Chemical confinement of short-chain sulfur into hierarchical porous hard carbon for ultra-stable high-capacity sodium-ion storage

• • The SHHC anode delivers a high reversible capacity of ~807 mAh g−1 at 0.03 A g−1, approximately three times that of conventional amorphous carbon, addressing the capacity bottleneck in SIB anodes. • • The composite achieves almost 100% capacity retention after 2000 cycles at 1.0 A g−1, demonstrating ultra-stable long-term cycling performance critical for grid-scale energy storage. • • The hierarchical porous structure with built-in cavities effectively accommodates electrode volume expansion, ensuring fast electrode kinetics and outstanding cyclability, which is essential for practical high-rate applications. • • The chemical confinement of ~25 wt% short-chain sulfur into the carbon matrix enables a surface-dominated storage mechanism, contributing to high capacity and superior rate capability, as evidenced by the high sulfur content and redox reactivity.