Design And Performance Research Of Textile-Based Flexible Supercapacitors

Flexible supercapacitors not only have the characteristics of ordinary capacitors,such as fast charge/discharge,long cycle life,and safety,but also have the advantages of lightweight,high flexibility,and integrability,which meet the development needs of flexible smart wearable electronics in energy storage.Although research on flexible supercapacitors has made rapid progress,there are still common problems,such as complicated preparation methods,low production efficiency,poor integration,and mechanical properties,which limit the development of flexible supercapacitors in wearable fields.Therefore,it is of great significance and practical value to develop suitable preparation processes to efficiently prepare flexible supercapacitors with excellent electrochemical and mechanical properties and enhance their integration.Textile technology is becoming increasingly sophisticated,and the structure of textiles is highly variable.It is feasible to apply the structural characteristics of textiles to the design of flexible supercapacitors.Therefore,in this paper,a series of novel flexible supercapacitors are constructed through suitable material selection and simple preparation methods,and structural design combined with textile technology,which provides a new strategy for developing smart wearable energy storage devices.The specific research contents of this thesis are concluded as follows:（1）In view of the low specific capacitance of fibrous supercapacitors,uniform and dense manganese and nickel co-substituted cobalt carbonate hydroxide nanoneedle arrays（MnNiCo-CH NNAs）are grown directly on the surface of CNT yarn by a simple and mild one-step hydrothermal method as the anode of asymmetric supercapacitor.MnNiCo-CH NNAs provide a high specific surface area and many redox reaction active sites,which effectively promote charge transfer and redox reaction.The MnNiCo-CH NNAs@CNT cathode exhibits high specific capacitance(1721.7m F cm^-2 at 0.4 A)and excellent electrochemical stability（99.3%capacitance retention after 10000charge/discharge cycles）.Activated carbon anode（AC@CNT）matching the charge of MnNiCo-CH NNAs@CNT cathode is prepared by a simple“dip-coating and drying”method.The assembled asymmetric fibrous supercapacitor with parallel structure has a voltage window of 1.5 V,excellent electrochemical performance(84.4 mF cm^-2 at 0.4 mA;25.5μWh cm^-2 at 602.4μW cm^-2)and cycling stability（83.2%capacitance retention after 5000 charge/discharge cycles）.Two series-connected devices can light up 65 LEDs with the“DHU 70”pattern,demonstrating their value in the field of energy storage.（2）Aiming at the disadvantages of complex,low efficiency,and non-scalability of coaxial asymmetric fibrous supercapacitor preparation methods,a novel one-step braiding method is developed to efficiently prepare coaxial asymmetric fibrous supercapacitors with excellent mechanical and electrochemical properties.The coaxial asymmetric fibrous supercapacitor（CAFSC）is prepared by the one-step braiding method on a high-speed braiding machine,where non-conducting polyester yarns are selected as the braiding/separator yarns,MnNiCo-CH NNAs@CNT cathode and AC@CNT anode are used as the axial yarns and core yarns,respectively.The braided CAFSC exhibits a one-dimensional structure in the axial direction and a tight core-sheath structure in the lateral direction.Benefiting from this braided structure,the CAFSC exhibits high specific capacitance(162.4 mF cm^-2 at 4 mA;46.33μWh cm^-2 at 1.75 m W cm^-2),high cycling stability（91.6%capacitance retention after 10000 charge/discharge cycles）,excellent bending stability（90.1%capacitance retention after 1500 bending cycles）,and outstanding mechanical properties（capable of freely bending and lifting a weight of 200 g）.In addition,the CAFSC demonstrates excellent weaveability and wearability.The flexible energy storage watchband prepared using textile weaving technology can provide a stable power source for the watch.The efficient and scalable one-step braiding technology offers a promising strategy for next-generation energy storage devices for wearable electronics.（3）To address the problem that the structure of conventional one-dimensional supercapacitors cannot be fully integrated with other functional devices into an integrated fibrous self-powered multifunctional wearable device,a novel asymmetric one-dimensional tubular supercapacitor with braided structure is prepared by a rational morphological structure design using a one-step braiding technique.The MnO₂@CNT cathode and MoS₂@CNT anode with matching charges are prepared by electrochemical deposition and hydrothermal methods,respectively.The braided-based asymmetric tubular supercapacitor（BATSC）is prepared by the one-step braiding method.The silica tube is used as the core yarn.The polyester yarns are used as the braided yarn,and the MnO₂@CNT cathodes and MoS₂@CNT anodes are used as the axial yarn and arranged alternately.The BATSC exhibits a one-dimensional structure in the axial direction and a double-shelled hollow structure in the lateral direction,and demonstrates excellent electrochemical properties(58.8 mF cm^-1 at 0.2 mA;23.5μWh cm^-1 at 67.8μW cm^-1)and excellent electrochemical stability performance（92.2%capacitance retention after 6000 bending-recovering cycles;the initial capacitance remains almost constant at dynamic bending different angles）.The CNT/PRBT fibrous strain sensor is prepared by a simple“dip-coating and drying”method employing polyester/rubber braided thread（PRBT）as the stretchable substrate material,which exhibits a sensitivity of up to 15.0 and a 50%sensing range,the fast response time（about 268 ms）,and good durability（2500 repeated stretching-releasing cycles of 10%strain）.The integrated wearable fibrous self-powered strain sensing device is constructed by the BATSC and CNT/PRBT strain sensors,and the CNT/PRBT strain sensor can be driven by the stored power of the BATSC.The fibrous self-powered strain sensing device has reliable self-powered sensing performance and can be sewn onto textile or directly as a portable self-powered strain sensor for real-time detection of human joint motion（fingers,elbows,and knees）,which has potential applications in wearable intelligent motion monitoring and rehabilitation training areas.The design and integration strategy of the fibrous self-powered sensing device provides new insights for the development of fibrous multifunctional wearable products.（4）To address the decay of electrochemical performance of flexible supercapacitors in wearable applications due to mechanical deformation caused by adaptation to human physiological activities,and materials and structures are reasonably selected and designed.The poly（3,4-ethylenedioxythiophene）/reduced graphene oxide@SSM（PEDOT/RGO@SSM）electrode is prepared by the simple two-step electrodeposition methods using stainless-steel mesh（SSM）with a diamond-shaped warp-knitted grid structure as the flexible and stretchable conductive substrate,and assembled into the symmetrical stretchable supercapacitor.The diamond-shaped SSM is knitted by ultrafine stainless-steel fibers with a diameter of 30μm,which endows high flexibility,stretchability,conductivity,and lightweight.The assembled symmetrical stretchable supercapacitor not only y exhibits good energy density(4.7μWh cm^-2 at 40μW cm^-2),but also demonstrates excellent flexibility（bending and stretching）,bending stability（CV curves have no change under different bending angles;94.7%capacitance retention after 100 charge/discharge cycles at 90°bend）,tensile stability（78.4%and 70.1%capacitance retention after 500 tensile cycles at 10%and 25%strain,respectively）,and lightweight.The series-connected devices are encapsulated with PDMS film and laminated to the garment,which can light up LED,showing the potential of the prepared stretchable supercapacitor as a wearable energy storage device.This simple and low-cost preparation method provides a promising novel idea for the large-scale production of lightweight,stretchable,and high-performance wearable supercapacitors.