Structure and electrochemical properties of La0.7Mg0.3Ni2.45-xCo0.75Mn0.1Al0.2WxLa0.7Mg0.3Ni2.45-xCo0.75Mn0.1Al0.2Wx(x=0–0.15)(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)Ni3(La,Mg)Ni3 phase and the LaNi5LaNi5 phase. The Co7W6Co7W6 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)(x=0) to 319.5 mAh/g (x=0.15)(x=0.15) with increasing xx due to the formation of new phases Co7W6Co7W6 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)(x=0) to 61.5% (x=0.1)(x=0.1). In addition, as x=0.05x=0.05, the alloy electrode exhibits the optimum kinetics property.