Dynamic EXAFS study of discharging nickel hydroxide electrode with non-integer Ni valency

Abstract

A dynamic in situ X-ray absorption study, in the energy dispersive mode, has revealed short-range structural changes taking place during the discharge of a nickel hydroxide film electrode. A Jahn–Teller distortion has been identified in the first Ni–O shell at overcharge, which diminishes during the discharge process. Throughout discharge, the first Ni–Ni shell moves antagonistically to Ni–O coordination. These structural changes and Ni K-edge shifts have been used as measures of Ni valency during film discharge. Correlation of the results with electrode charge leads to a simple mechanism, in terms of electron population at Ni sites, for the discharge process.