A molecular-scale regulation strategy for designing asphalt-based hard carbon for superior sodium storage

Abstract

The air pre-oxidation strategy has been proven to effectively inhibit the graphitization of asphalt during carbonization. Nonetheless, traditional air pre-oxidation methods mainly introduce oxygen-containing functional groups on the surface of asphalt aromatic molecules, which may result in a “trapping effect” on sodium ions. Additionally, due to incomplete oxidation reactions between the oxygen atoms introduced and carbon atoms within the planar molecules, asphalt tends to undergo slight liquid-phase melting during high-temperature carbonization. Therefore, this study proposed a molecular-scale regulation strategy that utilized a novel gradient pre-oxidation process to promote more oxygen atoms to crosslink with the internal carbon atoms of aromatic molecules. Consequently, the prepared asphalt-based hard carbon material exhibited a more disordered microstructure and richer defects. Additionally, the hard carbon material demonstrated excellent cycling stability (retaining a discharge specific capacity of 308.60 mA h g⁻¹ after 150 cycles at a current density of 1C) and rate performance (a discharge specific capacity of 181.79 mA h g⁻¹ at 10C) in sodium-ion half cells. Furthermore, the full battery assembled with Na₃V₂(PO₄)₃ had a specific discharge capacity of 208.30 mA h g⁻¹ after 200 cycles at 1C, demonstrating its high practical application value.