Study On Performance Of Ionic Liquid Supercapacitor Based On Conductive Metal-Organic Framework Ni₃（HITP）₂

Electric energy storage is one of the key technologies related to the development and utilization of new energy resource such as solar energy and wind energy.As a new type of electrical energy storage device,supercapacitors have the advantages of high power density,fast charge and discharge speed,long service life and environmental friendliness.However,supercapacitors still have the problem of low energy density.In order to solve this problem,metal-organic framework materials with good conductivity have received more and more attention,expected to become more suitable electrode materials for supercapacitors than activated carbon.By selecting Ni₃（HITP）₂,a kind of two-dimensional metal-organic framework material with good conductivity,as the electrode and three kinds of common ionic liquids[BMIM][PF₆],[BMIM][BF₄]and[EMIM][BF₄]as electrolyte,the performance of supercapacitors composed of conductive metal organic framework materials and ionic liquids was explored in this article.Firstly,through the combination of experimental characterization and structural calculation,the theoretical structure of Ni₃（HITP）₂ is confirmed to have parallel stacking and two-dimensional honeycomb graphene-like structure.The lattice parameters,pore size distribution,specific surface area,X-ray diffraction pattern,X-ray photoelectron spectroscopy and Raman spectroscopy of Ni₃（HITP）₂powder were obtained.Thus,the characteristics of Ni₃（HITP）₂powder,especially the porosity,were better understood.The optimization of the synthesis method greatly improved the specific surface area and crystallinity of Ni₃（HITP）₂ powder,and the highest specific surface area reached 732 m²/g,which exceeded the maximum value of the existing Ni₃（HITP）₂powder.Then the supercapacitors were assembled with Ni₃（HITP）₂ powder and three kinds of ionic liquids.It is found that among the three kinds of ionic liquid,[EMIM][BF₄]performs best without adding conductive agent.In this case,the capacitance performance is close to the level of activated carbon.It is also found that at the same scan rate,the specific area capacitance of supercapacitors which composed of electrode materials with different specific surface areas is the same and higher than that of commercial activated carbon,indicating that the Ni₃（HITP）₂exerts very high adsorption efficiency,fully demonstratting the advantage of the crystalline material of the conductive metal-organic framework material in supercapacitors.Finally,the acetonitrile solution of ionic liquid was selected as the electrolyte during the assembly of the supercapacitor.After the ionic liquid was dissolved in acetonitrile,both the capacitance performance and the impedance performance of the capacitor were significantly improved with a significant increase in solution conductivity,and[BMIM][PF₆]was the most significant improvement.By exploring the relationship between the capacitance performance and solution conductivity with[BMIM][PF₆]at a series of concentrations,it is found that the capacitance value of the superapacitor has a strong positive correlation with the conductivity of the solution.