Alkaline cells having low toxicity rechargeable zinc electrodes
View Patent ↗A nickel zinc alkaline cell has a zinc oxide negative electrode supported on a conductive substrate, an alkaline electrolyte, and a positive electrode having nickel hydroxide paste supported on a conductive substrate. The negative zinc oxide electrode comprises 85% to 95% zinc oxide powder, 1% to 10% bismuth oxide, 1% to 2% of a binder, and 0.05% to 5% by weight of a fluoride salt chosen from the group consisting of: sodium, potassium, rubidium, caesium, lithium, and mixtures thereof. Typically, the fluoride salt is potassium fluoride, in the amount of 0.5% by weight of the zinc oxide.
1. A nickel zinc alkaline cell having a zinc oxide negative electrode supported on a conductive substrate, an alkaline electrolyte, and a positive electrode having nickel hydroxide paste supported on a conductive substrate;
wherein said negative zinc oxide electrode comprises 85% to 95% zinc oxide powder, 1% to 10% bismuth oxide, 1% to 2% of a binder, and 0.05% to 5% by weight of a fluoride salt; and
wherein said fluoride salt is a salt of a metal chosen from the group consisting of: sodium, potassium, rubidium, caesium, lithium, and mixtures thereof.
2. The nickel zinc alkaline cell of claim 1 , wherein said fluoride salt is potassium fluoride.
3. The nickel zinc alkaline cell of claim 1 , wherein said fluoride salt is potassium fluoride in the amount of 0.05% to 4.5% by weight of said zinc oxide.
4. The nickel zinc alkaline cell of claim 1 , wherein said fluoride salt is potassium fluoride in the amount of 0.5% by weight of said zinc oxide.
5. The nickel zinc alkaline cell of claim 3 , wherein said bismuth oxide is present in the amount of 3% to 9% by weight of said zinc oxide.
6. The nickel zinc alkaline cell of claim 4 , wherein said bismuth oxide is present in the amount of 3% to 9% by weight of said zinc oxide.
7. The nickel zinc alkaline cell of claim 1 , wherein said positive electrode further comprises a conductivity enhancement additive chosen from the group consisting of: 2% to 3% by weight of nickel metal powder, 2% to 3% by weight of cobalt metal powder, and mixtures thereof.
8. The nickel zinc alkaline cell of claim 4 , wherein said positive electrode further comprises a conductivity enhancement additive chosen from the group consisting of: 2% to 3% by weight of nickel metal powder, 2% to 3% by weight of cobalt metal powder, and mixtures thereof.
9. The nickel zinc alkaline cell of claim 1 , wherein said alkaline electrolyte comprises a mixture of sodium hydroxide, potassium hydroxide, lithium hydroxide, and an acid chose from the group consisting of: boric acid, phosphoric acid, and mixtures thereof:
wherein when boric acid is present, it has a concentration of 0.6 to 1.3 moles per liter;
wherein the stoichiometric excess of alkali hydroxide is between 2.5 moles and 5.0 moles; and
wherein the electrolyte contains 0.05 to 3.0 moles of lithium hydroxide.
10. The nickel zinc alkaline cell of claim 4 , wherein said alkaline electrolyte comprises a mixture of sodium hydroxide, potassium hydroxide, lithium hydroxide, and an acid chose from the group consisting of: boric acid, phosphoric acid, and mixtures thereof,
wherein when boric acid is present, it has a concentration of 0.6 to 1.3 moles per liter;
wherein the stoichiometric excess of alkali hydroxide is between 2.5 moles and 5.0 moles; and
wherein the electrolyte contains 0.05 to 3.0 moles of lithium hydroxide.
11. A nickel zinc alkaline cell having a zinc oxide negative electrode supported on a conductive substrate, alkaline electrolyte, and a positive electrode supported on a conductive substrate; wherein said negative electrode as- constructed comprises zinc oxide, a binder, and 0 . 043 % to 3 . 8 % by weight of a fluoride salt; and wherein said fluoride salt is a salt of a metal chosen from the group consisting of: sodium, potassium, rubidium, caesium, lithium, and mixtures thereof.
12. The nickel zinc alkaline cell of claim 11 , wherein said fluoride salt is potassium fluoride.
13. The nickel zinc alkaline cell of claim 11 , wherein said fluoride salt is potassium fluoride in the amount of 0 . 05 % to 4 . 5 % by weight of said zinc oxide.
14. The nickel zinc alkaline cell of claim 13 , wherein said negative electrode further comprises bismuth oxide in the amount of 1 % to 10 % by weight.
15. The nickel zinc alkaline cell of claim 11 , wherein said positive electrode further comprises a conductivity enhancement additive selected from the group consisting of 2 % to 3 % by weight of nickel metal powder, 2 % to 3 % by weight of cobalt metal powder, and mixtures thereof.
16. The nickel zinc alkaline cell of claim 11 , wherein the alkaline electrolyte comprises hydroxide in stoichiometric excess over an acid selected from the group consisting of boric acid, phosphoric acid, and mixtures thereof.
17. The nickel zinc alkaline cell of claim 16 , wherein the alkaline electrolyte comprises hydroxide in stoichiometric excess over phosphoric acid.
18. The nickel zinc alkaline cell of claim 11 , wherein said fluoride is 0 . 05 % to 1 . 5 % by weight of the negative electrode.
19. The nickel zinc alkaline cell of claim 11 , wherein said fluoride is about 0 . 5 % by weight of the negative electrode.
20. A negative electrode supported on a conductive substrate comprising zinc oxide, bismuth oxide, a binder, and 0 . 043 % to 3 . 8 % by weight of a fluoride salt; and wherein said fluoride salt is a salt of a metal chosen from the group consisting of: sodium, potassium, rubidium, caesium, lithium, and mixtures thereof.
21. The negative electrode of claim 20 , wherein said fluoride salt is potassium fluoride.
22. The negative electrode of claim 20 , wherein said fluoride salt is potassium fluoride in the amount of 0 . 05 % to 4 . 5 % by weight of said zinc oxide.
23. The negative electrode of claim 20 , wherein said bismuth oxide is present in the amount of 1 % to 10 % by weight.