Application And Modification Of Metal Organic Frameworks (MOFs) In Lithium-sulfur Batteries

At present,the commercialization process of lithium-sulfur batteries has been greatly hindered.This is mainly due to the following problems: elemental sulfur is an insulator,and the electronic conductivity is low,which tends to lead to lower rate performance of the battery;The polysulfide easily dissolves,leading to a large loss of the positive electrode active material,resulting in an increase in capacity attenuation;the inherent "shuttle effect" of lithium-sulfur batteries will cause the corrosion of the negative electrode material,and the coulomb efficiency and cycle performance will decline.Therefore,compounding a material with strong conductivity and large specific surface area with elemental sulfur to improve the conductivity of sulfur and reduce the dissolution of polysulfides can accelerate the application of lithium-sulfur batteries.Metal-organic framework materials(MOFs)are widely used in various fields due to their high porosity,controllable structure,and adjustable redox activity.However,it is well known that metal-organic framework materials have a common disadvantage of poor electrical conductivity.Therefore,this article chooses two types of metal-organic frame materials were modified,and the two metal-organic frame materials were modified with different carbon materials.The modified MOFs/carbon material composite was used as the main body of the lithium-sulfur battery cathode material.This combines the dual advantages of MOFs and carbon materials at the same time,which is conducive to obtaining high-performance lithium-sulfur batteries.In this paper,two kinds of carbon materials modified MOFs are used as the main research object of lithium-sulfur battery cathode materials.The following three aspects have been carried out.(1)In order to obtain a high-performance lithium-sulfur battery,the strong chemical bond formed by the bimetal MOF-174 In/Mn in the lithium-sulfur battery positive electrode material is far greater than that of other metals,which can effectively fix sulfur.;Mn element can support the structure of the material during the reaction process,to a certain extent,can inhibit the shuttle effect in the lithium sulfur battery and the volume expansion during the reaction process.Therefore,on the one hand,the work focuses on the bimetal MOF-174 In/Mn,which is modified with different carbon materials and the modified MOF/carbon material composite is used as the cathode material for lithium-sulfur batteries.further research.(2)Similarly,due to the special micro-porous/meso-porous composite structure of Ce-MOF-808 and the metal oxide Ce O2 present in it,Ce O2 nanoparticles can well adsorb and catalyze the conversion of polysulfides.On the one hand,Ce-MOF-808 was selected as the main research object,and different carbon materials were used to modify them,and the modified MOF/carbon material composites were formed as cathode materials for lithium-sulfur batteries from morphological characterization and electrochemical testing.And other related research.(3)Finally,it is clear from the experimental and test results of the first two aspects that compared with other composite materials studied in this paper,Ce-MOF-808@S/PPy is a composite material that is used as a positive electrode for lithiumsulfur batteries.The material shows more excellent performance,so the last part of this article further studies the effect of different content of pyrrole monomer on the final performance of lithium-sulfur batteries during the preparation of Ce-MOF-808@S/PPy.