Covalently coupled hybrid of graphitic carbon nitride with reduced graphene oxide as a superior performance lithium-ion battery anode

Abstract

An in situ chemical synthetic approach has been designed for the fabrication of a covalently coupled hybrid consisting of graphitic carbon nitride (g-C₃N₄) with reduced graphene oxide (rGO) with differing g-C₃N₄/rGO ratio. The epoxy groups of graphene oxide (GO) undergo a nucleophilic substitution reaction with dicyandiamide (C₂H₄N₄) to form the C₂H₄N₄–GO composite via a covalent C–N bond, and then both the in situ polymerization of C₂H₄N₄ and the thermal reduction of GO can be achieved at higher temperatures, forming the covalently coupled g-C₃N₄–rGO. FT-IR, CP-MAS NMR and XPS analyses, clearly revealed a covalent interaction between the g-C₃N₄ and rGO sheets. The g-C₃N₄–rGO exhibits an unprecedented high, stable and reversible capacity of 1525 mA h g⁻¹ at a current density of 100 mA g⁻¹ after 50 cycles. Even at a large current density of 1000 mA g⁻¹, a reversible capacity of 943 mA h g⁻¹ can still be retained. The superior electrochemical performance of g-C₃N₄–rGO is attributed to the specific characteristics of the unique nanostructure of g-C₃N₄–rGO and the concerted effects of g-C₃N₄ and rGO, including covalent interactions between the two moieties, the good conductivity and high special surface area of the nanocomposite, as well as the template effect of the planar amino group of g-C₃N₄ for the dispersed decoration of Li⁺ ions.