Electrochemical properties of (La1-xTix)0.67Mg0.33Ni2.75Co0.25 (x=0-0.20, at%) hydrogen storage alloys

(La1-xTix.)(0.67)Mg0.33Ni2.75Co0.25 (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 PuNi3-type structure and LaNi5 phase with the hexagonal CaCu5-type structure. However, when the Ti content is higher than 0.10, a little amount of TiNi3 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. (C) 2010 Elsevier Ltd. All rights reserved.