Enhancing High-Capacity and High-Rate Sodium-Ion Storage through Synergistic N,S Dual Doping of Hard Carbon

Hard carbon, as the most promising commercial anode materials of sodium-ion batteries (SIBs), has suffered from the coupling limitations on initial Coulombic efficiency (ICE), capacity, and rate capability. Herein, to break such coupling limitations, sulfur-rich nitrogen-doped carbon nanomaterials (S-NC) were synthesized by a synergistic modification strategy, including structure/morphology regulation and dual heteroatom doping. The small specific surface area of S-NC is beneficial for inhibiting excessive growth of solid electrolyte interphase (SEI) film and irreversible interfacial reaction. The covalent S can serve as active electrochemical sites by Faradaic reactions and provide extra capacity. Benefit by N, S co-doping, S-NC shows large interlayer spacing, high defects, good electronic conductivity, strong ion adsorption performance, and fast Na⁺ ion transport, which combined with a more significant pore volume result in speedier reaction kinetics. Hence, S-NC possesses a high reversible specific capacity of 464.7 mAh g^-1 at 0.1 A g^-1 with a high ICE of 50.7%, excellent rate capability (209.8 mAh g^-1 at 10.0 A g^-1 ), and superb long-cycle capability delivering a capacity of 229.0 mAh g^-1 (85% retention) after 1800 cycles at 5.0 A g^-1 .