A rechargeable lithium–oxygen battery with dual mediators stabilizing the carbon cathode

At the cathode of a Li–O₂ battery, O₂ is reduced to Li₂ O₂ on discharge, the process being reversed on charge. Li₂ O₂ is an insulating and insoluble solid, leading ultimately to low rates, low capacities and early cell death if formed on the cathode surface. Here we show that when using dual mediators, 2,5-Di-tert-butyl-1,4-benzoquinone [DBBQ] on discharge and 2,2,6,6-tetramethyl-1-piperidinyloxy [TEMPO] on charge, the electrochemistry at the cathode surface is decoupled from Li₂ O₂ formation/decomposition in solution. Capacities of 2 mAh cm⁻² areal are demonstrated, and up to 40 mAh cm⁻² at rates ≫1 mA cm⁻² areal areal can be devised. One of the major barriers to the progress of Li–O₂ at 1 mA cm−2 with low polarization on charge/discharge areal are anticipated if suitable gas diffusion electrodes cells is decomposition of the carbon cathode. By forming/decomposing Li₂ O₂ in solution and avoiding high charge potentials, the carbon instability is significantly mitigated (<0.008% decomposition per cycle compared with 0.12% without mediators).