Bituminous Coal-Derived Carbon Anode: Molten Salt-Assisted Synthesis and Enhanced Performance in Sodium-Ion Battery

The high-efficiency and clean utilization of coal resources is a key strategy for new energy development, and converting coal into carbon materials offers a promising route to valorize bituminous coal. However, fabricating high-performance bituminous coal-derived carbon for sodium ion (Na+) insertion/extraction remains a major challenge, as it is difficult to regulate the carbon’s microstructural properties to match Na+ storage demands. Herein, we propose a molten salt-assisted carbonization strategy to prepare bituminous coal-derived hard carbon (HC) for use as a sodium-ion battery (SIB) anode material, and we focus on regulating the structure of carbon. The results show that as-prepared HC exhibits significantly enhanced electrochemical performance for Na+ storage when the molar ratio of NaCl to KCl is 1:1. The optimized material achieves a reversible capacity of 366.7 mAh g−1 at the current density of 100 mA g−1 after 60 cycles and retains 99% of its initial capacity after 500 cycles at a current density of 1 A g−1. The main finding is that the lattice spacing can be regulated by tuning the composition of the molten salt, and anode performance is enhanced remarkably by changes in the HC structure. This work provides a feasible strategy for designing and preparing a bituminous coal-derived carbon anode material for use in the energy storage field.