Modeling Electrochemical Decomposition of Fluoroethylene Carbonate on Silicon Anode Surfaces in Lithium Ion Batteries

Abstract

Fluoroethylene carbonate (FEC) shows promise as an electrolyte additive for\nimproving passivating solid-electrolyte interphase (SEI) films on silicon\nanodes used in lithium ion batteries (LIB). We apply density functional theory\n(DFT), ab initio molecular dynamics (AIMD), and quantum chemistry techniques to\nexamine excess-electron-induced FEC molecular decomposition mechanisms that\nlead to FEC-modified SEI. We consider one- and two-electron reactions using\ncluster models and explicit interfaces between liquid electrolyte and model\nLi(x)Si(y) surfaces, respectively. FEC is found to exhibit more varied reaction\npathways than unsubstituted ethylene carbonate. The initial bond-breaking\nevents and products of one- and two-electron reactions are qualitatively\nsimilar, with a fluoride ion detached in both cases. However, most one-electron\nproducts are charge-neutral, not anionic, and may not coalesce to form\neffective Li+-conducting SEI unless they are further reduced or take part in\nother reactions. The implications of these reactions to silicon-anode based LIB\nare discussed.\n