Selecting the molecular components of a pitch to produce a hard carbon anode with a high sodium storage capacity

Pitch is an excellent precursor for the production of hard carbon, with pre-oxidation crucial process in the fabrication. The structural changes in the different molecular components of pitch during thermochemical treatment are a key factor in determining the sodium-ion storage of pitch-based hard carbon anodes. We investigated the effects of the different molecular structures in the asphaltene precursor, including aromatic rings and aliphatic chains, on the sodium-ion storage behavior of the resulting carbon. We found that polar oxygen functional groups limit the steric hindrance caused by the aromatic rings in pitch, and thus facilitate the introduction of cross-linked structures. During high-temperature carbonization, aromatic rings form a rigid carbon framework that prevents the rearrangement of ordered carbon layers, leading to a short-range disordered carbon structure and promotes the production of closed pores. For example, a material prepared from asphaltene, which contains a large number of oxygen-containing functional groups and macromolecular aromatic rings, using pre-oxidation at 300 °C and carbonization at 1200 °C had a reversible capacity of 316.7 mAh g−1 when used as the anode for sodium ion batteries. Our research provides a theoretical basis for the selection of raw materials for the development of high-quality pitch-based hard carbons.