Phase Structure and Electrochemical Characteristics of Ml(Ni 3.55Co 0.75Mn 0.40Al 0.30) 5 x ( x = 0.88, 0.92, 0.96, 1.00) Hydrogen Storage Alloys

Abstract

The phase structure and electrochemical characteristics of Ml (Ni 3.55Co 0.75Mn 0.40Al 0.30) 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 LaNi 5 phase with the hexagonal CaCu 5 structure. But a few of the diffraction peaks of La 2Ni 7 phase on XRD pattern are observed when x < 0.92, and with decreasing x, the intensity of La 2Ni 7 diffraction peaks increases and the values of lattice parameters a and cell volume increase, c and c/a of LaNi 5 phase decrease gradually. When x >0.96, La 2Ni 7 phase disappears and the alloys become single CaCu 5-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.