Confined Carbonization of Pitch Assists the Closed Pore Engineering of Coal-Based Carbon for Superior Na-Ion Storage

Coal-based carbons have garnered interest as cost-effective anodes for sodium-ion batteries (SIBs) owing to their widespread availability and economic practicality. However, the inherent limitations in their microstructure, including insufficient active sites for Na-ion storage, restrict their potential for high-performance applications. Herein, a pitch-assisted coating treatment through confined carbonization is employed to transform open micropores in coal-based activated carbon into closed pores, resulting in more compact and efficient active sites for Na-ion storage. Complementary ex situ Raman and X-ray photoelectron spectroscopy analyses elucidate that Na filling within closed pores significantly influences the low-voltage plateau capacity, validating the critical role of closed pores in enhancing sodium storage efficiency. The engineered coal-based carbon anodes demonstrate a sodium storage capacity of 290.0 mAh g^-1 and an initial coulombic efficiency of 78.0%, along with exceptional cycling stability and rate performance. In combination with an O3-NaNi_1/3Fe_1/3Mn_1/3O₂ cathode, the assembled full cell achieves a remarkable energy density of 251.2 Wh kg^-1, determined by using the total mass of the cathode and anode. This work provides novel perspectives on the structural engineering of coal-based carbon materials, establishing a foundation for their commercialization in high-performance SIBs.