Graphene materials and their preparation methods, graphene composite materials, electronic devices

Abstract

The application relates to a graphene material and a preparation method thereof, a graphene composite material and an electronic device. The graphene material has a pore structure, and a tearing strength of the graphene material is greater than or equal to 30 gf / 25 mm in a thickness direction of the graphene material. The graphene material provided by the application has macroscopic structure, mechanical strength and excellent thermal performance.

Description

Technical Field

[0001] This invention relates to the field of heat dissipation materials technology, and in particular to graphene materials and their preparation methods, graphene composite materials, and electronic devices. Background Technology

[0002] Currently, graphene's extremely high thermal conductivity gives it a unique advantage in the field of thermal management materials. Graphene films are interconnected porous materials prepared by chemical vapor deposition, solution mixing, porous template methods, lyotropic plasticizing foaming, or a combination of these methods. Graphene films effectively reduce the contact thermal resistance between the layers, thereby improving the thermal performance of composite materials.

[0003] Due to limitations in graphene slurry formulation, coating, and foaming processes, existing graphene thermal conductive materials exhibit low structural mechanical strength and poor structural stability when exceeding a certain thickness, thus restricting their applications. Currently, the method of preparing thick graphene films using reducing agents through foaming is simple and easy; however, due to limitations in the original film thickness, thick films are often prepared by increasing the reducing agent concentration or extending the foaming time. This can easily lead to excessive film expansion, resulting in weakened pore wall structure strength or even collapse.

[0004] Therefore, how to make graphene materials possess both macroscopic structure and mechanical strength, as well as excellent thermal properties, is a problem that needs to be solved. Summary of the Invention

[0005] The purpose of this application is to provide graphene materials and their preparation methods, graphene composite materials, and electronic devices. The graphene materials possess both macroscopic structure and mechanical strength, as well as excellent thermal properties, and can be used as graphene foam / aerogel in fields such as fire retardancy, heat insulation and resilience, and heat conduction and dissipation.

[0006] In a first aspect, this application provides a graphene material having a porous structure and a thickness ≥1mm; along the thickness direction of the graphene material, the tear strength of the graphene material is ≥30gf / 25mm.

[0007] In some embodiments, the compressive strength of the graphene material is ≥5 MPa.

[0008] In some embodiments, the density of the graphene material is 0.1 g / cm³. 3 ~0.3g / cm 3 .

[0009] In some embodiments, the pore structure of the graphene material is distributed in a three-dimensional network.

[0010] In some embodiments, the compression resilience of the graphene material is 90% to 95%.

[0011] In some embodiments, the horizontal thermal conductivity of the graphene material is >30 W / m·K, and the vertical thermal conductivity of the graphene material is >1 W / m·K.

[0012] In some embodiments, the carbon content in the graphene material is ≥99.9% by mass.

[0013] In some embodiments, the average pore size of the pores in the graphene material is 1 μm to 200 μm.

[0014] Secondly, this application provides a method for preparing graphene material, comprising the following preparation steps:

[0015] The original graphene oxide film was immersed in an interface enhancement solution for wetting treatment. After wetting, N original graphene oxide films were stacked to obtain N layers of pre-expanded graphene oxide film, where N≥2.

[0016] The N-layer graphene oxide pre-expanded film is dried and graphitized to obtain a graphene material with a tear strength ≥30gf / 25mm.

[0017] In some embodiments, the thickness of the single-layer graphene oxide porous original film is 50 μm to 1000 μm.

[0018] In some embodiments, the mass ratio of carbon atoms to oxygen atoms in the original graphene oxide film is (1-3):1.

[0019] In some embodiments, the original graphene oxide film includes oxygen-containing functional groups.

[0020] In some embodiments, the original graphene oxide film includes oxygen-containing functional groups, which include at least one of epoxy groups, hydroxyl groups, and carboxyl groups.

[0021] In some embodiments, the graphene oxide film has a three-dimensional network of pores, the average pore size of which ranges from 1 μm to 200 μm.

[0022] In some embodiments, at least a portion of the graphene oxide in the original graphene oxide film is oriented in a horizontal or vertical direction.

[0023] In some embodiments, adjacent layers of the graphene oxide pre-expanded film are connected by at least one of hydrogen bonds, covalent bonds, and π-π non-covalent bonds.

[0024] In some embodiments, the interface-enhancing solution includes an additive, which includes at least one of hydrogen-bonded compounds, non-covalently bonded compounds, and covalently bonded compounds.

[0025] In some embodiments, the interface-enhancing solution includes an additive, which includes at least one of polyamic acid, graphene oxide quantum dots, graphene quantum dots, polymer quantum dots, polyvinyl alcohol, and polyacrylic acid.

[0026] In some embodiments, the solid content of the interface enhancement solution is 0.1% to 1%.

[0027] In some embodiments, the immersion treatment time is 5s to 60s.

[0028] In some embodiments, the drying process is carried out at a temperature of 60°C to 400°C.

[0029] In some embodiments, the heating rate of the drying process is ≤10℃ / min.

[0030] In some embodiments, the drying process takes 5 to 20 hours.

[0031] In some embodiments, the graphitization treatment temperature is 2700°C to 3100°C.

[0032] In some embodiments, the graphitization process takes 14 to 50 hours.

[0033] In some embodiments, the heating rate of the graphitization treatment is ≤5℃ / min.

[0034] In some embodiments, the graphitization process is performed under hot pressing.

[0035] In some embodiments, the hot-pressing pressure of the graphitization treatment is ≤100 kPa.

[0036] Thirdly, this application provides a graphene composite material, which includes the graphene material described above or the graphene material prepared according to the above-described method for preparing graphene material, and a phase change material, wherein at least a portion of the phase change material is located within the pore structure.

[0037] In some embodiments, the phase change material includes at least one of organic and inorganic phase change materials.

[0038] In some embodiments, the phase change material includes an organic phase change material, which includes at least one of paraffin, n-hexadecane, n-octadecane, n-eicosane, stearic acid, and palmitic acid.

[0039] In some embodiments, the thickness of the graphene composite material is ≥1 mm.

[0040] In some embodiments, the density of the graphene composite material is 1.0 g / cm³. 3 ~1.5g / cm 3 .

[0041] In some embodiments, the horizontal thermal conductivity of the graphene composite material is ≥35 W / m·K, and the vertical thermal conductivity of the graphene composite material is ≥2 W / m·K.

[0042] In some embodiments, the phase transition enthalpy of the graphene composite material is ≥150 J / g.

[0043] Fourthly, an electronic device comprising electronic components and the aforementioned graphene composite material.

[0044] Compared with the prior art, the present invention has at least the following beneficial effects:

[0045] The graphene material proposed in this application has a thickness ≥1mm and a tear strength ≥30gf / 25mm along the thickness direction. The graphene material provided in this application has strong bonding force along the thickness direction, so that the graphene material with a large thickness can still have macroscopic structure and mechanical strength, as well as excellent thermal properties. It can be used as graphene foam / aerogel in the fields of fireproofing and flame retardancy, heat insulation and rebound, and heat conduction and heat dissipation.

[0046] The method for preparing graphene material provided in this application involves immersing a graphene oxide pre-film in an interface enhancement solution, then stacking N pre-films of graphene oxide to obtain an N-layer pre-expanded graphene oxide film; finally, through graphitization treatment, a multi-layered graphene material is obtained. This material can achieve a tear strength ≥30gf / 25mm at a relatively large thickness, ensuring the thermal properties of the material and improving its mechanical strength and excellent thermal properties.

[0047] The graphene composite material provided in this application combines graphene material with phase change material to obtain an ultra-thick graphene composite material. The graphene composite material still has macroscopic structure, mechanical strength, and excellent thermal properties. Attached Figure Description

[0048] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0049] Figure 1 A schematic flowchart illustrating the preparation method of graphene material provided in the embodiments of this application;

[0050] Figure 2 This is a SEM image of the graphene material provided in Example 1 of this application at a magnification of 30x.

[0051] Figure 3 This is a SEM image of the graphene material provided in Example 1 of this application at 100x magnification.

[0052] Figure 4 This is a SEM image of the graphene composite material provided in Example 1 of this application at a magnification of 200x. Detailed Implementation

[0053] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0054] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0055] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0056] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0057] Currently, due to limitations in graphene slurry formulation, coating, and foaming processes, existing graphene thermal conductive materials exhibit low structural mechanical strength and poor structural stability when exceeding a certain thickness, thus restricting their applications. While preparing thick graphene films using reducing agents via foaming is a simple and easy method, it is often limited by the original film thickness. This often results in thick films being prepared by increasing the reducing agent concentration or extending the foaming time, which can easily lead to excessive film expansion, weakening the pore wall structure and even causing collapse.

[0058] Therefore, how to make graphene materials possess both macroscopic structure and mechanical strength, as well as excellent thermal properties, is a problem that needs to be solved.

[0059] This application provides a graphene material having a porous structure and a thickness ≥1mm; along the thickness direction of the graphene material, the tear strength of the graphene material is ≥30gf / 25mm.

[0060] The graphene material proposed in this application has a thickness of ≥1mm and a tear strength of ≥30gf / 25mm along the thickness direction. The graphene material provided in this application has a strong bonding force along the thickness direction, so that the graphene material with a large thickness can still have both macroscopic structure and mechanical strength, as well as excellent thermal properties.

[0061] In some embodiments, the thickness of the graphene material can be 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, 2.5 mm, 2.8 mm, 3 mm, 3.5 mm or 4 mm, etc., and is not limited here.

[0062] In some embodiments, the tear strength of the graphene material can be 30gf / 25mm, 31gf / 25mm, 33gf / 25mm, 34gf / 25mm, 35gf / 25mm, 36gf / 25mm, 37gf / 25mm, 38gf / 25mm, 39gf / 25mm, or 40gf / 25mm, etc., and is not limited here.

[0063] In some embodiments, the compressive strength of the graphene material is ≥5 MPa. Controlling the compressive strength of the graphene material within this range ensures its mechanical strength, preventing structural breakage or pore collapse under pressure.

[0064] In some embodiments, the density of the graphene material is 0.1 g / cm³. 3 ~0.3g / cm 3 Specifically, it could be 0.1 g / cm³. 3 0.15g / cm 3 0.16 g / cm 3 0.18g / cm 3 0.2g / cm 3 0.21g / cm 3 0.25g / cm 3 0.26g / cm 3 0.28g / cm 3 or 0.3g / cm 3 Graphene materials, etc., are not limited here. They have low expansion properties.

[0065] In some embodiments, the pore structure of the graphene material is distributed in a three-dimensional network.

[0066] In some embodiments, the compression resilience of the graphene material is 90% to 95%, specifically 90%, 91%, 92%, 93%, 94%, 95%, etc., and is not limited here.

[0067] In some embodiments, the horizontal thermal conductivity of the graphene material is >30 W / m·K, and the vertical thermal conductivity of the graphene material is >1 W / m·K;

[0068] In some embodiments, the carbon content in the graphene material is ≥99.9% by mass.

[0069] In some embodiments, the average pore size of the pores in the graphene material is 1μm to 200μm, specifically 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm, etc., and is not limited here.

[0070] This application also provides a graphene composite material, which includes the graphene material described above, and a phase change material, wherein at least a portion of the phase change material is located within the pore structure.

[0071] In some embodiments, the phase change material includes at least one of organic phase change materials and inorganic phase change materials;

[0072] In some embodiments, the organic phase change material includes at least one of paraffin, n-hexadecane, n-octadecane, n-eicosane, stearic acid, and palmitic acid;

[0073] In some embodiments, the thickness of the graphene composite material is ≥1mm; specifically, it can be 1mm, 1.2mm, 1.5mm, 1.7mm, 1.9mm, 2mm, 2.5mm, 2.9mm, 3mm, 4mm, 5mm, etc., and is not limited thereto. It is understood that, because the graphene material provided in this application is used as a framework, and a phase change material is composited within the graphene material, the resulting graphene composite material can also possess both high mechanical strength and excellent thermal properties. The graphene composite material of this application can be used as graphene foam / aerogel in fields such as fire retardancy, heat insulation and resilience, and thermal conductivity and heat dissipation.

[0074] In some embodiments, the density of the graphene composite material is 1.0 g / cm³. 3 ~1.5g / cm 3 Specifically, it could be 1.0 g / cm³. 3 1.4g / cm 3 1.2g / cm 31.35g / cm 3 1.4g / cm 3 Or 1.5g / cm 3 Graphene composites have a low density, making them suitable for use in electronic devices with high weight reduction requirements.

[0075] In some embodiments, the horizontal thermal conductivity of the graphene composite material is ≥35 W / m·K, and the vertical thermal conductivity of the graphene composite material is ≥2 W / m·K.

[0076] In some embodiments, the phase transition enthalpy of the graphene composite material is ≥150 J / g, specifically it can be 150 J / g, 160 J / g, 170 J / g, 180 J / g, 190 J / g, 200 J / g, 210 J / g or 220 J / g, etc., and is not limited here.

[0077] Secondly, this application provides a method for preparing graphene materials, such as... Figure 1 As shown, the preparation steps include the following:

[0078] Step S10: The graphene oxide original film is immersed in the interface enhancement solution for wetting treatment. After wetting, N graphene oxide original films are stacked to obtain N layers of graphene oxide pre-expanded film, where N≥2.

[0079] Step S20: The N-layer graphene oxide pre-expanded film is dried and graphitized to obtain a graphene material with a tear strength ≥30gf / 25mm.

[0080] The method for preparing graphene material provided in this application involves immersing a graphene oxide pre-film in an interface enhancement solution, then stacking N pre-films of graphene oxide to obtain an N-layer pre-expanded graphene oxide film; finally, through graphitization treatment, a multi-layered graphene material is obtained. This material can achieve a tear strength ≥30gf / 25mm at a relatively large thickness, ensuring the thermal properties of the material and improving its mechanical strength and excellent thermal properties.

[0081] The following is a detailed introduction to this solution:

[0082] Prior to step S10, the method further includes preparing a graphene oxide pre-film.

[0083] In some embodiments, the original graphene oxide film can be prepared by any one of the following methods: reducing agent foaming expansion, template method, and directional freezing method.

[0084] In some embodiments, the step of preparing the graphene oxide precursor film includes preparing a slurry containing graphene oxide and performing a film-forming treatment on the slurry to obtain the graphene oxide precursor film.

[0085] In some embodiments, the particle size of graphene oxide in the slurry is 1μm to 5μm, specifically 1μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm, etc., and is not limited here.

[0086] In some embodiments, the slurry further includes a support material, which includes at least one of carbon nanotubes, carbon fibers, and polymer fibers. Specifically, the polymer fibers can be aramid fibers, polyamide fibers, etc. Understandably, adding a graphitizable support material to a graphene oxide-containing slurry helps to repair lattice defects in graphene during high-temperature graphitization. Furthermore, the support material enhances the mechanical properties of the graphene material, providing support between the upper and lower layers of the graphene sheet structure and giving the graphene material better compressibility and resilience.

[0087] In some embodiments, the viscosity of the slurry is 10,000 cps to 50,000 cps, specifically 10,000 cps, 20,000 cps, 30,000 cps, 35,000 cps, 40,000 cps, 45,000 cps or 50,000 cps, etc., and is not limited here.

[0088] In some embodiments, the thickness of the original graphene oxide film is 50 μm to 1000 μm, specifically it can be 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 500 μm, 600 μm, 700 μm, 800 μm or 1000 μm, etc., and is not limited here.

[0089] In some embodiments, the mass ratio of carbon atoms to oxygen atoms in the graphene oxide film is 1 to 3, specifically 1.0, 1.2, 1.4, 1.6, 1.7, 1.8, 2.0, 2.2, 2.3, 2.4, 2.6, 2.8, or 3.0, etc., and is not limited thereto. Preferably, the atomic ratio of carbon atoms to oxygen atoms in the graphene oxide film is 1.4 to 2.6.

[0090] In some embodiments, the mass content of solid particles in the slurry is 0.5% to 5%, specifically 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc., and is not limited here.

[0091] In some embodiments, the original graphene oxide film includes oxygen-containing functional groups;

[0092] In some embodiments, the oxygen-containing functional groups include at least one of epoxy groups, hydroxyl groups, and carboxyl groups. Understandably, these oxygen-containing functional groups can interact with additives in the interface-enhancing solution, specifically by forming at least one of hydrogen bonds, covalent bonds, and π-π non-covalent bonds, thereby enhancing the bonding force between adjacent layers of pre-expanded graphene oxide films.

[0093] In some embodiments, the graphene oxide film has a three-dimensional network of pores, the average pore size of which ranges from 1 μm to 200 μm. The specific range of the average pore size can be 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm, etc., and is not limited thereto.

[0094] In some embodiments, at least a portion of the graphene oxide in the original graphene oxide film is oriented in a horizontal or vertical direction.

[0095] Step S10: The graphene oxide original film is immersed in the interface enhancement solution for wetting treatment. After wetting, N graphene oxide original films are stacked to obtain N layers of graphene oxide pre-expanded film, where N≥2.

[0096] In some embodiments, the interface-enhancing solution includes an additive, which includes at least one of hydrogen-bonded compounds, non-covalently bonded compounds, and covalently bonded compounds.

[0097] Understandably, hydrogen-bonded compounds can form strong hydrogen bonds with oxygen-containing functional groups on the surface of the original graphene oxide film, while covalently bonded compounds can form covalent bonds with oxygen-containing functional groups on the surface of the original graphene oxide film. Non-covalently bonded compounds can form π-π non-covalent bonds with the benzene ring structure of graphene oxide, which greatly enhances the bonding force between the pre-expanded graphene oxide films, thereby improving the structural strength and mechanical strength of graphene materials.

[0098] In some embodiments, adjacent layers of the graphene oxide pre-expanded film are connected by at least one of hydrogen bonds, covalent bonds, and π-π non-covalent bonds.

[0099] In some embodiments, the interface-enhancing solution includes additives, which include at least one of polyamic acid, graphene oxide quantum dots, graphene quantum dots, polymer quantum dots, polyvinyl alcohol, and polyacrylic acid. Understandably, the addition of these additives can increase the carbon content, density, and mechanical strength of the graphene material.

[0100] In some embodiments, the solvent in the interface enhancement solution includes water, methanol, ethanol, etc., and preferably, the solvent is water.

[0101] In some embodiments, the solid content of the interface enhancement solution is 0.1% to 1%, specifically 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc., and is not limited here.

[0102] In some embodiments, the soaking time is 5s to 60s, specifically 5s, 10s, 15s, 20s, 25s, 30s, 35s, 40s, 45s, 50s, 55s or 60s, etc., and is not limited here.

[0103] Step S20: The N-layer graphene oxide pre-expanded film is dried and graphitized to obtain a graphene material with a tear strength ≥30gf / 25mm.

[0104] Understandably, low-temperature drying can effectively remove solvents from the multilayer graphene oxide pre-expanded film, including water and solvents in the interface enhancement solution.

[0105] In some embodiments, the drying temperature is 60℃ to 400℃, specifically 60℃, 80℃, 100℃, 150℃, 200℃, 250℃, 300℃ or 400℃, etc., and is not limited here.

[0106] In some embodiments, the heating rate of the drying process is ≤10℃ / min, and may specifically be 10℃ / min, 9℃ / min, 8℃ / min, 7℃ / min, 6℃ / min, 5℃ / min, 3℃ / min or 2℃ / min, etc., which are not limited here.

[0107] Understandably, by controlling the immersion time, concentration, and additives of the interface enhancement solution, the surfaces of adjacent graphene oxide films can be connected by hydrogen bonds and / or covalent bonds. Then, by low-temperature drying, the interface connection between the adjacent graphene oxide films becomes tighter, achieving a molecular-level "welding" effect. Furthermore, drying helps maintain the structural stability of the pore structure within the multilayer graphene oxide film, making the pore structure less prone to collapse during normal use.

[0108] In some embodiments, the temperature of the graphitization treatment is 2700℃~3100℃, specifically 2700℃, 2800℃, 2900℃, 3000℃, 3050℃ or 3100℃, etc., which are not limited here.

[0109] In some embodiments, the graphitization treatment time is 14h to 50h, specifically 14h, 15h, 20h, 25h, 30h, 40h or 50h, etc., and is not limited here.

[0110] After step S20, the method further includes:

[0111] Step S30: Graphene material is combined with phase change material to obtain graphene composite material.

[0112] In some embodiments, the phase change material includes at least one of organic phase change materials and inorganic phase change materials;

[0113] In some embodiments, the organic phase change material includes at least one of paraffin, n-hexadecane, n-octadecane, n-eicosane, stearic acid, and palmitic acid.

[0114] Specifically, phase change materials (PCMs) can be composited with graphene materials through processes such as vacuum infusion and vacuum permeation. In graphene composite materials, PCMs can be adsorbed into the pores of graphene materials through capillary action, achieving a phase change between endothermic and exothermic states, thereby improving the thermal properties of the material.

[0115] In some embodiments, the thickness of the graphene composite material is ≥1mm; specifically, it can be 1mm, 1.2mm, 1.5mm, 1.7mm, 1.9mm, 2mm, 2.5mm, 2.9mm, etc., and is not limited here.

[0116] In some embodiments, the density of the graphene composite material is 1.0 g / cm³. 3 ~1.5g / cm 3 Specifically, it could be 1.0 g / cm³. 3 1.4g / cm 3 1.2g / cm 3 1.35g / cm 3 1.4g / cm 3 Or 1.5g / cm 3 Graphene composites have a low density, making them suitable for use in electronic devices with high weight reduction requirements.

[0117] In some embodiments, the horizontal thermal conductivity of the graphene composite material is ≥35 W / m·K, and the vertical thermal conductivity of the graphene composite material is ≥2 W / m·K.

[0118] In some embodiments, the phase transition enthalpy of the graphene composite material is ≥150 J / g, specifically it can be 150 J / g, 160 J / g, 170 J / g, 180 J / g, 190 J / g, 200 J / g, 210 J / g or 220 J / g, etc., and is not limited here.

[0119] This application also provides an electronic device, which includes electronic components and the above-described graphene composite material.

[0120] Electronic devices can be any of the following: mobile phones, computers, laptops, iPads, wearable devices, and in-vehicle electronic devices. These electronic devices are highly integrated and require strong heat dissipation.

[0121] In some implementations, graphene composite materials can also be used in combination with heat spreaders, heat-conducting sheets, etc., without limitation.

[0122] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0123] Example 1

[0124] A 1000-micrometer-thick graphene oxide pre-film with a carbon-to-oxygen ratio of 1:1 was immersed in a polyamic acid solution with a solid content of 0.5% for 10 seconds. The immersed graphene oxide pre-film was then stacked in three layers to obtain an ultra-thick graphene oxide pre-expanded film with a thickness of 3000 micrometers.

[0125] Under a hot-pressing pressure of 5 kPa, the material was dried at 400°C for 5 h at a heating rate of 5°C / min, and then graphitized at 3100°C for 20 h at a high temperature to obtain graphene material.

[0126] Graphene composite materials were obtained by vacuum infusing paraffin into graphene materials as a framework.

[0127] Figure 2 This is a SEM image of the graphene material provided in Example 1 of this application at a magnification of 30x. Figure 3 This is a SEM image of the graphene material provided in Example 1 of this application at 100x magnification; as shown... Figure 2 and Figure 3 As shown, the graphene material exhibits tight bonding at the interfaces, without delamination or discontinuity. The graphene material is 3 mm thick, and the average pore size is 150 μm (e.g., Figure 3 As shown), its density is 0.15 g / cm³. 3 The horizontal thermal conductivity is 35 W / (m·K), and the vertical thermal conductivity is 2 W / (m·K).

[0128] Figure 4 This is a SEM image of the graphene composite material provided in Example 1 of this application at a magnification of 200x, as shown below. Figure 4 As shown, the phase change material fully fills the pores of the graphene material. The graphene composite material has a thickness of 3 mm and a density of 1.1 g / cm³. 3 The horizontal thermal conductivity is 38 W / mK, the vertical thermal conductivity is 2.5 W / mK, and the phase transition enthalpy is 210 J / g.

[0129] Example 2

[0130] A 300-micrometer-thick graphene oxide pre-film with a carbon-to-oxygen ratio of 2:1 was immersed in a 0.1% polyvinyl alcohol aqueous solution for 20 seconds. The immersed graphene oxide pre-film was then stacked in four layers to obtain an ultra-thick graphene oxide pre-expanded film with a thickness of 1200 micrometers.

[0131] Under a hot-pressing pressure of 5 kPa, the material was dried at 400°C for 5 h at a heating rate of 5°C / min, and then graphitized at 3100°C for 15 h at a heating rate of 4°C / min to obtain graphene material.

[0132] Graphene composite materials were obtained by vacuum infusing paraffin into graphene materials as a framework.

[0133] Example 3

[0134] A 200-micrometer-thick graphene oxide pre-film with a carbon-to-oxygen ratio of 3:1 was immersed in a 1% solid content graphene quantum dot aqueous solution for 50 seconds. The immersed graphene oxide pre-film was then stacked in 5 layers to obtain an ultra-thick graphene oxide pre-expanded film with a thickness of 1000 micrometers.

[0135] Under a hot-pressing pressure of 2 kPa, the material was dried at 400°C for 5 h at a heating rate of 5°C / min, and then graphitized at 3100°C for 25 h at a heating rate of 2°C / min to obtain graphene material.

[0136] Graphene composite materials were obtained by vacuum infusing paraffin into graphene materials as a framework.

[0137] Example 4

[0138] Unlike Example 1, the graphitization treatment temperature was 2700°C.

[0139] Example 5

[0140] Unlike Example 1, the heating rate for graphitization treatment was 1 °C / min.

[0141] Example 6

[0142] Unlike Example 1, the graphene oxide film was immersed in an aqueous solution of polyacrylic acid with a solid content of 0.5% for 20 seconds.

[0143] Example 7

[0144] Unlike Example 1, the graphene oxide pre-film with a carbon-to-oxygen ratio of 1:1 was immersed in a polyamic acid solution with a solid content of 1.5%.

[0145] Example 8

[0146] Unlike Example 1, the graphitization treatment temperature was 2600°C.

[0147] Example 9

[0148] Unlike Example 1, the heating rate for graphitization treatment was 10 °C / min.

[0149] Comparative Example 1

[0150] Unlike Example 1, no soaking treatment was performed.

[0151] Comparative Example 2

[0152] Unlike Example 1, the carbon-to-oxygen ratio of the original graphene oxide film is 5:1.

[0153] Comparative Example 3

[0154] Unlike Example 1, the thickness of the original graphene oxide film is 2000 micrometers.

[0155] Comparative Example 4

[0156] Unlike Example 1, the average pore size of the graphene oxide original film ranges from 200 micrometers.

[0157] Comparative Example 5

[0158] Unlike Example 1, the hot pressing pressure is 1 MPa.

[0159] Test method:

[0160] The testing methods corresponding to the performance mentioned above.

[0161] 1. Horizontal thermal conductivity test

[0162] The equipment used was an LFA-467 Hyper Flash; referring to ASTM-E1461, "Standard Test Method for Determining Fixed Thermal Conductivity by Flash Method", the sample was cut into a circular disc with a diameter of 25.4 mm to measure the thermal diffusivity of graphene materials. Thermal conductivity = thermal diffusivity * density * specific heat capacity (specific heat capacity: 0.85) was calculated.

[0163] 2. Vertical thermal conductivity test

[0164] The equipment used was an LW-9389 steady-state heat flow thermal conductivity tester; referring to ASTM-D5470 "Standard Test Method for Thermal Transfer Properties of Thermally Conductive and Electrically Insulating Materials", the sample was cut into a 3mm×3mm square piece, and the thermal conductivity of the graphene material was tested under a pressure of 30psi by selecting the thermally conductive sheet-thermal conductivity test mode.

[0165] 3. Electron microscopy test:

[0166] Scanning electron microscopy was used to confirm the morphology of the material and the average pore size.

[0167] 4. Compressive strength test of graphene materials:

[0168] The equipment used was an AGS-X electronic universal tensile testing machine; referring to ASTM D3574-17, a 25×25mm graphene material was taken, and then pressure was applied at a rate of 5mm / min until the rate of pressure increase on the graphene material decreased significantly. The stress at this abrupt change point was taken as the maximum compressive strength.

[0169] 5. Tear strength test of graphene materials:

[0170] The equipment used was an AGS-X electronic universal tensile testing machine; referring to ASTM D3574-17, ① the sample length was cut to 120mm and the width to 25±0.5mm. The sample thickness and height were tested at least three points, and the average value was taken. ② A 10mm long slit was cut in the middle of the sample, and then it was clamped on the testing machine. A load was applied at a rate of 10mm / min to tear the sample. The data after fracture or tearing at least 20mm were recorded, and the average value was taken.

[0171] 6. Compression resilience test of graphene materials:

[0172] The equipment used was an AGS-X electronic universal tensile testing machine. Referring to GB / T 34336-2017, the samples were cut into 100mm × 100mm square pieces. The initial thickness h1 of the samples was measured using a thickness gauge, accurate to 0.01mm. The compression speed of the testing machine was 2mm / min. Compression was stopped when the sample was compressed to (100±5) kPa, and the machine was held in this position for 5 minutes. After 5 minutes of recovery, the recovered thickness h2 of the sample was measured using a thickness gauge, accurate to 0.01mm. The compression rebound rate was calculated as (h2 / h1) × 100%.

[0173] 7. Phase transition enthalpy test

[0174] The equipment used was a DSC2500; referring to GB / T 19466.3—2004, the phase transition enthalpy was tested. The test procedure was as follows: ① Pre-clean with nitrogen for 5 min, hold the initial temperature for 5 min, ② Increase the temperature at a rate of 10℃ / min. Heat the sample dish to a sufficiently high temperature (default is 150℃, the specific temperature depends on the sample condition), then hold the temperature for 5 min, and then cool down at the same rate to eliminate the previous thermal history of the test material. This is usually about 30℃ above the melt extrapolation termination temperature (Tm). The thermal history and morphology of the sample and specimen have a significant impact on the DSC test results of the polymer. Perform a preheating cycle and a second temperature scan. ③ After cooling with the instrument, remove the sample dish and observe whether the dish is deformed or the sample has overflowed. ④ If there is any mass loss, a chemical change should be suspected; open the dish and inspect the sample. If the sample has degraded, discard the test results and retest at a lower upper limit temperature.

[0175] Table 1. Properties of graphene materials prepared in comparative examples and embodiments

[0176]

[0177] Table 2. Properties of graphene composite materials prepared in comparative examples and embodiments

[0178]

[0179]

[0180] Comparing Examples 1 to 9 in Tables 1 and 2, it can be seen that by immersing the original graphene oxide film in an interface enhancement solution, and then stacking N layers of graphene oxide pre-expanded films, N layers of graphene oxide pre-expanded films are obtained. The adjacent two layers of graphene oxide pre-expanded films are connected by at least one of hydrogen bonds, covalent bonds, and π-π non-covalent bonds, which can enhance the bonding force between the individual graphene oxide pre-expanded films. Finally, through graphitization treatment, a multilayered graphene material is obtained. This material can achieve a tear strength ≥30gf / 25mm at a relatively large thickness, which can effectively protect the thermal properties of the graphene material and improve its mechanical strength.

[0181] In Example 7, during the preparation process, a graphene oxide pre-film with a carbon-to-oxygen ratio of 1:1 was immersed in a polyamic acid solution with a solid content of 1.5%. The concentration of the interface reinforcing agent was too high. On the one hand, this resulted in a high viscosity of the interface reinforcing agent solution, making it difficult to uniformly penetrate to the surface of the graphene oxide pre-film. On the other hand, the high concentration caused excessive concentration of interfacial mechanics, resulting in a decrease in the uniformity of film performance. At the same time, the pore structure of the graphene oxide pre-film was partially blocked, which would further affect the filling of the phase change material.

[0182] In Example 8, the graphitization temperature was only 2600℃ during the preparation process, resulting in a low degree of graphitization of the graphene material and a decrease in the thermal conductivity of the graphene material compared to Example 1.

[0183] In Example 9, the graphitization rate was 10°C / min. During the graphitization process, the orderliness of graphite crystal growth decreased, and defect repair was incomplete. The thermal conductivity of the graphene material was lower than that in Example 1.

[0184] In Comparative Example 1, the original graphene oxide film was not soaked in an interface enhancement solution during the preparation process. The graphene material obtained by graphitization after multilayer stacking was prone to delamination, making it impossible to prepare a thick film. There was no force at the composite interface, and the tear strength was significantly reduced. In other words, the graphene material was prone to delamination, making it difficult to infuse phase change materials.

[0185] In Comparative Example 2, the carbon-to-oxygen ratio of the original graphene oxide film used in the preparation process was 5 / 1, which resulted in an excessively high carbon atom content. This reduced the number of oxygen-containing functional groups on the surface of the original film and the number of active reaction points, leading to a weakening of the interaction between the original graphene oxide film and the interface reinforcing agent. Consequently, the interlayer interaction between adjacent pre-expanded graphene oxide films was weakened, the stacking effect was slightly reduced, the graphene material was prone to delamination, and the tear strength of the graphene material decreased.

[0186] In Comparative Example 3, the thickness of the original graphene oxide film used in the preparation process was 2000 micrometers. The original graphene oxide film was prepared by a foaming process. The foaming thickness of the original graphene oxide film was too thick, that is, the original film was over-expanded. The pore structure in the original graphene oxide film was large and loose, resulting in poor pore mechanical strength. The interlayer force of the graphene material prepared from it was weakened, which led to a decrease in the compressive strength and tear strength of the graphene material. In addition, the horizontal thermal conductivity and vertical thermal conductivity of the graphene material were both reduced.

[0187] In Comparative Example 4, the average pore size of the graphene oxide film used in the preparation process ranged from 200 micrometers. Similar to Comparative Example 3, the pore size of the graphene oxide film was too large, resulting in excessive expansion and a smaller contact area between the graphene sheets. Simultaneously, the effective overlap between the vertical and horizontal graphene sheets was poor, and the excessive expansion in the vertical direction led to poor mechanical support. The interlayer forces of the graphene material prepared in this way were weakened, resulting in a decrease in the compressive and tear strength of the graphene material, and a reduction in both the horizontal and vertical thermal conductivity.

[0188] In Comparative Example 5, the hot-pressing pressure was too high compared to Example 1 during the preparation process, which caused the pre-expanded graphene oxide film to collapse under pressure. The porous structure of the prepared graphene material collapsed in large quantities, making it difficult to meet the filling requirements of the phase change material. The phase change enthalpy was extremely low, and it did not have compressibility resilience.

[0189] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A graphene material, characterized in that, The graphene material has a porous structure and a thickness ≥1 mm; along the thickness direction of the graphene material, the tear strength is 30 gf / 25 mm ~ 40 gf / 25 mm; the graphene material has at least one chemical bond selected from hydrogen bonds, covalent bonds, and π-π non-covalent bonds; the carbon content in the graphene material is ≥99.9% by mass; the horizontal thermal conductivity of the graphene material is 30 W / m•K ~ 40 W / m•K; the vertical thermal conductivity of the graphene material is 1.2 W / m•K ~ 2.5 W / m•K; and the compression resilience of the graphene material is 90% ~ 95%.

2. The graphene material according to claim 1, characterized in that, The compressive strength of the graphene material is ≥5MPa.

3. The graphene material according to claim 1 or 2, characterized in that, The graphene material includes at least one of the following characteristics: (1) The density of the graphene material is 0.1 g / cm³. 3 ~0.3 g / cm 3 ; (2) The pore structure of the graphene material is distributed in a three-dimensional network; (3) The average pore size of the pores in the graphene material is 1μm~200μm.

4. A method for preparing the graphene material according to any one of claims 1 to 3, characterized in that, The preparation steps include the following: A graphene oxide pre-film is immersed in an interface enhancement solution for wetting treatment. After wetting, N graphene oxide pre-films are stacked to obtain an N-layer graphene oxide pre-expanded film, wherein N≥2. The solute of the interface enhancement solution includes additives, which include at least one of polyamic acid, graphene oxide quantum dots, graphene quantum dots, polymer quantum dots, polyvinyl alcohol, and polyacrylic acid. The solvent of the interface enhancement solution includes at least one of water, methanol, and ethanol. The thickness of the graphene oxide pre-film is 50μm~1000μm. The mass ratio of carbon atoms to oxygen atoms in the graphene oxide pre-film is (1~3):

1. The graphene oxide pre-film has a three-dimensional network of pores, and the average pore size ranges from 1μm to 150μm. The N-layer graphene oxide pre-expanded film is dried and graphitized to obtain a graphene material. The tear strength of the graphene material is ≥30gf / 25mm. The graphitization is carried out under hot pressing conditions, and the hot pressing pressure of the graphitization is ≤100 kPa.

5. The preparation method according to claim 4, characterized in that, The method includes at least one of the following features: (1) The original graphene oxide film includes oxygen-containing functional groups; (2) The original graphene oxide film includes oxygen-containing functional groups, which include at least one of epoxy groups, hydroxyl groups and carboxyl groups; (3) At least a portion of the graphene oxide in the original graphene oxide film is oriented in a horizontal or vertical direction; (4) The two adjacent layers of the graphene oxide pre-expanded film are connected by at least one of hydrogen bonds, covalent bonds, and π-π non-covalent bonds; (5) The solid content of the interface enhancement solution is 0.1%~1%.

6. The preparation method according to claim 4, characterized in that, The method includes at least one of the following features: (1) The soaking time is 5s~60s; (2) The drying temperature is 60℃~400℃; (3) The heating rate of the drying process is ≤10℃ / min; (4) The drying time is 5h~20h.

7. The preparation method according to claim 4, characterized in that, The method includes at least one of the following features: (1) The temperature of the graphitization treatment is 2700℃~3100℃; (2) The graphitization treatment time is 14h~50h; (3) The heating rate of the graphitization treatment is ≤5℃ / min.

8. A graphene composite material, characterized in that, The graphene composite material includes the graphene material according to any one of claims 1 to 3 or the graphene material prepared by the method according to any one of claims 4 to 7, and a phase change material, wherein at least a portion of the phase change material is located within the pore structure.

9. The graphene composite material according to claim 8, characterized in that, The graphene composite material includes at least one of the following characteristics: (1) The phase change material includes at least one of organic phase change materials and inorganic phase change materials; (2) The phase change material includes organic phase change materials, which include at least one of paraffin, n-hexadecane, n-octadecane, n-eicosane, stearic acid and palmitic acid; (3) The thickness of the graphene composite material is ≥1 mm; (4) The density of the graphene composite material is 1.0 g / cm³. 3 ~1.5 g / cm 3 ; (5) The horizontal thermal conductivity of the graphene composite material is ≥35 W / m•K, and the vertical thermal conductivity of the graphene composite material is ≥2 W / m•K; (6) The phase transition enthalpy of the graphene composite material is ≥150 J / g.

10. An electronic device, characterized in that, The electronic device includes electronic components and the graphene composite material according to any one of claims 8 or 9.

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