An enhanced natural graphite composite film and a method for preparing the same

Abstract

This invention discloses an enhanced natural graphite composite film and its preparation method. The preparation method includes the following steps: activating the surface of a natural graphite film through plasma treatment to obtain a pretreated natural graphite film; preparing a nano-silicon carbide dispersion, uniformly spraying the nano-silicon carbide dispersion onto the surface of the pretreated natural graphite film, and drying it under low-temperature heat treatment to obtain a natural graphite film with an interface reinforcement layer; preparing a graphene oxide dispersion, coating the graphene oxide dispersion onto the surface of the natural graphite film with the interface reinforcement layer, and performing low-temperature reduction treatment to obtain a graphene-natural graphite composite film; placing the graphene-natural graphite composite film in a pressing mechanism for hot pressing treatment to obtain the enhanced natural graphite composite film. This invention, through rational design of the preparation process and selection of materials, achieves improved performance of the enhanced natural graphite composite film, exhibiting excellent thermal conductivity, chemical stability, mechanical strength, and heat resistance.

Description

Technical Field

[0001] This invention relates to the field of graphite film material technology, specifically to an enhanced natural graphite composite film and its preparation method. Background Technology

[0002] Natural graphite, as an excellent thermal conductive material, possesses characteristics such as high thermal conductivity, light weight, and low cost, and has broad application prospects in the field of heat dissipation. However, with the rapid development of modern electronic technology, the performance requirements for materials are becoming increasingly demanding. Traditional natural graphite films are no longer able to meet the needs of high-end applications in some aspects, such as higher thermal conductivity, better mechanical strength, and more stable chemical properties.

[0003] Graphene, as a novel two-dimensional material, possesses extremely high thermal conductivity (theoretically up to 5000 W / m·K) and excellent mechanical strength. Combining graphene with natural graphite films not only compensates for the shortcomings of natural graphite films in terms of grain boundary defects and structural uniformity but also enhances their overall mechanical properties. Especially given the increasing demands for thin, lightweight, and highly efficient thermal conductive materials in electronic devices, this composite technology holds great promise for future applications.

[0004] Chinese patent CN 111526695A discloses a double-sided graphene heat dissipation film and its preparation method. The steps are as follows: Graphene oxide is soaked in water and ultrasonically stirred to form a graphene oxide solution; the back side of a natural graphite roll is adhered to a PET double-sided silicone film to form a natural graphite adhesive roll; the graphene oxide solution is coated onto the front side of the natural graphite roll and continuously dried and reduced to form an upper graphene layer; the PET double-sided silicone film is peeled off from the resulting single-sided graphene heat dissipation film roll; the graphene oxide solution is coated onto the back side of the natural graphite layer and continuously dried and reduced to form a lower graphene layer, thereby obtaining a double-sided graphene heat dissipation film roll. This invention uses a graphene oxide solution coating and drying reduction method, which has a simple process and is easy to operate; however, the graphene layer is formed by graphene oxide coating and reduction, and its interfacial bonding force with natural graphite may be weak, especially under high temperature or repeated thermal cycling conditions, which may lead to delamination or performance degradation. Summary of the Invention

[0005] To address the problems existing in the background technology, this invention provides an enhanced natural graphite-graphene composite film material and its preparation method that retains the original advantages of natural graphite films while achieving significant performance improvements through the addition of a graphene layer. This composite material needs to possess higher thermal conductivity, enhanced mechanical strength, and good chemical stability, while maintaining low cost and ease of processing.

[0006] This invention is implemented through the following technical solutions:

[0007] This invention provides a method for preparing an enhanced natural graphite composite film, comprising the following steps:

[0008] S1. The surface of the natural graphite film is activated by plasma treatment to obtain a pretreated natural graphite film;

[0009] S2. Prepare a nano-silicon carbide dispersion, spray the nano-silicon carbide dispersion evenly onto the surface of the pretreated natural graphite film, and dry it under low temperature heat treatment to obtain a natural graphite film with an interface reinforcement layer.

[0010] S3. Prepare a graphene oxide dispersion, coat the graphene oxide dispersion on the surface of a natural graphite film with an interface reinforcement layer, and perform low-temperature reduction treatment to obtain a graphene-natural graphite composite film.

[0011] S4. Place the graphene-natural graphite composite film in a pressing mechanism and perform hot pressing to obtain the reinforced natural graphite composite film.

[0012] Furthermore, in step S1, the plasma treatment is performed using argon gas at a low pressure of 50-100 Pa and a power of 100-200 W for 15-30 minutes.

[0013] Plasma treatment makes the surface of the natural graphite film more active, which helps the bonding between the graphene layer and the natural graphite film and improves the overall stability of the composite film. In addition, the natural graphite film after plasma treatment has better mechanical strength and wear resistance, which can increase the long-term service life of the composite film.

[0014] Furthermore, in step S2, the concentration of the nano-silicon carbide dispersion is 0.5-2 mg / mL, the solvent is ethanol, and the coating method is spin coating or spray coating.

[0015] Nano-silicon carbide possesses excellent thermal conductivity and chemical stability, which can effectively regulate the interface between natural graphite film and graphene layer, forming a tighter interface structure, improving the bonding force between natural graphite film and graphene layer, optimizing the thermal conductivity between the two, and reducing the impact of thermal expansion.

[0016] Furthermore, the temperature for low-temperature heat treatment drying in step S2 is 40-60℃.

[0017] Furthermore, in step S3, the concentration of the graphene oxide dispersion is 0.5-2 mg / mL, and the solvent is deionized water.

[0018] The reduction process transforms graphene oxide into graphene, restoring its excellent thermal conductivity and further enhancing the thermal conductivity of the composite film. The reduced graphene oxide forms a stronger chemical bond with the nano-silicon carbide interface, improving the adhesion between the graphene layer and the natural graphite film, and increasing the mechanical strength and stability of the composite film.

[0019] Furthermore, the graphene oxide dispersion in step S3 also includes vitamin C, silane coupling agent KH550, and polyvinyl alcohol; the concentration of vitamin C is 0.01-0.03 mg / mL, the concentration of silane coupling agent KH550 is 0.01-0.03 mg / mL, and the concentration of polyvinyl alcohol is 0.02-0.05 mg / mL.

[0020] During the reduction process, vitamin C acts as a reducing agent, effectively reducing oxygen functional groups in graphene oxide while maintaining the high-quality structure of graphene and preventing over-reduction or degradation. The synergistic effect of silane coupling agent KH550 and polyvinyl alcohol further modulates the interfacial chemical properties, establishing a tighter interfacial bonding network at the molecular scale.

[0021] Furthermore, in step S3, the low-temperature reduction treatment is carried out at a temperature of 120-135℃ for 1-2 hours.

[0022] Furthermore, in step S4, the hot pressing temperature is 150-200℃, the pressure is 10-20MPa, and the processing time is 15-30min.

[0023] Furthermore, the pressing mechanism includes: a pressing frame, which is a frame with openings at the front and back; a support plate is fixedly connected to the inner wall of the pressing frame; a telescopic cylinder II is fixedly installed at the top of the inner wall of the pressing frame; a pressing groove is opened at the bottom of the inner wall of the pressing frame; a through hole is opened at the center of the support plate; the movable end of the telescopic cylinder II passes through the through hole and is fixedly fitted with a pressure plate; a heating head is installed at the bottom of the pressure plate; the fixed end of the telescopic cylinder I is fixedly connected to the bottom of the support plate; the movable end of the telescopic cylinder I is fixedly connected to the support body; a return spring is provided between the support body and the bottom of the inner wall of the pressing frame; a pressing insulation cavity is provided in the middle of the support body; several sets of drive motors are installed on the vertical sections on both sides of the support body; a threaded rod is fixedly connected to the output end of each set of drive motors; the end of the threaded rod away from the drive motor is rotatably connected to the outer wall of the pressing insulation cavity; an anti-detachment component is movably sleeved on the outer wall of the threaded rod; and the anti-detachment component and the threaded rod are connected by threads; the top of the anti-detachment component extends towards the pressing insulation cavity to form an inclined pressing end.

[0024] Hot pressing causes the molecules in the composite film to rearrange and recombine through high temperature and high pressure, further optimizing the film's density, mechanical strength, and thermal conductivity. Hot pressing not only promotes the adhesion of the graphene layer but also improves the overall stability of the composite film.

[0025] A second aspect of the present invention provides an enhanced natural graphite composite film, prepared by the above method, comprising a natural graphite layer and a graphene layer; wherein the thickness of the natural graphite layer is 0.025-0.25 mm, and the thickness of the graphene layer is 0.01-0.025 mm.

[0026] The beneficial effects of this invention are:

[0027] 1. This invention combines natural graphite film and graphene, and then forms an enhanced natural graphite composite film with excellent performance through hot pressing. Graphene, due to its unique two-dimensional structure and atomic-level thickness, possesses very high thermal conductivity, which can significantly improve the vertical thermal conductivity of the composite film. The addition of graphene greatly enhances the thermal conductivity of the composite film, enabling more effective heat transfer under high heat loads and preventing localized overheating. The addition of the graphene layer allows the composite film to better disperse and transfer stress under stress, avoiding localized stress concentration and improving the strength and toughness of the composite film. Furthermore, graphene itself has strong antioxidant capabilities, resisting common chemical corrosion and maintaining its excellent thermal conductivity and structural stability. The graphene layer forms an effective barrier in the composite film, preventing the film material from degrading due to environmental factors during long-term use.

[0028] 2. Nano-silicon carbide itself has high thermal conductivity, and as an interface reinforcement layer, it alleviates the difference in thermal expansion between graphene and natural graphite, thereby improving the thermal conductivity efficiency of the composite film. The micron-sized size and good dispersibility of nano-silicon carbide enable it to provide a more uniform heat conduction path, which helps to improve the overall thermal conductivity performance of the composite film.

[0029] 3. After the graphene layer and the natural graphite film are tightly bonded together through a hot-pressing process, a continuous and efficient heat conduction channel is formed, further improving the heat conduction efficiency of the composite film. The thermal conductivity of the composite film is significantly improved, meeting the requirements of high thermal conductivity applications, such as heat dissipation materials for electronic devices and thermal management films.

[0030] 4. During the low-temperature reduction stage, vitamin C reduces the oxidized functional groups of graphene oxide to graphene through its reducing hydrogen atoms, maintaining the structural integrity of the graphene layer. The amino groups in the silane coupling agent KH550 promote the chemical bonding between graphene and nano-silicon carbide, thereby improving the interfacial bonding force. Polyvinyl alcohol (PVA), as a binder, further enhances the stability of the graphene layer and the toughness of the composite film. The hydrophilicity and film-forming properties of PVA help improve the uniformity of the graphene film, while reducing potential cracks or inhomogeneities in the graphene layer during reduction. The combined use of silane coupling agent KH550 and PVA not only improves the interfacial bonding between the graphene layer and silicon carbide but also enhances the structural stability and thermal conductivity of the graphene layer. Silane coupling agent KH550 provides the chemical bonding pathway, while PVA enhances the uniformity of the graphene film through adhesion and film-forming effects.

[0031] 5. The process steps of this invention are relatively simple and efficient. The choice of a low-temperature reduction process not only avoids graphene damage at high temperatures but also reduces energy consumption and improves production efficiency. The combination of plasma treatment and hot pressing not only enhances the performance of the composite film but also reduces additional processing steps to a certain extent, thereby increasing production efficiency and lowering production costs. These steps can be easily implemented in industrial production. Attached Figure Description

[0032] The accompanying drawings are provided to further explain the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0033] Figure 1 This is a schematic cross-sectional view of the pressing mechanism in this invention;

[0034] Figure 2 This is a three-dimensional schematic diagram of a portion of the pressing mechanism of the present invention. Figure 1 ;

[0035] Figure 3 This is a three-dimensional schematic diagram of a portion of the pressing mechanism of the present invention. Figure 2 ;

[0036] Figure 4 This is a three-dimensional schematic diagram of a portion of the pressing mechanism of the present invention. Figure 3 ;

[0037] Figure 5 This is a schematic diagram of the natural graphite composite film structure of the present invention;

[0038] In the diagram: 1. Pressing frame; 2. Support plate; 3. Telescopic cylinder one; 4. Drive motor; 5. Support body; 6. Return spring; 7. Pressing groove; 8. Telescopic cylinder two; 9. Pressure plate; 10. Heating head; 11. Chamfer; 12. Through hole; 13. Lower pressure insulation cavity; 14. Threaded rod; 15. Anti-detachment component; 16. Slanted pressure end; 17. Natural graphite layer; 18. Graphene layer. Detailed Implementation

[0039] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0040] In the embodiments and comparative examples of the present invention, the thickness of the natural graphite layer 17 in the prepared composite film is 0.25 mm, and the thickness of the graphene layer 18 is 0.025 mm.

[0041] Example 1: A method for preparing an enhanced natural graphite composite film, comprising the following steps:

[0042] S1. The surface of the natural graphite film is activated by plasma treatment. High-purity argon gas is used to treat the film for 30 minutes under low pressure of 50 Pa and power of 200 W to obtain the pretreated natural graphite film.

[0043] S2. Prepare a nano-silicon carbide dispersion with a concentration of 1 mg / mL (ethanol as solvent), uniformly spray the nano-silicon carbide dispersion onto the surface of the pretreated natural graphite film, and dry it at a low temperature of 50℃ to obtain a natural graphite film with an interface reinforcement layer.

[0044] S3. Prepare a graphene oxide dispersion using deionized water as the solvent. The concentration of the graphene oxide dispersion is 2 mg / mL, the concentration of vitamin C is 0.02 mg / mL, the concentration of silane coupling agent KH550 is 0.02 mg / mL, and the concentration of polyvinyl alcohol is 0.04 mg / mL. Spin-coating the graphene oxide dispersion onto the surface of a natural graphite film with an interface reinforcement layer is used. The film is then subjected to a low-temperature reduction treatment at 130℃ for 1.5 h to obtain a graphene-natural graphite composite film.

[0045] S4. Place the graphene-natural graphite composite film in a pressing mechanism and perform hot pressing treatment. The hot pressing treatment temperature is 180℃, the pressure is 15MPa, and the treatment time is 20min to obtain the reinforced natural graphite composite film.

[0046] Example 2

[0047] In this embodiment, step S3 involves preparing a graphene oxide dispersion using deionized water as the solvent. The concentration of the graphene oxide dispersion is 1.5 mg / mL, the concentration of vitamin C is 0.02 mg / mL, the concentration of silane coupling agent KH550 is 0.02 mg / mL, and the concentration of polyvinyl alcohol is 0.03 mg / mL. The remaining steps are the same as in Example 1.

[0048] Comparative Example 1

[0049] In this comparative example, the step of uniformly spraying the nano-silicon carbide dispersion onto the surface of the pretreated natural graphite film is not included. Instead, the graphite oxide dispersion is directly coated onto the pretreated natural graphite film. All other steps are the same as in Example 1.

[0050] Comparative Example 2

[0051] In this comparative example, step S3 involves preparing a graphene oxide dispersion using deionized water as the solvent. The concentration of the graphene oxide dispersion is 2 mg / mL, excluding vitamin C, silane coupling agent KH550, and polyvinyl alcohol. The remaining steps are the same as in Example 1.

[0052] Comparative Example 3

[0053] In this comparative example, step S3 involves preparing a graphene oxide dispersion using deionized water as the solvent. The concentration of the graphene oxide dispersion is 2 mg / mL, and the concentration of vitamin C is 0.02 mg / mL. The dispersion does not include silane coupling agent KH550 and polyvinyl alcohol. All other steps are the same as in Example 1.

[0054] Comparative Example 4

[0055] In this comparative example, in step S3, the graphene oxide dispersion was prepared using deionized water as the solvent. The concentration of the graphene oxide dispersion was 2 mg / mL, the concentration of vitamin C was 0.02 mg / mL, and the concentration of silane coupling agent KH550 was 0.02 mg / mL. Polyvinyl alcohol was not included. The remaining steps were the same as in Example 1.

[0056] Comparative Example 5

[0057] In this comparative example, step S1 involves cleaning the natural graphite film with ethanol and deionization to obtain a pretreated natural graphite film. The remaining steps are the same as in Example 1.

[0058] Comparative Example 6

[0059] This comparative example is a natural graphite film.

[0060] Test case

[0061] The performance of the natural graphite composite films prepared in Examples 1-2 and Comparative Examples 1-5, and the natural graphite film in Comparative Example 6 were tested.

[0062] Thermal diffusivity test: The thermal diffusivity of the natural graphite composite film was tested using Netzsch LFA467. The test temperature was set at room temperature (25℃), the voltage was 260V, the sampling time was 30ms, the detection area was 14mm, and the test sample size was a circular piece with a diameter of 2.54cm.

[0063] Density test: calculated using the weight and size method;

[0064] Thermal conductivity: calculated based on thermal diffusivity, density, and specific heat capacity (0.85 J / g*K);

[0065] The test results are shown in Table 1.

[0066] Table 1

[0067] Group <![CDATA[Thermal diffusivity (mm 2 / s)]]> <![CDATA[Density (g / cm 3 ).]]> Thermal conductivity (W / m*K) Example 1 421.43 2.32 831 Example 2 408.98 2.29 796 Comparative Example 1 354.51 2.21 666 Comparative Example 2 362.26 2.18 671 Comparative Example 3 374.40 2.23 710 Comparative Example 4 386.29 2.28 749 Comparative Example 5 359.83 2.16 661 Comparative Example 6 267.15 2.20 500

[0068] As can be seen from the data in Table 1, the natural graphite composite film prepared in the embodiments of the invention has excellent thermal conductivity. The natural graphite layer 17 and graphene layer 18, combined with the interface reinforcement layer and the nano-silicon carbide layer, are tightly bonded through a hot-pressing process, forming a continuous and efficient heat conduction channel, thus improving the thermal conductivity of the composite film. In Comparative Example 1, there is no nano-silicon carbide interface reinforcement. Nano-silicon carbide, as an interface reinforcement, can improve the vertical thermal conductivity of the composite film, especially in terms of the interfacial bonding. Removing nano-silicon carbide weakens the interfacial heat transfer capacity, reduces the interfacial bonding force, and affects the heat transfer path, resulting in a significant decrease in the thermal diffusivity of the composite film. In Comparative Example 2, vitamin C, silane coupling agent KH550, and polyvinyl alcohol were not added when preparing the graphene oxide dispersion. This means that the degree of interfacial chemical bonding and functionalization modification is weakened, thereby affecting the dispersibility and interfacial bonding of nano-silicon carbide and graphene oxide. Without these additives, the reduction of graphene oxide may not be as thorough as in Example 1, resulting in poor dispersion and uniformity of graphene layer 18 in the composite film, leading to a slight decrease in the density of the composite film, and possibly even the presence of tiny pores or uneven interfacial regions. In Example 1, vitamin C promotes the reduction of graphene oxide, and silane coupling agent KH550 and polyvinyl alcohol assist in the formation of chemical bonds between the reduced graphene and nano-silicon carbide interfaces, enhancing the thermal conductivity between graphene layer 18 and natural graphite layer 17. However, in Comparative Example 2, the lack of these additives leads to incomplete reduction of graphene oxide, and the bonding between graphene layer 18 and natural graphite layer 17 is not as tight as in Example 1, resulting in poorer thermal conductivity at the interface and a lower thermal diffusivity of the composite film. In Comparative Example 3, the graphene oxide dispersion does not include silane coupling agent KH550 and polyvinyl alcohol, and in Comparative Example 4, the graphene oxide dispersion does not include polyvinyl alcohol; both result in poor thermal conductivity at the interface between graphene layer 18 and natural graphite layer 17, and a lower thermal diffusivity of the composite film. In Comparative Example 5, the natural graphite film was treated only with ethanol and deionized water, rather than with plasma treatment to activate the surface. Plasma treatment can effectively remove organic matter, oxides, and impurities from the surface of the natural graphite film, increase its surface active groups, and improve the surface roughness and hydrophilicity of the natural graphite film. This helps to enhance the adhesion of materials such as graphene oxide and nano-silicon carbide, allowing them to be more uniformly distributed on the graphite film surface, ultimately forming a denser composite film. Although ethanol and deionized water cleaning can remove impurities from the graphite film surface, it does not increase surface active groups or improve the surface structure. Therefore, the surface activity of the natural graphite film is low, which leads to reduced adhesion performance of nano-silicon carbide and graphene, and the interfacial bonding is not as good as the treatment in Example 1. This results in poorer composite film density, discontinuous heat conduction paths, increased heat conduction resistance, and reduced thermal diffusivity.

[0069] Example 3

[0070] Based on Example 1, please refer to Figures 1-5 The pressing mechanism includes: a pressing frame 1, which is an open frame at the front and back; a support plate 2 fixedly connected to the inner wall of the pressing frame 1; a telescopic cylinder 8 fixedly installed at the top of the inner wall of the pressing frame 1; a pressing groove 7 opened at the bottom of the inner wall of the pressing frame 1; a through hole 12 opened at the center of the support plate 2; the movable end of the telescopic cylinder 8 passes through the through hole 12 and is fixedly fitted with a pressure plate 9; a heating head 10 is installed at the bottom of the pressure plate 9; the fixed end of the telescopic cylinder 3 is fixedly connected to the bottom of the support plate 2; and the movable end of the telescopic cylinder 3 is fixedly connected to the support body 5. A reset spring 6 is provided between the bottom of the inner wall of the pressing frame 1. A pressure insulation cavity 13 is provided in the middle of the support body 5. Several sets of drive motors 4 are installed on the vertical sections on both sides of the support body 5. Each set of drive motors 4 has a threaded rod 14 fixedly connected to its output end. The end of the threaded rod 14 away from the drive motor 4 is rotatably connected to the outer wall of the pressure insulation cavity 13. The anti-detachment part 15 is movably sleeved on the outer wall of the threaded rod 14, and the anti-detachment part 15 and the threaded rod 14 are connected by threads. The top of the anti-detachment part 15 extends towards the pressure insulation cavity 13 to form an inclined pressure end 16.

[0071] The working principle and beneficial effects of the above scheme are as follows: When in use, after placing the graphene-natural graphite composite film in the pressing groove 7 of the pressing frame 1, the telescopic cylinder 3 is activated to push the support body 5 down until the lower insulation cavity 13 enters the pressing groove 7 and is pressed against the graphene-natural graphite composite film inside, thereby achieving the initial pressing effect. Subsequently, the telescopic cylinder 28 is activated to push the pressure plate 9 down until the heating head 10 enters the pressure insulation chamber 13. Then, the drive motor 4 is activated to drive the threaded rod 14 to rotate, thereby causing the two sets of anti-detachment parts 15 to move towards the pressure insulation chamber 13 until the inclined pressing end 16 of the anti-detachment part 15 matches the chamfer 11 of the pressure plate 9, thus ensuring stability during the pressing process. As the temperature of the heating head 10 rises until the temperature of the entire pressure insulation chamber 13 reaches the required 150-200℃, and with the cooperation of the telescopic cylinder 13 and the telescopic cylinder 28, the pressure on the graphene-natural graphite composite film is maintained between 10-20MPa. After 20 minutes, an enhanced natural graphite composite film is obtained.

[0072] Finally, it should be noted that the above embodiments are merely illustrative of several implementations of the present invention and are not intended to limit the scope of the invention. For those skilled in the art, any modifications, equivalent substitutions, or improvements made without departing from the concept of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing an enhanced natural graphite composite film, characterized in that, Includes the following steps: S1. The surface of the natural graphite film is activated by plasma treatment to obtain a pretreated natural graphite film; S2. Prepare a nano-silicon carbide dispersion, spray the nano-silicon carbide dispersion evenly onto the surface of the pretreated natural graphite film, and dry it under low temperature heat treatment to obtain a natural graphite film with an interface reinforcement layer. S3. Prepare a graphene oxide dispersion, coat the graphene oxide dispersion on the surface of a natural graphite film with an interface reinforcement layer, and perform low-temperature reduction treatment to obtain a graphene-natural graphite composite film. S4. Place the graphene-natural graphite composite film in a pressing mechanism and perform hot pressing to obtain the reinforced natural graphite composite film.

2. The method for preparing the enhanced natural graphite composite film according to claim 1, characterized in that, In step S1, the plasma treatment is performed using argon gas at a low pressure of 50-100 Pa and a power of 100-200 W for 15-30 minutes.

3. The method for preparing the enhanced natural graphite composite film according to claim 1, characterized in that, In step S2, the concentration of the nano-silicon carbide dispersion is 0.5-2 mg / mL, and the solvent is ethanol.

4. The method for preparing the enhanced natural graphite composite film according to claim 1, characterized in that, The temperature for low-temperature heat treatment and drying in step S2 is 40-60℃.

5. The method for preparing the enhanced natural graphite composite film according to claim 1, characterized in that, In step S3, the concentration of the graphene oxide dispersion is 0.5-2 mg / mL, the solvent is deionized water, and the coating method is spin coating or spray coating.

6. The method for preparing the enhanced natural graphite composite film according to claim 1, characterized in that, The graphene oxide dispersion in step S3 also includes vitamin C, silane coupling agent KH550, and polyvinyl alcohol; the concentration of vitamin C is 0.01-0.03 mg / mL, the concentration of silane coupling agent KH550 is 0.01-0.03 mg / mL, and the concentration of polyvinyl alcohol is 0.02-0.05 mg / mL.

7. The method for preparing the enhanced natural graphite composite film according to claim 1, characterized in that, In step S3, the low-temperature reduction treatment is carried out at a temperature of 120-135℃ for 1-2 hours.

8. The method for preparing the enhanced natural graphite composite film according to claim 1, characterized in that, In step S4, the hot pressing temperature is 150-200℃, the pressure is 10-20MPa, and the processing time is 15-30min.

9. The method for preparing the enhanced natural graphite composite film according to claim 1, characterized in that, The pressing mechanism includes: a pressing frame (1), which is a frame with openings at the front and back; a support plate (2) is fixedly connected to the inner wall of the pressing frame (1); a telescopic cylinder (8) is fixedly installed at the top of the inner wall of the pressing frame (1); a pressing groove (7) is opened at the bottom of the inner wall of the pressing frame (1); a through hole (12) is opened at the center of the support plate (2); the movable end of the telescopic cylinder (8) passes through the through hole (12) and is fixedly installed with a pressure plate (9); a heating head (10) is installed at the bottom of the pressure plate (9); the fixed end of the telescopic cylinder (3) is fixedly connected to the bottom of the support plate (2); the movable end of the telescopic cylinder (3) is fixedly connected to the support body (5); and the support body (5) A reset spring (6) is provided between the bottom of the inner wall of the pressing frame (1) and the support body (5). A pressure insulation cavity (13) is provided in the middle of the support body (5). Several sets of drive motors (4) are installed on the vertical sections on both sides of the support body (5). Each set of drive motors (4) has a threaded rod (14) fixedly connected to its output end. The end of the threaded rod (14) away from the drive motor (4) is rotatably connected to the outer wall of the pressure insulation cavity (13). The anti-detachment part (15) is movably sleeved on the outer wall of the threaded rod (14), and the anti-detachment part (15) and the threaded rod (14) are connected by threads. The top of the anti-detachment part (15) extends towards the pressure insulation cavity (13) to form an inclined pressure end (16).

10. An enhanced natural graphite composite film, characterized in that, Prepared by the method described in any one of claims 1-9, comprising a natural graphite layer (17) and a graphene layer (18), wherein the thickness of the natural graphite layer is 0.025-0.25 mm and the thickness of the graphene layer is 0.01-0.025 mm.

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