Abstract:
A unitary lid for the casing of an electrochemical energy storage device is described. The lid has a terminal lead ferrule and a fill port formed from a single blank in a machine process. The lid does not require any welding except for securing it to the open end of a casing container. The ferrule supports a terminal lead insulated therefrom by glass. A thermoplastic insulator material encases the ferrule and a portion of the terminal lead extending below the lid. In that manner, the insulator helps prevent contact between the anode and the cathode in the vicinity of the lid.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part application of Ser. No. 10/339,478, filed Jan. 9, 2003, which is a continuation-in-part of application Ser. No.  09 / 837 , 778 , now abandoned, which claims priority on U.S. provisional application Ser. No. 60/198,175, filed Apr. 19, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to electrical energy storage devices, such as electrochemical cells and capacitors. More particularly, the present invention relates to lids or covers for casings housing electrical energy storage devices and feedthrough assemblies supported by the lids.  
         BACKGROUND OF THE INVENTION  
         [0003]    Electrochemical cells and capacitors typically include a container with an opening that is closed by a lid or cover welded to the container to form a casing for the electrical energy storage device. The lid must provide access to the interior of the casing for at least two purposes. First, a terminal lead connected to the anode or the cathode current collector must pass through one of the lid openings to a position exterior of the casing. Second, the electrolyte must be filled into the housing through the other lid opening. Conventionally, two openings are defined in the lid for this purpose. The openings usually have structures connected to the lid to aid in sealing them.  
           [0004]    The container and the lid are of an electrically conductive material and serve as a contact for either the anode or the cathode electrode, typically the anode. The other of the anode and cathode electrodes not in contact with the casing, typically the cathode, is connected to a terminal lead electrically insulated from the casing by a glass-to-metal seal. The insulating glass is typically supported in the lid by a ferrule and the ferrule/insulating glass/terminal lead is referred to as a feedthrough assembly. A fill port sleeve/closure assembly is used for sealing the fill opening.  
           [0005]    The provision of a sleeve-shaped terminal lead ferrule and fill port sleeve secured in respective openings in the lid introduces manufacturing steps into the process, which adds cost. The present lid and feedthrough assembly eliminates many of the conventional manufacturing steps by machining the lid from a metal blank. Not only does this save production costs, but also the machining process roughens the inner surface of the terminal ferrule, which, in turn, benefits adhesion of the glass-to-metal seal to the ferrule material. Then, this assembly is easily loaded into a mold assembly to provide a thermoplastic insulating enclosure encasing the ferrule and part of the terminal lead. The thusly-formed insulator helps segregate the anode from the cathode in the vicinity of the lid.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a unitary lid including a terminal ferrule and a fill port structure formed from a single blank of conductive material. A starting blank is provided with a thickness sufficient to meet the design features for a particular electrical energy storage device. The terminal ferrule and fill port are then created in the blank via a machining process such that the junctions where both the terminal lead ferrule and the fill port structure meet with the under side of the lid are at right angles. The process of the present invention eliminates the need for welding of the sleeve-shaped terminal lead ferrule and fill port, and requires fewer handling operations while optimizing the cell&#39;s internal volume. To further isolate the anode from the cathode, a thermoplastic material encases the ferrule and a portion of the length of the terminal lead.  
           [0007]    These and other aspects of the present invention will become increasingly more apparent to those skilled in the art by reference to the following description and the appended drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a cross-sectional, side elevational view of a unitary lid of the present invention.  
         [0009]    [0009]FIG. 2 is a cross-sectional view taken along line  2 - 2  of FIG. 1.  
         [0010]    [0010]FIG. 3 is a cross-sectional, side elevation view of an exemplary electrochemical cell with the unitary lid of the present invention supporting a feedthrough assembly for a terminal lead connected to one of the electrodes and with the lid attached to a container to provide a casing for the cell.  
         [0011]    [0011]FIG. 4 is a cross-sectional, side elevational view of the lid supporting the feedthrough assembly.  
         [0012]    [0012]FIG. 5 is a cross-sectional view of a mold assembly for providing an insulator material encapsulating a ferrule and part of a terminal lead for the feedthrough assembly.  
         [0013]    [0013]FIG. 6 is a cross-sectional view taken along line  6 - 6  of FIG. 5 prior to the insulator material being injected into the mold.  
         [0014]    [0014]FIG. 7 is a cross-sectional view similar to FIG. 6, but with the insulator material encasing the ferrule and terminal lead.  
         [0015]    [0015]FIG. 8 is a cross-sectional view illustrating a further embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0016]    Throughout this description the terms “lid” and “cover” are used interchangeably to refer to the member shown in FIGS. 1 and 2 that is attached to the open end of a container or housing to form a casing for an electrical energy storage device.  
         [0017]    Electrochemical cells or batteries generate electrical current from chemical energy. Capacitors are used to store relatively large quantities of electrical energy for subsequent discharge. Often, these types of electrical energy storage devices are used in medical devices such as heart pacemakers, cardiac defibrillators, neurostimulators, cochlear implants, and the like. In that light, the lid of the present invention is a compact unitary member with space saving right angle surfaces at the junction of the lid body and both the terminal ferrule and the fill port. As will be described hereinafter, this makes the present lid particularly applicable for electrical energy storage devices intended for incorporation into implantable medical devices.  
         [0018]    Turning now to the drawings, FIG. 1 shows a unitary lid or cover  10  according to the present invention formed by machining a rectangular blank (not shown) of an electrically conductive material such as stainless steel, titanium, nickel, aluminum, and the like. Lid  10  has generally opposing major planar upper and lower surfaces  12  and  14 . When in place closing the open end of the container  16  of a casing  18  (FIG. 3), the upper surface  12  is an exterior surface and inner or lower surface  14  is an interior surface.  
         [0019]    Lid  10  is formed of generally three portions or regions: a main body portion  20  having the opposed upper and lower surfaces  12 ,  14 , a terminal ferrule portion  22 , and a fill port portion  24 . The terminal lead ferrule  22  and the fill port portion  24  are completely integral or unitary with main body portion  20 . As used herein, completely integral means being of a single continuous body of material. In other words, by machining the lid  10  from a suitable blank, the terminal ferrule  22  and the fill port portion  24  are not separate or discrete parts, but rather are completely unitary with the main body portion  20  forming a single part.  
         [0020]    Lid  10  terminates along a peripheral edge  26  that is generally perpendicular to the planar upper and lower lid surfaces  12 ,  14 . In the embodiment shown, main body portion  20  is generally rectangular in peripheral shape. The terminal ferrule  22  is a sleeve-shaped portion having a generally cylindrically shaped surrounding sidewall  28  with a series of annular rings  30  extending from the inner surface  14  to a distal end thereof. The cylindrically shaped inner surface  32  of the surrounding sidewall has a machined roughened texture. In other words, the inner surface  32  is not threaded, but is roughened by the action of a rotating machining bit removing material from the blank to form the cylindrically shaped opening. The machined roughness enhances the integrity of the glass-to-metal seal by providing scoring marks that serve as attachment structures for the glass  33  (FIG. 8) to fill and anchor into.  
         [0021]    The ferrule sidewall  28  meets the lower surface  14  of the lid main body portion  20  at a right angle or a normal orientation. Similarly, the fill port  24  is a sleeve-shaped portion having a cylindrically shaped opening provided by a surrounding sidewall  34 . The cylindrical outer surface  36  of the fill port sidewall  34  meets the lower surface  14  of the lid main body portion  20  at a right angle.  
         [0022]    While the upper ends of the terminal ferrule  22  and the fill port  24  are shown co-planar with the upper surface  12  of the lid  10 , the present invention should not be so limited. In that respect, these structures can extend above the upper lid surface  12 . What is important is that they are unitary with the main body portion  20 .  
         [0023]    It will be understood by those of ordinary skill in the art that the main body portion  20  of the lid  10  may be of any suitable shape to mate with and close an opening in the container  16  for the casing  18 , which also may be of any suitable shape. Therefore, the present invention contemplates any configuration of two portions of an electrical energy storage device casing which when mated form a cavity therein. This includes casings of a cylindrical shape, prismatic shape, button shape and a casing formed of mating “clam shell” portions, such as described in U.S. application Ser. No. 09/757,232, filed Jan. 9, 2001. This application is assigned to the assignee of the present invention and incorporated herein by reference.  
         [0024]    Either one of such portions of the casing  18 , i.e., the lid  10  or the container  16 , or either one of the mating clam shell portions of the above-referenced patent application, may include the terminal ferrule portion  22  and the fill port portion  24  and be formed as a single part. What is important is that the respective cylindrically-shaped sidewalls  28 ,  36  of the terminal ferrule  22  and the fill port  24  meet the lower or inner surface  14  of the lid main body portion  20  at a normal orientation. This means that as little internal casing volume as possible is occupied by the unitary lid  10 . Such a construction benefits volumetric cell efficiency, which is especially important in electrical energy storage devices intended for incorporation in implantable medical devices.  
         [0025]    [0025]FIG. 3 shows an illustrative exemplary electrochemical cell incorporating a lid or cover  10  according to the present invention. The exemplary cell is described in U.S. Pat. No. 5,750,286 to Paulot et al., which is assigned to the assignee of the present invention and incorporated herein by reference. The cell includes the casing  18  made of metal, such as stainless steel, titanium, nickel, aluminum, or other suitable electrically conductive material. Casing  18  is formed of two portions: the container  16  and the lid  10 . Container  16  has a sidewall  38  terminating at a peripheral edge or rim  40  defining an opening leading into the container. Lid  10  closes this opening when it is attached to the peripheral edge  40 , such as by welding.  
         [0026]    As shown in FIGS.  3  to  7 , the terminal ferrule  22  supports a glass-to-metal seal  42  for a terminal lead  44  connected to the current collector  46  of one of the electrodes, for example the cathode electrode  48 . The anode (not shown) is segregated from the cathode by a separator  50 . The anode/cathode electrode assembly is then activated by an electrolyte (not shown) filled in the casing, and sealed therein by a closure means, such as ball  52  and sealing disc  54  sealed in the fill port portion  24  of the lid  10 . Those skilled in the art will understand that the present invention is not limited to any particular closure structure.  
         [0027]    [0027]FIG. 4 further shows a thermoplastic insulator  56  encasing the ferrule  22  and a portion of the terminal lead  44 . A preferred thermoplastic material is a fluoropolymer, for example polytetrafluoroethylene (PTFE) that surrounds the ferrule  22  from the lower surface  14  of the lid  10  and continues along a portion of the length of the terminal lead  44  to a distance spaced from the ferrule. The annular rings  30  of the ferrule  22  provide a discontinuous pathway that helps maintain a hermetic seal between the thermoplastic insulator and the ferrule. Also, thermoplastic materials generally flow better around and into annular rings than traditional threads. A lower portion  58  of the terminal lead  44  is left uncovered for subsequent connection to the cathode current collector  46 , as described above. The primary function of the insulator  56  is to help segregate the anode from the cathode adjacent in the vicinity of the lid  10 .  
         [0028]    [0028]FIGS. 5 and 6 illustrate a mold assembly  60  for providing the thermoplastic insulator  56  surrounding the ferrule  22  and terminal lead  44 . The mold assembly  60  has a cavity  62  sized to precisely enclose the lid  10 . The mold  60  provides an annulus  64  about the ferrule  22  and the terminal pin  44 . The annulus  64  is only present about the terminal pin  44  to the length that is desired for the insulator to encase the terminal pin. The mold  60  receives a plug  66  that blanks off the inner surface of the ferrule  22  above the glass-to-metal seal insulating the terminal lead  44  from the ferrule.  
         [0029]    [0029]FIG. 5 also illustrates an alternate embodiment of the terminal lead  44 A (shown in dashed lines) having a right angle bend partway through that portion of its length that will be encased by insulator  56 . Those skilled in the art will understand that the terminal lead can have various orientations and still be at least partially encased by the insulator material.  
         [0030]    [0030]FIG. 7 shows the insulator material  56  having been injected into the mold assembly  60  through a sprue  68  and gate  70  leading to the annulus  64 . The thermoplastic material  56  fills the entire void of the annulus  64  to surround the ferrule  22  including the annular rings  30  and a portion of the length of the terminal lead  44 . In this manner, the insulator  56  encases the terminal lead  58  supported by the glass-to-metal seal  42 , which, in turn, is supported by the ferrule portion  22  of the unitary lid  10 . The insulator  56  in conjunction with the separator  50  prevents the anode electrode from contacting the cathode electrode.  
         [0031]    [0031]FIG. 8 illustrates a further embodiment of the present invention. An annul ring  72  surrounds and contacts the thermoplastic material  56  encasing the annular rings  30  of terminal ferrule  22 . The annual ring  72  is preferably of a metal material and promotes hermetically between the thermoplastic material  56  and the terminal ferrule.  
         [0032]    In accordance with the previous description, it will be evident that the present invention is applicable to any type of electrical energy storage device in which a housing is used that has a container portion with an open side and a lid for closing the container, thereby forming a casing for the storage device. In that respect, the present invention is applicable to low rate, medium rate, high rate, case negative and case positive electrochemical cells of both primary and secondary chemistries. Examples of such cells include lithium iodine cells, lithium thionychloride cells, lithium silver vanadium oxide cells, lithium carbon monofluoride cells, lithium manganese dioxide cells, and secondary cells containing lithium cobalt oxide, and the like.  
         [0033]    It will further be recognized that such cells may take one of various configurations. For example, depending on the type of cell, the configuration of the anodes, cathodes, terminal lead ferrule portions, fill ports, etc. will vary. Also, for example, depending on the cell, the materials housed in the casing will vary. Such materials may take the form of a liquid or a solid depending on the type of cell. Therefore, it should be clear that the present invention is in no manner limited to the illustrative cell described herein and is applicable to all types of electrochemical chemistries.  
         [0034]    The present invention is also applicable to capacitors, such as those described in U.S. Pat. Nos. 5,926,362 and 6,334,879, both to Muffoletto et al. These patents are assigned to the assignee of the present invention and incorporated herein by reference.  
         [0035]    It is appreciated that various modifications to the inventive concepts described herein may be apparent to those of ordinary skill in the art without departing from the spirit and scope of the present invention as defined by the appended claims.