High-Capacity and Stable Li-O Batteries Enabled by a Trifunctional Soluble Redox Mediator.

Li-O 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 and alleviate the rigorous oxidative environment of Li-O batteries. Thanks to the strong solvation effect of DBDMB towards Li and O , it not only reduces the formation of by-products (a high Li O yield of 96.6 %), but also promotes the solution growth of large-sized Li O particles, avoiding the passivation of cathode as well as enabling a large discharge capacity. Moreover, DBDMB makes the oxidization of Li O and the decomposition of main by-products (Li CO and LiOH) proceed in a highly effective manner, prolonging the stability of Li-O batteries (243 cycles at 1000 mAh g and 1000 mA g ).