Structural regulation of asphalt-based hard carbon microcrystals based on liquid-phase crosslinking to enhance sodium...

Air-oxidation is an effective strategy to obtain promising carbon materials from asphalt for sodium-ion batteries. However, this method would generate a vast amount of gaseous pollutant, which pose challenges for recycling. Herein, a simple, cost-effective and environmentally friendly liquid-phase oxidation method is proposed. The oxygen-containing functional groups (-NO₂) are introduced into asphalt, which effectively prevents the melting of asphalt and rearrangement of carbon layers during subsequent carbonization process. As a result, a carbon material with notable disorder degree, large interlayer spacing and abundant closed pores, is prepared. The as-prepared product demonstrates an impressive initial Coulombic efficiency of 88.3 % and an enhanced specific capacity of 317.0 mA h g^-1, which is 2.6 times that of the pristine product. Moreover, when assembled with a Na_3.32Fe_2.34(P₂O₇)₂ cathode, the full-cell delivers a high reversible capacity of 271.7 mA h g^-1 at 30 mA g^-1 with superb cycle life. This study offers a novel oxidation strategy and provides a solution for producing highly disordered carbon anodes from soft carbon precursors.