Effects of Phase Transformation on Electrochemical Properties of A5B19-type Hydrogen Storage Alloy
A5B19-type La-Mg-Ni-based hydrogen storage alloys developed in recent years have shown great application po-tential as anode materials for Ni-MH batteries.But their capacity and cycle stability still need to be improved.In the present study,the superlattice La0.7Mg0.3Ni3.0Co0.55Al0.15 alloy with the(La,Mg)5Ni19 main phase has been prepared by keeping the as-cast alloy at 1223 K for 30 h,and the effects of phase transformation on the electrochemical properties and the functioning mechanism are studied.It is found that the main phase of the alloy before phase transformation is LaNi5,and the secondary phases include(La,Mg)5Ni19,(La,Mg)2Ni7 and LaMgNi4.During phase transformation,the LaNi5 phase reacts with the LaMgNi4 liquid phase through peritectic reaction,and reacts with the(La,Mg)2Ni7 phase through solid diffusion reaction.Electrochemical testing results show that the transformation of LaMgNi4 and LaNi5 phases to(La,Mg)5Ni19 phase improves the alloy's discharge capacity,and the Cmax increases from 361 to 381 mAh g-1.The transformation of(La,Mg)5Ni19,(La,Mg)2Ni7 and LaMgNi4 phases to(La,Mg)5Ni19 phase enhances the anti-pulverization/amorphization and anti-oxidation/corro-sion resistance of the alloy.As a positive result,the capacity retention after 150 cycles increases significantly from 65.6％to 80.8％.
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