Biomimetic Superoxide Disproportionation Catalyst for Anti-Aging Lithium–Oxygen Batteries

Abstract

Reactive oxygen species or superoxide (O₂^-), which damages or ages biological cells, is generated during metabolic pathways using oxygen as an electron acceptor in biological systems. Superoxide dismutase (SOD) protects cells from superoxide-triggered apoptosis by converting superoxide to oxygen and peroxide. Lithium-oxygen battery (LOB) cells have the same aging problems caused by superoxide-triggered side reactions. We transplanted the function of SOD of biological systems into LOB cells. Malonic acid-decorated fullerene (MA-C₆₀) was used as a superoxide disproportionation chemocatalyst mimicking the function of SOD. As expected, MA-C₆₀ as the superoxide scavenger improved capacity retention along charge/discharge cycles successfully. A LOB cell that failed to provide a meaningful capacity just after several cycles at high current (0.5 mA cm^-2) with 0.5 mAh cm^-2 cutoff survived up to 50 cycles after MA-C₆₀ was introduced to the electrolyte. Moreover, the SOD-mimetic catalyst increased capacity, <i>e</i>.<i>g</i>., more than a 6-fold increase at 0.2 mA cm^-2. The experimentally observed toroidal morphology of the final discharge product of oxygen reduction (Li₂O₂) and density functional theory calculation confirmed that the solution mechanism of Li₂O₂ formation, more beneficial than the surface mechanism from the capacity-gain standpoint, was preferred in the presence of MA-C₆₀.