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 La ₂MgMn_0.3Ni_8.7-x(Co_0.5Al _0.5)_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.