Binder-regulated interfacial carbonization and pore evolution in coal/sucrose-microsphere-derived hard carbons for sodium storage

Coal-derived hard carbon is a promising anode material for sodium-ion batteries, but the coordinated regulation of carbon-layer stacking, pore architecture, and interfacial chemistry remains challenging. Here, coal and pre-carbonized sucrose microspheres were assembled using different binder systems and subsequently converted into hard carbons. Structural and thermal analyses show that the chitosan/NaOH-assisted system regulates precursor integration, volatile evolution, interfacial carbonization, and local carbon-layer rearrangement. The resulting HC-CHS exhibits a spatially differentiated carbon architecture comprising a relatively disordered outer coating, an interconnected interfacial carbon region, and an inner coal-derived framework. This architecture combines moderate accessible porosity with internal nanovoids and confined pore-related domains. Bulk elemental analysis confirms higher N content, while XPS identifies surface/near-surface N-containing functionalities in HC-CHS. Consequently, HC-CHS delivers a reversible capacity of 328.8 mAh g -1 and an initial Coulombic efficiency of 92.57%, with the low-voltage plateau capacity of 224.8 mAh g -1 . In situ XRD, in situ EIS, and distribution of relaxation times analyses indicate reversible local carbon-layer adjustment, a comparatively stable interfacial response, and coordinated Na transport during sodiation/desodiation. Low-temperature measurements and pouch full-cell tests further demonstrate the retention of low-voltage storage and reversible full-cell operation. DFT calculations suggest that enhanced charge redistribution, reduced interlayer displacement, and a lower Na migration barrier facilitate reversible Na storage in HC-CHS. These findings establish a relationship between binder-regulated interfacial carbonization, spatial carbon architecture, pore evolution, and sodium-storage behavior in coal-derived hard carbon.