Nitrogen and sulfur co-doping mesoporous carbon for high-rate and long-cycle sodium-ion storage

Carbon materials are considered as promising anodes of sodium-ion batteries (SIBs) due to their low cost, high conductivity, and tunable interlayer spacing. However, the low specific capacity, inferior rate capability, and poor initial Coulombic efficiency (ICE) limit the practical applications. Heteroatom doping is a feasible strategy to address such issues, and the synergistic effect enables dual-element co-doping to further enhance SIBs performances. Here, we synthesize a unique nitrogen (N) and sulfur (S) co-doped mesoporous carbon (SNC) using mesoporous silica as the hard stencil. The ingenious S doping enlarges interlayer spacings, increases defect densities, and enriches active sites. In parallel, the presence of S anions readjusts the center of p-band position in pyridinic-N and the electronic configuration of isolated N atom. Outstanding sodium-ion storage performance is achieved in SNC featured with remarkable ICE (83.8%), high-rate capability (150.0 mAh·g⁻¹ at 40 A·g⁻¹), and long-cycle stability (241.6 mAh·g⁻¹ at 5 A·g⁻¹ after 1600 cycles). The sodium-ion storage mechanism is clarified by combining theory calculations and in-situ/ex-situ experimental characterizations. This work provides a new approach to synthesising dual-element co-doped carbon anodes for enhancing SIBs performances.