Correlations between Molecular Structure, Solvation Topology, and Transport Properties of Aqueous Organic Flow Battery Electrolyte Solutions

Aqueous organic redox flow batteries (AORFBs) are considered promising technologies for storing energy generated from renewable resources. However, designing organic electrolyte molecules is limited by gaps between fundamental understanding of coupling between solvation structure and dynamics and macroscopic transport properties like viscosity. Herein, we used molecular dynamics simulations to understand correlations among ionic molecular structures, ion clustering, and transport properties in 2,3-dihydrophenazine (2,3-DHP), a promising AORFB anolyte. We show that experimentally measured viscosity can be reproduced from simulations at relevant concentrations and that the asymmetric structure of 2,3-DHP leads to a unique inhomogeneity in the solvation topology. However, order parameters and metrics need to be developed for better correlations over spatiotemporal scales with careful consideration of the inhomogeneity of organic anolyte molecules. We show that the increased size and asymmetry of the anolyte lead to breakdown of assumptions within methods for determining ion transport mechanisms previously developed for Li-ion batteries.