High‐Capacity and Stable Li‐O 2 Batteries Enabled by a Trifunctional Soluble Redox Mediator

Li‐O 2 batteries with ultrahigh theoretical energy densities usually suffer from low practical discharge capacities and inferior cycling stability owing to the cathode passivation caused by insulating discharge products and by‐products. Here, a trifunctional ether‐based redox mediator, 2,5‐di‐tert‐butyl‐1,4‐dimethoxybenzene (DBDMB), is introduced into the electrolyte to capture reactive O 2 − and alleviate the rigorous oxidative environment of Li‐O 2 batteries. Thanks to the strong solvation effect of DBDMB towards Li + and O 2 − , it not only reduces the formation of by‐products (a high Li 2 O 2 yield of 96.6 %), but also promotes the solution growth of large‐sized Li 2 O 2 particles, avoiding the passivation of cathode as well as enabling a large discharge capacity. Moreover, DBDMB makes the oxidization of Li 2 O 2 and the decomposition of main by‐products (Li 2 CO 3 and LiOH) proceed in a highly effective manner, prolonging the stability of Li‐O 2 batteries (243 cycles at 1000 mAh g −1 and 1000 mA g −1 ).