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

Abstract

The aprotic Li-O₂ battery has attracted a great deal of interest because theoretically it can store more energy than today's Li-ion batteries. However, current Li-O₂ batteries suffer from passivation/clogging of the cathode by discharged Li₂ O₂ , high charging voltage for its subsequent oxidation, and accumulation of side reaction products (particularly Li₂ CO₃ and LiOH) upon cycling. Here, an advanced Li-O₂ battery with a hexamethylphosphoramide (HMPA) electrolyte is reported that can dissolve Li₂ O₂ , Li₂ CO₃ , 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-O₂ batteries, improved capacity, rate capability, voltaic efficiency, and cycle life are achieved for the HMPA-based Li-O₂ cells. More importantly, a combination of advanced research techniques provide compelling evidence that operation of the HMPA-based Li-O₂ battery is backed by nearly reversible formation/decomposition of Li₂ O₂ with negligible side reactions.