EFFECTS OF SUBSTITUTION OF OTHER ELEMENTS FOR NICKEL IN MECHANICALLY ALLOYED MG50NI50 AMORPHOUS-ALLOYS USED FOR NICKEL METAL HYDRIDE BATTERIES

It was recently found that Mg-Ni amorphous alloys prepared by mechanic al alloying exhibit a very high electrochemical discharge capacity, bu t because of corrosion those alloys show very bad durability during el ectrochemical cycling. In this paper, more than ten different amorphou s alloys, in which nickel had been partially replaced by other element s, have been prepared to improve their electrochemical properties. Exp erimental results show that the partial substitution of Ti for Ni in M g50Ni50 increases both the discharge capacity and degradation rate. Th e substitution of Zn for Ni shows no effect on the discharge capacity but increases the deterioration rate. The substitution of Fe, W, Cu, M n, Cr, Al or C for Ni decreases both the deterioration rate and discha rge capacity. The substitution of Se, Sb, Co, or Si decreases both the discharge capacity and cycling life. Optimum ternary alloys with reas onable discharge capacities and cycling lives are Mg50Ni45M5 (M=Mn, Cu or Fe), with maximum capacities of 345 mAh.g(-1), 343.3 mAh.g(-1), an d 273.3 mAh.g(-1) respectively. The capacity degradation after 9 cycle s is 57.5%, 51.4% and 40.5% respectively. This is far below the requir ement for practical usage. (C) 1997 Elsevier Science S.A.