KR102411615B1 - Flexible super capacitor and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a supercapacitor and a method for manufacturing the same, and one aspect of the present invention includes the steps of preparing a primary carbon fiber bundle in which two or more carbon fibers are twisted; surface-treating the primary carbon fiber bundle with an acidic solution; forming an encapsulated carbon fiber bundle by first coating the surface of the surface-treated primary carbon fiber bundle with a gel electrolyte; and twisting two or more of the encapsulated carbon fiber bundles to form a secondary carbon fiber bundle, and secondary coating with a gel electrolyte.

Description

Flexible supercapacitor and manufacturing method thereof

The present invention relates to a supercapacitor and a manufacturing method thereof, and more particularly, to a surface-activated carbon fiber-based supercapacitor and a manufacturing method thereof.

Recently, various types of wearable devices are emerging as technologies such as artificial intelligence (AI), cloud computing, Internet of Things (IoT), and big data develop, and parts and materials technologies such as semiconductors, sensors, and displays develop. Smart watches and fitness bands worn on the wrist in connection with smartphones are already gaining popularity, gradually becoming vests, shoes-type clothing, earwear such as Apple's AirPods, Microsoft's HoloLens, Google Glass, etc. Wearable devices worn on various types of bodies are being developed. In the future, it is expected that the products will be expanded to bioimplantable devices that can perform special tasks such as specialized medical services.

Powering wearable electronics requires directly integrated energy storage devices and materials with mechanical flexibility along with high energy and power densities. Smart textiles, which are being recently developed, are new materials that can be applied to multifunctional wearable electronic devices, have excellent elasticity, and are easy to manufacture in various shapes, so their application to future textiles and clothing is expected to expand.

On the other hand, among various energy storage devices, supercapacitors can be charged and discharged faster than batteries and have a long life cycle, so they are suitable for use as energy storage devices for wearable electronic devices, and it is one of the fields where smart fibers can be applied. .

Supercapacitors can be generally divided into electric double layer capacitors (EDLCs), pseudocapacitors, and hybrid supercapacitors according to the energy storage mechanism. Most of the recently developed wearable energy storage devices use EDLCs and have.

However, in the case of EDLC, there is a disadvantage in that it cannot provide a large energy density because the electric charge is simply stored by the adsorption/desorption of electrolyte ions in the surface region of the carbon-based electrode material.

Therefore, it is necessary to develop a supercapacitor made of a flexible fiber-based material capable of realizing high energy storage performance.

The above-mentioned background art is possessed or acquired by the inventor in the process of deriving the disclosure of the present application, and cannot necessarily be said to be a known technology disclosed to the general public prior to the present application.

SUMMARY OF THE INVENTION The present invention is to solve the above problems, and an object of the present invention is to provide a supercapacitor having flexibility while realizing high energy storage performance and a method for manufacturing the same.

However, the problems to be solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

One aspect of the present invention, comprising the steps of preparing a primary carbon fiber bundle in the form of two or more carbon fibers twisted; surface-treating the primary carbon fiber bundle with an acidic solution; forming an encapsulated carbon fiber bundle by first coating the surface of the surface-treated primary carbon fiber bundle with a gel electrolyte; and twisting two or more of the encapsulated carbon fiber bundles to form a secondary carbon fiber bundle, and secondary coating with a gel electrolyte.

According to an embodiment, the primary carbon fiber bundle may be in a form in which two or more carbon fibers are twisted in a Z-shape or S-shape and tightened.

According to one embodiment, the acidic solution is nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), phosphoric acid (H ₃ PO ₄ ), perchloric acid (HClO ₄ ), acetic acid (CH ₃ COOH) and carbonic acid (H ₂ ) CO ₃ ) It may include one or more selected from the group consisting of.

According to an embodiment, the surface-treated primary carbon fiber bundle includes an oxygen-containing functional group, and the oxygen-containing functional group includes at least one selected from the group consisting of a carbonyl group, a carboxyl group and a hydroxyl group. .

According to an embodiment, the surface-treated primary carbon fiber bundle may include oxygen in an amount of 10 atomic% to 40 atomic%.

According to one embodiment, the gel electrolyte, polyvinyl alcohol (PVA), phosphoric acid (H ₃ PO ₄ ), sulfuric acid (H ₂ SO ₄ ), sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca (OH) ₂ ) and magnesium hydroxide (Mg(OH) ₂ ) may include one or more selected from the group consisting of.

According to one embodiment, the secondary carbon fiber bundle, two or more of the encapsulated carbon fiber bundle may be twisted in an S-shape or Z-shape.

According to an embodiment, the encapsulated carbon fiber bundle may act as a positive electrode, a negative electrode, or a current collector.

According to one embodiment, the thickness of the secondary coated gel electrolyte may be formed to be 1 to 2 times the diameter of the secondary carbon fiber bundle.

According to an embodiment, the diameter of the encapsulated carbon fiber bundle may be 300 μm to 800 μm.

Another aspect of the present invention provides an electrode comprising a secondary carbon fiber bundle in which two or more encapsulated carbon fiber bundles are twisted; and a gel electrolyte coating layer formed on the surface of the secondary carbon fiber bundle, wherein the encapsulated carbon fiber bundle is coated with an electrolyte gel by twisting two or more primary carbon fibers.

According to one embodiment, the encapsulated carbon fiber bundle may have an oxygen-containing functional group on the surface.

According to an embodiment, the contact angle with respect to water may be 104° or less.

According to an embodiment, the specific capacitance at a voltage of 0 V to 1 V and a current density of 2 μA/cm ² to 15 μA/cm ² may be 2 mF/cm ² to 30 mF/cm ² have.

The method for manufacturing a flexible supercapacitor according to the present invention has an effect of manufacturing a supercapacitor with improved energy density, power density, thermal stability, and mechanical properties by using carbon fiber with an activated surface.

In addition, the flexible supercapacitor according to the present invention has an effect that can be applied to an energy storage device of a multifunctional wearable device.

1 is a diagram schematically illustrating a method of manufacturing a supercapacitor electrode according to an embodiment of the present invention.
2 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) of low magnification SEM images (top) and A high-magnification SEM image (bottom) is shown.
3 is a photograph of the manufactured supercapacitor and SEM images of a low-magnification cross-section and a high-magnification cross-section of Example 3 (F-SSEE@30).
4 is a TGA analysis result of the comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) supercapacitors.
5 is an XRD analysis result of the supercapacitors of Comparative Example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), and Example 3 (F-SSEE@30).
6 is an XPS analysis result of the supercapacitors of Comparative Example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), and Example 3 (F-SSEE@30).
7 is an XPS integrated analysis result of a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) supercapacitors .
8 is a diagram showing the surface of the carbon fiber into which oxygen-containing functional groups are introduced.
9 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) showing the contact angle at the supercapacitor interface will be.
10 shows a schematic configuration of a supercapacitor according to an embodiment of the present invention.
11 is a Nyquist plot according to the comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) supercapacitor EIS analysis. to be.
12 is a Bode plot of the supercapacitors of Comparative Example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), and Example 3 (F-SSEE@30).
13 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) 2 μA / cm ² of supercapacitors This is the charge/discharge curve at the current density.
14 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) 0 V to 1 V of supercapacitors The potential and specific capacity at 2 μA/cm ² to 15 μA/cm ² current density are shown.
15 is a Ragone plot of Example 3 (F-SSEE@30) supercapacitors associated with energy and power densities ranging from 4 μW/cm ² to 30 μW/cm ² .
16 shows the capacity retention rate when the flexible supercapacitor according to an embodiment of the present invention is changed into various shapes.
Figure 17 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) 2 μA / cm2 current of supercapacitors Cycling stability test results at density.
18 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) After heating the supercapacitors, EIS analysis It is a Nyquist plot according to
19 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) After heating the supercapacitor, 10,000 cycles capacity retention rate during the
20 shows an electrochemical storage mechanism of a supercapacitor according to an embodiment of the present invention.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, since various changes may be made to the embodiments, the scope of the patent application is not limited or limited by these embodiments. It should be understood that all modifications, equivalents and substitutes for the embodiments are included in the scope of the rights.

The terms used in the examples are used for the purpose of description only, and should not be construed as limiting. The singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprise" or "have" are intended to designate that a feature, number, step, operation, component, part, or a combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiment belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

In addition, in the description with reference to the accompanying drawings, the same components are given the same reference numerals regardless of the reference numerals, and the overlapping description thereof will be omitted. In describing the embodiment, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the embodiment, the detailed description thereof will be omitted.

In addition, in describing the components of the embodiment, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are only for distinguishing the elements from other elements, and the essence, order, or order of the elements are not limited by the terms. When it is described that a component is "connected", "coupled" or "connected" to another component, the component may be directly connected or connected to the other component, but another component is between each component. It will be understood that may also be "connected", "coupled" or "connected".

Components included in one embodiment and components having a common function will be described using the same names in other embodiments. Unless otherwise stated, descriptions described in one embodiment may be applied to other embodiments as well, and detailed descriptions within the overlapping range will be omitted.

One aspect of the present invention, comprising the steps of preparing a primary carbon fiber bundle in the form of two or more carbon fibers twisted; surface-treating the primary carbon fiber bundle with an acidic solution; forming an encapsulated carbon fiber bundle by first coating the surface of the surface-treated primary carbon fiber bundle with a gel electrolyte; and twisting two or more of the encapsulated carbon fiber bundles to form a secondary carbon fiber bundle, and secondary coating with a gel electrolyte.

In the method for manufacturing a flexible supercapacitor according to the present invention, an encapsulated carbon fiber bundle is obtained by using a primary carbon fiber bundle in which a plurality of carbon fibers are twisted, and a secondary carbon fiber is obtained by twisting two or more encapsulated carbon fiber bundles again. By forming a bundle, an electrode is formed, and a flexible supercapacitor is manufactured by coating the surface of the twisted secondary carbon fiber bundle with a gel electrolyte to form a gel electrolyte layer.

In addition, by activating the carbon fiber surface, wettability at the electrode interface is improved to promote ion diffusion, improve thermal stability, and generate a pseudocapacitive Faraday redox reaction to secure high energy and high power density. It has the characteristics to secure excellent flexibility and thermal stability.

Hereinafter, the manufacturing method of the flexible supercapacitor according to the present invention will be described in detail step by step.

In the method for manufacturing a flexible supercapacitor according to the present invention, the first step is to prepare a primary carbon fiber bundle in which two or more carbon fibers are twisted as an electrode material.

Carbon fiber is a very thin fiber whose main component is carbon, and the atoms constituting the carbon fiber are attached in the form of hexagonal ring crystals along the length direction of the fiber, and have strong physical properties due to this molecular arrangement structure. In addition, carbon fiber has characteristics such as high tensile strength, light weight, and low coefficient of thermal expansion, and thus can be used as a material in various fields.

The primary carbon fiber bundle, in the form of a plurality of carbon fibers twisted, is an electrode material for obtaining excellent energy storage ability and flexibility. In addition, it has high electrical conductivity and can operate as a current collector.

According to one embodiment, the primary carbon fiber bundle may use a carbon fiber bundle composed of 3K filaments.

According to an embodiment, the primary carbon fiber bundle may be in a form in which two or more carbon fibers are twisted in a Z-shape or S-shape and tightened.

In the primary carbon fiber bundle, the carbon fiber is twisted in a Z-shape or S-shape and tightened, thereby improving the flexibility and mechanical stability of the surface area.

Next, the step of surface-treating the primary carbon fiber bundle with an acidic solution is a step of activating the surface by surface-treating the prepared primary carbon fiber bundle with an acidic solution.

For example, after immersing the primary carbon fiber bundle in an acidic solution, the surface can be treated by maintaining it for a certain time. At this time, by immersing the carbon fiber bundle in the acidic solution, the carbon fiber surface activation can be sufficiently achieved. .

According to an embodiment, the acidic solution may include a compound having an oxygen atom, and through this, an oxygen-containing functional group may be introduced to the surface of the carbon fiber.

According to one embodiment, the acidic solution is nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), phosphoric acid (H ₃ PO ₄ ), perchloric acid (HClO ₄ ), acetic acid (CH ₃ COOH) and carbonic acid (H ₂ ) CO ₃ ) It may include one or more selected from the group consisting of.

According to an embodiment, the acidic solution may further include at least one of hydrofluoric acid (HF) and hydrochloric acid (HCl).

According to one embodiment, the surface treatment step may be performed for 1 minute to 30 minutes.

If the time range of the surface treatment step is less than the above range, the oxygen-containing functional group may not be sufficiently introduced to the surface, and if it exceeds the above range, the difference in effect due to the surface treatment is not large, so unnecessary process time may be taken, It is possible to change the mechanical properties of carbon fibers.

According to an embodiment, the surface-treated primary carbon fiber bundle includes an oxygen-containing functional group, and the oxygen-containing functional group includes at least one selected from the group consisting of a carbonyl group, a carboxyl group and a hydroxyl group. .

The oxygen-containing functional group may improve wettability on the carbon fiber surface to promote ion diffusion at the electrode interface, thereby improving charge connection at high current density. In addition, thermal stability can be improved by forming a stable interface between the electrode and the gel electrolyte, and the specific capacity of the supercapacitor can be increased by performing a pseudocapacitive Faraday redox reaction with protons of the electrolyte on the carbon fiber surface.

According to an embodiment, the surface-treated primary carbon fiber bundle may include oxygen in an amount of 10 atomic% to 40 atomic%.

If the oxygen is included below the above range, the effect of improving the electrochemical performance according to the oxygen-containing functional group may be insignificant. can decrease.

The next step, forming the encapsulated carbon fiber bundle, is a step of first coating the surface of the surface-treated primary carbon fiber bundle with a gel electrolyte.

The encapsulated carbon fiber bundle, finally, may act as a positive electrode and a negative electrode of a supercapacitor, and a current collector.

According to one embodiment, the gel electrolyte, polyvinyl alcohol (PVA), phosphoric acid (H ₃ PO ₄ ), sulfuric acid (H ₂ SO ₄ ), sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca (OH) ₂ ) and magnesium hydroxide (Mg(OH) ₂ ) may include one or more selected from the group consisting of.

The primary coating with the gel electrolyte can maximize electrochemical performance and improve mechanical stability by reducing the void space in the supercapacitor.

According to an embodiment, the thickness of the first coated gel electrolyte may be 0.01 mm to 5.00 mm.

If, if the thickness of the first coated gel electrolyte is less than the above range, the carbon fiber bundle coated electrolyte? It may be exposed and cause an electrical short of the supercapacitor, and if it exceeds the above range, it may not be easily twisted and it may be difficult to form a secondary carbon fiber bundle.

A subsequent step is a step of twisting two or more of the encapsulated carbon fiber bundles to form a secondary carbon fiber bundle, and secondary coating with a gel electrolyte.

According to one embodiment, the secondary carbon fiber bundle, two or more of the encapsulated carbon fiber bundle may be twisted in an S-shape or Z-shape.

The secondary carbon fiber bundle in which the encapsulated carbon fiber bundle is twisted may improve structural stability.

In addition, through two or more twisting (twisting) processes of the carbon fiber, it is possible to maximize the activation area by minimizing the void space in the supercapacitor as well as mechanical stability.

According to an embodiment, the encapsulated carbon fiber bundle may act as a positive electrode, a negative electrode, or a current collector.

According to an embodiment, the secondary carbon fiber bundle may be formed by twisting the two encapsulated carbon fiber bundles in an S shape.

At this time, one of the encapsulated carbon fiber bundles may act as a cathode, and the other may act as an anode.

According to one embodiment, the thickness of the secondary coated gel electrolyte may be formed to be 1 to 2 times the diameter of the secondary carbon fiber bundle.

According to an embodiment, the diameter of the encapsulated carbon fiber bundle may be 300 μm to 800 μm.

Preferably, the diameter of the encapsulated carbon fiber bundle may be 400 μm to 700 μm, and more preferably, 450 μm to 600 μm.

The encapsulated carbon fiber bundle may act as an electrode of a supercapacitor.

The method for manufacturing a flexible supercapacitor according to the present invention can optimize the electrochemical performance, mechanical properties and flexibility of the supercapacitor by adjusting the diameter of the encapsulated carbon fiber bundle forming the electrode and the thickness of the gel electrolyte layer within the above ranges. can

Another aspect of the present invention provides an electrode comprising a secondary carbon fiber bundle in which two or more encapsulated carbon fiber bundles are twisted; and a gel electrolyte coating layer formed on the surface of the secondary carbon fiber bundle, wherein the encapsulated carbon fiber bundle is coated with an electrolyte gel by twisting two or more primary carbon fibers.

According to one embodiment, the encapsulated carbon fiber bundle may have an oxygen-containing functional group on the surface.

According to an embodiment, the contact angle with respect to water may be 104° or less.

According to an embodiment, the contact angle with respect to water may be 95° or less, and preferably, 62° or less.

That is, the wettability is improved because the contact angle for water at the interface is lower than that of the carbon fiber without surface treatment, and the improvement of the wettability promotes ion diffusion between the electrode and the electrolyte, thereby improving the electrochemical performance of the supercapacitor.

According to an embodiment, the surface-treated primary carbon fiber bundle includes an oxygen-containing functional group, and the oxygen-containing functional group includes at least one selected from the group consisting of a carbonyl group, a carboxyl group and a hydroxyl group. .

According to an embodiment, the specific capacitance at a voltage of 0 V to 1 V and a current density of 2 μA/cm ² to 15 μA/cm ² may be 2 mF/cm ² to 30 mF/cm ² have.

According to an embodiment, the capacity retention rate after 10,000 charge/discharge cycles at a current density of 250 μA/cm ² may be 90% or more.

According to one embodiment, after heating at 50° C. to 80° C. for 30 minutes to 120 minutes, the capacity retention rate after 10,000 charge/discharge cycles at a current density of 250 μA/cm ² may be 92% or more.

The supercapacitor according to the present invention has excellent cycling stability and, in particular, exhibits excellent cycling stability even after heating, thereby exhibiting improved thermal stability.

According to an embodiment, the flexible supercapacitor may be an electric double layer capacitor (EDLC).

The flexible supercapacitor according to the present invention exhibits an electric double layer behavior and a pseudocapacitive Faraday redox reaction at the same time, thereby increasing the amount of electroactive sites to improve energy storage ability.

The flexible supercapacitor according to the present invention has characteristics of maintaining electrochemical performance and flexibility even in a shape deformation such as a straight line, bending, knotting, folding or rolling state. Therefore, it has the advantage of being applicable to various wearable electronic applications.

Hereinafter, the present invention will be described in more detail by way of Examples and Comparative Examples.

However, the following examples are only for illustrating the present invention, and the content of the present invention is not limited to the following examples.

<Example>

The carbon fiber bundles were twisted in a Z-shape and immersed in nitric acid (HNO ₃ ) for a certain time (5 minutes, 15 minutes, 30 minutes) and then rinsed with distilled water. A gel electrolyte (PVA, H ₃ PO ₄ ) was applied to the carbon fiber bundle surface-treated with nitric acid, and then dried. After that, the carbon fiber bundle encapsulated with the gel electrolyte was twisted again and coated with the gel electrolyte to prepare a supercapacitor.

1 is a diagram schematically illustrating a method of manufacturing a supercapacitor electrode according to an embodiment of the present invention.

Referring to FIG. 1 , first, a primary carbon fiber bundle in a tightened form is prepared by twisting carbon fibers, and immersing it in an acidic solution to activate the surface. After washing the surface-activated primary carbon fiber bundle, PVA-H ₃ PO ₄ gel electrolyte is applied with a brush to obtain an encapsulated carbon fiber bundle. Then, after twisting the encapsulated carbon fiber bundle again, PVA-H ₃ PO ₄ gel electrolyte is applied with a brush to obtain a final supercapacitor.

<Comparative example>

A supercapacitor was manufactured using a polymer gel composed of polyvinyl alcohol (PVA) and phosphoric acid (H ₃ PO ₄ ) as an electrolyte and carbon fiber as a positive electrode, negative electrode, or current collector.

<Experimental Example 1> Confirmation of morphological characteristics of supercapacitors

In order to confirm the morphological characteristics of the supercapacitors, the morphologies of Comparative Examples and Examples were confirmed by SEM images.

In the case of Examples, SEM images of supercapacitors each manufactured according to the surface treatment time were checked.

2 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) of low magnification SEM images (top) and A high magnification SEM image (bottom) is shown, and FIG. 3 is a photograph of the manufactured supercapacitor and an SEM image of a low magnification cross section and a high magnification cross section of Example 3 (F-SSEE@30).

Referring to FIG. 2 , it can be confirmed that the diameter of the individual carbon fibers constituting the manufactured capacitor is about 8 μm to 9 μm, and it can be confirmed that no morphological change occurs due to the surface treatment.

Referring to FIG. 3 , it can be seen that in Example 3 (F-SSEE@30), the diameter of each electrode is 450 μm to 600 μm, and the total outer diameter of the supercapacitor including the gel electrolyte coating layer is 1.5 mm.

In addition, it can be confirmed that the interface between the electrode composed of carbon fibers and the gel electrolyte is densely attached without empty space, and thus it can be seen that excellent mechanical properties can be secured.

<Experimental Example 2> Analysis of components and crystal structure of supercapacitors

In order to confirm the composition and crystal structure of the supercapacitor, Comparative Example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) Thermogravimetric analysis (TGA) and X-ray diffraction analysis (XRD) were performed on the supercapacitor.

The thermogravimetric analysis was performed at a temperature between 200 °C and 900 °C in air.

4 is a TGA analysis result of the comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) supercapacitors.

Referring to FIG. 4 , it can be seen that 100% weight loss of all fibers occurs, which shows that only one carbon phase exists without impurities.

In addition, the weight loss curve was found to shift as the temperature increased, indicating that oxygen-containing functional groups were introduced to the carbon fiber surface.

5 is an XRD analysis result of the supercapacitors of Comparative Example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), and Example 3 (F-SSEE@30).

Referring to FIG. 5 , the crystal structures of all supercapacitors exhibited diffraction peaks at about 26°, which corresponds to the (002) plane of graphite.

<Experimental Example 3> XPS spectrum of supercapacitor

In order to analyze the chemical bonding state of the carbon fiber surface according to the surface modification, X-ray photoelectron spectroscopy (XPS, X-ray Photoelectron Spectroscopy) was performed.

6 is an XPS analysis result of the comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), and Example 3 (F-SSEE@30) supercapacitors.

Referring to FIG. 6 , in the upper C 1s spectrum, it can be seen that the concentration of oxygen atoms increases as the surface activation time increases, and in particular, it can be seen that the increase of the C=O group is remarkably increased.

In addition, looking at the O 1s spectrum at the bottom, it can be seen that the peak is decomposed into chemically adsorbed oxygen at 535.3 eV, C = O bond at 531.3 eV, and C-O bond at 533.5 eV, Example 3 rather than Comparative Example (F-S) It can be seen that the intensity of the C=O binding peak clearly increases in the (F-SSEE@30) spectrum, which is consistent with the corresponding C 1s spectrum.

7 is an XPS integrated analysis result of a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) supercapacitors .

Referring to FIG. 7 , as the surface activation time increased, the ratio of oxygen-containing functional groups decreased in Comparative Examples (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15) and Examples. It can be seen that 3 (F-SSEE@30) gradually increases to 33 %, 43 %, 55 %, and 65 % in the order.

In addition, it can be seen that the percentage of carbonyl groups gradually increases as the surface activation time increases. These results show that the surface activation process effectively introduces carbonyl and carboxyl groups to the surface of carbon fibers.

8 is a diagram showing the surface of the carbon fiber into which oxygen-containing functional groups are introduced.

Referring to FIG. 8 , it is shown that introduction of oxygen-containing functional groups on the surface promotes redox reaction with protons in an acidic electrolyte, leading to high capacitance.

<Experimental Example 4> Evaluation of wettability at the supercapacitor interface

In order to confirm the wettability improvement effect according to the surface modification, Comparative Example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) The contact angle with respect to water at the supercapacitor interface was confirmed.

9 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) showing the contact angle at the supercapacitor interface will be.

Referring to FIG. 9 , the contact angle at the interface of the comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) supercapacitor It can be seen that these appear as 115 °, 104 °, 93 °, and 62 °, respectively.

This is because the increase in oxygen-containing groups improves the wettability between the electrode and the electrolyte, leading to favorable ion transport during cycling, thereby improving capacitance.

<Experimental Example 5> Evaluation of electrochemical performance of supercapacitors

To evaluate the electrochemical performance of the supercapacitor, it was analyzed through electrochemical impedance spectroscopy (EIS).

EIS was performed in a frequency range of 10 ⁵ to 10 ^-2 Hz with an AC signal of 5 mV, and cyclic voltammetry (CV) was performed using a potentiostat/galvanostat.

10 shows a schematic configuration of a supercapacitor according to an embodiment of the present invention.

Referring to FIG. 10 , in the supercapacitor according to an embodiment of the present invention, it is confirmed that the encapsulated carbon fiber bundle constitutes two electrodes, exhibits an electric double layer behavior, and a redox reaction is performed by an oxygen-containing functional group on the surface. can

11 is a Nyquist plot according to the comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) supercapacitor EIS analysis. to be.

Referring to FIG. 11 , Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) supercapacitors exhibited a linear slope in the low-frequency region, so that the electrolyte and It shows ion diffusion at the interface between the electrodes, and in particular, Example 3 (F-SSEE@30) shows the steepest slope, so it can be seen that the ion diffusion performance is the best.

12 is a Bode plot of the supercapacitors of Comparative Example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), and Example 3 (F-SSEE@30).

Referring to FIG. 12 , it can be seen that capacitive behavior at low frequencies is related to ion diffusion, and a phase angle approaching -90° represents an ideal capacitive behavior.

When the relaxation time constant (τ ₀ ) is calculated using the equation τ ₀ = 1/f ₀ , Comparative Example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) was reduced to 1.2 sec, 0.8 sec, 0.5 sec, and 0.2 sec in the order, and it can be seen that a fast response time was obtained as a result of faster charge transfer due to improved wettability.

13 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) 2 μA / cm ² of supercapacitors This is the charge/discharge curve at the current density.

Referring to FIG. 13 , it can be confirmed that the charging/discharging curve of the embodiment shows the general curve characteristics of the supercapacitor, and shows excellent reversibility because the charging and discharging processes have almost the same time.

14 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) 0 V to 1 V of supercapacitors The potential and specific capacity at 2 μA/cm ² to 15 μA/cm ² current density are shown.

14, Comparative Example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) 2 μA / of supercapacitors The specific capacity at cm ² was calculated as 5 mF/cm ² , 16 mF/cm ² , 20 mF/cm ² , and 26 mF/cm ² , respectively, confirming that the specific capacity increased as the surface treatment time increased. have. This is due to the pseudocapacitive reaction of the oxygen-containing functional group.

In addition, although the specific capacity decreases as the current density increases, the specific capacity of the supercapacitor of Example 3 (F-SSEE@30) is 14 mF/cm ² It can be seen that high performance is maintained, and the capacity retention rate is It can be seen that F-SSEE@30) shows the highest value.

These results indicate that the surface modification of the carbon fiber promotes ion diffusion as the wettability is improved, thereby improving the charge connection at high current density.

<Experimental Example 4> Evaluation of energy density, power density and cycling stability of supercapacitors

The energy density and power density of the supercapacitor were calculated using the charge/discharge curve and specific capacity obtained in Example 3 (F-SSEE@30) supercapacitor.

15 is a Ragone plot of Example 3 (F-SSEE@30) supercapacitors associated with energy and power densities ranging from 4 μW/cm ² to 30 μW/cm ² .

Referring to FIG. 15 , Example 3 (F-SSEE@30) exhibits high energy densities in the range of 3.5 - 2.0 μWh/cm ² and excellent power densities in the range of 4 - 30 μW/cm ² , much higher than the reported supercapacitors. You can check what you have.

16 shows the capacity retention rate when the flexible supercapacitor according to an embodiment of the present invention is changed into various shapes.

Referring to FIG. 16 , it can be confirmed that the capacity of the supercapacitor is maintained in a straight line, bent, knotted, folded, and wound state, thereby exhibiting excellent mechanical flexibility.

In addition, it can be seen that the surface activation method is a method capable of manufacturing a flexible fiber-based supercapacitor without impairing electrochemical performance.

17 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) 2 μA / cm ² of supercapacitors Cycling stability test results at current density.

Referring to FIG. 17 , it can be seen that all examples have excellent cycling stability than comparative examples, and in the case of Example 3 (F-SSEE@30) supercapacitors exhibit excellent cycling stability by maintaining 95% capacity even after 10,000 cycles. can

This is a result of improved ion diffusion through improved wettability.

<Experimental Example 5> Evaluation of thermal stability of supercapacitors

To evaluate the thermal stability of the supercapacitors, Comparative Examples (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) supercapacitors was heated in an oven at 70 ° C. for 1 hour, and then electrochemical performance was evaluated through EIS analysis.

18 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) After heating the supercapacitor, EIS analysis It is a Nyquist plot according to

Referring to FIG. 18 , it can be seen that the initial ion diffusion performance is maintained in the case of the supercapacitor of Example 3 (F-SSEE@30).

19 is a comparative example (FS), Example 1 (F-SSEE@5), Example 2 (F-SSEE@15), Example 3 (F-SSEE@30) After heating the supercapacitor, 10,000 cycles capacity retention during the period.

Referring to FIG. 19 , it can be seen that the capacity retention ratio of all examples is higher than that of the comparative example, and in particular, in the case of Example 3 (F-SSEE@30) supercapacitor, it can be seen that the supercapacitor exhibits a high capacity retention ratio of 92% even after heating.

Through this, it can be seen that the increase in oxygen-containing functional groups on the carbon fiber surface improves the thermal stability at the interface between the electrode and the gel electrolyte.

20 shows an electrochemical storage mechanism of a supercapacitor according to an embodiment of the present invention.

Referring to FIG. 20 , the combination of the electric double layer and the pseudocapacitance substantially increases the amount of electrically active sites to improve the energy storage capacity, and the improved wettability of the surface-treated carbon fiber promotes ion diffusion during cycling, resulting in high current density. It can be seen that the high-speed performance, cycle life and thermal stability can be improved by improving the charge connection in

As described above, although the embodiments have been described with reference to the limited drawings, those skilled in the art may apply various technical modifications and variations based on the above. For example, the described techniques are performed in an order different from the described method, and/or the described components of the system, structure, apparatus, circuit, etc. are combined or combined in a different form than the described method, or other components Or substituted or substituted by equivalents may achieve an appropriate result.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (11)

Preparing a primary carbon fiber bundle in the form of two or more carbon fibers twisted in a Z-shape or S-shape;
surface-treating the primary carbon fiber bundle with an acidic solution;
forming an encapsulated carbon fiber bundle by first coating the surface of the surface-treated primary carbon fiber bundle with a gel electrolyte; and
Twisting two or more of the encapsulated carbon fiber bundles in an S-shape or Z-shape to form a secondary carbon fiber bundle, and secondary coating with a gel electrolyte;
The surface-treated primary carbon fiber bundle includes an oxygen-containing functional group on the surface,
The oxygen-containing functional group will include at least one selected from the group consisting of a carbonyl group, a carboxyl group and a hydroxyl group,
A method for manufacturing a flexible supercapacitor.
delete According to claim 1,
The acidic solution is
At least one selected from the group consisting of nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), phosphoric acid (H ₃ PO ₄ ), perchloric acid (HClO ₄ ), acetic acid (CH ₃ COOH), and carbonic acid (H ₂ CO ₃ ) which includes,
A method for manufacturing a flexible supercapacitor.
According to claim 1,
The surface-treated primary carbon fiber bundle, which includes oxygen in an amount of 10 to 40 atomic% on the surface,
A method for manufacturing a flexible supercapacitor.
According to claim 1,
The gel electrolyte is
Polyvinyl alcohol (PVA), phosphoric acid (H ₃ PO ₄ ), sulfuric acid (H ₂ SO ₄ ), sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH) ₂ ), and magnesium hydroxide (Mg( OH) ₂ ) comprising at least one selected from the group consisting of,
A method for manufacturing a flexible supercapacitor.
delete According to claim 1,
The encapsulated carbon fiber bundle,
Which acts as a positive electrode, negative electrode or current collector,
A method for manufacturing a flexible supercapacitor.
According to claim 1,
The thickness of the secondary coated gel electrolyte is,
Which is formed in 1 to 2 times the diameter of the secondary carbon fiber bundle,
A method for manufacturing a flexible supercapacitor.
According to claim 1,
The diameter of the encapsulated carbon fiber bundle is,
300 μm to 800 μm,
A method for manufacturing a flexible supercapacitor.
an electrode comprising a secondary carbon fiber bundle in which two or more encapsulated carbon fiber bundles are twisted in an S-shape or a Z-shape; and
Including; a gel electrolyte coating layer formed on the surface of the secondary carbon fiber bundle;
The encapsulated carbon fiber bundle, the primary carbon fiber bundle is coated with a gel electrolyte,
The primary carbon fiber bundle is a form in which two or more primary carbon fibers are twisted into an S-shape or a Z-shape,
The primary carbon fiber bundle includes an oxygen-containing functional group on the surface,
The oxygen-containing functional group will include at least one selected from the group consisting of a carbonyl group, a carboxyl group and a hydroxyl group,
Flexible supercapacitors. delete

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