Reducing the electrochemical capacity decay of milled Mg–Ni alloys: The role of stabilizing amorphous phase by Ti-substitution

MgNi-based alloys have high electrochemical capacity as anode of nickel-metal hydride (Ni/MH) battery (≥500 mAh g −1 ). However the capacity decay seriously in charge-discharge cycling, which is previously ascribed to the corrosion of Mg. To solve this problem and reveal the related mechanism, the electrochemcial properties of Mg 0.50 Ni 0.50 , Mg 0.45 Ti 0.05 Ni 0.05 and Mg 0.40 Ti 0.10 Ni 0.50 alloys are studied in combination with their hydrogen storage properties and microstuctural evolution during cycling. This work demonstrates the amorphous phase in milled Mg 0.45 Ti 0.05 Ni 0.50 and Mg 0.40 Ti 0.10 Ni 0.50 alloys has higher resistance to hydrogenation-induced crystallization than milled Mg 0.50 Ni 0.50 alloy. Thus, they show better hydrogen absorption/desorption reversibility and contribute to the reversible electrochemical capacity. Therefore, the cycle performance of the Mg 0.50 Ni 0.50 alloy electrodes shows obvious improvement after partially substituting Mg by Ti. The capacity retention rate increases from 24.0% (Mg 0.50 Ni 0.50 ) to 55.7% (Mg 0.40 Ti 0.10 Ni 0.50 ) after 30 cycles. In addition, the Ti addition results in the formation of TiNi phase, and thus, the alloys show better electrochemical reaction kinetics and their high-rate dischargeability (HRD) is significantly improved. At 300 mA g −1 , the HRD values of Mg 0.50 Ni 0.50 , Mg 0.45 Ti 0.05 Ni 0.50 and Mg 0.40 Ti 0.10 Ni 0.50 alloys are 41.7%, 83.7% and 90.3%, respectively. At higher discharge current density of 1200 mA g −1 , the HRD values are 26.7%, 34.8% and 46.2%, respectively.