Construction And Properties Of Metal Oxide Cathode Materials For Lithium-Sulfur Batteries

As one of the most promising new-generation energy storage devices,lithium-sulfur batteries have received widespread attention because of their high energy density,high specific capacity,low cost and environmental friendliness.However,the commercialization of lithium-sulfur batteries is still facing many basic scientific problems,such as low conductivity of sulfur cathode and Li₂S/Li₂S₂,serious volume expansion of cathode after discharge,shuttle effect of intermediate products polysulfide and lithium dendrites of the anode,which lead to serious degradation of the performance of lithium-sulfur batteries during use.In order to cope with these problems,it is necessary to design and construct new cathode materials in order to obtain long-cycle,high-capacity lithium-sulfur batteries,which have become one of the promising and practical research topics in the field of energy storage.The research content of this thesis is as follows:1.Ta₂O₅ and V₂O₅ were prepared by the solvothermal and liquid-phase methods,and the V₂O₅/Ta₂O₅ complex was innovatively used as an interlayer for lithium-sulfur batteries to suppress the shuttle effect of polysulfides.The V₂O₅/Ta₂O₅ interlayer exhibits a strong adsorption effect on polysulfides.At the same time,the intermediate layer has a bi-directional catalytic effect on the charging and discharging processes of the battery,and the sulfur cathode modified with the intermediate layer exhibits higher sulfur utilization and better cycling stability,with an initial discharge-specific capacity of 1299 m Ah g^-1 at a surface loading of 1.0 mg cm^-2 and a reversible specific capacity of 867 m Ah g^-1 after 100 cycles,which is much higher than that of the comparison sample.This indicates that the designed V₂O₅/Ta₂O₅ interlayer catalyzes the conversion of polysulfides efficiently,suppressing the shuttle effect while accelerating the reaction kinetics of polysulfide conversion.2.Ta₂O₅/TaO₂@CNF（CNF is carbon nanofiber）nanofiber interlayer was prepared by a combination of an electrostatic spinning with a solvothermal method.This interlayer plays a dual role of physical hindrance and chemical adsorption to limit the shuttle of polysulfides.Meanwhile,the carbon fiber matrix of this interlayer material solves the defect of poor conductivity of metal oxides while exposing more active sites of metal oxides.The cathode modified with the interlayer exhibits better rate performance and better cycling stability.The Ta₂O₅/TaO₂@CNF modified interlayer of the lithium-sulfur battery has a discharge-specific capacity of 732 m Ah g^-1 in the first cycle at a surface loading of 1.0 mg cm^-2 and 1 C.After100 cycles,the discharge-specific capacity of the battery can still reach 570 m Ah g^-1,with a capacity decay rate of 0.22%per cycle.This indicates that the Ta₂O₅/TaO₂@CNF interlayer has a non-negligible effect on enhancing the performance of lithium-sulfur batteries.3.Multifunctional Ta₂O₅/PAN nanofiber film with adsorption and catalytic effects was modified in situ on the sulfur cathode surface by an electrostatic spinning technique using carbon black as the conductive agent,Ta₂O₅ as the adsorption catalyst,glucose as the binder,and PAN as the templating agent,which can be used as the cathode modified film to increase the Ta₂O₅ active sites by using nanofibers to enhance the Ta₂O₅ for polysulfide adsorption and catalytic effect of Ta₂O₅ on polysulfides.At the same time,the initial discharge capacity of 780 m Ah g^-1 was achieved at a current density of 1 C using only 5 wt%of the total mass of the modified membrane,and the effective discharge capacity of 622 m Ah g^-1 was maintained after 200 cycles,with a capacity decay rate of 0.10%per cycle,showing the improved electrochemical catalytic performance via micro-regulation and good cycling performance.