Research Of ZIF 67 Derived Carbon Based Composite Material And Its Inhibition Of Polysulfide Shuttle Effect

With the rapid development of the new energy automobile industry and electronic products,the industry has increasingly higher requirements for cruising range and running time.The current battery system cannot meet people's needs due to high cost and limited capacity.Lithium-sulfur(Li-S)battery have received widespread attention due to their high-capacity advantages.However,due to the shuttle effect,the commercialization of Li-S batteries has not been carried out completely.Therefore,three kinds of Co and N-doped porous carbon-based composite materials with different structures derived from ZIF 67 are proposed,which are used to suppress the shuttle effect after being prepared as a modified layer of the separator.The main contents are as follows:Based on the physical adsorption of polysulfides by traditional conductive carbon,we synthesized the ZIF 67/KB composite precursor material in an aqueous solution.After carbonization,a conductive porous carbon material with a large number of Co and N active sites was obtained,and it was prepared as a PE membrane coating layer.The abundant active sites and high conductivity in the coating layer can quickly adsorb and catalytically convert polysulfides.The results show that the battery with Co-N/KB modified separator has lower resistance.In addition,while the Co-N/KB coating layer provides a physical barrier,Co and N doping also provide chemical adsorption and conversion promotion effects on polysulfides.Therefore,compared with KB modified separator and PE separator,the lithium-sulfur battery using Co-N/KB modified separator has better cycle performance.On the basis of the first part of the research,ZIF 67 is epitaxially grown on the surface of the ZIF 8 template,the hollow structure Co-N-C material can be obtained after high temperature carbonization.In addition,the carbon nanotubes generated by the displacement of the Co nanoparticles can increase the conductivity of the material.The hollow Co-N-C material inhibits the shuttle effect through its physical structure,and the large amount of Co and N doping inside can promote the conversion of polysulfide through chemical action.The research results show that the battery using the Co-N-C modified separator can stably cycle more than 400 times under the conditions of a high sulfur loading of 4.7 mg cm^-2 and a high discharge rate of 1 C.The ZIF 8@67 precursor was further optimized to obtain the Zn S@Co-N-C dual-core shell structure.Electrochemical tests show that Zn S increases the chemical adsorption of polysulfides.The unique dual-core shell structure facilitates the penetration of electrolyte into the material and promotes the migration of lithium ions.Therefore,the Li-S battery can be work stably for more than 530 cycles under the conditions of sulfur loading of 3 mg cm^-2 at 1 C.