Atomistic Insights into Fluorinated/Chlorinated Ether-Based LHCEs on Lithium Metal: Decomposition Mechanisms via Multiscale Simulations

The interfacial stability of localized high-concentration electrolytes (LHCEs) with fluorinated (F2DEE) or chlorinated (Cl2DEE) ether solvents critically controls lithium metal battery performance. However, atomistic mechanisms driving their solid electrolyte interphase (SEI) formation remain unclear. We systematically compare the decomposition pathways of 1LiFSI-1.6F2DEE-3TTE and 1LiFSI-1.6Cl2DEE-3TTE on Li metal using multiscale simulations: classical molecular dynamics (CMD), ab initio molecular dynamics (AIMD), and density functional theory (DFT). CMD simulations show unique electric double layer (EDL) reorganization under charging; both LHCEs retain FSI^- anions within 6 Å of the Li anode, contrasting with conventional low-concentration electrolytes. This spatial selectivity enables AIMD simulations with two configurations (FSI^--near and FSI^--far interfaces). Results reveal that FSI^- reduction (with solvent participation) dominates over TTE dissociation, with calculated SEI fragment ratios (F/Cl/S) matching the experimental XPS trend. Electronic structure analysis via projected density of states, bond evolution, and Bader charge transfer clarifies decomposition sequences. DFT identifies key dehalogenation differences: F2DEE requires 0.11 eV energy barrier for defluorination, while Cl2DEE undergoes spontaneous barrierless dechlorination. This explains higher organic carbon content in Cl2DEE-derived SEI observed experimentally. Our work establishes a multiscale framework correlating solvation evolution, EDL dynamics, and SEI mechanisms, providing atomistic design guidelines for stable high-voltage lithium battery electrolytes.