RuO2 nanoparticles supported on Ni and N co-doped carbon nanotubes as an efficient bifunctional electrocatalyst of lithium-oxygen battery

Li2O2, as the discharge product of Li-O2 batteries on cathode, is difficult to be electrochemically decomposed, which will lead to short cycling lifespan of the batteries. In this study, the cycling lifespan of Li-O2 battery was prolonged significantly by an efficient bifunctional catalyst. The Ni and N co-doped carbon nanotubes (NiNCs) were synthesized firstly, and then RuO2 nanoparticles were deposited on NiNCs by a hydrothermal route to synthesize RuO2/NiNC catalysts. Transmission electron microscopy and X-ray diffraction characterizations demonstrated that part of metallic Ni was converted into NiO and Ni(OH)2 after loading RuO2, and the existence of NiO layer can prevent further oxidation of metallic Ni. The Li-O2 battery with RuO2/NiNC as the cathode catalyst exhibits an overpotential of 0.43 V, which is much lower than the value of 1.03 V measured with the Li-O2 battery using NiNC as the cathode catalyst. At a rate of 200 mA g−1, the Li-O2 battery with the RuO2/NiNC cathode can maintain a reversible capacity of 500 mA h g−1 for 260 cycles, and 117 cycles with a higher reversible capacity of 1000 mA h g−1. The superior property of the RuO2/NiNC bifunctional catalyst could be ascribed to the high activity of RuO2 and the rich carbon nanotube structure of NiNC for deposition and decomposition of Li2O2.