Preparation And Electrochemical Performance Of Vanadium Oxide-based Electrode Materials For Flexible Supercapacitor

Among numerous electrodes of supercapacitors,Faraday pseudocapacitive electrode materials produce excellent capacitance through rapid and reversible redox reactions.Metal oxides,such as VO₂and V₂O₅,which are one of the Faraday pseudocapacitive electrode materials,own the problems of laminated crystal structure collapse,particle agglomeration,low conductivity,poor multiplication performance,and circulation stability.Therefore,the electrochemical properties of VO₂and V₂O₅can be improved by modifying constituents,improving microstructures,or combining them with other substances that possess remarkable conductivity.In this paper,three different methods including chemical bath deposition,hydrothermal method,and electrochemical deposition were implemented by introducing carbon fiber felt which holds three-dimensional porous structure as a flexible growth/load substrate.CFF@VO₂（one dimensional nanobelt）,CFF@V₂O₅（two dimensional nanoplate）,and of CFF@V₂O₅@PIn（three dimensional nano-ball）were respectively obtained and studied on energy storage mechanisms and electrochemical properties.The flexible all-solid-state supercapacitors（FASCs）were assembled using respective composites.The electrochemical performances and working performances of the FASC were studied and analyzed,which provides an important reference for the follow-up study on supercapacitor electrode materials and devices.First,one dimensional VO₂nanobelts were deposited on the surface of the activated carbon fiber felt by a simple chemical bath deposition.VO₂provides a large electrical capacity as a pseudocapacitive material,while carbon fiber felt can optimize the distribution and appearance of VO₂.Its three-dimensional porous structure provides a wide space for rapid transmission of ions/electrons,avoiding a large number of VO₂stacking.Meanwhile,the introduction of carbon fiber felt has boosted the composite more active sites,showing more redox peaks,and its electrochemical properties have been more fully played.It is shown that CFFVO-60 with a deposition time of 60 min has optimum electrochemical properties and a capacitance of 1148m F/cm²under the current density of 1 m A/cm².Then,a flexible all-solid-state symmetrical supercapacitor was assembled using CFFVO-60 as the anode,ultra-thin activated carbon（AC）as the cathode,and PVA/Li Cl as the gel electrolyte.When the current density is 10 m A/cm²,the device achieves the capacitance of 1051 m F/cm²and a maximum energy density of 0.715 m Wh/cm³.Two devices linked in series could light a yellow LED of 1.8 V for 2 min successfully,demonstrating the good practicality of the FASC.Second,two dimensional V₂O₅nanoplates were grown on activated carbon felt straightly.Compared with VO₂from the chemical bath deposition,the V₂O₅prepared by hydrothermal method are more uniform,more diverse morphology and more uniform size.When they were tested in the same electrolyte,and under the same voltage and current density,the CFF@V₂O₅exhibits better capacitance（1465 m F/cm²）than the CFF@VO₂（1148 m F/cm²）,which can be attributed to the two-dimensional plane structure of V₂O₅with larger surface area,providing more active sites for ion participation in the reaction,while its surface-rich pores facilitate the rapid transmission of ions/electrons.With the CFF@V₂O₅as anode,the assembled flexible all-solid supercapacitor demonstrates better energy density（0.928 m Wh/cm³）and practical performance,maintaining good stability on the conditions of bending,folding,etc.It can be attributed to the fact that comparing with one-dimensional or two-dimensional growth substrates,the three-dimensional structured carbon fiber felt has a good advantage of volume and a large number of pores,which greatly promotes the full contact and reaction between the gel electrolyte and the electrode material,endowing the device with superior energy density and electrochemical performance.Two devices linked in series can light a red LED of 2.2 V for 2.5 min,indicating that the practicability of the device has been effectively improved comparing with the previous chapter.Third,a layer of PIn nanospheres were anchored on the surface of the CFF@V₂O₅by the electrochemical deposition,naming as CFF@V₂O₅@PIn.The V₂O₅nanoplates,which are grown on the surface of carbon fiber felt,have a large number of pores and voids providing favorable conditions for the formation and growth of PIn.Owing to the three-dimensional PIn nanospheres,it emerges larger surface area,more reaction points,smaller ion transmission resistance,and shorter transmission distance.The introduction of PIn has brought additional capacitance.Through the synergy effects of V₂O₅and PIn,the CFF@V₂O₅@PIn demonstrates better electrochemical performance than the CFF@V₂O₅,increasing its area capacitance from 1465 m F/cm²to 2254 m F/cm².The assembly of flexible asymmetric devices achieve an energy density of 1.68 m Wh/cm³,not only a device can successfully light a 1.8 V yellow LED,but also two devices linked in series can make a 3.5 V LED set lighted for 2 min normally,indicating that the practicality of the device compared to the above two chapters have been significantly enhanced.In this paper,vanadium oxides are served as the constituent to provide remarkable capacity owing to its significant faraday oxidation,and the flexible carbon fiber felt is introduced as a reinforcement.By conceiving different experimental methods and variables,enhancing the microstructures of electrode materials,improving the appearance of electrode materials,optimizing the interface design,the electrochemical properties of supercapacitor electrode materials and its operating voltage,energy density and working performance are evidently improved.