Influences of Rapid Quenching on the Structures and Electrochemical Performances of La0.7Mg0.3Co0.45Ni2.55-xFex (x=0-0.4) Electrode Alloys

The influences of rapid quenching on the structures and electrochemical behaviors of La-Mg-Ni system (PuNi3-type) La0.7Mg0.3Co0.45Ni2.55-xFex (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys were systemically investigated. The results show that the rapid quenching, instead of changing the phase structures of the alloys, leads to c axis enlarged and the a axis and cell volumes of the LaNi5 and (La, Mg)Ni-3 major phases decreased slightly. The morphologies of the as-quenched alloys exhibit a massive structure, which differ from that of the as-quenched AB(5)-type alloy. The rapid quenching clearly impairs some electrochemical performances of the alloys, involving discharge capacity, high rate discharge ability (HRD) and discharge potential, but it significantly prolongs the cycle life of the alloy. With an increase in the quenching rate from 0 (As-cast was defined as quenching rate of 0 m/s) to 30 m/s, the discharge capacity of the alloy (x = 0.4) decreases from 351.06 to 313.36 mAh/s, the HRD from 69.36 to 50.54%, whereas its cycle life increases from 106 to 166 cycles at a charging discharging current density of 600 mA/g.