Tuning the carbon morphology by pyrolysis in AlCl3–NaCl molten salt from coal tar pitch

Pitch-based carbon materials (PCMs) such as carbon microspheres and carbon fibers have gained great attention and obtained many applications. However, how to prepare PCMs via a simple route and modulate PCMs morphology is still a big challenge. In this study, we found and systematically elucidate the transition from carbon microspheres to fibrous carbons (FCs) in AlCl3–NaCl molten salt (ANMS) using coal tar pitch as the carbon precursor, and investigated the associated transition mechanism based on morphological analysis. Based on this mechanism and dispersion state analysis of pitch in molten salt, we achieved pitch-based carbon microspheres and FCs through a simple one-step approach using the ANMS as reaction medium. It was found that the reaction temperature and the ANMS formulation determines the morphology of PCMs. Spherical PCMs with the mean diameter of 4 μm were obtained when the molten salt is in liquid phase. Fibrous carbon are obtained when the molten salt coexists in gas-liquid two-phases. We propose a method to manipulate the reaction temperature and the composition of ANMS to control the static or dynamics of the reaction system, enabling the successful synthesis of carbon microspheres and FCs. Furthermore, our carbon microspheres maintain a specific capacity of 350mAh/g after 400 cycles, reaching the level of commercial MCMB. Our work further perfects the structure and morphology mechanism of PCMs in molten salt and provides new insights for a simple and shape-controllable method to design and develop the competitive PCMs.