Influence of over-stoichiometry on hydrogen storage and electrochemical properties of Sm-doped low-Co AB5-type alloys as negative electrode materials in nickel-metal hydride batteries

Abstract The La0.582Ce0.191Zr0.025Sm0.202(Ni0.849Co0.032Mn0.05Al0.069)5+x (x = 0.00, 0.10, 0.20, 0.35 or 0.47) hydrogen storage alloys are firstly synthesized to explore the influence of over-stoichiometry on crystal structure and electrochemical performance for nickel-metal hydride (Ni-MH) battery anodes. These alloys possess major CaCu5-type AB5 and minor BiF3-type Ni2MnAl phases. The decreasing of cell volume and charge acceptance ability of the alloy electrodes reduces capacity and peak power density. Meanwhile, the decreasing of MH stability results in the poorer charge retention rate. The enhanced anti-pulverization property of larger anisotropic factor (c/a) and the weakened electrode polarization promote the cycle stability. Moreover, the higher discharge plateau potential is beneficial to the discharge capacity at − 20 and − 40 °C. The high rate discharge ability (HRD) and initial voltage drop decrease at first and then increase because of the changing rate-determining factor of HRD with the shifted x.