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 mechanical alloying exhibit a very high electrochemical discharge capacity, but because of corrosion those alloys show very bad durability during electrochemical cycling. In this paper, more than ten different amorphous alloys, in which nickel had been partially replaced by other elements, have been prepared to improve their electrochemical properties. Experimental results show that the partial substitution of Ti for Ni in Mg50Ni50 increases both the discharge capacity and degradation rate. The substitution of Zn for Ni shows no effect on the discharge capacity but increases the deterioration rate. The substitution of Fe, W, Cu, Mn, Cr, Al or C for Ni decreases both the deterioration rate and discharge capacity. The substitution of Se, Sb, Co, or Si decreases both the discharge capacity and cycling life. Optimum ternary alloys with reasonable 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), and 273.3 mAh.g(-1) respectively. The capacity degradation after 9 cycles is 57.5%, 51.4% and 40.5% respectively. This is far below the requirement for practical usage. (C) 1997 Elsevier Science S.A.