Effects of Stoichiometric Ratio on the Microstructure and Electrochemical Properties of Ml<sub>0.96</sub>Mg<sub>0.04</sub>(Ni<sub>0.846</sub>Co<sub>0.014</sub>Mn<sub>0.08</sub>Al<sub>0.06</sub>)<sub>x</sub> (x=5.0-5.3) Alloys

Abstract

The as-cast Ml0.96Mg0.04(Ni0.846Co0.014Mn0.08Al0.06)x (x=5.0, 5.1, 5.2, 5.3) hydrogen storage alloys were prepared by vacuum induction melting method under argon atmosphere. Crystal structure, hydrogen absorption, desorption properties and electrochemical properties were investigated by means of XRD, SEM, EDS, PCT (Pressure Composition isotherms) and tri-electrode tests. The XRD and SEM results showed that the alloy were consisted of CaCu5-type phase as the main phase and (Al, Mn)(Ni, Co)2-type phase as the secondary phase. The content of the second phase increased as the stoichiometric ratio increased. PCT results indicated that the amount of hydrogen absorption decreased, while the hydrogen-desorption plateau pressure increased as the stoichiometric ratio increased. The electrochemical test results exhibited that the alloys had excellent activation performance at the second cycle, and the maximum capacity of the alloys were 341.2 mAh/g, 336.5 mAh/g, 333.6 mAh/g, 330.3 mAh/g as the stoichiometric x=5.0, 5.1, 5.2, 5.3, respectively. In addition, the cycle life increased slightly as the stoichiometric ratio increased. ML0.96Mg0.04(Ni0.846Co0.014Mn0.08Al0.06)5.0 had the best performance due to the combine action of trace Mg and stoichiometric ratio.