Solid electrolytic capacitor containing a poly(3,4-ethylenedioxythiophene) quaternary onium salt

1. A solid electrolytic capacitor comprising:

an anode body;

a dielectric overlying the anode body;

a solid electrolyte overlying the dielectric; and

a conductive coating that overlies the solid electrolyte, wherein the conductive coating includes nanoparticles formed from a poly(3,4-ethylenedioxythiophene) quaternary onium salt, wherein the conductive coating is generally free of poly(styrene sulfonic acid).

2. The solid electrolytic capacitor of claim 1 , wherein the poly(3,4-ethylenedioxythiophene) quaternary onium salt has the following general structure:

wherein,

R is (CH 2 ) a —O—(CH 2 ) b ;

a is from 0 to 10;

b is from 0 to 18;

Z is a negatively charged ion;

X is nitrogen or phosphorous;

R 1 , R 2 , R 3 , and R 4 are independently selected from the group consisting of hydrogen, substituted or unsubstituted C 1 -C 10 alkyl groups, substituted or unsubstituted C 3 -C 14 cycloalkyl groups, substituted or unsubstituted C 1 -C 10 alkenyl groups, substituted or unsubstituted C 2 -C 10 alkynyl groups, substituted or unsubstituted C 1 -C 10 alkoxy groups, substituted or unsubstituted aryl groups, substituted or unsubstituted heteroaryl groups, and combinations thereof; and

n is from 2 to 2,000.

3. The solid electrolytic capacitor of claim 2 , wherein “a” is from 1 to 2 and “b” is from 2 to 6.

4. The solid electrolytic capacitor of claim 2 , wherein Z is SO 3 − .

5. The solid electrolytic capacitor of claim 2 , wherein X is nitrogen.

6. The solid electrolytic capacitor of claim 2 , wherein R 1 , R 2 , R 3 , and R 4 are independently selected from the group consisting of hydrogen, C 1 -C 6 alkyl groups, and combinations thereof.

7. The solid electrolytic capacitor of claim 1 , wherein the poly(3,4-ethylenedioxythiophene) quaternary onium salt has the following general structure:

wherein,

R is (CH 2 ) a —O—(CH 2 ) b ;

a is from 1 to 6;

b is from 1 to 10;

R 1 , R 2 , R 3 , and R 4 are independently selected from the group consisting of hydrogen and C 1 -C 10 alkyl groups; and

n is from 4 to 1000.

8. The solid electrolytic capacitor of claim 1 , wherein the poly(3,4-ethylenedioxythiophene) quaternary onium salt has the following structure:

9. The solid electrolytic capacitor of claim 1 , wherein the poly(3,4-ethylenedioxythiophene) quaternary onium salt has one of the following structures:

10. The solid electrolytic capacitor of claim 1 , wherein the solid electrolyte contains a conductive polymer.

11. The solid electrolytic capacitor of claim 10 , wherein the conductive polymer of the solid electrolyte includes poly(3,4-ethylenedioxythiophene).

12. The solid electrolytic capacitor of claim 1 , wherein the nanoparticles have an average size of from about 2 to about 100 nanometers.

13. The solid electrolytic capacitor of claim 1 , wherein the thickness of the conductive coating is from about 1 μm to about 40 μm.

14. The solid electrolytic capacitor of claim 1 , wherein the anode body includes tantalum, niobium, or an electrically conductive oxide thereof.