Temperature stable solid electrolytic capacitor
A capacitor whose electrical properties can be stable under a variety of different conditions is provided. The solid electrolyte of the capacitor is formed from a combination of an in situ polymerized conductive polymer and a hydroxy-functional nonionic polymer. One benefit of such an in situ polymerized conductive polymer is that it does not require the use of polymeric counterions (e.g., polystyrenesulfonic anion) to compensate for charge, as with conventional particle dispersions, which tend to result in ionic polarization and instable electrical properties, particularly at the low temperatures noted above. Further, it is believed that hydroxy-functional nonionic polymers can improve the degree of contact between the polymer and the surface of the internal dielectric, which unexpectedly increases the capacitance performance and reduces ESR.
1. A solid electrolytic capacitor comprising:
a sintered porous anode;
a dielectric layer that overlies the anode body; and
a solid electrolyte overlying the dielectric layer, wherein the solid electrolyte comprises an in situ polymerized conductive polymer and a hydroxy-functional nonionic polymer, wherein the conductive polymer is a substituted polythiophene, and wherein the hydroxy-functional nonionic polymer is a polyalkylene glycol; and
further comprising an external polymer coating that overlies the solid electrolyte, wherein the external polymer coating contains a plurality of pre-polymerized conductive polymer particles.
2. The solid electrolytic capacitor of claim 1 , wherein the hydroxy-functional nonionic polymer has a molecular weight of from about 300 to about 1,200 grams per mole.
3. The solid electrolytic capacitor of claim 1 , wherein the solid electrolyte contains a first layer that overlies the dielectric layer and a second layer that overlies the first layer, the first layer containing the in situ polymerized conductive polymer and the second layer containing the hydroxy-functional nonionic polymer.
4. The solid electrolytic capacitor of claim 3 , wherein the second layer further contains a plurality of pre-polymerized conductive polymer particles.
5. The solid electrolytic capacitor of claim 4 , wherein the particles contain poly(3,4-ethylenedioxythiophene).
6. The solid electrolytic capacitor of claim 4 , wherein the particles contain a monomeric or polymeric counteranion.
7. The solid electrolytic capacitor of claim 1 , wherein the external polymer coating contains a first layer that overlies the solid electrolyte and a second layer that overlies the first layer, wherein the first layer contains a crosslinking agent and the second layer contains the pre-polymerized conductive polymer particles.
8. The solid electrolytic capacitor of claim 1 , further comprising an anode termination that is electrically connected to the anode and a cathode termination that is electrically connected to the solid electrolyte.
9. The solid electrolytic capacitor of claim 1 , wherein the capacitor exhibits an equivalence series resistance of about 100 mohms or less at a temperature of −55° C. and an operating frequency of 100 kHz.
10. A method for forming a solid electrolytic capacitor, the method comprising:
anodically oxidizing a sintered porous anode to form a dielectric, layer that overlies the anode;
forming a solid electrolyte over the dielectric layer by a process that includes chemically polymerizing a monomer in situ to form a conductive polymer, and thereafter, applying a hydroxy-functional nonionic polymer, wherein the conductive polymer is a substituted polythiophene, and wherein the hydroxy-functional nonionic polymer is a polyalkylene glycol; and
forging an external polymer coating that overlies the solid electrolyte, wherein the external polymer coating contains a plurality of pre-polymerized conductive polymer particles.
11. The method of claim 10 , wherein the hydroxy-functional nonionic polymer has a molecular weight of from about 300 to about 1,200 grams per mole.
12. The method of claim 10 , wherein hydroxy-functional nonionic polymer is applied in the form of a dispersion that contains a plurality of pre-polymerized conductive polymer particles.
13. The method of claim 10 , wherein the hydroxy-functional nonionic polymer is applied in the font of a solution.