Joule Heating Triggered Interfacial Engineering of Biomass Hard Carbon for High‐Performance Sodium‐Ion Batteries

ABSTRACT Biomass‐derived hard carbon (HC) has emerged as a promising low‐cost anode material for sodium‐ion batteries (SIBs). However, conventional pyrolysis typically results in narrow graphene interlayer spacing and disordered microstructures, which impede Na + diffusion kinetics and restrict low‐voltage plateau capacity. Herein, we develop an iron‐mediated Joule heating strategy to precisely engineer the microstructure of bamboo‐derived HC on ultrafast timescales. Rapid carbon atom reconstruction, combined with Fe‐catalyzed graphitization, simultaneously achieves enlarged interlayer spacing, well‐developed closed pores, and extended graphite microcrystals with long‐range order, collectively promoting faster Na + diffusion and storage. Notably, trace residual Fe further modulates interfacial chemistry by reducing the electrolyte decomposition barrier, facilitating the formation of a thin, uniform, and inorganic‐rich solid electrolyte interphase. Benefiting from this dual regulation of microstructure and interfacial chemistry, the resulting HC delivers a reversible capacity of 395 mAh g −1 at 0.05 A g −1 , including a high plateau capacity of 297 mAh g −1 , and retains 84% of its initial capacity over 5000 cycles, superior to the reported biomass‐derived HC anodes. By converting metal residues from perceived impurities into functional interfacial regulators, this work provides a rapid and scalable route to high‐performance biomass‐based HC anodes for SIBs.