Finally, the first lithium-based oxygen battery was operated at high temperatures . The negative electrode was made from a porous alloy of Li, Si, and Fe and the electrolyte was a hybrid of molten LiF-LiCl-Li2O (lithium ion conductor) and a CaO doped ZrO2 (oxygen ion conductor). It showed an average voltage of 2.2V, changing with the state of lithiation of the negative electrode. The peak areal power density on discharge was about 200 mW/cm 2 based on the area of the negative electrode. While the electrochemical performance of this device was quite good, the energy density of the device is quite low, due to the use of the Li-Fe-Si alloy, which both lowers the average voltage and also increases the mass of the active components.