Electrochemical behaviour of nanostructured Mm(Ni,Al,Co)5 alloy as MHx electrode

The electrochemical properties of nanocrystalline MmNi3.5Al0.8Co0.7 alloy, which has the hexagonal CaCu5 type structure, were investigated. This material was prepared by mechanical alloying (MA) followed by annealing and used as a negative electrode for a Ni–MHx battery. MA process transforms the starting mixture of the elements into an amorphous phase without other phase formation. Heating the MA sample at 1020 K for 0.5 h resulted in the formation of the hexagonal CaCu5-type structure. It was found that the electrodes prepared from the nanocrystalline powders had almost similar discharge capacities, compared with the negative electrode prepared from polycrystalline powders. In the annealed nanocrystalline MmNi3.5Al0.8Co0.7 powders discharging capacities up to 135 mAh g-1 (at 160 mA g-1 discharge current) were measured (note, that the lanthanum content in mischmetal was only 25 wt%).