Synthesis of coal-based functional carbon materials and its application in energy storage

Coal and its derivatives from the thermal conversion processes such as coke production are important chemical resources. The production of coal-based functional carbon materials (CFCMs) enabled by the theory and techniques of the molecular chemical engineering and the multi-dimensional carbon engineering, is an effective way to realize an efficient and clean utilization of coal resources. Coal and coal tar pitch feature the characteristics of polycyclic aromatic hydrocarbons at the molecular level. The controllable synthesis of zero-dimensional, one-dimensional, two-dimensional, and three-dimensional CFCMs can be enhanced by the physical fields such as microwave and plasma via molecular chemical cutting, hybridization , and interface assembly, promoting the applications of the CFCMs in energy storage fields. Firstly, the sources, types, and physicochemical properties of coal and its derivatives from the thermal conversion processes are introduced in detail in terms of the synthesis of CFCMs. Then, the preparation methods, advantages, and disadvantages of various CFCMs such as carbon dots, carbon fibers, carbon nanotubes, graphene, carbon nanosheets, porous carbon, carbon aerogels, and carbon foam are summarized systematically. After that, the applications of CFCMs in energy storage are discussed in terms of hard carbon, soft carbon, porous carbon, and heteroatom doped carbon, and the impacts of carbon layer orientation regulation, heteroatom doping, and confined space construction on the ion storage capability are highlighted. Next, the methods of making hybrids by combining coal-based functional carbon materials with transition metals are summarized, and the structural regulation effect of coal-based carbon sources on the electrode materials with high capacity but significant volume change is discussed. The key issues related to the CFCMs in terms of controlled fabrication, the tuning and evolution of molecular structure and activity of the precursors, and the synthesis methods are addressed. Finally, the perspective and future directions of the CFCMs are outlined, which will be pushed forward by the theory and techniques originated from the molecular chemical engineering and the enhanced mass and heat transfer strategies.