Force-field parameters for vanadium ions (+Â 2, +Â 3, +Â 4, +Â 5) to investigate their interactions within the vanadium redox flow battery electrolyte solution

With a long term objective of investigating the molecular interactions of vanadium ions with different moieties in the conventional vanadium redox flow battery (VRFB) aqueous electrolyte solution, as well as with the additives in the electrolyte, force-field parameters for vanadium ions are proposed. The parameterization of vanadium ions is performed on the basis of first solvation shell structure for vanadium ions in water obtained by density functional theory (DFT) calculations. Car-Parrinello molecular dynamics (CPMD) simulations were performed to benchmark the proposed force field parameters in the condensed phase environment. The water-vanadium interactions obtained by the proposed parameters are also compared with the extended X-ray absorption fine structure (EXAFS) data in the literature. (Krakowiak et al., Inorganic Chemistry. 51, 2012, 9598-9609.) The regular octahedral structure of oxygen atoms around V2 + and V3 + and distorted octahedral structure of oxygen atoms around V4 + and V5 +, as revealed by EXAFS, are reproduced accurately by the suggested force-field parameters. These validated parameters can now be used to perform molecular dynamics simulations on the VRFB electrolyte solution to obtain fundamental understanding of the effect of different additives on solubility and thermal stability of vanadium ions within the VRFB electrolyte.