Effect of Mn content on the structure and electrochemical characteristics of La0.7Mg0.3Ni2.975−xCo0.525Mnx (x = 0–0.4) hydrogen storage alloys

The effect of Mn content on the crystal structure and electrochemical characteristics of La0.7Mg0.3Ni2.975−xCo0.525Mnx (x = 0, 0.1, 0.2, 0.3, 0.4) alloys has been studied systematically. The results of the Rietveld analyses show that all these alloys mainly consist of two phases: the La(La,Mg)2Ni9 phase with the rhombohedral PuNi3-type structure and the LaNi5 phase with the hexagonal CaCu5-type structure. The pressure–composition isotherms shows that the partial substitution of Mn for Ni results in lower desorption plateau pressure and steeper pressure plateau of the alloy electrodes. For a Mn content of x = 0.3, the electrochemical performances, including specific discharge capacity, high rate chargeability (HRC) and high rate dischargeability (HRD), of the alloy are preferable. Moreover, the data of the polarization resistance Rp and the exchange current density I0 of the alloy electrodes is consistent with the results of HRC and HRD. The hydrogen diffusion coefficient D increases with increasing Mn content, and thereafter increases the low temperature dischargeability (LTD) of the alloy electrodes.