In situ Raman investigation of hydrous nickel oxide films with various additives in concentrated alkaline electrolytes

Electroprecipitated thin-film nickel composite electrodes with cobalt and lithium additives were characterized in detail by in situ Raman spectroscopy, and the effects of repeated charge-discharge cycling on the structure of the discharged and charged films were investigated in concentrated alkaline electrolytes. Electrochemical measurements showed that the presence of hydrous cobalt hydroxide in the electrode active firm reduces the threshold potential for the Ni(II) oxidation react-on and inhibits the phase transitions which usually occur in the film during prolonged cycling. On the other hand, lithium additions improve the reversibility of the nickel redox reaction and prevent capacity fading during long-term cycling. Analyses of the Raman spectra confirmed that cobalt is incorporated in the Ni(OH)(2) lattice on nickel sites. Lithium additions led to significant structural modifications represented by two new vibrational bands at 615 and 660 cm(-1) in the Raman spectra of the reduced film. It was found that films with both Co and Li additives exhibit properties which constitute a superposition of effects observed in single-additive composite nickel electrodes, and these properties do not depend on the electrolyte concentration.