Synergistic integration of phosphorus doping and closed-pore architecture in starch-derived hard carbon for advanced sodium-ion storage

Engineering high-efficiency hard carbon anodes remains a crucial frontier in sodium-ion battery technology development, yet simultaneously optimizing its rate performance and plateau capacity remains a significant challenge. Heteroatom doping and closed-pore engineering are recognized effective strategies, but they are typically achieved through complex, multi-step processes. Herein, a novel precursor engineering strategy is presented, where corn starch is cross-linked by sodium trimetaphosphate (STMP) and then carbonized to produce the hard carbon material. The optimized 10%-SOHC incorporates phosphorus heteroatoms and presents a high closed-pore volume of 0.42 cm³/g. Phosphorus doping effectively increases the interlayer spacing, promotes ion diffusion, and enhances Na⁺ adsorption. In addition, the abundant closed-pores provide substantial active sites for the low-voltage plateau region. Benefiting from this unique structure, 10%-SOHC delivers a high reversible capacity of 341.3 mAh g⁻¹, an initial coulombic efficiency (ICE) of 86.9%, excellent rate performance, and remarkable cycling durability. This study offers a scalable and versatile synthesis paradigm for designing advanced biomass-derived carbon anodes with tailored microstructures for efficient energy storage.