Structure and electrochemical properties of La0.7Mg0.3Ni2.45-xCo0.75Mn0.1Al0.2Wx (x=0-0.15) hydrogen storage alloys

The structure and electrochemical properties of La0.7Mg0.3Ni2.45-xCO0.75Mn0.1Al0.2Wx (x = 0, 0.02, 0.05, 0.1, 0.15) hydrogen storage alloys were studied systematically. X-ray powder diffraction and Rietveld analyses indicate that all the alloys mainly consist of the (La, Mg)Ni-3 phase and the LaNi5 phase. The Co7W6 phase and the separate W phase are formed with increasing x. Electrochemical studies show that the maximum discharge capacity decreases monotonously from 355.5 mAh/g (x = 0) to 319.5 mAh/g (x = 0.15) with increasing x due to the formation of new phases Co7W6 and W which cannot absorb hydrogen. However, the cycling stability is markedly improved, that is, after 150 charge/discharge cycles, the discharge capacity retention increases from 51.8% (x = 0) to 61.5% (x = 0.1). In addition, as x = 0.05, the alloy electrode exhibits the optimum kinetics property. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.