| Recently,the portable and wearable electronic devices are becoming a hotspot in the flexible electronics studies.The flexible sensor systems with small-size and low-cost can be used for medical,logistics,climate detection and other applications.To achieve long-term and efficient operation of the sensor/sensor array,the miniaturized power devices of high power/energy densities are imperative.Therefore,the micro-power devices become one of the core issues for the development of micro-sensing system.Compared to micro-batteries,the microsupercapacitors?MSCs?have higher power density and longer lifespan.Around the subjects of novel technologies and new materials for MSCs applications,intensive research works have been done.In this dissertation,based on surface ion exchange self-metallization?SMIE?technology,the formation and mechanism of high-performance supercapacitors,fabricated on flexible polymer and paper substrate,were carefully studied.The main contents of this dissertation are as follows:First,the state-of-the-art of flexible supercapacitor is discussed.Based on W.Othuis battery constant equation and B.E.Conway electrochemical model,an analytical equation of MSC is established.The factors like geometrical parameters,specific capacitance and internal resistance on the electrochemical behaviors of devices were discussed by simulating the cyclic voltammetry curves,which can provide the guidance for MSC design.Moreover,a new standard is proposed which can be used to evaluate the MSC's performance through the linear relationship of the characteristic discharging voltage.Second,MSCs were fabricated on the flexible polyimide films at room temperature by SMIE technology with photosensitive dry film patterning and ink-jet printing.The all-solid-state MSCs,processed at room temperature,is composed of interdigitated silver electrode as current collector and multi-walled carbon nanotubes?MWNTs?as active materials.With PVA/H3PO4 gel electrolyte,the flexible MSC has the maximum specific capacitance of 2.64 mF cm-2 and can operate at the charge/discharge rate of 200 V s-1.The energy and power densities obtained can be up to 0.001 Wh cm-3 and 57.8 W cm-3,respectively.In addition,the devices also exhibited the superior electrochemical and mechanical stabilities,which can withstand 15,000 charge/discharge cycles and 16000 times of mechanical bending testing without obvious performance loss.Combined with the theoretical model,the working mechanism effectively is discussed.Third,the combination of SMIE technology and immersion plating had been applied to prepare the Au-on-Ag?i.e.,Ag@Au or AOA?flexible electrodes,which is considered as a potential substitute of the commonly used gold current collector.Compared to the SMIE-based silver electrode,the AOA is not only more flexible,but also shows more stable chemical properties and better inertness to electrochemical erosion.The sandwich-structured AOA supercapacitor showed a max.specific capacitance of 5.7 mF cm-2.The maximum phase angle of the capacitor is-75° and the characteristic frequency is 3 Hz with the electrochemical impedance spectroscopy.The planar AOA supercapacitor with electrode gap of 50?m was obtained by simple blade cutting method.After 15000 charge/discharge cycles,the capacitance retention of this device is up to 96.5%.This study also provides a solution for large-scale production of high-performance,high-stability,and low-cost flexible current collectors.Fourth,the application of polyimide acid?PAA?is explored to achieve patterned MSC.The silver electrode is fabricated at low-temperature with solution method.Combined with photolithography and SMIE technique,the minimum linewidth?10?m,is achieved.Two types of growth models are proposed,and the mechanism of electrode metallization is discussed in detail.The electroplating strategy is used to enhance the chemical stability of silver further.Compared to the bulk silver,the surface area of silver film prepared by PAA arises to 310%-450%.With the increase of the plating time,the electrode surface area decreases gradually to 150%-290%.MSCs with different geometric parameters were prepared and the systematic study of charge/discharge characteristics was conducted.Fifth,the paper-based supercapacitors?PBSs?,with the pencil graphite as electrode material,is prepared with dry method.With mechanical method,the scheme of assembling graphite@MWNT composite structure can be directly achieved.With graphite@MWNT composite as the electrode,the graphite@MWNT/paper/graphite@MWNT sandwich structure is innovatively proposed as integrated-type paper supercapacitor.Paper acts as both substrate and electrolyte membrane.The prepared PBSs showed a max.specific capacitance of 13.2 mF cm-2.It can operate at scan rate of 150 V s-1,with the power density up to 15.1 W cm-3,which is the highest one in the reported PBSs.The practical applications,like to lighten LED and to drive Bluetooth sensor system,are also shown.The dissertation also evaluates the possibility of combining this technology with MnO2,graphene and other materials to explore new energy devices.The research methods and achievements of this dissertation are significant to the development of low-cost,integrated sensor system with integrated micro-powers. |
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