High-Capacity and High-Rate Discharging of a Coenzyme Q10 -Catalyzed Li-O2 Battery.

Discharging of the aprotic Li-O2 battery relies on O2 reduction to insulating solid Li2 O2 , which can either deposit as thin films on the cathode surface or precipitate as large particles in the electrolyte solution. Toward realizing Li-O2 batteries with high capacity and high rate capability, it is crucially important to discharge Li2 O2 in the electrolyte solution rather than on the cathode surface. Here, a soluble electrocatalyst of coenzyme Q10 (CoQ10 ) that can efficaciously drive solution phase formation of Li2 O2 in current benchmark ether-based Li-O2 batteries is reported, which would otherwise lead to Li2 O2 surface-film growth and premature cell death. In the range of current densities of 0.1-0.5 mA cm-2areal , the CoQ10 -catalyzed Li-O2 battery can deliver a discharge capacity that is ≈40-100 times what the pristine Li-O2 battery could achieve. The drastically enhanced electrochemical performance is attributed to the CoQ10 that not only efficiently mediates the electron transfer from the cathode to dissolve O2 but also strongly interacts with the newly formed Li2 O2 in solution retarding its precipitation on the cathode surface. The mediated oxygen reduction reaction and the bonding mechanism between CoQ10 and Li2 O2 are understood with density functional theory calculations.