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

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_1/3Fe_1/3Mn_1/3O₂ (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. © 2026 Wiley-VCH GmbH.