High-thermal-conductivity and high-thickness graphene composite film and preparation method therefor

Abstract

The present invention provides a high-thermal-conductivity and high-thickness graphene composite film and a preparation method therefor. The graphene composite film has a thickness of 1-2 mm, a thermal conductivity in the horizontal direction of 1500-1800 W / m•K and a thermal conductivity in the vertical direction of 100-200 W / m•K. The graphene composite film is obtained by mixing, coating, drying and sintering raw materials comprising a graphene oxide slurry, carbon fibers, carbon nanotubes and an adhesive dispersant, wherein on the basis of the mass of the graphene oxide slurry, the mass percentage of the carbon fibers is 4-7%, the mass percentage of the carbon nanotubes is 5-10%, and the mass percentage of the adhesive dispersant is 5-10%. The graphene composite film uses graphene oxide as a base material, and carbon fibers and carbon nanotubes of a certain length and diameter are added thereto to create a thermal conduction channel in the vertical direction. The synergistic combination of the three raw materials solves the current defect of it being difficult to balance the thickness and axial thermal conduction performance of a graphene film.

Description

High-thermal-conductivity high-thickness graphene composite film and preparation method thereof TECHNICAL FIELD

[0001] The present application belongs to the field of graphene film material preparation, and particularly relates to a high-thermal-conductivity high-thickness graphene composite film and a preparation method thereof. BACKGROUND

[0002] In the field of high-temperature thermal field applications, aerospace, military equipment, and highly integrated electronic devices, the demand for heat dissipation is increasingly high, and it is urgent to develop a heat-conducting material that can achieve high-speed heat conduction and heat dissipation in a limited internal space. Carbon materials are a very ideal new type of thermal management material, such as graphene, which has a thermal conductivity of up to 5300 W / m·K, and excellent mechanical strength and good flexibility. At present, a large number of graphite or graphene films are used for heat field environment and electronic device heat dissipation components. However, the current mature graphite or graphene heat dissipation film has a horizontal thermal conductivity of 1300-1500 W / m·K, and an axial thermal conductivity of less than 10 W / m·K, and the thickness is usually less than 300 microns, and the poor heat flux results in poor heat conduction effect. The existing manufacturing technology is difficult to obtain thicker graphene films, although the thermal conductivity of the film is high, but the heat flux is not enough, and it is difficult to dissipate more heat, and the application is further limited. The film composed of natural graphite mixed with adhesive has more grain boundaries and impurities, although the film can be thickened, but its thermal conductivity is generally in the range of 600-800 W / m·K, and the overall heat conduction capacity is still poor. More importantly, the axial thermal conductivity of any film is very poor, only 10-20 W / m·K, especially in the application of high-temperature thermal field, the performance is greatly limited.

[0003] CN 114634177 B discloses a preparation method of a graphite film, and the main preparation process comprises copper infiltration treatment. The specific steps of copper infiltration treatment are as follows: a copper ion solution is prepared by using inorganic copper salt; the selected graphene film is completely immersed in a container containing the copper ion solution, so that the copper ions penetrate into the graphene film; the container with the graphene film immersed is transferred to a vacuum oven; the saturated infiltrated graphene film is taken out and clamped by a metal clamp as a cathode connected with a negative electrode of an external circuit, and a graphite rod is used as an anode connected with a positive electrode of the external circuit, and direct current is input to reduce the copper ions in the graphene film and load them in the graphene film, and then the reduced graphene film is dried; the above-mentioned copper infiltration treatment is repeated for multiple times, so that the copper ions are reduced as much as possible between the layers of the graphene film. By infiltrating copper into the graphene, a large number of heat conduction nodes in the Z-axis direction are constructed in the graphene film, and the heat conduction performance of the graphene film in the Z-axis direction is improved. The technology uses copper infiltration to infiltrate a large number of copper particles between the layers of the graphene film, so as to improve the axial thermal conductivity, which is as high as 28-135 W / m·K. However, since the copper particles are discontinuous points, and the thermal conductivity of copper is limited, the improvement effect on the overall performance is not great.

[0004] The existing graphene-based materials generally have low heat flux or insufficient thermal conductivity, which cannot meet the needs of more application scenarios. Therefore, how to make graphene have high thickness and high thermal conductivity, especially improve the axial thermal conductivity, is a problem to be solved.

[0005] SUMMARY

[0006] In view of the problems of the prior art, the present application provides a graphene composite film with high thermal conductivity and high thickness. The graphene composite film uses graphene oxide as a base material, adds carbon fibers and carbon nanotubes with certain length and diameter to create vertical heat conduction channels, and the synergistic combination of the three raw materials solves the defect that the thickness and axial thermal conductivity of the graphene film are difficult to be considered at the same time.

[0007] The technical scheme of the present application is as follows:

[0008] The present application provides a graphene composite film with high thermal conductivity and high thickness. The thickness of the graphene composite film is 1-2 mm, the horizontal thermal conductivity is 1500-1800 W / m·K, and the vertical thermal conductivity is 100-200 W / m·K.

[0009] Further, the graphene composite film is obtained by mixing, coating, drying and sintering raw materials containing graphene oxide slurry, carbon fibers, carbon nanotubes and adhesive dispersants. The mass percentage of the carbon fibers is 4-7%, the mass percentage of the carbon nanotubes is 5-10%, and the mass percentage of the adhesive dispersant is 5-10%, based on the mass of the graphene oxide slurry.

[0010] Further, the graphene oxide has an oxygen content of 26-30 at% and a sheet size of 30-50 μm.

[0011] Further, the carbon fiber has a diameter of 5-10 μm and a length of 80-100 μm.

[0012] Further, the carbon nanotube has a diameter of 1-3 μm and a length of 10-20 μm.

[0013] Further, the adhesive dispersant is any one or more of polyvinyl butyral resin, carboxymethyl cellulose, and polyvinyl pyrrolidone.

[0014] Further, in the graphene composite film, the carbon fiber and the carbon nanotube are arranged perpendicularly or obliquely to the graphene sheet.

[0015] Further, in the graphene composite film, the carbon fiber and the carbon nanotube are arranged obliquely at 45° to the graphene sheet.

[0016] The present application also provides a method for preparing the aforementioned graphene composite film, which comprises the following steps:

[0017] Step 1: Preparation of graphene oxide slurry:

[0018] The graphene oxide is dispersed in water to prepare a stable dispersed graphene oxide slurry with a concentration of 8-10 wt%;

[0019] Step 2: Preparation of mixed solution of carbon fiber and carbon nanotube:

[0020] The carbon fiber with a diameter of 5-10 μm and a length of 80-100 μm and the carbon nanotube with a diameter of 1-3 μm and a length of 10-20 μm are mixed together and added to water, and an adhesive dispersant is added to the water to form a uniform mixed solution;

[0021] Step 3: The graphene oxide slurry of Step 1 and the mixed solution of Step 2 are mixed in a mass ratio of (7:3)-(9:1), and fully stirred to break the self-orientation of the graphene oxide and mix the carbon fiber and the carbon nanotube in the graphene oxide slurry to form a mixed slurry;

[0022] Step 4: Coating and baking:

[0023] The mixed slurry formed in Step 3 is coated on a release film as a substrate to a thickness of 2-6 mm, and then baked at 80-100°C to form a first layer of coating film, and then a second layer of coating film is screen printed on the first layer of coating film to a total thickness of 4-8 mm;

[0024] Step 5: Drying and sintering:

[0025] The coated film after increasing the thickness again is dried together until all the moisture is removed, and then the coated film is vacuum sintered at a temperature of 2500-3500 DEG C to obtain a graphene film with high axial thermal conductivity and high thickness.

[0026] Further, in step 1, the oxygen content of the graphene oxide is 26-30 at%, and the size of the sheet layer is 30-50 mu m.

[0027] Further, in step 1, the graphene oxide slurry is dispersed by using a homogenizing dispersing device for 1-3 h.

[0028] Further, in step 2, the mass percentage of the carbon fiber is 4-7% based on the mass of the graphene oxide slurry.

[0029] Further, in step 2, the mass percentage of the carbon nanotube is 5-10% based on the mass of the graphene oxide slurry.

[0030] Further, in step 2, the mass percentage of the adhesive dispersing agent is 5-10% based on the mass of the graphene oxide slurry.

[0031] Further, in step 2, the mixed system of the carbon fiber, the carbon nanotube and the adhesive dispersing agent is dispersed by using a ball milling device and a homogenizing dispersing device for 3-10 h.

[0032] Further, in step 4, the release film is PET.

[0033] Further, in step 4, the thickness ratio of the first layer of the coated film to the second layer of the coated film is 5:3.

[0034] Further, in step 4, the mixed slurry is taken out when the whole weight is reduced by 20% during baking.

[0035] Further, in step 5, the coated film is clamped by using a graphite plate and is vacuum sintered in a high-temperature graphitization furnace for 8-20 h.

[0036] The beneficial effects of the present application are as follows:

[0037] (1) The application adopts the form of composite of multiple carbon materials, wherein graphene is used as the main heat-conducting component and occupies the largest proportion. The graphene composite film uses graphene oxide as raw material to prepare a dense film material, and carbon nanotubes and carbon fibers are added to create vertical heat-conducting channels. Among them, the carbon fiber is a rigid fiber, and the use of a carbon fiber material with a length greater than the size of the graphene sheet and a relatively thick carbon fiber material can ensure that the carbon fiber will not be completely wrapped by the graphene to cause horizontal arrangement, so that vertical arrangement or inclined arrangement is easily formed during the drying of the slurry, thereby creating vertical heat-conducting channels in the graphene composite film, which is beneficial to the significant improvement of the axial thermal conductivity. The application of carbon nanotubes just supplements the pores caused by the arrangement of carbon fibers and graphene. Based on the specific selection and matching of the sizes of the three materials, perfect filling between the pores of the film can be achieved. At the same time, the carbon fiber is a flexible fiber, which can connect the horizontal direction and the vertical direction of the graphene composite film during the preparation process and supplement the weak heat-conducting capacity of the vertical direction, thereby further improving the axial heat-conducting capacity of the graphene composite film.

[0038] (2) The application mainly selects three high-thermal-conductivity carbon materials, which are allotropes of each other, have no repulsion between each other, and are easy to combine. In addition, the sizes of the three selected materials are matched appropriately, can form horizontal and vertical orientations during film formation, and can fill the internal pores with each other. The film coating is performed twice to increase the overall thickness of the material and improve the heat flux of the final product.

[0039] (3) The thickness of the graphene composite film of the application is 1-2 mm, the horizontal thermal conductivity is 1500-1800 W / m·K, and the axial heat-conducting capacity is as high as 100-200 W / m·K, which is more suitable for vertical heat conduction in the fields of photovoltaic, military, aerospace, etc. BRIEF DESCRIPTION OF DRAWINGS

[0040] Fig. 1 is a structural schematic diagram of the graphene composite film of the application.

[0041] Fig. 2 is a scanning electron microscope image of the surface morphology of the composite film of the application (the magnification is 3k times).

[0042] Fig. 3 is a further enlarged scanning electron microscope image of the surface morphology of the composite film of the application (the magnification is 10k times).

[0043] Reference signs: 1-graphene; 2-carbon fiber; 3-carbon nanotube. DETAILED DESCRIPTION

[0044] The application will be further described below in conjunction with examples, but the application is not limited to the following examples.

[0045] The horizontal thermal conductivity and the vertical thermal conductivity of the application are tested by using a laser thermal conductivity tester.

[0046] Embodiment 1

[0047] A high-thermal-conductivity high-thickness graphene composite film has a thickness of 2 mm, a horizontal thermal conductivity of 1800 W / m·K, and a vertical thermal conductivity of 200 W / m·K.

[0048] The preparation method is as follows:

[0049] Step 1: graphene oxide with an oxygen content of 30 at% and a sheet size of 50 μm is dispersed in water to prepare a concentrated graphene oxide slurry with a concentration of 10 wt%, and the concentrated graphene oxide slurry is dispersed for 2 h by using a homogenizing dispersion device to form a stable dispersed concentrated graphene oxide slurry;

[0050] Step 2: carbon fibers with a length of 80 μm and a diameter of 5 μm are mixed into water at a proportion of 4 wt%, and carbon nanotubes with a length of 10 μm and a diameter of 3 μm are mixed into water at a proportion of 5 wt%, and carboxymethyl cellulose is added to the mixed system at a proportion of 5 wt%, and the mixed system is dispersed for 4 h by using a ball milling device and a homogenizing dispersion device to form a uniform mixed liquid;

[0051] Step 3: the concentrated graphene oxide slurry in Step 1 and the mixed liquid in Step 2 are mixed at a mass ratio of 9:1, and are fully stirred to break the self-orientation of the graphene oxide, and the carbon fibers and the carbon nanotubes are fully mixed in the graphene oxide slurry to form a mixed slurry;

[0052] Step 4: the mixed slurry in Step 3 is coated on a coating machine with a PET release film as a substrate, and the coating thickness of the slurry is 5 mm, and then the coated slurry is placed in an oven at 80℃ to form a first layer of coating film, and the first layer of coating film is taken out when the overall weight of the first layer of coating film is reduced by 20%, and then the first layer of coating film is further screen printed to a thickness of 3 mm.

[0053] Step 5: the coating film with the increased thickness is dried together until all the water is removed, and then the coating film is clamped with graphite plates on both sides and is placed in a high-temperature graphitization furnace for vacuum sintering at a temperature of 2800℃ for 12 h to obtain an axial high-thermal-conductivity high-thickness graphene composite film.

[0054] As shown in FIG. 1, in the structural schematic diagram of the graphene composite film of the application, the carbon fibers and the carbon nanotubes are arranged vertically or obliquely with the graphene sheet layers.

[0055] Figure 2 is a scanning electron microscope image of the surface morphology of the graphene composite film of the present application (3k magnification), which shows that the surface is an interlaced structure of multiple materials (graphene, carbon nanotubes, carbon fibers). The effective combination of lines and surfaces makes the connection between graphene, carbon nanotubes and carbon fibers more compact, and this interlaced structure can achieve the connection and heat conduction of the graphene composite film in the vertical direction, improving the overall heat conduction and strength of the material.

[0056] Figure 3 is a further enlarged surface morphology scanning electron microscope image of the graphene composite film of the present application (10k magnification), which shows that the interlaced crosslinking of graphene, carbon nanotubes and carbon fibers is more clearly visible.

[0057] Figures 2 and 3 illustrate that in the graphene composite film of the present application, the combination of graphene, carbon fibers and carbon nanotubes forms a very firm porous structure, and the carbon fibers and carbon nanotubes are arranged vertically or obliquely to the graphene layers, which is conducive to improving the axial heat conduction capacity of the graphene composite film and also improving the shear strength in all directions. The existing similar products have poor axial heat conduction capacity (usually less than 10 W / m·K) and strength.

[0058] Example 2

[0059] A high-thermal-conductivity high-thickness graphene composite film with a thickness of 1 mm, a horizontal-direction thermal conductivity of 1500 W / m·K and a vertical-direction thermal conductivity of 100 W / m·K.

[0060] The preparation method is as follows:

[0061] Step 1: Disperse graphene oxide with an oxygen content of 26 at% and a layer size of 50 μm in water to prepare a concentrated graphene oxide slurry with a concentration of 8 wt%, and disperse for 2 h using a homogenizing dispersion device to form a stable dispersed concentrated graphene oxide slurry;

[0062] Step 2: Based on the mass of the above graphene oxide slurry, mix 4 wt% of carbon fibers with a length of 80 μm and a diameter of 5 μm, and 5 wt% of carbon nanotubes with a length of 10 μm and a diameter of 3 μm together in water, and add 10 wt% of carboxymethyl cellulose to the mixed system, and disperse the mixed system for 4 h using a ball milling device and a homogenizing dispersion device to form a uniform mixed liquid;

[0063] Step 3: Mix the graphene oxide concentrated slurry of step 1 and the mixed liquid of step 2 in a mass ratio of 7:3, and fully stir to break the self-orientation of the graphene oxide, and fully mix the carbon fibers and carbon nanotubes in the graphene oxide slurry to form a mixed slurry;

[0064] Step 4: The mixed slurry in step 3 is coated on a coating machine with a PET release film as the base, and the coating thickness of the slurry is 2 mm. Then the coated slurry is placed in an oven at 80°C to form a first layer of coating film. When the overall weight of the first layer of coating film is reduced by 20%, it is taken out. Then the first layer of coating film is further screen printed with a thickness of 3 mm.

[0065] Step 5: The coating film with increased thickness is dried together until all the water is removed. Then the coating film is clamped with graphite plates on both sides and placed in a high-temperature graphitization furnace for vacuum sintering at a temperature of 2800°C for 12 hours. Thus, an axially high-thermal-conductivity high-thickness graphene composite film is obtained.

[0066] Example 3

[0067] A high-thermal-conductivity high-thickness graphene composite film with a thickness of 2 mm, a horizontal-direction thermal conductivity of 1700 W / m·K, and a vertical-direction thermal conductivity of 150 W / m·K.

[0068] The preparation method is as follows:

[0069] Step 1: Oxidized graphene with an oxygen content of 30 at% and a sheet size of 50 μm is dispersed in water to prepare a concentrated slurry with a concentration of 10 wt%. The slurry is dispersed for 2 hours by using a homogenizing dispersion device to form a stable and concentrated oxidized graphene slurry.

[0070] Step 2: Carbon fibers with a length of 100 μm and a diameter of 5 μm are mixed with carbon nanotubes with a length of 20 μm and a diameter of 1 μm at a ratio of 7 wt% and 10 wt%, respectively. Carboxymethyl cellulose is added to the mixture at a ratio of 6 wt%. The mixture is dispersed for 4 hours by using a ball milling device and a homogenizing dispersion device to form a uniform mixture.

[0071] Step 3: The oxidized graphene slurry in step 1 and the mixture in step 2 are mixed at a mass ratio of 8:2, and stirred thoroughly to break the self-orientation of the oxidized graphene and mix the carbon fibers and carbon nanotubes in the oxidized graphene slurry to form a mixed slurry.

[0072] Step 4: The mixed slurry in step 3 is coated on a coating machine with a PET release film as the base, and the coating thickness of the slurry is 6 mm. Then the coated slurry is placed in an oven at 80°C to form a first layer of coating film. When the overall weight of the first layer of coating film is reduced by 20%, it is taken out. Then the first layer of coating film is further screen printed with a thickness of 8 mm.

[0073] Step 5: Dry the coating film with the increased thickness together until all the water is removed, then clamp the coating film with graphite plates on both sides, and place it in a high-temperature graphitization furnace for vacuum sintering at a temperature of 2800℃ for 12h to obtain a graphene composite film with high axial thermal conductivity and high thickness.

[0074] Comparative Example 1

[0075] A graphene film without the addition of carbon fibers and carbon nanotubes, with a thickness of 1.5mm, a horizontal thermal conductivity of 1800W / m·K, and a vertical thermal conductivity of 15W / m·K.

[0076] The preparation method is as follows:

[0077] (1) Disperse graphene oxide with an oxygen content of 30at% and a sheet size of 50μm in water to prepare a slurry with a concentration of 10wt%, and disperse it for 2h using a homogenizing dispersion device to form a stable and thick graphene oxide slurry.

[0078] (2) Coating the graphene oxide slurry in step (1) on a coating machine with a PET release film as the base, with a coating thickness of 5mm, then placing the coated slurry in an oven at 80℃ to form a first layer of coating film, and removing it when the overall weight of the first layer of coating film is reduced by 20%, and then continuing to screen print a thickness of 3mm on the first layer of coating film.

[0079] (3) Dry the slurry with the increased thickness together until all the water is removed, then clamp it with graphite plates on both sides, and place it in a high-temperature graphitization furnace for vacuum sintering at a temperature of 2800℃ for 12h to obtain a thick graphene film.

[0080] In Comparative Example 1, without the addition of carbon fibers and carbon nanotubes, the carbon materials inside the graphene composite film are laid horizontally, and the vertical thermal conductivity is naturally low.

[0081] Comparative Example 2

[0082] A graphene film with a thickness of 0.8mm, a horizontal thermal conductivity of 1300W / m·K, and a vertical thermal conductivity of 10W / m·K.

[0083] The preparation method is as follows:

[0084] (1) Disperse graphene oxide with an oxygen content of 30at% and a sheet size of 50μm in water to prepare a slurry with a concentration of 10wt%, and disperse it for 2h using a homogenizing dispersion device to form a stable and thick graphene oxide slurry.

[0085] (2) based on the mass of the graphene oxide slurry, carbon fibers with a length of 8 μm and a diameter of 1 μm are mixed together in a proportion of 4%, and carbon nanotubes with a length of 10 μm and a diameter of 3 μm are mixed together in a proportion of 5%, and then added to water, and 5% of carboxymethyl cellulose is added to the mixed system, and the mixture is dispersed for 4 h by a ball milling device and a homogenizing dispersion device to form a uniform mixed solution;

[0086] (3) the graphene oxide concentrated slurry in step (1) and the mixed solution in step (2) are mixed in a proportion of 9:1, and stirred thoroughly to break the self-orientation of the graphene oxide and to mix the carbon fibers and the carbon nanotubes in the graphene oxide slurry to form a mixed slurry.

[0087] (4) the mixed slurry in step (3) is coated on a PET release film as a substrate on a coating machine, and the coating thickness of the slurry is 5 mm, and then the coated slurry is placed in an oven at 80°C to be baked to form a first layer of coating film, and the first layer of coating film is removed when the overall weight of the first layer of coating film is reduced by 20%, and then the first layer of coating film is further screen printed to a thickness of 3 mm;

[0088] (5) the slurry with the increased thickness is dried by an instrument until all the water is removed, and then the coating film is clamped with graphite plates on both sides and placed in a high-temperature graphitization furnace for vacuum sintering at a temperature of 2800°C for 12 h to obtain a graphene film with high axial thermal conductivity and high thickness.

[0089] As can be seen from the results of Comparative Example 2, when the length and diameter of the carbon fibers are less than the range of the present application, the horizontal thermal conductivity of the final product is 1300 W / m·K, and the vertical thermal conductivity is only 10 W / m·K.

[0090] Because the length and diameter of the carbon fibers are too small, they cannot form a connection in the vertical direction in the form of a through hole in the graphene composite film, resulting in that the carbon materials inside the graphene composite film are still laid horizontally, and the horizontal laying structure of the graphene is also affected during the preparation process, thereby blocking the heat conduction and reducing the thermal conductivity of the graphene composite film.

[0091] The above description is only a preferred embodiment of the present application, and is not intended to limit the present application in any other form, and any modification or equivalent change made according to the technical essence of the present application still falls within the scope of the present application.

Claims

1. A high thermal conductive high thickness graphene composite film, characterized in that, The graphene composite film has a thickness of 1-2 mm, a horizontal direction thermal conductivity of 1500-1800 W / m·K, and a vertical direction thermal conductivity of 100-200 W / m·K.

2. The graphene composite film according to claim 1, wherein, The graphene composite film is obtained by mixing, coating, drying and sintering raw materials containing graphene oxide slurry, carbon fibers, carbon nanotubes and adhesive dispersants, the mass percentage of the carbon fibers being 4-7%, the mass percentage of the carbon nanotubes being 5-10%, and the mass percentage of the adhesive dispersant being 5-10%, based on the mass of the graphene oxide slurry.

3. The graphene composite film according to claim 1 or 2, wherein The graphene oxide has an oxygen content of 26-30 at% and a sheet size of 30-50 μm.

4. The graphene composite film according to claim 1 or 2, wherein The carbon fibers have a diameter of 5-10 μm and a length of 80-100 μm.

5. The graphene composite film according to claim 1 or 2, wherein The carbon nanotubes have a diameter of 1-3 μm and a length of 10-20 μm.

6. The graphene composite film according to claim 1 or 2, wherein The adhesive dispersant is any one or more of polyvinyl butyral resin, carboxymethyl cellulose and polyvinyl pyrrolidone.

7. The graphene composite film according to claim 1 or 2, wherein In the graphene composite film, the carbon fibers and carbon nanotubes are arranged vertically or obliquely with respect to the graphene sheet.

8. The graphene composite film according to claim 7, wherein, In the graphene composite film, the carbon fibers and carbon nanotubes are arranged obliquely at 45° with respect to the graphene sheet.

9. A method of producing the graphene composite film according to any one of claims 1 to 8, characterized by, The preparation method comprises the following steps: Step 1: Preparation of graphene oxide slurry Stable dispersed graphene oxide slurry with a concentration of 8-10 wt% is prepared by dispersing graphene oxide in water; Step 2: Preparation of mixed solution of carbon fibers and carbon nanotubes Carbon fibers with a diameter of 5-10 μm and a length of 80-100 μm and carbon nanotubes with a diameter of 1-3 μm and a length of 10-20 μm are mixed together and added to water, and an adhesive dispersant is added to the water to form a uniform mixed solution; Step 3: Mixing of the graphene oxide slurry of Step 1 and the mixed solution of Step 2 in a mass ratio of (7:3)-(9:1), and sufficient stirring to break the self-orientation of the graphene oxide and mix the carbon fibers and carbon nanotubes in the graphene oxide slurry to form a mixed slurry; Step 4: Coating and baking The mixed slurry formed in Step 3 is coated to a thickness of 2-6 mm on a release film as a substrate, and then baked at 80-100 °C to form a first layer of coating film, and then a second layer of coating film is screen printed on the first layer of coating film to a total coating film thickness of 4-8 mm; Step 5: Drying and sintering The coating films with increased thickness are dried together until all the water is removed, and then the coating films are vacuum sintered at a temperature of 2500-3500 °C to obtain a graphene film with high axial thermal conductivity and high thickness.

10. The method of claim 9, wherein, The thickness ratio of the first layer of coating film to the second layer of coating film is 5:3.

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