Study On The Supercapacitive Performance Of Mn Co₂O₄ And Its Composite Electrode Materials Prepared By Molten Salt Synthesis

With the rapid development of the global economy,the expedite consumption of fossil fuels and the deterioration of environmental pollution have greatly affected human life and work.Therefore,the development of clean energy storage devices is a major problem to be resolved urgently.As a new type of green energy storage device,the supercapacitor has attracted researchers'attention for its short charging time,high power density,extraordinary safety and long cycle life.In this thesis,MnCo₂O₄ submicron particles were prepared by molten salt synthesis.MnCo₂O₄/NiO supercapacitor electrode materials were prepared by hydrothermal method.X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and other characterization techniques were employed to research phase compositions and microstructures of electrode materials.The electrochemical behavior of electrode materials was investigated by galvanostatic charge discharge,cyclic voltammetry and electrochemical impedance spectroscopy.The main contents of this thesis are as follows:?1?MnCo₂O₄ was synthesized by the NaNO₃-KNO₃ molten salt system.The effect of reaction conditions on the structure and supercapacitive capacitance of MnCo₂O₄ electrode materials was studied.The results show that MnCo₂O₄ electrode materials with better crystallinity,higher purity and highest electrochemical performance can be synthesized when the mass ratio of raw materials?MnCl₂ and CoCl₂·6H₂O?to molten salt is 1:20 at 350?C for 4h.The specific capacitance of MnCo₂O₄ was investigated in different electrolytes.In comparation with other electrolytes,the results indicate that MnCo₂O₄ have outstanding electrochemical performance in 3 M KOH solution.The asymmetric supercapacitor based on MnCo₂O₄ as a positive electrode in combination with activated carbon?AC?as a negative electrode was assembled.And the factors influencing the performance of the MnCo₂O₄/AC asymmetric supercapacitor were studied.The results show that MnCo₂O₄/AC asymmetric supercapacitor has better electrochemical performance in the mixed solution of 2.5 M KOH and 0.5 M LiOH when the mass ratio of MnCo₂O₄ to AC is 1.5:1.Its specific capacitance is72.5 F·g^-11 at a current density of 1 A·g^-1.?2?MnCo₂O₄/NiO composite electrode materials were prepared by molten salt synthesis and hydrothermal method.The effect of synthesis conditions on the electrochemical performance and structure of the electrode materials was explored.The best electrochemical property is observed on the MnCo₂O₄/NiO when the amount of MnCo₂O₄ prepared by molten salt synthesis,NiCl₂·6H₂O and urea is 10,20 and 40 mmol at 150?C for 12 h and 500?C for2 h respectively.The addition of NiO significantly improves the electrochemical performance of MnCo₂O₄.When the current density is 1 A·g^-1,the specific capacitance of the MnCo₂O₄/NiO composite electrode material is 46%higher than individual MnCo₂O₄.Therefore,the electrode material with NiO is suitable to be charged/discharged at great current,having better capacitance performance.When hybrid supercapacitor was composed of MnCo₂O₄/NiO and AC,the specific capacitance and energy density of MnCo₂O₄/NiO were higher than that of MnCo₂O₄.[MnCo₂O₄/NiO]/AC asymmetric supercapacitors are promising practical applications for electric vehicles with high power density and high energy density.