Regulating Pores and Carbonyl Groups of Biomass‐Derived Hard Carbon for Enhanced Sodium Storage

Abstract This study investigates the impact of sulfuric acid‐assisted hydrothermal pretreatment on the structural and electrochemical properties of biomass‐derived hard carbon for sodium‐ion batteries. Advanced characterization demonstrates that sulfuric acid‐mediated hydrothermal strategy promotes the formation of crosslinked small molecules within the precursor. This process yields optimized hard carbon exhibiting pore‐orifice nanoconfinement, enriched C═O functional groups at pore interface, and increased proportion of closed pores after carbonization. Collectively, these structural refinements synergistic enable exceptional sodium storage performance through accelerated desolvation kinetics, reduced nucleation energy barriers, and enhanced closed pore utilization efficiency to boost specific capacity. Specifically, the SAHTC‐1300 anode delivers a remarkable reversible capacity of 386 mAh g −1 at 50 mA g −1 , maintains 270 mAh g −1 at 2 A g −1 , and retains 90% capacity after 1000 cycles at 1 A g −1 , outperforming control samples (HTC‐1300 and SCG‐1300). The work demonstrates the efficacy of sulfuric acid‐assisted hydrothermal carbonization for synthesizing high‐performance biomass‐derived hard carbon anodes, offering valuable insights for the design of advanced biomass‐based energy storage materials.