Despite the promise of extremely high theoretical capacity (2Li + 02 Li2O2, 1675 mAh per gram of oxygen), many challenges currently impede development of Li/O-2 battery technology. Finding suitable electrode and electrolyte materials remains the most elusive challenge to date. A radical new approach is to replace volatile, unstable and air -intolerant organic electrolytes common to prior research in the field with alkali metal nitrate molten salt electrolytes and operate the battery above the liquidus temperature (>80 degrees C). Here we demonstrate an intermediate temperature Li/O-2, battery using a lithium anode, a molten nitrate -based electrolyte (e.g., LiNO3-KNO3 eutectic) and a porous carbon 02 cathode with high energy efficiency (similar to 95%) and improved rate capability because the discharge product, lithium peroxide, is stable and moderately soluble in the molten salt electrolyte. The results, supported by essential state-of--the-art electrochemical, and analytical techniques such as in situ pressure and gas analyses, scanning electron microscopy, rotating disk electrode voltammetry, demonstrate that Li2O2 electro-chemically forms and decomposes upon cycling with discharge/charge overpotentials as low as life of such batteries is limited only by carbon reactivity and by the uncontrolled precipitation of Li2O2, which eventually becomes electrically disconnected from the O-2 electrode.