Study On Conducting Polymers Nanocomposites Electrodes And Devices With High Specific Capacitances

As a promising energy storage device, supercapacitors has gotten more attentions due to its advantages such as their high specific energy, high specific power, short charge/discharge time, long cycling life-time, excellent cycling efficiency and so on. Currently, the research of supercapacitors has focused on electrode materials with high specific capacitance, which are key components to fabricate high performance supercapacitors. Due to the high specific capacitance, good thermal stability and high conductivity, conducting polymer poly（3,4-ethylenedioxythiophene）（PEDOT） is a ideal electrode materials for supercapacitor electrodes. However, the low mechanical properties of PEDOT results in reducing the cycling life of PEDOT electrodes. The improved mechanical capability of PEDOT can be obtained by compositing PEDOT with inorganic nanomaterials. As a result, this paper mainly studied the PEDOT and its nanocomposites in the application of the supercapacitor electrode. The main contents are as follows:1. A chemical in situ polymerization method is used to prepare PEDOT/activated carbon（AC） composites with different mass ratio are investigated, as well as the morphology and electrochemical performance of these composites. The results show that the PEDOT/AC composite（with a mass ratio of AC to EDOT monomer about 20%）, has a 176.3 F/g specific capacitance at the current density of 0.5 A/g, and a remains of 90.2% specific capacitance after 4000 cycles of charge/discharge, indicating the good capacitance stability of this electrode. Further investigation shows that the high capacitance keeping rate of electrode of approximately 92.5% is obtained at a 3 A/g higher current density, revealing the high charge/discharge current performance of composite electrode during energy storage process. Furthermore, based on the composite electrodes above, a supercapacitor（2.3V/25F） is assembled and its energy storage performance is investigated. The results reveal that the device shows an energy density of 5.04 Wh/kg and exhibits a good electrochemical reversibility after 10000-cycle charge/discharge process.2. A conducting polymer poly（3,4-ethylenedioxythiophene）/poly（styrenesulfonate）（PEDOT/PSS） is demonstrated as a substitute binder of common poly（vinylidene fluoride） PVDF during the preparation of composite electrodes, and the influences of PEDOT/PSS on electrochemical performance of as-prepared PEDOT-PSS/AC electrodes is discussed. The results reveal that the PEDOT-PSS exhibits a good bonding effect and the composite electrode shows a specific capacitance of 108.8 F/g at a 0.5 A/g current density, and a capacitance losing rate about 9.93% after a 4000-cycle, which indicates a good capacitance cycling stability of PEDOT-PSS/AC electrode. At a higher current density of 5 A/g, the composite electrode also exhibits a 10.4% low capacitance losing rate（about 97.5 F/g）, which means good capacitance stability of composite electrode. The PEDOT-PSS/AC electrode based supercapacitor（2.3V/10F） also exhibits a good electrochemical reversibility, and only 1.3% loss of specific energy and no change of power energy of device are found after 10000-cycle charge/discharge process.3. Different MnO₂ thin film electrodes were prepared by electrochemical cyclic voltammetry（CV） and galvanostatic electrodeposition（GE） methods. The scanning electron microscope（SEM） investigation shows that the MnO₂ electrode film prepared by the CV method exhibits a layered and packing nanoflat structure, offering high a specific surface area for charge storage. The specific capacitance of MnO₂ electrode is 263.3 F/g at a current of 1 A/g, and a capacitance keeping rate about 74.98% after 4000 cycles charge/discharge. A MnO₂-PEDOT composite film is also deposited on the ITO surface through CV method. This composite film shows a 221.6 F/g specific capacitance, and keeps 84.93% of original capacitance after 4000-cycle charge/discharge. Subsequently, this MnO₂/PEDOT electrode was deposited on the carbon fiber sheet through CV method, and its electrochemical performance was investigated. It has been found that the MnO₂/PEDOT deposited carbon fiber exhibits a three-ring coaxial structure and shows a specific capacitance about 196.4 F/g, and a capacitance maintenance rate of 95.1% after 4000-cycle. For flexible device applications, the composite electrode assembled a flexible supercapacitor and this device shows energy density about 5.27 Wh/kg, and keeps more than 90% of original capacitance after 500 times charge/discharge.4. A modified Hummers method and a hydrazine hydrate reduction method were utilized to prepare reduced graphene oxide（RGO）, and an in situ polymerization method was subsequently used to prepare PEDOT-PSS/RGO self-supporting electrode. The optimized mass ratio of EDOT monomer to RGO was investigated to obtain high performance electrodes. It has been found that when at a mass ratio of EDOT monomer to RGO about 1:1, the as-prepared composite electrode shows a specific capacitance of 193.7 F/g, and a capacitance losing rate of 13.1% after 4000-cycle charge/discharge. The further investigation indicates that the electrode keeps more than 81.3% of original capacitance at a higher current density of 3A/g.5. A porous PEDOT nanostructure is firstly constructed on a RGO Langmuir-Blodgett（LB） film through an in situ polymerization method. By controlling the polymerizing temperature and heating rate during the polymerization, the optimized porous structure of PEDOT is obtained. It has been found that under a heating rate of 30℃/min, the as-prepared PEDOT/RGO shows continuous and ordered microstructures, and a high conductivity about 306.2 S/cm. The electrochemical performance investigation reveals that the porous structure of electrode results in complete and fast interaction between electrolyte ions and electrode surface, therefore this composite electrode shows a 267.1F/g high specific capacitance at a 0.5 A/g current density. The further investigation reveals that the porous electrode maintains 90% of original capacitance after 4000-cycle charge/discharge, and a capacity maintaining ability close to 82.97% at a higher 1.5 A/g current density.6. Conducting polymers poly-9,10-anthraquinone（PAQ） and poly-1,2-amino-9,10-anthraquinone（PAAQ） were synthesized by solution polymerization method and their electrochemical properties are studied. The results show that PAQ and PAAQ electrodes express a specific capacitance about 28.6 F/g and 69.8F/g respectively. The further investigation reveals that both PAQ and PAAQ electrodes exhibit good capacitance stability due to the plane conjugated molecule structure of conducting polymer. The capacitance maintenance rate above 90% is obtained after a 4000-cycle charge/discharge process. The PAAQ modified AC composite electrode was prepared through an in situ chemical polymerization method. This conducting polymer modified electrode shows a specific capacitance about 207.8 F/g at a 100 mA/g current density. The capacity retention rate of this composite electrode is above 90% after 4000 times of constant current charge/discharge. The results also reveal that the specific capacitance loss of PAAQ/AC electrode is about 10.4% at a higher 500 mA/g current density, indicating the stable electrochemical performance of composite electrode during the energy storage process.