Nitrogen and phosphorus codoped hierarchically porous carbon as an efficient sulfur host for Li-S batteries

For the first time, nitrogen and phosphorus codoped hierarchically porous carbon (NPHPC) has been explored as an efficient host for sulfur. The material is fabricated based on a scalable, one-step process involving the pyrolysis of melamine polyphosphate synthesized via a simple and versatile organic approach by using low cost industrial raw materials (melamine and polyphosphoric acid). The key features of NPHPC are the hierarchically porous structure and high surface area (1398 m² g⁻¹) that not only benefit for maximum sulfur loading but also capable of suppressing the dissolution of polysulfides through physisorption. Meanwhile, the N and P codopants together with the thermally stable functionalities are favorable for binding polysulfides via chemisorption. Benefitting from the synergistic effect of structural confinement (physisorption) and chemical binding (chemisorption), the NPHPC/S composite with a high sulfur content of 73 wt% delivers high capacity (1580 mAh g⁻¹ at 0.02 C) and long lifespan (200 cycles with 71% retention) for Li-S batteries. The present work highlights the importance of adopting heteroatom-doped hierarchically porous carbon for improving the performance of Li-S batteries, which may further stimulate more efforts in exploring advanced carbon-based hosts in the near future.