Design,Fabrication And Electrochemical Performance Of Titanium Dioxide/Carbon Composites For Lithium-Sulfur Batteries

The development and utilization of low-carbon,environmentally-friendly and abundant renewable energy can alleviate the global traditional energy exhaustion and pollution.Rechargeable batteries with energy density and long cycle performance are highly sought-after for electric vehicles and large-scale electrochemical energy-storage sysytems.However,current Li-ion batteries cannot satisfy this demand in terms of specific energy.The lithium-sulfur batteries(Li-S batteries),with a very high energy density(2600 Wh.kg-1)and cost effectiveness,have become one of the most promising candidates for next-generation high-energy rechargeable batteries.However,its commercial application has been hindered by several issues,the major one is the undesirable shuttle effect originating from the dissolution of lithium polysulfide intermediates in the electrolyte and their migration to Li anode through the separator,which results in low capacity and rapid capacity fading.In this dissertation,focussing on the key problem,we developed high performance Li-S batteries based on the construction of conductive network and surface modification.The results provide insight into design and development of long cycling performance Li-S batteries.The main results are summarized as follows:(1)We fabricated novel polysulfide barrier layers composed of TiO2/CNT in which the mesoporous TiO2 particles were threaded by CNTs to improve the performance of Li-S batteries.The threaded structure provides excellent interfacial contact between TiO2 and CNTs allowing CNTs to provide fast and continuous electron pathway toward the TiO2-polysulfide polar adsorption interface,thus dynamically accelerating the redox conversion of the trapped polysulfides.As a result of the synergetic effect,the cathode exhibits a high sulfur utilization and long cycle life.(2)By utilizing the self-weaving characteristic feature of the TiO2/carbon materials,we developed a lightweight capping layer directly coated onto the surface of sulfide cathode.The capping layer on the sulfur cathode allows the battery to benefit from the sulfur cathode is in direct contact with an electrically conducting layer to form a cathodic "subcell" for capturing and reducing polysulfide species.It is noteworthy that the weight density of the TiO2/CNT capping layers is much lower than in interlayers.High specific capacity and long cylcle life were achieved,demonstrating a prototype fpractically reliable Li-S batteries.