Quantum chemical methods have been used to study reduction mechanisms of ethylene carbonate (EC), propylene carbonate (PC), and vinylethylene carbonate (VEC), in electrolyte solutions. The feasibility of direct two-electron reduction of these species was assessed, and no barrier to reaction was found for the formation of Li2CO3 and 1,4-butadiene from VEC. In contrast EC and PC have barriers to reaction on the order of 0.5 eV. The ready formation of Li2CO3 when VEC is reduced may explain why it acts as a good passivating agent in lithium-ion cells. (C) 2003 The Electrochemical Society.