Patent Publication Number: US-6334879-B1

Title: Method for providing a hermetically sealed capacitor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part application of U.S. application Ser. No. 08/847,948, filed May 1, 1997, now U.S. Pat. No. 5,926,362 to Muffoletto et al. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a capacitor, and more particularly, to a capacitor having a substantially flat, planar geometry. Still more particularly, the present invention relates to a metallic substrate provided with capacitive material contacted thereto and incorporated into a hermetically sealed casing to provide at least one of the electrodes for the capacitor. The metallic substrate can provide at least one of the casing side walls itself or be connected to the side wall. A most preferred form of the capacitor has the conductive substrate provided with a pseudocapacitive material formed from an ultrasonically generated aerosol. 
     2. Prior Art 
     Standard capacitor construction consists of a cylindrically shaped case housing an anode electrode and a cathode electrode. For example, standard wet slug tantalum capacitors generally have a cylindrically shaped conductive casing serving as the terminal for the cathode electrode with the tantalum anode connected to a terminal lead electrically insulated from the casing by a glass-to-metal insulator and seal structure. The anode insulator and seal structure is disposed either internally or externally of the casing. The opposite end of the casing is also typically provided with an insulator structure. The cylindrical shape limits the internal volume inside the capacitor and the closing seal structures occupy volume that detracts from the capacitor&#39;s volumetric efficiency. 
     Furthermore, the capacitor of the present invention having a flat, planar shape can comprise either an electrochemical type capacitor or electrolytic type capacitor. The anode and/or the cathode in a typical electrochemical capacitor or the cathode in an electrolytic capacitor generally include a substrate of a conductive metal such as titanium or tantalum having a capacitive material provided thereon. In that respect, the capacitive material may be in the form of an anodized-etched foil, a sintered active material with or without oxide, a double layer capacitive material such as a carbonaceous capacitive material or platinum black, a semiconductive material, pseudocapacitive material such as a redox or under potential material, and conducting polymers. Commonly used coating techniques for contacting these materials to the substrate include dipping, sputtering and pressurized air atomization spraying of a solution of the capacitive material onto the substrate. Capacitance values for electrodes made by these prior art techniques are lower in specific capacitance than an electrode coated with an ultrasonically generated aerosol of active material according to the present invention. Sol-gel deposition is another prior art method of coating a substrate, and this method also provides capacitor electrodes lower in specific capacitance than ultrasonically generated aerosol coatings. 
     SUMMARY OF THE INVENTION 
     The present invention provides a hermetically sealed capacitor housed in a casing having a generally flat, planar profile. Additionally, the present capacitor having the flat, planar shape provided by spaced apart side walls joined by a surrounding intermediate wall includes an anode electrode and a cathode electrode, at least one of which is comprised of a conductive substrate having capacitive properties itself or, a capacitive material contacted thereto. The active material may be contacted to the substrate in the form of an ultrasonically generated aerosol of the active material. The conductive substrate is fabricated to the desired shape of the casing side wall serving as one electrode terminal with the active material in electrical association with a counter electrode or, the conductive substrate is electrically connected to the casing. 
     These and other aspects of the present invention will become more apparent to those skilled in the art by reference to the following description and the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan, cross-sectional view of a capacitor  10  according to the present invention. 
     FIG. 2 is an elevational, cross-sectional view of the capacitor  10  shown in FIG.  1 . 
     FIG. 3 is an elevational, cross-sectional view of the capacitor  10  shown in FIG. 2 rotated 90 degrees. 
     FIGS. 4 to  7  are fragmentary, cross-sectional views of alternate embodiments of insulator and seal structures for a terminal lead  34  for the capacitor  10 . 
     FIG. 8 is an elevational, cross-sectional view of an electrode lead-to-lead construction for a capacitor according to the present invention. 
     FIG. 9 is an elevational, cross-sectional view of an alternate embodiment of a lid  104  closing the capacitor casing. 
     FIGS. 10,  10 A and  11  are fragmentary, cross-sectional views of various embodiments of closure structures for the capacitor  10 . 
     FIGS. 12 to  15  are elevational, cross-sectional views of various alternate embodiments of capacitors according to the present invention. 
     FIG. 16 is an elevational, cross-sectional view of side-by-side capacitors  188  and  190  connected in parallel. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, FIGS. 1 to  3  illustrate an exemplary capacitor  10  according to the present invention. Capacitor  10  comprises an anode  12  and a cathode  14  housed inside of a hermetically sealed casing  16 . The capacitor electrodes are activated and operatively associated with each other by an electrolyte contained inside the casing  16 , as will be described in detail hereinafter. It should be pointed out that the capacitor  10  can be of either an electrochemical type wherein both the anode and the cathode electrodes are provided by conductive substrates having a capacitive material contacted thereto according to the present invention or, of an electrolytic type wherein the cathode electrode is provided by a conductive substrate having capacitive properties. The exemplary capacitor  10  illustrated in FIGS. 1 to  3  is of the latter type, however, this should not be construed as limiting. 
     Casing  16  includes a deep drawn can  18  having a generally rectangular shape comprised of spaced apart side walls  20  and  22  extending to and meeting with opposed end walls  24  and  26  extending from a bottom wall  28 . A lid  30  is secured to the side walls  20 ,  22  and the end walls  24 ,  26  by a weld  32  to close the casing  16 . Casing  16  is of a conductive metal and as such serves as one terminal or contact for making electrical connection between the capacitor and its load. The weld is provided by any conventional means, however, a preferred method is by laser welding. 
     The other electrical terminal or contact for the capacitor  10  is provided by a conductor or lead  34  extending from within the capacitor  10  through casing  16  and in particular through lid  30 . Lead  34  is insulated electrically from the metal lid  30  by an insulator and seal structure  36 , which will be described in detail presently. An electrolyte fill opening  38  in lid  30  is closed by a closure structure  40 , in a manner which will be described in detail hereinafter. 
     The cathode electrode  14  is spaced from the anode electrode  12  housed inside the casing and comprises an electrode active material  42  provided on a conductive substrate. The active material has a thickness of about a hundred Angstroms to about 0.1 millimeters. When the casing  16  serves as one terminal or contact for the capacitor, the casing, and in particular the can  18 , serves as the conductive substrate or, the conductive substrate provided with the active material  42  is electrically connected to the can  18 . In either case, the conductive substrate is selected from the group consisting of tantalum, titanium, nickel, molybdenum, niobium, cobalt, stainless steel, tungsten, platinum, palladium, gold, silver, copper, chromium, vanadium, aluminum, zirconium, hafnium, zinc and iron, and mixtures and alloys thereof. The lid  30  is also preferably of one of the above conductive materials. Preferably the conductive substrate has a thickness of about 0.001 to 2 millimeter. 
     Preferably the substrate is cleaned of contaminants by lubricants from handling equipment or body oils from hands and the like and roughened by chemical or mechanical means to increase its surface area prior to being contacted with the active material  42 . If desired, the electrical conductivity of the uncoated substrate can be improved by a technique described in U.S. application Ser. No. 08/847,946 entitled “Method of Improving Electrical Conductivity of Metals, Metal Alloys and Metal Oxides”, which is assigned to the assignee of the present invention and the disclosure of which is incorporated herein by reference. 
     After preparation, the active material  42  is contacted to the conductive substrate preferably after but possibly before the prepared substrate is cut, shaped or otherwise fabricated into the desired geometry. To provide a capacitor electrode, the substrate may be of an anodized-etched conductive material, have a sintered active material with or without oxide contacted thereto, be contacted with a double layer capacitive material, for example a finely divided carbonaceous material such as graphite or carbon or platinum black, a semiconductive material, a redox, pseudocapacitance or an under potential material, or an electroactive conducting polymer such as polyaniline, polypyrole, polythiophene and polyacetylene, and mixtures thereof. As will be described in detail hereinafter, the capacitive material is preferably contacted to the conductive substrate in the form of an ultrasonically generated aerosol of the conductive material. In the case of the can  18  serving as the conductive substrate, an articulating spray head of a well known type is used to coat the interior surfaces of the can  18  with the ultrasonically generated aerosol of the desired material. FIGS. 1 to  3  show that the majority of side walls  20  and  22  are provided with the electrode active material  42 . Other configurations of active material contacted to the conductive side walls are contemplated by the scope of the present invention as needed for a particular capacitor application. 
     According to one preferred aspect of the present invention, the redox active material  42  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 of the first metal 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. 
     The redox active material  42  may also include a second or more metals. The second metal is in the form of an oxide, a nitride, a carbon nitride or a carbide, and is not essential to the intended use of the conductive substrate as a capacitor electrode and the like. 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 active material product  42  includes oxides of ruthenium or ruthenium and tantalum. 
     In accordance with one embodiment of the present invention, the fabricated can  18  is provided with the active material  42  containing at least the first pseudocapacitive metal and possibly the second or more metals deposited on the side walls  20  and  22  of can  18  (FIG. 3) serving as the conductive substrate. Alternatively and as will be described in detail hereinafter, a conductive substrate of one of the enumerated materials is first provided with the redox active material coating and the thusly processed substrate is then contacted to the casing side walls (FIGS. 12 to  16 ). As previously discussed, the processed conductive substrate can provide the anode and/or the cathode in an electrochemical capacitor, or the cathode in an electrolytic capacitor. The exemplary capacitor shown in FIGS. 1 to  3  is of the electrolytic type and the cathode active material preferably coats the side walls beginning at a position spaced from the bottom wall of the casing to a distance spaced from the lid. Such a coating is accomplished by providing the conductive substrate with a masking material in a known manner so that only an intended area of the substrate is contacted with active material. The masking material is removed from the substrate prior to capacitor fabrication. Preferably, the cathode active material is substantially aligned in a face-to-face relationship with the anode major surfaces. 
     A preferred coating process is described in U.S. Pat. No. 5,894,403 to Shah et al., entitled “Ultrasonically Coated Substrate For Use In A Capacitor And Method Of Manufacture” or, by the coating process described in U.S. Pat. No. 5,920,455 to Shah et al., entitled “One Step Ultrasonically Coated Substrate For Use In A Capacitor”. These applications are both assigned to the assignee of the present invention and the disclosures thereof are incorporated herein by reference. In that manner, the ultrasonically generated active material contacted to the conductive substrate 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. 
     The anode electrode  12  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 having an anode lead  34  extending therefrom, and sintered under a vacuum at high temperatures. The porous body is then anodized in a suitable electrolyte to fill the pore with the electrolyte and to form a continuous dielectric oxide film on the sintered body. The assembly is then reformed to a desired voltage, as is well known by those skilled in the art to produce an oxide layer over the terminal lead/anode lead weld. The anode can also be of an etched aluminum or titanium foil or, a sintered aluminum or titanium body. 
     A separator structure of electrically insulative material is provided between the anode  12  and the cathode  14  to prevent an internal electrical short circuit between the electrodes. The separator material also 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 flow therethrough of the electrolyte during the electrochemical reaction of the capacitor  10 . 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 SOLUPOR (DMS Solutech), a polytetrafluoroethylene membrane commercially available under the designation ZITEX (Chemplast Inc.), a polypropylene membrane commercially available under the designation CELGARD (Celanese Plastic Company, Inc.) 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 use, the separator can be treated to improve its wettability, as is well known by those skilled in the art. 
     FIGS. 1 to  3  illustrate one embodiment of a separator structure according to the present invention wherein spaced apart sheets of  44 ,  46  of one of the above-referenced separator materials, for example sheets of microporous, polyolefinic film, are connected to a polymeric ring  48 . The sheets  44  and  46  are disposed intermediate the anode  12  and the coated side walls  20  and  22 , respectively, serving as the cathode electrode  14 . The microporous structure provides for ion flow therethrough during charge and discharge cycles while the polymeric ring  48  frames the sheets  44 ,  46  to provide structural support for them. Alternatively, the polymeric ring can be eliminated and the separator sheets  44 ,  46  are sealed to each other in a known manner at their peripheries to envelope the anode  12 . 
     As shown in enlarged detail in FIG. 4, the insulator and seal structure  36  for the terminal lead  34  comprises a header or ferrule element  50  defining an internal cylindrical through bore or passage  52  of constant inside diameter. An outwardly facing step  54  is provided at the upper end of ferrule  50  having an outer surface sized to fit in an opening  56  (FIGS. 2 and 3) in lid  30  with the upper end of ferrule  50  secured therein by welding and the like. The terminal lead  34  is secured and sealed within ferrule by a series of sealing materials. A first layer is provided by a disc or plug  58  of synthetic polymeric material having an annular groove  60  that receives the lower end of the ferrule  50  seated therein. A second layer  62  is of synthetic polymeric material such as elastomeric materials that are capable of sealing between lead  34  and the inner surface of ferrule  50  and which can be the same as or different than the first layer. The second layer  62  is provided in ferrule  50  contacting the plug  58  and a suitable material is, for example Master-Sil  151  made by Master Bond. Finally, a glass layer  66  provides a hermetic seal between the inside of the ferrule  50  and the terminal lead  34 . The glass used is, for example Elan Type  88  or Mansol Type  88 . The anode terminal lead  34  preferably comprises the same material as the anode  12 . 
     FIG. 5 shows another embodiment of an insulator and seal structure  66  for terminal lead  34  according to the present invention wherein a cup-shaped synthetic polymeric member  68  receives the ferrule  50  resting on a base portion of the cup  68 . A compression ring  70  is sized to surround the annular wall of cup member  68  thereby biased in a sealing engagement with the outer surface of ferrule  50 . A second, polymeric layer  72 , a third, polymeric layer  74  and fourth, glass layer  76  are then provided in the ferrule  50  sealing between bore  52  and lead  34  in a similar manner as previously described with respect to the seal structure  36  shown in FIG.  4 . 
     FIG. 6 illustrates another embodiment of an insulator and seal structure  78  for terminal lead  34  according to the present invention including a first layer  80  of synthetic polymeric material, a second, synthetic polymeric layer  82 , a third, polymeric layer  84  and a fourth, glass layer  86  provided successively in the ferrule  50  sealing between bore  52  and lead  34  in a manner similar to the insulator and seal structures shown in FIGS. 4 and 5. 
     FIG. 7 shows an alternate embodiment of an insulator and seal structure  88  according to the present invention including a metal sleeve  90  fitted around and along a portion of the terminal lead  34  inside the ferrule  50 . Sleeve  90  has an inner diameter that is somewhat greater than the outer diameter of lead  34 . The first and second synthetic polymeric layers  92  and  94  and a portion of a third, polymeric layer  96  seal between lead  34  and the bore  52  of the ferrule  50 . An upper portion of the third, polymeric layer  96  and a fourth, glass layer  98  seal between bore  52  and the outer surface of sleeve  90 . A weld  100  between sleeve  90  and lead  34  at their upper ends completes the hermetic structure. Insulator and seal structure  88  provides for economy of manufacture as it can be secured in ferrule by layers  96 , 98  before capacitor assembly. Then, the terminal lead  34  is moved through the sleeve  90 , layers  92  and  94  are filled into the ferrule and the terminal lead  34  is welded to the sleeve  90  at  100 . 
     FIGS. 2 and 3 show the insulator and seal structure  36  of FIG. 4 incorporated into the capacitor  10 . The anode  12  is provided with a notch forming a step  102  adjacent to end wall  26  of can  18 . Step  102  provides clearance for the insulator and seal structure  36 . In that manner, the portion of anode terminal lead  34  extending outside the capacitor  10  for connection to the load is hermetically sealed from the interior of the capacitor  10  and insulated from the can  18  and lid  30  serving as the terminal for the cathode electrode  14 . 
     It will be apparent to those skilled in the art that in addition to constructing the capacitor having the various insulator and seal structures disposed inside the casing with the upper end of ferrule  50  slightly protruding or flush with the lid  30 , the insulator and seal structures can also be mounted on the lid  30 . For example, in the insulator and seal structure  66  shown in FIG. 5, the compression ring  70  can be welded to the lid  30  surrounding the opening  54 . In the case of the insulator and seal structures  78  and  88  shown in FIGS. 6 and 7, respectively, the lower end of ferrule  50  can be welded to the upper surface of lid  30  such that the ferrule surrounds the opening  54 . Furthermore, it should be understood that the various synthetic polymeric materials need not necessarily be in the exact arrangements shown. These materials can be provided in any order desired or, they may be provided independently as required to protect the glass layer from the electrolyte and from voltage breakdown. Also, the encapsulate layers used in the terminal ferrule can be filled therein either before or after the anode  12  and lead  34  are connected together and formed to a desired voltage. 
     FIG. 8 shows an alternate embodiment of the capacitor  10  according to the present invention having a terminal lead  34 A provided with a U-shaped portion  34 B disposed inside the casing  18 . The lead  34 A is insulated from the can  18  and lid  30  by the insulator and seal structure  78  shown in FIG.  6 . The anode  12  is provided with an anode conductor  101  connected to U-shaped terminal lead portion  34 B by a weld  103 . This lead-to-lead construction can be used in addition to the insulator and seal structures shown in FIGS. 4 to  7 . 
     After the cathode electrode  14  is disposed inside the can  18 , the anode electrode  12  and the lid  30  as an assembly are fitted to the upper end of the can  18  and welded in place to provide a hermetic seal between the can and the lid. As shown in FIGS. 2 and 3, the lid  30  comprises a plate member having a shape sized to fit snugly inside the inner surface of the open end of can  18  and flush with the upper end thereof. The lid  30  is then secured in place by weld  32 . In an alternate embodiment shown in FIG. 9, a lid  104  has a first, larger body portion  106  and a second, smaller body portion  108  which meet at a step  110  which is sized to be received by the upper end of a can  112 . In that position, the surrounding wall of the first lid portion  106  is flush with the outer side wall of the can  112  and the surrounding wall of the second lid portion is in a snug-fitting relationship with the inner surface of can  112 . A weld  114  hermetically secures the lid to the can. Also can  112  is shown having a curved bottom wall. 
     The anode electrode  12  and cathode electrode  14  are activated and operatively associated with each other by an electrolyte solution filled in the casing through the electrolyte fill opening  38 . Any electrolyte that is known to activate the particular anode and cathode active materials selected to provide acceptable capacitive performance over a desired operating range is contemplated by the scope of the present invention. Suitable electrolytes include sulfuric acid in an aqueous solution. Specifically, a 38% sulfuric acid solution has been shown to perform well at voltages of up to about 125 volts. A 10% to 20% phosphoric acid/water solution is known to provide an increased equivalent series resistance (ESR) and breakdown voltage. Other suitable electrolytes are contemplated that provide desired performance characteristics. 
     Referring to FIG. 2, lid  30  is provided with the closure structure  40  for the electrolyte fill opening  38  preferably having a slightly inwardly closing taper that receives a metal ball  116  secured therein by weld  118 . Alternate embodiments of the closure structure are shown in FIGS. 10 and 11. In FIG. 10, a ring  120  having a cylindrical opening is secured to the under surface of lid  30  disposed coaxially with opening  38 . Metal ball  116  is wedged in the opening of ring  120  to prevent out gassed by-products as a closure plate  122  is disposed in the opening in a snug fitted relationship and secured therein by weld  124 . 
     FIG. 10A shows a plug  121  having an enlarged head  123  and a curved end  125  welded at  127 . If desired, plug  121  does not require the enlarged head  123  and/or the curved end  125  to provide a suitable closure for the electrolyte fill opening  38 . 
     FIG. 11 illustrates another embodiment of the seal structure wherein the portion of lid  30 A immediately adjacent to the fill opening  38  is deformed to have an annularly curved portion  126  that matches the curvature of ball  116 . Ball  116  is received in the curved portion  126  and secured in place by weld  128  to complete the seal. For a more detailed discussion of closure structures suitable for use with the present invention, reference is made to U.S. Pat. No. 5,776,632 to Honegger, entitled “Hermetic Seal For An Electrochemical Cell”, which is assigned to the assignee of the present invention and the disclosure of which is incorporated herein by reference. 
     FIGS. 12 to  15  illustrate alternate embodiments of capacitors according to the present invention having generally flat, planar geometries including side walls provided with electrode active material. Other than the various casing structures which are described immediately below, the capacitors of FIGS. 12 to  15  are similar to the capacitor  10  shown in FIGS. 1 to  3 . FIG. 12 shows a capacitor  130  having side walls  132  and  134  which are welded to a ring  136  after being selectively provided with the electrode active material  42  in a similar manner as previously described with respect to capacitor  10 . 
     FIG. 13 shows another embodiment of a capacitor  140  according to the present invention fabricated from an electrode active material  42  selectively contacted to a substrate provided in the shape of a cup having an annular side wall  142  extending from a bottom wall  144 . The side wall  142  forms into an annular rim  146  which is generally normal to the plane of side wall  142 . The rim  146  is connected to lid  148  by weld  150  to complete the enclosure. 
     FIG. 14 shows another embodiment of a capacitor  152  according to the present invention fabricated from an electrode active material  42  selectively contacted to a substrate provided in the shape of tray members  154  and  156 . An annular back-up ring  158  fits inside the side wall portions of the trays  154 ,  156  to provide support when the trays are connected together along their respective edges by weld  160  to complete the casing enclosure. 
     FIG. 15 illustrates an alternate embodiment of a capacitor  170  according to the present invention fabricated from a first substrate provided with an electrode active material  42  selectively contacted thereto and formed to provide a side wall  172  disposed intermediate opposed bottom and lid walls  174  and  176 , respectively. A second substrate selectively contacted with an electrode active material  42  is formed to provide a second side wall  178  disposed intermediate opposed bottom wall  180  and lid  182 . Second side wall  178  is somewhat shorter in length than side wall  172  so that bottom wall  180  and lid  182  are overlapped by bottom wall  174  and lid wall  176  secured therein by welds  184  and  186 . Again, opposed end walls (not shown) complete the casing enclosure. 
     FIG. 16 shows an embodiment of side-by-side capacitor cells  188  and  190  connected in parallel according to the present invention. The capacitor cells are housed in a deep drawn can  192  having the capacitive cathode active material  42  contacted to the opposed side walls  194  and  196 . An intermediate side wall  198  extends from a mid-point of the bottom wall  200  and is provided with the cathode active material  42  on the opposed sides thereof. Anode active pellets  12 A and  12 B are disposed between the side wall  194  and intermediate wall  198  and between the intermediate wall and side wall  196 , respectively. The anodes  12 A and  12 B are enveloped in respective separators  202  and  204 . Terminal lead  34  extends from anode  12 B which in turn is connected in parallel to anode  12 A via lead  206 . The insulator and seal structure  78  shown in FIG. 6 isolates the terminal lead  34  from the lid  30 B connected to can  192  by a weld  208 . An electrolyte (not shown) is filled in the casing to operatively associate and activate the capacitors. This side-by-side capacitor cells construction provides for reduced ESR in comparison to the capacitors shown in FIGS. 1 to  3  and  12  to  15 , and further provides a construction by which increased cathode active material may be housed inside of a casing. Of course, those skilled in the art will realize that the capacitor embodiment shown in FIG. 16 need not be limited to two side-by-side capacitor cells but that two or more cells as desired may be connected in parallel according to the present invention. 
     The present capacitor constructions having the generally flat, planar geometry have been shown to improve the volumetric efficiency of a capacitor by about 15% to about 80% over that of standard cylindrically shaped capacitors of a comparable casing size. Further, it has been determined that the capacitance obtained from an electrode made from an ultrasonically generated aerosol of active material contacted to a generally flat, planar geometry according to the present invention is on the order of about 2 F/sq. in. as measured by AC impedance spectroscopy. 
     It is appreciated that various modifications to the inventive concepts described herein may be apparent to those skilled in the art without departing from the spirit and the scope of the present invention defined by the hereinafter appended claims.