EFFECT OF IRON ON THE ELECTROCHEMICAL PROPERTIES OF THE NICKEL-HYDROXIDE ELECTRODE

New hydrated iron-substituted nickel hydroxides obtained either by precipitation (alpha) or by chimie douce (alpha*) have been tested as positive electrode materials in Ni/Cd cells. The gamma/alpha system is completely stabilized during long-term electrochemical cycling as a result of the stability of the Fe3+ ions in the reduced variety. Moreover, the substitution of iron results in a noticeable increase in the cell voltage, which can be correlated with the strong oxidizing character of the gamma oxidized phases due to the presence of tetravalent iron ions. The competition between electrolyte decomposition and effective oxidation of the electrode material leads to a decrease of the chargeability, which is all the more pronounced as the iron concentration becomes higher. The electrochemical behavior of these iron-substituted materials is discussed with regard to previous observations in our laboratory for the homologous cobalt phases.