Hollow carbon nanofibers for high-performance and flexible supercapacitor electrodes and their manufacturing methods

Abstract

One embodiment of the present invention provides a high-performance flexible supercapacitor electrode material based on hollow-structured activated carbon nanofibers having an excellent specific surface area through an ammonia atmosphere carbonization process, and a method for manufacturing the same. According to an embodiment of the present invention, a high-performance flexible supercapacitor electrode material based on hollow-structured activated carbon nanofibers having an excellent specific surface area can be manufactured through an ammonia atmosphere carbonization process. The hollow carbon nanofiber material synthesized by such a method can be utilized as an electrode for a flexible supercapacitor without a separate binder and exhibits excellent electrochemical performance and performance stability against bending.

Description

Technology Field

[0001] The present invention relates to hollow carbon nanofibers for high-performance and flexible supercapacitor electrodes and a method for manufacturing the same. More specifically, it relates to a high-performance flexible supercapacitor electrode material based on hollow activated carbon nanofibers having an excellent specific surface area through an ammonia atmosphere carbonization process, and a method for manufacturing the same. Background Technology

[0003] Carbon materials are being actively utilized as electrodes for energy storage devices due to their high specific surface area and electrical conductivity. In particular, much research is being conducted on them as electrode materials for supercapacitors, which possess high power density and long lifespan.

[0004] Carbon nanofibers possess high electrical conductivity and a nanostructure that facilitates ion diffusion, and are attracting attention as a promising supercapacitor electrode material because they can be synthesized in sheet form through an electrospinning process capable of mass production.

[0005] Conventional porous carbon materials are synthesized using degradable materials such as SiO2, PMMA, and PVP, or through activation processes utilizing KOH, CO2, etc. However, most of these existing pore structure improvement processes require additional processing after the carbon material is synthesized.

[0006] Accordingly, in order to dramatically improve the energy storage performance of carbon nanofiber-based materials, it is required to synthesize porous carbon nanofibers without an additional activation process through an ammonia atmosphere carbonization process, and furthermore, to develop carbon materials with excellent specific surface area by optimizing the etching process through the control of the ammonia flow rate. Prior art literature

[0008] (Patent Document 0001) KR 10-2021-0155102 A The problem to be solved

[0009] The technical problem that the present invention aims to solve is to develop a hollow carbon nanofiber material with a high specific surface area that can be utilized as an electrode for a high-performance flexible supercapacitor, and to provide a simple and mass-producible manufacturing method.

[0010] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below. means of solving the problem

[0012] To achieve the above technical objectives, one embodiment of the present invention provides a method for manufacturing porous hollow carbon nanofibers, comprising the steps of producing core-shell polymer nanofibers through electrospinning, heat-treating the core-shell polymer nanofibers, and carbonizing the heat-treated core-shell polymer nanofibers in an ammonia atmosphere, wherein the core-shell polymer nanofibers are characterized in that the core is composed of a polymer capable of thermal decomposition and the shell is composed of a polymer capable of carbonization, and the step of carbonizing in an ammonia atmosphere is characterized in that it forms the core-shell polymer nanofibers into a hollow shape and induces porosity by controlling the flow rate of ammonia that acts as an etching agent.

[0013] In an embodiment of the present invention, the pyrolyzable polymer may be characterized by including poly(methyl methacrylate), PMMA.

[0014] In an embodiment of the present invention, the carbonizable polymer may be characterized by including polyacrylonitrile (PAN).

[0015] In an embodiment of the present invention, the step of heat-treating the core-shell polymer nanofiber may be characterized as a step of stabilizing the core-shell polymer nanofiber.

[0016] In an embodiment of the present invention, the step of heat-treating the core-shell polymer nanofiber may be characterized as being performed at 250 to 300 ℃.

[0017] In an embodiment of the present invention, the step of carbonizing in an ammonia atmosphere may be characterized by being performed at an ammonia flow rate of 10 to 100 sccm (mL / min).

[0018] In an embodiment of the present invention, the step of carbonizing in an ammonia atmosphere may be characterized in that the specific surface area of ​​the porous hollow carbon nanofiber improves as the flow rate of ammonia increases.

[0019] To achieve the above technical problem, another embodiment of the present invention provides porous hollow carbon nanofibers manufactured according to a manufacturing method.

[0020] To achieve the above technical problem, another embodiment of the present invention provides a flexible supercapacitor comprising an electrode made of porous hollow carbon nanofibers and a gel electrolyte. Effects of the invention

[0023] According to an embodiment of the present invention, a high-performance flexible supercapacitor electrode material based on hollow-structured activated carbon nanofibers having an excellent specific surface area can be manufactured through an ammonia atmosphere carbonization process. By varying the flow rate of ammonia during the ammonia atmosphere carbonization process, the micro- and mesoporous pore structures of the activated hollow carbon nanofibers can be maximized and the specific surface area can be dramatically improved. The hollow carbon nanofiber material synthesized by this method can be utilized as an electrode for a flexible supercapacitor without a separate binder and exhibits excellent electrochemical performance and performance stability against bending.

[0024] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims. Brief explanation of the drawing

[0026] Figure 1 shows (a) SEM and (b) TEM images of hollow activated carbon nanofibers and (c) SEM and (d) TEM images of activated carbon nanofibers. Figure 2 is a graph analyzing the N 1s spectrum measured by photoelectron spectroscopy of active hollow carbon nanofiber materials synthesized according to ammonia flow rate changes (a) 10 sccm, (b) 50 sccm, and (c) 100 sccm. Figure 3 is a graph showing (a) nitrogen adsorption / desorption curves and (b) pore size distribution of hollow carbon nanofiber materials. Figure 4 is a graph showing (a) a comparison of specific capacitance, (b) cyclic amperage curves, and (c) Nyquist plots of hollow carbon nanofibers and carbon nanofibers. Figure 5 is a graph showing (a) the cyclic amperometric curve and (b) the cycle life characteristics of active hollow carbon nanofibers synthesized according to an ammonia flow rate of 100 sccm. Figure 6 is a graph showing (a) an image confirming flexibility, (b) a cyclic current curve according to the bending angle, and (c) bending durability performance of active hollow carbon nanofibers synthesized according to an ammonia flow rate of 100 sccm. Specific details for implementing the invention

[0027] The present invention will be described below with reference to the attached drawings. However, the present invention may be implemented in various different forms and is therefore not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0028] Throughout the specification, when it is stated that a part is "connected (connected, in contact, combined)" with another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members interposed between them. Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion of additional components.

[0029] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0030] Embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0032] The terms used in this specification are defined as follows.

[0033] “ECNF” stands for Etched Carbon Nanofiber.

[0034] “EHCNF” stands for Etched Hollow Carbon Nanofiber.

[0035] “EHCNF 10” refers to an etched hollow carbon nanofiber material synthesized according to an ammonia flow rate of 10 sccm.

[0036] “EHCNF 50” refers to an etched hollow carbon nanofiber material synthesized according to an ammonia flow rate of 50 sccm.

[0037] “EHCNF 100” refers to an etched hollow carbon nanofiber material synthesized according to an ammonia flow rate of 100 sccm.

[0038] “ECNF 100” refers to an etched carbon nanofiber material synthesized according to an ammonia flow rate of 100 sccm.

[0040] A method for manufacturing porous hollow carbon nanofibers according to an embodiment of the present invention is described.

[0041] A method for manufacturing porous hollow carbon nanofibers according to one embodiment of the present invention comprises the steps of producing core-shell polymer nanofibers through electrospinning, heat-treating the core-shell polymer nanofibers, and carbonizing the heat-treated core-shell polymer nanofibers in an ammonia atmosphere, wherein the core-shell polymer nanofibers may be composed of a polymer capable of thermal decomposition and a polymer capable of carbonization, and the step of carbonizing in an ammonia atmosphere may be characterized as a step of forming the core-shell polymer nanofibers into a hollow shape and inducing porosity by controlling the flow rate of ammonia that acts as an etching agent.

[0042] The first step is to fabricate core-shell polymer nanofibers through electrospinning. Coaxial nozzle electrospinning allows for the mass production of core-shell polymer nanofibers in the form of large-area sheets. They can be utilized as electrodes for energy storage devices without the need for a separate binder.

[0043] The above-mentioned pyrolytic polymer may include poly(methyl methacrylate), PMMA, but is not limited thereto. PMMA is colorless and transparent, has excellent optical properties, has a heat deformation temperature of approximately 70-110°C, and can be heat-processed at approximately 95-110°C. Since the core is made of a pyrolytic polymer, a hollow structure can be formed through a carbonization process.

[0044] The above carbonizable polymer may include, but is not limited to, polyacrylonitrile (PAN). PAN is a synthetic polymer widely used to make carbon fibers.

[0045] Conventional porous carbon materials can be synthesized using degradable materials such as SiO2, PMMA, and PVP, or through activation processes utilizing KOH, CO2, etc. However, most of these existing pore structure improvement processes required additional processing after the synthesis of the carbon material; in contrast, carbon nanofibers produced through an ammonia atmosphere carbonization process can synthesize porous carbon nanofibers without an additional activation process.

[0046] The next step is to heat-treat the above-mentioned core-shell polymer nanofiber.

[0047] The step of heat-treating the core-shell polymer nanofiber may be a step of stabilizing the core-shell polymer nanofiber. By performing heat treatment in air at a temperature of 250 to 300 ℃, thermal stability is improved through oxidation and polymer chain cross-linking.

[0048] The next step is to carbonize the heat-treated core-shell polymer nanofibers in an ammonia atmosphere. The step of carbonizing in an ammonia atmosphere is to form the core-shell polymer nanofibers into a hollow shape and induce porosity by controlling the flow rate of ammonia, which acts as an etching agent.

[0049] Porosity can be induced on the surface of hollow carbon nanofibers by supplying ammonia gas, which acts as an etching agent during the high-temperature carbonization process.

[0050] The step of carbonizing in the above ammonia atmosphere can be performed at an ammonia flow rate of 10 to 100 sccm, but preferably a wider range depending on other conditions.

[0051] Generally, porous carbon nanofibers synthesized through an ammonia atmosphere carbonization process have a specific surface area of ​​up to approximately 2,000 m² 2 The theoretical specific surface area of ​​graphene in / g (2,630 m²) 2 It is at a level lower than (g). Therefore, in order to dramatically improve the energy storage performance of carbon nanofiber-based materials, it is required to develop carbon materials with excellent specific surface area by optimizing the ammonia atmosphere carbonization process.

[0052] In the step of carbonizing in an ammonia atmosphere, the specific surface area of ​​the porous hollow carbon nanofibers can be improved as the flow rate of ammonia increases. The minimum flow rate point is 10 sccm and the maximum flow rate point is 100 sccm, and the specific surface area of ​​the porous hollow carbon nanofibers can be improved within this range, but the flow rate range may preferably be wider depending on other conditions.

[0053] By inducing nitrogen doping on the surface of hollow carbon nanofibers through ammonia-based activation, hydrophilicity and pseudocapacitance effects can be induced, thereby enhancing energy storage capacity in aqueous electrolytes. In other words, by utilizing ammonia gas during the carbonization process, the pore structure of carbon nanofibers can be controlled while simultaneously inducing nitrogen doping.

[0054] Micro and mesoporous structures can be maximized by controlling the ammonia flow rate during the ammonia atmosphere carbonization process. Active hollow carbon nanofibers with micro and mesoporous pore structures exhibit a high specific surface area and excellent electrochemical performance, and due to their hollow structure, they can demonstrate higher performance compared to conventional carbon nanofibers.

[0056] Porous hollow carbon nanofibers manufactured according to the above manufacturing method according to another embodiment of the present invention are described below.

[0057] Porous carbon nanofibers synthesized through a conventional ammonia atmosphere carbonization process have a specific surface area of ​​up to approximately 2,000 m² 2 The theoretical specific surface area of ​​graphene in / g (2,630 m²) 2 It is at a level lower than (g). Therefore, in order to dramatically improve the energy storage performance of carbon nanofiber-based materials, it is required to develop carbon materials with excellent specific surface area by optimizing the ammonia atmosphere carbonization process.

[0058] At this time, the specific surface area can be significantly improved by changing the ammonia flow rate during the ammonia atmosphere carbonization process. Through the ammonia atmosphere carbonization process, 3,000 m² 2 It is possible to manufacture active hollow carbon nanofibers having an excellent specific surface area of ​​more than / g.

[0060] A flexible supercapacitor comprising an electrode made of the porous hollow carbon nanofiber and a gel electrolyte according to another embodiment of the present invention is described below. The gel electrolyte may be a PVA / H3PO4 gel electrolyte.

[0061] The hollow porous carbon nanofiber material produced by the above manufacturing method can be utilized as an electrode for a flexible supercapacitor without a separate binder, and can exhibit excellent electrochemical performance and performance stability against bending.

[0063] Figure 1 shows (a) SEM and (b) TEM images of hollow activated carbon nanofibers and (c) SEM and (d) TEM images of activated carbon nanofibers. Referring to Figure 1, it can be seen that both carbon nanofibers have a diameter of about 100 nm, and the hollow activated carbon nanofibers have a hollow structure with a hollow of about 50 nm.

[0065] Figure 2 is a graph analyzing the N 1s spectrum measured by photoelectron spectroscopy of active hollow carbon nanofiber materials synthesized according to ammonia flow rates of 2a) 10 sccm, 2b) 50 sccm, and 2c) 100 sccm. Referring to Figure 2, it can be confirmed that as the ammonia flow rate increases, both Pyridinic N and Pyrrolic N, which exhibit pseudo-capacitor characteristics and hydrophilicity, are possessed. These nitrogen functional groups are formed by ammonia carbonization, which acts as an etching agent during the synthesis process.

[0067] Figure 3 is a graph showing 3a) nitrogen adsorption / desorption curves and 3b) pore size distribution of hollow carbon nanofiber materials.

[0068] Referring to Fig. 3a), the active hollow carbon nanofiber material has a maximum diameter of approximately 3,617 m due to its hollow shape and the ammonia atmosphere carbonization process. 2 It can be confirmed that it exhibits an excellent specific surface area of ​​ / g.

[0069] Referring to Fig. 3b), it can be seen that the active hollow carbon nanofibers have developed micro and mesoporous structures, with pores smaller than 10 nm mainly distributed. Since the pore structure smaller than 10 nm develops further as the ammonia flow rate increases, it can be confirmed that the ammonia atmosphere carbonization process is effective for developing micro and mesoporous pore structures on the surface of carbon nanofibers.

[0071] Figure 4 is a graph showing 4a) specific capacitance comparison, 4b) cyclic amperometric curve, and 4c) Nyquist plot of active hollow carbon nanofibers and active carbon nanofibers. It compares the results of measuring the electrochemical performance of active hollow carbon nanofibers and active carbon nanofibers using a two-electrode system in a 6M KOH electrolyte.

[0072] Referring to Figures 4a) and 4b), the charge-discharge measurement results show that as the flow rate of ammonia increases, the specific surface area of ​​the hollow carbon nanofiber improves, resulting in a high specific capacitance value. It can be confirmed that the active hollow carbon nanofiber (EHCNF 100) exhibits a high specific capacitance of 209.7 F / g in the discharge curve at a current density of 1 A / g. It can be confirmed that the active hollow carbon nanofiber (EHCNF 100) exhibits superior electrochemical performance compared to the active carbon nanofiber (ECNF 100) in both cyclic amperage and charge-discharge measurement results due to its hollow structure.

[0073] Referring to Fig. 4c), it can be confirmed in the Nyquist plot that hollow carbon nanofibers exhibit lower charge transfer resistance than carbon nanofibers due to their hollow structure.

[0075] Figure 5 is a graph showing 5a) the cyclic amperometric curve and 5b) the cycle life characteristics of active hollow carbon nanofibers synthesized according to an ammonia flow rate of 100 sccm.

[0076] Referring to Fig. 5a), it can be confirmed that the active hollow carbon nanofiber exhibits excellent electrochemical properties, with the circulating current curve appearing nearly square even at high scanning speeds.

[0077] Referring to Fig. 5b), it can be seen that excellent cycle life stability is demonstrated by showing a specific capacitance value of 93.8% compared to the first cycle even after 6,000 cycles.

[0079] Figure 6 shows 6a) an image confirming flexibility, 6b) a cyclic amperage curve according to bending angle, and 6c) a graph showing the bending endurance performance of a flexible supercapacitor using active hollow carbon nanofibers synthesized at an ammonia flow rate of 100 sccm. The flexible supercapacitor was fabricated using a PVA / H3PO4 gel electrolyte.

[0080] Referring to Fig. 6a), it can be seen that the active hollow carbon nanofiber (EHCNF 100) is flexible enough to bend 140°.

[0081] Referring to Fig. 6b), it can be seen that the flexible supercapacitor exhibits performance similar to that before bending even at bending angles of 70° and 140° in the cyclic current method curve at a scan rate of 20 mV / s.

[0082] Referring to Fig. 6c), it can be seen that it exhibits bending durability that maintains 96.15% of performance even after 500 cycles of 140° bending.

[0084] Active hollow carbon nanofibers having micro and mesoporous pore structures manufactured through an embodiment of the present invention exhibit a high specific surface area and excellent electrochemical performance, and due to their hollow structure, they demonstrate higher performance compared to conventional carbon nanofibers. The flexible carbon nanofiber sheet can be realized as a flexible supercapacitor and can be confirmed to exhibit excellent electrochemical performance and performance stability against bending.

[0086] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0087] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

Claim 1 A method for manufacturing porous hollow carbon nanofibers, comprising the steps of: producing core-shell polymer nanofibers through electrospinning; heat-treating the core-shell polymer nanofibers; and carbonizing the heat-treated core-shell polymer nanofibers in an ammonia atmosphere, wherein the core-shell polymer nanofibers are characterized in that the core is composed of a polymer capable of thermal decomposition and the shell is composed of a polymer capable of carbonization, and the step of carbonizing in an ammonia atmosphere is characterized in that the core-shell polymer nanofibers are formed into a hollow shape and porosity is induced by controlling the flow rate of ammonia that acts as an etching agent, and wherein the flow rate of ammonia in the step of carbonizing in an ammonia atmosphere is greater than 50 to 100 sccm and the specific surface area of ​​the porous hollow carbon nanofibers improves as the flow rate of ammonia increases. Claim 2 A method for manufacturing porous hollow carbon nanofibers according to claim 1, characterized in that the pyrolyzable polymer comprises poly(methyl methacrylate), PMMA. Claim 3 A method for manufacturing porous hollow carbon nanofibers according to claim 1, characterized in that the carbonizable polymer comprises polyacrylonitrile (PAN). Claim 4 A method for manufacturing porous hollow carbon nanofibers according to claim 1, wherein the step of heat-treating the core-shell polymer nanofiber stabilizes the core-shell polymer nanofiber. Claim 5 A method for manufacturing porous hollow carbon nanofibers according to claim 4, characterized in that the step of heat-treating the core-shell polymer nanofiber is performed at 250 to 300 ℃. Claim 6 delete Claim 7 delete Claim 8 Porous hollow carbon nanofibers manufactured according to the manufacturing method of claim 1. Claim 9 A flexible supercapacitor comprising an electrode made of porous hollow carbon nanofibers according to claim 8; and a gel electrolyte.

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