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 electical connection to the thin metal film battery cell.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/071,786 filed Jan. 19, 1998. 
    
    
     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. Pat. No. 5,198,313 issued Mar. 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 charactrized 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 
     FIG. 1 is an exploded view in perspective of a battery using the straps of the present invention; 
     FIG. 1A is a perspective view of a battery using the straps of the present invention; 
     FIG. 2 is a bottom view of the battery of FIG. 1 with a top removed; 
     FIG. 3 is a top view of the battery of FIG. 1 with a bottom removed; 
     FIG. 4 is a perspective view of a battery cell with the straps of the present invention; and 
     FIGS. 5-9 are plan views of alternative shapes for the strap of the present invention. 
     FIG. 10 is a cross-sectional view of the battery of FIG. 1A taken along the plane  5 - 5 - 5  of FIG.  1 A. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The basic battery construction shown in the drawings is the subject of a co-pending patent application Ser. No. 09/008,719 now U.S. Pat. No. 6,051,336 of Thomas J. Dougherty, Michael G. Andrew, Gerald K. Bowen, and Jeffrey Zagrodnik for “Battery Case for Thin Metal Film Cells” filed Jan. 19, 1998, and assigned to the assignee of this application. The disclosure of the co-pending application is incorporated herein by reference as though fully set forth. 
     Briefly, the battery  8  illustrated in the drawings includes a case  10  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 Ser. No. 08/870,803, filed Jun. 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  26   a  and  26   b  fabricated of lead which is cast in place and connects the projecting edges of one of the positive or negative plates. As shown in FIG. 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  26   a  and  26   b  has a flat body  25   a  and  25   b , respectively, from which extend an integral tombstone portion forming a tab  27   a  and  27   b , respectively. As shown in FIG. 3, the tabs  27   a  and  27   b  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 FIGS. 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  86  and  88 . In FIGS. 2 and 3, the two cells  18   c  and  18   d  that are remote from the terminals  86  and  88  have their tabs offset by 90°. The remaining cells  18   a ,  18   b ,  18   e , and  18   f  have the tabs offset by 180°. 
     As shown in FIGS. 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 FIGS. 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. 
     The connection between cells can be described as follows. 
     With reference to FIGS. 1,  1 A,  2  and  3 , the body  12  includes exterior side walls  30  and  32  and exterior end walls  34  and  36  as well as a plurality of partition walls generally indicated by reference numeral  38 . Partition walls  38  interconnect exterior side walls  30  and  32  and exterior end walls  34  and  36  in a modified honeycomb configuration that includes a plurality of generally octagonal shaped cell cavities  40 . The honeycomb configuration includes a flat surface within each cavity to facilitate alignment of the cells within the cavity and the electrical interconnection of the cells such as by welding. Specifically, partition walls  38  include a plurality of first planar segments  46  and a plurality of second planar segments  48  oriented orthogonal to first planar segments  46 . The second planar segments  48  are further orthogonal to first and second exterior end walls  34  and  36  and parallel to first and second exterior side walls  30  and  32 . In a similar manner, each of first planar segments  46  are parallel to first and second exterior end walls  34  and  36  and perpendicular to side walls  30  and  32 . A plurality of arcuate connector segments  50  interconnect the first and second planar segments  46  and  48  as well as couple the planar segments to the respective exterior side and end walls  30 ,  32 ,  34 , and  36 . Each of the arcuate connector segments  50  are integral with one or three other arcuate connector segments to define a plurality of roughly diamond shaped passages  52  or half diamond shaped passages  53 , each with rounded corners as shown. 
     The flat surfaces provided by planar segments  46  and  48  facilitate the proper alignment of each cell within its respective cavity and provide a flat surface for complete electrical interconnection of the cells by welding as hereinafter described. More particularly, as best illustrated in FIGS. 2 and 3, the tabs  27   a  and  27   b  of the cells  18   a - 18   f  are disposed within the cells  40  adjacent one of the planar surfaces  46  and  48 . The welding interconnection between adjacent tabs within the battery case occurs through an orifice  71  formed in the planar segments  46  and  48  as hereinafter described and as illustrated in FIG.  10 . Those skilled in the art will appreciate that a complete weld connection between adjacent tabs is facilitated by the planar configuration of surfaces  46  and  48 . 
     As shown in FIGS. 2 and 10, the body  12  further includes a plurality of semicircular stops  62  integral with and extending inwardly from arcuate connector segments  50  and truncated planar corner segments  54 . Stops  62  are recessed from lower end  60  of these respective segments to properly position the cells  18  within cell cavities  40  thereby facilitating the electrical interconnection of the cells  18  as hereinafter described. The electrical interconnection of the cells  18  within the case  10  can be described with reference to FIGS. 2,  3  and  10 . As illustrated in FIG. 10, flat planar segment  48  separating cells  18   c  and  18   d  is provided with an orifice  71  for electrically connecting tabs  27   a  and  27   b  in a manner generally known in the art such as welding. Those skilled in the art will appreciate that the electrical interconnection of each of the plurality of cells  18   a - 18   f  occurring through planar segments  46  are made in a manner substantially the same as that illustrated in FIG. 10 for connection to planar segment  48 . 
     As indicated above, the position of each cell  18   a - 18   f  within its respective cavity  40  is dictated by the positioning of stops  62  as best illustrated in FIGS. 2 and 10. More particularly, each of the cells are disposed within the respective cavity  40  until one of the straps  26   a  and  26   b  connected thereto engage the stops  62  projecting inwardly into the cavity. The stops  62  facilitate the proper positioning of the TMF cells relative to one another to allow precise electrical interconnection, as described above, with relative ease and simplicity.