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

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 NaNi₁/₃Fe₁/₃Mn₁/₃O₂ 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.