Lithium-oxygen (Li-O-2) batteries have attracted much attention owing to the high theoretical energy density afforded by the two-electron reduction of O-2 to lithium peroxide (Li2O2). We report an inorganic-electrolyte Li-O-2 cell that cycles at an elevated temperature via highly reversible four-electron redox to form crystalline lithium oxide (Li2O). It relies on a bifunctional metal oxide host that catalyzes O-O bond cleavage on discharge, yielding a high capacity of 11 milliampere-hours per square centimeter, and O-2 evolution on charge with very low overpotential. Online mass spectrometry and chemical quantification confirm that oxidation of Li2O involves transfer of exactly 4 e(-)/O-2. This work shows that Li-O-2 electrochemistry is not intrinsically limited once problems of electrolyte, superoxide, and cathode host are overcome and that coulombic efficiency close to 100% can be achieved.