▎ 摘　　要

Low-cost three-dimensional coal-based graphite microcrystal/graphene composites (3D-CGC/G) were synthesized via a one-step hydrothermal method. The high content of various oxygen functional groups and defects in this 3D architecture, induced by the graphite microcrystal, can provide plentiful reactive sites to adsorb Na+, while insertion and pore-filling of Na+ are negligible in this material. The high capacitance contribution (50.5-83.5%) of 3D-CGC/G suggests that the induced oxygen functional groups on the carbon surface could rapidly capture Na+ through a fast surface redox reaction at large current density, leading to good rate performance. When used as a sodium ion battery anode, the 3D-CGC/G1 composite exhibits a good reversible specific capacity of 254 mA h g(-1) after 350 different electrochemical rate cycles and 101 mA h g(-1) at 2 A g(-1) after 2000 cycles, demonstrating the good rate performance and electrochemical stability of coal-based carbon materials.