Phase Structure and Electrochemical Characteristics of Ml(Ni3.55Co0.75Mn0.40Al0.30)5x (x = 0.88, 0.92, 0.96, 1.00) Hydrogen Storage Alloys

The phase structure and electrochemical characteristics of Ml (Ni3.55Co0.75Mn0.40Al0.30)5x (x = 0.88, 0.92, 0.96, 1.00) hydrogen storage alloys were studied. The effect of the stoichiometric ratio on the phase structure and electrochemical characteristics was analyzed. The results of XRD reveal that all the alloys consist mainly of LaNi5 phase with the hexagonal CaCu5 structure. But a few of the diffraction peaks of La2Ni7 phase on XRD pattern are observed when x < 0.92, and with decreasing x, the intensity of La2Ni7 diffraction peaks increases and the values of lattice parameters a and cell volume increase, c and c/a of LaNi5 phase decrease gradually. When x >0.96, La2Ni7 phase disappears and the alloys become single CaCu5-type. The electrochemical tests show that the maximum discharge capacity, high rate dischargeability and low temperature dischargeability are improved to different degrees by adjusting the stoichiometric ratio.