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

Abstract

Lithium–oxygen batteries (LOBs) have usually been investigated at low current densities and low areal capacities due to small amounts of active materials supported on carbon papers, though they theoretically have high energy density. In addition, studies on catalysts have usually been conducted in the absence of redox mediators. In this study, we have investigated various catalysts at a high current density (0.4 mA cm–2), at a high areal capacity (4 mAh cm–2), and in the presence of dual redox mediators (RMs) of NO3– and Br–, using Ketjen black free-standing sheets (KBFSs; thickness: 270 μm) of high areal weight (6 mg cm–2). The RMs reduced the charge overvoltage even in the presence of catalysts, and catalysts also promoted Li2O2 decomposition in the presence of RMs. RuO2/KBFS, Ir-Co/N-KBFS, and Co/KBFS improved both cyclability and overvoltages compared with KBFS. RuO2/KBFS and Ir-Co/N-KBFS decomposed Li2CO3 at lower voltages than KBFS and exhibited less Li2CO3 residue after charge than KBFS. However, catalysts were coated with byproducts even in the presence of RMs during the discharge/charge tests.