In this work, suberonitrile (SUN) is investigated as both an additive and co-solvent to improve the cycling performance of lithium-rich cathode material such as Li[Li0.2Ni0.56Mn0.16Co0.08]O-2. It is found that using SUN as co-solvent will not improve the cycling performance, but actually deteriorate performance. However, when using SUN as an additive in the electrolyte, cycling performance of the cathode is significantly enhanced. Linear sweep voltammetry (LSV) data indicates that SUN can improve the oxidation potential of mixed solvents. Electrochemical measurements show that the cycling performance of the lithium-rich cathode material Li[Li0.2Ni0.56Mn0.16Co0.08]O-2 in electrolyte with 1% added SUN is better than the performance of the reference system, with a capacity retention of 77.4% after 200 cycles for the former compared with 66.8% for the latter at a current density of 180 mAg(-1). However, the 10% SUN system yields only 22.9% capacity retention after 200 cycles. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) demonstrate that the enhanced electrochemical performance of the cells by using SUN as additive can be ascribed to the modification of the cathode surface layer by the adsorption of SUN. The different effects and acting modes of SUN as an additives and solvent have been discussed and proposed. (C) 2015 The Electrochemical Society. All rights reserved.