Electrolytes for capacitors

Abstract

The present invention is directed to an electrolyte for an electrolytic capacitor. The capacitor has an electrolytic anode and an electrochemical cathode. The electrolyte has water, a water soluble organic salt, and a relatively weak organic acid. This electrolyte is chemically compatible to aluminum and tantalum oxide dielectrics and withstands higher voltage while maintaining good conductivity. This makes the electrolyte especially useful for high voltage applications, such as occur in an implantable cardiac defibrillator.

What is claimed is: 
     
      
       1. An electrolyte for an electrical energy storage device, the electrolyte consisting essentially of: 
       
         a) water; 
         b) an organic acid; and 
         c) an ammonium salt of the organic acid. 
       
      
     
     
      
       2. The electrolyte of  claim 1  wherein the water present in a range of, by weight, anout 1% to about 80%. 
      
     
     
      
       3. The electrolyte of  claim 1  wherein the acid has the general formula of c n H 2+n O 2  (where n=2 to 7). 
      
     
     
      
       4. The electrolyte of  claim 1  wherein the acid is selected from the group consisting of isobutyric acid, butyric acid, propionic acid, valeric acid, methylbutyric acid, trimethylacetic acid, and mixtures thereof. 
      
     
     
      
       5. The electrolyte of  claim 1  wherein the acid is present in a range of, by weight, about 1% to about 80%. 
      
     
     
      
       6. The electrolyte of  claim 1  wherein the ammonium salt is selected from the group consisting of ammonium isobutyrate, ammonium butyrate, ammonium propionate, ammonium valerate, ammonium methylbutyrate, ammonium trimethylacetate, and mixtures thereof. 
      
     
     
      
       7. The electrolyte of  claim 1  wherein the ammonium salt is present in a range of, by weight, 0.5% to about 50%. 
      
     
     
      
       8. An electrolyte for a capacitor, the electrolyte comprising: 
       
         a) water; 
         b) an organic solvent; 
         c) an organic acid; and 
         d) an ammonium salt of the organic acid. 
       
      
     
     
      
       9. The electrolyte of  claim 8  wherein the organic solvent is selected from the group consisting of glycols, glycol ethers, polyethylene glycols, amides, esters, nitriles, linear carbonates, cyclic carbonates, and mixtures thereof. 
      
     
     
      
       10. The electrolyte of  claim 9  wherein the glycol is selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, and mixtures thereof. 
      
     
     
      
       11. The electrolyte of  claim 9  wherein the glycol ether is selected from the group consisting of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol methyl ether, diethylene glycol methyl ether, dipropylene glycol methyl ether, glycol monobutyl ether, and mixtures thereof. 
      
     
     
      
       12. The electrolyte of  claim 9  wherein the amide is selected from the group consisting of formamide, dimethyl formamide, diethyl formamide, ethyl formamide, dimethyl acetamide, methyl acetamide, and mixtures thereof. 
      
     
     
      
       13. The electrolyte of  claim 9  wherein the ester is selected from the group consisting of γ-butyrolactone, γ-valerolactone, N-methyl-2-pyrrolidone, and mixtures thereof. 
      
     
     
      
       14. The electrolyte of  claim 9  wherein the nitrile is selected from the group consisting of acetonitrile, propionitrile, and mixtures thereof. 
      
     
     
      
       15. The electrolyte of  claim 9  wherein the linear and cyclic carbonates are selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl propyl carbonate, methyl propyl carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, and mixtures thereof. 
      
     
     
      
       16. The electrolyte of  claim 8  wherein the organic acid is selected from the group consisting of isobutyric acid, butyric acid, propionic acid, valeric acid, methylbutyric acid, trimethylacetic acid, and mixtures thereof. 
      
     
     
      
       17. The electrolyte of  claim 8  wherein the ammonium salt is selected from the group consisting of ammonium isobutyrate, ammonium butyrate, ammonium propionate, ammonium valerate, ammonium methylbutyrate, ammonium trimethylacetate, and mixtures thereof. 
      
     
     
      
       18. A capacitor, which comprises: 
       
         a) an anode of a valve metal; 
         b) an electrochemical cathode selected from the group consisting of a transition metal oxide, a transition metal nitride, a transition metal carbide and a transition metal carbon nitride; and 
         c) an electrolyte for the anode and the cathode, the electrolyte comprising:
 i) water; 
 ii) an organic solvent; 
 iii) an organic acid; and 
 iv) an ammonium salt of the organic acid. 
 
       
      
     
     
      
       19. The capacitor of  claim 18  wherein the organic acid is selected from the group consisting of isobutyric acid, butyric acid, propionic acid, valeric acid, methylbutyric acid, trimethylacetic acid, and mixtures thereof. 
      
     
     
      
       20. The capacitor of  claim 18  wherein the ammonium salt is selected from the group consisting of ammonium isobutyrate, ammonium butyrate, ammonium propionate, ammonium valerate, ammonium methylbutyrate, ammonium trimethylacetate, and mixtures thereof. 
      
     
     
      
       21. The capacitor of  claim 18  wherein the organic solvent is selected from the group consisting of glycols, glycol ethers, polyethylene glycols, amides, esters, nitriles, linear carbonates, cyclic carbonates, and mixtures thereof. 
      
     
     
      
       22. The capacitor of  claim 21  wherein the glycol is selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, and mixtures thereof. 
      
     
     
      
       23. The capacitor of  claim 21  wherein the glycol ether is selected from the group consisting of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol methyl ether, diethylene glycol methyl ether, dipropylene glycol methyl ether, glycol monobutyl ether, and mixtures thereof. 
      
     
     
      
       24. The capacitor of  claim 21  wherein the amide is selected from the group consisting of formamide, dimethyl formamide, diethyl formamide, ethyl formamide, dimethyl acetamide, methyl acetamide, and mixtures thereof. 
      
     
     
      
       25. The capacitor of  claim 21  wherein the ester is selected from the group consisting of y-butyrolactone, γ-valerolactone, N-methyl-2-pyrrolidone, and mixtures thereof. 
      
     
     
      
       26. The capacitor of  claim 21  wherein the nitrile is selected from the group consisting of acetonitrile, propionitrile, and mixtures thereof. 
      
     
     
      
       27. The capacitor of  claim 21  wherein the linear and cyclic carbonates are selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl propyl carbonate, methyl propyl carbonate, propylene carbonate, ethylene carbonate, butylenes carbonate, vinylene carbonate, and mixtures thereof. 
      
     
     
      
       28. The capacitor of  claim 18  wherein the valve metal is selected from the group consisting of tantalum, vanadium, niobium, aluminum, titanium, zirconium, hafnium, and mixtures thereof. 
      
     
     
      
       29. The capacitor of  claim 18  wherein the transition metal is selected from the group consisting of ruthenium, cobalt, manganese, molybdenum, tungsten, tantalum, iron, niobium, iridium, titanium, zirconium, hafnium, rhodium, vanadium, osmium, palladium, platinum, nickel, and mixtures thereof. 
      
     
     
      
       30. The capacitor of  claim 18  wherein the cathode is of ruthenium oxide and the anode is of tanatlum. 
      
     
     
      
       31. The capacitor of  claim 18  wherein the electrolyte includes at least one of the group consisting of phosphoric acid, trimethylphosphate, triethylphosphate, and triisopropylphosphate. 
      
     
     
      
       32. The capacitor of  claim 18  wherein the electrolyte includes a nitroaromatic compound selected from the group consisting of 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2-nitrobenzonic acid, 3-nitrobenzonic acid, 4-nitrobenzonic acid, 2-nitroacetophenone, 3-nitroacetophenone, 4-nitroacetophenone, 2-nitroanisole, 3-nitroanisole, 4-nitroanisole, 2- nitrobenzaldehyde, 3-nitrobenzaldehyde, 4-nitrobenzaldehyde, 2-nitrobenzyl alcohol, 3-nitrobenzyl alcohol, 4-nitrobenzyl alcohol, 2-nitrophthalic acid, 3-nitrophthalic acid, 4-nitrophthalic acid, and mixtures thereof. 
      
     
     
      
       33. A method for providing an electrolyte, consisting essentially of the steps of: 
       
         a) providing water; 
         b) providing an organic acid; and 
         c) providing an ammonium salt of the organic acid. 
       
      
     
     
      
       34. The method of  claim 33  including selecting the organic acid from the group consisting of isobutyric acid, butyric acid, propionic acid, valeric acid, methylbutyric acid, trimethylacetic acid, and mixtures thereof. 
      
     
     
      
       35. The method of  claim 33  including providing ammounium hydroxide therein to provide the ammonium salt. 
      
     
     
      
       36. The method of  claim 33  including selecting the ammonium salt from the group consisting of ammonium isobutyrate, ammonium butyrate, ammonium propionate, ammonium valerate, ammonium methylbutyrate, ammonium trimethylacetate, and mixtures thereof. 
      
     
     
      
       37. The method of  claim 33  further including an organic solvent selected from the group consisting of glycols, glycol ethers, polyethylene glycols, amides, esters, nitriles, linear carbonates, cyclic carbonates, and mixtures thereof. 
      
     
     
      
       38. The method of  claim 37  including selecting the glycol from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, and mixtures thereof. 
      
     
     
      
       39. The method of  claim 37  including selecting the glycol ether from the group consisting of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol methyl ether, diethylene glycol methyl ether, dipropylene glycol methyl ether, glycol monobutyl ether, and mixtures thereof. 
      
     
     
      
       40. The method of  claim 37  including selecting the amide from the group consisting of formamide, dimethyl formamide, diethyl formamide, ethyl formamide, dimethyl acetamide, methyl acetamide, and mixtures thereof. 
      
     
     
      
       41. The method of  claim 37  including selecting the ester from the group consisting of γ-butyrolactone, γ-valerolactone, N-methyl-2-pyrrolidone, and mixtures thereof. 
      
     
     
      
       42. The method of  claim 37  including selecting the nitrile from the group consisting of acetonitrile, propionitrile, and mixtures thereof. 
      
     
     
      
       43. The method of  claim 37  including selecting the linear and cyclic carbonates from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl propyl carbonate, methyl propyl carbonate, propylene carbonate, ethylene carbonate, butylenes carbonate, vinylene carbonate, and mixtures thereof. 
      
     
     
       44. An electrolyte for a capacitor comprising a tantalum anode, the electrolyte consisting of:
 a) water;   b) an organic acid and an ammonium salt of the organic acid, wherein the ammonium salt and its corresponding acid are selected from the group consisting of: ammonium isobutyrate and isobutyric acid, ammonium butyrate and butyric acid, ammonium propionate and propionic acid, ammonium valerate and valeric acid, ammonium methylbutyrate and methylbutyric acid, and ammonium trimethylacetate and trimethylacetic acid; and   c) a nitroaromatic compound selected from the group consisting of 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2-nitrobenzonic acid, 3-nitrobenzonic acid, 4-nitrobenzonic acid, 2-nitroacetophenone, 3-nitroacetophenone, 4-nitroacetophenone, 2-nitroanisole, 3-nitroanisole, 4-nitroanisole, 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, 4-nitrobenzaldehyde, 2-nitrobenzyl alcohol, 3-nitrobenzyl alcohol, 4-nitrobenzyl alcohol, 2-nitrophthalic acid, 3-nitrophthalic acid, 4-nitrophthalic acid, and mixtures thereof,   d) wherein the electrolyte has:
 i) a conductivity in the range of 6.9 to 11.5 mS/cm; 
 ii) a pH in the range of 4.9 to 6.7; 
 iii) an anode breakdown voltage in the range of 370 to 400 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode; and 
 iv) does not generate gas at 105° C. 
   
     
     
       45. The electrolyte of claim 44, wherein the water is present in a range of, by weight, about 1% to about 80%. 
     
     
       46. The electrolyte of claim 44, wherein the acid is present in a range of, by weight, about 1% to about 80%. 
     
     
       47. The electrolyte of claim 44, wherein the ammonium salt is present in a range of, by weight, 0.5% to about 50%. 
     
     
       48. The electrolyte of claim 44, wherein the ammonium salt and its corresponding acid are ammonium isobutyrate and isobutyric acid; and
 wherein the electrolyte having a pH of 4.9 and an anode breakdown voltage of 395 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode.   
     
     
       49. The electrolyte of claim 48, having a conductivity of 7.1 mS/cm. 
     
     
       50. The electrolyte of claim 44, wherein the ammonium salt and its corresponding acid are ammonium isobutyrate and isobutyric acid; and
 wherein the electrolyte having a pH of 5.4 and an anode breakdown voltage of 400 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode.   
     
     
       51. The electrolyte of claim 47, having a conductivity of 6.9 mS/cm. 
     
     
       52. The electrolyte of claim 44, wherein the ammonium salt and its corresponding acid are ammonium isobutyrate and isobutyric acid; and
 wherein the electrolyte having a pH of 5.2 and an anode breakdown voltage of 388 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode.   
     
     
       53. The electrolyte of claim 52, having a conductivity of 7.9 mS/cm. 
     
     
       54. The electrolyte of claim 44, wherein the ammonium salt and its corresponding acid are ammonium isobutyrate and isobutyric acid; and
 wherein the electrolyte having a pH of 5.7 and an anode breakdown voltage of 380 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode.   
     
     
       55. The electrolyte of claim 54, having a conductivity of 11.5 mS/cm. 
     
     
       56. The electrolyte of claim 45, wherein the ammonium salt and its corresponding acid are ammonium isobutyrate and isobutyric acid; and
 wherein the electrolyte having a pH of 6.7 and an anode breakdown voltage of 370 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode.   
     
     
       57. The electrolyte of claim 56, having a conductivity of 10.8 mS/cm. 
     
     
       58. An electrolyte for a capacitor comprising a tantalum anode, the electrolyte consisting of:
 a) water;   b) an organic solvent selected from the group consisting of glycols, glycol ethers, polyethylene glycols, amides, esters, nitriles, linear carbonates, cyclic carbonates, and mixtures thereof, wherein:
 i) the glycol is selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, and mixtures thereof; 
 ii) the glycol ether is selected from the group consisting of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol methyl ether, diethylene glycol methyl ether, dipropylene glycol methyl ether, glycol monobutyl ether, and mixtures thereof; 
 iii) the amide is selected from the group consisting of formamide, dimethyl formamide, diethyl formamide, ethyl formamide, dimethyl acetamide, methyl acetamide, and mixtures thereof; 
 iv) the ester is selected from the group consisting of γ-butyrolactone, γ-valerolactone, N-methyl-2-pyrrolidone, and mixtures thereof; 
 v) the nitrile is selected from the group consisting of acetonitrile, propionitrile, and mixtures thereof; and 
 vi) the linear and cyclic carbonates are selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl propyl carbonate, methyl propyl carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, and mixtures thereof; and 
   c) an organic acid and an ammonium salt of the organic acid, wherein the ammonium salt and its corresponding acid are selected from the group consisting of: ammonium isobutyrate and isobutyric acid, ammonium butyrate and butyric acid, ammonium propionate and propionic acid, ammonium valerate and valeric acid, ammonium methylbutyrate and methylbutyric acid, and ammonium trimethylacetate and trimethylacetic acid; and   d) a nitroaromatic compound selected from the group consisting of 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2-nitrobenzonic acid, 3-nitrobenzonic acid, 4-nitrobenzonic acid, 2-nitroacetophenone, 3-nitroacetophenone, 4-nitroacetophenone, 2-nitroanisole, 3-nitroanisole, 4-nitroanisole, 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, 4-nitrobenzaldehyde, 2-nitrobenzyl alcohol, 3-nitrobenzyl alcohol, 4-nitrobenzyl alcohol, 2-nitrophthalic acid, 3-nitrophthalic acid, 4-nitrophthalic acid, and mixtures thereof,   e) wherein the electrolyte has:
 i) a conductivity in the range of 6.9 to 11.5 mS/cm; 
 ii) a pH in the range of 4.9 to 6.7; 
 iii) an anode breakdown voltage in the range of 370 to 400 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode; and 
 iv) does not generate gas at 105° C. 
   
     
     
       59. A capacitor, which comprises:
 a) an anode of tantalum;   b) an electrochemical cathode of ruthenium oxide; and   c) an electrolyte for the anode and the cathode, the electrolyte consisting of:
 i) water; 
 ii) an organic solvent selected from the group consisting of glycols, glycol ethers, polyethylene glycols, amides, esters, nitriles, linear carbonates, cyclic carbonates, and mixtures thereof, wherein:
 A) the glycol is selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, and mixtures thereof; 
 B) the glycol ether is selected from the group consisting of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol methyl ether, diethylene glycol methyl ether, dipropylene glycol methyl ether, glycol monobutyl ether, and mixtures thereof; 
 C) the amide is selected from the group consisting of formamide, dimethyl formamide, diethyl formamide, ethyl formamide, dimethyl acetamide, methyl acetamide, and mixtures thereof; 
 D) the ester is selected from the group consisting of γ-butyrolactone, γ-valerolactone, N-methyl-2-pyrrolidone, and mixtures thereof; 
 E) the nitrile is selected from the group consisting of acetonitrile, propionitrile, and mixtures thereof; and 
 F) the linear and cyclic carbonates are selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ethyl propyl carbonate, methyl propyl carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, and mixtures thereof; and 
 
 iii) an organic acid and an ammonium salt of the organic acid, wherein the ammonium salt and its corresponding acid are selected from the group consisting of: ammonium isobutyrate and isobutyric acid, ammonium butyrate and butyric acid, ammonium propionate and propionic acid, ammonium valerate and valeric acid, ammonium methylbutyrate and methylbutyric acid, and ammonium trimethylacetate and trimethylacetic acid; 
 iv) a nitroaromatic compound selected from the group consisting of 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2-nitrobenzonic acid, 3-nitrobenzonic acid, 4-nitrobenzonic acid, 2-nitroacetophenone, 3-nitroacetophenone, 4-nitroacetophenone, 2-nitroanisole, 3-nitroanisole, 4-nitroanisole, 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, 4-nitrobenzaldehyde, 2-nitrobenzyl alcohol, 3-nitrobenzyl alcohol, 4-nitrobenzyl alcohol, 2-nitrophthalic acid, 3-nitrophthalic acid, 4-nitrophthalic acid, and mixtures thereof; 
 v) an additive selected from the group consisting of phosphoric acid, trimethylphosphate, triethylphosphate, and triisopropylphosphate; and 
 vi) wherein the electrolyte has:
 A) a conductivity in the range of 6.9 to 11.5 mS/cm; 
 B) a pH in the range of 4.9 to 6.7; 
 C) an anode breakdown voltage in the range of 370 to 400 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode; and 
 D) does not generate gas at 105° C. 
 
   
     
     
       60. The capacitor of claim 59, wherein the ammonium salt and its corresponding acid for the electrolyte are ammonium isobutyrate and isobutyric acid; and
 wherein the electrolyte has a pH of 4.9 and an anode breakdown voltage of 395 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode.   
     
     
       61. The capacitor of claim 60, wherein the electrolyte has a conductivity of 7.1 mS/cm. 
     
     
       62. The capacitor of claim 59, wherein the ammonium salt and its corresponding acid of the electrolyte are ammonium isobutyrate and isobutyric acid; and
 wherein the electrolyte has a pH of 5.4 and an anode breakdown voltage of 400 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode.   
     
     
       63. The capacitor of claim 62, wherein the electrolyte has a conductivity of 6.9 mS/cm. 
     
     
       64. The capacitor of claim 59, wherein the ammonium salt and its corresponding acid of the electrolyte are ammonium isobutyrate and isobutyric acid; and
 wherein the electrolyte has a pH of 5.2 and an anode breakdown voltage of 388 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode.   
     
     
       65. The capacitor of claim 64, wherein the electrolyte has a conductivity of 7.9 mS/cm. 
     
     
       66. The capacitor of claim 59, wherein the ammonium salt and its corresponding acid of the electrolyte are ammonium isobutyrate and isobutyric acid; and
 wherein the electrolyte has a pH of 5.7 and an anode breakdown voltage of 380 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode.   
     
     
       67. The capacitor of claim 66, wherein the electrolyte has a conductivity of 11.5 mS/cm. 
     
     
       68. The capacitor of claim 59, wherein the ammonium salt and its corresponding acid of the electrolyte are ammonium isobutyrate and isobutyric acid; and
 wherein the electrolyte has a pH of 6.7 and an anode breakdown voltage of 370 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode.   
     
     
       69. The capacitor of claim 68, wherein the electrolyte has a conductivity of 10.8 mS/cm. 
     
     
       70. An electrolyte for a capacitor comprising a tantalum anode, the electrolyte consisting of:
 a) water;   b) ammonium isobutyrate and isobutyric acid; and   c) 4-nitrophenol (p-nitrophenol),   d) wherein the electrolyte has:
 i) a conductivity in the range of 6.9 to 11.5 mS/cm; 
 ii) a pH in the range of 4.9 to 6.7; 
 iii) an anode breakdown voltage in the range of 370 to 400 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode; and 
 iv) does not generate gas at 105° C. 
   
     
     
       71. A capacitor, which comprises:
 a) an anode of tantalum;   b) an electrochemical cathode of ruthenium oxide; and   c) an electrolyte for the anode and the cathode, the electrolyte consisting of:
 i) water; 
 ii) an organic solvent; 
 iii) ammonium isobutyrate and isobutyric acid; and 
 iv) 4-nitrophenol (p-nitrophenol), 
 v) wherein the electrolyte has:
 A) a conductivity in the range of 6.9 to 11.5 mS/cm; 
 B) a pH in the range of 4.9 to 6.7; 
 C) an anode breakdown voltage in the range of 370 to 400 volts when the electrolyte is at room temperature and the breakdown voltage is measured using a tantalum anode; and 
 D) does not generate gas at 105° C.