Preparation And Application Of Carbon Materials By Molten Salt Method In Lithium-sulfur Battery

Lithium-sulfur battery is considered as one of the most promising energy storage devices because of its advantages of low cost,high energy density and environmental protection.However,due to the insulation of sulfur and discharge product Li₂S,the volume change and shuttle effect of sulfur cathode during charge and discharge,it is difficult to commercialize lithium-sulfur batteries.In order to solve these problems,sulfur must be combined with materials with high conductivity,rich catalytic active sites,large specific surface area and rich pores to improve the utilization rate of active sulfur.In this paper,a new type of sulfur-carbon composite cathode was designed and prepared by doping and modifying three-dimensional graded porous carbon materials.The main work is as follows:（1）Through the two-step pyrolysis method,a composite structure containing Fe₃C nanoparticles embedded in N-doped carbon nanotubes and N-doped three-dimensional porous carbon networks interspersed with each other（NCNT/NPNCs）was prepared.Nitrogen-doped carbon nanotubes embedded in Fe₃C nanoparticles in the material not only inhibit shuttle effect,but also have high conductivity,providing a transport channel for rapid electron/ion transfer,and the porous carbon network can fully load and fix sulfur.The reversible capacity of NCNT/NPNCs is 1125 m Ah g^-1 and 489 m Ah g^-1 at 0.2 C and 1 C current densities,respectively.（2）Three-dimensional porous N-doped carbon networks embedded with Co clusters（Co/PNC）were prepared by pyrolysis of nitrogen-containing precursors and cobalt precursors in molten Na Cl at high temperature.The composite structure of micro-meso-macropores in the material is beneficial to inhibit lithium polysulfide shuttle effect through physical adsorption,and the doping of N and Co nanoclusters also anchor polysulfides through chemical adsorption and high catalytic activity.At 0.2 C current density,the initial specific capacity of Co/PNC battery is 1105.4 m Ah g^-1,and only with a fading capacity of 0.064% per cycle after 300 cycles under 1 C.（3）Nitrogen-doped three-dimensional porous carbon material supported with Co Se₂catalyst（Co Se₂-PNC）was prepared by high temperature calcination selenization method as the cathode of lithium-sulfur battery,and it was proved that the combination of Co Se₂and PNC with high catalytic activity and conductivity can enhance the redox kinetics during charge and discharge.The composite electrode exhibits a good specific discharge capacity of 1139.6 m Ah g^-1 at a current density of 0.2 C,and still has 865.7 m Ah g^-1 after 100 cycles,with a high capacity retention rate of 75.97%,showing excellent electrochemical performance.