Topology‐Derived Closed Pores in Hard Carbon Boost Sodium‐Ion Storage

ABSTRACT The closed‐pore architecture of hard carbon governs reversible capacity, initial Coulombic efficiency (ICE), and Na‐storage kinetics, but its precise regulation and the underlying mechanism remain elusive. To address such issues, a molecular‐cavity engineering strategy is developed using cyclic molecular precursors, whose inherent cavities are preserved by low‐temperature cross‐linking, to construct topology‐derived intrinsic closed pores in hard carbon during carbonization. Using β‐cyclodextrin as a model precursor, the resulting hard carbon (β‐ICHC) delivers a reversible capacity of 410.2 mAh g −1 , an ICE of 94.7% and 99.7% capacity retention over 300 cycles. Combined theoretical and in situ/ex situ analyses reveal that intrinsic closed pores simultaneously enable high reversible capacity, high ICE, and fast Na‐storage kinetics: the intrinsic closed pores with sub‐0.35 nm electrolyte‐sieving mouths can not only serve as reversible Na‐storage spaces to increase capacity but also suppress irreversible Na + consumption to enhance ICE; the pseudo‐graphitic walls with enlarged interlayer spacing enable fast Na + transport and provide additional capacity. Furthermore, a three‐stage Na‐storage mechanism of surface/defect adsorption, closed‐pore‐wall adsorption, and closed‐pore filling is supported by the combined experimental and theoretical results. This work provides a paradigm for hard‐carbon structural design and offers new insight into sodium‐storage mechanisms.