Degradation behavior of foamed nickel positive electrodes of Ni-MH batteries

The extrusion mechanism has been demonstrated to be the major cause for the capacity decay of the positive electrodes during cycling. However, based o n our SEM and EPMA observations on cycled electrodes we found that some act ive material on the foamed nickel electrodes came off into scales especiall y as the electrodes cycled at IC rate of discharge. This phenomena is sugge sted as another important cause for the capacity decay of positive electrod es and may be explained by the internal stress induced by the different vol ume change at the outer layer and the core due to phase and structure trans formation during cycling. (C) 1999 Elsevier Science S.A. All rights reserve d.