| With the rapid development of industrial civilization in modern society and electronic information devices,as well as the decrease of fossil fuels,the exploit and application of new type of energy storage devices are becoming more and more important.As a new type of energy storage device,supercapacitors have been given tremendous attentions owing to not only the combined advantages of secondary battery and traditional capacitors such as high energy density and power density,also their rate capability,environment friendly,cycling stability and so on.They now are playing an irreplaceable role in aviation,transportation,military,medical and other fields.Active materials are the main factor affecting the performance of supercapacitor,such as rate capability,cycle life and theoretical capacity.Among materials for supercapacitor electrode,transition metal oxides have attracted lots of attention because of their high theoretical capacity,good electrochemical activity and adjustable morphology.Nickel oxide(Ni O)is among the most promising active materials for supercapacitor owing to abundant resources,environmental friendliness and high theoretical specific capacitance.Furthermore,the nickel oxide is handled easily to construct specific morphology or microstructure.Based on the above present,we intend to carry out the preparation of high performance capacitor electrode material.So this paper mainly focuses on a simple and convenient route to prepared hierarchical nickel oxide with controlled morphology and enhanced performance.Through a series of reasonable experiment design,3D flower-like Ni O was prepared as supercapacitor electrode material.The hierarchical and mesoporous Ni O was obtained from the sintered nickel hydroxide which was synthesized through ethanol or methanol assisted hydrothermal process.On the basis of SEM,XRD,TEM,BET contents,the morphology formation mechanism was explored by the varying amount of active agent addition and experiment parameter adjustment.And the relationship between electrochemical properties and hierarchical structure was studied.In turn,the best preparation process for high-performance electrode materials was determined.Based on the above matters,the future development of new materials and mechanism for supercapacitor may be conjectured.The main contents of this paper are as follows:On one hand,complex hierarchical 3D porous structure nickel oxide has been synthesized through an ethanol-based hydrothermal method followed by a sintering process.As a supercapacitor electrode material,the electrochemical performance of samples was tested.The results show that by adjusting the various experimental parameters of hydrothermal synthesis,such as changing the length of hydrothermal time,controlling the volume ratio of surfactant,etc,the structure,morphology,crystallinity and capacitive properties of the prepared samples are deeply influenced.1.The XRD map shows that there are recrystallization and polycrystallization processes in the hydrothermal process.SEM and TEM images prove that the morphology and microstructure of the sample are the most favorable when the hydrothermal duration is 120 min.the morphology of the sample is complex hierarchical 3D porous flower-like ball,with a diameter of about 2 ?m,a specific surface area of 164.05 m2/g,and a thin slice of 63 nm assembled from all directions.The pore size is mainly in the range of 30-60 nm analyzed by BET.in terms of electrochemical performances,the capacity of the sample can reach 678.4 F/g at a discharge current density of 1 A/g.After experienced 5000 cycles,the capacitance of the sample still maintained 94.8% of its initial capacity.2.With the organic solvent volume increase of in the preparation,flower-like morphology of the samples is more and more obvious,such as the number of petals and its thickness.When the volume of ethanol increased from 0 m L to 9 m L,the capacitances rise from 520.2 to 671.3 F/g,and the rate capability is improved,too.3.The sample prepared during 120 min hydrothermal process seems like a watershed of the performance of the tested samples,with the maximum capacitance and the best reversibility.In order to explore the influence of different types of surfactants on samples' morphologies and properties in the process of sample preparation,another organic solvent,methanol,is selected as the main experimental variable.Then through identical tests,the following conclusions are obtained.1.In the process of hydrothermal synthesis,the types of organic solvents may affect the sample's morphology,structure and properties in varying degrees.The samples prepared by using methanol are about 2-3 m in diameter,with a specific surface area of 126.47 m2/g,and the pore size of the sample is mainly about 5-20 nm.2.The morphology of the nickel oxide can be influenced by the amount of methanol during the hydrothermal process.With the increase of volume,the thickness of nanoscale thin film decreases,but the degree of aggregation increases until the flower clusters formed.3.Adopting methanol as surfactant,the difference of redox potential at the scan rate of 50 m V/s is close to 162 m V,specific capacitance at the discharge current density of 1 A/g discharge capacity can reach 578.6 F/g.After 5000 cycles charge /discharge,the capacitance can be kept up to 94.3%.4.The process of increasing the volume ratio of organic solvents is the process of continuous improvement of electrochemical performances.That is,with the increase of the volume ratio of organic solvents,the changes on the nickel oxide morphology benefit the sample's specific capacitance and cycling life.It is generally believed that morphology,structure,specific surface area,pore size and distribution,and ion diffusion channel play key part to determine performances of supercapacitor electrode.The advantages of hierarchical porous 3D architecture are favor of effective contact between electrolyte and active material,reducing transfer resistance,diffusion of charges and ions in electrolyte,and supply of active sites,consequently,prompting supercapacitive performances. |
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