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 Li2O2, high charging voltage for its subsequent oxidation, and accumulation of side reaction products (particularly Li2CO3 and LiOH) upon cycling. Here, an advanced Li-O-2 battery with a hexamethylphosphoramide (HMPA) electrolyte is reported that can dissolve Li2O2, Li2CO3, and LiOH up to 0.35, 0.36, and 1.11 x 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 Li2O2 with negligible side reactions.