Oxidation‐Induced Molecular Structural Transformations in Pitches with Different Softening Points Toward High Performance Sodium Storage

Abstract Pre‐oxidation treatment is a key process in producing pitch‐derived hard carbon for sodium‐ion battery anodes, however, the oxidative crosslinking mechanism of pitch remains elusive. This study aims to delve into the influence of softening points of pitches and pre‐oxidation durations on the variability of pitch oxidation behavior. The results demonstrate that the oxidation of pitch is due to the interconnection of polycyclic aromatic hydrocarbons and the presence of methyl groups that are directly attached to the aromatic rings. These structural features make pitches with higher softening points more susceptible to oxidation regardless of reaction period. Specifically, they are transformed into branched structures via ring‐opening, increasing the likelihood of oxidation. Further oxidation reactions generate functional groups such as esters and carboxylic acids, promoting the crosslinking of pitch, thus converting pitch from soft carbon to hard carbon, and increasing the reversible capacity from 105.1 to 259.6 mAh g −1 . However, the pitch with a low softening point featured by low aromatic hydrocarbon linkage failed to be pre‐oxidized. The results of this research provide a profound comprehension of the oxidation mechanisms of pitch, which guide the design to transform pitch improving the pre‐oxidation processes for obtaining pitch‐derived hard carbon for high performance sodium‐ion batteries.