Preparation of phosphorus-doped graphitic carbon nitride and its application in lithium-sulfur batteries

Graphite-phase carbon nitride (g-C₃N₄) was prepared by heat shrinkage polymerization method using urea as raw material, and phosphorus-doped g-C₃N₄ with different phosphorus content (xP-CN) was prepared by using hydrogen phosphate diamine as a phosphorus source. The effect of doping on the microstructure, morphology, and electrochemical performance of xP-CN/S composites as cathode materials for lithium-sulfur batteries was studied. The studies show that the layer spacing of xP-CN increases after phosphorus doping, the electrical conductivity increases, and the specific surface area becomes larger. The specific surface area of the 10% P-CN reaches 101.741 m²·g⁻¹. The initial discharge specific capacity of the 10% P-CN/S composite at 0.05 C (1 C=1675 mA·h·g⁻¹) reaches 1383.8 mA·h·g⁻¹. The reversible specific capacity after 100 cycles at 0.2 C is 860.0 mA·h·g⁻¹, the reversible specific capacity of g-C₃N₄/S composite is only 178.3 mA·h·g⁻¹; The specific capacity of 10% P-CN/S composite can be restored to 93.6% at 0.2 C after the rate test, showing good cycle performance and rate performance.