Aqueous Solution Synthesis of Sulfur-Ketjen Black Cathode Materials Without Heat Treatment for High-Performance Li-S Batteries

A sulfur-Ketjen Black (KB) composite was prepared by encapsulating sulfur into the micro/meso pores of commercial KB via an aqueous solution synthesis route without heat treatment. The sulfur-KB composite was characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and thermogravimetric measurements. The microstructural characterization suggested that elemental sulfur was well dispersed within the micro/meso pores of KB with the use of a peristaltic pump. Large reversible capacities and excellent cycling performances were demonstrated by the galvanostatic discharge charge process and cyclic voltammetry for Li-S batteries using the sulfur-KB composite as cathode material. The sulfur-KB composite displayed initial discharge capacities of 1409 mAh g(-1) and 1057 mAh g(-1) with good cycling stabilities at a current density of 0.2 C and 1 C, respectively. In addition, it exhibited high rate capability as the current density increased from 0.2 C to 2 C. Furthermore, electrochemical impedance spectroscopy was performed to analyze the influence of the microstructure of sulfur-KB composite on the electrochemical reaction. Based on the above studies, the improved electrochemical characteristics of the sulfur-KB composite has been attributed to the well dispersed sulfur loading morphology, which enhanced the charge transfer conductance and the constraint of lithium polysulfide.