Preperation And Electrochemical Performance Of S/C And S/TiO₂Cathode Composite For Lithium/Sulfur Battery

Lithium sulfur battery is a most promising energy storage system due to its high theoretical energy density, low cost and environmental friendliness. However, there are still a number of problems in Li/S batteries, such as the low active material utilization and poor cycle life, which are due to the high electrical resistivity of sulfur and lithium sulfide, and the high solubility of the charge-discharge products in the electrolytes. To overcome these problems, enormous efforts have been done on structure design and preparing method of cathode material. Many materials were used to prepare composite with sulfur such as carbon materials, conducting polymers and nano-oxides.Preparing methods have great influence on the performance of composite. S/C composites were prepared by different methods using sublimed sulfur and SP. The preparing methods are ball milling, heating at vacuum, heating in closed reactor and solution method. The structures of composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), the electrochemical performances were measured by galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS). The results indicate that the morphology of S/C composite was controlled by preparing method and sulfur content of composite. And the sample prepared by heating at vacuum with50%sulfur content showed the best electrochemical performance. The initial discharge capacity of the composite at0.1C,0.5C and1C is951.8,685.8,630.3mAh/g respectively, after50cycles, the capacity retention rate is71.3%. Even more the composite has excellent rate performance.When combined with metal oxide to prepare composite, the electrochemical performance of sulfur cathode was promoted. S/TiO2composites with different sulfur content were prepared by solution method and ball milling using sublimed sulfur and nano-TiO2. The composites were characterized and the electrochemical performances were evaluated. From the results, we confirmed that metal oxide has limited effect on modifying the performance of sulfur cathode if it was used as additive agent.Mesoporous TiO2was prepared by Evaporation-Induced Self-Assembly (EISA) using Ti(OC4H9)4and CTAB. Then S/mesoporous TiO2composite was prepared by heating in closed reactor using sublimed sulfur and mesporous TiO2. The structure and electrochemical performance were investigated. The results indicate that the structure of mesoporous TiO2was determined by concentration of CTAB and calcination temperature. When concentration of CTAB was0.5mol/L and calcination temperature was500℃, the pore size of mesoporous TiO2was10nm, and electrochemical performance of the prepared S/mesoporous TiO2composite was excellent. The initial discharge capacity of the composite at0.1C,0.2C,0.5C1C and2C is1043,900.4,770,700.3and625.8mAh/g respectively, after50cycles, the capacity retention rate is66.7%.68figures,4tables,126references.