Owing to its high theoretical specific
energy, the Li-oxygen battery
is one of the fundamentally most promising energy storage systems,
but also one of the most challenging. Poor rechargeability, involving
the oxidation of insoluble and insulating lithium peroxide (Li<sub>2</sub>O<sub>2</sub>), has remained the “Achilles’
heel” of this electrochemical energy storage system. We report
here on a new redox mediator tris[4-(diethylamino)phenyl]amine
(TDPA), thatat 3.1 Vexhibits the lowest and closest
potential redox couple compared to the equilibrium voltage of the
Li-oxygen cell of those reported to date, with a second couple also
at a low potential of 3.5 V. We show it is a soluble “catalyst”
capable of lowering the Li<sub>2</sub>O<sub>2</sub> charging potential
by >0.8 V without requiring direct electrical contact of the peroxide
and that it also facilitates high discharge capacities. Its chemical
and electrochemical stability, fast diffusion kinetics, and two dynamic
redox potentials represent a significant advance in oxygen-evolution
catalysis. It enables Li–O<sub>2</sub> cells that can be recharged
more than 100 cycles with average round-trip efficiencies >80%,
opening
a new avenue for practical Li-oxygen batteries