Molten salt assisted fabrication of coal-based carbon anode materials for efficient Na ion storage

The development of high-performance and low-cost anode materials plays a crucial role in the commercialization of sodium-ion batteries (SIBs). Coke coal is an excellent carbon precursor with high carbon content, wide distribution, and abundant reserves. Nevertheless, the microcrystalline structure of coke coal-based pyrolytic carbon is relatively regular with narrow interlayer spacing, resulting in poor electrochemical performance. Herein, a coal-based carbon microcrystalline heterostructure with greatly improved structural disordering was fabricated via the cross-linking reaction between functional groups of coke coal and sucrose with the assistance of a molten salt system. Unlike coke coal-based pyrolytic carbon (BCoal-700), the coal-based carbon microcrystalline heterostructure material (BCoal-SM-700) exhibited a significantly increased Na-storage capacity from 125.4 to 286.5 mA h g(-1), with excellent cycle and rate performance. When assembled into a sodium-ion hybrid capacitor, it exhibited an energy density of 103 W h kg(-1) at a power density of 216 W kg(-1). The molten salt procedure offers a simple, eco-friendly, and recyclable approach for the synthesis of coal/sucrose microcrystalline heterostructure carbon materials that can exhibit excellent Na-storage performance, making them promising candidates for SIBs.