Design Of High Performance Micro-Supercapacitor

With rapid development of miniaturized and portable electronic devices,it raises higher requirements on the miniaturization of energy storage devices.Because of the low energy density and poor cycling stability,micro-batteries often fail to meet the requirements of fast charging/discharging and long life span.Micro-supercapacitors?MSCs?become micro-battery auxiliary power supplies or even replace micro-batteries due to their high power density,excellent cycling stability and safety of use.However,more researches are based on thin-film MSCs.The main disadvantages are the ultra-low areal energy density,and its energy storage capacity cannot meet the practical application.To solve this problems,the MSC is required to increase the load of the active material per unit area.In this paper,we have designed two kinds of MSCs,which all show excellent surface capacitance and energy density.Furthermore,the flexible MSC is fabricated after the introducing graphene as the electrode material substrate.The main research contents of this thesis are as follows:?1?Construct 3D ITO current collector to improve the load of active materials:In order to prepare MSCs with high areal capacitance and areal energy density,we introduce indium tin oxide nanowires?ITO NWs?into the electrodes as a three-dimensional?3D?conductive current collector of the active material.Due to the design of the 3D structure and the strong combination between ITO nanowire and substrate,the active material loading can be greatly improved.After the ITO nanowires were prepared on ITO conductive glass by CVD method,the manganese dioxide?MnO₂?was loaded on it by electrodeposition,and the electrode structure was prepared by laser etching.Moreover,there is no need to introduce conductive layer or adhesive in the preparation process.We investigated the electrochemical performance of devices with different MnO₂ loading.The areal capacitance of this ITO NWs@MnO₂ based device can reach 193.8 mF/cm².In addition,its areal energy density can reach 26.94?Wh/cm²at a current density of 0.3 mA/cm²,and the areal power density can reach 15.07mW/cm² at a current density of 30 mA/cm² which are superior to those of most reported MnO₂ based MSCs.At the same time,the series and parallel connection of the devices can be easily realized by laser etching.Therefore,this method of using ITO nanowires as a 3D conductive current collector provides an idea for fabricating high-load MSCs.However,this structural design is rigid and cannot be bent,and cannot meet the flexible and wearable demands of current popular electronic devices.?2?Layer coat graphene paper to improve load of active material and introduce high flexibility:In order to introduce bendable properties into the devices while increasing the active material loading of the device,we introduce graphene as the basics of electrode material.The graphene oxide film prepared by the Hummers method and electrophoretic deposition possesses excellent mechanical properties and good electrical conductivity after being reduced by hydroiodic acid.So we use it as the substrate for the whole electrode and the conductive current collector of the active material.MnO₂ is grown on the reduced graphene paper by hydrothermal method.Due to the excellent mechanical properties of the graphene paper,we could assemble the MnO₂-loaded graphene paper?MGF?by layer coating method to increase the mass loading per unit area of the device.Finally we use laser etching method to prepare the finger electrode.We have explored the effect of MnO₂ loading on device performance.The device with a hydrothermal time of 60 min shows the best performance.The double-layer device performs an areal capacitance of 31.5 mF/cm² and exhibits excellent flexibility.The electrochemical performance remain stable at almost any bending angle,and even the device is completely folded in half,the device performance is not lost.After being bent for 4000 times?with a radius of curvature of 0.51 cm?,the performance of device is still not attenuated.When the number of MGF reaches 5,the areal capacitance device reaches 144.3 mF/cm²,and the areal energy density can reach20?Wh/cm².