Electrochemical properties of (La_(1-x)Ti_x)_(0.67)Mg_(0.33)Ni_(2.75)Co_(0.25) (x = 0-0.20, at%) hydrogen storage alloys

摘要

(La_(1-x)Ti_x)_(0.67)Mg_(0.33)Ni_(2.75)Co_(0.25) (x = 0,0.05,0.10,0.15 and 0.20, at%) alloys are synthesized by arc-melting and subsequent heat solid-liquid diffusing techniques, and the crystalline structures and electrochemical properties of the alloys are investigated systematically. The structural analysis results show that all the alloys mainly consist of (La, Mg)Ni_3 phase with the rhombohedral PuNi_3-type structure and LaNi_5 phase with the hexagonal CaCu_5-type structure. However, when the Ti content is higher than 0.10, a little amount of TiNi_3 phase start to form. Electrochemical measurements show that the alloy electrodes could be activated to their maximum discharge capacity within four cycles, the maximum discharge capacity is around 321.9-384.6 mAh g~(-1), both the cyclic stability and the high-rate discharge ability first increased and then decrease with increasing x. All the results show that a little amount of Ti substitution for La in AB_(3-) type hydrogen storage alloys is effective to the improvement of the overall electrochemical properties.