A high-capacity Li-ion/Li-oxygen hybrid cathodeElectronic supplementary information (ESI) available: Material synthesis, electrochemical measurements, characterization equipment, methods and the influence of the Super P ratio. See DOI: 10.1039/c5ta03299g

A hybrid Li-ion/Li-oxygen cathode is demonstrated. With a stable ionic liquid electrolyte, the capacity of a conventional LiCoO 2 cathode is greatly enhanced by the Li-oxygen mechanism. Furthermore, the Li-ion mode operation helps to improve the cyclability of the Li-oxygen mode. The Li-oxygen capacity can be a backup power source for occasional usage. The capacity of a conventional LiCoO 2 cathode is greatly enhanced by the Li-oxygen mechanism.