KR100675923B1 - Metal oxide incorporated activated carbon nanofibers by co-electrospinning, their applications of electrode for supercapacitors, and the producing method of the same - Google Patents

Abstract

A metal oxide incorporated activated carbon nano fiber, an electric double layer super-capacitor electrode and a manufacturing method thereof are provided to manufacture a high-performance electrode due to the Faraday reaction. The metal compound is added into the carbon fiber precursor polymer and dissolved by the respective precursor polymer solvent so that the spinning solution is manufactured. The spinning solution is spun by an electric spinning manner so that the ultra micro-fiber web is formed. The temperature of the fiber web is increased until 350 degrees in centigrade and stabilized at the oxidation gas atmosphere. The stabilized fiber is carbonated at 500 -1500 degrees in centigrade under the inert gas atmosphere so that the ultra micro-fiber containing the metal oxide is manufactured.

Description

Metal oxide composite nano activated carbon fibers and electrodes for electric double layer supercapacitors using the same, and methods for manufacturing the same.Metal oxide incorporated activated carbon nanofibers by co-electrospinning, their applications of electrode for supercapacitors, and the producing method of the same}

1 is a simplified schematic diagram of the production of ruthenium oxide-containing nanofibers by electrospinning.

Figure 2 is a scanning electron micrograph of a ruthenium oxide (10, 20%) containing ultra-fine polyacrylonitrile fiber prepared according to an embodiment of the present invention.

Figure 3 is an X-ray diffraction analysis of ruthenium oxide / carbon fiber prepared according to an embodiment of the present invention.

Figure 4 is a table of the results of elemental analysis of ruthenium oxide-containing nanocomposite activated carbon fibers by EDX analysis.

Figure 5 is a scanning electron micrograph of the nanocomposite activated carbon fiber 30 minutes steam activation at 800 ℃ of the ruthenium oxide-containing composite fiber prepared according to another embodiment of the present invention.

FIG. 6 is a graph of a constant current discharge using 20 wt.% Of the nanocomposite activated carbon fiber prepared according to another embodiment of the present invention in an electrode. FIG.

7 is a CV (cyclic voltammogram) graph of a supercapacitor electrode manufactured according to another embodiment of the present invention.

The present invention relates to a metal oxide composite nano-activated carbon fiber, an electrode for an electric double layer supercapacitor using the same, and a method of manufacturing the same. More specifically, metal oxides such as ruthenium oxide or ruthenium precursor solution are dispersed and mixed in a carbon fiber precursor solution. After the composite electrospinning to produce a ruthenium oxide-containing ultra-fine fibers having a fiber diameter of less than 500 nm and to oxidatively stabilize them, and to carbonized or activated to produce electrodes of ruthenium oxide-containing activated carbon fibers having an ultra-high specific surface area.

In general, energy storage systems are divided into primary and secondary batteries using an electrochemical reaction accompanied by a redox reaction and lithium-based secondary batteries using a rocking chair system of lithium ions. It can be divided into an electrochemical supercapacitor using the electric double layer principle formed at the interface of the phase. The electrochemical capacitor has a specific capacitance (F / g) of 100 to 1000 times higher than that of a conventional electrostatic capacitor, which is a supercapacitor or ultra-capacitor. According to the electrode material used, it is divided into a supercapacitor using an electric double layer principle (EDLC) and a pseudocapacitor expressing a capacity by a Faradaic reaction. An electric double layer capacitor is a device using electric charges accumulated in an electric double layer generated between a solid electrode and an electrolyte, and attracts attention from various fields in terms of use and application. In particular, capacitors have a lower energy density than batteries, but have excellent characteristics in terms of power density that exerts momentary power, and are expected to be applied to various fields due to almost semi-permanent lifespan exceeding several hundred thousand times.

As the electrode material for EDLC, an activated carbon-based carbon material having a large specific surface area, electrochemically stable and high conductivity is used, and an electrode material for pseudocapacitors is mainly metal oxide, polypinol, polyaniline, and polyacene. It can be divided into conductive polymers. RuO ₂ , IrO ₂ , NiO, CoO _x , MnO ₂ , WO _3, etc. have been developed as metal oxide electrode materials, showing excellent energy density comparable to that of secondary batteries, but low cycle life and high price and manufacturing process of electrode active materials. Due to difficulties, development is delayed.

Ruthenium oxide and iridium oxide are mainly used as metal oxide electrode materials, and ruthenium oxide is mainly classified into anhydrous and hydrate type, and anhydrous ruthenium oxide electrode for supercapacitor is mainly used for pyrolysis. In the case of hydrate, it is a general method to manufacture by sol-gel method. Although the specific capacitance of a supercapacitor using ruthenium oxide-based active material is about 600-650 F / g, it is known that the manufacturing process is complicated, requires a long time, and the cycle characteristics are lower than that of an EDLC carbon material. It is pointed out that the electrode material is expensive.

Currently, electrochemical capacitors used in memory back-up or parts requiring instantaneous peak power in various industries have higher output density than secondary batteries, and have semi-permanent cycle life and low environmental load. It is expected to be used in various industrial fields, but the energy density is lower than that of secondary batteries.

In order to improve the energy density of the EDLC, various researches are being conducted. The development of pseudocapacitors using Faraday reactions together with the structural control of carbon materials and the search for new carbon materials, parallel with various secondary batteries, and the positive electrode (+) Research into hybrid capacitors having different electrode materials of negative and negative electrodes has been actively conducted. Carbon materials for electrochemical capacitors mainly use coal, petroleum pitch, phenol resin, wood and carbon precursor precursor polymers as starting materials and activate at a temperature of less than 1200 ℃ using oxidizing gas or inorganic salts and have high specific surface area. Activated carbon and activated carbon fibers are used. In particular, in the case of activated carbon fibers, the pore distribution is more uniform than that of activated carbon, and high specific surface area characteristics can be produced in paper, felt, and non-woven fabrics, thereby making it possible to make higher-performance electrode active materials. However, active carbon fibers currently produced and sold are mainly polyacrylonitrile (PAN), pitch (Pitch), by expensive melt-spinning or melt-blown spinning equipment. Fiber is manufactured by phenolic resin (phenolic-resin) and then oxidative stabilization, carbonization or activation, but the fiber produced by the conventional spinning method is made of about 10㎛ diameter of about 10㎛ in diameter There is a limit to effectively improving the surface area.

In addition, when used as an electrode active material, the fiber is crushed to add a binder or a conductive material, and then applied to a current collector. In the case of a fabric, the fabric is used after weaving the manufactured fiber and then activating the fiber. Due to its relatively large diameter, the electrode has a low density and thus has a disadvantage in that high-speed charging and discharging or high output characteristics are degraded.

Accordingly, the present invention has been made to solve the problems of the prior art as described above, the object of the present invention is to produce a metal oxide composite ultra-fine activated carbon fiber, such as ruthenium oxide by electrospinning method and using it as a conductive agent or binder It is to provide a metal oxide composite nano-active carbon fiber used as an electrode for an electric double layer supercapacitor, an electrode for an electric double layer supercapacitor using the same, and a method of manufacturing the same, without the addition, grinding, and weaving process.

It is still another object of the present invention to manufacture carbon fiber to overcome the disadvantages of metal oxide electrode materials having low cycle life, high electrode active material price, and difficult manufacturing process, and EDLC capacitors have low energy density compared to secondary batteries. By adding a metal oxide to the spinning solution to increase the energy density, it is made of ultra-fine fibrous web through electrospinning to shorten the electrode manufacturing process and high energy density due to high electrode density and high energy density due to the amount of use (Faraday reaction) with the electric double layer. It is to provide a method for producing an electrode easily and inexpensively.

According to a feature of the present invention for achieving the above object, the present invention in the production of ultrafine activated carbon fibers containing metal oxide, the first step is to add a metal oxide to the carbon fiber precursor polymer solvent of each precursor polymer Preparing a spinning solution by dissolving in a second step, and electrospinning the spinning solution to form an ultrafine fibrous web. In a third step, the fibrous web is heated to 350 ° C. to be stabilized by incompatibility under an oxidizing gas atmosphere. In the step, the fourth step is carbonizing the stabilized fibers at 500 ℃ to 1500 ℃ in an inert gas atmosphere or vacuum to form a metal oxide-containing ultra-fine carbon fiber, the fifth step is the metal oxide-containing ultra-fine carbon fiber 600 ℃ ~ 1200 using oxidizing gas such as water vapor, carbon dioxide or inorganic salts such as KOH, ZnCl ₂ , H ₃ PO ₄ and NaOH Activating in the temperature range of ℃ includes the step of producing a metal oxide-containing ultra-fine activated carbon fiber.

Preferably, the metal oxide of the first step is RuO ₂ , IrO ₂ , NiO, CoO _x , MnO ₂ , WO ₃ One selected from the group consisting of metal oxides such as 1 to 50% by weight compared to the carbon fiber precursor material, when the carbon fiber precursor is polyacrylonitrile (PAN) solvent is dimethylformamide (DMF) or dimethylacetamide (DMAc) and PAN was dissolved in DMF or DMAc 5-30% by weight to prepare a spinning solution.

More preferably, a voltage of (+) and (-) 5 kV to 60 kV is applied to the nozzle and the focusing roller of the electrospinning apparatus of the second stage, respectively, and the distance between the nozzle and the focusing roller is 5 to 35 cm to maintain the discharge speed. Is electrospun at 1 to 5 ml / hr and winding speed at 5 to 1500 m / min.

More preferably, the metal oxide-containing ultrafine fiber web spun in the third step is heated to 350 ° C. at a temperature increase rate of 1 to 5 ° C./min and maintained for 1 hour to supply compressed air at 0.5 to 20 ml per minute. In the fourth step, the stabilized fiber is carbonized while maintaining the temperature for 1 hour after heating up to 700-1000 ° C. at 5 ° C./min under an inert atmosphere such as nitrogen and argon gas.

Even more preferably, in the fifth step, the stabilized fiber or carbonized fiber is activated in a temperature range of 700 to 1200 ° C. using nitrogen gas and steam having a ratio of nitrogen gas and steam of 0.5 to 99% by volume. Containing ultrafine activated carbon fibers.

According to a preferred embodiment of the present invention, the nonwoven fabric of the metal oxide-containing ultrafine activated carbon fiber prepared by the above manufacturing method is placed on the current collector, a cellulose separator is sandwiched between the positive electrode and the negative electrode, and a water-soluble electrolyte solution is used. The electrode for the electric double layer supercapacitor can be manufactured.

The nonwoven fabric of the metal oxide-containing ultrafine activated carbon fiber prepared by the above manufacturing method was cut and placed on a nickel foil current collector, sandwiched with a cellulose separator between the positive electrode and the negative electrode, and impregnated with a 6M KOH aqueous electrolyte solution. By using a pouch treated with aluminum lining, the electrode for the electric double layer supercapacitor can be manufactured.

The nonwoven fabric of the metal oxide-containing ultrafine activated carbon fiber prepared by the above manufacturing method is placed on the current collector, and a cellulose separator is sandwiched between the positive electrode and the negative electrode, and an electrode for an electric double layer supercapacitor is prepared by using an organic electrolyte solution. Can be.

In addition, the metal oxide-containing ultra-fine activated carbon fiber produced by the above production method may be used for electrodes of fuel cells, industrial filters, and the like.

According to the metal oxide composite nano active carbon fiber and the electrode for electric double layer supercapacitor using the same according to the present invention and a method for manufacturing the same, the metal oxide is contained in the precursor of the ultrafine active carbon fiber having excellent specific surface area to volume ratio. By dispersing and spinning, high energy density due to electric double layer and pseudocapacity is possible, and weaving process can be omitted after manufacturing in web state by electrospinning, and it does not need to go through the process of adding binder or conductive agent. Since the process can be shortened, an electrode for an electric double layer supercapacitor capable of achieving high energy density with excellent specific surface area characteristics can be produced at low cost.

Hereinafter, a preferred embodiment of the metal oxide composite nano active carbon fiber according to the present invention having the configuration as described above, an electrode for an electric double layer supercapacitor using the same, and a manufacturing method thereof will be described in detail with reference to the accompanying drawings.

First, the general manufacturing process of the metal oxide composite nano activated carbon fiber according to the present invention will be described. After adding a metal oxide to the carbon fiber precursor polymer, it is dissolved in a solvent compatible with the precursor polymer used to form a spinning solution. Emission by electrospinning In the short fiber manufacturing process by the electrospinning method, a short fiber is prepared by introducing a polymer solution into a high-voltage electric field. Specifically, the polymer solution is spun (sprayed) through a spinning nozzle having a + (-) electrode. It is a method for producing ultra-fine short fibers by collecting with a suction collector having a-(+) electrode. The diameter of the fiber produced by such a method is used in medical suture nonwoven fabrics, industrial filters and the like as ultra-fine fibers of less than ~ 1㎛. The fiber on the web produced by the electrospinning method may be stabilized, carbonized, and activated to produce nanometer-sized carbon nanofibers and activated carbon nanofiber webs. The carbon fiber and activated carbon fiber on the web prepared in this way have high electrical conductivity and ultra-high specific surface area, so that secondary processing and binders are unnecessary when manufacturing the electrode, and can be applied to an electrode for a large-capacity electric double layer capacitor.

Looking at an embodiment of the present invention with reference to Figure 1, first, ruthenium oxide hydrate is mixed with 1 to 50% by weight of polyacrylonitrile (polyacrylonitrile), a carbon fiber precursor polymer dimethylformamide (N, N -dimethylformaide, DMF) dissolved in 5 to 30% by weight of the solvent to prepare a spinning solution (a). The prepared spinning solution prepares a ruthenium oxide-containing polyacrylonitrile composite fiber nonwoven fabric having a fiber diameter of less than 500 nm through an electrospinning method with a high voltage generator (b). At this time, a voltage of (+) and (-) 5 kV to 60 kV, preferably 30 kV is applied to the nozzle and the focusing roller of the electrospinning apparatus, respectively (c), and the distance between the nozzle and the focusing roller is 5 to 35 cm (d ), The discharge speed is 1 ~ 5 ml / hr, the winding speed is 5 ~ 1500 m / min.

The ruthenium oxide-containing polyacrylonitrile composite fiber produced by the electrospinning is trapped in the current collector in a disordered nonwoven fabric and the density of the collected fibers increases when the speed of the focusing roller is increased, wherein the portion containing ruthenium It takes the form dispersed in this bead (bead), Figure 2 (a) is a scanning microscope picture when the ruthenium content is 10%, (b) is a scanning microscope picture when the ruthenium content is 20% As the ruthenium content increases, the droplet phase increases.

As shown in FIG. 3, X-ray diffraction analysis of the ruthenium oxide-containing nanocomposite activated carbon fiber shows that as the ruthenium content increases, the diffraction pattern due to the ruthenium oxide appears to be stronger. ((A) is RuO ₂ 0% by weight, (b) shows 10% by weight of RuO ₂ , (c) shows 15% by weight of RuO ₂ , and (d) shows 20% by weight of RuO _2. )

In addition, as can be seen through Figure 4, EDX analysis results, such as X-ray diffraction shows that the content of ruthenium (Ru) and oxygen (O) gradually increases as the ruthenium oxide content increases. (The weight percent shown in Figure 4 represents the RuO ₂ content relative to polyacrylonitrile, the carbon fiber precursor material.)

The composite fiber thus prepared is heated to 350 ° C. at an elevated rate of 1 to 5 ° C. per minute using an electric furnace and maintained for 1 hour to infusibilize and oxidatively stabilize.

The scanning micrograph shown in FIG. 5 relates to a metal oxide-containing activated carbon fiber. FIG. 5A shows a RuO ₂ in a precursor state. 5B shows the carbonized RuO ₂ containing ultrafine fibers, respectively. At this time, as the oxidizing gas, compressed air is supplied at 0.5 to 20 ml per minute, and the stabilized fiber is carbonized while maintaining the temperature for 1 hour after raising the temperature to 700-1000 ° C. at 5 ° C./min under an inert atmosphere (nitrogen, argon gas). The ultrafine ruthenium oxide-containing carbon fiber web was prepared. At this time, the yield of the carbon fiber production is high as 30 ~ 70% depending on the carbonization temperature, the diameter of the fiber constituting the ultra-fine carbon fiber web made is mostly less than 500 nm. In addition, the stabilized fiber is activated in the temperature range of 700 ~ 1200 ℃ using nitrogen gas and steam, wherein the ratio of the nitrogen gas and steam used is 0.5 ~ 99% by volume, 77K nitrogen isothermal adsorption of the prepared composite fiber The BET specific surface area is about 800 to 2000 m 2 / g depending on the activation temperature and the ratio of steam, and the average pore size is concentrated in the micropore region of about 0.2 nm or less.

According to another embodiment of the present invention, the ruthenium oxide-containing activated nanocarbon fiber nonwoven fabric electrospun by the method of Example 1 was cut to a size of 1.5 cm × 1.5 cm and placed on a nickel foil current collector. A cellulose separator is sandwiched between the positive electrode and the negative electrode, impregnated with 6M KOH aqueous electrolyte solution, and sealed using an aluminum-lized pouch to prepare a supercapacitor. The electrolyte solution can also be used as an organic solution.

As shown in FIG. 6, the supercapacitor manufactured by the above method is measured in the range of charge voltage 0.0-0.9 V, charge and discharge current 1-20 mA / cm 2 using a constant current charge / discharge method, and time-voltage The specific capacitance C is calculated from the discharge curve using the following equation (1).

.....................................................(1)

........................................ ...(One)

The specific storage capacity calculated from Equation (1) is highly dependent on the ruthenium oxide content and the specific surface area by activation conditions, and represents about 250-600 F / g, which is an electrospun polyacryl with no ruthenium added. A capacity increase of about 100-500% is shown compared to the same experimental conditions of nitrile activated carbon fibers.

In order to examine the ruthenium oxide redox reaction of the ruthenium oxide-containing activated carbon fiber nonwoven electrode, the supercapacitor prepared above was subjected to a cyclic voltammogram (CV) voltage range of 0.0-0.9 V and a scan rate of 1 mV / When the redox reaction to the ruthenium content was measured by measuring in the range of S-500 mV / S, as shown in FIG. 7, as the ruthenium oxide content increased, the capacity of the redox reaction increased but the ruthenium oxide content was increased. If the amount exceeds 50%, the specific surface area of the composite fiber is relatively decreased, and the capacity of the electric double layer decreases, so that the total capacity is 15 to 30%. In addition, if the content of ruthenium oxide is more than 50%, the viscosity of the solution during the spinning is sharply increased, which shows a disadvantage that the radioactivity is significantly reduced, the cycle characteristics of the supercapacitor electrode is also reduced.

As described above, in the present invention, a metal oxide such as ruthenium oxide was added to the precursor spinning solution of carbon fiber to improve pseudocapacity by Faraday reaction, and then stabilized after spinning the ultrafine fibers of nano units by electrospinning method. It can be seen that the technical idea is to inexpensively produce ultrafine activated carbon fibers containing metal oxides, which have excellent specific surface area characteristics and high energy density by undergoing carbonization and activation. Within the scope of the basic technical idea of the present invention, many other modifications will be possible to those skilled in the art.

As described above, according to the configuration of the present invention, the following effects can be expected.

First, in the present invention, the activated carbon fibers used in the electrode material of the conventional electrochemical capacitors are manufactured by melt spinning or melt spraying, so that the fiber diameter stays within about 10 μm, which effectively limits the specific surface area to volume. After adding a metal oxide to the precursor of the fiber, nanofibers may be manufactured by spinning using electrospinning to provide a fiber having excellent specific surface area to volume characteristics.

Secondly, the present invention enables high energy density due to the electric double layer and pseudocapacity by dispersing metal oxide inside the precursor of carbon fiber.

Third, since the carbon fiber precursor is manufactured in a web state using electrospinning, the weaving process can be omitted afterwards, and when used as an electrode active material, it is not necessary to grind the fiber and add a binder or a conductive agent. There is an advantage that can be shortened.

Net material, the present invention can realize a high energy density and excellent specific surface area through the shortened manufacturing process as described above it is possible to produce an electrode for an electric double layer supercapacitor at low cost.

Claims (12)

In the production of metal oxide-containing ultra-fine activated carbon fibers, the metal oxide-containing ultra-fine activated carbon fibers, characterized in that produced through the following steps; The first step is to prepare a spinning solution by adding a metal oxide to the carbon fiber precursor polymer dissolved in a solvent of each precursor polymer The second step is to electrospin the spinning solution to form an ultrafine fiber web In the third step, the fiber web is heated up to 350 ° C. to stabilize the fiber web in an oxidizing gas atmosphere to stabilize it. The fourth step is to carbonize the stabilized fibers at 500 ℃ to 1500 ℃ in an inert gas atmosphere or vacuum to form a metal oxide-containing ultra-fine carbon fibers In the fifth step, the metal oxide-containing ultrafine carbon fiber is activated using an oxidizing gas such as water vapor, carbon dioxide, or an inorganic salt such as KOH, ZnCl ₂ , H ₃ PO _4, and NaOH in a temperature range of 600 ° C. to 1200 ° C. Preparing ultrafine activated carbon fibers containing. The method of claim 1, In the first step, the metal oxide is RuO ₂ , IrO ₂ , NiO, CoO _x , MnO ₂ , WO ₃ Metal oxide-containing ultra-fine activated carbon fiber, characterized in that containing 1 to 50% by weight relative to the carbon fiber precursor material as one selected from the group consisting of metal oxides. The method of claim 1, In the first step, the carbon fiber precursor is a polyacrylonitrile (PAN), a metal spinning solution prepared by dissolving 5-30% by weight in solvent dimethylformamide (DMF) or dimethylacetamide (DMAc) Oxide containing ultrafine activated carbon fiber. The method of claim 1, A voltage of (+) and (-) 5kV ~ 60kV is applied to the nozzle and the focusing roller of the electrospinning device of the second stage, respectively, and the distance between the nozzle and the focusing roller is 5 ~ 35cm, and the discharge speed is 1-5ml / hr, the winding speed is 5 ~ 1500 m / min, the metal oxide-containing ultra-fine activated carbon fiber, characterized in that the electrospun. The method of claim 1, In the third stage, the spun metal oxide-containing ultrafine fiber web is heated to 350 ° C at a temperature increase rate of 1 to 5 ° C / min, maintained for 1 hour, and is fired under an oxidizing gas atmosphere such as supplying compressed air at 0.5 to 20 ml per minute. Metal oxide-containing ultra-fine activated carbon fibers characterized in that stabilized by fusion. The method of claim 1, The fourth step is a carbon oxide containing ultrafine activated carbon fiber, characterized in that the stabilized fiber is carbonized while maintaining the temperature for 1 hour after heating up to 700-1000 ℃ at 5 ℃ / min in an inert atmosphere such as nitrogen, argon gas. The method of claim 1, The fifth step is a metal oxide containing characterized in that the stabilized fiber or carbonized fiber is activated in the temperature range of 700 ~ 1200 ℃ using nitrogen gas and steam with a nitrogen gas and steam ratio of 0.5 to 99% by volume Ultrafine activated carbon fiber. In the electrode for electric double layer supercapacitor,  The nonwoven fabric of the metal oxide-containing ultrafine activated carbon fiber prepared by the method of claim 1 is placed on a current collector, a cellulose-based separator is sandwiched between the positive electrode and the negative electrode, and an electric double layer is produced using a water-soluble electrolyte solution. Supercapacitor electrode. In the electrode for electric double layer supercapacitor,  The nonwoven fabric of the ultrafine activated carbon fiber containing the metal oxide prepared by the method of claim 1 is cut and placed on a nickel foil current collector, a cellulose separator is sandwiched between the positive electrode and the negative electrode, and a 6M KOH aqueous electrolyte solution is prepared. An electrode for an electric double layer supercapacitor, comprising: a supercapacitor produced by impregnating and sealing a pouch treated with aluminum lining. In the electrode for electric double layer supercapacitor,  The nonwoven fabric of the metal oxide-containing ultrafine activated carbon fiber prepared by the method of claim 1 is placed on a current collector, a cellulose separator is sandwiched between a positive electrode and a negative electrode, and an electric double layer is produced using an organic electrolyte solution. Supercapacitor electrode. In the electrode of the fuel cell,  An electrode of a fuel cell, wherein the metal oxide-containing ultrafine activated carbon fiber prepared by the method of claim 1 is used for electrode production. In the industrial filter, An industrial filter comprising a metal oxide-containing ultra-fine activated carbon fiber prepared by the method of claim 1 as a material.

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