Abstract
TiV-based two-phase hydrogen storage alloys are promising candidates for negative electrode materials of Ni/MH batteries. In this work, phase structures and electrochemical properties of the Ti 0.8Zr 0.2V 2.7Mn 0.5Cr x Ni 1.75 ( x = 0 ∼ 0.7 ) alloys were systematically investigated to get an overall evaluation of Cr in the TiV-based alloys. It was found by XRD and Rietveld analysis that all the alloys consisted of a C14 Laves phase with hexagonal structure and a V-based solid solution phase with BCC structure. With the increasing Cr contents, the abundance of V-based phase increased while the C14 Laves phase decreased gradually. Electrochemical investigations indicated that besides the anticipated improvement of cyclic life, the increasing Cr content also lead to a better high rate dischargeability (HRD) in a certain range, but the discharge capacity decreased with excessive Cr content, which can be attributed to the variation of the composition, abundance and distribution of the two phases in the alloys. Electrochemical impedance spectroscopy (EIS), linear polarization, anode polarization and potentiostatic discharge were employed to study the kinetic properties and the results indicated that HRD of the alloy electrodes were controlled mainly with the hydrogen diffusion resistance inside the alloy particles.
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