Synthesis of graphitic carbon nitride at different thermal-pyrolysis temperature of urea and it application in lithium–sulfur batteries

Graphitic carbon nitride (g-C₃N₄) was produced by the direct thermal-pyrolysis of urea at different temperatures without additive assistance. The physical properties of porous g-C₃N₄ were characterized by various measurement methods: X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area measurements, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ay photoelectron spectroscopy (XPS). The effect of thermal-pyrolysis temperature on electrochemical behaviors of was researched as the sulfur matrices in lithium–sulfur batteries. The g-C₃N₄ prepared at 550 °C with sulfur matrix exhibits the superior electrochemical performances. As the result, the sulfur/CN-550 composite cathode exhibits a high initial discharge capacity of 1262.1 mAh g⁻¹ and delivers a specific capacity of 605.4 mAh g⁻¹ over 500 cycles at 0.39 mA cm⁻². The excellent electrochemical behavior of the g-C₃N₄ could be ascribed to the effective utilization of sulfur and the combination of polysulfides dissolution through physical and chemical interactions to achieve long-term circulation of the composite cathode in lithium–sulfur batteries.