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

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. © 2026 Wiley-VCH GmbH.