MmNi3.55Co0.75Mn0.4Al0.3B0.3 hydrogen storage alloys for high-power nickel/metal hydride batteries

Non-stoichiometric La-rich MmNi3.55Co0.75Mn0.4Al0.3B0.3 hydrogen storage alloys using B–Ni or B–Fe alloy as additive and Ce-rich MmNi3.55Co0.75Mn0.4Al0.3B0.3 one using pure B as additive have been prepared and their microstructure, thermodynamic, and electrochemical characteristics have been examined. It is found that all investigated alloys show good activation performance and high-rate dischargeability though there is a certain decrease in electrochemical capacities compared with the commercial MmNi3.55Co0.75Mn0.4Al0.3 alloy. MmNi3.55Co0.75Mn0.4Al0.3B0.3 alloys using B–Ni alloy as additive or adopting Ce-rich mischmetal show excellent rate capability and can discharge capacity over 190 mAh/g even under 3000 mA/g current density, which display their promising use in the high-power type Ni/MH battery. The electrochemical performances of these MmNi3.55Co0.75Mn0.4Al0.3B0.3 alloys are well correlated with their microstructure, thermodynamic, and kinetic characteristics.