Enhanced Performance of Lithium–Sulfur Batteries with Co-Doped g-C3N4 Nanosheet-Based Separator

Lithium–sulfur batteries are considered as one of the most potential energy storage devices in the future owing to their ideal theoretical energy density and specific capacity. However, the shuttle of soluble polysulfides and sluggish redox kinetics of polysulfides lead to insufficient use efficiency of active sulfur and the rapid capacity fading. In this study, novel Co-doped g-C3N4 (Co–CN) nanosheets are fabricated by a simple calcination process. The high discharge capacity of the commercial bulk S cathode with the Co–CN-modified separator is 1121 mAh g–1 at 0.2C with a satisfying rate performance of up to 3C. The Co–CN-modified separator also leads to excellent stability (640 mAh g–1 after 250 cycles) with high Coulombic efficiency of over 98%. At the sulfur mass loading of 3 mg cm–2, the cell can still deliver a discharge capacity of 719 mAh g–1 after 100 cycles with a high capacity retention of 95%. The improved performance can be attributed to the effective restriction of polysulfides shuttle due to the enhanced adsorption and catalytic conversion of polysulfides by the Co–CN nanosheet-modified separator. This work shares a simple and highly efficient strategy for increasing the performance of lithium–sulfur batteries.