Effect of Mixed EC/DMC Solvent Composition and Temperature on Structure and Ion Transport in a Lithium Bis(fluorosulfonyl)imide Salt-Based Battery Electrolyte

Carbonate-based lithium battery electrolytes are chosen due to their excellent chemical stability and electrochemical performance. In this work, using several computational methods, we have investigated the effect of ethyl carbonate (EC)-dimethyl carbonate (DMC) composition (and temperature) mixed with a lithium bis(fluorosulfonyl)imide salt (LiFSI). Density Functional Theory (DFT) calculations predict the relative stability of several Li + -(solvent/anion) complexes. The calculations show that EC-rich Li + -(solvent) complexes are more stable compared to DMC-rich complexes. Classical Molecular Dynamics (MD) simulations demonstrate that interactions between Li + ions and EC/DMC solvents are stronger compared to Li + –FSI – interactions. The diffusion of Li + ions and FSI – ions is higher in DMC-rich compared to EC-rich environments. The qualitative trends in ionic conductivity agree with experiments, where a maximum value of ionic conductivity is obtained at an EC mole fraction of 0.3–0.4. Overall, results from DFT, MD simulations, and correlation analysis show that an interplay between stability, structure, and ion transport shows an optimum EC/DMC composition as a suitable solvent for battery electrolytes.