Structural Design And Performance Research Of Flexible Electrode Materials In Wearable Supercapacitors

With the rapid development of science and technology,more and more wearable electronic products spring up in the modern society.Due to the merits of simple assembly,fast charging–discharging and long cycle life,supercapacitors?SCs?are being considered as an attractive class of energy-storage devices.Therefore,wearable SCs have been widely explored as a strategy to meet the demand of wearable electronics.At present,wearable SCs have made rapid progress,from two-dimensional sandwich structure to one-dimensional linear structure,a wide variety of wearable SCs have emerged.However,the electrochemical performance of wearable SCs is unsatisfactory,owing to the insufficient specific capacity and cycle stability of the flexible electrodes.To solve this problem,we have adopted rational structural design to obtain high volumetric capacitance of flexible film electrode with abundant porous channels in ionic liquid electrolyte.Meanwhile,we have developed high conductive metal carbides nanofibers to improve specific capacity and cycle stability of flexible film electrode.While enhancing the electrochemical behavior of wearable SCs by improving the performance of the flexible electrode,we also extend the functionalization of the wearable SCs.In order to meet the complex external force changes,we designed a highly elastic linear electrode based on double-covered yarns for wire-shaped wearable SCs,which show effective elastic stretchability and size adjustability.Then,we designed a shape memory linear electrode to solve the problem of irreversible plastic deformation of wearable SCs.Finally,in order to realize the reasonable utilization of renewable energy,we used carbon fiber tows with vertical nanosheets arrays as linear electrode for wearable SCs.The fabricated devices can be repeatedly charged by harvesting wind energy,which can truly realize the recycling of renewable energy.The main research progresses are as follows:?1?Research on flexible film electrodes in wearable SCs.A novel flexible film electrode has been prepared based on g-C₃N₄nanosheets and conductive CNTs by simple vacuum filtration.Benefiting from the abundant porous channels,the resultant film electrode represents excellent electrochemical performance especially in ionic liquid electrolyte.The maximum volume capacitance of 25 F/cm³ can be obtained.Meanwhile,the resultant film electrode shows good cycling stabilities with high capacitance retention over 80%after 5000 cycles under straight and bending states.In addition,electrospining technology has been widely used as a large-scale approach to prepare continuous fiber membranes.We have developed a flexible film electrode based on conductive metal carbide nanofibers.Benefiting from these features,the resultant film electrode exhibits superior electrochemical performance,especially represents a large specific capacity of 430 F/g and excellent cycle stability with a high capacitance retention of92.6%after 5000 cycles.?2?Functional design of flexible linear electrodes in wearable SCsA novel kind of elastic linear electrode based on double-covered yarns for wire-shaped SCs has been put forward.The fabricated devices exhibit excellent electrochemical performance and high stretchability.Such superior energy storage performance and steady electrochemical behaviors under high strain?150%maximum?have almost never been reported before.As a result,the wire-shaped SCs distinctly represent the available self-stretchable and size-adjustable ability.Besides,a shape memory linear electrode based on NiTi alloy wire for wire-shaped SCs has been put forward.The integrated devices exhibit ultrahigh volumetric energy density?8.9 mWh/cm³?,which is much higher than that of currently reported wire-shaped SCs.More importantly,the wire-shaped SCs distinctly represent the available recoverable ability to effectively solve the problem of irreversible plastic deformation.When irreversible plastic deformations happen,the deformed shape of the devices can automatically resume the initial presupposed shape in the warm environment?about 35°C?.Finally,we used vertical nanosheets arrays coated carbon fiber tows as yarn electrodes for wire-shaped SCs.Benefiting from the intriguing configuration,the fabricated devices exhibit low resistance and high volumetric energy density.As a result,the devices can be repeatedly charged by harvesting wind energy,which provides a feasible idea for realizing the rational utilization of renewable energy.