| With the exploration and utilization of renewable energy such as solar energy,wind energy,hydrogen energy and tidal energy,and the rapid development of new portable electronic equipment and flexible energy storage devices,the traditional energy storage system has been unable to meet the integrated demand of low cost,high power density,high energy density and high reliability.In recent years,research in the field of energy storage is shifting to materials and systems with novel electrochemical energy storage mechanisms.Hybrid supercapacitor with its unique structure combines the advantages of the high power and high energy density have been extensively studied,among which the main factor determining the performance of the supercapacitor is the electrode material.At present,the study of supercapacitor cathode materials has been reported very much,but little is known about its negative electrode materials.In this thesis,the electrochemical properties of iron oxide-based nano-anode materials were studied.The electrochemical properties of the supercapacitor were improved by means of surface modification and material composite,and the chemical composition and surface morphology were studied by XRD and SEM.The structural design was proposed to improve the performance of the supercapacitor.The main contents of this paper are as follows:1.The Fe2O3 negative electrode was prepared by hydrothermal method and heat treatment technique with ultra thin titanium as base.Then,carbon coated with different concentrations of glucose solution(0.05,0.1,0.25 and 0.5 M/L)to obtain Fe2O3@C electrode.Carbon coating can not only improve the conductivity of Fe2O3,but also can reduce its dissolved in the water-based electrolyte and improve its stability.The Rs values were calculated to be 2.69,2.17,3.26 and 3.83 ?,respectively,which were less than the Rs value(7.77 ?)of the pure Fe2O3 electrode,which indicated that the carbon coating could improve the conductivity of Fe2O3.At the same time,it was found that too much glucose concentration will reduce the specific capacity of Fe2O3,but it was helpful to improve its rate performance.2.The experimental method of synthesizing Fe3O4-Bi2O3 composite on carbon cloth was studied by two-step hydrothermal method.Then,by controlling the secondary hydrothermal time(1,2,3,4,5 and 6 h)and the different quality of bismuth nitrate(0.5,0.75,1.0,1.25 and 1.5 times)respectively to explore the electrochemical performance of the composite electrode with different growth content of Bi2O3,and to explore the optimum preparation conditions.Directly on the flexible carbon cloth growth of active materials,not only can ensure that the electrode material and the collector of good contact,and can make the electrode has excellent mechanical properties.By adding a glucose solution to the surface of the electrode,the Fe3O4-Bi2O3@C negative electrode was obtained by high temperature annealing.The "carbon glue" formed on the surface of the composite material can relieve the volume expansion in the constant current cycle charge and discharge process and protect the active material from falling off in the liquid electrolyte.The electrochemical test results show that the optimum conditions for the secondary hydrothermal growth of Bi2O3 are hydrothermal reaction for 5 h,and the mass of Bi(NO3)3 · 5H2O is 2.5875 g,which is 1.25 times of the original formula.Compared with Fe3O4@C electrode,the specific capacity of Fe3O4-Bi2O3@C electrode after composite Bi2O3 is greatly improved and the rate capability is excellent.The Fe3O4-Bi2O3@C composite electrode obtained under the optimum preparation conditions has a discharge capacity of about 8243 mF/cm2 at a current density of 1.5 mA/cm2,which is much higher than the specific capacity of a single Fe3O4@C electrode(1698 mF/cm2).At the same time,under current density of 9 mA/cm-2,our composite electrode demonstrating 104%energy retention after 1000 cycles,indicating that Fe3O4-Bi2O3@C electrode has a very excellent cycle stability. |
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