EFFECTS OF PRETREATMENT ON THE ACTIVATION BEHAVIOR OF ZR(V0.25NI0.75)2 METAL HYDRIDE ELECTRODES IN ALKALINE-SOLUTION

Metal hydrides used as negative electrodes in rechargeable batteries are covered with surface oxides during preparation of the electrode. They inhibit or slow down the absorption rate of hydrogen and have to be dissolved or made conductive in an activation process. In order to minimize the activation cycles we have investigated the influence of the pretreatments of the metal hydride powder Zr(V0.25Ni0.75), with KOH and fluoride-containing solutions on the surface composition of the alloy grains by means of X-ray photoelectron spectroscopy. The study establishes the relationship between the surface composition of the hydrogen-storing material and the electrode performance, eg. discharge capacity and high-rate dischargeability. The speed of activation increased with increasing nickel content in the top surface layers (30 angstrom) of the metal hydride.