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

Abstract

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^-2_areal , 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.