Nonionic surfactant for use in a solid electrolyte of an electrolytic capacitor

1. A solid electrolytic capacitor comprising:

a sintered porous anode;

a dielectric layer that overlies the anode body;

a solid electrolyte overlying the dielectric layer, wherein the solid electrolyte contains a first layer comprising pre-polymerized conductive polymer particles and a second layer that overlies the first layer, wherein the second layer is formed from a blend comprising pre-polymerized conductive polymer particles and a nonionic surfactant having a hydrophilic/lipophilic balance (“HLB”) of from about 10 to about 20 and a molecular weight of from about 100 to about 10,000 grams per mole, and wherein the nonionic surfactant has a hydrophobic base and a hydrophilic chain that contains alkoxy moieties and wherein the concentration of nonionic surfactants in the first layer is about 2 wt. % or less; and

an external polymer coating overlying the solid electrolyte, wherein the external polymer coating contains a plurality of pre-polymerized conductive polymer particles, and wherein a ratio of an average size of the pre-polymerized conductive polymer particles employed in the external polymer coating to an average size of the pre-polymerized conductive polymer particles employed in the second layer of the solid electrolyte is from about 1.5 to about 30.

2. The solid electrolytic capacitor of claim 1 , wherein the nonionic surfactant has an HLB of from about 14 to about 18.

3. The solid electrolytic capacitor of claim 1 , wherein the nonionic surfactant has a molecular weight of from about 500 to about 2,500 grams per mole.

4. The solid electrolytic capacitor of claim 1 , wherein the nonionic surfactant is an ethoxylated or propoxylated alkylphenol, ethoxylated or propoxylated C 6 -C 24 fatty alcohol, polyoxyethylene glycol alkyl ether, polyoxyethylene glycol alkyl phenol ether, polyoxyethylene glycol ester of a C 8 -C 24 fatty acid, polyoxyethylene glycol ether of a C 8 -C 24 fatty acid, block copolymer of polyethylene glycol and polypropylene glycol, or a combination thereof.

5. The solid electrolytic capacitor of claim 1 , wherein the hydrophilic chain of the nonionic surfactant contains ethoxy moieties.

6. The solid electrolytic capacitor of claim 1 , wherein the nonionic surfactant is a polyoxyethylene glycol sorbitan alkyl ester.

7. The solid electrolytic capacitor of claim 1 , wherein the conductive polymer particles include a substituted polythiophene.

8. 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.

9. 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.

10. The solid electrolytic capacitor of claim 1 , wherein the concentration of the nonionic surfactant in the layer is from about 5 wt. % to about 40 wt. %.

11. The solid electrolytic capacitor of claim 1 , wherein the particles of the second layer contain poly(3,4-ethylenedioxythiophene).

12. 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 forming a first layer that contains pre-polymerized conductive polymer particles, and thereafter forming a second layer that overlies the first layer, wherein the second layer is formed from a blend that comprises pre-polymerized conductive polymer particles and a nonionic surfactant having a hydrophilic/lipophilic balance (“HLB”) of from about 10 to about 20 and a molecular weight of from about 100 to about 10,000 grams per mole, and wherein the nonionic surfactant has a hydrophobic base and a hydrophilic chain that contains alkoxy moieties, and wherein the concentration of nonionic surfactants in the first layer is about 2 wt. % or less; and

forming an external polymer coating over the solid electrolyte, wherein the external polymer coating contains a plurality of pre-polymerized conductive polymer particles, and wherein a ratio of an average size of the pre-polymerized conductive polymer particles employed in the external polymer coating to an average size of the pre-polymerized conductive polymer particles employed in the second layer of the solid electrolyte is from about 1.5 to about 30.

13. The method of claim 12 , wherein the first layer is generally free of the nonionic surfactant.

14. The method of claim 12 , wherein the nonionic surfactant is an ethoxylated or propoxylated alkylphenol, ethoxylated or propoxylated C 6 -C 24 fatty alcohol, polyoxyethylene glycol alkyl ether, polyoxyethylene glycol alkyl phenol ether, polyoxyethylene glycol ester of a C 8 -C 24 fatty acid, polyoxyethylene glycol ether of a C 8 -C 24 fatty acid, block copolymer of polyethylene glycol and polypropylene glycol, or a combination thereof.

15. The method of claim 12 , wherein the hydrophilic chain of the nonionic surfactant contains ethoxy moieties.

16. The method of claim 12 , wherein the nonionic surfactant is a polyoxyethylene glycol sorbitan alkyl ester.

17. The method of claim 12 , wherein the conductive polymer particles include a substituted polythiophene.

18. The method of claim 12 , wherein the nonionic surfactant is applied in the form of a solution.