Enhancing Salt Diffusivity of Battery Electrolytes: Insights from Dynamic Ion Correlation Analysis

Abstract Playing a critical role in electrolyte ion transport, ion correlations influence concentration polarization and ultimately contribute to the rate performance of Li‐ion batteries. This study demonstrates that introducing monoglyme co‐solvent into a carbonate‐based electrolyte enhances salt diffusivity (D_salt) by 30%, effectively mitigating concentration polarization and improving the rate capability of a LiCoO₂ symmetric cell by 70% at 4C operation. Dynamic ion correlation analysis reveals that the improvement in D_salt is driven by increased positive self‐correlations of cations and anions, which represent enhanced random movement of ions, facilitated by reduced viscosity and smaller solvation shell sizes. Conversely, introducing diglyme co‐solvent reduces D_salt and deteriorates the rate capability. Although diglyme also improves self‐correlations through reduced viscosity, its stronger Li‐ion solvation increases cation–cation anti‐correlation, resulting in an unfavorable balance between the correlation terms that suppresses overall salt diffusivity. These findings underscore the significant influence of microscopic ion correlations on macroscopic transport properties, a crucial aspect in optimizing battery performance.