Wet capacitor cathode containing an alkyl-substituted poly(3,4-ethylenedioxythiophene)
A wet electrolytic capacitor that contains an anodically oxidized porous anode body, a cathode containing a metal substrate coated with a conductive coating, and a working electrolyte that wets the dielectric on the anode. The conductive coating contains an alkyl-substituted poly(3,4-ethylenedioxythiophene) having a certain structure. Such polymers can result in a higher degree of capacitance than many conventional types of coating materials. Further, because the polymers are generally semi-crystalline or amorphous, they can dissipate and/or absorb the heat associated with the high voltage. The degree of surface contact between the conductive coating and the surface of the metal substrate may also be enhanced in the present invention by selectively controlling the manner in which the conductive coating is formed.
1. A wet electrolytic capacitor comprising:
an anode comprising a sintered porous anode body that is coated with a dielectric, wherein the anode body comprises tantalum;
a cathode that comprises a metal substrate over which is disposed a conductive polymer coating, wherein the conductive polymer coating contains an alkyl-substituted poly(3,4-ethylenedioxythiophene) having the following general structure:
wherein R 2 is hydrogen or an alkyl group, n is from 1 to 2,000, and y is from 1 to 10; and
a fluid working electrolyte in communication with the anode and the cathode, wherein the electrolyte has a pH of from about 4.5 to about 7.0.
2. The wet electrolytic capacitor of claim 1 , wherein the conductive coating contains hydroxyethylated poly(3,4-ethylenedioxythiophene), hydroxymethylated poly(3,4-ethylenedioxythiophene), or a combination thereof.
3. The wet electrolytic capacitor of claim 1 , wherein the metal substrate includes titanium, tantalum, or steel.
4. The wet electrolytic capacitor of claim 1 , wherein the electrolyte contains water and ethylene glycol.
5. The wet electrolytic capacitor of claim 4 , wherein the electrolyte contains an ammonium salt of an organic acid.
6. The wet electrolytic capacitor of claim 5 , wherein the electrolyte contains phosphoric acid.
7. The wet electrolytic capacitor of claim 6 , wherein the electrolyte contains an organic acid.
8. The wet electrolytic capacitor of claim 1 , wherein the electrolyte has a pH of from about 5.0 to about 6.5.
9. The wet electrolytic capacitor of claim 1 , wherein the substrate is in the form of a casing within which the anode and the fluid electrolyte are positioned.
10. The wet electrolytic capacitor of claim 1 , wherein the anode body contains a sidewall positioned between a proximal end and an opposing distal end, wherein a plurality of longitudinally extending channels recessed into the sidewall.
11. The wet electrolytic capacitor of claim 1 , wherein the anode further comprises an anode lead wire.
12. The wet electrolytic capacitor of claim 1 , wherein the conductive coating is formed by electrochemical polymerization.