Stabilization of Sulfur Species in Coal-Derived Hard Carbon via Micropore Confinement and Chemical Bonding for Enhanced Sodium Storage
Hard carbon anodes for sodium-ion batteries suffer from limited capacity, low initial Coulombic efficiency, and poor long-term cycling stability. To address these issues, we report a dual-stabilization strategy that combines micropore confinement and chemical bonding to control sulfur species in coal-derived hard carbon. Bituminous coal, with its naturally condensed aromatic framework, serves as the carbon precursor. A two-step thermal process first constructs a microporous carbon framework, followed by gas-phase sulfidation to introduce sulfur. The sulfur is confined within micropores and forms stable covalent C–S bonds with the carbon matrix, providing synergistic physical–chemical stabilization. This suppresses sulfur migration, prevents interfacial side reactions, and introduces additional redox-active sites. The optimized sample (HC-10) delivers a high reversible capacity of 450 mAh/g after 800 cycles at a current density of 1 A/g, with excellent rate capability and cycling stability. Mechanistic analysis reveals that the stabilized sulfur species reversibly participate in sodium-ion storage and improve interfacial kinetics. This work provides an effective strategy for stabilizing sulfur in coal-derived carbon materials and offers insights into the design of high-performance anodes for sodium-ion batteries.