Oxygen etching-modulated defect-dependent pore structure of hard carbon for enhanced sodium-ion storage performance

Hard carbon (HC), a highly promising anode material for sodium-ion batteries, faces critical bottlenecks in improving sodium storage performance, primarily due to challenges in the precise construction of closed pore structures and the targeted regulation of carbon defects. To address this issue, a defect-oriented mild oxygen etching (DMOE) strategy is proposed to achieve synergistic optimization of the microstructure and sodium storage performance of hard carbon. Based on the resin intermediates generated by medium-temperature carbonization, combined with the DMOE strategy, the carbon‑oxygen radicals are effectively localized around defect sites, enabling directional regulation of sub-nanometer pores and microstructures. The optimized hard carbon material achieves a reversible specific capacity of 405.2 mAh g⁻¹, with a platform capacity of 303.1 mAh g⁻¹ and an initial coulombic efficiency of 90.4%. Long-term cycling stability is demonstrated by a retained capacity of 226.1 mAh g⁻¹after 800 cycles at a current density of 1 A g⁻¹. This study elucidates the defect-mediated closed pore formation mechanism and the structure-property relationship of hard carbon for sodium storage, providing a feasible design strategy for the controllable preparation of high-performance hard carbon anodes for sodium-ion batteries.