Nitrogen-doped activated microporous carbon spheres as a sulfur matrix for advanced lithium-sulfur batteries

Highlights: • A novel NAMCS/S composite is synthesized via a controllable solvothermal route. • NAMCS possess strong chemical and physical adsorption to immobilize polysulfides. • The nitrogen-doped can be beneficial to excellent cycling performance. A kind of nitrogen-doped activated microporous carbon sphere/sulfur composite (NAMCS/S) is deliberately designed and prepared via a controllable solvothermal method and a liquid phase in-situ sulfur deposition technology. The structure characteristic and composition analysis of samples are conducted with X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), field-emission scanning electron microscopy (FESEM) and high resolution transmission electron microscope (HRTEM). The electrochemical performances are characterized by galvanostatic charge-discharge (GCD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The results show that the nitrogen-doped activated microporous carbon spheres (NAMCS) present uniform spherical morphology, abundant nitrogen content of 9.64 wt%, and large specific surface areas of 1578.6 m²/g. Compared with the activated microporous carbon sphere/sulfur (AMCS/S) composite, the NAMCS/S composite with same sulfur loading of 64 wt% can deliver a higher initial capacity of 1004.6 mAh/g and a stable capacity retention of 79.1% after 100 cycles at 0.1 C rate as well as a remarkable Coulombic efficiency of 93% and relative low capacity decay of 0.2% per cycle. These effective improvements are attributed to the change of surface physicochemical property, chemical interaction between nitrogen functionality and polysulfides and the physical adsorption of abundant microporous structure.