Oxidation-Assisted ZnCl2 Activation of Pitch-Derived Hard Carbon with Abundant Closed Pores for Efficient Sodium Storage

As a low-cost precursor for hard carbon (HC) anodes in sodium-ion batteries, oxidized asphalt (OP) suffers from excessive carbon-layer ordering and insufficient development of closed-pore structure during pyrolysis, which limits low-voltage sodium storage and initial Coulombic efficiency. Herein, a synergistic strategy combining HNO3 oxidation with ZnCl2 activation is developed to regulate the microstructure of oxidized asphalt-derived HC. The oxygen-containing functional groups introduced by oxidation promote the anchoring of Zn species and facilitate the in situ generation of ZnO intermediates during pyrolysis, thereby reconfiguring the activation process and carbonization behavior. As a result, the ordered stacking of carbon layers is effectively suppressed, leading to an enlarged interlayer spacing of 0.391 nm and a closed-pore-rich structure. The obtained N–Zn–OP exhibits a defect-rich turbostratic framework with a specific surface area of 359.67 m2 g–1. Benefiting from the cooperative optimization of carbon layers and pore structure, the N–Zn–OP anode delivers a reversible capacity of 403.52 mAh g–1 at 15 mA g–1, with 51.13% of the capacity contributed by the low-voltage plateau, and retains 90% of its capacity after 100 cycles at 0.1C.