Performance of Air Electrode Catalysts in the Presence of Redox Mediators for High-Capacity Li-O₂ Batteries

Lithium-oxygen batteries (LOBs) have usually beeninvestigatedat low current densities and low areal capacities due to small amountsof active materials supported on carbon papers, though they theoreticallyhave high energy density. In addition, studies on catalysts have usuallybeen conducted in the absence of redox mediators. In this study, wehave investigated various catalysts at a high current density (0.4mA cm(-2)), at a high areal capacity (4 mAh cm(-2)), and in the presence of dual redox mediators (RMs)of NO3 (-) and Br-, usingKetjen black free-standing sheets (KBFSs; thickness: 270 mu m)of high areal weight (6 mg cm(-2)). The RMs reducedthe charge overvoltage even in the presence of catalysts, and catalystsalso promoted Li2O2 decomposition in the presenceof RMs. RuO2/KBFS, Ir-Co/N-KBFS, and Co/KBFS improved bothcyclability and overvoltages compared with KBFS. RuO2/KBFSand Ir-Co/N-KBFS decomposed Li2CO3 at lowervoltages than KBFS and exhibited less Li2CO3 residue after charge than KBFS. However, catalysts were coated withbyproducts even in the presence of RMs during the discharge/chargetests.