All-carbon elastic thermal interface material with multilevel structure and preparation method of all-carbon elastic thermal interface material

Abstract

The invention discloses an all-carbon elastic thermal interface material with a multilevel structure and a preparation method of the all-carbon elastic thermal interface material, which are characterized in that a mixture of graphene oxide and a polymer in different mass ratios and PVA which can be decomposed under a heating condition are subjected to centrifugal spin coating and multilayer overlapping to obtain a composite film, and then the composite film is subjected to heat treatment to obtain graphene aerogel. And then slicing the aerogel, carrying out plasma etching on the slices to etch off the low-graphitized graphene layer on the surface of the material, and further carrying out hot pressing to obtain the all-carbon elastic thermal interface material with the multilevel structure. The thermal interface material prepared by the method has relatively high elasticity, does not contain polymers, has relatively good weather resistance and cannot be stiff and aged after working for a long time, so that the performance of the material is greatly improved, and the service life of the material is greatly prolonged.

Description

Technical Field

[0001] The present invention belongs to the field of thermal interface materials, and in particular relates to a multi-level structured all-carbon elastic thermal interface material and a preparation method thereof. Background Art

[0002] With the continuous advancement of electronic information technology, the improvement of computer performance, and the emergence of new products such as wearable devices, the functional integration of CPUs continues to increase, and a trend towards miniaturization is emerging. This trend has led to a gradual reduction in the heat dissipation space of electronic devices, while the heat generated continues to increase, and the demand for heat dissipation is increasing. Traditional thermal interface materials, such as silicone grease, are gradually unable to meet the heat dissipation requirements of high-performance chips, becoming a major issue restricting the development of high-performance chips. In addition, thermal interface materials have broad application prospects in 5G, consumer electronics, automotive electronics, wearable devices, the Internet of Things, and other fields.

[0003] Graphene is a two-dimensional carbon nanomaterial with extremely high electron mobility and thermal conductivity. Graphene's thermal conductivity is much higher than that of traditional thermally conductive materials such as copper and silicone grease, making it an ideal choice for the preparation of high-performance thermal interface materials. Graphene-based thermal interface materials primarily use graphene as a thermally conductive skeleton and fillers such as epoxy resin, silicone oil, silicone rubber, and polyurethane as an elastic matrix. Through a specific preparation process, a vertically oriented thermal interface structure is created. Preparation methods include wrinkle orientation and stacking. After vertically aligning the graphene, a polymer filler is introduced to provide elasticity to the carbon material skeleton and to fill the surface roughness of the chip and heat sink.

[0004] Despite the significant performance advantages and application prospects of graphene-based thermal interface materials, their research and application still face some challenges. Existing carbon-based thermal interface materials still rely on polymers as a source of elasticity. However, polymers have poor weather resistance and become rigid and aged after prolonged operation, significantly reducing material performance and service life. Summary of the Invention

[0005] In response to the problem that current graphene-based thermal interface materials inevitably rely on polymers to provide elasticity, which leads to the problem that thermal interface materials are prone to aging, the present invention proposes a multi-level structured all-carbon elastic thermal interface material and a preparation method thereof. Compared with existing polymer thermal interface materials, the lifespan of the all-carbon elastic thermal interface material of the present invention is increased by more than three times. On the basis of solving the aging problem, through structural optimization, it also overcomes the contradictions of high density and high thermal conductivity, warping structure adaptability and low elastic modulus of thermal interface materials, which is of great significance for promoting the industrial application of all-carbon thermal interface materials.

[0006] The all-carbon elastic thermal interface material of the present invention is composed of highly graphitized graphene layers and low-graphitized graphene layers alternately stacked in a horizontal direction, with a density of 0.3-0.7 g / cm 3 The highly graphitized graphene layer includes a continuous first fold structure formed in the middle and skin structures formed at the upper and lower ends. The low-graphitized graphene layer includes only a second fold structure formed in the middle and nested with the first fold structure. The first and second fold structures form the main layer of the thermal interface material of the present application. The fold structure is Σ-shaped.

[0007] The highly graphitized graphene layer is formed by continuously overlapping highly graphitized graphene sheets, and the low graphitized graphene layer is formed by continuously overlapping low graphitized graphene sheets. High graphitization means a graphitization degree of >96%, and low graphitization means a graphitization degree of 75-90%. The density of the interface material of the present invention is 0.7-1g / cm 3 The highly graphitized graphene layers and the low graphite layers are continuous in the vertical direction, which can achieve vertical thermal conductivity, and the contact thermal resistance can reach 0.03. The continuous bending structure and the nested structure of high and low graphitization successfully solve the problem of excessively high elastic modulus of high-density and high-thermal conductivity interface materials; in addition, the aerogel structure of high and low graphitized layers, the flexibility of a large number of SP3 structures inside the low graphitized graphene structure, and the excellent flexibility and lubricity of the highly graphitized part of the cortex can provide elasticity for the material to achieve adaptive filling of the warping structure and friction microstructure, effectively reducing the contact thermal resistance.

[0008] The thickness of the full-carbon elastic thermal interface material of the present invention is generally 0.2-0.5 mm, wherein the thickness of the skin layer is 1-5 μm.

[0009] To construct the aforementioned high-density, high-thermal-conductivity, warpage-adaptive, and low-elastic-modulus thermal interface material, the present invention introduces a roller to create a highly oriented, alternating stack of high and low graphitized layers. Furthermore, a PVA layer is introduced to create a gas escape channel, preventing the high and low graphitized layers from peeling off due to gas expansion during heat treatment. Finally, precise hot pressing is used to release pressure and create a continuously flexing structure. Specifically, the present invention includes the following steps: (1) Using a roller centrifugal spin coating method, the coating is dripped into a horizontally arranged centrifugal roller, and under the action of centrifugal force, a first composite layer with a thickness of 20-80nm, a second composite layer with a thickness of 5-10nm, and a PVA layer with a thickness of 5-50nm are successively spin-coated on the inner wall of the centrifugal roller in sequence; the coating of the first composite layer is composed of a mixture of graphene oxide and polymer in a mass ratio of 3:7-8:2, and the coating of the second composite layer is composed of a mixture of graphene oxide and polymer in a mass ratio of 1:10-2:8; the polymer is one or more of polyacrylonitrile, polyimide, furan resin, phenolic resin, and lignin; wherein the first composite layer is used to prepare a high thermal conductivity skeleton, and graphene with a high graphitization (>96%) can be obtained at high temperature. The second composite layer is used to prepare a high thermal conductivity elastic structure, and graphene with a relatively low graphitization degree of 75-90% can be obtained at high temperature. The use of the centrifugal spin coating method can make the prepared graphene have orientation, and the orientation structure will increase the orderliness of the molecular arrangement, promote the directional fusion of molecules, and increase the graphitization degree. Nano-thick, highly graphitized carbon materials become more slippery due to the weakening of interlayer interactions, thus exhibiting flexibility. As the degree of graphitization decreases, the interlayer interactions strengthen, and the material exhibits elasticity.

[0010] (2) Repeat step 1 multiple times to obtain a composite film consisting of a first composite layer, a second composite layer, and a PVA layer stacked alternately.

[0011] (3) The composite film is hot-pressed in a nitrogen environment at 270-300°C with a pressure of 1-5 MPa, and then heat-treated in an argon atmosphere at 2700-3000°C in a confined space to obtain graphene aerogel with a density of 0.2-0.5 g / cm 3 Among them, the polymer and PVA layers are completely decomposed at a subsequent high temperature. During the decomposition of PVA, a gas escape channel is created, which can inhibit the delamination of structural units and enable the macroscopic material to form an arched airbag structure.

[0012] (4) Slice the graphene aerogel perpendicular to the graphene orientation direction to a thickness of 0.2-0.5 mm.

[0013] (5) The upper and lower surfaces of the slice are treated with plasma to first expose the uniform vertically oriented graphene structure, and then the low-graphitized graphene on the upper and lower surfaces of the slice is etched away to form a cortex consisting of a highly graphitized layer.

[0014] (6) Placing the slices after plasma treatment in an argon environment and sintering them at a high temperature of 2000-3000°C; the surface of the graphene treated by plasma is damaged, and it can be repaired by high-temperature sintering.

[0015] (7) The treated slices are pressed at a pressure of 0.2-2 MPa for 2-20 seconds. The density of the obtained product is 0.7-1 g / cm 3 The highly graphitized layer of the cortex changes from a vertical direction to a horizontal direction, and the high and low graphitized layers of the main layer form a mutually nested bending structure.

[0016] The third technical solution of the present invention is to provide another method for preparing a multi-level structured all-carbon elastic thermal interface material: (1) The coating is dripped into a horizontally arranged centrifugal drum by using a drum centrifugal spin coating method, and a first composite layer of 2-5 nm, a second composite layer of 20-80 nm, a third composite layer of 2-5 nm and a PVA layer of 5-50 nm are successively spin-coated on the inner wall of the centrifugal drum under the action of centrifugal force; the coating of the first composite layer is formed by a mixture of graphene oxide and polymer in a mass ratio of 1:10-3:7, the coating of the second composite layer is formed by a mixture of graphene oxide and polymer in a mass ratio of 3:7-8:2; the coating of the third composite layer is formed by a mixture of graphene oxide and polymer in a mass ratio of 1:10-2:8, and the polymer is one or more of polyacrylonitrile, polyimide, furan resin, phenolic resin and lignin.

[0017] (2) Repeat step 1 multiple times until the thickness reaches the product requirements, and obtain a composite film consisting of the first composite layer, the second composite layer, the third composite layer, and the PVA layer stacked alternately.

[0018] (3) The composite film is hot-pressed in a nitrogen environment at 270-300°C with a pressure of 1-5 MPa, and then heat-treated in an argon atmosphere at 2700-3000°C in a confined space to obtain a graphene aerogel with a density of 0.2-0.5 g / cm 3 .

[0019] (4) Slice the graphene aerogel perpendicular to the graphene orientation direction to a thickness of 0.2-0.5 mm.

[0020] (5) The upper and lower surfaces of the slice are treated with plasma to first expose the uniform vertically oriented graphene structure, and then the low-graphitized graphene on the upper and lower surfaces of the slice is etched away to form a cortex consisting of a highly graphitized layer.

[0021] (6) Place the slices after plasma treatment in an argon environment and sinter at a high temperature of 2000-3000℃; plasma treatment will damage the surface structure of the material, which needs to be repaired by high temperature.

[0022] (7) The treated slices are pressed at a pressure of 0.2-5 MPa for 2-20 seconds. The density of the obtained product is 0.7-1 g / cm 3The high graphitization layer of the cortex changes from a vertical direction to a horizontal direction, and the high and low graphitization layers of the main layer form a nested bending structure.

[0023] In the preparation process of the above two thermal interface materials, continuous spin coating means: after the first coating is sprayed, the second coating is sprayed immediately. As a result, the second coating is compounded before the first coating is completely dry, and the two coatings are effectively fused, which is conducive to a continuous heat conduction channel.

[0024] During the preparation of the two thermal interface materials, the low-graphitization material, due to its greater number of defects, disordered regions, and dangling bonds, exhibits a more active surface and readily reacts with active species in the plasma. In contrast, the highly graphitized material, due to its structure closer to the ideal graphite lattice, exhibits greater chemical and thermal stability and is less susceptible to reactions with active species in the plasma, such as ions and free radicals. Furthermore, the highly graphitized material has better conductivity, effectively shielding the plasma from the effects, thereby reducing the etching rate. However, the low-graphitized material, due to its poorer conductivity, is more susceptible to the plasma etching process. Therefore, during the plasma treatment in step 5, the low-graphitized material generally exhibits faster etching rates and greater etching selectivity than the highly graphitized material. During plasma etching, the highly graphitized layer is less etched, while the low-graphitized layer is more etched, forming a cortex layer where portions of the highly graphitized graphene sheets extend upward and downward. The graphene density in the cortex layer is reduced by half, increasing flexibility and gap-filling capability.

[0025] In the preparation process of the above two thermal interface materials, the slicing method is one of laser etching slicing and wire cutting slicing.

[0026] Beneficial effects of the present invention: (1) This material does not have polymer to provide elasticity, and the thermal interface life is increased by more than three times; (2) The design of the skin-core structure inside the structural unit provides good support, elasticity and filling properties without affecting the heat conduction path; (3) The density of the thermal interface skin is lower than that of the middle layer, and only the part with a high degree of graphitization is retained. It has good flexibility, lubricity and filling performance, which greatly reduces the contact thermal resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a physical diagram of the present invention.

[0028] Figure 2 This is a schematic diagram of the effect of step 6 of the present invention.

[0029] Figure 3 (a) is a SEM image of the cross section of Example 1, Figure 3 (b) is a SEM image of the upper surface of Example 1.

[0030] Figure 4 This is a partial enlarged view of Example 1.

[0031] Figure 5 is the compressive strain after multiple stress cycles of Example 1. DETAILED DESCRIPTION

[0032] The following examples are used to further illustrate the present invention. Their purpose is to illustrate the present invention and should not be construed as limiting the scope of the present invention. Unless otherwise specified, all references are by weight and weight percentage.

[0033] Unless otherwise specified, the raw materials used in the present invention are conventional commercial products; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0034] The roller centrifugal spin coating described in the present invention can refer to the prior art such as 202410407489.8.

[0035] The contact thermal resistance of the present invention is tested by a TIM-Tester thermal interface material testing system.

[0036] The embodiments of the present invention are further described below with reference to a number of embodiments.

[0037] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0038] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0039] Example 1 (1) Graphene oxide and polyacrylonitrile were mixed in a mass ratio of 3:7 to obtain a first coating; graphene oxide and polyacrylonitrile were mixed in a mass ratio of 1:10 to obtain a second coating. PVA was dispersed in deionized water to prepare a third coating with a mass fraction of 1%.

[0040] (2) The first coating, the second coating, and the third coating are continuously dripped into a horizontally arranged centrifugal drum, and the dosage of each injection is controlled. Under the action of centrifugal force, a 20 nm first composite layer, a 10 nm second composite layer, and a 5 nm PVA layer are formed on the inner wall of the centrifugal drum in sequence.

[0041] (3) Repeat step 2 several times to obtain a 2 cm thick composite film.

[0042] (4) The composite membrane was hot pressed in a nitrogen environment at 270°C (pressure 1 MPa), and then heat treated in an argon environment at 2700°C in a confined space to obtain a 5 cm thick membrane with a density of 0.25 g / cm 3 of graphene aerogel.

[0043] (5) Slice the graphene aerogel into slices with a thickness of 0.2 mm.

[0044] (6) Plasma is used to treat the upper and lower surfaces of the slice to first expose the uniform vertically oriented graphene structure, and then the low-graphitized graphene on the upper and lower surfaces of the slice is etched away to form a cortex consisting of a highly graphitized layer.

[0045] (7) Place the slices after plasma treatment in an argon environment and sinter at a high temperature of 3000°C; (8) The processed slices were pressed at a pressure of 0.2 MPa for 20 seconds.

[0046] The overall thickness of the obtained interface material is 0.17 mm and the density is 0.8 g / cm 3 ; Its cross-sectional and surface diagrams are as follows Figure 3 As shown, from Figure 3 As can be seen in the figure, the central main layer has a continuous Σ-shaped kink structure. Based on the composite structure, we can determine that it is a nested kink structure formed by a first kink structure formed by a highly graphitized graphene layer and a second kink structure formed by a less graphitized graphene layer. The skin layer is approximately 4μm thick and extends primarily horizontally. It is formed by the highly graphitized graphene layer under pressure.

[0047] Figure 4 This is a local enlarged view of the bending position. It can be seen that under the action of micro-pressure, the graphene only delaminates without breaking, and the elastic modulus is released while ensuring a continuous heat conduction path.

[0048] According to tests, the contact thermal resistance of this embodiment is 0.06K·cm2 / W, the service life can reach 3000 hours, and the strain recovery is still perfect after multiple cycles. The material has good elasticity and stability.

[0049] Example 2 (1) Graphene oxide and polyimide in a mass ratio of 8:2 were mixed evenly to obtain a first coating; graphene oxide and polyimide in a mass ratio of 2:8 were mixed evenly to obtain a second coating; and PVA was dispersed in deionized water to prepare a third coating with a mass fraction of 1%.

[0050] (2) The first coating, the second coating, and the third coating are continuously dripped into a horizontally arranged centrifugal drum, and the dosage of each injection is controlled. Under the action of centrifugal force, a first composite layer of 80 nm, a second composite layer of 5 nm, and a PVA layer of 50 nm are formed on the inner wall of the centrifugal drum in sequence.

[0051] (3) Repeat step 2 several times to obtain a composite film with a thickness of 1.2 cm.

[0052] (4) The composite membrane was hot pressed in a nitrogen environment at 300 °C (pressure 5 MPa), and then heat treated in an argon environment at 3000 °C in a confined space to obtain a 4 cm thick membrane with a density of 0.2 g / cm 3 graphene aerogel.

[0053] (5) Slice the graphene aerogel into slices with a thickness of 0.5 mm.

[0054] (6) Plasma is used to treat the upper and lower surfaces of the slice to first expose the uniform vertically oriented graphene structure, and then the low-graphitized graphene on the upper and lower surfaces of the slice is etched away to form a cortex consisting of a highly graphitized layer.

[0055] (7) Place the slices after plasma treatment in an argon environment and sinter at a high temperature of 2000°C; (8) The processed slices were pressed at a pressure of 4 MPa for 20 seconds. The high graphitized layer of the cortex changed from vertical to horizontal, and the high and low graphitized layers of the main layer formed a mutually nested bending structure. The overall thickness of the material was 0.37 mm and the density was 1 g / cm 3 , the cortex thickness is about 3μm.

[0056] According to tests, the contact thermal resistance of this embodiment is 0.1K·cm2 / W and the service life exceeds 3000 hours.

[0057] Example 3 (1) Graphene oxide and furan resin in a mass ratio of 1:10 were mixed evenly to obtain a first coating; graphene oxide and furan resin in a mass ratio of 3:7 were mixed evenly to obtain a second coating; graphene oxide and phenolic resin in a mass ratio of 1:10 were mixed evenly to obtain a third coating; PVA was dispersed in deionized water to prepare a fourth coating with a mass fraction of 1%.

[0058] (2) The first coating, the second coating, the third coating, and the fourth coating are continuously dripped into a horizontally arranged centrifugal drum, and the dosage of each injection is controlled. Under the action of centrifugal force, a first composite layer of 2 nm, a second composite layer of 20 nm, a third composite layer of 2 nm, and a PVA layer of 5 nm are formed on the inner wall of the centrifugal drum in sequence.

[0059] (3) Repeat step 2 to obtain a 3 cm thick composite film.

[0060] (4) The composite membrane was hot pressed in a nitrogen environment at 270°C (pressure 1 MPa), and then heat treated in an argon environment at 2700°C in a confined space to obtain a 4 cm thick membrane with a density of 0.5 g / cm 3 of graphene aerogel.

[0061] (5) Slice the graphene aerogel into slices with a thickness of 0.4 mm.

[0062] (6) Plasma is used to treat the upper and lower surfaces of the slice to first expose the uniform vertically oriented graphene structure, and then the low-graphitized graphene on the upper and lower surfaces of the slice is etched away to form a cortex consisting of a highly graphitized layer.

[0063] (7) Place the slices after plasma treatment in an argon environment and sinter at a high temperature of 2500°C; (8) The processed slices were pressed at a pressure of 3 MPa for 15 seconds. The high graphitized layer of the cortex changed from vertical to horizontal, and the high and low graphitized layers of the main layer formed a mutually nested bending structure. The overall thickness of the material was 0.28 mm and the density was 0.7 g / cm 3 , the cortex thickness is about 5μm.

[0064] According to tests, the contact thermal resistance of this embodiment is 0.04K·cm2 / W and the service life exceeds 3000 hours.

[0065] Example 4 (1) Graphene oxide and lignin in a mass ratio of 3:7 were mixed evenly to obtain a first coating; graphene oxide and lignin in a mass ratio of 8:2 were mixed evenly to obtain a second coating; graphene oxide and polyimide in a mass ratio of 2:8 were mixed evenly to obtain a third coating; PVA was dispersed in deionized water to prepare a fourth coating with a mass fraction of 1%.

[0066] (2) The first coating, the second coating, the third coating, and the fourth coating are continuously dripped into a horizontally arranged centrifugal drum, and the dosage of each injection is controlled. Under the action of centrifugal force, a first composite layer of 5 nm, a second composite layer of 80 nm, a third composite layer of 5 nm, and a PVA layer of 50 nm are formed on the inner wall of the centrifugal drum in sequence.

[0067] (3) Repeat step 2 to obtain a composite film with a thickness of 2.15 cm.

[0068] (4) The composite membrane was hot pressed in a nitrogen environment at 300 °C (pressure 5 MPa), and then heat treated in an argon environment at 3000 °C in a confined space to obtain a 5 cm thick membrane with a density of 0.3 g / cm 3 of graphene aerogel.

[0069] (5) Slice the graphene aerogel into slices with a thickness of 0.5 mm.

[0070] (6) Plasma is used to treat the upper and lower surfaces of the slice to first expose the uniform vertically oriented graphene structure, and then the low-graphitized graphene on the upper and lower surfaces of the slice is etched away to form a cortex consisting of a highly graphitized layer.

[0071] (7) Place the slices after plasma treatment in an argon environment and sinter at a high temperature of 2000°C; (8) The treated slices were pressed at a pressure of 5 MPa for 20 seconds. The high graphitized layer of the cortex changed from vertical to horizontal, and the high and low graphitized layers of the main layer formed a mutually nested bending structure. The overall thickness of the material was 0.3 mm and the density was 0.7 g / cm 3 , the cortex thickness is about 1μm.

[0072] According to tests, the contact thermal resistance of this embodiment is 0.05K·cm2 / W and the service life exceeds 3000 hours.

[0073] The above embodiments describe in detail the structure, features and effects of the present invention. The above are only preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which do not exceed the scope covered by the specification, should be within the scope of protection of the present invention.

Claims

1. A multi-level all-carbon elastic thermal interface material, characterized in that: It is composed of highly graphitized graphene layers and low-graphitized graphene layers stacked alternately in the horizontal direction, with a density of 0.3-0.7g / cm 3 ; The highly graphitized graphene layer includes a continuous first bending structure formed in the middle and a cortical structure formed at the upper and lower ends; the low graphitized graphene layer only includes a second bending structure formed in the middle and nested with the first bending structure; the first bending structure and the second bending structure form the main layer of the thermal interface material; the bending structure is Σ-shaped; the highly graphitized graphene layer is formed by continuously overlapping highly graphitized graphene sheets, and the low graphitized graphene layer is formed by continuously overlapping low graphitized graphene sheets, high graphitization means a graphitization degree >96%, and low graphitization means a graphitization degree of 75-90%.

2. The all-carbon elastic thermal interface material according to claim 1, characterized in that: The thickness of the cortex is 1-5 μm.

3. A method for preparing a multi-level structured all-carbon elastic thermal interface material, characterized in that: The following steps are involved: (1) Using a roller centrifugal spin coating method, the coating is dripped into a horizontally arranged centrifugal roller, and under the action of centrifugal force, a first composite layer with a thickness of 20-80 nm, a second composite layer with a thickness of 5-10 nm, and a PVA layer with a thickness of 5-50 nm are successively spin-coated on the inner wall of the centrifugal roller; the coating of the first composite layer is composed of a mixture of graphene oxide and a polymer in a mass ratio of 3:7-8:2, and the coating of the second composite layer is composed of a mixture of graphene oxide and a polymer in a mass ratio of 1:10-2:8; the polymer is one or more of polyacrylonitrile, polyimide, furan resin, phenolic resin, and lignin; (2) Repeating step 1 multiple times to obtain a composite film consisting of a first composite layer, a second composite layer, and a PVA layer alternately stacked; (3) The composite film was hot-pressed in a nitrogen environment at 270-300°C, and then heat-treated in an argon atmosphere at 2700-3000°C in a confined space to obtain a graphene aerogel with a density of 0.2-0.5 g / cm 3 ; (4) Slicing the graphene aerogel perpendicular to the graphene orientation direction to a thickness of 0.2-0.5 mm; (5) Plasma treatment of the upper and lower surfaces of the slice first exposes a uniform vertically oriented graphene structure, and then etches away the low-graphitized graphene on the upper and lower surfaces of the slice to form a cortex consisting of a highly graphitized layer; (6) Place the slices after plasma treatment in an argon environment and sinter at a high temperature of 2000-3000℃; (7) The treated slices are pressed at a pressure of 0.2-2 MPa for 2-20 seconds. The density of the obtained product is 0.7-1 g / cm 3 .

4. A method for preparing a multi-level structured all-carbon elastic thermal interface material, characterized in that: The following steps are involved: (1) Using a roller centrifugal spin coating method, the coating is dripped into a horizontally arranged centrifugal roller, and under the action of centrifugal force, a first composite layer of 2-5 nm, a second composite layer of 20-80 nm, a third composite layer of 2-5 nm, and a PVA layer of 5-50 nm are successively spin-coated on the inner wall of the centrifugal roller in sequence; the coating of the first composite layer is composed of a mixture of graphene oxide and a polymer in a mass ratio of 1:10-3:7, the coating of the second composite layer is composed of a mixture of graphene oxide and a polymer in a mass ratio of 3:7-8:2; the coating of the third composite layer is composed of a mixture of graphene oxide and a polymer in a mass ratio of 1:10-2:8, and the polymer is one or more of polyacrylonitrile, polyimide, furan resin, phenolic resin, and lignin; (2) Repeating step 1 multiple times to obtain a composite film consisting of a first composite layer, a second composite layer, a third composite layer, and a PVA layer stacked alternately; (3) The composite film is hot-pressed in a nitrogen environment at 270-300°C, and then heat-treated in an argon atmosphere at 2700-3000°C in a confined space to obtain a graphene aerogel with a density of 0.2-0.5 g / cm 3 ; (4) Slicing the graphene aerogel perpendicular to the graphene orientation direction to a thickness of 0.2-0.5 mm; (5) The upper and lower surfaces of the slice are treated with plasma to first expose the uniform vertically oriented graphene structure, and then the low-graphitized graphene on the upper and lower surfaces of the slice is etched away to form a cortex consisting of a highly graphitized layer.

5. (6) Place the plasma-treated slices in an argon environment and sinter at a high temperature of 2000-3000°C; (7) The treated slices are pressed at a pressure of 0.2-2 MPa for 2-20 seconds. The density of the obtained product is 0.7-1 g / cm 3 .

6. The preparation method according to claim 3 or 4, characterized in that The slicing method is laser etching slicing or wire cutting slicing.

7. The preparation method according to claim 3 or 4, characterized in that The pressure of hot pressing is 1-5 MPa.

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