Design And Synthesis Of Mesoporous Carbon-based Functional Materials And Their Application In Lithium-Sulfur Batteries

Lithium-sulfur（Li-S）batteries are considered to be one of the most promising candidates for the next generation of rechargeable batteries due to their significantly high energy density,low cost,and environment-friendly properties.However,the poor conductivity of sulfur and final discharge products,the so-called"shuttle effect"caused by the migration of soluble lithium polysulfide and other problems seriously hinder the practical application of Li-S batteries.The development of new sulfur-based composite cathode materials can solve the problems of Li-S batteries.In view of this,this paper improves the performance of Li-S batteries by reasonably designing and functionalization of mesoporous carbon-based materials.The main research contents are as follows:1.A novel nitrogen-doped ordered mesoporous carbon coated hierarchical porous carbon material anchored by CoSe nanoparticles electrocatalyst（mNC@HPC-CoSe）was successfully prepared through interfacial polymerization and micelle-mediated coassembly strategy.Its unique hierarchical porous structure is conducive to fully carrying sulfur and alleviating volume expansion during charging and discharging cycle,as well as ion/electron transport.The outer mesoporous carbon shell has the function of maintaining the internal hierarchical porous structure and limiting the outward diffusion of LiPSs.The introduction of polar CoSe nanoparticles provides enough chemical adsorption sites for anchoring LiPSs,and shows enhanced chemical adsorption effect on LiPSs.At the same time,it acts as an electrocatalyst to accelerate the redox transformation kinetics of LiPSs,thus inhibiting the shuttle effect of LiPSs more effectively.Under the synergistic effect of polar CoSe nanoparticles and nitrogen-doped ordered mesoporous carbon coated hierarchical porous carbon nanostructures,the Li-S cell assembled by mNC@HPC-CoSe as the sulfur host material（mNC@HPC-CoSe/S）shows high sulfur utilization,high rate performance and long-lasting excellent cycling stability.After 800cycles at 1C,the capacity remained at 645.3 mAh g^-1 with an average decay rate of only0.04%per cycle.2.A unique 2D mesoporous nitrogen-doped carbon-coated graphene nanosheet anchored by bimetallic CoNi nanoparticles（mNC-CoNi@rGO）was successfully prepared through a coordinated interfacial polymerization and micellar mediated coassembly strategy.The obtained functional material has a unique sandwich-like mesoporous structure,which is conducive to fully carrying sulfur and alleviating volume expansion during charging and discharging cycle.At the same time,the coated graphene as a conductive substrate and the nitrogen-doped ordered mesoporous carbon layer facilitates ion/electron transport.The introduction of polar bimetallic CoNi nanoparticles provides enough chemical adsorption sites for anchoring LiPSs,and shows enhanced chemical adsorption effect on LiPSs.At the same time,it acts as an electrocatalyst to accelerate the redox transformation of LiPSs,thus inhibiting the shuttle effect of LiPSs more effectively.Density functional theory（DFT）calculations show that the chemical adsorption energy of LiPSs on CoNi（111）surface is stronger than that on Co（111）surface,and the energy barrier to be overcome is lower.Due to the synergistic effect of bimetallic CoNi nanoparticles and ordered mesoporous carbon coated graphene conductive layer,the Li-S cell assembled by mNC-CoNi@rGO as the sulfur host material shows high sulfur utilization,high rate performance and long-lasting excellent cycling stability.Even with a high sulfur load of up to 5.0 mg cm^-2,the capacity can be maintained at 5.1 mAh cm^-2after 100 cycles at 0.2C.