Graphene and preparation method thereof

Abstract

The invention relates to the technical field of preparation of carbon nanomaterials, and discloses graphene and a preparation method thereof.The preparation method comprises the following steps that an asphalt raw material is subjected to Soxhlet extraction and evaporation through an organic solvent and then carbonized at the temperature of 1000-1500 DEG C, and a carbonized intermediate of a lamellar structure is obtained; mechanically ball-milling and activating the carbonized intermediate, mixing the activated carbonized intermediate with an intercalator containing anhydrous ferric chloride, and carrying out constant-temperature reaction in an inert atmosphere under a heating condition; and carrying out acid pickling on the reaction product to remove metal salt, washing and freeze-drying to obtain a graphene product. A high-quality precursor is obtained through a solvent purification and carbonization process, damage of a strong oxidant to crystal lattices is avoided by utilizing a non-oxidation molten salt intercalation system, and lamellar agglomeration is effectively inhibited in cooperation with freeze drying; the process is simple and environment-friendly, the obtained graphene keeps a complete intrinsic structure and has the characteristics of few defects, good dispersity and the like, and high-valued utilization of cheap asphalt is realized.

Description

Technical Field

[0001] This invention relates to the field of carbon nanomaterial preparation technology, specifically to a graphene and its preparation method. Background Technology

[0002] Graphene is a type of graphene composed of carbon atoms arranged in sp... 2 Two-dimensional carbon nanomaterials with hexagonal honeycomb lattices composed of hybrid orbitals have broad application prospects in energy storage, composite materials and electronic devices due to their excellent optical, electrical and mechanical properties.

[0003] In the large-scale preparation of graphene, the selection of raw materials and cost control are key factors for achieving industrial application. Coal tar pitch, as a major by-product in the coal tar processing process, is widely available and has a high carbon content, making it an ideal low-cost carbon source. However, pitch components are extremely complex, containing a large number of non-aromatic hydrocarbons, quinoline insolubles, and metal impurities. Direct carbonization often leads to disordered product structure, low graphitization degree, and difficulty in controlling interlayer spacing, making it difficult to directly prepare high-quality graphene products through conventional methods.

[0004] Currently, the mainstream processes for preparing graphene include redox methods (such as the Hummers process) and liquid-phase exfoliation. Although redox methods have a high yield, they require the use of large amounts of strong acids and oxidants such as concentrated sulfuric acid and potassium permanganate during the reaction. This not only generates a large amount of difficult-to-treat acidic waste liquid and places extremely high demands on the corrosion resistance of the equipment, but also the strong oxidation will destroy the conjugated structure on the surface of graphene, introducing a large number of oxygen-containing functional groups and lattice defects, resulting in a decrease in the electrical and thermal conductivity of the final product. In addition, the selection of intercalating agents and subsequent exfoliation processes are also important factors that restrict the quality of graphene. Conventional chemical intercalation methods often have long reaction cycles, and the diffusion resistance of intercalating agent molecules between carbon layers is large, resulting in uneven intercalation or incomplete exfoliation.

[0005] On the other hand, strong van der Waals forces exist between graphene sheets, making them prone to irreversible secondary stacking and agglomeration during preparation and subsequent drying. This causes the prepared material to revert to a graphite-like layered structure, thus losing the unique high specific surface area and excellent physicochemical properties of single-layer or few-layer graphene. Existing drying processes, such as forced-air drying, exacerbate this agglomeration phenomenon under the contraction force at the gas-liquid interface, resulting in poor powder dispersibility. This makes it difficult to meet the requirements for graphene dispersion in high-performance composite materials and other fields. Therefore, developing a graphene preparation method with low raw material costs, green and environmentally friendly processes, and effective avoidance of product defects and agglomeration is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a graphene and its preparation method, which solves the problems of structural defects in products caused by numerous impurities in raw materials, damage to the crystal lattice structure and environmental pollution caused by traditional strong oxidation intercalation, and the easy occurrence of secondary agglomeration during product drying in existing pitch-based graphene preparation processes.

[0007] To achieve the above objectives, the present invention provides a method for preparing graphene, comprising the following steps: S1. Preparation of carbonization intermediate: The asphalt raw material is mixed with an organic solvent and extracted using Soxhlet extraction. The solvent is evaporated from the extracted product to obtain the precursor. The precursor is then subjected to high-temperature carbonization under an inert atmosphere to obtain the carbonization intermediate. S2, Intercalation reaction: The carbonized intermediate is mechanically ball-milled to obtain intermediate powder, the intermediate powder is mixed with an intercalating agent, and a constant-temperature reaction is carried out under an inert atmosphere and heating conditions to obtain the reaction product; the intercalating agent contains anhydrous ferric chloride; S3. Post-processing: After the reaction is completed, the reaction product is acid-washed to remove residual intercalating agent and by-products, washed with water until neutral, and finally dried to obtain graphene product.

[0008] By adopting the above technical solution, this invention achieves low-cost, large-scale preparation of pitch-based high-quality graphene. Its main mechanism and beneficial effects are as follows: First, in response to the problem that asphalt raw materials contain a large number of non-aromatic components and low molecular weight impurities, step S1 uses Soxhlet extraction to remove saturated hydrocarbons and low molecular weight components, thereby increasing the content and orientation of aromatic components in the precursor.

[0009] Secondly, the high-temperature carbonization process in step S1 transforms the precursor into a carbonized intermediate with a disordered layer structure, retaining the graphene-like six-membered ring framework. At the same time, its interlayer spacing is larger than that of an ideal graphite crystal, and the interlayer van der Waals forces are weak, which lowers the energy barrier of the subsequent intercalation reaction.

[0010] Furthermore, the S2 step differs from the strong oxidation system of the traditional Hummers process. Instead, it utilizes anhydrous potassium chloride as a Lewis acid, which acts as an electron acceptor under anhydrous and oxygen-free heating conditions. This promotes the entry of intercalator molecules or complex ions into the carbon atom interlayer to form graphite intercalation compounds. During this process, the shear force generated by mechanical ball milling pre-disrupts some of the interlayer forces and provides mechanical energy to overcome the diffusion resistance of the intercalator, promoting its uniform distribution and deep exfoliation between carbon layers.

[0011] Finally, step S3, combined with acid washing and drying processes, removes residual metal salts between layers while preventing the stacking of sheets caused by the contraction force at the gas-liquid interface, thereby maintaining the highly dispersed, low-layer structure of graphene.

[0012] Preferably, in step S1, the organic solvent is selected from toluene, pyridine, N,N-dimethylformamide, or n-hexane; The mass ratio of the asphalt raw material to the organic solvent is 1:5 to 1:8; The Soxhlet extraction temperature is 120℃~170℃.

[0013] By adopting the above technical solution, the selective dissolution effect of solvents with different polarities is utilized, along with a specific extraction temperature and solvent ratio, to effectively remove non-graphitized components and obtain a high-purity precursor with uniform composition, providing a raw material basis for the formation of a homogeneous carbon layer structure.

[0014] Preferably, in step S1, the specific process of the high-temperature carbonization treatment is as follows: Heat to 1000℃~1500℃ at a heating rate of 2~5℃ / min, and hold for 1~2 hours; Alternatively, the high-temperature carbonization treatment can employ a segmented heating process: First, raise the temperature to 1000℃, then raise it to 1250℃~1500℃ and hold it thereafter.

[0015] By adopting the above technical solution, by controlling the heating rate and the final temperature, structural collapse or micropore blockage caused by the rapid escape of volatiles due to excessive heating rate can be prevented. The temperature range of 1000℃-1500℃ keeps the material in the stage of semi-coke to coke conversion, and the resulting intermediate has a suitable graphite microcrystal size and interlayer spacing for intercalation and exfoliation.

[0016] Preferably, in step S2, the rotation speed of the mechanical ball milling process is 500-800 r / min, and the ball milling time is 8-12 hours; The intercalating agent is composed of anhydrous potassium chloride and a second chloride salt; The second chloride salt is selected from one or a combination of several of ferric chloride, anhydrous aluminum chloride, or sodium chloride.

[0017] By adopting the above technical solution, a eutectic molten salt system is formed by introducing a second chloride salt and ferric chloride, which reduces the melting point and viscosity of the intercalating agent and enhances the fluidity and diffusion rate of the intercalating agent between carbon layers.

[0018] Preferably, in step S2, the specific composition of the intercalating agent satisfies one of the following conditions: The intercalating agent is composed of anhydrous potassium chloride and ferric chloride in a mass ratio of 5:4. The intercalating agent is composed of anhydrous potassium chloride and anhydrous aluminum chloride, with a mass ratio of 5:4 to 7:2. The intercalating agent is composed of anhydrous potassium chloride, aluminum chloride and sodium chloride in a mass ratio of 2:1:1.

[0019] By adopting the above technical solution, a stable eutectic molten salt system can be formed by specific component ratios, ensuring that the intercalating agent is in a good molten active state at the reaction temperature, promoting the full intercalation reaction, and improving the peelability of the product.

[0020] Preferably, in step S2, the total mass ratio of the intermediate powder to the intercalating agent is controlled to be 1:8 to 1:11; The isothermal reaction is carried out at a temperature of 150℃ to 300℃ for 8 to 12 hours.

[0021] By adopting the above technical solution, a sufficient amount of intercalating agent helps shift the intercalation reaction equilibrium towards the formation of intercalated compounds; suitable temperature and time ensure the completeness of the reaction while meeting the requirements of reaction kinetics.

[0022] Preferably, in step S3, the acid solution used for pickling is hydrochloric acid solution, sulfuric acid solution or nitric acid solution, and the acid concentration is 0.5 to 1 mol / L; the drying treatment specifically adopts a freeze-drying process.

[0023] By employing the above technical solution, dilute acid washing converts and removes the interlayer metal chlorides into soluble ions. Freeze-drying allows water to sublimate directly from the solid to the gaseous state, eliminating the capillary contraction caused by the surface tension of liquid water and effectively preventing secondary agglomeration of graphene sheets during the drying process, thereby obtaining high-quality graphene in a fluffy powder form.

[0024] This invention provides a method for preparing graphene. It has the following beneficial effects: 1. This invention uses industrial byproducts such as coal tar pitch or mesophase pitch as raw materials, and prepares carbonized intermediates with suitable interlayer spacing through solvent extraction purification and high-temperature carbonization control. This effectively removes impurity components in pitch that hinder graphitization, improves the structural regularity of the precursor, and realizes the high-value utilization of inexpensive carbon raw materials, thereby reducing the preparation cost of high-performance graphene.

[0025] 2. This invention uses a metal chloride molten salt system for intercalation reaction, avoiding the use of strong acids and oxidants such as concentrated sulfuric acid and potassium permanganate in traditional redox methods. The reaction conditions are mild, avoiding oxidation and damage to the graphene carbon lattice, preserving the intrinsic structure and excellent conductivity of graphene. At the same time, it significantly reduces the difficulty of waste liquid treatment and the corrosion resistance requirements of production equipment, improving the safety and environmental protection of the production process.

[0026] 3. This invention effectively overcomes the diffusion resistance of the intercalating agent between carbon layers through the synergistic effect of mechanical ball milling and molten salt intercalation, thereby improving the exfoliation efficiency. Combined with subsequent dilute acid cleaning and freeze-drying processes, it effectively inhibits the secondary agglomeration of graphene sheets while removing residual intercalating agent. The resulting graphene product has the characteristics of low defect density, good dispersibility, and high powder bulkiness. Attached Figure Description

[0027] Figure 1 This is a SEM image of the graphene prepared in Comparative Example 1 of the present invention. Figure 2 This is a SEM image of the graphene prepared in Comparative Example 5 of the present invention. Figure 3 This is a SEM image of the graphene prepared in Example 1 of the present invention; Figure 4 This is a SEM image of the graphene prepared in Example 3 of the present invention; Figure 5 This is a SEM image of the graphene prepared in Example 4 of the present invention; Figure 6 This is a SEM image of the graphene prepared in Example 5 of the present invention. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Preparation Examples 1-4: Preparation Example 1: This preparation example provides a carbonization intermediate B, the preparation process of which includes the following steps: Coal tar pitch was used as raw material. The coal tar pitch and toluene were mixed in a mass ratio of 1:6. The Soxhlet extraction method was used to extract the mixture at 160°C under magnetic stirring until the reflux liquid was colorless. The extracted product was evaporated at 120°C for 10 hours to obtain precursor A; Precursor A was placed in a tube furnace and carbonized under argon protection. The temperature was increased to 1000°C at a rate of 5°C / min, and then increased to 1400°C at a rate of 2°C / min. After holding at this temperature for 2 hours, the furnace was cooled to obtain intermediate B.

[0030] Preparation Example 2: This preparation example provides a carbonization intermediate B, the preparation process of which includes the following steps: Mesophase pitch was used as raw material and mixed with pyridine at a mass ratio of 1:8. The Soxhlet extraction method was used to extract the mixture at 130°C under magnetic stirring until the reflux liquid was colorless. The extracted product was evaporated at 120°C for 10 hours to obtain precursor A; Precursor A was placed in a tube furnace and carbonized under argon protection. The temperature was increased to 1000℃ at a rate of 5℃ / min, held for 2 hours, and then cooled in the furnace to obtain intermediate B.

[0031] Preparation Example 3: This preparation example provides a carbonization intermediate B, the preparation process of which includes the following steps: Coal tar pitch was used as raw material. The coal tar pitch and N,N-dimethylformamide were mixed in a mass ratio of 1:5. The Soxhlet extraction method was used to extract the mixture at 170°C under magnetic stirring until the reflux liquid was colorless. The extracted product was evaporated at 150°C for 8 hours to obtain precursor A; Precursor A was placed in a tube furnace and carbonized under argon protection. The temperature was increased to 1000°C at a rate of 5°C / min, and then increased to 1500°C at a rate of 2°C / min. After holding at this temperature for 1 hour, the furnace was cooled to obtain intermediate B.

[0032] Preparation Example 4: This preparation example provides a carbonization intermediate B, the preparation process of which includes the following steps: Mesophase pitch was used as raw material and mixed with n-hexane at a mass ratio of 1:7. The Soxhlet extraction method was used to extract the mixture at 120°C under magnetic stirring until the reflux liquid was colorless. The extracted product was evaporated at 100°C for 9 hours to obtain precursor A; Precursor A was placed in a tube furnace and carbonized under argon protection. The temperature was increased to 1000°C at a rate of 5°C / min, and then increased to 1250°C at a rate of 2°C / min. After holding at this temperature for 2 hours, the furnace was cooled to obtain intermediate B.

[0033] Examples 1-6: Example 1

[0034] This embodiment provides a method for preparing graphene, including the following steps: Take intermediate B obtained in Preparation Example 1, place it in a ball mill, and ball mill it for 10 hours at a speed of 600 r / min to obtain intermediate powder; The intermediate powder is mixed with the intercalating agent, which is composed of anhydrous potassium chloride and ferric chloride in a mass ratio of 5:4, and the total mass ratio of the intermediate powder to the intercalating agent is controlled to be 1:9. The mixed materials were placed in a reaction vessel and heated to 200°C under argon protection, and reacted at a constant temperature for 12 hours. After the reaction was completed, the product was cooled to room temperature, soaked in a 1 mol / L hydrochloric acid solution and stirred for 12 hours, the solid was separated by filtration, and the product was repeatedly washed with deionized water until the filtrate was neutral. The wet filter cake was placed in a freeze dryer for freeze drying to obtain powdered graphene product (see appendix for details). Figure 3 ). Example 2

[0035] This embodiment provides a method for preparing graphene, including the following steps: Take intermediate B obtained in Preparation Example 2, place it in a ball mill, and ball mill it for 10 hours at a speed of 600 r / min to obtain intermediate powder; The intermediate powder is mixed with the intercalating agent, which is composed of anhydrous potassium chloride and ferric chloride in a mass ratio of 5:4, and the total mass ratio of the intermediate powder to the intercalating agent is controlled to be 1:9. The mixed materials were placed in a reaction vessel and heated to 200°C under argon protection, and reacted at a constant temperature for 12 hours. After the reaction was completed, the product was cooled to room temperature, soaked in a 1 mol / L hydrochloric acid solution and stirred for 12 hours, the solid was separated by filtration, and the product was repeatedly washed with deionized water until the filtrate was neutral. The wet filter cake was placed in a freeze dryer for freeze drying to obtain powdered graphene product. Example 3

[0036] This embodiment provides a method for preparing graphene, including the following steps: Take intermediate B obtained in Preparation Example 1, place it in a ball mill, and ball mill it for 9 hours at a speed of 650 r / min to obtain intermediate powder; The intermediate powder is mixed with the intercalating agent, which is composed of anhydrous potassium chloride and anhydrous aluminum chloride in a mass ratio of 5:4, and the total mass ratio of the intermediate powder to the intercalating agent is controlled to be 1:10. The mixed materials were placed in a reaction vessel and heated to 220°C under argon protection, and reacted at a constant temperature for 10 hours. After the reaction was completed, the product was cooled to room temperature, soaked in 0.8 mol / L hydrochloric acid solution and stirred for 10 hours, the solid was separated by filtration, and the product was repeatedly washed with deionized water until the filtrate was neutral. The wet filter cake was placed in a freeze dryer for freeze drying to obtain powdered graphene product (see appendix for details). Figure 4 ). Example 4

[0037] This embodiment provides a method for preparing graphene, including the following steps: Take intermediate B obtained in Preparation Example 4, place it in a ball mill, and ball mill it for 12 hours at a speed of 500 r / min to obtain intermediate powder; The intermediate powder is mixed with the intercalating agent, which is composed of anhydrous potassium chloride and anhydrous aluminum chloride in a mass ratio of 7:2, and the total mass ratio of the intermediate powder to the intercalating agent is controlled to be 1:11. The mixed materials were placed in a reaction vessel and heated to 150°C under argon protection, and reacted at a constant temperature for 12 hours. After the reaction was completed, the product was cooled to room temperature, soaked in a 0.5 mol / L sulfuric acid solution and stirred for 12 hours. The solid was separated by filtration and washed repeatedly with deionized water until the filtrate was neutral. The wet filter cake was placed in a freeze dryer for freeze drying to obtain powdered graphene product (see appendix for details). Figure 5 ).

[0038] Example 5: This example provides a method for preparing graphene, including the following steps: Take intermediate B obtained in Preparation Example 3, place it in a ball mill, and ball mill it for 8 hours at a speed of 800 r / min to obtain intermediate powder; The intermediate powder is mixed with the intercalating agent, which is composed of anhydrous potassium chloride and anhydrous aluminum chloride in a mass ratio of 7:2, and the total mass ratio of the intermediate powder to the intercalating agent is controlled to be 1:8. The mixed materials were placed in a reaction vessel and heated to 300°C under argon protection, and reacted at a constant temperature for 8 hours. After the reaction was completed, the product was cooled to room temperature, soaked in 1 mol / L nitric acid solution and stirred for 8 hours, the solid was separated by filtration, and washed repeatedly with deionized water until the filtrate was neutral. The wet filter cake was placed in a freeze dryer for freeze drying to obtain powdered graphene product. Example 6

[0039] This embodiment provides a method for preparing graphene, including the following steps: Take intermediate B obtained in Preparation Example 2, place it in a ball mill, and ball mill it for 10 hours at a speed of 700 r / min to obtain intermediate powder; The intermediate powder is mixed with the intercalating agent, which is composed of anhydrous potassium chloride, potassium chloride and sodium chloride in a mass ratio of 2:1:1. The total mass ratio of the intermediate powder to the intercalating agent is controlled to be 1:9.5. The mixed material is placed in a reaction vessel and heated to 250°C under argon protection and reacted at a constant temperature for 10 hours. After the reaction was completed, the product was cooled to room temperature, soaked in 0.8 mol / L hydrochloric acid solution and stirred for 10 hours, the solid was separated by filtration, and the product was repeatedly washed with deionized water until the filtrate was neutral. The wet filter cake was placed in a freeze dryer for freeze drying to obtain powdered graphene product (see appendix for details). Figure 6 ).

[0040] Comparative Examples 1-7: Comparative Example 1: Compared with Example 1, the difference lies in that the solvent extraction and evaporation steps were omitted in the preparation of intermediate B. The coal tar pitch raw material was directly carbonized according to the carbonization procedure of Preparation Example 1. Everything else was the same. The resulting product was still a multi-layered stacked block, and no graphene was observed (see Appendix for details). Figure 1 ).

[0041] Comparative Example 2: Compared with Example 1, the difference is that the intercalating agent used in the step was replaced with sodium nitrate and potassium nitrate (mass ratio 1:1), and all other steps were the same. The resulting product was still a multi-layered stacked block, and no graphene was observed.

[0042] Comparative Example 3: Compared with Example 1, the difference is that the intercalating agent used in the step was replaced with sodium chloride and potassium chloride (mass ratio 1:1), and all other steps were the same. The resulting product was still a multi-layered stacked block, and no graphene was observed.

[0043] Comparative Example 4: Compared with Example 5, the difference is that the ball milling step of intermediate B was omitted, and the block intermediate B was directly mixed with the intercalating agent for reaction. Everything else was the same, and the resulting product was still a multi-layered stacked block, with no graphene present.

[0044] Comparative Example 5: Compared with Example 5, the difference lies in controlling the total mass ratio of intermediate powder to intercalating agent to be 1:3 in the steps, while all other steps are the same. The resulting product is still a multi-layered stacked block, and no graphene is observed. However, the delamination phenomenon at the edge of the block is intensified (see Appendix for details). Figure 2 ).

[0045] Comparative Example 6: Compared with Example 5, the difference is that the final drying step was dried in an 80°C forced-air drying oven instead of freeze drying. All other steps were the same, and no graphene was observed.

[0046] Comparative Example 7: Compared with Example 1, the difference is that the highest carbonization temperature during the preparation of intermediate B is 800°C, while the rest are the same, and no graphene is observed.

[0047] Test Example 1-2: Test Example 1: The products prepared in Examples 1-6 and Comparative Examples 1-7 were characterized in terms of performance. Powder samples were dispersed in ethanol, sonicated for 30 minutes, and the supernatant was dropped onto the surface of mica sheets. After drying, the thickness of the sheets was measured using atomic force microscopy (AFM). The average value of 50 sheets was calculated and the number of layers was converted.

[0048] The D peak (1350 cm⁻¹) was recorded using a micro Raman spectroscopy system at an excitation wavelength of 532 nm. -1 ) and G peak (1580cm) -1 ) strength and calculate The ratio is used to characterize the degree of defect.

[0049] The powder sample was pressed into a disc with a diameter of 13 mm under a pressure of 20 MPa, and the conductivity was measured using the four-probe method. The mass of the freeze-dried powder and the mass of the added carbonized intermediate were weighed, and the mass yield was calculated. The test results for each sample are shown in Table 1.

[0050]

[0051] The average thickness of Comparative Example 6 in Table 1 is marked as - because the sample was dried in a forced-air drying oven, which caused severe irreversible hard agglomeration between the graphene sheets. During AFM sample preparation and dispersion, it could not be effectively separated into individual sheets, thus making it impossible to measure an accurate thickness value for each sheet. Comparative Example 3 had a high yield of 98.2%, indicating that the product did not undergo significant exfoliation and remained a graphite-like powder.

[0052] Conclusion and analysis: The average thickness of the graphene products prepared in Examples 1-6 is between 0.8-1.6 nm (approximately 2-5 layers). The ratios were all below 0.3, and the conductivity was above 1000 S / m. Example 5, using a precursor carbonized at 1500℃ in conjunction with a ferric chloride / aluminum chloride system, reacted at 300℃, obtaining the lowest defect degree (0.11) and the highest conductivity. This indicates that the intermediate obtained through solvent purification combined with carbonization at a specific temperature, under the action of molten metal chloride, can be reacted without destroying the sp... 2 Interlayer stripping is achieved under the premise of a conjugate structure.

[0053] In Comparative Example 1, omitting the solvent extraction step resulted in a product thickness of 4.52 nm and a decrease in conductivity. Impurities and non-aromatic components in the raw material interfered with the ordered arrangement of graphite crystals, hindering the diffusion and reaction of the intercalating agent between layers.

[0054] Comparative Example 7 reduced the carbonization temperature to 800℃, and the product... The ratio increased to 0.88, and the electrical conductivity was only 112.4 S / m. Under conditions below 1000℃, the precursor failed to form graphite microcrystalline domains of sufficient size, and the high content of amorphous carbon led to numerous lattice defects and obstructed electron transport, making it impossible to prepare high-quality graphene.

[0055] Comparative Example 2 used a nitrate system, and although the product thickness was smaller, The conductivity is as high as 0.98, which is a decrease. The strong oxidizing property of nitrates destroys the carbon atom lattice and introduces oxygen-containing defects. In contrast, the metal chloride system used in this application utilizes an electron transfer complexation mechanism, which is a non-destructive intercalation. This is also the reason why the sample in the example maintains high conductivity.

[0056] Comparative Example 3, which used only alkali metal chlorides, produced a thick product, indicating that it failed to be exfoliated. This confirms that the system must contain transition metal chlorides with Lewis acidity to overcome interlayer van der Waals forces.

[0057] Comparative Examples 4 and 5 verified the effects of mechanical activation and intercalator dosage, respectively. Omitting ball milling resulted in insufficient reaction kinetics and an increase in the number of product layers; too low an intercalator dosage led to incomplete exfoliation.

[0058] Comparative Example 6 was dried in an oven, and severe agglomeration was observed by AFM, indicating that freeze drying is necessary to maintain the dispersion of the powder.

[0059] Test Example 2: The powders prepared in Examples 1-6 and Comparative Examples 1-7 were selected as electrode active materials for electrochemical performance testing. Graphene powder, acetylene black and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) was added to prepare a slurry. The slurry was coated on the surface of a nickel foam current collector, vacuum dried and then pressed into a sheet to obtain the working electrode.

[0060] A three-electrode testing system was constructed, with a platinum sheet as the counter electrode, a saturated calomel electrode as the reference electrode, and a 6 mol / L potassium hydroxide solution as the electrolyte.

[0061] Constant current charge-discharge (GCD) tests were performed using an electrochemical workstation, with the voltage window set from -1.0V to 0V. Specific capacity data were recorded at different current densities, and capacity retention was determined by performing 5000 charge-discharge cycles at a current density of 5A / g. Electrochemical test data for each sample are shown in Table 2.

[0062]

[0063] Conclusion Analysis: The specific capacities of the samples in Examples 1-6 at a current density of 1 A / g ranged from 158 to 216 F / g. When the current density was increased by 10 times, the rate retention remained above 74%, and the capacity retention after 5000 cycles exceeded 90%. Among them, Example 5 showed the best performance, which was attributed to its high degree of graphitization and few-layer structure. The few-layer characteristics provided abundant double-layer adsorption interfaces, while the complete carbon lattice structure ensured the rapid migration of electrons during charging and discharging, thereby reducing the internal resistance of the electrode and improving the rate performance.

[0064] The specific capacity and rate performance of Comparative Example 1 were both lower than those of the Example. Residual impurities in the raw materials not only reduced the effective specific surface area but also hindered the rapid diffusion of electrolyte ions.

[0065] Comparative Example 2, employing nitrate oxidation intercalation, exhibited a certain specific capacity at low rates, but its rate retention was only 56.9%, and cycle retention dropped to 68.5%. The oxidation process introduced oxygen-containing functional groups and lattice defects into the carbon framework, increasing electron transport impedance. Furthermore, this highly defective structure is prone to structural collapse during repeated charge-discharge cycles. In contrast, the data from the examples demonstrate the advantages of metal chloride non-oxidative intercalation technology in maintaining material structural stability and conductivity.

[0066] Comparative Example 3, due to the lack of effective stripping, has a small specific surface area and exhibits extremely low specific capacity, thus lacking practical value for capacitor energy storage.

[0067] Comparative Example 7, due to its low carbonization temperature, mainly consists of amorphous carbon with poor conductivity, resulting in severe polarization during high-current charge and discharge, and a rate performance of only 32.2%.

[0068] Comparative Example 6 did not employ freeze drying, resulting in powder agglomeration, which reduced the effective solid-liquid contact area and decreased the specific capacity by approximately 40-50% compared to the examples under the same conditions. This demonstrates the importance of the drying process in maintaining active sites.

Claims

1. A graphene, characterized in that, include: It is prepared by intercalation reaction of the following raw materials in parts by weight under an inert atmosphere and under heating conditions: Carbonized intermediate powder: 100 parts; Intercalating agent: 800-1100 parts.

2. A method for preparing graphene, characterized in that, The method for preparing the graphene according to claim 1 includes the following steps: S1. Preparation of carbonization intermediate: The asphalt raw material is mixed with an organic solvent and extracted using Soxhlet extraction. The solvent is evaporated from the extracted product to obtain the precursor. The precursor is then subjected to high-temperature carbonization under an inert atmosphere to obtain the carbonization intermediate. S2, Intercalation reaction: The carbonized intermediate is mechanically ball-milled to obtain intermediate powder, the intermediate powder is mixed with an intercalating agent, and a constant-temperature reaction is carried out under an inert atmosphere and heating conditions to obtain the reaction product; the intercalating agent contains anhydrous potassium chloride; S3. Post-processing: After the reaction is completed, the reaction product is acid-washed to remove the intercalating agent, washed with water until neutral, and finally dried to obtain the graphene product.

3. The method for preparing graphene according to claim 2, characterized in that, In step S1, the organic solvent is selected from toluene, pyridine, N,N-dimethylformamide, or n-hexane; The asphalt raw material includes one of medium-temperature coal tar pitch, mesophase asphalt, coated asphalt, and high softening point asphalt. The mass ratio of the asphalt raw material to the organic solvent is 1:5 to 1:8; The Soxhlet extraction temperature is 120℃~170℃.

4. The method for preparing graphene according to claim 2, characterized in that, In step S1, the specific process of the high-temperature carbonization treatment is as follows: Heat to 1000℃~1500℃ at a heating rate of 2~5℃ / min, and hold for 1~2 hours; Alternatively, the high-temperature carbonization treatment can employ a segmented heating process: First, raise the temperature to 1000℃, then raise it to 1250℃~1500℃ and hold it thereafter.

5. The method for preparing graphene according to claim 2, characterized in that, In step S2, the rotation speed of the mechanical ball milling process is 500-800 r / min, and the milling time is 8-12 hours.

6. The method for preparing graphene according to claim 2, characterized in that, In step S2, the intercalating agent is composed of anhydrous potassium chloride and a second chloride salt; The second chloride salt is selected from one or a combination of several of ferric chloride, anhydrous aluminum chloride, or sodium chloride.

7. The method for preparing graphene according to claim 4, characterized in that, The specific composition of the intercalating agent satisfies one of the following conditions: The intercalating agent is composed of anhydrous potassium chloride and ferric chloride in a mass ratio of 5:

4. The intercalating agent is composed of anhydrous potassium chloride and anhydrous aluminum chloride, with a mass ratio of 5:4 to 7:

2. The intercalating agent is composed of anhydrous potassium chloride, aluminum chloride and sodium chloride in a mass ratio of 2:1:

1.

8. The method for preparing graphene according to claim 2, characterized in that, In step S2, the total mass ratio of the intermediate powder to the intercalating agent is controlled to be 1:8 to 1:

11.

9. The method for preparing graphene according to claim 2, characterized in that, In step S2, the temperature of the isothermal reaction is 150℃~300℃, and the reaction time is 8~12 hours.

10. A method for preparing graphene according to claim 2, characterized in that, In step S3, the acid solution used for pickling is hydrochloric acid solution, sulfuric acid solution or nitric acid solution, and the acid concentration is 0.5 to 1 mol / L; In step S3, the drying process specifically employs a freeze-drying process.

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