Microstructure and electrochemical characteristics of non-stoichiometric hydrogen-absorbing alloys with a composition of Mm(Ni0.64Co0.20Al0.04Mn0.12)4.76

Four kinds of Mm (Ni0.64Co0.2Al0.04Mn0.12)(4.76) alloy for a negative electrode of nickel-metal hydride secondary batteries were prepared by induction melting with/without annealing and rapid quenching with/without annealing. Their microstructure and electrochemical characteristics, discharge capacity add charge-discharge cycle performance were examined. The microstructure was observed by using an electron-probe micro analyzer and an X-ray powder diffractometer. Discharge capacity was measured by using a half cell, while charge-discharge cycle performance was measured by using an AA size test cell. As the results the Mm (Ni0.64Co0.20Al0.04Mn0.12)(4.76) alloy obtained by rapid quenching with annealing was found to have the most homogenized microstructure, flattest plateau slope in the P-C isotherms and largest hydrogen content, which lead to the highest discharge capacity of 328 mAh.g(-1) in the half cell and the best charge-discharge cycle performance of 18 % degradation after 800 cycles in the AA size test cell.