Eco-friendly method for manufacturing graphene

Abstract

A method for manufacturing graphene according to the present invention can manufacture high-purity, high-quality graphene through an electrochemical non-oxidative exfoliation method by applying a voltage to a working electrode and a counter electrode placed in an electrolyte containing sodium chloride (NaCl). Furthermore, compared to conventional manufacturing methods that commonly use ammonium sulfate ((NH4)2SO4) as the electrolyte, the method for manufacturing graphene according to the present invention is not only more environmentally friendly, but also significantly reduces the amount of wastewater generated during the graphene production process, thereby preventing a decrease in productivity and an increase in cost due to wastewater treatment, thereby enhancing price competitiveness.

Description

Eco-friendly method for producing graphene

[0001] The present invention relates to an eco-friendly method for producing graphene by an electrochemical non-oxidative exfoliation method, which uses an eco-friendly electrolyte containing sodium chloride (NaCl) to produce high-purity / high-quality graphene while drastically reducing the generation of wastewater generated during the production process, and to graphene produced thereby.

[0002]

[0003] Graphene is a carbon atom sp 2 Graphene is a two-dimensional, planar, hexagonal crystal lattice structure formed by hybrid bonds. Graphene, with this structure, not only possesses exceptional physical strength but also exceptional thermal conductivity and electron mobility. It is attracting attention as a dream new material for diverse applications in fields such as semiconductors, displays, energy, and the environment.

[0004] For graphene with such outstanding properties to be commercially viable, high-purity graphene must be economically mass-produced. Known methods for producing graphene include mechanical exfoliation, chemical exfoliation, exfoliation-reinsertion-expansion, chemical vapor deposition (CVD), and electrochemical exfoliation.

[0005] Here, the mechanical exfoliation method involves bonding adhesive tape to a graphite sheet and then removing it to obtain graphene. This method was also the first to discover graphene. However, this mechanical exfoliation method takes too long to manufacture, the resulting graphene has an inconsistent shape, and it is impossible to obtain large-area graphene. Furthermore, its yield is extremely low, making it unsuitable for industrial applications.

[0006] Chemical exfoliation involves oxidizing graphite to create graphene oxide, which is then reduced back to graphene using a reducing agent. However, chemical exfoliation suffers from limitations, as the chemical reaction occurs under highly acidic conditions or at high temperatures and pressures. This can lead to irregular carbon bond breakage and difficulty in completely reducing the oxidized graphene. Due to these limitations, the resulting graphene inevitably contains numerous defects, significantly reducing its unique properties.

[0007] In addition, the peeling-reinsertion-expansion method or chemical vapor deposition method using fuming sulfuric acid and surfactants is performed at very high temperatures, so it is not economical in terms of energy input, and the process is difficult to handle due to the complicated process and the yield is low, which limits mass production.

[0008] To improve the problems of these conventional methods, the electrochemical exfoliation method has recently been attracting attention as a graphene manufacturing method. The electrochemical exfoliation method is a method in which a graphite cathode and a metal anode are immersed in an electrolyte and then a voltage is applied. It has the advantages of a relatively short exfoliation time, a simple process, and a large surface area and few defects of the obtained graphene.

[0009] These electrochemical stripping methods typically use sulfate (SO4) such as ammonium sulfate ((NH4)2SO4) or potassium sulfate (K2SO4) as the electrolyte. 2- ) or nitrates such as lithium nitrate (LiNO3) (NO 3- ), or phosphates such as ammonium phosphate ((NH4)3PO4), potassium phosphate (K3PO4), or sodium phosphate (Na3PO4) (PO4 3-) are being used. However, these electrolytes are not only toxic substances, which are harmful to the working environment, but also cause environmental problems due to the large amount of wastewater generated after graphene production. Furthermore, additional wastewater treatment processes are required to treat the wastewater, which in turn incurs a lot of costs, making it difficult to supply graphene at a low price.

[0010]

[0011] [Prior Art Literature]

[0012] [Patent Document]

[0013] (Patent Document 1) Korean Patent Registration No. 10-2289201

[0014] Accordingly, as a result of the research conducted by the present inventors, the electrochemical non-oxidative exfoliation method is performed by applying a voltage to the working electrode and counter electrode placed in the electrolyte, and by using an electrolyte containing sodium chloride (NaCl) as the electrolyte, it was confirmed that it is much more environmentally friendly than the conventional electrolyte such as ammonium sulfate ((NH4)2SO4), and that work stability can be secured, and further, the generation of wastewater generated during the graphene manufacturing process can be drastically reduced. In addition, it was confirmed that high-purity / high-quality graphene can be manufactured even when an electrolyte containing sodium chloride (NaCl) is used.

[0015] Accordingly, the object of the present invention is to provide a method for producing high-purity, high-quality graphene using an electrochemical non-oxidative exfoliation method, while also providing an economical and environmentally friendly method for producing graphene without generating wastewater during the production process.

[0016]

[0017] In order to achieve the above object, the present invention provides a method for producing graphene by an electrochemical non-oxidative exfoliation method, wherein the electrochemical non-oxidative exfoliation method is performed by applying a voltage to a working electrode and a counter electrode placed in an electrolyte, the electrolyte includes a solvent and an electrolyte, and the electrolyte includes sodium chloride (NaCl).

[0018] In a method for manufacturing graphene according to one embodiment of the present invention, the molar concentration of sodium chloride (NaCl) included in the electrolyte may be 0.1 M to 1.5 M.

[0019] In another embodiment of the present invention, a method for producing graphene may include the solvent including water.

[0020] In another embodiment of the present invention, a method for manufacturing graphene may include the electrolyte solution including a sodium chloride (NaCl) aqueous solution.

[0021] A method for producing graphene according to another embodiment of the present invention comprises the steps of: 2- ), nitrate (NO3 - ) and phosphate (PO4 3- ) may not be included.

[0022] According to another embodiment of the present invention, a method for producing graphene comprises: the electrolyte comprises lithium ions (Li) as cations; + ), potassium ions (K + ), barium ion (Ba 2+ ), calcium ions (Ca 2+ ), copper ions (Cu 2+ ), zinc ion (Zn 2+ ), aluminum ion (Al 3+ ), iron ion (Fe 2+ ), magnesium ions (Mg 2+ ) and ammonium ion (NH4 + ) may not be included.

[0023] According to another embodiment of the present invention, a method for manufacturing graphene comprises: the electrolyte comprises a solvent selected from the group consisting of 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), tetraethylene glycol dimethyl ether (TEGDME), poly(ethylene glycol) dimethyl ether (PEGDME), diethylene glycol dibutyl ether (DEGDBE), 2-ethoxyethyl ether (EEE), sulfone, sulfolane, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, gamma-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate (EA), propyl formate (PF), methyl formate (MF), toluene, xylene, methyl acetate (MA), fluoroethylene carbonate (FEC), May not contain vinylene carbonate (VC), allyl ethyl carbonate (AEC), and hydrofluoroether.

[0024] According to another embodiment of the present invention, a method for producing graphene may be provided in which the working electrode is a graphite electrode and the counter electrode is a stainless steel or nickel electrode.

[0025] According to another embodiment of the present invention, a method for manufacturing graphene may be performed by applying the electrochemical non-oxidative exfoliation method at a current of 0.5 to 40 A and a voltage of 1 to 200 V.

[0026] Furthermore, the present invention provides graphene manufactured according to the above manufacturing method.

[0027]

[0028] The manufacturing method according to the present invention is not only more environmentally friendly than the manufacturing method using ammonium sulfate ((NH4)2SO4), which is mainly used as a conventional electrolyte, by using an electrolyte containing sodium chloride (NaCl), but also allows for the production of a large quantity of high-purity / high-quality graphene.

[0029] Furthermore, since the manufacturing method according to the present invention uses a sodium chloride aqueous solution (i.e., brine) as an electrolyte, it can drastically reduce the generation of wastewater generated during the graphene manufacturing process compared to conventional processes, thereby suppressing a decrease in productivity and an increase in cost due to wastewater treatment, thereby improving price competitiveness.

[0030]

[0031] Figure 1 is a photograph showing the process of manufacturing graphene using an electrochemical non-oxidative exfoliation method according to one embodiment of the present invention.

[0032] Figure 2 shows the Raman spectra measured by Raman spectroscopy for graphene powders manufactured in examples and comparative examples.

[0033] Figures 3 and 4 show the results of XPS (X-ray photoelectron spectroscopy) analysis of graphene powders manufactured in examples and comparative examples.

[0034] Figure 5 is a field emission scanning electron microscope (FE-SEM) image of graphene powders manufactured in examples and comparative examples.

[0035] Figure 6 shows the results of XRD (X-ray Diffraction) analysis for graphene powders manufactured in examples and comparative examples.

[0036] In the following description of the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the embodiment, the detailed description will be omitted.

[0037] The terms used herein to refer to each component are used to distinguish it from other components and are not intended to limit the embodiments. Furthermore, the singular expressions used herein include the plural expressions unless the context clearly dictates otherwise.

[0038] The word "comprising" or "including" in this specification is intended to specify a feature, region, step, process, element, or component, and does not exclude the presence or addition of other features, regions, steps, processes, elements, or components, unless specifically stated to the contrary.

[0039] In the numerical ranges that limit the size, physical properties, etc. of the components described in this specification, if a numerical range limited only to the upper limit and a numerical range limited only to the lower limit are separately exemplified, it should be understood that a numerical range in which these upper and lower limits are combined is also included in the exemplary range.

[0040]

[0041] A method for producing graphene according to one embodiment of the present invention is a method for producing graphene using an electrochemical non-oxidative exfoliation method. The electrochemical non-oxidative exfoliation method is performed by applying a voltage to a working electrode and a counter electrode placed in an electrolyte solution, wherein the electrolyte solution includes a solvent and an electrolyte, and the electrolyte includes sodium chloride (NaCl).

[0042] Graphene as used herein refers to isolated graphene, and may include single-layer graphene, or bilayer or multilayer graphene having 2 to 10 hexagonal carbon atom intermediate layers or graphene planes. More preferably, it may include bilayer or multilayer graphene having 5 or fewer layers or 3 or fewer layers.

[0043]

[0044] Referring to FIG. 1, the method for producing graphene by the electrochemical non-oxidative exfoliation method according to the present invention can be performed in a reaction chamber having a predetermined volume in which a working electrode and a counter electrode are arranged inside and an electrolyte can be accommodated.

[0045] The working electrode and the counter electrode disposed inside the reaction chamber may be disposed at a predetermined interval, respectively, and one or more working electrodes and one or more counter electrodes may be used. When a plurality of working electrodes and a plurality of counter electrodes are used, the working electrodes and the counter electrodes may be disposed crosswise at a predetermined interval from each other, or multiple working electrodes may be disposed at a predetermined interval between the counter electrodes. Furthermore, the electrochemical non-oxidation peeling method according to the present invention can be applied regardless of the specific arrangement structure of the working electrodes and the counter electrodes, as long as the plurality of working electrodes and the plurality of counter electrodes have a structure in which they are electrochemically connected.

[0046] The working electrode used in the method for producing graphene according to the present invention may be a graphite electrode, and specifically, the graphite used as the working electrode may include at least one selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesocarbon microbead, hard carbon, soft carbon, petroleum coke, resin sintered body, carbon fiber, and pyrolytic carbon.

[0047] Additionally, the counter electrode used in the method for producing graphene according to the present invention may be a stainless steel or nickel electrode. Platinum (Pt) electrodes, used in most electrochemical reactions, are very expensive and have the disadvantage of being difficult to control in shape and size. However, stainless steel or nickel electrodes are relatively inexpensive compared to platinum electrodes and exhibit excellent electrical activity, making them suitable for use as counter electrodes. Other metal electrodes besides stainless steel or nickel electrodes may also be used.

[0048] The shape of the counter electrode and the working electrode may be various in consideration of the shape of the reaction chamber, reaction conditions, etc., and specifically, the counter electrode and the working electrode may each independently have a sheet, foil, plate, or rod shape, but is not limited thereto. However, since the working electrode has a larger surface area in contact with the electrolyte, which is advantageous in terms of the production volume of graphene, a sheet, foil, or plate shape with a large surface area per unit volume is preferable. Specifically, the working electrode has a unit volume (mm 3 Surface area per mm 2 ) ratio (i.e., the surface area of ​​the working electrode (mm 2 ) / volume of working electrode (mm) 3 ) ) may be 2 or more, preferably 2.5 or more, 3 or more, 3.5 or more or 4 or more, and more preferably 4 or more.

[0049]

[0050] The electrolyte used in the electrochemical non-oxidative peeling method according to the present invention includes a solvent and an electrolyte.

[0051] In particular, the method for manufacturing graphene according to the present invention is characterized by including sodium chloride (NaCl) as the electrolyte. Sodium chloride (NaCl) is a compound of chlorine and sodium, the main component of salt, and the substance that accounts for the largest proportion of salts in seawater. Therefore, it has the advantages of being readily available, inexpensive, and environmentally friendly compared to other salt compounds.

[0052] In addition, the electrolyte may not contain any electrolyte other than sodium chloride. Specifically, the electrolyte may not contain any electrolyte such as a sulfate electrolyte, a nitrate electrolyte, and / or a phosphate electrolyte, and more specifically, any electrolyte such as ammonium sulfate ((NH4)2SO4) or potassium sulfate (K2SO4). 2-) electrolyte or nitrate (NO) such as lithium nitrate (LiNO3) 3- ) electrolyte, or phosphates (PO4) such as ammonium phosphate ((NH4)3PO4), potassium phosphate (K3PO4), or sodium phosphate (Na3PO4). 3- ) may not contain electrolyte.

[0053] In other words, the electrolyte used in the method for producing graphene according to the present invention contains sulfate (SO4) as an anion. 2- ), nitrate (NO3 - ) and phosphate (PO4 3- ) may not be included. In addition, the electrolyte may contain lithium ions (Li) as cations. + ), potassium ions (K + ), barium ion (Ba 2+ ), calcium ions (Ca 2+ ), copper ions (Cu 2+ ), zinc ion (Zn 2+ ), aluminum ion (Al 3+ ), iron ion (Fe 2+ ), magnesium ions (Mg 2+ ) and ammonium ion (NH4 + ) may not be included.

[0054] That is, the electrolyte used in the method for manufacturing graphene according to the present invention may only use sodium chloride (NaCl) as an electrolyte, and may not include any electrolyte other than sodium chloride (NaCl). For reference, the electrolyte referred to in the present invention is a salt-type compound that accounts for the largest proportion among the substances included in the electrolyte, and is a substance distinct from reducing agents or other additives that may be added in trace amounts. The method for manufacturing graphene according to the present invention is more environmentally friendly because it does not use any salt-type compound other than sodium chloride (NaCl), and since there is no wastewater generated during the manufacturing process, the cost of wastewater treatment can be reduced.

[0055] The method for producing graphene according to the present invention may be such that the molar concentration of the sodium chloride (NaCl) included in the electrolyte may be 0.1 M to 2.0 M. Specifically, the sodium chloride included in the electrolyte may have a molar concentration of 0.1 M to 2.0 M, 0.1 M to 1.8 M, 0.1 M to 1.5 M, 0.1 M to 1.35 M, or 0.15 M to 1.35 M. When the molar concentration of sodium chloride is within an appropriate range, the exfoliation of graphene can proceed smoothly, thereby obtaining a desired amount of graphene.

[0056]

[0057] The solvent used in the method for producing graphene according to the present invention may include water. Specifically, the electrolyte used in the method for producing graphene according to the present invention may include water as a solvent and sodium chloride (NaCl) as an electrolyte. More specifically, the electrolyte used in the method for producing graphene according to the present invention may include an aqueous sodium chloride solution.

[0058] In addition, the method for manufacturing graphene according to the present invention may not include a solvent other than water as the electrolyte. Specifically, the electrolyte solution comprises 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), tetraethylene glycol dimethyl ether (TEGDME), poly(ethylene glycol) dimethyl ether (PEGDME), diethylene glycol dibutyl ether (DEGDBE), 2-ethoxyethyl ether (EEE), sulfone, sulfolane, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, gamma-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate (EA), propyl formate (PF), methyl formate (MF), toluene, xylene, methyl acetate (MA), fluoroethylene carbonate (FEC), vinylene carbonate (VC), allyl Ethyl carbonate (AEC), and hydrofluoroether may not be included. In other words, the electrolyte used in the method for producing graphene according to the present invention uses only water as a solvent, and no organic solvents other than water may be used. In the past, various organic solvents listed above were used in addition to water as solvents for electrolytes to dissolve the electrolyte well and enhance the electrochemical reaction. However, these organic solvents are not only harmful, but also can have a harmful effect on the human body of workers by vaporizing during the production process. However, the method for producing graphene according to the present invention is more environmentally friendly and can provide a safer work environment by not using organic solvents other than water, and can reduce the cost of wastewater treatment because there is no wastewater generated during the production process.

[0059]

[0060] The method for producing graphene according to the present invention may further comprise a reducing agent in the electrolyte solution. The reducing agent can be electrochemically decomposed to generate activated ions. That is, the reducing agent is electrochemically decomposed by the current applied during the graphene production process to generate activated ions (i.e., radicals), thereby assisting in the exfoliation of graphene and preventing surface oxidation of graphene. Specifically, in the case of an electrochemical non-oxidative exfoliation method using an aqueous electrolyte, hydroxyl radicals are formed through electrochemical decomposition. If a large number of such radicals are formed, carbon bonds are irregularly broken or the proportion of graphene oxide having oxygen functional groups on the surface increases. However, the reducing agent suppresses the formation of such hydroxyl radicals, thereby assisting in the production of high-quality graphene.

[0061] The reducing agent may include, but is not limited to, TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl), ascorbic acid, sodium borohydride, hydrazine, etc. In addition, the reducing agent may be included in an amount of 0.1 wt% or more based on the total weight of the electrolyte included in the electrolyte solution, specifically, 0.2 wt% or more, 0.3 wt% or more, 0.4 wt% or more, 0.5 wt% or more, 0.8 wt% or more, or 1 wt% or more, and may be included in an amount of 15 wt% or less, 13 wt% or less, 12 wt% or less, 10 wt% or less, 8 wt% or less, 7 wt% or less, or 6 wt% or less.

[0062]

[0063] A method for producing graphene according to one embodiment of the present invention may include the steps of (1) arranging a working electrode and a counter electrode in a reaction chamber at a predetermined interval and introducing an electrolyte; (2) immersing the working electrode and the counter electrode in the electrolyte for a predetermined period of time; (3) applying a voltage to exfoliate graphite; (4) filtering the exfoliated graphite and ultrasonically treating it; and (5) drying to obtain graphene powder.

[0064] In the above step (1), the separation distance between the working electrode and the counter electrode may be 0.5 cm or more, 1 cm or more, or 2 cm or more, and may be 20 cm or less, 15 cm or less, or 10 cm or less. The working electrode and the counter electrode must maintain an appropriate distance so that the exfoliation of graphite occurs well, and the size of the reaction chamber and the amount of electrolyte can be maintained within an appropriate range, which is advantageous from an economic perspective.

[0065] The above step (2) is a step of immersing the working electrode and the counter electrode in an electrolyte for a predetermined period of time. The immersion step may be performed for 1 minute or more, 2 minutes or more, 3 minutes or more, or 5 minutes or more. By immersing for a predetermined period of time or more, the graphite sheet, which is the working electrode, is sufficiently wetted so that smooth peeling can occur when voltage is applied, and the peeling time can be shortened.

[0066] The above step (3) is a step of applying voltage to peel off graphite. The voltage applied in the above step (3) may be 1 V to 200 V, and specifically, a voltage of 1 V to 150 V, 1 V to 100 V, 1 V to 50 V, 5 V to 25 V, or 5 V to 20 V may be applied. In addition, a current of 1 A to 50 A may be applied while the voltage is applied, and specifically, a current of 5 A to 45 A, 7 A to 43 A, or 10 A to 40 A may be applied. More specifically, the electrochemical non-oxidation peeling method according to the present invention may be performed by applying a current of 0.5 A to 40 A at a voltage of 1 V to 200 V.

[0067] The above step (4) is a step of filtering and ultrasonicating the exfoliated graphite. The filtering of the exfoliated graphite can be performed using a vacuum filtration device. Thereafter, the filtered exfoliated graphite is placed in deionized water and ultrasonicated. The ultrasonication can be performed at room temperature for 10 minutes or more, 20 minutes or more, 30 minutes or more, 40 minutes or more, 50 minutes or more, 1 hour or more, 2 hours or more, or 3 hours or more, and can be performed at a frequency of 5 kHz or more, 7 kHz or more, or 8 kHz or more. Through the ultrasonication, the exfoliated graphite can be more effectively separated into graphene having an area of ​​about 10 micrometers and consisting of 3 to 5 layers.

[0068] The above step (5) is a step of drying the exfoliated graphene to obtain graphene powder. The drying can be performed at a temperature of 70°C or higher, 80°C or higher, 90°C or higher, or 100°C or higher for 1 hour or longer, 2 hours or longer, 3 hours or longer, 5 hours or longer, 7 hours or longer, or 10 hours or longer.

[0069] Furthermore, in the method for manufacturing graphene according to one embodiment of the present invention, the electrolyte remaining after filtering the exfoliated graphite in step (4) can be reused by reintroducing it into the electrolyte of step (1). The electrolyte used in the present invention is not only environmentally friendly but can also be reused multiple times, thereby more effectively reducing process costs.

[0070]

[0071] High-quality graphene can be obtained through the method for producing graphene according to one embodiment of the present invention.

[0072] Graphene manufactured through the method for manufacturing graphene of the present invention has a defect density (D peak intensity (I D ) / G peak intensity (I G )) may be 0.7 or less. More specifically, the graphene manufactured through the method for manufacturing graphene of the present invention may have a defect density of 0.7 or less, and specifically, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.15 or less, or 0.1 or less. In addition, the graphene manufactured through the method for manufacturing graphene of the present invention may have a degree of graphitization (intensity of 2D peak (I 2D ) / G peak intensity (I G )) may be 0.3 or more, and specifically 0.35 or more, 0.4 or more, 0.45 or more, or 0.5 or more. In addition, the graphene has a ratio of defect density to graphitization degree (defect density / graphitization degree; i.e., intensity of D peak (I D ) / 2D peak intensity (I 2D )) may be 1 or less, and specifically may be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, or 0.3 or less. Here, the G peak, the D peak, and the 2D peak are peaks that appear in the spectrum analyzed by measuring the graphene powder using Raman spectroscopy, and are peaks in the range of 1500 to 1700 cm -1The G peak measured in the wavelength range of 1250 to 1450 cm is the main characteristic peak of graphene, which is a peak due to the in-plane vibration of sp2 hybridized carbon atoms. -1 The D peak measured in the wavelength range of 2600 to 2800 cm is the disordered vibration peak of graphene. -1 The 2D peak measured in the wavelength range refers to the two-phonon resonance second-order Raman peak.

[0073] In addition, the graphene manufactured through the method for manufacturing graphene of the present invention may have a carbon content ratio (atomic ratio) of 90% or more, and specifically, may be 91% or more, 92% or more, 93% or more, or 94% or more. In addition, the graphene may have an oxygen content ratio (atomic ratio) of less than 10%, and specifically, may be less than 9%, less than 8%, less than 7%, less than 6%, or less than 5%. In addition, the graphene may have an oxygen to carbon atomic ratio (O / C ratio) of less than 0.1, and specifically, may be less than 0.9, less than 0.8, less than 0.7, less than 0.6, or less than 0.5. Conversely, the graphene may have an atomic ratio of carbon to oxygen (C / O ratio) of 8 or more, and specifically, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, 15 or more, 16 or more, 17 or more, 18 or more, or 19 or more. Furthermore, the graphene manufactured through the method for manufacturing graphene of the present invention may not include a C=O functional group. Accordingly, the graphene manufactured through the method for manufacturing graphene of the present invention has a very low content of oxygen contained therein and thus has superior quality.

[0074]

[0075] Although the following examples are described, the scope of implementation is not limited to these.

[0076]

[0077] Example 1: Preparation of graphene

[0078] Stainless steel was used as a counter electrode, and a graphite sheet (area: 110 mm X 100 mm, thickness: 0.5 mm, weight: approximately 3.7 g) was used as a working electrode. One working electrode was placed between two counter electrodes in a reaction tank at a distance of 2.5 cm (see Fig. 1). Then, 3 L of 0.3 M NaCl aqueous solution as an electrolyte (NaCl 52.60 g) was added to the reaction tank. After the working electrode was immersed in the electrolyte for approximately 5 to 10 minutes, a DC voltage of +10 V was applied to the graphite electrode for 60 minutes to exfoliate the graphite. Thereafter, the exfoliated graphite was filtered using a vacuum filtration device, and deionized water was mixed with the filtered exfoliated graphite and ultrasonic treatment (25°C, 10,000 Hz) was performed for 3 hours. Afterwards, it was dried in a vacuum oven at 120°C for 12 hours to obtain a final 0.270 g of graphene powder.

[0079]

[0080] Examples 2 and 3

[0081] Graphene powders weighing 0.261 g and 0.254 g, respectively, were manufactured in the same manner as in Example 1, except that 0.15 M and 1.0 M NaCl aqueous solutions were used as electrolytes, respectively.

[0082]

[0083] Examples 4 and 5

[0084] Graphene powders of final weights of 0.248 g and 0.274 gg were manufactured in the same manner as in Example 1, except that 1 wt% and 5.7 wt% (based on the weight of NaCl) of TEMPO were added to the electrolyte as reducing agents, respectively.

[0085]

[0086] Examples 6 to 8

[0087] Graphene powders weighing 0.255 g, 0.268 g, and 0.150 g, respectively, were manufactured in the same manner as in Example 1, except that ascorbic acid, sodium borohydride, and hydrazine 1 wt% (based on the weight of NaCl) were each added to the electrolyte as reducing agents.

[0088]

[0089] Example 9

[0090] A final 0.240 g of graphene powder was manufactured using the same method as in Example 1, except that the remaining electrolyte solution after obtaining the graphene powder in Example 1 was reused.

[0091]

[0092] Comparative Examples 1 to 3

[0093] Graphene powder was manufactured in the same manner as in Example 1, except that 0.3 M ammonium sulfate ((NH4)2SO4) aqueous solution, potassium sulfate (K2SO4) aqueous solution, and sodium perchlorate (NaClO4) aqueous solution were used as electrolytes, respectively.

[0094]

[0095] The solvents, electrolytes, and additives used in the examples and comparative examples and the amount of graphene obtained are summarized in the table below.

[0096]

[0097] Solvent Electrolyte Additive Graphene Example 1 Water 0.3 M NaCl - 0.270 g Example 2 Water 0.15 M NaCl - 0.261 g Example 3 Water 1.0 M NaCl - 0.254 g Example 4 Water 0.3 M NaCl TEMPO 1 wt% 0.248 g Example 5 Water 0.3 M NaCl TEMPO 5.7 wt% 0.274 g Example 6 Water 0.3 M NaCl Ascorbic acid 1 wt% 0.255 g Example 7 Water 0.3 M NaCl Sodium borohydride 1 wt% 0.268 g Example 8 Water 0.3 M NaCl Hydrazine 1 wt% 0.150 g Example 9 Water (reused) 0.3 M NaCl (reused) - 0.240 g Comparative Example 1 Water 0.3 M (NH4)2SO4-2.70 gComparative Example 2WaterK2SO4-1.80 gComparative Example 3WaterNaClO4-1.076 g

[0098]

[0099] Test Example 1: Evaluation of Defect and Graphitization Degrees

[0100] The graphene powders manufactured in the above examples and comparative examples were subjected to Raman spectrometry using an inVia Raman spectrometer (514 nm, Ar) from Renishaw (UK). + The graphene powder was analyzed using a ion laser (see Fig. 2), and the defects and graphitization degree of the graphene powder manufactured using this were evaluated.

[0101] Raman spectroscopy of graphene powder is a widely used analytical method for the analysis of carbon materials, and the Raman spectrum of graphene materials can be mainly composed of several peaks, namely G, D, and G'. The G peak is the main characteristic peak of graphene, which is due to the in-plane vibration of sp2 hybridized carbon atoms, and can effectively reflect the number of graphene layers in the graphene sample. The D peak is generally considered to be the disordered vibration peak of graphene, which is used to characterize the structural defects of the graphene sample, and the 2D peak is the two-phonon resonance second-order Raman peak. The 2D peak can be used to characterize the interlayer stacking mode of carbon atoms in the graphene sample. In the Raman spectrum of graphene powder, the peak height is I D1250 to 1450 cm -1 The D peak is measured in the wavelength range of , and the peak height is I G 1500 to 1700 cm -1 The G peak is measured in the wavelength range of , and the peak height is I 2D 2600 to 2800 cm -1 The 2D peak is measured in the wavelength range of . Raman spectroscopy has the advantage of characterizing defects in graphene materials. In general, the defect density is expressed as the intensity of the "D peak (I D ) / G peak intensity (I G ) is thought to be proportional to I D / I G A lower value means fewer defects. Also, the intensity of the 2D peak (I 2D ) / G peak intensity (I G )" is a measure of the degree of graphitization.

[0102]

[0103] Category I D / I G I 2D / I G I D / I 2D Example 10.160.530.30 Example 30.10.530.19 Example 40.050.540.09 Comparative Example 10.770.531.45 Comparative Example 30.860.283.07

[0104]

[0105] Specifically, in the case of the graphene powder manufactured in the above example, the defect density (i.e., the intensity of the D peak (I)) was higher than that of the comparative example. D ) / G peak intensity (I G )) was measured to be very low, confirming that high-quality graphene with relatively few defects can be produced. Furthermore, in the case of Examples 3 and 4 using a reducing agent, graphene of even better quality can be produced compared to Example 1.

[0106] In addition, in the case of the graphene powder manufactured in the above example, the degree of graphitization (i.e., the intensity of the 2D peak (I 2D ) / G peak intensity (I G )) It can be confirmed that graphene of 3 to 5 layers was produced with a degree of graphitization of 0.53 or 0.54, and it was confirmed that higher quality graphene could be produced compared to Comparative Example 3, in which the degree of graphitization was measured to be 0.28.

[0107]

[0108] Test Example 2: Oxidation Evaluation

[0109] The graphene powders manufactured in the above examples and comparative examples were subjected to XPS (X-ray photoelectron spectroscopy) analysis using an X-ray photoelectron spectrometer (ThermoFisher K-ALPHA) (see Fig. 3), and the oxidation degree of the manufactured graphene powders was evaluated based on this.

[0110] The oxygen (O) content ratio of graphene material can be confirmed through the C 1s peak and O 1s peak measured by X-ray photoelectron spectroscopy. Generally, when graphene is manufactured using an electrochemical exfoliation method, the possibility of electrooxidation increases due to the long-term electrochemical reaction, which reduces the processability and the quality of the produced graphene. Therefore, the lower the oxygen content in the graphene, the better the quality of the graphene can be evaluated.

[0111] Examining the deconvolution peaks in Fig. 4, unlike the comparative example, the graph of the embodiment does not exhibit a peak for the C=O functional group, and the peak for the C-OH functional group also has a relatively low intensity. Therefore, it can be evaluated that the graphene manufactured in the embodiment has a much lower oxygen content within the graphene than the comparative example using a conventional electrolyte, and that graphene of superior quality has been manufactured.

[0112]

[0113] Classification C (%) O (%) C / O ratio O / C ratio Example 192.19 5.95 15.49 0.065 Example 393.62 5.55 16.87 0.059 Example 494.78 4.8 19.75 0.051 Comparative Example 187.11 11.55 7.54 0.133 Comparative Example 384.48 14.45 5.85 0.17

[0114]

[0115] Specifically, in the case of the graphene powder manufactured in the above example, the content ratio (atomic ratio) of carbon was measured to be 92% or more and the content ratio (atomic ratio) of oxygen was measured to be less than 6%, whereas in the comparative example, the content ratio (atomic ratio) of carbon was measured to be less than 90% and the content ratio (atomic ratio) of oxygen was measured to be more than 10%, confirming that high-quality graphene with relatively few defects can be manufactured.

[0116]

[0117] Test Example 3: Size and Thickness Evaluation

[0118] The size of the graphene powder manufactured in the above examples and comparative examples was analyzed using a field emission scanning electron microscope (FE-SEM) (Carl Zeiss Leo SUPRA 55) (see Fig. 5).

[0119] In addition, XRD (X-ray Diffraction) analysis of the graphene powder manufactured in the above examples and comparative examples was performed using an X-ray diffractometer (D8 Advance from Bruker) (see Fig. 6), and the thickness of the manufactured graphene powder was evaluated based on this.

[0120] The above XRD analysis was performed using a 2θ test range of 10 to 70°, a scan rate of 6° / min, a tube voltage of 40 KV, a current of 40 mA, and a Cu-Kα radiation source.

[0121] Referring to Fig. 6, a peak was observed around 2θ = 26.4° for both graphene manufactured in the examples and comparative examples through X-ray diffraction. The thickness of the manufactured graphene can be qualitatively evaluated through the intensity of each peak, and the weaker the intensity of the peak, the thinner the graphene.

[0122]

[0123] Discrete size (μm) Relative peak intensity Example 12.36.4 Example 3212.1 Example 4164.4 Comparative example 181

[0124]

[0125] Specifically, in the case of the graphene powder manufactured in Comparative Example 1, graphene with a thin layer and a size of 8 μm was manufactured, and in comparison, it was confirmed that Examples 3 and 4 could manufacture graphene powder with a wider size. Through this, it was confirmed that when some reducing agent is added, it is possible to prevent some oxidation of graphene during the graphene manufacturing process while simultaneously controlling the size and thickness of graphene, so that high-quality graphene with relatively few defects can be manufactured.

Claims

1. A method for producing graphene by electrochemical non-oxidative exfoliation, The above electrochemical non-oxidative peeling method is performed by applying voltage to a working electrode and a counter electrode placed in an electrolyte. The above electrolyte contains a solvent and an electrolyte, A method for producing graphene, wherein the electrolyte comprises sodium chloride (NaCl).

2. In paragraph 1, A method for producing graphene, wherein the molar concentration of sodium chloride (NaCl) contained in the electrolyte is 0.1 M to 2.0 M.

3. In paragraph 1, A method for producing graphene, wherein the solvent comprises water.

4. In paragraph 1, A method for producing graphene, wherein the electrolyte comprises a sodium chloride (NaCl) aqueous solution.

5. In paragraph 1, The above electrolyte contains sulfate (SO4) as an anion. 2- ), nitrate (NO3 - ) and phosphate (PO4 3- ) does not include a method for producing graphene.

6. In paragraph 1, The above electrolyte contains lithium ions (Li) as cations. + ), potassium ions (K + ), barium ion (Ba 2+ ), calcium ions (Ca 2+ ), copper ions (Cu 2+ ), zinc ion (Zn 2+ ), aluminum ion (Al 3+ ), iron ion (Fe 2+ ), magnesium ions (Mg 2+ ) and ammonium ion (NH4 + ) does not include a method for producing graphene.

7. In paragraph 1, The electrolyte solution is a solvent comprising 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), tetraethylene glycol dimethyl ether (TEGDME), poly(ethylene glycol) dimethyl ether (PEGDME), diethylene glycol dibutyl ether (DEGDBE), 2-ethoxyethyl ether (EEE), sulfone, sulfolane, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, gamma-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate (EA), propyl formate (PF), methyl formate (MF), toluene, xylene, methyl acetate (MA), fluoroethylene carbonate (FEC), vinylene carbonate (VC), allyl A method for producing graphene, which does not include ethyl carbonate (AEC) and hydrofluoroether.

8. In paragraph 1, A method for producing graphene, wherein the electrolyte further comprises a reducing agent.

9. In paragraph 1, The above working electrode is a graphite electrode, A method for producing graphene, wherein the counter electrode is a stainless steel or nickel electrode.

10. In paragraph 1, A method for producing graphene, wherein the above electrochemical non-oxidative exfoliation method is performed by applying a current of 0.5 to 40 A at a voltage of 1 to 200 V.

11. Graphene manufactured by the method of paragraph 1.

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