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

摘要

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_2Ni 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 210mAh/g, respectively. After 20 cycles, the amorphous electrode retained 11 percent of the initial discharge capacity while the composite electrode maintained 64 percent 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.