Lithium-air batteries have attracted extensive attention in the general energy field. To enhance the practical applicability of lithium-air batteries, the overpotential caused by the diffusion of oxygen in the cathode, a significant component of the total overpotential, should be well comprehended. In this work, a wetted model is derived to evaluate the energy loss associated with liquid electrolytes. The oxygen diffusion in both electrolytes and porous cathodes is investigated systematically by taking oxygen concentration distribution into account. By analyzing the factors associated with cathode overpotential, such as the cathode thickness of and the viscosity of electrolyte, our work facilitates the improvement in the electrochemical performance of lithium-air batteries. (C) 2015 Elsevier Ltd. All rights reserved.