CN110073458B

CN110073458B - Preparation method of corrugated graphene composite, composite prepared by preparation method and supercapacitor containing composite

Info

Publication number: CN110073458B
Application number: CN201780076905.9A
Authority: CN
Inventors: 张喜栋; 蒋韩权; 崔志赫; 吉大燮; 金亨锡; 裵仁国; 徐宙范; 赵恩姬
Original assignee: Korea Institute of Geoscience and Mineral Resources KIGAM
Current assignee: Korea Institute of Geoscience and Mineral Resources KIGAM
Priority date: 2016-12-12
Filing date: 2017-03-29
Publication date: 2022-07-08
Anticipated expiration: 2037-03-29
Also published as: WO2018110776A1; CN110073458A

Abstract

The present invention relates to a method for producing a corrugated graphene composite including the steps of spray-drying and heat-treating a solution containing graphene oxide and a conductive material, a graphene composite produced thereby, and a supercapacitor suitable for an electrode containing the same.

Description

Preparation method of corrugated graphene composite, composite prepared by preparation method and supercapacitor containing composite

Technical Field

The present invention relates to a method for preparing a corrugated graphene composite, a graphene composite prepared thereby, and a supercapacitor including the same, and more particularly, to a method for preparing a corrugated graphene composite including a step of spray-drying and heat-treating a solution including graphene oxide and a conductive material, a graphene composite prepared thereby, and a supercapacitor including the same.

Background

As the demand for energy storage devices having high energy and high power density increases, super capacitors are receiving attention as one of the new generation of environmentally friendly energy storage devices. Compared with the existing secondary battery, the super capacitor has the advantages of high power density, charge and discharge efficiency, semi-permanent cycle life, stability to current change and no explosion hazard. Therefore, it is actively utilized for portable electronic devices or power packs that need to provide stable energy, for instantaneous acceleration of electric vehicles, and for storage backup. In addition, since the supercapacitor uses a carbon material as an electrode active material, it can be called an energy backup and storage device having characteristics of environmental protection and excellent safety.

The electrochemical performance of the supercapacitor may depend on the electrode material, but needs to satisfy requirements such as high conductivity, wide specific surface area, high temperature stability, uniform pore structure, low cost, etc. Mainly uses carbon materials including active carbon, carbon nano tubes and graphene as electrode materials of the super capacitor. Among them, activated carbon is widely used as a material for a supercapacitor due to its wide specific surface area and low cost. However, even if the activated carbon electrode has a large number of micro/large voids, its electrolyte adsorption performance on the electrode surface is low, and there is a problem of low specific capacitance. Therefore, it has a wide specific surface area (theoretical value of 2600 m)²(g), rapid electron mobility, and excellent mechanical properties, graphene is receiving attention as a material for an energy storage device. Besides supercapacitors, the graphene is expected to be used in the fields of solar cells, electrochemical sensors and the like.

Recently, many studies for preparing a graphene electrode having pores have been reported to improve the proximity between an electrolyte and the surface of an electrode substance. However, these electrodes have a lower storage capacity per volume than conventional activated carbon electrodes due to extensive air holes and blind layering of graphene sheets.

In korean laid-open patent No. 10-2015-0044359, there are provided a graphene layer interval adjusting method and a supercapacitor using the same, and in particular, a method for preparing graphene for adjusting an interlayer interval of a supercapacitor, comprising: a step of adding a surfactant to a solution containing graphene oxide to disperse the graphene oxide; adding a reducing agent to a solution containing the dispersed graphene oxide to form reduced graphene oxide; and adding N-terminated groups to the solution containing the reduced graphene oxide₂ ⁺An activated pillar material (pillarmaterial) and an aryl group contained in the pillar materialAnd adjusting the interlayer distance between the reduced graphene oxides by connecting the original graphene oxides to the support members, wherein the interlayer distance between the reduced graphene oxides is adjusted according to the number of the aryl groups or the number of carbons of alkyl groups connecting two or more aryl groups. However, the above-mentioned production method also requires a reducing agent such as hydrazine for reducing graphene oxide, and thus requires a complicated process through a plurality of steps, and when the structure thus produced is applied to a capacitor, there is a problem that the specific capacitance decreases at a high current density (2A/g or more).

On the other hand, as a method for improving the approach of the specific capacitance of a supercapacitor, studies have been made on the preparation of a graphene composite containing carbon-based materials such as carbon nanotubes and activated carbon. However, since the graphene sheets having a two-dimensional structure are always re-laminated and aggregated, the electrolyte hardly permeates into the composite electrode. Further, an aggregation phenomenon occurs between the carbon nanotubes due to van der waals attractive force between the carbon nanotubes, so that a tendency arises that specific capacitance decreases as current density increases.

Therefore, studies for maintaining specific capacitance at high current density and for improving power density based thereon by solving the problems of re-stacking and agglomeration occurring when two-dimensional graphene and carbon nanotubes are applied are actually required.

Disclosure of Invention

Technical problem

The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide a method for preparing a self-assembled corrugated graphene composite through spray drying and heat treatment processes.

It is still another object of the present invention to provide a corrugated graphene composite in which carbon nanotubes form physical cross-linking points in graphene and have a high specific surface area.

Another object of the present invention is to provide a supercapacitor using the composite, which can effectively maintain specific capacitance even at a high current density.

It is still another object of the present invention to provide a method for preparing an electrode in which a graphene composite having pores with a wrinkle is prepared by a simpler process and fixed to a current collector by using graphene.

Means for solving the problems

In order to achieve the above object, in a first embodiment of the present invention, there is provided a method for preparing a corrugated graphene-carbon nanotube composite, including: preparing a colloid mixed solution formed by mixing an acid-treated carbon nanotube, graphene oxide and a solvent (step 1); and spray-drying the mixed solution and performing heat treatment (step 2).

In one embodiment, the carbon nanotube may be a multi-walled carbon nanotube (MWCNT).

In one embodiment, the acid treatment of the carbon nanotubes may be performed by dispersing the carbon nanotubes in an acid solution containing sulfuric acid and nitric acid.

In an embodiment, the mixing weight ratio of the carbon nanotubes and the graphene oxide in the step 1 may be 0.01: 1 to 0.4: 1.

in an embodiment, the graphene oxide concentration of the mixed solution of step 1 may be 0.10 weight percent to 0.50 weight percent.

In an embodiment, the step 2 may include: spraying the mixed solution of step 1 in the form of aerosol droplets through an upper two-fluid nozzle (step 2 a); and transferring the sprayed droplets to a heating furnace to dry the droplets, and forming a self-assembled wrinkled graphene-carbon nanotube complex by heat treatment (step 2 b).

In one embodiment, the diameter of the two-fluid nozzle of step 2a may be 1.0mm to 3.0 mm.

In one embodiment, the heat treatment of step 2 or step 2b may be performed at a temperature of 200 ℃ to 500 ℃.

In one embodiment, the heat treatment of step 2 or step 2b may be performed for 1 hour to 10 hours.

In order to achieve the above object, a further first embodiment of the present invention provides a corrugated graphene-carbon nanotube composite prepared by the above method for preparing a corrugated graphene-carbon nanotube composite, the corrugated graphene-carbon nanotube composite including corrugated graphene sheets; and a carbon nanotube contained in the graphene sheet, wherein the wrinkled graphene-carbon nanotube complex is spherical and has an average particle size of 1 to 10 μm.

In order to achieve the above object, another first embodiment of the present invention provides a supercapacitor electrode comprising the above-described wrinkled graphene-carbon nanotube composite.

In order to achieve the above object, a first embodiment of the present invention provides an ultracapacitor comprising: a pair of electrodes facing each other and containing an active material; an electrolyte disposed between the pair of electrodes; and a separation membrane provided between the pair of electrodes and configured to suppress an electrical short, wherein the active material includes the wrinkled graphene-carbon nanotube composite.

In order to achieve the above object, a second embodiment of the present invention provides a method for preparing a corrugated graphene-carbon nanotube-polymer composite, including: preparing a mixed solution obtained by mixing the carbon nanotube treated by the acid, the graphene oxide, the conductive polymer monomer and the solvent (step i); polymerizing the monomers of the mixed solution (step ii); and spray-drying the polymerization-reacted mixed solution and performing heat treatment (step iii).

In an embodiment, the mixing weight ratio of the carbon nanotubes and the graphene oxide in the step i may be 0.01: 1 to 0.5: 1.

in one embodiment, the monomer concentration of the mixed solution of step i may be 5mM to 50 mM.

In one embodiment, the conductive polymer monomer in step i may be one or more selected from the group consisting of aniline, pyrrole, thiophene, acetylene, furan, phenylene, and derivatives thereof.

In one embodiment, the step ii may be performed by adding a polymerization initiator to the mixed solution and treating ultrasonic waves.

In one embodiment, the step iii may include: spraying the above-mentioned mixed solution subjected to the polymerization reaction in the form of aerosol droplets through a two-fluid nozzle (step iiia); and transferring the sprayed droplets to a heating furnace to dry the droplets, and forming a self-assembled wrinkled graphene-carbon nanotube-polymer composite by heat treatment (step iiib).

In one embodiment, the diameter of the two-fluid nozzle of step iiia may be 1.0mm to 3.0 mm.

In one embodiment, the heat treatment of step iii or step iiib may be performed at a temperature of 200 ℃ to 500 ℃ for 1 hour to 10 hours.

In order to achieve the above-mentioned object, a second embodiment of the present invention provides a method for preparing a corrugated graphene-carbon nanotube-polymer composite, the method comprising: a graphene sheet in an accordion shape; a carbon nanotube contained in the graphene sheet; and a conductive polymer, wherein the corrugated graphene-carbon nanotube-polymer composite is spherical, and the average particle size is 1-10 μm.

In one embodiment, the conductive polymer may be one selected from the group consisting of polyaniline, polypyrrole, polythiophene, polyacetylene, polyfuran, and polyparaphenylene.

In order to achieve the above object, a second embodiment of the present invention provides a supercapacitor electrode comprising the above-described corrugated graphene-carbon nanotube-polymer composite.

In order to achieve the above object, a second embodiment of the present invention provides a corrugated graphene-carbon nanotube-polymer composite, including: a pair of electrodes facing each other and containing an active material; an electrolyte disposed between the pair of electrodes; and a separation membrane provided between the pair of electrodes and configured to suppress an electrical short circuit, wherein the active material includes the wrinkled graphene-carbon nanotube-polymer composite.

In order to achieve the above object, a third embodiment of the present invention provides a method for preparing a supercapacitor electrode comprising a corrugated graphene composite, including: preparing a mixed solution obtained by mixing the carbon nanotube treated by the acid, the graphene oxide, the conductive polymer monomer and the solvent (step i); polymerizing the monomers of the mixed solution (step ii); spray-drying the polymerization-reacted mixed solution, and preparing a folded graphene composite by heat treatment (step iii); and mixing the composite, graphene oxide, and a solvent, applying the mixture to a current collector, and then performing heat treatment (step iv).

In one embodiment, in step iv, the complex: the mixing weight ratio of the graphene oxide may be 1: 0.02 to 1: 0.5.

in one embodiment, the heat treatment of the above step iv may be performed at a temperature of 200 ℃ to 500 ℃ for 1 hour to 10 hours.

In order to achieve the above object, a further third embodiment of the present invention provides a supercapacitor electrode comprising: the corrugated graphene-carbon nanotube-polymer composite comprises a corrugated graphene sheet, a carbon nanotube and a conductive polymer, wherein the carbon nanotube and the conductive polymer are contained in the graphene sheet, and the corrugated graphene-carbon nanotube-polymer composite is spherical and has an average particle size of 1-10 μm; a current collector having a plurality of the above-described composites formed on one surface thereof; and a graphene sheet for fixing the current collector and the composite, and for fixing the composite and the composite.

In order to achieve the above object, another third embodiment of the present invention provides an ultracapacitor comprising: a pair of electrodes facing each other; an electrolyte disposed between the pair of electrodes; and a separation membrane provided between the pair of electrodes for suppressing an electrical short circuit, wherein the electrode is the supercapacitor electrode as described above.

ADVANTAGEOUS EFFECTS OF INVENTION

In the first embodiment of the present invention, a self-assembled, wrinkled graphene-carbon nanotube composite may be prepared by spray-drying and heat-treating a mixed colloidal solution of carbon nanotubes and graphene, and the thus prepared composite may allow the carbon nanotubes to form physical cross-linking points between graphenes and increase the inter-plane distance of the graphenes. When the electrode including the prepared composite is applied to a capacitor, the electrode has low interfacial resistance with an electrolyte, good conductivity, and excellent specific capacity retention at high current density.

In the second embodiment of the present invention, the carbon nanotubes introduced into the colloidal solution in which the graphene oxide, the carbon nanotubes and the conductive polymer monomer are mixed act as a cross-linking function between the graphene sheets of the prepared composite, and thus the electrolyte access can be improved when the capacitor is applied due to the improvement of the conductivity and the increase of the inter-plane distance. Further, since the corrugated graphene-carbon nanotube-polymer composite having a three-dimensional spherical shape and uniform pores formed therein has high conductivity and is capable of undergoing a redox reaction, a capacitor to which the composite is applied can exhibit both high power density and energy density.

In the third embodiment of the present invention, the corrugated graphene-carbon nanotube-polymer composite having a three-dimensional spherical shape and uniform pores formed therein is fixed to the current collector through graphene, so that an electrode can be prepared without a binder and exhibits both high power density and energy density when used in a capacitor.

It is to be understood that the effects of the present invention are not limited to the effects described above, and include all the effects that can be derived from the detailed description of the present invention or the structure of the invention described in the claims.

Drawings

Fig. 1 is a schematic diagram illustrating an example of a method for producing a wrinkled graphene-carbon nanotube composite according to a first embodiment of the present invention.

Fig. 2 is a schematic view showing an example of a method for producing a wrinkled graphene-carbon nanotube composite according to a first embodiment of the present invention.

Parts (a1) to (d1) of fig. 3 are photographs taken by a scanning electron microscope (FE-SEM) of the composite prepared in examples 1 to 3 of the present invention and comparative example 1.

Parts (a2) to (d2) of fig. 3 are photographs taken with a Transmission Electron Microscope (TEM) of the composite prepared in examples 1 to 3 of the present invention and comparative example 1.

Fig. 4 is a graph showing the results of X-ray diffraction (XRD) analysis of the composite bodies, graphene oxide, and multi-walled carbon nanotubes prepared in examples 1 to 3 of the present invention and comparative example 1.

Fig. 5 is a graph showing raman spectroscopy analysis results of the composites prepared in examples 1 to 3 of the present invention and comparative example 1.

Fig. 6 is a graph showing the results of analysis of the cycle voltage current, charge and discharge and impedance characteristics of the supercapacitors prepared in examples 4 to 6 of the invention and comparative example 2.

Fig. 7 is a schematic diagram illustrating an example of a method for producing a wrinkled graphene-carbon nanotube-polymer composite according to a second embodiment of the present invention.

Fig. 8 is a schematic view showing another example of the method for producing the wrinkled graphene-carbon nanotube-polymer composite according to the second embodiment of the present invention.

The pictures of the materials prepared in example i, comparative example i and comparative example ii of the present invention were taken by a scanning electron microscope (FE-SEM) in the portion a of fig. 9 to the portion c of fig. 9.

The photographs of the materials prepared in example i, comparative example i, and comparative example ii of the present invention were taken by a Transmission Electron Microscope (TEM) in the section d of fig. 9 to the section f of fig. 9.

Part a of fig. 10 is a graph showing the results of X-ray diffraction (XRD) analysis of the materials prepared in example i, comparative example i, and comparative example ii of the present invention.

Part b of fig. 10 is a graph showing the results of raman spectroscopy analysis of the substances prepared in example i, comparative example i and comparative example ii of the present invention.

Fig. 11 is a graph showing the results of mercury porosimetry (mercuryporimeter) analysis of the substances prepared in example i, comparative example i, and comparative example ii of the present invention.

Parts a to d of fig. 12 are graphs showing the results of analysis of the cycle voltage current, charge and discharge, and impedance characteristics of the supercapacitors prepared in example iv, comparative example iii, and comparative example iv of the present invention.

Parts a to d of fig. 13 are graphs showing the results of analysis of the cycle voltage current, charge and discharge and impedance characteristics of the supercapacitors produced in examples iv to vi of the present invention.

Fig. 14 is a schematic diagram showing an example of a method for producing a supercapacitor electrode including a wrinkled graphene composite according to a third embodiment of the present invention.

Fig. 15 is a schematic view showing another example of the method for producing a supercapacitor electrode including a wrinkled graphene composite according to the third embodiment of the present invention.

Parts a to f of fig. 16 are photographs taken by a scanning electron microscope (FE-SEM) of the materials prepared in examples i + to iii + of the present invention.

Parts a to f of fig. 17 are photographs taken by a Transmission Electron Microscope (TEM) of the substances prepared in examples i + to iii + of the present invention.

Part a of fig. 18 is a graph showing the results of X-ray diffraction analysis of the materials prepared in examples i + to iii + of the present invention, wrinkled graphene, and polyaniline.

Part b of fig. 18 is a graph showing raman spectrum analysis results of the materials prepared in examples i + to iii + of the present invention, the wrinkled graphene, and the polyaniline.

Parts a to c of fig. 19 are graphs showing the cycle voltage current, the charge and discharge characteristic analysis results of the supercapacitors produced in examples iv + to vi + of the present invention.

Parts a to c of fig. 20 are graphs showing the cycle voltage current and the result of the charge and discharge characteristic analysis of the supercapacitors prepared in example iv +, example vii + and example viii + of the present invention.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The advantages, features, and methods of accomplishing the same of the present invention will become more apparent with reference to the following examples.

However, the present invention is not limited to the embodiments disclosed below, and can be implemented in various ways different from each other, and the embodiments are provided to enable those skilled in the art to fully understand the scope of the present invention, which is defined only by the scope of the claims.

Further, in explaining the present invention, a detailed description thereof will be omitted in a case where it is considered that the gist of the present invention is obscured by related well-known technologies and the like.

A first embodiment of the present invention provides a method for preparing a corrugated graphene-carbon nanotube composite, including: preparing a colloid mixed solution (step 1) in which the carbon nanotubes treated with the acid, the graphene oxide, and the solvent are mixed (S10); and spray-drying the mixed solution and performing a heat treatment (step 2) (S20).

In the conventional study of graphene-carbon nanotube composites, since the phenomenon of re-stacking and aggregation occurs between graphene sheets having a two-dimensional structure, it is difficult for an electrolyte to permeate into a composite electrode. Also, an aggregation phenomenon occurs between the carbon nanotubes due to van der waals attractive force between the carbon nanotubes, and thus a tendency arises that specific capacitance decreases as current density increases.

The present inventors have developed a method for preparing a corrugated graphene-carbon nanotube composite that maintains specific capacitance at a high current density and can improve power density when applied to a capacitor in order to solve the problems of re-lamination and agglomeration of two-dimensional graphene and carbon nanotubes, and thus have completed the present invention.

Hereinafter, the method for producing the wrinkled graphene-carbon nanotube composite according to the first embodiment of the present invention will be described in detail for each step.

In the method for producing a wrinkled graphene-carbon nanotube composite according to the first embodiment of the present invention, a colloid-mixed solution in which an acid-treated carbon nanotube, graphene oxide and a solvent are mixed is prepared in step 1 (S10).

The carbon nanotube of the above step 1 may be one selected from the group consisting of a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), and a multi-walled carbon nanotube, preferably a multi-walled carbon nanotube (MWCNT).

The carbon nanotube acid treatment of the above step 1 may be performed by dispersing the carbon nanotubes in an acid solution containing sulfuric acid and nitric acid. Specifically, the compound can be prepared by reacting sulfuric acid: nitric acid is mixed with 2: 1 to 4: 1 and stirring at a temperature of 50 to 80 ℃ for 1 to 10 hours.

When the carbon nanotube acid treatment of the above step 1 is performed, the carbon nanotube: the solid to liquid ratio (g/mL) of the acid solution may be 1: 150 to 1: 250.

the step 1 may further include a step of washing the carbon nanotubes treated with the acid with a hydrochloric acid solution and drying the washed carbon nanotubes.

The acid-treated carbon nanotubes of the above step 1 can improve the dispersibility to water compared to before the acid treatment.

The mixing weight ratio of the carbon nanotubes and the graphene oxide in the step 1 may be 0.01: 1 to 0.4: 1, preferably may be 0.05: 1 to 0.1: 1. the mixing weight ratio of the carbon nano tube to the graphene oxide is less than 0.01: 1, there may be a problem in that, in the prepared corrugated graphene-carbon nanotube composite, carbon nanotubes may be insufficient to form physical cross-linking points in graphene, and the specific capacity retention rate of a supercapacitor including the same may be decreased. When the mixing weight ratio of the carbon nano tube to the graphene oxide is more than 0.4: 1, there may be a problem in that, in the prepared corrugated graphene-carbon nanotube composite, the carbon nanotubes may agglomerate, and the interfacial resistance between the electrolyte and the electrode of the supercapacitor including the same increases.

The solvent of the above step 1 may be one or more selected from the group consisting of distilled water, acetone, methyl ethyl ketone, methanol, ethanol, isopropanol, butanol, ethylene glycol, polyethylene glycol, tetrahydrofuran, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, hexane, cyclohexanone, toluene, chloroform, dichlorobenzene, xylene, trimethylbenzene, pyridine, methylnaphthalene, nitromethane, acrylonitrile, octadecylamine, aniline and dimethyl sulfoxide, and preferably distilled water may be used.

The graphene oxide concentration of the mixed solution of the above step 1 may be 0.10 to 0.50 weight percent, and preferably may be 0.15 to 0.35 weight percent. If the graphene oxide concentration of the mixed solution is less than 0.10 wt%, the amount of the composite produced per unit time in the following step is small, and thus the production efficiency may be reduced, and if the graphene oxide concentration of the mixed solution is greater than 0.50 wt%, there may be a problem that the wrinkled graphene-carbon nanotube composite cannot be formed by the spraying step.

The step 1 may further include a step of dispersing the prepared colloid mixed solution by ultrasonic treatment.

In the method for preparing a wrinkled graphene-carbon nanotube composite according to the first embodiment of the present invention, the mixed solution is spray-dried and heat-treated in the step 2 (S20).

The spray drying and heat treatment of step 2 may specifically include the following steps 2a and 2 b.

The step 2 may include: spraying the mixed solution of step 1 in the form of aerosol droplets through a two-fluid nozzle (step 2 a); and transferring the sprayed droplets to a heating furnace to dry the droplets, and forming a self-assembled wrinkled graphene-carbon nanotube complex by heat treatment (step 2 b).

The diameter of the two-fluid nozzle of step 2a above may be 1.0mm to 3.0mm, and preferably may be 1.0mm to 2.0 mm. If the diameter of the two-fluid nozzle is less than 1.0mm, there is a possibility that droplets may not smoothly come out of the nozzle, and if the diameter of the two-fluid nozzle is greater than 3.0mm, there is a possibility that fine particles may not be easily generated from the mixed solution passing through the step 1.

The two-fluid nozzle of the above step 2a can atomize the liquid by mixing dispersion caused by collision of the liquid and the gas. Unlike the conventional nozzle using a direct pressurization method, the two-fluid nozzle has an advantage of maintaining an ultra-fine spray even at a low pressure.

In the step 2b, the droplets may be transferred to the heating furnace by one or more gases selected from the group consisting of argon, helium and nitrogen, preferably by argon.

When the droplets are transferred to the heating furnace in the above step 2b, the flow rate of the gas may be 5L/min to 15L/min, preferably 5L/min to 10L/min.

The temperature of the heating furnace of the above step 2b may be 150 to 250 c, and preferably may be 180 to 220 c. If the temperature of the heating furnace is less than 150 ℃, the solvent in the droplets may remain without being partially evaporated, and the wrinkled graphene oxide-carbon nanotube complex may not be formed, and if the temperature of the heating furnace is greater than 250 ℃, excessive energy may be wasted in forming the wrinkled graphene oxide-carbon nanotube complex.

When the solvent present in the droplets is evaporated due to the drying by the transfer to the heating furnace in the above step 2b, the graphene oxide sheets are aggregated with each other by a capillary molding (capillary molding) phenomenon, and thus the wrinkled graphene oxide-carbon nanotube composite may be prepared.

The dried composite body subjected to the above step 2b may be collected in a filter by cyclone, and then may be subjected to a heat treatment for reduction of graphene oxide.

The heat treatment of the above step 2b may be performed at a temperature of 200 to 500 ℃, preferably 200 to 300 ℃. If the heat treatment temperature is less than 200 ℃, there may be a problem in that the graphene oxide may not be efficiently reduced, and if the heat treatment temperature is greater than 500 ℃, there may be an excessive energy waste in reducing the graphene oxide.

The heat treatment of the above step 2b may be performed in a muffle furnace (muffle furnace), and may be performed under one or more gas atmospheres selected from the group consisting of argon, helium, and nitrogen, and preferably may be performed under an argon atmosphere.

The heat treatment of the above step 2b may be performed for 1 hour to 10 hours, and preferably may be performed for 1 hour to 3 hours. If the heat treatment time is less than 1 hour, graphene oxide may not be efficiently reduced, and if the heat treatment time is greater than 10 hours, excessive energy may be wasted in reducing graphene oxide.

The finally prepared wrinkled graphene-carbon nanotube complex through the steps 1 to 2 can inhibit re-lamination of graphene and agglomeration of carbon nanotubes through complementary bonding of the preparation method. Furthermore, the carbon nanotubes located on the surface and edges of graphene can act as cross-linking between graphene sheets, and thus, when the electrode including the above-described composite is applied to a capacitor, the electrical conductivity can be improved and the electrolyte access can be promoted by increasing the inter-plane distance.

In a further first embodiment of the present invention, there is provided a corrugated graphene-carbon nanotube composite prepared by the method (

steps

1 and 2, S10, and S20), the corrugated graphene-carbon nanotube composite including: a graphene sheet in an accordion shape; and a carbon nanotube contained in the graphene sheet, wherein the wrinkled graphene-carbon nanotube complex is spherical and has an average particle size of 1 to 10 μm.

In the wrinkled graphene-carbon nanotube composite according to the first embodiment of the present invention, the carbon nanotubes are preferably multi-walled carbon nanotubes (MWCNTs).

The carbon nanotubes contained within the aforementioned corrugated graphene-carbon nanotube composite may serve as physical crosslinks between graphene sheets.

The wrinkled graphene-carbon nanotube composite may satisfy the following equation 1.

[ mathematical formula 1]

0.70<I_d/I_g<0.95

(in the above mathematical formula 1, I_dTo show the graphene sp in the corrugated graphene-carbon nanotube composite²Raman spectral peak intensity of absence, substitution or disorder (dissorder) of structure, I_gTo show the raman spectral peak intensity of carbon of graphite. )

The wrinkled graphene-carbon nanotube composite may have a characteristic of increasing an inter-graphene spacing (interlayer spacing), which may be caused by an oxygen functional group and a carbon nanotube, etc., remaining in graphene of the composite. Specifically, the graphene interplanar spacing of the wrinkled graphene-carbon nanotube composite may be 0.35nm to 0.38 nm.

Another first embodiment of the present invention provides a supercapacitor electrode comprising the above-described corrugated graphene-carbon nanotube composite.

When an electrode including the composite is applied to a capacitor, the electrode can have a characteristic of reducing contact resistance with a water-soluble electrolyte due to a high contact area caused by an increase in the graphene interplanar spacing of the composite.

The electrode may further include a binder supporting the composite, and the binder may be one or more selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), carboxymethyl cellulose (CMC), Styrene Butadiene Rubber (SBR), Polyimide (PI), and polyvinyl alcohol (PVA), but is not limited thereto.

Yet another first embodiment of the present invention provides an ultracapacitor comprising: a pair of electrodes facing each other and containing an active material; an electrolyte disposed between the pair of electrodes; and a separation membrane provided between the pair of electrodes and configured to suppress an electrical short, wherein the active material includes the wrinkled graphene-carbon nanotube composite.

The pair of electrodes may further include current collectors disposed on respective sides in electrical contact.

The electrolyte may be one selected from the group consisting of an acid-based electrolyte containing sulfuric acid, a base-based electrolyte containing potassium hydroxide, and a neutral electrolyte containing sodium sulfate, but is not limited thereto.

The current collector may be a metal foil or a metal thin film containing one or more metals selected from the group consisting of copper, nickel, aluminum, and stainless steel, and may be a porous paper based on carbon having conductivity, but is not limited thereto as long as it has chemical and electrochemical corrosion resistance.

The separation membrane may be a nonwoven fabric, Polytetrafluoroethylene (PTFE), porous membrane, kraft paper, cellulose electrolyte, rayon fiber, or the like, but is not limited thereto.

The supercapacitor according to the first embodiment of the present invention can increase the specific capacitance by reducing the interfacial resistance between the electrode and the electrolyte through a high contact area due to an increase in the graphene interplanar spacing of the composite. Specifically, the specific capacitance of the supercapacitor according to the first embodiment of the present invention may be 130F/g to 200F/g at a current density of 0.1A/g, and the above specific capacitance may be substantially maintained even at a high current density. Specifically, the specific capacitance at a current density of 4A/g may be 70% to 90% relative to the specific capacitance at a current density of 0.1A/g.

A second embodiment of the present invention provides a method for preparing a corrugated graphene-carbon nanotube-polymer composite, including: preparing a mixed solution (step i) of the acid-treated carbon nanotube, graphene oxide, a conductive polymer monomer, and a solvent (S100); polymerizing the monomers of the mixed solution (step ii) (S200); and spray-drying the polymerization-reacted mixed solution and performing a heat treatment (step iii) (S300).

Hereinafter, a method for preparing a wrinkled graphene-carbon nanotube-polymer composite according to a second embodiment of the present invention will be described in detail in terms of steps.

In the method for producing a wrinkled graphene-carbon nanotube-polymer composite according to the second embodiment of the present invention, in step i (S100), a mixed solution in which an acid-treated carbon nanotube, graphene oxide, a conductive polymer monomer, and a solvent are mixed is prepared.

The carbon nanotube of step i may be one or more carbon nanotubes selected from the group consisting of a single-walled carbon nanotube, a double-walled carbon nanotube, and a multi-walled carbon nanotube, and preferably is a multi-walled carbon nanotube.

The carbon nanotube acid treatment of the above-described step i may be performed by dispersing the carbon nanotubes in an acid solution including sulfuric acid and nitric acid.

Specifically, the compound can be prepared by reacting sulfuric acid: nitric acid is mixed with 2: 1 to 4: 1 and stirring at a temperature of 50 to 80 ℃ for 1 to 10 hours.

When the carbon nanotube acid treatment of the above step i is performed, the carbon nanotube: the solid-to-liquid ratio (g/mL) of the acid solution may be 1: 150 to 1: 250.

the step i may further include a step of washing the carbon nanotubes treated with the acid with a hydrochloric acid solution and drying the washed carbon nanotubes.

The acid-treated carbon nanotubes of the above step i may have improved dispersibility to water compared to before the acid treatment.

The mixing weight ratio of the carbon nanotubes and the graphene oxide in the step i may be 0.01: 1 to 0.5: 1, preferably may be 0.05: 1 to 0.1: 1. when the mixing weight ratio of the carbon nano tube to the graphene oxide is less than 0.01: 1, there may be a problem in that, in the prepared corrugated graphene-carbon nanotube-polymer composite, carbon nanotubes may not be sufficient to form physical cross-linking points in graphene, and the specific capacity retention rate of a supercapacitor including the same may be decreased. The mixing weight ratio of the carbon nano tube to the graphene oxide is more than 0.5: 1, there may be a problem in that, in the prepared corrugated graphene-carbon nanotube-polymer composite, the carbon nanotubes may agglomerate, and the interfacial resistance between the electrolyte and the electrode of the supercapacitor including the same increases.

The solvent of the step i may be one or more selected from the group consisting of distilled water, an acid solution, acetone, methyl ethyl ketone, methanol, ethanol, isopropanol, butanol, ethylene glycol, polyethylene glycol, tetrahydrofuran, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, hexane, cyclohexanone, toluene, chloroform, dichlorobenzene, xylene, trimethylbenzene, pyridine, methylnaphthalene, nitromethane, acrylonitrile, octadecylamine, aniline, and dimethylsulfoxide, and preferably a hydrochloric acid solution may be used.

The graphene oxide concentration of the mixed solution of the above step i may be 0.10 to 0.50 weight percent, and preferably may be 0.15 to 0.35 weight percent. If the graphene oxide concentration of the mixed solution is less than 0.10 wt%, the amount of the composite produced per unit time in the following step is small, and thus the production efficiency may be reduced, and if the graphene oxide concentration of the mixed solution is greater than 0.50 wt%, there may be a problem that the wrinkled graphene-carbon nanotube-polymer composite cannot be formed by the spraying step.

The monomer concentration of the mixed solution of the above step i may be 5mM to 50mM, and preferably may be 10mM to 30 mM. If the monomer concentration is less than 5mM, the content of the conductive polymer in the prepared composite is small, and thus there is a possibility that the specific capacitance is decreased when the composite is applied to a capacitor, and if the monomer concentration is more than 50mM, the conductive polymer is excessively generated in the prepared composite, and therefore there is a possibility that the contact resistance with the electrolyte is increased when the composite is applied to a capacitor.

The conductive polymer monomer in step i may be one or more selected from the group consisting of aniline, pyrrole, thiophene, acetylene, furan, phenylene, and derivatives thereof, and a monomer for forming one polymer selected from the group consisting of polyaniline, polypyrrole, polythiophene, polyacetylene, polyfuran, and polyparaphenylene may be used.

In the method for preparing a wrinkled graphene-carbon nanotube-polymer composite according to the second embodiment of the present invention, in the step ii (S200), a step of polymerizing monomers in the mixed solution is performed.

The step ii may be performed by adding a polymerization initiator to the mixed solution and treating the ultrasonic waves.

The ultrasonic treatment of the above step ii may be performed for 0.5 to 10 hours, preferably for 1 to 3 hours. If the ultrasonic treatment time is less than 0.5 hours, there may be a problem that the mixed solution prepared in the step i is not sufficiently dispersed and polymerization of the monomers is not completely performed, and if the ultrasonic treatment time is more than 10 hours, excessive energy may be consumed in the dispersion and polymerization processes of the mixed solution.

The polymerization initiator in the step ii may be a known initiator which can be used for polymerization of the above-mentioned monomer.

In the step ii, when the monomer is aniline, a common initiator used in polymerization may be used, and preferably, one or more polymerization initiators selected from the group consisting of ammonium persulfate, potassium persulfate, sodium persulfate, and lithium persulfate may be used.

The polymerization initiator of the above step ii may be added in an amount of 10 to 100 parts by weight, preferably 20 to 80 parts by weight, relative to 100 parts by weight of the monomer.

In the step ii, a conductive polymer selected from the group consisting of polyaniline, polypyrrole, polythiophene, polyacetylene, polyfuran, and polyparaphenylene may be formed in the mixed solution.

In the method of preparing the wrinkled graphene-carbon nanotube-polymer composite according to the second embodiment of the present invention, the mixed solution after the polymerization reaction is spray-dried and heat-treated in the step iii (S300).

Specifically, the spray drying and heat treatment of step iii may include the following steps iiia and iiib.

The step iii may include: spraying the above-mentioned mixed solution subjected to the polymerization reaction in the form of aerosol droplets through a two-fluid nozzle (step iiia); and transferring the sprayed droplets to a heating furnace to dry the droplets, and forming a self-assembled wrinkled graphene-carbon nanotube-polymer composite by heat treatment (step iiib).

The diameter of the two-fluid nozzle of the above step iiia may be 1.0mm to 3.0mm, and preferably may be 1.0mm to 2.0 mm. If the diameter of the two-fluid nozzle is less than 1.0mm, there is a possibility that droplets may not smoothly come out from the nozzle, and if the diameter of the two-fluid nozzle is greater than 3.0mm, there is a possibility that fine particles may not be easily generated from the mixed solution passing through the step ii.

The two-fluid nozzle of the above-described step iiia may atomize the liquid by mixing dispersion caused by collision of the liquid and the gas. Unlike the conventional nozzle using a direct pressurization method, the two-fluid nozzle has an advantage of maintaining an ultra-fine spray even at a low pressure.

In the step iiib, the droplets may be transferred to the heating furnace by one or more gases selected from the group consisting of argon, helium and nitrogen, preferably by argon.

When the droplets are transferred to the heating furnace in the above-mentioned step iiib, the flow rate of the gas may be 5L/min to 15L/min, and preferably may be 5L/min to 10L/min.

The temperature of the heating furnace of the above step iiib may be 150 to 250 c, and preferably may be 180 to 220 c. If the temperature of the heating furnace is less than 150 ℃, the solvent in the droplets may remain due to partial non-evaporation, and the wrinkled graphene oxide-carbon nanotube-polymer composite may not be formed, whereas if the temperature of the heating furnace is greater than 250 ℃, the wrinkled graphene oxide-carbon nanotube-polymer composite may be formed with excessive energy.

If the solvent present in the droplets is evaporated due to the drying by transferring to the heating furnace in the above-described step iiib, the graphene oxide sheets are aggregated with each other by a capillary formation phenomenon, and thus the wrinkled graphene oxide-carbon nanotube-polymer composite may be prepared.

The dried composite subjected to the above-described step iiib may be collected in a filter by cyclone, and then may be subjected to a heat treatment for reduction of graphene oxide.

The heat treatment of the above-described step iiib may be performed at a temperature of 200 to 500 ℃, and preferably may be performed at a temperature of 200 to 300 ℃. If the heat treatment temperature is less than 200 ℃, there may be a problem in that the graphene oxide may not be efficiently reduced, and if the heat treatment temperature is greater than 500 ℃, there may be an excessive energy waste in reducing the graphene oxide.

The heat treatment of the above-mentioned step iiib may be performed in a muffle furnace, may be performed under one or more gas atmospheres selected from the group consisting of argon, helium, and nitrogen, and preferably may be performed under an argon atmosphere.

The heat treatment of the above step iiib may be performed for 1 hour to 10 hours, and preferably may be performed for 1 hour to 3 hours. If the heat treatment time is less than 1 hour, graphene oxide may not be efficiently reduced, and if the heat treatment time is greater than 10 hours, excessive energy may be wasted in reducing graphene oxide.

The finally prepared wrinkled graphene-carbon nanotube-polymer composite through the steps i to iii can inhibit the re-lamination of graphene and the agglomeration of carbon nanotubes through the complementary bonding of the preparation method. Furthermore, the carbon nanotubes located on the surface and edges of graphene can act as cross-linking between graphene sheets, and thus, when the electrode including the above-described composite is applied to a capacitor, the electrical conductivity can be improved and the electrolyte access can be promoted by increasing the inter-plane distance. The power density and energy density of the capacitor can be increased by the conductive polymer contained in the composite.

In a second embodiment of the present invention, there is provided a corrugated graphene-carbon nanotube-polymer composite prepared by the method (steps i to iii, S100 to 300), wherein the corrugated graphene-carbon nanotube-polymer composite includes: a graphene sheet in an accordion shape; a carbon nanotube contained inside the graphene sheet; and a conductive polymer, wherein the corrugated graphene-carbon nanotube-polymer composite is spherical, and the average particle size is 1-10 μm.

The carbon nanotube may be one selected from the group consisting of a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), and a multi-walled carbon nanotube (MWCNT), and is preferably a multi-walled carbon nanotube.

The conductive polymer may be one selected from the group consisting of polyaniline, polypyrrole, polythiophene, polyacetylene, polyfuran, and polyparaphenylene, and may preferably be polyaniline.

The wrinkled graphene-carbon nanotube-polyaniline composite may have a characteristic of an increase in the inter-graphene plane distance, which may be caused by oxygen functional groups, carbon nanotubes, conductive polymers, and the like remaining in graphene of the composite.

Another second embodiment of the present invention provides a supercapacitor electrode comprising the above-described wrinkled graphene-carbon nanotube-polymer composite.

When an electrode including the composite is applied to a capacitor, the electrode may have a characteristic of reducing contact resistance with a water-soluble electrolyte due to a high contact area caused by an increase in the graphene interplanar spacing of the composite, and may have a high power density and a specific capacitance due to a conductive polymer in the composite.

The electrode may further include a binder supporting the composite, and the binder may be one or more selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride hexafluoropropylene, carboxymethyl cellulose, styrene butadiene rubber, polyimide, and polyvinyl alcohol, but is not limited thereto.

Yet another second embodiment of the present invention provides a supercapacitor comprising: a pair of electrodes facing each other and containing an active material; an electrolyte disposed between the pair of electrodes; and a separation membrane provided between the pair of electrodes for suppressing an electrical short circuit, wherein the active material includes the wrinkled graphene-carbon nanotube-polymer composite.

The separation membrane may be a nonwoven fabric, polytetrafluoroethylene, porous membrane, kraft paper, cellulose electrolyte, rayon fiber, or the like, but is not limited thereto.

With a supercapacitor of a polyaniline-carbon nanotube-oxidized graphene and a reduced graphene-carbon nanotube-polyaniline complex prepared by growing polyaniline in a reduced graphene-carbon nanotube complex prepared by a simple liquid phase reaction, as polyaniline grows on the surface of the reduced graphene-carbon nanotube, the electrolyte proximity may be reduced due to a decrease in pore volume in an electrode, and the specific capacitance may have a low value of 50% or less due to a decrease in active surface area caused by an oxidation-reduction reaction in polyaniline.

Meanwhile, in the liquid phase reaction, an active material electrode including a complex having pores may be prepared by growing polyaniline on a porous graphene-carbon nanotube prepared using Polystyrene (PS) as an organic template. However, this process has a disadvantage in that it is somewhat complicated because it requires a high-temperature heat treatment to remove the polystyrene organic template used for forming the pores.

In contrast, the supercapacitor according to the second embodiment of the present invention can increase the specific capacitance by reducing the interfacial resistance between the electrode and the electrolyte through a high contact area due to an increase in the graphene interplanar spacing of the composite. Furthermore, the conductive polymer in the composite can have the performance of both an electric double layer and a super capacitor. Specifically, the specific capacitance of the above-described supercapacitor may be 200F/g to 350F/g at a current density of 0.1A/g, and the above-described specific capacitance may be substantially maintained even at a high current density. Specifically, the specific capacitance at a current density of 4A/g may be 70% to 90% relative to the specific capacitance at a current density of 0.1A/g.

A third embodiment of the present invention provides a method for preparing a supercapacitor electrode comprising a corrugated graphene composite, including: preparing a mixed solution (step i) of the acid-treated carbon nanotube, graphene oxide, a conductive polymer monomer, and a solvent (S100); polymerizing the monomers of the mixed solution (step ii) (S200); spray-drying the polymerization-reacted mixed solution, and preparing a folded graphene composite by heat treatment (step iii) (S300); and mixing the composite, graphene oxide, and a solvent, applying the mixture to a current collector, and then performing a heat treatment (step iiii) (S400).

Hereinafter, a method for manufacturing a supercapacitor electrode including a wrinkled graphene composite according to a third embodiment of the present invention will be described in detail by steps.

In the method for manufacturing a supercapacitor electrode including a wrinkled graphene composite according to the third embodiment of the present invention, the above steps i to iii may be the same as the above steps i to iii of the second embodiment.

In the third embodiment of the present invention, in order to prepare a supercapacitor exhibiting high specific capacitance and specific capacitance retention by increasing the electron transfer rate and increasing the active material content, a capacitor electrode is prepared without using a binder, and the following steps are performed.

In the method for manufacturing a supercapacitor electrode including a wrinkled graphene composite according to the third embodiment of the present invention, in the step iv (S400), the composite, graphene oxide, and a solvent are mixed, applied to a current collector, and then heat-treated.

In step iv above, the complex: the mixing weight ratio of the graphene oxide may be 1: 0.02 to 1: 0.5, preferably, the above complex: the weight ratio of graphene oxide may be 1: 0.05 to 1: 0.3. in the above-described composite: the weight ratio of the graphene oxide is less than 1: 0.02, there are problems that the composite cannot be effectively fixed to the current collector and that the composite cannot be partially fixed to each other, and that: the weight ratio of the graphene oxide is more than 1: in the case of 0.5, the active surface area of the prepared electrode is reduced, and thus the specific capacitance of the capacitor may be reduced.

The heat treatment of the above step iv may be performed at a temperature of 200 to 500 ℃, preferably 200 to 300 ℃. If the heat treatment temperature is less than 200 ℃, there is a problem in that the graphene oxide mixed in the step iv cannot be efficiently reduced, and if the heat treatment temperature is more than 500 ℃, excessive energy may be wasted in reducing the graphene oxide mixed in the step iv.

The heat treatment of the above step iv may be performed for 1 hour to 10 hours, preferably for 1 hour to 3 hours. If the heat treatment time is less than 1 hour, there is a problem in that the graphene oxide mixed in the step iv cannot be efficiently reduced, and if the heat treatment time is more than 10 hours, excessive energy may be wasted in reducing the graphene oxide mixed in the step iv.

The current collector of the above step iv may be a metal foil or a metal thin film containing one or more metals selected from the group consisting of copper, nickel, aluminum, and stainless steel, and may be a porous paper based on carbon having conductivity, but is not limited thereto as long as it has chemical and electrochemical corrosion resistance.

The solvent of the above step iv may be one or more selected from the group consisting of distilled water, acid solution, acetone, methyl ethyl ketone, methanol, ethanol, isopropanol, butanol, ethylene glycol, polyethylene glycol, tetrahydrofuran, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, hexane, cyclohexanone, toluene, chloroform, dichlorobenzene, xylene, trimethylbenzene, pyridine, methylnaphthalene, nitromethane, acrylonitrile, octadecylamine, aniline and dimethylsulfoxide, and preferably an N-methyl-2-pyrrolidone solvent may be used.

The coating of the above step iv may be performed by coating a thickness of 50 μm to 200 μm on the above current collector, and preferably may be made to be 75 μm to 125 μm. If the coating thickness is less than 50 μm, there is a risk that the interface resistance between the prepared electrode and the water-soluble electrolyte increases, and if the coating thickness is more than 200 μm, there is a possibility that the specific capacitance cannot be increased and the composite and graphene may be wasted when the prepared electrode is applied to a capacitor.

The electrode prepared through the above steps i to iv may have a fast electron movement characteristic, and since the content of the active material is increased without using a binder, the specific capacitance and the specific capacitance retention rate may be improved when applied to a capacitor.

Yet another third embodiment of the present invention provides a supercapacitor electrode comprising: the corrugated graphene-carbon nanotube-polymer composite comprises a corrugated graphene sheet, a carbon nanotube and a conductive polymer, wherein the carbon nanotube and the conductive polymer are contained in the graphene sheet, and the corrugated graphene-carbon nanotube-polymer composite is spherical and has an average particle size of 1-10 μm; a current collector having a plurality of the above-described composites formed on one surface thereof; and a graphene sheet for fixing the current collector and the composite, and for fixing the composite and the composite.

The carbon nanotube may be one selected from the group consisting of a single-walled carbon nanotube, a double-walled carbon nanotube and a multi-walled carbon nanotube, and is preferably a multi-walled carbon nanotube.

The conductive polymer may be one selected from the group consisting of polyaniline, polypyrrole, polythiophene, polyacetylene, polyfuran, and polyparaphenylene, and preferably may be polyaniline.

When an electrode including the composite is applied to a capacitor, the electrode can have a characteristic of reducing contact resistance with a water-soluble electrolyte due to a high contact area caused by an increase in the graphene interplanar spacing of the composite. In the electrode, the composite is fixed to a current collector by graphene instead of the binder supporting the composite, so that the specific capacitance and the specific capacitance retention rate of the capacitor can be improved.

Another third embodiment of the present invention provides an ultracapacitor comprising: a pair of electrodes facing each other; an electrolyte disposed between the pair of electrodes; and a separation membrane provided between the pair of electrodes for suppressing an electrical short circuit, wherein the electrode is the supercapacitor electrode as described above.

The supercapacitor according to the third embodiment of the present invention can increase the specific capacitance by reducing the interfacial resistance between the electrode and the electrolyte through a high contact area due to an increase in the graphene interplanar spacing of the composite. Furthermore, the conductive polymer in the composite can have the performance of both an electric double layer and a super capacitor. Further, when the electrode is prepared by fixing the composite to a current collector through graphene without a binder, and thus is applied to a capacitor, it may have higher specific capacitance and specific capacitance retention rate. Specifically, the specific capacitance of the supercapacitor according to the third embodiment of the present invention may be 250F/g to 500F/g, or 400F/g to 500F/g, at a current density of 0.1A/g. The above specific capacitance can be substantially maintained even at a high current density. Specifically, the specific capacitance at a current density of 4A/g may be 85% to 95% relative to the specific capacitance at a current density of 0.1A/g.

Hereinafter, the first embodiment of the present invention will be described in further detail by examples and experimental examples. However, the following examples and experimental examples are only intended to illustrate the first embodiment of the present invention, and the scope of the first embodiment of the present invention is not limited thereto.

<Example 1>Preparation of wrinkled graphene-carbon nanotube complex 1

Graphene Oxide (GO) used as a raw material for preparing graphene is prepared by dispersing in distilled water after being prepared from graphite according to a modified HumMer's method.

Step 1: to increase the multi-walled carbon nanotubes (purity of 95%)NANOLAB) to water, acid treated. 1g of multi-walled carbon nanotubes was dispersed in 150mL of sulfuric acid (H)₂SO₄99.5%) and 50mL of nitric acid (HNO)₃) After mixing the solution, the mixture was stirred at a temperature of 70 ℃ for 2 hours. Subsequently, the mixture was washed with a 5% hydrochloric acid (HCl) solution by filtration and dried in the air. The weight ratio (weight ratio) of the multi-walled carbon nanotubes subjected to acid treatment to graphene oxide was 0.01: and 1, preparing a mixed solution by using distilled water as a solvent. At this time, the graphene oxide concentration of the mixed solution was made 0.25 weight percent.

Step 2 a: to prepare the multi-walled carbon nanotube-graphene oxide composite, an aerosol reactor was used and the reaction scheme is shown in fig. 2. The mixed solution containing the acid-treated multi-walled carbon nanotubes and graphene oxide was aerosol-jetted through a two-fluid nozzle having a diameter of 1.4mm to form droplets.

And step 2 b: the sprayed droplets were transferred to a 200 ℃ furnace by argon gas at a flow rate of 8L/min, thereby evaporating the solvent. The prepared sample was collected in a filter by cyclone, thereby obtaining a multiwalled carbon nanotube-graphene oxide composite prepared in a three-dimensional corrugated shape. In order to reduce the graphene oxide of the prepared multi-walled carbon nanotube-graphene oxide composite, after heat treatment is carried out in a muffle furnace at 250 ℃ for 2 hours in an argon atmosphere (1L/min), a corrugated graphene-multi-walled carbon nanotube (MWCNT-GR) composite is finally prepared.

<Example 2>Preparation of wrinkled graphene-carbon nanotube composite 2 (Multi-walled carbon nanotube: graphene oxide heavy) The amount ratio is 0.05: 1)

in step 1 of example 1 above, except that the multi-walled carbon nanotubes: the weight ratio of the graphene oxide is changed to 0.05: 1 except for preparing a mixed solution, a corrugated graphene-multiwall carbon nanotube composite was prepared in the same manner as in example 1 above.

<Example 3>Preparation of Pleated graphene-carbon nanotube Complex 3 (multiwall carbon nanotube: graphene oxide heavy weight) The quantity ratio is 0.1: 1)

in step 1 of example 1 above, except that the multi-walled carbon nanotubes: the weight ratio of the graphene oxide is changed to 0.1: 1 except for preparing a mixed solution, a corrugated graphene-multiwall carbon nanotube composite was prepared in the same manner as in example 1 above.

<Comparative example 1>Preparation of wrinkled graphene-carbon nanotube composite 4 (multiwall carbon nanotube: graphene oxide heavy) The quantity ratio is 0.5: 1)

in step 1 of example 1 above, except that the multi-walled carbon nanotubes: the weight ratio of the graphene oxide is changed to 0.5: 1 except for preparing a mixed solution, a corrugated graphene-multiwall carbon nanotube composite was prepared in the same manner as in example 1 above.

<Example 4>Preparation of a supercapacitor 1

To prepare the active substance, the ratio of 9: 1 by weight ratio, the corrugated graphene-carbon nanotube composite prepared in example 1 and a polyvinylidene fluoride (PVDF) binder were mixed and sufficiently stirred with an N-methyl-2-pyrrolidone (N-methyl-2-pyrrolidone, NMP, Micropure-EG) solvent for 20 minutes by a stirrer. The active material solution subjected to stirring was applied to a carbon paper (AvCarb P50, FuelCellsEtc, USA) as a current collector at a thickness of 100 μm. Drying the coated active substance at 80 deg.C for 2 hr, and cutting into 2cm pieces²The weight per unit electrode was measured to be about 5 mg. A Filter paper (Filter paper, Whatman 1822-110Grade GF/C) was cut to a diameter of 14mm and used as a separation membrane (separator) and potassium hydroxide was used as an electrolyte at a concentration of 5M. Finally, a supercapacitor was prepared using HS FLAT CELL (HOHSEN corp., Japan) as a two-electrode.

<Example 5>Preparation of supercapacitor 2

In the above example 4, a supercapacitor was prepared in the same manner as in the above example 4, except that the complex prepared in the above example 2 was used in the preparation of an active material.

<Example 6>Preparation of a supercapacitor 3

In the above example 4, a supercapacitor was prepared in the same manner as in the above example 4, except that the complex prepared in the above example 3 was used in the preparation of an active material.

<Comparative example 2>Preparation of supercapacitor 4

In the above example 4, a supercapacitor was prepared in the same manner as in the above example 4, except that the composite prepared in the above comparative example 1 was used in the preparation of an active material.

<Experimental example 1>Surface and morphological evaluation of graphene-multiwalled carbon nanotube composite

The structures and shapes of the wrinkled graphene-multi-walled carbon nanotubes prepared in examples 1 to 3 and comparative example 1 were photographed by a field emission scanning electron microscope (FE-SEM, Sirion, FEI) and a transmission electron microscope (TEM, JEM-ARM200F, JEOL), and the results are shown in fig. 3 from (a1) to (d1) and fig. 3 from (a2) to (d 2).

As shown in parts (a1) to (d1) of fig. 3, all the composites prepared were in the form of graphene sheets folded (crumped) in a three-dimensional shape, having a diameter of about 4 μm to 6 μm.

As a result of observation by a transmission electron microscope, as shown in parts (a2) to (d2) of fig. 3, it was confirmed that multi-walled carbon nanotubes were present in the wrinkled graphene sheet, and it was found that the content of multi-walled carbon nanotubes present in the graphene sheet increased as the weight ratio of multi-walled carbon nanotubes/graphene oxide increased during the preparation. It was confirmed that the following properties were observed in the case of multi-walled carbon nanotubes: the weight ratio of the graphene oxide is 0.01: 1 to 0.1: 1, in the prepared graphene-multi-walled carbon nanotube complex, multi-walled carbon nanotubes are uniformly dispersed among graphene sheets. However, in the case of multi-walled carbon nanotubes: the weight ratio of the graphene oxide is 0.5: 1, it was confirmed that the amount of the multi-walled carbon nanotubes present in the graphene sheet was large, and the aggregation of the (bundles) multi-walled carbon nanotubes occurred, thereby increasing the number of the aggregated (bundles) multi-walled carbon nanotubes.

<Experimental example 2>X-ray diffraction analysis of graphene-multiwalled carbon nanotube composites

The graphene-multiwall carbon nanotube composites prepared in examples 1 to 3 and comparative example 1 were analyzed by X-ray diffraction (SmartLab, Rigaku Co.), and the results are shown in fig. 4.

As shown in fig. 4, X-ray diffraction peaks (peak) of all the graphene-multiwalled carbon nanotube composites prepared occurred in the vicinity of about 23.5 ° and 42.9 ° in a large range. This is because the graphene oxide peak existing at 10 ° is reduced and moved to the graphene peak. The X-ray diffraction peak of the reduced graphene-multiwall carbon nanotube composite is shifted to the left of the peak of graphite, because the graphene surface spacing (interlayer spacing) of the composite increases due to the introduction of the multiwall carbon nanotubes and various oxygen functional groups remaining in the graphene. The results of calculating the surface pitches according to Bragg's law formula (the following mathematical formula 2) show that the surface pitches of the graphene-multiwall carbon nanotube composites of examples 1, 2, 3 and comparative example 1 were 0.37nm, 0.36nm and 0.34nm, respectively, and all samples were increased relative to the surface pitch of graphite of 0.33 nm. On the other hand, the weight ratio (multi-walled carbon nanotube: graphene oxide) in the preparation of the composite was 0.5: in comparative example 1 of 1, the surface distance was decreased compared to other graphene-multiwall carbon nanotube composites because the surface distance of the composites decreased due to the aggregation of the multiwall carbon nanotubes as the amount of multiwall carbon nanotube injection increased.

[ mathematical formula 2]

d₀₀₂＝nλ/2sinθ

<Experimental example 3>Raman spectrum determination of graphene-multi-walled carbon nanotube complex

Raman spectroscopy (Lambda Ray, LSI Dimension P1) analysis was performed on the graphene-multiwall carbon nanotube composites prepared in examples 1 to 3 and comparative example 1, and the results are shown in fig. 5.

As shown in FIG. 5, it was confirmed from the results of Raman analysis of the prepared graphene-multiwalled carbon nanotube composite that the thickness was 1350cm in each case^-1、1600cm^-1A D peak and a G peak representing graphene were observed. Wherein the G peak is a peak indicating carbon of graphite, and the D peak is a peak indicating graphene sp²Structural deletion (defect) and substitution or disorder (disorder). Therefore, the defect degree of graphene can be confirmed from the intensity ratio of the D peak and the G peak. The D/G band (band) ratio of the prepared graphene-multiwall carbon nanotube composite decreases as the multiwall carbon nanotube/graphene oxide weight ratio increases upon preparation. This indicates that the degree of defects in the composite is reduced due to the introduction of multi-walled carbon nanotubes having a relatively lower degree of defects than graphene sheets.

<Experimental example 4>Evaluation of i) circulating voltage and current, ii) charging and discharging, and iii) impedance characteristics of supercapacitor

The cyclic voltage current, charge and discharge, and impedance characteristics of the supercapacitors prepared in the above examples 4 to 6 and comparative example 2 were measured by Potentiostat (VSP, Bio-logics), and the results thereof are shown in parts (a) to (d) of fig. 6.

Generally, an electric double layer capacitor using an aqueous potassium hydroxide solution as an electrolyte has a pattern shape close to a rectangle due to an electric double layer effect by adsorption of surface ions, and the specific capacitance increases as the area of the rectangle increases.

i) Therefore, as shown in part (a) of fig. 6, the cycling voltage current test results for evaluating the performance of the supercapacitor made of the graphene-multiwall carbon nanotube composite show that there is ideal driving of the electric double layer capacitor in all electrodes. Also, as the multi-walled carbon nanotube/graphene oxide weight ratio was increased from 0.01 to 0.1 when preparing the composite, the area of the circulating current-voltage curve was increased, but the area was decreased under the condition of 0.5. This is probably because the increase in the amount of the multi-walled carbon nanotube implantation into which graphene is introduced increases the degree of high conductivity and the interfacial distance of graphene, so that electrolyte ions do not feel large resistance and are well arranged at the electrode substance interface. On the other hand, in the case where the multi-walled carbon nanotube/graphene oxide weight ratio is 0.5 or more when preparing the composite body, the agglomeration between the multi-walled carbon nanotubes causes the inter-plane distance of graphene to decrease and slows down the ion transfer rate of the electrolyte.

ii) part (b) of fig. 6 shows the charge-discharge test results and the specific capacitance thus calculated as a function of the scan speed. The charge/discharge test results showed that all the electrodes exhibited charge/discharge curves showing reversible symmetry, and in this case, the specific capacitance was obtained by the following equation 3.

[ mathematical formula 3]

C_p＝4IΔt/mΔV

Where I is a discharge current, Δ t is a discharge time, m is a mass of the active material, and Δ V is a measurement voltage range. As shown in fig. 6 (c), the specific capacitance of the capacitors including the graphene-multiwall carbon nanotube composite was 137F/g, 144F/g, 192F/g, and 109F/g, respectively, at a current density of 0.1A/g, in examples 4, 5, 6, and 2, and the specific capacitance increased as the weight ratio of multiwall carbon nanotubes/graphene oxide was increased from 0.01 to 0.1 when the composite was prepared, but decreased when the weight ratio of multiwall carbon nanotubes/graphene oxide was 0.5. In the case of example 6, in which the weight ratio of the multi-walled carbon nanotube/graphene oxide was 0.1 when the composite was prepared, a high specific capacitance was exhibited while maintaining the high specific capacitance as the scanning speed increased. From this, it is understood that there are optimum conditions for the mixing ratio of the multiwalled carbon nanotube and the graphene oxide. This is because, as described above as a result of the cyclic voltage current, the increase in the surface distance due to the introduction of the multi-walled carbon nanotube improves the penetration of electrolyte ions into the inside of the electrode and improves the conductivity, thereby maintaining the specific capacitance even at a high scanning speed. On the other hand, when the weight ratio of the multi-walled carbon nanotube/graphene oxide was 0.5 in the preparation of the composite, it was not obvious that the specific capacitance decreased as the current density increased, but it was found that the specific capacitance was somewhat lower at all current densities. This is considered to be because the specific capacitance of the composite is decreased due to an increase in the interfacial resistance of the electrolyte caused by the aggregation phenomenon of the multi-walled carbon nanotubes observed under a transmission electron microscope with the multi-walled carbon nanotubes having a low specific capacitance introduced in excess relative to graphene.

iii) as shown in part (d) of fig. 6, as shown in the experiment performed to investigate the interface resistance of the electrode and the electrolyte, as the multi-walled carbon nanotube/graphene oxide weight ratio was increased when preparing the composite, the bulk resistance (bulk resistance, corresponding to the intercept value of the Z' axis of part (d) of fig. 6) was substantially similar except for comparative example 2, but the interface resistance (interfacial resistance, corresponding to the diameter of a semicircle in the nyquist plot (nyquist plot) of part (d) of fig. 6) was decreased as the injection amount of the multi-walled carbon nanotube was increased. This is probably because not only the resistance is reduced due to the rapid conductivity of the multi-walled carbon nanotube, but also the contact area with the electrolyte is increased due to the increase in the interfacial distance with graphene, so that the interface resistance based on the ionic conductivity can be reduced.

Thus, the graphene-multi-walled carbon nanotube (graphene-multi-walled carbon nanotube) composite of the example of the first embodiment of the present invention is prepared in a spherical three-dimensional shape having an average particle size of 1 μm to 10 μm, and the multi-walled carbon nanotube is dispersed between graphene sheets. The evaluation of the performance of the supercapacitor comprising the graphene-multiwalled carbon nanotube composite revealed that the specific capacitance was 192F/g, which was the highest, at a multiwalled carbon nanotube/graphene oxide weight ratio of 0.1 when the composite was prepared, and that the specific capacitance was well maintained even at high current densities. Therefore, it is considered that the introduction of the multi-walled carbon nanotube into graphene can improve characteristics such as conductivity, ionic conductivity, and increase in graphene interfacial distance. In particular, the specific capacitance can be well maintained even at a high current density (4A/g) because the multi-walled carbon nanotube additionally forms a physical cross-linking point in graphene, and the air holes in the graphene-multi-walled carbon nanotube composite prepared in a three-dimensional shape cause interfacial resistance between an electrode and an electrolyte.

Hereinafter, the second embodiment of the present invention will be described in further detail by way of examples and experimental examples. However, the following examples and experimental examples are only intended to illustrate the second embodiment of the present invention, and the scope of the second embodiment of the present invention is not limited thereto.

<Example i>Preparation of wrinkled graphene-carbon nanotube-polymer complex 1

Graphene oxide used as a raw material for preparing graphene is prepared by dispersing in distilled water after being prepared from graphite by a modified HumMer's method.

Step i: in order to improve the dispersibility of multi-walled carbon nanotubes (95% purity, NANOLAB) in water, an acid treatment was performed. 1g of multi-walled carbon nanotubes was dispersed in 150mL of sulfuric acid (H)₂SO₄99.5%) and 50mL of nitric acid (HNO)₃) After mixing the solution, it was stirred at a temperature of 70 ℃ for 2 hours. Subsequently, the mixture was washed with a 5% hydrochloric acid (HCl) solution by filtration and dried in the air. The mixing weight ratio of the multi-walled carbon nano-tube treated by acid to the graphene oxide is 0.01: 1, adding 1M hydrochloric acid solution. At this time, the graphene oxide concentration of the hydrochloric acid solution was made 0.25 weight percent. Then, aniline, which is a conductive polymer monomer, was added to the hydrochloric acid solution to make the concentration thereof 20mM, thereby preparing a mixed solution.

Step ii: ammonium persulfate (APS; 98% purity, Sigma-Aldrich) was added as an initiator so that the aniline monomer of the above mixed solution: the weight ratio of the initiator is 4: and 1, subjecting the mixed solution to ultrasonic treatment for 1 hour to polymerize the polymer.

Step iiia: in order to prepare the multi-walled carbon nanotube-graphene oxide-polyaniline complex, an aerosol reactor is used, and the reaction scheme is shown in fig. 8. A mixed solution containing acid-treated multi-walled carbon nanotubes, graphene oxide and polyaniline was dispersed in an aerosol spray manner through a two-fluid nozzle having a diameter of 1.4mM to form droplets.

Step iiib: the sprayed droplets were transferred to a 200 ℃ furnace by argon gas at a flow rate of 8L/min, thereby evaporating the solvent. The prepared sample was collected in a filter by cyclone, thereby obtaining a multiwalled carbon nanotube-graphene oxide-polyaniline composite prepared in a three-dimensional corrugated shape. In order to reduce the prepared graphene oxide of the multi-walled carbon nanotube-graphene oxide-polyaniline composite, the corrugated graphene-multi-walled carbon nanotube-polyaniline (MWCNT-GR-PANI) composite is finally prepared after heat treatment for 2 hours in a muffle furnace at the temperature of 250 ℃ in an argon atmosphere (1L/min).

<Example ii>Preparation of wrinkled graphene-carbon nanotube-polymer complex 2 (multiwall carbon nanotube: oxidation) The weight ratio of the graphene is 0.05: 1)

in step i of example i above, except that the multi-walled carbon nanotubes: the weight ratio of the graphene oxide is changed to 0.05: 1 except for preparing the mixed solution, the corrugated graphene-multiwalled carbon nanotube-polyaniline composite was prepared in the same manner as in example i above.

< example iii > preparation of wrinkled graphene-carbon nanotube composite 3 (multi-walled carbon nanotube: graphene oxide weight ratio 0.1: 1)

In step i of example i above, except that the multi-walled carbon nanotubes: the weight ratio of the graphene oxide is changed to 0.1: 1 except for preparing a mixed solution, a corrugated graphene-multiwalled carbon nanotube-polyaniline composite was prepared in the same manner as in example i above.

<Comparative example i>Preparation of corrugated graphene balls

In step i of example i above, wrinkled graphene spheres (wrinkled graphene (CGR)) were prepared in the same manner as in example i above, except that the carbon nanotubes and the conductive polymer monomer were not added and step ii was omitted.

<Comparative example ii>Preparation of wrinkled graphene-carbon nano tube

In step i of the above example i, a wrinkled graphene-carbon nanotube composite was prepared in the same manner as in the above example i, except that the conductive polymer monomer was not added and step ii was omitted.

<Example iv>Preparation of a supercapacitor 1

To prepare the active substance, the ratio of 9: 1 weight ratio of the pleats prepared in example 1 aboveThe wrinkled graphene-carbon nanotube-polymer composite and a polyvinylidene fluoride (KUREHA co., Japan) binder were thoroughly stirred with an N-methyl-2-pyrrolidone (Micropure-EG) solvent for 20 minutes using a stirrer. The active material solution, which was completed stirring, was coated on a carbon paper (AvCarb P50, FuelCellsEtc, USA) as a current collector at a thickness of 100 μm. Drying the coated active substance at 80 deg.C for 2 hr, and cutting into 2cm pieces²The weight per unit electrode was measured to be about 5 mg. The filter paper (Whatman 1822-110Grade GF/C) was cut to a diameter of 14mM and used as a separation membrane, and 5M concentrated potassium hydroxide was used as an electrolyte. Finally, a supercapacitor was prepared using HS FLAT CELL (HOHSEN corp., Japan) as a two-electrode.

<Example v>Preparation of supercapacitor 2

In the above example iv, a supercapacitor was prepared in the same manner as in the above example iv except that the composite prepared in the above example ii was used in the preparation of an active material.

<Example vi>Preparation of a supercapacitor 3

In the above example iv, a supercapacitor was prepared in the same manner as in the above example iv, except that the composite prepared in the above example iii was used in the preparation of an active material.

<Comparative example iii>Preparation of supercapacitor 4

In the above example iv, a supercapacitor was prepared in the same manner as in the above example iv, except that the wrinkled graphene prepared in the above comparative example i was used in the preparation of an active material.

<Comparative example vi>Preparation of supercapacitor 5

In the above example iv, a supercapacitor was prepared in the same manner as in the above example iv except that the composite prepared in the above comparative example ii was used in the preparation of an active material.

<Experimental example i>Graphene-multiwalled carbon nanotube-polyphenylSurface and morphological evaluation of amine Complex

The structures and shapes of the substances prepared in example i, comparative example i, and comparative example ii were photographed by a field emission scanning electron microscope and a transmission electron microscope, and the results thereof are shown in portions a to c of fig. 9 and portions d to f of fig. 9.

As shown in parts a to c of fig. 9, all the composites prepared were in the form of folded graphene sheets of three-dimensional shapes, having diameters of about 4 to 6 μm. At this time, the shape was not changed by the addition of the carbon nanotubes and aniline, and it was considered that the carbon nanotubes and polyaniline were present between the graphene sheets.

As shown in the sections d to f of fig. 9, it was confirmed from the observation results of the transmission electron microscope that multi-walled carbon nanotubes were present in the wrinkled graphene sheet, and that polyaniline was generated on the surfaces of the carbon nanotubes and graphene after the addition of aniline.

<Experimental example ii>X-ray diffraction analysis of graphene-multiwalled carbon nanotube-polyaniline complex

The X-ray diffraction (SmartLab, Rigaku Co.) analysis of the materials prepared in example i, comparative example i and comparative example ii above showed the results shown in part a of fig. 10.

As shown in fig. 10 a, the samples of the wrinkled graphene and the carbon nanotube/graphene prepared according to the X-ray diffraction analysis results of the wrinkled graphene (CGR) of the comparative example i, the graphene-carbon nanotube of the comparative example ii, and the graphene-carbon nanotube-polyaniline composite of the example i have graphene and carbon nanotube peaks at 23.5 ° and 26.4 °. On the other hand, the graphene-carbon nanotube-polyaniline complex has polyaniline peaks at 19.7 ° and 25.3 ° together with the graphene and carbon nanotube peaks. Therefore, it was confirmed that graphene, carbon nanotubes, and polyaniline were successfully produced in the prepared wrinkled graphene, graphene-carbon nanotube complex, and graphene-carbon nanotube-polyaniline complex.

<Experimental example iii>Raman spectrum determination of graphene-multiwalled carbon nanotube-polyaniline complex

Raman spectroscopy (Lambda Ray, LSI Dimension P1) analysis was performed on the graphene-multiwalled carbon nanotube-polyaniline composite prepared in example i, comparative example i, and comparative example ii, and the results are shown in part b of fig. 10.

As shown in part b of FIG. 10, the concentrations of the samples prepared in example i, comparative example i and comparative example ii were 1350cm in length, respectively^-1、1600cm^-1A D peak and a G peak were observed as graphene peaks, and in this case, the G peak was a peak indicating carbon of graphite and the D peak was a peak indicating graphene sp²Deletion and substitution or deregulation peaks of the structure. On the other hand, the graphene-carbon nanotube-polyaniline composite is 1163cm^-1、1250cm^-1、1478cm^-1Peaks indicating C — H bonding of polyaniline were observed, and from these results, it was confirmed that polyaniline was successfully produced in the prepared composite.

<Experimental example iv>Mercury porosimetry determination of graphene-multiwalled carbon nanotube-polyaniline complex

The graphene-multiwalled carbon nanotube-polyaniline composites prepared in example i, comparative example i, and comparative example ii were analyzed by mercury porosimetry (AutoPore IV, Micromeritics), and the results are shown in fig. 11.

As shown in fig. 11, the average pore diameters (nm) of the wrinkled graphene of comparative example i, the graphene-carbon nanotube of comparative example ii, and the graphene-multiwall carbon nanotube-polyaniline composite of example i were measured to be 340nm, 657nm, and 824nm, respectively. At this time, it is considered that the introduction of the carbon nanotube and the polyaniline increases the pore size in the composite, and the increased pore size improves the proximity of the electrolyte to the composite electrode.

<Experimental example v>Evaluation of i) circulating voltage and current, ii) charging and discharging, and iii) impedance characteristics of supercapacitor

The cyclic voltage current, charge and discharge characteristics and impedance characteristics of the supercapacitors prepared in example iv, comparative example iii and comparative example iv were measured by potentiostat (VSP, Bio-logics), and the results are shown in parts (a) to (d) of fig. 12.

i) Referring to part a of fig. 12, it can be seen from the results of the cyclic current voltage test of the prepared sample that there is an ideal electric double layer capacitor driving in all the electrodes. Also, this rectangular area increases in the order of corrugated graphene, graphene-carbon nanotube-polyaniline, which is thought to be because diffusion of the electrolyte in the electrode increases and the moving resistance decreases due to the introduction of the carbon nanotube and polyaniline. This can be confirmed by the presence of an oxidation-reduction peak as a result of cycling voltage current and the appearance of a weak congested region (Plateau) in the charge-discharge curve of part b of fig. 12. These results indicate that the graphene-carbon nanotube-polyaniline composite has both an electrical double layer and a pseudocapacitor.

ii) section c of fig. 12 shows the specific capacitance calculated by the charge-discharge test results as a function of the scan speed. The wrinkled graphene, graphene-carbon nanotube and graphene-carbon nanotube-polyaniline samples have specific capacitances of 121F/g, 192F/g and 294F/g under the condition of 0.1A/g respectively. At this time, the spherical shape of the graphene-carbon nanotube-polyaniline composite, the increase in surface area caused by the introduction of the carbon nanotube, and the excellent conductivity characteristics improve the penetration of electrolyte ions on the electrode surface, having the highest specific capacitance when the characteristics of the pseudo capacitor caused by the introduction of polyaniline.

iii) as shown in part d of fig. 12, an impedance test was performed at a frequency range of 100kHz to 0.01Hz, and ion diffusion in a spherical graphene-carbon nanotube-polyaniline electrode was investigated. Referring to nyquist plots of wrinkled graphene, graphene-carbon nanotube, and graphene-carbon nanotube-polyaniline samples, the graphene-carbon nanotube-polyaniline electrode is linear in a low frequency region and semicircular in a high frequency region, compared to other electrodes. Thus, the polyaniline is generated in the graphene and the carbon nanotubes, and the fast diffusibility is maintained.

<Experimental example vi>I) cyclic voltage current, ii) charge and discharge of supercapacitors according to the carbon nanotube content and iii) evaluation of impedance characteristics

The cyclic voltage current, charge and discharge, and impedance characteristics of the supercapacitors prepared in the above examples iv to vi were measured by a potentiostat (VSP, Bio-logics), and the results thereof are shown in parts a to d of fig. 13.

i) As shown in a portion of fig. 13, it can be confirmed from the cycle voltage current test result that the cycle voltage current curve area increases as the addition amount of the carbon nanotube increases. This is because an increase in the addition amount of the carbon nanotubes introduced into the graphene inhibits the high conductivity and recombination of the graphene sheets, thereby increasing the ion transfer rate of the electrolyte in the prepared electrode.

ii) sections b and c of fig. 13 show the charge-discharge test and the specific capacitance calculated therefrom as a function of the scanning speed. The results of the charge and discharge tests confirmed that all the electrodes had the characteristics of an electric double layer and a pseudocapacitor, and the specific capacitances were 250F/g, 266F/g, and 294F/g, respectively, at a current density of 0.1A/g. This is because the specific capacitance increases with the increase in the amount of carbon nanotubes added, and the specific capacitance has the highest retention rate even when the amount of addition is such that the multiwall carbon nanotube/graphene oxide weight ratio is 0.1 when preparing the composite, as the current density increases.

iii) as shown in part d of fig. 13, as a result of an interfacial resistance test for investigating an electrode and an electrolyte, as the amount of the carbon nanotube added increases, the carbon nanotube is linear in a low frequency region and semicircular in a high frequency region. This indicates that the resistance of the carbon nanotube is reduced due to the rapid conductivity, and at the same time, the inhibition of recombination between graphene sheets increases the contact area of the electrolyte, thereby greatly reducing the interface resistance due to ion conduction.

The present inventors prepared a Graphene-multiwall Carbon Nanotube-polyaniline spherical composite having a three-dimensional structure by a single process using a colloidal solution in which a multiwall Carbon Nanotube (CNT), Graphene Oxide (GO), and aniline were mixed in the example of the second embodiment by an Aerosol Spray (ASP) process. And (e) the multi-walled carbon nanotubes put into the mixed colloidal solution in the step (i) have a crosslinking effect among graphene sheets, so that the conductivity is improved, the surface distance is increased, the electrolyte proximity is improved, a complex prepared by adding polyaniline is in a three-dimensional spherical shape, uniform air holes are formed in the complex, and the power density and the energy density are improved simultaneously by means of the high conductivity and the redox reaction of the polyaniline.

Hereinafter, a third embodiment of the present invention will be described in more detail by way of examples and experimental examples. However, the following examples and experimental examples are only intended to illustrate the third embodiment of the present invention, and the scope of the third embodiment of the present invention is not limited thereto.

<Example i +>Preparation of wrinkled graphene-carbon nanotube-polymer complex 1

Step i: in order to improve the dispersibility of multi-walled carbon nanotubes (95% purity, NANOLAB) in water, an acid treatment was performed. 1g of multi-walled carbon nanotubes was dispersed in 150mL of sulfuric acid (H)₂SO₄99.5%) and 50mL of nitric acid (HNO)₃) After mixing the solution, it was stirred at a temperature of 70 ℃ for 2 hours. Subsequently, the solution was washed by filtration with a 5% hydrochloric acid (HCl) solution and dried in the air. Mixing the multi-wall carbon nano tube subjected to acid treatment and graphene oxide in a weight ratio of 0.1: 1, adding 1M hydrochloric acid solution. At this time, the hydrochloric acid solution was such that the graphene oxide concentration was 0.25 weight percent. Then, aniline, which is a conductive polymer monomer, was added to the hydrochloric acid solution to make the concentration thereof 20mM, thereby preparing a mixed solution.

Step ii: ammonium persulfate (APS; 98% purity, Sigma-Aldrich), aniline monomer of the above mixed solution: the weight ratio of the initiator is 4: and 1, subjecting the mixed solution to ultrasonic treatment for 1 hour to polymerize the polymer.

Step iiia: in order to prepare the multi-walled carbon nanotube-graphene oxide-polyaniline composite, an aerosol reactor was used, and a reaction scheme as shown in fig. 15 was used to form droplets by dispersing a mixed solution containing the acid-treated multi-walled carbon nanotube, graphene oxide and polyaniline in an aerosol spray manner through a two-fluid nozzle having a diameter of 1.4 mm.

Step iiib: the sprayed droplets were transferred to a 200 ℃ furnace by argon gas at a flow rate of 8L/min, thereby evaporating the solvent. The prepared sample was collected in a filter by cyclone, thereby obtaining a multiwalled carbon nanotube-graphene oxide-polyaniline composite prepared in a three-dimensional corrugated shape. In order to reduce the prepared graphene oxide of the multi-walled carbon nanotube-graphene oxide-polyaniline composite, the corrugated graphene-multi-walled carbon nanotube-polyaniline composite is finally prepared after heat treatment for 2 hours in a muffle furnace at the temperature of 250 ℃ in an argon atmosphere (1L/min).

<Example ii +>Preparation of wrinkled graphene-carbon nanotube-polymer complex 2 (aniline concentration 10mM)

In step i of the above example i +, a wrinkled graphene-multi-walled carbon nanotube-polyaniline complex was prepared in the same manner as in the above example i + except that the aniline concentration of the mixed solution was made to be 10 mM.

<Example iii +>Preparation of wrinkled graphene-carbon nanotube-polymer composite 3 (aniline concentration 40mM)

In step i of the above example i +, a wrinkled graphene-multi-walled carbon nanotube-polyaniline complex was prepared in the same manner as in the above example i + except that the aniline concentration of the mixed solution was made 40 mM.

<Example iv +>Preparation of a supercapacitor 1

Step iv: to prepare the electrodes, the electrodes were measured at 9.5: 0.5 (1: 0.053) by weight of the mixture of the corrugated graphene-carbon nanotube-polymer composite prepared in example i + and graphene oxide, and mixing the mixture with a stirrerN-methyl-2-pyrrolidone (Micropure-EG) solvent was stirred well together for 20 minutes. The solution, the stirring of which was completed, was coated on a carbon paper (AvCarb P50, FuelCellsEtc, USA) as a current collector at a thickness of 100 μm. The coated material was heat-treated at 250 ℃ for 2 hours and cut into 2cm pieces²The weight per unit electrode was measured to be about 1.5 mg.

The filter paper (Whatman 1822-110Grade GF/C) was cut to a diameter of 14mm and used as a separation membrane, and 5M concentrated potassium hydroxide was used as an electrolyte. Finally, a supercapacitor was prepared using HS FLAT CELL (HOHSEN corp., Japan) as a two-electrode.

<Example v +>Preparation of supercapacitor 2

In step iv of example iv + above, a supercapacitor was prepared in the same manner as in example iv + above, except that the composite prepared in example ii + above was used.

<Example vi +>Preparation of a supercapacitor 3

In step iv of example iv + above, a supercapacitor was prepared in the same manner as in example iv + above, except that the composite prepared in example iii + above was used.

<Example vii +>Preparation of supercapacitor 4

In step iv of the above example iv +, the weight ratio of the composite and the graphene oxide is set to 9: 1 (1: 0.111), a supercapacitor was prepared in the same manner as in example iv + above.

<Example viii +>Preparation of supercapacitor 5

In step iv of the above example iv +, except that the weight ratio of the composite and the graphene oxide is set to 8: 2 (1: 0.25), a supercapacitor was prepared in the same manner as in example iv + above.

<Experiment example i +>Surface and morphological evaluation of graphene-multiwalled carbon nanotube-polyaniline complex

The structures and shapes of the composite prepared in examples i + to iii + above were photographed by a field emission scanning electron microscope (FE-SEM, Sirion, FEI) and a transmission electron microscope (JEM-ARM200F, JEOL), and the results thereof are shown in parts a to f of fig. 16 and parts a to f of fig. 17.

As shown in parts a to f of fig. 16, field emission scanning electron microscope observation results show that the graphene-carbon nanotube-polyaniline composites prepared in examples 1 to 3 are three-dimensional spherical (spherical) particles and have a diameter of about 5 μm. At this time, when the electrode was prepared, the shape did not change with the change in the aniline injection amount, and it was considered that the carbon nanotube existed between the graphene sheets. Further, it was found that the amount of growth of polyaniline-like protrusions on the surface of graphene increased with the increase in the amount of aniline injected when preparing the electrode.

As shown in portions a to f of fig. 17, the presence or absence of carbon nanotubes and polyaniline in the prepared sample was observed from a transmission electron microscope and a mapping image (mapping image), and it was confirmed that the carbon nanotubes were uniformly dispersed in the graphene sheet. Also, when preparing an electrode, the amount of polyaniline generated on the surfaces of carbon nanotubes and graphene increases as the amount of aniline injected increases.

<Experiment example ii +>X-ray diffraction analysis of graphene-multiwalled carbon nanotube-polyaniline complex

The composites prepared in examples i + to iii + above were subjected to X-ray diffraction (SmartLab, Rigaku Co.) analysis, the results of which are shown in part a of fig. 18.

As shown in part a of fig. 18, it can be confirmed that polyaniline peaks at 23.5 °, 26.4 ° and 19.7 ° and 25.3 ° of the composites prepared in examples i + to iii + together with graphene and carbon nanotube peaks. Therefore, it was confirmed that graphene, carbon nanotubes, and polyaniline were successfully produced in the produced composite.

<Experiment example iii +>Raman spectrum determination of graphene-multiwalled carbon nanotube-polyaniline complex

The complexes prepared in examples i + to iii + were analyzed by raman spectroscopy (Lambda Ray, LSI Dimension P1), and the results are shown in part b of fig. 18.

As shown in part b of FIG. 18, the composites prepared in examples i + to iii + above were at 1350cm^-1、1600cm^-1A D peak and a G peak were observed as graphene peaks. And, at 1163cm^-1、1250cm^-1、1478cm^-1Peaks indicating C — H bonding of polyaniline were observed, and from these results, it was confirmed that polyaniline was successfully produced in the sample.

<Experimental example iv +>Evaluation of i) circulating Voltage Current and ii) Charge-discharge characteristics of supercapacitors based on Aniline concentration Price of

The cycling voltage current and the charge and discharge characteristics of the supercapacitors prepared in examples iv + to vi + above were measured by potentiostat (VSP, Bio-logics), and the results are shown in parts a to c of fig. 19.

i) Referring to part a of fig. 19, it can be confirmed that there are electric double layer capacitor driving and oxidation-reduction peaks of the electrodes in all the electrodes prepared. And, when preparing an electrode, the aniline concentration of 20mM has the widest area of the cyclic voltage current. However, when preparing an electrode, in the case where aniline has a high concentration of 40mM, the area of the circulating voltage current is rather reduced, which is considered to be because the increase in the content of polyaniline in the complex causes an increase in the diffusion distance of electrolyte ions into the inside of the electrode, thereby affecting the capacitor performance.

ii) as shown in part b of fig. 19, it was confirmed that the curve congestion region was more pronounced as the aniline injection amount was increased at the time of electrode preparation in the charge and discharge curve, and these results indicate that the graphene-carbon nanotube-polyaniline-graphene composite exhibited both the electrical double layer and the pseudocapacitor characteristics. Referring to part c of FIG. 19, when preparing the electrodes, the electrodes having aniline concentrations of 10mM, 20mM, and 40mM have specific capacitances of 354F/g, 456F/g, and 256F/g, respectively, at a current density of 0.1A/g. At this time, the electrode of example i + has the highest specific capacitance, and also maintains a high specific capacitance as the current density increases. From this, it was found that the optimum condition for the aniline concentration was present when preparing the composite electrode. Moreover, the introduction of the carbon nanotubes in the composite electrode has a crosslinking effect among the graphene sheets, so that the conductivity is improved, and the specific capacitance based on the conductivity is improved. However, it is known that when preparing an electrode, the supercapacitor of example vi + which is suitable for the graphene-carbon nanotube-polyaniline-graphene electrode of example iv + prepared in the presence of high concentration (40mM) of aniline, has a relatively low specific capacitance at all current densities. This is considered to be because the migration of electrolyte ions into the electrode is suppressed due to the growth of polyaniline caused by the injection of excess aniline at the time of preparing the electrode, and the active surface area of the electrode according to the redox reaction decreases, affecting the specific capacitance.

<Experiment example v +>I) circulating voltage current and ii) charging and discharging of supercapacitor according to addition amount of graphene oxide Evaluation of characteristics

The cycle voltage current and the charge and discharge characteristics of the supercapacitors prepared in example iv +, example vii + and example viii + were measured by potentiostat (VSP, Bio-logics), and the results are shown in sections a to c of fig. 20.

i) As shown in part a of fig. 20, it can be confirmed that all the electrodes prepared have an electric double layer capacitor drive and an oxidation-reduction peak caused by polyaniline introduction exists. At this time, it can be seen that the area of the graph is 9.5 in terms of the mixed weight ratio of the graphene-carbon nanotube-polyaniline complex and the graphene oxide when the electrode is prepared: 0.5, 9: 1. 8: the 2 order decreased, which is believed to be because the active surface area of the prepared sample decreased due to the increased graphene oxide implantation.

ii) as can be confirmed from the charge and discharge tests and the non-storage calculation results of the parts b and c of fig. 20, the weight ratio of the graphene-carbon nanotube-polyaniline composite to the graphene oxide when the electrode is manufactured is 9.5: 0.5, 9: 1. 8: when the prepared composite electrode was applied to a capacitor, the specific capacitances were 471F/g, 456F/g, and 432F/g at a current density of 0.1A/g, respectively. And when the graphene-carbon nanotube-polyaniline composite is applied to preparing an electrode, the mixing weight ratio of the graphene-carbon nanotube-polyaniline composite to the graphene oxide is 9.5: 0.5, the weight ratio of the graphene-carbon nanotube-polyaniline complex to the graphene oxide to be mixed when the electrode is suitably prepared is 9: 1, the specific capacity retention decreases as the current density increases. From these results, it was confirmed that there is an optimum condition for the ratio of the graphene-carbon nanotube-polyaniline complex to the graphene oxide when preparing the electrode. Therefore, in the absence of a binder, the composite electrode incorporating the graphene sheets results in an increase in the specific capacitance of the supercapacitor and the retention of the specific capacitance due to rapid electron movement of the electrode and an increase in the active material content.

The present inventors prepared a Graphene-carbon nanotube-polyaniline composite by mixing a colloidal solution of multi-wall Carbon Nanotubes (CNTs), Graphene Oxide (GO), and aniline in the example of the third embodiment using an Aerosol Spray (ASP) process, and added Graphene oxide to prepare a Graphene-carbon nanotube-polyaniline-Graphene composite electrode having a three-dimensional structure. At this time, the influence of the prepared composite electrode on the performance of the supercapacitor was investigated according to the supercapacitor performance with the change in the aniline concentration and the adjustment of the graphene oxide injection amount. Confirming that the specific capacity of the supercapacitor is improved due to smooth electron movement inside the electrode and the increase of the content of the electrode active substances. The physical properties (shape, crystallinity, and defects) of graphene-carbon nanotube-polyaniline, which varied with the aniline concentration when the electrode was prepared, were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and raman analysis, and the supercapacitor characteristics of the electrode prepared from the composite were carried out.

Although specific examples of the method of preparing the corrugated graphene composite body, the composite body prepared thereby, and the supercapacitor including the composite body according to the first to third embodiments of the present invention have been described, it will be apparent that various modifications may be made without departing from the scope of the present invention.

Accordingly, the scope of the invention should not be construed as limited to the described embodiments, but should be determined by the appended claims along with their full scope of equivalents.

That is, it should be understood that the foregoing embodiments are illustrative in all aspects and should not be construed as limiting, the scope of the invention is shown by the appended claims rather than the detailed description, and all changes and modifications derived from the meaning and scope of the claims and their equivalents are intended to be included in the scope of the invention.

Claims

1. A preparation method of a supercapacitor electrode containing a corrugated graphene composite is characterized by comprising the following steps:

step i: preparing a mixed solution formed by mixing the carbon nano tube subjected to acid treatment, the graphene oxide, the conductive high polymer monomer and a solvent;

step ii: polymerizing the monomers in the mixed solution;

step iii: spray-drying the mixed solution subjected to the polymerization reaction, and preparing a corrugated graphene composite through heat treatment; and

step iv: the composite, graphene oxide, and a solvent are mixed, applied to a current collector, and then subjected to heat treatment.

2. The method for preparing the supercapacitor electrode comprising the corrugated graphene composite according to claim 1, wherein in the step iv, the composite: the mixing weight ratio of the graphene oxide is 1: 0.02 to 1: 0.5.

3. the method for preparing the supercapacitor electrode including the wrinkled graphene composite according to claim 1, wherein the heat treatment of the step iv is performed at a temperature of 200 to 500 ℃ for 1 to 10 hours.

4. A supercapacitor electrode, comprising:

a corrugated graphene-carbon nanotube-polymer composite including a first corrugated graphene sheet, a carbon nanotube contained in the first corrugated graphene sheet, and a conductive polymer, wherein the corrugated graphene-carbon nanotube-polymer composite is spherical and has an average particle size of 1 to 10 μm;

a current collector having a plurality of the above-described composites formed on one surface thereof; and

and a second graphene sheet for fixing the composite to the current collector and fixing the composite to the composite.

5. A super capacitor is characterized in that the super capacitor is provided with a plurality of capacitors,

the method comprises the following steps:

a pair of electrodes facing each other;

an electrolyte disposed between the pair of electrodes; and

a separation membrane disposed between the pair of electrodes for suppressing an electrical short circuit,

the electrode is the supercapacitor electrode according to claim 4.