Reduced graphene oxide powder

Abstract

The application provides a reduced graphene oxide powder, which is obtained through carbonization after twice oxidation-reduction processes. After one-time low-degree oxidation-reduction and secondary high-degree oxidation, large-diameter graphene is inserted deeper in the oxidation process, and the oxidation is more sufficient, so that the reduced graphene oxide with low powder resistivity and high specific surface area is obtained.

Description

Technical Field

[0001] This invention relates to the field of graphene materials technology, and more specifically to a reduced graphene oxide powder, which is obtained by carbonization after two oxidation-reduction processes. Background Technology

[0002] Oxidation-reduction (ORR) is currently the mainstream process for preparing graphene, with most processes involving a single OCR step, while two OCR steps are rarely reported. The specific surface area and resistivity of graphene prepared using traditional OCR processes are a pair of competing parameters. This is mainly because obtaining a high specific surface area requires sufficient oxidation during the oxidation stage. However, sufficient oxidation leads to the introduction of numerous pore defects during the subsequent high-temperature reduction stage due to deoxidation and carbon etching, as well as residual oxygen atoms from strong bonding, which disrupts the long-range order of graphene and reduces its conductivity. While reducing the degree of oxidation can improve the conductivity of graphene, low-oxidation graphene carries fewer oxygen-containing groups, making it difficult to obtain graphene with a high specific surface area during the expansion and reduction stages.

[0003] Graphene powder obtained through a single oxidation-reduction process has a specific surface area that is difficult to exceed 600 m². 2 The / g value is attributed to the fact that the initial raw material for preparing graphene is usually flake graphite. The van der Waals interactions between the flake graphite layers are strong. The oxidation process of the first oxidation-reduction process is a permeation intercalation oxidation process. The edge and surface areas of the flake graphite are oxidized more fully, while the oxidation degree in the middle area is less and there are fewer oxygen-containing functional groups. It is difficult to obtain graphene with a high exfoliation rate in the first expansion process stage. There are a large number of thick graphene nanosheets with few layers of graphene stacked together, so it is difficult to obtain graphene with a high specific surface area.

[0004] To obtain graphene with a high specific surface area, the flake graphite needs to be fully oxidized during the oxidation stage. Common practices include: ① Delaying the oxidation time: This often results in a large number of pore defects and oxygen heteroatom doping, leading to poor conductivity of the graphene powder; ② Using small-particle-size flake graphite raw materials: This causes carbon atoms to react during the oxidation process, resulting in a low yield of the final product. Moreover, neither of these methods makes it easy to obtain graphene with a large flake size, low powder resistivity, and high specific surface area. Summary of the Invention

[0005] Based on the above reasons, a reduced graphene oxide powder with low powder resistivity and high specific surface area is provided.

[0006] Specifically, the graphene oxide powder is carbonized after two oxidation-reduction processes. These two processes consist of a primary oxidation reaction, low-temperature expansion reduction, a secondary oxidation reaction, and a high-temperature expansion reduction. The significance of this two-stage oxidation-reduction process is as follows: Typically, the preparation of reduced graphene oxide powder involves a single, thorough oxidation-reduction process followed by staged temperature increases. The oxidation process in a single oxidation-reduction process is a penetrating intercalation oxidation process, where the graphite raw material is first oxidized at the edges and surface, then at the center. To completely open the graphite sheets in a single oxidation process requires a large amount of oxidant, leading to defect introduction, excessive porosity, and thus higher powder resistivity. Furthermore, excessive oxidant also makes the cleaning process more stringent. The graphene with low powder resistivity and high specific surface area provided by this invention, through a low-degree oxidation-reduction followed by a higher-degree oxidation, allows for deeper intercalation of large-diameter graphene sheets during the oxidation process, resulting in more complete oxidation, and ultimately, less oxidant is used.

[0007] Furthermore, the primary oxidation reaction and / or the secondary oxidation reaction are selected from any one of the Hummers oxidation process, Brodie oxidation process, Staudenmaier oxidation process, or modified Hummers oxidation process, Brodie oxidation process, Staudenmaier oxidation process.

[0008] Furthermore, the oxidant used in the secondary oxidation reaction is 4-8 times the mass of the oxidant used in the primary oxidation reaction. Preferably, the oxidant is potassium permanganate. The first oxidation is a low-level, light oxidation, the purpose of which is to control the oxidation as much as possible as an edge oxidation, so as not to affect the overall integrity of the graphene. Moreover, the first expansion can open up the interlayer gaps of the flake graphite to a certain extent by utilizing the edge oxidation, providing a convenient channel for subsequent secondary oxidation.

[0009] Furthermore, the low-temperature expansion reduction process involves an expansion temperature of 200-500℃ and an expansion time of 2-10 minutes. Within the temperature range of 200-400℃, hydroxyl groups in graphene oxide can be effectively removed. This means that during the low-temperature expansion reduction stage, the low-bond-energy carbon-oxygen single-bond oxygen-containing groups (such as hydroxyl groups) on graphene oxide are consumed first and detached as water molecules. This avoids the removal of double-bond oxygen-containing groups (such as carboxyl groups) caused by direct high temperatures, which would lead to in-situ carbon etching and introduce excessive defects.

[0010] Furthermore, the high-temperature expansion reduction process involves an expansion temperature of 500-1000℃ and an expansion time of 2-6 minutes. This temperature range of 500-1000℃ allows for the removal of double-bonded oxygen-containing functional groups such as carbonyl and carboxyl groups from the edges. Generally, graphene oxide at the edges has higher activity sites due to the presence of pore defects, making it easier for oxygen-containing functional groups to detach under high-temperature conditions compared to the central region. During the detachment of double-bonded oxygen-containing functional groups, in addition to water molecules, CO and CO2 molecules also detach, i.e., etching in-situ C atoms and leaving vacancies and structural defects. This may affect the mechanical and electrical properties of the reduced product.

[0011] Furthermore, aniline compounds or mixtures are added during the secondary oxidation reaction. Preferably, the aniline compounds or mixtures are one or more of dopamine hydrochloride, benzidine, m-phenylenediamine, and diphenylamine. The aniline compounds or mixtures can replace the double-bonded oxygen atoms at the edge of the graphene oxide with their own nitrogen atoms, causing the oxygen atoms to detach as water.

[0012] The mass of aniline compounds or mixtures should be controlled within an appropriate range. Aniline compounds or mixtures can be introduced in the form of an aqueous solution with a mass fraction of 0.1-1%, and the mass ratio of the aniline compounds or mixtures to the graphene oxide slurry in the secondary oxidation reaction process is aniline compounds or mixtures: graphene oxide slurry = 2:1-6. If the content is too low, the double bond oxygen at the edges cannot be completely replaced; if the content is too high, ① the aniline compounds or mixtures will affect the cleanliness of the product due to their attachment to the load, and after carbonization, they will exist in the form of hard carbon, affecting performance; ② the mechanism by which the expansion process can increase the specific surface area of ​​reduced graphene oxide lies in the abundance of oxygen-containing functional groups between the graphene oxide layers. During heating, the internal oxygen-containing functional groups break and release, thereby increasing the internal pressure of the graphene sheets and causing expansion. The replacement of the oxygen-containing groups (carbonyl groups, carboxyl groups) in the middle will affect the final specific surface area of ​​the product.

[0013] The resistivity of the reduced graphene oxide powder described in this application is <5Ω·cm, preferably <4Ω·cm.

[0014] The reduced graphene oxide powder described in this application also takes into account the specific surface area, which is >700m². 2 / g, preferably, with a specific surface area >750m² 2 / g.

[0015] Thanks to its excellent specific surface area and resistivity parameters, reduced graphene oxide powder can be used in new energy batteries.

[0016] The beneficial effects of this invention are as follows:

[0017] 1. The present invention provides a graphene with low powder resistivity and high specific surface area. Compared with the traditional single oxidation-reduction process, the graphene obtained by the two-stage oxidation-reduction strategy has a larger specific surface area.

[0018] 2. The graphene with low powder resistivity and high specific surface area provided by the present invention is made by a second high-level oxidation after a first low-level oxidation-reduction process, so that the large-diameter graphene has a deeper intercalation depth and more complete oxidation during the oxidation process.

[0019] 3. The present invention provides a graphene with low powder resistivity and high specific surface area. Through the dehydration condensation reaction of aniline compounds, the oxygen-containing groups on the graphene oxide are consumed in advance, so as to avoid the introduction of too many defects in the graphene due to in-situ carbon etching during the high-temperature reduction stage, thereby improving the powder conductivity of graphene.

[0020] This invention provides a graphene with low powder resistivity and high specific surface area. The preparation process is suitable for graphite raw materials of 20-2000 mesh. Compared with the reduced graphene oxide prepared by the traditional process, it can take into account the graphene sheet size, powder resistivity and specific surface area parameters, and realize the customized preparation of graphene. Attached Figure Description

[0021] Figure 1 This is a 10,000x magnified SEM image of the reduced graphene oxide powder obtained in Example 1.

[0022] Figure 2 The reduced graphene oxide powder was subjected to ultrasonic treatment and then spin-coated onto a silicon wafer. The image is a 6000x magnified SEM image.

[0023] Figure 3 The image is a 10,000x magnified SEM image of reduced graphene oxide powder after ultrasonic treatment and spin-coating onto a silicon wafer.

[0024] Figure 4 This is a 20,000x magnified SEM image of the reduced graphene oxide powder obtained in Example 1. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments, but these should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field, and there are no specific restrictions on their sources; they can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0026] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0027] The technical solution of the present invention is illustrated below through specific embodiments. It should be understood that the one or more steps mentioned in the present invention do not preclude the existence of other methods and steps before or after the combined steps, or that other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, and not for limiting the order of each method or limiting the scope of the present invention. Changes or adjustments to their relative relationships, without substantial changes to the technical content, can also be considered as within the scope of the present invention.

[0028] In the embodiments and comparative examples of this application, the methods for testing the resistivity and specific surface area of ​​the powder are as follows:

[0029] Powder resistivity: Measured using an ST2722-SZ four-probe powder resistivity tester.

[0030] Powder specific surface area: tested using a JW-BK200B instrument under the following conditions: 250℃ / 2.5h treatment, with adsorption using high-purity nitrogen. Example 1

[0031] A reduced graphene oxide powder is obtained by carbonization after two oxidation-reduction processes. The specific preparation method is as follows:

[0032] S1. Preparation of graphene oxide cake: Graphene oxide was prepared using a modified Hummer method. 20g of 500-mesh sieved flake graphite powder and 10g of potassium nitrate were mixed evenly, and 900g of concentrated sulfuric acid was added. The mixture was stirred for 15 minutes, and 10g of potassium permanganate was slowly added under ice bath and stirring conditions. After ice bath for 2 hours, the mixture was transferred to a 40℃ oven and reacted under magnetic stirring conditions for 30 minutes. After the solution turned brown, it was transferred to room temperature. Under stirring conditions, 1000g of deionized water was slowly added to carry out hydrolysis reaction. When the solution temperature was below 70℃, 100g of hydrogen peroxide solution was added under stirring conditions. The mixture was reacted for 2 hours until the slurry turned completely bright yellow. The mixture was first washed 8 times with 5% dilute hydrochloric acid aqueous solution, and then washed with deionized centrifugation until the pH was neutral. The graphene oxide cake was obtained by vacuum filtration or pressure filtration.

[0033] S2. First expansion treatment: The graphene oxide cake obtained in step S1 is pressed into thin strips, baked in an oven at 60-80℃ for 4 hours, and then simply crushed to obtain dry graphene oxide. It is then expanded in a microwave expansion furnace at a temperature of 350℃ for 6 minutes. Nitrogen gas is used for atmosphere protection during the expansion process to obtain first expanded graphene powder.

[0034] S3. Second oxidation treatment: Using the first-expanded graphene powder obtained in step S2 as raw material, 20g of the first-expanded graphene powder and 10g of potassium nitrate were mixed evenly, and 900g of concentrated sulfuric acid was added. The mixture was stirred for 15 minutes, and 60g of potassium permanganate was slowly added under ice bath and stirring conditions. After ice bath for 2 hours, the mixture was transferred to a 40℃ oven and reacted under magnetic stirring conditions for 30 minutes. After the solution turned brown, it was transferred to room temperature. Under stirring conditions, 1000g of deionized water was slowly added to carry out hydrolysis reaction. When the solution temperature was below 70℃, 100g of hydrogen peroxide solution was added under stirring conditions. The mixture was reacted for 2 hours until the slurry turned completely bright yellow. The slurry was first washed 8 times with 5% dilute hydrochloric acid aqueous solution and then washed with deionized centrifugation until the pH was neutral to obtain a graphene oxide slurry with a solid content of 1%. Prepare a 0.2% (w / w) aqueous solution of dopamine hydrochloride and add it to the graphene oxide slurry at a 1:1 (w / w) ratio under stirring. Transfer the slurry to a 50°C oven and keep it warm for 3 hours. Then obtain the graphene oxide cake by pressure filtration or vacuum filtration.

[0035] S4. Second puffing treatment: The graphene oxide cake obtained in step S3 is pressed into thin strips using a dough press. After baking in a 70℃ oven for 4 hours, it is ground and crushed to obtain graphene oxide powder. The powder is then puffed in a microwave puffing oven at a temperature of 900℃ for 4 minutes. Nitrogen gas is used for atmosphere protection during the puffing process to obtain second-expanded graphene powder.

[0036] S5. Carbonization treatment: The second expanded graphene powder obtained in step S4 is loaded into a graphite crucible and transferred to a carbonization furnace. The temperature is increased to 600℃ at a heating rate of 15℃ / min and held for 0.5h. Then, the temperature is increased to 1000℃ at a heating rate of 5℃ / min and held for 0.5h. Finally, the temperature is increased to 1350℃ at a heating rate of 2℃ / min and held for 10h. Then, it is naturally cooled to room temperature. Nitrogen gas is used for atmosphere protection during the carbonization process to obtain reduced graphene oxide powder.

[0037] The test results of the obtained reduced graphene oxide powder showed that its specific surface area was 859.4 m². 2 / g, its powder resistivity is 2.42mΩ·cm.

[0038] The obtained reduced graphene oxide powder was characterized by SEM, and the characterization results are as follows: Figure 1 As shown in the figure, the graphene interlayer exfoliation effect is very ideal;

[0039] SEM images of reduced graphene oxide powder after ultrasonic treatment and spin-coating onto silicon wafers at different magnifications are shown below. Figure 2 , Figure 3 As shown in the figure, graphene is easy to peel off, and the thickness of the peeled graphene layer is very small and the size is large. Highly peelable and dispersed ultrathin graphene can be obtained without high-strength treatment. Example 2

[0040] The difference between this embodiment and Example 1 is that deionized water was used instead of the 0.2% dopamine hydrochloride aqueous solution in step S3. The remaining steps are the same as in Example 1. The purpose is to investigate the effect of washing with the dopamine hydrochloride aqueous solution on the properties of reduced graphene oxide. The test results show that its specific surface area is 777.3 m² / g, which is similar to the BET value of the reduced graphene oxide obtained in Example 1. This can be attributed to the fact that dopamine hydrochloride in Example 1 provided some detachable hydrogen and oxygen, resulting in a higher BET value for the graphene powder in Example 1. Its powder resistivity is 4.03 mΩ·cm, which is much higher than that of the reduced graphene oxide powder obtained in Example 1. This can be attributed to the increased defects introduced by carbon etching during the high-temperature expansion and carbonization stages.

[0041] Examples 3-6

[0042] The difference between this embodiment and Embodiment 1 is that in step S2, the first expansion treatment is performed at 300℃, 400℃, 450℃, and 500℃ respectively. The remaining steps are the same as in Embodiment 1. The purpose is to investigate the effect of the first expansion temperature on the properties of graphene. This embodiment investigates the effect of the first expansion temperature on the properties of graphene by controlling variables. The test results are shown in the table below:

[0043] First expansion temperature 300℃ 400℃ 450℃ 500℃ BET value (m2 / g) 843.9 865.3 876.4 933.0 Powder resistivity (mΩ·cm) 2.12 2.74 3.12 3.66

[0044] Test results show that increasing the temperature during the low-temperature expansion stage is beneficial for increasing the specific surface area of ​​the reduced graphene oxide powder. This can be attributed to the fact that the higher the temperature during the low-temperature expansion stage, the larger the interlayer spacing of the graphene, which is conducive to subsequent secondary intercalation and oxidation. However, as the temperature during the low-temperature expansion stage increases, the resistivity of the reduced graphene oxide powder increases and its conductivity deteriorates. This can be attributed to the fact that as the temperature during the low-temperature expansion stage increases, the double-bonded oxygen elements gradually fall off, resulting in carbon etching, which is not conducive to improving the conductivity of the reduced graphene oxide.

[0045] Comparative Example 1

[0046] The difference between this comparative example and Example 1 is the absence of steps S2 and S3; the remaining steps are the same as in Example 1. The purpose is to investigate the effect of the secondary oxidation and expansion process on the properties of reduced graphene oxide. Test results show that its specific surface area is 254.7 m². 2 / g, its powder resistivity is 2.68mΩ·cm. The low resistivity can be attributed to the low amount of potassium permanganate used, resulting in a low degree of oxidation and fewer defects such as pores and heteroatoms, thus preserving most of the intrinsic conductivity of graphene. However, SEM characterization of the obtained reduced graphene oxide powder yielded the following results: Figure 4 As shown in the SEM image, the graphene interlayer exfoliation effect is poor, and the interlayer thickness is relatively thick. Comparative Example 2

[0047] The difference between this comparative example and Example 1 is that in step S1, the mass of potassium permanganate added is 40g; the remaining steps are the same as in Example 1. Test results show that its specific surface area is 881.30 m². 2 The powder has a resistivity of 5.62 mΩ·cm. Excessive addition of potassium permanganate during the primary oxidation process resulted in a higher degree of oxidation, introducing more pores and heteroatoms, thus increasing the powder resistivity. However, due to more complete intercalation, the specific surface area of ​​the powder also increased accordingly. Comparative Example 3

[0048] The difference between this comparative example and Example 1 is that in step S1, during the cleaning stage of the graphene oxide after primary oxidation, a 0.2% (w / w) aqueous solution of dopamine hydrochloride is prepared and added to the graphene oxide slurry in a 1:1 (w / w) ratio under stirring. The slurry is then transferred to a 50°C oven and kept at that temperature for 3 hours. Finally, the graphene oxide cake is obtained by pressure filtration or vacuum filtration.

[0049] Test results show that its specific surface area is 542.84 m². 2 / g, its powder resistivity is 2.85 mΩ·cm.

[0050] Because the addition of dopamine hydrochloride in the first oxidation stage causes a dehydration condensation reaction with the oxygen-containing groups of graphene oxide, it largely consumes the number of oxygen-containing groups in graphene oxide. This is not conducive to opening the interlayer gaps of flake graphite in the first stage, making the penetration oxidation process of the second oxidation stage difficult and resulting in insufficient overall oxidation uniformity. Therefore, it is impossible to increase the specific surface area of ​​the reduced graphene oxide powder through the second oxidation stage. At the same time, because the first oxidation is a light oxidation and both the first and second oxidation stages use dopamine hydrochloride, the excess dopamine hydrochloride usually exists in the form of amorphous carbon after carbonization. Although the precursor defects are reduced, it does not play a role in reducing the resistivity of the powder in the subsequent stages. Comparative Example 4

[0051] The difference between this comparative example and Example 1 is that in step S3, the dopamine solution is 5 times the amount of graphene slurry; the remaining steps are the same as in Example 1. Test results show that its specific surface area is 254.73 m². 2 The resistivity of the powder is 5.94 mΩ·cm. This is because the excessive dopamine hydrochloride solution replaced the oxygen-containing groups (carbonyl and carboxyl groups) in the middle, thus affecting the final specific surface area of ​​the product; and the attachment load of dopamine hydrochloride affected the cleanliness of the product, resulting in an increase in the resistivity of the powder. Comparative Example 5

[0052] The difference between this comparative example and Example 1 is that in step S2, the low-temperature puffing reduction temperature is 700 degrees Celsius; the remaining steps are the same as in Example 1. Test results show that the specific surface area of ​​the prepared powder is 1056.83 m². 2 / g, the powder resistivity is 6.02mΩ·cm. Increasing the temperature during the low-temperature expansion stage is beneficial for increasing the specific surface area of ​​the reduced graphene oxide powder. This can be attributed to the fact that a higher temperature during the low-temperature expansion stage results in a larger interlayer spacing of graphene, which is conducive to subsequent secondary intercalation and oxidation. However, as the temperature during the low-temperature expansion stage increases, the resistivity of the reduced graphene oxide powder increases, and its conductivity deteriorates. This can be attributed to the fact that at higher temperatures during the low-temperature expansion stage, double-bonded oxygen elements gradually detach, resulting in carbon etching, which is detrimental to improving the conductivity of the reduced graphene oxide. Comparative Example 6

[0053] The specific preparation method for conventional reduced graphene oxide powder is as follows:

[0054] S1. Preparation of graphene oxide cake: Graphene oxide was prepared using a modified Hummer method. 20g of 500-mesh sieved flake graphite powder and 10g of potassium nitrate were mixed evenly, and 900g of concentrated sulfuric acid was added. The mixture was stirred for 15 minutes, and 80g of potassium permanganate was slowly added under ice bath and stirring conditions. After ice bath for 2 hours, the mixture was transferred to a 40℃ oven and reacted under magnetic stirring conditions for 30 minutes. After the solution turned brown, it was transferred to room temperature. Under stirring conditions, 1000g of deionized water was slowly added to carry out the hydrolysis reaction. When the solution temperature was below 70℃, 100g of hydrogen peroxide solution was added under stirring conditions. The mixture was reacted for 2 hours until the slurry turned completely bright yellow. The mixture was first washed 8 times with 5% dilute hydrochloric acid aqueous solution, and then washed with deionized centrifugation until the pH was neutral. The graphene oxide cake was obtained by vacuum filtration or pressure filtration.

[0055] S2. Expansion treatment: The graphene oxide cake obtained in step S1 is pressed into thin strips, baked in an oven at 60-80℃ for 4 hours, and then simply crushed to obtain dry graphene oxide. It is then expanded in a microwave expansion furnace at a temperature of 800℃ for 6 minutes. Nitrogen gas is used for atmosphere protection during the expansion process to obtain expanded graphene powder.

[0056] S3. Carbonization treatment: The second expanded graphene powder obtained in step S2 is loaded into a graphite crucible and transferred to a carbonization furnace. The temperature is increased to 600℃ at a heating rate of 15℃ / min and held for 0.5h. Then, the temperature is increased to 1000℃ at a heating rate of 5℃ / min and held for 0.5h. Finally, the temperature is increased to 1350℃ at a heating rate of 2℃ / min and held for 10h. Then, it is naturally cooled to room temperature. Nitrogen gas is used for atmosphere protection during the carbonization process to obtain reduced graphene oxide powder.

[0057] The test results of the obtained reduced graphene oxide powder showed that its specific surface area was 382.76 m². 2 / g, its powder resistivity is 2.94mΩ·cm.

[0058] The oxidation process in a single oxidation-reduction process is a permeation intercalation oxidation process. The edges and surface areas of the flake graphite are oxidized more fully, while the oxidation degree in the middle area is less and there are fewer oxygen-containing functional groups. It is difficult to obtain graphene with a high exfoliation rate in the single expansion process stage. There are a large number of thick graphene nanosheets with few layers of graphene stacked together, so it is difficult to obtain graphene with a high specific surface area. Comparative Example 7

[0059] Another conventional method for preparing reduced graphene oxide powder is as follows:

[0060] S1. Preparation of graphene oxide cake: Graphene oxide was prepared using a modified Hummer method. 20g of 500-mesh sieved flake graphite powder and 10g of potassium nitrate were mixed evenly, and 900g of concentrated sulfuric acid was added. The mixture was stirred for 15 minutes, and 80g of potassium permanganate was slowly added under ice bath and stirring conditions. After ice bath for 2 hours, the mixture was transferred to a 40℃ oven and reacted under magnetic stirring conditions for 30 minutes. After the solution turned brown, it was transferred to room temperature. Under stirring conditions, 1000g of deionized water was slowly added to carry out the hydrolysis reaction. When the solution temperature was below 70℃, 100g of hydrogen peroxide solution was added under stirring conditions. The reaction was carried out for 6 hours. The mixture was first washed 8 times with 5% dilute hydrochloric acid aqueous solution, and then washed with deionized centrifugation until the pH was neutral. The graphene oxide cake was obtained by vacuum filtration or pressure filtration.

[0061] S2. Expansion treatment: The graphene oxide cake obtained in step S1 is pressed into thin strips, baked in an oven at 60-80℃ for 4 hours, and then simply crushed to obtain dry graphene oxide. It is then expanded in a microwave expansion furnace at a temperature of 800℃ for 6 minutes. Nitrogen gas is used for atmosphere protection during the expansion process to obtain expanded graphene powder.

[0062] S3. Carbonization treatment: The second expanded graphene powder obtained in step S2 is loaded into a graphite crucible and transferred to a carbonization furnace. The temperature is increased to 600℃ at a heating rate of 15℃ / min and held for 0.5h. Then, the temperature is increased to 1000℃ at a heating rate of 5℃ / min and held for 0.5h. Finally, the temperature is increased to 1350℃ at a heating rate of 2℃ / min and held for 10h. Then, it is naturally cooled to room temperature. Nitrogen gas is used for atmosphere protection during the carbonization process to obtain reduced graphene oxide powder.

[0063] The test results of the obtained reduced graphene oxide powder showed that its specific surface area was 687.73 m². 2 / g, its powder resistivity is 6.39mΩ·cm.

[0064] A longer oxidation time can yield reduced graphene oxide powder with a higher specific surface area, but full oxidation can also lead to more product defects and increased powder resistivity.

[0065] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A reduced graphene oxide powder, characterized in that, It is obtained by carbonization after two oxidation-reduction processes, specifically a primary oxidation reaction, a low-temperature puffing reduction, a secondary oxidation reaction, and a high-temperature puffing reduction. The oxidant used in the secondary oxidation reaction is 4-8 times the mass of the oxidant used in the primary oxidation reaction. In the secondary oxidation reaction, aniline compounds or mixtures are also added. The low-temperature puffing reduction has a puffing temperature of 200-500℃ and a puffing time of 2-10 min; the high-temperature puffing reduction has a puffing temperature of 500-1000℃ and a puffing time of 2-6 min.

2. A reduced graphene oxide powder as described in claim 1, characterized in that, The primary oxidation reaction and / or the secondary oxidation reaction are selected from any one of the Hummers oxidation process, Brodie oxidation process, Staudenmaier oxidation process, or modified Hummers oxidation process, Brodie oxidation process, Staudenmaier oxidation process.

3. A reduced graphene oxide powder as described in claim 1, characterized in that, The mass fraction of the aniline compound or mixture is 0.1-1%, and the mass ratio of the aniline compound or mixture to the graphene oxide slurry in the secondary oxidation reaction process is 2:1-6.

4. A reduced graphene oxide powder as described in claim 1, characterized in that, The resistivity of the reduced graphene oxide powder is <5Ω·cm.

5. A reduced graphene oxide powder as described in claim 4, characterized in that, The resistivity of the reduced graphene oxide powder is <4Ω·cm.

6. A reduced graphene oxide powder as described in claim 1, characterized in that, The specific surface area of ​​the reduced graphene oxide powder is >700 m². 2 / g.

7. A reduced graphene oxide powder as described in claim 6, characterized in that, The specific surface area of ​​the reduced graphene oxide powder is >750 m². 2 / g.

8. The application of the reduced graphene oxide powder according to any one of claims 1-7 in new energy batteries.

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