Tris(pentafluorophenyl)silane as a Solid Electrolyte Interphase (SEI)-Forming Agent for Graphite Electrodes

Abstract

Tris(pentafluorophenyl)silane (TPFPS) is examined as a solid electrolyte interphase (SEI)-forming agent for a graphite electrode. The surface film (SEI layer) generated from a conventional carbonate-based electrolyte (TPFPS-free) is so poorly passivating that continued reductive electrolyte decomposition and concomitant film deposition are employed to increase its thickness. Thus, the electrode develops more sluggish kinetics. An electrochemical quartz crystal microbalance (EQCM) study demonstrates that TPFPS is preferentially electroreduced before the organic carbonate solvents on the copper electrode, as predicted from ab initio calculations. Preferential electroreduction of TPFPS over the carbonate-based electrolyte is also observed after first lithiation of the graphite electrode. This gives a more compact and evenly covered SEI layer. The passivating ability of the resulting SEI layer is so high that additional electrolyte decomposition/film deposition is greatly suppressed. Consequently, both Li/graphite half-cell and graphite/LiCoO2 full-cell show higher Coulombic efficiency and better capacity retention in the TPFPS-added electrolyte.