KR102585145B1 - Surface-activated carbon fiber electrode, manufacturing method of the same, flexible fibrous supercapacitor comprising the same and manufacturing method of flexible fibrous supercapacitor - Google Patents

Abstract

The present invention relates to a surface-activated carbon fiber electrode, a manufacturing method thereof, a flexible fiber-type supercapacitor, and a method of manufacturing a flexible fiber-type supercapacitor. The surface-activated carbon fiber electrode according to an embodiment of the present invention is a carbon fiber electrode. It contains oxygen-containing groups on its surface and has micropores.

Description

Surface-activated carbon fiber electrode, manufacturing method thereof, flexible fiber-type supercapacitor, and manufacturing method of flexible fiber-type supercapacitor FIBROUS SUPERCAPACITOR}

The present invention relates to a surface-activated carbon fiber electrode, a manufacturing method thereof, a flexible fiber-type supercapacitor, and a method of manufacturing a flexible fiber-type supercapacitor.

Flexible fiber-based e-textiles are considered to provide a future intelligent platform with substantial potential to expand the range of electronic applications in wearable technologies. In this regard, energy storage devices composed of flexible fibers are a key feature for efficient powering and operation of wearable electronic textiles in bent, knotted and rolled states.

Recently, much research has been conducted to obtain electrode materials suitable for flexible supercapacitors that can withstand extreme situations such as bent, knotted, and rolled states. Carbon fiber, as a flexible fiber-based electronic fiber, has excellent flexibility and mechanical properties. Its strength makes it an ideal candidate for electrode material in flexible supercapacitors. In addition, carbon fiber can serve as an active material and a current collector at the same time, and can be advantageous in the production of a fibrous flexible supercapacitor (FFS) with high flexibility, wearability, and excellent mechanical properties by twisting several fibers. there is. Additionally, carbon fiber based on electrical double layer capacitors (EDLC) can further meet the requirements of flexible energy storage systems due to its easy manufacturing process, high power density, and excellent long-term stability. Therefore, these advantages can be easily applied to wearable electronic systems, making fiber-type supercapacitors a desirable alternative to existing supercapacitors and LIBs (lithium-ion batteries).

However, the application of fibrous supercapacitors composed of carbon fiber electrodes and gel electrolytes has the disadvantages of low capacitance, low rate performance, and low lifetime stability due to inefficient use of the interface between electrodes as well as low mechanical flexibility.

Therefore, there is an urgent need for the development and research of flexible fiber-based electronic fibers, namely carbon fibers, that can improve electrochemical performance and mechanical properties for application to wearable device systems.

In order to solve the above-mentioned problems, the present invention provides a surface-activated carbon fiber electrode with long-term cycling stability and improved energy storage performance by increasing the surface area, increasing the specific surface area, increasing the oxygen containing group, and increasing wettability, a manufacturing method thereof, and a flexible A method for manufacturing a fiber-type supercapacitor and a flexible fiber-type supercapacitor is provided.

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 description below.

The surface-activated carbon fiber electrode according to an embodiment of the present invention includes oxygen-containing groups on the surface of the carbon fiber and has micropores.

In one embodiment, the oxygen-containing group includes a hydroxyl group and a carbonyl group, and the content of the oxygen-containing group in the surface-activated carbon fiber electrode is 10 at. % to 60 at. It may be %.

In one embodiment, the oxygen-containing group is formed by a carbonized or graphitized polymer on the surface of the carbon fiber, and the polymer is polyvinylpyrrolidone (PVP) or polyvinylidene fluoride. ; PVDF), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polystyrene (PS), polymethyl methacrylate (PMMA), poly(n-butyl acrylate) )(poly(n-butyl acrylate); PBA), polyacrylonitrile (PAN), polyaniline (PANi), polyacrylic acid (PAA), polyester-amides (PEA) , polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyurethane (PU), polychloroprene, polyisoprene and poly It may contain at least one selected from the group consisting of butadiene (polybutadiene).

In one embodiment, the oxygen-containing group includes C-O, -OH, O-C=O, and -COOH bonds, and the C-O bond is 8 at. % to 15 at. %, the -OH bond is 4 at. % to 10 at. %, the O-C=O bond is 4 at. % to 10 at. %, and the -COOH bond is 2 at. % to 5 at. It may be %.

In one embodiment, the carbon fiber electrode may be made of two or more strands of carbon fiber twisted or woven.

In one embodiment, the carbon fiber electrode may have a Z-shaped twist structure, with a twist spacing of 10 ㎛ to 50 ㎛ and a twist angle of 25 ° to 75 °.

In one embodiment, the carbon fiber is a bundle of 1,000 to 10,000 filaments, and the individual fiber diameter of the carbon fiber may be 1 ㎛ to 50 ㎛.

In one embodiment, the carbon fiber has a specific surface area of 100 m ² g ^-1 to 300 m ² g ^-1 , a pore volume of 0.01 cm ³ g ^-1 to 0.20 cm ³ g ^-1 , and pores of 1 nm to 5 nm. It may include at least one of size and pore volume fraction of 35% to 40%.

A method of manufacturing a surface-activated carbon fiber electrode according to another embodiment of the present invention includes the steps of impregnating carbon fibers in a polymer solution and coating the carbon fibers with a polymer; and heat-treating the polymer-coated carbon fiber.

In one embodiment, before the step of impregnating the carbon fibers in a polymer solution and coating the carbon fibers with the polymer, the step of purifying the carbon fibers by immersing them in an acid solution, wherein the acid solution includes, It may contain at least one selected from the group consisting of nitric acid, phosphoric acid, and hydrofluoric acid.

In one embodiment, the polymer solution includes a polymer and a solvent, and the polymer is polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), and polyvinyl alcohol (polyvinyl alcohol). alcohol; PVA), polyvinyl acetate (PVAc), polystyrene (PS), polymethyl methacrylate (PMMA), poly(n-butyl acrylate) ; PBA), polyacrylonitrile (PAN), polyaniline (PANi), polyacrylic acid (PAA), polyester-amides (PEA), polyethylene (PE), poly selected from the group consisting of polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyurethane (PU), polychloroprene, polyisoprene, and polybutadiene It includes at least one, and the solvent may include at least one selected from the group consisting of ethanol, methanol, propanol, butanol, and isopropanol.

In one embodiment, the heat treatment of the polymer-coated carbon fiber is performed at a temperature of 300°C to 900°C; and air, or an atmosphere containing at least one of N ₂ to Ar.

In one embodiment, the step of twisting or weaving the heat-treated carbon fiber may be further included.

A flexible fiber-type supercapacitor according to another embodiment of the present invention includes a surface-activated carbon fiber electrode of an embodiment of the present invention; and a gel electrolyte coated on the surface-activated carbon fiber electrode.

In one embodiment, the gel electrolyte is polyvinyl alcohol (PVA), vanadium sulfate (VOSO ₄ ), zinc sulfate (ZnSO ₄ ), phosphoric acid (H ₃ PO ₄ ), sulfuric acid (H ₂ SO ₄ ), and sodium hydroxide. It may include at least one selected from the group consisting of (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH) ₂ ), and magnesium hydroxide (Mg(OH) ₂ ).

In one embodiment, there are at least two surface-activated carbon fiber electrodes coated with the gel electrolyte, and the two surface-activated carbon fiber electrodes coated with the gel electrolyte may be twisted into an S-shaped twist.

In one embodiment, the flexible fiber-type supercapacitor has an energy density of 500 μW h cm ^-2 to 1,000 μW h cm ^-2 at a current density ranging from 50 μW cm ^-2 to 500 μW cm ^-2 and 300 μW cm The capacitance retention rate may be 90% or more at a current density ranging from ^-2 to 500 μW cm ^-2 .

A method of manufacturing a flexible fiber-type supercapacitor according to another embodiment of the present invention includes the steps of impregnating carbon fibers in a polymer solution and coating the carbon fibers with a polymer; Preparing surface-activated carbon fiber by heat treating polymer-coated carbon fiber; and coating a gel electrolyte on the surface-activated carbon fiber.

In one embodiment, the step of coating the gel electrolyte on the surface-activated carbon fiber includes twisting or weaving the surface-activated carbon fiber and then coating the gel electrolyte on the surface-activated carbon fiber, or A gel electrolyte is coated on surface-activated carbon fiber, and the coating may include brush painting, spray coating, spin coating, or dip coating. there is.

The surface-activated carbon fiber electrode according to the present invention has an increased surface area due to the dehydrogenation reaction of the polymer by heat treatment, and the number of electrochemically active sites and ion diffusion are increased due to the increase in surface area and the oxygen-containing group on the surface of the carbon fiber, respectively. This can be improved. Additionally, improved wettability can be achieved in relation to the increase in the number of oxygen-containing groups on the surface of the carbon fiber.

The flexible fiber-type supercapacitor according to an embodiment of the present invention can provide a high-performance fiber-type flexible supercapacitor with high electrochemical performance and mechanical flexibility by applying a surface-activated carbon fiber electrode and a redox gel electrolyte. The surface area increases due to the dehydrogenation reaction of the polymer by heat treatment, and the number of electrochemically active sites and ion diffusion can be improved by increasing the surface area and increasing the oxygen-containing groups on the surface of the carbon fiber, respectively. In addition, the enhanced wettability associated with the increase in the number of oxygen-containing groups on the surface of the carbon fiber can effectively utilize the interface between the denser electrode and the electrolyte to improve ultra-high-speed cycling stability. Additionally, the introduction of redox gel electrolyte and reaction with hydroxyl and carbonyl groups on the carbon surface through oxygen transfer improved the charge storage ability.

Therefore, the microporosity of surface-activated carbon fiber not only provides excellent electrochemical dynamics and energy storage performance, but also provides excellent capacitance retention in stretching, bending, knotting, folding, and curling states due to excellent mechanical flexibility.

Figure 1 is a schematic diagram of a surface-activated carbon fiber electrode according to an embodiment of the present invention.
Figure 2 is a schematic diagram of the manufacturing process of a surface-activated carbon fiber electrode according to an embodiment of the present invention.
Figure 3 is a schematic diagram of a flexible fiber-type supercapacitor according to an embodiment of the present invention.
Figure 4 is a schematic diagram showing the manufacturing process of a flexible fiber supercapacitor (FFS-SARE) including a surface-activated carbon fiber electrode and a redox electrolyte according to an embodiment of the present invention.
Figure 5 is a diagram showing the shape and structural characteristics of carbon fiber and surface-activated carbon fiber according to an embodiment of the present invention.
Figure 6 is a diagram showing the chemical composition and wettability of carbon fiber and surface-activated carbon fiber according to an embodiment of the present invention.
Figure 7 is a diagram showing the surface properties and thermal properties of carbon fiber and surface-activated carbon fiber according to an embodiment of the present invention. This is a graph showing the results of (a) BET method, (b) micropore analysis, and (c) differential scanning calorimetry.
Figure 8 is a photograph and (b) a Raman spectrum of a vial containing (a) deionized water, H ₃ PO ₄ -PVA gel electrolyte, and VOSO ₄ -H ₃ PO ₄ -PVA gel electrolyte according to an embodiment of the present invention; c) Ionic conductivity of H ₃ PO ₄ -PVA VOSO ₄ -H ₃ PO ₄ -PVA gel electrolyte, (d) photograph of fabricated supercapacitor, (e) low magnification SEM image and (f) low magnification and (g) FFS- This is a high-magnification cross-sectional SEM image of SARE.
9 shows CV curves, (c) charge of (a) H ₃ PO ₄ -PVA and (b) VOSO ₄ -H ₃ PO ₄ -PVA aqueous electrolytes obtained using a three-electrode system according to an embodiment of the present invention. This is a diagram showing the oxidation-reduction reaction between hydroxyl and carbonyl groups on the ^surface of surface-activated carbon fiber and VO ²⁺ /VO ₂₊ during the discharge process.
Figure 10 shows the results of electrochemical dynamics analysis according to an embodiment of the present invention.
Figure 11 shows the results of an energy storage performance test according to an embodiment of the present invention.
Figure 12 shows (a) the capacitance retention rate of the straight, bent, knotted, folded, and wound states of the FFS-SARE, (b) the mechanical characteristics of the FFS-SARE during 100 repetitions in the flat and bent states, according to an embodiment of the present invention. Flexibility, (c) a photograph showing the large-scale weaving of three FFS-SARE devices into a fabric, (d) a diagram showing the capacitance retention of FFS-SARE devices woven into a fabric for different fabric states (straight and crumpled).
Figure 13 is a schematic diagram showing the increase in electrochemically active sites, efficient ion diffusion, and reversible Faraday reaction of FFS-SARE according to an embodiment of the present invention.

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

The terms used in the examples are for descriptive purposes only and should not be construed as limiting. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, 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 generally understood by a person of ordinary skill in the technical field to which the embodiments belong. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and unless explicitly defined in the present application, should not be interpreted in an ideal or excessively formal sense. No.

In addition, when describing with reference to the accompanying drawings, identical components will be assigned the same reference numerals regardless of the reference numerals, and overlapping descriptions thereof will be omitted. In describing the embodiments, if it is determined that detailed descriptions of related known technologies may unnecessarily obscure the gist of the embodiments, the detailed descriptions are omitted.

Additionally, in describing the components of the embodiment, terms such as first, second, A, and B may be used. These terms are only used to distinguish the component from other components, and the nature, sequence, or order of the component is not limited by the term.

Components included in one embodiment and components including common functions will be described using the same names in other embodiments. Unless stated to the contrary, the description given in one embodiment may be applied to other embodiments, and detailed description will be omitted to the extent of overlap.

The surface-activated carbon fiber electrode according to an embodiment of the present invention includes oxygen-containing groups on the surface of the carbon fiber and has micropores.

Figure 1 is a schematic diagram of a surface-activated carbon fiber electrode according to an embodiment of the present invention.

As shown in FIG. 1, the surface-activated carbon fiber electrode according to an embodiment of the present invention may be microporous and include a plurality of micropores.

In one embodiment, the oxygen-containing groups include a hydroxyl group and a carbonyl group, and the content of the oxygen-containing groups in the surface-activated carbon fiber electrode is 10 at. % to 60 at. It may be %.

In one embodiment, the oxygen-containing group may improve wettability of the surface-activated carbon fiber.

In one embodiment, the oxygen-containing group may be formed by a carbonized or graphitized polymer on the surface of the carbon fiber.

In one embodiment, the surface area increases due to the dehydrogenation reaction of the polymer by heat treatment, and the number of electrochemically active sites and ion diffusion can be improved due to the increase in surface area and the increase in oxygen-containing groups on the surface of the carbon fiber, respectively. .

In one embodiment, the polymer is polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and polyvinyl acetate (polyvinyl acetate). PVAc), polystyrene (PS), polymethyl methacrylate (PMMA), poly(n-butyl acrylate) (PBA), polyacrylonitrile (PAN) ), polyaniline (PANi), polyacrylic acid (PAA), polyester-amides (PEA), polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene It may contain at least one selected from the group consisting of polyvinylidene chloride (PVDC), polyurethane (PU), polychloroprene, polyisoprene, and polybutadiene.

In one embodiment, the polymer may be preferably polyvinylpyrrolidone (PVP).

In one embodiment, the oxygen-containing group includes C-O, -OH, O-C=O, and -COOH bonds, and the C-O bond is 8 at. % to 15 at. %, the -OH bond is 4 at. % to 10 at. %, the O-C=O bond is 4 at. % to 10 at. %, and the -COOH bond is 2 at. % to 5 at. It may be %.

In one embodiment, when the percentage of C-O, -OH, O-C=O and -COOH bond atoms among the oxygen-containing groups is outside the above range, surface activation is not effective and the redox reaction is not promoted even when a redox electrolyte is introduced. This may result in a decrease in energy storage ability.

In one embodiment, the carbon fiber electrode may be in the form of a yarn with a twisted structure or may be a fabric in which the carbon fibers are woven. The fabric may be woven with the carbon fiber alone or with other fibers.

In one embodiment, the carbon fiber electrode may be made of two or more strands of carbon fiber twisted or woven.

In one embodiment, the carbon fiber electrode may be twisted into a Z-shaped twist structure. Additionally, the weave may be made of carbon fiber or the twisted carbon fiber, and if necessary, other fibers other than the carbon fiber according to the present invention may be further included.

In one embodiment, it has a Z twist configuration, for example, the twist spacing may be 10 μm to 50 μm and the twist angle may be 25° to 75°. If the twist interval and twist angle are within the range, it may be advantageous for improved electrochemical development and utilization of carbon fiber while maintaining mechanical properties and flexibility.

In one embodiment, the carbon fiber may be a bundle of 1,000 to 10,000 filaments.

In one embodiment, the number of carbon fibers is 1,000 to 8,000, 1,000 to 5,000, 1,000 to 3,000, 2,000 to 10,000, 2,000 to 8,000, 2,000 to 5,000, and 3,000 to 3,000. It may be a bundle of 10,000, 3,000 to 5,000 filaments.

Preferably, the carbon fiber may be a bundle of 3,000 or more filaments.

In one embodiment, the individual fiber diameter of the carbon fiber may be 1 ㎛ to 50 ㎛. If the diameter is within the above range, improved electrochemical performance of carbon fiber can be provided while maintaining mechanical flexibility. In other words, by adjusting the porous structure, the electrochemical reaction area can be expanded to improve the electrochemical active site and ion diffusion ability.

In one embodiment, the carbon fiber has a specific surface area of 100 m ² g ^-1 to 300 m ² g ^-1 , a pore volume of 0.01 cm ³ g ^-1 to 0.20 cm ³ g ^-1 , and pores of 1 nm to 5 nm. It may include at least one of size and pore volume fraction of 35% to 40%. The size may be length, diameter, thickness, etc. depending on the shape. In other words, the specific surface area can be increased by adjusting the porosity, and the pore size, volume fraction, etc. can be controlled by forming mesoporosity. If it is contained within the above-mentioned range, the electrochemical active site and ion diffusion ability can be improved, thereby improving capacity, high-rate performance, etc.

In one embodiment, the carbon fiber electrode may be used as an anode and/or a cathode.

A method of manufacturing a surface-activated carbon fiber electrode according to another embodiment of the present invention includes the steps of impregnating carbon fibers in a polymer solution and coating the carbon fibers with a polymer; and heat-treating the polymer-coated carbon fiber.

Figure 2 is a schematic diagram of the manufacturing process of a surface-activated carbon fiber electrode according to an embodiment of the present invention.

Referring to Figure 2, initial carbon fiber is prepared, a polymer such as PVP is coated on the carbon fiber, and heat treatment is performed to produce activated carbon fiber.

In one embodiment, before the step of impregnating the carbon fibers in a polymer solution and coating the carbon fibers with the polymer, the step of purifying the carbon fibers by immersing them in an acid solution may be further included.

In one embodiment, the acid solution may include at least one selected from the group consisting of nitric acid, phosphoric acid, and hydrofluoric acid.

Preferably, the acid solution may be nitric acid.

In one embodiment, the polymer solution may include a polymer and a solvent.

In one embodiment, the polymer is polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and polyvinyl acetate (polyvinyl acetate). PVAc), polystyrene (PS), polymethyl methacrylate (PMMA), poly(n-butyl acrylate) (PBA), polyacrylonitrile (PAN) ), polyaniline (PANi), polyacrylic acid (PAA), polyester-amides (PEA), polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene It may contain at least one selected from the group consisting of polyvinylidene chloride (PVDC), polyurethane (PU), polychloroprene, polyisoprene, and polybutadiene.

Preferably, the polymer may be polyvinylpyrrolidone (PVP).

In one embodiment, the solvent may include at least one selected from the group consisting of ethanol, methanol, propanol, butanol, and isopropanol.

Preferably, the solvent may be ethanol.

In one embodiment, the heat treatment of the polymer-coated carbon fiber is performed at a temperature of 300°C to 900°C; More than 30 minutes; More than 1 hour; 2 hours or more; 4 hours or more; 4 to 10 hours; Alternatively, it may be performed for 4 to 6 hours and in an atmosphere containing at least one of air or N ₂ to Ar. If it is within the above range, it is advantageous for the expression of a synergistic effect due to mesopore formation and diatomic co-doping, which may be advantageous for improving the electrochemical and mechanical properties and flexibility of surface-activated carbon fibers as well as improving energy storage performance.

Preferably, the heat treatment is performed at a temperature of 300°C to 500°C; And it may be performed in an air atmosphere.

In one embodiment, hydrogen and oxygen may be lost due to dehydrogenation of the polymer due to the heat treatment, and the surface may be formed into a fine pore structure during the dehydrogenation process involving carbon consumption.

In one embodiment, the step of twisting or weaving the heat-treated carbon fiber may be further included. For example, after the heat treatment step, the heat-treated carbon fibers can be twisted or woven, and two or more carbon fibers can be twisted or knotted in various twisted forms, or fabric can be formed using a generally known fiber weaving method. You can. The weaving method can be woven with the twisted carbon fibers and other fibers, or with the twisted carbon fibers, if necessary.

A flexible fiber-type supercapacitor according to another embodiment of the present invention includes a surface-activated carbon fiber electrode of an embodiment of the present invention; and a gel electrolyte coated on the surface-activated carbon fiber electrode.

Figure 3 is a schematic diagram of a flexible fiber-type supercapacitor according to an embodiment of the present invention.

Referring to FIG. 3, the flexible fiber-type supercapacitor 100 according to an embodiment of the present invention includes a surface-activated carbon fiber electrode 110 and a gel electrolyte 120.

In one embodiment, the surface-activated carbon fiber electrode 110 is manufactured by using a surface-activated carbon fiber electrode according to an embodiment of the present invention or a method of manufacturing a surface-activated carbon fiber electrode according to an embodiment of the present invention. It may be a surface-activated carbon fiber electrode manufactured by.

In one embodiment, the gel electrolyte is polyvinyl alcohol (PVA), vanadium sulfate (VOSO ₄ ), zinc sulfate (ZnSO ₄ ), phosphoric acid (H ₃ PO ₄ ), sulfuric acid (H ₂ SO ₄ ), and sodium hydroxide. It may include at least one selected from the group consisting of (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH) ₂ ), and magnesium hydroxide (Mg(OH) ₂ ).

In one embodiment, there are at least two surface-activated carbon fiber electrodes coated with the gel electrolyte, and the two surface-activated carbon fiber electrodes coated with the gel electrolyte may be twisted into an S-shaped twist.

In one embodiment, the flexible fiber-type supercapacitor has an energy density of 500 μW h cm ^-2 to 1,000 μW h cm ^-2 at a current density ranging from 50 μW cm ^-2 to 500 μW cm ^-2 and 300 μW cm It has a capacitance retention rate of more than 90% at a current density ranging from ^-2 to 500 μW cm ^-2 and can provide excellent ultra-high-speed cycling stability of more than 5,000 cycles and 10,000 cycles.

In one embodiment, the surface-activated carbon fiber electrode coated with the gel electrolyte has the functions of an anode, a cathode, and a current collector, and the carbon fibers are electrochemically separated through coating of the gel electrolyte, which leads to the anode and the anode. This may mean that the cathode is separated by the electrolyte.

The flexible fiber-type supercapacitor according to an embodiment of the present invention can provide improved electrochemical performance such as specific capacitance, rate performance, capacitance maintenance, and cycling stability.

A method of manufacturing a flexible fiber-type supercapacitor according to another embodiment of the present invention includes the steps of impregnating carbon fibers in a polymer solution and coating the carbon fibers with a polymer; Preparing surface-activated carbon fiber by heat treating polymer-coated carbon fiber; and coating a gel electrolyte on the surface-activated carbon fiber.

Figure 4 is a schematic diagram showing the manufacturing process of a flexible fiber supercapacitor (FFS-SARE) including a surface-activated carbon fiber electrode and a redox electrolyte according to an embodiment of the present invention.

Figure 4 shows (a) carbon fiber, (b) polymer-coated carbon fiber, (c) surface-activated carbon fiber, (d) VOSO ₄ gel electrolyte coating on the fiber surface, and (e) prepared FFS-SARE. .

In one embodiment, the step of coating the gel electrolyte on the surface-activated carbon fiber includes twisting or weaving the surface-activated carbon fiber and then coating the gel electrolyte on the surface-activated carbon fiber, or The gel electrolyte may be coated on the surface-activated carbon fiber.

In one embodiment, before the step of impregnating the carbon fibers in a polymer solution and coating the carbon fibers with the polymer, the step of purifying the carbon fibers by immersing them in an acid solution may be further included.

In one embodiment, the acid solution may include at least one selected from the group consisting of nitric acid, phosphoric acid, and hydrofluoric acid.

Preferably, the acid solution may be nitric acid.

In one embodiment, the polymer solution may include a polymer and a solvent.

In one embodiment, the polymer is polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and polyvinyl acetate (polyvinyl acetate). PVAc), polystyrene (PS), polymethyl methacrylate (PMMA), poly(n-butyl acrylate) (PBA), polyacrylonitrile (PAN) ), polyaniline (PANi), polyacrylic acid (PAA), polyester-amides (PEA), polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene It may contain at least one selected from the group consisting of polyvinylidene chloride (PVDC), polyurethane (PU), polychloroprene, polyisoprene, and polybutadiene.

Preferably, the polymer may be polyvinylpyrrolidone (PVP).

In one embodiment, the solvent may include at least one selected from the group consisting of ethanol, methanol, propanol, butanol, and isopropanol.

Preferably, the solvent may be ethanol.

In one embodiment, the coating may include brush painting, spray coating, spin coating, or dip coating.

In one embodiment, the polymer solution can be coated to the surface and/or interior of the carbon fiber using various coating methods, for example, a spray injection process, an impregnation (or immersion) process, etc. can be used.

In one embodiment, the heat treatment of the polymer-coated carbon fiber is performed at a temperature of 300°C to 900°C; More than 30 minutes; More than 1 hour; 2 hours or more; 4 hours or more; 4 to 10 hours; Alternatively, it may be performed for 4 to 6 hours and in an atmosphere containing at least one of air or N ₂ to Ar. If it is within the above range, it is advantageous for the expression of a synergistic effect due to mesopore formation and diatomic co-doping, which may be advantageous for improving the electrochemical and mechanical properties and flexibility of surface-activated carbon fibers as well as improving energy storage performance.

Preferably, the heat treatment is performed at a temperature of 300°C to 500°C; And it may be performed in an air atmosphere.

In one embodiment, hydrogen and oxygen may be lost due to dehydrogenation of the polymer due to the heat treatment, and the surface may be formed into a fine pore structure during the dehydrogenation process involving carbon consumption.

In the step of coating the gel electrolyte on the surface-activated carbon fiber, the coating includes brush painting, spray coating, spin coating, or dip coating. It may be.

In one embodiment, the gel electrolyte can be used to coat the surface and/or the inside of the surface-activated carbon fiber with a polymer solution using various coating methods, for example, a spray process, impregnation (or immersion). ) process, etc. can be used.

In one embodiment, the gel electrolyte is polyvinyl alcohol (PVA), vanadium sulfate (VOSO ₄ ), zinc sulfate (ZnSO ₄ ), phosphoric acid (H ₃ PO ₄ ), sulfuric acid (H ₂ SO ₄ ), and sodium hydroxide. It may include at least one selected from the group consisting of (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH) ₂ ), and magnesium hydroxide (Mg(OH) ₂ ).

Preferably, the coating may be done by coating the gel electrolyte on the surface-activated carbon fiber using a brush painting method.

In one embodiment, the step of twisting or weaving the heat-treated carbon fiber may be further included. For example, after the heat treatment step, the heat-treated carbon fibers can be twisted or woven, and two or more carbon fibers can be twisted or knotted in various twisted forms, or fabric can be formed using a generally known fiber weaving method. You can. The weaving method can be woven with the twisted carbon fibers and other fibers, or with the twisted carbon fibers, if necessary.

The flexible fiber-type supercapacitor according to an embodiment of the present invention can provide a high-performance fiber-type flexible supercapacitor with high electrochemical performance and mechanical flexibility by applying a surface-activated carbon fiber electrode and a redox gel electrolyte. In other words, the surface area increases due to the dehydrogenation reaction of the polymer, which can improve the number of electrochemically active sites and ion diffusion due to the increase in surface area and oxygen-containing groups on the surface of the carbon fiber, respectively. In addition, the enhanced wettability associated with the increase in the number of oxygen-containing groups on the surface of the carbon fiber can effectively utilize the interface between the denser electrode and the electrolyte to improve ultra-high-speed cycling stability. Additionally, the introduction of redox gel electrolyte and reaction with hydroxyl and carbonyl groups on the carbon surface through oxygen transfer improved the charge storage ability.

Therefore, the microporosity of surface-activated carbon fiber not only provides excellent electrochemical dynamics and energy storage performance, but also provides excellent capacitance retention in stretching, bending, knotting, folding, and curling states due to excellent mechanical flexibility.

Hereinafter, the present invention will be described in more detail through 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.

Manufacturing of fiber-type flexible supercapacitors

To activate the surface of carbon fiber, the carbon fiber was first purified by immersing it in nitric acid. The coating solution was prepared using 2g of PVP in ethanol, and was uniformly applied to the fiber using a brush painting method. Then, the PVP-coated carbon fiber was heated to 500 °C in air to induce dehydrogenation and create a microporous structure with a high surface area. In this way, the surface of carbon fiber was successfully activated.

For the manufacture of flexible fibrous supercapacitors comprising surface-activated carbon fibers and a redox electrolyte (FFSs-SARE), 0.8 M zinc sulfate (ZnSO ₄ ) and 2.0 M phosphoric acid were used. A gel electrolyte was prepared by mixing (H ₃ PO4) and 2 g of polyvinyl alcohol (PVA) in deionized water (DI water). After slowly coating the gel electrolyte on the carbon fiber thread using a brush painting method, the coated fiber was twisted into a Z shape and tightly twisted to be used as an active material and current collector in each electrode (anode and cathode). Finally, the twisted flexible fiber supercapacitor was coated with gel electrolyte and dried. For comparison of electrochemical properties according to surface activation and redox electrolyte use, carbon fibers without surface activation (FSS), surface-activated carbon fibers (FFS-SA), and oxidation A flexible fibrous supercapacitor composed of redox-electrolyte-coated carbon fibers (FFS-RE) was fabricated.

Characteristic measurements

The structural characteristics and morphology of carbon fiber and fibrous supercapacitors were investigated using field-emission scanning electron microscopy (FESEM, Gyeongsang National University Core Facility Center). The composition of the carbon fiber was determined by thermogravimetric analysis (TGA) at temperatures ranging from 100° C. to 900° C. in air. The crystal structure and chemical bonding state of carbon fiber were investigated by X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS), and the wettability of carbon fiber was measured by contact angle measurement. It was measured through.

The specific surface area, average pore size, and total pore volume of the manufactured carbon fiber were evaluated through Brunauer-Emmett-Teller (BET) method and micropore (MP) analysis using N ₂ gas. The chemical properties of the gel electrolyte were measured by Raman spectroscopy at a laser excitation wavelength of 532.1 nm, and the ionic conductivity of the gel electrolyte was evaluated by electrochemical impedance spectroscopy (EIS). Cyclic voltammetry (CV) was performed using a potentiostat/galvanostat. EIS measurements were performed to investigate the electrochemical dynamics. Speed performance tests were performed in a potential range of 0.0 V to 1.0 V at current densities from 70 μA cm ^-2 to 400 μA cm ^-2 . Long-term cycling tests were performed at a current density of 400.0 μA cm ^-2 for up to 5,000 cycles.

Results and Discussion

The manufacturing process of a flexible fiber-type supercapacitor containing surface-activated carbon fiber and a redox electrolyte is schematically shown in FIG. 4.

First, 3,000 carbon fiber filaments (Figure 4(a)) were prepared to be used as electrodes and current collectors due to their high flexibility and high electrical conductivity. PVP was coated on carbon fiber using a brush painting method, as shown in Figure 4 (b). After drying, the fiber was dehydrogenated, and the PVP decomposed as the temperature increased to form oxygen.

Oxygen combined with carbon to form products such as carbon monoxide and carbon dioxide, resulting in the formation of a micropore structure with a high surface area (Figure 4(c)). A gel electrolyte was coated on the surface of the surface activated carbon fiber using a brush painting method to separate the active area and the lead area (Figure 4(d)). Then, as shown in Figure 4(e), the anode and cathode were separated to reduce the empty space inside the supercapacitor, and the two electrolyte-coated fibers were twisted into an S shape.

Figure 5 is a diagram showing the shape and structural characteristics of carbon fiber and surface-activated carbon fiber according to an embodiment of the present invention. This diagram shows low-magnification (a and b) and high-magnification (c and d) SEM images of carbon fiber and surface-activated carbon fiber, (e) XRD pattern, and (f) TGA curves of two types of carbon fiber.

Low-magnification SEM images of carbon fiber (Figure 5(a)) and surface-activated carbon fiber (Figure 5(b)) show the one-dimensional structure of individual fibers with a diameter of approximately 7 ㎛-9 ㎛. The specific surface area shape of each fiber is clearly shown in Figure 5 (c) and Figure 5 (d). While the carbon fiber (Figure 5(c)) had a smooth surface without flaws, the surface-activated carbon fiber (Figure 5(d)) had an uneven surface suggesting the presence of pores. These results show that surface activation through dehydrogenation of PVP can induce the formation of pores with high specific surface area, directly increasing the number of electrochemically active sites and improving ion diffusion ability.

The XRD pattern in Figure 5(e) shows two broad peaks at approximately 26° and 43°, which can be attributed to the (002) and (100) planes of amorphous carbon, respectively. The TGA analysis results are shown in Figure 5(g), and the 100% weight loss of all fibers shows that only one phase of carbon is present. Additionally, the weight loss curve of the surface-activated carbon fiber was clearly shifted compared to that of the carbon fiber, indicating that oxygen-containing groups were introduced to the surface.

Figure 6 is a diagram showing the chemical composition and wettability of carbon fiber and surface-activated carbon fiber according to an embodiment of the present invention. (a and b) C 1s XPS spectra, (c) percentage of oxygen-containing groups in the C 1s peak, (d and e) O 1s . (i) Schematic diagram of the oxygen-containing group in the carbon lattice structure.

Figures 6 (a) to 4 (f) show XPS results for carbon fiber and surface-activated carbon fiber. In the case of the C 1s spectrum of carbon fiber (Figure 6(a)) and surface activated carbon fiber (Figure 6(b)), the signals at 284.5 eV, 285.6 eV, 287.1 eV and 288.5 eV are C-C, C-O, C =O and O-C=O belong to the group. Additionally, after surface activation, the proportion of oxygen-containing groups such as hydroxyl and carbonyl groups on the surface increased from 25.1% for carbon fiber to 35.1% for surface-activated carbon fiber (Figure 6(c)). The O 1s spectra of carbon fiber and surface-activated carbon fiber are shown in Figure 6 (d) and Figure 6 (e), and the signals at 531.1 eV, 532.1 eV, 533.2 eV, and 535.2 eV are C-O, -OH, and O-C. =O and -COOH bonds. Quantitative analysis of these O 1s peaks is shown in (f) of Figure 6. The atomic percentages of C-O, -OH, O-C=O and -COOH bonds in surface-activated carbon fibers increased obviously after surface activation, with a value of 9.6 at. %, 5.5 at. %, 5.6 at. % and 2.9 at. % was; On the other hand, the values for carbon fiber were 7.6 at.%, 3.6 at.%, 3.8 at.%, and 1.7 at.%, respectively. The wettability of carbon fiber and surface-activated carbon fiber can be determined by contact angle measurements in Figures 6(g) and 6(h), respectively. The contact angle of the surface-activated carbon fiber ((g) in Figure 6) was 72°, which was lower than the contact angle (104°) of the carbon fiber ((h) in Figure 6). These XPS and contact angle results show that surface activation efficiently introduces hydroxyl and carbonyl groups to the carbon surface. In addition, according to the results in Figure 6 (i), the introduction of oxygen-containing functional groups on the carbon surface promotes redox reactions caused by redox electrolytes, thereby improving energy storage ability.

Figure 7 is a diagram showing the surface properties and thermal properties of carbon fiber and surface-activated carbon fiber according to an embodiment of the present invention. This is a graph showing the results of (a) BET method, (b) micropore analysis, and (c) differential scanning calorimetry.

The type of porous structure of carbon fiber and surface-activated carbon fiber was measured through N ₂ adsorption/desorption measurement and micropore analysis using the BET method, and the results are shown in Figure 7 (a) and Figure 7 (b). indicated.

The isotherms of carbon fiber and surface-activated carbon fiber show type I characteristics, which means the presence of micropores (pore width < 2 nm) according to the International Union of Pure and Applied Chemistry. In the entire pressure range, the adsorption volume of surface-activated carbon fiber was larger than that of carbon fiber, meaning that N ₂ gas was adsorbed over a larger area. Figure 7(b) shows the pore volume and pore size distribution obtained from micropore measurements.

Surface-activated carbon fibers showed improved pore volume in the size range of 0.8 nm to 1.8 nm, consistent with SEM results. The specific BET results are shown in Table 1 below.

note S _BET
[m ² g ^-1 ] total pore volume
(Total pore volume)
( p / p ₀ = 0.990)
[ ^cm3 g ^-1 ] average pore diameter
(Average pores
Diameter)
[nm] carbon fiber 2.2 0.009 15.7 Surface activated carbon fiber 107.0 0.066 2.4

The higher specific surface area of surface-activated carbon fiber increases the number of electrochemically active sites and provides favorable ion diffusion ability, which is expected to improve the energy storage performance of fibrous supercapacitors. The thermal response of PVP in the heating process was investigated by performing differential scanning calorimetry analysis in the temperature range of 30 ℃ to 400 ℃ in air, and the results are shown in Figure 7 (c). Carbon fiber did not show a melting peak because there was no PVP on the surface. On the other hand, pure PVP and PVP-coated carbon fibers showed reduced heat flow at 80 °C-90 °C, indicating melting of PVP. Additionally, the endothermic peak started at 390 °C due to the loss of hydrogen and oxygen due to dehydrogenation of PVP. Therefore, the surface may have formed into a microporous structure during the dehydrogenation process involving carbon consumption.

Figure 8 is a photograph and (b) a Raman spectrum of a vial containing (a) deionized water, H ₃ PO ₄ -PVA gel electrolyte, and VOSO ₄ -H ₃ PO ₄ -PVA gel electrolyte according to an embodiment of the present invention; c) Ionic conductivity of H ₃ PO ₄ -PVA VOSO ₄ -H ₃ PO ₄ -PVA gel electrolyte, (d) photograph of fabricated supercapacitor, (e) low magnification SEM image and (f) low magnification and (g) FFS- This is a high-magnification cross-sectional SEM image of SARE.

A photograph showing DI water, homogeneous H ₃ PO ₄ -PVA electrolyte and VOSO ₄ -H ₃ PO ₄ -PVA electrolyte is shown in Figure 8 (a), and Figure 8 (b) shows this gel. It shows the Raman spectrum. In both electrolytes, a distinct Raman peak at approximately 891.3 cm ^-1 can be assigned to P(OH) ₃ . In the VOSO ₄ -H ₃ PO ₄ -PVA electrolyte an additional peak is evident at 985.6 cm ^-1 and is attributed to SO ₄ ² . These results confirm that VOSO ₄ exists as a redox mediator in the gel electrolyte, and the presence of this compound can lead to improved electrochemical performance of fibrous supercapacitors.

Additionally, VOSO ₄ in the gel electrolyte can significantly increase ionic conductivity at the electrode-electrolyte interface, thereby improving ion diffusion dynamics during cycling (see (c) in Figure 8). Therefore, VOSO ₄ is a good candidate as a redox mediator for fiber-type supercapacitors. A photograph of the assembled fiber-type supercapacitor containing an active region for energy storage function and a lead region for electrical operation is shown in Figure 8 (d). The diameter of FFS-SARE was measured to be approximately 1.1 mm (see Figure 8(e)). Cross-sectional SEM analysis was performed to investigate the structural properties of FFS-SARE, and the obtained SEM images are shown in Figure 8 (f) and Figure 8 (g). Each electrode of the fiber-type supercapacitor had a diameter of 550 ㎛ to 600 ㎛ (FIG. 8(f)). In addition, the SEM image in Figure 8 (g) shows that the gel electrolyte and electrode material are in close contact with no empty space, effectively leading to excellent mechanical properties.

9 shows CV curves, (c) charge of (a) H ₃ PO ₄ -PVA and (b) VOSO ₄ -H ₃ PO ₄ -PVA aqueous electrolytes obtained using a three-electrode system according to an embodiment of the present invention. This is a diagram showing the oxidation-reduction reaction between hydroxyl and carbonyl groups on the ^surface of surface-activated carbon fiber and VO ²⁺ /VO ₂₊ during the discharge process.

To investigate the reversible Faradaic redox mechanism between surface-activated carbon fibers and VOSO _4, a three-electrode system was used for the potential range from 0.0 V to 1.0 V at a scan rate of 5 mV s ^-1 to 50 mV s ^-1 . A CV curve was obtained. As shown in Figure 9 (a), the surface-activated carbon fiber showed a flat and round redox peak when an aqueous H ₃ PO ₄ solution was used as an electrolyte, which indicates the presence of hydroxyl and carbonyl groups on the fiber surface. It means that an oxidation-reduction reaction occurred. In addition, in order to induce a reversible Faradaic redox reaction of VO ²⁺ / ^VO ₂₊ , it is very important that hydroxyl groups and carbonyl groups exist on the surface. In the case of VOSO ₄ -H ₃ PO ₄ aqueous solution, sharp redox pairs were observed as the current density increased (Figure 9(b)), indicating improved electrochemical behavior. The potentials of the oxidation and reduction peaks correspond well to the redox reaction of VO ²⁺ / ^VO ₂₊ .

Based on the CV results, the reversible Faradaic redox mechanism between surface-activated carbon fiber and VOSO ₄ can be explained by Equation 1 below and (c) in Figure 9.

[Equation 1]

VO ²⁺ + H ₂ O ↔ VO ₂ ⁺ + 2H ⁺ + e ^-

Additionally, the Faradaic redox reaction between VO ²⁺ /VO ₂₊ and the hydroxyl and carbonyl groups on the surface occurred through oxygen transfer ^. In particular, during the charging process of the hydroxyl group, VO ²⁺ adsorbed on the electrode surface interacts with H ⁺ of the hydroxyl group to form a bond. Next, the oxygen atoms are rearranged and form VO ₂ ⁺ on the electrode surface by liberating H ⁺ and e ^- . Eventually, VO ₂₊ diffuses into the bulk solution, displacing H ^{+ from} the bulk solution. Conversely, in the case of a carbonyl group, the adsorbed VO ²⁺ forms a transition state with the carbonyl group. VO ₂₊ then interacts with H ₂ O while diffusing back into ^the bulk electrolyte. Additionally, because the discharging process is the reverse of the charging process, the functional hydroxyl and carbonyl groups on the surface of the electrode with VOSO ₄ electrolyte can participate in the reversible Faradaic redox reaction of VO ²⁺ /VO ₂ ⁺ , thereby improving the energy storage performance of the fiber-type supercapacitor. This improves.

Figure 10 shows the results of electrochemical dynamics analysis according to an embodiment of the present invention. (a) Schematic diagram including the electrical double layer and redox behavior of the fiber supercapacitor, (b) electrochemical impendance spectrum, (c) Bode plot, (d) CV curve, and (e) charge/discharge curve.

The energy storage behavior of FFS-SARE is schematically shown in Figure 10(a) in terms of functional electric double layer and reversible Faradaic redox reaction. Importantly, the introduction of oxygen-containing groups and redox mediators can improve the specific capacitance by inducing a quasi-capacitance Faradaic reaction. The EIS Nyquist plot of FSS, FSS-SA, FSS-RE and FSS-SARE is shown in (b) of Figure 10. Here the linear trend in the low-frequency region reflects the ion diffusion behavior at the interface between the electrode and the gel electrolyte (referred to as Warburg impedance).

Therefore, compared to the slopes of FSS and FSS-RE in Figure 10 (b), the steeper slopes of FSS-SA and FSS-SARE show that the surface-activated carbon fibers have lower Warburg impedance. This leads to superior ion diffusion rates in the fibrous supercapacitor due to the improved wettability of the electrode material. This behavior was further investigated based on the frequency dependent phase angle plot (Bode plot) in Figure 10(c), where the capacitive behavior at low frequencies is associated with ion diffusion. Additionally, a phase angle approaching -90° indicates ideal capacitive operation. Calculating the relaxation time constant (τ ₀ ) from the equation τ ₀ = 1/f ₀ , τ ₀ of FSS-SARE (2.4 s) is similar to that of FSS (17.8 s), FSS-SA (4.0 s), and FSS-RE (8.3 s). shorter, showing that the faster response time indicates faster charge transport due to the introduction of redox mediators and improved wettability of the electrode surface.

Additionally, CV measurements were performed to investigate the electrochemical behavior of FSS, FSS-SA, FSS-RE and FSS-SARE in the voltage range from 0.0 V to 1.0 V at a scan rate of 10 mV s ^-1 (Figure 10 (d)). The confined CV area of FSS-SA was larger than that of FSS and FSS-RE, indicating that the increased specific surface area provided more electroactive sites during the charge and discharge process. A round redox peak was observed in FSS-SARE, implying additional charge storage capacity due to the reversible Faradaic redox behavior associated with the high specific surface area of the carbon electrode with oxygen-containing groups.

Figure 10(e) shows the galvanic charge/discharge curve of the manufactured supercapacitor. All devices show similar galvanostatic charge and discharge at a current density of 70.0 μA cm ^-2 , indicating similar rates and excellent reversibility. The charge/discharge curve of FSS-SARE showed significant redox humps and the longest time among all devices. This result may be the result of an additional pseudocapacitance contribution due to the reversible Faradaic redox reaction of VOSO ₄ with the hydroxyl and carbonyl groups and a general capacitance contribution due to the electric double layer capacitance properties.

Figure 11 shows the results of an energy storage performance test according to an embodiment of the present invention. (a) Speed performance, (b) comparison of speed performance with previously reported fiber supercapacitors, (c) Ragone plot of FFS-SARE with respect to energy and power density in the range 126 to 720 μW cm ^-2 and (d) 400 μA. This is a diagram showing the cycle stability for up to 5,000 cycles at a high current density of cm ^-2 .

The speed performance of the fabricated supercapacitor at potentials ranging from 0.0 V to 1.0 V at a current density range of 70 μA cm ^-2 to 400 μA cm ^-2 is shown in Figure 11 (a). FSS-SARE was 891 mF cm ^-2 at current densities of 70 μA cm ^-2 , 100 μA cm ^-2 , 150 μA cm ^-2 , 200 μA cm ^-2 , 300 μA cm ^-2 and 400 μA cm ^-2 , respectively. It showed surprising specific capacitances of 658 mF cm ^-2 , 550 mF cm ^-2 , 454 mF cm ^-2 , 410 mF cm ^-2 and 399 mF cm ^-2 . The speed performance of this device is even more remarkable when compared to previously reported fiber-type supercapacitors (Figure 11(b)).

The increased specific capacitance of FSS-SARE compared to other supercapacitors is due to (i) the machined surface of microporous carbon fiber providing many electrochemically active sites and improving ion diffusion ability, and (ii) VOSO ₄ and hydroxyl groups and Additional pseudocapacitive contribution due to the reversible Faradaic redox reaction of the carbonyl group improved the energy storage performance. The appropriate power and energy density of FSS-SARE for actual application as a fiber-type supercapacitor are shown in Figure 11 (c). The device exhibited maximum energy densities of 110 47 μW h cm ^-2 and 47 47 μW h cm ^-2 at power densities of 126 μW cm ^-2 and 720 μW cm ^-2 , respectively, both of which were similar to those of the previously reported fiber-type devices. It is considerably higher than a supercapacitor. In addition, FSS-SARE showed excellent cycling stability with a capacitance retention rate of 91% even after 5,000 cycles due to improved ion diffusion due to improved electrode surface wettability.

Figure 12 shows (a) the capacitance retention rate of the straight, bent, knotted, folded, and wound states of the FFS-SARE, (b) the mechanical characteristics of the FFS-SARE during 100 repetitions in the flat and bent states, according to an embodiment of the present invention. Flexibility, (c) a photograph showing the large-scale weaving of three FFS-SARE devices into a fabric, (d) a diagram showing the capacitance retention of FFS-SARE devices woven into a fabric for different fabric states (straight and crumpled).

35 cm) 슈퍼커패시터를 제조했다 (도 12의 (c)). 도 12의 (c)의 사진은 준비된 슈퍼커패시터가 일반 스웨터와 같은 직물로 쉽게 짜여질 수 있음을 명확하게 보여준다. 또한, FSS-SARE는 구겨진 경우에도 우수한 정전 용량 유지를 보였다 (도 12의 (d)).The mechanical flexibility of fibrous supercapacitors is a key factor determining their suitability for use as wearable energy storage devices. The excellent mechanical flexibility of FSS-SARE in the bent, knotted, folded, and rolled states was clearly observed, as shown in Figure 12 (a). Figure 12 (b) shows the capacitance maintenance of FSS-SARE after 100 repetitions at a current density of 400.0 μA cm ^-2 in straight and bent states. It shows the excellent mechanical performance and high flexibility of the device. To further investigate the practical applicability of FSS-SARE, three large-scale (

35 cm) supercapacitor was manufactured (FIG. 12(c)). The photo in Figure 12(c) clearly shows that the prepared supercapacitor can be easily woven into a fabric such as a regular sweater. Additionally, FSS-SARE showed excellent capacitance maintenance even when crumpled (Figure 12(d)).

Overall, our results demonstrate the compatible effects of surface tuning of carbon electrodes and generation of reversible Faradaic reactions on the electrochemical performance of flexible fiber supercapacitors.

Figure 13 is a schematic diagram including increase in electrochemically active sites, efficient ion diffusion, and reversible Faraday reaction of FFS-SARE according to an embodiment of the present invention.

As schematically shown in Figure 13, the surface area increased due to the dehydrogenation reaction of PVP, which improved the number of electrochemically active sites and ion diffusion due to the increase in surface area and oxygen-containing groups on the surface of the carbon fiber, respectively. The improved wettability associated with the increase in the number of oxygen-containing groups on the surface of the carbon fiber effectively utilized the interface between the denser electrode and the electrolyte, contributing to improved ultra-high-speed cycling stability. Finally, the introduction of a redox electrolyte containing VOSO ₄ improved energy ^storage performance by inducing a reversible Faradaic reaction of VO ²⁺ /VO ₂₊ with hydroxyl and carbonyl groups on the carbon surface through oxygen transfer. Due to these multiple synergistic effects, FSS-SARE exhibited excellent specific capacitance, excellent cycling stability, and excellent energy density. In addition, the possibility of practical application in a wearable energy storage device with improved energy storage performance and excellent mechanical properties was confirmed. In particular, its potential to be woven into textiles has been demonstrated.

result

A flexible fibrous supercapacitor (FFS-SARE) composed of surface-activated carbon fiber and redox electrolyte was fabricated for use in wearable energy storage devices. Multiple synergistic effects resulting from surface tuning of the carbon electrode and introduction of the reversible Faradaic reaction are clearly evident. FFS-SARE demonstrated excellent electrochemical performance, including remarkable specific capacitances of 891 mF cm ^-2 and 399 mF cm ^-2 at current densities of 70.0 μA cm ^-2 and 400 μA cm ^-2 , respectively, and 400.0 μA cm ^-2 It provides excellent ultra-fast cycling stability for 5,000 cycles with 92% capacitance retention at a current density of ² .

These results are due to the following factors: (i) dehydrogenation of PVP increased the surface area and oxygen-containing groups of the carbon fiber surface, thus increasing the number and wettability of electrochemically active sites, resulting in a lower overall specific capacitance; increased. (ii) Introduction of a redox electrolyte containing VO ²⁺ /VO ₂₊ and reaction with hydroxyl and carbonyl groups on ^the carbon surface through oxygen transfer improved the charge storage ability. (iii) It exhibits ultra-fast cycling stability by effective utilization of the interface between the electrode and electrolyte due to efficient ion diffusion. The excellent mechanical flexibility and realistic applicability of FFS-SARE were demonstrated by weaving the electrodes and performing charge-discharge tests. Therefore, the implementation of the present invention shows that using surface activated carbon as an electrode and VOSO ₄ as a redox electrolyte in a gel electrolyte for flexible fiber-type supercapacitors can present a path and strategy for advanced design of wearable energy storage devices. This has been proven in examples.

Although the embodiments have been described with limited drawings as described above, those skilled in the art can apply various technical modifications and variations based on the above. For example, the described techniques are performed in a different order than the described method, and/or components of the described system, structure, device, circuit, etc. are combined or combined in a different form than the described method, or other components are used. Alternatively, appropriate results may be achieved even if substituted or substituted by an equivalent.

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

100: Flexible fiber supercapacitor
110: Surface activated carbon fiber electrode
120: Gel electrolyte

Claims (19)

Contains oxygen-containing groups on the surface of the carbon fiber,
A carbon fiber electrode having micropores,
The carbon fiber is a bundle of 1,000 to 10,000 filaments,
The carbon fiber electrode is made of two or more strands of carbon fiber twisted or woven,
The carbon fiber electrode has a Z-shaped twist structure, a twist spacing of 10 ㎛ to 50 ㎛ and a twist angle of 25 ° to 75 °,
The carbon fiber has a specific surface area of 100 m ² g ^-1 to 300 m ² g ^-1 , a pore volume of 0.01 cm ³ g ^-1 to 0.20 cm ³ g ^-1 , a pore size of 1 nm to 5 nm, and a pore size of 35% to 40%. Containing at least one of the % pore volume fraction,
Surface-activated carbon fiber electrode.
According to paragraph 1,
The oxygen-containing group includes a hydroxyl group and a carbonyl group,
The content of oxygen-containing groups in the surface-activated carbon fiber electrode is 10 at. % to 60 at.%,
Surface-activated carbon fiber electrode.
According to paragraph 1,
The oxygen-containing group is formed by carbonized or graphitized polymer on the surface of the carbon fiber,
The polymers include polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), and polystyrene. ; PS), polymethyl methacrylate (PMMA), poly(n-butyl acrylate) (PBA), polyacrylonitrile (PAN), polyaniline (polyaniline). PANi), polyacrylic acid (PAA), polyester-amides (PEA), polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) ), polyurethane (PU), polychloroprene, polyisoprene, and polybutadiene, which includes at least one selected from the group consisting of,
Surface-activated carbon fiber electrode.
According to paragraph 1,
The oxygen-containing group includes CO, -OH, OC=O and -COOH bonds,
The CO bond is 8 at. % to 15 at. %,
The -OH bond is 4 at. % to 10 at. %,
The OC=O bond is 4 at. % to 10 at. %, and
The -COOH bond is 2 at. % to 5 at. %,
Surface-activated carbon fiber electrode.
delete delete According to paragraph 1,
The individual fiber diameter of the carbon fiber is 1 ㎛ to 50 ㎛,
Surface-activated carbon fiber electrode.
delete Impregnating carbon fibers in a polymer solution and coating the carbon fibers with the polymer; and
Heat treating the polymer-coated carbon fiber;
Including,
A method for manufacturing the surface-activated carbon fiber electrode of claim 1.
According to clause 9,
Before impregnating the carbon fiber with a polymer solution and coating the carbon fiber with the polymer,
Purifying the carbon fiber by immersing it in an acid solution;
It further includes,
The acid solution contains at least one selected from the group consisting of nitric acid, phosphoric acid, and hydrofluoric acid,
Method for manufacturing surface-activated carbon fiber electrodes.
According to clause 9,
The polymer solution includes a polymer and a solvent,
The polymers include polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), and polystyrene. ; PS), polymethyl methacrylate (PMMA), poly(n-butyl acrylate) (PBA), polyacrylonitrile (PAN), polyaniline (polyaniline). PANi), polyacrylic acid (PAA), polyester-amides (PEA), polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) ), polyurethane (PU), polychloroprene, polyisoprene, and polybutadiene;
The solvent includes at least one selected from the group consisting of ethanol, methanol, propanol, butanol, and isopropanol.
Method for manufacturing surface-activated carbon fiber electrodes.
According to clause 9,
The step of heat treating the polymer-coated carbon fiber is,
temperature between 300°C and 900°C; and air, or an atmosphere containing at least one of N ₂ to Ar;
Method for manufacturing surface-activated carbon fiber electrodes.
According to clause 9,
twisting or weaving the heat-treated carbon fiber;
Containing more,
Method for manufacturing surface-activated carbon fiber electrodes.
The surface-activated carbon fiber electrode of claim 1; and
A gel electrolyte coated on the surface-activated carbon fiber electrode;
Including,
Flexible fiber supercapacitor.
According to clause 14,
The gel electrolyte is,
Polyvinyl alcohol (PVA), vanadium sulfate (VOSO ₄ ), zinc sulfate (ZnSO ₄ ), phosphoric acid (H ₃ PO ₄ ), sulfuric acid (H ₂ SO ₄ ), sodium hydroxide (NaOH), potassium hydroxide (KOH), hydroxide Containing at least one selected from the group consisting of calcium (Ca(OH) ₂ ) and magnesium hydroxide (Mg(OH) ₂ ),
Flexible fiber supercapacitor.
According to clause 14,
There are at least two surface-activated carbon fiber electrodes coated with the gel electrolyte,
The two surface-activated carbon fiber electrodes coated with the gel electrolyte are twisted into an S-shaped twist.
Flexible fiber supercapacitor.
According to clause 14,
The flexible fiber supercapacitor,
At a current density ranging from 50 μW cm ^-2 to 500 μW cm ^-2 , the energy density is 500 μW h cm ^-2 to 1,000 μW h cm ^-2 ,
A capacitance retention rate of 90% or more at a current density ranging from 300 μW cm ^-2 to 500 μW cm ^-2 ,
Flexible fiber supercapacitor.
Impregnating carbon fibers in a polymer solution and coating the carbon fibers with the polymer;
Preparing surface-activated carbon fiber by heat treating polymer-coated carbon fiber; and
Coating a gel electrolyte on the surface-activated carbon fiber;
Including,
Method for manufacturing the flexible fiber-type supercapacitor of claim 14.
According to clause 18,
The step of coating the gel electrolyte on the surface-activated carbon fiber,
After twisting or weaving the surface-activated carbon fiber, a gel electrolyte is coated on the surface-activated carbon fiber, or a gel electrolyte is coated on the surface-activated carbon fiber,
The coating includes brush painting, spray coating, spin coating or dip coating methods,
Manufacturing method of flexible fiber-type supercapacitor.