Study on the phase structures and electrochemical performances of La_0.6Gd_0.2Mg_0.2Ni_3.15-xCo_0.25Al_0.1Mn_x (x = 0-0.3) alloys as negative electrode material for nickel/metal hydride batteries

La_0.6Gd_0.2Mg_0.2Ni_3.15-xCo_0.25Al_0.1Mn_x(x = 0-0.3) hydrogen storage alloys are prepared by induction melting followed by annealing treatment at 1173 K for 8 hours and the effects of partial substitution Mn for Ni on the phase structures and electrochemical properties are studied. The phase structure analyses show that (La, Mg)₂Ni₇ phase with Ce₂Ni₇-type structure, (La, Mg) Ni₃ phase with PuNi₃-type structure and LaNi₅ phase with CaCu₅-type structure are the main phases. The increase in Mn content results in the expansion of the lattice parameters and the cell volumes of the alloys. The electrochemical analyses show that a proper amount of Mn substitution for Ni (x = 0.1) can increase the maximum discharge capacity and improve the cyclic stability of the alloy electrodes. Additionally, the kinetic properties of the alloy electrodes are improved because of the lower charge transfer resistance on alloy surface and the faster hydrogen diffusion rate in alloy bulk after Mn partial substitution for Ni.