The outcome of cobalt in the nickel-cobalt oxyhydroxide electrodes of alkaline batteries

The evolution of cobalt hydroxide used as a coating for nickel hydroxide electrodes has been studied as a function of the redox potential window and upon cycling. From both chemical and electrochemical studies, it is shown that (i) upon deep discharges cobalt tends to migrate from the coating to the current collector and (ii) upon heavy cycling in the limited 1-1.4 V potential range a complete reorganization of the active material occurs. In the latter case, using X-ray diffraction, electron microscopy, and potentiodynamic intermittent technique, we identified the formation of a Ni1-xCox(OH)(2)(CO3)(z).rH(2)O-type phase through dissolution reprecipitation processes involving both cobalt and nickel species. From these findings, the conditions required to preserve the benefits of cobalt additives are given. (C) 2001 Elsevier Science.