Research And Development Of High-performance Supercapacitors Based On MOF Derived Transition Metal Oxides/Sulfides

Supercapacitor as a new energy storage device,has many advantages,such as fast charge and discharge speed,high power density and so on.However,the problems of low energy density and poor cycle life exist in the practical application of super capacitor,which seriously limits its application in practice.Therefore,it is necessary to improve the energy density and cycle stability by developing excellent electrode materials.There are many factors affecting electrode materials,such as specific surface area,conductivity and stability of electrode materials.Through the preparation of organometallic framework and its derivatives,the electrochemical properties of electrode materials can be significantly improved by using its adjustable chemical composition,size and internal structure.Based on this,this paper focuses on the preparation of nicoo electrode materials with hollow structure based on metal organic framework.In order to further improve its conductivity,Nicos was obtained by sulfurization and its electrochemical performance was tested.The main research work is as follows:?1?We have prepared a core-shell structure with adjustable chemical composition and structure.This core-shell structure can increase the active sites needed for electrode materials to participate in oxidation-reduction reaction,increase the contact area between electrode materials and electrolyte,and then improve the specific capacity of electrode materials,so as to solve the problem of low energy density of metal organic frame derivatives used in supercapacitors.In addition,the core-shell structure can fully release the generated stress in the process of oxidation-reduction,which solves the problem of poor cycle life of super capacitor.Using the metal organic framework ZIF-67 as the template,we have successfully prepared electrode materials with bimetal core-shell structure by Kendal ion exchange technology.At the current density of 1 A/g,the specific capacity of core-shell nicoo electrode material can reach 42 mAh/g,while the metal organic framework derivative Co₃O₄ with simple structure is only 14 mAh/g at the current density of 1 A/g.NiCoO electrode materials were subjected to 5000 cycles at low current density?1 A/g?,and the attenuation was only 20%.The results show that the core-shell NiCoO electrode material has higher energy density and longer cycle stable life.?2?The poor conductivity of metal oxide results in poor specific capacity and cycle stability of electrode materials.Metal sulfides have good electrical conductivity and show good performance as electrode materials of supercapacitors.On the basis of the nicoo electrode material based on MOF framework,the nano materials were vulcanized,doped with nitrogen and coated with carbon by means of high temperature annealing to improve the conductivity and cycle stability.In the experiment,ZIF-67was used as the precursor,Ni?NO₃?₂·6H₂O as the nickel source,and Kendal ion exchange method was used to carry out the ion exchange of ZIF-67.Sulfur powder was used as the sulfur source to vulcanize the core-shell structure organic framework,and Nicos was prepared by mild annealing in ar.The specific capacity of Nicos electrode material can reach 136 mAh/g at 1 A/g current density and 42 mAh/g at 1A/g NiCoO.The NiCoS electrode material was cycled 10000 times at low current density?1 A/g?,and the capacity retention rate was still 90%.The results show that the core-shell structure NiCoS as electrode material has higher specific capacity and cycle life.