Nitrogen-doped expanded graphite derived from spent graphite induce uniform growth of lithium peroxide for high-performance Li-oxygen battery

Clean treatment and recycling of retired graphite are of great significance to void environmental pollution and resource waste. For this reason, a simple chemical intercalation process combined melamine-assisted expansion strategy is used to prepare nitrogen-doping expanded graphite (N-EG) with a worm-like structure from waste graphite as an ideal lithium-oxygen (Li-O2) battery cathode. The pyrolysis of melamine during annealing can realize the reduction and nitrogen-doping of the expanded graphite in one step, so as to improve the conductivity and electrocatalytic activity of expanded graphite. Moreover, the continuous multilayer hierarchical porous structure of worm-like expanded graphite can not only provide sufficient free-space for the storage of discharge products but also facilitate the mass transfer for battery reactions. As a proof of concept, the as-prepared N-EG have been used as the cathode in Li-O2 battery and achieve excellent electrochemical performances, including high specific capacity, excellent rate performance and long cycle stability. Furthermore, by combining density functional theory (DFT) calculations with experimental data, we demonstrate that the introduction of N-doping in expanded graphite can induce surface combine solution-mediated growth of Li2O2 on the cathode. Such a universal method provides an environmentally friendly approach for the reuse of waste graphite to construct high-performance Li-O2 battery cathode.