A copper-based graphene composite material and its preparation method and application

Abstract

The present invention provides a copper-based graphene composite material, its preparation method, and application, comprising the following steps: copper coating is performed on both sides of ion-cleaned graphene paper using magnetron sputtering to obtain Cu-GP; copper foil is placed on either side of the Cu-GP, and vacuum hot pressing is performed to obtain the copper-based graphene composite material. This method, through magnetron sputtering deposition and vacuum hot pressing, results in a composite material with excellent in-plane and inter-plane thermal conductivity, thermal responsiveness, and excellent mechanical properties, such as toughness and fracture strength.

Description

Technical Field

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

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

[0003] Some studies have fabricated graphene oxide-copper composite films through electrodeposition, ultrasonic spraying, and annealing heat treatment, and have improved thermal conductivity by introducing Cu-OC covalent bonds and a nickel-silver transition layer at the interface. However, graphene agglomeration and its poor wettability with most metals have made it difficult to achieve good dispersion of carbon nanoparticles, which has long been a research focus on carbon nanoparticle-reinforced metal matrix composites. Summary of the Invention

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

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

[0006] Magnetron sputtering was used to deposit copper films on both sides of the ion-cleaned graphene paper to obtain Cu-GP.

[0007] Copper foils were placed on both sides of the Cu-GP and vacuum hot-pressed to obtain a copper-based graphene composite material.

[0008] Preferably, the magnetron sputtering adopts the following conditions:

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

[0010] Preferably, 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 minutes.

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

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

[0013] Preferably, the volume proportion 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 a single layer of copper foil is 0.01~0.1mm.

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

[0017] The copper-based graphene composite material is a sandwich structure, comprising 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 The inter-surface thermal conductivity is 8.2 W·m -1 ·K -1 .

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

[0021] The present invention provides a method for preparing a copper-based graphene composite material, comprising the following steps: using magnetron sputtering to plate copper films on both sides of ion-cleaned graphene paper to obtain Cu-GP; placing copper foil on both sides of the Cu-GP, and vacuum hot pressing to obtain a copper-based graphene composite material. This method uses magnetron sputtering deposition and vacuum hot pressing technology to ensure that the prepared composite material has excellent in-plane thermal conductivity and inter-plane thermal conductivity; it also has thermal responsiveness and excellent mechanical properties, such as toughness and fracture strength. 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 ) reached 805.8 W·m -1 ·K -1 , which is 118.6% higher than pure copper, and its inter-surface thermal conductivity (k ⊥ ) is 8.17 W·m -1 ·K -1;Cu / GP-66.7% has a toughness of 6.45 MJ / m 3 , a nine-fold improvement over the original GP, approaching that of pure copper foil, significantly enhancing the mechanical strength of graphene paper. Compared to pure copper foil, the surface temperature of a Cu / GP-66.7% composite material of the same thickness rose from 16.1°C to 71.7°C in 4 seconds on an 80°C heating table, and dropped to room temperature in 8 seconds, demonstrating excellent heat transfer properties and 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 of graphene paper before and after copper coating in Example 1 of the present invention;

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

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

[0026] Figure 5 This is a physical picture of the composite material prepared in Example 1 of the present invention;

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

[0028] Figure 7 for Figure 6 EDX characterization of the area shown in a;

[0029] Figure 8 The Raman spectra of GP and Cu / GP in Example 1 of the present invention are shown below:

[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 ~900cm -1 )picture;

[0031] Figure 10 Figure 2 is a transmission electron microscope (TEM) image of the copper / graphene (GP / Cu) interface, where Figure b is a high-resolution TEM image of Figure a, and Figure c is a high-resolution TEM image of the dotted box in Figure b;

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

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

[0034] Figure 13 The tensile strength test graphs of GP, Cu Foil and Cu / GP composite materials;

[0035] Figure 14 The fracture strain, Young's modulus and toughness test graphs of GP, Cu Foil and Cu / GP composites;

[0036] Figure 15 Schematic diagram of the heat transfer effect within and between the surfaces of the composite material prepared in Example 1 (k || and k ⊥ denote the in-plane and inter-plane thermal conductivities, respectively);

[0037] Figure 16 This is the temperature drop image change diagram of the composite material at room temperature within 10s;

[0038] Figure 17 The temperature change curves of different samples during the test and the infrared thermal imaging changes of Cu / GP;

[0039] Figure 18 are 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 Comparison of the in-plane and inter-plane thermal conductivity of each Cu / GP of Examples 1 to 5 of the present invention and reported Cu-based composite materials;

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

[0042] Figure 21 The figure shows the effect of hot pressing time on thermal conductivity of Examples 7-8 of the present invention and Comparative Examples 2-3. DETAILED DESCRIPTION

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

[0044] Magnetron sputtering was used to deposit copper films on both sides of the ion-cleaned graphene paper to obtain Cu-GP.

[0045] Copper foils were placed on both sides of the Cu-GP and vacuum hot-pressed to obtain a copper-based graphene composite material.

[0046] The present invention innovatively prepared a copper / graphene paper / copper sandwich structure composite material through magnetron sputtering deposition and vacuum hot pressing technology; the interface characteristics and thermal conductivity behavior of the composite material were systematically studied. The research shows that the composite material has excellent in-plane thermal conductivity (k ll ) and inter-surface thermal conductivity (k ⊥ ). Furthermore, transient thermal testing demonstrated excellent thermal response. Furthermore, the composite exhibited exceptional mechanical properties, particularly toughness approaching that of pure copper. This composite, while maintaining structural stability while exhibiting high thermal conductivity, offers an effective strategy for the development of new high-performance metal-matrix composites.

[0047] The present invention adopts magnetron sputtering to plate copper films on both sides of the graphene paper after ion cleaning to obtain Cu-GP.

[0048] The present invention cuts graphene paper into the required size, fixes it, and then performs ion cleaning to remove surface impurities. The present invention uses ion cleaning of graphene paper. Ion cleaning generates surface defects in graphene (GP), which in turn allows high-energy Cu particles deposited by magnetron sputtering to penetrate the graphene defects. The subsequent hot pressing process causes Cu atoms to diffuse through these defects or along the edges of graphene, ultimately leading to interlayer expansion, thereby enhancing the sealing of the heterogeneous interface and making the heterogeneous interface present an atomic-level interlocking structure. Its alternating distribution of Cu-C configuration significantly enhances the interface bonding strength. GP maintains its typical layered morphology and has high crystallinity, ensuring excellent thermal conductivity. This ultra-thin and 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 adopted for ion cleaning are: current 38~42mA, specifically 38mA, 39mA, 40mA, 41mA or 42mA; argon gas flow rate is 18~22sccm, specifically 18sccm, 19sccm, 20sccm, 21sccm or 22sccm; vacuum degree is less than 1Pa; ion cleaning time is 18~22min, specifically 18min, 19min, 20min, 21min or 22min.

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

[0051] The present invention first copper-plated one side of the GP and then copper-plated the other side; the thickness of the single-layer copper film was 1.5±0.5μm; the arithmetic mean roughness of the copper film was R a The root mean square roughness R is 35~38nm. q The copper film with a certain roughness in the present invention facilitates uniform heat conduction, reduces heat dissipation in the heat conduction path, and generally reduces the interfacial contact thermal resistance. The above-mentioned roughness also improves interfacial bonding strength, facilitating the subsequent VHP process to prepare the Cu / GP composite film.

[0052] After obtaining Cu-GP, the present invention places copper foil (Cu Foil) on either side of the Cu-GP and vacuum hot-presses the resulting copper-based graphene composite material. The present invention stacks the copper-coated graphene paper (Cu-GP) and copper foil in the order of Cu Foil / Cu-GP / Cu Foil and vacuum hot-presses the resulting material in a graphite mold.

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

[0054] The present invention controls the copper foil thickness and multi-layer stacking architecture to precisely control the volume fraction and interface compatibility of the graphene film, providing an innovative solution for thermal management during high power periods under extreme conditions.

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

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

[0057] The thickness of the single-layer copper foil is 0.01-0.1 mm, specifically 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] The volume proportion of graphene paper in the copper-based graphene composite material of the present invention is 16.7% to 66.7%. In a specific embodiment, the volume proportion of graphene paper in the copper-based graphene composite material is 40.0%, 33.3%, 28.6%, 16.7% or 66.7%. The present invention achieves the change of graphene volume by different thicknesses. As the volume content of graphene increases from 16.7% to 66.7%, its in-plane thermal conductivity increases from 554.4 W·m -1 ·K -1 Increased to 805.8 W·m -1 ·K -1 ( Figure 18 In a), the linear fitting results show R 2 =0.965, which proves that the addition of graphene linearly improves the thermal conductivity of Cu / GP.

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

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

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

[0062] The copper-based graphene composite material in the present invention is 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 / coated graphene paper / copper foil / coated 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 The inter-surface thermal conductivity is 8.2 W·m -1 ·K -1 .

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

[0065] The surface and interfacial bonding of graphene-reinforced copper-based composites (Cu / GP) were analyzed using a scanning electron microscope (SEM, Oxford, X-Max80) equipped with an energy-dispersive X-ray spectrometer (EDX). SEM cross-sections were prepared using an ion beam sectioner (Leica EM TIC 3X, Germany). Raman spectra were recorded using a Renishaw Invia reflectometer using a 532 nm laser beam. To further analyze the composite's interfacial microstructure, field emission transmission electron microscopy (TEM, Japan JEM-F200) was used for characterization. Samples were prepared using a focused ion beam (FIB, Guoyi Quantum DB500, China) at 3 kV. Mechanical tensile testing was performed at room temperature using a homemade tensile tester. Before testing, samples were cut into I-shaped sections with a total length of 35 mm, with a central region of 15 mm long and 3 mm wide. The ends of the samples were affixed to a paper frame to prevent damage during clamping. The gauge length was set to 15 mm, and the paper frame legs were cut off after sample loading. The tensile stress-strain curves were obtained under a loading rate of 4 μm / s.

[0066] Thermal conductivity testing method in the present invention:

[0067] Thermal diffusivity (α, mm) was measured using a NETZSCH LFA 467 Hyper-Flash instrument. 2 s –1), the in-plane and out-of-plane thermal conductivities were tested using the in-plane mode of AGLF (sample holder: in-plane 25.4 mm circular piece, lamp voltage: 260 V; pulse width: 0.05 ms, sample temperature: 25 ℃) and the standard mode of AGLF-TIM (sample holder: between-plane 25.4 mm circular piece; lamp voltage: 250 V; pulse width: 0.02 ms; sample temperature: 25 ℃). Before the test, a thin layer of graphite was sprayed on both sides of the sample to ensure consistent emissivity and high signal-to-noise ratio, thereby accurately determining the thermal diffusivity. At the same time, the specific heat capacity (Cp, J·g) of the sample was measured in a nitrogen atmosphere using a NETZSCH DSC 204F1Phoenix instrument. -1 K -1 In addition, the mass density (ρ) was measured at 25 °C using an analytical balance based on the Archimedean principle (MD-224, DST, Co., Ltd). The mass of the sample weighed in air (m a ), completely immersed in deionized water and weighed (m b ), the density ρ is calculated by the following formula:

[0068]

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

[0070] k = α × ρ × c p

[0071] Heat application exploration method in the present invention:

[0072] 25.4 mm diameter discs of Cu / GP (thickness ~70 μm), Cu foil (thickness ~70 μm), and Cu / GP-D (thickness ~140 μm) were cut. A thin layer of conductive graphite coating was evenly sprayed onto the test surface of the sample to ensure consistent emissivity and a high signal-to-noise ratio. The samples were placed on a heat source maintained at 80°C, and the flatness of the contact surface was inspected to ensure uniform heat transfer. Infrared images were recorded over a 30-second heating period. The heating stage was then removed, and images were recorded over a 10-second cooling period at room temperature.

[0073] To further illustrate the present invention, a copper-based graphene composite material provided by the present invention, a preparation method thereof, and applications thereof are described in detail below in conjunction with examples, but they should not be construed as limiting the scope of protection 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 Fuen 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] 42 μm thick graphene paper (GP) was cut into 40 × 40 mm dimensions and fixed at its four corners using a homemade fixture. Subsequently, the fixed GP was placed in a magnetron sputtering machine. Ion cleaning was performed for 20 min at a current of 40 mA, an argon flow rate of 20 s ccm, and a high vacuum (less than 1 Pa) to remove impurities on the GP surface. Next, copper plating was performed on one side of the GP at a sputtering power of 200 W, an argon flow rate of 20 sccm, and a high vacuum (less than 1 Pa) for 80 min. Finally, the other side of the GP was sputter-plated with copper using the same conditions, and the sample was named Cu-GP.

[0078] Step 2: Preparation of Cu / GP

[0079] Cu-GP was cut into a circular sample with a diameter of 38 mm and placed in the center, with copper foils of 38 mm in diameter and 0.01 mm thick placed on both sides (stacked in the order of Cu Foil / Cu-GP / Cu Foil). The assembly was placed in a graphite mold and heated to 650 ° C at a heating rate of 10 ° C / min under a pressure of 40 MPa and maintained for 25 minutes. At the same time, 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 to finally obtain a Cu / GP composite material. In this embodiment, the volume proportion of GP in the composite material is 66.7%, and the sample is referred to as Cu / GP, Cu / GP-66.7% or Cu / GP-25 M.

[0080] In order to achieve high thermal conductivity and ultra-stability of Cu / GP composite materials, this application proposes a reliable magnetron sputtering copper plating and vacuum hot pressing process ( Figure 1 ), designed to effectively eliminate interfacial porosity and enhance interfacial bonding. Specifically, before sputtering copper plating on the GP surface, ion cleaning is performed to remove surface contaminants, thereby ensuring the adhesion and uniformity of the copper plating layer. After pre-treatment, copper is plated on both sides of the GP using magnetron sputtering, forming a copper film approximately 1.5μm thick. Figure 2Figures a and b show the surface optical morphology of GP before and after copper plating in Example 1. Before copper plating, the GP surface exhibits a regular grid-like texture. This is because GP is composed of multiple layers of graphene stacked together to form a multi-layered structure. Furthermore, due to the interlayer bonding via van der Waals forces, its non-uniformity leads to uneven stress distribution between the layers, resulting in stress concentration in local areas. This, in turn, produces localized micro-deformations in the stress concentration areas, 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 improves its surface morphology to a certain extent. Furthermore, the copper film can form a metal-metal bond (such as atomic diffusion and metallurgical bonding) with the copper foil during the subsequent hot pressing process, optimizing inter-surface thermal conductivity through strong interfacial bonding.

[0081] Figure 3 a and b are SEM images of GP and Cu-GP, respectively; Figure 3 Figure b shows that copper, as a highly conductive metal, provides a good conductive path, improving the clarity and contrast of the SEM image. Figure 3 In Figure a, granular copper clusters are clearly observed on the surface of the Cu-GP, particularly concentrated in the wrinkle protrusions. This is due to the higher atomic and electron density in these areas, which leads to the tendency of copper atoms to aggregate in these areas. Furthermore, the natural steric hindrance caused by the roughness reduces the migration rate of copper atoms in these areas, leading to further concentration of copper atoms.

[0082] Figure 4 Figures a and b show AFM images of the GP and Cu-GP surfaces, respectively. Comparison reveals a reduction in the surface roughness of the Cu-GP, with Ra (arithmetic mean roughness) and Rq (root mean square roughness) dropping from 63.1nm and 82.2nm to 36.6nm and 47.3nm, respectively. This indicates that the coating, by partially covering the micron-scale recessed areas on the GP surface, effectively reduces the density of sharp surface protrusions, while also reducing air gaps and defects at the interface. Furthermore, lower roughness facilitates uniform heat conduction, reduces scattering in the heat conduction path, and overall reduces interfacial contact thermal resistance. Maintaining a certain degree of roughness also helps enhance interfacial bonding, facilitating the subsequent VHP process for preparing Cu / GP composite films.

[0083] After magnetron sputtering, the copper film was stacked in the order of Cu Foil / Cu-GP / Cu Foil and vacuum hot pressed at 650°C and 40 MPa for 25 min to obtain the composite material (Cu / GP) of this example. Figure 5 The image a shows the Cu / GP composite film after preparation in this example. It is a thin disc with a diameter of 38 mm. The mold hot pressing marks can be seen on the edge. The copper foil on both sides wraps the copper-plated GP. The surface is basically smooth except for a few wrinkles. The GP lines can be observed with the naked eye on the copper foil surface. Figure 5 Figure b shows that after vacuum hot pressing, the Cu / GP composite film exhibits significant flexibility and can withstand large deformation during bending. This mechanical behavior is mainly attributed to the high strength and flexibility of graphene paper and the ductility of copper foil.

[0084] Figure 6 (a) and (b) show the SEM cross-sectional image and a magnified view (scale bar = 50μm) of a Cu / GP-66.7% composite film sample after ion beam cutting. The top and bottom layers of the sample are made of copper foil of equal thickness (~10μm), with the middle and Cu-GP layers having thicknesses of 22.9μm, 36.3μm, and 12.1μm, respectively, from top to bottom. The increased cross-sectional thickness of the top copper foil layer may be due to the interaction between the high-energy ion beam and the copper foil surface during FIB cutting, triggering a deposition effect during the cutting process. Specifically, due to the bombardment of the high-energy ion beam, copper atoms may rearrange and deposit on the sample surface or the cut edge. This deposition effect may cover part of the graphene paper cross-section, causing the upper copper foil layer to appear thicker.

[0085] Figure 7 for Figure 6 Energy Dispersive X-Ray Spectroscopy (EDX) characterization results for the region shown in (a). Copper is primarily distributed in the copper foil layer, carbon is primarily concentrated in the Cu-GP layer, and no significant oxygen distribution is detected throughout the entire characterization area, indicating that oxidation reactions may have been effectively avoided during the composite film preparation process. A Cu-C diffusion layer may exist at the interface between the copper foil and Cu-GP, but direct observation of this elemental doping or diffusion layer is difficult at a magnification of 50μm.

[0086] like Figure 6 As shown in b, there is no obvious micro-void at the Cu-C interface of Cu / GP material. Figure 7 EDX analysis of the distribution of Cu and C elements on the cross section further demonstrated the seamless and tight bonding of the Cu-C interface. A strong interfacial bond is crucial for ensuring the structural stability and reliable thermal conductivity of the Cu / GP under long-term extreme environmental conditions. Considering the weak van der Waals forces of the graphene interlayer and the low permeability between graphene and copper, the present invention designed an interface with a sputtered copper layer to enhance the seamless bonding between the copper foil and graphene and ensure low interfacial thermal resistance.

[0087] pass Figure 8 In Figures a and b, we can compare the Raman spectra of GP and Cu / GP. Figure 8 b is the Raman spectra of Cu / GP. Figure 8 The GP Raman line shown in a is at 1580 cm -1There is a wide and small bulge at the point with a large peak width, which may be a manifestation of the weakening of the G peak of graphene. Copper foil, as a metal material, has strong reflection and absorption capabilities for lasers. Especially when the copper foil is thick, it is difficult for the laser to penetrate the copper foil and reach the graphene paper underneath. Therefore, the laser signal may not be able to effectively stimulate the Raman scattering of the graphene paper, resulting in the G peak signal being significantly suppressed, the G peak becoming wider and the intensity decreasing. This phenomenon is also manifested in other graphene characteristic peaks, such as the 2D peak. Due to the decrease in the intensity 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 mean that the defect density of graphene increases. At the same time, for standard graphene, the 2D peak is usually located at 2670cm in the Raman spectrum. -1 As can be seen from Figure 8a, the 2D peak position of GP is blue-shifted (located at 2722cm -1 It can be verified by combining the peak intensity ratio IG / I2D that the GP used in the present invention is mainly composed of multi-layer graphene stacking.

[0088] For further comparison, we prepared Cu-GP-EP by electrochemical copper plating, and then prepared the composite material Cu / GP-EP by the same hot pressing process as Example 1, namely Comparative Example 1.

[0089] Comparative Example 1

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

[0091] Comparative samples were prepared using electrochemical copper plating. First, a 1.07 mol / L CuSO₄ solution was prepared. Specifically, 800 g of CuSO₄·5H₂O was dissolved in 100 mL of H₂SO₄ and deionized water was added to make up to 3 L. Electroplating (EP) was performed at 45°C, using a 40×40 mm graphene paper as the cathode and a copper electrode as the anode, applying a 5 A current for 10 minutes. After the experiment, the sample was rinsed with distilled water and dried. It is named Cu-GP-EP.

[0092] Step 2: Cut the Cu-GP-EP into a circular sample with a diameter of 38 mm and place it in the center. Flanked by two copper foils with a diameter of 38 mm and a thickness of 0.01 mm (Cu Foil / Cu-GP-EP / Cu Foil). This assembly is placed in a graphite mold and heated to 650°C at a rate of 10°C / min under a pressure of 40 MPa. The temperature is maintained at this temperature for 25 minutes. A vacuum (less than 1 Pa) is applied during the hot pressing process to prevent oxidation at high temperatures. The sample is then cooled naturally to room temperature and the pressure is reduced to yield a copper-based graphene composite.

[0093] Figure 9Comparison 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 ~900cm -1 ) figure, through the analysis of characteristic peaks, it can be seen that Cu / GP-EP prepared by electroplating is more likely to generate copper oxides such as CuO and Cu2O. These copper oxides will hinder the mutual diffusion of copper atoms during the Cu-Cu hot pressing bonding process, reduce the interface bonding strength, and also have a certain impact on the thermal conductivity efficiency of the interface.

[0094] In contrast, the Raman spectroscopy analysis of the hot-pressed Cu / GP sample of Example 1 shows that the graphene layer hardly exhibits a D peak ( Figure 9 ), which indicates that the graphene layer was not damaged during the hot pressing process.

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

[0096] High-resolution SEM images show a continuous and dense Cu-C interface transition zone. Combined with EDX elemental distribution analysis, this confirms a seamless and tightly bonded Cu / C interface. Raman spectroscopy further demonstrates that the Cu / GP maintains a high degree of crystalline properties after hot pressing, confirming that the process does not damage the graphene structure, providing a structural foundation for high thermal conductivity.

[0097] In order to further 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). Figure 10 As shown in (a), the heterojunction interface exhibits an atomic-level interlocking structure, and its alternating distribution of Cu-C configuration significantly enhances the interface bonding strength. Figure 10High-resolution TEM (HR-TEM) images in middle b and c show that the carbon interlayer spacing at the interface has expanded to 0.454 nm, which is 36% larger than the theoretical value of graphene (0.334 nm). This may be due to the defect generation during the ion cleaning process ( Figure 8 (a) allows the high-energy Cu particles deposited by magnetron sputtering to penetrate graphene defects. The subsequent hot pressing process promotes the diffusion of Cu atoms through these defects or along the edges of the graphene, ultimately leading to interlayer expansion. At the same time, the bulk Cu near the interface shows a (111) lattice fringe spacing of 0.202 nm, consistent with the face-centered cubic (FCC) copper structure. Figure 11 The selected area electron diffraction (SAED) pattern confirmed the polycrystalline nature of Cu, which was marked as (111), (200) and (220) crystal planes, showing polycrystalline characteristics, thereby enhancing the sealing of the heterogeneous interface. Figure 12 X-ray diffraction (XRD) analysis further confirmed that both Cu and GP exhibited exposed pure copper crystal faces (JCPDS 04-0836), with no apparent copper oxide formation. Notably, GP maintained its typical (002) layered morphology and high crystallinity, ensuring excellent thermal conductivity. This ultrathin, seamless heterogeneous interface significantly enhances the material's structural stability, demonstrating great potential for extreme thermal management applications.

[0098] Based on the well-characterized structural characteristics of Cu / GP layered materials, it is crucial to study their mechanical behavior under applied loads. Although graphene-based materials generally exhibit limited mechanical strength due to weak interlayer interactions, this study achieved significant improvements in mechanical properties by preparing sandwich structure composites using hot pressing of copper foil. Figure 13 and Figure 14 As shown in the figure, 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 the composite material reaches 6.45 MJ / m³, which is 9.0 times higher than that of GP and close to the 7.45 MJ / m³ of pure copper foil. 3 This excellent mechanical synergistic effect may originate from the effective load transfer achieved by the Cu-GP interfacial bonding structure.

[0099] Figure 15 Schematic diagram of the heat transfer effect within and between surfaces of the material (k || and k ⊥ In-plane thermal conductivity and inter-plane thermal conductivity respectively. ||) is extremely high. This is due to the unique two-dimensional honeycomb structure of graphene and the strong covalent bonds between carbon atoms. Phonons are rarely scattered during transmission. This structure allows heat to be transferred quickly and efficiently within the graphene plane. In contrast to the in-plane thermal conductivity, the inter-plane (k ⊥ ) has a relatively low thermal conductivity. This is because the interaction between graphene layers is weak (van der Waals forces), which greatly hinders heat transfer between layers. The in-plane and inter-plane thermal conductivity test results of Example 1 show that after hot-press bonding of graphene paper with a material with 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 , the inter-surface thermal conductivity is 8.2W·m -1 ·K -1 .

[0100] In order to further compare the heat transfer capabilities of Cu / GP and Cu foil, discs of Cu / GP (thickness ~80μm), Cu foil (thickness ~80μm) and Cu / GP-D (thickness ~134μm) with a diameter of 25.4mm were cut respectively. A thin layer of conductive graphite coating was sprayed evenly on the test surface of the sample to ensure consistent emissivity and high signal-to-noise ratio. These samples were placed on a heat source with a constant temperature of 80℃, and the flatness of the contact surface was checked to ensure uniform heat conduction. The temperature increase image changes were recorded within 30s, and then the heating stage was removed and the temperature decrease image changes were recorded within 10s at room temperature (see Figure 16 ). Figure 17 Figures 2 and 3 show the temperature curves of different samples during the test, as well as the infrared thermal imaging changes of Cu / GP. Compared with Cu Foil, the surface temperature of Cu / GP-66.7%, which has a similar thickness, rises faster during heating, from 16.1°C to 71.7°C within 4 seconds, 13.8°C higher than Cu Foil. It also decreases faster during cooling. The heating curve of Cu / GP-D in the first 3 seconds largely overlaps with that of Cu / GP, but its heating and cooling rates are slightly lower than those of Cu / GP. This is likely due to the shorter heat conduction path and smaller volume of Cu / GP, resulting in a smaller heat capacity, lower thermal inertia, and lower interfacial thermal resistance, resulting in a faster response to temperature changes in rapid heating scenarios.

[0101] In summary, thanks to the reliable sputtering copper-plated optimized interface design of Cu / GP, a strong interface bonding between Cu and GP in the composite material was achieved, and excellent thermal conductivity was 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 needs.

[0103] Example 2

[0104] This embodiment is substantially the same as embodiment 1, except that the thickness of the copper foil on both sides is 0.03 mm. In this embodiment, the volume proportion of GP in the composite material is 40.0%, and the sample is referred to as Cu / GP-40.0%.

[0105] Example 3

[0106] This example is essentially the same as Example 1, differing only in that the thickness of the copper foil on one side is 0.03 mm and on the other side is 0.05 mm. In this example, the volume fraction of GP in the composite material is 33.3%, and the sample is referred to as Cu / GP-33.3%.

[0107] Example 4

[0108] This embodiment is substantially the same as embodiment 1, except that the thickness of the copper foil on both sides is 0.05 mm. In this embodiment, the volume proportion of GP in the composite material is 28.6%, and the sample is referred to as Cu / GP-28.6%.

[0109] Example 5

[0110] This embodiment is substantially the same as embodiment 1, except that the thickness of the copper foil on both sides is 0.10 mm. In this embodiment, the volume proportion of GP in the composite material is 16.7%, and the sample is referred to as Cu / GP-16.7%.

[0111] Example 6

[0112] In order to further increase the thickness of Cu / GP to adapt to different environmental requirements, this embodiment uses double layers of Cu / GP-66.7% stacked and hot-pressed to prepare a double-layer sandwich structure material. The preparation process of this embodiment is basically the same as that of Example 1, except that in step 2, the two sheets of Cu / GP are hot-pressed together under the same conditions, that is, they are first stacked to form a structure of copper foil / coated graphene paper / copper foil / copper foil / coated graphene paper / copper foil, and then 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 an excellent thermal conductivity of 1073.0 W·m -1 ·K -1 The in-plane thermal conductivity of Cu-GP after magnetron sputtering copper plating still maintains 987.5 W·m -1 ·K -1 This lays the foundation for high thermal conductivity Cu / GP composite materials. Figure 18As shown in Figure 2, the in-plane and inter-plane thermal conductivities of Cu / GP with five different graphene volume contents in Examples 1 to 5 were tested. As the graphene volume content increased from 16.7% to 66.7%, the in-plane thermal conductivity increased from 554.4 W·m -1 ·K -1 Increased to 805.8 W·m -1 ·K -1 ( Figure 18 In a), the linear fitting results show R 2 =0.965, which proves that the addition of graphene linearly improves the thermal conductivity of Cu / GP.

[0114] However, the analysis shows that with the increase of graphene volume content, the interfacial thermal conductivity k of Cu / GP increases. ⊥ From 26.7 W·m -1 ·K -1 Reduced to 8.2 W·m -1 ·K -1 ( Figure 18 This is reasonable because the in-plane alignment of graphene creates a large amount of thermal resistance along the perpendicular planes, which significantly reduces the interplanar thermal conductivity.

[0115] Figure 19 The figure shows a comparison of the in-plane and inter-plane thermal conductivity coefficients of each Cu / GP in Examples 1 to 5 and reported Cu-based composite materials. As can be seen from the figure, in addition to the ultra-high in-plane thermal conductivity of the graphene-based thick film material (GTF-SBA: Graphene-thickfilm Seamless-bonding Assembly) due to the ordered arrangement of graphene and strong interfacial adhesion (the graphite film layer is sintered by Ag / Cu to form an atomic seamless bonding interface), the thermal conductivity of the Cu / GP composite film provided by the present invention is superior to that of most currently known Cu-based thermal conductive composite materials by optimizing the volume fraction of graphene paper. In addition, compared with the copper / graphene composite materials reported for thermal management, the k value of the composite material of the present invention changes with the change of graphene content. ll The high thermal conductivity is always shown, which is entirely due to the ideal interface structure of Cu / GP.

[0116] In addition, the in-plane thermal conductivity of the double-layer sandwich structure material (Cu / GP-D) of Example 6 is 816.1 W·m -1 ·K -1 , indicating that there is no significant difference in the in-plane thermal conductivity of the single-layer and double-layer Cu / GP composite films ( Figure 20), indicating that the added film layer did not significantly increase the interfacial thermal resistance. This is because, regardless of the single-layer or double-layer configuration, the extremely high thermal conductivity of graphene paper makes it the primary heat conduction pathway for the composite film. The added film layer did not significantly increase the heat conduction pathway or introduce excessive interfacial thermal resistance (the interfacial thermal resistance is low after thermal bonding between copper foils).

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

[0118] Example 7

[0119] This embodiment is basically the same as embodiment 3, except that the hot pressing time in step 2 is 5 minutes, and the sample is referred to as Cu / GP-5 M.

[0120] Example 8

[0121] This embodiment is basically the same as embodiment 3, except that the hot pressing time in step 2 is 15 minutes, and the sample is referred to as Cu / GP-15 M.

[0122] Comparative Example 2

[0123] This embodiment is basically the same as embodiment 3, except that the hot pressing time in step 2 is 35 minutes, and the sample is referred to as Cu / GP-35 M.

[0124] Comparative Example 3

[0125] This embodiment is basically the same as embodiment 3, except that the hot pressing time in step 2 is 45 minutes, and the sample is referred to as Cu / GP-45 M.

[0126] The results show that with the increase of hot pressing time, the in-plane thermal conductivity reaches the maximum value at 25 min and then begins to decrease ( Figure 21 This may be because as the hot pressing time increases, the local stress in the Cu-C interface increases, which causes the phonon thermal resistance at the interface to increase, thereby reducing the thermal conductivity of Cu / GP. A similar phenomenon also occurs in Cu / GP-33.3% k ⊥ The changes in the heat treatment time further prove that a reasonable hot pressing time is conducive to the formation of Cu-C interface ( Figure 21 Middle b).

[0127] As can be seen from the above examples, the present invention prepares copper / copper-plated graphene paper (Cu / GP) sandwich structure composite materials through magnetron sputtering and vacuum hot pressing technology, and systematically studies its interface characteristics and thermal conductivity behavior. The sputtering process deposits a dense copper layer of about 1.5 μm on the GP surface to form a metallurgical bond. 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%), anisotropic thermal conductivity optimization is achieved, k ll Increase linearly to 805.8 W·m -1 ·K -1 , increased by 118.6% compared with pure copper, k ⊥ Maintain 8.17 W·m -1 ·K -1 The Cu / GP-D multilayer structure reaches 816.1W·m -1 ·K -1 There is no accumulated interfacial thermal resistance, demonstrating excellent scalability. Mechanical testing showed that the tensile strength, fracture strain, and Young's modulus of Cu / GP-66.7% were 3.1 times, 2.4 times, and 4.4 times higher than those of pure GP, respectively. Furthermore, the toughness reached 6.45 MJ / m³, a 9.0-fold increase over GP. In a transient thermal test at 80°C, Cu / GP-66.7% heated to 71.7°C within 4 seconds, 13.8°C higher than the equilibrium temperature of copper foil of the same thickness, and cooled to room temperature within 8 seconds. This interface engineering strategy provides a universal solution for the development of thermo-mechanically synergistically enhanced graphene metal matrix composites.

[0128] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a copper-based graphene composite material, comprising the following steps: Copper films were plated on both sides of the ion-cleaned graphene paper by magnetron sputtering to obtain Cu-GP. The magnetron sputtering was performed under the following conditions: a magnetron sputtering power of 200±50W, an argon flow rate of 18-22sccm, and a vacuum degree of less than 1Pa. Placing copper foil on both sides of the Cu-GP and hot pressing in vacuum to obtain a copper-based graphene composite material; The vacuum hot pressing temperature is 650±10°C, the pressure is 40±5MPa, and the time is 5~25min; The volume proportion of graphene paper in copper-based graphene composites is 16.7~66.7%; The thickness of the single-layer copper film in the copper-based graphene composite material is 1.5±0.5μm; The thickness of a single layer of copper foil is 0.01~0.1mm.

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

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

4. A copper-based graphene composite material, prepared by the preparation method according to any one of claims 1 to 3; The copper-based graphene composite material is a sandwich structure, comprising copper foil / coated graphene paper / copper foil arranged in sequence.

5. The copper-based graphene composite material according to claim 4, characterized in that The copper-based graphene composite material is a stacked sandwich structure.

6. The copper-based graphene composite material according to claim 4, 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 .

7. Use of a copper-based graphene composite material prepared by the preparation method according to any one of claims 1 to 3 in rapid heat dissipation of high power density electronic devices.

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