Studys On Titanium Oxide Supercapacitor Based On Electrospinning

Supercapacitor,also known as electrochemical capacitor,is a new kind of energy storage device between traditional capacitor and electrochemical cell.This device has the advantages of high discharge power,short charging time,long cycle life and no pollution.It has a great application prospect in high load devices,such as hybrid electric vehicles,high power equipment and mobile electronic devices.The supercapacitor consists of electrode material,electrolyte,separator and collector,and the electrode material is the main part.The key to improve the electrochemical performance of supercapacitors is to improve the specific surface area,electrical conductivity and electrochemical activity of electrode materials.Transition metal oxide TiO₂ with anatase,rutile and brookite three kinds of crystal structure,the bandwidth is 3-3.2 eV,it also has obvious characteristics of capacitance comparing with other metal oxides.Therefore,the research on the substitution of noble metal RuO₂ as the electrode material of the pseudo capacitor has been widely studied,but due to poor electrochemical activity,low conductivity,TiO₂ is still not used to practical application,a new method of preparing nanometer TiO₂ and its corresponding modification research has important significance.This study is mainly prepared TiO₂ nanofibers by electrospinning and study on the crystal structure,surface appearance and electrochemical propreties of annealing treatment on TiO₂ nanofibers,getting the best conditions of subsequent annealing treatment.In order to improve the electrochemical performance of electrode materials based on surface area,conductivity and electrochemical activity,respectively,further study on preparation of TiO₂nanotubes,TiO₂ mesoporous nanofibers,activated carbon?AC?modified nano TiO₂ and TiO₂-NiO composite nanofiber and tested the supercapacitor.The main research contents and results are as follows:Firstly,TiO₂ nanowires were prepared by electrospinning technique as the electrode materials of supercapacitors.The results show that annealing treatment has great influence on structure and electrochemical properties of TiO₂ nanowires.In the atmosphere,when the holding time is 3 hours,with the increase of the annealing temperature?400?-800??,Ti O₂changes from low temperature anatase to high temperature of rutile structure.When the annealing temperature is 500 degrees,the TiO₂ nanowires are anatase and the pseudocapacitive properties of it is the best.The specific capacitance is 23.85m F/cm² or 9.54F/g,the equivalent resistance is 11.7?and the energy density is 0.95Wh/kg.At the same time,under the conditions of O₂ atmosphere and vacuum,the annealing temperature was increased from 450 to 600 degree and the holding time was about 3 hours.Under the condition of O₂atmosphere annealing,the crystal structure of TiO₂ nanowires is anatase at 450 degree to 600degree and the electrochemical properties of the material are the best when annealing temperature is 450 degree.The specific capacitance of the electrode material is 28.34mF/cm²,the equivalent resistance is 9.7?and the energy density is 1.45Wh/kg.Vacuum annealing conditions,organic polymer of polyvinyl pyrrolidone?PVP?spinning of the precursor complete carbonization,TiO₂ nanowire electrode was black,SEM displayed on the surface of TiO₂ nanowires carbide nanowires attached and XRD showed no obvious diffraction peak.After carbonization,the activity of the nanofiber membrane is low,and the electrochemical performance of the electrode material is poor,mainly in the high resistance and low specific capacitance.With the increase of electrospinning time,the quality of electrode material increases linearly,but the specific capacitance of the material increases firstly and then decreases.When the spinning time is 20min,the quality of the electrode is 11mg,the maximum of the CV cycle curve,the specific capacitance of the electrode material is21.7mF/cm² or 8.7F/g,the equivalent resistance is 11.7?and the energy density is0.993Wh/kg.Secondly,prepared the TiO₂ nanotubes and TiO₂ mesoporous nanofibers by adjusting the ratio of the precursor and the spinneret.The experimental results show that the spinning voltage is about 12.0V,and the advancing speed is 1:7,the receiving distance was 13cm,the annealing temperature is 500 degrees,the holding time is 3 hours,Ti O₂ nanotubes prepared better,spinning fiber distribution,tube outer tube diameter is about 300nm and the diameter of the inner tube is about 200nm.The equivalent resistance of the electrode material is 78.1?,the specific capacitance is 11.7m F/cm² or 4.7F/g.CV for 1000 cycles,the electrical stimulation and ion infiltration effect decreased,CV cycle curve area still increases slowly,illustrating the cycle stability of TiO₂ nanotube electrode.Adding 2ml paraffin oil in the precursor solution,when the spinning voltage is about 14.0V,and the advancing speed is 1:6,the receiving distance was 12cm,the annealing temperature is 500 degrees centigrade,the holding time is 3 hours,the TiO₂ nanotube surface has obvious pore,namely TiO₂mesoporous nanofibers.But the influence of paraffin oil on the electrochemical activity of TiO₂ mesoporous nanofibers,resulting in a small area of CV cycle curve,lower than the electrical capacity.It is not suitable for supercapacitor electrode material.Finally,the conductivity and electrochemical activity of TiO₂ nanofibers were improved by the combination of activated carbon?AC?and NiO respectively.The activated carbon coating on the surface of TiO₂ nanowires using biaxial spinning process,SEM test showed that the activated carbon distributed evenly on the surface of the nanowires,the activated carbon particle size is about 10 nm,TiO₂ nanowires with diameter about 150nm,the combination of activated carbon enhances the double layer effect of electrode materials,the specific capacitance of electrode material for 36m F/cm²,the equivalent resistance is 17.6?,the energy density is 0.87Wh/kg,compared to TiO₂ nanowire electrode improves 33%.TiO₂composite NiO nanofiber membrane was canary yellow,the size of nanowires was about300nm,and the specific capacitance of the electrode material was less than 13mF/cm² or5.1F/g,compared to Ti O₂ nanowire electrode decreased by 50%,However,the redox peak of the electrode material is obvious,which indicates that the comples NiO enhances the electrochemical activity of TiO₂.