Low freezing electrolyte for an electrolytic capacitor
View Patent ↗An electrolytic capacitor comprising an anode, cathode and an electrolyte. The electrolyte comprises: about 35-60%, by weight water; about 10-55%, by weight organic solvent; about 0.05 to 10%, by weight, sulphuric acid; about 0.05 to 10%, by weight, boric acid; and about 0.05 to 10%, by weight, phosphorus oxy acid.
1. A method for providing a capacitor comprising the steps of:
providing a tantalum anode;
providing a cathode;
activating said anode and said cathode with an electrolyte comprising:
about 35-60%, by weight water;
about 10-55%, by weight organic solvent excluding ethylene glycol, formamide, dimethyl formamide and γ-butyrolactone;
about 0.05 to 30%, by weight, at least one acid selected from sulphuric, boric acid and phosphorus oxy acid;
wherein said electrolyte has a pH below about 5 and a freezing point below about −30° C.
2. A method according to claim 1 wherein said phosphorus oxy acid is orthophosphoric acid.
3. A method according to claim 1 wherein said phosphorus oxy acid is phosphorous acid.
4. A method according to claim 1 wherein said electrolyte has a pH of less than about 4 .
5. A capacitor prepared by the method according to claim 1 .
6. A method according to claim 1 wherein said acid comprises sulphuric acid and at least one acid selected from boric acid and phosphorus oxy acid.
7. A method according to claim 6 wherein said acid comprises sulphuric acid, boric acid and phosphorus oxy acid.
8. A method according to claim 7 wherein said electrolytic solution comprises: about 0.05 to 10%, by weight, sulphuric acid;
about 0.05 to 10%, by weight, boric acid; and
about 0.05 to 10%, by weight, phosphorus oxy acid.
9. A method according to claim 1 wherein said solvent is selected from a group consisting of glycerol, 1,3-propane diol; 2-methyl-1,3-propane diol;
propylene glycol; polyethylene glycol monomethyl ether; N-alkyl-2-pyrrolidone and diethylene glycol.
10. A method according to claim 9 wherein said solvent is glycerol.
11. A method according to claim 9 wherein said solvent is 1,3-propane diol.
12. A method according to claim 9 wherein said solvent is 2-methyl-1,3-propane diol.
13. A method according to claim 9 wherein said solvent is propylene glycol.
14. A method according to claim 9 wherein said solvent is polyethylene glycol monomethyl ether.
15. A method according to claim 9 wherein said cathode is a conductive metal provided with a semiconductive or metal-like conductive coating.
16. A method according to claim 15 wherein said cathode comprises a porous ruthenium oxide film provided on a titanium substrate.
17. A method according to claim 15 wherein said cathode is at least one element chosen from a group consisting of an oxide, a nitride, a carbide of a metal or an activated carbon.
18. A method according to claim 17 wherein said cathode comprises a metal selected from a group consisting of tantalum, titanium, nickel, iridium, platinum, palladium, gold, silver, cobalt, molybdenum, ruthenium, manganese, tungsten, iron, zirconium, hafnium, rhodium, vanadium, osmium and niobium.
19. A method according to claim 18 wherein when said acid comprises sulphuric acid, sufficient buffering material is added to raise the pH to a level sufficient to avoid dissolution of components of manufacture of said capacitor.