Structure and electrochemical properties of hydrogen storage alloys

The structure and electrochemical properties of La 0.7 Mg 0.3 Ni 2.45 - x Co 0.75 Mn 0.1 Al 0.2 W x ( 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 LaNi 5 phase. The Co 7 W 6 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 Co 7 W 6 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.