Low-energy-consumption green expandable graphite processing method

Abstract

The invention relates to the field of preparation of expandable graphite, in particular to a low-energy-consumption green expandable graphite processing method which comprises the following steps: firstly, carrying out microwave irradiation treatment on natural flake graphite to generate thermal stress cracks; and then the treated graphite serves as an anode and is placed in a composite electrolyte for constant-voltage electrochemical intercalation treatment. The electrifying duration and the initial voltage are adjusted in real time by detecting the settling velocity and the interlayer spacing of the intercalated graphite. Then, the intercalated graphite reaching the standard is placed in an organic solvent to be subjected to solvent replacement and auxiliary ultrasonic treatment, wormlike precursor graphite is obtained, and the preheating power of microwave expansion equipment is adjusted according to the turbidity of the replaced solution; and finally, determining the expansion duration by detecting the specific surface area of the precursor graphite. According to the method, the problem that in the prior art, the product quality is unstable due to the fact that the low-energy-consumption green expandable graphite electrolyte is prone to being excessively oxidized is solved through the process parameter adjusting procedure for detecting the expandable graphite.

Description

Technical Field

[0001] This invention relates to the field of expandable graphite preparation technology, and in particular to a low-energy-consumption and green expandable graphite processing method. Background Technology

[0002] Expandable graphite is an important deep-processed graphite product. Due to its rich layered structure, adjustable interlayer spacing, and good chemical stability, it is widely used in sealing materials, adsorbent materials, energy storage materials, and flame-retardant materials. Expanded graphite is typically produced by intercalating natural flake graphite to form graphite interlayer compounds, followed by rapid expansion under high temperature or microwave irradiation. Its expansion ratio is one of the core indicators for evaluating product quality.

[0003] Currently, the preparation methods for expandable graphite are mainly divided into two categories: chemical methods and electrochemical methods. Traditional chemical oxidation methods typically use strong oxidizing acids such as potassium permanganate, concentrated sulfuric acid, concentrated nitric acid, or perchloric acid to oxidize and intercalate graphite. However, this method has many shortcomings: on the one hand, the use of strong oxidizing acids poses serious safety hazards during production and generates large amounts of acidic wastewater, resulting in a heavy environmental burden and failing to meet the current requirements for green chemical development; on the other hand, traditional processes have high requirements for the particle size of graphite raw materials, and the intercalation process is unstable, leading to large fluctuations in the product expansion ratio and poor batch-to-batch consistency, making it difficult to meet the stable demand for high-performance expandable graphite in high-end applications.

[0004] To overcome the environmental and safety issues of traditional chemical methods, electrochemical intercalation has been proposed and gradually developed. This method uses graphite as the anode and performs oxidative intercalation in an electrolyte, reducing the use of strong oxidants. However, existing electrochemical methods still suffer from low intercalation efficiency and often rely on traditional electrolyte systems such as sulfuric acid and nitric acid, failing to fundamentally address the issue of process greening. Furthermore, process parameters in electrochemical treatment largely depend on empirical settings, lacking adjustments based on the state of intermediate products, resulting in unstable intercalation effects that directly impact the product quality of subsequent expansion processes. Summary of the Invention

[0005] Therefore, the present invention provides a low-energy-consumption, green, expandable graphite processing method to overcome the problem of unstable product quality caused by excessive oxidation of low-energy-consumption, green, expandable graphite electrolyte in the prior art.

[0006] Existing technologies suffer from problems such as unstable expansion ratios, high energy consumption, large environmental impact, and a lack of process control mechanisms.

[0007] To achieve the above objectives, the present invention provides a low-energy, green, expandable graphite processing method, comprising: Microwave irradiation was applied to natural flake graphite to obtain thermally stressed cracked flake graphite. A unit volume of the thermally stressed cracked flake graphite was selected as the anode and placed in a composite electrolyte for constant voltage electrochemical intercalation testing to obtain test intercalated graphite. The composite electrolyte comprises persulfate intercalating agent, carboxylic acid complexing agent, and deionized water. The intercalated graphite sample was placed in anhydrous ethanol solution, and the settling velocity and interlayer spacing of the intercalated graphite were detected. The energizing time and initial voltage of the constant voltage electrochemical intercalation treatment were adjusted according to the settling velocity and the interlayer spacing. The thermally stressed cracked flake graphite was used as the anode and placed in a composite electrolyte for constant-voltage electrochemical intercalation treatment according to the energizing time and the initial voltage to obtain intercalated graphite. The intercalated graphite was placed in an organic solvent for solvent replacement treatment and then subjected to auxiliary ultrasonic treatment to obtain worm-like precursor graphite. The preheating power of the microwave expansion device is determined based on the turbidity of the solution after solvent replacement treatment. The specific surface area of ​​expandable graphite precursor is detected, and the expansion time of the microwave expansion device is determined based on the specific surface area. The precursor graphite is placed in a microwave expansion device and expanded under the protection of an inert gas to obtain an expandable graphite product.

[0008] Further, adjusting the energizing duration of the constant-voltage electrochemical intercalation treatment based on the settling velocity and the interlayer spacing includes, The settlement velocity is compared with a preset settlement velocity threshold, and the interlayer spacing is compared with a preset interlayer spacing threshold. If the settling velocity is less than the preset settling velocity threshold, it is determined that the sulfate intercalating agent has undergone self-decomposition and oxygen production, and the energizing time of the constant voltage electrochemical intercalation treatment is reduced according to the difference between the preset settling velocity threshold and the settling velocity. If the interlayer spacing is less than the preset interlayer spacing threshold, the intercalation reaction is determined to be insufficient, and the intercalating agent molecules have not fully entered the graphite interlayer. The initial voltage of the constant voltage electrochemical intercalation treatment is increased according to the difference between the preset interlayer spacing threshold and the interlayer spacing.

[0009] Furthermore, the reduction in the energizing time of the constant voltage electrochemical intercalation treatment is positively correlated with the difference between the preset sedimentation velocity threshold and the sedimentation velocity.

[0010] Furthermore, the initial voltage increase of the constant voltage electrochemical intercalation treatment is positively correlated with the difference between the preset interlayer spacing threshold and the interlayer spacing.

[0011] Further, determining the preheating power of the microwave expansion device based on the turbidity of the solution after solvent displacement treatment includes, The turbidity of the solution is compared with a preset turbidity threshold. If the turbidity of the solution is less than the preset turbidity threshold, it is determined that a situation has occurred that leads to a high content of interlayer impurities, and the preheating power of the microwave expansion device is increased according to the difference between the preset turbidity threshold and the turbidity of the solution. If the turbidity of the solution is greater than or equal to the preset turbidity threshold, then the solvent replacement treatment is determined to meet the standard, and the preheating power of the microwave expansion device is the preset power.

[0012] Furthermore, the turbidity of the solution is a characterization value of the degree of light scattering by suspended particles in the mixed system after solvent replacement treatment.

[0013] Furthermore, the increase in preheating power is positively correlated with the difference between the preset solution turbidity threshold and the solution turbidity.

[0014] Further, determining the expansion duration of the microwave expansion device based on the specific surface area includes: The specific surface area is compared with a preset specific surface area threshold. If the specific surface area is less than a preset specific surface area threshold, it is determined that the interlayer structure expansion potential of the precursor graphite is limited, and the expansion time of the microwave expansion device is extended according to the difference between the preset specific surface area threshold and the specific surface area. If the specific surface area is greater than or equal to a preset specific surface area threshold, it is determined that the interlayer structure of the precursor graphite is well developed, and the expansion time of the microwave expansion device adopts a preset expansion time.

[0015] Furthermore, the extension of the expansion duration is positively correlated with the difference between the preset specific surface area threshold and the specific surface area.

[0016] Furthermore, the organic solvent used for solvent replacement treatment is selected from anhydrous ethanol, acetone or isopropanol, and the volume ratio of the organic solvent to the intercalated graphite is 4:1.

[0017] Compared with existing technologies, the advantages of this invention are as follows: By pretreating natural flake graphite with microwave irradiation, this invention utilizes the rapid volumetric heating characteristics of microwaves to generate a non-uniform thermal stress distribution within the graphite flakes, promoting the formation of microcracks and defect sites in the graphite crystal structure. These thermal stress cracks not only increase the specific surface area of ​​graphite, providing more active sites for subsequent electrochemical intercalation reactions, but also reduce the diffusion resistance of intercalator molecules into the graphite interlayers, thereby improving the intercalation efficiency.

[0018] Furthermore, this invention uses persulfate as an intercalating agent, combined with a carboxylic acid complexing agent to form a composite electrolyte system, avoiding the use of traditional strong oxidizing acids such as concentrated sulfuric acid and concentrated nitric acid. Under electrochemical oxidation conditions, persulfate can generate active oxygen species, achieving gentle oxidative intercalation between graphite layers. The introduction of the carboxylic acid complexing agent stabilizes metal ion impurities during the intercalation process, preventing their deposition between graphite layers. Simultaneously, the carboxylic acid molecules themselves enter the graphite interlayer, helping to widen the interlayer spacing.

[0019] Furthermore, this invention determines the occurrence of self-decomposition and oxygen production in the sulfate intercalating agent and judges whether the intercalation reaction is sufficient by measuring the settling velocity and interlayer spacing of the intercalated graphite. The settling velocity directly reflects the density and interlayer structural integrity of the intercalated graphite: when the sulfate intercalating agent undergoes self-decomposition and oxygen production, some of the generated oxygen molecules escape from the interlayer and form a gas film encapsulation effect on the graphite sheet surface, leading to a decrease in overall particle density and an increase in settling resistance, manifested as a significant slowdown in settling velocity; simultaneously, the retention of oxygen bubbles disrupts the homogeneity of the interlayer compounds, reducing subsequent expansion performance. The interlayer spacing, as a direct structural characterization of the intercalation reaction depth, indicates insufficient ion intercalation kinetics under electric field drive when it is below a threshold. This necessitates increasing the initial voltage to enhance the anodic oxidation driving force and promote the directional migration and intercalation of persulfate ions into the graphite interlayer.

[0020] Furthermore, the turbidity of the solution was used to determine whether the solvent replacement treatment met the standards, and the preheating power of the microwave expansion equipment was adjusted accordingly. Solution turbidity directly reflects the content of residual impurities and incompletely exfoliated agglomerates after solvent replacement of the intercalated graphite. When the turbidity is too low, it indicates that the organic solvent has not effectively penetrated deep into the interlayer, and the residual inorganic salt intercalating agent and complexing agent molecules will undergo violent decomposition during high-temperature expansion, generating a large amount of gas that causes a sudden increase in local pressure. This not only causes uneven expansion or even "deflagration," but also reduces product purity due to carbonized residues of impurities. Increasing the preheating power can accelerate the gentle pre-decomposition of interlayer residues, avoid stress concentration during the main expansion stage through staged gas release, and promote the pre-activation of interlayer compounds, making subsequent instantaneous high-temperature expansion more uniform and controllable.

[0021] Furthermore, the expansion time of the microwave expansion device is adjusted based on the specific surface area of ​​the expandable graphite precursor to determine whether the expansion potential of the interlayer structure of the precursor graphite is limited. Specific surface area directly reflects the degree of development of the graphite interlayer structure, and is related to the integrity of the intercalation reaction and the uniformity of the distribution of interlayer compounds. When the specific surface area is lower than a preset threshold, it indicates that the interlayer embedding depth of the precursor graphite is insufficient or that there is local aggregation of interlayer compounds, leading to uneven gas release kinetics and insufficient lamellar peeling during high-temperature expansion. Extending the expansion time provides more sufficient thermal action time for the gradual decomposition of interlayer compounds, promoting the complete volatilization of residual intercalating agents and the full expansion of lamellars, avoiding volume loss due to incomplete expansion. When the measured specific surface area is lower than the lower limit of the threshold, it indicates that the interlayer development of the precursor graphite is insufficient, and the expansion potential is limited, requiring an extended expansion time to promote the full development of the deep structure. After expansion, inert gas is used for rapid cooling to below 80°C before discharge to avoid product oxidation and structural collapse caused by high-temperature holding. Attached Figure Description

[0022] Figure 1 This is a flowchart of a low-energy, green, expandable graphite processing method according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating the process of adjusting the energizing time in the constant voltage electrochemical intercalation treatment according to an embodiment of the present invention. Figure 3 A flowchart of the preheating power of the microwave expansion device is determined for embodiments of the present invention; Figure 4 A flowchart for determining the expansion time of a microwave expansion device in an embodiment of the present invention. Detailed Implementation

[0023] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0024] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0025] Please see Figure 1-4 The following are flowcharts respectively: a low-energy-consumption, green, expandable graphite processing method according to an embodiment of the present invention; a flowchart of adjusting the energizing time of constant voltage electrochemical intercalation treatment according to an embodiment of the present invention; a flowchart of determining the preheating power of the microwave expansion device according to an embodiment of the present invention; and a flowchart of determining the expansion time of the microwave expansion device according to an embodiment of the present invention.

[0026] An embodiment of the present invention provides a low-energy, green, expandable graphite processing method, comprising: Step S1: Microwave irradiation is performed on natural flake graphite to obtain thermal stress cracked flake graphite. Step S2: Select a unit volume of the thermally stressed cracked flake graphite as the anode and place it in a composite electrolyte for constant voltage electrochemical intercalation testing to obtain test intercalated graphite. Step S3: Place the test intercalated graphite sample in anhydrous ethanol solution, detect the sedimentation rate of the test intercalated graphite and the interlayer spacing of the intercalated graphite, and adjust the energizing time and initial voltage of the constant voltage electrochemical intercalation treatment according to the sedimentation rate and the interlayer spacing. Step S4: The thermally stressed cracked flake graphite is used as the anode and placed in a composite electrolyte for constant voltage electrochemical intercalation treatment according to the energizing time and the initial voltage to obtain intercalated graphite. Step S5: The intercalated graphite is placed in an organic solvent for solvent replacement treatment and then subjected to auxiliary ultrasonic treatment to obtain worm-like precursor graphite. Step S6: Determine the preheating power of the microwave expansion device based on the turbidity of the solution after solvent replacement treatment; Step S7: Detect the specific surface area of ​​the expandable graphite precursor, and determine the expansion time of the microwave expansion device based on the specific surface area; Step S8: The precursor graphite is placed in a microwave expansion device and microwave expanded under the protection of an inert gas to obtain an expandable graphite product.

[0027] The composite electrolyte comprises persulfate intercalating agent, carboxylic acid complexing agent, and deionized water.

[0028] Specifically, the microwave irradiation treatment described in this embodiment uses an industrial-grade microwave reactor, with the microwave frequency set to 2450MHz, the irradiation power density controlled within the range of 2W / g-5W / g, and the irradiation duration of 3min-8min. During this treatment, the instantaneous heating generates thermal stress within the natural flake graphite, causing microcracks to form at the edges and defects of the graphite flakes. These microcracks provide channels for the entry of the intercalating agent during the subsequent electrochemical intercalation process, effectively reducing intercalation resistance and improving intercalation uniformity.

[0029] Specifically, the particle size range of the thermally stressed cracked flake graphite is 50-100 mesh. After microwave irradiation treatment, the surface crack density increases by 30%-50% compared with the untreated raw material, and the crack depth is 10%-20% of the thickness of the graphite flakes.

[0030] Specifically, the persulfate intercalating agent in the composite electrolyte is selected from ammonium persulfate or potassium persulfate, with a concentration of 0.5 mol / L to 1.5 mol / L; the carboxylic acid complexing agent is selected from citric acid or tartaric acid, with a concentration of 0.1 mol / L to 0.3 mol / L. The carboxylic acid complexing agent effectively inhibits the deposition of metal impurities on the anode surface during electrolysis by forming stable complexes with metal ions, maintaining electrode activity. Simultaneously, its weakly acidic environment slows down the spontaneous decomposition rate of persulfate, extending the effective service life of the electrolyte.

[0031] Specifically, the constant-voltage electrochemical intercalation treatment uses an anolyte current density of 50 mA / cm²-150 mA / cm², an initial voltage of 3V-6V, an electrolysis temperature of 25℃-45℃, and an energizing time of 30min-90min. During electrolysis, persulfate ions migrate directionally to the graphite interlayer under the influence of an electric field, undergoing an oxidation intercalation reaction. Carboxylic acid complexing agents synergistically maintain the stability of the electrolysis system, preventing uneven intercalation caused by drastic local pH fluctuations. The thermally stressed cracked flake graphite undergoes anodic oxidation in the composite electrolyte, and persulfate ions are embedded in the graphite interlayer under the influence of an electric field, forming a sulfate-graphite interlayer compound.

[0032] Specifically, the constant-voltage electrochemical intercalation test involves placing 0.5g-1.0g of the thermally stressed cracked flake graphite in the anode region of an electrolytic cell, using a graphite plate as the cathode, with the electrode spacing controlled at 2cm-4cm, and performing electrolysis under constant-voltage mode. During electrolysis, the current density change curve is monitored in real time. When the initial current density decays to 85% of its stable value, the intercalation reaction is considered to have entered a steady-state stage. A graphite sample at this point is then taken as the test intercalated graphite for subsequent analysis of sedimentation velocity and interlayer spacing. This electrolysis test step can effectively evaluate the intercalation reaction kinetics of different batches of raw materials, providing a basis for optimizing formal electrolysis process parameters.

[0033] Specifically, the sedimentation velocity is detected as follows: 10 mL of intercalated graphite sample is placed in 100 mL of anhydrous ethanol and allowed to stand in a constant temperature water bath at 25°C. The time required for the sample to settle from the liquid surface to the bottom is recorded, and the sedimentation distance per unit time is calculated as the sedimentation velocity. The interlayer spacing is measured using an X-ray diffractometer with a diffraction angle scanning range of 5°-30° and a scanning rate of 2° / min. When the interlayer spacing increases from 0.335 nm in the original graphite to more than 0.60 nm, it indicates that persulfate ions have successfully intercalated into the graphite interlayer and formed a stable interlayer compound structure. The expansion volume is determined according to the national standard GB / T 10698-1989. The dried intercalated graphite sample is placed in a muffle furnace at 950°C and heated for 30 seconds. The ratio of its expanded volume to its original mass is measured, with the unit being mL / g. In this embodiment, the expansion volume of expandable graphite after constant voltage electrochemical intercalation treatment reaches 250mL / g-350mL / g, which is 15%-25% higher than that of traditional chemical oxidation method, and the batch stability deviation is controlled within 5%.

[0034] Specifically, the microwave irradiation treatment in this embodiment uses an industrial-grade multi-cavity microwave reactor with a working frequency of 2450MHz±50MHz and an output power that is continuously adjustable from 3kW to 10kW. It is equipped with a rotating material tray to achieve uniform irradiation. The microwave reactor cavity is made of stainless steel lined with a polytetrafluoroethylene coating to effectively avoid microwave reflection and metal contamination. The effective volume of the cavity is 20L-50L to meet the needs of large-scale production. During the microwave irradiation treatment stage, the wet graphite filter cake after constant-voltage electrochemical intercalation is directly placed in the microwave reactor, controlling the material thickness to 2cm-5cm. Low-temperature rapid drying is performed under vacuum conditions of -0.08MPa to -0.06MPa. The microwave irradiation power density is set to 1W / g-3W / g of material, the irradiation time is 5min-15min, and the material temperature is monitored in real time and controlled within the range of 80℃-120℃ to avoid local overheating that could lead to premature decomposition and escape of the intercalating agent.

[0035] Specifically, the microwave irradiation treatment rapidly heats the polar molecules and interlayer compounds within the intercalated graphite through dipole rotation and ion conduction mechanisms. Moisture, under negative pressure, has its boiling point reduced to 60°C-80°C and is vaporized and removed, resulting in 40%-60% energy savings compared to traditional hot air drying. Simultaneously, the microwave electromagnetic field exerts a non-thermal effect on persulfate ions in the graphite interlayers, promoting their uniform distribution and enhancing their interaction with π electrons in the carbon layers, creating more favorable interlayer stress conditions for subsequent high-temperature expansion. After drying, the material's moisture content drops below 0.5%, allowing it to directly enter the high-temperature expansion process without intermediate cooling and transfer, achieving a compact process flow.

[0036] Specifically, the auxiliary ultrasonic treatment employs an ultrasonic cleaner or a tank-type ultrasonic reactor with a frequency of 20kHz-40kHz, an ultrasonic power density of 0.5W / cm²-2.0W / cm², and a treatment duration of 10-30 minutes. The ultrasonic treatment is performed simultaneously with the solvent replacement process. Utilizing the cavitation effect of ultrasound to generate localized high-pressure microjets, it effectively removes residual intercalating agent crystals and complexing agent molecules between the graphite flakes, promoting deep penetration of the organic solvent into the interlayer space, achieving efficient elution of impurities and sufficient relaxation of the interlayer structure. During the ultrasonic treatment, the solvent temperature is controlled within the range of 35℃-55℃ to avoid solvent evaporation and thermal decomposition of the intercalating agent due to excessively high temperatures.

[0037] Specifically, the microwave expansion device employs a single-cavity or traveling-wave microwave tube reactor, with a magnetron array as the microwave source. The total output power is 5kW-20kW, and the frequency stability is better than ±0.01%. The device is equipped with reaction tubes made of quartz glass or silicon nitride ceramic, with an inner diameter of 50mm-150mm and an effective heating section length of 500mm-1500mm, capable of withstanding instantaneous temperature shocks up to 1000℃. The inert gas protection system uses high-purity nitrogen or argon gas at a flow rate of 5L / min-20L / min to ensure that the oxygen content in the expansion chamber is below 50ppm, preventing the oxidation and burning of graphite at high temperatures.

[0038] Specifically, adjusting the energizing duration of the constant-voltage electrochemical intercalation treatment based on the settling velocity and the interlayer spacing includes, The settlement velocity is compared with a preset settlement velocity threshold, and the interlayer spacing is compared with a preset interlayer spacing threshold. If the settling velocity is less than the preset settling velocity threshold, it is determined that the sulfate intercalating agent has undergone self-decomposition and oxygen production, and the energizing time of the constant voltage electrochemical intercalation treatment is reduced according to the difference between the preset settling velocity threshold and the settling velocity. If the interlayer spacing is less than the preset interlayer spacing threshold, the intercalation reaction is determined to be insufficient, and the intercalating agent molecules have not fully entered the graphite interlayer. The initial voltage of the constant voltage electrochemical intercalation treatment is increased according to the difference between the preset interlayer spacing threshold and the interlayer spacing. If the settling velocity is greater than or equal to a preset settling velocity threshold and the interlayer spacing is greater than or equal to a preset interlayer spacing threshold, then the intercalation reaction is determined to meet the standard, and the constant voltage electrochemical intercalation treatment adopts a preset energizing time and initial voltage.

[0039] Specifically, in this embodiment, the preset sedimentation velocity threshold is set to 0.8 cm / min, and the preset interlayer spacing threshold is set to 0.65 nm. The sedimentation velocity and interlayer spacing of the intercalated graphite are used to determine whether the sulfate intercalating agent exhibits self-decomposition and oxygen production, and to assess the sufficiency of the intercalation reaction. With this setting, the sedimentation velocity directly reflects the density and interlayer structural integrity of the intercalated graphite: when the sulfate intercalating agent undergoes self-decomposition and oxygen production, some of the generated oxygen molecules escape from the interlayer and form a gas film encapsulation effect on the graphite sheet surface, leading to a decrease in overall particle density and an increase in sedimentation resistance, manifested as a significant slowdown in sedimentation velocity; simultaneously, the retention of oxygen bubbles disrupts the uniformity of the interlayer compounds, reducing subsequent expansion performance. As a direct structural characterization of the intercalation reaction depth, when the interlayer spacing is below the threshold, it indicates insufficient ion intercalation kinetics driven by the electric field. It is necessary to increase the initial voltage to enhance the anodic oxidation driving force and promote the directional migration and intercalation of persulfate ions into the graphite interlayer.

[0040] Specifically, the reduction in the energizing time of the constant-voltage electrochemical intercalation treatment is positively correlated with the difference between the preset sedimentation velocity threshold and the sedimentation velocity. It is understood that the positive correlation can be linear or nonlinear, and is not specifically limited. The slope of the linear positive correlation is also not specifically limited and can be set according to the actual preparation conditions, as long as the larger the difference between the preset sedimentation velocity threshold and the sedimentation velocity, the greater the reduction in the energizing time of the constant-voltage electrochemical intercalation treatment. For example, if the reduction in the energizing time of the constant-voltage electrochemical intercalation treatment is set to ΔM, and the difference between the preset sedimentation velocity threshold and the sedimentation velocity is set to Δμ, then ΔM = γ × Δμ + M0, where γ is the duration conversion coefficient, set to 1.16, M0 is the duration compensation reference value, and M0 is set to... 0取值为 5 minutes.

[0041] Specifically, the increase in the initial voltage of the constant-voltage electrochemical intercalation treatment is positively correlated with the difference between the preset interlayer spacing threshold and the interlayer spacing. It is understood that the positive correlation can be linear or nonlinear, and is not specifically limited. The slope of the linear positive correlation is also not specifically limited and can be set according to the actual fabrication conditions, as long as the difference between the preset interlayer spacing threshold and the interlayer spacing is larger, the increase in the initial voltage of the constant-voltage electrochemical intercalation treatment is larger. For example, if the increase in the initial voltage of the constant-voltage electrochemical intercalation treatment is set to ΔT, and the difference between the preset interlayer spacing threshold and the interlayer spacing is set to Δλ, then ΔT = α × Δλ + T0, where α is the voltage conversion coefficient, set to 1.12, and T0 is the initial voltage compensation reference value, set to 5V.

[0042] Specifically, determining the preheating power of the microwave expansion device based on the turbidity of the solution after solvent replacement treatment includes, The turbidity of the solution is compared with a preset turbidity threshold. If the turbidity of the solution is less than the preset turbidity threshold, it is determined that a situation has occurred that leads to a high content of interlayer impurities, and the preheating power of the microwave expansion device is increased according to the difference between the preset turbidity threshold and the turbidity of the solution. If the turbidity of the solution is greater than or equal to the preset turbidity threshold, then the solvent replacement treatment is determined to meet the standard, and the preheating power of the microwave expansion device is the preset power.

[0043] Specifically, the turbidity of the solution is used to determine whether the solvent replacement treatment meets the standards, and the preheating power of the microwave expansion equipment is adjusted accordingly. In this setting, the turbidity of the solution directly reflects the content of residual impurities and incompletely exfoliated agglomerates in the intercalated graphite after solvent replacement. When the turbidity is too low, it indicates that the organic solvent has not effectively penetrated deep into the interlayer. The residual inorganic salt intercalating agent and complexing agent molecules will undergo violent decomposition during high-temperature expansion, generating a large amount of gas and causing a sudden increase in local pressure. This not only causes uneven expansion or even "explosion," but also reduces product purity due to carbonized residues of impurities. Increasing the preheating power can accelerate the gentle pre-decomposition of interlayer residues, avoid stress concentration during the main expansion stage through staged gas release, and promote the pre-activation of interlayer compounds, making subsequent instantaneous high-temperature expansion more uniform and controllable. In this embodiment, the preset solution turbidity threshold is set to 80 NTU-120 NTU, and a turbidimeter is used to directly measure the supernatant after replacement at 25°C. The preheating power of the microwave expansion equipment is set to 3 kW-5 kW.

[0044] Specifically, solution turbidity is a characterization value of the degree of light scattering by suspended particles in the mixed system after solvent replacement treatment. The turbidity of the solution after solvent replacement treatment is monitored online using a turbidimeter with a measurement wavelength of 860nm±30nm, a range of 0NTU-200NTU, and a resolution of 0.1NTU. The preset solution turbidity threshold is set at 15NTU-25NTU, which corresponds to the critical concentration of suspended particles after thorough washing of intercalated graphite. When the measured turbidity is below the lower limit of the threshold, it indicates that the amount of interlayer impurities is too high, and the preheating power of the microwave expansion equipment needs to be increased to enhance the volatilization and removal effect of impurities during the subsequent expansion process; when the measured turbidity is within the threshold range, it indicates that the solvent replacement effect is good, and the microwave expansion equipment can be operated at the preset power.

[0045] Specifically, the heating rate of the microwave expansion is controlled in segments by adjusting the microwave output power: in the preheating stage, the temperature is increased to 150℃-180℃ at a rate of 10℃ / min-20℃ / min and maintained for 2min-5min to uniformly activate the interlayer compounds; in the rapid expansion stage, the temperature is increased to the target temperature of 250℃-300℃ at a rate of 30℃ / min-50℃ / min, during which the interlayer compounds rapidly decompose and release gases, driving the graphite sheets to violently peel off along the c-axis to form a worm-like structure. The preset expansion time is 90s, which is adjusted based on the specific surface area measurement results of the expandable graphite sample. The specific surface area is measured using the nitrogen adsorption BET method. Before testing, the sample is degassed under vacuum at 150℃ for 2h, and the relative pressure range is measured to be 0.05-0.30.

[0046] Specifically, the increase in preheating power is positively correlated with the difference between the preset solution turbidity threshold and the solution turbidity. It is understood that the positive correlation can be linear or nonlinear, and there is no specific limitation. The slope of the linear positive correlation is also not limited and can be set according to the actual preparation conditions, as long as the increase in preheating power is greater than the difference between the preset solution turbidity threshold and the solution turbidity. For example, if the increase in preheating power is set as ΔF, and the difference between the preset solution turbidity threshold and the solution turbidity is set as Δσ, then ΔF = β × Δσ + F0, where β is the power conversion coefficient, set to 0.96, and F0 is the power compensation benchmark value, set to 0.8kW. The power compensation benchmark value F0 is set based on the following: when the solution turbidity is critically low, it is necessary to ensure that the preheating power has a basic boosting capability to meet the minimum energy requirements for the pre-decomposition of interlayer impurities, avoiding carbonization and deposition of residues due to insufficient power increment.

[0047] Specifically, determining the expansion time of the microwave expansion device based on the specific surface area includes: The specific surface area is compared with a preset specific surface area threshold. If the specific surface area is less than a preset specific surface area threshold, it is determined that the interlayer structure expansion potential of the precursor graphite is limited, and the expansion time of the microwave expansion device is extended according to the difference between the preset specific surface area threshold and the specific surface area. If the specific surface area is greater than or equal to a preset specific surface area threshold, it is determined that the interlayer structure of the precursor graphite is well developed, and the expansion time of the microwave expansion device adopts a preset expansion time.

[0048] Specifically, the expansion time of the microwave expansion device is adjusted based on the specific surface area of ​​the expandable graphite precursor to determine whether the expansion potential of the interlayer structure of the precursor graphite is limited. This setting allows the specific surface area to directly reflect the degree of development of the graphite interlayer structure, relating to the integrity of the intercalation reaction and the uniformity of the distribution of interlayer compounds. When the specific surface area is below a preset threshold, it indicates insufficient interlayer embedding depth of the precursor graphite or local aggregation of interlayer compounds, leading to uneven gas release kinetics and insufficient lamellar peeling during high-temperature expansion. Extending the expansion time provides more sufficient thermal time for the gradual decomposition of interlayer compounds, promoting the complete volatilization of residual intercalating agents and the full expansion of lamellars, avoiding volume loss due to incomplete expansion. In this embodiment, the preset specific surface area threshold is set to 15 m² / g-25 m² / g, which corresponds to the typical structural characteristics of high-quality expandable graphite precursor. When the measured specific surface area is below the lower threshold, it indicates that the interlayer development of the precursor graphite is insufficient, limiting its expansion potential. The expansion time needs to be extended to promote the full development of the deep structure. When the measured specific surface area reaches or exceeds the threshold, it indicates that the interlayer structure is well-developed, and efficient expansion can be completed within the preset time. After expansion, inert gas is used for rapid cooling to below 80°C before discharge to avoid product oxidation and structural collapse caused by high-temperature storage.

[0049] Specifically, the extension of the expansion duration is positively correlated with the difference between the preset specific surface area threshold and the specific surface area. It is understood that the positive correlation can be linear or nonlinear, and there is no specific limitation. The slope of the linear positive correlation is also not specifically limited and can be set according to the actual preparation conditions, as long as the larger the difference between the preset specific surface area threshold and the specific surface area, the larger the extension of the expansion duration. For example, if the extension of the expansion duration is set to ΔA, and the difference between the preset specific surface area threshold and the specific surface area is set to Δη, then ΔA = φ × Δη + A0, where φ is the duration conversion coefficient, set to 1.24, and A0 is the duration compensation baseline value, set to 10 minutes.

[0050] Specifically, the organic solvent used for solvent replacement is selected from anhydrous ethanol, acetone, or isopropanol, with a volume ratio of organic solvent to intercalated graphite of 4:1. The equipment used for solvent replacement is a centrifugal filter or a vacuum filtration device with a filter cloth pore size of 1μm-5μm to ensure efficient solid-liquid separation while avoiding loss of fine particles through filtration. A three-stage countercurrent washing process is employed during replacement, with fresh solvent added from the final stage, contacting the intercalated graphite counter-currently, gradually increasing the concentration gradient of the washing liquid until the final concentration of residual intercalating agent in the replacement liquid is less than 0.1wt%. After replacement, nitrogen purging or vacuum drying is used to remove surface-adhered solvent. The nitrogen dew point is below -40℃, the vacuum degree is maintained between -0.08MPa and -0.095MPa, and the processing time is 15-30 minutes, reducing the residual solvent content on the material surface to below 0.5wt%, meeting the safe feeding requirements of the microwave expansion process.

[0051] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-energy, green, expandable graphite processing method, characterized in that, include: Microwave irradiation was applied to natural flake graphite to obtain thermally stressed cracked flake graphite. A unit volume of the thermally stressed cracked flake graphite was selected as the anode and placed in a composite electrolyte for constant voltage electrochemical intercalation testing to obtain test intercalated graphite. The composite electrolyte comprises persulfate intercalating agent, carboxylic acid complexing agent, and deionized water. The intercalated graphite sample was placed in anhydrous ethanol solution, and the settling velocity and interlayer spacing of the intercalated graphite were detected. The energizing time and initial voltage of the constant voltage electrochemical intercalation treatment were adjusted according to the settling velocity and the interlayer spacing. The thermally stressed cracked flake graphite was used as the anode and placed in a composite electrolyte for constant-voltage electrochemical intercalation treatment according to the energizing time and the initial voltage to obtain intercalated graphite. The intercalated graphite was placed in an organic solvent for solvent replacement treatment and then subjected to auxiliary ultrasonic treatment to obtain worm-like precursor graphite. The preheating power of the microwave expansion device is determined based on the turbidity of the solution after solvent replacement treatment. The specific surface area of ​​expandable graphite precursor is detected, and the expansion time of the microwave expansion device is determined based on the specific surface area. The precursor graphite is placed in a microwave expansion device and expanded under the protection of an inert gas to obtain an expandable graphite product.

2. The low-energy, green, expandable graphite processing method according to claim 1, characterized in that, The step of adjusting the energizing duration of the constant-voltage electrochemical intercalation treatment based on the settling velocity and the interlayer spacing includes, The settlement velocity is compared with a preset settlement velocity threshold, and the interlayer spacing is compared with a preset interlayer spacing threshold. If the settling velocity is less than the preset settling velocity threshold, it is determined that the sulfate intercalating agent has undergone self-decomposition and oxygen production, and the energizing time of the constant voltage electrochemical intercalation treatment is reduced according to the difference between the preset settling velocity threshold and the settling velocity. If the interlayer spacing is less than the preset interlayer spacing threshold, the intercalation reaction is determined to be insufficient, and the intercalating agent molecules have not fully entered the graphite interlayer. The initial voltage of the next batch of constant voltage electrochemical intercalation treatment is increased according to the difference between the preset interlayer spacing threshold and the interlayer spacing.

3. The low-energy, green, expandable graphite processing method according to claim 2, characterized in that, The reduction in the energizing time of the constant voltage electrochemical intercalation treatment is positively correlated with the difference between the preset sedimentation velocity threshold and the sedimentation velocity.

4. The low-energy, green, expandable graphite processing method according to claim 3, characterized in that, The initial voltage increase of the constant-voltage electrochemical intercalation treatment is positively correlated with the difference between the preset interlayer spacing threshold and the interlayer spacing.

5. The low-energy, green, expandable graphite processing method according to claim 4, characterized in that, The step of determining the preheating power of the microwave expansion device based on the turbidity of the solution after solvent displacement treatment includes, The turbidity of the solution is compared with a preset turbidity threshold. If the turbidity of the solution is less than the preset turbidity threshold, it is determined that a situation has occurred that leads to a high content of interlayer impurities, and the preheating power of the microwave expansion device is increased according to the difference between the preset turbidity threshold and the turbidity of the solution. If the turbidity of the solution is greater than or equal to the preset turbidity threshold, then the solvent replacement treatment is determined to meet the standard, and the preheating power of the microwave expansion device is the preset power.

6. The low-energy, green, expandable graphite processing method according to claim 5, characterized in that, Solution turbidity is a characterization value of the degree of light scattering by suspended particles in the mixed system after solvent replacement treatment.

7. The low-energy, green, expandable graphite processing method according to claim 6, characterized in that, The increase in preheating power is positively correlated with the difference between the preset solution turbidity threshold and the solution turbidity.

8. The low-energy, green, expandable graphite processing method according to claim 7, characterized in that, The expansion time of the microwave expansion device is determined based on the specific surface area. include, The specific surface area is compared with a preset specific surface area threshold. If the specific surface area is less than a preset specific surface area threshold, it is determined that the interlayer structure expansion potential of the precursor graphite is limited, and the expansion time of the microwave expansion device is extended according to the difference between the preset specific surface area threshold and the specific surface area. If the specific surface area is greater than or equal to a preset specific surface area threshold, it is determined that the interlayer structure of the precursor graphite is well developed, and the expansion time of the microwave expansion device adopts a preset expansion time.

9. The low-energy, green, expandable graphite processing method according to claim 8, characterized in that, The extent of the expansion duration is positively correlated with the difference between the preset specific surface area threshold and the specific surface area.

10. The low-energy, green, expandable graphite processing method according to claim 9, characterized in that, The organic solvent used for solvent replacement treatment is selected from anhydrous ethanol, acetone or isopropanol, and the volume ratio of the organic solvent to the intercalated graphite is 4:1.

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