Preparation Of Gasphase Silica/Sulfur Composite Cathode Materials And Its Lithium Storage Properties

Lithium sulfur?Li/S?battery is expected to be widely used in the field of electric vehicles and portable electronic devices,because of the high theoretical energy density?2600W·h/kg?and long battery life.In recent years,more and more researchers pay attention to it.In this thesis,the gas phase silica/sulfur composites with different mass ratios were prepared by solid state melting method.Both the structure and electrochemical properties of the composite materials are studied,and the composite materials was coated by polyethylene glycol 4000?PEG?and doped with carbon nanotubes?CNTs?,respectively.Based on the certain mass ratios improving the discharge voltage,reversibility and cycling performance of Li/S batteries.The structure and thermal stability of the composite materials were characterized by the X-ray diffraction?XRD?,scanning electron microscopy?SEM?and thermogravimetric analysis?TG?.The cyclic voltammetry?CV?,electrochemical impedance spectroscopy?EIS?were tested by the electrochemical workstation,besides the LAND battery test system was used to test the cycle performance as well as rate performance of the composite materials.The electrochemical properties of CV,EIS,cycle performance and rate performance were studied in depth,the specific research contents are as follows:1.The gas phase silica?GPSiO₂?was served as the carrier to load sulfur.The gas phase silica and sulfur composites?GPSiO₂/S?with different mass ratios are prepared by solid-state molten.It was found that GPSiO₂/S composites were ice wrapped structure,and the surface morphology of the cathode was coral reef after the cycling.The GPSiO₂/S composite with 3:7mass ratio possess the best electrochemical performance,which has a high initial discharge specific capacity of 1610mA·h/g,equivalent to 96%of sulfur utilization.And the specific capacity still remains at 814mA·h/g after 50 cycles.The results may be due to the composite material has relatively low impedance.2.The PEG-coated gas phase silica/sulfur composite?GPSiO₂/S@PEG?was prepared by coating polyethylene glycol 4000?PEG?onto the GPSiO₂/S composite?with the mass ratio of3:7?.And the results show that the structure of the GPSiO₂/S@PEG composite is core-shell structure.The initial discharge specific capacity of the composite decreased significantly after coating.But the reversibility and discharge voltage of the composite were improved.In the100th cycling,the specific capacity of the GPSiO₂/S@PEG composite was increased by 16%.The reason for the decrease is that the PEG,as a"shell",hinders the electron transport of the composite,which makes the charge and ion transfer resistance larger.3.The carbon nanotubes?CNTs?doped gaseous-phase silica/sulfur composite?GPSiO₂-CNTs/S?was prepared by doping different mass ratio of carbon nanotubes to GPSiO₂/S composite?with the mass ratio of 3:7?.The study displays the composite doping with CNTs can form a special three-dimensional network.And the reversibility and cycle performance of the GPSiO₂-CNTs/S composite with the mass ratio of 3:1:7 are significantly improved,but its initial discharge specific capacity decreased slightly.In the 100th cycling,the discharge specific capacity of the composite material was increased by 27%when compared with the GPSiO₂/S composite material.Due to this space structure,the electron transport properties of the composites increases,so the electrochemical performance of Li/S cells can be improves.