A high-energy-density lithium-oxygen battery based on a reversible four-electron conversion to lithium oxide

Lithium-oxygen (Li-O₂) batteries have attracted much attention owing to the high theoretical energy density afforded by the two-electron reduction of O₂ to lithium peroxide (Li₂O₂). We report an inorganic-electrolyte Li-O₂ 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 O₂ evolution on charge with very low overpotential. Online mass spectrometry and chemical quantification confirm that oxidation of Li₂O involves transfer of exactly 4 e^-/O₂ This work shows that Li-O₂ 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.