Synthesis Of Porous Carbon/Sulfur Composite Cathodic Materials For Lithium-Sulfur Secondary Batteries

Lithium-sulfur (Li-S) secondary batteries have attracted much attention because its sulfur electrode has the low cost, high specific capacity (1672mAh/g) and environmental benignity. However, sulfur is highly electrically and ionically insulated at room temperature (5×10-30S/cm), which is a great obstacle to the practical application. It has been proved that constructing sulfur composite electrodes via the surface modification is an efficient strategy to overcome the kinetic limitations and structural instability of sulfur electrodes. In this work, a simple and cost-effective method was developed to prepare porous carbon materials, which can be used as the conductive matrix to fabricate S-C composite for high-performance Li-S batteries.In Chapter3, highly mesoporous carbon foams (MCF) have been successfully synthesized via a facile, cost-effective and template-free Pechini Sol-gel method. The as-prepared MCF exhibited high specific surface area of1478.55m2/g and a commendable pore size distribution for impregnating sulfur. In Chapter4, MCF/S composites were synthesized by a common heat-treatment. The relationship between pore size distribution of mesoporous carbon foam/sulfur nanocomposite (MCF/S) and the content of loaded sulfur were investigated in detail, which had great impacts on the lithium storage performances. The as-prepared MCF/S (57.22wt%) could deliver a high initial discharge of1285mAh/g, and retain878mAh/g after50cycles. Compared with pristine sulfur, MCF/S cathodes showed enhanced electrochemical performances, which can be attributed to high specific surface area, high porosity and excellent conductivity of MCF matrix.In Chapter5, the activated carbon made by coconut shell was prepared, which also could be used as the conductive matrix for S-C composites. A series of tests and characterizations confirmed that high quality activated carbon derived from coconut shell can be fabricated with the weight ratio of C/KOH=1:1.5. However, the electrochemical properties of these S-C composites were not satisfied, which should be improved in the future.