Herein, we report the use of inorganic calcium tetrafluoroborate (Ca(BF4)(2)) as an electrolyte additive to achieve a significant improvement in the reversible capacities of graphite anodes at high rates for lithium ion batteries (LIBs). Even in a low concentration (0.01 M), the addition of Ca(BF4)(2) distinctively modifies the composition of a solid-electrolyte-interface (SEI) film on a graphite surface. While maintaining solid-state diffusivity, the SEI film modified by Ca(BF4)(2) enables facile Li+ transport, which leads to a noticeable decrease in over-potentials for Li+ intercalation/de-intercalation and finally to a remarkable increase in reversible capacities at high rates. For example, the capacity enhancement by ca. 80% can be achieved by adding Ca(BF4)(2) at 0.3 A.g(-1) (346 vs. 192 mAhg(-1)). The Ca(BF4)(2) additive effect is not graphite-morphology dependent. This beneficial effect of Ca(BF4)(2) is ascribed to a synergistic combination of Ca2+ cations and BF4- anions. Ca2+ salts with either different anionic species (Ca(TFSI)(2) and Ca(ClO4)(2)) or different cationic species (LiBF4) also show a certain improvement in capacities, but not as significant as that of Ca(BF4)(2). We hope that the formation of a robust and more ionically conductive SEI layer via this simple addition of Ca(BF4)(2) will be useful in designing fast-charging LIBs. (C) 2019 The Electrochemical Society.