Graphene paper based on multi-stage cooperative heat treatment and preparation method and application thereof

Abstract

This invention belongs to the field of graphene paper technology, specifically disclosing a graphene paper based on multi-stage synergistic heat treatment, its preparation method, and its application. The preparation method includes the following steps: filtering a graphene oxide dispersion into a film, drying, and peeling it to obtain a self-supported graphene oxide film; subjecting the obtained self-supported graphene oxide film to a first hot pressing at 250-350℃ and 25-35 MPa; after the first hot pressing, performing programmed temperature annealing in an inert atmosphere; subjecting the annealed graphene oxide film to a second hot pressing at 250-350℃ and 25-35 MPa; after the second hot pressing, performing rapid Joule heat treatment in an inert atmosphere at 2600-3000℃ for 30-90 seconds, and then cooling to obtain the graphene paper. Through multi-stage synergistic heat treatment, while ensuring the macroscopic structural integrity and mechanical stability of graphene paper, the interlayer interface contact is significantly enhanced and the interlayer contact thermal resistance is reduced. On the other hand, the interlayer order is improved through ultra-high temperature treatment, reducing defect scattering and interface scattering, thereby enhancing the effective phonon transport capacity of the material and achieving a significant improvement in the in-plane thermal conductivity of graphene paper.

Description

Technical Field

[0001] This invention belongs to the field of graphene paper technology, specifically relating to a graphene paper based on multi-stage synergistic heat treatment, its preparation method and application, which can significantly improve the in-plane thermal conductivity of graphene paper. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Graphene, a two-dimensional crystalline material composed of carbon atoms, possesses excellent intrinsic thermal transport properties. Studies have shown that under ideal structural conditions, the thermal conductivity of monolayer suspended graphene can reach 3000-5000 W / (m·K). Based on this property, assembling graphene sheets into macroscopic graphene paper is considered an important approach to realizing high-performance thermal management materials.

[0004] Currently, common preparation routes for graphene paper mainly include graphene oxide dispersion, film formation (such as coating, filtration, self-assembly, etc.), and subsequent reduction and graphitization treatments. For example, by adding catalysts (such as iron, copper, etc.) to GO, microwave reduction combined with high-temperature graphitization (2000~3000℃) is used after coating to form a film, aiming to reduce the graphitization temperature and improve thermal conductivity. However, this still requires high-temperature and long-term processing, and the optimization of the interlayer stacking structure is limited. Another approach is to first dry, pulverize, then press, and finally graphitize (1800~2500℃, 10h), aiming to improve the gas discharge path and reduce foaming through pulverization and subsequent compaction. However, this relies on traditional long-term high-temperature graphitization, resulting in low energy efficiency.

[0005] In addition, existing technologies mainly focus on graphitization and defect repair of the internal structure of graphene paper sheets. They have limited ability to improve the interlayer pore structure, interface contact state and macroscopic heat transfer pathway continuity formed during the film formation stage. As a result, the overall thermal conductivity of graphene paper materials is limited by interlayer thermal resistance and structural discontinuity, which has become a key factor restricting the further improvement of its thermal conductivity. Summary of the Invention

[0006] To address the problems of high energy consumption, long process cycle, and difficulty in simultaneously achieving layer densification, interface thermal resistance optimization, and graphitization improvement in existing graphene paper preparation processes, this invention provides a graphene paper based on multi-stage synergistic heat treatment, its preparation method, and its application. By rationally designing the process steps and sequence of multi-stage heat treatment, while ensuring the macroscopic integrity and structural stability of the graphene paper, the invention synergistically reduces the interlayer contact thermal resistance and constructs a continuous and stable macroscopic heat transfer path, thereby achieving a significant improvement in the thermal conductivity of the graphene paper.

[0007] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a method for preparing graphene paper based on multi-stage synergistic heat treatment, comprising the following steps: filtering a graphene oxide dispersion into a film, drying and peeling it off to obtain a self-supporting graphene oxide film. The obtained self-supported graphene oxide film was subjected to a hot pressing at 250-350℃ and 25-35 MPa; after the hot pressing, it was annealed in an inert atmosphere with programmed temperature rise. The annealed graphene oxide film was subjected to a second hot pressing at 250-350℃ and 25-35 MPa pressure. After the second hot pressing, rapid Joule heat treatment is carried out in an inert atmosphere at 2600-3000℃ for 30-90 seconds. After cooling, the product is obtained.

[0008] Secondly, the present invention provides a graphene paper based on multi-stage synergistic heat treatment, which is prepared by the aforementioned preparation method.

[0009] Thirdly, the present invention provides the application of the graphene paper based on multi-level synergistic heat treatment in the field of heat dissipation of electronic devices.

[0010] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: This invention achieves multi-scale synergistic optimization in terms of sheet densification, interface thermal resistance reduction and intrinsic heat transport capacity through the synergistic effect of two hot pressings, staged annealing and rapid Joule heat treatment, so that the thermal conductivity of the prepared graphene paper can reach 600 W / (m·K).

[0011] The hot pressing temperature used in this invention is moderate, and the rapid Joule heat treatment holding time is extremely short. While significantly improving performance, it also takes into account process controllability and energy efficiency, and has good prospects for engineering applications. Attached Figure Description

[0012] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0013] Figure 1 This is a process flow diagram of an embodiment of the present invention; Figure 2 These are digital photographs of the graphene paper prepared in Example 1 and Comparative Examples 1-5 of the present invention, wherein a is the graphene paper prepared in Example 1, b is the graphene paper prepared in Comparative Example 1, c is the graphene paper prepared in Comparative Example 2, d is the graphene paper prepared in Comparative Example 3, e is the graphene paper prepared in Comparative Example 4, and f is the graphene paper prepared in Comparative Example 5. Figure 3 This is a bar chart comparing the in-plane thermal conductivity of graphene paper prepared in Example 1 of the present invention with that of Comparative Examples 1-5. Figure 4 The images show a cross-sectional scanning electron microscope (SEM) comparison of the graphene paper prepared in Example 1 and Comparative Example 1 of the present invention, where a is the graphene paper prepared in Comparative Example 1 and b is the graphene paper prepared in Example 1. Detailed Implementation

[0014] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0015] In view of the technical problems mentioned in the background art, the present invention provides a method for preparing graphene paper based on multi-level synergistic heat treatment, comprising the following steps: filtering graphene oxide dispersion into a film, drying and peeling it off to obtain a self-supporting graphene oxide film; The obtained self-supported graphene oxide film was subjected to a hot pressing at 250-350℃ and 25-35 MPa; after the hot pressing, it was annealed in an inert atmosphere with programmed temperature rise. The annealed graphene oxide film was subjected to a second hot pressing at 250-350℃ and 25-35 MPa pressure. After the second hot pressing, rapid Joule heat treatment is carried out in an inert atmosphere at 2600-3000℃ for 30-90 seconds. After cooling, the product is obtained.

[0016] A first hot pressing process causes the GO sheets to undergo initial rearrangement and compaction under the combined action of heat and force, forming a continuous and dense layered stacked structure. First, a large number of oxygen-containing functional groups are removed at 350-450℃, achieving initial reduction and forming a stable carbon framework. Then, a prolonged holding time (≥1.5h) at 1150-1250℃ further repairs the sp2 carbon network and improves the thermal transport structure within the sheets. A second hot pressing is performed at 250-350℃ and 25-35 MPa pressure to eliminate micropores and interfacial gaps formed during annealing and reduction due to gas escape and sheet relaxation, achieving re-densification of the sheets and strengthening of interfacial contact, thereby reducing interlayer contact thermal resistance. The ultra-high temperature rapid thermal field of rapid Joule heat treatment is beneficial for improving the graphitization degree of the material and improving the orderliness and phonon transport behavior of graphite microregions, thus promoting the overall thermal conductivity of graphene paper.

[0017] The first hot pressing provides a structurally stable heat transfer framework for subsequent high-temperature processing through pre-densification; the annealing stage completes the construction of the carbon framework and the initial formation of the thermally conductive network under relatively mild conditions; the second hot pressing re-densifies the interface defects formed during reduction and annealing, ensuring that the film entering the Joule heat treatment stage has a good interfacial contact state; rapid Joule heat treatment, based on the stability of the interface and structure, promotes the graphitization degree and microscopic order of the graphene paper through short-time ultra-high temperature treatment. The steps are mutually coupled and their order is irreplaceable, forming a significant synergistic enhancement effect.

[0018] In some embodiments, the solid content of the graphene oxide dispersion is 2-5 mg / mL.

[0019] Excessive solid content increases the viscosity of the dispersion, making GO sheets prone to aggregation. This leads to uneven thickness and localized defects during film formation, affecting the uniformity of the film's microstructure. A solid content of 2-5 mg / mL allows the GO sheets to form a relatively ordered initial stacked structure during filtration, resulting in a self-supporting film with a certain thickness and density after drying. This provides a stable foundation for subsequent heat treatment and structural control processes.

[0020] In some embodiments, the filter membrane used in the filtration membrane formation is a nylon filter membrane.

[0021] Nylon filter membranes exhibit excellent chemical resistance and high compatibility with aqueous systems and potentially residual trace acid / alkali components in graphene oxide (GO) dispersions. They do not swell or chemically degrade, preventing contamination or structural damage to the GO sheets and ensuring the purity of the film formation process. Nylon filter membranes also possess moderate mechanical strength and flexibility. After vacuum filtration and drying, the adhesion between the GO film and the nylon filter membrane is weak, facilitating non-destructive peeling to obtain a complete self-supporting GO film. This reduces the risk of film damage during subsequent processing and ensures the smooth execution of hot pressing, annealing, and other processes.

[0022] In some embodiments, the temperature of a single hot pressing is 280-320°C, the pressure is 25-35 MPa, and the hot pressing time is 0.5-1.5 h.

[0023] In some embodiments, the temperature of the secondary hot pressing is 280-320℃, the pressure is 25-35 MPa, and the hot pressing time is 0.5-1.5h.

[0024] If the temperature of the first and second hot pressing is below 280℃, the thermal activation energy is insufficient, the movement of the sheets is restricted, and the densification effect is poor; if it is above 320℃, it may lead to an increase in edge defects of GO sheets or local cracking, which will damage the macroscopic integrity of the film.

[0025] In some embodiments, the programmed temperature rise annealing process is as follows: first, hold at 350-450℃ for 10-60 min, and then hold at 1150-1250℃ for at least 1.5 h.

[0026] First, a large number of oxygen-containing functional groups are removed at 350-450℃ to achieve preliminary reduction and form a stable carbon skeleton; then, the carbon is kept at 1150-1250℃ for a longer period of time (≥1.5h) to further repair the sp2 carbon network and improve the heat transport structure within the lamellar structure.

[0027] Preferably, the programmed temperature rise annealing process is as follows: first, hold at 350-450℃ for 20-40 minutes, and then hold at 1150-1250℃ for 1.5-3 hours.

[0028] In some embodiments, the heating rate of rapid Joule heat treatment is 4-10 °C / s.

[0029] Experiments show that when the heating rate reaches approximately 4℃ / s, the graphitization degree of graphene paper can be significantly improved, enhancing the orderliness and phonon transport behavior of graphite micro-regions and thus improving thermal conductivity. If the heating rate is below 4℃ / s, interlayer gas accumulation and structural disturbances easily occur, leading to porosity formation or weakening of interlayer interfaces, thereby affecting the reconstruction of graphite micro-regions and the continuity of thermal transport. At rates exceeding 10℃ / s, localized overheating may cause carbonization or volatilization at the sheet edges, disrupting the interlayer stacking structure. A rate of 4-10℃ / s is beneficial for uniform temperature distribution, ensuring graphitization on a substrate with good interfacial contact (after secondary hot-pressing pretreatment). The dense structure formed by two hot-pressing processes followed by annealing allows for rapid heating, reducing the high-temperature dwell time (only 30-90s), lowering energy consumption while maintaining micro-region structural stability, thereby preserving the uniformity and controllability of thermal transport in the material.

[0030] Preferably, during rapid Joule heat treatment, the graphene paper is placed in a graphite clamp.

[0031] Graphite clamps possess excellent electrical and thermal conductivity, enabling uniform transfer of Joule heat to the entire graphene paper, preventing overheating or ablation caused by localized current concentration. At ultra-high temperatures of 2600-3000℃, graphene paper is prone to wrinkling or cracking due to thermal expansion. Graphite clamps maintain the flatness of the film through their clamping action, while their layered structure buffers thermal stress, reducing the risk of sample deformation. Graphite exhibits extremely high chemical stability in an inert atmosphere, preventing reactions with graphene paper or the introduction of impurities. Furthermore, the clamps isolate the sample from external environments (such as airflow disturbances within the protective chamber), preventing surface oxidation or impurity adsorption and ensuring the purity of the final product.

[0032] Secondly, the present invention provides a graphene paper based on multi-stage synergistic heat treatment, which is prepared by the preparation method described above, and has an in-plane thermal conductivity of not less than 500 W / (m·K), preferably not less than 600 W / (m·K).

[0033] Thirdly, the present invention provides the application of the graphene paper based on multi-level synergistic heat treatment in the field of heat dissipation of electronic devices.

[0034] The present invention will be further described below with reference to the embodiments.

[0035] The graphene oxide powder used in the following examples was provided by JiaCai Technology Co., Ltd. The hot press was a vacuum hot press, the annealing was performed using a tube furnace, and the rapid Joule heat treatment was conducted using a Joule ultrafast heating device. Thermal conductivity was measured using the laser flare method (LFA) to determine the in-plane thermal diffusivity, and calculated as thermal diffusivity × density × specific heat capacity.

[0036] Example 1 A method for preparing graphene paper based on multi-stage synergistic heat treatment, such as... Figure 1 As shown, it includes the following steps: S1: Take a certain amount of graphene oxide powder, disperse it in deionized water, and sonicate it at 150 W for 5 minutes to obtain a graphene oxide (GO) dispersion with a concentration of 3 mg / mL. Then, centrifuge the dispersion at 3000 rpm for 20 minutes to remove large particles that are not fully exfoliated, and obtain a purified GO dispersion.

[0037] The purified GO dispersion was vacuum filtered through a 0.45 μm nylon-66 membrane to form a film. The wet membrane, along with the filter membrane, was placed in an oven at 80°C for 30 minutes and then carefully peeled off to obtain a self-supporting GO film.

[0038] S2: The GO film is placed in the mold of a vacuum hot press and hot-pressed at 300°C and 30MPa for 1 hour, then cooled to room temperature with the equipment. This step allows the GO sheets to initially align and compact under heat and pressure.

[0039] S3: The film, after the first hot pressing treatment, is transferred to a tube furnace for programmed temperature annealing under an argon atmosphere. First, the temperature is increased from room temperature to 400°C at a rate of 5°C / min and held at this temperature for 30 minutes to achieve initial removal of oxygen-containing functional groups. Then, the temperature is increased to 1200°C at a rate of 5°C / min and held at this high temperature for 2 hours to further repair the carbon framework and form a preliminary thermally conductive network. After processing, the film is naturally cooled to room temperature under argon protection.

[0040] S4: The film after annealing and reduction in step S3 is placed back into the vacuum hot press and subjected to a second hot pressing treatment at 300℃ and 30MPa for 1 hour. This step aims to re-compact the micropores and sheet relaxation that may have occurred during the reduction process, thereby strengthening the surface-to-surface contact between graphene sheets.

[0041] S5: The thin film sample, after the second hot-pressing treatment, is clamped between two graphite electrodes in a high-temperature Joule heat treatment system, with the entire system placed in a protective chamber filled with argon gas. A direct current is applied to the sample, controlling its rapid heating at an average rate of approximately 5°C / s, reaching a peak temperature of 2800°C within about 10 minutes. This temperature is maintained for 1 minute, after which the power is cut off, and the sample is rapidly cooled to room temperature under argon protection. This yields the final graphene paper product.

[0042] Example 2 A method for preparing graphene paper based on multi-stage synergistic heat treatment includes the following steps: S1: Take a certain amount of graphene oxide powder, disperse it in deionized water, and sonicate it at 200 W for 5 minutes to obtain a graphene oxide (GO) dispersion with a concentration of 3 mg / mL. Then, centrifuge the dispersion at 3000 rpm for 20 minutes to remove large particles that have not been fully exfoliated, and obtain a purified GO dispersion.

[0043] The purified GO dispersion was vacuum filtered through a 0.45 μm nylon-66 membrane to form a film. The wet membrane, along with the filter membrane, was placed in an oven at 80°C for 30 minutes and then carefully peeled off to obtain a self-supporting GO film.

[0044] S2: The GO film is placed in the mold of a vacuum hot press and hot-pressed at 320°C and 35MPa for 1 hour, then cooled to room temperature with the equipment. This step allows the GO sheets to initially align and compact under heat and pressure.

[0045] S3: The film, after the first hot pressing treatment, is transferred to a tube furnace for programmed temperature annealing under an argon atmosphere. First, the temperature is increased from room temperature to 450°C at a rate of 5°C / min and held at this temperature for 40 minutes to achieve initial removal of oxygen-containing functional groups. Then, the temperature is increased to 1150°C at a rate of 5°C / min and held at this high temperature for 2.5 hours to further repair the carbon framework and form a preliminary conductive and thermally conductive network. After processing, the film is naturally cooled to room temperature under argon protection.

[0046] S4: The film after annealing and reduction in step S3 is placed back into the vacuum hot press and subjected to a second hot pressing treatment at 320℃ and 25MPa for 1.5 hours. This step aims to re-compact the micropores and sheet relaxation that may have occurred during the reduction process, thereby strengthening the surface-to-surface contact between graphene sheets.

[0047] S5: The thin film sample, after the second hot-pressing treatment, is clamped between two graphite electrodes in a high-temperature Joule heat treatment system, with the entire system placed in a protective chamber filled with argon gas. A direct current is applied to the sample, rapidly heating it to a peak temperature of 2900°C at an average heating rate of approximately 7°C / s, and maintaining this temperature for 80 seconds. The power is then cut off, and the sample is rapidly cooled to room temperature under argon protection. This yields the final graphene paper product.

[0048] Example 3 A method for preparing graphene paper based on multi-stage synergistic heat treatment includes the following steps: S1: Take a certain amount of graphene oxide powder, disperse it in deionized water, and sonicate it at 180 W for 5 minutes to obtain a graphene oxide (GO) dispersion with a concentration of 3 mg / mL. Then, centrifuge the dispersion at 3000 rpm for 20 minutes to remove large particles that have not been fully exfoliated, and obtain a purified GO dispersion.

[0049] The purified GO dispersion was vacuum filtered through a 0.45 μm nylon-66 membrane to form a film. The wet membrane, along with the filter membrane, was placed in an oven at 80°C for 30 minutes and then carefully peeled off to obtain a self-supporting GO film.

[0050] S2: The GO film is placed in the mold of a vacuum hot press and hot-pressed at 280°C and 28MPa for 1 hour, then cooled to room temperature with the equipment. This step allows the GO sheets to initially align and compact under heat and pressure.

[0051] S3: The film, after the first hot pressing treatment, is transferred to a tube furnace for programmed temperature annealing under an argon atmosphere. First, the temperature is increased from room temperature to 370°C at a rate of 5°C / min and held at this temperature for 40 minutes to achieve initial removal of oxygen-containing functional groups. Then, the temperature is increased to 1200°C at a rate of 5°C / min and held at this high temperature for 2.5 hours to further repair the carbon framework and form a preliminary conductive and thermally conductive network. After processing, the film is naturally cooled to room temperature under argon protection.

[0052] S4: The film after annealing and reduction in step S3 is placed back into the vacuum hot press and subjected to a second hot pressing treatment at 280℃ and 35MPa for 0.5 hours. This step aims to re-compact the micropores and sheet relaxation that may have occurred during the reduction process, thereby strengthening the surface-to-surface contact between graphene sheets.

[0053] S5: The thin film sample, after the second hot-pressing treatment, is clamped between two graphite electrodes in a high-temperature Joule heat treatment system, with the entire system placed in a protective chamber filled with argon gas. A direct current is applied to the sample, rapidly heating it to a peak temperature of 2700°C at an average heating rate of approximately 10°C / s, and maintaining this temperature for 50 seconds. The power is then cut off, and the sample is rapidly cooled to room temperature under argon protection. This yields the final graphene paper product.

[0054] Comparative Example 1 A method for preparing graphene paper includes the following steps: S1: Same as step S1 in Example 1, to obtain a self-supporting GO film; S2: Directly perform thermal reduction on the self-supporting GO film without any hot pressing or subsequent rapid Joule heating. The thermal reduction conditions are as follows: under argon protection, heat to 400℃ at 5℃ / min and hold for 30 minutes, then heat to 1200℃ at 5℃ / min and hold for 2 hours, followed by natural cooling.

[0055] Comparative Example 2 The difference from Example 1 is that the second hot pressing and rapid Joule heat treatment are not performed, i.e., steps S4 and S5 are omitted. Everything else is the same as in Example 1.

[0056] Comparative Example 3 The difference from Example 1 is that the first hot pressing and rapid Joule heat treatment are not performed, i.e., steps S2 and S5 are omitted. Everything else is the same as in Example 1.

[0057] Comparative Example 4 The difference from Example 1 is that rapid Joule heat treatment is not performed, i.e., step S5 is omitted. Everything else is the same as in Example 1.

[0058] Comparative Example 5 The difference from Example 1 is that the first and second hot pressing are omitted, i.e., steps S2 and S4 are omitted. Everything else is the same as in Example 1.

[0059] Comparative Example 6 The difference from Example 1 is that the first hot pressing is omitted, i.e., step S2 is omitted. Everything else is the same as in Example 1.

[0060] Comparative Example 7 The difference from Example 1 is that the second hot pressing is not performed, i.e., step S4 is omitted. Everything else is the same as in Example 1.

[0061] Comparative Example 8 The difference from Example 1 is that in step S3, during annealing, the temperature is increased from room temperature to 400°C at a rate of 5°C / min, and held at this temperature for 2 hours and 30 minutes. Everything else is the same as in Example 1.

[0062] Comparative Example 9 The difference from Example 1 is that in step S3, during annealing, the temperature is increased from room temperature to 1200°C at a rate of 5°C / min, and held at this temperature for 2 hours and 30 minutes. Everything else is the same as in Example 1.

[0063] Table 1 Performance Testing and Result Analysis

[0064] From Table 1 and Figure 3 It can be seen that the thermal conductivity of the graphene paper prepared in Example 1 (complete process chain) (~600 W / (m·K)) is much higher than that of Comparative Example 1 (~105 W / (m·K)), which proves the advantages of multi-stage synergistic processing.

[0065] Comparing Comparative Example 4 (with S4) and Comparative Example 2 (without S4), it can be seen that, under the condition that both S2 and S3 steps are present, adding the S4 step significantly increases the thermal conductivity from 139.2 W / (m·K) to 256.7 W / (m·K). This indicates that the second hot pressing performed after high-temperature annealing and reduction (S3) can effectively eliminate the microstructure relaxation and new porosity caused by functional group removal and thermal stress release. This step provides a dense precursor structure with good interfacial contact for the subsequent rapid Joule heat treatment (S5), allowing the high-temperature graphitization efficiency of S5 to be fully utilized. Without this step, interfacial defects would become the main bottleneck limiting the final thermal conductivity.

[0066] Comparing Comparative Example 4 (with S2) and Comparative Example 3 (without S2), it can be seen that, under the condition that steps S3 and S4 are both present, adding the initial S2 step increases the thermal conductivity from 152.4 W / (m·K) to 256.7 W / (m·K). This indicates that the first hot pressing in the GO thin film stage has a role far beyond preliminary compaction. More importantly, by applying pressure at a lower temperature, it enables the GO sheets to achieve pre-alignment and pre-densification, forming a uniform and tightly stacked physical substrate. This uniform and stable substrate is crucial for subsequent high-temperature processing (especially S3 annealing). It effectively avoids large-size defects, cracks, or severe structural distortions caused by the loose and uneven structure of the original GO thin film at high temperatures, laying an irreplaceable foundation for the smooth progress of the entire process chain and the integrity of the final structure.

[0067] Comparing the schemes containing step S5 (Comparative Example 5, Example 1) with those without step S5 (Comparative Examples 1-4), a significant increase in thermal conductivity can be observed (from a maximum of 256.7 W / (m·K) to over 516.0 W / (m·K)). This demonstrates that the rapid ultra-high temperature treatment of step S5 plays a crucial role in repairing defects in the carbon framework and significantly improving the crystallinity of graphene crystals.

[0068] Comparing Comparative Example 6 (without S2) with Example 1 (with S2), it can be seen that even though subsequent steps S3, S4, and S5 are included, the absence of the initial S2 still causes the thermal conductivity to decrease from 602.0 W / (m·K) to 571.9 W / (m·K). This result further illustrates that the initial structural uniformity established by S2 has the characteristic of "precursor irreversibility," and its absence cannot be completely compensated for by subsequent high-temperature densification and graphitization processes, thus limiting the overall continuity of the final heat conduction pathway.

[0069] Comparing Comparative Example 7 (without S4) with Example 1, it can be seen that, even with steps S2, S3, and S5 present, the introduction of S4 still further increases the thermal conductivity from 563.4 W / (m·K) to 602.0 W / (m·K). This indicates that the second hot pressing, which re-densifies the material structure and reconstructs the interface before Joule heat treatment, helps to fully utilize the potential of the high-temperature graphitization stage in S5, thereby significantly improving the upper limit of thermal conductivity.

[0070] Comparing Comparative Example 8 with Example 1, it can be seen that, under the condition of having steps S2, S4, and S5, simplifying S3 from staged annealing to a single-temperature long-term treatment significantly reduced the thermal conductivity to 332.5 W / (m·K). This indicates that staged heating is crucial for achieving gradual removal of functional groups, progressive stress release, and orderly rearrangement of lamellar layers; a coarsened annealing path weakens the synergistic effect of subsequent densification and graphitization.

[0071] Furthermore, comparing Comparative Example 9 with Example 1, it can be seen that, under the same conditions including S2, S4, and S5, directly introducing a high-temperature treatment of 1200°C for a long time in stage S3 results in a thermal conductivity of only 485.4 W / (m·K). This indicates that applying high temperature too early will cause rapid shrinkage and structural reconstruction before the layers have completed gradual reduction and stress regulation, reducing stacking uniformity and overall continuity, thereby limiting further improvement in the final thermal conductivity.

[0072] Depend on Figure 2 Macroscopic morphological observation, Example 1 ( Figure 2 The graphene paper prepared in (a) is generally flat and dense with regular edges, and its surface is a uniform dark black with a slight metallic luster. The film has good self-support, indicating that a stable and continuous structural connection has been formed between the layers. Comparative Example 1 ( Figure 2 Sample b) underwent only low-temperature annealing. Macroscopically, the film is loose overall with obvious edge warping, a matte black surface that is rough and uneven, and exhibits weak mechanical integrity, making it prone to delamination and localized damage. Comparative Example 2 ( Figure 2 After one hot pressing and annealing treatment, the overall flatness of the film in sample c) was improved, but slight warping and surface undulations still existed at local edges, indicating insufficient interlayer densification.

[0073] Comparative Example 3 ( Figure 2 Sample d) underwent a second hot-pressing treatment after annealing. The film flatness was improved compared to Comparative Example 1, but uneven compaction areas were still visible in some areas, and the overall uniformity was still inferior to that of Example 1. Comparative Example 4 ( Figure 2 Sample (e) underwent two hot-pressing and annealing treatments, resulting in a significantly enhanced overall film density and a relatively smooth and uniform surface. However, its gloss was lower than that of Example 1, indicating that the degree of crystalline graphitization was still limited. Comparative Example 5 ( Figure 2 Sample f) was subjected to rapid Joule heat treatment only. The film has a slight metallic luster and a high degree of graphitization, but the overall flatness is still not as good as that of Example 1. There are local undulations and slight warping, which reflects that the interlayer porosity and interface adhesion are not fully optimized.

[0074] Further SEM cross-sectional observations showed that, in Comparative Example 1 ( Figure 4 Sample a) has a large interlayer gap and obvious interface separation, with a large number of discontinuous pores and structural fracture areas, resulting in frequent interruptions of the heat transfer path and a significant increase in interfacial thermal resistance; while Example 1 ( Figure 4Sample b) exhibits a highly oriented and tightly stacked layered structure, with significantly reduced interlayer gaps and good interfacial continuity. No obvious through-holes were observed, forming a continuous and stable in-plane thermal conductivity pathway. The aforementioned differences in macroscopic morphology and microstructure correspond to the thermal conductivity test results of each sample, fully demonstrating the crucial role of the multi-stage synergistic heat treatment process in densifying the sheets, improving interfacial continuity, and enhancing intrinsic heat transport capacity.

[0075] In summary, the specific multi-level synergistic process chain provided by this invention, consisting of "first hot pressing (S2) → staged annealing (S3) → second hot pressing (S4) → rapid Joule heat treatment (S5)," systematically solves key problems such as loose structure, poor interfacial contact, and numerous crystal defects in the preparation of high-performance graphene paper from GO precursors. Experimental data demonstrate that each step is unique and irreplaceable, and the steps are interconnected and executed sequentially, producing a significant synergistic gain effect. Ultimately, high-quality graphene paper with an in-plane thermal conductivity exceeding 600 W / (m·K) was successfully prepared.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing graphene paper based on multi-stage synergistic heat treatment, characterized in that: The process includes the following steps: filtering the graphene oxide dispersion into a film, drying and peeling it off to obtain a self-supported graphene oxide film; The obtained self-supported graphene oxide film was subjected to a hot pressing at 250-350℃ and 25-35 MPa; after the hot pressing, it was annealed in an inert atmosphere with programmed temperature rise. The annealed graphene oxide film was subjected to a second hot pressing at 250-350℃ and 25-35 MPa pressure. After the second hot pressing, rapid Joule heat treatment is carried out in an inert atmosphere at 2600-3000℃ for 30-90 seconds. After cooling, the product is obtained.

2. The method for preparing graphene paper based on multi-stage synergistic heat treatment according to claim 1, characterized in that: The solid content of the graphene oxide dispersion is 2-5 mg / mL.

3. The method for preparing graphene paper based on multi-stage synergistic heat treatment according to claim 1, characterized in that: The filter membrane used in the filtration membrane formation process is a nylon filter membrane.

4. The method for preparing graphene paper based on multi-stage synergistic heat treatment according to claim 1, characterized in that: The temperature for one hot pressing is 280-320℃, the pressure is 25-35 MPa, and the hot pressing time is 0.5-1.5h.

5. The method for preparing graphene paper based on multi-stage synergistic heat treatment according to claim 1, characterized in that: The temperature for the second hot pressing is 280-320℃, the pressure is 25-35 MPa, and the hot pressing time is 0.5-1.5h.

6. The method for preparing graphene paper based on multi-stage synergistic heat treatment according to claim 1, characterized in that: The programmed temperature annealing process is as follows: first, hold at 350-450℃ for 10-60 minutes, and then hold at 1150-1250℃ for at least 1.5 hours.

7. The method for preparing graphene paper based on multi-stage synergistic heat treatment according to claim 6, characterized in that: The programmed temperature annealing process is as follows: first, hold at 350-450℃ for 20-40 minutes, and then hold at 1150-1250℃ for 1.5-3 hours.

8. The method for preparing graphene paper based on multi-stage synergistic heat treatment according to claim 1, characterized in that: The heating rate of rapid Joule heat treatment is 4-10℃ / s.

9. A graphene paper based on multi-stage synergistic heat treatment, characterized in that: Prepared by any one of the preparation methods described in claims 1-8, the in-plane thermal conductivity is not less than 500 W / (m·K).

10. The application of the graphene paper based on multi-level synergistic heat treatment as described in claim 9 in the field of heat dissipation of electronic devices.

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