Low electronic conduction is expected to be a main limiting factor in the performance of reversible lithium-air, Li-O(2), batteries. Here, we apply density functional theory and non-equilibrium Green's function calculations to determine the electronic transport through lithium peroxide, Li(2)O(2), formed at the cathode during battery discharge. We find the transport to depend on the orientation and lattice matching of the insulator-metal interface in the presence of Au and Pt catalysts. Bulk lithium vacancies are found to be available and mobile under battery charging conditions, and found to pin the Fermi level at the top of the anti bonding peroxide pi*(2p(x)) and pi*(2p(y)) levels in the Li(2)O(2) valence band. Under an applied bias, this can result in a reduced transmission, since the anti bonding sigma*(2p(z)) level in the Li(2)O(2) conduction band is found to couple strongly to the metal substrate and create localized interface states with poor coupling to the Li(2)O(2) bulk states. These observations provide a possible explanation for the higher overpotential observed for charging than discharge. (c) 2010 Elsevier B.V. All rights reserved.