Influence of substitution of Al for Mg on the electrochemical cyclic stability of La2MgNi7.5Co1.5 hydrogen storage alloy

In this paper, the influence of small quantity substitution of Al for Mg (x=0.1) on electrochemical cyclic stability of La2Mg1-xAlxNi7.5Co1.5 hydrogen storage alloy has been investigated. After electrochemical charge-discharge cycle, LaNi3 and alpha La2Ni7 phase still remain PuNi3-type structure and Ce2Ni7 type structure, however, a small amount new phase La(OH)(3), Mg(OH)(2) and Ni appear in La2Mg1-xAlxNi7.5Co1.5(x=0, 0.1) alloys. The structure of hydride for LaNi3 and alpha La2Ni7 phase after hydrogenizing also remain PuNi3-type structure and Ce2Ni7 type structure. The expansion of LaNi3 cell and aLa2Ni7 phase cell in La2MgNi7.5Co1.5 hydride are anisotropic, but the rate of anisotropic expansion and volume expansion of the former is larger than that of the latter. Compared with the La2MgNi7.5Co1.5 hydride, the repression of volume expansion of alpha La2Ni7 phase in La2Mg0.9Al0.1Ni7.5Co1.5 alloy with substitution of Al for Mg is very weak, but the expansion of c axis and cell volume v of LaNi3 phase lowers obviously due to Al substitution. The change of particle size and micrograph of the alloys after electrochemical charge-discharge cycles show that the performance of anti-pulverization of La2Mg0.9Al0.1Ni7.5Co1.5 is superior to that of La2MgNi7.5Co1.5 alloy. That is main reason of improvement of electrochemical cyclic stability of La2MgNi7.5Co1.5 alloy due to substitution of Al for Mg.