Ultrafine NbN nanoparticle decorated nitrogen-doped carbon nanosheets with efficient polysulfide catalytic conversion for superior Li–S batteries

Lithium-sulfur batteries are considered as one of the most promising energy storage systems beyond commercial lithium-ion batteries, but the practical application of lithium-sulfur batteries is still hindered by the severe polysulfides dissolution and sluggish redox reaction kinetics with low areal capacity. Herein, ultrafine NbN decorated nitrogen-doped porous carbon nanosheets are reported via C3N4 sacrifice template using phenolic resol as carbon precursor. The ultrafine NbN nanoparticles and nitrogen-doped carbons guarantee efficient polysulfides trapping and fast redox reaction kinetics even with a high sulfur content of 75 wt%. In addition, porous carbon nanosheets and NbN nanoparticles provide more active sites for Li2S nucleation and serve as a second host for the reuse of sulfur. Hence, the lithium-sulfur cells with NbN@CNS-5 modified multifunctional separator deliver a high initial capacity of 1252 mAh g−1 @ 0.2 C, 683 mAh g−1 @ 4 C, and high capacity retention of 84.5% after 200 cycles at 0.2 C. Furthermore, a high initial capacity of 4.95 mAh cm−2 and 4.01 mAh cm−2 @0.2 C after 200 cycles are achieved at a sulfur loading of 4.2 mg cm−2. These findings open up a new method for the practical application of lithium-sulfur batteries with superior sulfur utilization and a long lifespan.