To develop reversible Li-O-2 batteries, the need for novel carbon-free cathode materials is evident. In this study, we present the hydrothermal synthesis of highly conductive crystalline antimony doped tin oxide (ATO) nanoparticles, the fabrication of ATO electrodes with high surface area, and their application as cathodes in aprotic Li-O-2 cells. We use a pressure transducer and an online electrochemical mass spectrometer to quantify consumed and evolved gases during discharge and charge of Li-O-2 cells. Solid discharge products on the cathode are identified by infrared spectroscopy and quantified by acid-base titration and UV-vis spectroscopy. Thus we demonstrate an unprecedented cell chemistry: In contrast to carbon cathodes, ATO cathodes enable the formation of Li2O and prevent the formation of carbonates on the cathode surface. Formed Li2O can be recharged at high potentials, which leads to the evolution of oxygen. These new mechanistic insights provide implications for cathode design concepts that might enable the reversible cycling of Li-O-2 cells. (C) The Author(s) 2017. Published by ECS. All rights reserved.