Abstract:
An electrolytic capacitor comprising a plurality of polymeric structures molded about the periphery of the anode pellet is described. The polymeric structures contact between a weld strap surrounding the butt seam between mating “clamshell” casing portions and the anode pellet sidewall. That way, the anode pellet is restrained from moving along both an x- and y-axes inside the casing. Having the cathode active material contacting the opposed major casing sidewalls being in a closely spaced relationship with the anode pellet through an intermediate separator prevents movement along the z-axis. The resulting capacitor is particularly well suited for use in high shock and vibration conditions.

Description:
BACKGROUND OF THE INVENTION 
   The present invention generally relates to a capacitor and, more particularly, to a capacitor capable of being subjected to high shock and vibration forces without failing. 
   SUMMARY OF THE INVENTION 
   Capacitors are used frequently in applications where high shock and vibration levels are experienced. A notable example is in the oil and gas industry where “measurement while drilling” applications can cause severe stress forces to a capacitor. Under high shock and vibration conditions, capacitors without adequate stabilization are capable of failing due to movement of the electrodes within the case, for example the anode pellet in an electrolytic capacitor. This movement can result in mechanical failure of the anode pellet lead rendering the capacitor inoperative. In that respect, mechanical stabilization of the anode pellet inside the casing is important for improving the reliability and safety of capacitors subjected to high shock and vibration conditions. 
   The capacitor of the present invention provides such mechanical stabilization through a plurality of polymeric point restraints that contact between the casing sidewall and the anode pellet sidewall to lock the anode in place. Alternatively, the polymeric point restraints contact between a weld strap surrounding the butt seam between mating “clam shell” casing portions and the anode pellet sidewall. This structure prevents the anode pellet from moving along both an x- and y-axes. Having the cathode active material coating the opposed major casing sidewalls being in a closely spaced relationship with the anode pellet through an intermediate separator prevents movement along the z-axis. 
   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 to the appended drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a capacitor  10  according to the present invention. 
       FIG. 2  is a side elevational view of an anode  12  having an embedded anode wire  34  extending from a notch  32  thereof. 
       FIG. 3  is a cross-sectional view of a glass-to-metal seal  38  for an anode lead  36 . 
       FIG. 4  is a side elevational view of the anode lead  36  including the glass-to-metal seal  38  connected to the embedded wire  34  of anode  12 . 
       FIG. 5  is a plan view of the anode  12  including the glass-to-metal seal  38  received in a fixture  48  surrounded by a weld strap  50  and with polymeric material being injected at selected locations between the anode and weld strap to form point restraints  58 A to  58 C. 
       FIG. 6  is a side elevational view showing the anode  12  held in position inside the weld strap  50  by the polymeric point restraints  58 A to  58 D. 
       FIG. 7  is a side elevational view of a casing portion  20  supporting a cathode active material  14  on a face wall  28  thereof. 
       FIG. 8  is a side elevational view showing the assembly of  FIG. 6  comprising the anode  12 , polymeric point restraints  58 A to  58 D and weld strap  50  after having being nested in the casing portion  20  of  FIG. 7 . 
       FIG. 9  is a cross-sectional view of the fully assembled capacitor  10 . 
       FIG. 9A  is an embodiment similar to the view shown in  FIG. 9 , but with the capacitor housed in different casing. 
       FIG. 10  is a side elevational view showing the anode  12  held in position in a casing portion by polymeric point restraints  58 E to  58 G, but without a weld strap. 
       FIG. 10A  is a cross-sectional view of  FIG. 10 . 
       FIG. 11  is a side elevational view showing the anode  12  held in position in a casing portion by a continuous polymeric restraint  58 , but without a weld strap. 
       FIG. 12  is a side elevational view showing the anode  12  held in position in a casing portion by polymeric point restraints  62 A to  62 C at the anode face walls. 
       FIG. 13  is a cross-sectional view along line  13 — 13  of  FIG. 12 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings,  FIG. 1  is a perspective view showing a capacitor  10  according to the present invention. The capacitor  10  comprises an anode  12  ( FIG. 2 ) of an anode active material and a cathode of a cathode active material  14  ( FIG. 7 ) housed inside a hermetically sealed casing  16 . The capacitor electrodes are operatively associated with each other by a working electrolyte (not shown) contained inside the casing, as will be described in detail hereinafter. The capacitor  10  is of an electrolytic type with the cathode comprising a conductive substrate having capacitive properties. 
   As particularly shown in  FIGS. 1 ,  7  to  9  and  13 , the casing  16  is of a metal material comprising first and second casing portions  18  and  20 . Casing portion  18  comprises a surrounding sidewall  22  extending to a face wall  24 . Similarly, casing portion  20  comprises a surrounding sidewall  26  extending to a face wall  28 . Sidewall  26  is sized so that sidewall  22  is in an overlapping relationship therewith. Then, the casing portions  18 ,  20  are hermetically sealed together by welding the overlapping sidewalls  22 ,  26  where they contact. The weld  30  is provided by any conventional means; however, a preferred method is by laser welding. 
   The mating casing portions  18 ,  20  are preferably 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, iron, and mixtures and alloys thereof. Preferably, the face and sidewalls of the casing portions have a thickness of about 0.005 to about 0.015 inches. 
   The active material of the anode  12  is typically of a metal selected from the group consisting of tantalum, aluminum, titanium, niobium, zirconium, hafnium, tungsten, molybdenum, vanadium, silicon, 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 a notch  32  from which an embedded anode wire  34  ( FIGS. 2 ,  4  to  6 ,  8 ,  10 ,  11  and  13 ) extends. The anode wire  34  preferably comprises the same material as the anode active material. The anode pellet is sintered under a vacuum at high temperatures and then anodized in a suitable electrolyte. The anodizing electrolyte fills the pores of the pressed powder body and a continuous dielectric oxide is formed thereon. In that manner, the anode  12  and extending wire  34  are provided with a dielectric oxide layer formed to a desired working voltage. The anode can also be of an etched aluminum, niobium, or titanium foil. 
   After the anode  12  and extending wire  34  are anodized to the desired formation voltage, the dielectric oxide is removed from the wire and there connected to an anode lead  36  supported in an insulative glass-to-metal seal  38  (GTMS). The weld and lead are then re-anodized. The glass-to-metal seal  38  comprises a ferrule  40  defining an internal cylindrical through bore or passage  42  of constant inside diameter. An insulative glass  44  provides a hermetic seal between the bore  42  and the anode lead  36  passing there through. The anode lead  36  has a J-shaped proximal portion  36 A that is subsequently connected to a crook in the anode wire  34  such as by laser welding to secure them together. The glass  44  is, for example, ELAN® type  88  or MANSOL™ type  88 . As shown in  FIGS. 1 and 8 , in the final capacitor assembly the GTMS  38  electrically insulates the anode lead  36  connected to the anode wire  34  from the metal casing  18 . 
   A separator  46  ( FIG. 4 ) of electrically insulative material in the shape of a bag completely surrounds and envelops the anode  12  except the extending wire  34 . The separator  46  prevents an internal electrical short circuit between the anode  12  and cathode active materials  14  in the assembled capacitor and has a degree of porosity sufficient to allow flow there through of the working 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 used, the separator can be treated to improve its wettability, as is well known by those skilled in the art. 
   As shown in  FIG. 5 , the anode  12  connected to the anode lead  36  supported in the GTMS  38  is then positioned inside a fixture  48 . A metal weld strap  50  is also positioned in the fixture  48  in a generally enclosing, but spaced relationship with the anode  12 . The weld strap  50  is discontinuous at  52  to provide a space for the GTMS  38 . As will be described in detail hereinafter, the metal strap  50  serves as a backing to protect the anode  12  and separator  46  from laser welding light when the casing portions  18  and  20  are welded to each other during final capacitor assembly. 
   Once the anode  12  and GTMS  38  surrounded by the weld strap  50  are properly positioned in the fixture  48 , a plurality of spacer pegs  54 A to  54 D are located about the periphery of the anode. The spacer pegs contact both the weld strap and the anode to maintain uniform spacing between them. 
   A nozzle  56  is then used to inject a polymeric material at spaced locations between the weld strap  50  and the periphery of the anode sidewall. The thusly-formed polymeric restraints  58  are oval-shaped “point contact” structures that each extends a relatively short distance about the periphery of the anode. While oval-shaped structures are shown, that should not be construed as limiting. They can be of many different shapes in plan view as long as the polymeric structures are of a thickness that substantially matches that of the anode between its major face walls. The polymeric material of the point restraints is of a fast curing type including a polyolefin, a fluoropolymer, a hot melt adhesive, or a UV curable adhesive. A relatively slow curing silastic material is also useful. The anode  12  held in position inside the weld strap  50  by the polymeric point restraints  58 A to  58 D is then removed from the fixture  48  as an assembly ( FIG. 7 ). 
   The cathode active material  14  preferably coats the face walls  24 ,  28 , spaced from the respective sidewalls  22 ,  26 . The pad printing process described in U.S. patent application Ser. No. 10/920,942, filed Aug. 18, 2004, is preferred for making such a coating. 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., are also suitable deposition methods. These patents and patent application are assigned to the assignee of the present invention and incorporated herein by reference. 
   As shown in  FIG. 7 , casing portion  20  is provided with the cathode active material  14  coated on its face wall  28  in a pattern that generally mirrors the shape of the anode  12 . The cathode active material  14  has a thickness of about a few hundred Angstroms to about 0.1 millimeters and is either directly coated on the inner surface of the face wall  28  or it is coated on a conductive substrate (not shown) in electrical contact with the inner surface of the face wall. The other casing portion  18  has the cathode active material  14  similarly coated on its face wall  24  or on a conductive substrate secured to the inner surface of the face wall in electrical contact therewith. In that respect, the face walls  24 ,  28  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 redox, pseudocapacitive or an under potential material, or be an electroactive conducting polymer such as polyaniline, polypyrole, polythiophene, polyacetylene, and mixtures thereof. 
   According to one preferred aspect of the present invention, the redox or cathode active material  14  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. 
   The cathode active material  14  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 face walls  24 ,  28  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  14  includes an oxide of ruthenium or oxides of ruthenium and tantalum. 
   As shown in  FIG. 8 , the anode  12  held in position by the polymeric point restraints  58 A to  58 D and the weld strap  50  as an assembly is then nested in the casing portion  20  with the GTMS  38  received in an opening  60  ( FIG. 8 ) in the casing sidewall  26 . The ferrule  40  of the GTMS has a distal step  40 A ( FIG. 3 ) that fits into the casing opening  60  in a tight fitting relationship. The weld strap  50  is likewise sized to fit inside the perimeter of the casing sidewall  26  in a closely spaced relationship. The ferrule  40  is then secured to the casing sidewall  26  such as by laser welding. This provides the anode  12  secured inside the casing portion  20  by the polymeric point restraints  58 A to  58 D and the weld strap  50 . In this position, the anode major face wall  12  ( FIG. 9 ) is resting on the casing sidewall  26 . However, the intermediate separator  46  prevents direct contact between the anode  12  and the cathode active material  14 . 
   The other casing portion  18  is then mated to the casing portion  20  with their respective sidewalls  22  and  26  overlapping each other. The continuous weldment  30  provided about the perimeter of the casing sidewalls  22  and  26 , such as by laser welding, secures the casing portions  18  and  20  to each other. The weld strap  50 , however, prevents laser light from penetrating into the interior of the capacitor to damage the anode  12  and separator  46  among other heat sensitive components. 
   A working electrolyte (not shown) is then provided in the capacitor through an opening in one of the casing portions  18 ,  20 . A suitable working electrolyte for the capacitor  10  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. Pub. Nos. 2003/0090857 and 2003/0142464 describe other working electrolytes for the present capacitors. The working electrolyte of the former publication comprises water, a water-soluble inorganic and/or organic acid and/or salt, and a water-soluble nitro-aromatic compound while the latter relates to an electrolyte having de-ionized water, an organic solvent, isobutyric acid and a concentrated ammonium salt. These publications and patent are assigned to the assignee of the present invention and incorporated herein by reference. The electrolyte fill opening is then closed by a hermetic closure (not shown), as is well known by those skilled in the art. 
   The spaces formed between the polymeric point restraints  58 A to  58 D provide for the electrolyte to thoroughly wet the anode  12  including the enveloping separator  46  as well as the cathode active materials  14  to provide the capacitor  10  in a functional state. The weld strap  50  encloses and contacts the polymeric point restraints  58 A to  58 D that, in turn, contact the separator  46  at the anode sidewall. This prevents any movement of these components should the capacitor be subject to high shock and vibration conditions. 
   The casing  16 , including the portions  18 ,  20 , being of a conductive metal serves as the negative terminal for making electrical connection between the capacitor  10  and its load. A pin (not shown) is welded to one of the casing portions  18 ,  20  to provide this. The anode lead  36  extending outside the capacitor  10  is hermetically sealed from the interior of the capacitor and insulated from the mating casing portions  20 ,  22  by the GTMS  38  to serve as the positive terminal for the capacitor  10 . 
     FIG. 9A  shows an alternate embodiment of a casing for the present capacitor. The casing comprises portion  20 A having a surrounding sidewall  26 A extending to a face wall  28 A supporting cathode active material  14 . The sidewall  26 A has a step  26 B at its upper end that received a plate  24 A serving as a second face wall for supporting cathode active material  14 . The plate  24 A is nested in the step  26 B. A weld  30  secures the plate  24 A to the casing portion  20 A at the step with the upper surface of the plate being coplanar with the upper end of the sidewall  26 A. The remaining structure for this capacitor is as previously described. 
     FIGS. 10 and 10A  show another embodiment of a casing for the present capacitor. The casing comprises portion  20 B having a surrounding sidewall  26 C extending to a face wall  28 B supporting cathode active material  14 . A plate  24 A rests on the upper edge of the sidewall  26 C and serves as a second face wall for supporting cathode active material  14 . Plate  24 A extends a short distance out beyond the sidewall  26 C. A weld  30  then secures the plate  24 A to the casing portion  20 B where the plate overhangs or extends past the sidewall  26 C. Also, in this embodiment, the weld strap has been eliminated. Elimination of the weld strap is possible with the laser beam being aimed at the corner where the plate  24 A extends past the sidewall  26 C. The remaining structure for this capacitor is as previously described. 
     FIG. 11  shows an alternate embodiment of a polymeric restraint for a capacitor anode  12 . In this embodiment, the polymeric material  58  completely surrounds the anode sidewall. That is, the polymeric material restrains the anode by contacting the anode sidewall between its major face walls and the sidewall  26 C of the casing portion  20 B. Since there is no weld strap, the casing is similar to that shown in  FIGS. 10 and 10A . If desired, a weld strap can be provided as previously described. In this embodiment, the electrolyte wets the anode  12  including the separator  46  and the cathode active material  14  at the opposed face walls. 
     FIGS. 12 and 13  illustrate a further embodiment of the invention. The anode  12  is held or restrained in position by a plurality of polymeric point structures  62 A,  62 B and  62 C contacting between the separator  46  at each anode face wall and the cathode active material  14  provided at the casing face walls. Three polymeric point restraints are the preferred minimum number, although more can be provided if desired. Also, the polymeric structures  62 A to  62 C can be used in conjunction with the previously described polymeric point restraints provided at the anode sidewall between the opposed anode face walls. Finally, this embodiment is shown with a weld strap  50 , so the casing is similar to that shown in  FIGS. 1 ,  7  to  9  and  9 A. The polymeric structures  62 A to  62 C can also be provided in a casing similar to that shown in  FIGS. 10 and 10A  devoid of a weld strap. 
   Thus, various polymeric structures as point restraints have been shown and described. However, modifications may be readily apparent to those skilled in the art. For example, the polymeric point restraints  58 A to  58 D can be used in conjunction with the polymeric point restraints  62 A to  62 C to provide added protection against the anode  12  moving inside the capacitor  10  subjected to high shock and vibration forces. 
   Although the embodiments described herein show the polymeric restraints used with a single anode pellet that should not be construed as limiting. It is contemplate by the scope of the present invention that the polymeric restraints can be used with two or more side-by-side anodes provided in one of the previously described casings. Such a multiple anode design is shown in U.S. Pat. No. 6,850,405 to Mileham et al. This patent is assigned to the assignee of the present invention and incorporated herein by reference. 
   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.