Effects of Ni on the structural and electrochemical properties of Ti–V-based hydrogen storage alloys

Phase structures and electrochemical properties of the Ti0.8Zr0.2V2.7Mn0.5Cr0.8NixTi0.8Zr0.2V2.7Mn0.5Cr0.8Nix (x=0x=0–1.25) alloys were systematically investigated. It was found by XRD and Rietveld analysis that all of the alloys consisted of a C14 Laves phase with a hexagonal structure and a V-based solid solution phase with BCC structure. With increasing Ni content, the abundance, distribution and lattice parameters of the two phases changed markedly. Electrochemical investigations indicated that the maximum discharge capacity of the alloy electrodes first increased from 27.9 mAh/g (x=0.0)(x=0.0) to 373.7 mAh/g (x=0.75)(x=0.75) and then decreased to 328.6 mAh/g (x=1.25)(x=1.25). Also, increasing Ni content led to significant improvements in the high-rate dischargeability as well as the cyclic stability. Electrochemical impedance spectroscopy (EIS), linear polarization, anodic polarization and potentiostatic discharge tests showed that both the charge transfer resistance at the surface of the electrodes, and the hydrogen diffusion resistance inside the electrodes, decreased with increasing Ni content.