Preparation Of Co-based Ternary Transition Metal Oxygen/Sulfide Core-Shell Nanomaterials And Their Application In Supercapacitors

In recent years,the energy crisis and environmental problems have become increasingly serious,and the development of electrochemical energy storage devices has become the key to solving this problem.As a new type of energy storage device,supercapacitors have attracted attention in many fields such as electronic products,aerospace,and mobile communications because of their advantages such as fast charging speed,high power density,and environmental protection.To prepare supercapacitors with more excellent performance,the exploration of electrode materials is indispensable.As an electrode material for a new type of supercapacitor,transition metal oxygen/sulfide compounds are favored by researchers because of their large theoretical specific capacitance,low price,and simple preparation process.In this thesis,cheap nickel foam is used as the substrate,ternary transition metal oxide nanowires are used as the conductive framework,and a nanosheet is coated on the surface to obtain a unique core-shell nanostructure.In addition,the surface of the metal oxide is modified by a simple chemical reduction method to introduce an appropriate amount of oxygen vacancies on the surface of the metal oxide nanowire,and the electrochemical performance of the treated electrode material is significantly improved.The structure and morphology of the material were characterized by advanced testing methods such as XRD,SEM and TEM,and the electrochemical performance of different electrodes was tested using a three-electrode system.The specific research contents are as follows:(1)CuCo2O4@CoS,CuCo2O4@NiS and CuCo2O4@Ni-Co-S composite electrodes with core-shell structure were prepared on the nickel foam substrate by simple hydrothermal method and electrodeposition method.According to electrochemical analysis,CuCo2O4@Ni-Co-S material has the highest specific capacitance,the best conductivity and cycle performance.The electrode has a specific capacitance of 4.46 F cm-2 at 4 mA cm-2.In addition,after 5000 charges and discharges,only 5.4%of the specific capacitance was lost.(2)In order to obtain an electrode material with better performance,a core-shell r-MnCo2O4@Ni-Co-S composite electrode material was synthesized for the first time.Due to the synergistic effect of r-MnCo2O4 and Ni-Co-S materials,the electrochemical performance of their composite materials is excellent.Among them,at the same current density,the specific capacitance of the r-MnCo2O4 electrode containing an appropriate amount of oxygen vacancies is 111.9%higher than that of the untreated MnCo2O4 electrode.In addition,after the r-MnCo2O4 nano wires are coated with a layer of Ni-Co-S nanosheets,the composite electrode material has excellent conductivity and a specific capacitance as high as 6.19 F cm-2.In addition,after 5000 cycles,its capacity retention rate is as high as 95.5%.In order to prove the practicality of this electrode,this electrode was used as the positive electrode material and CNT was used as the negative electrode material,and an rMCO@Ni-Co-S//CNT asymmetric supercapacitor was obtained.The rMCO@Ni-Co-S//CNT asymmetric supercapacitor was obtained.The device has an energy density of up to 3.013 mWh cm-3 at a power density of 0.015 W cm-3.And after 8000 charges and discharges,the device showed a capacity retention rate as high as 92.3%.Finally,the two devices were connected in series,successfully lighting an 8 mm commercial red LED for more than 1 hour,and also successfully driving an electric motor.The above conclusions confirm that the different components in the unique core-shell structure composite electrode material can achieve efficient collaboration,and the introduction of appropriate oxygen vacancies in the metal oxide can also effectively modify the material,which shows that this work has certain application value in the field of supercapacitors.