| Summary: | <p>Although Li–air rechargeable batteries offer higher energy densities than lithium-ion batteries, the insulating Li<sub>2</sub>O<sub>2</sub> formed during discharge hinders rapid, efficient re-charging. Redox mediators are used to facilitate Li<sub>2</sub>O<sub>2</sub> oxidation; however, fast kinetics at a low charging voltage are necessary for practical applications and are yet to be achieved. We investigate the mechanism of Li<sub>2</sub>O<sub>2</sub> oxidation by redox mediators. The rate-limiting step is the outer-sphere one-electron oxidation of Li<sub>2</sub>O<sub>2</sub> to LiO<sub>2</sub>, which follows Marcus theory. The second step is dominated by LiO<sub>2</sub> disproportionation, forming mostly triplet-state O<sub>2</sub>. The yield of singlet-state O<sub>2</sub> depends on the redox potential of the mediator in a way that does not correlate with electrolyte degradation, in contrast to earlier views. Our mechanistic understanding explains why current low-voltage mediators (<+3.3 V) fail to deliver high rates (the maximum rate is at +3.74 V) and suggests important mediator design strategies to deliver sufficiently high rates for fast charging at potentials closer to the thermodynamic potential of Li<sub>2</sub>O<sub>2</sub> oxidation (+2.96 V).</p>
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