Solid electrolytic capacitor assembly

1. A capacitor assembly comprising a capacitor element, the capacitor element comprising;

a porous anode body that contains a valve metal compound;

a dielectric that overlies the anode body and includes an oxide of the valve metal compound;

a solid electrolyte that overlies the dielectric, wherein the solid electrolyte includes a conductive polymer and a hydroxy-functional polymer; and

an organofunctional silane compound that is bonded to the oxide of the dielectric and is capable of bonding to the hydroxy-functional polymer, wherein the organofunctional silane compound has the following general formula (I):

wherein

R 1 , R 2 , and R 3 are independently alkyl, alkenyl, aryl, heteroaryl, cycloalkyl, heterocyclyl, halo, haloalkyl, hydroxyalkyl, or a combination thereof; and

X is a functional group that is capable of bonding to a hydroxyl group or is capable of being converted into a functional group that is capable of bonding to a hydroxyl group; and

Z is an organic group that links the functional group X to the silicon atom.

2. The capacitor assembly of claim 1 , wherein at least one of R 1 , R 2 , and R 3 is a hydroxyalkyl.

3. The capacitor assembly of claim 1 , wherein Z is alkyl, aryl, or a combination thereof.

4. The capacitor assembly of claim 1 , wherein X is an isocyanate.

5. The capacitor assembly of claim 4 , wherein the organosilane compound includes 3-isocyantopropyltriethoxysilane, 3-isocyantopropyltrimethoxysilane, 3-isocyanantopropylmethyldiethoxysilane, 3-isocyanantopropylmethyldiethoxysilane, or a combination thereof.

6. The capacitor of claim 1 , wherein X is a protecting group that is capable of being converted into a functional group that can react with the hydroxy-functional polymer.

7. The capacitor of claim 6 , wherein the protecting group includes a thiocyanate group, carbamate group, isocyanurate group, or a combination thereof.

8. The capacitor of claim 6 , wherein the organosilane compound includes (thiocyanatomethyl)phenethyl-trimethoxysilane, 3-thiocyanatopropyltriethoxysilane, N-(3-triethoxysilylpropyl)-o-t-butylcarbamate, triethoxysilylpropylethylcarbamate, N-trimethoxysilylpropylmethylcarbamate, tris(3-trimethoxysilylpropyl)isocyanurate, or a combination thereof.

9. The capacitor assembly of claim 1 , wherein the anode body includes tantalum and the dielectric includes tantalum pentoxide.

10. The capacitor assembly of claim 1 , wherein the solid electrolyte contains an extrinsically conductive polymer and a sulfonyl counterion.

11. The capacitor assembly of claim 10 , wherein the extrinsically conductive polymer is poly(3,4-ethylenedioxythiophene).

12. The capacitor assembly of claim 11 , wherein the sulfonyl counterion is polystyrene sulfonic acid or a salt thereof.

13. The capacitor assembly of claim 1 , wherein the conductive polymer is an intrinsically conductive polymer.

14. The capacitor assembly of claim 13 , wherein the intrinsically conductive polymer is poly(4-(2,3-dihydrothieno-[3,4-b][1,4]dioxin-2-ylmethoxy)-1-butane-sulphonic acid, salt), poly(4-(2,3-dihydrothieno-[3,4-b][1,4]dioxin-2-ylmethoxy)-1-propanesulphonic acid, salt), or a combination thereof.

15. The capacitor assembly of claim 1 , wherein the solid electrolyte contains a layer formed from a dispersion of pre-polymerized conductive polymer particles.

16. The capacitor assembly of claim 15 , wherein the hydroxy-functional polymer is contained within the layer.

17. The capacitor assembly of claim 1 , wherein the hydroxy-functional polymer has a molecular weight of from about 300 to about 1,200 grams per mole.

18. The capacitor assembly of claim 1 , wherein the hydroxy-functional polymer is a polyalkylene ether.

19. The capacitor assembly of claim 18 , wherein the polyalkylene ether is a polyalkylene glycol.

20. The capacitor assembly of claim 1 , further comprising an external polymer coating that overlies the solid electrolyte and contains pre-polymerized conductive polymer particles and a cross-linking agent.

21. The capacitor assembly of claim 1 , further comprising:

an anode termination that is in electrical connection with the anode body;

a cathode termination that is in electrical connection with the solid electrolyte; and

a housing that encloses the capacitor element and leaves exposed at least a portion of the anode termination and the cathode termination.

22. The capacitor assembly of claim 21 , wherein the housing is formed from a resinous material that encapsulates the capacitor element.

23. The capacitor assembly of claim 21 , wherein the housing defines an interior cavity within which the capacitor element is positioned, wherein the interior cavity has a gaseous atmosphere that includes an inert gas.

24. A method for forming a capacitor element, the method comprising:

anodically oxidizing a sintered porous anode body to form a dielectric that includes an oxide of a valve metal compound;

applying a solution to the anode that includes an organofunctional silane compound;

applying a dispersion that contains conductive polymer particles and a hydroxy-functional polymer to form a conductive polymer layer; and

bonding the organofunctional silane compound to the oxide of the dielectric, wherein the organofunctional silane compound has the following general formula (I):

wherein

R 1 , R 2 , and R 3 are independently alkyl, alkenyl, aryl, heteroaryl, cycloalkyl, heterocyclyl, halo, haloalkyl, hydroxyalkyl, or a combination thereof; and

X is a functional group that is capable of bonding to a hydroxyl group or is capable of being converted into a functional group that is capable of bonding to a hydroxyl group; and

Z is an organic group that links the functional group X to the silicon atom.

25. The method of claim 24 , wherein the solution includes an organic solvent.