Molecular pre-cleavage in polysaccharide precursor to design high-performance hard carbon for sodium-ion batteries

Closed-pore structures are pivotal for achieving high specific capacity in hard carbon (HC) anodes for sodium-ion batteries. Yet, their precise formation remains poorly controlled due to limited molecular-level understanding. Here, renewable cellulose as a model precursor, and a molecular pre-cleavage strategy is introduced to synthesize HC with expanded interlayer spacing and abundant tunable closed pores. Experimental characterizations combined with kinetic simulations reveal that closed-pore formation is governed by site-selective anchored oxidation at defined molecular positions, while the pre-cleaved molecular architecture suppresses graphitization, yielding numerous closed pores enclosed by short-range graphitic domains that enhance plateau capacity. The optimized HC anode delivers a high reversible capacity of 373.7 mAh g −1 at 20 mA g −1 and retains up to 97.7% capacity over 800 cycles at 2 A g −1 . Furthermore, a full-cell with Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 exhibits 93.2% capacity retention after 900 cycles at 2C. This work provides molecular-level design principles for engineering high-performance HC anodes, offering a pathway toward advanced SIBs with superior energy storage capabilities.