Bifunctional Oxygen Electrocatalysts for Lithium−Oxygen Batteries

Lithium−oxygen batteries have attracted great attention over the last few decades owing to their extraordinarily high theoretical energy density, which can potentially exceed that of current state-of-art lithium-ion batteries. However, lithium−oxygen batteries exhibit poor cycle stability, relatively low power capability and significantly large polarizations for both, the oxygen reduction reaction (ORR, discharge) and the oxygen evolution reaction (OER, charge). To address these issues, various catalysts for aqueous and non-aqueous lithium−oxygen batteries have thus been introduced, and some recent developments of bifunctional catalysts could simultaneously facilitate the ORR and OER, leading to great advancements in the overall battery performance. Herein, we present a brief overview of recent progress in the development of bifunctional catalysts for lithium−oxygen batteries based on the current understanding of their working mechanism. Perovskite-type, spinel-type, and non-oxide catalysts and their use in aqueous lithium−oxygen batteries are reviewed. Recently reported bifunctional catalysts in non-aqueous lithium−oxygen batteries are also introduced, and the different roles of solid- and soluble-type catalysts are further discussed. Finally, we conclude by deliberating the design prospects and perspectives for efficient bifunctional catalysts for future lithium−oxygen batteries.