The stabilization of sulfur species in coal-derived hard carbon by micropore confinement and chemical bonding to improve sodium storage

Hard carbon is derived from bituminous coal, taking advantage of its naturally condensed aromatic framework. Using a two-step thermal process, a microporous carbon framework was constructed, followed by gas-phase sulfidation to introduce sulfur species.

The sulfur is confined in the micropores while forming stable covalent C-S bonds with the carbon matrix, which stabilizes the sulfur by both physical and chemical means and thus suppresses sulfur migration, which prevents interfacial side reactions and introduces additional redox-active sites. As a result, the sample 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.