Synergetic solvent extraction and ionic liquid engineering for one-step carbonization of coal tar pitch toward sodium-ion anodes

Sodium-ion batteries (SIBs) have emerged as a promising complement to lithium-ion batteries due to the natural abundance and low cost of sodium resources. However, the large ionic radius and sluggish kinetics of Na⁺ lead to slow diffusion and inferior electrochemical performance of conventional anode materials. Herein, we report a facile and sustainable strategy for the upcycling of coal tar pitch (CTP) into functional carbon anodes. N-Methyl-2-pyrrolidone (NMP) was first employed for solvent extraction of CTP, followed by incorporation of imidazolium-based ionic liquids, 1-butyl-3-methylimidazolium bromide ([BMIM]Br) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆). A single-step carbonization process enabled in situ heteroatom doping and structural regulation of the derived carbons. Systematic structural characterization and electrochemical evaluation reveal that CTP-NMP-[BMIM]Br possesses the highest nitrogen content (4.36 at%), delivers an initial coulombic efficiency of 55.43%, and exhibits excellent cycling stability with a reversible capacity of 153.2 mAh g^{− 1} after 500 cycles at 50 mA g^{− 1}. This better electrochemical performance is attributed to its larger interlayer spacing, better hierarchical pore structure, large pore volume and defect sites that promote better sodium ion storage and transport characteristics. This work presents a green and scalable approach for transforming coal tar pitch into high-value carbon materials and highlights the role of ionic liquids as effective modifiers for tailoring microstructure, heteroatom chemistry, and porosity, thereby enabling high-performance carbon anodes for SIBs.