Lithium Cyano Tris(2,2,2-trifluoroethyl) Borate as a Multifunctional Electrolyte Additive for High-Performance Lithium Metal Batteries

Lithium cyano tris(2,2,2-trifluoroethyl) borate (LCTFEB) has been synthesized and investigated as a new electrolyte additive for high-performance lithium metal batteries. LCTFEB is prepared by the reaction of tris(2,2,2-trifluoroethyl) borate with lithium cyanide. The incorporation of LCTFEB into a carbonate-based electrolyte has been investigated. The electrochemical performance of NCM523/Li cells and symmetric Li/Li cells is significantly improved upon the incorporation of LCTFEB (5 wt %) into the electrolyte. Various characterizations of the lithium metal morphology and the solid electrolyte interphase (SEI) on the lithium metal anode have been conducted using field-emission scanning electron microscopy, cryogenic transmission electron microscopy, and X-ray photoelectron spectroscopy, suggesting the generation of a thin (∼10 nm) LiF-rich SEI with low concentrations of B and N compounds. The different SEI structures are formed by the preferential reductive decomposition of LCTFEB, resulting in improved electrochemical performance. The new electrolyte additive provides insight into innovative approaches for multifunctional electrolyte additive design.