An electrolyte additive based on highly fluorinated phosphate ester structure was identified as being able to stabilize carbonate-based electrolytes on 5 V class cathode surfaces. The synthesis and structural analysis of the additive are described, and preliminary yet encouraging results from electrochemical characterization showed that this additive participates in forming a protective interphasial chemistry not only on transition metal oxide cathode at high voltage (similar to 5 V vs Li) but also on graphitic graphite at low voltage (similar to 0 V vs Li), making it possible to formulate an electrolyte supporting reversible Li+-intercalation chemistry in the coveted 5 V region. (C) 2011 The Electrochemical Society. [DOI:10.1149/1.3532047] All rights reserved.