Localized high concentration electrolytes decomposition under electron-rich environments

Localized high concentration electrolytes have been proposed as an effective route to construct stable solid-electrolyte interphase (SEI) layers near Li-metal anodes. However, there is still a limited understanding of the decomposition mechanisms of electrolyte components during SEI formation. In this work, we investigate reactivities of lithium bis(fluorosulfonyl)imide (LiFSI, salt), 1,2-dimethoxyethane (DME, solvent), and tris(2,2,2-trifluoroethyl)orthoformate (TFEO, diluent) species in DME + TFEO mixed solvents and 1M LiFSI/DME/TFEO solutions. By supplying an excess of electrons into the simulation cell, LiFSI is initially reduced via a four-electron charge transfer reaction yielding F^- and N(SO₂)₂ ^3-. The local solvation environment has little effect on the subsequent TFEO reaction, which typically requires 6 |e| to decompose into F^-, HCOO^-, CH₂CF^-, and ^-OCH₂CF₃. Besides, the TFEO dehydrogenation reaction mechanism under an attack of anions is also identified. Unlike salt and diluent, DME shows good stability with any excess of electrons. The energetics of most relevant reactions are characterized. Most reactions are thermodynamically favorable with low activation barriers.