An Investigation On The Self-discharge Property Of The La_0.65Mg_0.35Ni_x(x=3.0-3.5) Hydrogen Storage Alloy Electrodes

The application status,research and development of hydrogen storage alloy were comprehensively introduced in the first part of this paper.The new series of RE-Mg-Ni based AB_3.0-3.5-type alloys with PuNi₃-type structure had higher capacity than that of the AB₅-type alloys and thus were regarded as promising candidates for reversible hydrogen storage.In this work,the effect of the A/B ratio and annealing treatment on the structural,electrochemical properties and self-discharge property of the AB_3.0-3.5-type hydrogen storage alloys has been studied systematically.The La_0.65Mg_0.35Ni_x(X=3.0-3.5) hydrogen storage alloys is prepared by induction melting.The structure,electrochemical properties and self-discharge property of as-cast alloys have been studied systematically by X-ray diffraction(XRD),scanning electron microscope(SEM) and electrochemical experiments.It is found by XRD analysis that all these alloys mainly consist of three phases:the LaNi₅ phase, (La,Mg)Ni₃ phase and(La,Mg)₂Ni₄ phase.The abundance of the LaNi₅ phase increases and that of La(La,Mg)Ni₃ phase decreases with increasing x.The electrochemical studies show that as x increases the maximum discharge capacity of the alloy electrodes first increases from 350.6mAh·g^-1(x=3.0)to 351.2mAh·g^-1(x=3.1)and then decreases to 244.1mAh·g^-1(x=3.5).Moreover,the capacity retention rate of 72h self-discharge increases from 77.7%(x=3.0)to 79.5%(x=3.1),and then decreases to 63.5%(x=3.5).When x=3.1,the capacity retention rate of alloy electrode is the maximum.Besides,lectrochemical experiments show that the discharge capacity,high rate discharge performance,cycle stability and self-discharge property of the La_0.35Mg_0.65Ni_x(X=3.0-3.5) alloy electrodes were improved after annealing treatment at 1173K.