Waste Cigarette Butts-Derived Nitrogen-Doped Carbon Fibers Loaded with Ru Nanoparticles as an Efficient Cathode Catalyst for Lithium-Oxygen Batteries

Low catalytic activity and high cost of cathode catalysts hinder the large-scale commercial application of lithium-oxygen (Li-O2) batteries. In this work, waste cigarette butts, which inherently have a porous fiber structure, were selected as the precursor of the carbon material for the cathode catalyst of Li-O2 batteries. The porous nitrogen-doped carbon material was prepared by simple heat treatment of waste cigarette butts. The rich porous structure of the obtained carbon fiber material effectively enhances the diffusion of oxygen molecules and provides ample space for the discharge products. N doping in carbon fibers enhances the bifunctional catalytic activity toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which was corroborated by density functional theory (DFT) calculation. The assembled Li-O2 battery with C–N fibers-loaded Ru nanoparticles catalyst delivers an initial discharge capacity of up to 12 036.3 mA h g–1 and can be cycled stably for more than 800 cycles (4000 h) at a current density of 200 mA g–1 and a cutoff capacity of 500 mA h g–1. Even at a high current density of 500 mA g–1, the cells still show a high average discharge voltage of 2.28 V with excellent cycle stability and rate capability. XPS analysis proves that the cathode material can effectively inhibit the formation of Li2CO3 and Li2O byproducts. This work provides a cost-effective solution to solve the cathode catalyst problem of Li-O2 batteries and improve their cycling stability as well as environment protection.