Atomic Structure and Valency of Nickel in Some of its Oxycompounds

The structure of the higher oxide forms of nickel where Ni has a valency greater than 2 is of great interest from the standpoint, of developing advanced nickel batteries for consumer applications and for electric vehicle propulsion. In spite of the considerable research work that has been published, there is still much uncertainty and confusion as to the stoichiometry and structure of the various oxides hydroxides that are formed during the charging and discharging of the nickel electrode. The difficulty stems in part from the highly disordered or amorphous nature of the phases formed which makes structural determination by X-ray diffraction difficult. X-ray absorption spectroscopy XAS consisting of the X-ray absorption near edge structure XANES and the extended X-ray absorption fine structure EXAFS is an excellent technique for the characterization of such materials which have no long range order. Preliminary to using the technique for in-situ structural determinations in an electrochemical cell, we have used XAS to study a number of standard samples for subsequent use as reference. We report initial XANES and EXAFS results that give the valency and structure of nickel in some compounds of interest in battery work.