Oxidation Engineering of Pitch Precursors Enables High-Performance Hard Carbon Anodes for Superior Sodium Storage

Abstract The structural evolution of pitch precursors during oxidation plays a decisive role in determining the sodium-storage performance of hard carbon, yet the distinct functions of different oxidation pathways remain poorly understood. Herein, the evolution of pitch precursors regulated by sequential liquid- and gas-phase oxidation is systematically elucidated through comparative studies of individual and combined oxidation routes. Liquid-phase oxidation activates the precursor by introducing abundant oxygen-containing species, whereas subsequent gas-phase oxidation promotes intermolecular crosslinking, restraining excessive carbon ordering and facilitating the generation of enlarged interlayer distances, defect-rich structures, and abundant closed nanopores. Benefiting from this cooperative regulation, the HC-AO exhibits a high reversible capacity of 331 mAh g–1 at 20 mA g–1 and an initial Coulombic efficiency of 93.2%, while delivering a 92.1% capacity retention over 500 cycles at 1000 mA g–1. This work establishes a mechanistic framework linking oxidation pathway, precursor evolution, and hard carbon microstructure, providing guidance for the rational design of high-performance hard carbon anodes.