A High‐Performance Li–O2 Battery with a Strongly Solvating Hexamethylphosphoramide Electrolyte and a LiPON‐Protected Lithium Anode

The aprotic Li–O 2 battery has attracted a great deal of interest because theoretically it can store more energy than today's Li‐ion batteries. However, current Li–O 2 batteries suffer from passivation/clogging of the cathode by discharged Li 2 O 2 , high charging voltage for its subsequent oxidation, and accumulation of side reaction products (particularly Li 2 CO 3 and LiOH) upon cycling. Here, an advanced Li–O 2 battery with a hexamethylphosphoramide (HMPA) electrolyte is reported that can dissolve Li 2 O 2 , Li 2 CO 3 , and LiOH up to 0.35, 0.36, and 1.11 × 10 −3 m , respectively, and a LiPON‐protected lithium anode that can be reversibly cycled in the HMPA electrolyte. Compared to the benchmark of ether‐based Li–O 2 batteries, improved capacity, rate capability, voltaic efficiency, and cycle life are achieved for the HMPA‐based Li–O 2 cells. More importantly, a combination of advanced research techniques provide compelling evidence that operation of the HMPA‐based Li–O 2 battery is backed by nearly reversible formation/decomposition of Li 2 O 2 with negligible side reactions.