Composite graphene film and preparation method and application thereof

Abstract

The application provides a composite graphene film and a preparation method and application thereof. The composite graphene film comprises graphene and graphite fibers; at least some of the graphite fibers and at least some of the graphene are interpenetrated to form a three-dimensional network structure; the thickness of the composite graphene film is in the range of 130 mu m-250 mu m, the in-plane thermal conductivity of the composite graphene film is in the range of 1400 W / (m.k)-2000 W / (m.k), and the out-of-plane thermal conductivity of the composite graphene film is in the range of 5 W / (m.k)-12.5 W / (m.k). The composite graphene film has high in-plane and out-of-plane thermal conductivities, and has a large thickness, so that the composite graphene film can realize high heat flux and efficient heat dissipation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat-conducting materials, in particular to a composite graphene film and a preparation method and application thereof. BACKGROUND

[0002] In recent years, with the rapid development of new energy vehicles and communication equipment, the market needs higher and higher performance and endurance of them. The industry always tries to continuously improve the energy density of the batteries used in the above-mentioned equipment and continuously improve the integration degree of the system control chips used in the above-mentioned equipment, which will lead to a sharp increase in heat production during the operation of the above-mentioned equipment. Therefore, efficient heat dissipation is the key to ensuring the normal and stable operation of the above-mentioned equipment and ensuring its safety performance.

[0003] At present, carbon-based film materials, especially graphene-based film materials, are widely used as heat dissipation materials due to their high thermal conductivity and low density. However, the heat dissipation effect of graphene-based film materials is limited when the thickness is small. In theory, increasing the thickness of graphene-based film materials can improve their heat conduction capacity, but in practice, it will lead to a decrease in the degree of graphitization inside the film material, thereby causing a decrease in the thermal conductivity of the film material, especially a decrease in the out-of-plane thermal conductivity. The finally obtained graphene-based film material is still difficult to achieve efficient heat dissipation. Therefore, it is urgent to develop a material that can achieve efficient heat dissipation. SUMMARY

[0004] In view of this, the present application provides a composite graphene film which has high in-plane and out-of-plane thermal conductivities and a large thickness, so that the composite graphene film can achieve high heat flux and efficient heat dissipation.

[0005] The first aspect of the present application provides a composite graphene film, comprising graphene and graphite fibers; at least some of the graphite fibers and at least some of the graphene are interpenetrated to form a three-dimensional network structure; the thickness of the composite graphene film is in the range of 130 μm-250 μm, the in-plane thermal conductivity of the composite graphene film is in the range of 1400 W / (m·k)-2000 W / (m·k), and the out-of-plane thermal conductivity of the composite graphene film is in the range of 5 W / (m·k)-12.5 W / (m·k).

[0006] The composite graphene film has high in-plane and out-of-plane thermal conductivities even when the thickness is in the range of 130 μm-250 μm, so that the composite graphene film can achieve high heat flux and efficient heat dissipation.

[0007] The second aspect of the present application provides a preparation method of a composite graphene film, comprising the following steps:

[0008] (1) adding a composite graphite fiber precursor and graphene oxide into a solvent, and mixing thoroughly to obtain a dispersion liquid; wherein the composite graphite fiber precursor comprises a spinnable carbon source and a two-dimensional layered material; the two-dimensional layered material is used to promote graphitization of the composite graphite fiber precursor and the graphene oxide;

[0009] (2) preparing a composite graphene film precursor from the dispersion liquid, wherein the composite graphene film precursor comprises a three-dimensional network structure formed by interpenetration of the composite graphite precursor fibers and the graphene oxide;

[0010] (3) performing a heating treatment on the composite graphene film precursor, so that the composite graphite fiber precursor forms graphite fibers and the graphene oxide forms graphene, to obtain a composite graphene film.

[0011] The preparation method has simple steps, high process reliability, and high production efficiency, and can realize large-scale industrial production.

[0012] The third aspect of the application provides an application of the composite graphene film in a heat-conducting material. DETAILED DESCRIPTION

[0013] The embodiment of the application provides a preparation method of a composite graphene film, comprising the following steps:

[0014] S1, a composite graphite fiber precursor and graphene oxide are added into a solvent, and mixed thoroughly to obtain a dispersion liquid; wherein the composite graphite fiber precursor comprises a spinnable carbon source and a two-dimensional layered material; the two-dimensional layered material is used to promote graphitization of the composite graphite fiber precursor and the graphene oxide;

[0015] S2, the dispersion liquid is prepared into a composite graphene film precursor, wherein the composite graphene film precursor comprises a three-dimensional network structure formed by interpenetration of the composite graphite precursor fibers and the graphene oxide;

[0016] S3, a heating treatment is performed on the composite graphene film precursor, so that the composite graphite fiber precursor forms graphite fibers and the graphene oxide forms graphene, to obtain a composite graphene film.

[0017] The atomic arrangement structure in the two-dimensional layered material is similar to that of carbon atoms in graphene, which can catalyze and guide the carbon atom rearrangement in the spinnable carbon source to form graphite fibers, and also can catalyze the reduction of graphene oxide and the carbon atom rearrangement at the defect structure possibly existing therein, so as to greatly improve the graphitization degree of the final composite graphene film. At the same time, the non-carbon elements in the two-dimensional layered material will escape in the form of gas during the graphitization process, thereby taking away the heat generated during the graphitization process of the composite graphite fiber precursor, improving the looseness of the internal structure of the composite graphene film precursor, and being beneficial to further improving the graphitization degree of the final graphite fiber, especially being beneficial to improving the graphitization degree of the internal structure of the composite graphene film precursor with large thickness, so as to significantly improve the overall thermal conductivity of the composite graphene film; in addition, the functional groups on the surface of the composite graphite fiber precursor and the graphene oxide can crosslink to react, so as to greatly slow down the interface effect between the two-dimensional graphene oxide and the one-dimensional composite graphite fiber precursor, improve the mixing degree of the composite graphite fiber precursor and the graphene oxide, and more smoothly form a three-dimensional network structure in which the composite graphite precursor fibers and the graphene oxide are interpenetrated, so as to smoothly obtain a three-dimensional network structure in which graphite fibers and graphene are interpenetrated, while the density of the composite graphene film can be improved, so as to be beneficial to improving the in-plane and out-of-plane thermal conductivity of the final composite graphene film, so that the finally obtained composite graphene film not only has high in-plane and out-of-plane thermal conductivity, but also can realize high heat flux, and can realize efficient heat dissipation.

[0018] In addition, because the composite graphite fiber precursor contains the two-dimensional layered material which catalyzes the graphitization of the spinnable carbon source and promotes the formation of graphene from the graphene oxide, the energy barrier of the carbon atom rearrangement reaction of the spinnable carbon source and the carbon atom rearrangement reaction at the defect structure possibly existing in the graphene oxide is reduced, so that the graphitization temperature of the spinnable carbon source (i.e., the heating temperature of the composite graphene film precursor) can be reduced, thereby being beneficial to greatly reducing the production cost and improving the production efficiency.

[0019] The above preparation method has simple steps, strong process reliability, high production efficiency, and can realize large-scale industrial production.

[0020] In some embodiments of the present application, the two-dimensional layered material includes but is not limited to at least one of boron nitride, carbon nitride, black phosphorus and Mxene. Among them, the above Mxene material refers to a two-dimensional layered material derived from transition metal carbon / nitrogen / carbon nitride, specifically refers to a class of two-dimensional layered materials with M n+1 X n T xA material system composed of elements, wherein M represents a transition metal element, X represents a C element or a N element, T represents a group / modifier on the surface of the material (such as O, F, -OH, etc.), and n is usually in the range of 1-3. In some specific embodiments, the above-mentioned boron nitride can be graphite phase carbon nitride (abbreviated as g-C3N4). Thus, in each of the above-mentioned two-dimensional materials having a sheet structure, either a C element or a N element or a P element with a similar atomic radius to that of C is contained, and these three elements can all perform carbon compensation on the defect structure during the graphitization process of the composite graphite fiber precursor, and the above-mentioned materials can also react with other substances in the system to generate gas to escape, thereby further improving the graphitization degree of the graphite fibers in the final composite graphene film, and further improving the thermal conductivity of the composite graphene film. For example, boron nitride and carbon nitride can finally form substances such as NO to escape; the functional groups on the surface of black phosphorus can generate gases such as NO to escape; Mxene can generate gases such as CO or NO to escape; and the O element in each of the above-mentioned gases can come from the spinnable carbon source, graphene oxide, etc., or from the functional groups carried by the two-dimensional layered material itself.

[0021] In some embodiments of the present application, the graphene oxide can be commercially available graphene oxide; or can be graphene oxide prepared by using graphite powder as raw material and adopting the Hummers method, the improved Hummers method, the Brodie method or the Saudenmaier method.

[0022] In some embodiments of the present application, the preparation method of the composite graphite fiber precursor comprises:

[0023] S11, a first spinning solution containing a spinnable carbon source is prepared, and the two-dimensional layered material is added to the above-mentioned spinning solution, and after being fully mixed, a second spinning solution is obtained;

[0024] S12, a composite graphite fiber precursor is prepared by using a method of melt spinning, dry spinning, wet spinning, dry-jet wet spinning, electrospinning or liquid crystal spinning.

[0025] Alternatively, in the above-mentioned step S11, the spinnable carbon source and the two-dimensional layered material are directly added to the organic solvent together, and after being fully mixed, a second spinning solution is directly obtained.

[0026] In some embodiments of the present application, the above-mentioned organic solvent includes but is not limited to at least one of methanol, ethanol, propanol, butanol, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, gamma-butyrolactone, hexamethylphosphoramide, dimethyl sulfoxide and m-cresol.

[0027] In some embodiments of the present application, the ratio of the mass of the two-dimensional layered material to the mass of the spinnable carbon source is 1:(100-1000). For example, the ratio of the mass of the two-dimensional layered material to the mass of the spinnable carbon source can be 1:100, 1:200, 1:300, 1:400, 1:500, 1:600, 1:700, 1:800, 1:900, 1:1000, etc. In this way, the final graphite fiber can have both a high degree of graphitization to improve the thermal conductivity of the final composite graphene film and good strength, so that the final composite graphene film has both high heat dissipation efficiency and good mechanical strength.

[0028] In some embodiments of the present application, a foaming material is also added to the dispersion. The foaming material can expand during the heating process and later react with other substances to generate gas to escape, thereby further improving the looseness of the internal structure of the composite graphene film precursor, taking away more heat generated by the graphitization reaction, and thus facilitating further improvement of the graphitization degree of the final graphite fiber, thereby facilitating the obtaining of a composite graphene film with better thermal conductivity. In some specific embodiments, the foaming material includes but is not limited to calcium carbide. In some specific embodiments of the present application, the mass percentage of the foaming material in the dispersion is in the range of 0.1%-0.5%. For example, the mass percentage of the foaming material in the dispersion can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc.

[0029] In some embodiments of the present application, in step S1, the ratio of the mass of the composite graphite fiber precursor to the mass of the graphene oxide in the dispersion is 1:(4-20). For example, the ratio of the mass of the composite graphite fiber precursor to the mass of the graphene oxide can be 1:4, 1:5, 1:7, 1:10, 1:12, 1:15, 1:17, 1:20, etc. Controlling the mass ratio of the two within the above range is to control the ratio of graphite fiber to graphene in the composite graphene film. It can be understood that the thermal conductivity of graphene is higher than that of graphite fiber, but graphite fiber is needed as the skeleton material of the three-dimensional network structure, and also contributes to the thermal conductivity in the thickness direction of the composite graphene film. In addition, graphite fiber can also guide the orientation of graphene in the thickness direction of the composite graphene film, further improving the out-of-plane thermal conductivity of the composite graphene material. After balancing the above factors, controlling the mass ratio of the mass of the composite graphite fiber precursor to the mass of the graphene oxide within the above range can finally form a composite graphene film with high mechanical properties and good thermal conductivity.

[0030] In some embodiments of the present application, in step S1, the dispersion liquid is prepared by pressurized ultrasonic method. In some specific embodiments, the composite graphite fiber precursor and graphene oxide are added into the solvent simultaneously and then pressurized ultrasonic dispersion is performed to obtain the dispersion liquid. In some other specific embodiments, the composite graphite fiber precursor dispersion liquid and the graphene oxide dispersion liquid are prepared separately, and then mixed to obtain the above-mentioned dispersion liquid.

[0031] In some embodiments of the present application, in step S2, the method for preparing the composite graphene film precursor includes, but is not limited to, the following method (a) or method (b):

[0032] (a) freeze-drying the dispersion liquid to obtain a composite aerogel, and then pressing the composite aerogel to obtain the composite graphene film precursor. In some specific embodiments, the freeze-drying temperature is -65℃ to -30℃, and the freezing time is 48h to 72h. In some specific embodiments, the pressing is a hot pressing treatment, and the composite aerogel can be pressed at a temperature of 150℃ to 200℃. In some specific embodiments, the dispersion liquid can be evaporated and concentrated first to obtain a concentrated liquid with a solid content of about 50%, and then freeze-drying the concentrated liquid.

[0033] (b) filtering the dispersion liquid to obtain the composite graphene film precursor. Specifically, a vacuum filtration method can be used, and the micro-porous filter membrane is used to filter for 0.5h to 1h to obtain a filter cake attached to the filter membrane, and then the filter membrane is removed to obtain the composite graphene film precursor.

[0034] In some embodiments of the present application, in step S3, the heating treatment is performed at a temperature of 2500℃ to 3200℃ for 0.5h to 1h in a protective atmosphere. In some specific embodiments, the heating treatment is performed at a temperature of 2800℃ to 2950℃ for 0.5h to 1h, or at a temperature of 2500℃ to 2800℃ for 0.5h to 1h. For example, the heating treatment can be performed at a temperature of 2500℃, 2550℃, 2600℃, 2650℃, 2700℃, 2750℃, 2800℃, 2850℃, 2900℃, 2950℃, 3000℃, 3100℃, 3200℃, etc.

[0035] In some embodiments of the present application, in step S3, the heating treatment is performed at a temperature of 2500℃ to 3200℃ for 0.5h to 1h in a protective atmosphere. In some specific embodiments, the heating treatment is performed at a temperature of 2800℃ to 2950℃ for 0.5h to 1h, or at a temperature of 2500℃ to 2800℃ for 0.5h to 1h. For example, the heating treatment can be performed at a temperature of 2500℃, 2550℃, 2600℃, 2650℃, 2700℃, 2750℃, 2800℃, 2850℃, 2900℃, 2950℃, 3000℃, 3100℃, 3200℃, etc.

[0036] In some embodiments of the present application, in step S3, after the heating treatment, the product obtained by the heating treatment is rolled to obtain the final composite graphene film. In this way, the compactness of the final composite graphene film is good.

[0037] In the process of heating treatment, the composite graphene film precursor is converted into a graphite fiber, which causes volume shrinkage. The rolling process also makes the final composite graphene film densification. Therefore, the volume of the composite graphene film precursor, especially the thickness, is reduced. In some embodiments of the present application, the thickness of the composite graphene film precursor is in the range of 190 μm-400 μm. Thus, a composite graphene film with large thickness and high in-plane and out-of-plane thermal conductivity can be prepared. For example, the thickness of the composite graphene film precursor can be 190 μm, 195 μm, 200 μm, 225 μm, 250 μm, 275 μm, 300 μm, 325 μm, 350 μm, 375 μm, 400 μm, etc.

[0038] The present application also provides a composite graphene film, which comprises graphene and graphite fibers. At least some of the graphite fibers and graphene are interpenetrated to form a three-dimensional network structure. The thickness of the composite graphene film is in the range of 130 μm-250 μm. The in-plane (along the length or width direction of the composite graphene film) thermal conductivity of the composite graphene film is in the range of 1400 W / (m·k)-2000 W / (m·k). The out-of-plane (along the thickness direction of the composite graphene film) thermal conductivity of the composite graphene film is in the range of 5 W / (m·k)-12.5 W / (m·k).

[0039] Both graphite fibers and graphene have high thermal conductivity, and their thermal conductivity is anisotropic. The composite graphene film has a three-dimensional network structure formed by interpenetrating graphite fibers and graphene. The highly oriented and staggered graphite fibers can interpenetrate between the graphene layers, so that at least part of the graphene and graphite fibers can form an angle with the thickness direction of the composite graphene film greater than 0 and less than 180°. Therefore, both of them can contribute to the thermal conductivity in the thickness direction of the composite graphene film, so that the out-of-plane thermal conductivity of the composite graphene film can reach 12.5 W / (m·k), and the in-plane thermal conductivity can be as high as 2000 W / (m·k). More importantly, the thickness of the composite graphene film is as high as 130 μm-250 μm, so the composite graphene film has high heat flux in the length, width and thickness directions, thereby achieving efficient heat dissipation. In some embodiments of the present application, the thickness of the composite graphene film is in the range of 150 μm-250 μm.

[0040] Exemplarily, the thickness of the composite graphene film can be 130 μm, 135 μm, 140 μm, 145 μm, 150 μm, 155 μm, 160 μm, 165 μm, 170 μm, 180 μm, 190 μm, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, etc.

[0041] Exemplarily, the in-plane thermal conductivity of the composite graphene film can be 1400 W / (m·k), 1405 W / (m·k), 1425 W / (m·k), 1450 W / (m·k), 1475 W / (m·k), 1500 W / (m·k), 1550 W / (m·k), 1600 W / (m·k), 1650 W / (m·k), 1700 W / (m·k), 1750 W / (m·k), 1800 W / (m·k), 1850 W / (m·k), 1900 W / (m·k), 1950 W / (m·k), 2000 W / (m·k), etc.

[0042] Exemplarily, the out-of-plane thermal conductivity of the composite graphene film can be 5 W / (m·k), 5.5 W / (m·k), 6 W / (m·k), 6.5 W / (m·k), 7 W / (m·k), 7.5 W / (m·k), 8 W / (m·k), 8.5 W / (m·k), 9 W / (m·k), 9.5 W / (m·k), 10 W / (m·k), 10.5 W / (m·k), 11 W / (m·k), 11.5 W / (m·k), 12 W / (m·k), 12.5 W / (m·k), etc.

[0043] When the carbon material is subjected to Raman spectrum test, when the wavelength of 514 nm, 532 nm, 633 nm is selected as the excitation light source, the carbon material with ordered arrangement of carbon atoms has two characteristic peaks of D peak and G peak, the peak position of D peak is near 1300 cm -1 -1360 cm -1 , which represents the existence of defect structure in the carbon material, the position of G peak is near 1580 cm -1 -1600 cm -1 , which represents the existence of sp 2 hybridization in the carbon material (i.e., represents the existence of graphite structure), and the peak intensity ratio I D / I G of D peak and G peak can represent the graphitization degree of the carbon material.

[0044] In some embodiments of the present application, the Raman spectrum of the graphite fiber has I D / I GThe value of I / I can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc. D / I G The value of I / I can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc.

[0045] In some embodiments of the present application, the value of I / I of the Raman spectrum of the composite graphene film is in the range of 0.01-0.1. D / I G The value of I / I can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc. D / I G The value of I / I can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc. D / I G The value of I / I can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc. D / I G The value of I / I can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc. D / I G The value of I / I can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc. D / I G The value of I / I can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc.

[0046] The present application also provides an application of the composite graphene film in a heat-conducting material.

[0047] The technical solutions of the present application are further described in the following embodiments.

[0048] Embodiment 1

[0049] (1) 10 g of spinnable carbon source (specifically, polyacrylonitrile) is dissolved in 50 mL of N,N-dimethylformamide (DMF) to obtain a first spinning solution; 0.1 g of two-dimensional layered material (specifically, carbon nitride) is added to the first spinning solution, and after uniform dispersion, a second spinning solution is obtained; and a composite graphene fiber precursor is prepared by using an electrostatic spinning device.

[0050] (2) 5 g of the composite graphite fiber precursor was dispersed in 50 mL of tetrahydrofuran, and after pressure ultrasonic dispersion for 2 h, a composite graphite fiber precursor dispersion was obtained and reserved; 50 g of graphene oxide was added to 50 mL of tetrahydrofuran, and after pressure ultrasonic dispersion for 5 h, a graphene oxide dispersion was obtained. After mixing the composite graphite fiber precursor dispersion and the graphene oxide dispersion, a dispersion was obtained.

[0051] (3) The dispersion was concentrated by pressure distillation to a solid content of 50 wt%, and then transferred to a culture dish and freeze-dried at -50°C for 48 h to obtain a composite aerogel. The composite aerogel was then pressed at 150°C to obtain a composite graphene film precursor with a thickness of 200 μm.

[0052] (4) The composite graphene film precursor was transferred to a graphite furnace and heated under an argon atmosphere, and the temperature was raised to 2800°C at a rate of 10°C / min, and held for 1.5 h. The obtained product was then rolled to obtain a composite graphene film with a thickness of 155 μm.

[0053] Example 2

[0054] The difference from Example 1 is only that the spinnable carbon source is polyimide, and the thickness of the finally obtained composite graphene film is 159 μm.

[0055] Example 3

[0056] The difference from Example 1 is only that the dispersion contains 50 g of graphene oxide and 12.5 g of polyacrylonitrile.

[0057] The thickness of the finally obtained composite graphene film is 152 μm.

[0058] Example 4

[0059] The difference from Example 1 is only that the dispersion contains 50 g of graphene oxide and 2.5 g of polyacrylonitrile.

[0060] The thickness of the finally obtained composite graphene film is 160 μm.

[0061] Example 5

[0062] The difference from Example 1 is only that the dispersion contains 50 g of graphene oxide and 13 g of polyacrylonitrile.

[0063] The thickness of the finally obtained composite graphene film is 150 μm.

[0064] Example 6

[0065] The difference from Example 1 is only that in step (1), 10 g of spinnable carbon source (specifically, polyacrylonitrile) is dissolved in 50 mL of N,N-dimethylformamide (DMF) to obtain a first spinning solution; 0.01 g of two-dimensional layered material (specifically, carbon nitride) is added to the first spinning solution, and after uniform dispersion, a second spinning solution is obtained; and a composite graphite fiber precursor is prepared by using an electrostatic spinning device.

[0066] The thickness of the finally obtained composite graphene film is 152 pm.

[0067] Example 7

[0068] The difference from Example 1 is only that in step (1), 10 g of spinnable carbon source (specifically, polyacrylonitrile) is dissolved in 50 mL of N,N-dimethylformamide (DMF) to obtain a first spinning solution; 0.11 g of two-dimensional layered material (specifically, carbon nitride) is added to the first spinning solution, and after uniform dispersion, a second spinning solution is obtained; and a composite graphite fiber precursor is prepared by using an electrostatic spinning device.

[0069] The thickness of the finally obtained composite graphene film is 148 pm.

[0070] Example 8

[0071] The difference from Example 1 is only that the amount of each raw material is increased, but the ratio between each raw material remains the same as in Example 1, and the thickness of the prepared composite graphene film precursor is 400 pm, and the thickness of the finally obtained composite graphene film is 250 pm.

[0072] Example 9

[0073] The difference from Example 1 is only that the amount of the dispersion solution is adjusted, and the thickness of the prepared composite graphene film precursor is 190 pm, and the thickness of the finally obtained composite graphene film is 150 pm.

[0074] Example 10

[0075] The difference from Example 1 is that the dispersion solution also contains 0.72 g of foaming material (specifically, calcium carbonate). The thickness of the prepared composite graphene film precursor is 250 pm, and the thickness of the finally obtained composite graphene film is 170 pm.

[0076] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are set.

[0077] Comparative Example 1

[0078] (1) 10 g of spinnable carbon source (specifically, polyimide) is dissolved in 50 mL of N,N-dimethylformamide (DMF) to obtain a spinning solution; and a graphite fiber precursor is prepared by using an electrostatic spinning device.

[0079] (2) 5 g of graphite fiber precursor was dispersed into 50 mL of tetrahydrofuran, and after pressurized ultrasonic dispersion for 2 h, a composite graphite fiber precursor dispersion liquid was obtained and reserved; 50 g of graphene oxide was added into 50 mL of tetrahydrofuran, and after pressurized ultrasonic dispersion for 5 h, a graphene oxide dispersion liquid was obtained. After the composite graphite fiber precursor dispersion liquid and the graphene oxide dispersion liquid were mixed thoroughly, a dispersion liquid was obtained.

[0080] (3) The above dispersion liquid was concentrated by means of reduced pressure distillation to a solid content of 50 wt%, and then transferred into a culture dish and freeze-dried at -50°C for 48 h to obtain a composite aerogel. The composite aerogel was pressed at 150°C to obtain a composite graphene film precursor with a thickness of 200 μm.

[0081] (4) The composite graphene oxide film precursor was transferred into a graphite furnace, heated under an argon atmosphere, and heated to 2800°C at a rate of 8°C / min, and kept at 2800°C for 1.5 h to obtain a composite graphene film with a thickness of 155 μm.

[0082] Comparative Example 2

[0083] (1) 55 g of graphene oxide was added into 500 mL of DMF, and after pressurized ultrasonic dispersion for 6 h, a graphene oxide dispersion liquid was obtained.

[0084] (2) The graphene oxide dispersion liquid was filtered by means of vacuum distillation for 1.5 h to obtain a graphene film precursor with a thickness of 205 μm.

[0085] (3) The graphene film precursor was transferred into a graphite furnace, heated under an argon atmosphere, and heated to 2800°C at a rate of 8°C / min, and kept at 2800°C for 1 h to obtain a graphene film with a thickness of originally 166 μm.

[0086] Comparative Example 3

[0087] (1) 5 g of commercial graphite fiber was added into 60 mL of N,N-dimethylacetamide, and after pressurized ultrasonic dispersion for 6 h, a graphite fiber dispersion liquid was obtained. 50 g of graphene oxide was added into 500 mL of DMF, and after pressurized ultrasonic dispersion for 6 h, a graphene oxide dispersion liquid was obtained. The graphite fiber dispersion liquid and the graphene oxide dispersion liquid were mixed to obtain a third dispersion liquid.

[0088] (2) The third dispersion liquid was filtered by means of vacuum distillation for 1.5 h to obtain a composite graphene film precursor with a thickness of 205 μm.

[0089] (3) The composite graphene oxide film precursor was transferred to a graphite furnace and heated under argon atmosphere, and the temperature was raised to 2800℃ at a rate of 8℃ / min, and then kept for 1 h, to obtain a composite graphene film with a thickness of 163 μm.

[0090] Performance characterization test

[0091] 1. Raman test: The wavelength of the Raman spectrum excitation light source was 514 nm, and the resolution was 2 cm -1 . The Raman spectra of five points on the cross section of the composite graphene were measured respectively, and the I D / I G values were calculated, and the average value was taken. The results are shown in Table 1. The Raman spectra of the graphite fibers in each example and the comparative example were measured, and the I D / I G values were calculated, and the results are shown in Table 1.

[0092] 2. The in-plane and out-of-plane thermal conductivities of the materials in each example and the comparative example were measured according to the ASTM-E1461-131 test standard, and the results are shown in Table 1.

[0093] Table 1

[0094]

[0095] As can be seen from the data in Table 1, the composite graphene film provided by the examples of the present application still has high in-plane and out-of-plane thermal conductivities at a large thickness, and can achieve a high heat flux.

[0096] The above describes exemplary embodiments of the present application. It should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements are also considered to be within the scope of protection of the present application.

Claims

1. A method for preparing a composite graphene film, characterized in that, Includes the following steps: (1) The composite graphite fiber precursor and graphene oxide are added to a solvent and mixed thoroughly to obtain a dispersion; wherein the composite graphite fiber precursor includes a spinnable carbon source and a two-dimensional layered material; the spinnable carbon source includes at least one of polyimide, polyacrylonitrile and pitch; the two-dimensional layered material includes at least one of boron nitride, carbon nitride, black phosphorus and Mxene; (2) The dispersion is prepared into a composite graphene membrane precursor, wherein the composite graphene membrane precursor includes a three-dimensional network structure formed by the composite graphite fiber precursor and the graphene oxide. (3) The composite graphene film precursor is heated to form graphite fibers from the composite graphite fiber precursor and graphene oxide from graphene oxide, thereby obtaining a composite graphene film.

2. The preparation method according to claim 1, characterized in that, The thickness of the composite graphene film precursor is in the range of 190 μm to 400 μm.

3. The preparation method according to claim 1, characterized in that, In the composite graphite fiber precursor, the mass ratio of the two-dimensional layered material to the spinnable carbon source is 1:(100-1000).

4. The preparation method according to claim 1, characterized in that, In the dispersion, the mass ratio of the composite graphite fiber precursor to the graphene oxide is 1:(4-20).

5. The preparation method according to claim 1, characterized in that, In step (3), the heating conditions are: under a protective atmosphere, the temperature is maintained at 2500°C-3200°C for 0.5h-1.5h.

6. The preparation method according to claim 1, characterized in that, Step (1) also includes adding a foaming material to the dispersion; the foaming material includes calcium carbonate.

7. A composite graphene film, characterized in that, The composite graphene was prepared using the method described in any one of claims 1-6.

8. The composite graphene film according to claim 7, characterized in that, The composite graphene film comprises graphene and graphite fibers; at least some of the graphite fibers are interwoven with at least some of the graphene to form a three-dimensional network structure; the thickness of the composite graphene film is in the range of 130 μm-250 μm, the in-plane thermal conductivity of the composite graphene film is in the range of 1400 W / (m·k)-2000 W / (m·k), and the out-of-plane thermal conductivity of the composite graphene film is in the range of 5 W / (m·k)-12.5 W / (m·k).

9. The composite graphene film according to claim 8, characterized in that, The Raman spectrum of the composite graphene film I D / I G The value is in the range of 0.01-0.

1.

10. The composite graphene film according to claim 8, characterized in that, The Raman spectrum of the graphite fiber I D / I G The value is in the range of 0.01-0.

1.

11. The application of a composite graphene film prepared by the preparation method according to any one of claims 1-6 or the composite graphene film according to any one of claims 7-10 in thermally conductive materials.

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