A high thermal conductivity hexagonal boron nitride-based composite thin film and its preparation method

Abstract

This invention belongs to the field of high-performance thermal management materials technology, and discloses a high thermal conductivity hexagonal boron nitride-based composite film and its preparation method. The composite film consists of hexagonal boron nitride (h-BN) nanosheets and graphitized carbon layers formed by heat treatment of polyhydroxy aromatic compounds, wherein the graphitized carbon layers bridge the hexagonal boron nitride nanosheets. The preparation method includes: mixing h-BN nanosheets and polyhydroxy aromatic compounds in a solvent to form a mixed dispersion; using vacuum filtration technology to self-assemble the two into a highly oriented pre-film; drying; and then heat-treating under an inert atmosphere to graphitize the polyhydroxy aromatic compounds, thereby obtaining the composite film. The in-plane thermal conductivity of the film is greater than 200 W / (m·K), and it possesses both excellent flexibility and mechanical strength, making it particularly suitable for efficient heat dissipation in 5G communications, high-power chips, and flexible electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of high-performance thermal management materials technology, specifically relating to a high thermal conductivity hexagonal boron nitride-based composite thin film and its preparation method. Background Technology

[0002] With the rapid development of electronic devices towards miniaturization and high power density, the internal heat flux density of these devices has increased dramatically, severely impacting their performance, lifespan, and operational reliability. Against this backdrop, thermal management has become a core technological bottleneck restricting the development of the electronic information industry. Therefore, developing efficient, high-performance thermal management materials is crucial for ensuring the stable operation of electronic devices.

[0003] h-BN nanosheets, as a novel two-dimensional layered material, possess a graphene-like crystal structure and extremely high in-plane intrinsic thermal conductivity, theoretically reaching 200-2000 W / (m·K). They also exhibit excellent electrical insulation (band gap of approximately 5.9 eV), good chemical stability, and thermal stability, maintaining stable performance even under harsh environments such as high temperature and high pressure. Based on these properties, h-BN nanosheets are considered an ideal novel thermally conductive and insulating material with broad application prospects in the field of heat dissipation for electronic devices.

[0004] However, preparing macroscopic thermally conductive thin films that fully utilize the intrinsic high thermal conductivity of h-BN nanosheets still faces numerous technical challenges: First, achieving highly ordered in-plane orientation of h-BN nanosheets during macroscopic thermally conductive film preparation is difficult. Random stacking of nanosheets leads to significant interfacial scattering of phonons in the heat transfer path, resulting in a substantial increase in interfacial thermal resistance and severely weakening the thermal conductivity of the macroscopic thermally conductive film. Second, using high-filling-content h-BN nanosheets to improve thermal conductivity often results in insufficient internal structural density and interlayer aggregation, leading to problems such as... The increased brittleness and decreased flexibility of the film make it prone to cracking and breakage, making it unable to meet the heat dissipation requirements of flexible electronic devices or dynamic working components. Third, existing traditional preparation processes such as blade coating and casting have problems such as complex processes, high operational difficulty, and difficulty in accurately controlling the micro-arrangement of nanosheets, resulting in poor product performance consistency and restricting its large-scale production and practical application. Fourth, the dispersants or binders used in some modification methods have poor compatibility with h-BN nanosheets, which easily form defects at the interface, affecting not only thermal conductivity but also potentially reducing the mechanical strength and long-term stability of the film.

[0005] In existing technologies, related research has attempted to improve the performance of h-BN thermally conductive films through surface modification and optimized preparation processes, but many shortcomings remain. For example, some methods introduce organic binders to enhance interlayer bonding, but the low thermal conductivity of organic binders themselves significantly increases interfacial thermal resistance. Other studies have used high-temperature sintering to improve film density, but excessively high temperatures can damage the h-BN nanosheet structure and exacerbate film brittleness. Therefore, there is an urgent need in this field for a new material and process that can simultaneously resolve the contradiction between high thermal conductivity, low interfacial thermal resistance, and excellent flexibility and mechanical strength, in order to meet the increasingly stringent requirements of modern electronic devices for high-performance thermal management materials. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high thermal conductivity hexagonal boron nitride-based composite film and its preparation method. Through reasonable component design and optimized preparation process, the high thermal conductivity, excellent flexibility and good mechanical strength of the boron nitride-based composite film are synergistically unified, which can effectively solve the technical problems of traditional h-BN thermal conductive films and meet the heat dissipation requirements of modern electronic devices.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides a high thermal conductivity hexagonal boron nitride-based composite film, comprising hexagonal boron nitride (h-BN) nanosheets and a graphitized carbonaceous layer formed by heat treatment of a polyhydroxy aromatic compound, wherein the graphitized carbonaceous layer bridges the hexagonal boron nitride nanosheets.

[0009] Preferably, the in-plane thermal conductivity of the composite film is greater than 200 W / (m·K).

[0010] Preferably, the polyhydroxy aromatic compound is a polyhydroxy aromatic compound, and its specific structure includes, but is not limited to, 2,3,6,7,10,11-hexahydroxytriphenylene. , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , The polyhydroxy aromatic compound is graphitized after heat treatment, forming a graphene-like bridging structure between h-BN nanosheets. The graphitized polyhydroxy aromatic compound molecules have excellent thermal conductivity and structural stability, which can effectively fill the interlayer voids of hexagonal boron nitride nanosheets, reduce interfacial thermal resistance, and enhance the bonding force between the layers, thus synergistically improving the thermal conductivity and mechanical properties of the thermally conductive film.

[0011] Preferably, the thickness of the composite film is 30 μm to 90 μm. This thickness range ensures that the film has sufficient structural strength and heat conduction path, while also meeting the requirements of electronic devices for thinner and lighter heat dissipation materials.

[0012] Preferably, the hexagonal boron nitride (h-BN) nanosheets have an average size of 0.05 μm to 10 μm and a sheet thickness of 0.5 nm to 500 nm. h-BN nanosheets within this size range exhibit good dispersibility and orientation, enabling the formation of continuous heat transport pathways within the composite film while avoiding the stacking and agglomeration problems caused by excessively large nanosheet sizes.

[0013] A second aspect of the present invention provides a method for preparing the above-mentioned high thermal conductivity hexagonal boron nitride-based composite thin film, comprising the following steps:

[0014] S1: Hexagonal boron nitride nanosheets, polyhydroxy aromatic compounds and solvents are mixed to form a uniform mixed dispersion;

[0015] S2: The mixed dispersion is vacuum filtered, and the hexagonal boron nitride nanosheets self-assemble into a highly oriented pre-film under the action of polyhydroxy aromatic compounds.

[0016] S3: The preformed film is dried to obtain a dried preformed film;

[0017] S4: The dried pre-formed film is heat-treated under an inert atmosphere. During this process, the polyhydroxy aromatic compounds are graphitized to obtain a high thermal conductivity hexagonal boron nitride-based composite film.

[0018] Preferably, in step S1, the concentration of the hexagonal boron nitride nanosheets in the mixed dispersion is 0.05-0.5 mg / mL. Too low a concentration will result in low film-forming efficiency and difficulty in controlling the film thickness; too high a concentration will easily cause nanosheet aggregation, affecting the uniformity of dispersion.

[0019] Preferably, in step S1, the mass ratio of the hexagonal boron nitride nanosheets to the polyhydroxy aromatic compound is 10:1 to 1:1, more preferably, the mass ratio is 5:1, 3:1, 3:1.62, or 1:1. By adjusting the mass ratio, the thermal conductivity, flexibility, and mechanical strength of the thermally conductive film can be precisely controlled. When the mass ratio is too high, the content of the polyhydroxy aromatic compound is insufficient, making it difficult to effectively fill the gaps between the layers and enhance the bonding force; when the mass ratio is too low, excessive polyhydroxy aromatic compounds will form a thermal conductivity bottleneck in the film, reducing the overall thermal conductivity.

[0020] Preferably, in step S1, the solvent is water or isopropanol (IPA) with a purity of ≥99.5%, to avoid impurities from adversely affecting the dispersion effect and film performance.

[0021] Preferably, in step S1, the mixing process involves first stirring and mixing at 20-30 °C, followed by ultrasonic dispersion. The stirring rate is 300-500 rpm, the stirring time is 1-2 h, the ultrasonic dispersion time is 30-60 min, and the ultrasonic power is 100-300 W. Ultrasonic action breaks down the aggregates of hexagonal boron nitride nanosheets, ensuring uniform dispersion in the solvent. The synergistic effect of mechanical stirring and ultrasonic dispersion ensures that the hexagonal boron nitride nanosheets and the polyhydroxy aromatic compound are thoroughly and uniformly mixed in the solvent.

[0022] Preferably, in step S2, the vacuum degree of the vacuum filtration is -0.08 MPa to -0.09 MPa, and the temperature of the dispersion is maintained at 20-25 °C during the filtration process. Under vacuum pressure, hexagonal boron nitride nanosheets, guided by the π-π interactions and hydrogen bonds of polyhydroxy aromatic compound molecules, are highly oriented with their two-dimensional planes parallel to the membrane surface, self-assembling to form a dense pre-fabricated membrane, laying the structural foundation for obtaining high thermal conductivity in the subsequent process.

[0023] Preferably, in step S3, the drying process is carried out at a temperature of 50-70 °C for 30-60 min, and the drying method is either forced air drying or vacuum drying. Drying removes the solvent from the pre-formed film, preventing solvent residue from causing pores and defects inside the film, which would affect structural density and performance stability.

[0024] Preferably, in step S4, the inert atmosphere is nitrogen or argon with a purity ≥99.99%, to prevent oxidation of the hexagonal boron nitride nanosheets and polyhydroxy aromatic compounds during heat treatment. The heat treatment temperature is 800-1200 °C, the heating rate is 3-5 °C / min, the holding time is 3-8 h, and then the film is cooled to room temperature in the furnace at a cooling rate ≤10 °C / min. Suitable heat treatment temperature and heating / cooling rates ensure sufficient graphitization of the polyhydroxy aromatic compounds while avoiding internal stress and cracking of the film due to excessively rapid temperature changes.

[0025] Preferably, after step S4, a post-processing step is included: cleaning the heat-treated high thermal conductivity hexagonal boron nitride-based composite film with anhydrous ethanol or deionized water to remove residual impurities on the surface, and then drying it at 40-60 °C for 20-30 min to obtain a final product with a smooth surface and stable performance.

[0026] The composite film prepared by this invention achieves a synergistic improvement in high thermal conductivity, excellent flexibility and good mechanical strength, avoiding the problem of other performance degradation caused by optimizing a single performance. The product has excellent overall performance and can meet the heat dissipation requirements of electronic devices in different scenarios. The fundamental reason lies in the introduction of polyhydroxy aromatic compounds as dispersants and assembly guides, combined with vacuum filtration and heat treatment processes. Vacuum filtration allows hexagonal boron nitride nanosheets to align highly in a direction parallel to the film surface under the guidance of π-π interactions and hydrogen bonding of polyhydroxy aromatic compound molecules, self-assembling to form a dense pre-film. In subsequent heat treatment, the polyhydroxy aromatic compounds undergo in-situ graphitization, forming a graphitized carbon layer between the highly oriented hexagonal boron nitride nanosheets. The graphitized carbon layer acts as a "nano-adhesive" and "phonon bridge," greatly enhancing the mechanical interaction between the hexagonal boron nitride nanosheets, transforming the film from "brittle" to "tough," significantly improving its flexibility and mechanical strength. On the other hand, the graphitized carbon layer has excellent thermal conductivity, filling the phonon transport gaps between the layers and significantly reducing interfacial thermal resistance, thus achieving a simultaneous leap in thermal conductivity and mechanical properties.

[0027] Advantages and beneficial effects of the present invention:

[0028] (1) Ultra-high in-plane thermal conductivity: The composite film prepared by the present invention has a highly oriented hexagonal boron nitride nanosheet layer and a graphitized carbon layer, and its in-plane thermal conductivity is greater than 200 W / (m·K), which is far superior to the traditional hexagonal boron nitride thermal conductive film.

[0029] (2) Excellent flexibility and mechanical toughness: The composite film prepared by this invention has excellent flexibility and mechanical strength while achieving high thermal conductivity, successfully solving the industry pain points of traditional high-fill thermal conductive films being brittle and having poor flexibility.

[0030] (3) The process is simple and controllable, and easy to scale up production: The preparation method is simple and does not require complex and expensive equipment. Fine structure control at the nanoscale can be achieved through self-assembly and vacuum filtration. The process parameters are easy to control, the product performance is consistent, and it is suitable for large-scale industrial production.

[0031] (4) Strong stability and wide range of applications: The thermally conductive film prepared by this invention has good chemical and thermal stability. It can maintain excellent performance in harsh environments such as high temperature and high humidity, and also has electrical insulation properties. It can be widely used for efficient heat dissipation of various electronic devices such as 5G communication, artificial intelligence chips, high-power semiconductor devices, and flexible electronic devices. It can also be used as a heat dissipation pad, packaging material, etc. in various electronic devices, effectively solving the thermal management problems brought about by the miniaturization and high power density development of electronic devices. It has broad application prospects. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the crystal structure of hexagonal boron nitride.

[0033] Figure 2 This is a schematic diagram of the three-dimensional structure of HHTBP.

[0034] Figure 3 This is a schematic diagram of the self-assembly of HHTBP on the surface of hexagonal boron nitride nanosheets through π-π and hydrogen bonding interactions.

[0035] Figure 4 Raman spectra of h-BN nanosheets, HHTBP before calcination, HHTBP after calcination, and composite thin film after calcination. Detailed Implementation

[0036] The present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0037] The reagents used in the following examples and comparative examples, and their sources, are as follows:

[0038] Hexagonal boron nitride nanosheets (h-BN nanosheets): average size 0.05-4 μm, layer thickness 1-10 BN nanosheets, purchased from Muco Nanotechnology Co., Ltd., product number: MK503.

[0039] 2,3,6,7,10,11-Hexahydroxytriphenylene (HHTBP): Purity >98%, purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd., product number: BD65207-250mg.

[0040] Isopropanol (IPA): Purity ≥99.5%, purchased from Pusenrit (Tianjin) Biomedical Technology Co., Ltd., product number: I811927-2.5L.

[0041] Example 1

[0042] A method for preparing a high thermal conductivity hexagonal boron nitride-based composite thin film includes the following steps:

[0043] S1: Preparation of dispersion: Measure 6 mL of a 0.5 mg / mL h-BN nanosheet dispersion in IPA. Then weigh 1.62 mg of HHTBP and dissolve it in 54 mL of IPA to obtain an HHTBP solution. Mix the dispersion and HHTBP solution, stir at 400 rpm for 1 h at 25 °C, and then ultrasonically disperse at 200 W for 45 min to form a homogeneous mixed dispersion. A schematic diagram of the crystal structure of hexagonal boron nitride is shown below. Figure 1 As shown, the chemical structural formula of HHTBP is Its three-dimensional structural diagram is as follows Figure 2 As shown;

[0044] S2: Vacuum Filtration Self-Assembly: The above mixed dispersion was poured into a vacuum filtration device and filtered under a vacuum of -0.085 MPa, maintaining the dispersion temperature at 20 °C. This allowed the h-BN nanosheets to self-assemble under the control of HHTBP, forming a dense pre-film. A schematic diagram of the self-assembly of HHTBP on the surface of hexagonal boron nitride nanosheets through π-π and hydrogen bonding interactions is shown below. Figure 3 As shown;

[0045] S3: Drying: Place the obtained pre-formed membrane together with the filter membrane into a vacuum drying oven and dry at 60 ℃ for 30 min to remove the solvent and obtain the dried pre-formed membrane;

[0046] S4: Heat Treatment: The dried pre-formed membrane was carefully peeled off from the filter membrane, placed in a corundum mold, and then placed in a tube furnace. Under nitrogen protection (nitrogen purity ≥ 99.99%), the temperature was increased to 1000 ℃ at a rate of 5 ℃ / min and held for 3 h for heat treatment. Afterward, it was cooled to room temperature in the furnace. During this process, HHTBP was completely graphitized, resulting in a high thermal conductivity hexagonal boron nitride-based composite film.

[0047] S5: Clean the high thermal conductivity hexagonal boron nitride-based composite film with anhydrous ethanol, and then dry it at 50 °C for 25 min.

[0048] Example 2

[0049] A method for preparing a high thermal conductivity hexagonal boron nitride-based composite thin film includes the following steps:

[0050] S1: Preparation of dispersion: Measure 6 mL of a 0.5 mg / mL h-BN nanosheet dispersion in IPA. Then weigh 1.62 mg of HHTBP (2,3,6,7,10,11-hexahedroxytriphenylene) and dissolve it in 54 mL of IPA to obtain an HHTBP solution. Mix the dispersion and HHTBP solution, stir at 400 rpm for 1 h at 25 ℃, and then ultrasonically disperse at 200 W for 45 min to form a homogeneous mixed dispersion. A schematic diagram of the crystal structure of hexagonal boron nitride is shown below. Figure 1 As shown, the chemical structural formula of HHTBP is Its three-dimensional structural diagram is as follows Figure 2 As shown;

[0051] S2: Vacuum Filtration Self-Assembly: The above mixed dispersion was poured into a vacuum filtration device and filtered under a vacuum of -0.085 MPa, maintaining the dispersion temperature at 20 °C. This allowed the h-BN nanosheets to self-assemble under the control of HHTBP, forming a dense pre-film. A schematic diagram of the self-assembly of HHTBP on the surface of hexagonal boron nitride nanosheets through π-π and hydrogen bonding interactions is shown below. Figure 3 As shown;

[0052] S3: Drying: Place the obtained pre-formed membrane together with the filter membrane into a vacuum drying oven and dry at 60 ℃ for 30 min to remove the solvent and obtain the dried pre-formed membrane;

[0053] S4: Heat Treatment: The dried pre-formed membrane was carefully peeled off from the filter membrane, placed in a corundum mold, and then placed in a tube furnace. Under nitrogen protection (nitrogen purity ≥ 99.99%), the temperature was increased to 1100 ℃ at a rate of 5 ℃ / min and held for 6 h for heat treatment. Afterward, the furnace was cooled to room temperature. During this process, HHTBP was completely graphitized, resulting in a high thermal conductivity hexagonal boron nitride-based composite film.

[0054] S5: Clean the high thermal conductivity hexagonal boron nitride-based composite film with anhydrous ethanol, and then dry it at 50 °C for 25 min.

[0055] Comparative Example 1

[0056] A method for preparing a pure h-BN membrane, comprising the following steps:

[0057] S1: Preparation of dispersion: Measure 6 mL of 0.5 mg / mL h-BN nanosheet dispersion in IPA and drop it into a flask containing 54 mL IPA. Mix them and stir at 400 rpm for 1 h at 25 °C. Then, ultrasonically disperse at 200 W for 45 min to form a uniform mixed dispersion.

[0058] S2: Vacuum filtration self-assembly: Pour the above mixed dispersion into a vacuum filtration device and perform filtration under a vacuum of -0.085 MPa, keeping the dispersion temperature at 20 ℃ to form a pre-formed membrane.

[0059] S3: Drying: Place the obtained pre-made membrane together with the filter membrane into a vacuum drying oven and dry at 60 °C for 30 min to remove the solvent and obtain a pure h-BN membrane.

[0060] Comparative Example 2

[0061] A method for preparing a composite membrane, comprising the following steps:

[0062] S1: Preparation of dispersion: Measure 6 mL of h-BN nanosheets with a concentration of 0.5 mg / mL dispersed in IPA, then weigh 1.62 mg of HHTBP molecules and dissolve them in 54 mL of IPA to obtain HHTBP solution. Mix the dispersion and HHTBP solution and stir at 400 rpm for 1 h at 25 ℃. Then, ultrasonically disperse at 200 W power for 45 min to form a uniform mixed dispersion.

[0063] S2: Vacuum filtration self-assembly: The above mixed dispersion is poured into a vacuum filtration device and filtered under a vacuum of -0.085 MPa. The dispersion temperature is kept at 20 °C. Under the control of HHTBP, h-BN nanosheets self-assemble to form a dense pre-film.

[0064] S3: Drying: Place the obtained pre-made membrane together with the filter membrane into a vacuum drying oven and dry at 60 °C for 30 min to remove the solvent and obtain a dried composite membrane.

[0065] Comparative Example 3

[0066] A method for preparing an h-BN composite membrane, comprising the following steps:

[0067] S1: Preparation of dispersion: Measure 6 mL of a 0.5 mg / mL h-BN nanosheet dispersion in IPA. Then weigh 1.62 mg HHTBP and dissolve it in 54 mL of IPA to obtain an HHTBP solution. Mix the dispersion and HHTBP solution, stir at 400 rpm for 1 h at 25 ℃, and then sonicate at 200 W for 45 min to form a homogeneous mixed dispersion.

[0068] S2: Casting and Drying: Pour the above mixed dispersion into the casting machine tank. Under a constant temperature of 25 ℃, control the movement of the casting doctor blade at a speed of 5 mm / s to spread the dispersion evenly on a clean glass substrate. Then place the spread substrate in a ventilated oven and dry it at a constant temperature of 60 ℃ for 8 hours. After the solvent has completely evaporated, peel off the continuous film formed on the substrate surface to complete the casting process.

[0069] Comparative Example 4

[0070] A method for preparing an h-BN composite membrane with added organic binder, comprising the following steps:

[0071] S1: Preparation of dispersion: Measure 6 mL of h-BN nanosheets with a concentration of 0.5 mg / mL in IPA (isopropanol); weigh 1.62 mg of polyethylene glycol (PEG-6000, organic binder), dissolve it in 54 mL of IPA to obtain an organic binder solution; mix the above h-BN nanosheet dispersion with the organic binder solution, stir at 400 rpm for 1 h at 25 ℃, and then ultrasonically disperse at 200 W power for 45 min to form a uniform mixed dispersion.

[0072] S2: Vacuum filtration self-assembly: The above mixed dispersion is poured into a vacuum filtration device and filtered under a vacuum of -0.085 MPa. The temperature of the dispersion is kept at 20 °C, so that the h-BN nanosheets self-assemble to form a preform under the adhesion of the organic binder.

[0073] S3: Drying: Place the obtained pre-formed membrane together with the filter membrane into a vacuum drying oven and dry at 60 °C for 30 min to remove the solvent and obtain the dried pre-formed membrane.

[0074] S4: Heat treatment: Carefully peel the dried pre-made membrane from the filter membrane, place it in a corundum mold, and put it into a tube furnace; under nitrogen protection (nitrogen purity ≥99.99%), heat it to 1000 ℃ at a heating rate of 5 ℃ / min, hold it at that temperature for 6 h for heat treatment, and then cool it to room temperature with the furnace; during this process, the organic binder undergoes thermal decomposition to obtain the h-BN composite membrane.

[0075] S5: The above-mentioned h-BN composite membrane is ultrasonically cleaned with anhydrous ethanol for 5 min, and then dried at 50 ℃ for 25 min to form the final h-BN / adhesive residue composite membrane (a small amount of organic adhesive remains after thermal decomposition).

[0076] Performance Testing and Analysis

[0077] The in-plane thermal conductivity, bending radius, tensile strength and elongation at break of the products prepared in the examples and comparative examples were tested respectively, and the test results are shown in Table 1.

[0078] In-plane thermal conductivity was measured using a thermal conductivity meter from Netzsch Instruments GmbH, Germany.

[0079] The bending radius was tested using the Mandrel Bend Test.

[0080] Specific procedures: Prepare a series of cylindrical mandrels with known diameters. Attach or bend the film sample onto or around the surface of the mandrel. Start with the largest diameter mandrel and gradually change mandrels until cracks or fractures appear on the film surface. The smallest mandrel radius that will not cause damage is the minimum bending radius of the film.

[0081] Tensile strength and elongation at break were tested using a universal testing machine.

[0082] Specific procedures: Cut the film sample into a standard dumbbell shape and clamp it in the upper and lower fixtures of the testing machine. Stretch at a constant rate and simultaneously record the stress-strain curve. The tensile strength is the maximum stress value on the curve. The elongation at break is calculated from the displacement at fracture and the original gauge length.

[0083] Table 1. Test results of products prepared in the examples and comparative examples.

[0084]

[0085] As can be seen from the data in Table 1, the hexagonal boron nitride-based composite film prepared in the embodiments of the present invention has an in-plane thermal conductivity ≥200 W / (m·K), a bending radius ≤3 mm, an elongation at break ≥8%, a tensile strength ≥25 MPa, and a tensile modulus ≥6 GPa.

[0086] Compared with the h-BN thermally conductive film prepared in Comparative Example 1, the composite film prepared in Example 1 has an in-plane thermal conductivity that is increased by more than 200%, a bending radius that is reduced by more than 200%, and an elongation at break and tensile strength that are both increased by more than 50%. Compared with Comparative Example 4, the composite film of the present invention has an in-plane thermal conductivity that is increased by more than 300%, a significantly better thermal stability, and superior mechanical properties.

[0087] The thermal conductivity and mechanical properties of the pure h-BN film obtained in Comparative Example 1 were significantly inferior to those of the examples. Specifically, the in-plane thermal conductivity was ≤60 W / (m·K); the elongation at break was ≤5%, and the film was brittle and prone to breakage, failing to meet the requirements of practical thermal management applications for material mechanical stability and thermal conductivity. The results indicate that without HHTBP, the h-BN nanosheets lack effective interlayer connections, failing to construct interlayer thermal bridges and mechanical reinforcement networks, resulting in limited thermal conductivity and extremely poor mechanical properties.

[0088] The composite film obtained in Comparative Example 2 exhibits inferior thermal conductivity and mechanical properties compared to the examples. Its in-plane thermal conductivity is 60-70 W / (m·K); the elongation at break is 6%-8%. The results indicate that, without high-temperature graphitization, HHTBP containing HHTBP but omitting the heat treatment step cannot be transformed into a "graphene-like bridging structure," and can only play a limited role in dispersion and assembly. It cannot form efficient thermal bridges and a stable mechanical reinforcement network between h-BN nanosheets, thus significantly limiting its enhancement effect on film performance.

[0089] Comparative Example 3 used conventional casting to replace vacuum filtration self-assembly, and the resulting h-BN composite film had an in-plane orientation degree of 0.3, which was inferior to that of the example. The results indicate that vacuum filtration is crucial for promoting the preferred in-plane orientation of h-BN nanosheets. Without this process, h-BN nanosheets tend to stack randomly and disordered, failing to form continuous in-plane orientation pathways. This not only leads to a significant decrease in in-plane orientation degree but also hinders the efficient transport of phonons in the in-plane direction and the uniform dispersion of stress. Therefore, its effect on improving the in-plane core performance of the composite film is significantly limited.

[0090] Raman spectroscopy was performed on the h-BN nanosheets, HHTBP before calcination, HHTBP after calcination, and the composite film after calcination in Example 1. Figure 4 As shown, the Raman spectrum of the original HHTBP is at ~1284 cm⁻¹. -1 ~1463 cm -1 ~1510 cm -1 ~1559 cm -1 and ~1614 cm -1 A series of characteristic peaks were observed, attributed to CO stretching vibration, CH in-plane bending vibration, and C=C stretching vibration of the benzene ring skeleton, respectively. After calcination at 1000 °C, these organic characteristic peaks completely disappeared, replaced by peaks at ~1350 cm⁻¹. -1 and ~1580 cm -1 Two broad peaks appeared at the point, namely the characteristic D peak and G peak of carbon materials. The appearance of the D peak indicates that there are a large number of structural defects or grain boundaries in the generated carbon material, which originates from the disordered stacking during the precursor pyrolysis process. The presence of the G peak confirms that sp 2The formation of hybrid graphite domains. In contrast, the Raman spectrum of h-BN nanosheets is only at ~1367 cm⁻¹. -1 A sharp E2g characteristic peak is observed, which is distinctly different from the signal of carbon materials. The presence of characteristic peaks from both h-BN and HHTBP after calcination of the composite film indicates that the graphitized carbon layer of HHTBP bridges the hexagonal boron nitride nanosheets after calcination at 1000 °C.

[0091] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A high thermal conductivity hexagonal boron nitride-based composite thin film, characterized in that, The composite film comprises hexagonal boron nitride nanosheets and a graphitized carbonaceous layer formed by heat treatment of a polyhydroxy aromatic compound. The graphitized carbonaceous layer bridges the hexagonal boron nitride nanosheets. The in-plane thermal conductivity of the composite film is greater than 200 W / (m·K). The method for preparing the composite film includes the following steps: S1: Hexagonal boron nitride nanosheets, polyhydroxy aromatic compounds and solvents are mixed to form a uniform mixed dispersion; S2: The mixed dispersion is vacuum filtered, and the hexagonal boron nitride nanosheets self-assemble into a highly oriented pre-film under the action of polyhydroxy aromatic compounds. S3: The preformed film is dried to obtain a dried preformed film; S4: The dried pre-formed film is heat-treated in an inert atmosphere at a temperature of 800-1200 ℃, a heating rate of 3-5 ℃ / min, and a holding time of 3-8 h. Then, it is cooled to room temperature in the furnace. During this process, the polyhydroxy aromatic compound is graphitized to obtain a high thermal conductivity hexagonal boron nitride-based composite film. The inert atmosphere is nitrogen or argon with a gas purity ≥99.99%.

2. The high thermal conductivity hexagonal boron nitride-based composite thin film according to claim 1, characterized in that, The hexagonal boron nitride nanosheets have an average size of 0.05 μm to 10 μm and a sheet thickness of 0.5 nm to 500 nm.

3. The high thermal conductivity hexagonal boron nitride-based composite thin film according to claim 1, characterized in that, The thickness of the membrane is 30 μm to 90 μm.

4. The high thermal conductivity hexagonal boron nitride-based composite thin film according to claim 1, characterized in that, The polyhydroxy aromatic compound is selected from one or more of the following compounds: 2,3,6,7,10,11-hexahydroxytriphenylene, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , .

5. A method for preparing a high thermal conductivity hexagonal boron nitride-based composite thin film as described in any one of claims 1-4, characterized in that, Includes the following steps: S1: Hexagonal boron nitride nanosheets, polyhydroxy aromatic compounds and solvents are mixed to form a uniform mixed dispersion; S2: The mixed dispersion is vacuum filtered, and the hexagonal boron nitride nanosheets self-assemble into a highly oriented pre-film under the action of polyhydroxy aromatic compounds. S3: The preformed film is dried to obtain a dried preformed film; S4: The dried pre-formed film is heat-treated in an inert atmosphere at a temperature of 800-1200 ℃, a heating rate of 3-5 ℃ / min, and a holding time of 3-8 h. Then, it is cooled to room temperature in the furnace. During this process, the polyhydroxy aromatic compound is graphitized to obtain a high thermal conductivity hexagonal boron nitride-based composite film. The inert atmosphere is nitrogen or argon with a gas purity ≥99.99%.

6. The preparation method according to claim 5, characterized in that, In step S1, the concentration of the hexagonal boron nitride nanosheets in the mixed dispersion is 0.05-0.5 mg / mL; the mass ratio of the hexagonal boron nitride nanosheets to the polyhydroxy aromatic compound is 10:1 to 1:1; the solvent is water or isopropanol with a solvent purity ≥99.5%; the mixing is carried out by stirring at 20-30 °C and then by ultrasonic dispersion.

7. The preparation method according to claim 5, characterized in that, In step S2, the vacuum degree of the vacuum filtration is -0.08 MPa to -0.09 MPa, and the temperature of the mixed dispersion is maintained at 20-25 ℃ during the filtration process; in step S3, the drying temperature is 50-70 ℃, the time is 30-60 min, and the drying method is forced air drying or vacuum drying.

8. The preparation method according to claim 5, characterized in that, Step S4 is followed by a post-processing step: the high thermal conductivity hexagonal boron nitride-based composite film after heat treatment is sequentially cleaned and dried.

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