Morphology Contorl Of Ni₃S₂ And Study Of Its Supercapacitor Performance

Supercapacitor is a new type of green energy storage device that can solve the current environmental pollution.It has high energy density,power density and cycle stability.Supercapacitors can optimize the energy and power density gaps between batteries and dielectric capacitors,and it can be used in energy/power supply systems,hybrid vehicles,portable electronic devices,etc.The performance of supercapacitors mainly depends on the preparation and morphology control of its electrode materials.Ni₃S₂has high electrical conductivity and theoretical specific capacitance,and it is an excellent electrode material for supercapacitors.However,the specific capacitance of the ordinary Ni₃S₂electrode is very low,and the cycle stability is poor,which limits its application in the field of supercapacitors.In order to solve this problem,by properly designing the nanostructured Ni₃S₂,the electrochemically active sites required for the reaction can be increased,and the structural stability of the electrode material can be improved,thereby improving the specific capacitance and cycle stability of the supercapacitor.The specific research content is as follows:（1）Ni₃S₂electrodes with different morphologies were prepared by changing the content of glycerol in the reaction solvent using the hydrothermal method.The effects of different glycerol content on the structure and morphology of the samples were investigated.then electrochemical tests were used to analyze their supercapacitive properties.The results show that the glycerol content in the reaction solvent has a great effect on the morphology of the samples,and then affects its supercapacitor performance.The more wrinkled structures on the sample surface,the more contacts with the electrolyte,the more active sites can be provided,and the better the supercapacitor performance.When the ratio of glycerol/water/N-N dimethylformamide in the reaction solution is 2:1:1,the fold structure on the sheet Ni₃S₂is the most,and its specific capacitance value is 736.64 F·g^-1at a current density of 0.8 A·g^-1,after a 1000-cycle test,its specific capacitance retains 82%of the original.（2）Using electrochemical deposition methods,different morphologies of Ni₃S₂electrode materials were prepared by changing the deposition current.The effects of different deposition currents on the morphology,structure,and supercapacitor properties of the samples were investigated.It was found that when the deposition current was 30 m A,The surface of the Ni₃S₂sample is all composed of a wrinkled structure.At the same time,the sample has the best ultracapacitor performance.Its specific capacitance value is 1401F·g^-1at a current density of 1 A·g^-1,but its cycle stability is poor.After 400 charge and discharge tests,its specific capacitance has become 58%of the original.（3）Ni₃S₂electrode materials with different morphologies were prepared by changing the concentration of NH₄F in the electrolyte using an electrochemical deposition method.The effects of NH₄F concentration on the morphology and structure of the samples were investigated,and then electrochemical tests were used to analyze their supercapacitive properties.The results show that:when the concentration of NH₄F is 0.15 M,the nickel foam is completely composed of a layer of Ni₃S₂nanosheets that intersect with each other in an orderly manner.This ordered and cross-distributed nanosheet structure can greatly improve the structural stability of the electrode material,and then improve its cycle stability.At the same time,at a current density of 1 A·g^-1,its specific capacitance can reach 2172F·g^-1;At a current density of 2 A·g^-1,a capacitance of 744 F·g^-1can be retained for the Ni₃S₂nanosheets after 10000 cycles,corresponding to 93.%of the intial capacitance.