ELECTROCHEMICAL PROPERTIES OF MG2NI AND MG2NI2 PREPARED BY MECHANICALALLOYING

Crystallized Mg2Ni and Mg2Ni2 amorphous alloys synthesized by mechanic al 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 it s poor capacity retention upon cycling appears to originate from a fin e Ni dispersion within the Mg/Ni matrix. This dispersion enables a bet ter protection of the Mg against oxidation during cycling. We show, ho wever, that this protection of Mg by Ni is not sufficient to avoid a s trong corrosion of Mg in the KOH electrolyte during cycling, leading t o the formation of Mg(OH)(2).