A method for preparing graphene powder based on redox method

Abstract

The application discloses a method for preparing graphene powder based on an oxidation-reduction method, and comprises the following steps: preparing graphene oxide, wherein the number of layers of the graphene oxide is less than or equal to 3; preparing graphene oxide dispersion liquid by using the graphene oxide; reducing, spray drying and secondary drying the graphene oxide dispersion liquid to obtain fluffy reduced graphene oxide powder; and high-temperature calcining the fluffy reduced graphene oxide powder to obtain graphene powder. The graphene prepared by the method makes up for the gap between the graphene powder on the market and the theoretical graphene conductivity, further improves the practical application value of the graphene, provides favorable support for realizing high energy density and higher fast-charging performance of lithium batteries, realizes macro preparation of the few-layer graphene powder, and meets the requirements of downstream applications.

Description

Technical Field

[0001] This invention relates to the field of thin-layer graphene material preparation, and more particularly to a method for preparing graphene powder based on redox method. Background Technology

[0002] Graphene is a material composed of carbon atoms through sp... 2 The two-dimensional, honeycomb-like layered structure formed by hybridization is the basic structural unit of other carbon materials. Since its discovery, it has been a research hotspot in the field of materials science due to its outstanding physicochemical properties.

[0003] Oligolayer graphene generally refers to graphene with fewer than 5 layers. Compared to multilayer graphene, oligolayer graphene is thinner and more flexible, exhibiting outstanding performance in nanoelectronic devices and composite materials. Adding oligolayer graphene to batteries can increase conductivity, thereby enhancing battery capacity and cycle life.

[0004] There are various methods for preparing graphene, including mechanical exfoliation, liquid phase exfoliation, chemical oxidation, crystal epitaxial growth, chemical vapor deposition, organic synthesis, and carbon nanotube exfoliation.

[0005] Mechanical exfoliation overcomes the inter-sheet forces in graphite by mechanical means and uses photoresist to separate the graphite, successfully obtaining single-layer graphene. Although this method can produce graphene with fewer layers than conventional mechanical exfoliation, it still struggles to precisely control the purity of graphene and has extremely low yields, making large-scale graphene production difficult. Currently, commercially available mechanical exfoliation methods for preparing graphene slurries typically use mills, homogenizers, and other equipment to break down and exfoliate the graphite. The resulting graphene material is generally ≥10 layers thick, classifying it as multilayer graphene. This method cannot produce few-layer or oligolayer graphene. Furthermore, these methods require the addition of small amounts of dispersants to stabilize the graphene during the breaking down and exfoliation process. These dispersants can have adverse effects in downstream lithium-ion battery applications, hindering the development of more advanced graphene materials.

[0006] Liquid-phase exfoliation involves using ultrasonic waves, heating, or other methods to exfoliate graphite, preparing single-layer or multi-layer graphene solutions. This method requires the addition of numerous dispersants during graphene preparation. These dispersants stabilize the graphene sheets in the solution. However, in downstream lithium-ion battery manufacturing, the dispersants on the graphene surface, acting as conductive agents, cannot be separated, resulting in dispersants remaining in the electrodes during positive and negative electrode assembly. The presence of these dispersants reduces the high-voltage withstand capability of the assembled battery. The fundamental reason is that dispersants are often high-molecular-weight or low-molecular-weight materials that decompose under high voltage and high current, producing gases and undergoing cyclic expansion and other adverse phenomena. Therefore, they are unsuitable for high-current charging and discharging. In today's fast-paced lifestyle, the conductive agents in this method are insufficient to meet the demands of fast charging.

[0007] Chemical vapor deposition (CVD) involves decomposing carbon-containing chemicals (such as methane) at high temperatures. The resulting carbon atoms are deposited on a substrate, where they combine to form graphene. This method can produce single-layer or even monolayer graphene materials. Transparent graphene films can be used in electronic touchscreens, sensors, transistors, and more. The main hurdle is how to peel the graphene from the substrate without damage or contamination, which remains a key challenge. Furthermore, CVD is not suitable for preparing graphene powder materials, and the resulting graphene cannot be used as a conductive agent in lithium-ion batteries.

[0008] Epitaxial growth, organic synthesis, and carbon nanotube exfoliation are all methods that can produce single-layer and few-layer graphene materials, but cost and large-scale production remain limiting factors.

[0009] The oxidation-reduction method involves chemically oxidizing and exfoliating graphene to obtain graphene oxide (GO) with a high monolayer ratio, and then reducing GO to obtain graphene. This method is the optimal route for preparing graphene powder with a high monolayer ratio. Summary of the Invention

[0010] To address the above problems, this invention provides a method for preparing oligolayer graphene, comprising the following steps:

[0011] A method for preparing oligolayer graphene powder, characterized by comprising the following steps:

[0012] S1: Prepare graphene oxide, wherein the graphene oxide satisfies the following conditions:

[0013] The graphene oxide dispersion with a concentration of 50 ppm has an absorption peak at 230 nm ≥ 2.0;

[0014] S2: Prepare a graphene oxide dispersion using the graphene oxide from step S1;

[0015] S3: Reduce the graphene oxide dispersion in step S2 to obtain a reduced graphene oxide dispersion, then perform spray drying and secondary drying to obtain reduced graphene oxide powder;

[0016] S4: The reduced graphene oxide powder obtained in step S3 is calcined at high temperature to obtain graphene powder.

[0017] Preferably, in step S1, the method for preparing graphene oxide is as follows:

[0018] S11: Mix graphite, potassium permanganate, and concentrated sulfuric acid evenly to obtain a slurry, and place it into a reaction vessel;

[0019] S12: Under conditions of 25℃-40℃, react for 3-6 hours to obtain graphene oxide reaction solution;

[0020] S13: Add water to the graphene oxide reaction solution in step S12 and stir;

[0021] S14: Add hydrogen peroxide until no more bubbles are produced, separate and purify to prepare graphene oxide.

[0022] Preferably, the number of graphene oxide layers is ≤3.

[0023] Preferably, the graphene oxide dispersion with a concentration of 50 ppm has an absorption peak of 2.0-3.5 at 230 nm.

[0024] Preferably, in step S11, the purity of the potassium permanganate is ≥99.9 wt%, the mass fraction of the concentrated sulfuric acid is 95-98 wt%, and the graphite carbon content is ≥99 wt%.

[0025] Preferably, the graphite is one of flake graphite, acidified graphite, or expanded graphite, and the flake diameter of the graphite is 200-5000 mesh, preferably 325-2000 mesh.

[0026] Preferably, in step S11, the temperature at which the graphite, potassium permanganate, and concentrated sulfuric acid are mixed is -5 to 10°C; more preferably, the temperature is 2 to 8°C.

[0027] Preferably, in step S11, the mass ratio of the graphite, potassium permanganate, and concentrated sulfuric acid mixture is 1:(3.0-6.0):(55.2-73.6); more preferably, the mass ratio is 1:(3.0-4.5):(60-70).

[0028] Preferably, in step S13, the volume of water added is 1-10 times the volume of the graphene oxide reaction liquid; more preferably, it is 1-3 times.

[0029] Preferably, in step S13, the temperature of the graphene oxide reaction solution after adding water is not higher than 75°C, and more preferably, the temperature is 55-75°C.

[0030] Preferably, in step S13, the stirring time is 0.5-2 hours; more preferably, the stirring time is 1-2 hours.

[0031] Preferably, in step S14, the hydrogen peroxide has a mass fraction of 30%.

[0032] Preferably, the separation is performed by filtering, vacuum filtering, or pressure filtering the reaction solution to which hydrogen peroxide has been added until no more bubbles are produced, to obtain a filter cake.

[0033] Preferably, the purification method is to wash the filter cake with a dilute acid solution.

[0034] Preferably, the dilute acid solution is one or more of hydrochloric acid, sulfuric acid, and nitric acid.

[0035] Preferably, the mass fraction of the dilute acid solution is 0.1-3%.

[0036] Preferably, the temperature of the stirring and washing is 45-80℃, and the number of washing cycles is 1-5.

[0037] Preferably, in step S2, the solid content of the dispersion is ≤3.5wt%; more preferably, the solid content is 1-3.5wt%.

[0038] Preferably, the viscosity of the dispersion is ≤10000 mPa·s; more preferably, the viscosity of the dispersion is 5000-10000 mPa·s.

[0039] Preferably, in step S3, the method for reducing the graphene oxide dispersion in step S2 is: to use a redox method for reduction.

[0040] Preferably, the reducing agent used in the redox method is one or more of an organic compound containing -NH2, a phenol or alcohol containing -OH, a metal hydride, or a hydrogen halide.

[0041] Preferably, the mass ratio of graphene oxide to reducing agent is 1:(0.01-0.5); more preferably, the mass ratio is 1:(0.05-0.3).

[0042] Preferably, the reduction temperature is 70-100℃ and the stirring reaction time is 5-12h; more preferably, the reduction temperature is 70-90℃ and the stirring reaction time is 6-10h.

[0043] Preferably, in step S3, the spray drying method is as follows: the reduced graphene oxide dispersion is dried using a spray drying device.

[0044] Preferably, the outlet temperature of the spray drying equipment is ≤78℃; more preferably, the temperature is 60-75℃.

[0045] Preferably, the water content of the spray-dried reduced graphene oxide is ≥5 wt%; more preferably, the water content is 5-15 wt%.

[0046] Preferably, in step S3, the secondary drying is performed by using an oven at a temperature of 100-300°C; more preferably, the temperature is 200-300°C.

[0047] Preferably, the tap density of the reduced graphene oxide powder after secondary drying is ≤0.1 g / cm³. 3 Further preferably, it is 0.005-0.09 g / cm³. 3 .

[0048] Preferably, in step S4, the high-temperature calcination temperature is 1000-1500℃ and the calcination time is 2-6h; more preferably, the high-temperature calcination temperature is 1000-1300℃ and the calcination time is 2-4h.

[0049] The present invention also protects an oligolayer graphene powder, which is prepared by the above preparation method; preferably, the graphene powder has ≤5 layers.

[0050] The working principle of this invention is as follows: GO raw materials are prepared in batches using an improved Hummers method. By controlling the oxidative synthesis method, the mesh size of the graphite raw material, the holding temperature during the synthesis process, and the purification temperature during GO purification, the obtained GO can be used to prepare oligolayer graphene materials. Subsequently, a thin layer of GO is obtained by reducing the concentration of GO in water. During reduction, the GO is weakly reduced to prevent the rGO obtained after weak reduction from folding and agglomeration caused by π-π stacking after reduction. After reduction with chemical reagents, a thin layer of rGO dispersion is obtained, at which point the rGO can be stably dispersed in water. After drying, rGO powder is obtained. At this point, simple drying would result in rGO agglomerates due to the surface tension of water. Therefore, the rGO solution is spray-dried to the micron level and then instantly dried. By controlling the spray drying flow rate and gas pressure, the particle size of rGO can be controlled, resulting in fluffy rGO powder with a high specific surface area, placing the rGO powder in a few-layer or oligolayer state. Finally, this oligolayer or oligolayer rGO is directly repaired at high temperature to obtain graphene powder with ≤5 layers. In the above process, by controlling the preparation of thin-layer rGO and fluffing the rGO powder, the rGO powder before high-temperature repair achieves a thin-layer effect. Subsequently, high-temperature repair is used to prepare oligolayer graphene powder, realizing the large-scale preparation of oligolayer graphene powder to meet the requirements of downstream applications.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] (1) The development of oligolayer graphene powder materials has made up for some of the gap between the conductivity of graphene powder on the market and that of theoretical graphene, and further enhanced the practical application value of graphene.

[0053] (2) It provides favorable support for lithium batteries to achieve high energy density and higher fast charging performance;

[0054] (3) Achieve large-scale preparation of oligolayer graphene powder to meet the requirements of downstream applications. Attached Figure Description

[0055] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0056] Figure 1 This is a schematic diagram of the graphene preparation method provided by the present invention;

[0057] Figure 2 This is an atomic force microscope image of GO prepared according to the preparation method of the present invention;

[0058] Figure 3 This is a scanning electron microscope image of graphene obtained by the preparation method according to an embodiment of the present invention;

[0059] Figure 4 This is a transmission electron microscope image of graphene obtained by the preparation method of the present invention.

[0060] Figure 5 This is a polarized light microscope image of the GO dispersion at a concentration of 50 ppm prepared according to the preparation method of Example 1 of the present invention.

[0061] Figure 6 This is a polarized light microscope image of the GO dispersion at a concentration of 50 ppm prepared according to the preparation method of Example 2 of the present invention;

[0062] Figure 7 This is a polarized light microscope image of the GO dispersion at a concentration of 50 ppm prepared according to the preparation method of Example 3 of the present invention;

[0063] Figure 8 This is a polarized light microscope image of the GO dispersion at a concentration of 50 ppm prepared by the preparation method of Example 4 of the present invention.

[0064] Figure 9 This is a polarized light microscope image of the GO dispersion prepared by the preparation method of Example 5 of the present invention at a concentration of 50 ppm;

[0065] Figure 10 This is a polarized light microscope image of the GO dispersion prepared by the preparation method of Comparative Example 1 according to the present invention at a concentration of 50 ppm.

[0066] Figure 11 This is a polarized light microscope image of the GO dispersion prepared by the preparation method of Comparative Example 2 according to the present invention at a concentration of 50 ppm.

[0067] Figure 12 This is a polarized light microscope image of the GO dispersion prepared by the preparation method of Comparative Example 3 according to the present invention at a concentration of 50 ppm.

[0068] Figure 13 This is a polarized light microscope image of the GO dispersion at a concentration of 50 ppm prepared according to the preparation method of Comparative Example 4 of the present invention. Detailed Implementation

[0069] To facilitate understanding of the present invention, a more complete description will be provided below. Preferred embodiments of the invention are given below. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0070] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0071] This document refers to numerical ranges, which, unless otherwise specified, are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between them. Furthermore, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0072] Unless otherwise specified, the temperature parameters in this document can be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows for temperature fluctuations within the precision range controlled by the instrument.

[0073] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0074] like Figure 1 This is a schematic diagram of the method for preparing oligolayer graphene provided by the present invention.

[0075] This invention provides a method for preparing oligolayer graphene, comprising the following steps:

[0076] (1) Preparation of GO.

[0077] GO itself needs to be easily dispersed in water, so the GO itself needs to have a relatively high monolayer ratio. At the same time, GO has a high affinity for water, so the raw material GO needs to have a high degree of oxidation and a high degree of exfoliation.

[0078] Graphene oxide can be synthesized using the Brodie method, Staudenmaier method, Hummers method, and their improved methods.

[0079] GO is now prepared using an improved Hummer method.

[0080] ① Mix graphite, potassium permanganate, and concentrated sulfuric acid evenly to obtain a slurry.

[0081] Under conditions of -5℃ to 10℃, preferably 2-8℃, concentrated sulfuric acid (95-98wt%), graphite raw material (C content ≥99wt%), and potassium permanganate (≥99.9wt%) are stirred and mixed for 0.5-2h. The graphite used can be one of flake graphite, acidified graphite, expanded graphite (worm powder), etc. The flake diameter of the graphite raw material is selected as 200-5000 mesh, preferably 325-2000 mesh. The concentrated sulfuric acid and graphite can be mixed first, and then potassium permanganate can be added, or the potassium permanganate and concentrated sulfuric acid can be mixed first, and then graphite can be added. When mixing, the mass ratio of graphite, potassium permanganate and concentrated sulfuric acid is 1:(3.0-6.0):(55.2-73.6), preferably 1:(3.0-4.5):(60-70).

[0082] The particle size of graphite raw materials is between 200 and 5000 mesh, which is easy to oxidize and intercalate within this range. If the particle size is too large, oxidation is likely to be incomplete; if the particle size is too small, for example, oxidizing graphite raw materials with a particle size of 5000 mesh will consume a large portion of the oxidant due to the numerous edges, and it will also be difficult to separate the materials.

[0083] ② Prepare the graphene oxide reaction solution.

[0084] After mixing, the temperature is increased to 25-40℃, and the mixture is stirred for 3-6 hours to obtain a graphene oxide reaction solution.

[0085] The reaction temperature is 25–40℃. Within this temperature range, the reaction is more likely to be complete. When the temperature is below 25℃, the oxidation intercalation will be incomplete, and a high monolayer ratio of GO cannot be obtained. When the temperature is above 40℃, dangerous situations such as explosions may occur during intercalation oxidation because the reaction activity is too high and the reaction is difficult to control.

[0086] When the reaction time is less than 3 hours, incomplete oxidation intercalation will occur, and GO with a high monolayer ratio cannot be obtained; if the reaction time is too long, efficiency will be reduced and resources will be wasted.

[0087] ③ Add water and hydrogen peroxide to the graphene oxide reaction solution to obtain graphene oxide slurry.

[0088] Add water to the reaction solution, controlling the material temperature to be no higher than 75℃, preferably 55-75℃. The volume of water added should be 1-10 times the original volume of the reaction solution, preferably 1-3 times. After adding water, stir for 0.5-2 hours, preferably 1-2 hours, and gradually add hydrogen peroxide (H2O2 mass fraction of 30%) until no more bubbles are produced.

[0089] When the reaction temperature exceeds 75°C, the materials in the reaction solution will agglomerate, and ultimately GO that is well dispersed in water cannot be obtained.

[0090] ④ Separate and purify to obtain GO.

[0091] The above reaction solution is filtered, vacuum filtered, or pressure filtered to obtain a graphene oxide filter cake. A dilute acid (including one or more of hydrochloric acid, sulfuric acid, nitric acid, etc., with a mass fraction concentration of 0.1%-3%) is added to the filter cake, and the mixture is stirred and washed. The temperature of the washing liquid is controlled at 45℃-80℃. The filtrate is then removed by filtration to obtain the filter cake. This washing process is repeated 1-5 times to obtain a moist GO filter cake. The GO filter cake is characterized using atomic force microscopy, such as... Figure 2 As shown in the diagram, GO is mostly in a low-level state.

[0092] When the washing temperature is below 45℃, the diffusion rate of ions in water is low, which is not conducive to purification efficiency. When the washing temperature is above 80℃, some functional groups on the GO surface will begin to detach, and the reduction of functional groups is not conducive to the subsequent dispersion of GO in water.

[0093] To select the GO raw material with the required low number of layers, the method used is to test the solubility of GO in water. Specifically, GO is dispersed in water to obtain a dispersion with a concentration of 50 ppm. The absorption peak value of the dispersion at 230 nm is measured using a UV-Vis (ultraviolet-visible absorption spectrometer). When the absorption peak value is ≥2.0, it meets the requirement of good water dispersion of GO to a low number of layers; preferably, the absorption peak value range is 2.0-3.5. In this invention, the number of GO layers after dispersion is ≤3.

[0094] This invention utilizes the dispersion behavior of GO in water. As the concentration of GO in water increases, the GO dispersion gradually transforms from isotropic to anisotropic. Simultaneously, when anisotropy occurs, the phase behavior of GO gradually transforms from a nematic phase to a lamellar phase. Therefore, the dispersion effect of GO in water can be observed using a polarizing microscope. A weak dispersion method was used to disperse the aqueous GO solution in deionized water at a concentration of 50 ppm. The mixture was stirred at 150 rpm for 10 minutes and then placed in a transparent sample cell with a thickness of 0.5 mm. When the polarizing microscope showed GO with a nematic phase texture and no other rich colors, it indicates that GO is easily peeled off, indicating a low layer count. In this invention, the number of GO layers after dispersion is ≤3.

[0095] In this invention, the number of GO layers refers to the number of layers when GO is dispersed in a dispersion with a concentration of 50 ppm.

[0096] (2) Preparation of GO dispersion.

[0097] GO is prepared into an aqueous dispersion with a solid content ≤3.5wt%, preferably 1-3.5wt%. The GO dispersion is prepared into a dispersion with a viscosity ≤10000mPa·s, preferably 5000-10000mPa·s, by means of stirring dispersion, homogenization dispersion, microfluidization, etc., to ensure that GO can be uniformly dispersed in the aqueous solution.

[0098] The solid content mentioned above refers to the percentage by mass of the emulsion or coating remaining after drying under specified conditions.

[0099] When the solid content of the GO dispersion is ≤3.5wt%, the GO dispersion can remain stable. In subsequent steps, after being weakly reduced, it can still be stably dispersed in water without agglomeration. When the solid content of the GO dispersion is higher than 3.5wt%, the viscosity of the GO dispersion will be too high. After adding the reducing agent, the reducing agent will dissolve and cause uneven reduction due to the poor fluidity of the slurry.

[0100] (3) Reduce the GO dispersion.

[0101] Add a chemical reducing agent to the above GO dispersion, with a GO solid to chemical reducing agent mass ratio of 1:(0.01-0.5), preferably 1:(0.05-0.3); stir the reaction at a temperature of 70-100℃ for 5-12 hours to obtain a black liquid, preferably at a temperature of 70-90℃ and a stirring reaction time of 6-10 hours.

[0102] When the mass ratio of GO solid to chemical reducing agent, temperature, and stirring time are below the above ranges, the GO reduction will not meet the requirements of the subsequent high-temperature repair. During the high-temperature repair process, expansion and explosion will occur, and the thermal repair efficiency will also be reduced. When the mass ratio of GO solid to chemical reducing agent, temperature, and stirring time are above the above ranges, rGO will agglomerate, which will lead to the risk of continuous drying and overheating in the subsequent spray drying.

[0103] Among them, the chemical reducing agent is an organic compound containing -NH2, an alcohol and phenol containing -OH (monohydrin, polyhydrin, monohydric phenol, polyphenol), a metal hydride (NaBH4, LiAlH4, etc.), a hydrogen halide (hydroiodic acid, hydrobromic acid), etc., and can be one or a mixture of the above chemical reducing agents. In actual production, it can be selected according to actual needs.

[0104] (4) The black liquid is spray-dried (i.e. fluffing treatment) to obtain fluffy rGO powder.

[0105] The aforementioned black liquid is dried using a spray drying device. The spray drying process varies depending on the feed rate and the feed speed. The outlet temperature is controlled at ≤78℃, with a preferred temperature of 60-75℃. Meanwhile, in order to minimize the agglomeration of rGO (reduced graphene oxide), the feed speed is appropriately controlled according to the specifications of the equipment used.

[0106] rGO is atomized into micron-sized particles by spray drying equipment and then dried instantly. The particle size of rGO is controlled by controlling the flow rate and gas pressure of spray drying, thereby obtaining a fluffy rGO powder material with a high specific surface area, so that the rGO powder is in a oligolayer or few-layer state.

[0107] The feed rate can be adjusted according to the solid content of the material. The higher the solid content of the rGO solution, the lower the feed rate, so as to further ensure that the number of agglomerated layers of the dried rGO is smaller, thereby making the specific surface area of ​​the obtained rGO larger and the number of graphene layers obtained after calcination smaller.

[0108] The nozzles of spray drying equipment can be centrifugal or two-fluid.

[0109] If rGO is thoroughly dried, the apparent tap density of the sample will be less than 0.05 g / cc, resulting in extremely low yield when using a cyclone separator in a spray dryer. To maximize the rGO yield, it is necessary to maintain a certain moisture content during drying to increase its density. Therefore, the drying discharge temperature of rGO should be below 100℃, preferably ≤78℃, and more preferably 60-75℃. The rGO powder obtained by the above spray drying should have a moisture content ≥5wt%, preferably 5-15wt%. This moisture content level is also necessary to improve the yield. If the drying degree is higher than this, due to the large specific surface area and small particle size of rGO, the yield through the cyclone separator in the spray dryer will be very low, less than 50%, which is not conducive to the large-scale preparation of rGO powder.

[0110] (5) The spray-dried rGO powder is dried a second time.

[0111] The above-mentioned fluffy rGO powder is placed in an oven and dried at a temperature of 100-300℃, preferably 200-300℃, until constant weight is achieved.

[0112] The spray drying temperature of the above-mentioned rGO is below 100℃, and the moisture content of the rGO powder obtained by spray drying is ≥5%. Therefore, it is necessary to perform secondary drying to remove moisture before entering the high-temperature repair process.

[0113] The tap density of the reduced graphene oxide powder after secondary drying is ≤0.1 g / cm³. 3 Further preferably, it is 0.005-0.09 g / cm³. 3 .

[0114] After spray drying and secondary drying, the reduced graphene oxide powder is in a fluffy state. Within the above-mentioned tap density range, the number of reduced graphene oxide layers is very low, and excessive agglomeration will not occur during high-temperature graphitization, providing a basis for preparing graphene powder with no more than 5 layers.

[0115] Tapped density refers to the mass per unit volume of powder in a container after it has been tapped under specified conditions.

[0116] (6) High-temperature repair of fluffy rGO powder to obtain graphene powder.

[0117] Loose rGO powder is calcined in a high-temperature furnace under inert conditions, with the temperature increased to 1000–1500°C at a heating rate of 5°C / min, and heat-treated for 2–6 hours to obtain oligolayer graphene powder material; preferably, the high-temperature calcination temperature is 1000–1300°C, and the calcination time is 2–4 hours. Figure 3 , Figure 4 As shown.

[0118] The oligolayer graphene powder prepared by the above method was characterized and tested. The test methods are as follows:

[0119] The test method for the mass fraction of elements C and O is: DB32 / T 3595-2019.

[0120] The testing method for ID / IG is: Q / NGSIC 012-2020.

[0121] The test method for specific surface area (BET) is GB / T 7702.20-1997.

[0122] The test method for oil absorption value is GBT 3780.2-2007.

[0123] The conductivity testing method is described in Sasha Stankovich, Dmitriy A. Dikin, et al., Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide, Carbon 45 (2007): [lines 1558-1565]. The conductivity of oligolayer graphene powder was tested using the method described in this literature.

[0124] The test results are shown in Table 1.

[0125] Table 1 Performance data of the oligolayer graphene powder prepared by the method of the present invention

[0126]

[0127] As shown in Table 1, C (wt%) ≥ 97.4% and O (wt%) ≤ 0.05%, indicating that almost all GO raw materials were reduced to form graphene; ID / IG ≤ 1.12 indicates that the defect degree of the graphene after thermal repair is low; BET ≥ 750m 2 The / g indicates that the graphene prepared by this method has a large specific surface area, BET≥750m². 2 The / g indicates that the graphene prepared by this method has a relatively large specific surface area. Furthermore, based on the theoretical specific surface area calculation for graphene, a specific surface area of ​​750m² is considered optimal. 2 At a density of / g, the average number of graphene layers is around 3, indicating that the graphene powder has a BET ≥ 750m. 2 The graphene content is / g, indicating it is oligolayer graphene; the oil absorption value is between 3500 and 5500 ml / 100g, indicating that the graphene powder material has a large specific surface area, and the larger the oil absorption value, the larger the specific surface area, and vice versa; the electrical conductivity range is 10. 5 ~10 6 The S / m ratio indicates that the prepared oligolayer graphene powder has good electrical conductivity.

[0128] The present invention will be further described below with reference to specific embodiments.

[0129] Example 1:

[0130] A method for preparing graphene powder based on redox method:

[0131] At 2℃, 1104g of concentrated sulfuric acid (98wt%) and 20g of 325-mesh graphite raw material (flake graphite) (C content ≥99wt%) were stirred and mixed for 30min. Then, 80g of potassium permanganate (99.9wt%) was slowly added and stirred. After mixing, the temperature was increased to 30℃ and stirred for 6h to obtain a graphene oxide reaction solution. 1800mL of water was added to the reaction solution, and the material temperature was controlled not to exceed 75℃. After adding water, the mixture was stirred for 30min, and hydrogen peroxide (H2O2 mass fraction 30%) was gradually added until no more bubbles were generated. The solid was then separated and washed with a 0.27% mass fraction dilute sulfuric acid solution at 65℃. The solid was then separated again. This washing process was repeated 3 times to obtain a purified GO paste.

[0132] The GO paste was dispersed in deionized water to prepare a dispersion with a concentration of 50 ppm. After sonication for 5-10 minutes, the absorption peak of the GO solution at 230 nm was measured to be 2.01.

[0133] In addition, the GO paste was dispersed in deionized water to prepare a GO dispersion with a concentration of 50 ppm. The dispersion was stirred at 150 rpm for 10 min and then placed in a 0.5 mm thick transparent sample cell for characterization using a polarizing microscope. Figure 5 As shown.

[0134] 30g of GO (dry weight) was dispersed in 1.97kg of deionized water by stirring or homogenization to obtain a uniform GO dispersion with a solid content of 1.5%. 6g of vitamin C was added to the dispersion, and the mixture was stirred thoroughly until homogeneous. The mixture was then heated to 85℃ and stirred continuously for 6 hours to obtain a black liquid.

[0135] The obtained black liquid was dried using a spray dryer. 2 kg of the black liquid was fed into the sprayer using a peristaltic pump at a feed rate of 6 kg / h. The inlet temperature was 220°C and the outlet temperature was 75°C, resulting in fluffy rGO powder.

[0136] The loose rGO powder was dried twice to constant weight using an oven at 230℃. After drying, it was placed in a high-temperature calcination furnace and annealed at 1000℃ for 6 hours under nitrogen atmosphere at a heating rate of 5℃ / min to obtain graphene powder material. The material was then characterized, and the results are shown in Table 2.

[0137] Example 2:

[0138] A method for preparing graphene powder based on redox method:

[0139] At 5℃, 1288g of concentrated sulfuric acid (98wt%) and 20g of 1000-mesh graphite raw material (flake graphite) (C content ≥99wt%) were stirred and mixed for 30min. Then, 115g of potassium permanganate (99.9wt%) was slowly added and stirred. After mixing, the temperature was increased to 38℃ and stirred for 4h to obtain a graphene oxide reaction solution. 1800mL of water was added to the reaction solution, and the material temperature was controlled not to exceed 75℃. After adding water, the mixture was stirred for 60min, and hydrogen peroxide (H2O2 mass fraction 30%) was gradually added until no more bubbles were generated. The solid was then separated and washed with a 2.5% mass fraction dilute sulfuric acid solution at 45℃. The solid was then separated again. This washing process was repeated 4 times to obtain a purified GO paste.

[0140] The GO paste was dispersed in deionized water to prepare a dispersion with a concentration of 50 ppm. After sonication for 5-10 minutes, the absorption peak of the GO solution at 230 nm was measured to be 2.20.

[0141] In addition, the GO paste was dispersed in deionized water to prepare a GO dispersion with a concentration of 50 ppm. The dispersion was stirred at 150 rpm for 10 min and then placed in a 0.5 mm thick transparent sample cell for characterization using a polarizing microscope. Figure 6 As shown.

[0142] 30g of GO (dry weight) was dispersed in 2.97kg of deionized water by stirring or homogenization to obtain a uniform GO dispersion with a solid content of 1%. 6g of vitamin C was added to the dispersion, and the mixture was stirred thoroughly until homogeneous. The mixture was then heated to 85℃ and stirred continuously for 6 hours to obtain a black liquid.

[0143] The obtained black liquid was dried using a spray drying device. 3 kg of the black liquid was fed into the machine using a peristaltic pump at a feed rate of 10 kg / h, with an inlet temperature of 200°C and an outlet temperature of 72°C, to obtain fluffy rGO powder.

[0144] The fluffy rGO powder was dried twice to constant weight using an oven at 100℃. After drying, it was placed in a high-temperature calcination furnace and annealed at 1300℃ for 3 hours under nitrogen atmosphere at a heating rate of 5℃ / min to obtain graphene powder material. The material was then characterized, and the results are shown in Table 2.

[0145] Example 3:

[0146] A method for preparing graphene powder based on redox method:

[0147] At 5℃, 1288g of concentrated sulfuric acid (98wt%) and 20g of 5000-mesh graphite raw material (expanded graphite) (C content ≥99wt%) were stirred and mixed for 30min. Then, 120g of potassium permanganate (99.9wt%) was slowly added and stirred. After mixing, the temperature was increased to 35℃ and stirred for 3h to obtain a graphene oxide reaction solution. 2700mL of water was added to the reaction solution, and the material temperature was controlled not to exceed 65℃. After adding water, the mixture was stirred for 120min, and hydrogen peroxide (H2O2 mass fraction 30%) was gradually added until no more bubbles were generated. The solid was then separated and washed with a 0.5% mass fraction dilute hydrochloric acid solution at 50℃. The solid was then separated again. This washing process was repeated 4 times to obtain a purified GO paste.

[0148] The GO paste was dispersed in deionized water to prepare a dispersion with a concentration of 50 ppm. After sonication for 5-10 minutes, the absorption peak of the GO solution at 230 nm was measured to be 2.18.

[0149] In addition, the GO paste was dispersed in deionized water to prepare a GO dispersion with a concentration of 50 ppm. The dispersion was stirred at 150 rpm for 10 min and then placed in a 0.5 mm thick transparent sample cell for characterization using a polarizing microscope. Figure 7 As shown.

[0150] 30g of GO (dry weight) was dispersed in 9.97kg of deionized water by stirring or homogenization to obtain a uniform GO dispersion with a solid content of 0.3%. 4.5g of vitamin C was added to the dispersion, and the mixture was stirred thoroughly until homogeneous. The mixture was then heated to 85℃ and stirred continuously for 6 hours to obtain a black liquid.

[0151] The obtained black liquid was dried using a spray drying device. 10 kg of the black liquid was fed into the machine using a peristaltic pump at a feed rate of 8.3 kg / h, with the inlet temperature at 180°C and the outlet temperature at 73°C, to obtain fluffy rGO powder.

[0152] The fluffy rGO powder was dried twice to constant weight using an oven at 150℃. After drying, it was placed in a high-temperature calcination furnace and annealed at 1500℃ for 2 hours under nitrogen atmosphere at a heating rate of 5℃ / min to obtain graphene powder material. The material was then characterized, and the results are shown in Table 2.

[0153] Example 4:

[0154] A method for preparing graphene powder based on redox method:

[0155] At 5℃, 1470g of concentrated sulfuric acid (98wt%) and 20g of 500-mesh graphite raw material (expanded graphite) (C content ≥99wt%) were stirred and mixed for 30min. Then, 75g of potassium permanganate (99.9wt%) was slowly added and stirred. After mixing, the temperature was increased to 40℃ and stirred for 2.5h to obtain a graphene oxide reaction solution. 2000mL of water was added to the reaction solution, and the material temperature was controlled not to exceed 65℃. After adding water, the mixture was stirred for 60min, and hydrogen peroxide (H2O2 mass fraction 30%) was gradually added until no more bubbles were generated. The solid was then separated and washed with a 1.5% hydrochloric acid solution at 70℃. The solid was then separated again. This washing process was repeated 4 times to obtain a purified GO paste.

[0156] The GO paste was dispersed in deionized water to prepare a dispersion with a concentration of 50 ppm. After sonication for 5-10 minutes, the absorption peak of the GO solution at 230 nm was measured to be 2.05.

[0157] In addition, the GO paste was dispersed in deionized water to prepare a GO dispersion with a concentration of 50 ppm. The dispersion was stirred at 150 rpm for 10 min and then placed in a 0.5 mm thick transparent sample cell for characterization using a polarizing microscope. Figure 8 As shown.

[0158] 10g of dry GO was dispersed in 9.99kg of deionized water by stirring or homogenization to obtain a uniform GO dispersion with a solid content of 0.1%. 2g of hydrazine hydrate was added to the dispersion, and the mixture was stirred thoroughly until homogeneous. The mixture was then heated to 95℃ and stirred for another 6 hours to obtain a black liquid.

[0159] The obtained black liquid was dried using a spray drying device. 10 kg of the black liquid was fed into the machine using a peristaltic pump at a feed rate of 8.3 kg / h, with an inlet temperature of 170°C and an outlet temperature of 68°C, to obtain fluffy rGO powder.

[0160] The fluffy rGO powder was dried twice to constant weight using an oven at 200℃. After drying, it was placed in a high-temperature calcination furnace and annealed at 1100℃ for 5 hours under nitrogen atmosphere at a heating rate of 5℃ / min to obtain graphene powder material. The material was then characterized, and the results are shown in Table 2.

[0161] Example 5:

[0162] A method for preparing graphene powder based on redox method:

[0163] At -5℃, 1470g of concentrated sulfuric acid (98wt%) and 20g of 500-mesh graphite raw material (expanded graphite) (C content ≥99wt%) were stirred and mixed for 60min. Then, 75g of potassium permanganate (99.9wt%) was slowly added and stirred. After mixing, the temperature was increased to 25℃ and stirred for 5h to obtain a graphene oxide reaction solution. 2000mL of water was added to the reaction solution, and the material temperature was controlled not to exceed 65℃. After adding water, the mixture was stirred for 90min, and hydrogen peroxide (H2O2 mass fraction 30%) was gradually added until no more bubbles were generated. The solid was then separated and washed with 0.1% hydrochloric acid solution at 80℃. The solid was then separated again. This washing process was repeated twice to obtain a purified GO paste.

[0164] The GO paste was dispersed in deionized water to prepare a dispersion with a concentration of 50 ppm. After sonication for 5-10 minutes, the absorption peak of the GO solution at 230 nm was measured to be 2.08.

[0165] In addition, the GO paste was dispersed in deionized water to prepare a GO dispersion with a concentration of 50 ppm. The dispersion was stirred at 150 rpm for 10 min and then placed in a 0.5 mm thick transparent sample cell for characterization using a polarizing microscope. Figure 9 As shown.

[0166] 350 g of GO (dry weight) was dispersed in 9.65 kg of deionized water by stirring or homogenization to obtain a uniform GO dispersion with a solid content of 3.5%. 3.5 g of hydrazine hydrate was added to the dispersion, and the mixture was stirred thoroughly until homogeneous. The mixture was then heated to 70°C and stirred for 12 hours to obtain a black liquid.

[0167] The obtained black liquid was dried using a spray drying device. 10 kg of the black liquid was fed into the device using a peristaltic pump at a feed rate of 5 kg / h. The inlet temperature was 170°C and the outlet temperature was 65°C, resulting in fluffy rGO powder.

[0168] The fluffy rGO powder was dried twice to constant weight using an oven at 300℃. After drying, it was placed in a high-temperature calcination furnace and annealed at 1500℃ for 2 hours under nitrogen atmosphere at a heating rate of 5℃ / min to obtain graphene powder material. The material was then characterized, and the results are shown in Table 2.

[0169] Comparative Example 1:

[0170] A method for preparing graphene powder:

[0171] At 3℃, 1470g of concentrated sulfuric acid (98wt%) and 20g of 150-mesh graphite raw material (flake graphite) (C content ≥99wt%) were stirred and mixed for 30min. Then, 50g of potassium permanganate (99.9wt%) was slowly added and stirred. After mixing, the temperature was increased to 30℃ and stirred for 4h to obtain a graphene oxide reaction solution. 2000mL of water was added to the reaction solution, and the material temperature was controlled not to exceed 75℃. After adding water, the mixture was stirred for 30min, and hydrogen peroxide (H2O2 mass fraction 30%) was gradually added until no more bubbles were generated. The solid was then separated and washed with a 0.75% mass fraction dilute hydrochloric acid solution at 50℃. The solid was then separated again. This washing process was repeated 4 times to obtain a purified GO paste.

[0172] The GO paste was dispersed in deionized water to prepare a dispersion with a concentration of 50 ppm. After sonication for 5-10 minutes, the absorption peak of the GO solution at 230 nm was measured to be 1.52.

[0173] In addition, the GO paste was dispersed in deionized water to prepare a GO dispersion with a concentration of 50 ppm. The dispersion was stirred at 150 rpm for 10 min and then placed in a 0.5 mm thick transparent sample cell for characterization using a polarizing microscope. Figure 10 As shown.

[0174] 30g of dry GO was dispersed in 9.97kg of deionized water by stirring or homogenization to obtain a uniform GO dispersion with a solid content of 0.3%. 9g of hydrazine hydrate was added to the dispersion, stirred thoroughly until homogeneous, heated to 95℃, and the reaction was continued at this temperature with stirring for 6 hours to obtain a black liquid.

[0175] The obtained black liquid was dried using a spray drying device. 10 kg of the black liquid was fed into the machine using a peristaltic pump at a feed rate of 8.3 kg / h, with an inlet temperature of 170°C and an outlet temperature of 68°C, to obtain fluffy rGO powder.

[0176] The fluffy rGO powder was dried twice to constant weight using an oven at 200℃. After drying, it was placed in a high-temperature calcination furnace and annealed at 1300℃ for 3 hours under nitrogen atmosphere at a heating rate of 5℃ / min to obtain graphene powder material. The material was then characterized, and the results are shown in Table 2.

[0177] Comparative Example 2:

[0178] A method for preparing graphene powder:

[0179] At 3℃, 1470g of concentrated sulfuric acid (98wt%) and 20g of 325-mesh graphite raw material (flake graphite) (C content ≥99wt%) were stirred and mixed for 30min. Then, 75g of potassium permanganate (99.9wt%) was slowly added and stirred. After mixing, the temperature was increased to 30℃ and stirred for 4h to obtain a graphene oxide reaction solution. 1800mL of water was added to the reaction solution, and the material temperature was controlled at 90℃. After adding water, the mixture was stirred for 30min, and hydrogen peroxide (H2O2 mass fraction 30%) was gradually added until no more bubbles were generated. The solid was then separated and washed with a 1% mass fraction dilute hydrochloric acid solution at 75℃. The solid was then separated again. This washing process was repeated 4 times to obtain a purified GO paste.

[0180] The GO paste was dispersed in deionized water to prepare a dispersion with a concentration of 50 ppm. After sonication for 5-10 minutes, the absorption peak of the GO solution at 230 nm was measured to be 1.67.

[0181] In addition, the GO paste was dispersed in deionized water to prepare a GO dispersion with a concentration of 50 ppm. The dispersion was stirred at 150 rpm for 10 min and then placed in a 0.5 mm thick transparent sample cell for characterization using a polarizing microscope. Figure 11 As shown.

[0182] 30g of dry GO was dispersed in 9.97kg of deionized water by stirring or homogenization to obtain a uniform GO dispersion with a solid content of 0.3%. 9g of hydrazine hydrate was added to the dispersion, stirred thoroughly until homogeneous, heated to 95℃, and the reaction was continued at this temperature with stirring for 6 hours to obtain a black liquid.

[0183] The obtained black liquid was dried using a spray drying device. 10 kg of the black liquid was fed into the machine using a peristaltic pump at a feed rate of 8.3 kg / h, with an inlet temperature of 170°C and an outlet temperature of 68°C, to obtain fluffy rGO powder.

[0184] The loose rGO powder was dried twice to constant weight using an oven at 200℃. After drying, it was placed in a high-temperature calcination furnace and annealed at 1300℃ for 3 hours under nitrogen atmosphere at a heating rate of 5℃ / min to obtain graphene powder material. The material was then characterized, and the results are shown in Table 2.

[0185] Comparative Example 3:

[0186] A method for preparing graphene powder:

[0187] At 3℃, 1470g of concentrated sulfuric acid (98wt%) and 20g of 500-mesh graphite raw material (expanded graphite) (C content ≥99wt%) were stirred and mixed for 30min. Then, 75g of potassium permanganate (99.9wt%) was slowly added and stirred to mix. After mixing, the temperature was increased to 30℃ and stirred for 4h to obtain a graphene oxide reaction solution. 1800mL of water was added to the reaction solution, and the material temperature was controlled not to exceed 75℃. After adding water, the mixture was stirred for 30min, and hydrogen peroxide (H2O2 mass fraction 30%) was gradually added until no more bubbles were generated. The solid was then separated and washed with a 0.75% mass fraction dilute hydrochloric acid solution at 65℃. The solid was then separated again. This washing process was repeated 4 times to obtain a purified GO paste.

[0188] The GO paste was dispersed in deionized water to prepare a dispersion with a concentration of 50 ppm. After sonication for 5-10 minutes, the absorption peak of the GO solution at 230 nm was measured to be 2.07.

[0189] In addition, the GO paste was dispersed in deionized water to prepare a GO dispersion with a concentration of 50 ppm. The dispersion was stirred at 150 rpm for 10 min and then placed in a 0.5 mm thick transparent sample cell for characterization using a polarizing microscope. Figure 12 As shown.

[0190] 10g of GO (dry weight) was dispersed in 9.99kg of deionized water by stirring or homogenization to obtain a uniform GO dispersion with a solid content of 0.3%. 3g of hydrazine hydrate was added to the dispersion, and the mixture was stirred thoroughly until homogeneous. The mixture was then heated to 95℃ and stirred for another 6 hours to obtain a black liquid.

[0191] The obtained black liquid was separated to obtain a black rGO solid paste, which was then dried in an oven at 200℃. After drying, it was placed in a high-temperature calcination furnace and heated to 1300℃ under nitrogen atmosphere at a heating rate of 5℃ / min for 3 hours to obtain graphene powder material. The powder was then characterized, and the results are shown in Table 2.

[0192] Comparative Example 4:

[0193] A method for preparing graphene powder:

[0194] At 3℃, 1470g of concentrated sulfuric acid (98wt%) and 20g of 500-mesh graphite raw material (expanded graphite) (C content ≥99wt%) were stirred and mixed for 30min. Then, 75g of potassium permanganate (99.9wt%) was slowly added and stirred to mix. After mixing, the temperature was increased to 80℃ and stirred for 4h to obtain a graphene oxide reaction solution. 1800mL of water was added to the reaction solution, and the material temperature was controlled not to exceed 75℃. After adding water, the mixture was stirred for 30min, and hydrogen peroxide (H2O2 mass fraction 30%) was gradually added until no more bubbles were generated. The solid was then separated and washed with a 0.75% mass fraction dilute hydrochloric acid solution at 65℃. The solid was then separated again. This washing process was repeated 4 times to obtain a purified GO paste.

[0195] The GO paste was dispersed in deionized water to prepare a dispersion with a concentration of 50 ppm. After sonication for 5-10 minutes, the absorption peak of the GO solution at 230 nm was measured to be 1.69.

[0196] In addition, the GO paste was dispersed in deionized water to prepare a GO dispersion with a concentration of 50 ppm. The dispersion was stirred at 150 rpm for 10 min and then placed in a 0.5 mm thick transparent sample cell for characterization using a polarizing microscope. Figure 13 As shown.

[0197] 30g of dry GO was dispersed in 9.97kg of deionized water by stirring or homogenization to obtain a uniform GO dispersion with a solid content of 0.3%. 9g of hydrazine hydrate was added to the dispersion, stirred thoroughly until homogeneous, heated to 95℃, and the reaction was continued at this temperature with stirring for 6 hours to obtain a black liquid.

[0198] The obtained black liquid was dried using a spray drying device. 10 kg of the black liquid was fed into the machine using a peristaltic pump at a feed rate of 8.3 kg / h, with an inlet temperature of 170°C and an outlet temperature of 73°C, to obtain fluffy rGO powder.

[0199] The loose rGO powder was dried twice to constant weight using an oven at 150℃. After drying, it was placed in a high-temperature calcination furnace and annealed at 1000℃ for 6 hours under nitrogen atmosphere at a heating rate of 5℃ / min to obtain graphene powder material. The material was then characterized, and the results are shown in Table 2.

[0200] Table 2. Performance data of graphene prepared in the examples and comparative examples.

[0201]

[0202] In the GO synthesis process, the mesh size of the raw material graphene, the oxidation washing temperature, and the drying method directly affect the specific surface area and conductivity of the obtained graphene material. Therefore, only under the combined effect of specific conditions can oligolayer graphene materials be prepared.

[0203] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0204] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing graphene powder based on redox reaction, characterized in that, Includes the following steps: S1: Prepare graphene oxide, wherein the graphene oxide satisfies the following conditions: The absorption peak value of the graphene oxide dispersion with a concentration of 50 ppm at 230 nm is ≥2.

0. S2: Prepare a graphene oxide dispersion using the graphene oxide from step S1; S3: Reduce the graphene oxide dispersion obtained in step S2 to obtain a reduced graphene oxide dispersion, and then perform spray drying and secondary drying to obtain reduced graphene oxide powder. S4: The reduced graphene oxide powder obtained in step S3 is calcined at high temperature to obtain graphene powder. In step S3, the method for reducing the graphene oxide dispersion in step S2 is as follows: reduction is carried out by redox method; the mass ratio of graphene oxide to reducing agent is 1:(0.01-0.5); the temperature during reduction is 70-100℃, and the stirring reaction time is 5-12h. In step S3, the spray drying method is as follows: the reduced graphene oxide dispersion is dried using a spray drying device; the outlet temperature of the spray drying device is ≤78℃; and the water content of the spray-dried reduced graphene oxide is ≥5wt%.

2. The preparation method according to claim 1, characterized in that, In step S1, the method for preparing graphene oxide is as follows: S11: Mix graphite, potassium permanganate, and concentrated sulfuric acid evenly to obtain a slurry, and place it into a reaction vessel; S12: Under conditions of 25℃-40℃, react for 3-6 hours to obtain graphene oxide reaction solution; S13: Add water to the graphene oxide reaction solution in step S12 and stir; S14: Add hydrogen peroxide until no more bubbles are produced, separate and purify to prepare graphene oxide.

3. The preparation method according to claim 1, characterized in that, The number of graphene oxide layers is ≤3.

4. The preparation method according to claim 1, characterized in that, The graphene oxide dispersion with a concentration of 50 ppm has an absorption peak of 2.0-3.5 at 230 nm.

5. The preparation method according to claim 2, characterized in that, In step S11, the mass fraction of potassium permanganate is ≥99.9 wt%, the mass fraction of concentrated sulfuric acid is 95-98 wt%, and the carbon content of graphite is ≥99 wt%.

6. The preparation method according to claim 2, characterized in that, The graphite is one of flake graphite, acidified graphite, or expanded graphite, and the flake diameter of the graphite is 200-5000 mesh.

7. The preparation method according to claim 2, characterized in that, The flake size of graphite ranges from 325 to 2000 mesh.

8. The preparation method according to claim 2, characterized in that, The temperature at which the graphite, potassium permanganate, and concentrated sulfuric acid are mixed is -5 to 10°C.

9. The preparation method according to claim 2, characterized in that, The temperature at which the graphite, potassium permanganate, and concentrated sulfuric acid are mixed is 2~8℃.

10. The preparation method according to claim 2, characterized in that, In step S11, the mass ratio of the graphite, potassium permanganate, and concentrated sulfuric acid mixture is 1:(3.0-6.0):(55.2-73.6).

11. The preparation method according to claim 2, characterized in that, In step S11, the mass ratio of the graphite, potassium permanganate, and concentrated sulfuric acid is 1:(3.0-4.5):(60-70).

12. The preparation method according to claim 2, characterized in that, In step S13, the volume of water added is 1-10 times the volume of the graphene oxide reaction liquid.

13. The preparation method according to claim 2, characterized in that, In step S13, the volume of water added is 1-3 times the volume of the graphene oxide reaction liquid.

14. The preparation method according to claim 2, characterized in that, The temperature of the graphene oxide reaction solution after adding water should not exceed 75℃.

15. The preparation method according to claim 2, characterized in that, The temperature of the graphene oxide reaction solution after adding water is 55-75℃.

16. The preparation method according to claim 2, characterized in that, The stirring time is 0.5-2 hours.

17. The preparation method according to claim 2, characterized in that, The stirring time is 1-2 hours.

18. The preparation method according to claim 2, characterized in that, In step S14, the hydrogen peroxide has a mass fraction of 30%.

19. The preparation method according to claim 2, characterized in that, The separation process involves filtering, vacuum filtering, or pressure filtering the reaction solution containing added hydrogen peroxide until no more bubbles are produced, to obtain a filter cake.

20. The preparation method according to claim 2, characterized in that, The purification method is as follows: the filter cake is washed with a dilute acid solution.

21. The preparation method according to claim 20, characterized in that, The dilute acid solution is one or more of hydrochloric acid, sulfuric acid, and nitric acid.

22. The preparation method according to claim 20, characterized in that, The mass fraction of the dilute acid solution is 0.1-3%.

23. The preparation method according to claim 2, characterized in that, The temperature for stirring and washing is 45-80℃, and the number of washes is 1-5.

24. The preparation method according to claim 1, characterized in that, In step S2, the solid content of the dispersion is ≤3.5wt%.

25. The preparation method according to claim 1, characterized in that, In step S2, the solid content of the dispersion is 1-3.5 wt%.

26. The preparation method according to claim 1, characterized in that, The viscosity of the dispersion is ≤10000mPa·s.

27. The preparation method according to claim 1, characterized in that, The viscosity of the dispersion is 5000-10000 mPa·s.

28. The preparation method according to claim 1, characterized in that, The reducing agent used in the redox method is one or more of the following: organic compounds containing -NH2, phenols and alcohols containing -OH, metal hydrides, or hydrogen halides.

29. The preparation method according to claim 1, characterized in that, The mass ratio of graphene oxide to reducing agent is 1:(0.05-0.3).

30. The preparation method according to claim 1, characterized in that, The reduction temperature is 70-90℃, and the stirring reaction time is 6-10h.

31. The preparation method according to claim 1, characterized in that, The outlet temperature of the spray drying equipment is 60-75℃.

32. The preparation method according to claim 1, characterized in that, The water content of the spray-dried reduced graphene oxide is 5-15 wt%.

33. The preparation method according to claim 1, characterized in that, The secondary drying method is as follows: drying is performed using an oven at a temperature of 100-300℃.

34. The preparation method according to claim 1, characterized in that, The temperature is 200-300℃.

35. The preparation method according to claim 1, characterized in that, The tap density of the reduced graphene oxide powder obtained after secondary drying is ≤0.1 g / cm³. 3 .

36. The preparation method according to claim 1, characterized in that, The tap density of the reduced graphene oxide powder obtained after secondary drying is 0.005-0.09 g / cm³. 3 .

37. The preparation method according to claim 1, characterized in that, In step S4, the high-temperature calcination temperature is 1000-1500℃, and the calcination time is 2-6h.

38. The preparation method according to claim 1, characterized in that, The high-temperature calcination temperature is 1000-1300℃, and the calcination time is 2-4 hours.

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