Method for preparing few-layer-like graphene through bubble assistance-liquid phase mechanical exfoliation method

Abstract

The invention relates to the technical field of composite materials, in particular to a method for preparing few-layer-like graphene through a bubble assistance-liquid phase mechanical exfoliation method. The method comprises the following steps: S1, bubble generation and intercalation treatment: putting graphite slurry, a foaming agent and a dispersing agent into a reaction kettle, reacting at the reaction temperature of 80-100 DEG C, and continuously reacting until the graphite layer spacing is expanded to a preset range [01]; s2, crushing and washing treatment: putting the graphite slurry obtained in the step S1 into a high-shear washing device, carrying out crushing and washing treatment at a high rotating speed, and introducing pure water for cleaning until the measured value of a conductivity detector is 50 us / cm to 100 us / cm; the graphite washing material obtained in the second step and the second step is placed in a freeze dryer, expansion treatment is carried out through pre-freezing and sublimation drying, and the pre-freezing temperature ranges from-70 DEG C to-90 DEG C. According to the method, the layer number and the thickness of the few-layer-like graphene can be controlled by utilizing the synergistic effect of bubble expansion, mechanical shearing and freeze drying through multi-layer experimental design.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of composite materials, in particular to a method for preparing oligolayer graphene by a bubble-assisted liquid-phase mechanical exfoliation method. BACKGROUND

[0002] The development of two-dimensional carbon materials is reshaping the modern industrial technology landscape. Among them, oligolayer graphene (usually defined as 2-10 layers of graphene stacks) has become a core material for driving the innovation of energy storage, flexible electronic devices and advanced composites due to its unique electrical, thermal and mechanical properties. Studies have shown that the number of layers and the lateral size of graphene are key parameters that determine the upper limit of performance. Reducing the number of layers can significantly improve electrical conductivity - phonon scattering increases exponentially with layer thickness, causing the in-plane thermal conductivity of more than ten layers of graphene to drop to 60% of that of a single layer. There are still significant defects in the current industrialized production of high-quality oligolayer graphene.

[0003] Although the mechanical exfoliation method can produce low-defect graphene, the single batch processing time is more than 72 hours, and the yield is less than 0.1%, and it is difficult to control the layer distribution (usually 3-8 layers mixed); the chemical vapor deposition method (CVD) can realize wafer-level preparation, but it requires a copper / nickel substrate to react at a high temperature of 1000°C, and the energy consumption per square meter is more than 30kWh, and the subsequent acid etching and transfer process not only introduces crack and wrinkle defects, but also generates about 5L of heavy metal-containing waste liquid per square meter; Although the redox method is simple, the epoxy group generated in the strong oxidation stage destroys the sp2 lattice integrity, and even after hydrazine reduction, the residual hydroxyl group and vacancy defects still make the electrical conductivity decay to less than 10% of that of intrinsic graphene, and the number of layers of the product is uncontrollable (usually 3-8 layers stacked). Although the emerging liquid-phase exfoliation technology can control the number of layers by adjusting the surface energy of the solvent, the high-frequency mechanical impact generated by conventional ball milling and ultrasonic process leads to two contradictory effects: on the one hand, it causes irregular stacking of the layers to form a "nano origami" structure, and on the other hand, excessive shear produces a large number of nanoscale fragments, which seriously restricts the structural regularity of conductive materials.

[0004] Therefore, developing an efficient exfoliation technology that has uniform layer number, controllable flake size, low structural defects and green process has become a strategic demand to break through the bottleneck of industrial application of oligolayer graphene.

[0005] In view of the above industry pain points, the "bubble-assisted liquid-phase mechanical exfoliation method" proposed by the present application successfully solves the contradiction between efficiency and quality of traditional processes by synergistically regulating cavitation effect and shear dynamics to realize high-precision directional exfoliation of graphene. The product has 10-25 2-10

[03] layers, the proportion of which is more than 80%, the lateral size is concentrated in 0.5-2 microns, and the thickness is 0.6-3 nanometers. SUMMARY

[0006] This application provides a method for preparing oligolayer-like graphene using a bubble-assisted liquid-phase mechanical exfoliation method to solve the above-mentioned problems.

[0007] This application provides a method for preparing oligolayer-like graphene using a bubble-assisted liquid-phase mechanical exfoliation method, the method comprising: S1. Bubble generation and intercalation treatment: Graphite slurry, foaming agent and dispersant are placed in a reaction vessel and reacted at a reaction temperature of 80°C to 100°C. The reaction continues until the interlayer spacing of graphite expands to a preset range, which is 0.5 nm to 1.5 nm. S2. Crushing and washing treatment: The graphite slurry obtained in step S1 is placed in a high-shear washing device for crushing and washing at high speed, and then rinsed with pure water until the conductivity detector measures 50us / cm to 100us / cm. S3. Freeze-drying treatment: The graphite washing material obtained in step S2 is placed in a freeze dryer and expanded by pre-freezing and sublimation drying, wherein the pre-freezing temperature is -70℃ to -90℃. In the final product obtained through steps S1, S2 and S3, the proportion of 2-10 layer oligolayer graphene sheets is >80%, the lateral size is concentrated in 0.5-2 micrometers, and the thickness is 0.6-3 nanometers

[04] .

[0008] Through the aforementioned technical solution, the interlayer spacing of graphite is controllably expanded by the synergistic effect of bubble expansion and mechanical shearing. This results in a layer distribution of the obtained oligolayer-like graphene concentrated between 10 and 25 layers (2 to 10 layers, accounting for >80%), with lateral dimensions controlled between 0.5 μm and 2 μm, and thicknesses ranging from 3 nm to 0.6 nm to 34.5 nm. Furthermore, the electrical conductivity remains stable within the range of 50 μS / cm to 100 μS / cm, significantly improving the electrical consistency and structural integrity of the material. Compared to traditional methods, this method avoids high-temperature or strong oxidizing environments, reduces defect rates (such as vacancies and hydroxyl residues), and features low energy consumption and high yield, making it suitable for large-scale production.

[0009] Optionally, in step S1, the solid content of the graphite slurry is 10% to 15%, and the particle size range of the graphite slurry is 5 micrometers to 10 micrometers.

[0010] Through the above technical solution, the uniformity of bubble distribution and intercalation efficiency are significantly improved by synergistic control of solid content and particle size, making the process of expanding interlayer spacing highly repeatable; after subsequent high-shear crushing, the number of oligolayer graphene layers is concentrated between 10 and 25 layers and between 2 and 10 layers, the lateral size consistency is improved, and the electrical performance stability is enhanced.

[0011] Optionally, in step S1, the foaming agent is selected from at least one of the following: a combination of potassium bicarbonate and hydrochloric acid, a combination of sodium bicarbonate and citric acid, a combination of ammonium carbonate and acetic acid, a combination of hydrogen peroxide and manganese dioxide, and ammonium bicarbonate.

[0012] Through the above technical solution, the synergistic effect of multiple foaming agents was achieved to precisely control the bubble size and release rate, which improved the uniformity of graphite interlayer spacing by about 40%. The standard deviation of the number of layers of the exfoliated oligolayer graphene was reduced from ±5 layers in the traditional method to ±2 layers, and the crystal integrity (ID / IG≤0.08) was significantly better than that of a single foaming system.

[0013] Optionally, in step S1, the preferred combination of the foaming agent is a combination of potassium bicarbonate and hydrochloric acid, wherein the mass concentration of potassium bicarbonate is 0.5wt% to 1.5wt% and the concentration of hydrochloric acid is 0.7wt% to 2.5wt%.

[0014] By employing the above technical solution and matching the concentrations of potassium bicarbonate and hydrochloric acid, the gas generation rate and interlayer spacing expansion were synergistically controlled, improving the repeatability of the process and the uniformity of the graphene layer number. The resulting oligolayer-like graphene exhibits a more concentrated interlayer spacing distribution and a reduced defect rate, which is beneficial for improving the electrical consistency and subsequent application performance of the material.

[0015] Optionally, the reactor in step S1 is equipped with a temperature control system, a three-layer stirring paddle, a condenser, and an ultrasonic transmitter. The three-layer stirring paddle includes: A bottom impeller, a middle impeller, and a top impeller are arranged along different heights of the reactor via a concentric shaft sleeve structure. The bottom impeller is a disc turbine impeller, the middle impeller is a wide-bladed axial flow impeller, and the top impeller is a slanted blade. The bottom impeller is positioned below the middle impeller, and the middle impeller is positioned below the top impeller. The bottom impeller, the middle impeller, and the top impeller are all in contact with the graphite slurry inside the reactor.

[0016] Through the aforementioned technical solution, the synergistic effect of a three-layer stirring impeller and ultrasound enables efficient dispersion and intercalation of bubbles in graphite slurry, significantly improving the uniformity and controllability of interlayer spacing expansion. The temperature control system and condenser ensure the stability of the reaction process, avoiding the impact of temperature fluctuations or solvent loss on the intercalation effect. Ultimately, this configuration results in a layer distribution of oligolayer-like graphene concentrated between 10 and 25 layers and 2 to 10 layers, with reduced defect rate, improved electrical consistency, shortened reaction time, and increased yield.

[0017] Optionally, in step S1, the ratio of the diameter of the bottom impeller's disc turbine blade to the inner diameter of the bottom of the reactor is 0.3 to 0.5, and the rotational speed of the bottom impeller is 100 rpm to 200 rpm. The ratio of the blade width to the diameter of the wide-bladed axial-flow propeller of the middle propeller is 0.2 to 0.4, and the rotational speed of the middle propeller is 80 rpm to 150 rpm. The blade angle of the top propeller is 30 to 45 degrees, and the rotational speed of the top propeller is 50 to 100 rpm.

[0018] Through the above technical solution, the precise matching of the geometry and rotation speed of the three-layer stirring impeller achieves a high degree of control over the bubble dispersion and intercalation process, significantly improving the uniformity and repeatability of interlayer spacing expansion. The application of gradient shear force avoids the problems of excessive fragmentation or insufficient intercalation, resulting in a layer distribution of oligolayer-like graphene concentrated between 10 and 25 layers and 2 to 10 layers, while reducing the defect rate. Simultaneously, this configuration improves reaction efficiency, shortens processing time, and ensures the consistency of the product's electrical properties.

[0019] Optionally, the high-shear washing device in step S2 includes a frame assembly, a filter assembly, and a power assembly. The filter assembly consists of filter element 1 and filter element 2. Filter element 1 is a 316L stainless steel drum, and filter element 2 is a porous titanium drum. Filter element 1 and filter element 2 are arranged adjacent to each other and located within the frame assembly. The surface of filter element 1 is equipped with a shear groove design.

[0020] Through the above technical solution, the simultaneous efficient fragmentation and deep washing of graphite layers are achieved by the synergistic design of dual filter elements and the establishment of a high shear field. The grooved structure of filter element 1 significantly enhances local shear efficiency, avoiding the over-fragmentation problem common in traditional devices; the fine filtration of filter element 2 ensures the complete removal of impurity ions, keeping the conductivity of the final product stable within the range of 50 μS / cm to 100 μS / cm. This device improves washing efficiency by approximately 40% while maintaining the integrity of the graphite sheet structure, and the distribution of product layers is more concentrated.

[0021] Optionally, in step S2, the shear groove design of the filter element 1 of the high-shear washing device includes a plurality of V-shaped grooves arranged axially on the surface of the filter element 1, the depth of the V-shaped grooves being 2 mm to 5 mm, and the spacing between the V-shaped grooves being 5 mm to 10 mm.

[0022] Through the above technical solution, the precise parameter design of the V-shaped grooves achieves efficient and uniform shearing of graphite layers, significantly improving the exfoliation efficiency and layer consistency of oligolayer graphene (10-252-10 layer ratio > 80%), while reducing energy loss and defect rate. The groove structure enhances fluid mixing, avoids local overheating or blockage, improves process stability and repeatability, and the final product has better electrical properties (electrical conductivity stable at 50us / cm to 100us / cm) and structural integrity.

[0023] Optionally, in step S2, the pore size of the filter element 2 of the high-shear washing device is 500 nanometers.

[0024] Through the above technical solution, the precise control of the 500nm pore size makes the final oligolayer graphene layer distribution more concentrated (10-252-10 layers account for >80%), and the lateral size uniformity is improved by about 25%. At the same time, it significantly reduces impurity residue, stabilizes the product conductivity in the range of 50us / cm to 100us / cm, enhances the anti-clogging ability of the filter element, and increases the continuous operation time of the equipment.

[0025] Optionally, in step S1, the dispersant is sodium dodecyl sulfate.

[0026] The above technical solution, using sodium dodecyl sulfate as a dispersant, significantly improves the dispersion stability and bubble intercalation uniformity of graphite slurry, thereby achieving precise control of interlayer spacing. This effectively reduces the energy input required for subsequent high-shear washing, reduces structural defects in graphene sheets, and results in a final oligolayer-like graphene layer distribution concentrated between 10 and 25 layers and 2 to 10 layers, with high consistency in electrical properties (conductivity stable in the range of 50 μS / cm to 100 μS / cm). Furthermore, sodium dodecyl sulfate is easily removed by water washing, avoiding the impact of residual impurities on the conductivity of graphene, thus improving product purity and the environmental friendliness of the process.

[0027] Optionally, in step S2, the rotational speed of the high-shear washing device is 4000 rpm to 6000 rpm.

[0028] The above technical solution achieves a balance between exfoliation efficiency and product quality by optimizing rotation speed parameters. Within the 4000-6000 rpm range, oligolayer-like graphene with lateral dimensions of 0.5-2 μm and 10-252-10 layers can be obtained, with flakes of less than 10 layers accounting for less than 15%, effectively avoiding structural defects caused by excessive exfoliation. Compared to traditional ultrasonic exfoliation (energy consumption > 500 W / L), the unit energy consumption in this rotation speed range is reduced to 120-180 W / L, while washing efficiency is improved by approximately 40%. Resistance monitoring data indicates that this shear strength can effectively remove intercalating agent residue, maintaining the product conductivity at over 85% of that of intrinsic graphene.

[0029] Optionally, in step S2, the high-shear washing device is equipped with a jacket, and hot water is circulated inside the jacket to maintain the internal temperature of the high-shear washing device at 50°C to 80°C.

[0030] Through the above technical solution, a jacket temperature control system was used to achieve high reproducibility of process parameters, reducing the difference in the proportion of 10-252-10 layers between different batches from ±15% to ±5%. The isothermal conditions improved shearing efficiency, reduced unit energy consumption, and prevented graphite oxidation caused by localized overheating. The temperature-stable system facilitated deeper removal of impurity ions, reducing the fluctuation range of product conductivity.

[0031] Optionally, in step S3, the pre-freezing time of the freeze-drying process is 4 to 6 hours, and the sublimation drying time is 24 to 48 hours.

[0032] By employing the above technical solution and precisely controlling the freeze-drying sequence, the interlayer spacing retention rate of the final product is further improved. More importantly, the proportion of 10-252-10 layer oligolayer graphene is stabilized at >80%, effectively avoiding secondary stacking during the drying process. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a flowchart illustrating a method for preparing oligolayer-like graphene using a bubble-assisted liquid-phase mechanical exfoliation method, as provided in one embodiment of this application. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0036] Furthermore, the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article, unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship.

[0037] The embodiments of this application will now be described in further detail with reference to the accompanying drawings.

[0038] While mechanical exfoliation can prepare low-defect graphene, the single batch processing time exceeds 72 hours and the yield is less than 0.1%, and it is difficult to control the layer distribution (usually 3-8 layers mixed). Although chemical vapor deposition (CVD) can achieve wafer-level preparation, it requires a copper / nickel substrate to react at a high temperature of 1000℃, with an energy consumption of more than 30kWh per square meter. The subsequent acid etching and transfer process not only introduces cracks and wrinkles, but also generates about 5L of waste liquid containing heavy metals per square meter. While the redox method is simple, the epoxy groups generated during the strong oxidation stage disrupt the integrity of the sp² lattice. Even after reduction with hydrazine hydrate, the residual hydroxyl groups and vacancy defects still cause the conductivity to decrease to less than 10% of that of intrinsic graphene. Furthermore, the number of product layers is uncontrollable (typically 3-8 layers stacked). Although emerging liquid-phase exfoliation technology can control the number of layers through solvent surface energy, the high-frequency mechanical impact generated by conventional ball milling and ultrasonic processes leads to two contradictory effects: on the one hand, it causes irregular stacking of layers, forming a "nano-origami" structure; on the other hand, excessive shearing generates a large number of nano-fragments, severely restricting the structural regularity of conductive materials.

[0039] Based on this, this application provides a method for preparing oligolayer-like graphene using a bubble-assisted liquid-phase mechanical exfoliation method. Through the synergistic effect of bubble expansion and mechanical shearing, the interlayer spacing of graphite is controllably increased (from 0.5 nm to 1.5 nm), resulting in oligolayer-like graphene with a layer distribution concentrated between 10 and 25 layers (2 to 10 layers, accounting for >80%), lateral dimensions controlled between 0.5 μm and 2 μm, thickness between 3 nm and 0.6 nm and 4.53 nm, and electrical conductivity stabilized within the range of 50 μS / cm to 100 μS / cm. This significantly improves the electrical consistency and structural integrity of the material. Compared with traditional methods, this method avoids high-temperature or strong oxidizing environments, reduces defect rates (such as vacancies and hydroxyl residues), and features low energy consumption and high yield, making it suitable for large-scale production.

[0040] Figure 1 This is a flowchart illustrating a method for preparing oligolayer-like graphene using a bubble-assisted liquid-phase mechanical exfoliation technique, as provided in one embodiment of this application. Figure 1 As shown, the method includes: S1. Bubble generation and intercalation treatment: Graphite slurry, foaming agent and dispersant are placed in a reaction vessel and reacted at a reaction temperature of 80°C to 100°C. The reaction continues until the interlayer spacing of graphite expands to a preset range, which is 0.5 nanometers to 1.5 nanometers.

[0041] S2. Crushing and washing treatment: The graphite slurry obtained in step S1 is placed in a high-shear washing device for crushing and washing at high speed, and then rinsed with pure water until the conductivity detector measures 50us / cm to 100us / cm.

[0042] S3. Freeze-drying treatment: The graphite washing material obtained in step S2 is placed in a freeze dryer and expanded by pre-freezing and sublimation drying, wherein the pre-freezing temperature is -70℃ to -90℃.

[0043] In the final product obtained through steps S1, S2 and S3, the proportion of 2-10 layer oligolayer graphene sheets is >80%, the lateral size is concentrated in 0.5-2 micrometers, and the thickness is 0.6-3 nanometers

[05] .

[0044] Technical Background and Working Principle: This invention addresses the problems of precise control over the number of layers and interlayer spacing in existing oligolayer graphene preparation technologies, as well as the high defect rate and interlayer shrinkage caused by traditional mechanical exfoliation. Traditional methods such as mechanical exfoliation have low yields (<0.1%) and uneven layer distribution (3-8 layers mixed). Chemical vapor deposition (CVD) requires a high-temperature substrate (1000°C) and generates heavy metal waste liquid, while redox methods, although simple, suffer from strong oxidation processes that damage the sp² lattice integrity, leading to a sharp drop in conductivity. This invention utilizes a bubble-assisted liquid-phase mechanical exfoliation method. A foaming agent is introduced into the liquid phase to generate gas (such as CO2) in situ between graphite layers. The expansion force of the bubbles expands the interlayer spacing (within a preset range of 0.5 nm to 1.5 nm), weakening the interlayer van der Waals forces and thus reducing the shear energy required for subsequent mechanical exfoliation. Simultaneously, freeze-drying technology is used to avoid high-temperature oxidation through ice crystal sublimation, maintaining the expanded state of the graphite interlayer spacing during the drying process, ultimately obtaining oligolayer graphene with uniform layer number and low defect rate.

[0045] Technical Solution and Component Functions: This embodiment specifically includes the following steps: S1, Bubble Generation and Intercalation Treatment: Graphite slurry (solid content 10% to 15%, particle size 50μm to 100μm), foaming agent (such as a combination of potassium bicarbonate and hydrochloric acid, potassium bicarbonate concentration 0.5wt% to 1.5wt%, hydrochloric acid concentration 0.7wt% to 2.5wt%), and dispersant (sodium dodecyl sulfate) are placed in a self-developed reaction vessel and heated to 80°C to 100°C under a temperature control system for reaction, continuing until the graphite interlayer spacing expands to 0.5nm to 1.5nm; the reaction vessel is equipped with a three-layer stirring paddle (the bottom paddle is a disc vortex). The impeller, with a diameter-to-bottom-in-diameter ratio of 0.3 to 0.5 and a rotation speed of 100 to 200 rpm, is used for high-shear breaking of large bubbles; the middle impeller is a wide-bladed axial-flow impeller with a blade width-to-pipe diameter ratio of 0.2 to 0.4 and a rotation speed of 80 to 150 rpm, used for refining bubbles and enhancing liquid-phase circulation; the top impeller is an oblique-bladed impeller with a blade inclination angle of 30° to 45° and a rotation speed of 50 to 100 rpm, used to eliminate eddies and establish axial circulation throughout the vessel, condenser (for steam recovery), and ultrasonic transmitter (frequency 20 kHz to 40 kHz, for bubble refinement), working together to achieve uniform bubble distribution and full intercalation of graphite particles. S2. Crushing and Washing Process: The graphite slurry obtained in S1 is placed into a self-developed high-shear washing device for crushing and washing at a speed of 4000 rpm to 6000 rpm. The device includes a frame assembly (304 mirror stainless steel), a filter assembly (filter element 1 is a 316L stainless steel drum with V-shaped grooves along the axial direction on the surface, with a depth of 2 mm to 5 mm and a spacing of 5 mm to 10 mm, used to enhance shear force; filter element 2 is a porous titanium drum with a pore size of 500 nm, used for fine particle filtration) and a power assembly (motor power 3kW, explosion-proof design). Hot water is circulated through the outer jacket to maintain the internal temperature at 50°C to 80°C to reduce van der Waals forces. Pure water is circulated for washing until the conductivity stabilizes in the range of 50 μS / cm to 100 μS / cm. S3. Freeze-drying treatment: The graphite washing material obtained in S2 is placed in a freeze dryer and pre-frozen (-80°C, 4 to 6 hours) to allow water to crystallize. Then, it is sublimated and dried (500 Pa, 24 to 48 hours) to achieve ice crystal sublimation, avoid the collapse of the interlayer structure and maintain the expanded state.

[0046] Beneficial Effects: This embodiment achieves controllable expansion of the graphite interlayer spacing (0.5 nm to 1.5 nm) through the synergistic effect of bubble expansion and mechanical shearing. This results in a layer distribution of the obtained oligolayer-like graphene concentrated between 10 and 25 layers (2 to 10 layers, accounting for >80%), with lateral dimensions controlled between 0.5 μm and 2 μm, and thicknesses ranging from 3 nm to 0.6 nm to 4.53 nm. Furthermore, the electrical conductivity remains stable within the range of 50 μS / cm to 100 μS / cm, significantly improving the electrical consistency and structural integrity of the material. Compared to traditional methods, this method avoids high-temperature or strong oxidizing environments, reduces defect rates (such as vacancies and hydroxyl residues), and features low energy consumption and high yield, making it suitable for large-scale production.

[0047] In some embodiments, in step S1, the solid content of the graphite slurry is 10% to 15%, and the particle size of the graphite slurry is in the range of 5 micrometers to 10 micrometers.

[0048] Technical Background and Working Principle: In the field of oligolayer graphene preparation, the physical parameters of graphite slurry (such as solid content and particle size) directly affect the bubble intercalation efficiency and the quality of the final product. In traditional methods, excessively high solid content leads to excessive slurry viscosity, hindering uniform bubble distribution; excessively low solid content reduces processing efficiency. Too small a particle size easily causes excessive fragmentation, while too large a particle size results in insufficient intercalation. This invention, based on fluid dynamics and particle technology principles, discovers that a combination of 10% to 15% solid content and 5 to 10 micrometers particle size can optimize slurry rheology: a moderate solid content ensures uniform bubble migration between layers, while a specific particle size range provides sufficient specific surface area and intercalation channels, synergistically weakening van der Waals forces through bubble expansion, laying the foundation for subsequent mechanical exfoliation.

[0049] Technical solution and component function: In step S1, the solid content of the slurry is controlled at 10% to 15% by accurately measuring the ratio of graphite powder to water, and the graphite particle size is limited to 5 micrometers to 10 micrometers by sieving or ball milling pretreatment; the slurry is mixed with foaming agent and dispersant in the reactor, and the temperature control system maintains the reaction temperature at 80°C to 100°C. The three-layer stirring paddle (bottom paddle, middle paddle, and top paddle) achieves macro-mixing and local shearing through different rotation speeds and geometric designs, ensuring uniform suspension of particles and efficient intercalation of bubbles between layers, thereby expanding the interlayer spacing to the preset range.

[0050] Beneficial effects: This implementation method significantly improves the uniformity of bubble distribution and intercalation efficiency through the synergistic control of solid content and particle size, making the process of expanding interlayer spacing highly repeatable; after subsequent high-shear crushing, the number of oligolayer graphene layers is concentrated in the range of 10 to 25 layers and 2 to 10 layers, improving the lateral size consistency and enhancing the stability of electrical properties.

[0051] In some embodiments, in step S1, the foaming agent is selected from at least one of the following: a combination of potassium bicarbonate and hydrochloric acid, a combination of sodium bicarbonate and citric acid, a combination of ammonium carbonate and acetic acid, a combination of hydrogen peroxide and manganese dioxide, and ammonium bicarbonate.

[0052] Technical Background and Working Principle: In bubble-assisted exfoliation processes, the choice of foaming agent directly affects gas generation kinetics and interlayer expansion efficiency. Traditional single-foaming systems suffer from uncontrollable gas release rates and insufficient intercalation depths. This invention is based on a multi-mode foaming mechanism, employing multiple gas generation pathways, including acid-base reactions (sodium bicarbonate / citric acid, ammonium carbonate / acetic acid), catalytic decomposition (hydrogen peroxide / manganese dioxide), and thermal decomposition (ammonium bicarbonate), to construct a controllable gas release curve. Specifically, the acid-base combination generates CO2 in the liquid phase through ion exchange reactions, resulting in a concentrated bubble size distribution; the redox system produces oxygen, leading to higher bubble density; and the thermal decomposition of ammonium bicarbonate releases a mixture of ammonia and CO2, ensuring a consistently stable expansion pressure. This multi-mode foaming mechanism is adaptable to different graphite crystal forms and slurry viscosities, generating gradient expansion forces through the directional accumulation of bubbles between layers, significantly reducing the van der Waals barrier.

[0053] Technical solution and component function: In step S1, the selected foaming agent combination (sodium bicarbonate and citric acid, ammonium carbonate and acetic acid, hydrogen peroxide and manganese dioxide or ammonium bicarbonate) is added to graphite slurry with a solid content of 10%-15% according to the stoichiometric ratio. In a reactor equipped with a three-layer stirring paddle and an ultrasonic transmitter, the reaction temperature is maintained at 80-100℃ by a temperature control system. The bottom paddle's disc turbine paddle breaks large bubbles into microbubble clusters, the middle paddle's wide-bladed axial flow paddle enhances the mixing of the gas, liquid and solid three phases, the top paddle's oblique blades establish axial circulation, and the ultrasonic transmitter (20-40kHz) further refines the bubbles and promotes their penetration into the graphite interlayer. The reaction continues until the interlayer spacing expands to 0.5-1.5nm.

[0054] Beneficial effects: This implementation method achieves precise control of bubble size and release rate through the synergistic effect of multiple foaming agents, which improves the uniformity of graphite interlayer spacing by about 40%. The standard deviation of the number of layers of the exfoliated oligolayer graphene is reduced from ±5 layers in the traditional method to ±2 layers, and the crystal integrity (ID / IG≤0.08) is significantly better than that of a single foaming system.

[0055] In some embodiments, in step S1, the preferred combination of the foaming agent is a combination of potassium bicarbonate and hydrochloric acid, wherein the mass concentration of potassium bicarbonate is 0.5 wt% to 1.5 wt% and the concentration of hydrochloric acid is 0.7 wt% to 2.5 wt%.

[0056] Technical Background and Working Principle: The concentration ratio of the foaming agent directly determines the gas generation kinetics and interlayer expansion efficiency. The potassium bicarbonate-hydrochloric acid system generates CO2 bubbles in situ between graphite layers through an acid-base neutralization reaction (KHCO3 + HCl → KCl + H2O + CO2↑), and the expansion pressure is positively correlated with the reaction rate. When the concentration is too low (<0.5wt% KHCO3), insufficient gas production leads to inadequate interlayer expansion; when the concentration is too high (>1.5wt% KHCO3), bubble aggregation causes interlayer stress concentration, increasing the risk of structural defects. This invention experimentally verifies that a concentration window of 0.5-1.5wt% potassium bicarbonate and 0.7-2.5wt% hydrochloric acid can maintain the CO2 generation rate within an optimized range of 0.8-1.2 L / min·kg, ensuring sufficient expansion force to weaken van der Waals forces while avoiding excessive impact that could damage the integrity of the graphite lattice.

[0057] Technical solution and component function: In step S1, a potassium bicarbonate solution with a mass concentration of 0.5-1.5wt% is first added to a graphite slurry with a solid content of 10-15%, and then a hydrochloric acid solution with a concentration of 0.7-2.5wt% is slowly added dropwise. In a reactor equipped with three layers of stirring paddles, the reaction temperature is maintained at 80-100℃ by a temperature control system. The bottom paddle (disc turbine paddle, 100-200rpm) breaks the large CO2 bubbles into micron-sized bubbles, the middle paddle (wide-blade axial flow paddle, 80-150rpm) promotes the axial circulation of the bubble-graphite composite system, and the top paddle (oblique blade, 50-100rpm) eliminates the temperature gradient. At the same time, the ultrasonic transmitter (20-40kHz) promotes the penetration of bubbles into the interlayer, and the reaction continues until the interlayer spacing expands to 0.5-1.5nm.

[0058] Beneficial effects: This embodiment achieves synergistic control of gas generation rate and interlayer spacing expansion by matching the concentrations of potassium bicarbonate and hydrochloric acid, thus improving process repeatability and the uniformity of graphene layer number. The resulting oligolayer-like graphene has a more concentrated interlayer spacing distribution and a lower defect rate, which is beneficial for improving the electrical consistency and subsequent application performance of the material.

[0059] In some embodiments, the reactor in step S1 is equipped with a temperature control system, a three-layer impeller, a condenser, and an ultrasonic transmitter. The three-layer impeller includes a bottom impeller, a middle impeller, and a top impeller arranged along different heights of the reactor via a concentric shaft sleeve structure. The bottom impeller is a disc turbine impeller, the middle impeller is a wide-bladed axial flow impeller, and the top impeller is an inclined blade. The bottom impeller is located below the middle impeller, the middle impeller is located below the top impeller, and the bottom impeller, middle impeller, and top impeller are all in contact with the graphite slurry in the reactor.

[0060] Technical Background and Working Principle: In traditional oligolayer graphene preparation processes, the mixing uniformity and bubble distribution control of the reaction system are key challenges affecting interlayer spacing expansion. A single stirring structure cannot simultaneously achieve the synergistic effects of macroscopic flow, local shear, and bubble dispersion, leading to uneven interlayer intercalation, bubble aggregation or escape, and consequently affecting the controllability of interlayer spacing. Furthermore, solvent evaporation and temperature fluctuations during high-temperature reactions further reduce process stability. This invention addresses these problems by designing a dedicated reactor equipped with a temperature control system, three-layer stirring paddles, a condenser, and an ultrasonic transmitter. Utilizing the coupling of multi-layer mechanical stirring and acoustic cavitation effects, uniform bubble generation and efficient intercalation are achieved in the liquid phase. The three-layer stirring paddles, through combinations of different geometries and rotation speeds, are responsible for high-shear fragmentation of the bottom layer, bubble refinement of the middle layer, and axial circulation of the top layer, respectively. Ultrasonic waves promote the uniform nucleation and distribution of microbubbles, thereby achieving precise control of graphite interlayer spacing under mild conditions.

[0061] Technical Solution and Component Functions: In this embodiment, the reactor used in step S1 is equipped with a temperature control system, a three-layer stirring paddle, a condenser, and an ultrasonic transmitter. The temperature control system maintains the reaction temperature within a stable range of 80°C to 100°C using a PID controller, ensuring a consistent decomposition rate of the foaming agent. The condenser is connected to a reflux device to recover the solvent volatilized during the reaction, preventing material loss and environmental leakage. The ultrasonic transmitter operates at a frequency of 20kHz to 40kHz, generating a cavitation effect in the slurry to assist in the refinement and uniform dispersion of bubbles. The three-layer impeller system comprises a bottom impeller, a middle impeller, and a top impeller. The bottom impeller is a disc turbine impeller with a diameter-to-bottom inner diameter ratio of 0.3 to 0.5, operating at 100 to 200 rpm. It generates high shear force to break up large bubbles and delivers microbubble clusters to the middle layer. The middle impeller is a wide-bladed axial flow impeller with a blade width-to-diameter ratio of 0.2 to 0.4, operating at 80 to 150 rpm. It receives bottom-layer bubbles and enhances liquid-phase circulation, further refining the bubbles. The top impeller is a slanted blade with a blade inclination angle of 30 to 45 degrees, operating at 50 to 100 rpm. It establishes axial circulation throughout the reactor, eliminates local eddies, and ensures sufficient contact between bubbles and graphite particles. All components work together to form a multi-scale flow field, enabling bubbles to be uniformly intercalated between graphite layers, increasing the interlayer spacing to 0.5 to 1.5 nanometers.

[0062] Beneficial Effects: This embodiment achieves efficient dispersion and intercalation of bubbles in graphite slurry through the synergistic effect of three-layer stirring paddles and ultrasound, significantly improving the uniformity and controllability of interlayer spacing expansion. The temperature control system and condenser ensure the stability of the reaction process, avoiding the impact of temperature fluctuations or solvent loss on the intercalation effect. Ultimately, this configuration concentrates the layer distribution of oligolayer-like graphene to 10 to 25 layers and 2 to 10 layers, while reducing the defect rate, improving electrical consistency, shortening the reaction time, and increasing the yield.

[0063] In some embodiments, in step S1, the ratio of the diameter of the bottom impeller's disc turbine blade to the inner diameter of the bottom of the reactor is 0.3 to 0.5, and the rotational speed of the bottom impeller is 100 rpm to 200 rpm; the ratio of the blade width of the middle impeller's wide-blade axial flow blade to the diameter of the middle impeller is 0.2 to 0.4, and the rotational speed of the middle impeller is 80 rpm to 150 rpm; the blade inclination angle of the top impeller's oblique blade is 30 degrees to 45 degrees, and the rotational speed of the top impeller is 50 rpm to 100 rpm.

[0064] Technical Background and Working Principle: In the preparation of oligolayer-like graphene using the bubble-assisted liquid-phase mechanical exfoliation method, the matching of the impeller's geometric parameters and rotational speed is a core factor affecting bubble distribution and graphite layer intercalation efficiency. Traditional single-stirring structures often fail to simultaneously address macroscopic mixing and local shearing, resulting in uneven bubble size and inconsistent intercalation depth, leading to insufficient interlayer spacing or excessive fragmentation. Especially in high-viscosity slurry systems, inappropriate impeller design can easily generate flow dead zones or excessive eddies, reducing reaction uniformity. This invention addresses this bottleneck by precisely controlling the geometric proportions and rotational speed range of a three-layer impeller. Utilizing the synergistic effect of the bottom impeller's high-shear fragmentation, the middle impeller's bubble refinement, and the top impeller's axial circulation, gradient shear forces are generated at different flow field scales, ensuring uniform bubble intercalation between graphite layers. Its working principle is based on fluid dynamics optimization: the disk turbine structure of the bottom propeller generates strong radial flow at high speed, breaking up large bubbles; the wide-blade axial flow design of the middle propeller promotes liquid phase circulation and bubble refinement; the oblique blade configuration of the top propeller establishes stable axial flow and eliminates local eddies, thereby achieving a balance between multi-scale bubble dispersion and intercalation force.

[0065] Technical Solution and Component Functions: In this embodiment, the three-layer stirring impeller in step S1 adopts specific geometric parameters and rotation speed configuration: the bottom impeller is a disc turbine impeller, the ratio of its diameter to the inner diameter of the bottom of the reactor is controlled at 0.3 to 0.5, and it runs at a speed of 100 rpm to 200 rpm to generate high shear force to break the initial bubbles and deliver microbubble clusters to the middle layer; the middle impeller is a wide-blade axial flow impeller, the ratio of blade width to impeller diameter is set at 0.2 to 0.4, and it runs at a speed of 80 rpm to 150 rpm to receive the bottom layer bubbles and enhance slurry circulation, further refining the bubble size; the top impeller is an inclined blade, the blade inclination angle is maintained at 30 degrees to 45 degrees, and it runs at a speed of 50 rpm to 100 rpm to establish axial flow throughout the reactor, eliminate eddies that may remain in the middle impeller, and ensure sufficient contact between the bubbles and graphite particles. Each blade is independently controlled by an adjustable speed drive device. Combined with the temperature control system of the reactor (maintaining 80°C to 100°C) and the ultrasonic transmitter (20kHz to 40kHz), a synergistic flow field is formed, which allows bubbles to be uniformly intercalated between graphite layers, and the interlayer spacing is expanded to the preset range of 0.5 nanometers to 1.5 nanometers.

[0066] Beneficial Effects: This embodiment achieves a high degree of control over the bubble dispersion and intercalation process through precise matching of the geometry and rotation speed of the three-layer stirring impeller, significantly improving the uniformity and repeatability of interlayer spacing expansion. The application of gradient shear force avoids the problems of excessive fragmentation or insufficient intercalation, resulting in a layer distribution of oligolayer-like graphene concentrated between 10 and 25 layers and 2 to 10 layers, while reducing the defect rate. Simultaneously, this configuration improves reaction efficiency, shortens processing time, and ensures the consistency of the product's electrical properties.

[0067] In some embodiments, the high-shear washing device in step S2 includes a frame assembly, a filter assembly, and a power assembly. The filter assembly consists of filter element 1 and filter element 2. Filter element 1 is a 316L stainless steel drum, and filter element 2 is a porous titanium drum. Filter element 1 and filter element 2 are arranged adjacent to each other and located within the frame assembly. The surface of filter element 1 is provided with a shear groove design.

[0068] Technical Background and Working Principle: In the liquid-phase mechanical exfoliation process of oligolayer graphene, traditional washing devices often struggle to simultaneously meet the dual requirements of efficient crushing and fine filtration, leading to excessive damage to the graphite layers or residual impurities, affecting the uniformity of the final product's layers and electrical properties. Especially under high-speed conditions, a single filter structure is prone to flow dead zones or blockages, reducing washing efficiency. This invention addresses this technical bottleneck by designing a high-shear washing device integrating a frame assembly, filter assembly, and power assembly. It achieves simultaneous optimization of crushing and washing through the synergistic effect of dual filter elements. Its core working principle is based on the coupling effect of centrifugal filtration and surface shear: the groove design on the surface of filter element 1 generates localized high-shear zones during high-speed rotation, finely crushing the expanded graphite layers; the porous structure of filter element 2 achieves the retention of fine particles and the high-flux transmission of pure water, thereby efficiently removing ionic impurities remaining from the intercalation reaction while maintaining the integrity of the graphite sheet structure.

[0069] Technical Solution and Component Functions: In this embodiment, the high-shear washing device used in step S2 comprises three main modules: a frame assembly, a filter assembly, and a power assembly. The frame assembly is made of 304 mirror-finish stainless steel, providing structural support and a sealed environment. The power assembly consists of an explosion-proof motor and a belt drive system, outputting an adjustable speed of 4000 rpm to 6000 rpm to provide rotational power for the filter assembly. The filter assembly consists of adjacent filter elements 1 and 2. Filter element 1 is a 316L stainless steel drum with axially distributed V-shaped shear grooves (2-5 mm deep, 5-10 mm spacing) on ​​its surface, generating strong shear force during high-speed rotation to further peel off the graphite layer. Filter element 2 is a porous titanium drum, using its 500-nanometer pore size structure to trap fine graphite fragments and finely filter the washing liquid. Hot water at 50°C to 80°C is introduced into the outer jacket of the device to maintain a stable internal temperature, reduce van der Waals forces, and ensure that the spacing between the graphite layers remains expanded during the washing process.

[0070] Beneficial Effects: This embodiment achieves simultaneous high-efficiency fragmentation and deep washing of graphite layers through the synergistic design of dual filter elements and the establishment of a high shear field. The grooved structure of filter element 1 significantly enhances local shear efficiency, avoiding the over-fragmentation problem common in traditional devices; the fine filtration of filter element 2 ensures the complete removal of impurity ions, keeping the conductivity of the final product stable within the range of 50 μS / cm to 100 μS / cm. This device maintains the integrity of the graphite sheet structure while increasing washing efficiency by approximately 40%, and the product layer distribution is more concentrated.

[0071] In some embodiments, in step S2, the shear groove design of the filter element 1 of the high-shear washing device includes a plurality of V-shaped grooves arranged axially on the surface of the filter element 1, the depth of the V-shaped grooves being 2 mm to 5 mm, and the spacing between the V-shaped grooves being 5 mm to 10 mm.

[0072] Technical Background and Working Principle: In high-shear washing processes, graphite slurry needs to undergo efficient mechanical exfoliation to separate the graphite layers. However, the surface of a traditional smooth drum often fails to generate sufficient local shear force, leading to uneven exfoliation and low energy utilization. The V-groove design optimizes fluid dynamics through geometry. When the drum rotates at high speed, strong eddies and shear fields are generated at the groove edges, thereby enhancing the exfoliation effect on the graphite layers. This structure guides the slurry to form periodic disturbances between the grooves, generating high shear stress through local acceleration and deceleration regions. This effectively weakens the van der Waals forces between graphite layers while avoiding excessive fragmentation that could lead to the generation of nano-fragments, ensuring the uniformity and controllability of the exfoliation process.

[0073] Technical solution and component function: On the surface of the filter element 1 (316L stainless steel drum) of the high-shear washing device, multiple V-shaped grooves are uniformly machined along the axial direction. The groove depth is controlled within the range of 2mm to 5mm, and the spacing is controlled within the range of 5mm to 10mm. When the drum rotates at a speed of 4000rpm to 6000rpm, these grooves interact with the slurry to generate local high-shear zones, which efficiently break up the graphite layer. At the same time, the groove structure promotes the axial flow and distribution of the slurry, prevents particle deposition and clogging, and works with the filter element 2 (porous titanium drum) to achieve the separation and washing of impurities. The entire filter group operates under the drive of the power unit, the frame unit provides structural support, and the jacket is circulated with hot water to maintain the temperature at 50℃ to 80℃ to reduce the viscosity of the slurry and optimize the shearing effect and washing efficiency.

[0074] Beneficial effects: This implementation method achieves efficient and uniform shearing of graphite layers through precise parameter design of V-shaped grooves, significantly improving the exfoliation efficiency and layer consistency of oligolayer graphene (10-252-10 layer ratio > 80%), while reducing energy loss and defect rate; the groove structure enhances fluid mixing, avoids local overheating or blockage, improves process stability and repeatability, and the final product has better electrical properties (electrical conductivity stable at 50us / cm to 100us / cm) and structural integrity.

[0075] In some embodiments, in step S2, the pore size of the filter element 2 of the high-shear washing device is 500 nanometers.

[0076] Technical Background and Working Principle: In the preparation of oligolayer graphene, the slurry after high-shear washing requires precise solid-liquid separation for effective purification. If the filter pore size is too large, insufficiently exfoliated graphite fragments or impurities will pass through, reducing product purity; while if the pore size is too small, it will easily cause clogging, affecting washing efficiency and increasing energy consumption. The 500nm pore size design is based on in-depth research on the size distribution of graphite sheets: after bubble intercalation and preliminary shearing, the target oligolayer graphene sheets are mostly distributed in the range of 0.5-2µm. The 500nm pore size can effectively retain single-layer or few-layer graphene fragments, while allowing nanoscale impurities and washing liquid generated during the exfoliation process to pass through smoothly, achieving the best balance between selectivity and permeability.

[0077] Technical Solution and Component Functions: The filter element 2 of the high-shear washing device adopts a porous titanium drum with a pore size precisely controlled at 500nm. This element is arranged adjacent to the filter element 1 with V-shaped grooves on its surface. When the slurry circulates at a speed of 4000-6000rpm, the filter element 2 accurately sieves the sheared graphite fragments through its uniformly distributed microporous structure, effectively retaining the target size of oligolayer graphene-like material, while discharging impurity ions and residual foaming agent. The porous titanium material has both high mechanical strength and excellent corrosion resistance, ensuring long-term stable operation in a hot water jacket temperature environment of 50-80℃, and working in conjunction with the power unit and frame unit to achieve continuous washing and separation operations.

[0078] Beneficial effects: This embodiment achieves a more concentrated distribution of oligolayer graphene layers (10-252-10 layers account for >80%) through precise control of the 500nm pore size, improving the lateral size uniformity by about 25%; at the same time, it significantly reduces impurity residue, stabilizes the product conductivity in the range of 50us / cm to 100us / cm, enhances the anti-clogging ability of the filter element, and increases the continuous operation time of the equipment.

[0079] In some embodiments, in step S1, the dispersant is sodium dodecyl sulfate.

[0080] Technical Background and Working Principle: In the process of preparing oligolayer-like graphene using bubble-assisted liquid-phase mechanical exfoliation, the choice of dispersant has a decisive impact on the stability of the graphite slurry and the bubble intercalation efficiency. In traditional methods, graphite particles are prone to agglomeration in the liquid phase due to van der Waals forces, leading to uneven interlayer spacing and uneven bubble distribution, which in turn affects the subsequent mechanical exfoliation effect and the consistency of the product layer number. Sodium dodecyl sulfate (SDS), as an anionic surfactant, has a molecular structure containing hydrophilic sulfonic acid groups and hydrophobic alkyl chains. It can adsorb on the surface of graphite particles and form a negatively charged double layer, effectively inhibiting particle aggregation through electrostatic repulsion and steric hindrance. At the same time, SDS can significantly reduce the surface tension of the slurry, enhance the stability and dispersibility of bubbles, and enable bubbles to penetrate uniformly between graphite layers and generate continuous expansion force, laying the foundation for the controllable expansion of the interlayer spacing. This dispersion mechanism, combined with stirring and ultrasonic treatment in the reactor, ensures the uniformity and repeatability of the intercalation process.

[0081] Technical Solution and Component Functions: In step S1, during bubble generation and intercalation, sodium dodecyl sulfate is added to the graphite slurry at a mass concentration of 0.5 wt% to 2.0 wt%, and mixed with foaming agents (such as potassium bicarbonate and hydrochloric acid) and graphite particles in a reactor. The reactor temperature control system maintains the temperature at 80°C to 100°C, allowing the dispersant to dissolve rapidly under stirring and heating conditions, forming a stable emulsion system. Three layers of impellers (bottom impeller is a disc turbine impeller, middle impeller is a wide-bladed axial flow impeller, and top impeller is a slanted blade impeller) operate in coordination at different speeds. The bottom impeller (100 rpm to 200 rpm) achieves high-shear breaking of large bubbles, the middle impeller (80 rpm to 150 rpm) enhances liquid-phase circulation and bubble refinement, and the top impeller (50 rpm to 100 rpm) establishes axial flow throughout the reactor to eliminate eddies, ensuring uniform distribution of the dispersant and bubbles. An ultrasonic transmitter (frequency 20 kHz to 40 kHz) further assists in bubble micronization and graphite layer penetration. Through the spatial stabilizing effect of the dispersant, the graphite particles remain suspended, and bubbles are generated in situ between the layers, expanding the interlayer spacing to 0.5 to 1.5 nanometers, providing a pretreatment basis for subsequent crushing and washing.

[0082] Beneficial Effects: This embodiment, by using sodium dodecyl sulfate as a dispersant, significantly improves the dispersion stability and bubble intercalation uniformity of the graphite slurry, thereby achieving precise control of the interlayer spacing. This effectively reduces the energy input required for subsequent high-shear washing, reduces structural defects in the graphene sheets, and results in a final oligolayer-like graphene layer distribution concentrated between 10 and 25 layers and 2 to 10 layers, with high consistency in electrical properties (conductivity stable between 50 μS / cm and 100 μS / cm). Furthermore, sodium dodecyl sulfate is easily removed by water washing, avoiding the impact of residual impurities on the conductivity of the graphene, thus improving the purity of the product and the environmental friendliness of the process.

[0083] In some embodiments, in step S2, the rotational speed of the high-shear washing device is 4000 rpm to 6000 rpm.

[0084] Technical Background and Working Principle: In the high-shear washing process, the core challenge in preparing high-quality oligolayer-like graphene lies in balancing mechanical exfoliation efficiency with energy consumption control. Traditional ball milling or ultrasonic processes often require speeds exceeding 8000 rpm to achieve effective exfoliation. This not only leads to excessive fragmentation of graphite sheets, generating nano-fragments, but also causes "nano-origami" stacking defects due to high-frequency impacts. This invention significantly weakens interlayer van der Waals forces through pre-treatment with bubble intercalation, thereby greatly reducing the energy required for subsequent mechanical exfoliation. Limiting the high-shear washing device speed to the range of 4000 to 6000 rpm is based on a precise match between fluid shear dynamics and the interlayer binding energy of graphite: the shear stress generated within this speed range is sufficient to overcome the residual interlayer forces after pretreatment, while avoiding lateral size reduction caused by excessive shearing. Its physical essence lies in the velocity gradient generated in the Couette flow field formed by the gaps between the filter elements when the drum rotates at high speed, where the local shear rate reaches 10... 4 At the s⁻¹ level, directional exfoliation of graphite layers can be achieved rather than disordered fragmentation.

[0085] Technical Solution and Component Functions: In the crushing and washing process of step S2, the high-shear washing device operates at a speed of 4000 rpm to 6000 rpm driven by the motor of the power unit. Specifically, the intercalated graphite slurry obtained in step S1 is continuously injected into the drum cavity via a feed pump. Under the action of centrifugal force, the V-shaped grooves (depth 2-5 mm, spacing 5-10 mm) on the surface of filter element 1 (316L stainless steel drum) generate periodically changing fluid shear zones during rotation, applying alternating tensile and compressive stresses to the flowing graphite particles. The adjacent filter element 2 (porous titanium drum, pore size 500 nm) selectively traps the stripped fragments through precise pore size control. The outer jacket circulation system of the device maintains a temperature of 50-80℃, enhancing shear transfer efficiency by reducing the slurry viscosity. The entire system generates stable Taylor vortices and turbulent pulsations at a set rotation speed, enabling the graphite layer to be controllably exfoliated under the combined action of mechanical and fluid forces. At the same time, continuous pure water washing replaces impurity ions with conductivity of 50us / cm to 100us / cm.

[0086] Beneficial Effects: This embodiment achieves a balance between exfoliation efficiency and product quality by optimizing rotation speed parameters. Within the 4000-6000 rpm range, it yields oligolayer-like graphene with lateral dimensions of 0.5-2 μm and 10-252-10 layers, with less than 15% of the sheets having fewer than 10 layers, effectively avoiding structural defects caused by excessive exfoliation. Compared to traditional ultrasonic exfoliation (energy consumption > 500 W / L), the unit energy consumption in this rotation speed range is reduced to 120-180 W / L, while washing efficiency is improved by approximately 40%. Resistance monitoring data indicates that this shear strength can effectively remove intercalating agent residue, maintaining the product conductivity at over 85% of that of intrinsic graphene.

[0087] In some embodiments, in step S2, the high-shear washing device is equipped with a jacket on its outer layer, and hot water is circulated inside the jacket to maintain the internal temperature of the high-shear washing device at 50°C to 80°C.

[0088] Technical Background and Working Principle: During high-speed shear washing, the conversion of mechanical energy into heat energy leads to an increase in system temperature, and temperature fluctuations significantly affect the rheological properties and interlayer forces of graphite slurry. Traditional high-shear equipment lacks an effective temperature control mechanism, resulting in localized overheating (>90℃) that causes bubble rupture and graphite layer recombination. Simultaneously, van der Waals forces exhibit a nonlinear response to temperature changes, causing unstable peeling efficiency. This invention, by configuring a jacket on the outer layer of the high-shear washing device and circulating hot water, precisely maintains the internal temperature within the range of 50-80℃. This temperature range is designed based on the interfacial energy characteristics of the graphite-water system: above 50℃, the slurry viscosity can be effectively reduced (from 120 mPa·s to 45 mPa·s), enhancing shear force transmission efficiency; while the upper limit of 80℃ prevents violent vaporization of water from damaging bubble stability. Its thermodynamic principle lies in the fact that the jacket system compensates for frictional heat loss through conductive heat transfer, keeping the system in a dynamic thermal equilibrium state and ensuring the synergistic effect of the shear field and temperature field.

[0089] Technical Solution and Component Functions: In the crushing and washing process of step S2, the jacket system of the high-shear washing device is connected to the hot water circulation device. A proportional-integral-derivative (PID) temperature control module regulates the hot water temperature within the jacket to a range of 50-80℃, ensuring a stable slurry temperature inside the device. Specifically, the hot water circulates within the jacket cavity at a flow rate of 2-5 L / min, forming convective heat transfer with the frictional heat generated by the high-speed rotation of the drum at 4000-6000 rpm. A temperature sensor monitors the slurry temperature in real time and feeds the data back to the control system. When the temperature deviates from the set range, the opening of the hot water inlet valve is automatically adjusted. This temperature control mechanism works in conjunction with filter element 1 (a 316L stainless steel drum with V-grooves) and filter element 2 (a 500nm porous titanium drum) to achieve a stable shear viscosity ratio (≥0.8) under constant temperature conditions. This ensures that the graphite layer is peeled off under optimal rheological conditions, while continuous pure water washing ensures that its conductivity reaches the target of 50-100 μS / cm.

[0090] Beneficial effects: This implementation method achieves high reproducibility of process parameters through a jacket temperature control system, reducing the difference in the proportion of 10-252-10 layers between different batches from ±15% to ±5%. The isothermal conditions improve shearing efficiency, reduce unit energy consumption, and avoid graphite oxidation caused by localized overheating. The temperature-stable system is more conducive to the deep removal of impurity ions, reducing the fluctuation range of product conductivity.

[0091] In some embodiments, in step S3, the pre-freezing time of the freeze-drying process is 4 to 6 hours, and the sublimation drying process is 24 to 48 hours.

[0092] Technical Background and Working Principle: In the final forming stage of oligolayer graphene, the choice of drying method directly affects the maintenance of interlayer spacing and the integrity of the crystal structure. Traditional hot air drying or vacuum drying can cause irreversible stacking of graphite layers under capillary forces, resulting in the complete loss of the expansion effect obtained from the previous bubble intercalation. This invention employs freeze-drying technology, establishing an optimized process based on the balance between ice crystal growth kinetics and sublimation mass transfer by controlling the pre-freezing time (4-6 hours) and sublimation drying time (24-48 hours). The scientific principle is as follows: the duration of the pre-freezing stage (-80℃) determines the integrity of water crystallization. 4 hours can ensure that the water inside graphite particles with a particle size ≤50μm is completely solidified, while 6 hours is suitable for systems with larger particle sizes (100μm). The duration of the sublimation stage (500Pa) is designed based on the coupling model of Darcy's law and Knudsen diffusion. 24 hours can achieve the removal of 85% of the water, while 48 hours ensures the deep removal of residual bound water (≤0.8wt%), thereby maintaining the expanded structure to the maximum extent while avoiding interlayer collapse.

[0093] Technical Solution and Component Functions: In the freeze-drying process of step S3, the wet graphite material (moisture content 60-70%) after high-shear washing is evenly spread in the tray of the freeze dryer. It is first transferred to the pre-freezing chamber and treated at -80℃ for 4-6 hours to completely convert free and bound water into hexagonal ice crystals. Then it is transferred to the sublimation chamber and sublimated under a vacuum of 500Pa for 24-48 hours. This process is achieved through a multi-stage temperature control system and pressure gradient regulation: the pre-freezing stage uses programmed cooling (-10℃ / min) to prevent excessive ice crystal growth; the sublimation stage uses a heating plate to provide a latent heat of sublimation of 25-35℃, while the condenser maintains -85℃ to capture water vapor. The entire system monitors the sample mass change in real time using a mass sensor. The drying endpoint is determined when the mass loss per unit time is <0.1% / h, ultimately obtaining expanded graphene powder with a moisture content ≤1.5%.

[0094] Beneficial effects: This embodiment further improves the interlayer spacing retention rate of the final product by precisely controlling the freeze-drying sequence. More importantly, it stabilizes the proportion of 10-252-10 graphene layers at >80%, effectively avoiding secondary stacking during the drying process.

Claims

1. A method for preparing oligolayer-like graphene using a bubble-assisted liquid-phase mechanical exfoliation method, characterized in that, include: S1. Bubble generation and intercalation treatment: Graphite slurry, foaming agent and dispersant are placed in a reaction vessel and reacted at a reaction temperature of 80℃ to 100℃; S2. Crushing and washing treatment: The graphite slurry obtained in step S1 is placed in a high-shear washing device for crushing and washing at high speed, and then rinsed with pure water until the conductivity detector measures 50us / cm to 100us / cm. S3. Freeze-drying treatment: The graphite washing material obtained in step S2 is placed in a freeze dryer and expanded by pre-freezing and sublimation drying, wherein the pre-freezing temperature is -70℃ to -90℃. In the final product obtained through steps S1, S2, and S3, 2-10 layer oligolayer graphene sheets account for >80%, with lateral dimensions concentrated in the range of 0.5-2 micrometers and a thickness of 0.6-3 nanometers [02].

2. The method according to claim 1, characterized in that, In step S1, the solid content of the graphite slurry is 10% to 15%, and the particle size range of the graphite slurry is 5 micrometers to 10 micrometers.

3. The method according to claim 2, characterized in that, In step S1, the foaming agent is selected from at least one of the following: a combination of potassium bicarbonate and hydrochloric acid, a combination of sodium bicarbonate and citric acid, a combination of ammonium carbonate and acetic acid, a combination of hydrogen peroxide and manganese dioxide, and ammonium bicarbonate.

4. The method according to claim 3, characterized in that, In step S1, the preferred combination of the foaming agent is a combination of potassium bicarbonate and hydrochloric acid, wherein the mass concentration of potassium bicarbonate is 0.5wt% to 1.5wt% and the concentration of hydrochloric acid is 0.7wt% to 2.5wt%.

5. The method according to claim 4, characterized in that, In step S1, the reactor is equipped with a temperature control system, a three-layer stirring paddle, a condenser, and an ultrasonic transmitter. The three-layer stirring paddle includes: A bottom impeller, a middle impeller, and a top impeller are arranged along different heights of the reactor via a concentric shaft sleeve structure. The bottom impeller is a disc turbine impeller, the middle impeller is a wide-bladed axial flow impeller, and the top impeller is a slanted blade. The bottom impeller is positioned below the middle impeller, and the middle impeller is positioned below the top impeller. The bottom impeller, the middle impeller, and the top impeller are all in contact with the graphite slurry inside the reactor.

6. The method according to claim 5, characterized in that, In step S1, the ratio of the diameter of the bottom impeller's disc turbine blade to the inner diameter of the bottom of the reactor is 0.3 to 0.5, and the rotational speed of the bottom impeller is 100 rpm to 200 rpm. The ratio of the blade width to the diameter of the wide-bladed axial-flow propeller of the middle propeller is 0.2 to 0.4, and the rotational speed of the middle propeller is 80 rpm to 150 rpm. The blade angle of the top propeller is 30 to 45 degrees, and the rotational speed of the top propeller is 50 to 100 rpm.

7. The method according to claim 6, characterized in that, The high-shear washing device in step S2 includes a frame assembly, a filter assembly, and a power assembly. The filter assembly consists of filter element 1 and filter element 2. Filter element 1 is a 316L stainless steel drum, and filter element 2 is a porous titanium drum. Filter element 1 and filter element 2 are arranged adjacent to each other and located within the frame assembly. The surface of filter element 1 is equipped with shear groove design.

8. The method according to claim 7, characterized in that, In step S2, the shear groove design of the filter element 1 of the high-shear washing device includes a plurality of V-shaped grooves arranged axially on the surface of the filter element 1, the depth of the V-shaped grooves being 2 mm to 5 mm, and the spacing between the V-shaped grooves being 5 mm to 10 mm.

9. The method according to claim 8, characterized in that, In step S2, the pore size of the filter element 2 of the high-shear washing device is 500 nanometers.

10. The method according to claim 9, characterized in that, In step S1, the dispersant is sodium dodecyl sulfate.

11. The method according to claim 10, characterized in that, In step S2, the rotation speed of the high-shear washing device is 4000 rpm to 6000 rpm.

12. The method according to claim 11, characterized in that, In step S2, the high-shear washing device is equipped with a jacket on its outer layer, and hot water is circulated inside the jacket to maintain the internal temperature of the high-shear washing device at 50°C to 80°C.

13. The method according to claim 12, characterized in that, In step S3, the pre-freezing time of the freeze-drying process is 4 to 6 hours, and the sublimation drying process is 24 to 48 hours.

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