Synthesis And Performance Of Vanadium Oxide Nanorods Coated With Carbon Nanoshell For Supercapacitors

As an energy storage device,supercapacitors?SCs?have some unique advantages over rechargeable batteries,such as faster charge discharge rates,longer working life and higher power density.As an important member of transition metal oxides,vanadium oxides have attracted increasing interest as SCs electrodes materials,since their unique layered structure and multiple valence states?+5 to+2?guarantee high energy density and theoretical efficient ion diffusion.However,the practical low ionic diffusivity(10^-1313 to 10^-1212 cm² s^-1)and electrical conductivity(10^-33 to 10^-22 S cm^-1)limited their development and application for SCs electrodes.In order to solve the above-mentioned problems,in this paper,the modification of pure vanadium oxides was studied by means of nanometer material and comparing carbon materials and other aspects.The physical properties and electrochemical properties of the materials were discussed.The specific contents were as follows:1.VO_x@C composites were obtained by high temperature pyrolysis of V₆O₁₃@C,which was synthesized via sol-hydrothermal approach.The morphology,specific surface area and pore distribution and organic group types of carbon contained in the materials were studied.The electrochemical properties of two kinds of composite electrodes were determined and the effect of annealing temperature and the quality of initial pentaoxide on the electrochemical properties of V₆O₁₃@C and VO_x@C were ascertained.The physical structure characterization results show that the V₆O₁₃@C and VO_x@C composites are mesoporous material and the latter owned larger specific surface area than the former,their specific surface area was about131²82m²·g^-1;The carbon coated with vanadium oxide is organic carbon,and it contain a lot of organic group,such as-OH,C-H,C=O and C=C.While the mass of the raw materials of V₂O₅ is 0.8g,the sample V₆O₁₃@C own better electrochemical performance and while the calcination temperature is 700?,the sample VO_x@C have better electrochemical performance.The sample?S-0.8-700?exhibited a high specific capacitance of 548F·g^-11 at discharge current density 0.5A·g^-1.Moreover,the sample own excellent rate capability with retention rate of specific capacitance reach up to 83.3%at higher current rate 5A·g^-11 and furthermore,the sample own excellent cyclic stability with retention rate of specific capacitance reach up to 88.3%after 1000 cycles.2.Symmetric supercapacitors were successfully assembled with the sample S-0.8-700 as the anode and cathode materials and 1mol·L^-1Na₂SO₄ solution as electrolyte.The best voltage range and scan rate of symmetric supercapacitors are 0⁰.85V and 10mV·s^-1,respectively.The constant current charge and discharge results are as follows.The first,symmetric supercapacitors have big specific capacitance and good reversibility of charging and discharging(The charge and discharge specific capacitance are 119F·g^-11 and 109F·g^-1,respectively and reversibility of charging and discharging reach up to 91.6%).Then,it own excellent rate capability with retention rate of specific capacitance reach up to 81.1%at higher current rate 5A·g^-11 and furthermore,it own good rate capability with retention rate of specific capacitance reach up to 84.3%after 1000 cycles.The last,while the power density is2136W·kg^-1,the energy density reach up to 8.9Wh·kg^-1,and the energy density only decreased by 2Wh·Kg^-11 than biggest energy density,and the attenuation rate was less than18.4%.