Effects of carbon crystallinity on hydriding-dehydriding and charge-discharge characteristics of MgNi alloy-carbon material composites

Abstract

Hydriding-dehydriding and charge-discharge characteristics of amorphous MgNi alloys modified by ball-milling with different carbon materials were investigated with the intention of using them in nickel-metal hydride batteries. It was found that the ball-milling with carbon materials markedly improved hydriding-dehydriding and charge-discharge characteristics of the MgNi alloy, and an optimum ball-milling time was shortened by utilization of carbon material with lower crystallinity. However, ball-milling for longer than the optimum time led to a decrease in the amount of absorbed hydrogen and the discharge capacity, which was ascribed to the formation of MgNi3C. These results indicate that the characteristics of MgNi alloy-carbon material composites greatly depend on both crystallinity of carbon material used and ball-milling time.