STRUCTURAL AND TEXTURAL INVESTIGATIONS OF THE NICKEL-HYDROXIDE ELECTRODE

In order to understand the textural and structural modifications invol ved in the electrochemical cycling of the nickel hydroxide/oxyhydroxid e electrode (NOE), well defined divalent nickel hydroxides (alpha- and beta-types) have been prepared and characterized. The alpha-type phas es present a pseudo-bidimensional structure and each nickel hydroxide layer can be considered as a surface layer with water molecules and hy droxyl vacancies compensated by adsorbed anionic species from the moth er precipitation solution. Ageing of these phases in KOH electrolyte l eads to the alpha-->beta transformation by a dissolution-recrystalliza tion phenomenon via the electrolyte, and an Ostwald ripening in KOH is observed for these beta(ex alpha) phases. Textural and structural cha nges during the electrochemical cycling of NOE are studied: it is show n that the beta(II)-->gamma(III)-->beta(II) transformation occurs dire ctly in the solid state.