Oxygen Plasma-Treated Hard Carbon for High-Rate and Durable Sodium-Ion Storage

Tuning of oxygen functional groups in hard carbon (HC) is significant for optimizing sodium storage performance, but achieving precise modulation through effective strategies remains challenging. Herein, we introduce an oxygen plasma treatment strategy to enrich targeted carbonyl groups (C═O) on litchi wood-derived HC (OHC-1400). This surface modification method simultaneously regulates the electron conductivity and interface kinetics. Density functional theory (DFT) calculations and in situ Raman spectroscopy jointly reveal that C═O functionalities significantly reduce the charge transfer barrier and promote reversible adsorption-intercalation mechanisms. Furthermore, the C═O functionalized surface of HC facilitates the formation of a thin, inorganic-rich solid electrolyte interface (SEI) film, effectively inhibiting electrolyte degradation. Consequently, OHC-1400 exhibits high initial specific capacity (304.61 mAh g^–1) with an initial Coulombic efficiency (ICE) of 90.40% and excellent cycling stability (capacity retention of 94.2% after 950 cycles at 0.5 A g^–1). This study highlights the synergy between structural engineering and surface functionalization, providing a feasible pathway for utilizing biomass-derived HC to improve the performance of sodium ion batteries.