STRUCTURAL DEFECTS AND ELECTROCHEMICAL REACTIVITY OF BETA-NI(OH)(2)

Electrochemical reactivities and structural properties of several nick el hydroxide powders were analysed by X-ray diffraction, Raman spectro scopy and extended X-ray absorption fine structure (EXAFS). It is show n that the electrochemical efficiency of beta-Ni(OH)(2) is associated with the amount of proton vacancies included in the crystal lattice. T he number of those proton vacancies increases when the crystallite siz e decreases or when the ratio of co-precipitated cobalt increases. Pro ton vacancies shift the oxidation potential of beta-Ni(OH)(2) towards less anodic values and, therefore, improve the chargeability and the e lectrochemical efficiency of nickel hydroxide. It is shown that both R aman spectroscopy and X-ray diffraction techniques can be used to pred ict effectively the electrochemical efficiency of beta-Ni(OH)(2) hydro xide. EXAFS results indicate also that the oxidation level of nickel a toms inside the hydroxide is not modified by the existence of proton v acancies. It means probably that to maintain the electroneutrality in the whole crystal induces others singularities. Finally, the influence of co-precipitated additives such as cadmium and cobalt on the rate o f defects has been investigated.