Aromatic heterocyclic polymer-based graphite film with high vertical thermal conductivity and preparation method of aromatic heterocyclic polymer-based graphite film

Abstract

The invention belongs to the field of heat-conducting graphite materials, and particularly relates to a high-vertical-heat-conductivity aromatic heterocyclic polymer-based graphite film and a preparation method thereof. The graphite film is prepared by the following steps: preparing a base film from modified aromatic oxadiazole, carbonizing, graphitizing and carrying out cold pressing treatment. Wherein the modified polyaryloxadiazole is mainly prepared from the following raw materials: terephthalic acid, isophthalic acid, azobenzene dicarboxylic acid, carboxyl modified carbon nanotubes and hydrazinium.

Description

Technical Field

[0001] The present invention belongs to the field of thermally conductive graphite materials, and in particular relates to an aromatic heterocyclic polymer-based graphite film with high vertical thermal conductivity and a preparation method thereof. Background Art

[0002] In the era of booming modern technology, electronic devices are rapidly advancing toward higher performance, miniaturization, and greater multifunctionality. From mobile devices like smartphones and tablets to large-scale equipment like data centers and communication base stations, they all generate significant amounts of heat during operation. If this heat cannot be dissipated promptly and effectively, device performance will be severely impacted, significantly shortening their lifespan. Therefore, efficient thermal management technology has become a key factor in ensuring the stable operation of electronic devices, and graphite film, as a key material in this field, has attracted considerable attention.

[0003] Currently, the main technologies used to prepare graphene films include the organic precursor method and the graphite oxide method. The organic precursor method often uses polymers such as polyimide (PI) and polyoxadiazole (POD) as precursors, and prepares graphite film through preforming, carbonization, and high-temperature graphitization. This method can produce graphene thermally conductive films or fibers with high thermal conductivity, good crystallinity, and orientation, to a certain extent meeting some thermal management requirements. The graphite oxide method utilizes the thermal reduction properties of graphene oxide to prepare graphite film. Its process is relatively simple and has also been applied in some fields.

[0004] However, both mainstream graphite film preparation technologies suffer from a key drawback: low vertical thermal conductivity, typically below 3 W / (mK). This issue severely limits the application of graphite film in numerous applications requiring high vertical heat dissipation. In 5G communication base stations, as signal transmission frequencies continue to increase, the heat generated by base station equipment is rapidly increasing. Existing graphite films with low vertical thermal conductivity cannot quickly and effectively conduct heat away from the heat-generating components, leading to excessively high internal device temperatures, which in turn affects signal transmission stability and device reliability, increasing the risk of equipment failure. A similar dilemma exists in the CPU cooling modules of high-performance computers. CPUs generate significant amounts of heat during high-speed computing. If the graphite film has poor vertical thermal conductivity, heat will accumulate on the CPU chip surface, rapidly increasing chip temperatures, slowing CPU operations and potentially even causing serious problems such as system freezes. In electric vehicle battery thermal management systems, heat is generated during battery charging and discharging, and graphite film is required to conduct this heat vertically to the heat dissipation components. However, existing graphite films with low vertical thermal conductivity cannot meet this rapid heat dissipation requirement, potentially causing excessive battery temperatures, impacting battery charging and discharging efficiency and service life, and even posing safety risks.

[0005] Currently, researchers have made many attempts to improve the vertical thermal conductivity of graphite films. However, most existing improvement methods have limitations. While improving the vertical thermal conductivity, they often sacrifice the in-plane thermal conductivity of the graphite film. For example, when adding certain special fillers to improve the vertical thermal conductivity, these fillers may destroy the original in-plane crystal structure of the graphite film, resulting in a decrease in the in-plane thermal conductivity. This makes it difficult to find a balance between ensuring good vertical heat dissipation performance and maintaining high in-plane thermal conductivity in practical applications, greatly limiting the improvement of the overall performance of graphite films and their widespread application. Summary of the Invention

[0006] The present invention carboxylates carbon nanotubes and in-situ polymerizes them with poly(arylene oxadiazole) (POD) to obtain modified poly(arylene oxadiazole), thereby obtaining a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, which can take into account both horizontal and vertical thermal conductivity.

[0007] The technical solution of the present invention:

[0008] The first technical problem to be solved by the present invention is to provide a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, wherein the graphite film is first prepared by preparing a base film of modified polyaromatic oxadiazole, and then undergoing carbonization and graphitization treatment and cold pressing treatment; wherein the modified polyaromatic oxadiazole is prepared using terephthalic acid, isophthalic acid, azophthalic acid, carboxyl-modified carbon nanotubes and hydrazine salts as main raw materials.

[0009] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the modified polyarylene oxadiazole is prepared by the following preparation method: first, terephthalic acid, isophthalic acid, azophthalic acid, carboxyl-modified carbon nanotubes and hydrazine salt are reacted at 80-90°C under the action of fuming sulfuric acid until the reaction liquid is transparent; then the temperature is raised to 100-120°C and the reaction is carried out for 2-5 hours; benzoic acid is used to terminate the reaction; and then the reaction is continued at 120-135°C for 0.5-1 hour, and vacuum degassing and drying are carried out. The modified polyarylene oxadiazole is prepared; wherein the molar ratio of isophthalic acid to terephthalic acid is 0.05-0.55:0.95-0.45; the mass of azophthalic acid: the total mass of isophthalic acid and terephthalic acid is 0.01-0.10:1, the mass of carboxyl-modified carbon nanotubes: the total mass of isophthalic acid and terephthalic acid is 0.001-0.01:1, and the molar addition amount of hydrazine salt: the total molar amount of isophthalic acid and terephthalic acid is 1.10-1.20:1.

[0010] Preferably, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the mass of azophthalic acid: the total mass of isophthalic acid and terephthalic acid is 0.05:1.

[0011] Furthermore, in the aforementioned high perpendicular thermal conductivity heteroaromatic polymer-based graphite film, the carboxyl-modified carbon nanotubes are obtained by surface-functionalizing the carbon nanotubes with carboxyl groups using a mixed solution of concentrated sulfuric acid and concentrated nitric acid. Preferably, the volume ratio of the concentrated sulfuric acid to concentrated nitric acid is 3:1. The mass-to-volume ratio of the carbon nanotubes to the mixed acid is 1 g:50-100 mL (preferably 1 g:50 mL). The surface carboxyl-functionalization treatment is performed by stirring at 60-100°C (preferably 80°C) for 4-8 hours (preferably 6 hours). Preferably, the carbon nanotubes are 10-30 μm in length.

[0012] Furthermore, in the aforementioned high vertical thermal conductivity heteroaromatic polymer-based graphite film, the carboxyl-modified carbon nanotubes are obtained by functionalizing the carbon nanotubes with carboxyl groups on their surfaces using a mixed solution of concentrated sulfuric acid and concentrated nitric acid. After removing impurities (using a Buchner funnel to filter the solid), the carbon nanotubes are washed multiple times until neutral, and then incubated at 60-80°C until constant weight is reached (preferably for 8-12 hours). When single-walled carbon nanotubes are used as the starting material, the carbon nanotubes are designated SWCNT-COOH (carboxyl-modified single-walled carbon nanotubes); when multi-walled carbon nanotubes are used as the starting material, the carbon nanotubes are designated MWCNT-COOH (carboxyl-modified multi-walled carbon nanotubes).

[0013] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the hydrazine salt is hydrazine sulfate salt.

[0014] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the azophthalic acid is azobenzene-4,4'-dicarboxylic acid.

[0015] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the thickness of the graphite film is 30 to 100 μm.

[0016] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the density of the graphite film is 1.8 to 2.1 g / cm 3 .

[0017] Furthermore, in the above-mentioned aromatic heterocyclic polymer-based graphite film with high vertical thermal conductivity, the horizontal thermal conductivity of the graphite film is 1300 to 1700 W / (mK).

[0018] Furthermore, in the above-mentioned aromatic heterocyclic polymer-based graphite film with high vertical thermal conductivity, the vertical thermal conductivity of the graphite film is 3.5 to 12 W / (mK).

[0019] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the graphite film has a graphitization degree of 95-100%.

[0020] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the lattice spacing of the graphite film is 0.335 to 0.350 nm.

[0021] The second technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned aromatic heterocyclic polymer-based graphite film with high vertical thermal conductivity, comprising the following steps:

[0022] (1) Preparing a poly (aryl oxadiazole) (POD) stock solution: first reacting terephthalic acid, isophthalic acid, azophthalic acid, carboxyl-modified carbon nanotubes and hydrazine salt at 80-90°C under the action of fuming sulfuric acid until the reaction solution becomes transparent; then heating to 100-120°C and reacting for 2-5 hours; terminating the reaction with benzoic acid; then continuing the reaction at 120-135°C for 0.5-1 hour, and performing vacuum degassing and drying to obtain the modified poly (aryl oxadiazole) stock solution; The molar ratio of isophthalic acid to terephthalic acid is 0.05-0.55:0.95-0.45; the mass of azophthalic acid: the total mass of isophthalic acid and terephthalic acid is 0.01-0.10:1; the mass of carboxyl-modified carbon nanotubes: the total mass of isophthalic acid and terephthalic acid is 0.001-0.01:1; and the molar amount of hydrazine salt added: the total molar amount of isophthalic acid and terephthalic acid is 1.10-1.20:1.

[0023] (2) Preparation of wet poly (aryl oxadiazole) (POD) membrane: The obtained POD stock solution is passed through a wet film preparation device to prepare a wet POD membrane after solvent replacement;

[0024] (3) preparing a dry POD membrane from the obtained wet poly(arylene oxadiazole) (POD) membrane;

[0025] (4) Finally, the dry POD film is subjected to carbonization and graphitization treatment and cold pressing treatment to obtain the high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film.

[0026] Furthermore, in the above-mentioned method for preparing the high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, in step (1), the molar ratio of the terminator benzoic acid to the excess amount of hydrazine salt is 1:1.

[0027] Furthermore, in the above method for preparing the aromatic heterocyclic polymer-based graphite film with high vertical thermal conductivity, in step (1), the sulfur trioxide content in the fuming sulfuric acid is 20-40 wt %, preferably 25 wt %.

[0028] Furthermore, in the method for preparing the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, in step (2), the method for preparing a wet POD film from the obtained POD stock solution is as follows: the obtained POD stock solution is spread on a substrate at 60 to 120°C, and a wet film preparation device is used to scrape the film to obtain a wet film; then the substrate is placed in a 30 to 60 wt% sulfuric acid aqueous solution for solvent replacement, and the water-containing wet POD film is obtained after washing.

[0029] Furthermore, in the above-mentioned method for preparing the high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, in step (3), the wet POD film is annealed at 60 to 120° C. for 10 to 60 minutes to obtain a dry POD film.

[0030] Furthermore, in the above-mentioned method for preparing the aromatic heterocyclic polymer-based graphite film with high vertical thermal conductivity, in step (4), the carbonization temperature is 1200-1500°C, and the graphitization temperature is 2600-3000°C.

[0031] Preferably, in the above-mentioned method for preparing the aromatic heterocyclic polymer-based graphite film with high vertical thermal conductivity, in step (4), the carbonization treatment process is: under the protection of inert gas, the dry POD film is gradually heated from room temperature to 400-500°C at a heating rate of 2-5°C / min, and kept warm for 0.5h-2h, then the heating rate is reduced to 0.5-2°C / min (preferably 1°C / min) and the temperature is raised to 500-600°C, and the temperature is kept warm for 0.5h-2h; then the heating rate is increased to 2-5°C / min (preferably 2.5°C / min) and the temperature is raised to 1200-1500°C (preferably 1400°C) and kept warm for 0.5h-5h.

[0032] Preferably, in the above-mentioned method for preparing the aromatic heterocyclic polymer-based graphite film with high vertical thermal conductivity, in step (4), the graphitization treatment process is: heating to 2200-2300°C at a heating rate of 3-10°C / min, keeping warm for 0.5h-2h, then reducing the heating rate to 0.5-2°C / min and heating to 2400-2500°C, keeping warm for 0.5h-2h; then increasing the heating rate to 3-10°C / min and heating to 2600-3000°C and keeping warm for 0.5h-2h, and then naturally cooling to room temperature.

[0033] Furthermore, in the above-mentioned method for preparing the high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, in step (4), the cold pressing treatment is: first expelling the air in the film, then pressing at a pressure of 50 to 150 MPa for 1 to 2 hours, and then pressing at a pressure of 250 to 300 MPa for 5 to 10 hours.

[0034] Beneficial effects of the present invention:

[0035] The present invention carboxylates carbon nanotubes and in-situ polymerizes them with poly(arylene oxadiazole) (POD) to produce a modified poly(arylene oxadiazole). This results in a high vertical thermal conductivity heterocyclic polymer-based graphite film that balances both horizontal and vertical thermal conductivity. The graphite film has a thickness range of 30 to 100 μm and a density of 1.8 to 2.1 g / cm². 3 The horizontal thermal conductivity is 1300~1700 W / (mK), and the vertical thermal conductivity is 3.5~12 W / (mK), which achieves a significant improvement in the comprehensive performance of the graphite film. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Transmission electron microscope morphology image (a), elemental analysis image (b) of the carboxylated carbon nanotubes used in the examples of the present invention, and TEM morphology image (c) of the graphite film sample of Example 3.

[0037] Figure 2 Raman data of carbonized films at 1400°C of Examples 1-10 of the present invention and Comparative Example 1 (a) and the corresponding I D / I G Data analysis diagram (c), Raman data diagram of 3000℃ graphitized film (b) and corresponding I 2D / I G Data analysis diagram (d).

[0038] Figure 3 XRD data of the graphite films at 3000°C of Examples 1-10 of the present invention and Comparative Example 1 (a) and the corresponding d 002 and L c Data analysis diagram (b). DETAILED DESCRIPTION

[0039] The present invention proposes a method for improving the vertical thermal conductivity of a poly(arylene oxadiazole) (POD)-based graphite film using carboxyl-modified carbon nanotubes. The graphite film is first prepared by preparing a base film of modified poly(arylene oxadiazole), which is then subjected to carbonization and graphitization treatments and cold pressing. The structural formula of the modified poly(arylene oxadiazole) is shown as follows:

[0040] .

[0041] The method includes the following key steps:

[0042] 1) Preparation of POD polymer stock solution: A solution mixing copolymerization method was used, using fuming sulfuric acid as a solvent and dehydrating agent to promote the polymerization and cyclization reactions of the monomers. In this process, carboxyl-modified carbon nanotubes were added to the reaction system as a reactive monomer to ensure their uniform dispersion during the polymerization process.

[0043] 2) Preparation and drying of wet POD film: The obtained POD stock solution is spread on a substrate (such as a glass plate) at 60-120°C and scraped using a wet film preparation apparatus. Wet films of varying thicknesses can be prepared by adjusting the slit width of the wet film preparation apparatus. Subsequently, the substrate is placed in a 30-60 wt% (preferably 50 wt%) aqueous sulfuric acid solution for solvent replacement for 10-30 minutes. At this time, the solvent of the wet film changes from concentrated sulfuric acid to water, and the film gradually separates from the glass plate. The film is then transferred to deionized water for 10-30 minutes to remove the surface sulfuric acid. Finally, the film is transferred to flowing deionized water for rinsing for more than 12 hours to remove the remaining sulfuric acid, thereby obtaining a water-containing wet POD film.

[0044] 3) The wet POD film is then fixed with a nail board and dried to obtain a dry POD film of carboxyl-modified carbon nanotubes;

[0045] 4) Carbonization-graphitization treatment and cold pressing treatment: The POD dry film undergoes carbonization-graphitization treatment, in which carbon nanotubes act as a vertical phase in the film. Through in-situ polymerization, they can effectively improve the holes and defects caused by the different shrinkage during the carbonization process of the matrix; during the graphitization process, they do not interfere with the growth of graphite sheets, and act as a vertical phase heat conduction path between layers, thereby improving the vertical thermal conductivity of the graphite film; the graphitized film is then gradually cold pressed to improve its density and performance: a roller press is used to remove the air inside the film at low pressure, and then a cold press is used to press at 50-150 MPa for 1-2 hours, and finally at 250-300 MPa for 5-10 hours to obtain a flexible and dense graphite film. For example: first place the graphite film between two pieces of smooth release paper to ensure the smoothness of the graphite film surface after calendering and separation from the pressing surface, first use a roller press at low pressure to remove the air inside the film, then use a cold press at 100 MPa pressure for 1 hour, and finally use 300 MPa pressure for 5 hours to obtain a flexible and dense graphite film.

[0046] This invention achieves in-situ polymerization of carbon nanotubes and poly(arylene oxadiazole) (POD) by carboxylating carbon nanotubes and combining them with the strong dispersing and dehydrating properties of the poly(arylene oxadiazole) (POD) polymerization system. This fundamentally addresses the difficulty in dispersing carbon nanotubes and mitigates the disruption of graphite crystallite orientation caused by differential shrinkage during carbonization. The strong solubility and dispersibility of the poly(arylene oxadiazole) system combined with the dehydrating properties of fuming sulfuric acid significantly reduces defects and vacancies caused by differential shrinkage during carbonization of the carbon material and organic precursor, laying a key foundation for the preparation of high-performance graphite films.

[0047] The present invention constructs a composite bidirectional structure of carbon nanotubes and graphene: carbon nanotubes mainly exist between graphite microcrystal layers during the graphitization process, which neither affects the continuous growth and stacking of graphene sheets nor affects the continuous growth and stacking of graphene sheets. At the same time, they can serve as vertical phase heat conduction paths, forming a synergistic effect with the horizontal graphene sheet heat conduction paths, thus achieving a balance between horizontal and vertical thermal conductivity.

[0048] The performance of the graphite film of the present invention is significantly improved: the vertical thermal conductivity is increased by 300%, and the horizontal thermal conductivity decreases by less than 10%. When the thickness is 45 μm, the horizontal thermal conductivity reaches 1564 W / (mK) and the vertical thermal conductivity reaches 7.0 W / (mK). The overall product density is 1.8-2.1 g / cm 3 This effectively overcomes the current technical shortcoming of difficult-to-improve vertical thermal conductivity in thermally conductive graphite films, and addresses the issue of low vertical thermal conductivity in graphite films prepared from organic polymer precursors. The graphite film of the present invention can be widely used in electronics manufacturing, energy storage, aerospace, and other fields. It can achieve uniform heat distribution and rapid heat removal from heat-generating devices, significantly improving the thermal management efficiency of equipment and providing a better choice for the application of thermal management systems in different scenarios.

[0049] The examples will further illustrate the above embodiments. It should be emphasized that these examples are only used to illustrate the process and effects of the present invention and do not limit the scope of application of the present invention. Unless otherwise specified, the conditions, reagents, or equipment used in the experiments all follow industry standards or manufacturer's recommended specifications.

[0050] In the embodiments of the present invention, all raw materials are directly purchased industrial-grade raw materials.

[0051] Examples 1-5

[0052] 1) Stock Solution Synthesis: First, the raw materials were blended in the proportions shown in Table 1 and dissolved at 85°C for 0.5 hours. After the solids were dissolved, the temperature was raised to 90°C for 1 hour, and then further raised to 120°C for 3 hours. After the reaction, benzoic acid (in an amount equal to the molar amount of excess hydrazine sulfate) was used to terminate the reaction. The reaction was then continued at 120°C for 0.5 hours, followed by vacuum degassing for 12 hours to produce the POD stock solution. The carboxyl-modified carbon nanotubes were surface-functionalized with carboxyl groups in a mixture of concentrated sulfuric acid and concentrated nitric acid (3:1). After impurities were removed, the solution was washed multiple times until neutral, and then incubated at 60°C for 10 hours to obtain the carboxyl-modified carbon nanotubes, named MWCNT-COOH (carboxyl-modified multi-walled carbon nanotubes). The carbon nanotubes were selected to have a length of 10-30 μm.

[0053] Table 1 Ratio of each raw material (can be enlarged according to the usage amount)

[0054] raw material Mass or volume Terephthalic acid 20 g Isophthalic acid 5 g Azobenzene-4,4'-dicarboxylic acid 1.25 g Carboxyl-modified multi-walled carbon nanotubes 0.025 / 0.0625 / 0.125 / 0.1875 / 0.25 g Hydrazine sulfate 20.56 g concentrated sulfuric acid 80 mL Oleum (50%) 70 mL benzoic acid 0.9189 g

[0055] 2) Wet film formation: The POD stock solution was processed through a wet film preparation device. The specific operation was as follows: the POD stock solution was spread on a glass plate at 80 °C, and the film was scraped using a wet film preparation device with a 750 μm slit. After the film was separated from the glass plate by 50 wt% sulfuric acid solution for 20 minutes, it was rinsed with deionized water for more than 12 hours to remove the residual sulfuric acid to obtain a POD wet film.

[0056] 3) Preparation of dry film: Use a pin plate to fix the four sides of the POD wet film and dry the water in an oven at 100°C to obtain a POD dry film.

[0057] 4) Carbonization, graphitization and cold pressing treatment of POD dry film:

[0058] Carbonization treatment: Carried out in a graphite furnace; under the protection of argon at 5 L / min, first heated to 400°C at a rate of 2.5°C / min, held at that temperature for 0.5 hour, then adjusted to a heating rate of 1°C / min to 600°C, held at that temperature for 0.5 hour; then adjusted to a heating rate of 2.5°C / min to 1400°C and held at that temperature for 1 hour;

[0059] Graphitization treatment: first, heat to 2200°C at a rate of 5°C / min, hold for 0.5 hour, then adjust the heating rate to 1°C / min and raise to 2500°C, hold for 0.5 hour; then adjust the heating rate to 5°C / min and raise to 3000°C and hold for 1 hour; then naturally cool to room temperature to obtain the initial graphite film;

[0060] Cold pressing treatment: First, place the graphite film between two pieces of smooth release paper to ensure the smoothness of the graphite film surface after calendering and separation from the pressing surface. First, use a roller press at low pressure to remove the air inside the film, then use a cold press at 100 MPa pressure for 1 hour, and finally press at 300 MPa pressure for 5 hours to obtain a flexible and dense graphite film.

[0061] The obtained graphite films are named according to the amount of multi-walled carbon nanotubes added, namely Example 1-MWCNT0.1 (i.e., carboxyl-modified multi-walled carbon nanotubes account for 0.1 wt% of the total mass of terephthalic acid and isophthalic acid), Example 2-MWCNT0.25, Example 3-MWCNT0.5, Example 4-MWCNT0.75, and Example 5-MWCNT1.0. The thickness of the final prepared graphite film is 45 μm.

[0062] Examples 6-10

[0063] The preparation method is the same as that in Example 1, except that the multi-walled carbon nanotubes are replaced by single-walled carbon nanotubes. The obtained graphite films are named according to the amount of single-walled carbon nanotubes added, namely, Example 6-SWCNT0.1 (i.e., the carboxyl-modified single-walled carbon nanotubes account for 0.1 wt% of the total mass of terephthalic acid and isophthalic acid), Example 7-SWCNT0.25, Example 8-SWCNT0.5, Example 9-SWCNT0.75, and Example 10-SWCNT1.0.

[0064] Comparative Example 1

[0065] The preparation method is the same as that of Example 1, except that no carbon nanotubes are added during the preparation process; the graphite film is denoted as origin.

[0066] Comparative Example 2

[0067] The preparation method is the same as that of Example 3, except that the multi-walled carbon nanotubes added during the preparation process are not carboxylated.

[0068] Comparative Example 3

[0069] The preparation method is the same as that of Example 8, except that the single-walled carbon nanotubes added during the preparation process are not carboxylated.

[0070] Comparative Example 4

[0071] The preparation method is the same as that of Example 3, except that the carboxyl-modified multi-walled carbon nanotubes are replaced by graphene oxide during the preparation process.

[0072] Performance tests and their results:

[0073] Thermal conductivity testing: The thermal diffusivity of graphite films was measured using a NETZSCH LFA 467 at room temperature (25°C). The test sample was a 2.5 cm diameter disc, with graphite sprayed on both sides. The thermal conductivity test results for the graphite films obtained in the Examples and Comparative Examples are shown in Table 2.

[0074] Table 2 Performance comparison of graphite films

[0075] Serial number <![CDATA[Density (g·cm -3 )]]> <![CDATA[Horizontal thermal conductivity (W·m -1 ·K -1 )]]> <![CDATA[Vertical thermal conductivity (W·m -1 ·K -1 )]]> Comparative Example 1 2.08 1675.7 2.21 Example 1 2.06 1602.6 4.17 Example 2 2.04 1537.9 5.91 Example 3 2.01 1458.9 7.78 Example 4 1.95 1337.8 8.93 Example 5 1.9 1173.9 12.26 Comparative Example 2 1.87 1205.5 4.71 Example 6 2.04 1646.9 3.77 Example 7 2.01 1621.7 4.62 Example 8 1.95 1564.3 7.05 Example 9 1.85 1460.1 8.43 Example 10 1.77 1357.3 9.89 Comparative Example 3 1.82 1348.5 4.12 Comparative Example 4 1.88 1377.5 2.74

[0076] The thermal conductivity data in Table 1 show that the introduction of carbon nanotubes without carboxylation (Comparative Examples 2 and 3) leads to a more severe shrinkage mismatch during the carbonization process, causing a sharp drop in horizontal thermal conductivity and a negligible increase in vertical thermal conductivity. This effect is significantly reduced after carboxylation, and in Example 8, the use of carboxyl-modified single-walled carbon nanotubes maintains the horizontal thermal conductivity of the final graphite film above 1560 W·m -1 ·K -1At the same time, the vertical thermal conductivity is increased to 7 W·m -1 ·K -1 The above demonstrates the excellent effect of the present invention. However, when other carbon-based fillers such as graphene oxide are introduced (Comparative Example 4), the horizontal thermal conductivity is greatly reduced and the vertical thermal conductivity is not effectively improved.

[0077] Depend on Figure 1 a. Figure 1 b. Figure 1 Morphological and elemental analysis indicate that the carbon nanotubes have been successfully surface carboxylated after treatment, which facilitates their dispersion in the POD polymerization system and their participation in the polymerization reaction. Graphitization also reveals effective connections between graphene sheets, creating vertical thermal pathways.

[0078] Depend on Figure 2 a. Figure 2 b Raman data and Figure 2 c. Figure 2 dI D / I G The data analysis shows that the addition of carboxyl-modified carbon nanotubes affects the growth quality of graphite microcrystals during the carbonization process. This is mainly caused by the mismatch between the matrix and the carbon nanotubes' shrinkage. However, as long as this effect is controlled and weakened, it can be repaired during the graphitization process. Figure 2 b It can be seen that the defect peaks disappear after graphitization, which shows that the defects caused by the introduction of carbon nanotubes can be effectively reduced by this technology. 2D / I G It can be seen from the comparison that with the increase of the amount of carbon nanotubes introduced, I 2D / I G It will continue to increase, which means that the average stacking number of graphite sheets is decreasing. This is mainly because most of the carbon nanotubes are located between the layers, and this effect of multi-walled carbon nanotubes is greater than that of single-walled carbon nanotubes.

[0079] Depend on Figure 3 a XRD data and Figure 3 b of d 002 and L c The data analysis chart further shows that the intercalation effect after the introduction of carbon nanotubes, since most of the carbon nanotubes are inserted into the graphene sheets, leads to an increase in the interlayer spacing and a decrease in the average stacking thickness, and the intercalation effect of multi-walled carbon nanotubes is greater than that of single-walled carbon nanotubes.

[0080] In summary, this invention addresses the technical bottlenecks of low vertical thermal conductivity of existing graphite films and the tendency of fillers to reduce horizontal thermal conductivity by introducing fillers. By utilizing an in-situ polymerization process of carboxylated carbon nanotubes and poly (aryl oxadiazole) (POD), this process effectively addresses issues such as interfacial incompatibility between carbon-based materials and organic matrices, as well as heterogeneous shrinkage mismatch during high-temperature carbonization. Experimental results demonstrate that this invention significantly improves vertical thermal conductivity while maintaining the high horizontal thermal conductivity of the graphite film, significantly improving the overall thermal conductivity of the graphite film compared to conventional technologies. This invention provides a novel solution for the preparation of high-performance thermal management materials and has broad application prospects in electronics manufacturing, energy storage, aerospace, and other fields.

Claims

1. A high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, characterized in that: The graphite film is prepared by first preparing a base film of modified polyarylene oxadiazole, and then undergoing carbonization and graphitization treatment and cold pressing treatment; wherein the modified polyarylene oxadiazole is prepared using terephthalic acid, isophthalic acid, azophthalic acid, carboxyl-modified carbon nanotubes and hydrazine salt as main raw materials.

2. The high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 1, characterized in that: The modified polyaryl oxadiazole is prepared by the following preparation method: first, terephthalic acid, isophthalic acid, azophthalic acid, carboxyl-modified carbon nanotubes and hydrazine salt are reacted at 80-90° C. under the action of fuming sulfuric acid until the reaction solution becomes transparent; then the temperature is raised to 100-120° C. and the reaction is carried out for 2-5 hours; benzoic acid is used to terminate the reaction; and the reaction is continued at 120-135° C. for 0.5-1 hour, and vacuum degassing and drying are performed to obtain the modified polyaryl oxadiazole; The molar ratio of isophthalic acid to terephthalic acid is 0.05-0.55:0.95-0.45; the mass of azophthalic acid: the total mass of isophthalic acid and terephthalic acid is 0.01-0.10:1; the mass of carboxyl-modified carbon nanotubes: the total mass of isophthalic acid and terephthalic acid is 0.001-0.01:1; and the molar amount of hydrazine salt added: the total molar amount of isophthalic acid and terephthalic acid is 1.10-1.20:

1.

3. The high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 1 or 2, characterized in that: The carboxyl-modified carbon nanotubes are obtained by subjecting carbon nanotubes to surface carboxyl functionalization treatment using a mixed solution of concentrated sulfuric acid and concentrated nitric acid.

4. The high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 1 or 2, characterized in that: The thickness of the graphite film is 30 to 100 μm; or The density of the graphite film is 1.8-2.1 g / cm 3 ;or, The horizontal thermal conductivity of the graphite film is 1300 to 1700 W / (mK); or, The vertical thermal conductivity of the graphite film is 3.5 to 12 W / (mK); or, The graphitization degree of the graphite film is 95-100%; or, The lattice spacing of the graphite film is 0.335-0.350 nm.

5. The method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Prepare POD stock solution: first, react terephthalic acid, isophthalic acid, azophthalic acid, carboxyl modified carbon nanotubes and hydrazine salt at 80-90°C under the action of fuming sulfuric acid until the reaction solution is transparent; then heat to 100-120°C and react for 2-5 hours; terminate the reaction with benzoic acid; then continue to react at 120-135°C for 0.5-1 hour, and perform vacuum degassing and drying to obtain the modified polyoxadiazole stock solution; wherein, isophthalic acid The molar ratio of phthalic acid to terephthalic acid is 0.05-0.55:0.95-0.45; the mass of azophthalic acid: the total mass of isophthalic acid and terephthalic acid is 0.01-0.10:1; the mass of carboxyl-modified carbon nanotubes: the total mass of isophthalic acid and terephthalic acid is 0.001-0.01:1; the molar amount of hydrazine salt added: the total molar amount of isophthalic acid and terephthalic acid is 1.10-1.20:1; (2) Preparation of POD membrane: The obtained POD stock solution is passed through a wet film preparation device to prepare a wet POD membrane after solvent replacement; (3) The obtained wet POD membrane is then used to prepare a dry POD membrane; (4) Finally, the dry POD film is subjected to carbonization and graphitization treatment and cold pressing treatment to obtain the high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film.

6. The method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 5, characterized in that: In step (2), the method for preparing a wet POD film from the obtained POD stock solution is as follows: spreading the obtained POD stock solution on a substrate at 60 to 120°C, scraping the film using a wet film preparation device to obtain a wet film; then placing the substrate in a 30 to 60 wt% sulfuric acid aqueous solution for solvent replacement, and washing with water to obtain a water-containing wet POD film.

7. The method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 5, characterized in that: In step (3), the wet POD film is annealed at 60 to 120° C. for 10 to 60 minutes to obtain a dry POD film.

8. The method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 5, characterized in that: In step (4), the carbonization temperature is 1200-1500°C, and the graphitization temperature is 2600-3000°C.

9. The method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 5, characterized in that: In step (4), the carbonization treatment process is as follows: under the protection of inert gas, the dry POD film is gradually heated from room temperature to 400-500°C at a heating rate of 2-5°C / min, and kept warm for 0.5h-2h, then the heating rate is reduced to 0.5-2°C / min and the temperature is raised to 500-600°C, and the temperature is kept warm for 0.5h-2h; then the heating rate is increased to 2-5°C / min and the temperature is raised to 1200-1500°C and kept warm for 0.5h-5h.

10. The method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 5, characterized in that: In step (4), the graphitization treatment process is as follows: heating to 2200-2300°C at a heating rate of 3-10°C / min, keeping warm for 0.5h-2h, then reducing the heating rate to 0.5-2°C / min and heating to 2400-2500°C, keeping warm for 0.5h-2h; then increasing the heating rate to 3-10°C / min and heating to 2600-3000°C and keeping warm for 0.5h-2h, and then naturally cooling to room temperature.

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