Preparation process of high-expansion-ratio high-conductivity expandable graphite

Abstract

The application provides a preparation process of high-expansion-ratio high-conductivity expandable graphite, and belongs to the technical field of graphite preparation. The preparation process of the high-expansion-ratio high-conductivity expandable graphite comprises the following steps: pretreating high-purity natural graphite or artificial graphite powder to remove impurities; preparing an expanding agent; uniformly mixing the expanding agent into the graphite powder according to a proportion, to ensure that the expanding agent is in full contact with the graphite powder and uniformly distributed; placing the mixture of the mixed graphite and the expanding agent into a high-temperature furnace to perform multistage heat treatment, to form a graphite material with a porous structure; after the heat treatment is completed, screening the cooled expanded graphite to remove unreacted expanding agent; and performing surface modification treatment on the expanded graphite to enhance the conductivity of the expanded graphite. The application can solve the problems that the single heat treatment in the existing preparation process leads to poor structural stability of the graphite, and it is difficult to ensure the stability and mechanical properties of the expanded graphite.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of graphite preparation, and particularly relates to a preparation process of high-expansion-ratio high-conductivity expandable graphite. BACKGROUND

[0002] Expandable graphite is a material that increases the distance between graphite layers through a specific processing process, and is widely used in sealing, heat insulation, electrical conductivity and other fields. Graphite is a material with a layered structure, and its carbon atoms form a two-dimensional hexagonal lattice through covalent bonds, and the layers are combined by van der Waals force. Due to this structure, graphite has good electrical conductivity, thermal conductivity and mechanical strength. However, natural graphite does not have expansion capability at room temperature, so improving the expansion characteristics of graphite has become one of the research focuses. In order to make graphite have expansion capability, it is usually necessary to add an expanding agent to the graphite. The expanding agent can undergo a chemical reaction under heating conditions to release gas, causing the expansion of the graphite interlayer distance. The graphite treated by expansion has a larger interlayer distance and better electrical conductivity, and is widely used in the manufacture of conductive plastics, battery negative materials, etc.; due to its good elasticity and expansion characteristics, expandable graphite is often used in high-temperature sealing, heat exchange and other fields; due to the low thermal conductivity of expandable graphite, it is often used in high-temperature insulation materials.

[0003] The single heat treatment in the existing preparation process causes poor structural stability of the graphite, and it is difficult to ensure the stability and mechanical properties of the expanded graphite. SUMMARY

[0004] Therefore, the application provides a preparation process of high-expansion-ratio high-conductivity expandable graphite, which can solve the problem of poor structural stability of graphite caused by single heat treatment in the existing preparation process, and difficulty in ensuring the stability and mechanical properties of the expanded graphite.

[0005] The application is implemented as follows:

[0006] The application provides a preparation process of high-expansion-ratio high-conductivity expandable graphite, which includes the following specific steps:

[0007] S10: pretreating high-purity natural graphite or artificial graphite powder to remove impurities;

[0008] S20: preparing an expanding agent;

[0009] S30: uniformly mixing the expanding agent into the graphite powder in proportion to ensure sufficient contact and uniform distribution of the expanding agent and the graphite powder;

[0010] S40: placing the mixture of the mixed graphite and expanding agent in a high-temperature furnace for multi-stage heat treatment to form a graphite material with a porous structure;

[0011] S50: After the heat treatment is completed, the expanded graphite after cooling is screened to remove unreacted expanding agent;

[0012] S60: The expanded graphite is subjected to surface modification treatment to enhance its electrical conductivity, and the preparation of high-expansion-ratio high-conductivity expandable graphite is completed.

[0013] The specific steps of said surface modification treatment of the expanded graphite to enhance its electrical conductivity and complete the preparation of high-expansion-ratio high-conductivity expandable graphite include:

[0014] First, the expanded graphite is cleaned to remove possible oil stains, impurities or other contaminants on the surface to ensure the effect of subsequent modification treatment. Solvent or acid pickling method can be used to clean the graphite; the cleaned expanded graphite needs to be dried in an oven to remove water and solvent residues.

[0015] Second, the expanded graphite is subjected to surface modification by chemical method;

[0016] Third, the expanded graphite after surface modification needs to be subjected to high-temperature heat treatment at a temperature of 300°C to 800°C to further optimize its structure;

[0017] Fourth, the modified expanded graphite is subjected to a series of characterization analysis.

[0018] Common modifiers include oxidizing agents, fluorides, nitrides, etc. Common modification methods include:

[0019] Oxidation modification: using strong oxidizing agents (such as hydrogen peroxide, nitric acid, etc.) to oxidize the surface of the expanded graphite, generating oxygen-containing functional groups (such as carboxyl, hydroxyl, ether, etc.), which can enhance the hydrophilicity and electrical conductivity of the graphite surface.

[0020] Nitriding modification: through heat treatment under nitrogen atmosphere or nitriding agent (such as ammonia, silicon nitride) to treat the surface of the graphite, forming nitrogen-based functional groups to enhance the electrical conductivity of the graphite.

[0021] Surface coating: some materials with excellent electrical conductivity (such as carbon nanotubes, graphene, metal nanoparticles, etc.) are deposited on the surface of the expanded graphite by physical or chemical deposition method to improve its electrical conductivity. Common coating methods include:

[0022] Chemical vapor deposition (CVD): carbon nanotubes, graphene and other conductive materials are deposited on the surface of the expanded graphite by CVD technology.

[0023] Sol-gel method: conductive materials (such as metal oxides, graphene) are mixed with expanded graphite to form a composite through sol-gel reaction to improve the electrical conductivity.

[0024] On the basis of the above technical solutions, the preparation process of the high-expansion high-conductivity expandable graphite can be further improved as follows:

[0025] The specific steps for pre-treating the high-purity natural graphite or artificial graphite powder to remove impurities include:

[0026] First, mix the graphite powder with acid and perform acid washing to remove surface oxides, metal impurities and other soluble impurities;

[0027] Second, after acid washing, repeatedly rinse the graphite powder with deionized water to make the pH value of the graphite powder close to neutral;

[0028] Third, perform heat treatment on the graphite in a high-temperature environment to remove organic impurities and moisture; nitrogen is introduced during the heat treatment process to prevent further oxidation of the graphite;

[0029] Fourth, finely grind the graphite powder using a mechanical grinding device to make the particle size more uniform, remove larger impurity particles, and separate the ground powder by screening to separate impurities or larger particles of graphite with a particle size that is too large;

[0030] Fifth, perform ultrasonic cleaning on the graphite powder to remove fine impurities and particles attached to the surface of the graphite through high-frequency vibration of the ultrasonic waves;

[0031] Sixth, perform solvent extraction on the cleaned graphite to remove organic matter;

[0032] Seventh, completely dry the pre-treated graphite powder in a vacuum drying box to remove excess moisture.

[0033] Further, the specific steps for performing solvent extraction on the cleaned graphite to remove organic matter include:

[0034] First, add the solvent to a container to ensure that the volume of the solvent is greater than the volume of the graphite powder to ensure sufficient dissolution and extraction;

[0035] Second, add ions to the solvent and mix thoroughly to make the ions generate a turbulent electric field in the solvent;

[0036] Third, add the cleaned graphite powder to the solvent to ensure that the graphite is completely covered by the solvent and soak for 1-2 hours;

[0037] Fourth, continuously stir during the soaking process to make the solvent contact the organic matter on the surface of the graphite, promote the dissolution of the organic matter, and further introduce impurities into the solvent by the ions to improve the efficiency of the solvent extraction;

[0038] Fifth, filter the soaked impurities and repeatedly rinse them with deionized water;

[0039] The ion is one or more of Cl⁻, Na⁺, SO4²⁻, H⁺.

[0040] Further, the mechanical grinding device comprises an external drive assembly, a grinding bin, a grinding shaft, and a storage tube. The external drive assembly is arranged outside the grinding bin, the inner wall of the grinding bin is funnel-shaped, and the grinding shaft is arranged inside the grinding bin and has a spiral structure for grinding the graphite powder entering the mechanical grinding device through the extrusion between the grinding shaft and the inside of the grinding bin.

[0041] Further, the specific steps for completely drying the pretreated graphite powder by the vacuum drying oven to remove excess moisture include:

[0042] First, evenly distribute the pretreated graphite powder on the drying tray or grid plate of the drying oven, ensuring no stacking or overlapping;

[0043] Second, set the temperature of the drying oven to 60-70℃ and dry for 2-3 hours to start removing surface moisture from the graphite powder;

[0044] Third, heat the drying oven to 100-120℃ and dry for 4-6 hours to accelerate moisture evaporation;

[0045] Fourth, turn on the vacuum pump to ensure low pressure in the oven, further promoting moisture evaporation, and maintain the temperature in the vacuum oven at 80-100℃ for 2-3 hours to ensure the weight stability of the graphite powder;

[0046] Fifth, turn off the vacuum pump and gradually reduce the temperature of the drying oven to avoid excessive temperature difference causing sample moisture absorption, with a duration of about 1 hour.

[0047] Further, the specific steps for preparing the expanding agent include:

[0048] First, uniformly mix the expanding agent with the plasticizer and filler to ensure uniform distribution of the expanding agent and other ingredients;

[0049] Second, use a high-efficiency mixer for further mixing to ensure uniform mixing and prevent clumping or layering;

[0050] Third, place the mixed raw materials in an oven for 0.5-1 hours of thermal activation at a temperature of 80-120℃;

[0051] Fourth, place the expanding agent mixture in a vacuum drying oven to remove excess moisture in a vacuum environment, maintaining the vacuum drying temperature at 50-80℃ for 1-2 hours;

[0052] Step 5, use a pulverizer to crush the expanding agent material into fine powder, increase the surface area of the expanding agent, and enhance its expansion effect;

[0053] Step 6, screen out the larger particles by using a screen with a mesh size of 80-200.

[0054] Further, in the step of uniformly mixing the expanding agent into the graphite powder in a certain proportion, the proportion of the expanding agent added is between 8% and 10%.

[0055] Further, the specific steps of ensuring sufficient contact and uniform distribution of the expanding agent and graphite powder include:

[0056] Step 1, divide the expanding agent into multiple additions to the graphite powder, and thoroughly stir after each addition to avoid uneven contact between the expanding agent and the graphite powder when initially added;

[0057] Step 2, use a double or triple shaft mixer, start with low speed and gradually increase the stirring speed, so that the expanding agent penetrates better into each part of the graphite powder;

[0058] Step 3, after initial mixing, let it stand for a period of time to make the contact between the expanding agent and the graphite powder more uniform, and then perform a short subsequent mixing to ensure the final effect;

[0059] The overall temperature of the mixing process is set at 40-50℃, and the mixing time is 10-30 minutes.

[0060] Further, the specific steps of placing the mixture of mixed graphite and expanding agent in a high-temperature furnace for multi-stage heat treatment to form a graphite material with a porous structure include:

[0061] Step 1, evenly lay the dried mixture in a high-temperature resistant furnace tray or crucible to ensure uniform distribution of the material and avoid excessive accumulation; use a quartz crucible or ceramic crucible;

[0062] Step 2, slowly raise the furnace temperature from room temperature to 100-200℃ to gradually remove moisture and low-boiling-point volatiles from the material, avoiding violent expansion or decomposition of the material, and maintain for 30 minutes to 1 hour;

[0063] Step 3, raise the furnace temperature to the initial expansion temperature of the expanding agent, which is between 250-500℃, and the expanding agent starts to expand in the graphite powder; the temperature in this stage is set to 300-600℃ and maintained for 1-2 hours;

[0064] Fourth step, the temperature is raised to 600-1000℃, sintering treatment is carried out at this high temperature, and the temperature is kept for 2-4 hours, the structural stability of the graphite material is improved, and the reaction between the graphite and the expanding agent is further promoted at high temperature, forming a porous material with good porosity and stable structure;

[0065] Fifth step, after sintering is completed, the furnace temperature is gradually reduced to avoid cracks or damage to the material caused by sudden cooling, and the cooling rate is 20-50℃ per minute until the temperature returns to room temperature.

[0066] Further, after the heat treatment is completed, the expanded graphite after cooling is screened to remove unreacted expanding agent, and the specific steps include:

[0067] First step, use a vibrating screen device to finely screen the expanded graphite, so that the expanded graphite particles are separated by size; during the screening process, the unreacted expanding agent is easily separated due to its poor adhesion to the graphite particles;

[0068] Second step, use an air classifier to further process the screened material, and separate the light unreacted expanding agent from the heavier expanded graphite by adjusting the speed of the air flow and utilizing the difference in air flow.

[0069] The specific steps of using an air classifier to further process the screened material by adjusting the speed of the air flow and utilizing the difference in air flow to separate the light unreacted expanding agent from the heavier expanded graphite include:

[0070] First step, separate the expanded graphite and unreacted expanding agent by screening method to ensure that the particle size of the material in the air classifier is within a proper range. Generally speaking, smaller particle size materials (such as unreacted expanding agent) are suitable for separation by air classifier. Ensure that the material is free of moisture to avoid the influence of damp material on the classification effect of the air classifier. Drying or natural air drying methods can be used.

[0071] Second step, adjust the air flow speed of the air classifier according to the particle size and density of the material. The speed of the air flow determines the suspension time of the material in the classifier, affecting the classification effect. Light unreacted expanding agent is easily carried away by the air flow due to its small density, while heavier expanded graphite is relatively difficult to carry away. Adjust the direction and angle of the air flow according to the actual situation to ensure uniform distribution of the material in the air flow and achieve the best separation effect. The classification size range of the air classifier needs to be set according to the particle size distribution of the material to ensure that the target material can be effectively separated from the unwanted material during the classification process.

[0072] Third step, the screened and pretreated material is fed into the air classifier. After entering the classifier, the material is separated from the internal device by adjusting the airflow. The material is suspended in the airflow, and according to the particle size and density difference of the material, the lighter unreacted expanding agent is carried away by the airflow, while the heavier expanded graphite is collected by the collector below. The speed of the airflow and the internal setting of the air classifier control the accuracy of the separation.

[0073] Fourth step, the light material (unreacted expanding agent) carried away by the airflow enters the collector through the outlet of the airflow, usually using a bag dust collector or other suitable collection equipment for recycling. The heavier expanded graphite material falls into the collection container through the outlet at the bottom of the classifier, ensuring that the graphite particles are not wasted or excessively blown away.

[0074] Fifth step, the separated material is detected to ensure that the separation effect meets the expectations. The distribution and separation accuracy of the material can be verified by particle size analysis, weight measurement, etc. According to the separation effect, timely adjust the airflow speed, pressure and other parameters, optimize the working state of the classifier, further improve the separation efficiency.

[0075] Compared with the prior art, the preparation process of the high-expansion-ratio high-conductivity expandable graphite provided by the present application has the following advantages:

[0076] The high-purity natural or artificial graphite powder is pretreated to remove impurities, which ensures the purity of the graphite powder, removes surface oxides, metal impurities and other soluble impurities, and ensures the stability of the subsequent reaction and the quality of the graphite. Through steps such as acid pickling and ultrasonic cleaning, the graphite powder becomes more uniform and has higher reactivity.

[0077] The preparation steps of the expanding agent include mixing the expanding agent, plasticizer and filler, and heat-activating treatment to activate the expansion performance of the expanding agent. The final expanding agent removes excess water in a vacuum environment to ensure good expansion effect, and is crushed and sieved to ensure that the particle size of the expanding agent is suitable for mixing with the graphite powder.

[0078] The expanding agent is uniformly mixed with the graphite powder in proportion to ensure that the expanding agent and the graphite powder are in full contact and uniformly distributed. This step ensures that the expanding agent can fully penetrate the graphite powder by adding the expanding agent multiple times and using a double-shaft or triple-shaft mixer. Reasonable mixing can ensure that the expanding agent and the graphite powder are in full contact, thereby improving the expansion and conductivity performance.

[0079] By performing multi-stage heat treatment on the mixture of graphite and expanding agent in a high-temperature furnace, the expanding agent can expand in the graphite, and finally form a graphite material with a porous structure. In this process, the structural stability of the graphite is enhanced, and the pores formed are beneficial to improving its conductivity and expansion ratio.

[0080] After the heat treatment is completed and cooled, the unreacted expanding agent is removed by vibrating screen and air classifier. This can ensure that the final expanded graphite has high purity and avoid the negative impact of the expanding agent on the performance of the final product.

[0081] Surface modification treatment is a key step to enhance the electrical conductivity of expanded graphite. Through surface modification technology, the electrical conductivity of graphite can be effectively increased, further improving the application performance of graphite in battery, conductive material and other fields.

[0082] After acid washing and multi-step cleaning, the impurities of graphite powder are removed, and its surface becomes cleaner, ensuring the uniformity of subsequent reactions. Ultrasonic cleaning can remove small particles and improve the surface cleanliness of graphite. Solvent extraction of organic matter makes the graphite powder more pure, avoiding the interference of impurities on the expansion agent reaction.

[0083] Through mixing, thermal activation, vacuum drying and crushing, the particle size of the expanding agent is appropriate, and the expansion performance is improved. The treated expanding agent can better react with graphite in the heat treatment to form a porous structure.

[0084] Through uniform mixing, the expanding agent can be fully contacted with the graphite powder, so that the effect of the expanding agent is evenly distributed in the graphite powder, thereby improving the expansion ratio and electrical conductivity.

[0085] Through multi-stage heat treatment, the expanding agent expands in the graphite and forms pores. The temperature and time of heat treatment are set reasonably to ensure the stability of the pore structure of the graphite and improve its electrical conductivity.

[0086] Through fine screening, unreacted expanding agent is removed to ensure the quality of expanded graphite.

[0087] Surface modification treatment increases the electrical conductivity of graphite, so that it has good electrical conductivity performance at high expansion ratio. BRIEF DESCRIPTION OF DRAWINGS

[0088] Figure 1 A flowchart of a preparation process of high-expansion-ratio high-conductivity expandable graphite. DETAILED DESCRIPTION

[0089] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application.

[0090] As shown in Figure 1 A flowchart of a preparation process of high-expansion-ratio high-conductivity expandable graphite provided by the present application, which includes the following specific steps in the figure:

[0091] S10: pretreating high-purity natural graphite or artificial graphite powder to remove impurities;

[0092] S20: preparing an expanding agent;

[0093] S30: uniformly mixing the expanding agent into the graphite powder in a certain proportion to ensure sufficient contact and uniform distribution of the expanding agent and the graphite powder;

[0094] S40: placing the mixture of the mixed graphite and the expanding agent in a high-temperature furnace for multi-stage heat treatment to form a graphite material with a porous structure;

[0095] S50: after the heat treatment is completed, screening the expanded graphite after cooling to remove unreacted expanding agent;

[0096] S60: performing surface modification treatment on the expanded graphite to enhance its electrical conductivity, and completing the preparation of the high-expansion-ratio high-conductivity expandable graphite.

[0097] In the above technical solution, the specific steps for pretreating the high-purity natural graphite or artificial graphite powder to remove impurities include:

[0098] First, mix the graphite powder with acid for acid washing to remove surface oxides, metal impurities, and other soluble impurities;

[0099] Second, after acid washing, repeatedly rinse the graphite powder with deionized water to make the pH value of the graphite powder close to neutral;

[0100] Third, perform heat treatment on the graphite in a high-temperature environment to remove organic impurities and moisture; during the heat treatment, introduce nitrogen to prevent further oxidation of the graphite;

[0101] Fourth, use a mechanical grinding device to finely grind the graphite powder to make the particle size more uniform, remove larger impurity particles, and screen the ground powder to separate impurities or larger particles of graphite with excessively large particle size;

[0102] Fifth, perform ultrasonic cleaning on the graphite powder to remove fine impurities and particles attached to the surface of the graphite through high-frequency vibration of the ultrasonic waves;

[0103] Sixth, perform solvent extraction on the cleaned graphite to remove organic matter;

[0104] Seventh, completely dry the pretreated graphite powder in a vacuum drying box to remove excess moisture.

[0105] Further, in the above technical solution, the specific steps for performing solvent extraction on the cleaned graphite to remove organic matter include:

[0106] First, add solvent to the container, make sure the volume of the solvent is greater than the volume of the graphite powder, to ensure full dissolution and extraction;

[0107] Second, add ions to the solvent, mix well, so that the ions generate a turbulent electric field in the solvent;

[0108] Third, add the cleaned graphite powder to the solvent, make sure the graphite is completely covered by the solvent, soak for 1-2 hours;

[0109] Fourth, continuously stir during the soaking process, so that the solvent contacts the organic matter on the surface of the graphite, promoting the dissolution of the organic matter, and the ions further introduce impurities into the solvent, improving the efficiency of solvent extraction;

[0110] Fifth, filter the impurities after soaking and rinse repeatedly with deionized water;

[0111] The ions are one or more of Cl⁻, Na⁺, SO4²⁻, and H⁺.

[0112] Further, in the above technical solution, the mechanical grinding device includes an external drive assembly, a grinding bin, a grinding shaft, and a storage tube. The external drive assembly is arranged outside the grinding bin, the inner wall of the grinding bin is funnel-shaped, the grinding shaft is arranged inside the grinding bin, and the structure is spiral-shaped, used to grind the graphite powder entering the mechanical grinding device through the extrusion of the grinding shaft and the grinding bin.

[0113] Further, in the above technical solution, the specific steps for completely drying the pretreated graphite powder in the vacuum drying oven to remove excess moisture include:

[0114] First, evenly distribute the pretreated graphite powder on the drying tray or grid plate of the drying oven, ensuring no stacking or overlapping;

[0115] Second, set the temperature of the drying oven to 60-70℃, and dry for 2-3 hours to start removing the surface moisture of the graphite powder;

[0116] Third, heat the drying oven to 100-120℃, and dry for 4-6 hours to accelerate the evaporation of moisture;

[0117] Fourth, turn on the vacuum pump to ensure that the pressure in the oven is low, further promoting the evaporation of moisture, and maintain the temperature in the vacuum oven at 80-100℃ for 2-3 hours to ensure the weight stability of the graphite powder;

[0118] Fifth, turn off the vacuum pump and gradually reduce the temperature of the drying oven to avoid excessive temperature difference causing the sample to absorb moisture, and the duration is about 1 hour.

[0119] Further, in the above technical solution, the specific steps for preparing the expanding agent include:

[0120] First, uniformly mix the expanding agent with the plasticizer and the filler, and ensure uniform distribution of the expanding agent and other ingredients;

[0121] Second, use a high-efficiency mixer for further mixing to ensure uniform mixing and prevent clumping or layering;

[0122] Third, place the mixed raw materials in an oven and perform thermal activation at a temperature of 80-120°C for 0.5-1 hours;

[0123] Fourth, place the expanding agent mixture in a vacuum drying oven and remove excess moisture in a vacuum environment, maintaining a vacuum drying temperature of 50-80°C and a drying time of 1-2 hours;

[0124] Fifth, use a pulverizer to crush the expanding agent material into fine powder, increasing the surface area of the expanding agent and improving its expansion effect;

[0125] Sixth, screen the material through a screen with a mesh size of 80-200 to remove larger particles.

[0126] Further, in the above technical solution, the expanding agent is uniformly mixed into the graphite powder in a ratio of 8% to 10% to ensure full contact and uniform distribution of the expanding agent and the graphite powder.

[0127] Further, in the above technical solution, the specific steps for ensuring full contact and uniform distribution of the expanding agent and the graphite powder include:

[0128] First, divide the expanding agent into multiple additions to the graphite powder, and thoroughly stir after each addition to avoid uneven contact between the expanding agent and the graphite powder during the initial addition;

[0129] Second, use a double- or triple-shaft mixer to start stirring at low speed and gradually increase the stirring speed to allow the expanding agent to better penetrate into various parts of the graphite powder;

[0130] Third, after initial mixing, let the mixture stand for a period of time to allow the expanding agent and the graphite powder to make more uniform contact, and then perform a short period of subsequent mixing to ensure the final result;

[0131] The overall temperature of the mixing process is set to 40-50°C, and the mixing time is 10-30 minutes.

[0132] Further, in the above technical solution, the mixed mixture of graphite and expanding agent is placed in a high-temperature furnace for multi-stage heat treatment to form a graphite material with a porous structure, and the specific steps include:

[0133] First step, evenly spread the dried mixture in a high-temperature resistant furnace tray or crucible, ensure uniform distribution of materials, avoid stacking too high; use quartz crucible or ceramic crucible;

[0134] Second step, slowly raise the furnace temperature from room temperature to 100-200℃, for gradually removing moisture and low-boiling-point volatile substances in the material, avoid the material from swelling or decomposing violently, keep for 30 minutes to 1 hour;

[0135] Third step, raise the furnace temperature to the starting expansion temperature of the expanding agent, the activation temperature of the expanding agent is between 250-500℃, the expanding agent starts to expand in the graphite powder, the temperature in this stage is set to 300-600℃, and keep for 1-2 hours;

[0136] Fourth step, raise the temperature to 600-1000℃, sintering treatment is carried out at this high temperature, keep this temperature for 2-4 hours, improve the structural stability of the graphite material, and further promote the reaction between graphite and expanding agent at high temperature, form a porous material with good porosity and stable structure;

[0137] Fifth step, after sintering is completed, gradually reduce the furnace temperature, avoid sudden cooling leading to cracks or damage of the material, the cooling rate is 20-50℃ per minute, until the temperature returns to room temperature.

[0138] Further, in the above technical solution, after the heat treatment is completed, the expanded graphite after cooling is screened, and the specific steps of removing the unreacted expanding agent include:

[0139] First step, use a vibrating screen device to finely screen the expanded graphite, so that the expanded graphite particles are separated by size; during the screening process, the unreacted expanding agent is easily separated due to its poor adhesion to the graphite particles;

[0140] Second step, use an air classifier to further process the screened material, by adjusting the speed of the air flow, use the difference of air flow to separate the light unreacted expanding agent from the heavier expanded graphite.

[0141] Example 1: combination of natural graphite and expanding agent

[0142] Raw materials:

[0143] Natural graphite powder: 100g, particle size is 30 microns.

[0144] Expanding agent: 10g, use expanding agent with expansion rate of 500%.

[0145] Plasticizer: 2g.

[0146] Filler: 1g.

[0147] Steps:

[0148] Pre-treatment (S10): Wash the graphite powder with concentrated sulfuric acid (H2SO4) for 30 minutes to remove surface impurities, then rinse thoroughly with deionized water to remove acidic substances, and finally dry the graphite powder at 60°C for 12 hours to obtain high-purity graphite powder.

[0149] Expanding agent preparation (S20): Mix the expanding agent, plasticizer, and filler, grind them to a particle size of less than 50 microns using a ball mill, and then vacuum dry in a vacuum drying oven for 8 hours to remove excess moisture, obtaining granular expanding agent.

[0150] Mixing (S30): Mix 10g of expanding agent with 100g of graphite powder using a double-shaft mixer to ensure uniform distribution of the expanding agent. The mixing time is controlled at 30 minutes, and the stirring rate is 500 rpm.

[0151] Heat treatment (S40): Place the mixture in a high-temperature furnace for multi-stage heat treatment, initially heating to 300°C and maintaining for 1 hour, then heating to 700°C and maintaining for 2 hours to promote the reaction between the expanding agent and the graphite and form a porous structure.

[0152] Screening (S50): Use a vibrating screen to screen out unreacted expanding agent to ensure that the purity of the expanded graphite reaches more than 90%.

[0153] Surface modification (S60): Perform plasma surface modification using nitrogen and oxygen gases, with a treatment time of 30 minutes to improve the electrical conductivity of the graphite surface, ensuring that the electrical conductivity of the graphite reaches 1.2 × 10 4 S / m.

[0154] Example 2: Combination of artificial graphite with high-expansion-rate expanding agent

[0155] Raw materials:

[0156] Artificial graphite powder: 200g, particle size 20 microns.

[0157] High-expansion-rate expanding agent: 30g, expansion rate 700%.

[0158] Plasticizer: 5g.

[0159] Filler: 3g.

[0160] Steps:

[0161] Pre-treatment (S10): Perform acid-base neutralization treatment on the artificial graphite powder, first using concentrated sulfuric acid for acid washing, then using sodium hydroxide solution for neutralization, and finally cleaning with deionized water, drying to 80°C to remove moisture, obtaining high-purity graphite powder.

[0162] Preparation of the expansion agent (S20): The expansion agent and the plasticizer are mixed in proportion, and stirred for 30 minutes using a high-speed mixer to ensure uniform distribution of the expansion agent. Then, the water in the expansion agent is removed by vacuum drying.

[0163] Mixing (S30): 30g of the expansion agent is mixed with 200g of artificial graphite powder using a three-shaft mixer, with a stirring time of 45 minutes and a stirring rate of 600 rpm to ensure complete mixing of the expansion agent and the graphite powder.

[0164] Heat treatment (S40): Two-stage heat treatment is performed in a high-temperature furnace: the first stage is heating at 400°C for 1 hour; the second stage is heating to 900°C and maintaining for 3 hours, so that the expansion agent completely reacts with the graphite powder to form a porous structure.

[0165] Screening (S50): The screening operation uses a vibrating screen to remove unreacted expansion agent, and the final expanded graphite purity reaches more than 95%.

[0166] Surface modification (S60): The expanded graphite is surface modified, treated with 1% hydrogen fluoride (HF) solution for 10 minutes, so that the surface conductivity of the graphite is improved, and the final conductivity reaches 2.5 × 10 4 S / m.

[0167] Example 3: Mixing natural graphite with special expansion agent

[0168] Raw materials:

[0169] Natural graphite powder: 150g, particle size 40 microns.

[0170] Special expansion agent: 20g, expansion rate 600%.

[0171] Plasticizer: 3g.

[0172] Filler: 2g.

[0173] Steps:

[0174] Pre-treatment (S10): The natural graphite powder is treated by ultrasonic cleaning and acid pickling to ensure low impurity content and a graphite powder purity of 98%. Then, it is dried at 60°C for 12 hours.

[0175] Preparation of the expansion agent (S20): The expansion agent, plasticizer and filler are mixed in a ratio of 1:0.2:0.1, and fine grinding is performed using a ball mill to control the particle size to within 20 microns. After vacuum drying, the expansion agent is obtained.

[0176] Mixing (S30): The expanding agent and the natural graphite powder are uniformly mixed in proportion, and a double-shaft mixer is used for mixing, with a mixing time of 40 minutes to ensure uniform mixing.

[0177] Heat treatment (S40): The heat treatment is performed in a high-temperature furnace, with the temperature being raised to 350°C in the first stage and maintained for 1 hour, and then heated to 800°C in the second stage, and the heating is continued for 2 hours to ensure that the expanding agent expands in the graphite.

[0178] Screening (S50): The screening operation uses a 0.5mm screen to remove unreacted expanding agent, and finally the expanded graphite with a purity of up to 90% or more is obtained.

[0179] Surface modification (S60): Nitrogen modification treatment is used to improve the electrical conductivity of the expanded graphite, with a treatment time of 20 minutes, and the electrical conductivity reaches 1.8 × 10 4 S / m.

[0180] Specifically, the principle of the present application is as follows: when used, high-purity natural graphite or artificial graphite powder is pretreated to remove impurities; an expanding agent is prepared; the expanding agent is uniformly mixed into the graphite powder in proportion to ensure sufficient contact and uniform distribution of the expanding agent and the graphite powder; the mixture of the mixed graphite and the expanding agent is placed in a high-temperature furnace for multi-stage heat treatment to form a graphite material with a porous structure; after the heat treatment is completed, the expanded graphite after cooling is screened to remove unreacted expanding agent; and the expanded graphite is subjected to surface modification treatment to enhance its electrical conductivity, and the preparation of high-expansion-ratio high-conductivity expandable graphite is completed.

[0181] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A preparation process for expandable graphite with high expansion ratio and high conductivity, characterized in that, The specific steps include the following: S10: Pre-treat high-purity natural or artificial graphite powder to remove impurities; S20: Preparation of expanding agent; S30: Mix the expanding agent evenly into the graphite powder according to the specified ratio to ensure sufficient contact and uniform distribution between the expanding agent and the graphite powder; S40: The mixture of graphite and expanding agent is placed in a high-temperature furnace for multi-stage heat treatment to form a graphite material with a porous structure; S50: After heat treatment, the cooled expanded graphite is screened to remove unreacted expanding agent; S60: Surface modification treatment is performed on expanded graphite to enhance its conductivity, thus completing the preparation of high expansion ratio and high conductivity expandable graphite. The specific steps of S40 include: The first step is to evenly spread the dried mixture in a high-temperature resistant pan or crucible, ensuring uniform material distribution and avoiding excessive accumulation; use a quartz crucible or a ceramic crucible. The second step is to slowly raise the furnace temperature from room temperature to 100-200℃ to gradually remove moisture and low-boiling-point volatiles from the material, and to prevent the material from expanding or decomposing violently. This process is maintained for 30 minutes to 1 hour. The third step is to raise the furnace temperature to the initial expansion temperature of the expanding agent. The activation temperature of the expanding agent is between 250-500℃. The expanding agent begins to expand in the graphite powder. The temperature at this stage is set to 300-600℃ and maintained for 1-2 hours. The fourth step is to raise the temperature to 600-1000℃ and sinter at this high temperature for 2-4 hours to improve the structural stability of the graphite material and further promote the reaction between graphite and the expanding agent at high temperature to form a porous material with good porosity and stable structure. The fifth step is to gradually reduce the furnace temperature after sintering to avoid sudden cooling that could cause cracks or damage to the material. The cooling rate is 20-50°C per minute until the temperature returns to room temperature.

2. The preparation process of high expansion ratio and high conductivity expandable graphite according to claim 1, characterized in that, The specific steps of S10 include: The first step is to mix graphite powder with acid and perform acid washing to remove surface oxides, metallic impurities and other soluble impurities. The second step is to rinse the graphite powder repeatedly with deionized water after acid washing, so that the pH value of the graphite powder is close to neutral. The third step is to heat-treat the graphite at a high temperature to remove organic impurities and moisture; nitrogen gas is introduced during the heat treatment process to prevent further oxidation of the graphite. The fourth step is to use mechanical grinding equipment to finely grind the graphite powder to make the particle size more uniform, remove larger impurity particles, and then sieve the ground particles to separate the oversized impurities or larger graphite particles. The fifth step is to perform ultrasonic cleaning on the graphite powder, using the high-frequency vibration of ultrasound to remove fine impurities and particles attached to the graphite surface. The sixth step is to perform solvent extraction on the cleaned graphite to remove organic matter; The seventh step is to thoroughly dry the pretreated graphite powder in a vacuum drying oven to remove excess moisture.

3. The preparation process of high expansion ratio and high conductivity expandable graphite according to claim 2, characterized in that, The specific steps of the sixth step of S10 include: Step 1: Add the solvent to the container, ensuring that the volume of the solvent is greater than the volume of the graphite powder to ensure complete dissolution and extraction; Step 2: Add ions to the solvent and mix thoroughly to generate a disordered electric field in the solvent. Step 3: Add the cleaned graphite powder to the solvent, ensuring that the graphite is completely covered by the solvent, and soak for 1-2 hours. Step 4: Stir continuously during the soaking process to allow the solvent to come into contact with the organic matter on the graphite surface, promote the dissolution of the organic matter, and allow the ions to further introduce impurities into the solvent, thereby improving the efficiency of solvent extraction. Step 5: Filter the impurities after soaking and rinse them repeatedly with deionized water; The ions are one or more of Cl⁻, Na⁺, SO₄²⁻, and H⁺.

4. The preparation process of high expansion ratio and high conductivity expandable graphite according to claim 3, characterized in that, The mechanical grinding equipment includes an external drive assembly, a grinding chamber, a grinding shaft, and a storage pipe. The external drive assembly is located outside the grinding chamber, the inner wall of the grinding chamber has a funnel-like structure, and the grinding shaft is located inside the grinding chamber. It has a spiral structure and is used to grind the graphite powder entering the mechanical grinding equipment from the feed chamber by the extrusion between the grinding shaft and the inside of the grinding chamber.

5. The preparation process of high expansion ratio and high conductivity expandable graphite according to claim 4, characterized in that, The specific steps of the seventh step in S10 include: Step 1: Distribute the pretreated graphite powder evenly on the drying tray or grid plate of the drying oven, ensuring that there is no accumulation or overlap. Step 2: Set the temperature of the drying oven to 60-70℃ and dry for 2-3 hours to allow the graphite powder to begin to remove surface moisture. Step 3: Heat the drying oven to 100-120℃ and dry for 4-6 hours to accelerate the evaporation of moisture; Step 4: Turn on the vacuum pump to ensure that the pressure inside the chamber reaches a low level, further promoting the evaporation of moisture. Maintain the temperature inside the vacuum chamber at 80-100℃ for 2-3 hours to ensure the weight stability of the graphite powder. Step 5: Turn off the vacuum pump and gradually lower the temperature of the drying oven to avoid excessive temperature difference causing the sample to absorb moisture. This process should last for about 1 hour.

6. The preparation process of high expansion ratio and high conductivity expandable graphite according to claim 5, characterized in that, The specific steps of S20 include: The first step is to mix the expanding agent with the plasticizer and filler evenly to ensure that the expanding agent is evenly distributed with other components; The second step is to use a high-efficiency mixer to further mix the ingredients, ensuring a uniform mixture and preventing clumping or separation. The third step is to place the mixed raw materials into an oven and perform thermal activation at a temperature of 80-120℃ for 0.5-1 hour. The fourth step is to place the expansion agent mixture into a vacuum drying oven, remove excess moisture through a vacuum environment, maintain the vacuum drying temperature between 50-80℃, and dry for 1-2 hours. The fifth step is to use a pulverizer to break the expanding agent material into fine powder, thereby increasing the surface area of ​​the expanding agent and enhancing its expanding effect. The sixth step is to remove larger particles by sieving through a screen; the screen should have an aperture of 80-200 mesh.

7. The preparation process of high expansion ratio and high conductivity expandable graphite according to claim 6, characterized in that, In the step of uniformly mixing the expanding agent into the graphite powder according to the specified ratio to ensure sufficient contact and uniform distribution of the expanding agent with the graphite powder, the proportion of the expanding agent added is between 8% and 10%.

8. The preparation process of high expansion ratio and high conductivity expandable graphite according to claim 7, characterized in that, The specific steps of S30 include: The first step is to add the expanding agent to the graphite powder in multiple portions, stirring thoroughly after each addition to prevent uneven contact between the expanding agent and the graphite powder during the initial addition. The second step is to use a twin-shaft or tri-shaft mixer to start mixing at a low speed and gradually increase the mixing speed so that the expanding agent can better penetrate into all parts of the graphite powder. The third step is to let it stand for a period of time after the initial mixing to allow the contact between the expanding agent and the graphite powder to be more uniform, and then perform a short subsequent mixing to ensure the final effect. The overall temperature of the mixing process is set at 40-50℃, and the mixing time is 10-30 minutes.

9. The preparation process of high expansion ratio and high conductivity expandable graphite according to claim 8, characterized in that, The specific steps of S50 include: The first step is to use a vibrating screen to finely sieve the expanded graphite, separating the expanded graphite particles according to their size. During the sieving process, unreacted expanding agent is easily separated because it has poor adhesion to the graphite particles. The second step involves using an air classifier to further process the sieved material. By adjusting the airflow speed and utilizing the differences in airflow, the lighter unreacted expanding agent is separated from the heavier expanded graphite.

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