Wet electrolytic capacitor containing a cathode coating

• US 20070211413A1
• Filed: 03/09/2006
• Published: 09/13/2007
• Est. Priority Date: 03/09/2006
• Status: Active Grant

• Current Assignee: AVX Corporation (Kyocera Corporation)
• Original Assignee: AVX Corporation (Kyocera Corporation)
• Inventors: Ning, Gang, Fife, James, Sebald, Zebbie, Bates, James, Pease, Robert
• Granted Patent: US 7,511,943 B2
• Time in Patent Office: Days
• US Class Current: 361/516
• CPC Class Codes: H01G 9/0425 specially adapted for cathode
• CPC Class Codes: H01G 9/145 Liquid electrolytic capacitors H01G11/00 takes precedence

Abstract

A wet electrolytic capacitor that includes an anode, cathode, and an electrolyte is provided. The cathode contains a substrate and a coating overlying the substrate. The coating comprises a sintered body containing carbonaceous particles (e.g., activated carbon) and inorganic particles (e.g., NbO₂).

Claims

1. A wet electrolytic capacitor comprising:

an anode;

a cathode containing a substrate and a coating overlying the substrate, the coating comprising carbonaceous particles and inorganic particles, wherein the inorganic particles are sinter bonded to the carbonaceous particles and to the substrate; and

an electrolyte disposed between the cathode and anode.

2. The wet electrolytic capacitor of claim 1, wherein the carbonaceous particles contain activated carbon.

3. The wet electrolytic capacitor of claim 1, wherein the carbonaceous particles have a specific surface area of at least about 200 square meters per gram.

4. The wet electrolytic capacitor of claim 1, wherein the carbonaceous particles have a specific surface area of at least about 1500 square meters per gram.

5. The wet electrolytic capacitor of claim 1, wherein the carbonaceous particles have a median size of from about 5 to about 20 micrometers.

6. The wet electrolytic capacitor of claim 1, wherein the carbonaceous particles are porous.

7. The wet electrolytic capacitor of claim 1, wherein the inorganic particles have a resistivity of less than about 1×

10⁵ ohm-cm at about 20°

C.

8. The wet electrolytic capacitor of claim 1, wherein the inorganic particles contain a niobium oxide having an atomic ratio of niobium to oxygen of 1:

less than 2.5.

9. The wet electrolytic capacitor of claim 8, wherein the niobium oxide has an atomic ratio of niobium to oxygen of 1:

less than 1.5.

10. The wet electrolytic capacitor of claim 8, wherein the niobium oxide is selected from the group consisting of Nb_0.7, NbO_1.0, NbO_1.1, and NbO₂.

11. The wet electrolytic capacitor of claim 8, wherein the niobium oxide has an atomic ratio of niobium to oxygen of 1:

0.5±

0.2.

12. The wet electrolytic capacitor of claim 8, wherein the niobium oxide is NbO₂.

13. The wet electrolytic capacitor of claim 1, wherein the inorganic particles contain tantalum.

14. The wet electrolytic capacitor of claim 1, wherein the inorganic particles have a median size of less than about 20 micrometers.

15. The wet electrolytic capacitor of claim 1, wherein the inorganic particles have a median size of less than about 5 micrometers.

16. The wet electrolytic capacitor of claim 1, wherein the ratio of the median particle size of the carbonaceous particles to the median particle size of the inorganic particles is from about 1.5:

1 to about 50;

1.

17. The wet electrolytic capacitor of claim 1, wherein the ratio of the median particle size of the carbonaceous particles to the median particle size of the inorganic particles is from about 4:

1 to about 15;

1.

18. The wet electrolytic capacitor of claim 1, wherein the weight ratio of the inorganic particles to the carbonaceous particles in the coating is from about 0.5:

1 to about 50;

1.

19. The wet electrolytic capacitor of claim 1, wherein the coating contains a single layer.

20. The wet electrolytic capacitor of claim 1, wherein the coating contains two or more layers.

21. The wet electrolytic capacitor of claim 20, wherein one of the layers contains primarily inorganic particles and another layer contains a mixture of inorganic particles and carbonaceous particles.

22. The wet electrolytic capacitor of claim 1, wherein the carbonaceous particles are surrounded by the inorganic particles.

23. The wet electrolytic capacitor of claim 1, further comprising a plurality of metal particles overlying the substrate.

24. The wet electrolytic capacitor of claim 1, wherein the substrate comprises a metal selected from the group consisting of tantalum, niobium, aluminum, nickel, hafnium, titanium, copper, silver, and combinations thereof.

25. The wet electrolytic capacitor of claim 1, wherein the electrolyte is an aqueous solution containing an acid.

26. The wet electrolytic capacitor of claim 1, wherein the anode comprises tantalum or niobium.

27. The wet electrolytic capacitor of claim 26, wherein the anode comprises niobium oxide.

28. The wet electrolytic capacitor of claim 1, wherein the capacitor has an ESR of less than about 200 milliohms at a frequency of 120 Hertz.

29. The wet electrolytic capacitor of claim 1, wherein the ratio of the cathode capacitance to the anode capacitance is at least about 50.

30. The wet electrolytic capacitor of claim 1, wherein the ratio of the cathode capacitance to the anode capacitance is at least about 100.

31. A method for forming a wet electrolytic capacitor, the method comprising:

applying a coating formulation to a substrate of a cathode;

sintering the coating formulation to form a cathode coating, the cathode coating comprising carbonaceous particles and inorganic particles; and

disposing an electrolyte between the cathode and an anode.

32. The method of claim 31, wherein the inorganic particles contain a niobium oxide having an atomic ratio of niobium to oxygen of 1:

less than 2.5.

33. The method of claim 32, wherein the niobium oxide has an atomic ratio of niobium to oxygen of 1:

0.5±

0.2.

34. The method of claim 32, wherein the niobium oxide is NbO₂.

35. The method of claim 31, wherein the inorganic particles contain tantalum.

36. The method of claim 31, wherein the coating formulation has a solids content of from about 20% to about 80% by weight.

37. The method of claim 31, wherein the metal substrate is dipped into the coating formulation.

38. The method of claim 31, wherein the coating formulation is sintered at a temperature of from about 500°

C. to about 2400°

C.

39. The method of claim 31, wherein the coating formulation is sintered at a temperature of from about 900°

C. to about 1200°

C.

40. The method of claim 31, wherein the coating formulation is sintered at a pressure of less than about 200 millitorr.

41. The method of claim 31, wherein the coating formulation is sintered at a pressure of less than about 50 millitorr.

42. The method of claim 31, further comprising pre-coating the substrate with a plurality of metal particles prior to application of the coating formulation.