Molecular-level design and green process engineering: optimizing pseudo-graphitic domains in pitch-derived hard carbon for fast sodium storage†

This study leverages low-cost coal tar pitch (CTP) to enhance its application in hard carbon (HC) anodes for sodium-ion batteries (SIBs), offering significant environmental and economic benefits. Traditional CTP activation strategies often employ corrosive acids (e.g., H₂SO₄/HNO₃) or toxic oxidants to enhance solubility. Moreover, the inability to precisely regulate pseudo-graphitic domains during carbonization results in disordered structures with limited Na⁺ storage kinetics and low initial coulombic efficiency (ICE). Herein, a green oxidation (HCOOH/H₂O₂)–hydrothermal cascade strategy is employed to yield soluble oxidized CTP and controllably grow graphite nanodomains in situ within the amorphous phase. By controlling the size of these nanodomains, short-range ordered pseudo-graphitic domains with large interlayer spacing and an optimized pore structure were formed during carbonization. The resulting HC demonstrated exceptional rate performance, delivering capacities from 318 to 181 mA h g⁻¹ at current densities ranging from 0.03 to 2 A g⁻¹, and achieved a high ICE of 96.7% when using a carboxymethyl cellulose binder. By integrating molecular-level design with green process engineering, this strategy establishes a universal paradigm for sustainable carbon materials, bridging the gap between sustainable chemistry and high-energy-density batteries.