Effect of phosphorous-doped graphitic carbon nitride on electrochemical properties of lithium-sulfur battery

Various sulfur host materials have been developed to improve the performance of lithium-sulfur (Li-S) battery. In this work, we used phosphorus-doped graphitic carbon nitride (xP-g-C3N4) as a sulfur host material for the first time. xP-g-C3N4 was prepared with dicyandiamide as the precursor and 1-butyl-3-methylimidazole hexafluorophosphate as a phosphorus source. The effect of phosphorus doping on the electrochemical properties of xP-g-C3N4/S as cathode material for the Li-S battery was studied. The results show that decreasing lattice spacing improves the conductivity by doping phosphorus, and the specific surface area of 0.1P-g-C3N4 reaches 19.66 m2 g−1, which is about two times higher than that of g-C3N4. 0.1P-g-C3N4/S has 1344 mAh g−1 for the initial discharge specific capacity and 882 mAh g−1 for reversible specific capacity after 100 cycles with a capacity decay of 0.34% per cycle, exhibiting outstanding cycling performance and rate performance. Phosphorus-doped materials have a high specific capacity due to their own stronger physical adsorption and chemisorption of polysulfides and higher conductivity. This doping strategy proposed a new and efficient pathway for the fabrication of high-performance sulfur electrodes for Li-S batteries.