Promoting cross-linking reactivity of coal molecules via swelling strategy to realize high performance coal-derived hard carbon anode

Cross-linking of coal is an effective method for the preparation of modified coal-derived hard carbon (HCs). However, the complex molecular structure and the lower reactivity of coal hinder its cross-linking, which is not beneficial to the preparation of high-performance coal-derived hard carbon. Herein, a swelling strategy is proposed to improve the reactivity of coal molecules with their cross-linking mechanisms with sucroce. It is found that swelling destroys the hydrogen bonding network in coal molecules, producing aliphatic structures and carboxyl functional groups. Therefore, it improves coal molecular reactivity which is conducive to the formation of an abundant C=O/O=C–O three-dimensional structure and a stable cross-linking structure during the high temperature carbonization procedure. The swelling treatment further enlarges the layer spacing of the carbon material, leading to a greater disorder in the carbon structure, and facilitates the development of pore structure. The HCs with optimal structure exhibit a high initial coulombic efficiency of 88.4 %, a reversible capacity of 304.7 mAh g −1 , and a excellent rate performance (192 mAh g −1 at 1 A g −1 ). This work provides a molecular structure modulation strategy for the modification of coal-derived HCs with potential application in advanced sodium ion batteries.