Neutral electrolyte for a wet electrolytic capacitor

• US 7,460,356 B2
• Filed: 03/20/2007
• Issued: 12/02/2008
• Est. Priority Date: 03/20/2007
• Status: Active Grant

• Current Assignee: Kyocera AVX Components Corporation (Kyocera Corporation)
• Original Assignee: AVX Corporation (Kyocera Corporation)
• Inventors: Ning, Gang
• Primary Examiner(s): Thomas; Eric
• Assistant Examiner(s): Sinclair; David M
• Application Number:
  US11/725,965
• Publication Number:
  US 20080232029A1
• Time in Patent Office: 623 Days
• Field of Search: 252/62.2, 361/505, 361/503, 361/504, 361/507
• US Class Current: 361/507
• CPC Class Codes: H01G 9/035 Liquid electrolytes, e.g. impregnating materials H01G11/54 takes precedence
• CPC Class Codes: H01G 9/145 Liquid electrolytic capacitors H01G11/00 takes precedence

Abstract

A working electrolyte for use in a wet electrolytic capacitor is provided. The electrolyte is relatively neutral and has a pH of from about 5.0 to about 8.0, in some embodiments from about 5.5 to about 7.5, and in some embodiments, from about 6.0 to about 7.5. Despite possessing a neutral pH level, the electrolyte is nevertheless electrically conductive. For instance, the electrolyte may have an electrical conductivity of about 10 milliSiemens per centimeter (“mS/cm”) or more, in some embodiments about 30 mS/cm or more, and in some embodiments, from about 40 mS/cm to about 100 mS/cm, determined at a temperature of 25° C.

Claims

1. A wet electrolytic capacitor comprising:

an anode;

a cathode current collector; and

a working electrolyte disposed between the cathode current collector and the anode, wherein the working electrolyte comprises a nitroaromatic depolarizer in an amount of from about 10 to about 200 parts per million of the electrolyte, and wherein the electrolyte has a pH of from about 5.0 to about 8.0 and an electrical conductivity of from about 10 milliSiemens per centimeter or more, determined at a temperature of 25°

C.

2. The wet electrolytic capacitor of claim 1, wherein the pH is from about 5.5 to about 7.5.

3. The wet electrolytic capacitor of claim 1, wherein the pH is from about 6.0 to about 7.5.

4. The wet electrolytic capacitor of claim 1, wherein the electrical conductivity is about 30 milliSiemens per centimeter or more.

5. The wet electrolytic capacitor of claim 1, wherein the working electrolyte comprises an aqueous solvent.

6. The wet electrolytic capacitor of claim 5, wherein the aqueous solvent constitutes from about 30 wt. % to about 90 wt. % of the working electrolyte.

7. The wet electrolytic capacitor of claim 5, wherein the aqueous solvent includes deionized water.

8. The wet electrolytic capacitor of claim 1, wherein the working electrolyte includes an ionic compound, the ionic compound including an inorganic acid, organic acid, an anhydride or salt thereof, or mixtures of any of the foregoing.

9. The wet electrolytic capacitor of claim 1, wherein the working electrolyte further comprises a basic pH modifier.

10. The wet electrolytic capacitor of claim 1, wherein the working electrolyte has a freezing point of about −

20°

C. or less.

11. The wet electrolytic capacitor of claim 1, wherein the working electrolyte has a boiling point of about 85°

C. or more.

12. The wet electrolytic capacitor of claim 1, wherein the nitroaromatic depolarizer includes an alkyl-substituted nitrobenzoic acid, an anhydride or salt thereof, or mixtures of any of the foregoing.

13. The wet electrolytic capacitor of claim 12, wherein the alkyl-substituted nitrobenzoic acid includes 2-methyl-3-nitrobenzoic acid, 2-methyl-6-nitrobenzoic acid, 3-methyl-2-nitrobenzoic acid, 3-methyl-4-nitrobenzoic acid, 3-methyl-6-nitrobenzoic acid, or 4-methyl-3-nitrobenzoic acid.

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

15. The wet electrolytic capacitor of claim 1, wherein the anode includes a valve metal oxide having an atomic ratio of metal to oxygen of 1:

less than 1.5.

16. The wet electrolytic capacitor of claim 15, wherein the valve metal oxide includes niobium oxide.

17. The wet electrolytic capacitor of claim 1, further comprising a coating overlying the current collector that comprises electrochemically-active particles.

18. The wet electrolytic capacitor of claim 1, wherein the current collector includes a metal.

19. The wet electrolytic capacitor of claim 1, wherein the capacitor exhibits an ESR of about 1500 milliohms or less, measured at a frequency of 1000 Hz.

20. The wet electrolytic capacitor of claim 1, wherein the capacitor exhibits an ESR of about 500 milliohms or less, measured at a frequency of 1000 Hz.

21. A working electrolyte for an electrolytic capacitor comprising from about 1 to about 500 parts per million of a nitroaromatic depolarizer, the nitroaromatic depolarizer including an alkyl-substituted nitrobenzoic acid, an anhydride or salt thereof, or mixtures of any of the foregoing, wherein the working electrolyte has a pH of from about 5.0 to about 8.0.

22. The working electrolyte of claim 21, wherein the electrolyte has a pH of from about 5.5 to about 7.5.

23. The working electrolyte of claim 21, wherein the electrolyte has a pH of from about 6.0 to about 7.5.

24. The working electrolyte of claim 21, wherein the electrical conductivity is about 10 milliSiemens per centimeter or more.

25. The working electrolyte of claim 21, wherein the electrical conductivity is about 30 milliSiemens per centimeter or more.

26. The working electrolyte of claim 21, wherein the working electrolyte comprises an aqueous solvent.

27. The working electrolyte of claim 21, wherein the working electrolyte includes an inorganic acid, organic acid, an anhydride or salt thereof, or mixtures of any of the foregoing.

28. The working electrolyte of claim 21, wherein the working electrolyte has a freezing point of about −

20°

C. or less and a boiling point of about 85°

C. or more.

29. The working electrolyte of claim 21, wherein the nitroaromatic depolarizer includes 2-methyl-3-nitrobenzoic acid, 2-methyl-6-nitrobenzoic acid, 3-methyl-2-nitrobenzoic acid, 3-methyl-4-nitrobenzoic acid, 3-methyl-6-nitrobenzoic acid, 4-methyl-3-nitrobenzoic acid, an anhydride or salt thereof, or mixtures of any of the foregoing.

30. The working electrolyte of claim 21, wherein the nitroaromatic depolarizer constitutes 10 to about 200 parts per million of the working electrolyte.

31. The working electrolyte of claim 21, wherein the nitroaromatic depolarizer constitutes 20 to about 150 parts per million of the working electrolyte.