Synthesis Of Three Dimensional Vanadium Sulfide Nanomaterials And Their Supercapacitive Performance

Supercapacitors are fast charging/discharging energy storage devices that can meet the needs of society for high power output.The electrode materials of supercapacitors decide dominantly its charging/discharging performance.Recently,following transition metal oxides,transition metal sulfides has become a rising electrode material for supercapacitors.As representive transition metal sulfides,VS₄ has a chain-like 1D crystal structure while VS₂ has layered crystal structure in which layers connect with each other by Van de Waals force,both crystal stuctures of which are advantegous to the intercalation/disintercalation of electrolyte ions.When these two kinds of vanadium sulfides are utilized as electrode materials of supercapacitors,their crystal structure facilitates the charge transfer,together with the multiple valences of vanadium and the abundance in sulfur,leading to their high theoretical specific capacitances.However,at present,there are few researches about these vanadium sulfides as supercapacitor electrodes.To evaluate the application possiblity of these vanadium sulfides,their synthesis methods and supercapacitive performances have been systematically explored in this thesis.The major research contents are as follows:?1?In this thesis,using citric acid,ammonium orthovanadate and thioacetamide as raw materials,three-dimensional hydrangea-like VS₄ microspheres were successfully synthesized by hydrothermal method.The effects of raw material ratio,hydrothermal reaction temperature,solute concentration and hydrothermal reaction time on the morphology and phase composition of the products were investigated by SEM and XRD characterizations.The growth mechanism was studied in detail.The prepared spheroidal VS₄ microspheres were hollow with a specific surface area of 5 m²/g and an average pore diameter of 3 nm.The VS₄ microspheres were assembled into supercapacitor electrodes,and 0.5 M Na₂SO₃ aqueous solution was used as the electrolyte solution.The CV curve had good symmetry and the potential window was0.9 V.The specific capacity was as high as 533 F/g at 0.1 A/g.Coulomb efficiency was119.98%.The maximal energy density was 60 Wh/kg while the maximal power density was 125 W/kg.The VS₄ microspheres maintained 80%of initial specific capacitance after 500 cycles.?2?Using sodium orthovanadate and thioacetamide as raw materials,VS₂nanoflowers were synthesized by hydrothermal method.The VS₂ nanoflowers were mixed with minor VS₄ microspheres in good crystallinity.When assembled as electrode materials of supercapacitors,the VS₂ nanoflowers exhibited apotential window of 0.9 V in electrolyte of 1 M NaNO₃.Their specific capacity was 474.44 F/g at a current density of 1 A/g.Their maximal energy density was 53.38 Wh/kg at a power density of 125W/kg;the maximal power density was 500 W/kg at an energy density of 32 Wh/kg.Their specific capacity decreased to 64.4%of the initial value after 84 cycles.?3?By adding surfactant octadecylamine?ODA?or acetylene black?ACETO?into the precursor solution,VS₂ particle and nanoflower composites crystals and VS₂/ACETO composites were successfully prepared.According to the electrochemical characterization in electrolyte of 1 M NaNO₃,the specific capacities of VS₂ particle and nanoflower composites crystals and VS₂/ACETO composites can be 158.28 F/g and220.2 F/g,respectively.