Influence of Al Substitution for Mg on Phase Structure and Electrochemical Properties of La2MgNi7.5Co1.5 Hydrogen Storage Alloys

The phase structure and electrochemical properties of La2Mg1−xAlxNi7.5Co1.5 (x=0.0,0.1,0.3,0.5) alloys were investigated by means of X-ray diffraction (XRD), electron probe X-Ray microanalysis (EPMA) and electrochemical measurements. XRD and EPMA results show that small quantity replacement Mg by Al (x=0.1) does not change phase composition of La2MgNi7.5Co1.5 alloy, the alloy is still constituted with LaNi3 phase and αLa2Ni7 phase, but the abundance of LaNi3 phase decreases obviously and that of αLa2Ni7 increases in the La2Mg0.9Al0.1Ni7.5Co1.5 alloy. The more Al substitution will change phase composition of the alloy, resulting in LaNi3 phase disappearance. Influence of change of Al content on cell parameters of different phases of the La2Mg1−xAlxNi7.5Co1.5 alloy is different. Moreover, little replacement of Mg by Al (x=0.1) lowers scarcely hydrogen storage capacity and maximum electrochemical discharge capacity of the alloy, but with the increment of Al content in the La2Mg1−xMgxNi7.5Co1.5 alloy, hydrogen storage capacity, activation property and maximum electrochemical discharge capacity of the alloys decrease continuously. Al substitution for Mg can improve obviously electrochemical cyclic stability of La2MgNi7.5Co1.5 alloy electrode, and is beneficial to improve high rate dischargeability of the alloy electrode.