Modification Of Mesoporous Hollow Carbon Spheres And Their Application As Host Materials In Lithium Sulfur Batteries

With high theoretical energy density and theoretical cathode specific capacity,lithium-sulfur（Li-S）batteries also have the advantages of environmental soundness and low production cost.Nowadays,there are still some problems on the road to commercialization of Li-S batteries.To alleviate the impact of these problems,we modified mesoporous hollow carbon spheres rich in 3D pore structure as a substrate for sulfur host material.（1）The 3D hollow structure not only facilitates the redox reaction through better distribution of active materials and improved electrolyte penetration but also helps to buffer the volume variation during the cycling.Furthermore,VN nanoparticles can effectively catalyse Li PSs conversion and boost reaction kinetics through the desirable trapping and adsorption of Li PSs.By virtues of these merits,the S@VNHCS cathode has exhibited advantageous electrochemical performances including the high initial discharge capacity of 1453 m A h g^-1 at 0.1 C and the ultralow capacity fading rate of 0.0293%per cycle at 2 C.（2）Mesoporous hollow carbon spheres were modified with nitrides of niobium-vanadium（VNb NCS）using oxalic acid solution as solvent.This mesoporous hollow structure with metal-nitrogen coordination bonds has excellent electrocatalytic properties,which benefit from the bonding of the VN and Nb₄N₅ interfaces and the large number of exposed N and transition metal sites.Based on this,the initial discharge specific capacity of the S@VNb NCS sulfur cathode at a current of 0.1 C is 1322.9 m A h g^-1,and after 600 cycles at a current of 2 C,the specific capacity still has 602 m A h g^-1 with a capacity decay rate of 0.051%per cycle.（3）Nitrogen/cobalt Co-doped mesoporous carbon materials（Co/N@HCS）were prepared by growing ZIF-67 in the center of mesoporous hollow nitrogen-doped carbon spheres using an in-situ synthesis process.This core-shell structure has a ZIF-derived carbon with N/Co catalytic active sites as the core and a mesoporous carbon with N sites as the shell.Highly polar active sites in Co/N@HCS enhance the adsorption of Li PSs,promoting multilevel catalysis in the electrode reaction and alleviating the shuttle behavior of Li PSs.The initial specific capacity of the Co/N@HCS/S cathode at a current of 2 C was 719.2 m A h g-1.The specific capacity retention after 600 cycles was 76.3%,and the capacity decay rate per cycle was 0.0393%.After 600 charge/discharge cycles,the specific capacity retention rate was 76.3%,and the capacity decay rate per cycle was 0.0393%.