Conversion of aliphatic structure-rich coal maceral into high-capacity hard carbons for sodium-ion batteries

Pre-oxidation is an effective strategy for preparing high-capacity coal-derived hard carbons. However, the complex molecular structure of coal results in the uncontrollability of oxidation and structural evolution, which hinders the design of high-performance hard carbons. Herein, we are separating macerals to investigate the effects of molecular structural features of coal macerals on their oxidative reactivity, as well as the constitutive relationship between the cross-linked structures of the macerals and the structures of coal-derived hard carbons. According to molecular mechanics and Monte Carlo method simulations, the oxygen adsorption behavior of different coal molecules during increasing temperatures is revealed. The macerals with more aliphatic structures exhibit higher oxidative reactivity and have more adsorbed oxygen in the molecular model, contributing to a more cross-linked structure. The subsequent carbonization process limits the rearrangement of the carbon layers, resulting in a more disordered carbon layer structure and the formation of more ultra-micropores. Experimental results reveal that vitrinite-rich coal-derived hard carbons exhibit a capacity of 330.2 mAh/g higher than inertinite-rich coal-derived hard carbons capacity of 260 mAh/g. This work throws a light on the preparation of high-capacity coal-derived hard carbons, and provides theoretical guidance for other thermochemical research systems.