Tailoring Electrochemical Properties of Ether-Based Solvents through Fluorination-Driven Solvation Control

The solvation structure of electrolytes plays a crucial role in determining the performance of sodium-ion batteries (SIBs). In this study, we employ a combined atomistic modeling approach of molecular dynamics (MD) simulations and density functional theory (DFT) calculations to investigate the impact of fluorination on the solvation structure and reductive stability of a series of fluorinated diethyl ether (FDEE) solvents for SIBs. Our findings reveal that fluorination significantly influences the Na+ solvation environment, leading to a decrease in solvation strength and a shift toward anion-dominated solvates. However, bilaterally substituted FDEEs with a low degree of fluorination exhibit enhanced solvation due to favorable Na–F interactions. Highly fluorinated FDEEs promote the formation of clustered solvation shells, reminiscent of high-concentration electrolytes, which facilitate Na+ desolvation and enhance reductive stability. Furthermore, we demonstrate that the position and degree of fluorination significantly affect the LUMO levels and reduction potentials of FDEE molecules, providing insights into their electrochemical stability. This study elucidates the complex interplay between fluorination, solvation structure, and electrochemical properties in FDEE-based electrolytes, offering valuable insights into molecular features that influence high-performance electrolyte design.