Multi-Scale Synergistic Engineering of S/N Co-Doped Hard Carbon Derived from Coal Pitch with Hierarchical Porosity for High-Performance Sodium-Ion Storage

The development of robust hard carbon as sodium-ion batteries (SIBs) anode is often constrained by the trade-off between specific capacity, initial Coulombic efficiency (ICE), and rate performance. Here, a multiscale synergistic strategy is proposed to synthesize advanced hard carbon anodes using low-cost coal pitch as the precursor. This is achieved through a facile one-step pyrolysis process involving sodium thiosulfate as a combined sulfur source and porogen, magnesium oxide (MgO) as a hard template, and poly(vinylpyrrolidone) (PVP) as a versatile additive acting as a secondary porogen and nitrogen source. The optimized carbon material exhibits a unique structure characterized by S/N codoping, an enlarged interlayer spacing (0.385 nm), and a hierarchical pore architecture with a balanced surface area and pore volume. When employed as a SIBs anode, this electrode delivers a significant reversible capacity of 278.3 mAh g –1 with an outstanding ICE of 83.5%, remarkable rate performance (173.7 mAh g –1 at 3C), and excellent cycling durability. Electrochemical analysis reveals that the synergistic effects of heteroatom doping and optimized porosity enhance Na + adsorption, facilitate intercalation, and improve ion transport kinetics. Furthermore, a full cell configured with this anode and a Na 3 V 2 (PO 4 ) 3 cathode demonstrates a high operating voltage and prominent stability, retaining 63.6% capacity after 2000 cycles. This work provides a viable approach to design carbonaceous materials that break the performance coupling in SIB anodes.