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

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 (Li ₂ O ₂ ). 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 (Li ₂ O). 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 Li ₂ O 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.
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