Preparation Of Carbon-based Composite Materials Of Metal Nitrides And Sulfides And Their Applications In Lithium-sulfur Batteries

Lithium-sulfur batteries(Li-S)are considered to be the most promising next generation energy storage system due to their ultra-high theoretical specific capacity(1675 m Ah g^-1)and energy density(2600 W h kg^-1).However,many disadvantages hinder the further development of Li–S batteries,such as the insulating nature of the active materials,low utilization of the active materials,poor cycle stability,low capacity and poor safety performance,which hinder the practical application of Li-S batteries.Adding a bifunctional catalyst has emerged as a promising way to enhance the capacities,rate capabilities and cycling stabilities of Li–S batteries by coupling polar inorganic materials with carbonaceous materials.This thesis focus on the synthesis method of introducing polar metal nitrides and metal sulfides into carbon-based sulfur composite materials,structure control.In addition,the effects of the synthesized bifunctional composite materials on the electrochemical performance of sulfur cathodes and batteries were studied in depth(1)WN in-situ coated nitrogen-containing mesoporous carbon spheres.The interconnected S/WN-CNS composite is constructed,and the influence of the presence of a WN coating layer with conductivity and polarity on the electrochemical performance of carbon-based sulfur cathodes is revealed.(2)Synthesis of nitrogen-containing graphene-coated VN hollow nanospheres.A large number of defect sites were introduced on the graphene surface after nitriding,which strengthened the coating effect of VN hollow spheres and the carbon interface.The polar VN not only has ultra-high electrical conductivity,but also has a chemisorption effect on polysulfide ions,which inhibits the shuttle of lithium polysulfide.The effect of VN on the electrochemical performance of carbon-based sulfur cathode is revealed.(3)CNTs@Zn S composite material is formed by carbon nanotubes uniformly coated with Zn S.The CNTs@Zn S composite material effectively buffers the volume strain during the electrochemical reaction.The open hollow structure provides more active sites and maintains the stability of the CNTs@Zn S electrode structure.Sulfur cathode was successfully prepared by combining polar inorganic materials such as WN,VN and Zn S with carbon-based materials.The composite sulfur cathode enhances Li-S battery capacity,rate performance and cycle stability Bifunctional polar materials can not only capture dissolved polysulfides with strong binding energy,but also accelerate the conversion reaction of Li PSs,thereby inhibiting the dissolution of Li PSs and improving the utilization rate and cycle stability of active materials.