Cooperative effect of Co and Al on the microstructure and electrochemical properties of AB3-type hydrogen storage electrode alloys for advanced MH/Ni secondary battery

The crystal structure and electrochemical properties of the La2MgMn0.3Ni8.7−x(Co0.5Al0.5)x (x = 0, 1.0, 2.0 and 3.0, at%) hydrogen storage alloys are investigated systematically. The results show that all the alloys consist of (La, Mg)Ni3 and LaNi5 phases, the cyclic stability S60 increases from 61.2% (x = 0) to 78.7% (x = 3.0) after 60 charge/discharge cycles, and the peak high rate dischargeability (HRD) at the discharge current density of 1200 mA/g appears at the alloy of x = 2.0 with the value of 68.3%. Moreover, the electrochemical kinetic properties of the alloys are also improved at different extent with increasing x. All the results indicate that the substitution of Co and Al for Ni in AB3-type hydrogen storage alloys is effective to improving the overall electrochemical properties, and the optimum content is x = 2.0.