Copper-based graphene composite material and preparation method and application thereof

Abstract

The invention provides a copper-based graphene composite material as well as a preparation method and application thereof, and the preparation method comprises the following steps: plating copper films on two surfaces of graphene paper subjected to ion cleaning by adopting magnetron sputtering to obtain Cu-GP; placing copper foils on two sides of the Cu-GP, and performing vacuum hot pressing to obtain the copper-based graphene composite material. According to the method, through magnetron sputtering deposition and vacuum hot pressing technologies, the prepared composite material has excellent in-plane heat conductivity and inter-plane heat conductivity; and the material also has thermal responsiveness and excellent mechanical properties, such as toughness, breaking strength and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-efficiency thermal management materials, and particularly relates to a copper-based graphene composite material, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of electronic devices such as 5G communication chips and high-computing power processors towards high power density and miniaturization, their heat flux density has increased exponentially, posing a huge challenge to traditional thermal management materials. Copper, due to its isotropic high thermal conductivity (~387 W·m -1 ·K -1 ), and good processability, has become a widely used matrix for heat transfer materials. The thermal conductivity of graphene exceeds 5000 W·m -1 ·K -1 , making it one of the materials with the highest known thermal conductivity. Therefore, the combination of graphene and copper is considered an ideal choice for thermal management applications and has become a current research hotspot.

[0003] Some studies have prepared graphene oxide-copper layer composite films through electrodeposition, ultrasonic spraying, and annealing heat treatment, and improved the thermal conductivity by introducing Cu-O-C covalent bonds and nickel-silver transition layers at the interface. However, the agglomeration of graphene and its poor wettability with most metals have led to difficulties in achieving good dispersion of carbon nanoparticles, which has always been the focus of research on carbon nanoparticle-reinforced metal matrix composites. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a copper-based graphene composite material, a preparation method thereof, and an application thereof, and the composite material has excellent thermal conductivity.

[0005] The present invention provides a preparation method of a copper-based graphene composite material, comprising the following steps:

[0006] Copper films are respectively deposited on both sides of the graphene paper after ion cleaning by magnetron sputtering to obtain Cu-GP;

[0007] Copper foils are placed on both sides of Cu-GP, and vacuum hot pressing is performed to obtain a copper-based graphene composite material.

[0008] Preferably, the conditions for the magnetron sputtering are as follows:

[0009] The power of the magnetron sputtering is 200 ± 50 W, the flow rate of argon is 18 - 22 sccm, and the vacuum degree is less than 1 Pa.

[0010] Preferably, the temperature of the vacuum hot pressing is 650 ± 10 °C, the pressure is 40 ± 5 MPa, and the time is 5 - 25 min.

[0011] Preferably, the arithmetic mean roughness of the copper film is 35 - 38 nm.

[0012] Preferably, the conditions for ion cleaning are as follows: the current is 38 - 42 mA, the argon gas flow rate is 18 - 22 sccm, the vacuum degree is less than 1 Pa, and the ion cleaning time is 18 - 22 min.

[0013] Preferably, the volume ratio of graphene paper in the copper - based graphene composite material is 16.7 - 66.7%.

[0014] Preferably, the thickness of the single - layer copper film in the copper - based graphene composite material is 1.5 ± 0.5 μm;

[0015] The thickness of the single - layer copper foil is 0.01 - 0.1 mm.

[0016] The present invention provides a copper - based graphene composite material prepared by the preparation method described in the above technical solution;

[0017] The copper - based graphene composite material has a sandwich structure, including copper foil / coated graphene paper / copper foil arranged in sequence.

[0018] Preferably, the copper - based graphene composite material is a stacked sandwich structure.

[0019] Preferably, the in - plane thermal conductivity of the copper - based graphene composite material reaches 806 W·m -1 ·K -1 , and the through - plane thermal conductivity is 8.2 W·m -1 ·K -1 .

[0020] The present invention provides an application of the copper - based graphene composite material prepared by the preparation method described in the above technical solution in rapid heat dissipation of high - power - density electronic devices, 5G communication chips or high - computing - power processors.

[0021] The present invention provides a preparation method of a copper - based graphene composite material, including the following steps: magnetron sputtering is used to deposit copper films on both sides of the graphene paper after ion cleaning to obtain Cu - GP; copper foils are placed on both sides of Cu - GP, and vacuum hot pressing is carried out to obtain the copper - based graphene composite material. By means of magnetron sputtering deposition and vacuum hot pressing technologies, the prepared composite material has excellent in - plane thermal conductivity and through - plane thermal conductivity; it also has thermal responsiveness and excellent mechanical properties, such as toughness, fracture strength, etc. When the volume ratio of graphene paper in the composite material prepared by the present invention is 66.7%, the in - plane thermal conductivity (k ll ) of the composite material reaches 805.8 W·m -1 ·K -1 , which is 118.6% higher than that of pure copper, and its through - plane thermal conductivity (k ⊥ ) is 8.17 W·m -1 ·K -1; The toughness of Cu / GP-66.7% reaches 6.45 MJ / m 3 , which is 9 times higher than that of the original GP and close to that of pure copper foil, greatly improving the mechanical strength of the graphene paper. Compared with pure copper foil, for the Cu / GP-66.7% composite material with the same thickness, on an 80 °C heating table, the surface temperature rises from 16.1 °C to 71.7 °C within 4 seconds and can drop to room temperature within 8 seconds, showing excellent heat transfer performance and having high practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the preparation process of the copper-based graphene composite material of the present invention;

[0023] Figure 2 Surface optical morphology diagrams of the graphene paper before and after copper plating film in Example 1 of the present invention;

[0024] Figure 3 SEM diagrams before and after copper plating film in Example 1 of the present invention;

[0025] Figure 4 AFM diagrams before and after copper plating film in Example 1 of the present invention;

[0026] Figure 5 Physical diagram of the composite material prepared in Example 1 of the present invention;

[0027] Figure 6 SEM cross-section of Cu / GP in Example 1 of the present invention;

[0028] Figure 7 For Figure 6 EDX characterization diagram of the area shown in a in

[0029] Figure 8 Raman spectra of GP and Cu / GP in Example 1 of the present invention;

[0030] Figure 9 Comparison of Raman spectra of graphene, Cu / GP (sample prepared in Example 1), and Cu / GP-EP (sample prepared in Comparative Example 1) (100 cm -1 ~900 cm -1 );

[0031] Figure 10 Transmission electron microscope (TEM) diagram of the copper / graphene (GP / Cu) interface. Among them, Figure b is the high-resolution TEM diagram of Figure a, and Figure c is the high-resolution TEM diagram of the area indicated by the dashed box in Figure b;

[0032] Figure 11 Electron diffraction (SAED) pattern of the copper / graphene (GP / Cu) interface;

[0033] Figure 12 It is an X-ray diffraction (XRD) analysis diagram of the copper / graphene (GP / Cu) interface;

[0034] Figure 13 It is a tensile strength test diagram of GP, Cu Foil, and Cu / GP composites;

[0035] Figure 14 It is a test diagram of the fracture strain, Young's modulus, and toughness of GP, Cu Foil, and Cu / GP composites;

[0036] Figure 15 It is a schematic diagram of the in-plane and inter-plane heat transfer effects of the composite material prepared in Example 1 (k || and k ⊥ represent the in-plane and inter-plane thermal conductivities respectively);

[0037] Figure 16 It is a diagram of the change in the cooling image of the composite material within 10 s at room temperature;

[0038] Figure 17 It is the temperature change curve during the test of different samples and the infrared thermal imaging change of Cu / GP;

[0039] Figure 18 It is the in-plane and inter-plane thermal conductivities of Cu / GP with five different graphene volume contents in Examples 1 to 5 of the present invention;

[0040] Figure 19 It is a comparison of the in-plane and inter-plane thermal conductivity coefficients of each Cu / GP in Examples 1 to 5 of the present invention and the reported Cu-based composite materials;

[0041] Figure 20 It is the in-plane thermal conductivity test of the composite materials prepared in Example 1 and Example 6 of the present invention;

[0042] Figure 21 It is the influence of the hot pressing time on the thermal conductivity in Examples 7 to 8 and Comparative Examples 2 to 3 of the present invention. Detailed implementation mode

[0043] The present invention provides a preparation method of a copper-based graphene composite material, comprising the following steps:

[0044] Copper films are respectively plated on both sides of the ion-cleaned graphene paper by magnetron sputtering to obtain Cu-GP;

[0045] Copper foils are placed on both sides of Cu-GP, and vacuum hot pressing is carried out to obtain a copper-based graphene composite material.

[0046] The present invention innovatively prepares a copper / graphene paper / copper sandwich structure composite material through magnetron sputtering deposition and vacuum hot pressing technology; the interfacial characteristics and heat conduction behavior of this composite material are also systematically studied. The research shows that this composite material has excellent in-plane thermal conductivity (k ll ), and inter-plane thermal conductivity (k ⊥ ). In addition, transient thermal testing shows that it has excellent thermal response performance. Moreover, this composite material exhibits excellent mechanical properties, especially the toughness is close to that of pure copper. While having high thermal conductivity, this composite material can maintain structural stability, providing an effective strategy for the development of new high-performance metal matrix composites.

[0047] In the present invention, copper films are respectively deposited on both sides of the graphene paper after ion cleaning by magnetron sputtering to obtain Cu-GP.

[0048] In the present invention, the graphene paper is cut into required sizes, fixed and then subjected to ion cleaning to remove surface impurities. The present invention uses ion cleaning on the graphene paper. Through ion cleaning, surface defects are generated on the graphene (GP), so that the high-energy Cu particles deposited by magnetron sputtering can penetrate the graphene defects. In the subsequent hot pressing process, Cu atoms diffuse through these defects or along the edges of the graphene, ultimately leading to interlayer swelling, thereby enhancing the sealing of the heterogeneous interface and making the heterogeneous interface present an atomic-level interlocking structure. Its alternating Cu-C configuration significantly enhances the interfacial bonding strength. And GP maintains its typical layered morphology and has high crystallinity, ensuring excellent thermal conductivity. This ultra-thin seamless heterogeneous interface structure significantly improves the structural stability of the material and shows great potential in extreme thermal management applications.

[0049] In the present invention, the conditions for ion cleaning are as follows: the current is 38 - 42 mA, specifically it can be 38 mA, 39 mA, 40 mA, 41 mA or 42 mA; the argon flow rate is 18 - 22 sccm, specifically it can be 18 sccm, 19 sccm, 20 sccm, 21 sccm or 22 sccm; the vacuum degree is less than 1 Pa; the ion cleaning time is 18 - 22 min, specifically it can be 18 min, 19 min, 20 min, 21 min or 22 min.

[0050] In the present invention, the conditions for the magnetron sputtering include: the power of the magnetron sputtering is 200 ± 50 W, specifically it can be 150 W, 160 W, 170 W, 180 W, 190 W, 200 W, 210 W, 220 W, 230 W, 240 W or 250 W; the argon flow rate is 18 - 22 sccm, specifically it can be 18 sccm, 19 sccm, 20 sccm, 21 sccm or 21 sccm; the vacuum degree is less than 1 Pa.

[0051] In the present invention, copper plating is first performed on one side of the GP, and then on the other side; the thickness of the single-layer copper film is 1.5 ± 0.5 μm; the arithmetic mean roughness R a of the obtained copper film is 35 - 38 nm, and the root mean square roughness R q is 47 - 48 nm. In the present invention, forming a copper film with a certain roughness helps to evenly conduct heat, reduce heat dissipation in the heat conduction path, and generally reduce the interfacial contact thermal resistance; moreover, the above-mentioned roughness also helps with the interfacial bonding force, facilitating the subsequent preparation of the Cu / GP composite film by the VHP process.

[0052] After obtaining the Cu-GP, in the present invention, copper foils (Cu Foil) are placed on both sides of the Cu-GP, and vacuum hot pressing is performed to obtain a copper-based graphene composite material. In the present invention, the graphene paper (Cu-GP) after copper plating is stacked with the copper foils in the order of Cu Foil / Cu-GP / Cu Foil and placed in a graphite mold for vacuum hot pressing.

[0053] In the present invention, the temperature of the vacuum hot pressing is 650 ± 10 °C, specifically it can be 640 °C, 645 °C, 650 °C, 655 °C or 660 °C; the pressure is 40 ± 5 MPa, specifically it can be 35 MPa, 36 MPa, 37 MPa, 38 MPa, 39 MPa, 40 MPa, 41 MPa, 42 MPa, 43 MPa, 44 MPa or 45 MPa; the time of the vacuum hot pressing is 5 - 25 min, specifically it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min or 25 min. In the present invention, the time of the vacuum hot pressing has a great influence on the thermal conductivity of the Cu / GP. If the hot pressing time is too short, there will be gaps at the bonding interface, making it difficult to ensure the structural stability and reliable thermal conductivity of the Cu / GP in a long-term extreme environment. If the hot pressing time is too long, the local stress in the Cu-C interface increases, thereby causing an increase in the phonon thermal resistance at the interface, and further reducing the thermal conductivity of the Cu / GP. By limiting the hot pressing time to 5 - 25 min in the present invention, better mechanical properties and thermal conductivity can be achieved.

[0054] The present invention provides an innovative solution for high-power device thermal management under extreme conditions by regulating the copper foil thickness and the multi-layer stacking structure, and precisely controlling the volume fraction and interfacial compatibility of the graphene film.

[0055] The thickness of the single-layer copper film in the copper-based graphene composite material prepared by the present invention is 1.5 ± 0.5 μm, and specifically can be 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2.0 μm; the copper film with the above thickness can achieve a good physical interlocking effect between the graphene paper and the copper foil, achieving the dual effects of high interfacial bonding strength and low interfacial thermal resistance.

[0056] The thickness of a single sheet of graphene paper is 40 - 45 μm, and specifically can be 40 μm, 41 μm, 42 μm, 43 μm, 44 μm or 45 μm; in the actual operation of the present invention, the number of graphene sheets will be adjusted according to the graphene volume ratio.

[0057] The thickness of the single-layer copper foil is 0.01 - 0.1 mm, and specifically can be 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm or 0.1 mm.

[0058] In the copper-based graphene composite material of the present invention, the volume ratio of the graphene paper is 16.7 - 66.7%. In specific embodiments, the volume ratio of the graphene paper in the copper-based graphene composite material is 40.0%, 33.3%, 28.6%, 16.7% or 66.7%. The present invention realizes the change of the graphene volume by different thicknesses. As the graphene volume content increases from 16.7% to 66.7%, its in-plane thermal conductivity increases from 554.4 W·m -1 ·K -1 to 805.8 W·m -1 ·K -1 ( Figure 18 in a)), and the linear fitting result shows that R 2 = 0.965, proving that the addition of graphene linearly increases the thermal conductivity of Cu / GP.

[0059] The present invention can also construct a double-layer sandwich structure, that is, first stack to form a structure of copper foil / coated graphene paper / copper foil / copper foil / coated graphene paper / copper foil, and hot press under the same conditions to construct a double-layer sandwich structure material.

[0060] The present invention provides a copper-based graphene composite material prepared by the preparation method described in the above technical solution;

[0061] The copper-based graphene composite material is a sandwich structure, including copper foil / coated graphene paper / copper foil arranged in sequence.

[0062] The copper-based graphene composite material in the present invention has a stacked sandwich structure; in a specific embodiment, the number of stacked layers is 2, that is, the structure of the copper-based graphene composite material includes copper foil / crystallized graphene paper / copper foil / crystallized graphene paper / copper foil.

[0063] In the present invention, the in-plane thermal conductivity of the copper-based graphene composite material reaches 806 W·m -1 ·K -1 , and the through-plane thermal conductivity is 8.2 W·m -1 ·K -1 .

[0064] The present invention also provides an application of the copper-based graphene composite material prepared by the preparation method described in the above technical solution in rapid heat dissipation of high-power density electronic devices, 5G communication chips or high-computing power processors.

[0065] In the present invention, a scanning electron microscope (SEM, Oxford, X-Max80) equipped with an energy dispersive X-ray spectrometer (EDX) was used to analyze the surface layer and interfacial bonding of the graphene-reinforced copper-based composite material (Cu / GP). The SEM cross-section samples were prepared by an ion beam cutting machine (Leica EM TIC 3X, Germany). Raman spectra were recorded using a Renishaw Invia reflectometer with a 532 nm laser beam. To further analyze the interfacial microstructure of the composite material, a field emission transmission electron microscope (TEM, JEOL-F200, Japan) was used for characterization, and the samples were prepared using a focused ion beam (FIB, Guoyi Quantum DB500, China) device (3 KV). At room temperature, a mechanical tensile test was carried out using a self-made tensile tester. Before the test, the sample was cut into an I-shaped piece with a total length of 35 mm, where the middle region was 15 mm long and 3 mm wide. The two ends of the sample were pasted on a paper frame to prevent damage during clamping. The gauge length was set to 15 mm, and the legs of the paper frame were cut off after the sample was loaded. Under the condition of a loading rate of 4 μm / s, the tensile stress-strain curve was obtained.

[0066] The thermal conductivity test method in the present invention:

[0067] The thermal diffusivity (α, mm 2 s –1), the in-plane thermal conductivity was measured using the in-plane mode of AGLF (sample holder: 25.4 mm in-plane circular wafer, lamp voltage: 260 V; pulse width: 0.05 ms, sample temperature: 25 °C) and the standard mode of AGLF-TIM (sample holder: 25.4 mm between-plane circular wafer; lamp voltage: 250 V; pulse width: 0.02 ms; sample temperature: 25 °C) for in-plane and out-of-plane directions, respectively. Before the measurement, a thin layer of graphite was sprayed on both sides of the sample to ensure consistent emissivity and high signal-to-noise ratio for accurate determination of the thermal diffusivity. Meanwhile, the specific heat capacity (Cp, J·g -1 K -1 ), was measured using a NETZSCH DSC 204F1 Phoenix instrument in a nitrogen atmosphere. a ). In addition, at 25 °C, the mass density (ρ) was measured using an analytical balance (MD-224, DST, Co., Ltd) based on Archimedes' principle. The mass of the sample was weighed in air (m b ), fully immersed in deionized water and weighed again (m

[0068]

[0069] where ρ water =1.0 g cm -3 . The thermal conductivity (k, W m -1 K -1 ) at 25 °C was calculated according to the following formula:

[0070] k = α × ρ × c p

[0071] The method for exploring thermal applications in the present invention:

[0072] Circular wafers of Cu / GP (thickness ~70 μm), Cu foil (thickness ~70 μm), and Cu / GP-D (thickness ~140 μm) with a diameter of 25.4 mm were cut. A thin layer of conductive graphite coating was evenly sprayed on the sample test surface to ensure consistent emissivity and high signal-to-noise ratio. These samples were placed on a heat source at a constant temperature of 80 °C, and the flatness of the contact surface was checked to ensure uniform heat conduction. The change in the infrared image during heating within 30 s was recorded, and then the heating stage was removed, and the change in the cooling image within 10 s at room temperature was recorded.

[0073] To further illustrate the present invention, a copper-based graphene composite material and its preparation method and application provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0074] In the following examples and comparative examples, commercially pure copper foil (Cu) was purchased from Shenzhen Huateng New Materials Technology Co., Ltd., China. High thermal conductivity graphene paper (GP) was purchased from Changzhou Fu'en Technology Co., Ltd., China. The chemical reagents in Comparative Example 1 were purchased from Sinopharm Chemical Reagent Co., Ltd., China. All aqueous solutions were prepared using deionized water (≥18.25 MΩ).

[0075] Example 1

[0076] Step 1: Preparation of Cu-GP

[0077] The graphene paper (GP) with a thickness of 42 μm was cut into a size of 40×40 mm, and its four corners were fixed using a self-made fixture. Subsequently, the fixed GP was placed in a magnetron sputtering machine. Under the conditions of a current of 40 mA, an argon gas flow rate of 20 sccm, and a high vacuum (less than 1 Pa), ion cleaning was carried out for 20 min to remove impurities on the surface of GP. Then, under the conditions of a sputtering power of 200 W, an argon gas flow rate of 20 sccm, and a high vacuum (less than 1 Pa), copper plating was performed on one side of GP for 80 min. Finally, sputtering copper plating was carried out on the other side of GP under the same conditions, and the sample was named Cu-GP.

[0078] Step 2: Preparation of Cu / GP

[0079] The Cu-GP was cut into circular samples with a diameter of 38 mm and placed at the central position, and copper foils with a diameter of 38 mm and a thickness of 0.01 mm were placed on both sides (stacked in the order of Cu Foil / Cu-GP / Cu Foil). The assembly was placed in a graphite mold, heated to 650 °C at a heating rate of 10 °C / min under a pressure of 40 MPa, and held for 25 min. At the same time, a vacuum (less than 1 Pa) was applied during the hot pressing process to prevent high-temperature oxidation. Subsequently, the sample was naturally cooled to room temperature and the pressure was reduced, and finally the Cu / GP composite material was obtained. In this example, the volume ratio of GP in the composite material was 66.7%, and the sample was abbreviated as Cu / GP, Cu / GP-66.7% or Cu / GP-25 M.

[0080] To achieve the high thermal conductivity and super stability of the Cu / GP composite material, the present application proposes a reliable magnetron sputtering copper plating and vacuum hot pressing process ( Figure 1 ) aiming to effectively eliminate the interfacial porosity and enhance the interfacial bonding force. Specifically, before sputtering copper plating on the surface of GP, ion cleaning was first carried out to remove surface contaminants, thereby ensuring the adhesion and uniformity of the copper plating layer. The pretreated GP was copper-plated on both sides by magnetron sputtering to form a copper thin film with a thickness of about 1.5 μm. Figure 2Figures a and b of this are the surface optical morphologies of GP before and after copper plating in Example 1. Before coating, the surface of GP presented regular grid-like textures. This is because GP is composed of multiple layers of graphene stacked to form a multi-layered structure. And due to the interlayer bonding through van der Waals forces, its non-uniformity leads to uneven stress distribution between layers, resulting in stress concentration in local areas, causing local micro-deformations in these areas and forming wrinkles or ripples on the surface. After copper plating (named Cu-GP), a continuous and dense copper film layer is formed on its surface, which has a certain improvement on its surface morphology. Moreover, the copper film can form metal-metal bonds (such as atomic diffusion and metallurgical bonding) with the copper foil during the subsequent hot pressing process, optimizing the inter-plane heat conduction efficiency through strong interfacial bonding.

[0081] Figure 3 In which, a and b are the SEM images of GP and Cu-GP respectively; Figure 3 As shown in b in which, copper, as a highly conductive metal, provides a good conductive channel, improving the clarity and contrast of the SEM image. Compared with Figure 3 a in which, granular copper clusters can be clearly observed on the surface of Cu-GP, especially concentrated at the wrinkled protrusions. This is due to the higher atomic and electron densities in these areas, where copper atoms tend to aggregate. At the same time, due to the natural steric hindrance formed by the roughness, the migration rate of copper atoms in these areas is lower, resulting in further concentration of copper atoms.

[0082] Figure 4 In which, a and b are the AFM images of the surfaces of GP and Cu-GP respectively. By comparison, it is found that the surface roughness of Cu-GP decreases, and Ra (arithmetic mean roughness of the profile) and Rq (root mean square roughness) decrease from 63.1 nm and 82.2 nm to 36.6 nm and 47.3 nm respectively. This indicates that the coating effectively reduces the density of sharp protrusions on the surface by locally covering the micron-scale concave areas on the surface of GP, while also reducing the air gaps and defects at the interface. And the lower roughness helps the uniform conduction of heat, reducing the scattering in the heat conduction path, and generally reducing the interfacial contact thermal resistance. And retaining a certain roughness also helps to enhance the interfacial bonding force, facilitating the preparation of the Cu / GP composite film by the subsequent VHP process.

[0083] After magnetron sputtering copper film, stack them in the order of Cu Foil / Cu-GP / Cu Foil, and vacuum hot press at 650 °C and 40 MPa for 25 min to obtain the composite material (Cu / GP) of this example. Figure 5 As shown in a in which, the Cu / GP composite film prepared in this example is a thin round sheet with a diameter of 38 mm. Mold hot pressing marks can be seen at the edge. The copper foils on both sides wrap the copper-plated GP. The surface is basically smooth except for a small amount of wrinkles. The GP patterns embossed by pressing can be observed on the surface of the copper foil with the naked eye. AsFigure 5 As shown in b, after vacuum hot pressing, the Cu / GP composite film exhibits remarkable flexibility and can withstand large deformations during bending. This mechanical behavior is mainly attributed to the high strength and flexibility of the graphene paper and the ductility of the copper foil.

[0084] Figures 6a and 6b are respectively the SEM cross-sectional image and the partial enlarged view (scale bar = 50 μm) of the Cu / GP-66.7% composite film sample after ion beam cutting. The upper and lower layers of the sample are both copper foils with the same thickness (∼10 μm), and in the middle is the Cu-GP layer, with thicknesses of 22.9 μm, 36.3 μm, and 12.1 μm from top to bottom. The reason for the increased cross-sectional thickness of the top copper foil may be that during FIB cutting of the copper foil, the high-energy ion beam interacts with the copper foil surface, triggering a deposition effect during the cutting process, that is, due to the bombardment of the high-energy ion beam, copper atoms may rearrange and deposit on the sample surface or the cutting edge. This deposition effect may cover part of the cross-section of the graphene paper, making the thickness of the upper copper foil appear to increase.

[0085] Figure 7 For Figure 6 The EDX (Energy Dispersive X-Ray Spectroscopy) characterization results of the area shown in a. Among them, copper elements are mainly distributed in the copper foil layer, carbon elements are mainly concentrated in the Cu-GP layer, and no significant distribution of oxygen elements is detected almost throughout the characterization area, indicating that oxidation reactions may have been effectively avoided during the preparation of this composite film. There may be a Cu-C diffusion layer at the interface between the copper foil and the Cu-GP, but it is difficult to directly observe obvious element doping or diffusion layer at a magnification of 50 μm.

[0086] As Figure 6 shown in b, there are no obvious microvoids at the Cu-C interface of the Cu / GP material. Combining Figure 7 the EDX analysis of the distribution of Cu and C elements on the cross-section further proves the seamless and tight combination of the Cu-C interface. A strong interface bond is crucial for ensuring the structural stability and reliable thermal conductivity of Cu / GP in long-term extreme environments. Considering the weak van der Waals force of the graphene intermediate layer and the low permeability between graphene and copper, the present invention designs an interface with a sputtered copper layer to enhance the seamless combination of the copper foil and graphene and ensure low interface thermal resistance.

[0087] Through Figure 8 a and b, the changes in the Raman spectra of GP and Cu / GP can be compared. Figure 8b is the Raman spectrum of Cu / GP. Compared with Figure 8 the GP Raman spectrum shown in a, it has a peak at 1580 cm -1There is a wide and small bulge at this position, with a relatively large peak width, which may be a weakened manifestation of the G peak of graphene. As a metal material, copper foil has strong reflection and absorption capabilities for laser, especially when the copper foil is relatively thick, it is difficult for the laser to penetrate the copper foil to reach the graphene paper below. Therefore, the laser signal may not be able to effectively excite the Raman scattering of the graphene paper, resulting in significant suppression of the G peak signal, with the G peak becoming wider and its intensity decreasing. This phenomenon is also manifested in other graphene characteristic peaks, such as the 2D peak. Due to the decrease in the intensities of the G peak and the 2D peak, the proportion of the D peak in the overall spectrum in Figure 8b increases, which does not indicate an increase in the defect density of graphene. At the same time, for standard graphene, the 2D peak in the Raman spectrum is usually located at about 2670 cm -1 or so. As can be seen from Figure 8a, the 2D peak position of GP undergoes a blue shift (located at about 2722 cm -1 or so), and through the combined peak intensity ratio IG / I2D, it can be verified that the GP used in the present invention is mainly composed of multi-layer graphene stacked together.

[0088] For further comparison, we prepared Cu-GP-EP by electroplating copper, and then prepared the composite material Cu / GP-EP through the same hot pressing process as in Example 1, that is, Comparative Example 1.

[0089] Comparative Example 1

[0090] Step 1: Preparation of Cu-GP-EP

[0091] Prepare a comparative sample by electroplating copper. First, prepare a CuSO 4 solution with a concentration of 1.07 mol / L. The specific method is to dissolve 800 g of CuSO 4 ·5H 2 O in 100 mL of H 2 SO 4 , and add deionized water to make up 3 L. At an electrolysis temperature of 45 °C, use a 40×40 mm graphene paper as the cathode and a copper electrode as the anode, and apply a current of 5 A for electroplating (EP) for 10 min. After the experiment is completed, wash the sample with distilled water and dry it, and name it Cu-GP-EP.

[0092] Step 2: Cut the Cu-GP-EP into circular samples with a diameter of 38 mm and place them at the center position. Place copper foils with a diameter of 38 mm and a thickness of 0.01 mm on both sides (stacked in the order of Cu Foil / Cu-GP-EP / Cu Foil). Put this assembly into a graphite mold, heat it to 650 °C at a heating rate of 10 °C / min under a pressure of 40 MPa, and hold for 25 min. At the same time, apply a vacuum (less than 1 Pa) during the hot pressing process to prevent high-temperature oxidation. Subsequently, the sample is naturally cooled to room temperature and the pressure is released to obtain a copper-based graphene composite material.

[0093] Figure 9 Figure for the comparison of Raman spectra of graphene, Cu / GP (the sample prepared in Example 1), and Cu / GP-EP (the sample prepared in Comparative Example 1) (100 cm -1 ~900 cm -1 ). By analyzing the characteristic peaks, it can be seen that Cu / GP-EP prepared by the electroplating method is more likely to generate copper oxides such as CuO and Cu 2 O. These copper oxides will hinder the mutual diffusion of copper atoms during the Cu-Cu hot pressing bonding process, reduce the interfacial bonding strength, and also have a certain impact on the heat conduction efficiency of the interface.

[0094] On the contrary, by analyzing the Cu / GP sample formed by hot pressing in Example 1 through Raman spectroscopy, almost no D peak appears in the graphene layer ( Figure 9 ), indicating that the graphene layer is not damaged during the hot pressing process.

[0095] In summary, the microstructure characterization of Cu / GP shows that the magnetron sputtering copper plating and vacuum hot pressing processes optimize the interfacial composition and microstructure of the Cu / GP composite material, lay the foundation for seamless and tight assembly, and endow Cu / GP with excellent thermal conductivity and environmental adaptability. Scanning electron microscopy (SEM) reveals that the surface of GP presents characteristic wrinkles and layered stacking morphology. In addition, the almost invisible D peak (1350 cm -1 ) in the Raman spectrum confirms its high crystallinity and provides a structural basis for excellent thermal conductivity. Surface topography analysis shows that the roughness of Cu-GP after copper plating (Ra = 36.6 nm) is slightly lower than that of the original GP (Ra = 63.1 nm), a decrease of 41.8%, which is attributed to the dense coverage of the sputtered copper coating. This phenomenon indicates that the magnetron sputtering process significantly enhances the interfacial bonding strength by reducing the interfacial porosity and improving the metal-carbon interface coherency.

[0096] The high-resolution SEM image shows that the Cu-C interface transition region is continuous and dense. Combining with the EDX elemental surface distribution analysis, it is confirmed that there is a seamless and tightly bonded Cu / C interface at the interface. Further, Raman spectroscopy proves that the Raman spectrum of Cu / GP after hot pressing maintains high crystallinity characteristics, confirming that the graphene structure is not damaged during the process, providing a structural basis for high thermal conductivity.

[0097] To deeply explore the structural evolution of the copper / graphene (GP / Cu) interface, cross-sectional samples were prepared by focused ion beam (FIB) and characterized by transmission electron microscopy (TEM). As Figure 10 shown in a, the heterointerface presents an atomic-level interlocking structure, and its alternately distributed Cu-C configuration significantly enhances the interface bonding strength. Figure 10 The high-resolution TEM (HR-TEM) images in b and c show that the carbon layer spacing at the interface expands to 0.454 nm, which is 36% larger than the theoretical value of graphene (0.334 nm). This may be due to the generation of defects during the ion cleaning process ( Figure 8 shown in a), enabling the high-energy Cu particles deposited by magnetron sputtering to penetrate the graphene defects. The subsequent hot pressing process promotes the diffusion of Cu atoms through these defects or along the graphene edges, ultimately leading to interlayer swelling. At the same time, the bulk Cu near the interface shows a (111) lattice fringe spacing of 0.202 nm, which is consistent with the face-centered cubic (FCC) copper structure. Figure 11 The selected area electron diffraction (SAED) pattern of Figure 12 confirms the polycrystalline characteristics of Cu, which are indexed as the (111), (200), and (220) crystal planes, presenting polycrystalline characteristics, thus enhancing the sealing of the heterointerface.

[0098] Based on the clearly characterized structural features of the Cu / GP layered material, it is crucial to study its mechanical behavior under external loading. Although graphene-based materials usually exhibit limited mechanical strength due to weak interlayer interactions, in this study, a sandwich-structured composite material prepared by hot pressing copper foil has achieved a significant improvement in mechanical properties. As Figure 13 and Figure 14As shown, the tensile strength of the Cu / GP-66.7% composite material reaches 84.6 MPa, the fracture strain is 12.4%, and the Young's modulus is 2.15 GPa, which are 3.1 times, 2.4 times, and 4.4 times higher than those of pure GP, respectively. It is worth noting that the toughness of this composite material reaches 6.45 MJ / m³, which is 9.0 times higher than that of GP and close to 7.45 MJ / m of pure copper foil. 3 This excellent mechanical synergistic effect may be attributed to the effective load transfer achieved by the Cu-GP interfacial bonding structure.

[0099] Figure 15 Figure showing the effects of in-plane and inter-plane heat transfer of the material (k || and k ⊥ represent in-plane and inter-plane thermal conductivities, respectively). The in-plane thermal conductivity (k || ) of graphene paper is extremely high, which is due to the unique two-dimensional honeycomb structure of graphene and the strong covalent bonds between carbon atoms. Phonons are rarely scattered during the transfer process, and this structure enables heat to be transferred quickly and effectively within the graphene plane. In contrast to the in-plane thermal conductivity, the inter-plane (k ⊥ ) thermal conductivity of graphene paper is relatively low. This is because the interaction between graphene layers is weak (van der Waals force), resulting in a large hindrance to heat transfer between layers; the test results of the in-plane and inter-plane thermal conductivities of Example 1 show that after thermocompression bonding of graphene paper with materials having a lower thermal conductivity (such as copper foil), the overall in-plane thermal conductivity of the composite material can still reach 805.8 W·m -1 ·K -1 , and the inter-plane thermal conductivity is 8.2 W·m -1 ·K -1 .

[0100] To further compare the heat transfer capabilities of Cu / GP and Cu foil, discs with a diameter of 25.4 mm of Cu / GP (thickness ~80 μm), Cu foil (thickness ~80 μm), and Cu / GP-D (thickness ~134 μm) were cut. A thin layer of conductive graphite coating was evenly sprayed on the sample test surface to ensure consistent emissivity and high signal-to-noise ratio. These samples were placed on a heat source at a constant temperature of 80 °C, and the flatness of the contact surface was checked to ensure uniform heat conduction. The change in the heating image within 30 s was recorded, and then the heating stage was removed, and the change in the cooling image within 10 s at room temperature was recorded (see Figure 16 ). Figure 17Temperature change curves of different samples during the test and infrared thermal imaging changes of Cu / GP. Compared with Cu Foil, the surface temperature of Cu / GP-66.7% with a similar thickness rises faster during heating, from 16.1 °C to 71.7 °C within 4 s, 13.8 °C higher than that of Cu Foil, and drops faster during cooling. The heating curve of Cu / GP-D in the first 3 s basically coincides with that of Cu / GP, but its heating rate and cooling rate are slightly lower than those of Cu / GP. This may be because Cu / GP has a shorter heat conduction path and a smaller volume, resulting in a smaller heat capacity, lower thermal inertia, and less interfacial thermal resistance, so it shows a faster response to temperature changes in the rapid heating scenario.

[0101] In summary, thanks to the reliable sputtered copper-plated optimized interface design of Cu / GP, a strong interfacial adhesion between Cu and GP in the composite material is achieved, and excellent thermal conductivity is obtained.

[0102] The present invention also provides Cu / GP with different graphene contents (Examples 2 to 5) and scalable compatibility (Example 6) to meet future extreme thermal management requirements.

[0103] Example 2

[0104] This example is basically the same as Example 1, except that the thickness of the copper foils on both sides is 0.03 mm. In this example, the volume fraction of GP in the composite material is 40.0%, and the sample is abbreviated as Cu / GP-40.0%.

[0105] Example 3

[0106] This example is basically the same as Example 1, except that the thickness of one copper foil is 0.03 mm and the other is 0.05 mm. In this example, the volume fraction of GP in the composite material is 33.3%, and the sample is abbreviated as Cu / GP-33.3%.

[0107] Example 4

[0108] This example is basically the same as Example 1, except that the thickness of the copper foils on both sides is 0.05 mm. In this example, the volume fraction of GP in the composite material is 28.6%, and the sample is abbreviated as Cu / GP-28.6%.

[0109] Example 5

[0110] This example is basically the same as Example 1, except that the thickness of the copper foils on both sides is 0.10 mm. In this example, the volume fraction of GP in the composite material is 16.7%, and the sample is abbreviated as Cu / GP-16.7%.

[0111] Example 6

[0112] In order to further increase the thickness of Cu / GP to meet different environmental requirements, in this example, a double-layer Cu / GP-66.7% laminated hot pressing method is used to prepare a double-layer sandwich structure material. The preparation process of this example is basically the same as that of Example 1. The difference is that in Step 2, two pieces of Cu / GP are hot pressed and combined under the same conditions, that is, a structure of copper foil / carbon-coated graphene paper / copper foil / copper foil / carbon-coated graphene paper / copper foil is first stacked and hot pressed under the same conditions to construct a double-layer sandwich structure material, named Cu / GP-D.

[0113] The GP used in the present invention has excellent in-plane thermal conductivity of 1073.0 W·m -1 ·K -1 . And the Cu-GP after magnetron sputtering copper plating still maintains an in-plane thermal conductivity of 987.5 W·m -1 ·K -1 , which lays the foundation for the high thermal conductivity Cu / GP composite material. As Figure 18 shown, the in-plane and through-plane thermal conductivities of Cu / GP with five different graphene volume contents in Examples 1-5 were measured. As the graphene volume content increased from 16.7% to 66.7%, its in-plane thermal conductivity increased from 554.4 W·m -1 ·K -1 to 805.8 W·m -1 ·K -1 ( Figure 18 a in the figure), and the linear fitting result shows that R 2 = 0.965, proving that the addition of graphene linearly increases the thermal conductivity of Cu / GP.

[0114] However, the analysis shows that as the graphene volume content increases, the through-plane thermal conductivity k ⊥ of Cu / GP decreases from 26.7 W·m -1 ·K -1 to 8.2 W·m -1 ·K -1 ( Figure 18 b in the figure). This is reasonable because the in-plane alignment of graphene will generate a large amount of thermal resistance along the perpendicular plane, thus significantly reducing the through-plane thermal conductivity.

[0115] Figure 19Comparison of in-plane and through-plane thermal conductivities of each Cu / GP in Examples 1 - 5 and reported Cu-based composite materials. As can be seen from the figure, except for the graphene-based thick film material (GTF-SBA: Graphene-thickfilm Seamless-bonding Assembly) which has an ultra-high in-plane thermal conductivity due to the ordered arrangement of graphene and strong interfacial adhesion (forming an atomic seamless bonding interface by sintering graphite film layers through Ag / Cu), by optimizing the volume fraction of graphene paper, the thermal conductivity of the Cu / GP composite film provided by the present invention is superior to most currently known Cu-based thermal conductive composite materials. Moreover, compared with the reported copper / graphene composite materials used for thermal management, with the change of graphene content, the k ll of the composite material of the present invention always exhibits a relatively high thermal conductivity, which is entirely due to the ideal interfacial structure of Cu / GP.

[0116] In addition, the in-plane thermal conductivity of the double-layer sandwich structure material (Cu / GP-D) in Example 6 is 816.1 W·m -1 ·K -1 , indicating that there is no significant difference in the in-plane thermal conductivity between the single-layer and double-layer configurations of the Cu / GP composite film ( Figure 20 ), suggesting that the increased film layer does not significantly increase the interfacial thermal resistance. This is because whether it is a single-layer or double-layer configuration, due to the extremely high thermal conductivity of graphene paper, it becomes the main heat conduction path of the composite film. The increased film layer does not significantly increase the heat conduction path and does not introduce excessive interfacial thermal resistance (the interfacial thermal resistance is relatively low after thermal bonding of copper foils).

[0117] In addition, the present invention also uses Examples 3, 7 - 8 and Comparative Examples 2 - 3 to study the influence of hot pressing time on the in-plane and through-plane thermal conductivities of Cu / GP-33.3%.

[0118] Example 7

[0119] This example is basically the same as Example 3, and the only difference is that the hot pressing time in Step 2 is 5 min, and the sample is abbreviated as Cu / GP-5 M.

[0120] Example 8

[0121] This example is basically the same as Example 3, and the only difference is that the hot pressing time in Step 2 is 15 min, and the sample is abbreviated as Cu / GP-15 M.

[0122] Comparative Example 2

[0123] This example is basically the same as Example 3, and the only difference is that the hot pressing time in Step 2 is 35 min, and the sample is abbreviated as Cu / GP-35 M.

[0124] Comparative Example 3

[0125] This example is basically the same as Example 3, and the only difference is that the hot pressing time in Step 2 is 45 min, and the sample is abbreviated as Cu / GP-45 M.

[0126] The results show that as the hot pressing time increases, the in-plane thermal conductivity reaches the maximum value at 25 min and then begins to decrease ( Figure 21 in a)). This may be because as the hot pressing time prolongs, the local stress in the Cu-C interface increases, which causes an increase in the phonon thermal resistance at the interface, and then reduces the thermal conductivity of Cu / GP. A similar phenomenon also appears in the change of k of Cu / GP-33.3%, further proving that a reasonable hot pressing time is helpful for the formation of the Cu-C interface ( ⊥ in b)). Figure 21 in b)).

[0127] As can be seen from the above examples, the present invention prepares a copper / copper-plated graphene paper (Cu / GP) sandwich structure composite material by magnetron sputtering and vacuum hot pressing technologies, and systematically studies its interface characteristics and heat conduction behavior. The sputtering process deposits a dense copper layer of about 1.5 μm on the surface of GP to form a metallurgical bond, and ion cleaning increases the surface defects of GP and also improves the interface bonding strength. By precisely controlling the graphene volume fraction (16.7~66.7%), the anisotropic thermal conductivity is optimized, and k ll increases linearly to 805.8 W·m -1 ·K -1 , which is 118.6% higher than that of pure copper, and k ⊥ remains above 8.17 W·m -1 ·K -1 . The multi-layer structure of Cu / GP-D reaches 816.1 W·m -1 ·K -1 and does not accumulate interface thermal resistance, showing excellent scalability. Mechanical tests show that the tensile strength, fracture strain and Young's modulus of Cu / GP-66.7% are 3.1 times, 2.4 times and 4.4 times higher than those of pure GP respectively. And the toughness reaches 6.45 MJ / m³, which is 9.0 times higher than that of GP. In the 80 °C transient heat test, Cu / GP-66.7% heats up to 71.7 °C within 4 s, which is 13.8 °C higher than the equilibrium temperature of the copper foil with the same thickness, and cools down to room temperature within 8 s. This interface engineering strategy provides a universal solution for the development of graphene metal matrix composites with synergistic enhancement of heat and mechanics.

[0128] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a copper-based graphene composite material, comprising the following steps: The copper film was plated on both sides of the ion-cleaned graphene paper by magnetron sputtering to obtain Cu-GP. Copper foils are placed on both sides of the Cu-GP, and vacuum hot pressing is performed to obtain a copper-based graphene composite material.

2. The preparation method according to claim 1, characterized in that: The conditions adopted for the magnetron sputtering are: The power of magnetron sputtering is 200±50W, the flow rate of argon is 18~22sccm, and the vacuum degree is less than 1Pa; The vacuum hot pressing is performed at a temperature of 650±10° C., a pressure of 40±5 MPa, and a time of 5 to 25 min.

3. The preparation method according to claim 1, characterized in that: The arithmetic mean roughness of the copper film profile is 35~38nm.

4. The preparation method according to claim 1, characterized in that: The conditions used for ion cleaning are: current 38~42mA, argon gas flow rate 18~22sccm, vacuum degree less than 1Pa, and ion cleaning time 18~22min.

5. The preparation method according to claim 1, characterized in that: The volume proportion of graphene paper in copper-based graphene composites is 16.7~66.7%.

6. The preparation method according to claim 1, characterized in that: The thickness of the single-layer copper film in the copper-based graphene composite material is 1.5 ± 0.5 μm; The thickness of a single layer of copper foil is 0.01~0.1mm.

7. A copper-based graphene composite material, prepared by the preparation method according to any one of claims 1 to 6; The copper-based graphene composite material is a sandwich structure, comprising copper foil / coated graphene paper / copper foil arranged in sequence.

8. The copper-based graphene composite material according to claim 7, characterized in that: The copper-based graphene composite material is a stacked sandwich structure.

9. The copper-based graphene composite material according to claim 7, characterized in that: The in-plane thermal conductivity of the copper-based graphene composite material reaches 806 W·m -1 ·K -1 The inter-surface thermal conductivity is 8.2 W·m -1 ·K -1 .

10. An application of a copper-based graphene composite material prepared by the preparation method according to any one of claims 1 to 6 in rapid heat dissipation of high-power density electronic devices, 5G communication chips or high-computing power processors.

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