Influences of annealing treatment on electrochemical properties of La4MgNi17.5Co1.5 hydrogen storage alloy

摘要

The La4 Mg Ni17.5 Co1.5 hydrogen storage alloys were prepared by induction levitation melting under argon atmosphere and were annealed respectively at 1123K, 1173K for 8 h in vacuum. XRD diffraction analyses indicate that the as-cast alloy was composed of the LaNi5 and Pr5Co19 phases, and the annealed alloys were composed of the LaNi5, Pr$Co19 and Ce5 Co19 phases. The electrochemical studies reveal that the maximum discharge capacity of the alloys increased obviously with the rising of annealing temperature at 1123K (366.0mAh/g). When the annealing temperature increased to 1173K, the maximum discharge capacity of the alloys decreased to 33S.5mAh/g. That maybe related to the easier Mg evaporation at higher annealing temperature. After annealed treatment, there was little change about the high rate discharge ability, and the HRD900 of all alloy electrodes reached to above 90%. When annealed at 1123K, the capacity retention (S100) of alloy electrode decreased to 62.07% but increased to 69.09%when annealed at 1173K. It can be concluded that the ingredient homogeneity maybe help to improve the cyclic stability, but the variation of phase contents among LaNi5, Pr5Coi9 or Ce5Co19 phases would also influence the cyclic stability through changing the degree of the pulverization which could be observed by SEM images of alloy electrodes after cycled.