Braiding Fabrication And Evaluation Of High Performance Rope-Shaped Supercapacitor

Flexible supercapacitors,as one of the important branches of flexible energy storage systems,it provides the possibility of realizing smart textiles because of high flexibility,long cycle life,high power density and environmental friendliness.The wire supercapacitor can be processed as needed in the subsequent process due to the lower dimension,which can be better integrated to form a unified whole with the textile and can exert energy storage performance without affecting the fabric appearance.Therefore,wire supercapacitor is widely regarded as one of the most ideal devices in flexible energy storage devices.Although many scholars have done a lot of work for the preparation of linear supercapacitor,there are still many shortcomings.Specifically:?1?The bending stiffness of the fiber prepared by the spinning technique using carbon as the active material is poor,and it is difficult to mass-produce,which limits the subsequent processing and application.?2?A linear matrix material such as natural fiber or chemical fiber is used as a skeleton to prepare a linear superconductor,and the load of the active material is limited,and the linear superconducting energy storage performance is poor.?3?Although some scholars have prepared high-energy density linear super-electricity by constructing nanostructures of active materials,their volume is small and the total energy storage is small,which is difficult to be used as an energy storage device in practical use.?4?For the preparation of stretchable ultra-electricity,there are few proposals for developing new structure stretchable super-electricity.?5?There is not has good idea for no joint connection between fiber super-electricity so far.The paper first prepared a filament electrode with high active material loading and high energy density.The coaxial rope-shaped supercapacitor with high energy output,energy density independent with volume,and high stability is prepared by the textile weaving process.A novel coaxial stretchable rope-like supercapacitor structure was designed by using the braiding process.Finally,a high voltage self-series coaxial superconductor was designed and fabricated.The research content specifically includes the following aspects:?1?In order to solve the problem that the electrochemical properties of the fiber electrode is poor due to the small amount of active material supported on the fiber electrode,firstly,a fiber electrode with high active material load is prepared.Using polylactic acid PLA filament as matrix,FeCl₃ modified graphene oxide?GO?as active material coated on PLA filament,and conductive polypyrrole?PPy?was grown on the surface of PLA filament by in-situ polymerization to obtain a high active material loading fiber electrode.In this work,different mass ratios of FeCl₃ and GO that effect on the active material loading of the filament electrode were explored,and the reason and mechanism of the high loading active material were revealed.The results showed that the mass ratio of FeCl₃ to GO was 6:6,the loading on the filament electrode was largest.The reason was that with the increase of the mass of FeCl₃,much more Fe³⁺combined with GO,the active materials which absorbed on the surface of the filament could obtain more Fe³⁺ions.It could intiate a part of pyrrole polymerization in the pyrrole solution without introducing other oxidant ions.As a result,some oligomeric polypyrrole PPy could be formed to adhere on the filament substrate,which promoted the repolymerization of the subsequent pyrrole.The test results showed that filament electrode active material loading was increased from 53%to 72.4%compared with unmodification.In addition,it had excellent electrical and electrochemical properties.The filament conductivity could reach 652 S/m,and the specific capacitance was158.8 mF/cm²,energy density 3.5?Wh/cm²,power density 0.032 mW/cm².The filament supercapacitor device showed an excellent long-life performance up to 5000cycles with a retention of⁹0.7%.This supercapacitor was flexible and performs stably under bending deformation,which render them promising in many emerging fields such as portable and wearable electronics.?2?Although the fiber electrode has a high energy density,the total energy storage of the linear?fiber?supercapacitor is low,because the volume of fiber is small.In order to prepare high-energy storage fiber supercapacitor,this part is based on the modified filament electrode which is prepared above,and 12 modified filaments are braiding by textile braiding process to realize integrated formation of 12 filament electrodes.A high-energy coaxial supercapacitor?referred to as coaxial supercapacitor?is prepared by layer-braiding.A 12-yarn electrode is integrated into a rope by the textile braiding process.The obtained rope electrode realized energy density and the volume independent characteristics.Electrode energy is increased in proportion to the volume.The electrochemical properties of the rope electrode,the yarn electrode and the fiber electrode are analyzed by electrode dynamics under different scan rate.In addition,the performance of rope electrodes is compared by braiding and twisting two different methods.The results show that the electrical conductivity of the rope electrode is greatly increased compared with filament or fiber.The resistance of the rope electrode is only 85?/cm.The fiber,filament and rope electrodes specific capacitance are 92.1,95.9,87.8 F/cm³ respectively at a scan rate of 5 mV/s,and the discrepancies of specific capacitances between fiber and filament and between fiber and rope are both less than 10%in a scan rate range of 5 to 100 mV/s.Compared with fiber electrode,the volume of the rope electrode is increased by nearly 1500 times,so the energy is also nearly 1500 times higher which verifies volume-independent specific capacitance and also volume-independent energy density within the1500-fold volume increase.The kinetic analysis of three electrodes shows that fiber electrode,filament electrode and rope electrode have the same dynamics at the low scan rate.At the high scan rate,rope electrode is dominant by diffusion control.Compared with twisted electrode,braid electrode has better performance and faster charge transfer speed,which is due to larger effective electrode area of the braided electrode.It is calculated that the maximum specific capacitance of braided electrode is 87.8 F/cm³ and twisted electrode is only 68.7 F/cm³.?3?Coaxial supercapacitor can realize the integration of multiple fibers/yarns,and the obtained supercapacitor has excellent electrochemical performance.However,the coaxial supercapacitor separator layer generally adopts a commercial hydrophilic cellulose separator?NKK?.The separator is easily broken during the stretching process,causing short-circuit between the inner and outer electrodes.In order to the needs of stretchable products,this section designs a new type of coaxial stretchable supercapacitor based on coaxial supercapacitor and using a layer-by-layer braiding.Each of the inner-and outer-electrode was braided with 6 modified PLA yarns along a pre-stretched core yarn of spandex monofilament.The electrode could achieve 100%strain and a high capacitance of 68.7 mF/cm.Between the inner-and outer-electrode there was a stretchable separation membrane fabricated by braiding 12 spandex yarns on the surface of the inner-electrode,which featured a high stretchability and porosity.By injecting the electrolyte between the inner-and outer-electrode the assembly of the cord-shaped supercapacitor was completed.In this way,multiple yarn-electrodes could be integrated by braiding process,which endowed the cord-shaped supercapacitor an excellent areal capacitive performance of 60.1 mF/cm²?1.5 F/cm³;31.02 F/g?with the energy density 5.4?Wh/cm²?0.13 mWh/cm³;2.8 Wh/kg?,power density 0.52 mW/cm²?12.34 mW/cm³?.Very high capacitance retention of 99.8%could be achieved under the strain of 100%,demonstrating the application value of this stretchable cord-shaped supercapacitor.?4?The high-voltage and high-energy output can be realized between the energy storage components through the external circuit,although the high voltage and high energy output can be realized,but for the flexible energy storage component,a series of new problems,such as aesthetics and joint fastness,contact short circuit between devices,and so on.Therefore,based on coaxial supercapacitor,this section creatively designs a coaxial self-series rope-like supercapacitor?referred to as self-series supercapacitor?.A coaxial rope-like self-series supercapacitor?labeled as self-series supercapacitor?is designed and prepared.This rope supercapacitor can provide different voltage outputs according to the needs of the external circuit.This work prepared superconductors composed of different numbers of devices?X-unit,X=1,2,4,6,8 etc.?and tested their electrochemical performance.The results show that a single device can provide an output voltage of 0.8 V.As the number of coaxial supercapacitor increases,the output voltage of the whole device increases proportionally.The maximum output voltage of 8-unit devices can reach 6.4 V.In addition,a fast charge transfer and low internal resistant of a single device is evident for the rope due to its coaxial structure.1-uint,2-unit,4-unit and 8-unit rope supercapacitors produce capacitances of 83.0,41.8,22.1 and 11.0 mF at 0.1 mA,respectively,scaling down with the number of unit.As for the device energy,1-uint,2-unit,4-unit and 8-unit rope supercapacitors generate 7.4,14.9,31.4 and 62.6?Wh at 0.1 mA,respectively,scaling up with the number of unit.Particularly,the energy density of different devices is 189,195,208,209?Wh/cm³,and the difference is less than 10%,so this rope structure is stable.Additionally,the rope supercapacitors exhibit an excellent long-life performance,which can endure up to 10000 cycles.Compared with the monofilament fiber electrode,the volume of the 8-unit device is equivalent to an increase of nearly 12,000 times,so the energy storage performance is greatly improved.Through practical application,the 4-unit device can be used as the energy supply unit to realize the simultaneous illumination of 36 LED lights.It can also be inserted into the textile to prepare the energy storage strap to power the electronic watch.The 4-unit device can make the electronic watch worked 12 min,far exceeding the level reported in the existing literature.Therefore,the method provides a new solution for realizing high-voltage output and high-energy storage of linear super-power,and has certain guiding significance.