Unveiling the etching-repair dynamic interplay in pitch-derived carbon for high-performance sodium storage

Direct pyrolysis of pitch-a low-cost carbon precursor-invariably yields graphitizable soft carbon with narrow interlayer spacing and insufficient closed pores, limiting its sodium storage capacity. Herein, we unveil a temperature-directed etching-repair dynamic interplay during CO₂-mediated carbonization that fundamentally disrupts this graphitization trajectory. At the kinetically favorable temperature of 900 °C, CO₂ gasification preferentially occurs at reactive edge- and defect-associated carbon sites, outperforming thermally driven structural rearrangement; this "de-graphitization" process simultaneously fulfills three critical functions: expanding the interlayer spacing to 0.357 nm and enhancing structural disorder, constructing a closed-pore-dominated hierarchical pore system (0.5-2 nm), and dynamically enriching electroactive CO functional groups on internal pore surfaces. In contrast, at 1000 °C, thermodynamic carbon-layer re-stacking overwhelms CO₂ etching, triggering structural self-repair and pore collapse. Benefiting from this synergistic tripartite optimization achieved in a single atmospheric variable, the 900 °C-activated carbon delivers a high reversible capacity of 318.14 mAh·g^-1 and outstanding rate capability (116.6 mAh·g^-1 at 1.5 A·g^-1). Full-cell tests further confirm its good compatibility with an O3-type cathode, underscoring its practical application potential. This work establishes a generalizable mechanistic framework for converting low-cost soft carbon precursors into high-performance hard carbon anodes through precise kinetic control.