Study On La-Mg-Ni Based Hydrogen Storage Alloys Under Different Condition

In order to obtain high capacity La-Mg-Ni based hydrogen storage alloy which is easy to activate and have stable cycle capability, La0.67Mg0.33Ni2.77 and La0.88Mg0.12Ni2.94Mn0.12Co0.56Al0.2 hydrogen storage alloys were selected as the subject of this study. Treated with high energy milling, high temperature sintering, cold molding and by means of XRD, SEM, PPMS, Metal-lographic Microscope and electrochemical test methods, the effect of different experimental condition and additive content to the phase structure, micro-structure, resistance and electrochemical properties were studied systematically.XRD analysis showed that, La0.67Mg0.33Ni2.77 +x(wt.) %AB5 (x=10, 30, 50) hydrogen storage alloy became amorphous under high energy milling, and the lattice volume of La2Ni7 phase diminished which result in the reduce of capacity of the hydrogen storage alloy. Moreover the peak in the XRD pattern became more cuspate and the FWHM of the (116) peak of La2Ni7 phase was 0.366(not annealing), 0.256(annealing at 700℃) and 0.196 (annealing at 800℃). The amount of La2Ni7 phase reduced, but its lattice volume increased from 544.34?3 before annealing to 568.85?3 after annealing.Electrochemical test showed that high energy milling improve the activation capability of La0.67Mg0.33Ni2.77+x(wt.) %AB5(x=10, 30, 50) hydrogen storage alloy, and all alloys electrodes was activated at the first cycle. High temperature sintering decreased the capacity of La0.67Mg0.33Ni2.77+30(wt.)%AB5 hydrogen storage alloys, but its HRD was improved. When the molding pressure was increased, The I0 of La0.88Mg0.12Ni2.94Mn0.12Co0.56Al0.2+10%Co hydrogen storage alloys was reduced from 524.00mA/g at 300MPa to 356.85mA/g at 1000MPa. The limit current density IL was increased first and then decreased, also the resistance of alloy electrodes reduced. Metallographic Microscope and PPMS analysis showed that, when molding under 800MPa the grains inside La0.88Mg0.12Ni2.94Mn0.12Co0.56Al0.2+10%Co hydrogen storage alloy electrodes was symmetrical and there was less interspaces between grains, and the grains inside the alloy electrodes became plastically deforming and felted. Moreover there was few independent grains inside the alloy electrodes.