Preparation And Electrochemical Properties Of Oxide Modified Carbon-Sulfur Composite Cathode Materials

Lithium sulfur?Li-S?battery is now widely recognized as one of the most competitive secondary battery systems in the world,because of its super-high theoretical energy density?2600 Wh/kg?,abundance storage and cheap-price for its main electrode materials of sulfur.However,due to the poor electrical conductivity of element sulfur,the "shuttle" effects of intermediate polysulfide formed in the processes of discharge/charge and other well-established factors,significant capacity decay can often be observed during the electrode reactions,which hindered the practical applications of Li-S batteries.Considering the perspectives of the interface effect between polysulfide and metal oxide,in this dissertation,different kinds of metal oxide modified C-S composite electrodes were prepared,and the influences of microstructures,such as nanoparticle interfacial adsorption and oxide shell coating,on electrochemical properties of Li-S batteries,were investigated.The main content are as follows:?1?Preparation of antimony tin oxide?Sb:SnO₂,ATO?nanoparticle modified carbon nanotube-sulfur composite cathodes and investigate on their electrochemical properties.Commercial avaible CNT were used as conductive frameworks and host materials,which were mixed with ATO nanoparticles and further loaded with elemental sulfur by melting diffusion method to prepare the cathodes.Investigation indicated that the CNT network can improve the conductivity and the loading amount of sulfur,while the ATO particles can effective inhibit the "shuttle" throughout an adsorption related mechanism.For an optimized ATO incorporation amount of 2wt.%,the initial discharge capacity reached about 982 mAh/g,and the capacity retention is as high as 66.5% after 200 cycles,which showed an improvement of 43.8% for the pristine CNT modified sulfur electrode.?2?Preparation and investigate on electrochemical properties of MnO₂ coated carbonized polyethyleneimine-sulfur composite electrode materials by a wet chemical in situ oxidation synthesis method.Linear polyethyleneimine?LPEI?were used as template to prepare novel 3-D connected porous carbon networks,which were further loaded with elemental sulfur and oxidized with KMnO4 in solution to form a MnO₂ shell coated sulfur-carbon composite electrodes.Investigation indicated that the outside MnO₂ shell can significantly inhibit the diffusion and dissolution of polysulfide in electrolyte by an absorption and space confinement combined mechanism,which can improve the coulomb efficiency significantly.For a moderately oxidized sample,the specific capacity can maintain as high as 485 mAh/g after 200 cycles,with a stabilized coulomb efficiency of around 96%,while for sample without oxidation treatment,a severely decreased coulomb efficiency of only about 84% was obtained after 200 cycles.