INFLUENCE OF ELECTRODE THICKNESS ON CHARGE DISCHARGE BEHAVIOR OF AB(5)-TYPE METAL HYDRIDE ELECTRODES

Reversible alkaline batteries that use metal hydride alloys require a compacting procedure for fabricating the negative electrode. This is b ecause the intermetallic compounds used as the active material are bri ttle and disintegrate into powder upon hydride formation. The charge-d ischarge kinetics are expected to depend on the reaction mechanism and on the electrode morphology. The resistance of an electrode can be di vided into the following series resistances: the reaction resistance, given by the surface composition of the alloy and the real surface are a of the alloy grains, and the resistances due to the ionic conductivi ty of the electrolyte and the electrical conductivity of the metal hyd ride bed; these strongly depend on the porosity and the geometry of th e electrode. The total resistance defines the kinetic behaviour and th e loss of energy (Joule heating) during cycling. We have investigated the influence of the electrode thickness on the overpotential during c harge and discharge. The overpotential is described as a function of t he discharge time and thickness of the electrode.