Electrochemical properties of nanocrystalline and amorphous Mg-Y-Ni alloys applied to Ni-MH battery

The as-cast Mg2Ni-type Mg20−xYxNi10 (x=0, 1, 2, 3 and 4) electrode alloys were prepared by vacuum induction melting. Subsequently, the as-cast alloys were mechanically milled in a planetary-type ball mill. The analyses of scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveal that nanocrystalline and amorphous structure can be obtained by mechanical milling, and the amount of amorphous phase increases with milling time prolonging. The electrochemical measurements show that the discharge capacity of Y0 alloy increases with milling time prolonging, while that of the Y-substituted alloys has a maximum value in the same condition. The cycle stabilities of the alloys decrease with milling time prolonging. The effect of milling time on the electrochemical kinetics of the alloys is related to Y content. When x=0, the high rate discharge ability, diffusion coefficient of hydrogen atom, limiting current density and charge transfer rate all increase with milling time prolonging, but the results are exactly opposite when x=3.