Decoupling the influence of dielectric constant and electrolyte structure on ion transport and dissociation

The development of next generation water treatment, sustainable energy, and resource extraction technologies requires a fundamental understanding of complex electrolyte systems. Ion dissociation, or "ionicity", describes the extent to which cations and anions exist as individual, "free" species in electrolyte systems and serves as a powerful metric connecting molecular-level interactions to the electrochemical and thermophysical properties of these systems. While solvent polarity (i.e., dielectric constant) has a significant impact on ion dissociation and electrolyte ionic conductivity, isolating its continuum-scale effects from molecular-level solvent- and ion-specific interactions that promote higher order ion-clustering remains challenging. In the present study, we employ a combined experimental and theoretical approach to systematically elucidate the role of the continuum-scale solvent dielectric constant and molecular-level interactions in governing ion dissociation and transport in ternary lithium chloride-ethanol-water electrolytes. By varying the solvent composition, we systematically tune its dielectric constant and employ pulsed field gradient NMR, electrophoretic NMR, and molecular dynamics simulations to directly probe ion and solvent self-diffusivities, electrophoretic mobilities, and solvation environments. Through this approach, we reveal the importance of electrolyte structure and the strength of the hydrogen bonding network in governing transport properties across multiple length scales. We also establish a workflow that can be readily applied to inform the design of more complex electrolytes for applications including energy storage, water treatment, and chemical separation technologies.