Balancing the “disordered-ordered” microcrystalline structure to achieve high-performance of bituminous coal-based hard carbon anode for sodium-ion batteries

Bituminous coal, characterized by an optimal degree of metamorphism, volatile content, high aromaticity, and crosslinking potential, serves as an excellent precursor for the synthesis of hard carbon (HC). However, the ordered microcrystalline structure of derived HC increases the energy barrier for sodium-ion insertion, impairs diffusion kinetics, and restricts the localized storage of quasi-metallic sodium clusters, thereby significantly diminishing performance. Simple pyrolysis of resource-abundant while high aromatic bituminous coal induces highly graphitized carbon, exhibiting unsuitable microstructure for sodium storage. Herein, for the first time, the condensation reaction kinetics during the thermal treatment of bituminous coal were regulated, and the strong crosslinking network was optimized in-situ during the curing stage, establishing a “disordered-ordered” equilibrium state within the microcrystalline structure of the derived HC. The randomly arranged graphitic-like microcrystals facilitate sodium-ion adsorption, while the ordered graphitic domains provide efficient ion insertion sites and electronic conduction pathways. The coexistence of disordered and ordered domains generates structural mismatches at their interfaces, inducing carbon layer distortion that forms closed pores, which subsequently accommodate quasi-metallic sodium clusters. This balanced microstructural design enhances the sodium storage capacity of the bituminous coal-based HC anode from 225.6 mAh g −1 to 271.2 mAh g −1 , achieving an initial Coulombic efficiency (ICE) of 85.7%.