Interplay of Solvation Dynamics and Ion Transport in Concentrated LiFSA-Sulfone Electrolytes

Understanding how solvation dynamics govern lithium-ion transport is central to designing high-performance electrolytes. In this work, we combine molecular dynamics (MD) and metadynamics simulations with machine-learned force-field optimization to unravel the interplay between solvation structure, ligand-exchange kinetics, and macroscopic transport in concentrated lithium bis(fluorosulfonyl) amide (LiFSA)-sulfone electrolytes. The results reveal two distinct transport regimes: a solvent-dominated, highly ordered solvation environment in cyclic symmetric sulfolane (SL) that supports long-lived coordination and vehicular-like diffusion with intermittent hopping; and a dynamically flexible, hopping-dominated regime in acyclic and asymmetric solvents ethyl methyl sulfone (EMS), dimethyl sulfone (DMS), 3-methyl sulfolane (MSL) characterized by rapid ligand exchange and fluctuating coordination. Metadynamics free-energy surfaces (FES) confirm that SL stabilizes a deep, solvent-rich solvation basin, while EMS and MSL exhibit broader basins reflecting facile reorganization. The computed residence lengths and exchange rates quantitatively connect these microscopic dynamics to macroscopic trends in viscosity and conductivity, highlighting a tradeoff between solvation stability and dynamic mobility. Together, these insights establish a unified mechanistic framework that links solvation energetics and ion transport, providing molecular-level design principles for optimizing conductivity and stability in next-generation lithium electrolytes.