Study On Sythesis And Capacitance Performance Of V₂O₅ And LiV₃O₈

With the progress of science and technology, the development of energy storing and conversion devices have been motivated and received continuous attention. Supercapacitors have been further researched due to their higher power density than batteries and higher energy density compared to conventional capacitors. The preparation of electrode materials and electrolyte is very important because they are the main factors influencing the electrochemical performance of supereapacitor. V2O5 nanowires and LiV3O8 were synthesized in this work. The influence of experimental conditions on products was studied by X-ray powder diffraction, infrared radiation, scanning electron microscopy, transmission electron microscopy and isothermal nitrogen adsorption. Cyclic voltammetry and galvanostatic charge-discharge were used to characterize the electrochemical properties of the materials and analyze the effect of electrode on the materials. The main results are as follews:Ultrahigh-aspect-ratio V2O5 nanowires were successfully prepared using V2O5 and H2O2 as the starting materials by a facile template-free hydrothermal route. The X-ray powder diffraction and scanning electron microscopy results show that the conglomerated V2O5�nH2O sheets turned into uniform V2O5 nanowires with reaction time increased. After reacted at 96 h, the flexibility and uniform V2O5 nanowires were obtained with the length of about hundreds of micrometers, the width about 50 nm and the specific surface area of 25.6 m2�g-1. It's known that the material possesses high initial specific capacitance (351 F�g-1 at 2 A�g-1), good rate capability (272 F-�g-1 at 10 A�g-1), poor cyclic stability of the specific capacitance (only 15% of capacitance remained after 50 cycles) by cyclic voltammetry and galvanostatic charge-discharge. The cyclic stability of specific capacitance of the material after calcination is better and 55.6% of specific capacitance could be remained after 50 cycles.LiV3O8 was systhesized using V2O5, LiOH�H2O, H2O2 as the starting materials by a facile hydrothermal method. The raw material ratio of getting pure phase LiV3O8 and the combination of hydrothermal reaction time, calcining time and calcining temperature were obtained by X-ray powder diffraction and infrared radiation. The scanning electron microscopy and electrochemical test results show that the products are sheet or block structure stacked by LiV3Og layer with loose structure, poor crystallinity, high initial specific capacitance and poor cyclic stability at low calcination temperature but the product synthesized at high calcination temperature is just the opposite.In the work, the neutral solution was choosed as the electrolyte and the influences of the variety and the concentration of the electrolyte on electrochemical properties were researched. It's distinctly observed that chloride cann't be choosed as electrolyte in the system of nickel foam as current collector. The specific capacitance of the materials in Li+ solution are much higher than that in K+ and Na+ solutions and the electrochemical properties in NO3- solution are slightly higher than that in SO42- solution. If the electrolyte is consistent, the value of the specific capacitance increased and then decreased with the increase of electrolyte concentration.