A bidirectional high thermal conductivity graphene block and preparation method thereof

Abstract

The present invention discloses a bidirectional high-thermal-conductivity graphene block and its preparation method. Ion implantation is used to introduce trace metals onto the surface of a two-dimensional graphene film to improve the wettability of the graphene with the metals. Then, copper and silver nanolayers are sequentially deposited on the surface of the carbide-modified graphene film formed by the trace metals to obtain a metallized graphene film. Finally, the metallized graphene film is aggregated using spark plasma sintering technology to form a graphene block. This graphene block has excellent molecular interface structural stability that can adapt to extreme environments, bidirectional high thermal conductivity both in-plane and out-of-plane, and modular assembly features that are compatible with industrial production, making it easy to achieve large-scale production of materials of any thickness, area, and shape.

Description

Technical Field

[0001] The present invention belongs to the technical field of extreme environment thermal management material preparation, and specifically relates to a bidirectional high thermal conductivity graphene block material and a preparation method thereof. Background Art

[0002] The rapid development of high-power electronic devices in fields such as communications, aerospace, military, and energy storage has led to higher requirements for their integration and miniaturization. However, this inevitably creates localized hotspots with high heat flux density during the operation of these electronic devices, posing a significant threat to their stable and reliable operation. Furthermore, under extreme operating conditions, such as deep cryogenic-high temperature cycling, high-energy radiation, and high vacuum, traditional electronic thermal management modules face the risk of catastrophic structural failure. Therefore, the development of novel thermal management materials is crucial for exploring next-generation aerospace thermal control technologies to meet the stringent requirements of lightweight, high thermal conductivity, and excellent structural stability under these extreme application conditions.

[0003] Graphene-based films and bulk materials inherit the excellent properties of two-dimensional graphene sheet assembly units, such as high thermal conductivity, low density, high flexibility, low thermal expansion coefficient and stable physical and chemical properties. They are a class of carbon-based thermal management materials with great potential and have been favored in the aerospace and electronics fields in recent years. They are mainly obtained through various bottom-up macroscopic assembly methods such as wet coating, filtration, wet spinning, centrifugal casting, etc. However, traditional graphene films and bulk materials are subject to the intrinsic contradiction between high thermal conductivity and large thickness. Their own heat flux (the product of thermal conductivity and thickness) is still low, and they cannot effectively solve the high heat flux (usually higher than 1000 W / cm 2 ) problem, it is urgent to develop graphene bulk materials with high thermal conductivity and a thickness of hundreds of microns.

[0004] Specifically, graphite blocks prepared by directly pressing natural graphite powder have inherent multi-grain boundary defects that hinder internal phonon transmission, resulting in a macroscopic in-plane thermal conductivity below 600 W / mK, making it difficult to meet the needs of practical heat dissipation applications. Graphene blocks are also difficult to prepare by direct scraping from graphene-based solutions, primarily due to the low solids content of the solution, making it difficult to produce thicker graphene blocks. Furthermore, when graphene blocks undergo a liquid-solid drying transition, the inevitable capillary contraction effect causes poor orientation of the internal graphene sheets in the wet block and a long drying time. The resulting graphene blocks face bottlenecks in thermal conductivity and structural stability, making them difficult to meet practical application requirements.

[0005] Currently, graphene bulk materials are commonly produced by stacking and bonding several highly thermally conductive graphene films using a polymer adhesive. Porosity at the bonding interface is then eliminated through cold pressing or vacuum heating. However, graphene bulk materials produced using this method still face numerous challenges in practical applications. First, the bond between the graphene film and the polymer adhesive is primarily through van der Waals forces, resulting in weak interfacial bonding and numerous pores, which dramatically increases interfacial thermal resistance. Second, because graphene films are anisotropic materials, their out-of-plane thermal conductivity is extremely low (less than 5 W / (mK)). Even lower-conductivity polymer adhesives (1-2 W / (mK)) are unable to improve their out-of-plane heat transfer capabilities and further reduce out-of-plane phonon heat transfer, hindering rapid heat transfer. Third, graphene bulk materials produced using traditional polymer bonding methods have poor tolerance to extreme environments. After repeated cold / hot shocks, the polymer layer is prone to aging, leading to severe structural failure such as blistering, delamination, and surface wrinkling and brittleness, significantly reducing their thermal transfer performance. Furthermore, self-fusion mediated by the surface oxygen-containing functional groups of graphene oxide or electrothermal fusion can achieve effective bonding of multilayer graphene films, thereby enabling the preparation of graphene bulk materials. However, neither of these methods can guarantee the proper bonding of the graphene film's elementary interfaces, resulting in numerous interfacial pore defects. Furthermore, the interlayers of the graphene bulk material remain in van der Waals stacking, making efficient out-of-plane phonon transfer difficult, and their macroscopic perpendicular thermal conductivity remains limited to below 5 W / mK. Furthermore, this method is limited by the delicate handling required for bonding, making it difficult to implement on a large scale in industrial production.

[0006] Therefore, it is still a huge challenge to develop bidirectional high thermal conductivity and structurally stable graphene blocks with a thickness of more than hundreds of microns to ensure the long-term stable service performance of graphene blocks in extreme environments. Summary of the Invention

[0007] To address the aforementioned challenges in the prior art, the present invention proposes a bidirectionally highly thermally conductive graphene bulk material and its preparation method. This material features a seamless heterogeneous metal-bonded nanostructure, effectively eliminating the pore defects present in conventional graphene bonding interfaces and reducing the interfacial phonon scattering effect. This method achieves seamless covalent bonding at the graphene / metal heterointerface, ensuring a stable material structure after multiple extreme cold / heat shocks (77-573 K). Furthermore, the graphene bulk material benefits from the interlayer interface coupling effect, enabling efficient cross-layer phonon transmission, resulting in unique bidirectional high thermal conductivity both in-plane and out-of-plane. This overcomes the anisotropic limitations of existing graphene films and bulk materials, enabling greater heat flux and exhibiting superior practical heat dissipation capabilities.

[0008] One of the technical solutions of the present invention is to provide a method for preparing a bidirectional high-thermal-conductivity graphene bulk material. Ion implantation introduces trace amounts of titanium or a titanium-nickel mixture onto the surface of a graphene film to improve the wettability of the graphene with metals. The trace metal layer components include metal elements that can form covalent bonds with carbon atoms in the graphene to reduce the interfacial phonon thermal resistance. Then, copper and silver nanolayers are sequentially deposited by magnetron sputtering on the surface of the two-dimensional graphene film modified with the trace amount of titanium or the titanium-nickel mixture to obtain a metallized two-dimensional graphene film. Finally, the metallized two-dimensional graphene film is coalesced using spark plasma sintering technology to produce a graphene bulk material.

[0009] The specific steps are as follows:

[0010] (1) Clean the graphene membrane. Generally, ultrasonically clean it in acetone and alcohol solution for 15 minutes, then rinse it with deionized water and dry it naturally to remove various impurities introduced during the preparation process.

[0011] (2) metal ion implantation is performed on the upper and lower surfaces of the graphene film to form a carbide bridge layer; the metal ions are one or two of titanium, nickel, iron, and tungsten, and the thickness thereof is 10 nm;

[0012] (3) Then, a metal copper layer and a silver layer are sequentially deposited on the bridging layer; wherein the thickness of the copper layer is 10-250 nm, and the thickness of the silver layer is 10-50 nm; thereby obtaining a metallized graphene film;

[0013] (4) Cut the metallized graphene films and fill them into a clean graphite mold one by one. Use the spark plasma sintering process to vertically stack and solidify the multilayer metallized graphene films to make a bidirectional high thermal conductivity graphene block.

[0014] Furthermore, the graphene film in step (1) is one of a pure graphene film and a graphene-based composite film.

[0015] Furthermore, the ion implantation method in step (2) is to use a titanium target, a nickel target, an iron target, a tungsten target, or a titanium-nickel composite metal target to sputter a metal ion beam onto the surface of the graphene film. The incident ions undergo molecular covalent bridging with carbon atoms on the surface of the graphene film, thereby forming a carbide transition layer to enhance the interface bonding strength and eliminate interface pore defects, thereby laying an excellent interface structural foundation for a seamless and strong graphene / metal interface.

[0016] Furthermore, the vertical stacking solidification method in step (4) is a vacuum degree less than 1×10 -3Pa, and a thermocouple gradient heating method was used under the condition of applying a uniaxial pressure of 10 MPa, that is, from room temperature to 400 °C in 4 minutes, and then to 500 °C in another 4 minutes, and kept at 500 °C for 10 minutes, then the heating was stopped and naturally cooled in the cavity. The high vacuum condition remained unchanged during the whole process.

[0017] This method is mature and simple. Based on the modular design of stacking multiple metals, it can use the carbide bridging layer generated by covalent bonding to achieve seamless interface connection, thereby reducing the interfacial thermal resistance caused by the traditional van der Waals interface, improving the out-of-plane heat transfer performance of the graphene block and weakening the strong anisotropy of the graphene block.

[0018] The macroscopic heat transfer performance of graphene bulk materials is closely related to their internal graphene interface structure. The interlayer interactions of conventional graphene bulk materials are dominated by van der Waals forces, resulting in high interlayer phonon transport barriers and prone to boundary scattering effects. Furthermore, the interfaces of conventional polymer-bonded graphene bulk materials contain numerous structural defects. Point defect scattering of phonons at these interfaces significantly dominates the in-plane thermal conductivity, further reducing the thermal conductivity of carbonaceous materials at low temperatures. Integrating nano-heterogeneous metals with the graphene surface to create a seamless molecular interface bridging layer helps reduce interfacial nanopore defects, thereby effectively increasing the mean free path of phonons in the interlayer direction and reducing the out-of-plane interface thermal resistance.

[0019] At the same time, due to the atomic lattice mismatch between copper atoms and carbon atoms, the two are insoluble in each other, and it is impossible to directly achieve a strong interface seamless connection between the nano-copper layer and the graphene. The phonon vibration spectra of metallic copper and graphene are also very different, resulting in the existence of Kapitza thermal resistance. When high-energy phonons cross the interface of graphene-metallic copper, they need to transfer energy to the interface of the next layer of material through more coupled vibrations, which causes serious attenuation of phonon energy. Direct compounding will cause a huge interface thermal resistance, and the out-of-plane and in-plane heat transfer efficiency will be greatly affected. Therefore, the molecular carbide interface bridging layer can effectively match the phonon vibration spectrum of the graphene-metal interface and optimize the interface phonon transmission behavior, ensuring the mean free path and phonon transmission speed of phonons in the out-of-plane perpendicular direction.

[0020] In addition, traditional graphene blocks mainly rely on the phonon thermal conduction mechanism. The additionally introduced metal layer can also improve the electronic thermal conductivity contribution of the graphene block material, and has a dual phonon and electron transmission mechanism, thereby greatly improving the in-plane and out-of-plane thermal conductivity of the graphene block. At the same time, the multi-metal layer has better ductility and can be used as a packaging layer. It can also further reduce the structural instability of the traditional graphene block due to the easy dissociation of the layered structure caused by the weak van der Waals interaction, thereby improving the structural reliability of the graphene block under extreme use conditions and ensuring long-term and efficient heat dissipation performance.

[0021] A second technical solution of the present invention is to provide a bidirectional high-thermal-conductivity graphene block prepared using the aforementioned method. This block features a seamless heterogeneous metal-bonded nanostructure, effectively eliminating the pore defects present in traditional adhesive interfaces and reducing interfacial phonon scattering. The resulting bidirectional high-thermal-conductivity graphene block has controllable thickness, ranging from micrometers to millimeters, and boasts strong structural designability and high tolerance to extreme environments, demonstrating its potential for application in extreme thermal management.

[0022] The material is composed of alternating layers of micron-scale two-dimensional graphene films and nanoscale multi-element metal layers. Specifically, the two-dimensional graphene film has a thickness of 1 to 150 μm, an in-plane thermal conductivity of 1000 to 2000 W / (mK), and a volume fraction of 90 to 99.5% in the bulk material. The nanoscale multi-element metal layer includes a bridging layer, a thermal conductive layer, and a welding layer. The bridging layer is a 10 nm thick carbide of titanium carbide, nickel carbide, iron carbide, or tungsten carbide, or a 10 nm thick carbide of a titanium-nickel mixture. The mass fraction of nickel in the titanium-nickel mixture is 60%. The thermal conductive layer is metallic copper with a thickness of 10-250 nm. The welding layer is metallic silver with a thickness of 10-50 nm.

[0023] Beneficial effects of the present invention:

[0024] (1) Multiple two-dimensional graphene films are vertically stacked and solidified using multi-element nanometal layers, converting traditional van der Waals adhesion into heterogeneous metal covalent bonding, achieving seamless connection between high thermal conductivity two-dimensional graphene film elements, and making the graphene block have a lower interface pore defect structure and greatly improved interface connection strength.

[0025] (2) Based on this reliable seamless connection engineering, the graphene block material achieves high in-plane thermal conductivity and good out-of-plane heat transfer, making it a competitive new thermal management material.

[0026] (3) The obtained graphene block has good tolerance to extreme high and low temperature environments and structural stability. After hundreds of high / low temperature shocks (77 K ~ 573 K), it still maintains excellent assembly structure and thermal conductivity, and is expected to be used in aerospace and other fields.

[0027] (4) The obtained graphene block has a low density and controllable shape and size, and can be adjusted according to actual needs to adapt to more extreme thermal management application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Flowchart of the preparation of traditional glued graphene blocks and seamlessly bonded bidirectional high thermal conductivity graphene blocks;

[0029] Figure 2Scanning electron microscopy images of the surface and cross-section of a single metallized graphene film;

[0030] Figure 3 Physical picture of bidirectional high thermal conductivity graphene block;

[0031] Figure 4 Comparison of interface porosity between Example 1 and Comparative Example 1;

[0032] Figure 5 Effect of low temperature shock on the in-plane thermal conductivity of graphene bulk materials in Example 2 and Comparative Example 2;

[0033] Figure 6 Comparison of the effects of low-temperature shock on the appearance of graphene blocks in Example 2 and Comparative Example 2;

[0034] Figure 7 Effect of high temperature shock on the in-plane thermal conductivity of graphene bulk materials in Example 3 and Comparative Example 3;

[0035] Figure 8 Effect of high temperature shock on the appearance of graphene blocks in Example 3 and Comparative Example 3. DETAILED DESCRIPTION

[0036] 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.

[0037] 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.

[0038] The embodiments of the present invention are further described below with reference to a number of embodiments.

[0039] 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.

[0040] 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.

[0041] The purity of the metal target materials described in the present invention is >99%.

[0042] Example 1

[0043] (1) The graphene film (thickness 25 μm, in-plane thermal conductivity 1900 W / (mK)) was ultrasonically cleaned in acetone and alcohol solutions for 15 min, then rinsed with deionized water and dried naturally to remove various impurities introduced during the preparation process.

[0044] (2) Metal ion implantation on the surface of the graphene film. First, the graphene film is cleaned with argon ions and the vacuum degree in the cavity is less than 5 10 -3 The implantation was carried out at a pressure of 15 sccm, an argon flow rate of 150 sccm, a bias voltage of 400 V, a temperature of 150°C, an implantation energy of 30 kV, and a duration of 10 minutes. Subsequently, a titanium-60 wt% nickel composite metal target (purity >99%) was used. The implanted metal ions reacted in situ with the carbon atoms on the graphene film surface to form a 10 nm thick carbide transition layer.

[0045] (3) Multilayer metals were deposited on the graphene film modified with the titanium-nickel molecular bridge layer by magnetron sputtering technology. The output power was 2 kW, and a copper target (purity > 99%) and a silver target (purity > 99%) were used to deposit a copper layer with a thickness of 245 nm and a silver layer with a thickness of 25 nm. The entire process was carried out under vacuum protection. The two sides of the graphene film were treated in the same way to obtain a metallized graphene film (such as Figure 2 ).

[0046] (4) Cut a single metallized graphene film into discs to meet the thermal conductivity test requirements. Take 20 cut circular films, stack them vertically in a clean graphite mold, and use the spark plasma sintering process to obtain vertically stacked solidified graphene blocks (such as Figure 3 The curing and sintering process was carried out by a gradient heating method, that is, from room temperature to 400 °C for 4 minutes; then the temperature was raised to 500 °C in 4 minutes and kept at 500 °C for 10 minutes. Then the temperature was stopped and the cavity and sample were allowed to cool naturally. The vacuum degree was kept below 1×10 -3 Pa, and a vertical pressure of 10 MPa was applied to ensure that the curing was complete.

[0047] The thickness of the prepared graphene block is 505 μm, the in-plane thermal conductivity is 1649 W / (mK), the out-of-plane thermal conductivity is 8.88 W / (mK), and the in-plane electrical conductivity is 8.64×10 5 S / m. By Figure 4 It can be observed that this example has a dense and continuous graphene-metal interface layer and metal-metal interface layer. The filling of the pores by the carbide layer and metal atoms significantly eliminates interface defects, reducing the interface porosity to 1 / 6 of that of Comparative Example 1, effectively achieving a covalent and seamless connection between the graphene layer and the metal layer.

[0048] Example 2

[0049] The same as Example 1, except that 40 cut circular films are taken, stacked vertically one by one in a clean graphite mold, and a spark plasma sintering process is used to obtain vertically stacked and solidified graphene blocks.

[0050] After multiple low-temperature shocks, the macrostructure of this embodiment remains essentially unchanged ( Figure 6 )

[0051] Example 3

[0052] The same as Example 1, except that 60 cut circular films are taken, stacked vertically one by one in a clean graphite mold, and a spark plasma sintering process is used to obtain vertically stacked and solidified graphene blocks.

[0053] After 200 high temperature shock cycles (298 K ~ 573 K), the thermal conductivity of this embodiment still maintained 95%, and the original structure was still maintained after multiple high temperature thermal shocks ( Figure 8 ).

[0054] Example 4

[0055] The same as Example 1, except that the graphene film (thickness of 70 μm, in-plane thermal conductivity of 1700 W / (mK)) was used. Fifteen cut circular films were stacked vertically in a clean graphite mold, and a spark plasma sintering process was used to obtain a vertically stacked and solidified graphene block. The graphene block had a thickness of 1033 μm, an in-plane thermal conductivity of 1462 W / (mK), an out-of-plane thermal conductivity of 8.32 W / (mK), and an in-plane electrical conductivity of 7.68×10 5 S / m.

[0056] Example 5

[0057] Same as Example 1, except that the graphene film (thickness of 150 μm, in-plane thermal conductivity of 1500 W / (mK)) was used. Seven round films were cut and stacked vertically in a clean graphite mold. Spark plasma sintering was used to obtain a vertically stacked and solidified graphene block. The graphene block had a thickness of 1025 μm, an in-plane thermal conductivity of 1284 W / (mK), an out-of-plane thermal conductivity of 8.25 W / (mK), and an in-plane electrical conductivity of 6.75×10 5 S / m.

[0058] Example 6

[0059] The same as Example 1, except that iron is used as the bridging layer in step (2). The obtained graphene bulk material has an in-plane thermal conductivity of 1630 W / (mK) and an out-of-plane thermal conductivity of 8.18 W / (mK).

[0060] Example 7

[0061] Same as Example 1, except that tungsten is used as the bridging layer in step (2). The obtained graphene bulk material has an in-plane thermal conductivity of 1672 W / (mK) and an out-of-plane thermal conductivity of 8.68 W / (mK).

[0062] Example 8

[0063] The same as Example 1, except that the functional layer is made of high thermal conductivity copper metal with a thickness of about 10 nm; the welding layer is made of soft and low melting point silver metal with a thickness of about 10 nm.

[0064] Example 9

[0065] The same as Example 1, except that the functional layer is made of high thermal conductivity copper, 250 nm thick; the soldering layer is made of soft and low melting point silver, about 50 nm thick.

[0066] Comparative Example 1

[0067] The preparation method of conventional graphene bulk material specifically includes the following steps:

[0068] (1) The graphene film (thickness 25 μm, in-plane thermal conductivity 1900 W / (mK)) was ultrasonically cleaned in acetone and alcohol solutions for 15 min, then rinsed with deionized water and dried naturally to remove various impurities introduced during the preparation process.

[0069] (2) 20 graphene films were bonded layer by layer using a 1 μm thick ultra-thin polymer double-sided tape to obtain a polymer-bonded graphene block. The tape uses an ultra-thin polyethylene terephthalate transparent substrate and is coated on both sides with a polyacrylate-based polymer adhesive.

[0070] (3) Cold press the above samples at 10 MPa for 12 hours to improve the density. Cut the samples into disc shapes suitable for testing.

[0071] The thickness of the prepared graphene block is 513 μm, the in-plane thermal conductivity is 1513 W / (mK), the out-of-plane thermal conductivity is 1.82 W / (mK), and the in-plane electrical conductivity is 1.43×105 S / m (as shown in Table 1).

[0072] like Figure 4As shown, there are a large number of fine wrinkles on the surface of the graphene film, which is difficult to achieve conformal adhesion assembly with the polymer, so that the graphene of this comparative example and the polymer interface have a large number of pore defects, and the porosity can reach 12%. These unavoidable pores are easily filled with adiabatic air in actual use, so that there is huge interfacial thermal resistance inside the graphene block. And a large number of interfacial pore defects are easily formed under external force, which is the root cause of the destruction of the polymer adhesive-based graphene block structure under extreme conditions.

[0073] Comparative Example 2

[0074] The same as comparative example 1, except that 40 graphene films are bonded layer by layer.

[0075] The test results show that the thickness of Example 2 is 1009 μm, the in-plane thermal conductivity is 1507 W / (mK), the out-of-plane thermal conductivity is 8.53 W / (mK), and the in-plane electrical conductivity is 7.92×10 5 S / m; the thickness of Comparative Example 2 is 1024 μm, the in-plane thermal conductivity is 1228 W / (mK), the out-of-plane thermal conductivity is 1.67 W / (mK), and the in-plane electrical conductivity is 1.16×10 5 S / m.

[0076] like Figure 5 To verify the structural tolerance and performance stability of the resulting graphene bulk material in a low-temperature environment, a simulated low-temperature cyclic shock experiment was carried out using liquid nitrogen, and the graphene bulk material samples were tested multiple times in a temperature range of 77 K to 298 K. After 200 low-temperature shocks, the in-plane thermal conductivity of Comparative Example 2 decreased by 70%, while the in-plane thermal conductivity of Example 2 remained stable. This is due to the fact that the seamless metal nanolayer of Example 2 effectively reduced the interfacial porosity and blocked the penetration of liquid nitrogen molecules at the pore defects of the graphene membrane assembly interface, thereby avoiding the huge deformation of liquid helium molecules due to the gas-liquid phase transition, and suppressing the destructive damage that occurs to traditional polymer adhesive-based graphene bulk materials, such as bubbling between graphene layers and structural dissociation.

[0077] Comparative Example 3

[0078] The same as comparative example 1, except that 60 graphene films were bonded layer by layer to obtain a bonded graphene block. After testing, the thickness of Example 3 was 3026 μm, the in-plane thermal conductivity was 1336 W / (mK), the out-of-plane thermal conductivity was 8.11 W / (mK), and the in-plane electrical conductivity was 7.07×10 5 S / m; the thickness of Comparative Example 3 is 3073 μm, the in-plane thermal conductivity is 978 W / (mK), the out-of-plane thermal conductivity is 1.04 W / (mK), and the in-plane electrical conductivity is 0.92×10 5 S / m.

[0079] The thermal stability of graphene bulk is crucial to its performance and service life in high temperature scenarios. Figure 7 As shown in the figure, after 200 high-temperature shock cycles (298 K to 573 K), the in-plane thermal conductivity of Comparative Example 3 dropped sharply by nearly 80%, while that of Example 3 remained at 95%. This is because the polymer adhesive is susceptible to thermal decomposition at high temperatures. After multiple thermal shocks, Comparative Example 3 experienced interlayer debonding, significantly destroying the interlayer adhesion structure. However, Example 3, due to the seamless covalently bonded interface between the graphene film and the nanometal layer, retained its original structure after multiple high-temperature thermal shocks. This further demonstrates the excellent high-temperature tolerance of graphene monoliths assembled using covalent seamless bonding.

[0080] Comparative Example 4

[0081] The same as Comparative Example 1, except that the graphene film (thickness of 70 μm, in-plane thermal conductivity of 1700 W / (mK)) was used, 15 graphene films were bonded layer by layer to obtain a polymer adhesive-based graphene block.

[0082] The graphene block prepared in this comparative example has a thickness of 1049 μm, an in-plane thermal conductivity of 1251 W / (mK), an out-of-plane thermal conductivity of 1.46 W / (mK), and an in-plane electrical conductivity of 1.18×10 5 S / m.

[0083] Comparative Example 5

[0084] The same as Comparative Example 1, except that the graphene film (thickness of 150 μm, in-plane thermal conductivity of 1500 W / (mK)) was used, and seven graphene films were bonded layer by layer to obtain a polymer-bonded graphene block.

[0085] The graphene block prepared in this comparative example has a thickness of 1041 μm, an in-plane thermal conductivity of 1095 W / (mK), an out-of-plane thermal conductivity of 1.20 W / (mK), and an in-plane electrical conductivity of 1.03×10 5 S / m.

[0086] Comparative Example 6

[0087] Same as Example 1, except that in step 3, the metals were sputtered in the order of 245 nm silver layer and 25 nm copper layer. The resulting graphene bulk had an in-plane thermal conductivity of 1640 W / (mK) and an out-of-plane thermal conductivity of 7.88 W / (mK).

[0088] Comparative Example 7

[0089] Same as Example 1, except that in step 3, a 245 nm layer of iron was sputtered first, followed by a 25 nm layer of silver. The resulting graphene bulk had an in-plane thermal conductivity of 1554 W / (mK) and an out-of-plane thermal conductivity of 7.78 W / (mK).

[0090] Comparative Example 8

[0091] Same as Example 1, except that the thickness of the sputtered copper layer in step 3 is 5 nm. The obtained graphene bulk material has an in-plane thermal conductivity of 1354 W / (mK) and an out-of-plane thermal conductivity of 6.76 W / (mK).

[0092] Comparative Example 9

[0093] The same as Example 1, except that the thickness of the sputtered silver layer in step 3 is 100 nm. The obtained graphene bulk material has an in-plane thermal conductivity of 1454 W / (mK) and an out-of-plane thermal conductivity of 7.16 W / (mK).

[0094] Table 1 Thickness, density, thermal conductivity and electrical conductivity of each embodiment and comparative example

[0095] Material Thickness (μm) Density (g / cm3) In-plane thermal conductivity (W / mK) Out-of-plane thermal conductivity (W / mK) <![CDATA[In-plane conductivity (×10 5 S / m)]]> Example 1 505 2.45 1649±158 8.88±0.72 8.64±0.75 Comparative Example 1 513 1.91 1513±112 1.82±0.15 1.43±0.12 Example 2 1009 2.45 1507±148 8.53±0.77 7.92±0.51 Comparative Example 2 1024 1.91 1228±111 1.67±0.13 1.16±0.10 Example 3 3026 2.45 1336±132 8.11±0.64 7.07±0.43 Comparative Example 3 3073 1.91 978±87 1.04±0.09 0.92±0.07 Example 4 1033 2.27 1462±139 8.32±0.71 7.68±0.56 Comparative Example 4 1049 1.92 1251±105 1.46±0.10 1.18±0.11 Example 5 1025 2.21 1284±99 8.25±0.71 6.75±0.43 Comparative Example 5 1041 1.93 1095±83 1.20±0.11 1.03±0.09

[0096] As can be seen from Table 1, under the conditions of the same graphene film thickness and number of stacking layers, the graphene blocks prepared by the preparation method used in the present invention have significantly improved in-plane and out-of-plane thermal conductivity and in-plane electrical conductivity compared to the graphene blocks bonded by polymer using the traditional method.

[0097] Table 2 Effects of the types and thicknesses of the bridging layer, thermal conductive layer, and welding layer on the properties of graphene bulk

[0098] Material Bridge Layer Thermal conductive layer Welding layer Thermal conductive layer thickness (nm) Welding layer thickness In-plane thermal conductivity Out-of-plane thermal conductivity Example 1 Ti-Ni Cu Ag 245 25 1649±158 8.88±0.72 Example 6 Fe Cu Ag 245 25 1630±135 8.18±0.42 Example 7 W Cu Ag 245 25 1672±135 8.68±0.37 Comparative Example 6 Ti-Ni Ag Cu 245 25 1640±132 7.88±0.66 Comparative Example 7 Ti-Ni Fe Ag 245 25 1554±78 7.78±0.45 Comparative Example 8 Ti-Ni Cu Ag 5 25 1354±97 6.76±0.75 Comparative Example 9 Ti-Ni Cu Ag 245 100 1454±127 7.16±0.32

[0099] As shown in Table 2, the composition, thickness, and stacking order of the bridging layer, thermal conductive layer, and solder layer in the graphene bulk material have a significant impact on the graphene bulk. The formation of a covalent interfacial bridging layer and thermal conductive layers and solder layers of appropriate thickness in the graphene bulk prepared by the preparation method of the present invention significantly improves the in-plane and out-of-plane thermal conductivity and in-plane electrical conductivity of the graphene bulk material.

[0100] 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 method for preparing a bidirectional high thermal conductivity graphene block, characterized in that: The following steps are involved: (1) Clean the graphene film and let it dry naturally; (2) metal ion implantation is performed on the upper and lower surfaces of the graphene film to form a bridging layer; the metal ions are one or two of titanium, nickel, iron, and tungsten, and the thickness thereof is 10 nm; (3) Then, a metal copper layer and a silver layer are sequentially deposited on the bridging layer; wherein the thickness of the copper layer is 10-250 nm, and the thickness of the silver layer is 10-50 nm; thereby obtaining a metallized graphene film; (4) cutting the metallized graphene films and filling them into a graphite mold one by one, and vertically stacking and solidifying the multilayer metallized graphene films using a spark plasma sintering process to produce a bidirectional high thermal conductivity graphene block; The vertical stacking solidification method has a vacuum degree of less than 1×10 -3 Pa, and a thermocouple gradient heating method was used under the condition of applying a uniaxial pressure of 10 MPa, that is, from room temperature to 400 °C in 4 minutes, and then to 500 °C in another 4 minutes, and maintained at 500 °C for 10 minutes, and then the heating was stopped and naturally cooled in the cavity.

2. The preparation method according to claim 1, characterized in that The graphene film in step (1) is one of a pure graphene film and a graphene-based composite film.

3. The preparation method according to claim 1, characterized in that The ion implantation method in step (2) is to use a titanium target, a nickel target, an iron target, a tungsten target, or a titanium-nickel composite metal target to sputter a metal ion beam onto the surface of the graphene film.

4. A bidirectional high thermal conductivity graphene block prepared by the preparation method according to claim 1, characterized in that: It is composed of alternating graphene films and nanoscale multi-metal layers; the nanoscale multi-metal layers include a bridging layer, a thermal conductive layer, and a welding layer; the bridging layer is a carbide of one of titanium carbide, nickel carbide, iron carbide, tungsten carbide with a thickness of 10 nm, or a carbide of a titanium-nickel mixture with a thickness of 10 nm; the mass fraction of nickel in the titanium-nickel mixture is 60%; the thermal conductive layer is metallic copper with a thickness of 10-250 nm; the welding layer is metallic silver with a thickness of 10-50 nm.

5. The bidirectional high thermal conductivity graphene block according to claim 4, characterized in that: The volume fraction of the graphene film in the bidirectional high thermal conductivity graphene block is 90-99.5%.

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