LiCoO2/graphite and Li[Ni1/3Mn1/3Co1/3]O-2/graphite pouch cells and Li[Ni1-x-yMnxCoy]O-2/graphite 18650 cells were made with varying concentrations of vinylene carbonate (VC) and studied using high precision coulometry, extended cycling as well as electrochemical impedance spectroscopy (EIS). As expected, adding increased concentrations of VC (up to 6 wt%) to the control electrolyte resulted in improved coulombic efficiency, decreased charge endpoint, slippage and longer cycle life. However, high concentrations of VC led to larger charge transfer resistance, especially at the graphite negative electrode. Understanding how varying amounts of VC impact cell lifetime and impedance allows for optimized electrolyte formulations to be found for different applications that may balance lifetime and power demands. (C) 2013 The Electrochemical Society. All rights reserved.