Preparation And Performance Of Carbon Nanomaterials-based Supercapacitor Electrodes And Flexible Devices

Carbon nanotubes（CNTs）and graphene are the shinning materials‘star’within the past 30 years.These one-and two-dimensional structures composed of graphite layers,exhibit unique properties and broad application prospect.Their high conductivity and large specific surface area allow them to be a category of excellent supercapacitor electrodes.Besides,when they compose with metal oxides and conductive polymers,the capacitance and rate performance of the composites could be elevated due the conductivity improvement.In addition,these one-and two-dimensional structures have been widely used to prepare various flexible transparent electrodes and devices due to their high flexibility and transparency.Hence,focusing on the application of carbon nanomaterials to supercapacitors,we need carry out the synthesis research of electrode materials to increase the device performance.On the other hand,we could construct novel flexible transparent devices with carbon nanomaterials as energy supply for flexible electronics by taking advantage of their flexibility,transparency and conductivity.In this dissertation,we prepared graphene-based high capacitive supercapacitor electrodes by composing graphene with transition metal oxides and conductive polymers.Then we developed CNT wire-shaped electrodes and supercapacitors by growing CNT film onto metal wire via chemical vapor deposition（CVD）.On the basis of CNT transparent electrodes,finally,we proposed a novel approach to control the assembly of flexible transparent supercapacitors（FTSCs）.The main progress is summarized as follows:High-performance supercapacitor electrodes were constructed by composing graphene with high theoretical-capacitance Co₃O₄（3560 F/g）because of their synergistic effect.Co₃O₄ nanopetals were synthesized by varying the hydrothermal reaction temperature.The as-prepared graphene/Co₃O₄nanopetal composite exhibited excellent electrochemical performance.The specific capacitance value could reach up to 714 F/g at a scan rate of 2 m V/s tested by cyclic voltammetry.In galvanostatic charge/discharge measurement,besides,its capacitance was 841 F/g at a current density of 0.1 A/g.After galvanostatic charge-discharge 1000 laps at the current density of 0.4 A/g,the specific capacitance could keep 96.7%of original capacitive value,demonstrating its good cycling stability.The graphene/polyaniline（PANI）composite hydrogel was successfully prepared by a one-step hydrothermal method.The composite hydrogel,allowing to be facially processed by cutting,also combining the advantages of high conductivity of graphene and high pseudocapacitance of PANI,is an excellent supercapacitor electrode.The specific capacitance value is 258.5 F/g at a scan rate of 2m V/s and the specific capacitance value is up to 307 F/g at a current density of 0.2 A/g.The specific capacitance value can still maintain 90%of the initial value after repeating the galvanostatic charge–discharge for 1000 cycles at a current density of 1.0 A/g.These results showed the potential application of the graphene/PANI composite hydrogel electrode in supercapacitors.Metal wires only offer a limited cylindrical surface area when acted as substrate for the loading of CNTs.To resolve this issue,we deposited three-dimensional NiO nanowall arrays on metal wires,then prepared CNT films on the substrates via CVD deposition.The thickness of the CNT films is up to 6μm.The NiO nanowalls were reduced to Ni particles during the CNT growth.By using the prepared CNT/metal wires as electrodes,all-solid wire-shaped supercapacitors were assembled.The areal capacitance of the devices reached a high value of 12.5 m F/cm² at a current density of 10μA/cm.The energy density varied from 1.74 to 1.43μWh/cm² in a power density ranging from 0.064 to 0.746m W/cm²,which is higher than some reported carbon-based solid-state fiber supercapacitors.CNTs have been widely used as building blocks to fabricate FTSC electrodes.However,little attention has been paid to precisely control the electrode spacing during the device assembly.PVA-based gels have been generally used as both electrolytes and separators for FTSCs.However,these gels sandwiched between the electrodes in FTSCs are easily compressed under bending and compression duo to their viscous flow behavior,resulting in the deformation of electrode spacing and the unstable capacitance performance.To resolve this issue,herein we introduced monodispersed polystyrene（PS）microspheres into PVA-Li Cl polymer gel electrolyte as spacer to precisely control the electrode spacing during the assembly of FTSCs using SWCNTs/ITO-PET or MnO₂/MWCNTs/ITO-PET as transparent electrodes.The electrode spacing could be tuned by varying the diameter of PS microspheres,e.g.,20,40 and 80μm.More importantly,the PS microspheres spacers protected the gel electrolyte from squeeze when bending takes place,allowing the stable performance output by FTSCs under bending state.After repeating bending test,the capacitance remained 95.6%,indicating the high stability and flexibility of the devices with the assistance of PS microspheres spacers.