In recent years, the development of high performance hydrogen storage alloys as negative electrode active materials for Ni-MH batteries, a considerable attention has been paid to the research of Mg-based alloys, particularly amorphous Mg-Ni-type alloys prepared by mechanical alloying(MA) and Mechanical Grinding(MG) adopted different raw materials. Lei et al. synthesized it to use mainly low cost pure Mg and Ni metal by MA, Kohno et al. prepared it to choose the mixture of $Mg_2Ni$ and Ni by MG and Iwakura et al. also investigated it employing both. Extensive work has been carried on the discharge capacity and cycle life of alloy electrode. Although amorphous Mg-Ni type alloys can absorb and desorb electrochemically a large amount of hydrogen at room temperature, degradation of its discharge capacity is much faster than that of AB5, AB2 type metal hydride electrode. Using XRD and XPS, Lei et al indicted that serious oxidation of magnesium and nickel occurred, which was regarded as main reason for degradation of amorphous Mg-Ni alloy. Nevertheless, the degradation mechanism of amorphous alloy has not shown in detail. Liu et al have investigated more than ten different MgNi based amorphous alloys with partial replacement of nickel by the other elements (Zn, Ti, Mn, Cu, etc ) in order to improve the cycle life. In spite of this replacement the cycle life is far below the requirement for practical usage. Some results on amorphous alloy have also shown that the discharge performance is strongly dependent on the surface properties altered by various surface pre-treatments. Iwakura et al. have studied electrochemical characterization of MgNi alloys surface modified with graphite. Then the marked improvement of discharge capacity is achieved with surface modification of $Mg_{50}Ni_{50}$ alloy, but the tendency of degradation is similar to that without modification. The surface coating is not effective because MH alloy is pulverized during charging/discharging. So, new Mg-Ti-Ni alloy was developed. Mg was substituted with Ti in various content. $Mg_{0.9}Ti_{0.1}Ni_{1.0}$ has maximum discharge capacity (453mAh/g) at 1st cycle and $Mg_{0.7}Ti_{0.3}Ni_{1.0}$ has very good cycle life. It endures more than 30cycles without loss of discharge capacity. It is because the surface oxide depth of Mg-Ti-Ni alloy is decreased and Ni-subsurface layer is formed. $TiO_2$ film on the surface depress the oxidation of Mg in 6M KOH solution.
