Electrochemical and Raman Studies of Beta‐Type Nickel Hydroxides Ni1 − x Co x ( OH ) 2 Electrode Materials

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Abstract
A large variety of pure and cobalt‐substituted nickel hydroxides of well‐controlled chemical composition, particle size, and morphology have been prepared and characterized by x‐ray, transmission electron microscopy, electrochemical, and Raman spectrometry studies. The hydroxide particle size and its Co‐substituted content were found to govern the Ni‐electrode capacity. Once these parameters were controlled, β‐nickel hydroxide specimens able to reversibly exchange more than one electron per metal atom (Ni + Co) were routinely prepared. Raman spectra consists of five lines. The intensities of the ones located at 3605 and were found to change as a function of the particle size and the Co content. Indeed, the line at , ascribed to adsorbed water, appears and grows when the particle size decreases (e.g., when the surface/volume ratio increases), while the line located at is enhanced by the presence of coprecipitated cobalt. A direct correlation between the intensity of the Raman line and the electrochemical capacity of the nickel hydroxide sample is found. Raman spectroscopy can then be used as a powerful nondestructive tool to differentiate “high capacity” from low capacity nickel hydroxide samples.

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