Application Of Multifunctional Carbon-based Composite Materials In High-performance Lithium-sulfur Batteries

In order to speed up the construction of a resource-saving society,the state vigorously advocates the use of new energy vehicles with obvious energy saving and emission reduction effects.However,the current outstanding problem restricting its development is the lack of battery life,and the key factor to solve this problem is to develop and use electrode materials with higher energy density.Taking the lithium ion batteries?including lithium iron phosphate,lithium cobaltate,and lithium manganate?,which have the highest utilization rate in recent years,as an example,the theoretical capacity of the cathode material is insufficient to greatly limit the battery's endurance,so a higher specific capacity has been studied.The positive electrode material has important significance for promoting the development of new energy automobile industry.Research shows that the specific sulfur capacity is as high as 1675 m Ah g^-1,which is one of the most promising cathode materials.However,the conductivity of sulfur is extremely poor,and 80%of the volume change will occur during the cycle,and the lithium polysulfide?Li Ps?formed during charge and discharge is very soluble in organic electrolytes,these problems have seriously hindered its commercialization process.In order to solve the above problems,two flexible self-supporting composite materials were designed and prepared by electrospinning technology and other methods,making full use of the conductivity of porous carbon materials and the physical adsorption of Li Ps,as well as sulfides and oxides outside the carbon fiber To increase the chemical adsorption of Li Ps,enhance the cycle stability and rate performance of lithium-sulfur batteries.The specific method is as follows:?1?First obtain nanofibers by electrospinning,and then use the catalytic effect of iron oxide?Fe Ox?to obtain graphitized carbon nanofibers with good conductivity under high temperature carbonization.Sodium solution.After hydrothermal at 180?for 24h,molybdenum disulfide?Mo S₂?with a certain thickness and irregular nanosheet flower structure was grown on the surface of the fiber,and Fe O_x was removed by dilute nitric acid to make it into a rocky desertified porous carbon fiber structure?G-PCNFs?.Finally,the melting method is used to physically restrict the sulfur powder to the flower gap of the molybdenum disulfide sheet and the porous structure of the carbon nanofibers to obtain S/Mo S₂@G-PCNFs.The porous graphite carbon in the composite structure not only improves the conductivity of the positive electrode,but also slows down the volume change of sulfur during charge and discharge,and physically adsorbs soluble Li Ps.More importantly,the chemical adsorption of molybdenum disulfide nanosheets outside the porous carbon nanofibers further suppresses the shuttle effect caused by Li Ps,and the utilization rate of sulfur active materials is effectively improved.In addition,the positive electrode material has a flexible self-supporting structure and can be cut to any size for performance testing.Finally,we observed that the specific discharge capacity at the first cycle at 0.1 C was 1386 m Ah g^-1.At a large rate of 1.0 C,the specific discharge capacity in the first cycle is nearly 926 m Ah g^-1,and the average decay rate during 500 charge-discharge processes is only 0.089%.?2?In order to solve Mo S₂'s no contribution to capacity,the mass percentage of sulfur in the cathode material is reduced.The flexible graphite porous carbon fiber obtained in the previous experiment was coated with a certain amount of V2O5nanosheets on the surface of the fiber by hydrothermal method,and the molten method was used to inject sulfur into the porous structure.In the composite structure obtained in this way,V₂O₅ is a positive electrode material.The thiosulfate obtained during the discharge can not only produce strong chemical adsorption with Li Ps,but also contribute a certain capacity.