An Air‐Etching Strategy for Enlarging Plateau Capacity of Hard Carbon Anodes

ABSTRACT Hard carbon (HC) anodes are regarded as the most promising anodes for sodium‐ion batteries (SIBs), yet their energy density is severely limited by low‐voltage plateau capacity, which remains difficult to enhance without sacrificing Initial Coulombic efficiency (ICE) or structural integrity. Here, we report a convenient air‐etching strategy for the scalable synthesis of HC via a precursor‐independent pore evolution pathway. By introducing a mild air oxidation process within a narrow kinetic window, the oxidation of pre‐carbonized precursors preferentially occurs at edge and defect sites and suppresses over‐etching, generating closable ultra‐micropores (∼0.8 nm) without framework collapse. Upon graphitization, the ultra‐micropores evolve into uniform distributed closed nanopores (∼2.8 nm) while maintaining a low specific surface area. The resulting HC exhibits a plateau‐dominated sodium storage behavior and delivers a high ICE of 91.8% and a high reversible capacity of 460 mAh g −1 with a remarkably enlarged plateau capacity of 346.4 mAh g −1 , superior to most of HC reported previously. More importantly, the air‐etching approach is applicable to diverse precursors, offering a low‐cost and powerful route for achieving high‐energy‐density HC anodes and SIBs.