Solid electrolytic capacitor with improved performance at high temperatures and voltages

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

a sintered 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 at least one conductive polymer layer that contains a sulfonyl ion and wherein the conductive polymer layer contains an extrinsically conductive polymer and a sulfonyl counterion or an intrinsically conductive polymer;

an external polymer coating that overlies the solid electrolyte; and

an organofunctional silane that is covalently bonded to the oxide of the dielectric and is capable of bonding to the sulfonyl ion, wherein the organofunctional silane is a diaminofunctional silane having the following general formula (III):

wherein,

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

R 4 and R 5 are independently hydrogen, alkyl, independently alkyl, alkenyl, aryl, heteroaryl, cycloalkyl, heterocyclyl, halo, haloalkyl, hydroxyalkyl, or alternatively N, R 4 , and R 5 together with one or more additional atoms form a ring structure; and

Z 1 and Z 2 are independently an organic group;

wherein the organofunctional silane forms at least a first layer that contains a single silane compound;

wherein after being subjected to a hot atmosphere having a temperature of about 80° C. or more and a rated voltage for 90 seconds and a time of about 100 hours or more, the capacitor assembly exhibits a leakage current of from about 0.1 microamps to about 10 microamps as determined at the rated voltage; and

wherein a ratio of a capacitance of the capacitor assembly after being exposed to the hot atmosphere for about 500 hours to a capacitance value of the capacitor assembly when initially exposed to the hot atmosphere is from about 0.7 to 1.

2. The capacitor assembly of claim 1 , wherein the diaminofunctional silane is N-(2-aminoethyl)-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(6-aminohexyl)aminomethyltriethoxysilane, N-(6-aminohexyl)aminopropyltrimethoxysilane, N-(2-aminoethyl)-11-aminoundecyltrimethoxysilane), (aminoethylaminomethyl)-phenethyltrimethoxysilane, N-3-[(amino(polypropylenoxy)]-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylsilanetriol, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminoi sobutylmethyldimethoxysilane, or (aminoethylamino)-3-isobutyldimethylmethoxysilane.

3. The capacitor assembly of claim 2 , wherein the diaminofunctional silane is N-(2-aminoethyl)-aminopropyltrimethoxysilane.

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

5. The capacitor assembly of claim 1 , wherein the extrinsically conductive polymer has repeating units of the following formula:

wherein,

R 7 is a linear or branched, C 1 to C 18 alkyl radical; C 5 to C 12 cycloalkyl radical; C 6 to C 14 aryl radical; C 7 to C 18 aralkyl radical; and

q is an integer from 0 to 8.

6. The capacitor assembly of claim 1 , wherein the extrinsically conductive polymer is poly(3,4-ethylenedioxythiophene).

7. The capacitor assembly of claim 1 , wherein the sulfonyl counterion is polystyrene sulfonic acid or a salt thereof.

8. The capacitor assembly of claim 1 ,

wherein the conductive polymer layer contains an intrinsically conductive polymer having repeating units of the following formula:

wherein,

R is (CH 2 ) a —O—(CH 2 ) b ;

a is from 0 to 10;

b is from 1 to 18;

Z is an anion;

X is a cation.

9. The capacitor assembly of claim 8 , 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.

10. The capacitor assembly of claim 1 , wherein the conductive polymer layer is formed from a dispersion of pre-polymerized conductive polymer particles.

11. The capacitor assembly of claim 1 , wherein the solid electrolyte is generally free of in situ-polymerized conductive polymers.

12. The capacitor assembly of claim 1 , wherein the external polymer coating contains pre-polymerized conductive polymer particles and a cross-linking agent.

13. 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.

14. The capacitor assembly of claim 13 , wherein the housing is formed from a resinous material that encapsulates the capacitor element.

15. The capacitor assembly of claim 13 , 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.

16. The capacitor assembly of claim 1 , comprising a second layer of the organofunctional silane that contains a single silane compound that is the same or different from the silane compound of the first layer.

17. The capacitor assembly of claim 1 , wherein the hot atmosphere has a temperature of from about 105° C. to about 130° C.

18. The capacitor assembly of claim 1 , wherein the rated voltage is 15 volts or more.

19. The capacitor assembly of claim 1 , wherein the time is from about 300 hours to about 3000 hours.

20. A method for forming a capacitor assembly, 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 a single organofunctional silane compound, wherein the organofunctional silane is a diaminofunctional silane having the following general formula (III):

wherein,

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

R 4 and R 5 are independently hydrogen, alkyl, independently alkyl, alkenyl, aryl, heteroaryl, cycloalkyl, heterocyclyl, halo, haloalkyl, hydroxyalkyl, or alternatively N, R 4 , and R 5 together with one or more additional atoms form a ring structure; and

Z 1 and Z 2 are independently an organic group;

applying a dispersion that contains conductive polymer particles and a sulfonyl counterion to form a conductive polymer layer;

covalently bonding the organofunctional silane compound to the oxide of the dielectric, wherein the organofunctional silane compound is capable of bonding to the sulfonyl counterion; and

applying an external polymer coating that overlies the solid electrolyte;

wherein the conductive polymer layer contains an extrinsically conductive polymer and a sulfonyl counterion or wherein the conductive polymer layer contains an intrinsically conductive polymer having repeating units of the following formula:

wherein,

R is (CH 2 ) a —O—(CH 2 ) b ;

a is from 0 to 10;

b is from 1 to 18;

Z is an anion;

X is a cation;

wherein after being subjected to a hot atmosphere having a temperature of about 80° C. or more and a rated voltage for 90 seconds and a time of about 100 hours or more, the capacitor assembly exhibits a leakage current of from about 0.1 microamps to about 10 microamps as determined at the rated voltage; and

wherein a ratio of a capacitance of the capacitor assembly after being exposed to the hot atmosphere for about 500 hours to a capacitance value of the capacitor assembly when initially exposed to the hot atmosphere is from about 0.7 to 1.

21. The method of claim 20 , wherein the solution includes an organic solvent.