ELECTROCHEMICAL AND RAMAN STUDIES OF BETA-TYPE NICKEL HYDROXIDES NI1-XCOX(OH)(2) ELECTRODE MATERIALS

A large variety of pure beta-Ni(OH)(2) and cobalt-substituted nickel h ydroxides Ni1-xCox(OH)(2) of well-controlled chemical composition, par ticle size, and morphology have been prepared and characterized by x-r ay, transmission electron microscopy, electrochemical, and Raman spect rometry studies. The hydroxide particle size and its Co-substituted co ntent were found to govern the Ni-electrode capacity. Once these param eters were controlled, P-nickel hydroxide specimens able to reversibly exchange more than one electron per metal atom (Ni + Co) were routine ly prepared. beta-Ni1-xCox(OH)(2) Raman spectra consists of five lines . The intensities of the ones located at 3605 and 515 cm(-1) were foun d to change as a function of the particle size and the Co content. Ind eed, the line at 3605 cm(-1), 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 515 cm(-1) is enhanced by the presence of coprecipitated cobalt. A direct correlation between th e intensity of the 515 cm(-1) Raman line and the electrochemical capac ity of the nickel hydroxide sample is found. Raman spectroscopy can th en be used as a powerful nondestructive tool to differentiate ''high c apacity'' from low capacity nickel hydroxide samples.