Fe Powder Catalytically Synthesized C₃N₃ toward High-Performance Anode Materials of Lithium-Ion Batteries

Recently, carbon nitrides and their carbon-based derivatives have been widely studied as anode materials of lithium-ion batteries due to their graphite-like structure and abundant nitrogen active sites. In this paper, a layered carbon nitride material C₃N₃ consisting of triazine rings with an ultrahigh theoretical specific capacity was designed and synthesized by an innovative method based on Fe powder-catalyzed carbon-carbon coupling polymerization of cyanuric chloride at 260 °C, with reference to the Ullmann reaction. The structural characterizations indicated that the as-synthesized material had a C/N ratio close to 1:1 and a layered structure and only contained one type of nitrogen, suggesting the successful synthesis of C₃N₃. When used as a lithium-ion battery anode, the C₃N₃ material showed a high reversible specific capacity up to 842.39 mAh g^-1 at 0.1 A g^-1, good rate capability, and excellent cycling stability attributed to abundant pyridine nitrogen active sites, large specific surface area, and good structure stability. Ex situ XPS results indicated that Li⁺ storage relies on the reversible transformation of -C=N- and -C-N- groups as well as the formation of bridge-connected -C=C- bonds. To further optimize the performance, the reaction temperature was further increased to synthesize a series of C₃N₃ derivatives for the enhanced specific surface area and conductivity. The resulting derivative prepared at 550 °C showed the best electrochemical performance, with an initial specific capacity close to 900 mAh g^-1 at 0.1 A g^-1 and good cycling stability (94.3% capacity retention after 500 cycles at 1 A g^-1). This work will undoubtedly inspire the further study of high-capacity carbon nitride-based electrode materials for energy storage.