Abstract: Biomass-based hard carbon is considered a highly promising anode for sodium-ion batteries. Nevertheless, its practical deployment is often impeded by excessive specific surface area and an abundance of structural defects, which inevitably lead to limited initial coulombic efficiency and unsatisfactory sodium storage capacity. Herein, we report a pepper stalk-derived hard carbon engineered via temperature-mediated closed-pore tuning, delivering a reversible capacity of 302.3 mAh·g^–1 (initial coulombic efficiency of 86.7%) and remarkable cycling stability (87.6% capacity retention after 300 cycles). Systematic characterization reveals that carbonization at 1600°C optimally develops 3.48 nm closed pores and enhances graphite domains, achieving a high plateau capacity of 191.7 mAh·g^–1, which constitutes 63.4% of the total capacity attributed to efficient Na⁺ ion filling. A full cell paired with a Na₃V₂(PO₄)₃ cathode achieves an energy density of 271.0 Wh·kg^–1 based on the total mass of the active materials. This research provides a viable and industrial-scale methodology for pore-structure engineering, overcoming major hurdles to the market adoption of biomass-derived carbon materials.