Pore structure modulation and defect engineering of soft carbon@coal-derived hard carbon for enhanced sodium storage application in SIBs†

Hard carbon (HC) is regarded as the most promising commercial anode material for sodium-ion batteries (SIBs) due to its low cost, abundant sources, large reversible capacity, and suitability. Nevertheless, HC suffers from low initial coulombic efficiency (ICE), poor rate performance, and long-term cycling performance, significantly restricting its practical application. Herein, we proceed with defined regulation of the microcrystalline structure of coal-derived HC, which leads to reduced surface defects and increased interlayer spacing, further enhancing the sodium storage capacity of coal-derived HC as an anode material for SIBs by coating porous HC with soft carbon (SC). Meanwhile, we successfully synthesized high-performance SC@HC composite materials through chemical crosslinking reactions by innovatively adopting the sol–gel method and SC coating for the complex composition of coal. The SC@HC composite material as an anode in SIBs can deliver a reversible capacity of 320 mA h g⁻¹ at 0.01 A g⁻¹, a high ICE of 89%, and good cycling stability (capacity retention of 80% after 400 cycles at 1 A g⁻¹). This work can rationally guide the design of low-defect and much more closed pore coal-derived HC materials and provide a feasible route for the development of high-performance HC-based anode materials for SIB applications.