Oxygen Functional Groups and Pore Regulation of Sucrose-Derived Carbon for Enhancing Electrochemical Stability in the Cathode of RT Na-S Batteries

Sucrose-derived carbon spheres are promising host materials for cathode sulfur species in Room-Temperature (RT) Na-S batteries. Therefore, the morphology, micro-mesoporous structure, and oxygen-containing functional groups of sucrose-derived nanocarbon spheres were regulated to effectively accommodate sulfur species. This structural design facilitates sulfur confinement, improves charge/ion transport, and enhances the cycling stability of AC@S composites. With increasing activation temperature, the developed porous structure provides more storage sites for active sulfur species; however, excessive activation can reduce the content of oxygen- containing functional groups and weaken the chemical anchoring capability of the carbon framework. Among the prepared samples, AC@S-900 delivered the highest initial capacity of 1323.35 mAh g -1 at 1.0 C, whereas AC@S-750 exhibited superior cycling durability, delivering an initial specific capacity of 941.48 mAh g -1 and maintaining 566.04 mAh g -1 after 1500 cycles, corresponding to an ultralow capacity decay rate of 0.027% per cycle. DFT calculations further suggested that oxygen-containing functional groups can provide polar adsorption/catalytic sites, reduce the conversion energy barriers of Na 2 S x species. Specifically, the carbon framework's carbonyl (C=O) and epoxy (C-O-C) groups can enhance the sulfur redox kinetics. Download: Download high-res image (308KB) Download: Download full-size image