Charging a Li–O2 battery using a redox mediator

The non-aqueous Li–air (O2) battery is receiving intense interest because its theoretical specific energy exceeds that of Li-ion batteries. Recharging the Li–O2 battery depends on oxidizing solid lithium peroxide (Li2O2), which is formed on discharge within the porous cathode. However, transporting charge between Li2O2 particles and the solid electrode surface is at best very difficult and leads to voltage polarization on charging, even at modest rates. This is a significant problem facing the non-aqueous Li–O2 battery. Here we show that incorporation of a redox mediator, tetrathiafulvalene (TTF), enables recharging at rates that are impossible for the cell in the absence of the mediator. On charging, TTF is oxidized to TTF+ at the cathode surface; TTF+ in turn oxidizes the solid Li2O2, which results in the regeneration of TTF. The mediator acts as an electron–hole transfer agent that permits efficient oxidation of solid Li2O2. The cell with the mediator demonstrated 100 charge/discharge cycles.