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

A dynamic in situ X-ray absorption study, in the energy dispersive mode, ha s revealed short-range structural changes taking place during the discharge of a nickel hydroxide film electrode. A Jahn-Teller distortion has been id entified in the first Ni-O shell at overcharge, which diminishes during the discharge process. Throughout discharge, the first Ni-Ni shell moves antag onistically to Ni-O coordination. These structural changes and Ni K-edge sh ifts have been used as measures of Ni valency during film discharge. Correl ation of the results with electrode charge leads to a simple mechanism, in terms of electron population at Ni sites, for the discharge process. (C) 20 01 Elsevier Science Ltd. All rights reserved.