A preparation method and application of high vertical thermal conductivity graphene film

Abstract

The present invention proposes a method for preparing a high vertical thermal conductivity graphene film, which utilizes the internal defects of graphene oxide nanosheets to achieve carbon-carbon interlayer crosslinking at high temperature, builds a phonon transmission bridge between layers in the vertical direction, and thereby gives the graphene film excellent vertical thermal conductivity; in addition, due to the formation of interlayer covalent bonds, the electron transmission and shear resistance between graphene layers are also greatly improved, showing application potential in high thermal management fields such as high-power electronic components and high-power devices.

Description

Technical Field

[0001] The invention belongs to the technical field of functional materials, and specifically relates to a preparation method of a high vertical thermal conductive graphene film and application thereof. Background Art

[0002] Graphene is a two-dimensional crystal with a single atomic layer thickness composed of carbon atoms peeled off from graphite material. Graphene in a narrow sense refers to a single layer of graphite with a thickness of 0.335nm and only one layer of carbon atoms. Perfect graphene has an ideal two-dimensional crystal structure composed of a hexagonal lattice. Graphene has extremely strong thermal conductivity. The thermal conductivity of a single layer of graphene can reach 5000W / mK, which is 3 times that of pure diamond at room temperature and 12 times that of metallic copper. Graphene thermal conductive film is a heat dissipation film material obtained by macroscopic assembly of graphene oxide and high-temperature graphitization treatment. In the horizontal direction, the thermal conductivity of graphene can reach 1300~2000W / mK. The high thermal conductivity of graphene film makes it an ideal alternative material to traditional graphite heat dissipation film. It is widely used in heat dissipation of smart phones, tablets, high-power energy-saving LED lighting, ultra-thin LCD TVs, etc.

[0003] The high efficiency of heat transfer in graphene thermal conductive film is brought about by the strong sp2 bond connection in the graphene sheets. However, since there is only van der Waals force between the graphene film layers, the phonon transmission speed of the large π bond between the sheets is much lower than that of the chemical bond, resulting in low vertical thermal conductivity between the layers, and the thermal conductivity coefficient is only 5-20W / mK, which is about two orders of magnitude lower than the horizontal thermal conductivity. The van der Waals force between π bonds is lower than that of covalent bonds, so it is difficult to achieve the conversion between the two. Therefore, the low thermal conductivity of graphene thermal conductive film in the vertical direction has become a bottleneck restricting the development of thermal management materials, limiting its application in many high-power devices and other fields. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a high vertical thermal conductivity graphene film material with a vertical thermal conductivity of more than 10W / mK. The present invention controls the activation temperature to adjust the defects in the graphene oxide sheet to achieve interlayer crosslinking, thereby achieving high thermal conductivity of graphene in the vertical direction, solving the thermal conductivity shortcoming of anisotropic high thermal conductivity carbon materials such as graphene in the vertical direction; at the same time, the development of high vertical thermal conductivity graphene materials also provides more ways for heat dissipation, thereby meeting the urgent need for efficient and rapid heat dissipation in the field of thermal management.

[0005] Specifically, the technical solution of the present application is: a method for preparing a high vertical thermal conductivity graphene film, which comprises the following steps: wet assembling graphene oxide nanosheets to form a film, drying, and then high temperature carbon activation at 1600-2000 degrees Celsius for 30-240 minutes; while reducing the graphene oxide, the upper and lower graphene oxide nanosheets are cross-linked at the defects. In the temperature range of 1600-2000°C, the defects between the graphene oxide film sheets are activated, and chemical cross-linking is easily generated between the defects, which provides an efficient path for the transmission of phonons, thereby exhibiting a higher vertical thermal conductivity. When the high-temperature treatment temperature reaches above 2000℃, the graphene oxide is fully graphitized to form a three-dimensional graphite crystal. The single-layer graphite layers are connected in the form of non-covalent bonds, resulting in intense interlayer phonon scattering and low vertical thermal conductivity. When the heat treatment temperature is lower than 1600℃, there are a large number of internal defects between the layers of the graphene oxide film. Since the reaction thermodynamic energy at this time is reduced and the reaction activation energy between defects is not reached, phonons are easily captured by defect sites when transmitted in the vertical direction, resulting in extremely low vertical thermal conductivity.

[0006] In some embodiments of the present invention, the graphene oxide nanosheets have a thickness of less than 5 nm and a size ranging from 1 to 30 um. The smaller the size of the graphene oxide, the more edge defects can be exposed.

[0007] In some embodiments of the present invention, the edge defects are increased by reducing the size of the graphene oxide nanosheets to promote the interlayer crosslinking. For example, the size of the graphene oxide nanosheets is reduced by ultrasound, mechanical shearing, etc.

[0008] In certain embodiments of the present invention, the graphene oxide nanosheets are etched to increase the internal defects of the graphene nanosheets, thereby promoting the interlayer crosslinking. For example, etching is performed using hydrogen peroxide or potassium hydroxide. Specifically, the method is: mixing a graphene oxide suspension with a hydrogen peroxide or potassium hydroxide solution, and heating the mixture to react to prepare defects of different contents inside the sheet.

[0009] The present invention also relates to the application of the high vertical thermal conductivity graphene film prepared by the above method in the fields of electronic devices, heat pipe systems, high-temperature thermal protection, etc.

[0010] The beneficial effects of the present invention are:

[0011] (1) By controlling the heat treatment of graphene oxide, an sp2 covalent cross-linked structure is formed between the layers, providing a new development direction for the development of new graphene carbon materials.

[0012] (2) The existence of the interlayer cross-linking structure greatly improves the transmission of phonons in the vertical direction, enhances the vertical thermal conductivity of the graphene film, and further significantly improves the heat dissipation capacity of the graphene film, showing great development potential in the field of thermal management. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a spherical aberration electron microscope image of the interlayer cross-linked graphene film material. DETAILED DESCRIPTION

[0014] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0015] Example 1

[0016] The thickness is 2-5 nm, the average size is 20 μm, and the concentration is 10 mg / cm 3 A 1% hydrogen peroxide solution was added to the graphene oxide solution, and the mixture was heated at 60°C for 4 hours. After the reaction was completed, the graphene oxide solution was scraped and dried to form a film. The film was then heat treated at 1600°C for 4 hours. After the temperature was lowered, a graphene film material with high vertical thermal conductivity was obtained. Figure 1 It can be seen from the spherical aberration electron microscope image that in the graphene film, the graphene layers are sp2 covalently cross-linked. Further measurement shows that the vertical thermal conductivity of the graphene film is 20W / mK.

[0017] Example 2

[0018] The thickness is 2-5 nm, the average size is 20 μm, and the concentration is 10 mg / cm 3 A 1% by mass hydrogen peroxide solution was added to the graphene oxide solution, and the reaction was heated at 60°C for 4 hours. After the reaction was completed, the graphene oxide solution was scraped and dried to form a film. The film was then heat treated at 2000°C for 1 hour. After cooling, a graphene film material with high vertical thermal conductivity was obtained, wherein the vertical thermal conductivity of the graphene film was 35W / mK.

[0019] Example 3

[0020] The thickness is 2-5nm, the average size is 30um, and the concentration is 10mg / cm 3 1% potassium hydroxide by mass was added to the graphene oxide solution, and the reaction was heated at 60°C for 4 hours. After the reaction was completed, the graphene oxide solution was scraped and dried to form a film. The film was then heat treated at 1600°C for 30 minutes. After cooling, a graphene film material with high vertical thermal conductivity was obtained, wherein the vertical thermal conductivity of the graphene film was 17W / mK.

[0021] Example 4

[0022] The thickness is 2-5nm, the average size is 1um, and the concentration is 10mg / cm 3 The graphene oxide solution was scraped and dried to form a film, and then the film was heat treated at 1600°C for 4 hours. After cooling, a graphene film material with high vertical thermal conductivity was obtained, wherein the vertical thermal conductivity of the graphene film was 14.5W / mK.

[0023] Example 5

[0024] The thickness is 2-5 nm, the average size is 20 μm, and the concentration is 10 mg / cm 3 The graphene oxide solution was subjected to 300W ultrasonic treatment for 12 hours, then it was scraped and dried to form a film, and then the film was heat treated at 2000℃ for 4 hours. After cooling, a graphene film material with high vertical thermal conductivity was obtained, wherein the vertical thermal conductivity of the graphene film was 22.8W / mK.

[0025] Comparative Example 1

[0026] The thickness is 2-5 nm, the average size is 20 μm, and the concentration is 10 mg / cm 3 The graphene oxide solution was directly scraped and dried to form a film, and then the film was heat treated at 1600°C for 4 hours. After cooling, the graphene film material was obtained, and the vertical thermal conductivity was only 3.2W / mK.

[0027] Comparative Example 2

[0028] The thickness is 2-5 nm, the average size is 20 μm, and the concentration is 10 mg / cm 3 The graphene oxide solution was directly scraped and dried to form a film, and then the film was heat treated at 2000°C for 4 hours. After cooling, the graphene film material was obtained, and the vertical thermal conductivity was only 7.5W / mK.

[0029] Comparative Example 3

[0030] The thickness is 2-5 nm, the average size is 20 μm, and the concentration is 10 mg / cm 3 A 1% by mass hydrogen peroxide solution was added to the graphene oxide solution, and the reaction was heated at 60°C for 4 hours. After the reaction was completed, the graphene oxide solution was scraped and dried to form a film. The film was then heat treated at 2800°C for 4 hours. After cooling, the vertical thermal conductivity of the graphene film obtained was 8W / mK.

[0031] Comparative Example 4

[0032] The thickness is 2-5 nm, the average size is 20 μm, and the concentration is 10 mg / cm 3 A 1% by mass hydrogen peroxide solution was added to the graphene oxide solution, and the reaction was heated at 60°C for 4 hours. After the reaction was completed, the graphene oxide solution was scraped and dried to form a film. The film was then heat treated at 1000°C for 4 hours. After cooling, the vertical thermal conductivity of the graphene film obtained was 5W / mK.

[0033] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a high vertical thermal conductivity graphene film, wherein the vertical thermal conductivity of the graphene film is above 10 W / mK; characterized in that: The method comprises the following steps: assembling graphene oxide nanosheets by wet method, and after drying, performing high temperature carbon activation at 1600-2000 degrees Celsius for 30-240 minutes, so that the upper and lower graphene oxide nanosheets are cross-linked at the defects to obtain a high vertical thermal conductive graphene film; The graphene oxide nanosheets are etched with hydrogen peroxide or potassium hydroxide to increase internal defects of the graphene nanosheets and promote the interlayer crosslinking.

2. The method for preparing a high vertical thermal conductive graphene film according to claim 1, characterized in that: The graphene oxide nanosheet has a thickness of less than 5 nm.

3. The method for preparing a high vertical thermal conductive graphene film according to claim 1, characterized in that: The edge defects are increased by reducing the size of the graphene oxide nanosheets, promoting the interlayer cross-linking.

4. The method for preparing a high vertical thermal conductive graphene film according to claim 3, characterized in that: The size of the graphene oxide nanosheets is reduced by ultrasound or mechanical shearing.

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