Nitrogen and phosphorus co-doped porous carbons for high energy density and low shuttling Na/S batteries

Porous carbons with their abundant availability and high electrical conductivity present significant potential as cathode materials for Na–S batteries. In this study, we report the synthesis of nitrogen and phosphorus co-doped porous carbon (P–N co-doped PC) through a one-step carbonization process utilizing ammonium polyphosphate as the source of nitrogen and phosphorus. The average reversible capacities for P–N co-doped PC were 920, 861, 823 and 756 mA h g⁻¹ at current densities of 0.2, 0.5, 1.0 and 2.0 C, respectively. Notably, upon returning to current densities of 1.0, 0.5 and 0.2 C, the capacities were restored to 805, 853 and 906 mA h g⁻¹, highlighting the exceptional stability of the P–N co-doped PC. The pronounced capacitive storage mechanism of P–N co-doped PC can be attributed to the presence of numerous surface defects and active sites resulting from the co-doping of nitrogen and phosphorus. In particular, the remarkable cycling stability exhibited by the P–N co-doped PC can be ascribed to the exceptional stability of the surface layer that has undergone phosphorus doping, thereby facilitating the migration of ions. This research contributes valuable insights into the development of advanced Na–S batteries through the utilization of heteroatom-doped functionalized porous carbons.