A supercritical fluid-assisted carbonization process

Abstract

This invention discloses a supercritical fluid-assisted carbonization process and its application. Addressing the limitations of existing laser-induced graphene (LIG) technologies, such as the single structure and low specific surface area, this process pre-immersing a polymer matrix in a supercritical fluid environment under high pressure allows gas molecules to fully penetrate and be trapped within the matrix. Subsequently, laser-induced carbonization technology induces a "physical burst" effect of the internal gas, deeply synergizing with the "chemical carbonization" of the polymer. Results show that the graphene material prepared by this process possesses a multi-level hierarchical pore structure with interconnected micropores, mesopores, and macropores, significantly increasing the specific surface area and drastically reducing charge migration impedance. In the examples, the capacitance of the supercapacitor assembled from scN2-LIG can reach 2.4 times that of traditional LIG. This invention is simple, environmentally friendly, and applicable to the continuous production of various carbon precursors (such as PI, wood, and fiber paper), showing great industrial application potential in energy storage, sensing, catalysis, and environmental remediation.

Description

Technical Field

[0001] This invention belongs to the field of graphene carbonization technology, specifically relating to a method for preparing laser-induced graphene and laser-induced graphene carbonization materials. Background Technology

[0002] Graphene is a two-dimensional layered carbon material, obtained by processing bulk graphite crystals into single-layer graphite sheets. Its structure consists of sp2-hybridized carbon atoms, exhibiting a honeycomb-like two-dimensional plane containing regular hexagons. The connection mode of carbon atoms in its structure is the same as that of zero-dimensional fullerenes, one-dimensional carbon nanotubes, and three-dimensional graphite. Among these materials, three-dimensional porous graphene possesses a high surface area while maintaining high electron mobility and mechanical stability, showing broad application prospects.

[0003] Traditional methods for fabricating three-dimensional porous graphene structures mainly include: (1) assembling graphene oxide (GO) into foam, which requires the preparation of graphene oxide precursors via its oxidative acid synthesis route. (2) Chemical vapor deposition (CVD) on porous substrates can also produce three-dimensional porous graphene, but high-temperature conditions and subsequent etching and drying processes may hinder its large-scale production. (3) Recently, a simple and scalable method has been developed, namely, laser engraving of carbon-rich substrates to obtain three-dimensional porous graphene, which is also known as laser-induced graphene (LIG).

[0004] In 2014, Lin et al. (Reference: LIN J, PENG Z, LIU Y, et al. Laser-induced porous graphene films from commercial polymers[J]. Nature Communications,2014,5(1).) first used CO2 infrared laser irradiation to process porous graphene from polyimide (PI), a process known as laser-induced graphene (LIG). They found that the interaction between the laser and polyimide generates local high temperature and pressure, which breaks the CO, C=O, and NC bonds, leading to the rearrangement of carbon atoms and the formation of a graphene structure. The simple manufacturing process and low production cost of LIG make it more desirable in practical applications. In particular, the microstructure, function, and defect density of the LIG electrode can be controlled by adjusting the laser parameters, thereby controlling related properties.

[0005] Generally, the preparation process of laser-induced graphene (LIG) is as follows: Under normal environmental conditions, carbon-containing precursor materials, such as polyimide (PI), or materials containing cellulose or lignin, are irradiated with a certain laser power using a commercial CO2 infrared laser engraving machine. Through photochemical and thermochemical processes, the carbon-containing precursor is transformed into LIG, while the remaining components are emitted as gas. The generation of gas also promotes the formation of the porous structure of LIG. However, although traditional laser-induced graphene (LIG) technology has achieved rapid preparation of carbon materials, it has significant limitations in the control of microstructure. Under the instantaneous high temperature of the laser, the polymer matrix relies solely on the limited gas expulsion generated by its own thermal decomposition, which is insufficient to support a highly developed three-dimensional structure, often leading to carbon layer collapse or a single pore size distribution (mainly micropores). This structural defect severely limits the mass transfer efficiency and effective active site exposure of the material in fields such as supercapacitor energy storage, high-performance sensing, and industrial catalysis.

[0006] Supercritical fluids are gases whose temperature and pressure are both above their critical temperature and pressure. In the supercritical state, the fluid possesses the physicochemical properties of both gases and liquids; for example, its diffusion coefficient and viscosity are comparable to those of gases, while its density and solubility are similar to those of liquids. For CO2, its critical temperature and critical pressure are 31.1... o C is 7.22 MPa, while N2 is -147 MPa. o C and 3.4 MPa. In microporous foaming processes, supercritical fluids are often used. To ensure that gases such as CO2 and N2 dissolve into the polymer matrix within a specific time, the gases must be in a supercritical state (Reference: Ruiz JAR Marc-Tallon J, Pedros M, Dumon M. Two-step micro cellular foaming of amorphous polymers in supercritical CO2[J]. The Journal of Supercritical Fluids, 2011, 57(1): 87-94). After depressurization, the supercritical gas will gradually disappear in the polymer matrix over time (generally more than 48 hours). However, high-pressure fluids that are not in a supercritical state can also be incorporated into the polymer matrix, but the time is slower and less gas is dissolved (Reference: High-Pressure Fluid Autoclave Foaming of High-Performance Polymer Materials[M], 2020, Science Press, Zhai Wentao).

[0007] Although supercritical fluids (such as supercritical CO2 and N2) are often used in polymer microporous foaming processes to physically foam polymers by taking advantage of their high solubility and rapid diffusion, there are no reports on combining supercritical fluid impregnation technology with laser-induced graphene formation to regulate the pore structure of LIG by utilizing the synergistic effect of physical expansion and chemical carbonization.

[0008] Existing laser-induced carbonization or laser-induced graphene formation processes typically involve directly laser-treating carbon-containing precursor materials under ambient temperature, pressure, or ordinary atmosphere conditions. While these methods offer advantages such as simplicity, high processing speed, and ease of patterning, the formation of their pore structures primarily relies on the gases released during the pyrolysis of the precursor under laser irradiation. Consequently, limitations remain in terms of pore structure richness, tunable pore size distribution, and the construction of three-dimensional interconnected structures within the carbonized layer. Particularly in applications requiring a large carbonization depth, high specific surface area, and superior electrochemical performance, the pore structures formed by traditional methods are often relatively simple, failing to meet the demands of high-performance devices.

[0009] Furthermore, while pre-foaming the polymer material into a porous structure before laser carbonization can increase the initial porosity to some extent, the pre-foamed porous polymer itself tends to form a heat-insulating layer, hindering the conduction of heat generated by the laser to the material's interior. This results in a decrease in laser carbonization depth, poorer continuity of the carbonized layer, and affects the structural stability and electrical conductivity of the final carbonized material. Therefore, how to further construct carbonized materials with rich three-dimensional porous structures without significantly reducing the laser carbonization depth has become one of the technical problems that need to be solved in this field.

[0010] To address the technical problems of insufficient gas generation, uncontrollable and monolithic pore structure, and low specific surface area in existing laser-induced graphene (LIG) technologies, this invention provides a supercritical fluid-assisted carbonization process. This process involves pre-introducing a supercritical or high-pressure fluid into the polymer matrix. The core innovation of this process lies in the three-pronged synergistic mechanism of "pre-saturation-instantaneous expansion-in-situ carbonization." By permeating and "locking" the supercritical fluid into the gaps between polymer molecular chains, the matrix is ​​brought to a high-pressure saturated state. At the instant of laser induction, the extremely high energy input triggers a violent reaction in two dimensions: Physical dimension: Gas molecules dissolved within the matrix undergo rapid volume expansion upon heating, producing a "micro-physical explosion" effect that expands the polymer skeleton at the moment of carbonization; Chemical dimension: Polymer chemical bonds break and rearrange, forming a graphene lattice. This synergistic effect effectively prevents interlayer overlap during carbonization, constructing a multi-level hierarchical pore network from micropores (<2μm), mesopores (2-10μm) to macropores (>10μm). This allows for the preparation of high-performance graphene carbonization materials with abundant three-dimensional hierarchical porous structures. Summary of the Invention

[0011] In order to overcome the shortcomings of the prior art, the present invention aims to provide a supercritical fluid-assisted carbonization process to achieve the preparation of a large number of graphene three-dimensional hierarchical porous structures, thereby improving electrochemical performance.

[0012] This process does not simply involve laser treatment in an external atmosphere. Instead, before laser-induced carbonization, a fluid medium is introduced into the polymer material, temporarily storing it within the interstices of polymer molecular chains, interfacial regions, and / or internal micro-regions. Subsequently, during laser-induced carbonization, the fluid medium expands and escapes under localized rapid heating conditions, co-processing with the polymer's pyrolysis, carbonization, and grapheneization processes to construct a three-dimensional porous structure within the material. This synergistic process effectively avoids the insufficient pore formation caused by relying solely on polymer pyrolysis gas production, while also mitigating local collapse and interlayer stacking of the carbonized layer, thus facilitating the acquisition of carbonized materials with both significant carbonization depth and rich pore structure.

[0013] In this invention, the fluid medium is preferably a supercritical fluid, but it can also be a high-pressure fluid with near-supercritical properties. In practical applications, when a fluid reaches a true supercritical state, it typically exhibits superior penetration, diffusion, and swelling capabilities, making it more conducive to penetrating the interior of polymer materials. When the fluid does not reach a strictly true supercritical state but is under high pressure, it can still impregnate polymer materials and achieve an auxiliary pore-forming effect in subsequent laser processing; however, the impregnation time usually needs to be appropriately extended. Therefore, this invention is not limited to a strictly true supercritical fluid state; high-pressure fluids with near-supercritical properties are also within the scope of protection of this invention, provided that the impregnation and subsequent synergistic carbonization effects are satisfied.

[0014] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0015] A supercritical fluid-assisted carbonization process, characterized by comprising a polymer material, a laser, and further comprising the following steps during the carbonization process:

[0016] S1. Place the polymer material in a sealed high-pressure reactor, inject gas into the high-pressure reactor, set the temperature and pressure to make the gas in a supercritical fluid state or a high-pressure fluid state close to supercritical function, and perform impregnation treatment. After the impregnation time is reached, take it out to obtain the polymer material containing the gas.

[0017] S2. Laser-induced carbonization treatment is performed on the polymer material containing the gas using a laser.

[0018] S3. During the laser-induced carbonization process, the gas inside the polymer material expands and escapes due to heat, which works synergistically with the carbonization process of the polymer material to obtain a carbonized sample with a three-dimensional porous structure and different pore structures.

[0019] The supercritical fluid-assisted carbonization process provided by this invention includes at least the following steps: First, a polymer material is placed in a sealed high-pressure reactor, a selected gas is injected into it, and corresponding temperature and pressure conditions are set so that the gas is in a supercritical fluid state or a high-pressure fluid state close to supercritical function, thereby impregnating the polymer material and allowing fluid molecules to enter the interior of the polymer material; then, the impregnated polymer material is taken out and subjected to laser-induced carbonization treatment within an appropriate time; during the laser-induced process, due to the rapid increase in temperature in the local area, the fluid molecules that previously entered the interior of the polymer undergo rapid expansion and escape, which is carried out in synergy with the pyrolysis, carbonization, and grapheneization processes of the polymer itself, ultimately yielding a carbonized sample with a three-dimensional porous structure.

[0020] Unlike processes that involve foaming followed by laser treatment, in this invention, the escape of fluid molecules and the laser-induced carbonization process occur simultaneously. That is, the fluid is not completely released and forms a stable porous insulating structure before laser treatment; instead, it undergoes transient expansion and escape in the carbonization front region under laser irradiation. This promotes pore formation while ensuring continuous heat transfer from the laser into the material. Therefore, this synergistic approach is more advantageous in balancing carbonization depth and pore structure richness.

[0021] Preferably, the pressure of the high-pressure fluid is greater than or equal to 1 MPa. The inventors have found that when the fluid pressure is high, the gas typically exhibits significant penetration and impregnation capabilities into polymer materials, particularly when the gas reaches a supercritical fluid state. Therefore, it can penetrate the polymer interior and contribute to pore formation during subsequent laser processing. With further increases in pressure, the fluid's dissolution, diffusion, and temporary storage capabilities within the polymer material are typically enhanced, further facilitating the formation of richer porous structures. In a preferred embodiment, the fluid may reach a true supercritical state; in other embodiments, the fluid may be a high-pressure fluid that does not reach a true supercritical state but possesses near-supercritical functions.

[0022] Supercritical fluid is the ideal gas in this invention. However, in actual operation, the gas can be a non-supercritical high-pressure gas. These high-pressure gases can also impregnate the polymer, but the impregnation time will be greatly extended. This will prolong the process time, but it can be carried out at pressures lower than the actual supercritical conditions, thereby reducing equipment requirements to some extent.

[0023] Preferably, the gas is one or more of carbon dioxide, nitrogen, and water vapor, or a mixture thereof. Carbon dioxide has good permeability and swelling properties, making it easy to penetrate the interior of polymer materials, and is one of the preferred fluids of this invention. Nitrogen has small molecular size and relatively inert chemical properties, allowing it to enter the intersegments of polymer chains under high pressure, and plays a role in assisting pore formation and providing a local protective atmosphere during laser processing. Water vapor is widely available and inexpensive, and can also be used as an auxiliary fluid medium in the process of this invention under certain conditions. When using two or more gases to form a mixed gas, the mixture can be adjusted according to the type of precursor, impregnation efficiency, target pore structure, and end use to balance cost, impregnation capacity, and structural control effects.

[0024] In this invention, the gas can be a single gas or a mixture of gases. As long as it can enter the interior of the polymer material under set conditions and work synergistically with the carbonization reaction in the subsequent laser-induced carbonization process, the technical effect of this invention can be achieved.

[0025] Preferably, the polymer material is a polymer material containing a benzene ring structure, or a polymer material containing cellulose or lignin. Generally, polymer materials containing a benzene ring structure are more likely to form carbon structures or graphene structures with high order under laser irradiation, and are therefore preferred precursors of this invention; while materials containing cellulose or lignin are widely available, low in cost, and also have good carbonization potential, showing good application prospects in low-cost and green manufacturing applications. The above materials can be single-component materials or composite materials containing the aforementioned components.

[0026] The polymer materials containing benzene ring structures may include, but are not limited to, polyimide, polyetherimide, polybenzimidazole, phenolic resin materials and their composite systems; the materials containing cellulose or lignin may include, but are not limited to, wood, paper, cellulose films and other biomass-based precursors.

[0027] More preferably, the polymer material containing the benzene ring structure is a polyimide or a composite material containing a polyimide. Polyimides and their composite materials generally have high heat resistance, good carbon yield, and superior laser-induced graphene formation capability, and are therefore suitable as precursor materials for the present invention. The composite material containing a polyimide can be a composite system formed by polyimide and reinforcing fibers, or a composite structure formed by polyimide and fabrics, conductive skeletons, layered substrates, or other polymers.

[0028] In this application, if different types of polyimide materials are used in the embodiments, the specific materials described in each embodiment shall prevail; however, as long as the material has the conditions for synergistic effect of laser-induced carbonization and fluid impregnation, it can be applied to the present invention.

[0029] Preferably, the polymer material is in the form of a film, fiber, continuous filament, prepreg filament, prepreg tape, or fabric. For films and sheet materials, planar laser scanning and patterning are convenient, making them suitable for fabricating planar electrodes and patterned conductive areas. For fibers, continuous filaments, prepreg filaments, and prepreg tapes, continuous processing and winding are convenient, making them suitable for preparing fibrous or linear functional materials. For fabrics and other woven structures, flexibility, breathability, and large-area processing requirements can be considered, making them suitable for flexible energy storage, wearable devices, and structural-functional integrated materials.

[0030] This invention does not limit the specific dimensions and thickness of the polymer material, as long as it can absorb or temporarily store the fluid medium under immersion conditions and undergo synergistic carbonization and pore formation under subsequent laser action, this invention is applicable.

[0031] Preferably, the laser is an infrared laser. Infrared lasers have excellent thermal effects on polymer materials, enabling rapid heating in localized areas, thereby effectively inducing carbonization and / or graphene formation in the polymer material and promoting the expansion and escape of the internal fluid medium in a short time, which is beneficial for achieving the synergistic pore-forming effect described in this invention. Furthermore, infrared laser equipment is mature, the process is stable, and it is easy to achieve continuous and patterned processing, thus having good applicability in this invention.

[0032] In practical applications, parameters such as laser power, scanning speed, scanning spacing, focal length, and scanning mode can be adjusted according to the type of precursor material, material thickness, impregnation degree, and target hole structure. This invention does not impose any particular limitations on these parameters.

[0033] Preferably, the laser-induced carbonization treatment can be laser treatment of all materials or patterned partial laser treatment. When laser treatment is performed on all materials, a continuous porous carbonized structure can be obtained, which is suitable for the preparation of integral electrodes, self-supporting conductive layers, and integral reinforcing structures. When patterned partial laser treatment is used, conductive areas, functional areas, or electrode areas with predetermined patterns can be formed on the material surface or in local areas, which is suitable for the preparation of micro-devices, circuit structures, sensing units, and patterned energy storage devices.

[0034] The specific pattern form of the patterning process can be designed according to actual needs, such as strip, grid, array, snake or other arbitrary two-dimensional pattern, and the present invention does not limit it.

[0035] Preferably, the obtained carbonized sample is a graphene carbonized material, and its structure contains a large number of three-dimensional pores of different sizes, thereby forming a hierarchical pore structure network. In this application, "graphene carbonized material" refers to a porous carbon material containing a graphene-based carbon structure formed after laser-induced carbonization. It can be manifested as a continuous carbonized layer, a porous conductive framework attached to the substrate surface, or a fibrous, sheet-like, or fabric-like graphene-based carbon structure.

[0036] The pores of different sizes can originate from multiple synergistic processes: on the one hand, the polymer material undergoes pyrolysis and carbonization under laser irradiation, releasing gas and forming initial pores; on the other hand, the fluid medium that has pre-entered the polymer expands and escapes rapidly under the local high temperature of the laser, further promoting pore formation and channel connectivity. The combined effect of these physical and chemical carbonization processes is beneficial for forming a hierarchical pore structure with a large specific surface area and three-dimensional connectivity. Compared with conventional laser carbonization samples without fluid assistance, the materials obtained by this invention typically have richer pore structures, larger specific surface areas, lower stacking degree, and higher structural openness, thereby improving ion transport, specific surface area, and overall electrochemical performance.

[0037] The preferred type of hole is a combination of smaller-sized holes, medium-sized holes, and larger-sized holes.

[0038] In a preferred embodiment, the graphene carbonized sample can be a primary carbonized sample, or it can undergo multiple impregnation-laser cycle treatments based on the primary carbonized sample to further modify the formed graphene structure. The cycle treatment includes at least the following steps: placing the primary carbonized sample back into a high-pressure reactor and performing fluid impregnation treatment under set temperature and pressure conditions, allowing the fluid to re-enter the sample interior or pore structure; subsequently, performing laser-induced treatment on the impregnated sample again to obtain a secondary carbonized sample; depending on the target pore structure, degree of grapheneization, or material performance requirements, the above steps can be repeated to obtain a multiple carbonized sample.

[0039] The number of repetitions of the cyclic treatment is denoted as N, where N≥0. The number of repetitions can be set according to the existing carbonization degree of the sample, the target pore structure, the target conductivity, and the target application scenario. Through multiple immersion-laser cycles, the pore structure, surface active sites, grapheneization degree, and local defect state of the material can be further adjusted, thereby achieving secondary optimization of the final material properties.

[0040] The beneficial effects of this invention are as follows:

[0041] (1) Constructing a three-dimensional hierarchical porous structure to significantly increase specific surface area: This invention utilizes the excellent dissolution and diffusion capabilities of supercritical fluids in polymer matrices to pre-store gas molecules inside the matrix. Upon laser irradiation, the matrix temperature rises sharply, and the dissolved fluid instantly vaporizes and expands, generating a strong physical foaming effect. This dual physical and chemical gas-generating mechanism produces enormous internal pressure, effectively "exploding" the carbon layer and forming a rich hierarchical porous structure containing micropores, mesopores, and macropores. This significantly increases the specific surface area of ​​the material and addresses the problem of monolithic pore structures in conventional processes.

[0042] (2) Enhanced Electrochemical and Adsorption Performance: Thanks to its abundant hierarchical porous structure, the LIG material prepared in this invention, when used as a supercapacitor electrode, provides high-speed ion transport channels through macropores and a large number of active sites through mesopores and micropores, thereby significantly reducing ion transport impedance and improving specific capacitance and rate performance. Simultaneously, the high specific surface area also enhances its sensitivity in gas adsorption and sensing.

[0043] (3) It is beneficial to balance carbonization depth and pore structure control. Unlike the method of directly laser treating pre-foamed porous polymers, the fluid in this invention does not completely escape in front of the laser, but is released synchronously at the carbonization front under the action of the laser. Therefore, it is not easy to form a significant heat insulation layer, which helps to maintain a better laser carbonization depth.

[0044] (4) Flexible and highly controllable process: This invention can precisely control the pore size distribution and graphene degree of graphene by adjusting the supercritical fluid impregnation process (pressure, temperature, time) and parameters such as laser power and speed. In addition, by introducing a "multiple impregnation-laser" cycle process, the generated graphene structure can be modified again to further improve the material quality.

[0045] (5) Green and environmentally friendly with good versatility: The supercritical fluids used (such as CO2 and N2) are non-toxic and harmless, and have low cost. Moreover, the process is applicable to a variety of carbon-containing precursors (such as PI, wood, paper, etc.), and has good prospects for industrial application. The fluids used can be one or more of carbon dioxide, nitrogen, water vapor, etc., which are low in cost and applicable to a variety of polymer materials and their composites, including films, fibers, continuous filaments, prepreg filaments, prepreg tapes and fabrics, etc., and have good prospects for engineering application. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the supercritical fluid synergistic assisted carbonization process in Embodiments 1-3 of the present invention; Figure 2 These are comparative SEM images of the microstructure of the materials prepared in Examples 1-3 of this invention; Figure 3 This invention is based on the LIG material Raman diagram and density bar chart. Figure 4 This is a cyclic current-voltage characteristic curve of the supercapacitor assembled based on the materials in Examples 1-3. Detailed Implementation

[0047] The present invention will be further described below with reference to embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Experimental conditions and process parameters not specifically described can be based on conventional conditions in the art, or can be appropriately adjusted according to the specific material type, thickness and target structure.

[0048] The “laser-induced carbonization treatment” described in this application includes the carbonization process that occurs under laser irradiation and the accompanying grapheneization process; “graphene-carbonized material” refers to a porous carbon material containing a grapheneized carbon structure formed after laser-induced carbonization; “supercritical fluid” refers to a fluid medium that is above its critical temperature and critical pressure; “high-pressure fluid with near-supercritical function” refers to a fluid medium that, although it has not strictly reached the true supercritical state, can still produce a significant impregnation effect on polymer materials under high pressure and achieve an auxiliary pore-forming effect in subsequent laser treatment.

[0049] Unless otherwise stated, the laser processing parameters used in the following embodiments are pre-selected and determined parameters that enable the polymer material to undergo stable laser-induced carbonization; in different embodiments, the laser type, laser power, scanning speed, scanning mode and focal length are kept consistent in order to compare the effects of different fluid-assisted conditions on the structure and properties of the resulting carbonized material.

[0050] Example 1: Laser-induced graphene without supercritical fluid (control group) This example uses a traditional direct laser writing process without introducing any supercritical fluid assistance. The specific steps are as follows:

[0051] A 75 μm thick polyimide-based continuous carbon fiber cloth reinforced composite film was selected as the precursor material. The precursor material was flattened and fixed on a laser processing platform, and its surface was wiped with ethanol to remove oil and dust, then dried for later use.

[0052] Under normal temperature and pressure conditions, i.e., in an air atmosphere with an ambient temperature of 25°C and an ambient pressure of 0.1 MPa, the surface of the precursor material is subjected to grating scanning laser-induced carbonization treatment using pre-set general laser parameters to obtain a black conductive carbonized layer.

[0053] The resulting sample surface formed a three-dimensional porous carbonized structure, whose pore structure mainly originated from the pyrolysis and carbonization process of the polymer material under laser irradiation. Due to the lack of fluid assistance, the pore structure of the obtained sample was relatively simple, mainly exhibiting small-scale pore structures accompanied by a small number of larger pores.

[0054] The sample obtained in this embodiment is designated as control sample LIG.

[0055] Results Description: Under laser irradiation, photothermal conversion occurred on the surface of the PI film, resulting in the in-situ formation of black porous graphene material (LIG). This formed a three-dimensional graphene structure with microporous and a small number of macroporous structures, containing only uniform graphene micropores with a pore size <500 nm, and a very few mesopores and macropores, such as... Figure 2 a.

[0056] Performance testing: The prepared carbonized porous graphene was used as the positive electrode of a zinc-ion supercapacitor. The capacitance performance of the capacitor was tested as follows: Figure 4 As shown.

[0057] Example 2: Supercritical Carbon Dioxide (Sc-CO2) Assisted Laser-Induced Graphene (scCO2-LIG) This example uses supercritical CO2 as a physical blowing agent and auxiliary medium. The specific steps are as follows:

[0058] The same polyimide-based continuous carbon fiber cloth reinforced composite film as in Example 1 was selected as the precursor material, placed in a sealed high-pressure reactor, and high-purity carbon dioxide gas was injected into the high-pressure reactor after sealing.

[0059] The heating and pressurization system was turned on to adjust the environment inside the reactor to a supercritical carbon dioxide state. The impregnation conditions were set as follows: temperature 45℃, pressure 15 MPa, and impregnation time 24 h. Under these conditions, carbon dioxide molecules penetrated into the precursor material and achieved a high degree of impregnation.

[0060] After impregnation, the pressure was quickly released and the sample was removed. Within 30 minutes, the sample was transferred to the laser processing platform. Subsequently, the sample was subjected to laser-induced carbonization treatment using the same laser processing parameters as in Example 1.

[0061] Under the localized rapid heating effect of laser, carbon dioxide that has pre-entered the precursor material expands and escapes rapidly, co-existing with the pyrolysis and carbonization processes of the polymer material, thereby promoting the formation of a more open porous structure within the carbonized layer. The resulting sample exhibits obvious three-dimensional porous characteristics, with a richer pore structure than the control sample, showing the coexistence of larger-scale and smaller-scale pore structures, and improved overall structural openness of the material.

[0062] The sample obtained in this embodiment is denoted as scCO2-LIG.

[0063] Results Description: The high energy of the laser beam instantaneously disrupted the gas balance within the polymer. Simultaneously with laser-induced carbonization, CO2 molecules dissolved in the matrix underwent a violent phase transition and volume expansion (physical explosion effect). This localized rapid expansion and escape effect, synergistically with the gas production from polymer decomposition, significantly enriched the pore structure of graphene, forming a structure where macropores (>5μm) and micropores coexist, with very few mesoporous structures, such as... Figure 2 b.

[0064] Performance testing: The prepared three-dimensional carbonized porous graphene was used as the positive electrode of a zinc-ion supercapacitor. The capacitance performance of the capacitor was tested as follows: Figure 4 As shown.

[0065] Example 3: Supercritical Nitrogen (Sc-N2) Assisted Laser-Induced Graphene (scN2-LIG) This example uses supercritical N2 as a physical blowing agent and auxiliary medium. The specific steps are as follows:

[0066] The same polyimide-based continuous carbon fiber cloth reinforced composite film as in Example 1 was selected as the precursor material, placed in a high-pressure reactor, and high-purity nitrogen gas was injected into the reactor.

[0067] Because nitrogen has a low critical temperature, it exhibits near-supercritical fluid characteristics even under high pressure at room temperature. In this embodiment, the impregnation conditions were set as follows: temperature 25°C, pressure 15 MPa, and impregnation time 48 h. Considering that nitrogen's solubility and impregnation capacity in polymer materials is generally lower than that of carbon dioxide, the impregnation time was appropriately extended to increase the fluid content within the material.

[0068] After impregnation, the sample was removed and fixed on a laser processing platform, and laser-induced carbonization was performed using the same laser processing parameters as in Example 1.

[0069] During laser irradiation, the high-pressure nitrogen gas entering the precursor material rapidly expands and escapes, thus aiding in the formation of a porous structure. Simultaneously, nitrogen, as a relatively inert atmosphere, can mitigate the excessive oxidation of the carbide material to some extent within the local microenvironment. The resulting sample exhibits a richer three-dimensional hierarchical porous structure with superior structural connectivity compared to the control and carbon dioxide-assisted samples.

[0070] The sample obtained in this embodiment is denoted as scN2-LIG.

[0071] Results Description: N2 molecules are relatively small and embed into polymer chains under high pressure. During laser irradiation, the high-pressure N2 rapidly expands, aiding in pore formation. Furthermore, as an inert protective atmosphere, N2 reduces excessive oxidation of carbon materials to some extent in the local microenvironment, resulting in a hierarchical pore structure of macropores-mesopores (2-10 μm)-micropores, such as... Figure 2 c.

[0072] Performance testing: The prepared three-dimensional carbonized porous graphene was used as the positive electrode of a zinc-ion supercapacitor. The capacitance performance of the capacitor was tested as follows: Figure 4 As shown.

[0073] Performance display, such as Figure 3 The density of three-dimensional porous graphene prepared by scN2-LIG is 0.64 g / cm³, that prepared by scCO2-LIG is 0.76 g / cm³, and that prepared by LIG without supercritical fluid is 0.91 g / cm³. These results indicate that the overall structure of the scN2-LIG samples is more porous and open. Furthermore, the defect ratio (D / G) of the three-dimensional porous graphene prepared by scN2-LIG is smaller.

[0074] like Figure 4 The capacitance of three-dimensional carbonized porous graphene prepared by scN2-LIG is 2.4 times that of porous graphene prepared without supercritical fluid LIG and 1.3 times that of three-dimensional carbonized porous graphene prepared by scCO2-LIG.

[0075] Example 4: High-Pressure Nitrogen-Assisted Laser-Induced Carbonization of Continuous Filaments This example uses supercritical N2 as a physical foaming agent and auxiliary medium. The specific steps are as follows:

[0076] Supercritical impregnation: PEI-CCF prepreg yarns are placed in a high-pressure reactor and high-purity nitrogen (N2) is injected. Since nitrogen has an extremely low critical temperature (-147°C), it is in the supercritical fluid region even at room temperature and high pressure. The conditions set in this example are: temperature 25°C, pressure 15 MPa. Impregnation is maintained under this high-pressure environment for 48 hours (since the solubility of N2 in polymers is generally lower than that of CO2, the impregnation time can be appropriately extended or the pressure increased).

[0077] Decompression and transfer: Take out the impregnated PEI-CCF prepreg yarn and connect one end of the prepreg yarn to the continuous winding device. Pass the part that needs to be laser carbonized through the mold fixed on the laser processing platform. At the same time as the laser carbonization process, the winding device is started.

[0078] Laser induction: Laser treatment was performed using the same laser parameters as in Example 1.

[0079] The final product is a continuous graphene-CCF filament material obtained by continuous laser carbonization.

[0080] Example 5: Multiple Immersion-Laser Cyclic Treatment Example

[0081] The primary carbonized sample obtained in Example 2 or Example 3 is selected as the sample to be processed. The primary carbonized sample is placed in a high-pressure reactor again, and a selected fluid medium is injected into the reactor, so that the fluid re-enters the pore structure and internal region of the primary carbonized sample under set temperature and pressure conditions.

[0082] In one specific embodiment, the fluid medium is carbon dioxide or nitrogen; when carbon dioxide is used, the sample can be impregnated at 45°C and 15 MPa for 24 h; when nitrogen is used, the sample can be impregnated at 25°C and 15 MPa for 48 h. After impregnation, the sample is removed and subjected to laser-induced carbonization again to obtain a secondary carbonized sample.

[0083] Depending on the target pore structure, degree of graphene formation, and final application requirements, the above impregnation-laser process can be repeated multiple times to obtain multiple carbonized samples. Through multiple impregnation-laser cycle treatments, the pore structure, structural openness, surface active sites, and local defect state of the material can be further adjusted, thereby achieving further optimization of the final performance.

[0084] This embodiment demonstrates that the fluid-assisted process of the present invention is not only applicable to primary laser-induced carbonization, but can also be used for secondary or multiple modifications to the already formed graphene carbonized structure.

[0085] Example 6:

[0086] Direct laser processing of pre-foamed porous polymer materials

[0087] To illustrate the difference between the technical approach of this invention and direct laser treatment of pre-foamed materials, a comparative approach can be taken by directly laser-treating polymer materials with pre-formed porous structures. The inventors discovered that such materials, due to the presence of numerous static pores within them, are prone to forming a heat-insulating effect under laser irradiation, hindering heat transfer to the material's interior; therefore, the resulting carbonized layer depth is typically small.

[0088] In a comparative experiment, when pre-porous polymer materials were directly laser-treated, the resulting carbonized layer depth was only about 50 μm, significantly less than the carbonization depth of >100 μm typically achievable with conventional laser-induced graphene materials, and also less than the carbonization depth achievable with the fluid-assisted process of this invention. This result demonstrates that the present invention, through the method of "pre-impregnation, subsequent laser treatment, and simultaneous gas release," can promote pore formation while avoiding the pre-formation of a significant heat-insulating layer, thus better balancing carbonization depth and pore structure richness.

[0089] In summary, this invention constructs graphene carbonized materials with a three-dimensional porous structure by impregnating polymer materials with supercritical or near-supercritical high-pressure fluids before laser-induced carbonization. This allows the fluid medium to pre-enter the material and synergize with the carbonization process during subsequent laser treatment. Compared to conventional laser-induced carbonization processes without fluid assistance, the materials obtained by this invention exhibit richer pore structures, higher structural openness, and superior overall performance. Furthermore, they are suitable for various precursor forms, including thin films, continuous filaments, and composite materials, demonstrating promising application prospects.

[0090] Of course, the present invention is not limited to the above-described embodiments. Those skilled in the art can make equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A supercritical fluid-assisted carbonization process, characterized in that, Including polymer materials, lasers, and the following steps in the carbonization process: S1. Place the polymer material in a sealed high-pressure reactor, inject gas into the high-pressure reactor, and set the temperature and pressure to make the gas be in a supercritical fluid state or a high-pressure fluid state close to supercritical function, so as to impregnate the polymer material; after the impregnation time is reached, take it out to obtain the polymer material containing the gas. S2. Laser-induced carbonization treatment is performed on the polymer material containing the gas using a laser. S3. During the laser-induced carbonization process, the gas inside the polymer material expands and escapes due to heat, which works synergistically with the carbonization process of the polymer material to obtain a carbonized sample with a three-dimensional porous structure.

2. The supercritical fluid-assisted carbonization process according to claim 1, characterized in that, The gas is in a true supercritical state, or in a high-pressure fluid state close to supercritical function, and the pressure of the high-pressure fluid is greater than or equal to 1 MPa.

3. The carbonization process according to claim 1 or 2, characterized in that, The gas is one or more of carbon dioxide, nitrogen, and water vapor, or a mixture of these as the main components.

4. The carbonization process according to any one of claims 1 to 3, characterized in that, The polymer material is a polymer material containing a benzene ring structure, or a polymer material containing cellulose or lignin.

5. The carbonization process according to claim 4, characterized in that, The polymer material containing a benzene ring structure is a polyimide or a composite material containing a polyimide.

6. The carbonization process according to any one of claims 1 to 5, characterized in that, The polymer material is in the form of a film, fiber, continuous filament, prepreg filament, prepreg tape, or fabric.

7. The carbonization process according to any one of claims 1 to 6, characterized in that, The laser is an infrared laser.

8. The carbonization process according to any one of claims 1 to 7, characterized in that, The laser-induced carbonization process involves laser treatment of the entire material or laser treatment of a patterned portion of the material.

9. The carbonization process according to any one of claims 1 to 8, characterized in that, The carbonized sample is a graphene carbonized material, and its structure contains pores of different sizes to form a three-dimensional porous structure with a large specific surface area.

10. The carbonization process according to any one of claims 1 to 9, characterized in that, It also includes the following cyclical steps: The carbonized sample is placed in a high-pressure reactor for fluid immersion, and then subjected to laser-induced treatment again to obtain a secondary or multiple carbonized sample; the number of repetitions of the cycle step is N, where N is 0 or a positive integer.

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