Abstract:
A wet tantalum capacitor of either a single anode design or of multiple anode configurations having cathode active material supported on the casing and sealed in its own separator material is described. The separator “covers&#39; the cathode active material and is adhered directly to the casing. For a multiple anode design, an inner cathode foil positioned between opposed anode pellets is sealed in its own separator bag. Preferably, a polymeric restraining device prevents the anode from contacting the casing. The completed anode/cathode electrode assembly is sealed in the casing, which is filled with electrolyte thru a port. The fill port is hermetically sealed to complete the capacitor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. provisional patent application Ser. No. 62/248,695, filed on Oct. 30, 2015. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to a capacitor, and more particularly, to a capacitor having a cathode spaced from an anode. The cathode is of an active material supported on a casing sidewall or a conductive substrate in contact with the casing sidewall. The anode is typically in the form of a sintered valve metal pellet, such as a sintered tantalum pellet that has been anodized and subjected to a formation step. The anode and cathode are kept from direct physical contact with each other by a separator that covers the cathode with a margin of the separator secured to the casing sidewall adjacent to the cathode material. 
         [0004]    Conventional designs have the anode contained in a separator that surrounds and envelopes the anode pellet. 
         [0005]    2. Prior Art 
         [0006]      FIGS. 1 and 2  are side and top cross-sectional views respectively of a flat electrolytic capacitor  10  according to the prior art. The prior art capacitor  10  comprises an anode  12  and a cathode  14  housed inside a hermetically sealed casing  16 . The capacitor electrodes are contacted with a working electrolyte (not shown) contained inside casing  16 . Casing  16  includes a deep drawn can  18  having a generally rectangular shape comprised of spaced apart sidewalls  20  and  22  meeting with opposed end walls  24  and  26 , the sidewalls  20 ,  22  and end walls  24 ,  26  extending upwardly from a bottom wall  28 . A lid  30  is secured to sidewalls  20  and  22  and end walls  24  and  26  by a weld  32  to complete the casing  16 . Casing  16  is made of a conductive metal and serves as one terminal or contact for making electrical connection between the capacitor and its load. 
         [0007]    Anode  12  is in the form of a sintered pellet of a material selected from the group consisting of tantalum, aluminum, titanium, niobium, zirconium, hafnium, tungsten, molybdenum, vanadium, silicon, germanium, and mixtures thereof. As well known to those skilled in the art, after sintering, the anode pellet is anodized. 
         [0008]    Cathode  14  is spaced from the anode  12  and comprises conductive substrates  34  supporting a cathode active material  36 . In  FIGS. 1 and 2 , the conductive substrates  34  are the casing sidewalls  20 ,  22 . While not shown in the drawings, the conductive substrates  34  can alternatively be a separate conductive member that is contacted to the inner surface of the casing sidewalls  20 ,  22 . Ruthenium oxide is one of a number of suitable cathode active materials. 
         [0009]    A separator structure includes spaced apart sheets  38  and  40  of insulative material, for example a microporous polyolefinic film. The separator sheets  38  and  40  are connected to a polymeric ring  42  and disposed intermediate anode  12  and the coated sidewalls  20 ,  22  serving as the cathode. 
         [0010]    Alternatively, the polymer ring  42  is eliminated and the separator sheets  38 ,  40  are secured to each other adjacent to their edges. 
         [0011]    The other electrical terminal or contact is provided by a conductor or lead  44  extending from the anode  12  and through lid  30 . Lead  44  is electrically insulated from lid  30  by an insulator and seal structure  46 . The anode  12  is provided with a notch forming a step  48  adjacent to end wall  26  of can  18 . Step  48  provides clearance for the insulator and seal structure  46 . In that manner, the portion of anode terminal lead  44  extending outside the capacitor  10  for connection to the load is hermetically sealed from the interior of the capacitor  10  and electrically insulated from the can  18  and lid  30  serving as the terminal for the cathode  14 . 
         [0012]    An electrolyte fill opening is provided for filling an electrolyte (not shown) into the capacitor, after which this opening is sealed with closure member  50  that is preferably welded in place. 
         [0013]    While positioning the anode in a separator envelope to prevent the opposite polarity electrodes from contacting each other is acceptable, there is a desire to improve manufacturability of capacitors, for example electrolytic capacitors. Improved manufacturability is realized by covering the cathode with a separator material instead of containing a sintered pellet-type valve metal anode in a separator envelope. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention describes a structure and method for physically isolating the cathode material from the anode in a wet tantalum capacitor. The capacitor can be of either a single anode design or of multiple anode configurations. The cathode that is supported on the case, and or lid is sealed in its own separator material, which is adhered directly to the case or lid. For a multiple anode design, an inner cathode foil positioned between opposed anode pellets is sealed in its own separator bag. Preferably, a restraining device made of a polymeric material such as polypropylene, PTFE or polyester, but not limited to these materials is used to prevent the anode from contacting the case. The completed anode assembly is then inserted into a case half, such as in a mating clamshell case design and welded into place. The second case half is secured to the first case half, preferably with a hermetic seal and the casing is filled with electrolyte thru a port (not shown) and the fill port is hermetically sealed to complete the capacitor. 
         [0015]    An advantage of this design over conventional capacitors where the opposite polarity electrodes are prevented from direct physical contact with each other by enveloping the anode in its own separator bag is that the number of heat seal layers is minimized. This allows for larger anodes, thereby increasing packaging efficiency. 
         [0016]    These and other objects of the present invention will become increasingly more apparent to those skilled in the art by reference to the following detailed description and the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIGS. 1 and 2  are side and top cross-sectional views of an exemplary capacitor  10  according to the prior art. 
           [0018]      FIG. 3  is a side cross-sectional view of an exemplary capacitor  100  according to the present invention. 
           [0019]      FIG. 4  is a top cross-sectional view of the exemplary capacitor  100  shown in  FIG. 3  according to the present invention. 
           [0020]      FIG. 5  is a plan view showing an exemplary embodiment of a separator sheet  144  covering a cathode active material  142  contacted to a conductive substrate  120 ,  122 . 
           [0021]      FIG. 6  is a fragmentary, cross-sectional view of an insulator and seal structure  136  for a terminal lead  134  for the capacitor  100 . 
           [0022]      FIG. 7  is a top cross-sectional view of an exemplary capacitor  200  according to the present invention housed in a casing  202  of mating clamshells  204 ,  206 . 
           [0023]      FIG. 8  is a top cross-sectional view of an exemplary capacitor  300  according to the present invention having a dual anode design. 
           [0024]      FIG. 9  is a top cross-sectional view of another exemplary capacitor  300 A according to the present invention having a dual anode design. 
           [0025]      FIG. 10  is a fragmentary, top cross-sectional view of a dual anode capacitor design according to the present invention having anode leads  324 A,  324 B connected to a common lead  336  supported in an insulator and seal  136 . 
           [0026]      FIG. 11  is a fragmentary, top cross-sectional view of a dual anode capacitor design according to the present invention having anode leads  325 A,  325 B supported in respective insulator and seals  136 A,  136 B. 
       
    
    
       [0027]    The present invention will be described in connection with preferred embodiments, however, it will be understood that there is no intent to limit the invention to the embodiments described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Turning now to the drawings,  FIG. 3  is a perspective view of one embodiment of a capacitor  100  according to the present invention. The capacitor  100  is preferably an electrolytic-type capacitor comprising an anode  112  and a cathode  114  housed inside a hermetically sealed casing  116 . The capacitor electrodes are contacted with a working electrolyte (not shown) contained inside casing  116 . 
         [0029]    Casing  116  is a deep drawn can of a generally prismatic shape having a similar form factor as the casing  16  for the prior art capacitor  10  described above with respect to  FIGS. 3 and 4 , and comprises spaced apart sidewalls  120  and  122  meeting with opposed end walls  124  and  126 , the sidewalls  120 ,  122  and end walls  124 ,  126  extending upwardly from a bottom wall  128 . A lid  130  is secured to sidewalls  120  and  122  and end walls  124  and  126  by a weld  132 . Casing  116  is made of a conductive metal selected from the group consisting of tantalum, titanium, nickel, niobium, stainless steel, aluminum, zirconium, and mixtures and alloys thereof. Regardless the metal, casing  116  has a thickness of about 0.015 to about 0.5 millimeters and serves as one terminal or contact for making electrical connection between the capacitor and its load. 
         [0030]    The anode  112  is typically of a metal selected from the group consisting of tantalum, aluminum, titanium, niobium, zirconium, hafnium, tungsten, molybdenum, vanadium, silicon and germanium, and mixtures thereof in the form of a pellet. As is well known by those skilled in the art, the anode metal in powdered form, for example tantalum powder, is compressed into a pellet  133  having an anode lead  134  extending therefrom and sintered under a vacuum at high temperatures. 
         [0031]    A preferred tantalum material and method of manufacturing an anode pellet for the present capacitor, which is well suited for implantable cardiac device capacitor applications, is described in U.S. Pat. No. 9,312,075 to Liu et al., which is assigned to the assignee of the present invention and incorporated herein by reference. Other suitable capacitor grade tantalum powders are described in U.S. Pat. No. 9,312,075 to Liu et al., which is assigned to the assignee of the present invention and incorporated herein by reference. 
         [0032]    Before pressing, the tantalum powder is typically, but not necessarily, mixed with approximately 0 to 5 percent of a binder such as ammonium carbonate. This and other binders are used to facilitate metal particle adhesion and die lubrication during anode pressing. The powder and binder mixture are dispended into a die cavity and are pressed to a density of approximately 4 grams per cubic centimeter to approximately 8 grams per cubic centimeter. Binder is then removed from the anode pellet  133  either by washing in warm deionized water or by heating at a temperature sufficient to decompose the binder. Complete binder removal is desirable since residuals may result in high leakage current. The washed anode pellet is then vacuum-sintered at between about 1,350° C. to about 1,600° C. to permanently bond the metal anode particles. 
         [0033]    An oxide is formed on the surface of the sintered anode by immersing the anode in an electrolyte and applying a current. The electrolyte includes constituents such as water and phosphoric acid and perhaps other organic solvents. The application of current drives the formation of an oxide film that is proportional in thickness to the targeted forming voltage. A pulsed formation process may be used wherein current is cyclically applied and removed to allow diffusion of heated electrolyte from the internal pores of the anode. Intermediate washing and annealing steps may be performed to facilitate the formation of a stable, defect free, oxide. Preferably, the anode pellet  133  is anodized to a formation voltage formation voltage that is greater than zero up to 550 V. 
         [0034]    Cathode  114  is spaced from the anode  112  and comprises conductive substrates  140  supporting a cathode active material  142  having a thickness of about a few hundred Angstroms to about 0.1 millimeters. In  FIG. 3 , the clamshell casing sidewalls  120 ,  122  serve as the conductive substrates. While not shown in the drawing, the conductive substrates  140  can alternatively be a separate conductive member that is contacted to the inner surface of the clamshell sidewalls  120 ,  122 . The conductive substrates  140 , and hence the clamshell sidewalls  120 ,  122 , are selected from the group consisting of titanium, tantalum, nickel, niobium, stainless steel, aluminum, zirconium, and mixtures and alloys thereof. 
         [0035]    The cathode active material  142  may be selected from those described above or selected from the group including graphitic or glassy carbon on titanium carbide, carbon and silver vanadium oxide on titanium carbide, carbon and crystalline manganese dioxide on titanium carbide, platinum on titanium, ruthenium on titanium, barium titanate on titanium, carbon and crystalline ruthenium oxide on titanium carbide, carbon and crystalline iridium oxide on titanium carbide, silver vanadium oxide on titanium, and activated carbon. 
         [0036]    The cathode active material  142  contacted to the casing sidewalls  120 ,  122  serving as the conductive substrates  140  is preferably spaced from the bottom wall and upper edge at the lid  130 . Such a cathode active coating is accomplished by providing the conductive sidewalls  120  and  122  with a masking material in a known manner so that only the intended areas of the sidewalls are contacted with active material. The masking material is removed from the sidewalls  120 ,  122  prior to capacitor fabrication. As will be described in detail hereinafter, the masking material must leave an open area of the sidewalls  120 ,  122  that is sufficient for contact with a separator material according to the present invention. 
         [0037]    In that respect, the clamshell sidewalls  120  and  122  may support an anodized-etched conductive material, or have a sintered active material with or without oxide contacted thereto, or be contacted with a double layer capacitive material, for example a finely divided carbonaceous material such as graphite, carbon, activated carbon, or platinum black, or be contacted with a redox, pseudocapacitive or an under potential material, or an electroactive conducting polymer such as polyaniline, polypyrrole, polythiophene, and polyacetylene, and mixtures thereof. 
         [0038]    According to one preferred aspect of the present invention, the redox or cathode active material  142  includes an oxide of a first metal, the nitride of the first metal, the carbon nitride of the first metal, and/or the carbide of the first metal, the oxide, nitride, carbon nitride and carbide having pseudocapacitive properties. The first metal is preferably selected from the group consisting of ruthenium, cobalt, manganese, molybdenum, tungsten, tantalum, iron, niobium, iridium, titanium, zirconium, hafnium, rhodium, vanadium, osmium, palladium, platinum, nickel, and lead. 
         [0039]    The cathode active material  142  may also include a second or more metals. The second metal is in the form of an oxide, a nitride, a carbon nitride or carbide, and is not essential to the intended use of the conductive sidewalls  120  and  122  as a capacitor electrode. The second metal is different than the first metal and is selected from one or more of the group consisting of tantalum, titanium, nickel, iridium, platinum, palladium, gold, silver, cobalt, molybdenum, ruthenium, manganese, tungsten, iron, zirconium, hafnium, rhodium, vanadium, osmium, and niobium. In a preferred embodiment of the invention, the cathode active material includes an oxide of ruthenium or oxides of ruthenium and tantalum. 
         [0040]    As disclosed in U.S. Pat. No. 7,116,547 to Seitz et al., a preferred coating process is by pad printing. This patent is assigned to the assignee of the present invention and incorporated herein by reference. An ultrasonically generated aerosol, as described in U.S. Pat. Nos. 5,894,403, 5,920,455, 6,224,985, and 6,468,605, all to Shah et al., is also suitable for making a coating of the active materials. These patents are assigned to the assignee of the present invention and incorporated herein by reference. In that manner, the ultrasonically generated active material contacted to the conductive surfaces has a majority of its particles with diameters of less than about 10 microns. This provides an internal surface area for the active material of about 10 m 2 /gram to about 1,500 m 2 /gram. 
         [0041]    A separator  144  of electrically insulative material is provided between the anode  112  and the cathode  114  to prevent an internal electrical short circuit between the electrodes. The separator  144  is chemically unreactive with the anode and cathode active materials and both chemically unreactive with and insoluble in the electrolyte. In addition, the separator material has a degree of porosity sufficient to allow ionic conduction therethrough during charging and discharging of the capacitor  100 . 
         [0042]    According to the present invention, individual separator sheets  144  of electrically insulative material completely surround and envelop the cathode active material  142  contacted to the casing sidewalls  120 ,  122 . As shown in the plan view of  FIG. 5 , the exemplary separator  144  has height and width or “x” and “y” dimensions that are larger than the height and width or “a” and “b” dimensions of the cathode active material  142 , and is contacted to the casing sidewalls  120 ,  122  to cover the active material. The separator  144  has a perimeter edge or margin  144 A secured to the inner surface of the sidewall  120 ,  122  adjacent to a perimeter  142 A of the cathode active material  142 . It should be understood that the illustration of separator  144  covering the active material  142  in  FIG. 5  is exemplary. In practice, the active material can have a myriad of different shapes dictated by the form factor of a particular capacitor design. Regardless the specific shape of the active material  142  and its exemplary x and y dimensions, the separator  144  is sized and shaped to cover the cathode active material  142  with the margin  144 A secured to the conductive substrate  140  in a surrounding relationship. 
         [0043]    The separators  144  are secured to the inner surfaces of the respective casing sidewalls  120 ,  122  using any one of a number of materials including an adhesive  146 , such as hot melt glue (MasterBond MB514), epoxy (Tam Tech Polypropylene, polyethylene adhesive/glue), and PET tape with an acrylic adhesive (3M VBH Tapes). That way, the cathode active material  142  is contained in an envelope comprising the casing sidewall  120 ,  122  to which it is contacted (or a conductive substrate  140  in electrical contact with the inner surface of the casing sidewalls) and the covering separator  144  secured to the inner surface of the casing sidewall by the adhesive material  146  so that the separator  144  is in a surrounding relationship adjacent to a perimeter edge  142 A of the cathode active material  142 . 
         [0044]    Illustrative separator materials include woven and non-woven fabrics of polyolefinic fibers including polypropylene and polyethylene, or fluoropolymeric fibers including polyvinylidene fluoride, polyethylenetetrafluoroethylene, and polyethylenechlorotrifluoroethylene laminated or superposed with a polyolefinic or fluoropolymeric microporous film, non-woven glass, glass fiber materials and ceramic materials. Suitable microporous films include a polyethylene membrane commercially available under the designation SOLOPOR®, (DMS Solutech); a polytetrafluoroethylene membrane commercially available under the designation ZITEX®, (Chemplast Inc.) or EXCELLERATOR®, (W.L. Gore and Associates); a polypropylene membrane commercially available under the designation CELGARD®, (Celgard LLC); and a membrane commercially available under the designation DEXIGLAS®, (C. H. Dexter, Div., Dexter Corp.). Cellulose based separators also typically used in capacitors are contemplated by the scope of the present invention. Depending on the electrolyte used, the separator  144  can be treated to improve its wettability, for example with a surfactant, as is well known by those skilled in the art. 
         [0045]    The anode conductor or lead  134  preferably comprises the same material as the anode  112  and extends from within the capacitor through casing  116  and, in particular, through lid  130  to serve as the positive terminal or contact. As shown in  FIG. 6 , lead  134  is electrically insulated from lid  130  by the insulator and seal structure  136 . The anode  112  is provided with a notch forming a step  164  adjacent to one of the end walls  124 ,  126  of casing  116 . The anode step  164  provides clearance for the insulator and seal structure  136 . 
         [0046]    In one embodiment, the insulator and seal structure  136  for the terminal lead  134  comprises a header or ferrule element  150  defining an internal cylindrical through bore or passage  152 . An outwardly facing step  154  is provided at the upper end of ferrule  150  having an outer surface sized to fit in an opening  156  ( FIG. 3 ) in lid  130  with the upper end of ferrule  150  secured therein by welding and the like. 
         [0047]    The anode lead  134  is secured and sealed within ferrule by a series of sealing materials. A first layer  162  is provided by a synthetic polymeric material such as elastomeric materials that are capable of sealing between lead  134  and the inner surface of ferrule  150 . A suitable material for the first layer  162  is, for example Master-Sil 151 made by Master Bond. Finally, a glass layer  166  provides a hermetic seal between the inside of the ferrule  150  and the anode lead  134 . The glass is, for example, Elan Type 88 or Mansol Type 88. Alternatively, a suitable insulator and seal structure is provided without using glass  166 . While such a seal structure is not necessarily hermetic, acceptable isolation of the electrolyte from inside the casing  116  to the outside thereof is provided by the first polymer layer  162 . 
         [0048]    A fill opening or port in the casing  116  is provided for filling a working electrolyte (not shown) into the capacitor, after which this opening is sealed with closure member  168 , which is preferably welded in place. A suitable working electrolyte for the capacitor  100  is described in U.S. Pat. No. 6,219,222 to Shah et al., which includes a mixed solvent of water and ethylene glycol having an ammonium salt dissolved therein. U.S. Pat. No. 6,687,117 and U.S. Patent Application Pub. No. 2003/0090857, both to Liu et al., describe other electrolytes that are useful with the present capacitor  100 . The electrolyte of the latter publication comprises water, a water-soluble inorganic and/or organic acid and/or salt, and a water-soluble nitro-aromatic compound while the former relates to an electrolyte having de-ionized water, an organic solvent, isobutyric acid and a concentrated ammonium salt. These patents and publications are assigned to the assignee of the present invention and incorporated herein by reference. 
         [0049]    Filling is accomplished by placing the capacitor  100  in a vacuum chamber such that the electrolyte fill port extends into a reservoir of electrolyte. When the chamber is evacuated, pressure is reduced inside the capacitor. When the vacuum is released, pressure inside the capacitor re-equilibrates, and electrolyte is drawn through the fill port into the capacitor. 
         [0050]    Another embodiment of a capacitor  200  according to the present invention is illustrated in  FIG. 7 . Capacitor  200  includes a casing  202  comprising first and second mating metal clamshell-shaped casing members  204  and  206 . First clamshell member  204  comprises a first face wall  208  joined to a surrounding sidewall  210  extending to an edge  212 . Second clamshell member  206  is similar to the first casing member  204  and has a second face wall  214  joined to a surrounding sidewall  216  extending to an edge  218 . 
         [0051]    In a similar manner as described with respect to the capacitor  100  illustrated in  FIGS. 3 to 6 , the anode  220  for capacitor  200  comprises a sintered valve metal pellet  222  and a lead, for example embedded anode leads  324 A,  324 B ( FIG. 10 ) or weld connected leads  325 A,  325 B ( FIG. 11 ) extending therefrom. Although any one of the number of suitable anode materials described with respect to capacitor  100  are contemplated by this embodiment, tantalum is preferred. Before incorporation into the capacitor, the valve metal pellet  222 , and the weld ( FIG. 11 ) if it exists, is anodized in a suitable electrolyte and then subjected to formation protocol to a target operating voltage. 
         [0052]    Cathode  226  is spaced from the anode  220  and comprises a cathode active material  228 , for example ruthenium oxide, of a suitable thickness supported on an inner surface of the first and second face walls  208 ,  214 . 
         [0053]    According to the present invention, a separator  330  of insulative, but allowing ion transfer therethrough covers the cathode active material  228  supported on the inner surfaces of the first and second face walls  208 ,  214 . As with capacitor  100 , the separator  230  is sized and shaped to cover the cathode active material  228  with a peripheral margin  230 A contacting the inner surfaces of the face walls  208 ,  214  adjacent to a perimeter edge  228 A of the cathode active material  228 . The separator margin  230 A is secured to the inner surface of the first and second face walls  208 ,  214  by one of the suitable adhesives  232  described for that purpose with respect to capacitor  100 . 
         [0054]    After the anode  220  and cathode  226  are housed in the casing  202 , the first clamshell member  204  is mated with the second clamshell member  206  having their surrounding sidewalls  210 ,  216  in an overlapping relationship adjacent to their edges  212 ,  218 . An annular weld  234 , preferably a laser weld, hermetically secures the overlapping sidewalls  210 ,  216  together. Finally, a working electrolyte (not shown) is filled into the casing  202  and the fill opening is sealed with a plug (not shown). 
         [0055]      FIG. 8  illustrates another embodiment of a capacitor  300  according to the present invention. Capacitor  300  includes a casing  302  comprising mating first and second clamshell-shaped casing members  304 ,  306 . Casing member  304  comprises a first face wall  308  joined to a surrounding sidewall  310  extending to an edge  312 . Similarly, the second casing member  306  comprises a second face wall  314  joined to a surrounding sidewall  316  extending to an edge  318 . 
         [0056]    Cathode active material  320  is contacted to an inner surface of the face walls  308 ,  314 . A separator  322  of insulative, but allowing ion transfer therethrough covers the cathode active material  320  supported on the inner surfaces of the first and second face walls  308 ,  314 . According to the present invention, the separators  322  are sized and shaped to cover the cathode active material  320  with a peripheral margin  322 A contacting the face walls  308 ,  314  adjacent to a perimeter edge  320 A of the cathode active material. The separator margin  322 A is secured to the inner surface of the first and second casing member  304 ,  306  by one of the suitable adhesives  324  described for that purpose with respect to capacitors  100  and  200 . 
         [0057]    Capacitor  300  is of a dual anode design and further includes parallel connected sintered valve metal pellets  326  and  328 , preferably of tantalum, serving as the anode. As before, the valve metal pellets  326 ,  328  are anodized and subjected to a formation protocol prior to being incorporated into the capacitor. 
         [0058]    Capacitor  300  further includes cathode active material  320  supported on the opposed surfaces  330 A and  330 B of a cathode current collector  330  that is positioned intermediate the anode pellets  326 ,  328 . The cathode current collector  330  is preferably in the form of a foil. Two sheets of separator material  332 A and  332 B cover the cathode active material  320 . According to the present invention, the sheets  332 A,  332 B are sized and shaped so that their peripheral margins contact the cathode current collector  330  adjacent to a perimeter edge  320 A of the cathode active material. The separators  332 A,  332 B are secured to the opposed surfaces  330 A,  330 B of the cathode current collector  330  using one of the suitable adhesives  334  described for this purpose with respect to capacitors  100  and  200 . 
         [0059]    Tab  330 C of cathode current collector  330  is then welded to the inside surface of clamshell  304  to electrically connect the current collector to the casing  302 . 
         [0060]    After the anodes  326 ,  328  and cathode  320  are housed in the casing  302 , the first clamshell member  304  is mated with the second clamshell member  306  having their surrounding sidewalls  312 ,  216  in an overlapping relationship. An annular weld  334 , preferably a laser weld, hermetically secures the overlapping clamshell sidewalls  310 ,  316  together adjacent to their respective edges  312 ,  318 . Finally, a working electrolyte (not shown) is filled into the casing  302  and the fill opening is sealed with a plug (not shown). 
         [0061]      FIG. 9  illustrates another embodiment of a capacitor  300 A according to the present invention. Capacitor  300 A is similar to capacitor  300  described with respect to  FIG. 8  with the exception of the separator structure for the cathode portion disposed intermediate the anode pellets  326 ,  328 . In this embodiment, the separator is an envelope formed of at least two sheets  332 C,  332 D that are sealed to each other, such as at the location indicated by numerical designation  332 E in the cross-sectional view. At the opposite end of the cathode, the connected separator sheets  332 C,  3320  include an opening through which the current collector  330  extends to tab  330 C. This opening in the separator sheets may be additionally sealed with an adhesive material (not shown). The current collector tab  330 C is secured to the casing, such as by a weld so that the casing serves as a terminal for the intermediate cathode portion. 
         [0062]      FIG. 10  illustrates an exemplary embodiment for connecting anode leads  324 A,  324 B in parallel for a dual-anode design  326 ,  328  of the capacitor  300  illustrated in  FIG. 8 . Anode lead  324 A has a first portion  3240  that is embedded in the first pellet  326  and a second, outer portion  324 D. Similarly, anode lead  324 B for pellet  328  has a first portion  324 E that is embedded in therein and a second, outer portion  324 F. The outer portions  324 D,  324 F of the anode leads are bent toward and into contact with a feedthrough lead  336 . In particular, anode lead  324 A for the first pellet  326  contacts a first “side” of the feedthrough lead  336  opposite the anode lead  324 B for the second anode pellet  328 . The leads  324 A,  324 B are preferably laser welded to the feedthrough lead  236  extending through an insulator and seal structure  136  similar to that shown in  FIG. 6 . 
         [0063]      FIG. 10  further shows that the exemplary mating clamshell casing member  304 ,  306  are each provided with a portion of an opening that is sized and shaped to receive the ferrule  150  for the insulator and seal structure  136  ( FIG. 6 ). The casing member  304 ,  306  are preferably welded to the ferrule  150  as a hermetically sealed structure. 
         [0064]      FIG. 11  illustrates another exemplary embodiment for connecting anode leads  325 A,  325 B in parallel for a dual-anode design  326 ,  328 . Instead of the anode lead being connected to a common feedthrough lead  336 , however, this embodiment has the leads for anode pellets  326 ,  328  supported in respective insulator and seal structures  136 A,  136 B, which are both similar to the insulator and seal structure  136  illustrated in  FIG. 6 . As shown, the insulator and seal structures  136 A supporting anode lead  325 A is supported in an opening with surrounding sidewall of a first clamshell-shaped casing member. The insulator and seal structure  136 B supporting the anode lead  325 B for the second anode  328  is supported in an opening in the surrounding sidewall for the second clamshell-shaped casing member  306 . Distal portions of the anode leads  325 A,  325 E extend through an inner insulative plate  350  and an outer conductive plate  352  to thereby connect the anodes  326 ,  328  in parallel. Preferably, the distal ends of the anode leads  325 A,  325 B are flush with an outer surface of plate  352 , which provides a suitable surface for connecting the capacitor to a load or device that it is intended to power. 
         [0065]    It is noted that the exemplary embodiment shown in  FIG. 11 , the anode leads  325 A,  325 B are not embedded in the anode pellets  220 ,  222 . Instead, they are connected to the anode pellets  326 ,  328  by welds  354 . 
         [0066]    The capacitors  100 ,  200 ,  300  and  300 A of the present invention are not limited to single anode and dual anode designs. Instead, the capacitors may comprise additional anodes and cathode current collectors including cathode active material on the current collector faces thereof. Moreover, the anode active materials, cathode active material including coating processes, casing materials, separator materials and electrolytes described in detail with respect to capacitor  100  are equally applicable for use in capacitors  200 ,  300  and  300 A. 
         [0067]    Further, for a more detailed discussion regarding various casing constructions suitable for the present capacitors  100 ,  200 ,  300  and  300 A, reference is made to U.S. Pat. No. 7,012,799 to Muffoletto et al. This patent is assigned to the assignee of the present invention and incorporated herein by reference. 
         [0068]    Moreover, while not shown in the drawings, the various capacitors  100 ,  200 ,  300  and  300  preferably include a molded polymeric cradle or restraint for containing the anodes in the desired position should the capacitor experience high shock and vibration conditions. Suitable restraints are described in U.S. Pat. Nos. 7,085,126 to Muffoletto et al. and 7.092,242 to Gloss et al., which are assigned to the assignee of the present invention and incorporated herein by reference. 
         [0069]    Although several embodiments of the invention have been described in detail, for purposes of illustration, various modifications of each may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited, except as by the appended claims.