Thermodynamic strategies to increase solubility for higher energy density in organic redox flow batteries

Improving the solubility of redox-active organic molecules (ROMs) in electrolyte solutions is vital for boosting the energy density of redox flow batteries and avoiding precipitation issues. This study explores six thermodynamic strategies to enhance ROM solubility by lowering melting points or activity coefficients. Minor structural changes—such as tuning alkyl side chains, repositioning functional groups, or altering ROM ligands—introduce molecular asymmetry, consistently increasing solubility and energy density in various electrolyte solutions. Furthermore, tailored co-solvents or salting-in agents strengthen solute–solvent interactions, reducing activity coefficients. COSMO-RS proves effective for qualitatively assessing these modifications. These strategies collectively offer a structured approach to designing molecules and selecting solvent additives, optimizing ROM solubility and elevating battery performance. • Six thermodynamic strategies to enhance ROM solubility for higher battery energy density. • Molecular asymmetry increases solubility by lowering melting properties. • Task-specific co-solvents and salting-in agents optimize solute-solvent interactions. • COSMO-RS effectively screens structural modifications to predict solubility trends. • Guidelines for ion management improve ROM stability and electrolyte compatibility.