We report tris(pentafluorophenyl) borane (TPFPB) as a novel electrolyte additive for silicon (Si) thin film anodes in lithium ion batteries. The introduction of TPFPB into the electrolyte consisting of 1 M lithium perchlorate (LiClO4) in ethylene carbonate (EC)/diethyl carbonate (DEC) (1/1 volume) significantly enhances the capacity retention and coulombic efficiency. Specifically, TPFPB enables the improved properties by forming stable solid-electrolyte interphase (SEI) layers and suppressing surface pulverization. The SEI layers are thoroughly characterized by a variety of analytical tools including scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (X PS). (C) 2011 Elsevier Ltd. All rights reserved.