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 Mg2Ni-based hydrogen storage alloy by means of composite materials has been proposed. The new composites Mg2Ni-x mol% Mg3AlNi2 (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% Mg3AlNi2 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. (C) 2011 Elsevier Ltd. All rights reserved.