KR102572121B1 - Fabrication method of one-dimensional carbon-nanofiber membrane decorated with crystalline ceramic nanoparticles by joule heating process - Google Patents

Abstract

Disclosed is a one-dimensional carbon nanofiber membrane to which ceramic nanoparticles having crystallinity are bound using a Joule heating process and a manufacturing method thereof. In one embodiment, a spinning solution containing polyacrylonitrile is synthesized into a one-dimensional structure in the form of nanofibers through an electrospinning machine, and a primary stabilization process performed under an air atmosphere and a secondary carbonization process performed under an inert atmosphere After making carbon nanofibers with a one-dimensional nanostructure, at least one of various metal ions such as lanthanum, strontium, cobalt vanadium, etc. It is possible to bind ceramic nanoparticles having crystallinity by adjusting the atmospheric atmosphere of the Joule heating process, which can instantaneously generate ultra-high temperature heat from carbon nanofibers to which one or more types of metal ions are bound by being supported in a solution containing carbon nanofibers.

Description

One-dimensional carbon nanofiber membrane in which ceramic nanoparticles having crystallinity are bound using a Joule heating process and its manufacturing method

Embodiments of the present invention relate to a functional membrane having catalytic properties by regularly binding various ceramic nanoparticles having crystallinity to carbon nanofibers having a one-dimensional nanostructure using a Joule heating process and a manufacturing method thereof. More specifically, after dissolving polyacrylonitrile in a solvent, electrospinning and heat-treating carbon nanofibers, the surface is negatively charged through an oxygen plasma process, and then supported in a solution in which a metal salt is dissolved and atmospheric conditions are controlled. Provides a membrane and its manufacturing technology made by regularly binding crystalline ceramic nanoparticles to the surface of carbon nanofibers by instantaneously applying ultra-high temperature through a Joule heating process in the state of A carbon material-based membrane that can be used free-standing in an energy storage system by providing a one-dimensional nanostructure in which desired ceramic nanoparticles are regularly bound by freely changing the type of nanoparticles and a manufacturing method therefor. It is possible to provide a ceramic catalyst binding of an electrode and a manufacturing method thereof.

As interest in energy and the environment is rapidly increasing, interest in using eco-friendly energy is rapidly increasing rather than using fossil fuels, which are the main culprits of environmental pollution. Among various eco-friendly energy technologies, batteries are by far receiving great attention. Currently, battery technology has been commercialized with significant progress, and is applied not only to small devices such as mobile phones but also as a power source for automobiles. In particular, among various battery types, a lithium ion battery is the most widely used battery and is used in an electric vehicle based on recently advanced technology. However, such a lithium ion battery does not reach standard long-distance driving of 400 km or more while maintaining an appropriate weight of an automobile due to its low theoretical energy density. Therefore, in order to overcome the low energy density of a lithium ion battery, a lithium-air battery system having an energy density equivalent to that of gasoline and at least 10 times higher than that of a lithium ion battery is attracting attention as a next-generation battery system.

A lithium-air battery consists of a negative electrode, a separator, and a positive electrode, and has a system that uses oxygen in the air in the presence of lithium metal as the negative electrode material and carbon and non-carbon-based conductive membranes as the positive electrode material. It is a system in which lithium metal, the negative electrode, generates lithium ions as it oxidizes, and the air introduced into the battery causes an electrochemical reaction with lithium ions in the positive electrode material to store and use energy. In particular, the lithium-air battery is a next-generation battery that actively reacts with lithium ions and oxygen gas in the air, forms an oxide in the form of Li ₂ O ₂ on the surface of the cathode material, and has a high theoretical energy density of over 3500 Wh/kg. However, the lithium-air battery currently being studied has significantly lower lifespan compared to conventional lithium-ion batteries because of imperfect contact between materials inside the battery, high non-conductivity of lithium oxide, and lithium oxide that is not decomposed due to high overvoltage. In addition, the actual usable energy density also remains at a very low level compared to the theoretical value due to the low oxygen concentration in the air, undecomposed lithium oxide, and high overvoltage.

In order to solve this problem, various material groups and processing methods are being applied to solve the limitations of the current lithium-air battery system. As a currently used method, a cathode is being developed by sintering and hydration heat treatment of ceramics and metals. However, when this method is used, a relatively large particle size is formed, which reduces the activity of the catalyst, and a lot of time is required for the process. Being caught is a weakness. In order to solve these problems and improve the performance of lithium-air batteries, the present invention developed a catalyst by applying a Joule heating process. Instead of the existing process that requires a long time and large particle size is formed, the limitation was solved by using a Joule heating method that can bind multi-component nano-sized particles by adjusting the air conditions within a short time of several seconds, and furthermore, the metal composition ratio and It is expected that it will be possible to bind crystallized perovskite nanoparticles (ABO ₃ ) through optimization of air conditions.

Lithium-air batteries have the highest energy density among next-generation energy storage systems, but have a problem in that their lifespan is rapidly reduced (less than 50 cycles) due to side reactions that occur during charge/discharge and high overvoltage due to low charge/discharge efficiency. . In addition, when it is driven in the actual atmosphere, it is difficult to operate stably due to limitations in solubility and diffusion of oxygen and moisture in the air, so it has not reached the current commercialization stage. In particular, the oxygen reduction reaction (ORR) that occurs by generating lithium oxide (Li ₂ O ₂ , Li ₂ O) during discharge and the oxygen evolution reaction (OER) that occurs by decomposing these lithium oxides during charging This should occur reversibly, but when insulating particles having a solid phase are generated on the surface of the cathode due to the influence of reaction by-products, charging is inhibited and reaction efficiency is lowered. Lithium oxide that has not been decomposed in the reaction reacts with the carbon material of the cathode to generate irreversible side reaction materials such as Li ₂ CO ₃ and LiRCO ₃ , thereby inhibiting the reversible reaction of the battery and reducing life characteristics.

To solve this problem, a battery can reversibly participate in ORR and OER reactions during charge/discharge, research is being conducted to increase energy density, and various material groups such as ceramic materials, metal catalysts, and ceramic catalysts are being applied. However, when these materials are used as cathodes, they have the disadvantage that they are not suitable for mass production due to their low specific surface area and high weight. Currently, most of the materials with large particle sizes are applied by methods such as sintering and hydration heat treatment. Therefore, it not only requires a considerable amount of time for the reaction, but also becomes an obstacle to efficient battery operation.

In order to solve the above problems, the present invention provides a functional membrane having catalytic properties and a manufacturing method thereof by regularly binding various ceramic nanoparticles having crystallinity to carbon nanofibers having a one-dimensional nanostructure using a Joule heating process. do. In the present invention, in order to solve the limitations of existing technologies that are inefficient and require considerable time, it is possible to manufacture in a short time within a few seconds, and to maximize catalytic properties, microcatalysts of several to hundreds of nm in size are deposited on the surface of carbon nanofibers. stuck. By adjusting the internal air conditions, various metals were used to bind various ceramic nanoparticles with crystallinity, not limited to the binding of single atoms, and perovskite nanoparticles with crystallinity were controlled by adjusting the metal composition ratio and air conditions ABO ₃ structure) is expected to be concluded.

Joule heating that negatively charges the surface of carbon nanofibers through oxygen plasma, binds metal ions to the surface of carbon nanofibers by supporting them in a solution in which metal salts are dissolved, and controls current application time while atmospheric conditions are controlled. Through the process, it provides a carbon nanofiber membrane characterized in that ceramic nanoparticles having crystallinity are uniformly bound to the surface of the carbon nanofibers.

According to one side, the carbon nanofibers are a primary stabilization process in which a spinning solution containing polyacrylonitrile is randomly spun through an electrospinning machine under an air atmosphere and a secondary carbonization process in an inert atmosphere. It may be characterized in that carbon nanofibers made through the method are used as a matrix, and the diameter of the carbon nanofibers is included in the range of 300 nm to 800 nm.

According to another aspect, the metal salt includes at least one of lanthanum, strontium, cobalt, nickel, and vanadium, and heat is instantaneously applied to the carbon nanofibers through the Joule heating process to obtain lanthanum, strontium, cobalt, nickel and vanadium. It may be characterized in that ceramic nanoparticles composed of at least one metal of vanadium are bound to the surface of the carbon nanofibers in a crystalline state.

According to another aspect, the size of the ceramic nanoparticles may be adjusted according to at least one of internal air pressure and current application time in the joule heating process.

According to another aspect, the type of metal of the ceramic nanoparticles bound to the surface of the carbon fiber may be changed or added by changing or adding the type of metal salt included in the solution.

According to another aspect, the joule heating process may be characterized in that the internal air pressure is adjusted within a range of 10 mtorr to 760 torr.

According to another aspect, the degree of oxidation of the ceramic nanoparticles bound to the carbon nanofibers may be controlled through the Joule heating process.

(a) spinning a polymer solution and preparing carbon nanofibers through a heat treatment process; (b) negatively charging the surface of the prepared carbon nanofibers through an oxygen plasma process; (c) supporting carbon nanofibers whose surfaces are negatively charged in a solution in which a metal salt is dissolved; (d) drying the supported carbon nanofibers; (e) combining metal foils to lower contact resistance between both ends of the carbon nanofibers to which the metal salt is bound and electrodes; and (f) binding the crystalline ceramic particles to the carbon nanofibers through a Joule heating process under controlled atmospheric conditions.

According to one side, the solvent of the polymer solution or the solvent of the solution in which the metal salt is dissolved is formic acid, acetic acid, phosphoric acid, sulfuric acid, m-cresol, trifluoroacetanehydride/ Dichloromethane, water, N-methylmorpholine N-oxide, chloroform, tetrahydrofuran and aliphatic ketones methylisobutylketone, methylethylketone, aliphatic hydroxyl groups m-butyl alcohol, isobutyl alcohol, isopropyl Alcohol, methyl alcohol, ethanol, aliphatic compounds such as hexane, tetrachloroethylene, acetone, glycols such as propylene glycol, diethylene glycol, ethylene glycol, halogen compounds such as trichloroethylene, dichloromethane, aromatic compounds such as toluene, Xylene, cyclohexanone as an aliphatic ring compound group, cyclohexane as ester group, n-butyl acetate, ethyl acetate, aliphatic ether group as butylcellosalb, acetic acid 2-ethoxyethanol, 2-ethoxyethanol, amide It may be characterized by including one or more solvents selected from the group consisting of dimethylformamide, dimethylacetamide, and mixtures thereof.

According to another aspect, in the step (a), the first heat treatment of the spun nanofibers in the temperature range of 200 to 300 ° C. to control the cyclization and dehydrogenation reactions, thereby improving the structural stability and mechanical properties between nanofibers. It may be characterized in that the electrical conductivity and electron transfer ability are controlled by controlling the first heat treatment of the nanofibers in a second heat treatment within a temperature range of 800 to 1000 ° C.

According to another aspect, in step (b), defect elements on the surface of the carbon nanofibers are increased through an oxygen plasma process at an intensity of 10 W to 200 W, and the surface of the carbon nanofibers is negatively charged. do.

According to another aspect, the type of the metal salt is a metal form including chloride (-Cl), iodide (-I), nitrate (-NO ₃ ), acetate (-Ac.) or a hydrate of the corresponding salt ( n H ₂ O), including target metal ions that can be dissolved and ionized in the solvents, and the total concentration of the metal ion-based solution in the solution in which the metal salt is dissolved is in the range of 0.005 to 0.1 M, wherein the It is characterized in that the composition of the ceramic nanoparticles produced after the execution of the final process is controlled according to the type and composition of metal ions in the solution in which the metal salt is dissolved.

According to another aspect, in the step (c), the solution in which the metal salt is dissolved is transferred to a vial and a petri dish of an appropriate size so that the carbon nanofibers after the oxygen plasma process are completely immersed in the solution and impregnated for 1 second to 1 minute By doing so, it can be characterized in that the metal ions in the solution are uniformly dispersed and coated on the surface of the carbon nanofibers.

According to another aspect, in the step (d), the carbon nanofibers are heat-treated in a vacuum atmosphere at a temperature range of 60 to 150 ° C. to evaporate the solvent of the solution in which the metal salt is dissolved, and the solvent in the solution in which the metal salt is dissolved. Depending on the type, the degree of dispersion of the ceramic nanoparticles and the reduction ratio of metal ions after the final process may be adjusted.

According to another aspect, the metal foil includes at least one of copper, nickel, and tungsten, has a width ranging from 3 mm to 10 mm depending on the size of the carbon nanofibers, and the carbon nanofibers It may be characterized by having a vertical width included in the range of 2.5 to 4 times in proportion to the size of the membrane.

According to another aspect, the structure of the platform for the joule heating process includes a support that is not decomposed and damaged at 2000 ° C or higher, and the internal air pressure condition for the joule heating process is in the range of 10 mtorr to 760 torr, , The value of the applied current for the joule heating process is included in the range of 1 A to 10 A, and the current application time for the joule heating process is included in the range of 10 ms to 300 seconds.

According to another aspect, metal ions bound to the surface of the carbon nanofibers are ceramicized through heat treatment using the Joule heating process, and ceramic nanoparticles are bound to the surface of the carbon nanofibers to provide catalytic properties. can be done with

According to another aspect, the size of the ceramic nanoparticles bound to the surface of the carbon nanofibers by adjusting at least one of the type of the metal salt, the current application time for the joule heating process, and the internal air pressure condition for the joule heating process. It can be characterized by controlling.

According to another aspect, the ceramic nanoparticles may include nanoparticles having a perovskite structure of ABO ₃ , and the ratio of A and B may be 1:1.

According to another aspect, at least one of the metal A and the metal B may be made of two or more metals.

It is believed that the present invention will be utilized as a core technology necessary to solve the above-mentioned problems of the lithium-air battery. Existing lithium-air battery technology required a material that could reversibly drive ORR and OER reactions during charge/discharge and increase energy density. To solve this problem, various materials (ceramic, metal, etc.) were applied. . However, these materials have fatal weaknesses such as low specific surface area and high weight, and most of the materials with large particle sizes are synthesized through long-term reactions (sintering and hydration heat treatment, etc.).

The present invention is characterized in that a catalyst having a size of several to hundreds of nanometers capable of maximizing a catalytic effect in a short time within a few seconds is uniformly bound to carbon nanofibers in order to solve the limitations of the existing technology. The embodiment of the present invention has the advantage of being able to simply synthesize using various metal salts together with a solution, and has the advantage of being able to solve the reaction that required a considerable time due to the existing sintering and hydrothermal synthesis reaction in a short time. .

It is believed that the present invention will be able to replace the heavy metal current collector applied to the existing lithium-air battery cathode and overcome the slurry casting process of binding the catalyst using an expensive binder. Therefore, the lithium-air battery cathode developed through the present invention will be used as a key technology for commercialization of lithium-air batteries.

The accompanying drawings, which are included as part of the detailed description to aid understanding of the present invention, provide examples of the present invention and explain the technical idea of the present invention together with the detailed description.
1 is a drawing of the color and shape of the spun nanofibers, the nanofibers after the first heat treatment, and the nanofibers after the second heat treatment according to an embodiment of the present invention.
FIG. 2 is a flowchart of a method for manufacturing a carbon nanofiber membrane in which ceramic nanoparticles having crystallinity of several to hundreds of nm are regularly bound to a surface through a Joule heating process according to an embodiment of the present invention.
3 is a diagram illustrating a method of holding copper foils at both ends in order to lower the contact resistance between dried carbon nanofibers and an electrode according to an embodiment of the present invention and a shape of a sample after overall pre-treatment of joule heating.
4 shows (a) an image of a sample loaded in a jul heating device and (b) an image of a sample that emits high heat and bright light during the jul heating process.
5 shows (a) a scanning electron microscope image and (b) an energy dispersive spectroscopy image using a transmission electron microscope, in which a vanadium oxide ceramic according to an embodiment of the present invention regularly rises while covering carbon nanofibers. .
6 is a sample to which Joule heating was applied for 400 ms and (b) a sample to which Joule heating was applied for 200 ms in an air pressure atmosphere of 30 mtorr for three elements of lanthanum, strontium, and cobalt according to an embodiment of the present invention. A scanning electron microscope image is shown.
7 is an internal air pressure of (a) 30 mtorr, (b) 3 torr, (c) 30 torr, and (d) 300 torr for three elements of lanthanum, strontium, and cobalt according to an embodiment of the present invention and a comparative example. shows a scanning electron microscope image of a sample subjected to Joule heating for 400 ms at .
8 shows three elements of lanthanum, strontium, and cobalt according to an embodiment of the present invention and a comparative example fixed at an internal air pressure of 3 torr, (a) 400 ms line heating repeated 5 times at 100 ms intervals, and (b) ) 400 ms line heating was repeated 10 times at 100 ms intervals, and (c) 2 sec line heating and (d) 4 sec line heating are shown.
9 is (a) energy dispersive spectroscopy image and (b) projection of a material subjected to Joule heating of lanthanum, strontium, and cobalt three elements according to an embodiment and a comparative example of the present invention under conditions of an internal air pressure of 3 torr. An electron microscope image is shown.

The present invention can apply various transformations and can have various embodiments. Hereinafter, specific embodiments will be described in detail based on the accompanying drawings.

In describing the present invention, if it is determined that a detailed description of related known technologies may obscure the gist of the present invention, the detailed description will be omitted.

Terms such as first and second may be used to describe various components, but the components are not limited by the terms, and the terms are used only for the purpose of distinguishing one component from another. used

Hereinafter, a one-dimensional carbon nanofiber membrane to which ceramic nanoparticles having crystallinity are bound through a Joule heating process and a manufacturing method thereof will be described in detail with reference to the accompanying drawings.

In the embodiments of the present invention, a carbon nanofiber membrane having a one-dimensional nanostructure is immersed in a solution in which one or more types of metal salts are dissolved and dried to bind metal ions, followed by a Joule heating process in a controlled state of internal air conditions. by applying high energy instantaneously to carbon nanofibers, rapidly heating and rapidly cooling them to rapidly react with metal ions on the surface and oxygen in the air, resulting in uniform ceramic nanoparticles with crystallinity of several to hundreds of nm on the carbon nanofibers. It is characterized by manufacturing a high-mobility and high-conductivity carbon nanofiber membrane with maximized catalytic properties. The ceramic material on the membrane made through the Joule heating process is different from other membranes in which ceramic particles of several hundred nm to several μm in size are bound and made through conventional sintering and hydration heat treatment. Compared to the existing methods, it is possible to bind ceramic nanoparticles regularly with only a short heat treatment within a few seconds, so that the desired ceramic material can be bound on carbon nanofibers remarkably quickly.

Looking at the trend of existing ceramic particle manufacturing technology, studies have been attempted in a method of manufacturing ceramic particles by sintering and hydration heat treatment. However, since the heat treatment process is long and it is manufactured in several steps, it has been shown to be a limitation that it takes a long time to manufacture a desired material. In addition, since the particles grow and form large lumpy particles through a complicated heat treatment process, it is difficult to make small and uniform ceramic particles. In order to improve this, research is being conducted to limit the size during ceramic synthesis by continuously making the sol-gel particles smaller through the sonochemical method, but the limitation that the nanoparticles made has a size of at least several hundred nm is underway. still showing

Therefore, if small ceramic nanoparticles with a size of several to hundreds of nm are bound and synthesized on carbon nanofibers through a Joule heating process in a short time within a few seconds, they have excellent reproducibility, high porosity, high conductivity, and high catalytic activity, and are suitable for next-generation This will lead to the development of carbon nanofiber membranes that can be used as cathodes for lithium-air batteries, an energy system.

In the present invention, due to the ceramic nanoparticles having a size of several to hundreds of nm of various types with crystallinity that are evenly raised on the carbon nanofibers through the Joule heating process, they have high electrical conductivity, high porosity and high catalytic activity. A carbon nanofiber membrane synthesis method is provided. The membrane using the joule heating provided ceramic nanoparticles of a smaller size than ceramic particles manufactured by sintering and hydration heat treatment. In order to manufacture a carbon nanofiber membrane having the above characteristics, a carbon nanofiber membrane in which ceramic nanoparticles are uniformly bound through a fast, efficient and easy process and a manufacturing method thereof are characterized.

1 is a nanofiber 100 obtained through an electrospinning method according to an embodiment of the present invention, a nanofiber 101 obtained after a first heat treatment for structural stabilization of the obtained fiber, and a carbon nanofiber made after a second heat treatment ( 102) is a schematic diagram.

At this time, the diameter of the polymer nanofiber is preferably included in the range of 300 nm to 800 nm, and the diameter of the nanofiber is the viscosity and boiling point of the polymer composite solution, the size of the voltage applied to the electrospinning device, the discharge speed, and the nozzle Can be adjusted by radius. When the diameter of the opened nanofibers is several μm or more, not only the pores between the fibers are significantly lowered, but also the specific surface area is reduced, so that the flow with the outside air of the membrane may not be smooth, and the available contact with the chemical reactants of the energy system As the area becomes smaller, the electrochemical reaction effect may also be lowered. In addition, if the electrical resistance is too low due to the thick fiber, the energy generated by the flow of current is reduced, and ceramic production may not be smooth. That is, using a carbon nanofiber membrane composed of nanofibers having a diameter range of 300 nm to 800 nm is highly useful as a highly active high-porosity membrane, and is advantageous in the Joule heating process to be performed to bind ceramic nanoparticles. Additionally, when fabricating randomly arranged nanofibers by electrospinning, it is possible to adjust the spacing between fibers through the rotation speed and angle of the substrate on the conductive current collector, the discharge speed of the spinning solution, and the radius of the nozzle, , the distribution of pore sizes can be controlled in the range of 50 nm to 10 μm.

In addition, in order to uniformly incorporate the polyacrylonitrile polymer into the nanofibers, the polymer must be completely dissolved in a solvent. For this, formic acid, acetic acid, phosphoric acid, sulfuric acid, m-cresol, trifluoroacetanehydride/dichloromethane, water, N-methylmorpholine N-oxide , chloroform, tetrahydrofuran, aliphatic ketones methyl isobutyl ketone, methyl ethyl ketone, aliphatic hydroxyl groups m-butyl alcohol, isobutyl alcohol, isopropyl alcohol, methyl alcohol, ethanol, aliphatic compounds hexane, tetrachloroethylene, Acetone, propylene glycol, diethylene glycol, ethylene glycol as the glycol group, trichloroethylene, dichloromethane as the halogen compound group, toluene and xylene as the aromatic compound group, cyclohexanone, chlorohexane and ester as the aliphatic ring compound group Selected from the group consisting of n-butyl acetate, ethyl acetate, butyl cello salve as the aliphatic ether group, acetic acid 2-ethoxyethanol, 2-ethoxyethanol, amide as dimethylformamide, dimethylacetamide and mixtures thereof It is important to uniformly incorporate the polymer into the fibers using a solvent.

2 shows a flowchart of a method for manufacturing a carbon nanofiber membrane having a one-dimensional nanostructure in which ceramic nanoparticles are uniformly bound through a Joule heating process according to an embodiment of the present invention. As shown in the flow chart of FIG. 2, the method for manufacturing a nano-ceramic bonded carbon nanofiber membrane includes the steps of spinning a polymer solution and manufacturing carbon nanofibers through primary and secondary heat treatment processes (210), the prepared carbon nanofibers. negatively charging the surface through an oxygen plasma process (220), supporting carbon nanofibers whose surface is negatively charged in a solution in which a metal salt is dissolved (230), drying the supported carbon nanofibers in a vacuum oven Step 240, (e) step 250 of combining copper foil to lower the contact resistance between both ends of the carbon nanofibers to which the metal salt is bound and the electrode, and the Joule heating process under controlled atmospheric conditions. It may include a step 260 of binding the ceramic particles having crystallinity to the carbon nanofibers. In the following, each of the above steps will be described in more detail.

First, a step 210 of spinning a polymer solution and manufacturing carbon nanofibers through primary and secondary heat treatment processes will be described. The polymer for preparing the polymer solution may include polyacrylonitrile (PAN), and the molecular weight may be included in the range of 10,000 to 500,000 Da, preferably included in the range of 50,000 to 200,000 Da. More preferably, the molecular weight of the polymer may be included in the range of 100,000 to 150,000 Da, but is not limited thereto. A spinning solution is made by completely dissolving the selected polymer using a commercial solvent of N,N'-dimethylformamide. In order to prepare the spinning solution, the mass ratio of the polymer and the solvent is fixed at 1:6, and stirring is performed in a stirrer where heat is applied at a temperature of 70 ° C., 50 to 200 rpm between 6 and 20 hours (preferably 80 ~ 150 rpm) is sufficiently stirred so that the polymer is completely dissolved in the solvent phase. After transferring the prepared spinning solution to a syringe with an appropriate capacity, a syringe pump is used to apply pressure to the syringe at a constant speed so that a certain amount of solution is discharged at a certain time. The electrospinning system consists of a high voltage, a grounded conductive substrate with adjustable rotation and transport speed, a syringe, and a syringe nozzle. Here, the diameter of each of the plurality of nanofibers has a size distribution of 300 nm to 800 nm, and as the spacing between the nanofibers is in the range of 10 nm to hundreds of nm, pores with an average diameter of 10 nm to hundreds of nm are included. can do. As a more specific example, a voltage in the range of 15 to 20 kV is applied through a high voltage application device, the rotation speed of the conductive current collector is adjusted in the range of 50 rpm to 200 rpm, and the discharge rate of the solution is in the range of 5 to 20 μL/min. It is possible to obtain a nanofibrous membrane composed of a plurality of nanofibers. Next, the nanofiber membrane is subjected to a primary heat treatment for 2 hours at a temperature of 250 ° C. under atmospheric air conditions together with a conductive current collector substrate, causing a cyclization and dehydrogenation reaction of the polyacrylonitrile to improve heat resistance. A ladder structure with Next, the second heat treatment process of forming a conjugated structure in which six carbon atoms form a planar ring structure is performed at a temperature of 900 ° C. under an inert atmosphere. ) can obtain a carbon nanofiber membrane.

Next, a step 220 of negatively charging the surface of the produced carbon nanofibers through an oxygen plasma process will be described. After creating a vacuum inside the device, high energy is applied to create plasma to functionalize the surface of the material through the oxygen plasma process, which binds a large amount of oxygen radicals to the surface of the carbon nanofiber, thereby negatively charging the surface, and metal ions A carbon nanofiber membrane whose surface is functionalized so that it can be easily bound can be obtained.

Next, a step 230 of supporting carbon nanofibers whose surface is negatively charged in a solution in which a metal salt is dissolved will be described, and a step 240 of drying the supported carbon nanofibers in a vacuum oven. The desired metal salt is dissolved in water and ethanol at a concentration of 0.015 M to 0.03 M based on the metal ion to make a solution in which the metal salt is dissolved, and 2 × 0.5 cm carbon nanofibers are supported in 5 mL of the solution for 10 seconds to obtain a sufficient amount of metal. The ions can be bound to the surface of the carbon nanofibers, and quickly dried using a vacuum oven so that the metal ions on the surface can be evenly bound to the surface of the carbon nanofibers. A carbon nanofiber membrane in which metal ions required for a ceramic to be made are bound at once can be obtained by changing the type of metal salt such as lanthanum, strontium, cobalt, nickel, vanadium, etc. or by using two or more metal salts among them. Preferably, the type of metal salt is in the form of a metal including chloride (-Cl), iodide (-I), nitrate (-NO ₃ ), acetate (-Ac.) or a hydrate of the corresponding salt (.n H ₂ O) and/or a target metal ion that can be ionized by being dissolved in a solvent.

Next, a step 250 of combining copper foil to lower the contact resistance between both ends of the carbon nanofibers to which the metal salt is bound and the electrode will be described. In order to prevent the current applied to the carbon nanofiber from flowing only in a very small area through the part where the electrode is bitten and to lower the contact resistance between the electrode and the carbon nanofiber, copper foil with a size of 0.5 cm × 3 cm is passed on both ends to cover the entire area. A sample that has been pretreated with Joule heating, through which current can flow effectively, can be obtained.

Lastly, the step 260 of binding the crystalline ceramic nanoparticles to the carbon nanofibers by Joule heating the sample after the pretreatment of Joule heating under controlled atmospheric conditions will be described. During the Joule heating process, the pressure inside the device is adjusted within the range of 30 mtorr to 300 torr, and a current of 1 A is applied for 200 ms to 4 seconds, or the same current for 400 ms is repeated 5 or 10 times to several to hundreds of nm. A carbon nanofiber membrane to which ceramic nanoparticles are bound can be obtained. At this time, the carbon nanofibers that are momentarily exposed to ultra-high temperature heat through the Joule heating process increase overall electrical conductivity and provide excellent electron transfer ability.

In the following, the present invention will be described in detail through Examples and Comparative Examples. The examples and comparative examples are only for explaining the present invention, and the present invention is not limited to the following examples, and it is clear to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. It goes without saying that changes and modifications fall within the scope of the appended claims.

Example 1: Highly conductive carbon nanofibers consisting of one-dimensional nanofibers to which vanadium oxide ceramics are regularly bound

3 shows that both ends of a carbon nanofiber according to an embodiment of the present invention are placed on a copper foil having a size of 0.5 cm Х 3 cm, respectively (300), and then the copper foil is folded and both ends are bitten with the copper foil (301). It is a schematic diagram showing the preprocessing process to minimize the contact resistance with the electrode of the line heating device to be performed later. At this time, various metal foils can be used instead of copper foil, but unwanted side reactions are minimized by using foils made of metals with high melting and boiling points so that they do not melt or evaporate when momentarily exposed to high-temperature heat generated during joule heating. A way to do it. If the horizontal length of the copper foil passed on to the carbon nanofibers is longer than 1 cm, the distance between the electrodes through which the current must flow becomes too short, resulting in uneven joule heating throughout the carbon nanofibers. Even if the resistance of the carbon nanofiber is too low, heat cannot be generated sufficiently, so high reproducibility can be shown by measuring the resistance of the carbon nanofiber before proceeding with the pretreatment process.

Figure 4 shows the appearance of light and heat (401) during line heating by loading a sample into a line heating device according to an embodiment of the present invention (400) and applying a current of 1 A. The brightest light is emitted when the point resistance value at both ends of the sample is over 100 Ω, and when a short heat treatment time is applied in a relatively low oxygen partial pressure range, carbon nanofibers are burned inside the device or the carbon surface is oxidized. This rarely occurs, and the joule heating process proceeds stably.

5(a) and 5(b) show a 0.015 M solution based on metal ions made using vanadium chloride as a metal salt and water as a solvent in step 230, followed by steps up to step 260. It shows a scanning electron microscope image and an energy dispersive spectroscopy image obtained through a transmission electron microscope of carbon nanofibers bound with oxide ceramics. Through scanning electron microscope images, it can be confirmed that vanadium oxide is regularly attached to the surface of carbon nanofibers in the form of nanoparticles, and through transmission electron microscope images, particles of several nm in size are regularly attached to the surface of carbon nanofibers. You can check that it has been done.

Example 2: Highly conductive carbon nanofibers composed of one-dimensional nanofibers regularly bound with lanthanum, strontium, and cobalt ceramics, and size control of bound nanoparticles by controlling current application time

6(a) and 6(b) show the same mol numbers of lanthanum chloride, strontium chloride, and cobalt chloride as metal salts in step 220 and water as a solvent at a concentration of 0.015 M based on metal ions. The solution was used, the internal air pressure condition was fixed at 30 mtorr during Joule heating, and the current application time was adjusted to 400 ms and 200 ms, respectively, in step 260 to obtain lanthanum, strontium, and cobalt oxides with crystallinity of different sizes. This is a scanning microscope image of carbon nanofibers bound with ceramics. In the case of a current application time of 400 ms, the nanoparticles grew to a certain extent and grew to a size of about 20 nm, and in the case of a current application time of 200 ms, the nanoparticles did not grow sufficiently and grew to a size of about 13 nm. You can check.

Example 3: Highly conductive carbon nanofibers composed of one-dimensional nanofibers to which lanthanum, strontium, and cobalt ceramics are regularly bound and controlling the size of the bound nanoparticles by adjusting the air pressure inside the device during joule heating

7(a), 7(b), 7(c), and 7(d) show that in step 220, lanthanum chloride, strontium chloride, and cobalt chloride are used in the same mole number as metal salts, and as a solvent Crystalline lanthanum synthesized through a Joule heating process using a solution with a concentration of 0.015 M based on metal ions made using water and gradually increasing the internal air conditions to 30 mtorr, 3 torr, 30 torr, and 300 torr, respectively. This is a scanning microscope image of carbon nanofibers bound with ceramics containing , strontium and cobalt oxide. As the internal air pressure increased, it was confirmed that the size of the ceramic nanoparticles bound up to 30 torr grew from 2 nm to several tens and up to 200 nm. However, when joule heating is performed at 300 torr, the concentration of oxygen present in the air is relatively high, and an ignition phenomenon occurs in the carbon fiber with an instantaneous ignition phenomenon. , it can be confirmed that small, angular and relatively highly crystalline particles are bound.

Example 4: Highly conductive carbon nanofibers composed of one-dimensional nanofibers to which lanthanum, strontium, and cobalt ceramics are regularly bound and controlling the size of bound nanoparticles by adjusting the air pressure inside the device during joule heating

8(a), 8(b), 8(c), and 8(d) show that in step 220, lanthanum chloride, strontium chloride, and cobalt chloride are used as metal salts in the same mole number, and as a solvent A solution with a concentration of 0.015 M based on metal ions made using water was used, the internal air condition was fixed at 3 torr, and the current application time during the Joule heating process was 5 times of 400 ms each, 10 times of 400 ms each, 2 seconds This is a scanning microscope image of carbon nanofibers bonded with ceramics containing crystallized lanthanum, strontium, and cobalt oxides synthesized by controlling , 4 seconds. When the current is applied several times in a short period of time, it can be confirmed that as the number of times increases from 5 to 10, the particles are more uniformly bound to the surface of the carbon nanofibers, and the particle size also becomes smaller. In addition, when a current is applied for 2 seconds, it can be confirmed that the particle growth of the nanoparticles takes place for a long time, and the size of the particles increases and covers the surface of the carbon nanofibers. However, when a current was applied for 4 seconds, it was confirmed that the particles covering the surface were uniformly bound on the carbon nanofibers in the form of cubic nanoparticles with high crystallinity. The bound nanoparticles have a size of several to hundreds of nm, and in particular, the sample to which current was applied for 4 seconds had high crystallinity.

Figures 9 (a) and 9 (b) show energy dispersive spectroscopy images and high-resolution transmission electron microscope images of the sample to which current was applied for 4 seconds. As can be seen in the energy dispersive spectroscopy image, it can be seen that lanthanum, strontium, cobalt, and oxygen are evenly distributed in one nanoparticle. In addition, it can be confirmed through a high-resolution transmission electron microscope image that ceramic nanoparticles having a size of several to hundreds of nm are crystalline. Example 4 combines the optimal conditions of Examples 1, 2, and 3, and when multi-element metals such as lanthanum, strontium, and cobalt are used, under what air conditions and for how long a current is applied to the nanoparticles This is an example of confirming that metal nanoparticles have the highest crystallinity and are most uniformly bound to the surface. Furthermore, Embodiments 1, 2, 3, and 4 are characterized in that it is possible to experimentally and empirically predict how long a current application time should be passed in various metal elements, under what air conditions, by applying the previous results.

As another solution of the present invention, in the process from step 230 to step 260, the pressure inside the line heating device, the ratio of metal salts, the concentration of the solution in which the metal salt is dissolved, and the current application time during line heating are adjusted As a result, the ABO ₃ structured perovskite material can be bound on the carbon nanofibers in a size of several to hundreds of nm.

In addition, in a lithium-air battery composed of a lithium cathode, a separator, an air cathode, and an air diffusion layer for application as an eco-friendly energy technology, the carbon nanofiber material to which the ceramic nanoparticles developed in the present invention are evenly bound is used as a cathode material. The structure of an air anode suitable for a lithium-air battery can be designed.

In addition, the embodiments of the present invention are not only utilized in the green energy field, but can be applied to any field requiring nano-ceramic particles or a conductive material to which a catalytic material is bound as needed.

Unlike conventional hydrothermal synthesis or sintering reactions that take several hours to several tens of hours, the embodiments of the present invention can be produced remarkably quickly in a matter of seconds, and ceramic particles can be made into carbon nanoparticles in the form of very small nanoparticles with a size of several to hundreds of nm. It is very differentiated in that it can bind uniformly to the surface of fibers. In addition, since the embodiments of the present invention use a metal ion dissolving solution, the type of ceramic particles can be easily controlled, and the size of the ceramic particles to be bound is on the order of several to hundreds of nm and is uniformly bound to the surface of the carbon nanofibers. The catalytic properties can be maximized, and the carbon nanofiber itself is re-carbonized during the high-temperature heat treatment process of Joule heating, and the conductivity dramatically increases. It is expected that Furthermore, it is expected that the technology and manufacturing method provided by the embodiments of the present invention will be an important technology that enables to overcome the limitations of electric vehicles using lithium ion batteries that do not currently reach the target mileage. . In addition, it was experimentally confirmed that the conductivity of the entire electrode can be dramatically increased while binding various ceramic particles on the carbon nanofibers in a nanoscale. Based on these experimental results, it will be possible to regularly bind perovskite nanoparticles by adjusting the type of metal salt, air pressure inside the device, and applied current intensity and time. It will contribute to the realization of a high-capacity/long-life battery system and will be widely expandable beyond the energy field to industrial fields such as next-generation automobiles, which are often cited as application points for lithium-air batteries, thereby reducing environmental pollution and carbon dioxide. It will be able to contribute to environmental protection, such as preventing global warming.

As such, the carbon nanofiber membrane in which ceramic nanoparticles having crystallinity and containing various metal elements are uniformly bound using Joule heating can be used as an air electrode of a lithium-air battery, which is attracting attention as a next-generation energy storage system. However, it is synthesized based on the electrospinning process that can be synthesized in a large area and is highly likely to be commercialized and applied. In addition, when used in electric vehicle technology under an actual atmosphere, it can be applied as a very economical air electrode with low weight, high conductivity and high catalytic properties that can solve the limitations of conventional heavy metal or low conductivity carbon based air electrodes. there is. Furthermore, it can be used in various fields other than the energy field that require materials with various conductivity, low weight, and catalytic properties.

The above description is merely an example of the technical idea of the present invention, and various modifications and variations can be made to those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments described in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and are not limited to these embodiments. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the equivalent range should be construed as being included in the scope of the present invention.

Claims (20)

delete delete delete delete delete delete delete (a) spinning a polymer solution and preparing carbon nanofibers through a heat treatment process;
(b) negatively charging the surface of the prepared carbon nanofibers through an oxygen plasma process;
(c) supporting carbon nanofibers whose surfaces are negatively charged in a solution in which a metal salt is dissolved;
(d) drying the supported carbon nanofibers;
(e) combining metal foils to lower contact resistance between both ends of the carbon nanofibers to which the metal salt is bound and electrodes; and
(f) binding ceramic nanoparticles with crystallinity to carbon nanofibers through a Joule heating process under controlled atmospheric conditions
Method for producing a carbon nanofiber membrane comprising a. According to claim 8,
The solvent of the polymer solution or the solvent of the solution in which the metal salt is dissolved is formic acid, acetic acid, phosphoric acid, sulfuric acid, m-cresol, trifluoroacetanehydride/dichloromethane , water, N-methylmorpholine N-oxide, chloroform, tetrahydrofuran and aliphatic ketones methyl isobutyl ketone, methyl ethyl ketone, aliphatic hydroxyl group m-butyl alcohol, isobutyl alcohol, isopropyl alcohol, methyl alcohol , ethanol, aliphatic compounds such as hexane, tetrachloroethylene, acetone, propylene glycol, diethylene glycol, ethylene glycol as glycol groups, trichloroethylene, dichloromethane as halogen compounds, toluene, xylene, aliphatic compounds as aromatic compounds Cyclohexanone as a cyclic compound group, n-butyl acetate as cyclohexane and ester group, ethyl acetate, butylcellosalve as aliphatic ether group, 2-ethoxyethanol acetate, 2-ethoxyethanol as amide, dimethylformamide as amide, A method for producing a carbon nanofiber membrane comprising at least one solvent selected from the group consisting of dimethylacetamide and mixtures thereof. According to claim 8,
In step (a),
By first heat-treating the spun nanofibers within a temperature range of 200 to 300 ° C. to control the cyclization and dehydrogenation reactions, the structural stability and mechanical properties between the nanofibers are controlled,
A method for producing a carbon nanofiber membrane, characterized in that the second heat treatment of the first heat treatment nanofibers in the temperature range of 800 to 1000 ℃ to control the electrical conductivity and electron transfer ability. According to claim 8,
In step (b),
A method of manufacturing a carbon nanofiber membrane, characterized in that, through an oxygen plasma process of 10 W to 200 W, defect elements on the surface of the carbon nanofibers are increased and the surface of the carbon nanofibers is negatively charged. According to claim 8,
The type of the metal salt is a metal form including chloride (-Cl), iodide (-I), nitrate (-NO ₃ ), acetate (-Ac.) or a hydrate of the corresponding salt (· n H ₂ O) , containing a target metal ion that can be dissolved in solvents and ionized,
The total concentration of the metal ion-based solution in the solution in which the metal salt is dissolved is in the range of 0.005 to 0.1 M,
A method for producing a carbon nanofiber membrane, characterized in that the composition of the ceramic nanoparticles produced after the final process is adjusted according to the type and composition of metal ions in the solution in which the metal salt is dissolved. According to claim 8,
In step (c),
The solution in which the metal salt is dissolved is transferred to a vial and a petri dish of an appropriate size, and the carbon nanofibers after the oxygen plasma process are completely immersed in the solution for 1 second to 1 minute, so that the metal ions in the solution are on the surface of the carbon nanofibers. A method for producing a carbon nanofiber membrane, characterized in that it is uniformly dispersed and coated. According to claim 8,
In step (d),
The carbon nanofibers are heat treated in a vacuum atmosphere at a temperature range of 60 to 150 ° C. to evaporate the solvent of the solution in which the metal salt is dissolved,
A method for producing a carbon nanofiber membrane, characterized in that the degree of dispersion of the ceramic nanoparticles and the reduction ratio of metal ions after the final process is adjusted according to the type of solvent of the solution in which the metal salt is dissolved. According to claim 8,
The metal foil,
at least one of copper, nickel and tungsten;
It has a width in the range of 3 mm to 10 mm depending on the size of the carbon nanofibers,
Having a vertical width included in the range of 2.5 to 4 times in proportion to the size of the carbon nanofiber membrane
Method for producing a carbon nanofiber membrane, characterized in that. According to claim 8,
The structure of the platform for the joule heating process includes a support that is not decomposed and damaged at 2000 ° C or higher,
Internal air pressure conditions for the joule heating process are in the range of 10 mtorr to 760 torr,
The value of the applied current for the Joule heating process is included in the range of 1 A to 10 A,
The current application time for the Joule heating process is included in the range of 10 ms to 300 seconds
Method for producing a carbon nanofiber membrane, characterized in that. According to claim 8,
Carbon nanofiber membrane, characterized in that the metal ions bound to the surface of the carbon nanofiber are ceramicized through heat treatment using the Joule heating process, and ceramic nanoparticles are bound to the surface of the carbon nanofiber to provide catalytic properties. Manufacturing method of. According to claim 8,
Controlling the size of the ceramic nanoparticles bound to the surface of the carbon nanofibers by adjusting at least one of the type of the metal salt, the current application time for the joule heating process, and the internal air pressure condition for the joule heating process, characterized in that A method for producing a carbon nanofiber membrane. According to claim 8,
The ceramic nanoparticles include nanoparticles of a perovskite structure of ABO ₃ ,
The ratio of A and B is 1:1
Method for producing a carbon nanofiber membrane, characterized in that. According to claim 19,
A method for producing a carbon nanofiber membrane, characterized in that at least one of the A and the B is made of two or more metals.