The incorporation of additives designed to sacrificially react on the surface of cathode materials in lithium ion batteries has been investigated. Addition of low concentrations of either 2,5-dihydrofuran or gamma-butyrolactone to 1 M LiPF6 in 1: 1: 1 ethylene carbonate/diethyl carbonate/dimethyl carbonate improves the capacity retention of Li/Li1.17Mn0.58Ni0.25O2 cells cycled at 4.9 V vs Li. A surface analysis of the cathode materials (X-ray photoelectron spectroscopy and IR) suggests that the structure of the cathode surface film is modified by the presence of the additives resulting in a decrease in detrimental electrolyte oxidation reactions on the cathode surface. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3238486] All rights reserved.