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

To solve the problems of limited capacity, low initial coulombic efficiency, and poor long-term cycling stability in hard carbon anodes for sodium-ion batteries, a stabilization strategy is reported that uses both microporous confinement and chemical bonding to control the sulfur species. 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 gasphase 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. Analysis of the storage mechanism shows that the stabilized sulfur species can reversibly participate in the sodium-ion storage and improve interfacial kinetics. Download: Download high-res image (150KB) Download: Download full-size image