Pasted nickel hydroxide electrode for rechargeable nickel-zinc batteries
View Patent ↗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 nickel-zinc cell comprising:
(a) a zinc oxide negative electrode,
(b) a nickel oxide positive electrode which comprises nickel hydroxide particles coated with cobalt oxidized to at least a valence of 3.0, and added cobalt, and
(c) an alkaline electrolyte;
wherein the surface coating of the cobalt oxidized to at least a valence of 3.0 and added cobalt, together, constitute greater than about 2% by weight of the coated nickel oxide particles.
2. The nickel-zinc cell of claim 1 , wherein the nickel oxide positive electrode further comprises nickel powder and binding materials.
3. The nickel-zinc cell of claim 1 , wherein the cobalt oxidized to at least a valence of 3.0 has an oxidation state of about 3 to 3.25.
4. The nickel-zinc cell of claim 1 , wherein the cobalt concentration in the zinc oxide negative electrode is about 5 ppm to about 30 ppm.
5. The nickel-zinc cell of claim 1 , wherein the cobalt concentration in the zinc oxide negative electrode is less than about 10 ppm.
6. The nickel-zinc cell of claim 1 , wherein the zinc oxide negative electrode gassing rate after formation is less than 1 ml/hr.
7. The nickel-zinc cell of claim 1 , wherein the residual capacity of a fully charged cell after 28 days at 60° C. is greater than about 30% of the full capacity.