Effect of vanadium substitution in C14 Laves phase alloys for NiMH battery application

Vanadium, as the most important B-site modifier in (Zr,Ti)Ni2-based Laves phase alloy, was studied to optimize the performance of nickel metal hydride batteries. As the amount of V-substitution for Ni increases, the total hydrogen storage capacity increases, while the reversible hydrogen storage capacity decreases due to the formation of a stable hydride. Lattice constants increase with higher vanadium contents indicating the majority of vanadium atoms reside in the B-site. Broader X-ray diffraction peaks and higher pressure-concentration isotherm slope factors indicate a higher degree of disorder for alloys with a higher V-content. In the study of a series of alloys with various V, Ni, Ti, Zr contents (while maintaining a constant value of electronegativity), all alloys exhibit similar pressure-concentration isotherms and half-cell characteristics. The sealed NiMH battery performance indicates that in the pure C14 alloy family, low-vanadium alloys (12-13 at.%) are more favorable in regards to peak power stability, charge retention, and cycle life.