Fundamental Understanding of Oxidative Stability in Fluorinated Asymmetric Ethers for Li Batteries

Fluorination strategies for electrolyte solvents are widely used to improve the electrochemical performance and cycling stability of Li-metal batteries. Recently, β-fluorinated 1-ethoxy-2-methoxyethane (FxEME) has been designed and shown to exhibit excellent oxidative stability. However, solvent design remains largely empirical, and its atomistic-level effects are not fully understood. Here, we investigated how fluorination affects the oxidative stability of asymmetric ethers, (Fx)EME, using multiscale modeling with density functional theory (DFT), ab initio molecular dynamics (AIMD), and machine-learning force field (MLFF)-MD. DFT and AIMD capture fluorination-induced electronic-structure changes with high accuracy, while MLFF-MD enables exploration of interfacial reactions at larger time and length scales. Our results indicate that β-fluorination stabilizes ethoxy C-H bonds via inductive effects and weakens solvent-cathode (Li_0.5NiO₂) interactions through electron redistribution, mitigating oxidation and C-C activation. Furthermore, the increased dipole moment of F3EME drives a preferential orientation that shields the methoxy group. Overall, these three fluorination-induced effects confer FxEME significantly higher oxidative stability than EME. This work provides atomistic insights into fluorination-driven electronic and interfacial effects, supporting rational electrolyte design.