STRAP FOR SPIRALLY WOUND THIN METAL FILM BATTERY

Abstract: A thin metal film battery cell is formed by one or more plates wound in a spiral thereby forming a roll with two ends at which spiralled edges of the plates are exposed. Each end of the roll is covered by an end strap which includes a body of electrically conductive material from which a tab extends. The body contacts each convolution of the roll while leaving a portion of each convolution exposed so that an electrolyte is able to flow into the roll. The tab attached to and projecting outward from the body for making electrical connection to the thin metal film battery cell.

Description: STRAP FOR SPIRALLY WOUND THIN METAL FILM BATTERY Background of the Invention This invention relates to electric storage batteries and more particularly to a termination strap for thin metal film battery cells. A thin metal film battery cell includes plates made from very thin lead foil pasted with an active material on both surfaces. Plates with positive active material and plates with negative active material are separated by a separator strip and are spirally wound to form a roll. Unpasted edges of the positive plates extend in one direction while unpasted edges of the negative plates extend in an opposite direction from the roll. Terminations of lead or lead alloy are cast on or soldered to the ends of the spiral roll. U.S. Patent No. 5,198,313 issued March 30, 1993, for "Battery End Connector" describes one arrangement of cast-on end connectors for the two ends of a spiral roll. The present invention provides a termination for a thin metal film roll in the form of a cap-like strap which uses less lead than the terminations of the prior art and which facilitates improved exposure of each of the spiral layers, or convolutions, to electrolyte. The strap also facilitates high voltage extrusion welding of the straps of adjacent cells. Summary of the Invention In accordance with the invention, a cap-like strap is formed at an end of a spirally wound cell of alternating convoluted layers of positive and negative thin metal foil plates. The shapes of the straps are is characterized by the fact that the strap engages a portion of the projecting ends of each layer of the spiral, while leaving another portion of the projecting ends of each layer exposed. The strap is further characterized by an upstanding, integrally formed tombstone portion for connection to adjacent cells or to a terminal. A strap having the foregoing characteristics is formed at each end of the spiral roll. The strap can take a variety of configurations and is preferably cast in place on the end of the spiral roll. The foregoing and other objects and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate preferred embodiments of the invention. Brief Description of the Drawings Figure 1 is an exploded view in perspective of a battery using the straps of the present invention; Figure 2 is a top view of the battery of Figure 1 with a top removed; Figure 3 is a bottom view of the battery of Figure 1 with a bottom removed; Figure 4 is a perspective view of a battery cell with the straps of the present invention; and Figures 5-9 are plan views of alternative shapes for the strap of the present invention. Detailed Description of the Preferred Embodiments The basic battery construction shown in the drawings is the subject of a co- pending U.S. patent application Serial No. 09/008,719 filed January 19, 1998. The disclosure of the co-pending application is incorporated herein by reference as though fully set forth herein. Briefly, the battery illustrated in the drawings includes a case having a body 12 with a top 14 and a bottom 16 each joined to the body 12 in a manner known in the art, such as by heat sealing. The case is configured to accommodate a plurality of thin metal film cells 18 that include a spirally wound thin metal film roll 20 coiled in a manner generally known in the art. That is, thin lead foil plates coated with positive or negative active material are spirally wound with a separator layer between the plates. The positive and negative plates are wound axially off-set from each other so that the edges of the positive plate protrude axially from one end and the edges of the negative plate protrude axially from the other end. As thin metal film battery cells are generally known in the art, recognized techniques for manufacturing such cells and the manner in which they generate electricity will not be described herein. For a general description of such cells, reference may be had to U.S. Patent Application No. 08/870,803, filed June 6, 1997, entitled "Modular Electric Storage Battery", and assigned to the assignee of the present invention. The disclosure of such earlier filed application is incorporated herein by reference. Each end of the spirally wound roll of plates and separator is joined to a cap-like strap 26a and 26b fabricated of lead which is cast in place and connects the projecting edges of one of the positive or negative plates. As shown in Figure 1 , the straps 26 are configured in such a manner that they connect with all convolutions of the spirally wound roll but also expose an axial end portion of each spiral convolution. The result is that an electrical connection is established to the positive or negative plates while at the same time allowing electrolyte to pass axially into each convoluted layer of the roll. Each strap 26a and 26b has a flat body 25a and 25b, respectively, from which extend an integral tombstone portion forming a tab 27a and 27b, respectively. As shown in Figure 3, the tabs 27a and 27b on certain of the straps on opposite ends of the roll 20 are off-set by 180°. On other rolls 20, the tabs are off-set by 90°. The cells 18 are received in a honeycomb structure formed in the body 12. As shown in Figures 2 and 3, the positive and negative straps are arranged in the honeycomb case in such a manner that they can be serially connected to each other by welding in a known manner and also can connect to terminals 30 and 32. In Figures 2 and 3, the two cells 18c and 18d that are remote from the terminals 30 and 32 have their tabs offset by 90°. The remaining cells 18a, 18b, 18e, and 18f have the tabs offset by 180°. As shown in Figures 1-4, the preferred form of the cap-like strap utilizes a crescent shape with the opening of the crescent off-set from the centerline of the roll. Alternative strap configurations are shown in Figures 5-9. All of the shapes of the straps are characterized by the fact that the strap engages a portion of the projecting ends of each convolution of the spiral, while leaving another portion of the projecting ends of each convolution exposed. Each of the configurations also includes an upstanding tombstone tab for making electrical connections between adjacent cells and external terminals on the battery. Electrolyte is introduced into the battery through vents 34 in the top 14 that are centered over each cell. The cap-like strap of this invention allows the electrolyte to readily wet all the convoluted layers.

Claims: CLAIMS We claim: 1. An end strap for a thin metal film battery cell formed by a plate which is wound in a spiral thereby forming a roll with two ends at which spiralled edges of the plate are exposed, the end strap comprising: a body of electrically conductive material for abutting one end of the roll wherein the body contacts each convolution of the roll while leaving a portion of each convolution exposed so that an electrolyte is able to flow into each convolution of the roll; and a tab of electrically conductive material attached to and projecting outward from the body for making electical connection to the thin metal film battery cell. 2. The end strap as recited in claim 1 wherein the body has two major surfaces and at least one edge surface extending between the two major surfaces; and the tab projecting from one of the two major surfaces. 3. The end strap as recited in claim 1 wherein the body has two major surfaces and at least one edge surface extending between the two major surfaces; and the tab projecting from one of the two major surfaces at a location adjecent to the at least one edge surface . 4. The end strap as recited in claim 1 wherein the body has a crescent shape. 5. The end strap as recited in claim 1 wherein the body has a semicircular shape. 6. The end strap as recited in claim 1 wherein the body has a trapezoidal shape. 7. A battery cell comprising: a roll formed by first and second thin metal foil plates wound in a spiral with a spiral edge of the first thin metal foil plate protruding from a first end of the roll and a spiral edge of the second thin metal foil plate protruding from a second end of the roll; a first strap abutting the first end of the roll and including a first body of electrically conductive material contacting each convolution of the first thin metal foil plate while leaving a portion of each convolution first thin metal foil plate exposed so that an electrolyte is able to flow into the roll, and a first tab of electrically conductive material attached to and projecting outward from the first body for making electrical connection to the thin metal film battery cell; and a second strap abutting the second end of the roll and including a second body of electrically conductive material contacting each convolution of the second thin metal foil plate while leaving a portion of each convolution second thin metal foil plate exposed so that the electrolyte is able to flow into the roll, and a second tab of electrically conductive material attached to and projecting outward from the second body for making electrical connection to the thin metal film battery cell. 8. The battery cell as recited in claim 7 wherein the first tab is off-set from the second tab by 180°. 9. The battery cell as recited in claim 7 wherein the first tab is off-set from the second tab by 90°. 10. The battery cell as recited in claim 7 wherein each of the first body and the second body has two major surfaces and at least one edge surface extending between the two major surfaces; and a respective one of the first tab and the second tab projects from one of the two major surfaces. 11. The battery cell as recited in claim 7 wherein each of the first body and the second body has two major surfaces and at least one edge surface extending between the two major surfaces; and a respective one of the first tab and the second tab projects from one of the two major surfaces at a location adjecent to the at least one edge surface. 12. The battery cell as recited in claim 7 wherein the first and second bodies each have a crescent shape. 13. The battery cell as recited in claim 7 wherein the first and second bodies each have a semicircular shape. 14. The battery cell as recited in claim 7 wherein the first and second bodies each have a trapezoidal shape.

Inventors: ANDREW MICHAEL G, DOUGHERTY THOMAS J, ZAGRODNIK JEFFREY P, ANDREW, MICHAEL, G., DOUGHERTY, THOMAS, J., ZAGRODNIK, JEFFREY, P.
Applicants: JOHNSON CONTROLS TECH CO, JOHNSON CONTROLS TECHNOLOGY COMPANY
Application year: 1999
Main classification: H01M2
IPC codes: H01M2, H01M6, H01M10