Structural Engineering of Biomass‐Derived Hard Carbon With Architectured Closed Pores for Fast Sodium Storage

ABSTRACT Hard carbons are widely used as sodium‐ion battery (SIB) anode materials owing to their abundant resources, cost‐effectiveness, and excellent electrochemical performance, but their sluggish charge transfer kinetics limit fast‐charging applications. Herein, we synthesize porous spherical nanostructured hard carbon via acid‐assisted hydrothermal precarbonization of biomass sphagnum moss, followed by high‐temperature treatment. This microstructure engineering introduces interconnected closed pores, expands the interlayer distance to 0.43 nm, and forms a uniform spherical morphology, effectively reducing ion diffusion resistance and boosting reaction kinetics. The optimized anode delivers a reversible capacity of 108 mAh g −1 at 10 A g −1 . Assembled into a full cell with a NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 cathode, it retains 70% capacity after 1000 cycles at 300 mA g −1 , demonstrating superior cycling stability and fast‐charging capability. This work provides a feasible microstructure engineering strategy for high‐rate sodium storage in biomass‐derived carbons.