Sequential Dual‐Phase Oxidation Engineered Structure of Pitch‐Derived Hard Carbon towards Improved Sodium‐Ion Storage

ABSTRACT Pitch‐derived hard carbon is regarded as a highly promising anode material for sodium‐ion batteries (SIBs) due to its low‐cost precursors and high carbon yield. However, during high‐temperature carbonization, its aromatic structures tend to become ordered and undergo graphitization, leading to interlayer contraction and limited capacity, which significantly restricts sodium storage performance. Herein, we propose a sequential dual‐phase oxidation strategy that introduces a liquid‐phase oxidation step prior to gas‐phase oxidation, which effectively improves the uniformity and the depth of pitch oxidation, thereby promoting intermolecular crosslinking. The resulting highly crosslinked network leads to expanded interlayer spacing, increased defect density, and a hierarchically developed microporous and ultramicroporous structure in the derived hard carbons. Consequently, the optimized hard carbon exhibits improved Na ⁺ transport across the solid electrolyte interphase and within the bulk carbon framework, along with accelerated charge‐transfer kinetics. As a result, it delivers a high reversible capacity of 339.91 mAh g ⁻¹ , excellent rate capability (279.89 mAh g ⁻¹ at 100 mA g ⁻¹ ), and outstanding cycling stability with 77.19% capacity retention after 180 cycles at 150 mA g ⁻¹ . This work provides an effective and scalable approach for developing low‐cost, high‐performance pitch‐derived hard carbon anodes for advanced SIBs.