Synthesis of composite Mg–Ni–Ca metal hydride by mechanical alloying

Abstract Amorphous and composite Mg–Ni–Ca metal hydrides were synthesized by mechanical alloying. (Mg 0.5 Ca 0.5 )Ni 2 yielded the composite of Mg 2 Ni and CaNi 5 , while MgNi 0.95 Ca 0.05 produced the amorphous phase. The initial discharge capacities of the amorphous MgNi 0.95 Ca 0.05 alloy and the composite (Mg 0.5 Ca 0.5 )Ni 2 alloy were 460 and 210 mAh/g, respectively. After 20 cycles, the amorphous electrode retained 11% of the initial discharge capacity while the composite electrode maintained 64% of the initial discharge capacity. After 10 cycles, the XPS analysis showed that Mg spectra of the amorphous MgNi 0.95 Ca 0.05 alloy was shifted to a lower binding energy because Mg reacted with OH − of the electrolyte. However, Mg spectra of the composite (Mg 0.5 Ca 0.5 )Ni 2 alloy showed that the binding energy did not change during the cycle test. These results indicate that the amorphous phase had the highest discharge capacity and the composite formation improved the cyclic stability.