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

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.