Effect Of Ce Substitution For La On Phase Structure And Electrochemical Properties Of La₁₅Fe₇₇B₈ Type Hydrogen Storage Alloys

In this paper the La15-xCexFe14Ni64Mn5B2 (x=0,2,4,6) hydrogen storage alloys were prepared by vacuum melting and rapid quenching method. Through XRD, SEM, EDS and electrochemical tests, the effects of the partial substitution of La by Ce and annealing treatment on the phase structure and electrochemical performance of alloys were studied systemically.The result shows that all of the alloys consist of the LaNi5 phase, La3Ni13B2 phase and (Fe, Ni) phase. The electrochemical study indicates that cycling stability (S50) of alloy electrodes increase from 77.9%(x=0) to 86.4%(x=6), but the activation properties, the maximum discharge capacity and HRD decreases, retention rate of 72 h self-discharge and higher temperature (333K) electrochemical performance decreases with increasing Ce content.The lower temperature electrochemical performance first increases and then decreases with increasing Ce content. The capacity retention rate first increases from 16.9%(x=0) increases to 21.1%(x=2) and then decreases to 12.8%(x=6) when charge at 298K and discharge at 233 K and the capacity retention rate first increases from 22.0%(x=0) increases to 24.5%(x=2) and then decreases to 14.6%(x=6) when charge at 233 and discharge at 233 K.The annealed alloys were also systematically investigated. More homogeneous composition of alloy is obtained and the P-C-T plateau becomes flater. The electrochemical performances, such as activation, maximum discharge capacity, HRD, lower temperature discharge capability and high temperature discharge capability are increasesed. The capacity retention rate of 72h self-discharge increases except for x=6 but the cycling stability decreases after annealing heat treatment.