Defect‐Guided Etching of Coal Tar Pitch Toward Hierarchical Porous Carbon Cathodes for High‐Energy Sodium‐Ion Capacitors

Abstract

Sodium‐ion capacitors (SICs) are promising candidates for high‐power energy storage, yet their practical energy density is severely constrained by the limited anion‐storage capacity, sluggish interfacial kinetics, and insufficient cathode/electrolyte stability at high operating voltages. Herein, we present a defect‐guided etching strategy to construct high‐performance carbon cathodes from low‐cost coal tar pitch. This approach integrates acidification pre‐oxidation with in situ nitrogen doping, where the pre‐oxidation step suppresses pitch melt‐flow and promotes molecular cross‐linking, while melamine‐derived nitrogen dopants create defect‐rich carbon domains that serve as preferential sites for subsequent chemical etching. The optimized carbon boasts an ultrahigh specific surface area (1828.77 m 2 g −1 ), hierarchical micro/mesoporosity, and abundant nitrogen heteroatoms (12.6 at%), providing exceptional active sites and rapid ion‐transport channels. Mechanistic investigations reveal a surface‐controlled capacitive process dominated by reversible PF 6 − adsorption/desorption, stabilized by a Na‐F‐rich cathode‐electrolyte interphase. When coupled with a hard carbon anode, the SIC achieves an energy density of 119.4 Wh kg −1 at 574.6 W kg −1 (based on the total active mass of cathode and anode), and retains 94.1% of its initial capacity after 7000 long‐term cycles at 5 A g −1 . This work demonstrates a scalable route for designing coal‐pitch‐derived carbon materials toward high‐energy, high‐power energy storage systems.