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Doping Modification And Gel Structure Preparation Of VS2 Micro-Nano Materials And Their Supercapacitors Performances

Posted on:2020-01-08Degree:MasterType:Thesis
Country:ChinaCandidate:Q ZhangFull Text:PDF
GTID:2381330578462845Subject:Materials Science and Engineering
Abstract/Summary:PDF Full Text Request
Environmental pollution and energy shortage are the primary problems facing humanity.The use of natural green energy,such as solar and wind energy,is growing rapidly,and further development will require smart and versatile energy storage devices.Therefore,the development of energy storage equipment is of great significance to green energy production.Supercapacitors,as an important electrochemical energy storage device,have the advantages of high power density,fast charging and discharging speed,long cycle life and low cost.As an important part of supercapacitors,the electrode materials directly affect their performances.Therefore,it is urgent to find high performance electrode materials.Vanadium disulfide(VS2)is one of the transition metal sulfides with graphene-like layered structure.The results have shown that monolayer VS2 is of high specific surface area,high number of active sites,and excellent superelectric energy storage performance.The specific surface area and the number of active sites were reduced by the stacking of nano-sheets for flower-like VS2 synthesized by traditional hydrothermal method,which results in poor super-electrical performance.In this paper,the VS2 aerogel and molybdenum-doped vanadium disulfide(VS2-Mo)samples were prepared to improve the specific surface area and the number of active sites,and their phase characterization and electrochemical properties were tested.The main contents are as follows.(1)Flower-like VS2 materials were prepared by hydrothermal synthesis with thioacetamide,ammonia water and vanadate amine as a precursor.The VS2 aerogel materials were obtained by physical means of ultrasonic treatment and freeze drying.The phase,crystalline,layered structures,morphology,and elemental were characterized by XRD,Raman,FESEM,TEM,XPS,EDS,and the specific surface area and pore size distribution were measured by BET.The electrochemical performances were studied by using the electrochemical workstation with three-electrode test system.The results are as follows,the VS2 aerogel is a porous structure composed of several VS2 nanosheets,and has a specific surface area of up to 21.0948 m2/g.The VS2 aerogel electrode exhibits high specific capacitance of 218 F/g at the scan rate of 5 mV/s and excellent cycle stability with 92.78%capacitance retention after 1000 consecutive charge/discharge processes at the current density of 2 A/g.The high electrochemical performances of the VS2 aerogel electrode can be attributed to the following two reasons.Firstly,the VS2 aerogel structure with high specific surface area could provide more active sites.Secondly,the unique porous structure could buffer volume expansion to improve retention ability during charge/discharge cycles.(2)Vanadium disulfide nano-materials doped with molybdenum(VS2-Mo)were prepared by hydrothermal synthesis with thioacetamide,ammonia,vanadate and ammonium molybdate as a precursor.The phase,crystalline,porous/layered structures,morphology,and elemental were characterized by XRD,Raman,FESEM,TEM,XPS,EDS,and the specific surface area and pore size distribution were measured by BET.The electrochemical performances were studied by using the electrochemical workstation with three-electrode test system.The results are as follows,the size of the flowered VS2-Mo material is reduced,and the layer spacing of the(001)crystal plane is broadened up to 0.586 nm.The VS2-Mo electrode exhibits high specific capacitance of 236 F/g at the scan rate of 5 mV/s and excellent cycle stability with 88.66%capacitance retention after 3000 consecutive charge/discharge cycles at the current density of 2 A/g.The excellent electrochemical properties of VS2-Mo electrode can be attributed to the following three reasons.Firstly,VS2-Mo samples still retain the metallic property of 1T phase and have high conductivity.Secondly,the interlayer spacing of VS2-Mo samples on(001)crystal plane is widened to allow more ions embedding.Thirdly,the lattice distortion caused by the widening of interlayer spacing leads to many defects,which increases the number of active sites in VS2-Mo samples.
Keywords/Search Tags:Hydrothermal reaction, Sonication processing, Vanadium disulfide aerogel, Molybdenum doped Vanadium disulfide, Supercapacitor
PDF Full Text Request
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