Covalent Encapsulation of Sulfur in a MOF-Derived S, N-Doped Porous Carbon Host Realized via the Vapor-Infiltration Method Results in Enhanced Sodium–Sulfur Battery Performance

Practical applications of room temperature sodium–sulfur batteries are still inhibited by the poor conductivity and slow reaction kinetics of sulfur, and dissolution of intermediate polysulfides in the commonly used electrolytes. To address these issues, starting from a novel 3D Zn-based metal–organic framework with 2,5-thiophenedicarboxylic acid and 1,4-bis(pyrid-4-yl) benzene as ligands, a S, N-doped porous carbon host with 3D tubular holes for sulfur storage is fabricated. In contrast to the commonly used melt-diffusion method to confine sulfur physically, a vapor-infiltration method is utilized to achieve sulfur/carbon composite with covalent bonds, which can join electrochemical reaction without low voltage activation. A polydopamine derived N-doped carbon layer is further coated on the composite to confine the high-temperature-induced gas-phase sulfur inside the host. S and N dopants increase the polarity of the carbon host to restrict diffusion of sulfur, and its 3D porous structure provides a large storage area for sulfur. As a result, the obtained composite shows outstanding electrochemical performance with 467 mAh g⁻¹ (1262 mAh g⁻¹_(sulfur)) at 0.1 A g⁻¹, 270 mAh g⁻¹ (730 mAh g⁻¹_(sulfur)) after 1000 cycles at 1 A g⁻¹ and 201 mAh g⁻¹ (543 mAh g⁻¹_(sulfur)) at 5.0 A g⁻¹.