Abstract:
The apparatus of the present invention provides a cover for venting gases from thin metal film battery cells having vents disposed at the center of one end of the cells. The vents comprise cylindrical wells that recess into, and substantially fill, the top portions of battery cell cavities within a battery housing. The cavities are sized to hold the battery cells securely and are configured to provide an electrical serial connection. The wells include pipes which extend outward from the bottom of the wells and lead from openings in the bases of the wells. The openings in the pipes are covered with flexible valve caps and well lids cover the wells. The center point arrangement of the recessed wells permit gases from the battery cells to escape through the openings, yet restrict the electrolyte from exiting the housing. The base of the battery housing does not have vent openings and is interchangeable with the cover so that the battery housing may be oriented with the terminals near the top or the bottom of the case.

Description:
This application claims the benefit of U.S. provisional application No. 60/071,789, filed on Jan. 19, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to electric storage batteries, and more particularly to an arrangement for venting gases from thin metal film battery cells. 
     Thin metal film (TMF) battery technology provides a compact high power battery cell. Cells of this type are well known and their construction and manufacture have been described in, for example, U. S. Pat. Nos. 3,494,800; 5,045,086; 5,047,300; 5,198,313 and 5,368,961 the disclosures of which are hereby incorporated by reference. A thin metal film battery cell includes thin metal film plates sealed within a valve-regulated, sealed cell container. The cells include absorptive glass-mat (AGM) separator technology in an electrolyte starved system. The thin metal film plates are made from very thin lead film pasted on both surfaces with an active material. Plates having positive active material and plates having negative active material are spiral wound with separator material, and terminations are cast-on or soldered to the ends of the spiral roll. The roll is encapsulated in a container which is filled with electrolyte and then sealed. 
     When thin metal film batteries are charged, the excitation of the positive and negative active materials tends to heat the electrolytic fluid which causes some of the electrolytic fluid to change from a liquid to a gas. This gas accumulates and increases the pressure within the battery case. In extreme overcharging conditions, the accumulated gas can rupture the battery enclosure. Prior art inventions place openings in the battery enclosure to release the gas and prevent built-up pressure within the enclosure; however, the electrolyte may also exit through such openings. Thus, the present invention is directed to the venting of gases accumulated in a thin metal film battery housing while preventing electrolyte from exiting the housing. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, the apparatus includes a battery housing containing at least one cavity for holding a battery cell. The housing is enclosed by a cover having a vent opening at the base of a venting well that is substantially centered and recessed within one end of the cavity so as to substantially fill the top of the cavity. The venting well also includes a pipe, or well aperture, at its center extending outwardly from the vent opening. A baffle is disposed at an inner end of the well aperture that partially interrupts direct flow through the vent opening. 
     Preferably, a flexible valve cap is mounted on the top of, and seals to, the well aperture. The valve cap is preferably made of a flexible rubber material that expands at a venting pressure to allow gases from within the cavities to escape and contracts when below the venting pressure to reseal to the well aperture. A well lid or cover closes the top of the well. 
     Such a vent arrangement is provided above each cell in a multiple cell battery. The vent may be formed in a top that closes the body into which the cells are mounted. Preferably, the top is interchangeable with a bottom that does not include the vents. 
     The foregoing and other objects and advantages of the invention will be found in the detailed description that follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the battery with a center point vent cover according to the present invention with one lid removed; 
     FIG. 2 is an exploded perspective view of the battery illustrated in FIG. 1, showing one thin metal film battery cell and with no lids or caps; 
     FIG. 3 is a top plan view of the battery case illustrated in FIG. 1 with the top and bottom of the case removed for clarity, showing one thin metal film battery cell in each cavity; 
     FIG. 4 is a bottom plan view of the battery shown in FIG. 1 with the top and bottom of the case removed for clarity, showing one thin metal film battery cell in each cavity; 
     FIG. 5 is a cross-sectional view of the battery taken along the plane  5 — 5 — 5  shown in FIG. 1; 
     FIG. 6 is a cross-sectional view of the top of the battery case taken along the line  6 — 6  illustrated in FIG. 2; 
     FIG. 7 is a cross-sectional view of the bottom of the battery case taken along the line  7 — 7  shown in FIG. 2; and 
     FIG. 8 is an enlarged view in cross section of one vent in the top of the battery case. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As illustrated in FIG. 1 the battery  8  includes a case  10  having a body or housing  12  with a top  14  and a bottom  16  each coupled to the body in a manner known in the art such as by heat sealing. The case  10  is configured to accommodate a plurality of thin metal film cells  18  (FIG. 2) that include a thin metal film  20  coiled in a spiral in a manner generally known in the art (for illustration purposes, the spiral coil is shown in the figures as multiple concentric circles). The film  20  defines an outer cylindrical surface area generally indicated by reference numeral  21 , a first end  22 , and second end  24 . First  26  and second  28  conducting leads are coupled to the respective first  22  and second  24  ends of the coiled thin metal film  20  such as by welding or an equivalent technique known in the art. 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 which is incorporated herein by reference. 
     With reference to FIGS. 2 and 3, 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 . 
     In the illustrated embodiment, exterior walls  30 ,  32 ,  34 , and  36 , as well as each of the plurality of partition walls  38 , have the same wall thickness  41  (FIG. 3) thereby simplifying the manufacture of case  10 . Partition walls  38  include a plurality of first planar segments  46  and second planar segments  48  oriented orthogonal to first planar segments  46 . Second planar segments  48  are further orthogonal to first  30  and second  32  exterior side walls and parallel to first  34  and second  36  exterior end walls. In a similar manner, each of first planar segments  46  are orthogonal to first  34  and second  36  exterior end walls and parallel to first  30  and second  32  exterior side walls. A plurality of arcuate connector segments  50  interconnect first  46  and second  48  planar segments as well as couple the planar segments  46  and  48  to the respective exterior side  30  and  32  and end  34  and  36  walls. Each of the arcuate connector segments  50  are integral with one or three other arcuate connector segments  50  to define a plurality of roughly diamond shaped passages  52  or half diamond shaped passages  53 , each with rounded corners as shown. 
     The planar segments  46  and  48 , the exterior side and end walls, and the arcuate connector segments  50  cooperate to define the octagonal cell cavities  40  for accommodating cells  18 . As best illustrated in FIG. 3, cells  18   a - 18   f  are each disposed in a cavity  40  (FIG. 2) of body  12 . The arcuate configuration of segments  50  is predetermined to securely retain the cells  18  within each cavity  40 . More particularly, in the preferred embodiment, the overall size of each cavity  40  as well as the shape of arcuate segments  50  are predetermined so that during the insertion of each cell  18  within each cavity  40 , the arcuate segments  50  matingly engage the cell  18  along in excess of fifty percent (50%) of the exterior surface area  21  of film  20 . The uniform thickness of the exterior case walls  30 ,  32 ,  34 , and  36  and each partition wall  38  uniformly compresses the cell during insertion such as by compressing the glass fiber separators normally included therewithin. Accordingly, the cells  18  are securely nested and retained within the cavities  40 . Finally, as illustrated in FIG. 5, top  14  and stops  62 , described in detail below, longitudinally retain the cells  18  within the cavities  40  as shown. 
     As illustrated, the exterior side walls  30  and  32 , exterior end walls  34  and  36 , and partition walls  38  of body  12  are integral with one another. It is preferred that the walls  30 ,  32 ,  34 ,  36  and  38  are formed of a thermally resistant plastic material such as polypropylene through processes known in the art such as stamping, casting, or injection molding. 
     In order to further define generally octagonal cell cavities  40 , exterior side walls  30  and  32  are connected to exterior end walls  34  and  36  via truncated planar corner segments  54 . As best illustrated in FIG. 2, the exterior walls  30 ,  32 ,  34 , and  36  of body  12  are of a uniform length  56  defining an upper end  58  and a lower end  60 . Top  14  is coupled to the case  12  proximate to upper end  58  and bottom  16  is coupled proximate to lower end  60  thereof (FIG.  1 ). 
     In addition to the robustness, retention features, and moldability of the modified honeycomb configuration of the present invention, the flat surfaces provided by planar segments  46  and  48  facilitate the proper alignment of each cell  18  within its respective cavity  40  and provides a flat surface for complete electrical interconnection of the cells  18  by welding as hereinafter described. More particularly, as best illustrated in FIGS. 3 and 4, the upstanding tabs  27   a - 27   f  of the cells  18   a - 18   f  are disposed within the cavities  40  adjacent one of the planar surfaces  46  and  48 . The welded interconnection between adjacent tabs  27  within the battery case  10  occurs through an orifice  171  formed in the planar segments  46  and  48  as hereinafter described and as illustrated in FIG.  5 . Those skilled in the art will appreciate that a complete weld connection between adjacent tabs  27  is facilitated by the planar configuration of surfaces  46  and  48 . 
     As shown in FIGS. 4 and 5, 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  (FIG. 5) of these respective segments to properly position the cells  18  within the cell cavities  40  thereby facilitating the electrical interconnection of the cells  18  as hereinafter described. 
     The configuration of the top  14  will now be described with reference to FIGS. 1,  5 ,  6 , and  8 . The top  14  is preferably formed of the same plastic material as body  12  through stamping, casting, injection molding, or other method known in the art. The top  14  includes an upper planar member  64 , a connecting flange  66  extending downwardly from the periphery of upper member  64 , and a plurality of vents  68  (FIG. 6) disposable within the cell cavities  40  when the top  14  is connected to body  12  (FIG.  5 ). Vents  68  allow dissipation of gases generated within case  10  during the charging and discharging cycles of the cells. The vents  68  include venting passages  70  defined by upstanding cylindrical pipes  71  that selectively provide access to the cell cavities  40  for placement of an electrolyte within each of the cell cavities  40 . 
     The vents  68  are partially defined by a cylindrical well  72  interconnecting upper planar member  64  and a well bottom  73 . The cylindrical wells  72  of adjacent vents  68  are separated from one another so as to define a recessed cavity  74  that accommodates the upstanding tab  27  on conducting leads  26  or  28  for electrically interconnecting the cells  18  as hereinafter described. Upper  81  and lower  83  sets of ribs are integral with and protrude from the top and bottom surface respectively of each well bottom  73 . The ribs of each set  81  and  83  are aligned perpendicularly and extend from the edges of the wells  72  to provide structural support for the vents  68 . On separate, parallel planes, the upper ribs  81  bisect the angles formed by the lower ribs  83 . The ribs  81  and  83  are interrupted near their midpoints by the open venting passage  70  of each vent  68 . The ribs  81  and  83  and the recessed wells  72  increase the pressure handling capabilities of the case  10 . 
     The bottom of each venting passage  70  is defined by a baffle  75 . When adding electrolytic fluid to the battery  8 , the baffle  75  disperses the fluid laterally through the venting passage  70  preventing the stream of fluid from damaging the battery cells  18 . A vent opening  76  extends from the well bottom  73  to above and laterally around the baffle  75 . A rubber cap  77  is disposed on the top of the pipe  71  above the vent opening  76 . The rubber cap  77 , made of a polypropylene/polyethylene material such as EPDM, acts as a valve to maintain an air tight seal up to approximately 15 psi. The EPDM material allows the rubber cap  77  to expand and vent the gases at approximately 20 psi, and then reseal. Each well  72  is enclosed by a lid member  78  sealed to the open top of each cylindrical well  72 . The lids  78  have at least one laterally offset opening  78 ′ for the escape of gas from the vent. To reduce the likelihood of a rupture in extreme overcharge conditions, the lids  78  are designed to release at approximately 50-60 psi to rapidly vent the gases. The baffle  75 , caps  77  and lids  78  collectively work to prevent electrolytic fluid from exiting the battery  8  when vented or inverted. 
     As illustrated in FIG. 7, the bottom  16  is configured in a manner substantially similar to the top  14  and includes a lower planar member  79 , a connecting flange  80 , and upper members  82  recessed from the lower planar member  79  and connected thereto via tapered cylindrical connecting walls  84 . Protruding some thickness from the bottom and top surface respectively of the each upper member  82  are upper  85  and lower  87  sets of ribs, each set perpendicularly intersecting at the center of the upper members  82 , similar to ribs  81  and  83 . The bottom  16  does not include the vent arrangement formed in the top  14 . 
     The top  14  and the bottom  16  are connected to body  12  such as by heat sealing or other method known in the art. More particularly, connecting flanges  66  and  80  of top  14  and bottom  16 , respectively, are configured to operatively engage exterior side  30  and  32  and end  34  and  36  walls, whereupon the top  14  and the bottom  16  are heat sealed to the body  12  at raised surfaces  89  circumscribing the vents  68  to provide a sealed case that is vented through vents  68  in the top  14 . 
     The electrical interconnection of the cells  18  within the case  10  will now be described with reference to FIGS. 3 and 4. As illustrated, adjacent TMF cells are oppositely oriented in a manner generally known in the art for serial connection. Thus, cell  18   a  is electrically connected to exterior terminal  86  by second conducting lead  28   a  (FIG. 4) and is electrically connected to cell  18   b  via the connection of the respective first conducting leads  26   a  and  26   b . The serial electrical connection of the remaining cells  18   b - 18   f  is accomplished in a substantially similar manner and is illustrated in the drawings. 
     As illustrated in FIG. 5, planar segment  46  separating cells  18   c  and  18   d  is provided with an orifice  171  for electrically connecting upstanding tabs  27   c  and  27   d  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 second planar segments  48  are made in a manner substantially the same as that illustrated in FIG. 5 for connection to first planar segment  46 . As shown in FIG. 3, the serial electrical connection of cells  18   a - 18   f  is completed by electrically connecting the second lead of cell  18   f  in a manner generally known in the art to terminal  88  which is coupled to the exterior of battery case  12  and, more particularly, to end wall  34 . 
     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. 3 and 5. More particularly, each of the cells  18   a - 18   f  is disposed within a respective cavity  40  until one of the first  26  and second  28  leads connected thereto engage the stops  62  projecting inwardly into the cavity  40 . The stops  62  facilitate the proper positioning of the TMF cells  18  relative to one another to allow precise electrical interconnection, as described above, with relative ease and simplicity. 
     As seen from the above description and the accompanying drawings, each vent  68  is centered over one of the cells  18  and is recessed down toward the level of the top of a cell  18 . The result is that there is very little free space in which gas can accumulate without venting. The vent  68  accommodates the venting of gas but restricts the exit of electrolyte. Because the top  14  and bottom  16  contain identical structures for attachment to the body  12 , the terminals  86  and  88  can be located at the top by simply reversing the top  14  and bottom  16  before heat sealing to the body  12 . 
     Illustrative embodiments of the invention have been described in considerable detail for the purpose of disclosing practical, operative structures whereby the invention may be practiced advantageously. The designs described are intended to be illustrative only. The novel characteristics of the invention may be incorporated in other structural forms without departing from the scope of the invention as defined in the following claims.