High-Capacity and Stable Li-O2 Batteries Enabled by a Trifunctional Soluble Redox Mediator

Li-O2 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 O2− and alleviate the rigorous oxidative environment of Li-O2 batteries. Thanks to the strong solvation effect of DBDMB towards Li+ and O2−, it not only reduces the formation of by-products (a high Li2O2 yield of 96.6 %), but also promotes the solution growth of large-sized Li2O2 particles, avoiding the passivation of cathode as well as enabling a large discharge capacity. Moreover, DBDMB makes the oxidization of Li2O2 and the decomposition of main by-products (Li2CO3 and LiOH) proceed in a highly effective manner, prolonging the stability of Li-O2 batteries (243 cycles at 1000 mAh g−1 and 1000 mA g−1).