Efficiently Preparing of High-Rate Coal-Based Hard Carbon Anodes via Plasma Pre-Oxidation

Coal emerges as an exceptional candidate for hard carbon precursors, attributed to its three-dimensional (3D) structure and high carbon yield. Nevertheless, abundant aromatic rings in coal tend to form a highly ordered graphitic structure after high-temperature carbonization, which hinders sodium-ion (Na+) storage. Herein, glow discharge plasma is employed to effectively introduce oxygen-containing groups into coal effectively, facilitating the formation of a cross-linked structure, which is subsequently subjected to high-temperature carbonization to obtain structurally optimized coal-based hard carbon (HC). Compared with the traditional pre-oxidation method, the surface chemical composition and microstructure of coal-based HC (OCHC20) obtained after carbonized are effectively modified by oxygen plasma treatment. The OCHC20 exhibits a remarkable initial Coulombic efficiency (ICE) of 89.3% and a reversible capacity of 302 mAh g^{- 1} at 0.05 A g^-1, which is higher than the 263 mAh g^-1 reversible capacity of hard carbon (OCHC) prepared by traditional pre-oxidation. Particularly, OCHC20 displays superior rate performance with a capacity of 238 mAh g^-1 at 5 A g^-1, representing a 22.7% increase over OCHC (194 mAh g^-1). This study demonstrates the potential of plasma technology in the rational design of carbon-based anodes for high-performance sodium-ion batteries (SIBs).