Mechanistic Insight on the Stability of Ether and Fluorinated Ether Solvent-Based Lithium Bis(fluoromethanesulfonyl) Electrolytes near Li Metal Surface
Harender S. Dhattarwal, Jer‐Lai Kuo, Hemant K. Kashyap
Abstract
Recently, ether-based solvents and their fluorinated derivatives have shown extraordinary ability to facilitate the formation of a highly stable ultrathin solid-electrolyte interphase (SEI) layer in lithium metal batteries (LMBs). Herein, density functional theory based molecular dynamics (DFT-MD) simulations have been performed to provide a mechanistic insight on the stability of Li bis(fluoromethanesulfonyl)imide ([Li][FSI]) salt dissolved in dimethoxybutane (DMB) and fluorinated dimethoxybutane (FDMB) solvents near the surface of lithium metal which is employed as anode in LMBs. It is observed that because of the strong reducing nature of Li, the FSI anions in both of the electrolytes readily dissociate to form LiF, Li2O, and other species. Our analysis reveals that while the DMB molecules in the [Li][FSI]-DMB system are relatively stable against reductive dissociation, the FDMB molecules in the [Li][FSI]-FDMB system easily undergo reductive dissociation upon charge transfer from the Li surface. It is shown that the SF bonds of the FSI anions and CF bonds of FDMB molecules are the first ones to break upon their exposure to the Li metal surface. It is observed that the dissociated species of [Li][FSI]-FDMB electrolyte cover the Li surface completely, preventing further dissociation of other FSI anions and solvent molecules. It is found that the FDMB dissociation majorly contributes F atoms forming additional LiF which is an essential component for the formation of a uniform and robust SEI.