Highly efficient Ru/B4C multifunctional oxygen electrode for rechargeable Li O2 batteries

Irreversible parasitic reactions and the accumulation of insulating side products are two of the main barriers for practical application of rechargeable Li-O2 batteries. Therefore, it is critical to develop multifunctional oxygen electrodes suitable for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and decomposition of side reaction products. Here we report the application of ultrafine ruthenium-deposited boron carbide (Ru/B4C) with remarkably multifunctional activities as non-carbon-based oxygen electrodes for Li-O2 batteries. Li2CO3 and LiOH can be completely decomposed by Ru/B4C at 3.97 V and 4.1 V, respectively, within the stability window of the ether-based electrolyte. A Li-O2 battery using a Ru/B4C oxygen electrode achieves a high discharge voltage plateau of 2.8 V, a significantly low charge voltage of 3.7 V, and good cycling performance under a limited capacity of 300 mAh gRu/B4C-1. In-situ gas chromatography analysis reveals that O2 is the major gas product during charge. Only a negligible amount of CO2 is observed in the first charge, in either a shallowly or a deeply discharged cell. Therefore, Ru/B4C can be used as a very promising oxygen-electrode material for Li-O2 batteries and Li-air batteries operated in ambient air.