High-strength high-conductivity graphene / copper composite material and preparation method thereof

Abstract

The application discloses a high-strength and high-conductivity graphene / copper composite material and a preparation method thereof. A small amount of graphite is added into copper powder, chemical stripping is combined with high-pressure bonding to ensure uniform dispersion of graphene in the matrix, and strong interface bonding with the matrix is realized to form a three-dimensional interconnected graphene structure, which can effectively bear load under tensile stress and enhance the overall mechanical properties. The graphene three-dimensional structure enhances the charge transport efficiency of the copper matrix, fully plays the role of high conductivity of graphene, and makes the prepared copper graphene composite material have high strength and high conductivity, a shorter preparation process, higher preparation efficiency, lower industrial production cost, more energy saving and consumption reduction, and more technical advantages.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial production process of graphene / copper composite material, and particularly relates to a preparation method of high-strength and high-conductivity graphene / copper composite material. BACKGROUND

[0002] Graphene is considered to be the most potential reinforcing material in copper-based composite materials because it has excellent mechanical and physical properties, and the specific surface area reaches 2630 m 2 ·g -1 ·cm 2 ·v -1 ·s -1 ·K -1 ·K -1 .

[0003] In recent years, many scholars have carried out extensive research on graphene and metal composites. After introducing graphene into copper, aluminum and other substrates, the performance of the material can be effectively improved, and the prepared composite material has high strength, high thermal conductivity, high electrical conductivity, low friction coefficient and the like. It can be used for electrical contact materials, packaging materials, wear-resistant materials and corrosion-resistant materials, and has potential application value in many fields.

[0004] Generally, there are two ways to combine graphene and copper.

[0005] The first way is in-situ growth. For example, in the paper Adv. Funct. Mater. 2019, 29, 1806792, the team of Zhang Di of Shanghai Jiaotong University obtains graphene / copper foil by using chemical vapor deposition (CVD), and after hot pressing into a layered composite material, a graphene / copper product with high electrical conductivity of 117% IACS is obtained. In the paper Carbon. 2022, 186:303-312, the team of Gao Zhao-shun of the Institute of Electrical Engineering of the Chinese Academy of Sciences uses a liquid carbon source in combination with a hot pressing sintering method to generate graphene in-situ, and the mechanical properties of the composite material are greatly improved, but the electrical conductivity is slightly decreased.

[0006] The second is an external method: mixing graphene powder or graphite with copper to process, directly adding into the internal or coating on the surface of copper. For example, in the patent CN202110851980.6, Yang Zhiyu proposes a graphene / copper wire and its preparation method, after mixing few-layer graphene oxide powder and oxygen-free copper powder, low-temperature hot pressing sintering, adding auxiliary materials for vacuum melting to obtain graphene / copper composite material with volume content of 99.99% or more, and the thermal conductivity can reach 500-600 W / m·K, and the volume resistivity is reduced by 5-20%. In the paper Composites Part B: Engineering, 2021, 216: 108850, Chen uses graphite and copper for multi-pass rolling to prepare graphene / copper composite material, although the electrical conductivity decreases to a certain extent (68% IACS), but the mechanical properties are greatly improved.

[0007] The graphene / copper composite material prepared by in-situ growth method has complete graphene structure and few defects, and the graphene is combined closely with the surface of the copper matrix, but it needs high temperature close to 1000℃, and the carbonization and sintering process is very complicated, which greatly limits the application of the method and makes the industrialization difficult.

[0008] The external method is difficult to realize the uniform mixing of graphene and copper, and is easy to cause agglomeration, especially the graphene floating phenomenon is serious during the melting process, and the process is complex, so it is not conducive to batch production.

[0009] At present, there are few reports on the preparation of graphene / copper composite material by hydrothermal reduction method directly from graphite. Most researchers use one-step hydrothermal synthesis to obtain CuO / oxidized graphene (GO or RGO) composite material, and the remaining few researchers obtain graphene / copper composite material, but the raw material is oxidized graphene instead of simpler, more easily obtained and lower cost graphite. SUMMARY

[0010] In view of the shortcomings of the prior art, the purpose of the present application is to provide a preparation method of high-strength and high-conductivity graphene / copper composite material, which effectively uses low-cost graphite to realize industrial production of graphene / copper composite material, has shorter preparation process, higher preparation efficiency, lower industrial production cost, is more energy-saving and consumption-reducing, and has many technical advantages.

[0011] In order to achieve the above purpose, the technical scheme adopted by the present application is:

[0012] A preparation method of high-strength and high-conductivity graphene / copper composite material, which is prepared by combining chemical exfoliation method and hydrothermal method, including the following preparation steps and conditions,

[0013] Step S1, the copper powder and graphite powder are weighed according to the proportion by weight to obtain a mixed powder, wherein the mass ratio of the copper powder and the graphite powder is 1:0.01-0.03, alcohol is added to the mixed powder, and the mixed powder is uniformly mixed to obtain a mixture;

[0014] Step S2, a mixed solution is prepared, the adhesive organic matter is sealed and stirred with the solvent to prepare the mixed solution, the adhesive organic matter is selected from alcohol, the solvent is selected from at least one of DMF and NMP, the weight ratio of the adhesive organic matter to the solvent is 1:5-10, and the total mass of the mixed solution accounts for 10-20%;

[0015] Step S3, the mixture of step 1 and the mixed solution of step S2 are moved into a hydrothermal reaction kettle, the temperature in the hydrothermal kettle is controlled at 150-220 DEG C, and the hydrothermal reaction is carried out for 5-30 hours, after the hydrothermal reaction is completed, the hydrothermal reaction kettle is cooled to room temperature, and a graphene oxide coated copper powder composite material is obtained;

[0016] Wherein, DMF enters the graphite intercalation of the graphite powder and peels off the graphite into graphene oxide by the action of high temperature and high pressure in the hydrothermal reaction,

[0017] The adhesive organic matter makes the oxygen-containing groups on the surface of the formed graphene oxide produce hydrogen bonds or weak interactions with the surface of the copper powder by the action of high temperature and high pressure in the hydrothermal reaction,

[0018] The adhesive organic matter enhances the binding force between the graphene oxide and the copper powder while effectively dispersing the copper powder and the graphene oxide, and prevents the graphene oxide from agglomerating, so that the graphene oxide is tightly attached to the surface of the copper powder and uniformly coated on the surface of the copper powder,

[0019] The surface of the copper powder is uniformly coated with graphene oxide film with 3-5 layers of graphene oxide and in a sheet film structure, and no gap is generated, so as to form the graphene oxide coated copper powder composite material;

[0020] Step S4, the graphene oxide coated copper powder composite material of step S3 is sequentially subjected to suction filtration, washing and vacuum drying to obtain a pure graphene oxide coated copper powder composite material;

[0021] Step S5, the graphene oxide coated copper powder composite material is subjected to a reduction reaction using a reducing atmosphere, the reduction temperature is 200-450 DEG C, the reduction reaction time is 1-3 hours, the graphene oxide coated on the surface of the copper powder is reduced into graphene, and a graphene / copper composite material is obtained, wherein the surface of the copper powder is uniformly coated with 3-5 layers of graphene in a sheet film structure;

[0022] Step S6, the graphene / copper composite material of step S5 is subjected to vacuum hot pressing treatment to obtain a graphene / copper bulk body, the graphene / copper bulk body exhibits Cu(111), Cu(200) and Cu(220) crystal plane indexes, showing a polycrystalline copper structure, and the bulk conductivity of the graphene / copper bulk body is 97-107% IACS.

[0023] In a further technical solution, after the copper powder completely coated with graphene is subjected to hot pressing treatment, the graphene between the copper powder particles is connected to each other and exhibits a three-dimensional interconnected structure in the bulk body, and the graphene / copper bulk body obtained after the hot pressing treatment has no pores and holes on the surface.

[0024] In a further technical solution, the purity of the copper powder is greater than 99.9%, the particle size of the copper powder is 15-50 μm, and the input weight of the copper powder is 97-99% of the total mass of the raw materials composed of the mixed powders.

[0025] The particle size of the graphite powder is 20-50 μm, and the input weight of the graphite powder is 1-3% of the total mass of the raw materials composed of the mixture and the mixed solution.

[0026] The binder organic matter is at least one selected from ethylene glycol, polypropylene glycol and polyethylene glycol, and the input weight of the binder organic matter is 10-20% of the total mass of the raw materials composed of the mixture and the mixed solution.

[0027] In a further technical solution, in step S2, the binder organic matter is polyethylene glycol, and the solvent is DMF, and the mass ratio of polyethylene glycol to DMF is 1:5-10.

[0028] In step S3, the oxygen-containing group includes a hydroxyl group and a carboxyl group.

[0029] In step S5, the reduction temperature of the reduction reaction is 250-450°C, the reduction reaction time is 0.5-1 hour, part of the graphene formed after the reduction reaction has wrinkles, and the Raman characteristic peak I D / I G of the graphene / copper composite material is 0.16-0.18.

[0030] In a further technical solution, in step S3, the temperature in the hydrothermal kettle is controlled at 180-190°C, and the hydrothermal reaction is performed for 10-15 hours.

[0031] In step S5, the reduction temperature of the reduction reaction is 350°C and is maintained for 1 hour.

[0032] In step S6, the graphene / copper composite material is subjected to vacuum hot pressing treatment at a temperature of 800°C for 2 hours.

[0033] In a further technical solution, in the step S5, the mixed gas of nitrogen and hydrogen is used as the reducing atmosphere, the hydrogen accounts for 1-5% of the volume percentage of the reducing atmosphere, the temperature for reducing the graphene oxide coated copper powder composite is 300-600 DEG C, and the reducing time is 30-200 min.

[0034] In the step S6, the vacuum hot pressing temperature of the vacuum hot pressing treatment is 600 DEG C-1000 DEG C, and the vacuum hot pressing time is 1-12 hours.

[0035] In a further technical solution, in the step S5, the temperature for reducing the graphene oxide coated copper powder composite is 350 DEG C, and the reducing time is 60 min.

[0036] In the step S6, the vacuum hot pressing temperature of the vacuum hot pressing treatment is 800 DEG C, and the vacuum hot pressing time is 2 hours; the periphery of the polycrystalline copper structure has 3-5 layers of graphene, and the graphene between each polycrystalline copper structure is connected and presents a three-dimensional interconnected structure.

[0037] A high-strength and high-conductivity graphene / copper composite material, the graphene / copper bulk presents a polycrystalline copper structure, presents Cu(111), Cu(200) and Cu(220) crystal face indexes, the bulk conductivity of the graphene / copper bulk is 97-107% IACS, the periphery of the polycrystalline copper structure has 3-5 layers of graphene, and the graphene between each polycrystalline copper structure is connected and presents a three-dimensional interconnected structure. Part of the graphene at the periphery of the polycrystalline copper structure has a wrinkle, and the wrinkle is 6-8 layers of graphene.

[0038] Compared with the prior art, the application has the advantages that: the application effectively uses low-cost graphite to realize industrial production of high-strength and high-conductivity graphene / copper composite material, the preparation process is shorter, the preparation efficiency is higher, the industrial production cost is lower, and the energy consumption is reduced, and the application has many technical advantages.

[0039] The application adds a small amount of graphite to the copper material, uses chemical stripping and high-pressure bonding to ensure uniform dispersion of graphene in the matrix, realizes strong interface bonding with the matrix and forms a three-dimensional interconnected graphene structure, effectively bears the load under the action of tensile stress, and enhances the overall mechanical properties; the application enhances the charge transport efficiency of the copper matrix through the three-dimensional graphene structure, fully plays the role of high conductivity of graphene, and makes the prepared copper graphene composite material have high strength and high conductivity. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 It is the real object diagram of the raw material copper powder and the graphene coated copper powder in the examples.

[0041] Figure 2 Raman spectrum of graphene-coated copper powder prepared in the example.

[0042] Figure 3 Raman spectrum of graphene on the surface of copper powder after reduction in the example.

[0043] Figure 4 Optical microscope image of graphene-coated copper powder in the example.

[0044] Figure 5 Photo of hot-pressed graphene / copper bulk in the example.

[0045] Figure 6 XRD pattern of graphene / copper bulk prepared in the example. DETAILED DESCRIPTION

[0046] A method for preparing a high-strength and high-conductivity graphene / copper composite material, which is prepared by combining a chemical exfoliation method and a hydrothermal method, comprises the following preparation steps and conditions,

[0047] In step S1, copper powder and graphite powder are weighed according to a weight ratio to obtain a mixed powder, wherein the mass ratio of the copper powder to the graphite powder is 1:0.01-0.03, alcohol is added to the mixed powder, and the mixed powder is uniformly mixed to obtain a mixture.

[0048] The purity of the copper powder is greater than 99.9%, the particle size of the copper powder is 15-50 μm, and the input weight of the copper powder is 97-99% of the total mass of the mixed powder.

[0049] The particle size of the graphite powder is 20-50 μm, and the input weight of the graphite powder is 1-3% of the total mass of the raw materials of the mixed powder.

[0050] In step S2, a mixed solution is prepared by sealing and stirring a binder organic substance and a solvent to obtain the mixed solution, the binder organic substance is selected from alcohol, the solvent is selected from at least one of DMF and NMP, the weight ratio of the binder organic substance to the solvent is 1:5-10, and the total mass concentration of the mixed solution is 10-20%.

[0051] DMF is the chemical abbreviation of dimethylformamide (N,N-dimethylformamide), and NMP is the chemical abbreviation of N-methyl-2-pyrrolidone. Preferably, the binder organic substance is selected from polyethylene glycol, the solvent is selected from DMF, and the mass ratio of the polyethylene glycol to the DMF is 1:5-10.

[0052] The binder organic substance is selected from at least one of ethylene glycol, polypropylene glycol, and polyethylene glycol, and the input weight of the binder organic substance is 10-20% of the total mass of the mixed solution.

[0053] Step S3, the mixture of step 1 and the mixed solution of step S2 are moved into a hydrothermal reactor, the temperature in the hydrothermal reactor is controlled at 150-220℃, and the hydrothermal reaction is carried out for 5-30 hours, preferably, the temperature in the hydrothermal reactor is controlled at 180-190℃, and the hydrothermal reaction is carried out for 10-15 hours. After the hydrothermal reaction is completed, the hydrothermal reactor is cooled to room temperature to obtain a graphene oxide coated copper powder composite material;

[0054] In the process, DMF enters the graphite intercalation of the graphite powder and peels off the graphite into graphene oxide under the action of high temperature and high pressure of the hydrothermal reaction,

[0055] The adhesive organic matter makes the oxygen-containing groups (hydroxyl and carboxyl) on the surface of the formed graphene oxide produce hydrogen bonds or weak interactions with the surface of the copper powder under the action of high temperature and high pressure of the hydrothermal reaction, thereby enhancing the binding force between the graphene oxide and the copper powder, effectively dispersing the copper powder and the graphene oxide, preventing agglomeration, and helping to form a uniform composite material and improve the binding effect of the graphene oxide and the copper powder.

[0056] The adhesive organic matter enhances the binding force between the graphene oxide and the copper powder while effectively dispersing the copper powder and the graphene oxide, and prevents the graphene oxide from agglomerating, so that the graphene oxide is tightly attached to the surface of the copper powder and uniformly coated on the surface of the copper powder,

[0057] The use of polyethylene glycol helps the graphene oxide to combine with the surface of the copper powder and form a dense structure, and makes the graphene oxide tightly attached to the surface of the copper powder without voids, so that the surface of the copper powder is uniformly coated with graphene oxide film with 3-5 layers of graphene oxide and in the form of a sheet film structure, and no voids are generated, to form the graphene oxide coated copper powder composite material;

[0058] The use of a hydrothermal reactor vessel for high temperature and high pressure reaction can make the graphene oxide deposited on the copper powder, so that the graphene oxide is more uniformly distributed, and the copper powder is black before reduction, indicating that the copper powder is completely covered and the color of copper itself is not exposed, as shown in the accompanying Figure 1 , and the surface Raman characteristic peaks are as shown in the accompanying Figure 2 .

[0059] Step S4, the graphene oxide coated copper powder composite material of step S3 is sequentially subjected to suction filtration, washing and vacuum drying to obtain a pure graphene oxide coated copper powder composite material;

[0060] Step S5, using a reducing atmosphere to reduce the graphene oxide coated copper powder composite, using a mixed gas mixed by nitrogen and hydrogen as the reducing atmosphere, the hydrogen accounts for 1-5% of the volume percentage of the reducing atmosphere, the temperature for reducing the graphene oxide coated copper powder composite is 300-600 DEG C, the reducing reaction time is 30-200 min, preferably, the reducing temperature is controlled at 200-450 DEG C, the reducing reaction time is controlled at 1-3 hours, the graphene oxide coated on the surface of the copper powder is reduced to graphene, and the graphene / copper composite material with 3-5 layers of graphene coated on the surface of the copper powder and in the form of a sheet film structure is obtained;

[0061] The present application reduces the graphene oxide to graphene through the reducing reaction, removes all the organic solvents, and makes the graphene contact surface free of impurities, so that the physical properties are not affected.

[0062] The temperature of the thermal reduction reaction cannot be too high, the reducing temperature is 250-450 DEG C, and cannot exceed 500 DEG C, and the reducing reaction time is 0.5-1 hour, and when the temperature is too high, the graphene is etched in a hydrogen atmosphere and thus the remaining bare copper powder particles are etched, the copper powders are adhered to each other and affect the subsequent hot pressing process, especially the copper powders are adhered to each other and thus holes and gaps are generated between the copper-copper interfaces, the existence of the gaps greatly affects the conductivity and the thermal conductivity. When the temperature is low, the organic residues are easily generated, and a long heat treatment time is required, thus increasing the cost. Preferably, the reducing temperature is 350 DEG C and the reducing reaction is maintained for 1 hour, part of the graphene formed through the reducing reaction has wrinkles, the Raman characteristic peak I D / I G The ratio of the graphene / copper composite material is 0.16-0.18, and the graphene / copper bulk material obtained after the vacuum hot pressing treatment of step S6 has a thermal conductivity of 496 W / (m·K), an electrical conductivity of 106.8% IACS, and a tensile strength of 521 MPa.

[0063] Step S6, the graphene / copper composite material of step S5 is subjected to vacuum hot pressing treatment, the vacuum hot pressing temperature of the vacuum hot pressing treatment is 600 DEG C-1000 DEG C, and the vacuum hot pressing time is 1-12 hours, preferably, the vacuum hot pressing temperature is 800 DEG C, and the vacuum hot pressing treatment time is 2 hours, and the graphene / copper bulk material is obtained, and the graphene / copper bulk material obtained after the hot pressing has a metallic yellow color, as shown in the attached Figure 5 macroscopic photograph shows that no pores and holes appear on the surface of the sample after the hot pressing.

[0064] The copper powder completely coated by graphene is subjected to hot pressing treatment, the graphene is connected with each other between the copper powder particles and presents a three-dimensional connected structure in the bulk, the surface of the graphene / copper bulk obtained after the hot pressing treatment is free of pores and holes, the XRD of the graphene / copper bulk after the hot pressing treatment is shown in the attached Figure 6 figure, the graphene / copper bulk presents Cu(111), Cu(200) and Cu(220) crystal face indexes, and shows a polycrystalline copper structure, the bulk conductivity of the graphene / copper bulk is 97-107% IACS. The graphene is well coated on the surface of the copper powder, and the copper powder is not previously adhered, the graphene presents a sheet and granular coating on the surface, and the reduced graphene oxide is well coated, as shown in the attached Figure 4 figure.

[0065] A high-strength and high-conductivity graphene / copper composite material is prepared according to the above method, the graphene / copper bulk presents a polycrystalline copper structure, presents Cu(111), Cu(200) and Cu(220) crystal face indexes, and the bulk conductivity of the graphene / copper bulk is 97-107% IACS, the periphery of the polycrystalline copper structure has graphene with 3-5 layers, the graphene between the polycrystalline copper structures is connected with each other and presents a three-dimensional connected structure. Part of the graphene at the periphery of the polycrystalline copper structure has wrinkles, and the wrinkles are graphene with 6-8 layers.

[0066] The content of the graphite is appropriate, and too high content of the graphite will cause too much graphene oxide film to be deposited on the surface of the copper powder and generate more wrinkles or stacked thick film, thereby causing agglomeration, especially for the graphene oxide film with a thickness of more than 10 layers, which is not conducive to the improvement of the conductivity.

[0067] When the content of the graphite is low, the exfoliated graphene oxide film is less, and less single-layer graphene oxide will cause insufficient coverage of the graphene oxide on the surface of the copper powder, and the surface of the pure copper powder is not completely coated, which will cause the copper-copper interface to contact and diffuse during the hot pressing process, and finally cause the graphene to fail to form a three-dimensional connected structure, which is not conducive to the interface conduction characteristics of the graphene and the improvement of the overall conductivity. Preferably, 1.5 g of graphite is added per 100.0 g of copper powder, which is the most optimal, and the thickness of the graphene oxide film is 3-5 layers. After reduction by heat treatment, the reduced graphene completely coats the copper powder, and there is no bare metal copper, the color of the powder is similar to that of pure copper powder, which is metallic yellow, the number of layers of the graphene on the surface of the copper powder is mainly 3-5 layers, and the graphene presents a sheet film structure coated on the surface of the copper powder, part of the graphene has a certain wrinkle, and the Raman characteristic peak I D / I G is about 0.17.

[0068] Example 1

[0069] 100.0 g of copper powder was weighed into a 250 mL beaker, 1 g of graphite was added; then polyethylene glycol and DMF were added, the ratio of polyethylene glycol and DMF was 1:5, and the mass was 20 g.

[0070] The beaker was moved into a constant temperature water bath, the temperature was maintained at 45℃, and was moved into an autoclave for reaction at 160℃ for 12 h. After the reaction kettle was cooled to room temperature, it was sequentially subjected to suction filtration treatment, washing treatment and vacuum drying treatment, and then was placed in a mixed gas of argon and hydrogen for heat treatment at a temperature of 350℃ for 1 h.

[0071] Then, a mixed gas of nitrogen and hydrogen was used as a reducing atmosphere for reduction reaction at a temperature of 350℃ for 1 h, and then vacuum hot pressing treatment was performed at a temperature of 800℃ for 2 h to obtain a graphene / copper composite material.

[0072] The thermal conductivity of the material was measured by an experimental instrument to be 380 W / (m·K), the electrical conductivity was 103.3% IACS, and the tensile strength was 410 MPa.

[0073] Example 2

[0074] 100.0 g of copper powder was weighed into a 250 mL beaker, 2 g of graphite was added; then polyethylene glycol and DMF were added, the ratio of polyethylene glycol and DMF was 1:5, and the mass was 20 g.

[0075] The beaker was moved into a constant temperature water bath, the temperature was maintained at 45℃, and was moved into an autoclave for reaction at 160℃ for 12 h. After the reaction kettle was cooled to room temperature, it was sequentially subjected to suction filtration treatment, washing treatment and vacuum drying treatment, and then was placed in a mixed gas of argon and hydrogen for heat treatment at a temperature of 350℃ for 1 h.

[0076] Then, a mixed gas of nitrogen and hydrogen was used as a reducing atmosphere for reduction reaction at a temperature of 350℃ for 1 h, and then vacuum hot pressing treatment was performed at a temperature of 800℃ for 2 h to obtain a graphene / copper composite material.

[0077] The thermal conductivity of the material was measured by an experimental instrument to be 455 W / (m·K), the electrical conductivity was 102.6% IACS, and the tensile strength was 432 MPa.

[0078] Example 3

[0079] 100.0 g of copper powder was weighed into a 250 mL beaker, 1.5 g of graphite was added; then polyethylene glycol and DMF were added, the ratio of polyethylene glycol and DMF was 1:5, and the mass was 20 g.

[0080] The beaker is moved into a constant temperature water bath, the temperature is maintained at 45℃, and is moved into an autoclave for reaction at 160℃ for 12h. After the reaction kettle is cooled to room temperature, it is sequentially subjected to filtration treatment, washing treatment and vacuum drying treatment, and then is placed in a mixed gas of argon and hydrogen for heat treatment at a temperature of 350℃ for 1h.

[0081] The material is subjected to reduction reaction using a mixed gas of nitrogen and hydrogen as a reducing atmosphere, the reduction reaction temperature is 350℃ and is maintained for 1h, and then is subjected to vacuum hot pressing treatment, the vacuum hot pressing temperature is 800℃ and the time is 2h, to obtain a graphene / copper composite material.

[0082] The thermal conductivity of the material is measured to be 496W / (m·K), the electrical conductivity is 106.8%IACS, and the tensile strength is 521MPa.

[0083] Example 4

[0084] 100.0g of copper powder is weighed into a 250mL beaker, 3g of graphite is added, and then polyethylene glycol and DMF are added, the ratio of polyethylene glycol and DMF is 1:5, and the mass is 20g.

[0085] The beaker is moved into a constant temperature water bath, the temperature is maintained at 45℃, and is moved into an autoclave for reaction at 160℃ for 12h. After the reaction kettle is cooled to room temperature, it is sequentially subjected to filtration treatment, washing treatment and vacuum drying treatment, and then is placed in a mixed gas of argon and hydrogen for heat treatment at a temperature of 350℃ for 1h.

[0086] The material is subjected to reduction reaction using a mixed gas of nitrogen and hydrogen as a reducing atmosphere, the reduction reaction temperature is 350℃ and is maintained for 1h, and then is subjected to vacuum hot pressing treatment, the vacuum hot pressing temperature is 800℃ and the time is 2h, to obtain a graphene / copper composite material.

[0087] The thermal conductivity of the material is measured to be 56W / (m·K), the electrical conductivity is 99.1%IACS, and the tensile strength is 473MPa.

[0088] Example 5

[0089] 100.0g of copper powder is weighed into a 250mL beaker; then polyethylene glycol and DMF are added, the ratio of polyethylene glycol and DMF is 1:5, and the mass is 20g.

[0090] The beaker is moved into a constant temperature water bath, the temperature is maintained at 45℃, and is moved into an autoclave for reaction at 160℃ for 12h. After the reaction kettle is cooled to room temperature, it is sequentially subjected to filtration treatment, washing treatment and vacuum drying treatment, and then is placed in a mixed gas of argon and hydrogen for heat treatment at a temperature of 350℃ for 1h.

[0091] Then, the graphene / copper composite material is obtained by using mixed gas of nitrogen and hydrogen as reducing atmosphere for reduction reaction at 350 DEG C for 1 hour, and then vacuum hot pressing treatment at 800 DEG C for 2 hours,

[0092] The thermal conductivity of the material is 364 W / (m*K) measured by experimental instrument, the electrical conductivity is 100.3% IACS, and the tensile strength is 376 MPa.

[0093] Electrical conductivity (% IACS) Tensile strength (MPa) Thermal conductivity (W / (mK)) Example 1 103.3 410 380 Example 2 102.6 432 455 Example 3 106.8 521 496 Example 4 99.1 473 563 Example 5 100.3 376 364

[0094] Table 1: Material performance test comparison table

[0095] The test standards used in Table 1 are,

[0096] Tensile strength: The tensile strength of the sample is tested on an electronic universal mechanical property testing machine according to GB / T 228.1-2010 Metal Materials Tensile Test Part 1: Room Temperature Test Method.

[0097] Electrical conductivity: GB / T 32791-2016 Copper and Copper Alloy Electrical Conductivity Eddy Current Test Method is used to measure the electrical conductivity of the sample by using a Keithley power supply voltmeter through voltammetry.

[0098] Thermal conductivity: The thermal diffusivity is tested by a laser thermal conductivity instrument, and then the thermal conductivity is calculated according to the specific heat and density. XRD is used to analyze the phase; Raman spectrum is used to test the surface material of the copper powder; and light microscope is used to analyze the surface morphology.

[0099] From the results of the material performance test comparison table in Table 1, it can be seen that compared with the pure copper control group without adding graphite in Example 5, the graphene / copper composite material prepared by the hydrothermal method combined with reduction and hot pressing method has higher electrical conductivity and thermal conductivity, and the electrical conductivity, tensile strength and thermal conductivity are synergistically enhanced in Examples 1 to 3.

[0100] The advantages of the above technical solutions of the application are as follows:

[0101] (1) The graphene / copper composite material is prepared by the hydrothermal method combined with reduction and hot pressing treatment using graphite and copper powder as raw materials, which provides a new idea for the preparation of graphene / copper composite material.

[0102] (2) The preparation process is simple, and the reaction conditions are mild without high temperature calcination.

[0103] (3) The highest thermal conductivity of the prepared graphene / copper bulk material is 496 W / (m*K), and the maximum electrical conductivity is 106.8% IACS.

Claims

1. A method for preparing high-strength and high-conductivity graphene / copper composite material, characterized in that: The preparation is combined by chemical stripping method and hydrothermal method, including the following preparation steps and conditions, Step S1, copper powder and graphite powder are weighed according to the weight ratio to obtain a mixture powder, wherein the mass ratio of copper powder to graphite powder is 1:0.01-0.03, alcohol is added to the mixture powder, and the mixture powder is uniformly mixed to obtain a mixture; Step S2, a mixed solution is prepared, the adhesive organic matter is sealed and stirred with the solvent to prepare the mixed solution, the adhesive organic matter is selected from alcohol, the solvent is selected from at least one of DMF and NMP, the weight ratio of the adhesive organic matter to the solvent is 1:5-10, and the total mass of the mixed solution accounts for 10-20%; Step S3, the mixture of step 1 and the mixed solution of step S2 are moved into a hydrothermal reactor, the temperature in the hydrothermal reactor is controlled at 150-220 DEG C, and hydrothermal reaction is carried out for 5-30 hours, after the hydrothermal reaction is completed, the hydrothermal reactor is cooled to room temperature, and a graphene oxide coated copper powder composite material is obtained; Wherein, DMF enters the graphite intercalation of graphite powder by the action of high temperature and high pressure of hydrothermal reaction, and the graphite is stripped into graphene oxide, The adhesive organic matter makes the oxygen-containing groups on the surface of the formed graphene oxide produce hydrogen bonds or weak interactions with the surface of the copper powder by the action of high temperature and high pressure of the hydrothermal reaction, The adhesive organic matter enhances the binding force between graphene oxide and copper powder while effectively dispersing copper powder and graphene oxide, and prevents graphene oxide from agglomerating at the same time, so that graphene oxide is tightly attached to the surface of copper powder and uniformly coated on the surface of copper powder, The surface of the copper powder is uniformly coated with graphene oxide film with 3-5 layers of graphene oxide and a sheet film structure, no gap is generated, to form the graphene oxide coated copper powder composite material; Step S4, the graphene oxide coated copper powder composite material of step S3 is sequentially subjected to suction filtration, washing and vacuum drying to obtain a pure graphene oxide coated copper powder composite material; Step S5, a reducing atmosphere is used for reduction reaction of the graphene oxide coated copper powder composite material, the reduction temperature is 200-450 DEG C, the reduction reaction time is 1-3 hours, the graphene oxide coated on the surface of the copper powder is reduced into graphene, and a graphene / copper composite material with the surface of the copper powder uniformly coated with 3-5 layers of graphene and a sheet film structure is obtained; Step S6, the graphene / copper composite material of step S5 is subjected to vacuum hot pressing treatment to obtain a graphene / copper block, the graphene / copper block exhibits Cu(111), Cu(200) and Cu(220) crystal face indexes, showing a polycrystalline copper structure, and the block conductivity of the graphene / copper block is 97-107%IACS.

2. The method for preparing a high-strength, high-conductivity graphene / copper composite material according to claim 1, characterized in that: The copper powder coated with graphene is subjected to hot pressing treatment, the graphene is connected to each other between the copper powder particles and exhibits a three-dimensional interconnected structure in the block, and the surface of the graphene / copper block obtained by hot pressing treatment is free of pores and holes.

3. The method according to claim 1, wherein the method comprises the following steps: 1) preparing a graphene dispersion solution; 2) mixing the graphene dispersion solution with copper powder to form a mixture; 3) heating the mixture to a temperature of 600-800°C; 4) sintering the mixture to form a graphene / copper composite material. The purity of the copper powder is greater than 99.9%, the particle size of the copper powder is 15-50 μm, and the input weight of the copper powder accounts for 97-99% of the total mass of the mixture powder. The particle size of the graphite powder is 20-50 μm, and the input weight of the graphite powder is 1-3% of the total mass of the raw material composed of the mixture powder; The adhesive organic matter is at least one of ethylene glycol, polypropylene glycol and polyethylene glycol, and the input weight of the adhesive organic matter is 10-20% of the total mass of the raw solution composed of the mixed solution.

4. The method for preparing a high-strength, high-conductivity graphene / copper composite material according to claim 1, characterized in that: In the step S2, the adhesive organic matter is polyethylene glycol, and the solvent is DMF, and the mass ratio of polyethylene glycol to DMF is 1:5-10. In the step S3, the oxygen-containing group includes hydroxyl and carboxyl. The step S5, the reduction temperature of the reduction reaction is 250-450℃, the reduction reaction time is 0.5~1 hours, the part of graphene formed by the reduction reaction has wrinkle, the Raman characteristic peak of graphene / copper composite material I D / I G The ratio is 0.16-0.

18.

5. The method according to claim 1, wherein the method is characterized by: In the step S3, the temperature in the hydrothermal kettle is controlled at 180-190 ℃, and the hydrothermal reaction is performed for 10-15 hours. In the step S5, the reduction temperature of the reduction reaction is 350 ℃ and is maintained for 1 hour. In the step S6, the graphene / copper composite material is subjected to vacuum hot pressing treatment at a temperature of 800 ℃ for 2 hours.

6. The method according to claim 1, wherein the method is characterized by: In the step S5, a mixed gas composed of nitrogen and hydrogen is used as the reduction atmosphere, the volume percentage of nitrogen in the reduction atmosphere is 1-5%, the temperature for the reduction reaction of the graphene oxide coated copper powder composite material is 300-600 ℃, and the time for the reduction reaction is 30-200 min. In the step S6, the vacuum hot pressing temperature for the vacuum hot pressing treatment is 600-1000 ℃, and the vacuum hot pressing time is 1-12 hours.

7. The method according to claim 1, wherein the method is characterized by: In the step S5, the temperature for the reduction reaction of the graphene oxide coated copper powder composite material is 350 ℃, and the time for the reduction reaction is 60 min. In the step S6, the vacuum hot pressing temperature for the vacuum hot pressing treatment is 800 ℃, and the vacuum hot pressing time is 2 hours; the periphery of the polycrystalline copper structure has graphene with 3-5 layers, and the graphene between the polycrystalline copper structures is connected and presents a three-dimensional connected structure.

8. A high-strength high-conductivity graphene / copper composite material prepared according to any one of claims 1 to 7, characterized in that: The graphene / copper bulk material presents a polycrystalline copper structure, presents Cu(111), Cu(200) and Cu(220) crystal plane indexes, the bulk conductivity of the graphene / copper bulk material is 97-107% IACS, the periphery of the polycrystalline copper structure has graphene with 3-5 layers, and the graphene between the polycrystalline copper structures is connected and presents a three-dimensional connected structure.

9. The high-strength high-conductivity graphene / copper composite material according to claim 8, characterized in that: Part of the graphene at the periphery of the polycrystalline copper structure has wrinkles, and the wrinkles are graphene with 6-8 layers.

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