Graphene powder, method of preparing the same, and use thereof

Abstract

The present invention relates to graphene materials. Graphene powder, its preparation method and use are disclosed. Graphene powder is a stack of graphene sheets. In the Raman spectrum of the graphene powder, the peak heights are I D , I G There are D and G peaks, where I D / I G The graphene powder of the present disclosure can be applied to conductive composite materials, anticorrosive coatings, and heat dissipation composite materials, and in particular, when used in lithium ion batteries, it can significantly reduce the internal resistance of the electrodes and improve the stability of the batteries.

Description

Detailed Description of the Invention

[0001] 〔Technical Field〕 The present disclosure relates to graphene materials, particularly to graphene powder, and its preparation method and use.

[0002] 〔Background Art〕 Graphene is a carbon material having a single-layer two-dimensional honeycomb lattice structure connected by sp 2 hybrid carbon atoms. Graphene can have ultra-high conductivity (electron mobility of 10,000 cm 2 / (V·s)), ultra-high thermal conductivity (about 5000 W / (m·K)), and a large specific surface area. Graphene has the potential to be widely applied in fields such as electronics, aerospace, military, and new energy. Graphene is expected to trigger a new revolution in modern electronic technology. As a result of many years of research and development, great achievements have been obtained in the large-scale production technology, processing equipment, and product quality of graphene. However, there are still many important technical problems to be solved. For example, the current method for preparing graphene powder adopted by many enterprises is still the oxidation-reduction method, which may contain many strong acids and oxidizing substances, causing serious pollution problems. At the same time, the produced graphene powder contains a large number of defects, and the product quality cannot be controlled, so the downstream applications are limited, and the industrialization of graphene is significantly limited.

[0003] CN102838110B proposes a process including subjecting a mixed powder of magnesium powder and carbonate powder to combustion and synthesis to obtain graphene powder. This process is simple to operate and enables continuous production. However, this process requires high-purity magnesium powder. Since graphene uses carbonate as a carbon source, it is inferior in economy. Furthermore, the graphene powder may have low crystallinity and quality, so the downstream applications are limited to some extent.

[0004] CN107539973B proposes a process that involves obtaining a graphene rally from graphite, an intercalation expander, and chlorosulfonic acid using ultrasonic delamination, followed by freeze-drying to obtain graphene powder. The graphene obtained by this process may have a perfect crystalline structure. This process is easy to operate and low-cost. However, ultrasonic delamination is inefficient and can result in poor processing uniformity, and it is difficult to remove impurities other than carbon ions from the product, making large-scale application difficult.

[0005] CN105540575A discloses a method for preparing graphene by exfoliating it using a high-pressure homogenizer, in which graphite, an intercalation agent, and a dispersant are used as raw materials to obtain graphene powder using a high-pressure homogenizer. This method can yield high graphene yields. However, this method is complex, requires large amounts of organic solvents, and pollutes the environment. At the same time, the intercalation agent in the solution may remain in the graphene product, making purification difficult and potentially negatively affecting the quality of the graphene product. Therefore, large-scale application of this product in downstream businesses such as lithium-ion batteries may be difficult.

[0006] Therefore, developing graphene powder that exhibits excellent dispersion properties, is easy to prepare, inexpensive, and of high quality is a technical challenge in this field.

[0007] [Summary of the Invention] The objective of this invention is to address the low conductivity of graphene powder in the prior art. One or more of the following issues: non-uniform dispersion in the solvent, tendency to aggregate, complexity of preparation. The objective is to solve this problem. Therefore, this disclosure provides graphene powder, a method for preparing the same, and its use. The graphene powder of this disclosure has advantages such as having few defects and high conductivity, and can be applied to conductive composite materials, anticorrosion coatings, and heat dissipation composite materials. In particular, when used in lithium-ion batteries, it can significantly reduce the internal resistance of the electrodes and improve the stability of the battery at any current rate.

[0008] In a first aspect of this disclosure, a graphene powder is a laminate of graphene sheets, wherein the Raman spectrum of the graphene powder has peak heights of I D , I G It includes the D peak and G peak, I D / I G Graphene powder with a coefficient of 0.10 or less is provided.

[0009] In a second aspect of this disclosure, (1) A process of pre-expanding expandable graphite to obtain pre-expanded graphite; (2) After mixing the pre-expanded graphite obtained in step (1), a wetting agent, and a solvent, the resulting mixture is subjected to a first high-pressure homogenization and a second high-pressure homogenization to obtain a slurry containing graphene powder. Here, the pressure of the second high-pressure homogenization is 10-20 MPa higher than the pressure of the first high-pressure homogenization; A method for preparing graphene powder is provided, comprising the step of (3) drying the slurry containing the graphene powder obtained in step (2) to obtain graphene powder.

[0010] A third aspect of this disclosure provides the use of the above-described graphene powder or graphene powder prepared by the above-described method in a conductive composite material.

[0011] A fourth aspect of this disclosure provides the use of the above-described graphene powder or graphene powder prepared by the above-described method in an anticorrosive coating.

[0012] A fifth aspect of this disclosure provides the use of the above-described graphene powder or graphene powder prepared by the above-described method in a heat dissipation composite material.

[0013] Compared to conventional technology, the present invention provides the following technical advantages. (1) The graphene powder of this disclosure is formed by laminating graphene sheets. Preferably, the graphene sheets are loosely laminated, leaving voids in the laminate. Therefore, the graphene powder of this disclosure has a large contact surface with the solvent and can have good dispersibility in both aqueous and oil-based solvents. When used, the laminate can be dispersed in the corresponding graphene sheets. The graphene powder of this disclosure and the corresponding graphene sheets formed by the dispersion can have properties such as high purity, low defects, and high conductivity. The graphene powder of this disclosure can be suitably used in fields such as conductive composite materials, anticorrosive coatings (especially epoxy resin anticorrosive coatings), and heat dissipation composite materials. For example, when the graphene powder of this disclosure is used in anticorrosive coatings, the zinc content can be significantly reduced while improving the corrosion protection performance of the coating. When the graphene powder of this disclosure is applied to heat dissipation coatings, the thermal conductivity in the X and Y directions of the resulting heat dissipation film can be significantly improved. The graphene powder of this disclosure can be suitably used as a conductive agent in lithium batteries in particular. The graphene sheets contained in the graphene powder of this disclosure are complete and have a large radial size. Therefore, when the graphene sheets of this disclosure are used as a conductive agent, the dispersed, large-sized graphene sheets can increase the contact area between the graphene sheets and the electrode active material. This can provide many electron pathways to the electrode active material and facilitate the formation of a network for planar conduction of electrons within the electrode. The graphene sheets can reduce the internal resistance of the electrode and improve the rate performance and stability of the battery. (2) The preparation method of this disclosure employs homogenization by gradually increasing the pressure when peeling off graphite layer by layer, optionally selecting a specific wetting agent, and optionally selecting an appropriate expansion coefficient to expand the graphite. The lattice coherence of graphene in the graphene sheet is better maintained. As a result, the graphene powder obtained has a relatively complete graphene sheet, a larger radial size, a thinner thickness, higher purity, fewer defects, and higher conductivity. Furthermore, the graphene powder preparation method of the present invention does not require the use of reagents such as oxidizing agents, strong acids, or strong bases, and is environmentally friendly.

[0014] [Brief explanation of the drawing] [Figure 1] This is an SEM image of graphene powder G-1 obtained in Example 1. [Figure 2] TEM image of graphene powder G-1 obtained in Example 1. [Figure 3] HR-TEM image of graphene powder G-1 obtained in Example 1. [Figure 4] This is the Raman spectrum of graphene powder G-1 obtained in Example 1. [Figure 5] This is the XRD spectrum of graphene powder G-1 obtained in Example 1. [Figure 6] This is an SEM image of graphene powder G-2 obtained in Example 2. [Figure 7] HR-TEM image of graphene powder G-2 obtained in Example 2. [Figure 8] This is an SEM image of graphene powder DG-1 obtained in Comparative Example 1. [Figure 9] This figure shows the cycle performance at different current rates of a coin cell having a negative electrode containing graphene powder G-1 obtained in Example 1 as the negative electrode conductive material and a silicon-carbon material as the negative electrode active material. Figure 10 shows the cycle performance at different current rates of a coin cell in Comparative Example 4, which has a negative electrode containing Super P as the negative electrode conductive material and a silicon-carbon material as the negative electrode active material. [Figure 11] This is an SEM image (top view) of the negative electrode using graphene powder G-1 as the negative electrode conductive agent in Example 1. [Figure 12] This is an SEM image (top view) of the negative electrode of Comparative Example 4, which uses commercially available Super P as the negative electrode conductive agent. [Figure 13] In Example 5, the results of a neutral salt spray test were shown in which notches were made in the anticorrosive coating on a carbon steel substrate. The left side shows the results for a conventional anticorrosive coating (containing 80% zinc), and the right side shows the results for a coating using graphene powder (containing 30% zinc). [Figure 14] HR-TEM image of graphene powder DG-1 obtained in Comparative Example 1. [Figure 15] This is the Raman spectrum of graphene powder DG-1 obtained in Comparative Example 1. [Figure 16] This is the Raman spectrum of graphene powder G-4 obtained in Example 4. [Figure 17] This figure shows the cycle performance at different current rates of a coin cell using graphene powder G-4 obtained in Example 4 as the negative electrode conductive material and a silicon-carbon material as the negative electrode active material. [Figure 18] This figure shows the cycle performance at different current rates of coin cells using graphene powder DG-3 obtained in Comparative Example 3 as the negative electrode conductive material and a silicon-carbon material as the negative electrode active material. [Figure 19] shows the heat loss curves of different graphene material samples under an air atmosphere, where 1 is graphene powder G-1 obtained in Example 1, 2 is commercially available graphene powder (prepared by physical method), 3 is commercially available graphene oxide, and 4 is commercially available reduced graphene oxide. [Figure 20] This is an SEM image of commercially available graphene powder (prepared by a physical method). [Figure 21] This is a SEM image of commercially available graphene oxide. [Figure 22] This is a SEM image of commercially available reduced graphene oxide.

[0015] [Modes for carrying out the invention] It should be understood that the endpoints and any values ​​of the ranges disclosed herein are not limited to exact ranges or values, but rather encompass values ​​close to those ranges or values. Regarding ranges of values, one or more new numerical ranges can be obtained by combinations between the endpoint values ​​of each range, between the endpoint values ​​of each range and specific point values, and between specific point values, and these new numerical ranges are also considered to be specifically disclosed herein.

[0016] Except for the examples, all numerical values ​​in this specification should be understood to be modified in all cases by the term "approximately," regardless of whether "approximately" actually appears before the number.

[0017] In this specification, the term "graphene" refers to sp(s) stacked in a honeycomb structure. 2 This refers to a two-dimensional material composed of a single layer of hybridized carbon atoms. Graphene is typically prepared by methods such as mechanical exfoliation, oxidation-reduction reactions, and SiC epitaxial growth. Therefore, the term "graphene" also includes graphene oxide and reduced graphene oxide.

[0018] In this specification, the term "graphene sheet" refers to a layered aggregate of graphene, which may include one or more layers of graphene. Therefore, graphene sheets include single-layer graphene (sometimes simply called graphene), double-layer graphene, and low-layer graphene containing 3 to 10 layers of graphene. Generally, when the number of layers is 10 or less, the layered aggregate of graphene is considered to have properties similar to graphene (single-layer graphene). When the number of layers exceeds 10, the properties of the layered aggregate of graphene become closer to those of graphite. The thickness of a graphene sheet is on the nanoscale, while the other two dimensions are typically larger than the nanoscale.

[0019] In this specification, the term "expandable graphite" refers to a graphite material that can be used to form worm-shaped expanded graphite. For example, by chemical or physical means (such as heating), the graphite layers of the graphite material expand along the Z-axis direction at a high ratio (for example, an expansion ratio of 100 to 400 times), and worm-shaped expanded graphite is formed. "Expandable graphite" and "graphite intercalation compound" may have the same meaning.

[0020] In one aspect of the present disclosure, there is provided a graphene powder which is a laminate of graphene sheets, and in the Raman spectrum of the graphene powder, the peak heights are I D 、I G respectively for the D peak and the G peak, and a graphene powder in which I D / I G is 0.10 or less. In a modification, I D / I G may be 0.01 to 0.10, preferably 0.03 to 0.10. For example, it may be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, etc., but is not limited thereto. In a modification, voids are present in the graphene powder, such as voids between graphene sheets or voids within graphene sheets. The presence of voids means that the connection between the graphite layers is broken. In a modification, the particle size of the graphene powder is 15 to 35 μm.

[0021] Raman spectroscopy is widely used for the analysis of carbon materials. The Raman spectrum of a graphene material can mainly consist of a plurality of peaks of G, D, and G'. The G peak is the main characteristic peak of graphene, sp 2These peaks are due to in-plane vibrations of hybridized carbon atoms. The G peak effectively reflects the number of graphene layers in a graphene sample. The D peak is usually considered a disordered vibrational peak of graphene and is used to evaluate structural defects in graphene samples. The G' peak, also known as the 2D peak, is a second-order Raman peak of 2-phonon resonance and can be used to characterize the interlayer stacking of carbon atoms in a graphene sample. In the Raman spectrum of graphene powder, wavelengths 1250–1450 cm are observed. -1 Peak height I within the range D D peak, wavelength 1500-1700 cm -1 Peak height I within the range G The G peak is at a wavelength of 2600-2800 cm. -1 Peak height I within the range 2D A 2D peak is present. Raman spectroscopy has advantages in characterizing defects in graphene materials. Generally, the defect density is I D / I G It is thought to be proportional to the I of graphene powder. D / I G The lower value indicates fewer defects in the conductive composite material of graphene.

[0022] The conductivity of graphene powder can be 500 to 5000 S / cm, preferably 1500 to 4000 S / cm, and more preferably 2000 to 3500 S / cm. Examples include, but are not limited to, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, and 4000.

[0023] The specific surface area of ​​graphene powder is 50-300 m². 2 It can be / g, preferably 100-250m 2 / g is also acceptable.

[0024] The tap density of graphene powder is 0.02-0.04 g / cm³. 3 It is possible.

[0025] Based on the mass of the graphene powder, the carbon content of the graphene powder may be 99.50% or more, preferably 99.80 to 99.95%, and the oxygen content may be 300 ppm or less.

[0026] In one embodiment, a laminate of graphene sheets contains 1 to 10 layers of graphene. In one modification, the total thickness is 0.5 to 3.0 nm. In another modification, a laminate of graphene sheets has a median grain size of 5 to 15 μm, preferably 8 to 15 μm. The median grain size of the graphene sheet represents the dimension of the largest dimension of the graphene sheet. As described above, the graphene sheet has a nanoscale thickness, and the dimensions of the other two dimensions are usually larger than nanoscale. Correspondingly, the median grain size of the graphene sheet represents the dimension in the length / width (XY) direction.

[0027] In the Raman spectrum of the graphene sheet, the peak heights are I D , I G There are D peaks and G peaks, and I D / I G It may be 0.10 or less. In one modified example, I D / I G The value may be 0.01 to 0.10, preferably 0.03 to 0.10, and examples include, but are not limited to, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, etc.

[0028] In the Raman spectrum of graphene sheets, wavelengths of 1250-1450 cm are observed. -1 Peak height I within the range D D peak, wavelength 1500-1700 cm -1 Peak height I within the range G The G peak is at a wavelength of 2600-2800 cm. -1 Peak height I within the range 2D A 2D peak exists in the graphene sheet. D / I GThe low value indicates that there are few defects within the graphene sheet.

[0029] In thermogravimetric analysis, graphene sheets exhibit the following behavior. When a graphene sheet is heat-treated in an air atmosphere, the temperature at which thermal decomposition of the graphene sheet begins is 600°C or higher, preferably 700°C or higher. In one modified example, when heat-treated at 800°C in an air atmosphere, the heat loss rate of the graphene sheet is 10% or less, preferably 8% or less, more preferably 5% or less. Here, the heat loss rate is (weight of graphene sheet before heat treatment - weight of graphene sheet after heat treatment) / weight of graphene sheet before heat treatment. The temperature at which thermal decomposition begins is negatively correlated with the impurity content of the graphene material sample. In this respect, the higher the thermal decomposition start temperature, the lower the impurity content of the graphene material sample. The heat loss rate is positively correlated with the impurity content of the graphene material sample. In this respect, the lower the heat loss rate, the lower the impurity content of the graphene material sample.

[0030] The conductivity of the graphene sheet may be 500 to 5000 S / cm, preferably 1500 to 4000 S / cm, and more preferably 2000 to 3500 S / cm. Examples include, but are not limited to, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, and 4000.

[0031] In another aspect of this disclosure, (1) A process of pre-expanding expandable graphite to obtain pre-expanded graphite; (2) After mixing the pre-expanded graphite obtained in step (1), a wetting agent, and a solvent, the resulting mixture is subjected to a first high-pressure homogenization and a second high-pressure homogenization to obtain a slurry containing graphene powder. Here, the pressure of the second high-pressure homogenization is 10-20 MPa higher than the pressure of the first high-pressure homogenization; A method for preparing graphene powder is provided, comprising the step of (3) drying the slurry containing the graphene powder obtained in step (2) to obtain graphene powder.

[0032] In one modified example, the pre-expanded graphite obtained in step (1) has an expansion rate of 200 to 300 times that of expandable graphite.

[0033] Preferably, step (1) may include the steps of heating the expandable graphite to 800-950°C and expanding the expandable graphite for 10-60 seconds to obtain pre-expanded graphite. In one modified example, the expandable graphite may have a particle size of 70-100 mesh.

[0034] In one modified example, the wetting agent in step (2) is an aliphatic amine polyoxyethylene ether. Preferably, the HLB value of the aliphatic amine polyoxyethylene ether may be 12 or higher.

[0035] Preferably, the pre-expanded graphite obtained in step (1) and the wetting agent are supplied in step (2) in a mass ratio of 1:0.01 to 0.1. The solvent may be one or more of water or ethanol. The slurry containing graphene powder may have a solid content of 0.5 to 5.0% by weight.

[0036] More preferably, in step (2), the pressure for the first high-pressure homogenization is 30 to 40 MPa and the time is 20 to 60 minutes. The pressure for the second high-pressure homogenization is 40 to 50 MPa and the time is 10 to 30 minutes.

[0037] In a modified example, the graphene powder obtained in step (3) may have a residual solvent level of 0.1% by weight or less.

[0038] Preferably, the drying in step (3) is spray drying or freeze drying. In one variation, the conditions for spray drying are that the air inlet temperature is 300 to 350°C, the air inlet temperature is 200 to 250°C higher than the air outlet temperature, the air outlet temperature is 100 to 130°C, and the rotation speed of the centrifugal disk of the spray dryer is 20,000 to 30,000 rpm. In one variation, the conditions for freeze drying are that the cooling trap temperature is -65°C or lower, preferably -75 to -70°C, the shelf partition plate temperature is -55°C or lower, preferably -65 to -60°C, the heating rate is 0.1 to 0.5°C / min, the time to raise the temperature from the shelf partition plate temperature to 0°C is 24 hours or more, preferably 26 to 30 hours, and the vacuum level is 10 Pa or lower, preferably 0.5 to 5 Pa.

[0039] The graphene powder of this disclosure has characteristics such as good dispersibility, high purity, few defects, and high conductivity. The graphene powder of this disclosure can be suitably used in fields such as conductive composite materials, anticorrosive coatings (especially epoxy resin anticorrosive coatings), and heat dissipation composite materials.

[0040] In this regard, further embodiments of the present disclosure provide the use of the graphene powder of the present disclosure in conductive composite materials, anticorrosive coatings, particularly epoxy resin anticorrosive coatings, and heat dissipation composite materials.

[0041] The graphene powder of this disclosure can be used in lithium-ion batteries. Lithium-ion batteries may have structures well known to those skilled in the art. Generally, lithium-ion batteries may include a negative electrode, a positive electrode, a separator, and an electrolyte. The separator may be placed between the positive and negative electrodes. The positive electrode includes a positive electrode active material, and the negative electrode includes a negative electrode active material. The specific composition of the positive electrode active material is not particularly limited. The positive electrode active material may be a lithium-containing positive electrode active material commonly used in the art. The specific composition of the negative electrode active material is not particularly limited. Preferably, the negative electrode active material is a silicon-carbon negative electrode material. The graphene powder of this disclosure can be used in combination with the negative electrode active material or the positive electrode active material as a conductive agent in the corresponding battery electrodes.

[0042] The separator can be selected from various separators known to those skilled in the art and commonly used in lithium-ion batteries, such as polypropylene microporous film, polyethylene mat, glass fiber mat, or ultrafine glass fiber paper.

[0043] The electrolyte may be any of the conventional electrolytes, including non-aqueous electrolytes. A non-aqueous electrolyte is a solution formed by an electrolyte lithium salt in a non-aqueous solvent. Conventional non-aqueous electrolytes known to those skilled in the art can be used. For example, the electrolyte lithium salt may be at least one selected from the group consisting of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), and lithium hexafluorosilicate (LiSiF6). The non-aqueous solvent can be selected from the group consisting of linear esters, cyclic esters, and mixtures thereof. The linear ester may be at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), and dipropyl carbonate (DPC). The cyclic ester may be at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC).

[0044] [Structural and performance testing] This disclosure describes the characterization of material sample morphology using a scanning electron microscope (SEM). Specifically, the scanning electron microscope used is a TECNALG2F20 (200kv) from FEI Corporation, USA. The test method involves directly pressing the sample onto a sample stage containing conductive tape, inserting it into the electron microscope, and observing it. The observation magnification is 8,000x.

[0045] In this disclosure, the morphology of the material samples is characterized using a JEOL Ltd. JEM-2100 transmission electron microscope (TEM, HR-TEM). The test method involves placing the sample on a copper support mesh and inserting it into the electron microscope for observation. The observation magnifications are 17,000x and 380,000x.

[0046] In this disclosure, the median particle size of graphene sheets is characterized by dynamic light scattering using a Malvern Panalytical MS-3000 laser particle size analyzer. The test is performed by dispersing the sample in deionized water to a concentration of 0.01 mg / ml, sonicating it for 10 minutes, and then subjecting it to the test. The light shielding range of the analyzer is set to 5-20%.

[0047] In this disclosure, XRD analysis of material samples was performed using an X-ray diffractometer D / max-2200 / PC manufactured by Nippon Rigakusha. The test conditions included a 2θ test range of 10 to 70°, a scanning speed of 6° / min, a tube voltage of 40KV, a current of 40mA, and a Cu-Kα radiation source.

[0048] In this disclosure, the specific surface area of ​​the material sample is measured using the ASAP2010 specific surface area and pore distribution tester from Micromeritics, Inc., USA. The test conditions include a temperature of 77K and a nitrogen atmosphere.

[0049] In this disclosure, the heat loss curve is measured using a Pyris1 thermogravimetric analyzer from Perkin-Elmer, Inc. in the United States, under an air atmosphere, at a heating rate of 20°C / min.

[0050] In this disclosure, Raman spectra were obtained using an Invia / Reflrx Laser Micro-Raman spectrometer with a 785 nm wavelength laser as the excitation source, by placing the material sample on a slide.

[0051] In this disclosure, the expansion rate is measured as follows: A fixed amount of expandable graphite is weighed, and its volume is measured using a graduated cylinder. As described above, the expandable graphite is pre-expanded to obtain pre-expanded graphite. After the pre-expanded graphite is cooled to room temperature, its volume is detected using a graduated cylinder. The expansion rate is calculated using the following formula. Expansion rate = (Volume of pre-expanded graphite - Volume of expandable graphite) / Volume of expandable graphite.

[0052] In this disclosure, the residual solvent content is measured as follows: 1 g of the obtained graphene powder is used as a sample, dried in a vacuum oven at 60°C for 10 hours, and then the weight of the sample is measured. The residual solvent content is calculated using the following formula. Residual solvent percentage % = (1 - weight of sample after drying (g)) / 1 × 100%.

[0053] In this disclosure, tap density is measured using the FT-100E multi-function tap density tester from Rico instrument technology Co., LTD, at a test frequency of 200 Hz and a vibration frequency of 5000 times.

[0054] In this disclosure, conductivity is measured using the ST-2258C multifunction digital four-probe tester from Suzhou Jingge Electronic Co., Ltd. Samples are prepared by compression. Specifically, the obtained graphene powder sample is compressed into a 100 μm thin plate at a pressure of 10 MPa and tested using the tester.

[0055] In this disclosure, oxygen and carbon content are measured using a ThermoFisher FlashSmart-1120265 elemental analyzer, with He gas as the carrier gas and an injection volume of 1 mg.

[0056] In this invention, the electrochemical properties of assembled lithium-ion batteries are measured using the Wuhan Blue Battery Test System (CT2001B). The measurement conditions include a voltage range of 0.005V to 2V and a current range of 0.05A to 2A. Each sample consists of 10 assembled coin cells, and the battery performance is measured under the same voltage and current. The average value is used as the measurement result.

[0057] In this disclosure, a neutral salt spray test is performed using the Q-FOG cycle saline spray tester from Q-Lab, Inc., USA, in accordance with HG / T5573-2019. The test is performed in the following steps: A physiological saline solution containing (5±0.5%) sodium chloride with a pH of 6.5-7.2 is sprayed using a spray device, and the sprayed saline solution adheres to a test specimen with a cut. After 1440 hours, the corrosion state of the cut on the surface is observed. The corrosion protection effect is determined by detecting the corrosion distance of the cut.

[0058] [Examples] The present invention will be described in detail below with reference to examples.

[0059] In the following examples and comparative examples, the room temperature is 25°C.

[0060] In the following examples and comparative examples, the expandable graphite used was E-196403 from Aladdin Reagents Co., Ltd. The wetting agent was Surfonic T-10 from Huntsman Chemical Trading Co., Ltd.

[0061] [Example 1] (1) 100g of expandable graphite (75 mesh) was pre-expanded at 900°C for 20 seconds to obtain pre-expanded graphite. As measured by the above test, the expansion rate of the pre-expanded graphite was 220 times.

[0062] (2) 10 g of pre-expanded graphite obtained in step (1), 0.25 g of wetting agent (Surfonic T-10, HLB value 12.4, aliphatic amine polyoxyethylene ether), and 239.75 g of deionized water were added to a high-pressure homogenizer and homogenized at 30 MPa for 30 minutes, then the pressure was increased to 45 MPa and homogenized for 30 minutes to obtain a slurry containing graphene powder.

[0063] (3) The slurry was dried using a spray dryer. The air inlet temperature of the spray dryer was 350°C, the air outlet temperature was 100°C, and the rotation speed of the centrifugal disk of the spray dryer was 20,000 rpm. The powder recovered at the outlet was graphene powder G-1.

[0064] Figure 1 is an SEM image of graphene powder G-1 obtained in Example 1. As can be seen from Figure 1, G-1 has a structure formed by stacking graphene sheets, with a particle size of 20-30 μm, and there were voids between the graphene sheets.

[0065] Figure 2 is a TEM image of graphene powder G-1 obtained in Example 1. As can be seen from Figure 2, the graphene sheets are stacked, which is consistent with the result obtained from the SEM image in Figure 1. This indicates that G-1 is made up of stacked graphene sheets.

[0066] Figure 3 shows an HR-TEM image of graphene powder G-1 obtained in Example 1. As shown by the grid lines in Figure 3, the graphene sheet in G-1 is a thin-layer graphene having 4 to 6 layers of graphene, with a thickness of approximately 1.2 nm to 1.9 nm. The median particle size of the graphene sheet was 8.5 μm.

[0067] Figure 4 shows the Raman spectrum of graphene powder G-1 obtained in Example 1. As can be seen from Figure 4, the D peak of this graphene powder is 1354 cm⁻¹. -1 The G peak is 1574cm. -1 And the ratio of their peak heights (I D / I GThe ratio was 0.09, indicating that the G-1 had fewer defects. Furthermore, the G-1 also had a ratio of 2709 cm -1 A prominent 2D peak was observed, confirming that G-1 is a thin-layer graphene stack. This was consistent with the results in Figure 3.

[0068] Figure 5 shows the XRD spectrum of G-1. Only a prominent diffraction peak appeared at 26.63°, and no impurity peaks were observed. This indicates that G-1 does not contain an impurity phase formed by oxidation or doping with impurity elements.

[0069] Elemental analysis revealed that the carbon content of G-1 obtained in Example 1 was 99.95% by weight, and the oxygen content was 140 ppm.

[0070] As measured in the aforementioned tests, the thermal decomposition initiation temperature of G-1 was 640°C, the heat loss rate at 800°C was 6.5%, the conductivity was 3200 S / cm, and the tap density was 0.028 g / cm³. 3 The specific surface area is 180 m². 2 The concentration was / g, and the solvent retention rate was 0.1%.

[0071] The heat loss curve of graphene powder G-1 obtained in Example 1 is shown in Figure 19 and is designated as 1. For comparison, a commercially available product was used as a comparison sample, and its heat loss data and SEM image were obtained, and the results are shown in Figures 19 to 22. Comparison sample 2 (simply labeled 2 in the figure) is graphene powder from Shanghai Carbon Source Valley New Material Technology Co., Ltd. (graphene powder prepared by physical methods). Comparison sample 3 (simply labeled 3 in the figure) is SE-3521 (graphene oxide powder) from Changzhou Sixth Element Material Technology Co., Ltd. Comparison sample 4 (simply labeled 4 in the figure) is SE-1430 (redox-type graphene powder) from Changzhou Sixth Element Material Technology Co., Ltd. As shown in Figure 19, comparison sample 2 had a thermal decomposition start temperature of 560°C and a heat loss rate of 57% at 800°C. Comparative sample 3 had a thermal decomposition initiation temperature of 420°C and a heat loss rate of 68% at 800°C. Comparative sample 4 had a thermal decomposition initiation temperature of 50°C and a heat loss rate of 98% at 800°C.

[0072] Figure 20 shows an SEM image of comparative sample 2. As shown in Figure 20, the graphene sheet of this comparative sample had many layers, no voids between the graphene sheets, and was strongly bonded. In such a structure, solvent penetration is difficult, making it difficult to disperse the graphene.

[0073] Figure 21 shows an SEM image of comparison sample 3. As shown in Figure 21, the comparison sample is formed by stacking multiple graphene material sheets, but the sheets are thick, and the comparison sample contains many spherical particle impurities, resulting in low purity.

[0074] Figure 22 shows an SEM image of comparative sample 4. As shown in Figure 22, this comparative sample is also formed by stacking multiple graphene material sheets, but the sheets are thicker, and the comparative sample contains many spherical particle impurities, resulting in low purity.

[0075] [Assembly process] The graphene powder G-1 obtained in Example 1 was added to the negative electrode of a lithium-ion battery as a conductive agent. This lithium-ion battery has a metallic lithium sheet as the positive electrode, a polypropylene microporous film as the separator, and a 1 mol / L lithium hexafluorophosphate (LiPF6) solution as the electrolyte (using a mixture of vinyl carbonate and diethyl carbonate in a volume ratio of 3:7 as the solvent). The negative electrode contains the graphene powder G-1 obtained in Example 1 as a conductive agent and has a design capacity of 500 mAhg. -1 A CR2016 coin cell was assembled using a silicon-carbon anode active material with a mass ratio of 1:8 between the conductive agent and the silicon-carbon anode active material.

[0076] The assembled coin cells were subjected to the above tests, and their cycle performance at different current rates was characterized. The results are shown in Figure 9.

[0077] [Example 2] (1) 100g of expandable graphite (75 mesh) was pre-expanded at 900°C for 20 seconds to obtain pre-expanded graphite. As measured by the above test, the expansion rate of the pre-expanded graphite was 220 times.

[0078] (2) 10 g of pre-expanded graphite obtained in step (1), 0.25 g of wetting agent (Surfonic T-10, HLB value 12.4), and 239.75 g of deionized water were added to a high-pressure homogenizer and homogenized at 30 MPa for 30 minutes, then the pressure was increased to 45 MPa and homogenized for another 30 minutes to obtain a slurry containing graphene powder.

[0079] (3) The slurry was dried in a freeze-drying apparatus. The temperature of the cooling trap was -75°C, the temperature of the shelf divider was -60°C, the heating rate was 0.5°C / min, and the temperature was maintained at -60°C, -50°C, -40°C, -20°C, -10°C, and 0°C for 12 hours, 4 hours, 4 hours, 2 hours, 2 hours, and 2 hours, respectively. The vacuum level inside the shelf was maintained at 5 Pa at all times during the process. After the temperature of the shelf divider returned to room temperature, the obtained product was removed and named G-2.

[0080] Figure 6 shows an SEM image of graphene powder G-2 obtained in Example 2. As can be seen from Figure 6, G-2 has a structure formed by stacking graphene sheets, with a particle size of 22-25 μm, and there were voids between the graphene sheets.

[0081] Figure 7 shows an HR-TEM image of graphene powder G-2 obtained in Example 2. As shown by the grid lines in Figure 7, the graphene sheet in G-2 is a thin-layer graphene with 5 to 8 layers of graphene, and its thickness was approximately 1.5 nm to 2.4 nm. As measured in the above-described test, the median particle size of the graphene sheet was 6.7 μm. The D peak of product G-2 was 1346 cm⁻¹. -1 Therefore, the G peak is 1569cm. -1 And the ratio of their peak heights (I D / I G The ratio was 0.08, indicating that the G-2 had few defects. Furthermore, the G-2 had a length of 2692 cm. -1 A significant 2D peak also appeared, confirming that G-2 is a thin-layer graphene stack.

[0082] Furthermore, the XRD spectrum of G-2 was obtained through the aforementioned tests. The results showed only a prominent diffraction peak at 26.63°, and no impurity peaks were observed. This indicates that G-2 does not contain an impurity phase formed by oxidation or doping with impurity elements.

[0083] As measured in the above-mentioned tests, the carbon content of G-2 was 99.95% by weight, the oxygen content was 200 ppm, the thermal decomposition initiation temperature was 640°C, the heat loss rate at 800°C was 7%, the conductivity was 2000 S / cm, and the tap density was 0.021 g / cm³. 3 Its specific surface area is 220 m². 2 The concentration was / g, and the solvent residue rate was 0.1%.

[0084] [Example 3] (1) 100 g (75 mesh) of expandable graphite was pre-expanded at 900°C for 40 seconds to obtain pre-expanded graphite. As measured by the above test, the expansion rate of the pre-expanded graphite was 300 times.

[0085] (2) 10 g of pre-expanded graphite, 0.25 g of wetting agent (Surfonic T-10, HLB value 12.4), and 239.75 g of deionized water were added to a high-pressure homogenizer and homogenized at 30 MPa for 30 minutes, then the pressure was increased to 45 MPa and homogenized for another 30 minutes to obtain a slurry containing graphene powder.

[0086] (3) The slurry was dried in a spray dryer. The air inlet temperature of the spray dryer was 350°C, the air outlet temperature was 100°C, and the rotation speed of the centrifugal disk of the spray dryer was 20,000 rpm. The powder recovered at the outlet was graphene powder G-3.

[0087] The above-described tests yielded SEM images and XRD spectra of G-3. As can be seen from the SEM image of G-3, G-3 is a structure formed by stacking graphene sheets, with a particle size of 20-25 μm. There were voids between the graphene sheets. As can be seen from the HR-TEM results, the graphene sheets of G-3 are thin-layer graphene with 4-6 layers of graphene, and their thickness was approximately 1.2 nm-1.8 nm. As can be seen from the dynamic light scattering data, the median particle size of the graphene sheets was 10 μm. As shown in the Raman spectrum, the D peak of G-3 is at 1351 cm⁻¹. -1 Therefore, the G peak is 1572cm. -1 And the ratio of their peak heights (I D / I G The ratio was 0.09, indicating that the G-3 had fewer defects. Furthermore, the G-3 also had a ratio of 2702cm -1 A prominent 2D peak was observed, confirming that G-3 is a thin-layer graphene stack. Furthermore, the XRD spectrum of G-3 showed only a prominent diffraction peak at 26.63°, with no impurity peaks observed. This indicates that G-3 does not contain an impurity phase formed by oxidation or doping with impurity elements.

[0088] As measured in the aforementioned tests, the carbon content of G-3 was 99.82% by weight, the oxygen content was 260 ppm, the thermal decomposition initiation temperature was 655°C, the heat loss rate at 800°C was 8.4%, the electrical conductivity was 1800 S / cm, and the tap density was 0.031 g / cm³. 3 The specific surface area is 120 m². 2 The concentration was / g, and the solvent residue rate was 0.1%.

[0089] [Example 4] (1) 100 g (75 mesh) of expandable graphite was pre-expanded at 900°C for 40 seconds to obtain pre-expanded graphite. As measured by the above test, the expansion rate of the pre-expanded graphite was 300 times.

[0090] (2) 10 g of pre-expanded graphite, 0.25 g of wetting agent (Surfonic T-10, HLB value 12.4), and 239.75 g of deionized water were added to a high-pressure homogenizer and homogenized at 30 MPa for 60 minutes, then the pressure was increased to 45 MPa and homogenized for 30 minutes to obtain a slurry containing graphene powder.

[0091] (3) The slurry was dried in a spray dryer. The air inlet temperature of the spray dryer was 350°C, the air outlet temperature was 100°C, and the rotation speed of the centrifugal disk of the spray dryer was 20,000 rpm. The powder recovered at the outlet was graphene powder G-4.

[0092] The above-described tests yielded SEM images and XRD spectra of G-4. As can be seen from the SEM image of G-4, G-4 is a structure formed by stacking graphene sheets, with a particle size of 18-22 μm. There were voids between the graphene sheets. As can be seen from the HR-TEM results, the graphene sheets of G-4 are thin-layer graphene with 4-6 layers of graphene, and their thickness was approximately 1.2 nm-1.8 nm. As can be seen from the dynamic light scattering data, the median particle size of the graphene sheets was 10 μm. As shown in the Raman spectrum in Figure 16, the D peak of G-4 is at 1346 cm⁻¹. -1Therefore, the G peak is 1565cm. -1 And the ratio of their peak heights (I D / I G The ratio was 0.04, indicating that the G-4 had fewer defects. Furthermore, the G-4 also had a ratio of 2702 cm -1 A prominent 2D peak was observed, confirming that G-4 is a thin-layer graphene stack. Furthermore, the XRD spectrum of G-4 showed only a prominent diffraction peak at 26.63°, with no impurity peaks observed. This indicates that G-4 does not contain an impurity phase formed by oxidation or doping with impurity elements.

[0093] As measured in the aforementioned tests, the carbon content of G-4 was 99.85% by weight, the oxygen content was 140 ppm, the thermal decomposition initiation temperature was 640°C, the heat loss rate at 800°C was 6.7%, the electrical conductivity was 2000 S / cm, and the tap density was 0.029 g / cm³. 3 Its specific surface area is 140 m². 2 The concentration was / g, and the solvent residue rate was 0.1%.

[0094] A coin cell was assembled by repeating the assembly procedure of Example 1, except that graphene powder G-1 obtained in Example 1 was replaced with G-4 obtained in Example 4. This coin cell was then subjected to tests to characterize its cycle performance at different current rates. The results are shown in Figure 17.

[0095] [Comparative Example 1] (1) 100 g (75 mesh) of expandable graphite was pre-expanded at 900°C for 20 seconds to obtain pre-expanded graphite. As measured by the above test, the expansion rate of the pre-expanded graphite was 220 times.

[0096] (2) 10 g of pre-expanded graphite, 0.25 g of wetting agent (Teric N6, HLB value 10.9, alkylphenol polyoxyethylene ether), and 239.75 g of deionized water were added to a high-pressure homogenizer and homogenized at 30 MPa for 30 minutes, then the pressure was increased to 45 MPa and homogenized for 30 minutes to obtain a slurry containing graphene powder.

[0097] (3) The slurry was dried in a spray dryer. The air inlet temperature of the spray dryer was 350°C, the air outlet temperature was 100°C, and the rotation speed of the centrifugal disk of the spray dryer was 20,000 rpm. The powder recovered at the outlet was graphene powder DG-1.

[0098] The above-described tests yielded an SEM image of DG-1, which is shown in Figure 8. As can be seen from the figure, the graphene sheets of DG-1 were stacked in a disordered manner. DG-1 did not have a clearly defined particle size.

[0099] Figure 14 shows an HR-TEM image of DG-1. As can be seen from the figure, the graphene sheet of DG-1 has a layered structure with 15 to 20 layers of graphene and a thickness of approximately 4.5 nm to 6 nm.

[0100] Figure 15 shows the Raman spectrum of DG-1. As can be seen from the figure, the D peak of DG-1 is at 1351 cm⁻¹. -1 Therefore, the G peak is 1514cm. -1 And the ratio of their peak heights (I D / I G ) is 0.25, and the DG-1 is substantially more defective than the G-1. Furthermore, the DG-1 also has 2702cm -1 A 2D peak was observed, but this was a broad peak and not a prominent one. This confirmed that the graphene sheet of DG-1 has a layered structure containing more graphene layers.

[0101] As measured in the above-mentioned tests, the carbon content of DG-1 was 99.32% by weight, the oxygen content was 240 ppm, the thermal decomposition initiation temperature was 620°C, the heat loss rate at 800°C was 9.2%, the electrical conductivity was 800 S / cm, and the tap density was 0.042 g / cm³. 3 The specific surface area is 60 m². 2 The concentration was / g, and the solvent residue rate was 0.25%.

[0102] [Comparative Example 2] (1) 100g of expandable graphite (75 mesh) was pre-expanded at 900°C for 20 seconds to obtain pre-expanded graphite. As measured by the above test, the expansion rate of the pre-expanded graphite was 220 times.

[0103] (2) 10 g of pre-expanded graphite, 0.25 g of wetting agent (Surfonic T-10, HLB value 12.4), and 239.75 g of deionized water were added to a high-pressure homogenizer and homogenized at 30 MPa for 60 minutes to obtain a slurry containing graphene powder.

[0104] (3) The slurry was dried in a spray dryer. The air inlet temperature of the spray dryer was 350°C, the air outlet temperature was 100°C, and the rotation speed of the centrifugal disk of the spray dryer was 20,000 rpm. The powder recovered at the outlet was graphene powder DG-2.

[0105] The above-described tests yielded SEM images, HR-TEM images, and Raman spectra of DG-2. As can be seen from the SEM image of DG-2, the graphene sheets in DG-2 were stacked in a disordered manner. DG-2 did not have a distinct grain size. As can be seen from the HR-TEM image, the graphene sheets in DG-2 had a layered structure with 10 to 15 layers of graphene, and a thickness of approximately 3 nm to 4.5 nm. As can be seen from the Raman spectrum of DG-2, the D peak of DG-2 was at 1351 cm⁻¹. -1 Therefore, the G peak is 1514cm. -1 And the ratio of their peak heights (I D / I G The ratio was 0.2, indicating that the DG-2 had significantly more defects than the G-1. Furthermore, the DG-2 had 2702 cm². -1 A 2D peak was observed, but this was a broad peak, indicating the presence of a small amount of thin-layer graphene in DG-2.

[0106] The tests described above showed that DG-2 has a carbon content of 99.95% by weight, an oxygen content of 140 ppm, a thermal decomposition initiation temperature of 640°C, a heat loss rate of 7% at 800°C, an electrical conductivity of 500 S / cm, and a tap density of 0.08 g / cm³. 3 The specific surface area is 12m². 2 The concentration was / g, and the solvent residue rate was 0.1%.

[0107] [Comparative Example 3] (1) 100g of expandable graphite (75 mesh) was pre-expanded at 900°C for 20 seconds to obtain pre-expanded graphite. As measured by the above test, the expansion rate of the pre-expanded graphite was 220 times.

[0108] (2) 10 g of pre-expanded graphite, 0.25 g of wetting agent (Surfonic T-10, HLB value 12.4), and 239.75 g of deionized water were added to a high-pressure homogenizer and homogenized at 45 MPa for 60 minutes to obtain a slurry containing graphene powder.

[0109] (3) The slurry was dried using a spray dryer. The air inlet temperature of the spray dryer was 350°C, the air outlet temperature was 100°C, and the rotation speed of the centrifugal disk of the spray dryer was 20,000 rpm. The powder recovered at the outlet was graphene powder DG-3.

[0110] The above-described tests yielded SEM images, HR-TEM images, and Raman spectra of DG-3. As can be seen from the SEM image of DG-3, DG-3 did not have a distinct grain size. As can be seen from the HR-TEM image of DG-3, the graphene sheet of DG-3 was a thin-layer graphene with 4 to 6 layers of graphene, and its thickness was approximately 1.2 nm to 1.9 nm. As can be seen from the Raman spectrum of DG-3, the D peak of DG-3 was at 1354 cm⁻¹. -1 The G peak is 1574cm. -1 And the ratio of their peak heights (I D / I G The ratio was 0.13, indicating that DG-3 had fewer defects and was similar to G-1. Furthermore, DG-3 had a yield of 2709 cm².-1 showed a 2D peak, which was a sharp peak, indicating that the graphene sheet of DG-3 was few-layer graphene. Since DG-3 had a wide particle size distribution, it was disadvantageous for industrial applications.

[0111] As measured in the above-mentioned tests, the carbon content of DG-3 was 99.95 wt%, the oxygen content was 140 ppm, the thermal decomposition start temperature was 640 °C, the thermal loss rate at 800 °C was 7%, the conductivity was 1600 S / cm, and the tap density was 0.018 g / cm 3 and the specific surface area was 200 m 2 / g, and the solvent residue rate was 0.1%.

[0112] The assembly of Example 1 was repeated to assemble a coin cell except that the graphene powder G-1 obtained in Example 1 was replaced with DG-3 obtained in Comparative Example 3. A test was conducted on this coin cell to characterize the cycle performance at different current rates. The results are shown in Fig. 18.

[0113] 〔Comparative Example 4〕 The assembly of Example 1 was repeated to assemble a coin cell except that the graphene powder G-1 obtained in Example 1 was replaced with a commercially available Super P conductive agent. A test was conducted on this coin cell to characterize the cycle performance at different current rates. The results are shown in Fig. 10.

[0114] As shown in Fig. 9, when the graphene powder G-1 obtained in Example 1 was used as the conductive agent, the capacity retention rates of the coin cell were 100%, 97%, 90%, and 78% at the current rates of 0.1C / 0.2C / 0.5C / 1C, respectively. As shown in Fig. 10, when commercially available Super P was used as the conductive agent, the capacity retention rates were 96%, 92%, 68%, and 40% at the current rates of 0.1C / 0.2C / 0.5C / 1C, respectively. From the above results, it was shown that the graphene powder of the present disclosure made the coin cell more stable.

[0115] As shown in Figure 17, when G-4 was used as the conductive agent, the capacity retention rates of the coin cell were 100%, 91%, 83%, and 69% at current rates of 0.1C / 0.2C / 0.5C / 1C, respectively. As shown in Figure 18, when DG-3 was used as the conductive agent, the capacity retention rates of the coin cell were 95%, 89%, 64%, and 42% at current rates of 0.1C / 0.2C / 0.5C / 1C, respectively. Both capacity retention rates were lower than when G-1 was used as the conductive agent. When DG-3 was used as the conductive agent, stability decreased significantly at certain current rates.

[0116] Figure 11 shows the configuration of a negative electrode having graphene powder G-1 as a conductive agent in Example 1. Figure 12 shows the configuration of a negative electrode having Super P as a conductive agent. It was clear that there were significant differences between these two negative electrode configurations. As can be seen from Figure 11, the graphene sheets in the graphene powder of this disclosure are complete and have a large radial size. Therefore, when the graphene powder of this disclosure is used as a conductive agent, the dispersed, large-sized graphene sheets increased the contact area between them and the electrode active material. This provided more pathways for electron movement in the electrode active material, promoting the formation of a network for planar conduction of electrons within the resulting electrode, resulting in excellent conductivity (3200 S / cm), reduced internal resistance of the electrode, and improved battery rate performance. Furthermore, the flexibility associated with the graphene sheets buffered the volume expansion of the silicon-carbon negative electrode material during charge-discharge cycles, improving the battery cycle performance. As shown in Figure 12, Super P was dispersed between the silicon-carbon negative electrode material. Therefore, electrons were conducted linearly. Super P also did not have the effect of mitigating the volume expansion of the silicon-carbon anode material.

[0117] [Example 5] Preparation of zinc powder-containing epoxy corrosion-resistant resin The required amounts of epoxy resin and inorganic zinc powder were weighed and uniformly mixed to obtain a zinc powder-containing epoxy corrosion-resistant resin.

[0118] 1 g of graphene powder G-1 obtained in Example 1 was added to 999 g of zinc powder-containing epoxy corrosion inhibitor (zinc powder accounts for 30% by mass of the epoxy corrosion inhibitor). After uniform mixing, the mixture was applied to the surface of a washed carbon steel test piece to form a 90 μm thick film. Separately, 1000 g of zinc powder-containing epoxy corrosion inhibitor (zinc powder accounts for 80% by mass of the epoxy corrosion inhibitor) was applied to the surface of a washed carbon steel test piece to form a 90 μm thick film. Cross-shaped lines were cut into the coated surfaces of two carbon steel test pieces in accordance with HG / T5573-2019, and then a neutral salt spray test was performed in a salt spray test box. After 1440 hours, the corrosion state of the cuts on the carbon steel surface was observed. The results are shown in Figure 13. The left figure shows the results for a conventional zinc-containing epoxy corrosion inhibitor (zinc content 80%), where the corrosion diffusion distance of the cuts after the salt spray test was 5-20 mm. The figure on the right shows the results for a zinc-containing epoxy anticorrosion resin (containing 30% zinc) with added graphene powder. After the salt spray test, the corrosion diffusion distance of the cut was 2-3 mm. Comparing the two results, the diffusion distance in the figure on the right was clearly smaller than that in the figure on the left. Also, a clear corrosion pattern was observed on the lower part of the substrate in the figure on the left, but not in the figure on the right. From these results, it was shown that the corrosion resistance of epoxy resin anticorrosion coatings is significantly improved by the addition of graphene powder. Furthermore, the use of graphene powder as disclosed in this disclosure in (epoxy resin) anticorrosion coatings substantially reduced the amount of zinc used.

[0119] Specific embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical scope of the present invention, various simple modifications can be made to the embodiments of the present invention, and various technical features can be combined in any other suitable manner. These simple modifications and combinations are also disclosed herein and should be considered to be within the scope of protection of this disclosure. [Brief explanation of the drawing]

[0120] [Figure 1] This is an SEM image of graphene powder G-1 obtained in Example 1. [Figure 2] This is a TEM image of graphene powder G-1 obtained in Example 1. [Figure 3] This is an HR-TEM image of graphene powder G-1 obtained in Example 1. [Figure 4] This is the Raman spectrum of graphene powder G-1 obtained in Example 1. [Figure 5] This is the XRD spectrum of graphene powder G-1 obtained in Example 1. [Figure 6] This is an SEM image of graphene powder G-2 obtained in Example 2. [Figure 7] This is an HR-TEM image of graphene powder G-2 obtained in Example 2. [Figure 8] This is an SEM image of graphene powder DG-1 obtained in Comparative Example 1. [Figure 9] The cycle performance at different current rates of a coin cell having a negative electrode containing a silicon-carbon material as the negative electrode active material, with graphene powder G-1 obtained in Example 1 as the negative electrode conductive agent, is shown. [Figure 10] Comparative Example 4 shows the cycle performance at different current rates of a coin cell having a negative electrode containing Super P as the negative electrode conductive agent and a negative silicon-carbon material as the negative electrode active material. [Figure 11] This is an SEM image (top view) of the negative electrode using graphene powder G-1 as the negative electrode conductive agent in Example 1. [Figure 12] This is an SEM image (top view) of the negative electrode using commercially available Super P as the negative electrode conductive agent in Comparative Example 4. [Figure 13] Example 5 shows the results of a neutral salt spray test in which notches were made in the anticorrosive coating on a carbon steel substrate. The left side shows the results for a conventional anticorrosive coating (containing 80% zinc), and the right side shows the results for a coating using graphene powder (containing 30% zinc). [Figure 14] This is an HR-TEM image of graphene powder DG-1 obtained in Comparative Example 1. [Figure 15] This is the Raman spectrum of graphene powder DG-1 obtained in Comparative Example 1. [Figure 16] This is the Raman spectrum of graphene powder G-4 obtained in Example 4. [Figure 17] This example demonstrates the cycle performance at different current rates of a coin cell using graphene powder G-4 obtained in Example 4 as the negative electrode conductive material and a silicon-carbon material as the negative electrode active material. [Figure 18] Comparative Example 3 shows the cycle performance at different current rates of coin cells using graphene powder DG-3 as the negative electrode conductive agent and a silicon-carbon material as the negative electrode active material. [Figure 19] The heat loss curves of different graphene material samples under an air atmosphere are shown, where 1 is graphene powder G-1 obtained in Example 1, 2 is commercially available graphene powder (prepared by physical method), 3 is commercially available graphene oxide, and 4 is commercially available reduced graphene oxide. [Figure 20] This is a SEM image of commercially available graphene powder (prepared using a physical method). [Figure 21] This is a SEM image of commercially available graphene oxide. [Figure 22] This is a SEM image of commercially available reduced graphene oxide.

Claims

1. A graphene powder which is a laminate of graphene sheets, wherein the graphene sheets contain 1 to 10 layers of graphene, and in the Raman spectrum of the graphene powder, the peak heights are each I Ｄ , I Ｇ The Raman spectrum includes D and G peaks, and was tested using an Invia / Reflx Laser Micro-Raman spectrometer with a 785 nm wavelength laser as the excitation source. Ｄ / I Ｇ The ratio is 0.03 to 0.10, the graphene powder has voids between the graphene sheets, the particle size of the graphene powder measured by dynamic light scattering is 20 to 35 μm, the graphene powder has a carbon content of 99.50% or more and an oxygen content of 300 ppm or less, and the graphene powder has a specific surface area of ​​50 to 300 m². ２ Graphene powder, weighing / g.

2. The graphene powder has a specific surface area of ​​100 to 250 m². ２ The graphene powder according to claim 1, wherein the weight is / g.

3. The graphene powder has a tap density of 0.02 to 0.04 g / cm³. ３ The graphene powder according to claim 1.

4. The graphene powder according to claim 1, wherein the graphene powder has an electrical conductivity of 500 to 5000 S / cm as measured using an ST-2258C multi-function digital 4-probe tester.

5. The graphene powder according to any one of claims 1 to 4, wherein when the graphene sheet is heat-treated in an air atmosphere, the temperature at which the thermal decomposition of the graphene sheet begins is 600°C or higher.

6. The graphene powder according to any one of claims 1 to 4, wherein when the graphene sheet is heat-treated at 800°C in an air atmosphere, the heat loss of the graphene sheet is 10% or less.

7. (1) A step of pre-expanding expandable graphite to obtain pre-expanded graphite; (2) After mixing the pre-expanded graphite obtained in step (1), a wetting agent, and a solvent, the resulting mixture is subjected to a first high-pressure homogenization and a second high-pressure homogenization to obtain a slurry containing graphene powder. Here, the pressure of the second high-pressure homogenization is 10 to 20 MPa higher than the pressure of the first high-pressure homogenization; (3) The process includes a step of drying the slurry containing the graphene powder obtained in step (2) to obtain graphene powder, The wetting agent in step (2) is an aliphatic amine polyoxyethylene ether, and the HLB value of the aliphatic amine polyoxyethylene ether is 12 or higher. A method for preparing graphene powder according to any one of claims 1 to 4.

8. The method according to claim 7, wherein the pre-expanded graphite obtained in step (1) has an expansion rate of 200 to 300 times that of the expandable graphite before pre-expansion.

9. The method according to claim 7, wherein the pre-expansion in step (1) includes the steps of heating expandable graphite to 800 to 950°C and expanding the expandable graphite for 10 to 60 seconds to obtain pre-expanded graphite.

10. The method according to claim 7, wherein in step (2), the first high-pressure homogenization is performed at a pressure of 30 to 40 MPa for a duration of 20 to 60 minutes, and the second high-pressure homogenization is performed at a pressure of 40 to 50 MPa for a duration of 10 to 30 minutes.

11. The method according to claim 7, wherein the pre-expanded graphite obtained in step (1) and the wetting agent are supplied in step (2) in a mass ratio of 1:0.01 to 0.

1.

12. In step (3), drying is spray drying or freeze-drying. The conditions for the spray drying are that the air inlet temperature is 300 to 350°C, the air inlet temperature is 200 to 250°C higher than the air outlet temperature, the air outlet temperature is 100 to 130°C, and the rotation speed of the centrifugal disk of the spray drying apparatus is 20,000 to 30,000 rpm. The method according to claim 7, wherein the freeze-drying conditions are: a cooling trap temperature of -75 to -70°C, a shelf partition plate temperature of -65 to -60°C, a heating rate of 0.1 to 0.5°C / min, a time of 26 to 30 hours to raise the temperature from the shelf partition plate temperature to 0°C, and a vacuum level of 0.5 to 5 Pa.

13. Use of graphene powder according to any one of claims 1 to 4, or graphene powder prepared by the method according to any one of claims 7 to 12, in conductive composite materials, anticorrosive coatings, or heat dissipation composite materials.

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