NICKEL HYDROXIDE ELECTRODE FOR RECHARGEABLE BATTERIES
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 method of making a positive electrode for a battery, the method comprising:
(a) mixing a hydroxide solution and a strong oxidizing agent with nickel hydroxide particles coated with a cobalt compound at a temperature of between about 100° C. and 150° C. to produce a modified nickel hydroxide;
(b) separating the modified nickel hydroxide from a mixture resulting from (a);
(c) preparing an electrode mixture as a paste comprising the modified nickel hydroxide and cobalt metal; and
(d) incorporating the electrode mixture into a positive electrode.
2 . The method of claim 1 , further comprising, prior to (a), mixing nickel hydroxide powder with a first hydroxide and a cobalt salt solution to form the nickel hydroxide particles coated with the cobalt compound.
3 . The method of claim 2 , wherein mixing the nickel hydroxide powder with the first hydroxide and the cobalt salt solution is performed at a temperature of between about 40° C. and about 60° C.
4 . The method of claim 2 , wherein the nickel hydroxide particles coated with the cobalt compound comprise up to about 1 weight percent of the cobalt compound.
5 . The method of claim 1 , wherein the strong oxidizing agent is selected from the group consisting of a permanganate, a perchlorate, a persulfate, and ozone.
6 . The method of claim 5 , wherein the strong oxidizing agent is the persulfate as a salt and the hydroxide is an alkali metal hydroxide.
7 . The method of claim 1 , wherein the separating operation comprises
(i) washing the modified nickel hydroxide; and
(ii) drying the modified nickel hydroxide.
8 . The method of claim 1 , wherein the separating operation comprises
(i) filtering the modified nickel hydroxide; and
(ii) washing the filtered modified nickel hydroxide.
9 . The method of claim 1 , wherein operation (a) is performed at a temperature of about 120° C. to about 125° C.
10 . The method of claim 1 , wherein operation (a) is performed for a period of between about 5 minutes and 200 minutes.
11 . The method of claim 1 , wherein the positive electrode comprises between about 60 to 95% by weight of the modified nickel hydroxide and up to about 10% of cobalt, including cobalt metal and the cobalt compound.
12 . The method of claim 11 , wherein the cobalt compound is selected from the group consisting of cobalt oxide, cobalt hydroxide, cobalt oxyhydroxide and combinations thereof.