Pepper stalk hard carbon anodes with temperature-tailored closed pores for high-performance sodium-ion batteries

• Pepper stalk-derived hard carbon with temperature-tailored closed pores achieves a high reversible capacity of 302.3 mAh·g−1 and an initial coulombic efficiency of 86.7%. • Carbonization at 1600°C optimally develops 3.48 nm closed pores and enhances graphite domains, yielding a plateau capacity of 191.7 mAh·g−1 (63.4% of total capacity) through efficient Na+ filling. • Full cell with Na3V2(PO4)3 cathode delivers an energy density of 271.0 Wh·kg−1, demonstrating practical viability for sodium-ion batteries. • Provides an industrial-scale, low-cost methodology for pore-structure engineering of biomass-derived hard carbons, addressing barriers to commercialization.