Rapid Temperature Shock Suppresses Graphitized Stacking: Guiding Quasi-Ionic-Bonding Na Storage in Hard Carbon

Conventional coal pyrolysis tends to drive aromatic condensation and graphitic stacking, which limits closed-pore formation and leads to sluggish Na + transport, low plateau capacity and poor initial Coulombic efficiency (ICE) in coal-derived hard carbon. Here we develop a rapid temperature shock (RTS) strategy to redirect coal carbonization through a kinetically constrained thermal pathway. The rapid heating restrains graphitic rearrangement and secondary condensation, while promoting cross-linked disordered carbon reconstruction. The resulting RTS-HC exhibits an enlarged d 002 spacing of 0.392 nm, abundant closed nanopores and a turbostratic carbon framework. These structural features lower the Na + migration barrier to 0.38 eV and facilitate reversible low-potential Na storage. Density functional theory calculations further indicate that confined Na-carbon interactions with partial ionic character stabilize Na storage within closed pores. As a result, RTS-HC delivers a reversible capacity of 303.6 mAh g -1 at 30 mA g -1 , a high ICE of 89% and a plateau contribution of 67%. It also retains 80.4% of its capacity after 1000 cycles at 500 mA g -1 , outperforming the conventionally pyrolyzed counterpart. This work provides a kinetic carbonization strategy for converting coal into high-performance hard carbon anodes for sodium-ion batteries.