0086] A square shaped contact lead was made by cutting a piece of plane nickel foil (100 μm thick). The contact lead was positioned between the welding fixtures of an ultrasonic welder such that the welding zone was 1 mm from the tab edge. The welding zone was a rectangle (20×6 mm).

[0087] A battery with 9 lithium anodes, each of 100 μm thickness, was assembled. A stack of lithium contact tabs protruded from the battery. The stack of lithium contact tabs was formed and trimmed to produce a flat welding area and to ensure that each of the contact tabs, regardless of its position, in the stack used the minimum quantity of lithium. The trimmed edges of lithium tabs fully covered the welding zone at the nickel foil.

[0088] The stack of lithium contact tabs was then positioned on top of the contact lead, between the welding fixtures of an ultrasonic welder. The welding conditions are listed in Table 4. The welder is a NewPower Ultrasonic Electronic Equipment CO., LTD 40 kHz ultrasonic welder. A single weld was performed. Each of the 9 lithium layers were welded firmly to each other. A strong join was produced between the lithium and the nickel contact lead. This join had been tested per peel test procedure.

TABLE-US-00004 TABLE 4 Frequency 40 kHz Welding Time sectors: Delay 0.15 s Welding 0.18 s Take off 0.20 s Amplitude 50% (of 10 μm) Pressure 0.21 MPa Power 350 W Energy 350 J

Example 5 (Copper)

[0089] A square shaped contact lead was made by cutting a piece of plane copper foil (100 μm thick). The contact lead was positioned between the welding fixtures of an ultrasonic welder such that the welding zone was placed 1 mm from the tab edge. The welding zone was a rectangle (20×6 mm).

[0090] A battery with 9 lithium anodes, each of 100 μm thickness, was assembled. A stack of lithium contact tabs protruded from the battery. The stack of lithium contact tabs was formed and trimmed to produce a flat welding area and to ensure that each of the contact tabs, regardless of its position, in the stack used the minimum quantity of lithium. The trimmed edges of lithium tabs fully covered the welding zone at the copper foil.

[0091] The stack of lithium contact tabs was then positioned on top of the contact lead, between the welding fixtures of an ultrasonic welder. The welding conditions are listed in Table 5. The welder is a NewPower Ultrasonic Electronic Equipment CO., LTD 40 kHz ultrasonic welder. A single weld was then performed. Each of the 9 lithium layers were welded firmly to each other. A strong join was produced between the lithium and the copper contact lead. This join had been tested per peel test procedure.

TABLE-US-00005 TABLE 5 Frequency 40 kHz Welding Time sectors: Delay 0.15 s Welding 0.16 s Take off 0.20 s Amplitude 50% (of 10 μm) Pressure 0.20 MPa Power 300 W Energy 300 J

Example 6 (Stainless Steel, 316)

[0092] A square shaped contact lead was made by cutting a piece of plane stainless steel foil (58 μm thick). The contact lead was positioned between the welding fixtures of an ultrasonic welder such that the welding zone was placed 1 mm from the tab edge. The welding zone was a rectangle (20×6 mm).

[0093] A battery with 9 lithium anodes, each of 100 μm thickness, was assembled. A stack of lithium contact tabs protruded from the battery. The stack of lithium contact tabs was formed and trimmed to produce a flat welding area and to ensure that each of the contact tabs, regardless of its position, in the stack used the minimum quantity of lithium. The trimmed edges of lithium tabs fully covered the welding zone at the stainless steel foil.

[0094] The stack of lithium contact tabs was then positioned on top of the contact lead, between the welding fixtures of an ultrasonic welder. The welding conditions are listed in Table 6, were then entered into the NewPower Ultrasonic Electronic Equipment CO., LTD 40 kHz ultrasonic welder. A single weld was then performed. Each of the 9 lithium layers were welded firmly to each other. A strong join was produced between the lithium and the stainless steel contact lead. This join had been tested per peel test procedure.

TABLE-US-00006 TABLE 6 Frequency 40 kHz Welding Time sectors: Delay 0.15 s Welding 0.18 s Take off 0.20 s Amplitude 80% (of 10 μm) Pressure 0.21 MPa Power 350 W Energy 350 J

[0095] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0096] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0097] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.