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 Li ₂O₂ 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 Li₂O ₂, which results in the regeneration of TTF. The mediator acts as an electron-hole transfer agent that permits efficient oxidation of solid Li ₂O₂. The cell with the mediator demonstrated 100 charge/discharge cycles.