Effects of the substitution of Mn for Ni on structures and electrochemical performances of the as-cast and quenched electrode alloys

The effects of the substitution of Mn for Ni on the structures and electrochemical characteristics of the as-cast and quenched La 0.5 Ce 0.2 Mg 0.3 Co 0.4 Ni 2.6 - x Mn x ( x = 0 , 0.1, 0.2, 0.3, 0.4) alloys were studied systematically. The results obtained by XRD, SEM and TEM indicate that the as-cast and quenched alloys mainly consist of two major phases the ( La , Mg ) Ni 3 and LaNi 5 and a residual phase LaNi. With increasing Mn content in the alloys, the abundance of the ( La , Mg ) Ni 3 phase decreases and that of the LaNi 5 phase increases and both the lattice parameters and the cell volumes of major phases ( La , Mg ) Ni 3 and LaNi 5 increase. The as-quenched alloys display a nanocrystalline structure, and the grain sizes of the alloys are in a range of 20–30 nm. The results by the electrochemical measurements indicate that the discharge capacities of the as-cast and quenched alloys first increase and then decrease with the variety of Mn content and obtain the maximum values for a Mn content of x = 0.2 . The substitution of Mn for Ni clearly improves the high rate discharge abilities (HRDs) and the activation capabilities of the as-cast and quenched alloys, but it slightly impairs the cycle stabilities of the as-cast and quenched alloys.