The Research On The Capacitance Performance Of Polyaniline And Composite

Supercapacitors are new energy storage components between electrostatic capacitors and batteries,which have higher energy density than that of electrostatic capacitor and higher power density and longer cycle life than that of batteries.As a conducting polymer material,polyaniline can be doped by proton acid and lithium-ion,so higher conductivity could be achieved.Because of its capacity of storage charge within three-dimensional bulk, its application as supercapacitor materiall gradually becomes attractive.But the shortcomings of poor cycle life,the lower redox potential,which narrowed voltage window, limited the pace of its practical application.In order to overcome these shortcomings,first, methode synthesis of polyaniline,as well as preparation method of electrodes were further research to upgrade specific capacitance of polyaniline and polyaniline composite materials; second,hybrid capacitors were prepared using polyaniline/carbon(PANI/C) and polyaniline/manganese dioxide(PANI/MnO₂) composite material as cathode,activated carbon materials as anode to enlarge capacitor voltage window and energy density.In this paper,the properties of PANI and PANI/C as well as PANI/MnO₂ composite material were experimentally studied by the scanning electron microscopy,infrared spectroscopy,and cyclic voltammetry,electrochemical impedance,X-ray diffraction, constant current charge and discharge method.The electrolyte system included not only the commonly used acid,but also the organic electrolyte for lithium ion batteries.The pulse potential method was first adopted to prepare polyaniline material.The properties of PANI/C and PANI/MnO₂ composite materials in 1mol/L LiPF₆/EC+DMC organic solvents were also first studied in this paper.The results showed that the polyaniline prepared by chemical oxidation 1mol/L H₂SO₄ solution had a good capacitance performance,in 0-0.7V voltage range single electrode specific capacity was up to 654F/g,better than that of PANI prepared in HCl, HNO₃,HClO₄.PANI/C electrode and PANI-C hybrid capacitors in 1 mol/L H₂SO₄ solution operating voltage range upgrade to 1.2V,at 1mA/cm² current density,the capacity is 72.3F/g and the specific energy of 13.2Wh/kg were achived.After 1000 charge-discharge cycle at 5 mA/cm² current density,the specific capacity of hybrid capacitors from 53 F/g dropped to 46.4 F/g,about 12.01%rate of decay.Three electrochemical methods were performed to prepare polyaniline.By potentiostat polymerization method,the polymerization potential should be controlled at 750-800 mV,and electrode had the best electrochemical performance,the single electrode specific capacitance reached 398.10F/g.Single electrode specific capacitance reached 426.82 F/g;when 3 mA current was adopted in gavalnostat polymerization method.By using of pulse potential method,the pulse frequency and the pulse potential should be controlled at appropriate value,the greater the potential difference between the upper and lower limits,the better polyaniline capacitive performance.Pulse frequency of 0.05 Hz,the upper and lower limits for the potential 800mV and 200mV,respectively,specific capacitance of single electrode could reach 512.28F/g,increased 20.02%and 28.68% compared to that of potentiostat method and gavalnostat method.PANI/C composite materials had good capacitive performance in 1mol/L H₂SO₄ solution.Specific capacitance of single electrode was up to 448.7F/g,well above the 281F/g of activated carbon.The voltage window of PANI/C-C hybrid capacitor in 1mol/ L H₂SO₄ solution was up to 1.35V;specific capacity was 83.1F/g at 3mA/cm² discharge current density,82%higher than C-C capacitors and the energy density was higher 230%. After 1000 constant current charge-discharge cycles,the capacity maintained 89.1%of the initial capacity.Polyaniline modified carbon electrode(PANI/C) was prepared in 1mol/L H₂SO₄ solution using cyclic voltammetry in Tonghua activated carbon(2^#C).Compared to 82F/g of 2^# carbon electrode,single electrode specific capacitance was up to 175F/g,increased 113.41%,indicating the tremendous contribution of the Faraday pseudocapacitance.The specific capacity of PANI/C-C hybrid capacitor was 30.7F/g,higher 45.50%than that of carbon capacitor(21.1F/g).After 20000 charge-discharge cycles,the capacitance of PANI/C-C capacitor was decreased only 17%.The voltage windows of PANI-C capacitor in 1mol/Lol/L LiPF₆/EC+DMC electrolyte could be up to 1.5V,in 0.1 mA/cm² charge-discharge current,the specific capacity was 36.0F/g and specific energy was 11.3F/g.After 1100 charge-discharge cycle, capacitors capacity was retained 322F/g,94.2%of the initial capacity.The voltage window PANI/C-C capacitor in the 1 mol/L LiPF₆/EC+DMC organic solvents could be extended up to 2.5V,in 0.2 mA/cm² discharge current density,specific capacitance reached 30.72F/g and specific energy reached 27.86Wh/kg,144.95%higher than PANI-C capacitor.Specific capacitance of PANI/C-PANI/C symmetrical capacitor in the organic liquid was only 18.97F/g,lower than that of PANI/C-C and PANI-C capacitors.Using PANI/MnO₂ composite materials for hybrid capacitor in 1 mol/L LiPF₆/EC +DMC electrolyte,the voltage window was up to 2.5 V,good characteristics of a square was found in the cyclic voltammetry curves.Specific capacity of PANI/MnO₂ was up to 26.1 F/g,increased 2.62%compared to that of hybrid MnO₂-C(19.68F/g).Test results showed that,as a negative materiall,the performance of PANI and composite materials in organic solvents was poor,and it can not used capacitor anode material.