| Supercapacitors(SCs)with advantages of high power density,fast charge/discharge capability,long cycle life and safety,have been widely applied in various electric/hybrid devices as power sources,energy recovery devices or power compensation devices.Flexible SCs have attracted extensive interest and research to fulfill the requirements of flexibility,light-weight and miniaturization aroused from portable and wearable electronics.Novel nano materials especially nano composite materials with high specific capacitance have been constantly developed.Flexible two-dimensional(2D)tandem SCs,micro and fiber SCs have been successfully developed and a great progress has been gained.Despite this,some critical problems remained in flexible SCs,such as low volumetric specific capacitance and energy density,complex and costly fabrication process flexible devices,and lack of quantitative analysis of the stability of flexible SCs under dynamic deformation.To address these problems and enhance electrochemical and mechanical performance of flexible SCs,this thesis focuses attempts to fabricate high performance electrode materials,design novel structured devices,and simplify the fabrication process.The main content and results include:(1)Construction of flexible 2D tandem SCs based on carbon nanotube(CNT)/V2O5 layered composite films and performance study.V2O5 nanosheets are synthesized by hydrothermal method and then vacuum filtrated with CNT to form flexible composite films.The composite in the form of layered structure with Cdispersion between the V2O5 nanosheets.The thickness,density and conductivity of the composite films are tuned by the mass ratio of those two materials.When the mass ratio of MWCNTs is 10%,the gravimetric and volumetric specific capacitance of VC-10%composite films both reach the maximum value of 207.7 F g-1 and 521.0 F cm-3 respectively.Based on VC-10%films,the flexible all-solid-state SCs show a very high energy and power density of 17 Wh L-1(7.3 Whkg-1)and 10191 W L-1(4264 W kg-1).Meanwhile,the flexible SCs show very stable performance with less than 10%variation in the capacitance under different bending amplitudes.Layered composite films based on evenly mixed 2D pseudocapacitive and one-dimentional carbon materials show very high volumetric capacitance in present work,providing a great reference for construction of flexible two-dimentioanl tandem SCs with high volumetric energy density.(2)Construction of 2D in-plane SCs based on selective electrochemical deposition and performance study.Flexible micro SCs are assembled through drawing pattern,followed by successive electrochemical deposition of nickel interdigitated finger electrodes and Mn02 on the titanium foil.The flexible SCs demonstrate a maximum specific capacitance of 26.6 mF cm-2 and can remain about 70%initial capacitance after 12000 charge/discharge cycles.The capacitance remains nearly constant under different deformations,and 85%of initial capacitance can be retained after 1000 cycles of bending tests.Moreover,multiple devices can be connected in series or parallel without external circuit by changing the drawn pattern.This selective electrochemical method for 2D in-plane SCs possesses advantages of low-cost,simplicity,time-saving and flexibility,and can be applied in construction of other one dimentioanl(1D)electronic devices.(3)Construction of parallel double-helix structured 1D fiber SCs and performance study.The fiber SCs are assembled by twisting two titanium fiber@MnO2 fiber electrodes with a gap on a nylon fiber,while the electrodes are synthesized by electrochemical deposition of MnO2 nanosheets on the titanium fiber.The fiber SCs show an maximum areal capacitance of 15.6 mF cm-2,and a maximum energy and power density of 1.39 μWh cm-2和579μW cm-2,comparable or superior to some reported results.Meanwhile,the capacitance of SCs under static/dynamic deformations remain very stable,but fluctuations can be observed under dynamic bending and the extent and frequency of fluctuations are related with the bending frequency.Moreover,the fiber devices remain more than 88%of initial capacitance after 3500 bending cycles,showing very stable mechanical stability.The parallel double-helix structure can avoid short-circuit and guarantee the stability of fiber SCs under both static and dynamic deformations,showing great application potential.Quantitative study on the flexible fiber SCs reveals the law of output in dynamic deformation,providing references for precise performance evaluation and optimization of structure of flexible SCs.(4)Constrcution of flexible 1D fiber SCs based on a slicing method and performance study.A two dimensional tandem SC based on CNT films are slicing into size-controllable fiber SCs,avoiding the complex process of fabricating fiber electrodes and assembling fiber devices.The fiber SCs remain unchanging electrochemical performance under bending or knotted state or even after 1000 bending cycles.The specific capacitance and energy density of the fiber SC are enhanced by 5 times after incorporation of polyaniline.External circuit-free serial and parallel connected devices are also constructed with this slicing method.This novel slicing method for fiber supercapacitors is simple,fast and flexible,thus has great application potential and can be applied in other 1D electronic devices. |
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