PASTED NICKEL HYDROXIDE ELECTRODE FOR RECHARGEABLE NICKEL-ZINC BATTERIES
Active material for a positive electrode of a rechargeable alkaline electrochemical cell is made with nickel hydroxide particles or cobalt-coated nickel hydroxide particles treated with strongly oxidizing reagents such as alkali metal persulfate in alkaline solution. The active material also may be made with cobalt-coated nickel hydroxide particles having a high percentage of cobalt(III) on a surface or an average cobalt oxidation state of about 3 measured across the particles. The treated nickel hydroxide or cobalt-coated nickel hydroxide decreases the cobalt solubility in the alkaline electrolyte and increases the high-rate charge and discharge capability. The lower cobalt solubility decreases cobalt migration that can increase self discharge and lead to premature failure.
1 . A method of making a nickel containing positive electrode for a battery, the method comprising:
(a) mixing an alkali metal hydroxide solution, a strong oxidizing agent, and a nickel hydroxide or a cobalt-coated nickel hydroxide powder;
(b) separating the wet nickel hydroxide or a cobalt-coated nickel hydroxide powder from a reaction product or an unreacted oxidizing agent;
(c) preparing an active material paste using the separated nickel hydroxide or cobalt-coated nickel hydroxide powder and cobalt metal; and,
(d) incorporating the paste into a nickel electrode;
wherein the mixing operation is performed at a temperature of between about 20° C. and about 100° C.
2 . The method of claim 1 , wherein the separating operation comprises:
(a) washing the mixture; and,
(b) drying the mixture.
3 . The method of claim 1 , wherein the separating operation comprises:
(a) filtering the mixture; and,
(b) washing the filtered mixture.
4 . The method of claim 1 , wherein the alkali metal hydroxide solution is selected from the group consisting of sodium hydroxide solution, potassium hydroxide solution, and lithium hydroxide solution.
5 . The method of claim 1 , wherein the strong oxidizing agent is an alkali metal persulfate.
6 . The method of claim 1 , wherein the strong oxidizing agent is sodium persulfate or potassium persulfate.
7 . The method of claim 1 , wherein the strong oxidizing agent is selected from the group consisting of a persulfate, a perchlorate, ozone, and a permanganate.
8 . The method of claim 1 , wherein the mixing operation is performed at a temperature of about 20 to about 60° C.
9 . The method of claim 1 , wherein the mixing operation is performed at a temperature of about 60° C.
10 . The method of claim 1 , wherein the mixing operation is performed for a period of about 0.1 to about 3 hours.
11 . The method of claim 1 , wherein the mixing operation is performed for a period of about 0.1 to about 1 hour.
12 . The method of claim 1 , wherein the mixing operation is performed for a period of about 3 hours.