A method for preparing low-defect graphene powder by high-temperature molten salt intercalation and instantaneous expansion.

Abstract

This invention relates to the field of graphene preparation technology and provides a method for preparing low-defect graphene powder using a high-temperature molten salt intercalation and instantaneous expansion method. First, a graphite / molten salt composite electrode is prepared. Then, salt is intercalated into the graphite using an electrochemical intercalation method. Finally, the intercalated graphite is exfoliated into thin-layer graphene using a negative pressure high-power microwave exfoliation method or a normal pressure high-temperature quenching exfoliation method. The raw materials used in this invention are low-cost and environmentally friendly, and the production process is safe and efficient. Through the optimized combination of molten salt electro-assisted intercalation technology and the instantaneous expansion method, the prepared graphene not only has a layer count controlled at 3-5 layers and a flake size of 25-300 μm, but also exhibits few defects on the graphene flakes, providing strong technical support for promoting the high-quality development of related industries.

Description

Technical Field

[0001] This invention belongs to the field of graphene preparation technology, and particularly relates to a method for preparing low-defect graphene powder by high-temperature molten salt intercalation instantaneous expansion. Background Technology

[0002] Since its discovery in 2004, graphene has demonstrated broad application potential in various fields due to its exceptional physical properties. For example, its high thermal conductivity of 5300 W / mK has led to its use in heat dissipation for electronic chips, especially in portable electronic products; its high electrical conductivity and flexible two-dimensional structure have made it suitable for use in high-barrier, heavy-duty anti-corrosion paints. Undoubtedly, the preparation methods and production technologies of graphene are crucial prerequisites for its application, promotion, and development. The quality, physical properties, cost, impurity content, and environmental issues involved in graphene preparation all affect the development of downstream applications and product promotion, ultimately impacting technological development and diffusion. Therefore, a low-cost and low-pollution method for preparing high-quality graphene powder is essential.

[0003] Currently, there are three main methods for preparing graphene powder: 1) Mechanical exfoliation, which is the primary method used by some domestic manufacturers to produce non-redox graphene. This involves exfoliating graphite using equipment such as grinders, ball mills, and high-pressure homogenizers to obtain graphene or graphite nanosheets with more than ten layers. Its advantages include low cost, but it suffers from high energy consumption, long processing time, and the potential introduction of metallic impurities. Furthermore, the large number of graphene layers affects flexibility and conductivity, limiting product performance. 2) Redox method, which uses oxidants such as sulfuric acid and potassium permanganate to oxidize graphite into graphite oxide. This graphite oxide is then processed into graphene oxide, which is then chemically or thermally reduced to produce graphene. This method is technically mature and can achieve large-scale production (hundreds of tons per year). However, its production process involves hazardous substances such as concentrated sulfuric acid, posing safety and environmental pollution risks. Additionally, the prepared graphene contains metallic ion impurities, resulting in poor conductivity and difficulty in achieving ideal performance. 3) Vapor deposition methods, including epitaxial growth and metal-catalyzed vapor deposition, can produce high-quality graphene that closely resembles the theoretical state and exhibits excellent electrical conductivity. However, this method involves expensive equipment, low production efficiency, and high costs, making it difficult for businesses to use, and even research institutions only allow well-funded research groups to conduct application development and property exploration of such products. Therefore, a method for preparing low-defect graphene powder using high-temperature molten salt intercalation and instantaneous expansion is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing low-defect graphene powder by high-temperature molten salt intercalation and instantaneous expansion, which aims to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing low-defect graphene powder by high-temperature molten salt intercalation and instantaneous expansion includes the following steps:

[0007] Step 1: Preparation of graphite / molten salt composite electrode: Graphite powder and salt for intercalation are initially mixed using a mixing mixer. The initially mixed material is then fed into a single-screw mixer, where the salt is heated to a molten state to fully impregnate the graphite powder surface. The mixture is then poured into a mold, with an electrode current collector pre-placed at the bottom of the mold, and the mixture covering the current collector. After sealing the mold, it is placed on a flat vulcanizing machine for heating and molding, pressing the mixture and current collector into a single composite graphite electrode.

[0008] Step 2, Intercalation: The prepared composite graphite electrode is installed as the anode in a container, and the container is filled with salt for intercalation as the electrolyte, with the bulk graphite electrode as the cathode. After placing the anode, cathode, and electrolyte, the container is sealed and heated until the electrolyte melts. Pressure is applied from one end of the cathode into the container to maintain the pressure of the molten salt liquid within the range of 2-6 atmospheres. Then, current is applied under a low voltage of 0.5-1.2V and a high current of 5-40A to promote the intercalation reaction (low voltage controls the electrolyte from being oxidized and reduced, and high current promotes the efficiency of intercalation). After treatment, the composite graphite electrode of the anode will expand and some of it will detach and shed powder. The expansion and detachment of the composite graphite electrode of the anode are observed until all the intercalated expanded graphite is separated from the current collector.

[0009] Step 3: Instant peeling, using negative pressure high-power microwave peeling method or normal pressure high-temperature quenching peeling method;

[0010] The negative pressure high-power microwave exfoliation method is as follows: the intercalated graphite powder is placed in a sealed device that can simultaneously achieve vacuuming and microwave heating, and the graphite powder is instantly heated with a microwave power of 10-15KW, causing the intercalated material to instantly vaporize (decompose into gas), the graphite powder to instantly expand and explode, and the graphite is exfoliated into thinner graphene.

[0011] The atmospheric pressure high temperature quenching and stripping method is as follows: the intercalated graphite powder is instantly heated to above 1000℃ or burned by flame, so that the intercalated material is released instantly and the graphite is stripped. Because the intercalation of molten salt is used, compared with the intercalation of concentrated sulfuric acid and potassium permanganate oxidation, more salt will be inserted into the graphite layers. Even small-flake graphite can be stripped using this method.

[0012] Furthermore, in step 1, the molar ratio of graphite powder to the salt used for intercalation is (3-6):1; the salt used for intercalation is mainly sulfate.

[0013] Furthermore, in step 1, the current collector has a rough mesh structure, which facilitates the firm bonding of the powder to the current collector under molding. The current collector can be made of metals such as copper and aluminum, or carbon fiber materials.

[0014] Furthermore, in step 1, the composite graphite electrode is cylindrical or cuboid.

[0015] Furthermore, in step 1, during the heating and molding process, the pressure and temperature are adjusted according to the mesh size of the graphite flakes used and the type and amount of salt used. The heating temperature does not exceed the decomposition temperature or vaporization temperature of the salt.

[0016] Furthermore, in step 2, the heating temperature is higher than the melting temperature of the salt, but lower than the decomposition temperature or vaporization temperature.

[0017] Furthermore, in step 2, the container is a reactor with a ceramic insulating inner layer, or a reaction vessel with a polytetrafluoroethylene liner is selected according to the melting temperature of the salt.

[0018] Furthermore, in step 2, the molar ratio of electrolyte to graphite powder is (5-6):1.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. This invention develops a non-redox method for preparing low-defect graphene powder by high-temperature molten salt intercalation and instantaneous expansion. The number of graphene layers prepared can be controlled to be 3-5 layers, and the scale size can reach 25-300μm.

[0021] 2. In terms of raw material selection, this invention uses non-corrosive, environmentally friendly salt as a key material to ensure the safety and environmental friendliness of the production process. The environmentally friendly treatment of this type of salt is simple, greatly reducing the potential environmental impact. At the same time, the melting temperature of the selected salt is below 300-400℃, effectively reducing energy consumption during the intercalation process. Furthermore, as a common chemical raw material, its low price directly guarantees the cost-effectiveness of graphene production.

[0022] 3. This invention innovatively employs molten salt electro-assisted intercalation technology, improving the uniformity and quantity of the intercalation reagent distribution between graphite layers, thereby producing graphene with fewer layers and a narrower layer distribution range. Compared to graphene oxide preparation methods, this invention avoids the redox process, reducing defects on the graphene flakes; compared to mechanical exfoliation, the graphite raw material is not ground or crushed, retaining a larger flake size and improving product quality.

[0023] 4. This invention introduces an instantaneous expansion method, particularly negative pressure microwave technology, which operates at a pressure below one standard atmosphere. This significantly enhances the expansion force exerted on the graphite interlayers during the decomposition and vaporization of the intercalated material, achieving better exfoliation results and producing graphene with fewer layers. Because the number of intercalated materials increases, the force released during decomposition far exceeds the force generated during the expansion graphite preparation process. Therefore, secondary mechanical exfoliation is unnecessary, directly producing thin-layer graphene and improving production efficiency and product quality. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope image of the graphene prepared by the method in Example 1.

[0025] Figure 2 This is a scanning electron microscope image of the graphene prepared by the method in Example 2.

[0026] Figure 3 The images shown are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the graphene prepared by the method in Example 3; where a is a SEM image and b is a TEM image.

[0027] Figure 4 This is a scanning electron microscope image of the graphene prepared by the method in Example 4.

[0028] Figure 5 This is a diagram showing the scale size distribution of the graphene obtained by the method in Example 3.

[0029] Figure 6 This is a layer number distribution diagram of the graphene obtained by the method in Example 3. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0032] Example 1: A method for preparing low-defect graphene powder by high-temperature molten salt intercalation and instantaneous expansion, comprising the following steps:

[0033] 1) Ingredients: Ammonium bisulfate and 100-mesh graphite powder are used as raw materials. They are first mixed in a mixing machine at a molar ratio of 1:4, and then added to a single screw press. The heating temperature is controlled at 160℃ to heat the ammonium bisulfate to a molten state so that the molten salt can fully wet the surface of the graphite powder.

[0034] 2) Molding: The uniformly mixed graphite / molten salt powder is poured into a mold. An electrode current collector (metallic copper) is pre-placed at the bottom of the mold. The mixture covers the current collector and is compacted to ensure the powder fully fills the mold and adheres tightly to the current collector. After sealing the mold, it is heated and molded on a flat vulcanizing machine at a temperature of 160℃ and a pressure of 40 MPa. The mixed powder and current collector are pressed into a single cylindrical composite graphite electrode.

[0035] 3) Intercalation: The prepared composite graphite electrode is installed as the anode in a reaction vessel lined with polytetrafluoroethylene (PTFE). A certain amount of ammonium bisulfate is added as the electrolyte, with a molar ratio of electrolyte to graphite powder of 6:1. A bulk graphite electrode is used as the cathode. After placing the anode, cathode, and electrolyte, the container is sealed with silicone rubber or PTFE gaskets. The interior of the container is heated to 160°C, and pressure is applied from one end of the cathode to maintain the pressure of the molten salt liquid within the container at approximately 4 atmospheres. Then, the composite graphite electrode at the anode is intercalated using a voltage of 0.8V and a current of 15A. The heating temperature is maintained at approximately 160°C throughout this process.

[0036] 4) Instant exfoliation using a negative pressure high-power microwave exfoliation method: Intercalated graphite powder is placed in a ceramic crucible within a vacuum microwave reactor. After sealing the reactor, the pressure inside the chamber is evacuated to below 100 Pa. Then, instantaneous microwave heating begins at a power of 15 kW. The graphite expands and explodes instantaneously, exfoliating into graphene. The amount of sample in the crucible should not be excessive; it depends on the volume of the chamber, the pressure it can withstand, and the depth of microwave heating.

[0037] Scanning electron microscope image of graphene prepared by the method in Example 1 is shown below. Figure 1 As shown.

[0038] Example 2: A method for preparing low-defect graphene powder by high-temperature molten salt intercalation and instantaneous expansion, comprising the following steps:

[0039] The operations from 1) to 3) are consistent with those in Example 1. In step 4), the atmospheric pressure high-temperature quenching and exfoliation method is selected for instant exfoliation: the muffle furnace is heated to 1000°C, the ceramic sagger is placed inside, and after preheating to the same temperature, it is removed. A certain amount of graphite powder is added. The amount of graphite powder used here is related to the structure and bottom area of ​​the sagger. The graphite powder should cover the bottom of the sagger, with a thickness not exceeding 5mm. Considering both production efficiency and exfoliation effect, the thickness is best around 3mm. The sagger is then placed back into the muffle furnace and heated for 60 seconds. After all the graphite powder has expanded and turned red, it is removed to obtain graphene dry powder.

[0040] Scanning electron microscope image of graphene prepared by the method in Example 2 is shown below. Figure 2As shown.

[0041] Example 3: A method for preparing low-defect graphene powder by high-temperature molten salt intercalation and instantaneous expansion, comprising the following steps:

[0042] 1) Ingredients: Ammonium sulfate and 100-mesh graphite powder are used as raw materials. They are first mixed in a mixing machine at a molar ratio of 1:5, and then added to a single screw press. The heating temperature is controlled at 240℃ to heat the ammonium sulfate to a molten state so that the molten salt can fully wet the surface of the graphite powder.

[0043] 2) Molding: The uniformly mixed graphite / molten salt powder is poured into a mold. An electrode current collector (metallic copper) is pre-placed at the bottom of the mold. The mixture covers the current collector and is vibrated to ensure the powder fully fills the mold and adheres tightly to the current collector. After sealing the mold, it is heated and molded on a flat vulcanizing machine at a temperature of 240℃ and a pressure of 40 MPa. The mixed powder and current collector are pressed into a single cylindrical composite graphite electrode.

[0044] 3) Intercalation: The prepared composite graphite electrode is installed as the anode in a reaction vessel lined with polytetrafluoroethylene (PTFE). A certain amount of ammonium bisulfate is added as the electrolyte, with a molar ratio of electrolyte to graphite powder of 5:1. A bulk graphite electrode is used as the cathode. After placing the anode, cathode, and electrolyte, the container is sealed with silicone rubber or PTFE gaskets. The interior of the container is heated to 240°C, and pressure is applied from one end of the cathode to maintain the pressure of the molten salt liquid within the container at approximately 4 atmospheres. Then, the composite graphite electrode at the anode is intercalated using a voltage of 0.8V and a current of 15A. The heating temperature is maintained at approximately 240°C throughout this process.

[0045] 4) Negative Pressure Exfoliation: The intercalated graphite powder is placed in a ceramic crucible and then placed in a vacuum microwave reactor. After sealing the reactor, the pressure inside the chamber is evacuated to below 100 Pa. Then, instantaneous microwave heating begins at a power of 15 kW. The graphite will expand and explode instantaneously, exfoliating into graphene. The amount of sample in the crucible should not be excessive; it depends on the volume of the chamber, the pressure it can withstand, and the depth of microwave heating.

[0046] Scanning electron microscope image of graphene prepared by the method in Example 3 is shown below. Figure 3 As shown in Figure a, the transmission electron microscope image is as follows. Figure 3 As shown in Figure b, the layer number distribution and flake size distribution of graphene are respectively... Figure 6 He Ru Figure 5 As shown, the graphene has 3-5 layers and the scales are 25-300 μm in size.

[0047] Example 4: A method for preparing low-defect graphene powder by high-temperature molten salt intercalation and instantaneous expansion, comprising the following steps:

[0048] The operating procedure is the same as in Example 1, except that the salt used for intercalation is replaced with potassium bisulfate, and the melting heating temperature is 220°C.

[0049] Scanning electron microscope image of graphene prepared by the method in Example 4 is shown below. Figure 4 As shown.

[0050] Example 5: A method for preparing low-defect graphene powder by high-temperature molten salt intercalation and instantaneous expansion, comprising the following steps:

[0051] The operation procedure is the same as in Example 2, except that the salt used for intercalation is replaced with ammonium sulfate, and the melting heating temperature is 240°C.

[0052] In addition, the mesh size of the graphite powder used can be changed (50-300 mesh), which determines the size of the flakes used to produce graphene, or the current can be changed to improve the intercalation efficiency.

[0053] In general, the greater the amount of gas generated during the decomposition of the intercalating agent (molten salt), the better the exfoliation effect. The heat treatment method also affects the exfoliation effect to some extent. The negative pressure high-power microwave exfoliation method is superior to the atmospheric pressure high-temperature quenching exfoliation method, mainly because microwave heating has a more significant instantaneous heating effect, while high-temperature quenching involves heat conduction between materials, a process that causes some of the intercalating agent to slowly leak out. Therefore, Example 3 showed the best exfoliation effect, with thinner graphene layers, specifically 3-5 layers, and flake sizes of 25-300 μm.

[0054] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for preparing low-defect graphene powder by high-temperature molten salt intercalation and instantaneous expansion, characterized in that, Includes the following steps: Step 1: Preparation of graphite / molten salt composite electrode: Graphite powder and salt for intercalation are initially mixed using a mixing mixer. The initially mixed material is then fed into a single-screw mixer, where the salt is heated to a molten state to fully impregnate the graphite powder surface. The mixture is then poured into a mold, with an electrode current collector pre-placed at the bottom of the mold, and the mixture covering the current collector. After sealing the mold, it is placed on a flat vulcanizing machine for heating and molding, pressing the mixture and current collector into a single composite graphite electrode. Step 2, Intercalation: The prepared composite graphite electrode is installed as the anode in a container, and the container is filled with salt for intercalation as the electrolyte, with the bulk graphite electrode as the cathode. The container is sealed and heated until the electrolyte melts. Pressure is applied from one end of the cathode into the container to maintain the pressure of the molten salt liquid within the range of 2-6 atmospheres. Then, current is applied under a low voltage of 0.5-1.2V and a high current of 5-40A to promote the intercalation reaction. The expansion and detachment of the composite graphite electrode at the anode are observed until all the intercalated expanded graphite is detached from the current collector. Step 3: Instant peeling, using negative pressure high-power microwave peeling method or normal pressure high-temperature quenching peeling method; The negative pressure high-power microwave stripping method is as follows: the intercalated graphite powder is placed in a sealed device that can simultaneously achieve vacuuming and microwave heating, and the graphite powder is instantly heated with a microwave power of 10-15KW, causing the intercalated material to instantly vaporize, the graphite powder to instantly expand and explode, and the graphite is stripped off. The atmospheric pressure high temperature quenching and stripping method is as follows: the intercalated graphite powder is instantly subjected to heating above 1000℃ or flame burning, so that the intercalated material is released instantly and the graphite is stripped off.

2. The method for preparing low-defect graphene powder by high-temperature molten salt intercalation instantaneous expansion according to claim 1, characterized in that, In step 1, the molar ratio of graphite powder to the salt used for intercalation is (3-6):1; the salt used for intercalation is a sulfate.

3. The method for preparing low-defect graphene powder by high-temperature molten salt intercalation instantaneous expansion according to claim 1, characterized in that, In step 1, the current collector is a mesh frame structure, and the current collector is made of metal or carbon fiber material.

4. The method for preparing low-defect graphene powder by high-temperature molten salt intercalation instantaneous expansion according to claim 1, characterized in that, In step 1, the composite graphite electrode is cylindrical or cuboid.

5. The method for preparing low-defect graphene powder by high-temperature molten salt intercalation instantaneous expansion according to claim 1, characterized in that, In step 1, when performing heating molding, the heating temperature does not exceed the decomposition temperature or vaporization temperature of the salt.

6. The method for preparing low-defect graphene powder by high-temperature molten salt intercalation instantaneous expansion according to claim 1, characterized in that, In step 2, the heating temperature is higher than the melting temperature of the salt, but lower than the decomposition temperature or vaporization temperature.

7. The method for preparing low-defect graphene powder by high-temperature molten salt intercalation instantaneous expansion according to claim 1, characterized in that, In step 2, the container is a reactor with a ceramic insulating inner layer, or a reaction vessel with a polytetrafluoroethylene liner is selected according to the melting temperature of the salt.

8. The method for preparing low-defect graphene powder by high-temperature molten salt intercalation instantaneous expansion according to claim 1, characterized in that, In step 2, the molar ratio of electrolyte to graphite powder is (5-6):1.

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