Influence of Mg₃AlNi₂ content on the cycling stability of Mg₂Ni-Mg₃AlNi₂ hydrogen storage alloy electrodes

A novel method to improve the cycling capacity degradation of Mg ₂Ni-based hydrogen storage alloy by means of composite materials has been proposed. The new composites Mg₂Ni-x mol% Mg ₃AlNi₂ (x = 0, 15, 30, 60, 100) were prepared by means of combining electric resistance melting with isothermal evaporation casting process (IECP). Phase analysis and microstructure were investigated by SEM and TEM observations. Results showed that the cycling stability of the alloy with Mg₃AlNi₂ was superior to that of Mg₂Ni. XPS analysis revealed that the formation of an Al oxide film during cycling could enhance the anti-corrosion of the surface of the composites. Among the obtained capacity retaining rates, Mg₂Ni-15 mol% Mg₃AlNi ₂ composite had the best anti-corrosion performance. This composite has kept 76% of its maximum discharge capacity (50 mA hg^-1) at 25th cycle compared to 20% for Mg₂Ni. The enhancement of the cycling stability of the electrode alloy with 15 mol% Mg₃AlNi₂ can be ascribed to the decrease in the rate of pulverization of the alloy during cycling, which is considered as the factor in the improvement of the electrochemical properties of the Mg₃AlNi₂-containing alloys.