Design And Performance Study Of Cathode Materials And High-performance Separator Coatings For Lithium-sulfur Batteries

Lithium-sulphur batteries are one of the most promising battery energy storage systems available due to its high theoretical specific capacity(1675 m Ah g^-1)and energy density(2600Wh g^-1).However,the low electronic conductivity of the active material sulfur and discharge products,the volume expansion of sulfur during charging and discharging,the low utilization rate of the active material due to the shuttle effect of polysulfide formation in the positive and negative electrodes,and the lithium dendrites produced by lithium metal in the negative electrode have hindered large-scale application of lithium-sulfur batteries.Based on the above-mentioned main problems of lithium-sulfur batteries,in this paper,the preparation of the cathode sulfur carrier material and the design of the diaphragm coating material for lithium-sulfur batteries are researched,the performance of the prepared materials and lithium-sulfur batteries are analyzed and characterized.The main work is as follows:(1)Preparation and electrochemical properties of carbon-coated Halloysite/sulfur composite materialThe carbon coated Halloysite is used as the host material for the lithium-sulfur cathode.The carbon layer on the surface of Halloysite site can greatly increase the electron conductivity of Halloysite,enabling rapid electron transfer between the host material and sulfur.It is a natural inorganic material with tubular structure,and the inner layer of the pipe diameter is made of alumina,the outer wall of the pipe diameter is made of silica.,the dislocation of silica ions and aluminum ions makes it form charge structure of internal positive and external negative.Based on these structural features,Halloysite has a strong charge effect on the anions in polysulfides and can effectively inhibit the shuttle effect of polysulfides.The pore size structure of Halloysite not only can alleviate the volume expansion problem of sulfur during charging and discharging,but also can absorb more electrolyte and accelerate the migration of lithium ions in the positive and negative electrodes.The experimental results show that the lithium-sulfur battery has an initial specific capacity of 1108.1 m Ah g^-1at a multiplicity of 0.1 C,maintains a specific capacity of 698.3 m Ah g^-1at a high multiplicity of 3C,and maintains a specific capacity of 561.2 m Ah g^-1for 1000 cycles at 0.2 C,the capacity loss rate is only 0.044%per cycle.The experimental results demonstrate that the carbon-coated Halloysite can effectively suppress the shuttle effect of polysulfides and improve the electrochemical performance of lithium-sulfur batteries.(2)Preparation and electrochemical properties of cobalt-doped carbon nanotube composite separatorThe monatomic cobalt-loaded carbon nanotubes are produced by calcination of C₃N₄,glucose and melamine in an inert atmosphere at a certain mass ratio.The cobalt-doped carbon nanotubes are filtered by vacuum filtration onto a commercial polypropylene separator to act as a separator material for lithium-sulfur batteries.The high specific surface area of the carbon nanotubes can effectively adsorb polysulfides and the high catalytic activity of cobalt can reduce the conversion barrier of polysulfides and improve the reaction kinetics.The electrochemical test results show that the initial specific capacity of the cell is 1364.8 m Ah g^-1at 0.1 C,with a sulfur utilization rate of 81.5%,and the capacity is maintained at 775.9 m Ah g^-1at 3 C.After 500 cycles at 1 C,the capacity is 716.7 m Ah g^-1,the capacity retention rate is68.7%,the capacity decay rate is only 0.06%per cycle.The experimental results show that this composite separator can significantly improve the electrochemical performance of lithium-sulfur batteries.