Assembly And Capacitance Properties Of All-solid Flexible Manganese Dioxide Nanowire Bundle/single-walled Carbon Nanotube Composite Film Capacitor

In recent years,the electronic devices with efficient and flexible intelligent have attracted more and more attention from researchers.For the next generation of flexible electronic equipment,it is the key to solve the standby time short,poor portability and other issues for existing flexible electronic equipment.Flexible supercapacitor is suitable for using in flexible electronic equipment because of its high energy storage efficiency,good environmental stability,long cycle life and low production cost.The performance of flexible supercapacitor is mainly affected by its electrode material,and the flexible electrode materials can meet the requirements of good flexibility,high specific capacitance and excellent cycle stability.Manganese oxide is a typical pseudocapacitor electrode material because of its high theoretical specific capacity,wide voltage window,resource-rich and environmentally friendly.However,the poor conductivity of manganese oxide electrodes and own rigid characteristics restrict it application in flexible supercapacitor alone.The research results show that the conductivity and specific capacitance of the composite electrode can be improved by adding the carbon material with high conductivity and long cycle life through the synergistic effect.In this thesis,by using manganese oxide based electrode materials?MnO₂?with high performance and single-walled carbon nanotubes?SWCNT?with good conductivity as the assembled units,the manganese oxide nanowire/carbon nanotube hybrid film electrodes with good flexible and excellent electrochemical property are expected to be prepared,and manganese oxide nanowire/carbon nanotube film all solid-state flexible supercapacitor is looking forward to be assmbled by using this hybrid film electrode.The research thesis consists of five chapters.The first chapter introduced the preparation,structure,property and application of carbon nanotube,manganese dioxide,and all solid-state flexible supercapacitors.Chapter 2 to Chapter 4 were the experimental parts consisted of the preparation and characterization of manganese oxide nanowire/carbon nanotube film,the assembling of all solid-state flexible fiber supercapacitors and their capacitive property discussion.Chapter 5 was the summary of the thesis.The main research contents were as follows:Preparation and electrochemical properties of ?-MnO₂ nanowire and manganese oxide nanowire/single walled carbon nanotubes composite film electrodes.The low-crystalline layered manganese oxide was firstly prepared by rapid oxidation-reduction reaction.Then the low-crystalline layered manganese oxide was hydrothermally treated in 1 mol L"1 NaOH solution at 150? for 20 h,?-MnO₂ nanowires with large aspect ratio was prepared,and the effect of the hydrothermal treatment time on the morphology and electrochemical properties of ?-MnO₂ nanowires was also investigated.The prepared MnO₂ nanowires had a high specific capacitance of 259 F g-1 at a current density of 0.25 A g-1.By using ?-MnO₂ nanowires and SWCNT with different mass ratios,?-MnO₂ nanowires/SWCNT hybrid film electrodes with good flexibility and high capacitance were obtained via a simple vacuum filtration method.The electrochemical properties of the ?-MnO₂ nanowires/SWCNT hybrid film electrodes were measured in a three-electrode system.When the amount of SWCNT was 15 wt%,the ?-MnO₂/SWCNT-15 hybrid film electrode showed larger areal specific capacitance of 964 mF cm-2 at current density of 1 mA cm-2 and excellent capacity retention of 81%when the current density increases from 1 to 10 mA cm-2.Assembly and characterization of ?-MnO₂/SWCNT all-solid flexible supercapacitor.By using ?-MnO₂/S WCNT-15 film electrodes,a flexible all-solid-state?-MnO₂/SWCNT-15 hybrid supercapacitor was assembled by sandwiching PVA-KOH solid-state electrolyte without using other conductive additives,binders,and current collector.The assembled flexible all-solid-state ?-MnO₂/S WCNT-15 hybrid supercapacitor not only showed good flexibility and mechanical property,but also gave a high areal capacitance of 358 mF cm-2 at a current density of 2 mA cm-2,good capacitance retention of 90%,excellent Coulombic efficiency of 96%after 2,000 cycles,and high energy density of 31.8 ?Wh cm-2 at a power density of 0.815 mW cm-2.Meanwhile,the assembled device could withstand a large degree of bending and twisting,the device's electrochemical performance and impedance hardly changed after bending at 120° for 200 times.In addition,two ?-MnO₂/SWCNT-15 hybrid film supercapacitors were connected in series,and the resultant direct current circuit was powerful enough to light up a redlight-emitting diode?LED?at a voltage of 1.6 V when it was fully charged,demonstrating the potential application of the assembled device in energy storage for flexible/wearable electronics.