Ruthenium dioxide-decorated carbonized tubular polypyrrole as a bifunctional catalyst for non-aqueous lithium-oxygen batteries

Owing to large specific surface area, high electronical conductivity and low mass, carbon materials have been widely used as cathode for non-aqueous lithium-oxygen (Li-O₂) batteries. However, carbon cathodes usually present poor catalytic activities toward oxygen reduction and evolution reactions (ORR and OER), resulting in a large charge over-potential and a short cycling life. In this work, a non-aqueous Li-O₂ battery with a bifunctional catalyst, ruthenium dioxide (RuO₂)-decorated carbonized tubular polypyrrole, is reported. Compared with conventional catalysts, the bifunctional catalyst has two special features: i), a high content of graphitic N, and ii), a large number of RuO₂ nanoparticles. The battery with the novel bifunctional catalyst shows a large discharge capacity (10095 mAh g⁻¹ at a current density of 200 mA g⁻¹), a high rate capacity (6758 mAh g⁻¹ at a current density of 1000 mA g⁻¹) and a long cycling life (55 cycles at the current density of 500 mA g⁻¹). In addition, at the first cycle with a fixed capacity of 1000 mAh g⁻¹, the discharge and charge over-potentials are only 0.28 and 0.78 V, which are 180 and 360 mV lower than those of the batteries fitted with pristine carbonized tubular polypyrrole cathode.