Electrochemical properties of Mg2Ni and Mg2Ni2 prepared by mechanical alloying

Crystallized Mg₂Ni and Mg₂Ni₂ amorphous alloys synthesized by mechanical alloying at room temperature were found to present first discharge capacities of 270 mAh/g and 500 mAh/g, respectively. These capacities decrease upon subsequent cycling to reach 30 mAh/g and 70 mAh/g after 60 charge/discharge cycles. The largest initial capacity, measured for the Mg₂Ni₂ composition, is ascribed to its amorphous nature, while its poor capacity retention upon cyding appears to originate from a fine Ni dispersion within the Mg/Ni matrix. This dispersion enables a better protection of the Mg against oxidation during cycling. We show, however, that this protection of Mg by Ni is not sufficient to avoid a strong corrosion of Mg in the KOH electrolyte during cycling, leading to the formation of Mg(OH)₂. Received: 8 October 1997 / Accepted: 20 January 1998