Study on Sulfur Cathode Materials for High Performance Lithium/Sulfur Batteries

Rechargeable lithium/sulfur batteries have attracted significant attention due to their high theoretical specific capacity, high power density and low cost. Nevertheless, sulfur is very much an electrically insulating material, which leads to poor electrochemical accessibility and low utilization of the sulfur in the electrode. The polysulfide anions which are formed as the reaction intermediates are highly soluble in the organic electrolyte solvent, which results in low active material utilization, low coulombic efficiency and short cycle life of the sulfur electrode. Many approaches have been investigated for improving the performances of the sulfur cathode, such as synthesizing sulfur/carbon and sulfur/conducting polymer composites, adding adsorption additives into the electrodes, modification of the electrolyte, etc. Much attention has been paid to recent advances in the sulfur cathodes. In my doctoral work, honeycomb-like sulfur was synthesized via a soft template strategy for lithium/sulfur battery cathode, which has shown improved electrochemical performance compared to commercial sulfur particles. Another polypyrrole@sulfur@polypyrrole (PPy@S@PPy) composite with half-split tubular structure was prepared by the oxidative chemical polymerization method together with the chemical precipitation method. Moreover, the spray pyrolysis method was applied to synthesize a porous sulfur/dual-carbon composite with improved electrochemical performance, which shows great potential for the commercialization of lithium/sulfur batteries. Finally, an active carbon/nano-sulfur/polypyrrole composite with host-container architecture was prepared by the spray precipitation method and a subsequent oxidative chemical polymerization method for lithium/sulfur battery cathode.