Structural and electrochemical properties of hydrogen storage alloys Ti_0.8Zr_0.2V_2.7Mn_0.5Cr _0.8Ni_x (x = 1.50-2.25)

In this paper, the structural and electrochemical properties of the Ti _0.8Zr_0.2V_2.7Mn_0.5Cr _0.8Ni_x (x=1.50, 1.75, 2.00, 2.25) hydrogen storage alloys have been systematically investigated. It was found by XRD and Rietveld analysis that the former two alloys were composed of a C14 Laves phase and a V-based solid solution phase, but a small amount of an impurity phase appeared in the latter two ones. The lattice parameters and cell volumes of the two main phases shrank continuously with the increasing Ni content in the alloys. Electrochemical investigations indicated that the maximum discharge capacity of the alloy electrodes decreased from 327.5 (x=1.50) to 164.5mAh/g (x=2.25), while the cyclic stability improved with increasing Ni content. For the sample x=2.25, after 200 cycles the discharge capacity of the electrode still remained 96.78% of the maximum capacity. High rate dischargeability (HRD) of the alloy electrodes improved at first and then declined with increasing Ni content. Electrochemical impedance spectroscopy (EIS), linear polarization, anode polarization and potentiostatic discharge tests were employed to investigate the kinetic performance of the alloy electrodes.