Carbon nanotube hollow fiber-based electrode and preparation method and application thereof

Abstract

The invention discloses a carbon nanotube hollow fiber-based electrode and a preparation method and application thereof, the carbon nanotube hollow fiber-based electrode comprises a conductive substrate and an active material loaded on the conductive substrate, the conductive substrate is a carbon nanotube hollow fiber, the inner diameter of the carbon nanotube hollow fiber is 130-310 [mu] m, and the wall thickness of the carbon nanotube hollow fiber is 5-10 [mu] m. The carbon nanotube hollow fiber is used as a conductive substrate, and a stable conductive network structure is formed among the carbon nanotubes, so that the substrate has excellent conductivity, is beneficial to rapid transfer of charges between an electrode and an electrolyte, also has a high specific surface area, and provides more active sites for charge storage; the carbon nanotube hollow fiber is subjected to surface treatment, and oxygen-containing functional groups such as hydroxyl and carboxyl are introduced, so that hydroxide uniformly and orderly grows on the surface of the hollow fiber, a nanowire array structure is formed, a multi-channel diffusion path is provided, and ion diffusion is facilitated; and the prepared carbon nanotube hollow fiber-based electrode has high specific capacitance and excellent rate capability.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and particularly relates to a carbon nanotube hollow fiber-based electrode and its preparation method and application. Background Art

[0002] Supercapacitors have characteristics such as fast charge / discharge rate, long cycle life, high power density, and green safety. Among them, fibrous supercapacitors inherit a series of advantages of supercapacitors, and compared with traditional supercapacitors, they have the characteristics of light weight, flexibility, and weavability of fiber materials, which can meet the requirements of wearable electronic devices.

[0003] Among many fiber electrodes, carbon-based fibers have excellent electrical conductivity, flexibility, and a certain active material loading capacity, and are more suitable as flexible electrodes for application in fibrous supercapacitors. However, the specific capacitance and energy density of carbon-based fibrous supercapacitors are still relatively low, making it difficult to effectively meet the application requirements.

[0004] Although the specific capacitance of the electrode can be increased by loading active substances on the carbon-based fibers, a large amount of active substances are prone to agglomerate on the fiber surface, which in turn easily leads to slow kinetic reactions. Therefore, it is difficult for existing carbon-based fiber electrodes to achieve excellent rate performance at high current densities.

[0005] Therefore, it is still necessary to develop a fiber-based electrode with both high specific capacitance and excellent rate performance for application in flexible supercapacitors to meet the requirements of wearable electronic devices. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the present invention provides a carbon nanotube hollow fiber-based electrode and its preparation method and application. The surface-treated carbon nanotube hollow fiber is used as a conductive substrate and loaded with active materials, having a high specific capacitance and maintaining excellent rate performance at high current densities.

[0007] To solve the above technical problems, on the one hand, the present invention provides a carbon nanotube hollow fiber-based electrode, including a conductive substrate and active materials loaded on the conductive substrate. The conductive substrate is a carbon nanotube hollow fiber, and the inner diameter of the carbon nanotube hollow fiber is 130 - 310 μm, and the wall thickness is 5 - 10 μm.

[0008] The present invention uses carbon nanotube hollow fibers as the conductive substrate. The hollow fibers are completely composed of carbon nanotubes, and a stable conductive network structure is formed between the carbon nanotubes, enabling the hollow fiber substrate to have excellent electrical conductivity on the one hand, which is conducive to the rapid transfer of charges between the electrode and the electrolyte, and on the other hand, having a high specific surface area, which can provide more active sites for charge storage. The inner diameter and wall thickness of the carbon nanotube hollow fibers are defined. Because a smaller inner diameter generally helps to shorten the ion diffusion path, reduce the charge transfer impedance, and increase the specific surface area, but it cannot accommodate enough active materials; a larger inner diameter can provide more space to accommodate the volume expansion of the active materials, but it will reduce the specific surface area and active sites; a thin-wall structure is conducive to ion transport and rapid charge and discharge, but the strength is relatively insufficient; a thick-wall structure provides higher mechanical strength and cycling stability, but may increase the ion transport resistance. Therefore, the inner diameter and wall thickness of the carbon nanotube hollow fibers are controlled within an appropriate range to achieve the balance and optimization of the comprehensive performance of the carbon nanotube hollow fiber-based electrode.

[0009] Further, the active material is nickel-cobalt bimetallic hydroxide.

[0010] In the second aspect of the present invention, a method for preparing the carbon nanotube hollow fiber-based electrode described in the first aspect is provided, including the following steps:

[0011] S1. Mix and dissolve nickel nitrate hexahydrate, cobalt nitrate hexahydrate, urea, and a solvent to obtain a reaction solution;

[0012] S2. Place the carbon nanotube hollow fibers in the reaction solution and carry out a hydrothermal reaction in a closed environment to obtain a carbon nanotube hollow fiber-based electrode.

[0013] Further, in S2, before placing the carbon nanotube hollow fibers in the reaction solution, a surface treatment step is also included, specifically: heat-treat the carbon nanotube hollow fibers at 390 - 410 °C for 1 - 2 h, and then place them in an acidic solution for acid treatment for 2 - 3 h. After the surface treatment of the carbon nanotube hollow fibers, oxygen-containing functional groups such as hydroxyl and carboxyl groups are introduced on the surface of the carbon nanotube hollow fibers, which form hydrogen bond interactions or electrostatic attractions with the hydroxyl groups in the nickel-cobalt bimetallic hydroxide, helping the two to combine, enabling the hydroxide to grow uniformly and orderly on the surface of the hollow fibers and not easily agglomerate. At the same time, the metal hydroxide loaded on the fiber surface has a nanowire array structure, which can provide a multi-channel diffusion path, facilitating the diffusion of ions, and making the prepared carbon nanotube hollow fiber-based electrode have both a high specific capacitance and excellent rate performance.

[0014] Further, the acidic solution is an aqueous solution of hydrochloric acid or nitric acid.

[0015] Further, in S2, the carbon nanotube hollow fibers are vertically placed in the reaction solution, facilitating the vertical and orderly growth of nickel-cobalt bimetallic hydroxide on the surface of the hollow fibers to form a nanowire array structure, which is conducive to ion diffusion.

[0016] Further, in S2, the temperature of the hydrothermal reaction is 110 - 130 °C, and the time is 1 - 6 h.

[0017] Further, in S1, the concentration of nickel nitrate hexahydrate in the reaction solution is 0.01 - 0.025 M, the concentration of cobalt nitrate hexahydrate is 0.02 - 0.05 M, and the concentration of urea is 0.05 - 0.125 M.

[0018] Further, in S2, the carbon nanotube hollow fibers are prepared by coating carbon nanotubes on wet vinylon filaments and then soaking the vinylon filaments in water at 90 - 100 °C.

[0019] The third aspect of the present invention provides the application of the carbon nanotube hollow fiber-based electrode described in the first aspect or the carbon nanotube hollow fiber-based electrode prepared by the preparation method described in the second aspect in a flexible supercapacitor.

[0020] Advantages of the present invention:

[0021] The present invention uses carbon nanotube hollow fibers as the conductive substrate, and a stable conductive network structure is formed between the carbon nanotubes. On the one hand, the hollow fiber substrate has excellent conductivity, which is conducive to the rapid transfer of charges between the electrode and the electrolyte. On the other hand, it has a high specific surface area, which can provide more active sites for charge storage.

[0022] After the surface treatment of the carbon nanotube hollow fibers in the present invention, oxygen-containing functional groups such as hydroxyl and carboxyl groups are introduced on the surface of the carbon nanotube hollow fibers, which form hydrogen bond interactions or electrostatic attractions with the hydroxyl groups in the nickel-cobalt bimetallic hydroxide, helping the two to combine. This makes the hydroxide grow uniformly and orderly on the surface of the hollow fibers and not easily agglomerate. At the same time, the metal hydroxide loaded on the fiber surface has a nanowire array structure, which can provide a multi-channel diffusion path, facilitating ion diffusion. As a result, the prepared carbon nanotube hollow fiber-based electrode has both a high specific capacitance and excellent rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0024] Figure 1It is the scanning electron microscope image of the carbon nanotube hollow fiber-based electrode prepared in Example 1 of the present invention;

[0025] Figure 2 It is the scanning electron microscope image of the carbon nanotube hollow fiber-based electrode prepared in Example 2 of the present invention;

[0026] Figure 3 It is the galvanostatic charge-discharge curves of the carbon nanotube hollow fiber-based electrode prepared in Example 2 of the present invention at different current densities;

[0027] Figure 4 It is the mass specific capacitance of the carbon nanotube hollow fiber-based electrode prepared in Example 2 of the present invention at different current densities. Detailed implementation manners

[0028] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0029] This embodiment provides a carbon nanotube hollow fiber-based electrode, including a conductive substrate and an active material loaded on the conductive substrate. The conductive substrate is a carbon nanotube hollow fiber, the inner diameter of the carbon nanotube hollow fiber is 130 - 310 μm, the wall thickness is 5 - 10 μm, and the active material is nickel-cobalt bimetallic hydroxide.

[0030] Another embodiment provides a preparation method of the carbon nanotube hollow fiber-based electrode described in the above embodiment, including the following steps:

[0031] S1. Mix and dissolve nickel nitrate hexahydrate, cobalt nitrate hexahydrate, urea and a solvent to obtain a reaction solution;

[0032] S2. Place the carbon nanotube hollow fiber in the reaction solution and carry out a hydrothermal reaction in a closed environment to obtain a carbon nanotube hollow fiber-based electrode.

[0033] As a preferred implementation manner, in S1, the concentration of nickel nitrate hexahydrate in the reaction solution is 0.01 - 0.025 M, the concentration of cobalt nitrate hexahydrate is 0.02 - 0.05 M, and the concentration of urea is 0.05 - 0.125 M.

[0034] As a preferred embodiment, in S2, before placing the carbon nanotube hollow fiber in the reaction solution, a surface treatment step is further included, specifically: heat-treating the carbon nanotube hollow fiber at 390 - 410 °C for 1 - 2 h, and then performing acid treatment in an aqueous solution of hydrochloric acid or nitric acid for 2 - 3 h; the carbon nanotube hollow fiber is placed vertically in the reaction solution, facilitating the vertical and orderly growth of nickel-cobalt double metal hydroxide on the surface of the hollow fiber to form a nanowire array structure, which is beneficial to ion diffusion; the temperature of the hydrothermal reaction is 110 - 130 °C, and the time is 1 - 6 h.

[0035] As a preferred embodiment, in S2, the carbon nanotube hollow fiber is prepared by coating carbon nanotubes on a wet polyvinyl alcohol filament and then soaking it in water at 90 - 100 °C to remove the polyvinyl alcohol filament.

[0036] Another embodiment provides an application of the carbon nanotube hollow fiber-based electrode described in the above embodiment in a flexible supercapacitor.

[0037] Example 1

[0038] This example provides a preparation method of a carbon nanotube hollow fiber-based electrode, including the following steps:

[0039] (1) Prepare carbon nanotube hollow fiber and perform surface treatment on it:

[0040] First, prepare carbon nanotube tubes by the floating catalyst chemical vapor deposition method: feed a mixed solution prepared from ferrocene, thiophene, and ethanol through a peristaltic pump, and react it in a high-temperature furnace under the carrier of nitrogen to obtain carbon nanotube tubes. Among them, the mass ratio of ferrocene, thiophene, and ethanol is 0.9:0.6:98.5, and the reaction temperature is 1300 °C.

[0041] Wet the polyvinyl alcohol filament with ethanol, then contact the wet polyvinyl alcohol filament with carbon nanotubes to coat the carbon nanotubes on the surface of the polyvinyl alcohol filament; among them, the count of the polyvinyl alcohol filament is 40, and the number of wetting-coating repetitions is 4 times; finally, soak the carbon nanotube-coated polyvinyl alcohol filament in water at 90 - 100 °C for 1 h to remove the polyvinyl alcohol filament, and carbon nanotube hollow fiber is obtained. The inner diameter of the prepared carbon nanotube hollow fiber is 305 ± 5 μm, and the wall thickness is 6.5 ± 0.5 μm.

[0042] Heat-treat the prepared carbon nanotube hollow fiber at 400 °C for 1 h, and then perform acid treatment on it with 37 wt% hydrochloric acid for 2 h to perform surface treatment on the carbon nanotube hollow fiber.

[0043] (2) Load nickel-cobalt double metal hydroxide on the surface of the carbon nanotube hollow fiber:

[0044] Prepare a mixed aqueous solution of nickel nitrate hexahydrate, cobalt nitrate hexahydrate and urea. Pour the above mixed solution into a reaction kettle equipped with a polytetrafluoroethylene inner lining. Then vertically place the surface-treated carbon nanotube hollow fiber into the mixed solution. Seal the reaction kettle and put it into an oven for hydrothermal reaction. After the reaction is completed, wash and dry to obtain the carbon nanotube hollow fiber-based electrode. Among them, the concentration of nickel nitrate hexahydrate in the mixed aqueous solution is 0.025 M, the concentration of cobalt nitrate hexahydrate is 0.05 M, the concentration of urea is 0.125 M, the temperature of the hydrothermal reaction is 120 °C, and the time is 6 h. The cross-sectional SEM image of the carbon nanotube hollow fiber electrode obtained in this example is as Figure 1 shown, it can be seen that the surface of the carbon nanotube hollow fiber is uniformly coated with the active substance nickel-cobalt double metal hydroxide.

[0045] Use the carbon nanotube hollow fiber-based electrode prepared in this example for a flexible supercapacitor, and study its electrochemical performance through constant current charge-discharge tests. The results show that when the current density is 2 A / g, the specific capacitance of the prepared fiber electrode is 408.0 F / g, and when the current density increases to 50 A / g, its capacitance retention rate is 81.3%.

[0046] Example 2

[0047] The difference between this example and Example 1 is that:

[0048] In step (1), the count of the vinylon filament is 80, the number of repeated wetting-coating times is 3 times, the inner diameter of the prepared carbon nanotube hollow fiber is 135 ± 5 μm, and the wall thickness is 8.0 ± 0.5 μm;

[0049] In step (2), the concentration of nickel nitrate hexahydrate in the mixed aqueous solution is 0.02 M, the concentration of cobalt nitrate hexahydrate is 0.04 M, the concentration of urea is 0.1 M, and the hydrothermal reaction time is 3 h.

[0050] The surface SEM image of the carbon nanotube hollow fiber electrode obtained in this example is as Figure 2 shown, it can be seen that the surface of the carbon nanotube hollow fiber is uniformly coated with the active substance nickel-cobalt double metal hydroxide, and the nickel-cobalt double metal hydroxide is arranged orderly.

[0051] Use the carbon nanotube hollow fiber-based electrode prepared in this example for a flexible supercapacitor, and study its electrochemical performance through constant current charge-discharge tests. Referring to Figure 3 , it can be seen that at different current densities, the prepared carbon nanotube hollow fiber-based electrode has good electrochemical reversibility. According to Figure 3 calculation, when the current density is 2 A / g, the specific capacitance of the prepared fiber electrode is 1964 F / g, and when the current density increases to 100 A / g, its capacitance retention rate is 80.4%. Referring toFigure 4 Compared with Example 1, the performance of Example 2 is significantly improved. This is because, on the one hand, the smaller inner diameter of the hollow fiber is generally beneficial to shortening the ion diffusion path, reducing the charge transfer impedance, and increasing the specific surface area. On the other hand, the too high concentration of the hydrothermal reaction in Example 1 may lead to an accelerated reaction rate. Also, as the reaction time prolongs, although the loading amount of the active material increases, the binding force between the microscopic active materials may be greater than the binding force between the active material and the hollow fiber substrate, making the active material prone to falling off. And during the repeated charge-discharge process, with the expansion of the active material volume, its rate performance also decreases.

[0052] Example 3

[0053] The difference between this example and Example 2 is that in step (2), the hydrothermal reaction time is 1 h.

[0054] The carbon nanotube hollow fiber-based electrode prepared in this example is used in a flexible supercapacitor, and its electrochemical performance is studied through constant current charge-discharge tests. The results show that at a current density of 2 A / g, the specific capacitance of the prepared fiber electrode is 1159 F / g, and when the current density increases to 100 A / g, its capacitance retention rate is 74.2%. Due to the short hydrothermal reaction time, the loading of the active material is less, and the performance is correspondingly reduced.

[0055] Example 4

[0056] The difference between this example and Example 1 is that:

[0057] In step (1), the count of the vinylon filament is 80, the repeated wetting-coating times is 3 times, the inner diameter of the prepared carbon nanotube hollow fiber is 135 ± 5 μm, and the wall thickness is 8.0 ± 0.5 μm;

[0058] In step (2), the hydrothermal reaction time is 4 h.

[0059] The carbon nanotube hollow fiber-based electrode prepared in this example is used in a flexible supercapacitor, and its electrochemical performance is studied through constant current charge-discharge tests. The results show that at a current density of 2 A / g, the specific capacitance of the prepared fiber electrode is 700.4 F / g, and when the current density increases to 50 A / g, its capacitance retention rate is 82.9%. Compared with Example 1, the performance of Example 4 has a certain degree of improvement, which is because the smaller inner diameter of the hollow fiber is generally beneficial to shortening the ion diffusion path, reducing the charge transfer impedance, and increasing the specific surface area.

[0060] Example 5

[0061] The difference between this example and Example 2 is that:

[0062] In step (1), the denier of the vinylon filament is 60, the number of wetting - coating repetitions is 3, the inner diameter of the prepared carbon nanotube hollow fiber is 200 ± 5 μm, and the wall thickness is 7.0 ± 0.5 μm;

[0063] In step (2), the hydrothermal reaction time is 2 h.

[0064] The carbon nanotube hollow fiber - based electrode prepared in this example is used for a flexible supercapacitor, and its electrochemical performance is studied through constant - current charge - discharge tests. The results show that at a current density of 2 A / g, the specific capacitance of the prepared fiber electrode is 2015 F / g, and when the current density increases to 100 A / g, its capacitance retention rate is 81.3%. Compared with Example 2, the inner diameter and wall thickness of the carbon nanotube hollow fiber in this example are more suitable, and the performance is better.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that the step of surface - treating the carbon nanotube hollow fiber in step (1) is omitted.

[0067] The carbon nanotube hollow fiber - based electrode prepared in this comparative example is used for a flexible supercapacitor, and its electrochemical performance is studied through constant - current charge - discharge tests. The results show that at a current density of 2 A / g, the specific capacitance of the prepared fiber electrode is 378 F / g, and when the current density increases to 50 A / g, its capacitance retention rate is 59.5%. This is because without surface - treating the carbon nanotube hollow fiber, nickel - cobalt double - metal hydroxide cannot be orderly combined with the carbon nanotube hollow fiber, and it is easy to agglomerate, hindering ion diffusion.

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 2 is that in step (1), the number of wetting - coating repetitions is 6, the inner diameter of the prepared carbon nanotube hollow fiber is 135 ± 5 μm, and the wall thickness is 15.0 ± 0.5 μm.

[0070] The carbon nanotube hollow fiber - based electrode prepared in this comparative example is used for a flexible supercapacitor, and its electrochemical performance is studied through constant - current charge - discharge tests. The results show that at a current density of 2 A / g, the specific capacitance of the prepared fiber electrode is 1648 F / g, and when the current density increases to 100 A / g, its capacitance retention rate is 65.3%. This is because when the wall thickness of the carbon nanotube hollow fiber is too large, the ion - transport resistance increases.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 2 lies in that: in step (1), the count of the vinylon filament is 20, the repeated wetting-coating times is 5, the inner diameter of the prepared carbon nanotube hollow fiber is 400 ± 5 μm, and the wall thickness is 7.8 ± 0.5 μm.

[0073] The carbon nanotube hollow fiber-based electrode prepared in this comparative example was used in a flexible supercapacitor, and its electrochemical performance was studied through constant current charge-discharge tests. The results showed that at a current density of 2 A / g, the specific capacitance of the prepared fiber electrode was 823 F / g, and when the current density increased to 100 A / g, its capacitance retention rate was 62.5%. This is because when the inner diameter of the carbon nanotube hollow fiber is too large, although it can accommodate more active materials, it will lead to a decrease in specific surface area and active sites.

[0074] In summary, in the present invention, the carbon nanotube hollow fiber is used as a conductive substrate, and a stable conductive network structure is formed between the carbon nanotubes. On the one hand, the hollow fiber substrate has excellent electrical conductivity, which is conducive to the rapid transfer of charges between the electrode and the electrolyte. On the other hand, it has a high specific surface area, which can provide more active sites for charge storage. After surface treatment of the carbon nanotube hollow fiber, oxygen-containing functional groups such as hydroxyl and carboxyl groups introduced on the surface of the carbon nanotube hollow fiber form hydrogen bond interactions or electrostatic attractions with the hydroxyl groups in the nickel-cobalt bimetallic hydroxide, which helps the two to combine, enabling the hydroxide to grow uniformly and orderly on the surface of the hollow fiber and not easily agglomerate. At the same time, the metal hydroxide loaded on the fiber surface has a nanowire array structure, which can provide a multi-channel diffusion path, facilitating the diffusion of ions, so that the prepared carbon nanotube hollow fiber-based electrode has both high specific capacitance and excellent rate performance.

[0075] The present invention has been described in detail above in combination with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications or improvements can be made to the technical solutions and their implementation manners of the present invention, and these all fall within the scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A carbon nanotube hollow fiber-based electrode, characterized in that, It includes a conductive substrate and an active material supported on the conductive substrate. The conductive substrate is a carbon nanotube hollow fiber, and the inner diameter of the carbon nanotube hollow fiber is 130 - 310 μm, and the wall thickness is 5 - 10 μm.

2. The carbon nanotube hollow fiber-based electrode according to claim 1, characterized in that, The active material is nickel-cobalt double metal hydroxide.

3. A method for preparing a carbon nanotube hollow fiber-based electrode according to any one of claims 1-2, characterized in that, It includes the following steps: S1. Mix and dissolve nickel nitrate hexahydrate, cobalt nitrate hexahydrate, urea and a solvent to obtain a reaction solution. S2. Place the carbon nanotube hollow fiber in the reaction solution and carry out a hydrothermal reaction in a closed environment to obtain a carbon nanotube hollow fiber-based electrode.

4. The preparation method of the carbon nanotube hollow fiber-based electrode according to claim 3, characterized in that, In S2, before placing the carbon nanotube hollow fiber in the reaction solution, a surface treatment step is also included, specifically: heat-treat the carbon nanotube hollow fiber at 390 - 410 °C for 1 - 2 h, and then place it in an acidic solution for acid treatment for 2 - 3 h.

5. The preparation method of the carbon nanotube hollow fiber-based electrode according to claim 4, characterized in that, The acidic solution is an aqueous solution of hydrochloric acid or nitric acid.

6. The preparation method of the carbon nanotube hollow fiber-based electrode according to claim 3, wherein, In S2, the carbon nanotube hollow fiber is placed vertically in the reaction solution.

7. The preparation method of the carbon nanotube hollow fiber-based electrode according to claim 3, characterized in that, In S2, the temperature of the hydrothermal reaction is 110 - 130 °C, and the time is 1 - 6 h.

8. The preparation method of the carbon nanotube hollow fiber-based electrode according to claim 3, wherein In S1, the concentration of nickel nitrate hexahydrate in the reaction solution is 0.01 - 0.025 M, the concentration of cobalt nitrate hexahydrate is 0.02 - 0.05 M, and the concentration of urea is 0.05 - 0.125 M.

9. The preparation method of the carbon nanotube hollow fiber-based electrode according to claim 3, characterized in that, In S2, the carbon nanotube hollow fiber is obtained by coating the carbon nanotubes on the wetted vinylon filaments and then soaking them in water at 90 - 100 °C to remove the vinylon filaments.

10. Application of the carbon nanotube hollow fiber-based electrode according to any one of claims 1 - 2 or the carbon nanotube hollow fiber-based electrode prepared by the preparation method according to any one of claims 3 - 9 in a flexible supercapacitor.

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