Partial Oxidation Strategy Toward Carbonyl‐Dominated Surfaces for Enhanced Sodium Storage in Biomass‐Derived Hard Carbon

ABSTRACT The practical application of biomass‐derived hard carbon (HC) in sodium‐ion batteries (SIBs) remains hindered by low initial Coulombic efficiency (ICE) and limited rate capability, primarily caused by unstable surface functionalities and inefficient interfacial chemistry. In this study, we propose a facile precisely controlled partial oxidation strategy to selectively regulate the surface chemical environment of glucose‐derived hard carbon, enabling the transformation of unstable hydroxyl and carboxyl groups into more stable carbonyl functionalities without significantly altering the carbon framework. This mild, low‐temperature partial oxidation process partially unifies surface functional groups, promotes the formation of a thin and uniform solid electrolyte interphase (SEI), and enhances Na + adsorption and diffusion kinetics. The optimized sample (CS‐HO) exhibits a reversible capacity of 310.5 at 50 mA g –1 , a high ICE exceeding 70%, and excellent rate performance and cycling stability, with 73% capacity retention after 1000 cycles at 1 A g –1 . Mechanistic investigations, including in situ Raman spectroscopy and galvanostatic intermittent titration technique (GITT), reveal a dominant “adsorption–intercalation–pore filling” storage mechanism, attributed to the homogenized carbonyl‐rich surface and optimized porous environment. This study offers mechanistic insights into bond‐specific surface engineering and establishes a scalable, energy‐efficient, and chemically rational pathway toward the design of high‐performance SIB anode materials.