Structure Design And Energy Storage Mechanism Of High-Performance Wearable Aquaous Supercapacitors

The emergence of imperceptible wearable electroSICs has undated the people'scientific and technological?S&T?demands for intelligent lives in the future.With the rapid development of this field,to develop wearable energy storage devices suitable for them has become the key step during the realization of this S&T dream.Up to date,aqueous supercapacitors?SCs?became one of the important research hotspots of wearable energy storage devices because of their excellent safety.However the applications of aqueous SCs have been greatly limited by their low energy densities.So,it is urgent and important to improve the energy density of aqueous SCs.Generally,the spatial structure and energy storage mechanism of the electrodes are recognized as two main factors that inhibit the energy density of aqueous SCs.Herein,to settle down the problem in these two aspects,this dissertation has proposed two solutions to promote the energy density of wearable energy storage devices:1)as for the design of electrodes'structures,conductive hierarchical structures have been employed to extend the available space for energy storage in the electrodes;2)referring to ioSIC battery,introducing ioSIC energy-storage mechanism to solve the shortage in energy storage density of the traditional SCs.1)Firstly,carbon nanotubes?CNTs?were introduced as conductive hierarchical structures to extend the energy storage space of the electrode and to provide more sites for the loading of active materials.The introduction of CNT hierarchies increased the electrode's specific capacitance from3 to 9.1 mF/cm,increased the rate capability from 23.68%to 64.46%,increased the cycling stability from 31.7%to 84.8%?1000 cycles?.Moreover,a type of symmetric flexible SCs was packaged using the prepared MnO₂@CNT/SSW fiber-shaped electrodes.The assembled SCs show the highest energy density of 0.78 mW h/cm³,and exhibit excellent flexibility.These experimental designs and obtained data would indicate that the introduction of CNT hierarchies can not only enhance the electrochemical performances of the SCs,but also improve the mechaSICal flexibility of the devices.However,the cluster of pseudo-capacitor materials?MnO₂?on the CNT hierarchies inhibits the enhancement of devices'performances.2)To obtain better improvements in electrochemical performances from hierarchical y structure performance,conducting polymers?such as polypyrrole,Ppy?were tried to modify the surface of CNT hierarchies,which successfully realized the uniform coating of MnO₂ nanosheets on the CNT hierarchies.The modification via Ppy increased the electrode's specific capacitance from 293.4 F/g to 529.3 F/g,increased the cycle stability from 79.6%to 98.5%.Moreover,a type of planar asymmetric flexible SCs was packaged using the prepared CNT@Ppy@MnO₂ core-shell structure electrodes.The assembled SCs show the highest energy density of 38.42 W h/kg and excellent flexibility.This design indicates that the modification via Ppy plays an important role in solving the problem during coating processes between traditional pseudo-capacitance materials and nano-carbon materials?such as CNT?.And this work also provides a universal solution for the effective deposition of other materials on carbon nanomaterials.3)Referring to the energy storage mechanism in high-energy-density Li-ion batteries,a type of aqueous energy storage system via lithium ions,i.e.,Li-ion capacitors?LICs?,was innovatively developed to further improve the energy density of SCs,and their energy storage mechanism and advantages were also explored.In this work,a type of fiber-shaped LIC energy storage systems was constructed using the hydrogenated-Li₄Ti₅O₁₂?H-LTO?nanomaterials.The fabricated H-LTO fiber electrodes show a specific capacitance of 3.6 mF/cm,a wide voltage window of 1.4 V,and almost no decay after 100,000 cycles.More importantly,via the sweep-voltammetry analysis on cyclic voltammetry curves,it is demonstrated that the intercalation/deintercalation processes of Li⁺ions can also occur on the H-LTO electrodes in the aqueous electrolyte.Furthermore,a type of quasi-solid fiber-shaped LICs was packaged using H-LTO fiber electrodes.The assembled LICs show a high energy density of 18.44?W h/cm² and an excellent wearable performance.At the same manner,the energy storage mechanism of the assembled aqueous LICs was also demonstrated by the sweep-voltammetry analysis.This part of work innovatively proposes one new research direction for future wearable SCs.4)In order to further improve the energy density of SCs,the design of 3D space and energy storage mechanism via ions were integrated together to produce an excellent fiber-shaped ion capacitors?FICs?.As for the design of electrode space,a type of flexible and porous multi-ply carbonized cotton threads?CCTs?was used as the fiber frame,and a 5-?m TiN nanowire array was grown on CCTs to greatly expand the available space for energy storage;as for the energy storage mechanism via ions,the Li⁺or Na⁺-ion storage capacities of TiN was utilized to improve the energy density of FICs.The prepared TiN-NW@CCT electrodes show high specific capacitances of 40.9mF/cm?Li?and 39.6 mF/cm?Na?,which are higher than most of the reported data.Moreover,a type of symmetric FICs using two TiN-NW@CCT electrodes showed a wide voltage window of 2.2V.And the assembled FICs showed the highest energy density of 93.1?W h/cm²?Li⁺ions?and 52.5?W h/cm²?Na⁺ions?,which are nearly three times as high as the reported highest value.These results also demonstrated the synergistic effect of 3D space design and energy storage mechanism via ions in the enhancement of energy storage density of SCs.And this work provides the necessary technology for the development of high-performance capacitors in future.