Trifunctional soluble redox mediator enabled high-capacity and stable Li-O2 batteries

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, we firstly introduce a new kind of trifunctional ether-based redox mediator, 2,5-di-tert-butyl-1,4-dimethoxybenzene (DBDMB), into the electrolyte to capture the reactive O 2 - and alleviate the rigorous oxidative environment during cycling of Li-O 2 batteries. Thanks to the strong solvation of DBDMB towards Li + and O 2 - , it can not only reduce the formation of by-products (a high Li 2 O 2 yield of 96.6%), but also promote the solution growth of large-sized Li 2 O 2 particles, avoiding the passivation of cathode as well as enabling a large discharge capacity. More encouragingly, 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 ). DFT calculations also unravel the intrinsic functional mechanism of DBDMB for facilitating the reversible O 2 involved redox reactions. Our strategy of using trifunctional electrolyte additive to capture reactive discharge intermediates with reduced formation of by-products, regulate solution growth of Li 2 O 2 , and co-oxidize Li 2 O 2 and by-products, will open up a new avenue to promote the performance of Li-air batteries.