The Li-O2 cell can be thought of as a battery-fuel cell hybrid, although it is more a derivative of metal-air batteries (e.g. Zn-air). A schematic representation of the rechargeable non-aqueous Li-O2 cell is shown in Fig 1. On discharge, lithium ions formed at the lithium metal anode are transported across the electrolyte and into the pores of the air-cathode. O2 from the atmosphere enters the cathode, and dissolves into the electrolyte within the pores. It is then reduced at the porous carbon electrode surface by electrons from the external circuit and combines with Li+ from the electrolyte, leading to the formation of solid Li2O2 as the final discharge product. Surprisingly, the reaction is reversible, Li2O2 can be oxidised, releasing oxygen gas, thus making this an energy storage device: 2Li + O2 ↔ Li2O2.