Nickel hydroxide electrode for rechargeable batteries
View Patent ↗The nickel hydroxide particles for a nickel hydroxide electrode may be treated using an alkaline solution of a strong oxidizing agent such as sodium or potassium persulfate to modify the surface nickel hydroxide structure. The resulting modified surface structure has been found to impart various benefits to electrodes formed from the nickel hydroxide. It is believed that the oxidation of cobalt compounds at the surface of the nickel hydroxide particles results in a highly conductive cobalt compound that plays an important role in the high reliability, high stability and high capacity utilization of nickel electrodes as described herein.
1. A galvanic cell comprising:
(a) a zinc oxide based negative electrode;
(b) a nickel hydroxide positive electrode comprising:
nickel hydroxide particles having a modified surface comprising nickel in a higher oxidation state on average than is present in the bulk of the particles and
a coating of a cobalt compound on the nickel hydroxide particles, said coating also comprising added cobalt metal;
(c) a separator disposed between the positive electrode and the negative electrode and preventing electrical contact therebetween; and
(d) an alkaline electrolyte in contact with the negative electrode, the positive electrode and the separator;
wherein the cobalt content, including added cobalt metal and the cobalt compound, in the nickel hydroxide positive electrode is not significantly soluble in the alkaline electrolyte at room temperature and the coating of the cobalt compound on the surface of the nickel hydroxide particles is between about 0.1% and 1% by weight of the coated nickel hydroxide particles.
2. The cell of claim 1 , wherein the cobalt compound is selected from the group consisting of cobalt oxide, cobalt hydroxide, cobalt oxyhydroxide, and combinations thereof.
3. The cell of claim 1 , wherein the cell achieves a cycle life of at least about 500 cycles at a discharge rates of about 5 C or greater.
4. The cell of claim 1 , wherein the zinc oxide based negative electrode comprises no more than about 10 ppm cobalt.
5. The cell of claim 1 , wherein the nickel hydroxide positive electrode further comprises nickel metal powder, Y 2 O 3 , Ca(OH) 2 , and a binder.
6. The cell of claim 1 , wherein the nickel hydroxide particles comprise a coating of a cobalt compound and wherein at least about 90% by weight of the cobalt compound in the coating has a valence of 3 to 3.25.