In-situ self-generated graphene / copper composite material with oriented bimodal structure and preparation method thereof

Abstract

An in-situ self-generated graphene / copper composite material with an oriented bimodal structure and a preparation method thereof belong to the technical field of copper-based composite materials. The present invention aims to solve the problem of the incompatibility of strength, plasticity and conductivity of existing graphene-enhanced copper-based composite materials. The present invention uses dendritic copper powder and / or spherical copper powder and organic matter as main raw materials. During the heat treatment and sintering process, the organic matter on the surface of the copper powder is converted into graphene to limit the growth of grains, retain the fine copper particles (convex grain structure) on the surface of the copper powder, and realize the separation of copper powders of different particle sizes by graphene, and then obtain the oriented bimodal structure through processes such as rolling and extrusion deformation. The present invention can adjust the ratio of large and small grains in the oriented bimodal structure by changing the graphene content and the ratio of large and small grain copper powders, and obtain a graphene / copper composite material with high strength, high plasticity and high conductivity.

Description

Technical Field

[0001] The invention belongs to the technical field of copper-based composite materials, and in particular, relates to an in-situ self-generated graphene / copper composite material with an oriented bimodal structure, and a method for producing an in-situ self-generated graphene / copper composite material with an oriented bimodal structure. Background Art

[0002] Copper has been widely used in modern industry due to its excellent electrical conductivity. With the rapid development of conductive lead frames, electric vehicles and power electronics technology, higher requirements are placed on the comprehensive performance of copper. Improving mechanical strength without affecting its electrical conductivity and plastic deformation ability is an urgent challenge. Due to the high strength and electrical conductivity of graphene, graphene / copper composites are expected to achieve excellent overall performance. In the past decade, a variety of methods for preparing graphene / copper composites have been developed, including mechanical mixing, molecular mixing, stacking self-assembly and in-situ self-generation. In general, the performance of composites is determined by their microstructure, which is mainly affected by the preparation method of graphene, the distribution of graphene and the microstructure of the copper matrix. The performance can be improved by improving the microstructure of the composite.

[0003] Graphene can be roughly divided into two types according to the preparation method: top-down (derived from graphite or carbon nanotubes) or bottom-up (produced by carbonizing organic molecules through high temperature processes or electric fields). Graphene prepared by the top-down method is usually of high quality, but it is usually difficult to achieve uniform dispersion in the matrix. The quality of the graphene raw material will also be affected during the dispersion process, for example, a large number of defects will be introduced during ball milling and ultrasound. In contrast, graphene prepared by the bottom-up method is relatively easy to disperse, especially when organic matter is directly mixed with copper powder, it is easier to disperse evenly in the matrix. The in-situ autogenous method adopts the bottom-up method, which has the advantages of simple and rapid synthesis process and strong interface bonding with the copper matrix.

[0004] The oriented arrangement of graphene and copper matrix can optimize the structure of the composite material, thereby improving the mechanical and electrical properties. Kim et al. (Nat Commun 4 (2013) 2114) used chemical vapor deposition to grow a single layer of graphene on the copper surface and prepared a graphene / copper composite material with an alternating layer distribution and a strength of up to 1.5 GPa. Cao et al. (Advanced Functional Materials 29 (17) (2019)) achieved a laminated graphene / copper composite material with a conductivity of 117% IACS by growing graphene on both sides of copper foil and hot pressing and sintering. These findings emphasize the importance of oriented structural design in improving the performance of graphene / copper composites. However, these processes for preparing graphene and composites usually involve the use of complex techniques such as chemical vapor deposition and metal layer deposition.

[0005] Metal materials with a bimodal structure can improve strength without significantly affecting ductility and conductivity. Bimodal structural materials are composed of micron-sized coarse grains and nanometer-sized fine grains. Fine grains help to improve material strength, and coarse grains can improve material ductility by passivating microcracks, thereby improving the material's plastic deformation ability. Mesguich et al. (Scripta Mater 137 (2017) 78-82) demonstrated that the bimodal structure of carbon nanotube copper composites can improve mechanical properties while limiting the decrease in conductivity. However, the preparation of these materials usually involves low temperature (77K) and multiple deformation processes, which increases the complexity of the preparation process. In addition, there are no reports on the preparation of oriented bimodal graphene / copper composites. Summary of the invention

[0006] The purpose of the present invention is to provide a simple method for preparing a graphene / copper composite material with an oriented bimodal structure of copper grains by combining an in-situ autogenous method and a deformation process. The present invention uses copper powder (including a mixture of dendritic copper powder and / or spherical copper powder of two mesh sizes) and organic matter as raw materials. During the heat treatment and sintering process, the organic matter on the surface of the copper powder is converted into graphene to limit the growth of copper grains, and the fine copper particles on the surface of the dendritic copper powder (the convex grain structure on the surface of the dendritic copper powder) are retained to achieve the separation of copper particles of different particle sizes by graphene, and then the oriented bimodal structure is obtained by rolling and extrusion deformation processes to optimize the performance of the composite material. The present invention solves the problem of the uncoordinated strength, plasticity and conductivity of the existing graphene-enhanced copper-based composite material. The ratio of large and small grains in the oriented bimodal structure can be adjusted by changing the graphene content and the ratio of large and small grain copper particles to obtain a graphene / copper composite material with high strength, high plasticity and high conductivity.

[0007] The present invention first mixes a carbon source with copper powder and then coats the surface of the copper powder with organic matter, then undergoes heat treatment and sintering to obtain a graphene / copper composite material, and then undergoes deformation treatment to obtain a graphene / copper composite material with an oriented bimodal structure. The prepared composite material has excellent mechanical and electrical properties.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The method for in-situ self-generated graphene / copper composite material with oriented bimodal structure provided by the present invention is specifically achieved by the following steps:

[0010] Uniformly coating the carbon source on the surface of the dendritic copper powder and / or the spherical copper powder, heat treating under a protective gas atmosphere, cooling to room temperature; sintering; deforming; obtaining the graphene / copper composite material;

[0011] The carbon source includes organic matter or a mixture of organic matter and graphene; the organic matter is an organic matter composed of carbon-hydrogen, carbon-hydrogen-oxygen or carbon-hydrogen-nitrogen; and the graphene is a combination of one or more of mechanically exfoliated graphene, oxidized graphene and combustion synthesized graphene in any ratio.

[0012] It is further defined that the particle size of the dendritic copper powder (or dendritic copper powder, dendritic electrolytic copper powder) is 20 mesh-15000 mesh; the mesh size of the spherical copper powder is 20 mesh-15000 mesh; when only spherical copper powder is used, two spherical copper powders with average particle sizes greater than or equal to 3 are required, and the mass ratio of large particle size copper powder to small particle size copper powder is 1: (0.1-10).

[0013] It is further defined that the organic matter is a combination of one or more of macromolecular organic matter represented by polyacrylonitrile and polymethyl methacrylate, and small molecular organic matter represented by oleic acid and oleylamine in any ratio.

[0014] Further defined, an organic solvent such as N,N-dimethylformamide, cyclohexane or anhydrous ethanol may be used in the coating process.

[0015] It is further defined that the dispersion is carried out by magnetic stirring, mechanical stirring, ultrasound, ball milling, and rotary evaporation.

[0016] The heat treatment process parameters are further defined as follows: heat treatment temperature of 300°C-1000°C, holding time of 1min-60min, protective atmosphere of nitrogen, argon, or a mixture of hydrogen and argon, wherein the hydrogen gas volume fraction in the mixture is greater than 5%.

[0017] Further defined, the heat treatment can be carried out in stages, and the specific process is as follows: heat up to 200℃-250℃ at a rate of 5-10℃ / min, keep warm for 60min-120min, then heat up to 800℃-1000℃ at a rate of 5-10℃ / min, keep warm for 5min-10min.

[0018] It is further defined that the sintering is spark plasma sintering, vacuum hot pressing sintering, and vacuum sintering; the sintering is carried out at a temperature of 400° C. to 1050° C. and a pressure of 0 MPa to 200 MPa.

[0019] It is further defined that the deformation process is performed by rolling or extrusion.

[0020] It is further defined that the deformation temperature is controlled at 0-900° C. and the deformation ratio is 0-95%.

[0021] Another object of the present invention is to provide a graphene / copper composite material prepared by any one of the above methods.

[0022] It is further defined that the graphene / copper composite material has an oriented bimodal structure.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention is expected to solve the problem of uncoordinated strength, plasticity and electrical conductivity of existing graphene-enhanced copper-based composite materials. The present invention adjusts the ratio of large and small grains of a bimodal structure in a graphene / copper composite material by changing the graphene content and the ratio of large and small grain copper powders, thereby obtaining a composite material with an oriented bimodal structure, thereby achieving a balance between strength, plasticity and electrical conductivity in the graphene / copper composite material, improving the strength, plasticity and electrical conductivity of the material, and obtaining a graphene / copper composite material with high mechanical properties and high electrical conductivity.

[0025] The invention adopts organic matter and copper powder to mix in liquid phase, which can fully contact and evenly coat, has easy-to-obtain raw materials, simple equipment and operation, and is easy to carry out batch production.

[0026] In order to further understand the features and technical contents of the present invention, please refer to the following detailed description and drawings of the present invention. However, the attached drawings are only provided for reference and illustration and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The SEM photos of the 200-mesh dendritic electrolytic copper powder raw materials in Examples 1-4 and Comparative Example 1;

[0028] Figure 2The SEM photos of the composite copper powder after heat treatment and the graphene after corrosion treatment in Example 1;

[0029] Figure 3 The IPF diagram of the oriented bimodal structure of the graphene / copper composite material prepared by the method of Example 1;

[0030] Figure 4 This is a SEM photograph of the surface of the graphene / copper composite material prepared by the method of Example 1 after being corroded by 5% concentration of nitric acid;

[0031] Figure 5 The tensile curve of the graphene / copper composite material prepared by the method of Example 1;

[0032] Figure 6 The IPF diagram of the oriented bimodal structure of the graphene / copper composite material prepared by the method of Example 2;

[0033] Figure 7 The tensile curve of the graphene / copper composite material prepared by the method of Example 2;

[0034] Figure 8 This is the IPF diagram of the material prepared by the method of Comparative Example 1;

[0035] Fig. 9 This is the tensile curve of the material prepared by the method of Comparative Example 1. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0037] Example 1: The preparation method of the in-situ self-generated graphene / copper composite material with an oriented bimodal structure in this example is carried out according to the following steps:

[0038] Step 1, the copper powder selected is 200 mesh electrolytic copper powder (or called dendritic copper powder, dendritic electrolytic copper powder), 100 parts of N, N-dimethylformamide (DMF) are used as solvent to disperse 1 part of polyacrylonitrile (PAN), after stirring for 2 hours, 60 parts of copper powder are added, and then stirring is continued for 1 hour, the slurry obtained after filtration is placed in a copper boat, and then placed in a tubular heating furnace for heating, heating to 250°C at a rate of 10°C / min, keeping warm for 120 minutes, and then heating to 800°C at a rate of 10°C / min, keeping warm for 5 minutes, and the heating atmosphere is a mixture of hydrogen (17vol.%) and argon (83vol.%); after heating, cooling at room temperature is completed to obtain a graphene / copper composite powder;

[0039] Step 2, subjecting the graphene / copper composite powder obtained in step 1 to SPS sintering treatment, the sintering process being 700° C. for 5 min and the sintering pressure being 40 MPa;

[0040] Step 3, rolling the graphene / copper composite powder after the treatment in step 2, the rolling process is hot rolling, the temperature is 500° C., and the total rolling amount is 70%, to obtain the graphene / copper composite material.

[0041] The composite powder and composite material prepared in this embodiment were tested, and the results are as follows: Figure 1-4 shown.

[0042] The SEM photo of the 200-mesh dendritic copper powder raw material used in this embodiment is as follows: Figure 1 As shown by Figure 1 It can be seen that the copper powder raw material used in this embodiment is dendritic copper powder, the diameter of the copper powder is about 10 μm, and the grain size of the protruding part of the copper powder surface is about 1 μm-2 μm.

[0043] The SEM photos of the composite copper powder after heat treatment in step 1 and the graphene after corrosion treatment with nitric acid (5 vol.%) solution are as follows: Figure 2 As shown by Figure 2 (a) It can be seen that the composite powder obtained after in-situ coating and heat treatment in this embodiment can still maintain a dendritic structure on the surface; Figure 2 (b) It can be seen that the surface of the composite powder obtained in this embodiment is uniformly coated with a layer of graphene. After the dendritic copper powder used is in-situ coated and heat treated, the surface can still maintain a dendritic structure;

[0044] The IPF diagram of the oriented bimodal structure of the graphene / copper composite material prepared by the method of this embodiment is shown in FIG. Figure 3 As shown by Figure 3 It can be seen that the composite material prepared in this embodiment is composed of small grains with a diameter of 0.5-3 microns and large grains with a diameter of 5-20 microns. The volume ratio of small grains to large grains is about 1:1, and both large and small grains are elongated in the same direction, that is, an oriented bimodal structure.

[0045] The SEM photograph of the surface of the graphene / copper composite material prepared by the method of this embodiment after being corroded by nitric acid (5 vol.%) solution is shown in FIG. Figure 4 As shown by Figure 4 It can be seen that the small grains in this embodiment have obvious graphene-coated morphology, which shows that the physical barrier effect of graphene is conducive to the formation of a double-peak structure, and an oriented structure is formed during the subsequent hot rolling deformation process.

[0046] The tensile curve of the graphene / copper composite material prepared by the method of this embodiment is as follows Figure 5 As shown by Figure 5It can be seen that the oriented bimodal composite material of this embodiment has a tensile yield strength of 315 MPa, a tensile strength of 353 MPa, and an elongation at break of 12.4%, has high strength and fracture rate, and achieves strong-plastic matching.

[0047] In addition, the electrical properties of this embodiment were tested. The electrical conductivity was 95.7% IACS (International Annealed Soft Copper Standard) at 20°C, maintaining a high electrical conductivity, and the resistance temperature coefficient was 0.00384°C. -1 Compared with the international annealed soft copper of 0.00394℃ -1 There is a significant decrease compared to the

[0048] Example 2: The preparation method of the in-situ self-generated graphene / copper composite material with an oriented bimodal structure in this example is carried out according to the following steps:

[0049] Step 1, the copper powder selected is 200 mesh dendritic copper powder, 100 parts of N, N-dimethylformamide (DMF) are used as solvent to disperse 0.05 parts of mechanical exfoliation graphene and 0.5 parts of polyacrylonitrile (PAN), after magnetic stirring for 2 hours, 60 parts of copper powder are added, and stirring is continued for 1 hour, the slurry obtained after filtration is placed in a copper boat, and then placed in a tubular heating furnace for heating, heating to 250°C at a rate of 10°C / min, keeping warm for 120 minutes, and then heating to 800°C at a rate of 10°C / min, keeping warm for 5 minutes, and the heating atmosphere is a mixture of hydrogen (17 vol.%) and argon (83 vol.%); after heating, cooling at room temperature is completed to obtain a graphene / copper composite powder.

[0050] Step 2: The graphene / copper composite powder obtained in step 1 is subjected to SPS sintering treatment, the sintering process is 700° C. for 5 min, and the sintering pressure is 40 MPa.

[0051] Step 3: rolling the composite material after the treatment in step 2, wherein the rolling process is hot rolling, the temperature is 500° C., and the total rolling amount is 70%.

[0052] The IPF diagram of the oriented bimodal structure of the graphene / copper composite material prepared by the method of this embodiment is shown in FIG. Figure 6 As shown by Figure 6 It can be seen that the composite material prepared in this embodiment is composed of small grains with a diameter of 0.5-3 microns and large grains with a diameter of 5-20 microns. The volume ratio of small grains to large grains is about 1:5, and both large and small grains are elongated in the same direction, that is, an oriented bimodal structure.

[0053] The tensile curve of the graphene / copper composite material prepared by the method of this embodiment is as follows Figure 7 As shown by Figure 7It can be seen that the tensile yield strength of the composite material of this embodiment is 263MPa, the tensile strength is 321MPa, and the elongation at break is 14.5%. At 20°C, the electrical conductivity of the composite material is 96.0% IACS, and the temperature coefficient of resistance is 0.00388°C. -1 .

[0054] Example 3: The preparation method of the in-situ self-generated graphene / copper composite material with an oriented bimodal structure in this example is carried out according to the following steps:

[0055] Step 1, the selected copper powder is 200 mesh dendritic copper powder, first the copper powder is soaked in anhydrous formic acid, the soaking time is 30min, the carbon source mixture concentration is 0.025 parts of polyacrylonitrile (PAN) per 100 parts of N, N-dimethylformamide (DMF), after mechanical stirring for 2h, 60 parts of copper powder are added, and then stirring is continued for 1h, the slurry obtained after filtration is placed in a copper boat, and then placed in a tubular heating furnace for heating, heating to 250°C at a rate of 10°C / min, keeping warm for 120min, and then heating to 800°C at a rate of 10°C / min, keeping warm for 5min, the heating atmosphere is a mixture of hydrogen (17vol.%) and argon (83vol.%); after heating, it is cooled at room temperature to obtain a graphene / copper composite powder.

[0056] Step 2: The graphene / copper composite powder obtained in step 1 is subjected to SPS sintering treatment, the sintering process is 700° C. for 5 min, and the sintering pressure is 40 MPa.

[0057] Step 3: rolling the composite material after the treatment in step 2, wherein the rolling process is cold rolling, and the total rolling amount is 80%.

[0058] The composite material of this embodiment has a tensile yield strength of 410 MPa, a tensile strength of 440 MPa, an elongation at break of 5.7%, and an electrical conductivity of 96.7% IACS at 20°C.

[0059] Example 4: The preparation method of the in-situ self-generated graphene / copper composite material with an oriented bimodal structure in this example is carried out according to the following steps:

[0060] Step 1, the selected copper powder is 200 mesh dendritic copper powder, first the copper powder is soaked in anhydrous formic acid, the soaking time is 30min, the carbon source mixture concentration is 0.025 parts of polyacrylonitrile (PAN) per 100 parts of N, N-dimethylformamide (DMF), after mechanical stirring for 2h, 60 parts of copper powder are added, and then stirring is continued for 1h, the slurry obtained after centrifugation is placed in a copper boat, and then placed in a tubular heating furnace for heating, heating to 250°C at a rate of 10°C / min, keeping warm for 120min, and then heating to 800°C at a rate of 10°C / min, keeping warm for 5min, the heating atmosphere is a mixture of hydrogen (17vol.%) and argon (83vol.%); after heating, it is cooled at room temperature to obtain a graphene / copper composite powder.

[0061] Step 2: The graphene / copper composite powder obtained in step 1 is subjected to SPS sintering treatment, the sintering process is 700° C. for 5 min, and the sintering pressure is 40 MPa.

[0062] Step 3: Extruding the composite material processed in step 2, the extrusion process is hot extrusion, the extrusion temperature is 800° C., and the extrusion ratio is 25.

[0063] The electrical conductivity of the composite material with an oriented bimodal structure of this embodiment is 101% IACS at 20°C.

[0064] Example 5: The preparation method of the in-situ self-generated graphene / copper composite material with an oriented bimodal structure in this example is carried out according to the following steps:

[0065] Step 1. The selected copper powder is 325 mesh dendritic copper powder. First, the copper powder is soaked in anhydrous formic acid for 30 minutes. The concentration of the carbon source mixture is 1 part of oleic acid per 100 parts of cyclohexane. After mechanical stirring for 2 hours, 60 parts of copper powder are added, and then stirring is continued for 1 hour. The solid slurry obtained after rotary evaporation is placed in a copper boat, and then placed in a tubular heating furnace for heating. The temperature is increased to 700°C at a rate of 10°C / min and kept warm for 5 minutes. The heating atmosphere is a mixture of hydrogen (17vol.%) and argon (83vol.%); after heating, it is cooled at room temperature to obtain a graphene / copper composite powder.

[0066] Step 2: The graphene / copper composite powder obtained in step 1 is subjected to SPS sintering treatment, the sintering process is 700° C. for 5 min, and the sintering pressure is 40 MPa.

[0067] Step 3: rolling the composite material after the treatment in step 2, wherein the rolling process is hot rolling, the temperature is 600° C., and the total rolling amount is 70%.

[0068] Example 6: The preparation method of the in-situ self-generated graphene / copper composite material with an oriented bimodal structure in this example is carried out according to the following steps:

[0069] Step 1, the selected copper powder is 40 and 200 mesh spherical copper powder, which are mixed at a mass ratio of 1:1, and 100 parts of N, N-dimethylformamide (DMF) are used as a solvent to disperse 1 part of polyacrylonitrile (PAN). After stirring for 2 hours, 60 parts of the mixed copper powder are added, and then stirring is continued for 1 hour. The slurry obtained after filtration is placed in a copper boat, and then placed in a tubular heating furnace for heating, and the temperature is increased to 250°C at a rate of 10°C / min, and the temperature is kept for 120 minutes, and then the temperature is increased to 800°C at a rate of 10°C / min, and the temperature is kept for 5 minutes. The heating atmosphere is a mixture of hydrogen (17 vol.%) and argon (83 vol.%); after the heating is completed, it is cooled at room temperature to obtain a graphene / copper composite powder;

[0070] Step 2, subjecting the graphene / copper composite powder obtained in step 1 to SPS sintering treatment, the sintering process being 700° C. for 5 min and the sintering pressure being 40 MPa;

[0071] Step 3, rolling the graphene / copper composite powder treated in step 2, the rolling process is hot rolling, the temperature is 500° C., and the total rolling amount is 70%, to obtain the graphene / copper composite material with an oriented bimodal structure.

[0072] Comparative Example 1: The method is carried out according to the following steps:

[0073] Step 1, the copper powder selected is 200 mesh electrolytic copper powder (dendritic copper powder, i.e., dendritic electrolytic copper powder), 100 parts of N, N-dimethylformamide (DMF) are used as solvent, 60 parts of copper powder are added, and stirring is continued for 1 hour, the slurry obtained after filtration is placed in a copper boat, and then placed in a tubular heating furnace for heating, the temperature is increased to 250°C at a rate of 10°C / min, and the temperature is kept for 120 minutes, and then the temperature is increased to 800°C at a rate of 10°C / min, and the temperature is kept for 5 minutes, and the heating atmosphere is a mixture of hydrogen (17 vol.%) and argon (83 vol.%); after the heating is completed, it is cooled at room temperature to obtain a graphene / copper composite powder;

[0074] Step 2, subjecting the graphene / copper composite powder obtained in step 1 to SPS sintering treatment, the sintering process being 700° C. for 5 min and the sintering pressure being 40 MPa;

[0075] Step 3: rolling the graphene / copper composite powder processed in step 2, wherein the rolling process is hot rolling, the temperature is 500° C., and the total rolling amount is 70%.

[0076] The IPF diagram of the material prepared by the method of Comparative Example 1 is as follows Figure 8As shown by Figure 8 It can be seen that the materials prepared in this comparative example are all composed of large grains with a diameter of 5-20 μm, which is a uniform grain structure, which is significantly different from the oriented bimodal structure.

[0077] The tensile curve of the material prepared by the method of Comparative Example 1 is as follows Fig. 9 As shown by Fig. 9 It can be seen that the tensile yield strength of the material prepared in this comparative example is 227MPa, the tensile strength is 293MPa, and the elongation at break is 20.5%. The conductivity of the material at 20°C is 97.3% IACS, and the temperature coefficient of resistance is 0.00395°C. -1 Compared with the international annealed soft copper of 0.00394℃ -1 quite.

Claims

1. A method for preparing an in-situ self-generated graphene / copper composite material with an oriented bimodal structure, characterized in that: The preparation method is achieved by the following steps: The carbon source is uniformly coated on the surface of the dendritic copper powder and / or the spherical copper powder, heat-treated in a protective gas atmosphere, cooled to room temperature, sintered, and then deformed to obtain the graphene / copper composite material; Wherein, the carbon source is one of polyacrylonitrile and oleylamine; When only dendritic copper powder is present, the copper powder has a diameter of 10 μm, and the grain size of the protruding portion of the copper powder surface is 1 μm-2 μm; When only spherical copper powder is used, two types of spherical copper powders with average particle diameter ratio greater than or equal to 3 are required; The heat treatment process parameters are as follows: temperature of 300° C.-1000° C., holding time of 1 min.-60 min. The protective atmosphere is nitrogen, argon, or a mixture of hydrogen and argon, and the volume fraction of hydrogen in the mixture is greater than 5%.

2. The preparation method according to claim 1, characterized in that: In the process of coating the carbon source, an organic solvent is used, and the organic solvent is N, N-dimethylformamide, cyclohexane or anhydrous ethanol; magnetic stirring, mechanical stirring, ultrasound, ball milling and rotary evaporation are used for dispersion.

3. The preparation method according to claim 1, characterized in that: The particle size of the dendritic copper powder is 20 meshes to 15000 meshes; the particle size of the spherical copper powder is 20 meshes to 15000 meshes.

4. The preparation method according to claim 3, characterized in that: The sintering process includes spark plasma sintering, vacuum hot pressing sintering and vacuum sintering; the sintering process is carried out at a temperature of 400°C to 1050°C and a pressure of 0MPa to 200MPa.

5. The preparation method according to claim 1, characterized in that: The deformation process is carried out by rolling or extrusion.

6. The preparation method according to claim 1, characterized in that: The deformation temperature is controlled at 0-900℃; When the deformation process is carried out by rolling, the total rolling amount is 70% or 80%; When the deformation process adopts extrusion, the extrusion ratio is 25.

7. A graphene / copper composite material prepared by the preparation method according to any one of claims 1 to 6.

8. The graphene / copper composite material according to claim 7, characterized in that: The graphene / copper composite material presents an oriented bimodal structure.

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