Ethyl Acetate Vapor Induced Local Ordering in Hard Carbon for Stable Sodium‐Ion Batteries

ABSTRACT Biomass‐derived hard carbon (HC) is a promising anode material for sodium‐ion batteries (SIBs) owing to its high Na ⁺ storage capacity. However, the defects and disordered structures cause irreversible Na ⁺ storage and side reactions, inducing low initial Coulombic efficiency (ICE) and poor cyclability. Herein, we propose a novel in situ vapor‐phase structural engineering strategy that leverages the synergistic cross‐linking between the defect sites of HC and organic free radicals generated from the decomposition of ethyl acetate, thereby constructing a distinctive locally ordered structure. Mechanistic characterizations based on synchrotron radiation reveal that the modulated locally ordered nanodomains simultaneously enhance intercalated Na ⁺ storage and suppress interfacial side reactions, thereby minimizing irreversible Na ⁺ loss and facilitating the formation of a robust solid electrolyte interface. Consequently, the optimized walnut shell‐derived hard carbon (Et‐WNS) exhibits a superior ICE of 90.1%, a reversible capacity of 374 mAh g ⁻¹ , and 99.5% capacity retention over 500 cycles. The 1.3 Ah pouch cell assembled with NaNi _1/3 Fe _1/3 Mn _1/3 O ₂ (NFMO) || Et‐WNS delivers an energy density of 142 Wh kg ⁻¹ and 73% retention after 120 cycles. This work provides a simple, green, and low‐cost strategy to modulate the local order structure to optimize the electrochemical properties of biomass‐based HC for high‐performance SIBs.